Prof. Dr. Lars Borchardt
- +49 (234) 3229431
- personal website
- A guide to direct mechanocatalysis
Hwang, S. and Grätz, S. and Borchardt, L.
Chemical Communications 58 (2022)Direct mechanocatalysis (DM) describes solvent-free catalytic reactions that are initiated by mechanical forces in mechanochemical reactors such as ball mills. The distinctive feature of DM is that the milling materials, e.g. the milling balls themselves are the catalyst of the reaction. In this article we follow the historical evolution of this novel concept and give a guide to this emerging, powerful synthesis tool. Within this perspective we seek to highlight the impact of the relevant milling parameters, the nature of the catalyst and potential additives, the scope of reactions that are currently accessible by this method, and the thus far raised hypotheses on the underlying mechanisms of direct mechanochemical transformations. © The Royal Society of Chemistry.
view abstract 10.1039/d1cc05697b
- From Inert to Catalytically Active Milling Media: Galvanostatic Coating for Direct Mechanocatalysis
Wohlgemuth, M. and Mayer, M. and Rappen, M. and Schmidt, F. and Saure, R. and Grätz, S. and Borchardt, L.
Angewandte Chemie - International Edition (2022)
view abstract 10.1002/anie.202212694
- Mechanochemically-Assisted Synthesis of Polyimides
Rensch, T. and Fabig, S. and Grätz, S. and Borchardt, L.
ChemSusChem 15 (2022)Polyimides were obtained in 99 % yield in under 1 h through the “beat and heat” approach, involving solvent-free vibrational ball milling and a thermal treatment step. The influence of a plethora of additives was explored, such as Lewis acids, Lewis bases, and dehydrating agents, and the mechanochemical reaction was identified to run via a polyamic acid intermediate. The protocol was adopted to a range of substrates inaccessible through solution-based processes, including perylene tetracarboxylic acid dianhydride and melamine. Furthermore, quantum chemical calculations were conducted to identify the water removal as the crucial step in the reaction mechanism. The presented method is substantially faster and more versatile than the solution-based process. © 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH
view abstract 10.1002/cssc.202101975
- Potential of novel porous materials for capture of toluene traces in air under humid conditions
Pujol, Q. and Weber, G. and Bellat, J.-P. and Grätz, S. and Krusenbaum, A. and Borchardt, L. and Bezverkhyy, I.
Microporous and Mesoporous Materials 344 (2022)
view abstract 10.1016/j.micromeso.2022.112204
- Scale-Up of Solvent-Free, Mechanochemical Precursor Synthesis for Nanoporous Carbon Materials via Extrusion
Rensch, T. and Chantrain, V. and Sander, M. and Grätz, S. and Borchardt, L.
ChemSusChem (2022)The mechanochemical synthesis of nitrogen-rich nanoporous carbon materials has been scaled up using an extruder. Lignin, urea, and K2CO3 were extruded under heat and pressure to yield nanoporous carbons with up to 3500 m2 g−1 specific surface area after pyrolysis. The route was further broadened by applying different nitrogen sources as well as sawdust as a low-cost renewable feedstock to receive carbons with a C/N ratio of up to 15 depending on nitrogen source and extrusion parameters. The texture of obtained carbons was investigated by scanning electron microscopy as well as argon and nitrogen physisorption, while the chemical structure was analyzed by X-ray photoelectron spectroscopy. The received carbon was tested as a supercapacitor electrode, showing comparable performance to similar ball-mill-synthesized materials. Lastly, the space-time yield was applied to justify the use of a continuous reactor versus the ball mill. © 2022 The Authors. ChemSusChem published by Wiley-VCH GmbH.
view abstract 10.1002/cssc.202200651
- The Direct Mechanocatalytic Suzuki–Miyaura Reaction of Small Organic Molecules
Pickhardt, W. and Beaković, C. and Mayer, M. and Wohlgemuth, M. and Kraus, F.J.L. and Etter, M. and Grätz, S. and Borchardt, L.
Angewandte Chemie - International Edition (2022)The molecular Suzuki cross-coupling reaction was conducted mechanochemically, without solvents, ligands, or catalyst powders. Utilizing one catalytically active palladium milling ball, products could be formed in quantitative yield in as little as 30 min. In contrast to previous reports, the adjustment of milling parameters led to the complete elimination of abrasion from the catalyst ball, thus enabling the first reported systematic catalyst analysis. XPS, in situ XRD, and reference experiments provided evidence that the milling ball surface was the location of the catalysis, allowing a mechanism to be proposed. The versatility of the approach was demonstrated by extending the substrate scope to deactivated and even sterically hindered aryl iodides and bromides. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.
view abstract 10.1002/anie.202205003
- The impact of the physical state and the reaction phase in the direct mechanocatalytic Suzuki-Miyaura coupling reaction
Yoo, K. and Fabig, S. and Grätz, S. and Borchardt, L.
Faraday Discussions (2022)
view abstract 10.1039/d2fd00100d
- The mechanochemical Friedel-Crafts polymerization as a solvent-free cross-linking approach toward microporous polymers
Krusenbaum, A. and Geisler, J. and Kraus, F.J.L. and Grätz, S. and Höfler, M.V. and Gutmann, T. and Borchardt, L.
Journal of Polymer Science 60 (2022)Herein we report the mechanochemical Friedel-Crafts alkylation of 1,3,5-triphenylbenzene (TPB) with two organochloride cross-linking agents, dichloromethane (DCM) and chloroform (CHCl3), respectively. During a thorough milling parameter evaluation, the DCM-linked polymers were found to be flexible and extremely sensitive toward parameter changes, which even enables the synthesis of a polymer with a SSABET of 1670 m2/g, on par with the solution-based reference. Contrary, CHCl3-linked polymers are exhibiting a rigid structure, with a high porosity that is widely unaffected by parameter changes. As a result, a polymer with a SSABET of 1280 m2/g could be generated in as little as 30 minutes, outperforming the reported literature analogue in terms of synthesis time and SSABET. To underline the environmental benefits of our fast and solvent-free synthesis approach, the green metrics are discussed, revealing an enhancement of the mass intensity, mass productivity and the E-factor, as well as of synthesis time and the work-up in comparison to the classical synthesis. Therefore, the mechanochemical polymerization is presented as a versatile tool, enabling the generation of highly porous polymers within short reaction times, with a minimal use of chlorinated cross-linker and with the possibility of a post polymerization modification. © 2021 The Authors. Journal of Polymer Science published by Wiley Periodicals LLC.
view abstract 10.1002/pol.20210606
- The mechanochemical synthesis of polymers
Krusenbaum, A. and Grätz, S. and Tigineh, G.T. and Borchardt, L. and Kim, J.G.
Chemical Society Reviews 51 (2022)Mechanochemistry - the utilization of mechanical forces to induce chemical reactions - is a rarely considered tool for polymer synthesis. It offers numerous advantages such as reduced solvent consumption, accessibility of novel structures, and the avoidance of problems posed by low monomer solubility and fast precipitation. Consequently, the development of new high-performance materials based on mechanochemically synthesised polymers has drawn much interest, particularly from the perspective of green chemistry. This review covers the constructive mechanochemical synthesis of polymers, starting from early examples and progressing to the current state of the art while emphasising linear and porous polymers as well as post-polymerisation modifications. © 2022 The Royal Society of Chemistry
view abstract 10.1039/d1cs01093j
- Beyond the Scholl reaction-one-step planarization and edge chlorination of nanographenes by mechanochemistry
Baier, D.M. and Grätz, S. and Jahromi, B.F. and Hellmann, S. and Bergheim, K. and Pickhardt, W. and Schmid, R. and Borchardt, L.
RSC Advances 11 (2021)The edge chlorination of the benchmark nanographenes triphenylene and hexa-peri-hexabenzocoronene is conducted mechanochemically. This approach overcomes solubility limitations and eliminates the need for elaborate chlorination conditions. Additionally, the planarization of oligophenylenes and their edge-chlorination can be combined in a one-pot approach requiring as little as 60 minutes. © The Royal Society of Chemistry.
view abstract 10.1039/d1ra07679e
- Influence of surface wettability on methane hydrate formation in hydrophilic and hydrophobic mesoporous silicas
Casco, M.E. and Grätz, S. and Wallacher, D. and Grimm, N. and Többens, D.M. and Bilo, M. and Speil, N. and Fröba, M. and Borchardt, L.
Chemical Engineering Journal 405 (2021)The methane hydrate (MH) formation process in confinement was investigated using high-pressure methane sorption experiments on two wet materials with similar pore size distributions, B – PMO (hydrophobic) and MCM – 41 (hydrophilic). Their methane sorption isotherms possess two discrete methane gas consumption steps at ~10 bar and ~ 30 bar at 243 K. A systematic analysis reveals that external water and the so-called ‘core water’ inside the pore is rapidly consumed in the first step to form bulk-like hydrate, whereas adsorbed water is slowly consumed in the second step to form less stable confined hydrates at higher pressures. Synchrotron powder X-Ray results confirm methane hydrate structure I and reveal that bulk ice is swiftly and fully converted to hydrate in MCM – 41, whereas inactive bulk ice co-exists with MH in B – PMO at 6 MPa demonstrating the huge impact of the surface wettability on the water's behavior during MH formation. © 2020 Elsevier B.V.
view abstract 10.1016/j.cej.2020.126955
- Mechanochemically Assisted Synthesis of Hexaazatriphenylenehexacarbonitrile
Pickhardt, W. and Wohlgemuth, M. and Grätz, S. and Borchardt, L.
Journal of Organic Chemistry 86 (2021)1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT CN) was synthesized mechanochemically at room temperature. The coupling of hexaketocyclohexane and diaminomaleonitrile was conducted in 10 min by vibratory ball milling. The effects of milling parameters, acids, dehydrating agents, and liquid-assisted grinding were rationalized. With 67%, the yield of this mechanochemical approach exceeds that of state-of-the-art wet-chemical syntheses while being superior with respect to time-, resource-, and energy-efficiency as quantified via green metrics. © 2021 The Authors. Published by American Chemical Society.
view abstract 10.1021/acs.joc.1c00253
- Revealing the Impact of Hierarchical Pore Organization in Supercapacitor Electrodes by Coupling Ionic Dynamics at Micro- and Macroscales
Dvoyashkin, M. and Leistenschneider, D. and Evans, J.D. and Sander, M. and Borchardt, L.
Advanced Energy Materials 11 (2021)The rate of charging of supercapacitors depends on how quickly ions can reach and accommodate the surface of electrodes. Diffusivity, a parameter reflecting the speed of ions’ migration, is believed to be crucial in designing supercapacitor electrodes. Herein, this belief is questioned, shedding light on a puzzling and potentially critical feature of ionic dynamics denoted as confinement-induced ion–solvent separation. This effect can lead to a strong slowdown of the ion mobility inside hierarchical pore networks. Explanations for when such an effect occurs and how it can be circumvented are provided. Furthermore, this microscopic picture of diffusion seen by NMR is bridged with the macroscopic charging behavior of supercapacitors investigated by impedance spectroscopy. Quantifying the average residence time of ions within carbon particles shows that the nanopore environment may not be the rate-limiting factor for the overall ion mobility and thus performance of a cell—as commonly expected. Combining direct diffusion studies performed with neat and solvated ionic liquids and those on organic electrolytes, the so far lacking criteria for the rational selection of electrolyte–carbon systems is developed and recommendations for the preparation of transport-optimized materials for supercapacitors to minimize ionic diffusion limitations are given. © 2021 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH
view abstract 10.1002/aenm.202100700
- Titanium Niobium Oxide Ti2Nb10O29/Carbon Hybrid Electrodes Derived by Mechanochemically Synthesized Carbide for High-Performance Lithium-Ion Batteries
Budak, Ö. and Srimuk, P. and Aslan, M. and Shim, H. and Borchardt, L. and Presser, V.
ChemSusChem 14 (2021)This work introduces the facile and scalable two-step synthesis of Ti2Nb10O29 (TNO)/carbon hybrid material as a promising anode for lithium-ion batteries (LIBs). The first step consisted of a mechanically induced self-sustaining reaction via ball-milling at room temperature to produce titanium niobium carbide with a Ti and Nb stoichiometric ratio of 1 to 5. The second step involved the oxidation of as-synthesized titanium niobium carbide to produce TNO. Synthetic air yielded fully oxidized TNO, while annealing in CO2 resulted in TNO/carbon hybrids. The electrochemical performance for the hybrid and non-hybrid electrodes was surveyed in a narrow potential window (1.0–2.5 V vs. Li/Li+) and a large potential window (0.05–2.5 V vs. Li/Li+). The best hybrid material displayed a specific capacity of 350 mAh g−1 at a rate of 0.01 A g−1 (144 mAh g−1 at 1 A g−1) in the large potential window regime. The electrochemical performance of hybrid materials was superior compared to non-hybrid materials for operation within the large potential window. Due to the advantage of carbon in hybrid material, the rate handling was faster than that of the non-hybrid one. The hybrid materials displayed robust cycling stability and maintained ca. 70 % of their initial capacities after 500 cycles. In contrast, only ca. 26 % of the initial capacity was maintained after the first 40 cycles for non-hybrid materials. We also applied our hybrid material as an anode in a full-cell lithium-ion battery by coupling it with commercial LiMn2O4. © 2020 The Authors. ChemSusChem published by Wiley-VCH GmbH
view abstract 10.1002/cssc.202002229
- A comprehensive approach for the characterization of porous polymers using 13C and 15N dynamic nuclear polarization NMR spectroscopy
Grätz, S. and De Olivera Junior, M. and Gutmann, T. and Borchardt, L.
Physical Chemistry Chemical Physics 22 (2020)Most porous polymers are notoriously hard to characterize due to their amorphous and completely insoluble nature. On the other hand, they are an interesting class of materials for sorption, catalytic, and electrode applications, thus they warrant in-depth studies. In this contribution, we elaborate on the possibilities that dynamic nuclear polarization offers towards the investigation of the structure of porous polymers. We discuss the advantages and disadvantages of this technique in the investigation of model polymers. This journal is © the Owner Societies.
view abstract 10.1039/d0cp04010j
- Direct Mechanocatalysis: Using Milling Balls as Catalysts
Pickhardt, W. and Grätz, S. and Borchardt, L.
Chemistry - A European Journal 26 (2020)Direct mechanocatalysis describes catalytic reactions under the involvement of mechanical energy with the distinct feature of milling equipment itself being the catalyst. This novel type of catalysis features no solubility challenges of the catalysts nor the substrate and on top offering most facile way of separation. © 2020 The Authors. Published by Wiley-VCH GmbH
view abstract 10.1002/chem.202001177
- In Situ Generation of Electrolyte inside Pyridine-Based Covalent Triazine Frameworks for Direct Supercapacitor Integration
Troschke, E. and Leistenschneider, D. and Rensch, T. and Grätz, S. and Maschita, J. and Ehrling, S. and Klemmed, B. and Lotsch, B.V. and Eychmüller, A. and Borchardt, L. and Kaskel, S.
ChemSusChem 13 (2020)The synthesis of porous electrode materials is often linked with the generation of waste that results from extensive purification steps and low mass yield. In contrast to porous carbons, covalent triazine frameworks (CTFs) display modular properties on a molecular basis through appropriate choice of the monomer. Herein, the synthesis of a new pyridine-based CTF material is showcased. The porosity and nitrogen-doping are tuned by a careful choice of the reaction temperature. An in-depth structural characterization by using Ar physisorption, X-ray photoelectron spectroscopy, and Raman spectroscopy was conducted to give a rational explanation of the material properties. Without any purification, the samples were applied as symmetrical supercapacitors and showed a specific capacitance of 141 F g−1. Residual ZnCl2, which acted formerly as the porogen, was used directly as the electrolyte salt. Upon the addition of water, ZnCl2 was dissolved to form the aqueous electrolyte in situ. Thereby, extensive and time-consuming washing steps could be circumvented. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/cssc.202000518
- Mechanochemical Cyclodehydrogenation with Elemental Copper: An Alternative Pathway toward Nanographenes
Grätz, S. and Oltermann, M. and Vogt, C.G. and Borchardt, L.
ACS Sustainable Chemistry and Engineering 8 (2020)Elemental copper can be utilized to generate C-C bonds in order to synthesize nanographenes in a mechanochemical environment. Utilizing the solvent-free environment of a ball mill, we present a facile and highly sustainable concept for the internal C-C coupling in oligo-phenyls on the example of triphenylene and extend it to the transformation of hexaphenylbenzene into hexa-peri-hexabenzocoronene as a benchmark nanographene. © 2020 American Chemical Society.
view abstract 10.1021/acssuschemeng.0c02223
- Non-porous organic crystals and their interaction with guest molecules from the gas phase
Casco, M.E. and Krupp, F. and Grätz, S. and Schwenger, A. and Damakoudi, V. and Richert, C. and Frey, W. and Borchardt, L.
Adsorption 26 (2020)Some organic molecules encapsulate solvents upon crystallization. One class of compounds that shows a high propensity to form such crystalline solvates are tetraaryladamantanes (TAAs). Recently, tetrakis(dialkoxyphenyl)-adamantanes have been shown to encapsulate a wide range of guest molecules in their crystals, and to stabilize the guest molecules against undesired reactions. The term ‘encapsulating organic crystals’ (EnOCs) has been coined for these species. In this work, we studied the behavior of three TAAs upon exposition to different guest molecules by means of sorption technique. We firstly measured the vapor adsorption/desorption isotherms with water, tetrahydrofuran and toluene, and secondly, we studied the uptake of methane on dry and wet TAAs. Uptake of methane beyond one molar equivalent was detected for wet crystals, even though the materials showed a lack of porosity. Thus far, such behavior, which we ascribe to methane hydrate formation, had been described for porous non-crystalline materials or crystals with detectable porosity, not for non-porous organic crystals. Our results show that TAA crystals have interesting properties beyond the formation of conventional solvates. Gas-containing organic crystals may find application as reservoirs for gases that are difficult to encapsulate or are slow to form crystalline hydrates in the absence of a host compound. Wet tetraaryladamantane crystals take up methane in form of methane hydrate structure I, even though they appear non-porous to argon. [Figure not available: see fulltext.] © 2020, The Author(s).
view abstract 10.1007/s10450-020-00259-8
- Solid-state transformation of aqueous to organic electrolyte - Enhancing the operating voltage window of ‘in situelectrolyte’ supercapacitors
Leistenschneider, D. and Heß, L.H. and Balducci, A. and Borchardt, L.
Sustainable Energy and Fuels 4 (2020)We introduce a holistic concept where by-product salts, which are formed during the synthesis of activated carbons, are not considered as waste products but rather upcycled to an organic electrolyte for EDLC applications. In detail, inorganic salts such as KHCO3, which accumulate inside carbon pores during chemical activation with K2CO3, are converted to the organic electrolyte KTfSI by simply treating the composite with HTfSI. This mechanochemical solid-state reaction runs in as little as one minute and the resulting composite is directly used as an electrode according to the so-calledin situelectrolyte concept. Thereby, the waste production during the EDLC preparation is minimized greatly and the use of any additional electrolyte is made obsolete. EDLC electrodes are fabricatedviathe two most common procedures: slurry-coating on alumina foil and dry-processing with PTFE to form free-standing electrodes. The full cell devices show a good performance of 30 F g-1at high scan rates of 10 A g-1and a high capacitance retention of 74% after 16?000 cycles. By applying the concept the mass productivity can be increased by 15-fold. © The Royal Society of Chemistry 2020.
view abstract 10.1039/d0se00180e
- Sustainable and rapid preparation of nanosized Fe/Ni-pentlandite particles by mechanochemistry
Tetzlaff, D. and Pellumbi, K. and Baier, D.M. and Hoof, L. and Shastry Barkur, H. and Smialkowski, M. and Amin, H.M.A. and Grätz, S. and Siegmund, D. and Borchardt, L. and Apfel, U.-P.
Chemical Science 11 (2020)In recent years, metal-rich sulfides of the pentlandite type (M9S8) have attracted considerable attention for energy storage applications. However, common synthetic routes towards pentlandites either involve energy intensive high temperature procedures or solvothermal methods with specialized precursors and non-sustainable organic solvents. Herein, we demonstrate that ball milling is a simple and efficient method to synthesize nanosized bimetallic pentlandite particles (Fe4.5Ni4.5S8, Pn) with an average size of ca. 250 nm in a single synthetic step from elemental- or sulfidic mixtures. We herein highlight the effects of the milling ball quantity, precursor types and milling time on the product quality. Along this line, Raman spectroscopy as well as temperature/pressure monitoring during the milling processes provide valuable insights into mechanistic differences between the mechanochemical Pn-formation. By employing the obtained Pn-nanosized particles as cathodic electrocatalysts for water splitting in a zero-gap PEM electrolyzer we provide a comprehensive path for a potential sustainable future process involving non-noble metal catalysts. © 2020 The Royal Society of Chemistry.
view abstract 10.1039/d0sc04525j
- The mechanochemical Scholl reaction as a versatile synthesis tool for the solvent-free generation of microporous polymers
Krusenbaum, A. and Grätz, S. and Bimmermann, S. and Hutsch, S. and Borchardt, L.
RSC Advances 10 (2020)Herein we report the mechanochemical Scholl polymerization of 1,3,5-triphenylbenzene in a high speed ball mill. The reaction is conducted solvent-free, solely using solid FeCl3. The resulting porous polymer was obtained in >99% yield after very short reaction times of only 5 minutes and exhibits a high specific surface area of 658 m2 g-1, which could be further enhanced up to 990 m2 g-1 by liquid assisted grinding. Within this study we illuminate the origin of porosity by investigating the impact of various milling parameters and milling materials, temperature and pressure, and different liquids for LAG as well as post polymer milling. Finally we expand the procedure to different monomers and mills, to present the mechanochemical Scholl reaction as a versatile synthesis tool for porous polymers. © The Royal Society of Chemistry.
view abstract 10.1039/d0ra05279e
- An Asymmetric Supercapacitor–Diode (CAPode) for Unidirectional Energy Storage
Zhang, E. and Fulik, N. and Hao, G.-P. and Zhang, H.-Y. and Kaneko, K. and Borchardt, L. and Brunner, E. and Kaskel, S.
Angewandte Chemie - International Edition 58 (2019)A new asymmetric capacitor concept is proposed providing high energy storage capacity for only one charging direction. Size-selective microporous carbons (w<0.9 nm) with narrow pore size distribution are demonstrated to exclusively electrosorb small anions (BF4−) but size-exclude larger cations (TBA+ or TPA+), while the counter electrode, an ordered mesoporous carbon (w>2 nm), gives access to both ions. This architecture exclusively charges in one direction with high rectification ratios (RR=12), representing a novel capacitive analogue of semiconductor-based diodes (“CAPode”). By precise pore size control of microporous carbons (0.6 nm, 0.8 nm and 1.0 nm) combined with an ordered mesoporous counter electrode (CMK-3, 4.8 nm) electrolyte cation sieving and unidirectional charging is demonstrated by analyzing the device charge-discharge response and monitoring individual electrodes of the device via in situ NMR spectroscopy. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/anie.201904888
- Comparing pore structure models of nanoporous carbons obtained from small angle X-ray scattering and gas adsorption
Prehal, C. and Grätz, S. and Krüner, B. and Thommes, M. and Borchardt, L. and Presser, V. and Paris, O.
Carbon 152 (2019)The performance of nanoporous carbons, used for hydrogen storage, ionic charge storage, or selective gas separation, is strongly determined by their pore shape and size distribution. Two frequently used experimental techniques to characterize the nanopore structure of carbons are gas adsorption combined with quenched-solid density functional theory and small angle X-ray scattering. However, neither of the two techniques can unambiguously derive a valid pore model for disordered pore structures without making assumptions. Here, we quantitatively compare pore size distributions from X-ray scattering and gas adsorption data. We generate three-dimensional pore models of activated carbons using small angle scattering and the concept of Gaussian Random Fields. These pore models are used to generate pore size distributions inherently containing a slit-pore assumption, making them comparable to pore size distributions obtained from gas adsorption analysis. This is realized by probing the effective adsorption potential via sampling of the three-dimensional pore structure with a probing adsorbate and calculating a “Degree of Confinement” parameter accounting for local pore geometry effects. We also generate pore size distributions with an alternative definition of pore size and discuss intricacies of gas adsorption results, such as the general tendency to underestimate the pore size dispersity in disordered microporous carbons. © 2019 Elsevier Ltd
view abstract 10.1016/j.carbon.2019.06.008
- Direct Mechanocatalysis: Palladium as Milling Media and Catalyst in the Mechanochemical Suzuki Polymerization
Vogt, C.G. and Grätz, S. and Lukin, S. and Halasz, I. and Etter, M. and Evans, J.D. and Borchardt, L.
Angewandte Chemie - International Edition 58 (2019)The milling ball is the catalyst. We introduce a palladium-catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium-catalyzed C−C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4-bromo or 4-iodophenylboronic acid giving poly(para-phenylene). Surprisingly, we observe one of the highest degrees of polymerization (199) reported so far. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/anie.201911356
- Experimental Evidence of Confined Methane Hydrate in Hydrophilic and Hydrophobic Model Carbons
Casco, M.E. and Zhang, E. and Grätz, S. and Krause, S. and Bon, V. and Wallacher, D. and Grimm, N. and Többens, D.M. and Hauß, T. and Borchardt, L.
Journal of Physical Chemistry C 123 (2019)Methane hydrate confined in porous materials is postulated as an alternative energy storage strategy. By applying model carbons with ordered and uniformly sized pores and a combination of advanced in situ characterization techniques, we address fundamental questions on the formation mechanism of methane hydrate in confinement. Here, we provide experimental evidence for the presence of methane hydrate inside confined spaces by in situ small- and wide-angle neutron scattering, X-ray diffraction, and high-pressure gas adsorption techniques. Furthermore, we demonstrate how the carbon surface chemistry tremendously impacts the methane hydrate formation kinetics and storage capacity. Our findings represent a substantial step toward transforming a naturally occurring phenomenon into a feasible energy storage technology. © 2019 American Chemical Society.
view abstract 10.1021/acs.jpcc.9b06366
- Ionic liquid - Electrode materials interactions studied by NMR spectroscopy, cyclic voltammetry, and impedance spectroscopy
Zhang, E. and Fulik, N. and Paasch, S. and Borchardt, L. and Kaskel, S. and Brunner, E.
Energy Storage Materials 19 (2019)The interactions between two selected porous carbon materials and ionic-liquid based electrolyte solutions consisting of the ionic liquid 1-Ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4)diluted with acetonitrile are investigated within the present paper by combined use of cyclic voltammetry, electrochemical impedance spectroscopy, and NMR spectroscopy. The commercially available microporous YP50F and the hierarchically organized micro- and mesoporous OM-CDC (ordered mesoporous carbide derived carbon)are selected as model materials to achieve a better understanding of the electrolyte behavior, especially its mobility, in porous carbons. The ionic liquid chosen as electrolyte leads to high specific capacitance approaching 180 F g-1 for OM-CDC. Due to the hierarchical pore system, OM-CDC shows a better rate performance than YP50F. NMR analyses provide an understanding of the molecular processes giving rise to the above-mentioned observations. They reveal a limited accessibility of the narrow pores in YP50F for pure EmimBF4 in contrast to OM-CDC. It was found that about 30% of the entire pore volume of YP50F remain unfilled by electrolyte ions without dilution. Dilution with acetonitrile significantly increased the anion mobility as the NMR signal of adsorbed ions becomes narrower. A mixture containing 60% EmimBF4 and 40% acetonitrile was identified as the optimum for electrochemical applications. © 2019 Elsevier B.V.
view abstract 10.1016/j.ensm.2019.03.015
- Mechanochemical synthesis of hyper-crosslinked polymers: Influences on their pore structure and adsorption behaviour for organic vapors
Grätz, S. and Zink, S. and Kraffczyk, H. and Rose, M. and Borchardt, L.
Beilstein Journal of Organic Chemistry 15 (2019)This study elucidates a mechanochemical polymerization reaction towards a hyper-crosslinked polymer as an alternative to conventional solvent-based procedures. The swift and solvent-free Friedel-Crafts alkylation reaction yields a porous polymer with surface areas of up to 1720 m2g-1 and pore volumes of up to 1.55 cm3g-1. The application of LAG (liquid-assisted grinding) revealed a profound impact of the liquid's boiling point on the textural properties of the obtained polymer materials. Finally, the materials are characterized by vapour sorption experiments with benzene and cyclohexane. © 2019 Grätz et al.
view abstract 10.3762/bjoc.15.112
- Mechanochemical synthesis of N-doped porous carbon at room temperature
Casco, M.E. and Kirchhoff, S. and Leistenschneider, D. and Rauche, M. and Brunner, E. and Borchardt, L.
Nanoscale 11 (2019)We report the one-pot mechanochemical synthesis of N-doped porous carbons at room temperature using a planetary ball mill. The fast reaction (5 minutes) between calcium carbide and cyanuric chloride proceeds in absence of any solvent and displays a facile bottom-up strategy that completely avoids typical thermal carbonization steps and directly yields a N-doped porous carbon containing 16 wt% of nitrogen and exhibiting a surface area of 1080 m2 g-1. © 2019 The Royal Society of Chemistry.
view abstract 10.1039/c9nr01019j
- Nitrogen-Doped Biomass-Derived Carbon Formed by Mechanochemical Synthesis for Lithium–Sulfur Batteries
Schneidermann, C. and Kensy, C. and Otto, P. and Oswald, S. and Giebeler, L. and Leistenschneider, D. and Grätz, S. and Dörfler, S. and Kaskel, S. and Borchardt, L.
ChemSusChem 12 (2019)Nitrogen-doped carbons were synthesized by a solvent-free mechanochemically induced one-pot synthesis by using renewable biomass waste. Three solid materials are used: sawdust as a carbon source, urea and/or melamine as a nitrogen source, and potassium carbonate as an activation agent. The resulting nitrogen-doped porous carbons offer a very high specific surface area of up to 3000 m 2 g −1 and a large pore volume up to 2 cm 3 g −1 . Also, a high nitrogen content of 4 wt % (urea only) up to 12 wt % (melamine only) is generated, depending on the nitrogen and carbon sources. The mechanochemical reaction and the impact of different wood components on the porosity and surface functionalities are investigated by nitrogen physisorption and high-resolution X-ray photoelectron spectroscopy (XPS). These N-doped carbons are highly suitable as cathode materials for Li–S batteries, showing high initial discharge capacities of up to 1300 mAh g sulfur −1 (95 % coulombic efficiency) and >75 % capacity retention within the first 50 cycles at low electrolyte volume. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/cssc.201801997
- On the origin of mesopore collapse in functionalized porous carbons
Zhang, E. and Casco, M.E. and Xu, F. and Sheng, W.-B. and Oswald, S. and Giebeler, L. and Wegner, K. and Borchardt, L. and Kaskel, S.
Carbon 149 (2019)Heteroatom functionalization of ordered mesoporous carbon (OMC)represents an important strategy towards electrocatalytic and battery applications. Such functionalization frequently leads to degradation or even collapse of mesopores, which is generally attributed to the harsh conditions used or the successfully doped functional groups or the entrapment of guest species into mesopores. However, in this report, we find the structural deterioration of functionalized OMC is mainly induced by the water evaporation during the drying process, beyond the usually accepted concept mentioned above. We report two types of well-defined OMCs, resembling comparable pore architectures but varying in surface chemistry, namely the hydrophobic OMC (Cmeso)and hydrophilic one (HCmeso). After washing and drying processes, Cmeso remains intact regardless of the drying processes. In sharp contrast, HCmeso shows gradual porosity deterioration or even totally collapse under continuous washing-drying cycles. Lyophilization can however well preserve the porosity due to the reduced stress exerted by water on carbon walls. Such a distinct phenomenon is elaborately characterized by N2 physisorption, H2O physisorption, TEM and SAXS and further validated by well-known CMK-3, which undergoes surface functionalization by concentrated HNO3. Our finding reveals an important but neglected issue addressing the drying process in particular for polar functionalized porous carbons. © 2019 Elsevier Ltd
view abstract 10.1016/j.carbon.2019.04.116
- Tailoring the Adsorption of ACE-Inhibiting Peptides by Nitrogen Functionalization of Porous Carbons
Huettner, C. and Hagemann, D. and Troschke, E. and Hippauf, F. and Borchardt, L. and Oswald, S. and Henle, T. and Kaskel, S.
Langmuir 35 (2019)Bioactive peptides, such as isoleucyl-tryptophan (IW), exhibit a high potential to inhibit the angiotensin-converting enzyme (ACE). Adsorption on carbon materials provides a beneficial method to extract these specific molecules from the complex mixture of an α-lactalbumin hydrolysate. This study focuses on the impact of nitrogen functionalization of porous carbon adsorbents, either via pre- or post-treatment, on the adsorption behavior of the ACE-inhibiting peptide IW and the essential amino acid tryptophan (W). The commercially activated carbon Norit ROX 0.8 is compared with pre- and postsynthetically functionalized N-doped carbon in terms of surface area, pore size, and surface functionality. For prefunctionalization, a covalent triazine framework was synthesized by trimerization of an aromatic nitrile under ionothermal conditions. For the postsynthetic approach, the activated carbon ROX 0.8 was functionalized with the nitrogen-rich molecule melamine. The batch adsorption results using model mixtures containing the single components IW and W could be transferred to a more complex mixture of an α-lactalbumin hydrolysate containing a huge number of various peptides. For this purpose, reverse-phase high-pressure liquid chromatography with fluorescence detection was used for identification and quantification. The treatment with the three different carbon materials leads to an increase in the ACE-inhibiting effect in vitro. The modified surface structure of the carbon via pre- or post-treatment allows separation of IW and W due to the certain selectivity for either the amino acid or the dipeptide. © 2019 American Chemical Society.
view abstract 10.1021/acs.langmuir.9b00996
- Tailoring the porosity of a mesoporous carbon by a solvent-free mechanochemical approach
Leistenschneider, D. and Wegner, K. and Eßbach, C. and Sander, M. and Schneidermann, C. and Borchardt, L.
Carbon 147 (2019)The synthesis of mesoporous carbons with well-defined and tailored pores conventionally involves the use of solvents and proceeds via multiple synthesis steps such as template synthesis and precursor infiltration. In this work, a solvent-free mechanochemical polymerization is used to derive mesoporous carbons with narrow pore size distributions and specific surface areas of up to 1660 m 2 g −1 . The size of the mesopores can be tailored by simply adjusting milling parameters like the milling speed. Finally, the carbons have been applied as supercapacitors through a new approach - the ‘in situ electrolyte’ concept. This holistic concept does not treat the accumulating by-products of the carbon synthesis as waste, but rather utilizes them directly as electrolyte salts. With this, washing steps are circumvented and the use of any solvent becomes obsolete. © 2019 Elsevier Ltd
view abstract 10.1016/j.carbon.2019.02.065
- Upcycling of polyurethane waste by mechanochemistry: Synthesis of N-doped porous carbon materials for supercapacitor applications
Schneidermann, C. and Otto, P. and Leistenschneider, D. and Grätz, S. and Eßbach, C. and Borchardt, L.
Beilstein Journal of Nanotechnology 10 (2019)We developed an upcycling process of polyurethane obtaining porous nitrogen-doped carbon materials that were applied in supercapacitor electrodes. In detail, a mechanochemical solvent-free one-pot synthesis is used and combined with a thermal treatment. Polyurethane is an ideal precursor already containing nitrogen in its backbone, yielding nitrogen-doped porous carbon materials with N content values of 1-8 wt %, high specific surface area values of up to 2150 m2·g-1 (at a N content of 1.6 wt %) and large pore volume values of up to 0.9 cm3·g-1. The materials were tested as electrodes for supercapacitors in aqueous 1 M Li2SO4 electrolyte (100 F·g-1), organic 1 M TEA-BF4 (ACN, 83 F·g-1) and EMIM-BF4 (70 F·g-1). © 2019 Schneidermann et al.
view abstract 10.3762/bjnano.10.157
- Carbon onion/sulfur hybrid cathodes: Via inverse vulcanization for lithium-sulfur batteries
Choudhury, S. and Srimuk, P. and Raju, K. and Tolosa, A. and Fleischmann, S. and Zeiger, M. and Ozoemena, K.I. and Borchardt, L. and Presser, V.
Sustainable Energy and Fuels 2 (2018)A sulfur-1,3-diisopropenylbenzene copolymer was synthesized by ring-opening radical polymerization and hybridized with carbon onions at different loading levels. The carbon onion mixing was assisted by shear in a two-roll mill to capitalize on the softened state of the copolymer. The sulfur copolymer and the hybrids were thoroughly characterized in structure and chemical composition, and finally tested by electrochemical benchmarking. An enhancement of specific capacity was observed over 140 cycles at higher content of carbon onions in the hybrid electrodes. The copolymer hybrids demonstrate a maximum initial specific capacity of 1150 mA h gsulfur-1 (850 mA h gelectrode-1) and a low decay of capacity to reach 790 mA h gsulfur-1 (585 mA h gelectrode-1) after 140 charge/discharge cycles. All carbon onion/sulfur copolymer hybrid electrodes yielded high chemical stability, stable electrochemical performance superior to conventional melt-infiltrated reference samples having similar sulfur and carbon onion content. The amount of carbon onions embedded in the sulfur copolymer has a strong influence on the specific capacity, as they effectively stabilize the sulfur copolymer and sterically hinder the recombination of sulfur species to the S8 configuration. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c7se00452d
- Electrolyte mobility in supercapacitor electrodes – Solid state NMR studies on hierarchical and narrow pore sized carbons
Fulik, N. and Hippauf, F. and Leistenschneider, D. and Paasch, S. and Kaskel, S. and Brunner, E. and Borchardt, L.
Energy Storage Materials 12 (2018)Electrical double layer capacitors are in the special focus of current energy storage research due to their high power density. They store charge physically by quick electrosorption of electrolyte ions on the surface of porous carbon electrodes. However, fundamental insight into the storage mechanism, especially on a molecular level is limited despite of the crucial importance to understand and improve this promising technology. We have investigated and quantified the mobility of electrolyte ions in supercapacitor electrodes by means of solid-state nuclear magnetic resonance (NMR) spectroscopy. We could discriminate between the mobility of cations, anions, and solvent molecules. The exchange of these species between different pore systems as well as between pore system and external bulk environment is studied in detail by NMR spectroscopic methods. © 2017
view abstract 10.1016/j.ensm.2017.12.008
- Mechanochemical synthesis of porous carbon at room temperature with a highly ordered sp2 microstructure
Casco, M.E. and Badaczewski, F. and Grätz, S. and Tolosa, A. and Presser, V. and Smarsly, B.M. and Borchardt, L.
Carbon 139 (2018)Carbon nanostructures with a well-developed turbostratic sp2 structure and high porosity are synthesized at room temperature inside a planetary ball mill. The obtained carbons were analyzed in-depth by means of gas adsorption, wide-angle X-ray scattering (WAXS), Raman spectroscopy, and transmission electron microscopy (TEM). Our approach involves the solvent-free reaction between calcium carbide (CaC2) and hexachlorobenzene (C6Cl6) conducted under mechanochemical conditions. After certain mechanical activation time, the exothermic nature of the reaction (−492 kcal) provokes a combustion-like event that results in innocuous salt (CaCl2) and a carbonaceous material. Carbon with a high degree of structural order in the constituting graphene and the graphene stacks, possessing almost no internal surface, can be obtained after 5 min of milling time with a mass ratio CaC2/C6Cl6 of 0.9, while carbon exhibiting a surface area as high as 915 m2/g can be obtained after 2 h of milling time with a mass ratio CaC2/C6Cl6 of 5.1. WAXS results and TEM observations reveal a mixture of amorphous carbon and non-graphitic phases. Among the last one, spherical-shaped carbons and curved nanosized strips can be easily distinguished. © 2018 Elsevier Ltd
view abstract 10.1016/j.carbon.2018.06.068
- Methane Hydrate in Confined Spaces: An Alternative Storage System
Borchardt, L. and Casco, M.E. and Silvestre-Albero, J.
ChemPhysChem 19 (2018)Methane hydrate inheres the great potential to be a nature-inspired alternative for chemical energy storage, as it allows to store large amounts of methane in a dense solid phase. The embedment of methane hydrate in the confined environment of porous materials can be capitalized for potential applications as its physicochemical properties, such as the formation kinetics or pressure and temperature stability, are significantly changed compared to the bulk system. We review this topic from a materials scientific perspective by considering porous carbons, silica, clays, zeolites, and polymers as host structures for methane hydrate formation. We discuss the contribution of advanced characterization techniques and theoretical simulations towards the elucidation of the methane hydrate formation and dissociation process within the confined space. We outline the scientific challenges this system is currently facing and look on possible future applications for this technology. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/cphc.201701250
- Nanocasting in ball mills - Combining ultra-hydrophilicity and ordered mesoporosity in carbon materials
Zhang, E. and Hao, G.-P. and Casco, M.E. and Bon, V. and Grätz, S. and Borchardt, L.
Journal of Materials Chemistry A 6 (2018)A novel carbon material with an ultra-hydrophilic surface and an ordered arrangement of uniformly sized mesopores is synthesized via a solvent-free nanocasting approach conducted in a planetary ball mill. The synthesis involves a mechanochemical coordination reaction of bipyridine and copper chloride and its subsequent carbonization. Stemming from the synergistic effect of uniformly dispersed 34 wt% of heteroatoms and the highly ordered mesoporous structure (specific surface area >1000 m2 g-1, pore volume >1.2 cm3 g-1), the apparent water contact angle of the material is 0°-an unprecedented value for carbon materials. This novel type of carbon, with its tailorable pore structure, constitutes an ideal model material for fundamental investigations and can open new perspectives for advanced applications of porous carbons where polar wettability is crucial. Moreover, the solvent-free ball milling synthesis concept paves the way towards many novel materials, that syntheses are currently suffering from solubility issues in the nanocasting process. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c7ta10783h
- Nanoimprint lithography of nanoporous carbon materials for micro-supercapacitor architectures
Lochmann, S. and Grothe, J. and Eckhardt, K. and Leistenschneider, D. and Borchardt, L. and Kaskel, S.
Nanoscale 10 (2018)Nanoimprint lithography is proposed as a highly versatile method for the production of nanostructured supercapacitors (micro-supercapacitors, MSC). Liquid sucrose- and lignin-precursor printing produces patterns with high quality and a line width down to 500 nm. The liquid-carbon-precursor NIL-printing approach enables nitrogen doping to achieve an increased supercapacitor performance for aqueous electrolytes (Li2SO4). The lines are interconverted into nanoporous carbon materials (d ≈ 1 nm) with high specific surface area (>1000 m2 g-1) to form stable structures reaching specific resistivities as low as ρ = 3.5 × 10-5 Ωm and capacitances up to 7 F cm-3. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c8nr01535j
- Revising the Concept of Pore Hierarchy for Ionic Transport in Carbon Materials for Supercapacitors
Borchardt, L. and Leistenschneider, D. and Haase, J. and Dvoyashkin, M.
Advanced Energy Materials 8 (2018)Rapid motion of electrolyte ions is a crucial requirement to ensure the fast charging/discharging and the high power densities of supercapacitor devices. This motion is primarily determined by the pore size and connectivity of the used porous carbon electrodes. Here, the diffusion characteristics of each individual electrolyte component, that is, anion, cation, and solvent confined to model carbons with uniform and well-defined pore sizes are quantified. As a result, the contributions of micropores, mesopores, and hierarchical pore architectures to the overall transport of adsorbed mobile species are rationalized. Unexpectedly, it is observed that the presence of a network of mesopores, in addition to smaller micropores—the concept widely used in heterogeneous catalysis to promote diffusion of sorbates—does not necessarily enhance ionic transport in carbon materials. The observed phenomenon is explained by the stripping off the surrounding solvent shell from the electrolyte ions entering the micropores of the hierarchical material, and the resulting enrichment of solvent molecules preferably in the mesopores. It is believed that the presented findings serve to provide fundamental understanding of the mechanisms of electrolyte diffusion in carbon materials and depict a quantitative platform for the future designing of supercapacitor electrodes on a rational basis. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/aenm.201800892
- Solvent-free synthesis of a porous thiophene polymer by mechanochemical oxidative polymerization
Grätz, S. and Oltermann, M. and Troschke, E. and Paasch, S. and Krause, S. and Brunner, E. and Borchardt, L.
Journal of Materials Chemistry A 6 (2018)This study elucidates a mechanochemical approach to synthesize a microporous thiophene polymer via oxidative polymerization. Utilizing a design of experiments approach we optimized the reaction conditions leading to complete conversion and a polymer with a surface area of up to 1850 m2 g−1-almost twice as high as the material prepared by solution-based polymerization. Thus, our approach presents a solvent free, quick and scalable alternative for the production of porous polymers. © The Royal Society of Chemistry.
view abstract 10.1039/c8ta03684e
- The mechanochemical Scholl reaction-a solvent-free and versatile graphitization tool
Grätz, S. and Beyer, D. and Tkachova, V. and Hellmann, S. and Berger, R. and Feng, X. and Borchardt, L.
Chemical Communications 54 (2018)Herein, we report on the mechanochemical Scholl reaction of dendritic oligophenylene precursors to produce benchmark nanographenes such as hexa-peri-hexabenzocoronene (HBC), triangular shaped C60 and expanded C222 under solvent-free conditions. The solvent-free approach overcomes the bottleneck of solubility limitation in this well-known and powerful reaction. The mechanochemical approach allows tracking the reaction process by in situ pressure measurements. The quality of produced nanographenes has been confirmed by MALDI-TOF mass spectrometry and UV-Vis absorption spectroscopy. This approach paves the way towards gram scale and environmentally benign synthesis of extended nanographenes and possibly graphene nanoribbons suitable for application in carbon based electronics or energy applications. © 2018 The Royal Society of Chemistry.
view abstract 10.1039/c8cc01993b
- The “In Situ Electrolyte” Concept: Using Activation Chemicals as Electrolytes for Carbon-Based Supercapacitors
Leistenschneider, D. and Schneidermann, C. and Hippauf, F. and Grätz, S. and Borchardt, L.
Advanced Sustainable Systems 2 (2018)The “in situ electrolyte” concept displays a novel method for the fabrication of carbon-based supercapacitors. The synthesis is designed in such way that by-products formed during the carbon synthesis directly act as an electrolyte salt and contribute to the supercapacitor's functionality. The presented method produces materials competitive with conventional approaches but simplifies and economizes their whole synthesis and application. The concept shows how process steps can be rendered obsolete by taking a holistic view on the material synthesis and its respective application, by not treating by-products as waste, but rather as integral part of the desired application. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/adsu.201800087
- Carbon nano-composites for lithium–sulfur batteries
Borchardt, L. and Althues, H. and Kaskel, S.
Current Opinion in Green and Sustainable Chemistry 4 (2017)The lithium–sulfur battery is among the most promising next-generation energy storage technologies. Particularly carbon nano-composites display an important “piece of the puzzle” to enhance their performance. This short review addresses five major challenges the research field is currently confronted with. It discusses new developments of advanced carbon nanostructures and highlights strategies to improve the performances by cathode functionalization. It outlines current ambitions to gain a deeper understanding of carbon cathode chemistry by in situ characterization techniques, highlights the beneficial role of carbon nanostructures in anode and interfacial components and closes with recommendations for comprehensive and mandatory electrochemical characterization of Li–S cells. © 2017 Elsevier B.V.
view abstract 10.1016/j.cogsc.2017.02.008
- Carbon onion-sulfur hybrid cathodes for lithium-sulfur batteries
Choudhury, S. and Zeiger, M. and Massuti-Ballester, P. and Fleischmann, S. and Formanek, P. and Borchardt, L. and Presser, V.
Sustainable Energy and Fuels 1 (2017)In this study, we explore carbon onions (diameter below 10 nm), for the first time, as a substrate material for lithium sulfur cathodes. We introduce several scalable synthesis routes to fabricate carbon onion-sulfur hybrids by adopting in situ and melt diffusion strategies with sulfur fractions up to 68 mass%. The conducting skeleton of agglomerated carbon onions proved to be responsible for keeping active sulfur always in close vicinity to the conducting matrix. Therefore, the hybrids are found to be efficient cathodes for Li-S batteries, yielding 97-98% Coulombic efficiency over 150 cycles with a slow fading of the specific capacity (ca. 660 mA h g-1 after 150 cycles) in long term cycle test and rate capability experiments. © The Royal Society of Chemistry.
view abstract 10.1039/c6se00034g
- Hybrid N-Butylamine-Based Ligands for Switching the Colloidal Solubility and Regimentation of Inorganic-Capped Nanocrystals
Sayevich, V. and Guhrenz, C. and Dzhagan, V.M. and Sin, M. and Werheid, M. and Cai, B. and Borchardt, L. and Widmer, J. and Zahn, D.R.T. and Brunner, E. and Lesnyak, V. and Gaponik, N. and Eychmüller, A.
ACS Nano 11 (2017)We report on a simple and effective technique of tuning the colloidal solubility of inorganic-capped CdSe and CdSe/CdS core/shell nanocrystals (NCs) from highly polar to nonpolar media using n-butylamine molecules. The introduction of the short and volatile organic amine mainly results in a modification of the labile diffusion region of the inorganic-capped NCs, enabling a significant extension of their dispersibility and improving the ability to form long-range assemblies. Moreover, the hybrid n-butylamine/inorganic capping can be thermally decomposed under mild heat treatment, making this approach of surface functionalization well-compatible with a low-temperature, solution-processed device fabrication. Particularly, a field-effect transistor-based on n-butylamine/Ga-I-complex-capped 4.5 nm CdSe NC solids shows excellent transport characteristics with electron mobilities up to 2 cm2/(V·s) and a high current modulation value (>104) at a low operation voltage (<2 V). © 2017 American Chemical Society.
view abstract 10.1021/acsnano.6b06996
- Mechanochemical Friedel–Crafts Alkylation—A Sustainable Pathway Towards Porous Organic Polymers
Troschke, E. and Grätz, S. and Lübken, T. and Borchardt, L.
Angewandte Chemie - International Edition 56 (2017)This study elucidates an innovative mechanochemical approach applying Friedel–Crafts alkylation to synthesize porous covalent triazine frameworks (CTFs). Herein, we pursue a counterintuitive approach by utilizing a rather destructive method to synthesize well-defined materials with intrinsic porosity. Investigating a model system including carbazole as monomer and cyanuric chloride as triazine node, ball milling is shown to successfully yield porous polymers almost quantitatively. We verified the successful structure formation by an in-depth investigation applying XPS, solid-state NMR and FT-IR spectroscopy. An in situ study of pressure and temperature developments inside the milling chamber in combination with two-dimensional liquid-state NMR spectroscopy reveals insights into the polymerization mechanism. The versatility of this mechanochemical approach is showcased by application of other monomers with different size and geometry. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/anie.201702303
- Mechanochemical Suzuki polycondensation-from linear to hyperbranched polyphenylenes
Grätz, S. and Wolfrum, B. and Borchardt, L.
Green Chemistry 19 (2017)The mechanochemical Suzuki polycondensation constitutes a sustainable alternative to classical solvent-based polymerization reactions for poly(phenylene)s. In order to establish a basic understanding of the process, important reaction parameters like the milling material, halide type and polymerization system are investigated. Under optimized conditions, we have been able to synthesize linear polymers with an outstanding degree of polymerization of 164, in a ligand free environment-in as little as 30 minutes. In addition, the developed principle is broadened to a hyperbranched system with high temperature resistance and high yields in short reaction times. © 2017 The Royal Society of Chemistry.
view abstract 10.1039/c7gc00693d
- Mechanochemistry-assisted synthesis of hierarchical porous carbons applied as supercapacitors
Leistenschneider, D. and Jäckel, N. and Hippauf, F. and Presser, V. and Borchardt, L.
Beilstein Journal of Organic Chemistry 13 (2017)A solvent-free synthesis of hierarchical porous carbons is conducted by a facile and fast mechanochemical reaction in a ball mill. By means of a mechanochemical ball-milling approach, we obtained titanium(IV) citrate-based polymers, which have been processed via high temperature chlorine treatment to hierarchical porous carbons with a high specific surface area of up to 1814 m2 g−1 and well-defined pore structures. The carbons are applied as electrode materials in electric double-layer capacitors showing high specific capacitances with 98 F g−1 in organic and 138 F g−1 in an ionic liquid electrolyte as well as good rate capabilities, maintaining 87% of the initial capacitance with 1 M TEA-BF4 in acetonitrile (ACN) and 81% at 10 A g−1 in EMIM-BF4. © 2017 Leistenschneider et al.; licensee Beilstein-Institut.
view abstract 10.3762/bjoc.13.130
- Microporous novolac-derived carbon beads/sulfur hybrid cathode for lithium-sulfur batteries
Choudhury, S. and Krüner, B. and Massuti-Ballester, P. and Tolosa, A. and Prehal, C. and Grobelsek, I. and Paris, O. and Borchardt, L. and Presser, V.
Journal of Power Sources 357 (2017)Novolac-derived nanoporous carbon beads were used as conductive matrix for lithium-sulfur battery cathodes. We employed a facile self-emulsifying synthesis to obtain sub-micrometer novolac-derived carbon beads with nanopores. After pyrolysis, the carbon beads showed already a specific surface area of 640 m2 g−1 which was increased to 2080 m2 g−1 after physical activation. The non-activated and the activated carbon beads represent nanoporous carbon with a medium and a high surface area, respectively. This allows us to assess the influence of the porosity on the electrochemical performance of lithium-sulfur battery cathodes. The carbon/sulfur hybrids were obtained from two different approaches of sulfur infiltration: melt-infusion of sulfur (annealing) and in situ formation of sulfur from sodium thiosulfate. The best performance (∼880 mAh gsulfur−1 at low charge rate; 5th cycle) and high performance stability (>600 mAh gsulfur−1 after 100 cycles) were found for the activated carbon beads when using melt infusion of sulfur. © 2017 Elsevier B.V.
view abstract 10.1016/j.jpowsour.2017.05.005
- Salt templated synthesis of hierarchical covalent triazine frameworks
Troschke, E. and Grätz, S. and Borchardt, L. and Haubold, D. and Senkovska, I. and Eychmueller, A. and Kaskel, S.
Microporous and Mesoporous Materials 239 (2017)Covalent triazine framework (CTF-1) materials with hierarchical pore structures have been synthesised using a salt templating approach. As salt templates binary mixtures of ZnCl2 with various alkali chlorides (instead of only ZnCl2) in combination with a modified temperature protocol were utilised. The porosity of salt templated CTF-1 materials was analysed by means of argon physisorption at 87 K. In addition to microporosity, typical for CTF-1, the resulting materials show enhanced mesoporosity and have high total pore volumes of up to 2.1 cm3 g−1. The presented synthetic protocol provides an access to materials combining high nitrogen content, hierarchical pore structure, and high total pore volume, while established CTF syntheses at elevated temperatures used to increase the pore volume in general cause nitrogen loss. These new hierarchical CTFs are very promising cathode materials for lithium-sulphur batteries, where both characteristics (nitrogen content and mesoporosity) are crucial. © 2016 Elsevier Inc.
view abstract 10.1016/j.micromeso.2016.10.002
- Solvent-free hierarchization of zeolites by carbochlorination
Nichterwitz, M. and Grätz, S. and Nickel, W. and Borchardt, L.
Journal of Materials Chemistry A 5 (2017)Carbochlorination, a solvent-free top-down process, is a novel pathway for the hierarchization of zeolites. In contrast to other methods no further washing steps are required. The employed method should serve as a model system for the “upcycling” of coked and deactivated zeolites accumulated by the industry. In order to establish a basic understanding of the process, zeolite H-Y was taken as a model system and a thorough investigation of important reaction parameters, like chlorination temperature, time and concentration, carbon loading, and Si/Al ratio, was performed. Under optimized conditions, we have been able to hierarchize H-Y with high yield, doubling the mesopore volume while maintaining the crystallinity and surface area. © The Royal Society of Chemistry.
view abstract 10.1039/C6TA09145H
- Solvent-Free Mechanochemical Synthesis of Nitrogen-Doped Nanoporous Carbon for Electrochemical Energy Storage
Schneidermann, C. and Jäckel, N. and Oswald, S. and Giebeler, L. and Presser, V. and Borchardt, L.
ChemSusChem 10 (2017)Nitrogen-doped nanoporous carbons were synthesized by a solvent-free mechanochemically induced one-pot synthesis. This facile approach involves the mechanochemical treatment and carbonization of three solid materials: potassium carbonate, urea, and lignin, which is a waste product from pulp industry. The resulting nitrogen-doped porous carbons offer a very high specific surface area up to 3000 m2 g−1 and large pore volume up to 2 cm3 g−1. The mechanochemical reaction and the impact of activation and functionalization are investigated by nitrogen and water physisorption and high-resolution X-ray photoelectron spectroscopy (XPS). Our N-doped carbons are highly suitable for electrochemical energy storage as supercapacitor electrodes, showing high specific capacitances in aqueous 1 m Li2SO4 electrolyte (177 F g−1), organic 1 m tetraethylammonium tetrafluoroborate in acetonitrile (147 F g−1), and an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate; 192 F g−1). This new mechanochemical pathway synergistically combines attractive energy-storage ratings with a scalable, time-efficient, cost-effective, and environmentally favorable synthesis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/cssc.201700459
- Tailored Mesoporous Carbon/Vanadium Pentoxide Hybrid Electrodes for High Power Pseudocapacitive Lithium and Sodium Intercalation
Fleischmann, S. and Leistenschneider, D. and Lemkova, V. and Krüner, B. and Zeiger, M. and Borchardt, L. and Presser, V.
Chemistry of Materials 29 (2017)In this study, atomic layer deposition (ALD) is employed to synthesize hybrid electrode materials of especially tailored mesoporous carbon and vanadium oxide. The highly conformal and precise character of ALD allowed for depositing up to 65 mass % of vanadium oxide inside the 5-20 nm mesopores of the carbon particles, without substantially obstructing internal surface area. The deposited phase was identified as orthorhombic V2O5, and an increasing crystalline order was detected for higher mass loadings. Employing the hybrid material as lithium and sodium intercalation hosts at a rate of 0.5C yielded specific capacities of 310 and 250 mAh/g per V2O5, respectively, while showing predominantly pseudocapacitive behavior, that is, capacitor-like voltage profiles. C-rate benchmarking revealed a retention of about 50% of the maximum capacity for both lithium and sodium at a high rate of 100C. When testing for longevity in lithium-containing electrolyte, a steadily increasing capacity was observed to 116% of the initial value after 2000 cycles. In sodium electrolyte, the capacity faded to 75% after 2000 cycles, which represents one of the most stable performances for sodium intercalation in the literature. Homogeneously distributed vanadium oxide that is locally confined in the tailored carbon mesopores was identified as the reason for enhanced cyclability and rate behavior of the hybrid material. © 2017 American Chemical Society.
view abstract 10.1021/acs.chemmater.7b02533
- Toward a molecular design of porous carbon materials
Borchardt, L. and Zhu, Q.-L. and Casco, M.E. and Berger, R. and Zhuang, X. and Kaskel, S. and Feng, X. and Xu, Q.
Materials Today 20 (2017)The molecular design of porous solids from predefined building blocks, in particular metal-organic and covalent frameworks, has been a tremendous success in the past two decades approaching record porosities and more importantly was an enabler for integrating predefined molecular functionality (enantioselectivity, optical and catalytic properties) into pore walls. Recent efforts indicate that this concept could also be applicable to rationally design porous and nanostructured carbonaceous materials, a class of materials hitherto and especially in the past often considered as “black magic” in terms of pore-wall structure definition and surface functionality. Carbon precursors with structural and compositional information in their molecular backbone, pre-formed covalent bonds, or integrated functional groups enable the design of carbon materials that can be tailored for certain applications. We review this exciting field of synthetic approaches based on molecular building blocks such as ionic liquids, bio molecules, or organic precursor monomers enabling the design of advanced carbonaceous architectures such as porous carbons, porous carbon-rich polymers or graphene nanoribbons. Moreover, our review includes approaches using the reactive and thermal transformation of periodic crystalline structures such as metal-organic frameworks, or carbides into equally defined carbon material. Such molecularly designed carbons are not only ideal model materials for fundamental science but also emerge in applications with until now unattained functionality. © 2017 Elsevier Ltd
view abstract 10.1016/j.mattod.2017.06.002
- Carbon Materials for Lithium Sulfur Batteries - Ten Critical Questions
Borchardt, L. and Oschatz, M. and Kaskel, S.
Chemistry - A European Journal 22 (2016)Lithium-sulfur batteries are among the most promising electrochemical energy storage devices of the near future. Especially the low price and abundant availability of sulfur as the cathode material and the high theoretical capacity in comparison to state-of-the art lithium-ion technologies are attractive features. Despite significant research achievements that have been made over the last years, fundamental (electro-) chemical questions still remain unanswered. This review addresses ten crucial questions associated with lithium-sulfur batteries and critically evaluates current research with respect to them. The sulfur-carbon composite cathode is a particular focus, but its complex interplay with other hardware components in the cell, such as the electrolyte and the anode, necessitates a critical discussion of other cell components. Modern in situ characterisation methods are ideally suited to illuminate the role of each component. This article does not pretend to summarise all recently published data, but instead is a critical overview over lithium-sulfur batteries based on recent research findings. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/chem.201600040
- Design of Hierarchically Porous Carbons with Interlinked Hydrophilic and Hydrophobic Surface and Their Capacitive Behavior
Hao, G.-P. and Zhang, Q. and Sin, M. and Hippauf, F. and Borchardt, L. and Brunner, E. and Kaskel, S.
Chemistry of Materials 28 (2016)In this contribution, we report a general surface engineering strategy to transform nonpolar nanocarbons (e.g., carbon nanotube and graphene) into amphiphilic nanocarbons with unique ultrahydrophilic@ultrahydrophobic surface configuration and hierarchical structure by grafting a thin layer of metal-organic frameworks followed by pyrolysis and leaching. The outer ultrahydrophilic carbon layer features rich surface heterogeneity (B-/N-doping both up to ca. 10 at. %) and high density of microporosity, while the inner nonpolar CNT or graphene provides a high electronic conductivity. The unique bipolar surface and high heterogeneity as well as highly accessible hierarchical structures render this family of nanocarbons capable of a high surface efficiency under both aqueous and organic conditions, as it is reflected in the behavior of the electrodes for supercapacitors by comparing a wide range of highly porous nonpolar carbons. The bipolar hierarchical carbons' efficiency in terms of areal capacitance and energy density are 3-6 times and 2-3 times higher than that of typical benchmark materials (e.g., commercially popular YP-50F carbons, CNT, and graphene etc.). More importantly, the study of this series of model carbon materials may help researchers to understand in-depth how carbon surface chemistry with a high density of doping sites influences the wetting, transport, and electrosorption behavior of charged ions in aqueous and organic conditions. © 2016 American Chemical Society.
view abstract 10.1021/acs.chemmater.6b03964
- Illuminating solid gas storage in confined spaces-methane hydrate formation in porous model carbons
Borchardt, L. and Nickel, W. and Casco, M. and Senkovska, I. and Bon, V. and Wallacher, D. and Grimm, N. and Krause, S. and Silvestre-Albero, J.
Physical Chemistry Chemical Physics 18 (2016)Methane hydrate nucleation and growth in porous model carbon materials illuminates the way towards the design of an optimized solid-based methane storage technology. High-pressure methane adsorption studies on pre-humidified carbons with well-defined and uniform porosity show that methane hydrate formation in confined nanospace can take place at relatively low pressures, even below 3 MPa CH4, depending on the pore size and the adsorption temperature. The methane hydrate nucleation and growth is highly promoted at temperatures below the water freezing point, due to the lower activation energy in ice vs. liquid water. The methane storage capacity via hydrate formation increases with an increase in the pore size up to an optimum value for the 25 nm pore size model-carbon, with a 173% improvement in the adsorption capacity as compared to the dry sample. Synchrotron X-ray powder diffraction measurements (SXRPD) confirm the formation of methane hydrates with a sI structure, in close agreement with natural hydrates. Furthermore, SXRPD data anticipate a certain contraction of the unit cell parameter for methane hydrates grown in small pores. © the Owner Societies 2016.
view abstract 10.1039/c6cp03993f
- Interactions Between Electrolytes and Carbon-Based Materials—NMR Studies on Electrical Double-Layer Capacitors, Lithium-Ion Batteries, and Fuel Cells
Oschatz, M. and Borchardt, L. and Hippauf, F. and Nickel, W. and Kaskel, S. and Brunner, E.
Annual Reports on NMR Spectroscopy 87 (2016)Electrical double-layer capacitors, lithium-ion batteries, and fuel cells are among the most important devices for storage and conversion of electrochemical energy. Further improvement of these systems and their single components is needed to meet the future requirements in terms of higher energy and power densities. In all of these devices, the interactions between carbonaceous materials and electrolyte components play crucial roles. In electrical double-layer capacitors and lithium-ion batteries, electrolyte ions get in direct contact with carbon electrode materials for energy storage. In fuel cells, carbon-supported electrode catalysts and polymeric membranes are among the most important components. For a directed improvement of these devices, a profound understanding of the processes taking place on the carbon–electrolyte interfaces is crucial. Especially nuclear magnetic resonance spectroscopy is qualified for the characterization of these interactions due to its chemical specificity, the local nature of NMR-relevant interactions, the possibility to investigate both amorphous and crystalline compounds, and the potential to monitor dynamic processes that occur over a wide timescale. This review addresses recent NMR spectroscopic investigations of the interactions between electrolytes and carbon materials in electrical double-layer capacitors, lithium-ion batteries, and fuel cells. Structures and properties of the most important carbon nanomaterials relevant for these devices are discussed, and the general principles of the electrochemical energy storage systems are introduced. Fundamental principles as well as hardware aspects of in situ and ex situ NMR measurements are addressed. The relationships between the properties of the carbon materials, the electrochemical characteristics, and the NMR data are explained. NMR spectroscopy as the profound analytical method is considered in combination with the operating principles of the electrochemical energy storage devices. © 2016 Elsevier Ltd
view abstract 10.1016/bs.arnmr.2015.08.003
- Mechanochemical polymerization-controlling a polycondensation reaction between a diamine and a dialdehyde in a ball mill
Grätz, S. and Borchardt, L.
RSC Advances 6 (2016)The mechanochemical polycondensation between a diamine and a dialdehyde constitutes a sustainable alternative to classical solvent-based polymerization reactions. This process not only allows for a higher conversion and a shorter reaction time as compared to standard solvent-based syntheses of this conjugated polymer, but the reaction can also be adjusted by the energy introduced via the ball mill. © The Royal Society of Chemistry 2016.
view abstract 10.1039/c6ra15677k
- Self-supporting hierarchical porous PtAg alloy nanotubular aerogels as highly active and durable electrocatalysts
Liu, W. and Haubold, D. and Rutkowski, B. and Oschatz, M. and Hübner, R. and Werheid, M. and Ziegler, C. and Sonntag, L. and Liu, S. and Zheng, Z. and Herrmann, A.-K. and Geiger, D. and Terlan, B. and Gemming, T. and Borchardt, L. and Kaskel, S. and Czyrska-Filemonowicz, A. and Eychmüller, A.
Chemistry of Materials 28 (2016)Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems. © 2016 American Chemical Society.
view abstract 10.1021/acs.chemmater.6b01394
- The Formation and Morphology of Nanoparticle Supracrystals
Haubold, D. and Reichhelm, A. and Weiz, A. and Borchardt, L. and Ziegler, C. and Bahrig, L. and Kaskel, S. and Ruck, M. and Eychmüller, A.
Advanced Functional Materials 26 (2016)Supracrystals are highly symmetrical ordered superstructures built up from nanoparticles (NPs) via self-assembly. While the NP assembly has been intensively investigated, the formation mechanism is still not understood. To shed some light onto the formation mechanism, one of the most common supracrystal morphologies, the trigonal structures, as a model system is being used to investigate the formation process in solution. To explain the formation of the trigonal structures and determining the size of the supracrystal seeds formed in solution, the concept of substrate-affected growth is introduced. Furthermore, the influence of the NP concentration on the seed size is shown and our investigations from Ag toward Au are extended. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/adfm.201600186
- The Importance of Pore Size and Surface Polarity for Polysulfide Adsorption in Lithium Sulfur Batteries
Hippauf, F. and Nickel, W. and Hao, G.-P. and Schwedtmann, K. and Giebeler, L. and Oswald, S. and Borchardt, L. and Doerfler, S. and Weigand, J.J. and Kaskel, S.
Advanced Materials Interfaces 3 (2016)Polysulfide shuttling is a crucial factor in lithium sulfur batteries responsible for capacity fading and degradation. Liquid phase adsorption in combination with nuclear magnetic resonance and X-ray photoelectron spectroscopy are used to elucidate and quantify polysulfide retention in typical porous cathode materials used in lithium sulfur batteries without cell assembly to achieve a more fundamental understanding of liquid phase adsorption phenomena as a responsible mechanism for polysulfide retention. The individual impact of each pore size increment is quantified on the polysulfide adsorption (PSA). Ultramicropores show eight times higher PSA (1.48 mmol cm−3) than mesopores. Strong heteroatom-doped ultramicropores show even stronger interactions with polysulfides leading to 25 times higher adsorption compared to hydrophobic mesopores. These findings allow to precisely tailor pore structure and heteroatom distribution of cathode materials for next generation lithium sulfur batteries with prolonged cycle life and reduced capacity fading. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/admi.201600508
- Towards a continuous adsorption process for the enrichment of ACE-inhibiting peptides from food protein hydrolysates
Hippauf, F. and Huettner, C. and Lunow, D. and Borchardt, L. and Henle, T. and Kaskel, S.
Carbon 107 (2016)Bioactive peptides such as Ile-Trp show great potential as natural ACE (angiotensin-converting-enzyme)-inhibitors. A continuous process for the up-scaled enrichment of ACE-inhibiting peptides based on a columnar adsorber system with an activated carbon stationary phase was developed. The particle size of the adsorbent and the flow rate was investigated as key factors affecting adsorption kinetics and separation performance. Batch and column adsorption experiments of model adsorbate systems were successfully transferred to a more complex system of an α-lactalbumin hydrolysate containing a multitude of species. Ile-Trp was successfully enriched from the hydrolysate by a factor of 4 using the optimized carbon column. The enrichment was more selective using smaller adsorbent particles due to improved adsorption kinetics. © 2016 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2016.05.062
- ZnPd/ZnO Aerogels as Potential Catalytic Materials
Ziegler, C. and Klosz, S. and Borchardt, L. and Oschatz, M. and Kaskel, S. and Friedrich, M. and Kriegel, R. and Keilhauer, T. and Armbrüster, M. and Eychmüller, A.
Advanced Functional Materials 26 (2016)Many different aerogel materials are known to be accessible via the controlled destabilization of the respective nanoparticle suspensions. Especially for applications in heterogeneous catalysis such materials with high specific surface areas are highly desirable. Here, a facile method to obtain a mixed ZnPd/ZnO aerogel via a reductive treatment of a preformed Pd/ZnO aerogel is presented. Different morphologies of the Pd/ZnO aerogels could be achieved by controlling the destabilization of the ZnO sol. All aerogels show a high CO2 selectivity of up to 96% and a very good activity in methanol steam reforming that delivers hydrogen, which is one of the most important fuels for future energy concepts. The method presented is promising for different transition metal/metal oxide systems and hence opens a path to a huge variety of materials. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adfm.201503000
- Emulsion soft templating of carbide-derived carbon nanospheres with controllable porosity for capacitive electrochemical energy storage
Oschatz, M. and Zeiger, M. and Jäckel, N. and Strubel, P. and Borchardt, L. and Reinhold, R. and Nickel, W. and Eckert, J. and Presser, V. and Kaskel, S.
Journal of Materials Chemistry A 3 (2015)A new approach to produce highly porous carbide-derived carbon nanospheres of 20-200 nm diameter based on a novel soft-templating technique is presented. A platinum catalyst is used for the cross-linking of liquid (allylhydrido)polycarbosilane polymer chains with para-divinylbenzene within oil-in-water miniemulsions. Quantitative implementation of the pre-ceramic polymer can be achieved allowing precise control over the resulting materials. After pyrolysis and high-temperature chlorine treatment, the resulting particles offer a spherical shape, very high specific surface area (up to 2347 m2 g-1), and large micro/mesopore volume (up to 1.67 cm3 g-1). The internal pore structure of the nanospheres is controllable by the composition of the oil phase within the miniemulsions. The materials are highly suitable to be used as supercapacitor electrodes with high specific capacitances in aqueous 1 M Na2SO4 solution (110 F g-1) and organic 1 M tetraethylammonium tetrafluoroborate in acetonitrile (130 F g-1). © The Royal Society of Chemistry 2015.
view abstract 10.1039/c5ta03730a
- Enhancing ACE-inhibition of food protein hydrolysates by selective adsorption using porous carbon materials
Hippauf, F. and Lunow, D. and Huettner, C. and Nickel, W. and Borchardt, L. and Henle, T. and Kaskel, S.
Carbon 87 (2015)Bioactive peptides from food proteins such as natural ACE (angiotensin-converting enzyme)-inhibitors have attracted particular attention for their potential to prevent hypertension. ACE-inhibiting peptides were enriched from food protein hydrolysates prepared from α-lactalbumin and lysozyme by selective adsorption on microporous activated carbons. For the eluate, it was shown by liquid chromatography that the strongest inhibitor isoleucyl-tryptophan was enriched by a factor of 11.2 compared to the initial α-lactalbumin hydrolysate. Natural inhibitors derived from lysozyme hydrolysates (e.g., alanyl-tryptophan) were successfully enriched as well. Identification of the enriched peptide fraction by mass spectroscopy revealed the hydrophobic character of the enriched peptides. The molecular weight distribution of the enriched peptide fraction can be controlled by the pore size distribution of the chosen adsorbent, which was proven by size exclusion chromatography of enriched peptide fractions derived from three different model carbons differing in their pore size. The selective enrichment of natural ACE-inhibitors from the α-lactalbumin hydrolysate lead to a 6 times stronger in vitro ACE-inhibition demonstrating the high potential as ingredients for hypotensive functional foods with reduced side effects. © 2015 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2015.02.023
- Nanoporous Carbide-Derived Carbons as Electrode Materials in Electrochemical Double-Layer Capacitors
Oschatz, M. and Borchardt, L. and Hao, G. and Kaskel, S.
Nanocarbons for Advanced Energy Storage 1 (2015)Among the diverse established electrochemical energy storage systems, electrochemical double-layer capacitors (EDLCs) stand out due to their high power densities and ultra-long cycle life. The key components of EDLCs are the carbonaceous electrodes where the charge accumulation takes place by the electrosorption of electrolyte ions. It is of crucial importance to use carbon materials with well-defined pore architecture and therefore many different approaches for their synthesis have been developed. Traditional high-surface area carbon materials such as activated carbons often exhibit wormlike or ink-bottle shaped pores hindering efficient ion adsorption and therefore do not lead to optimized performance. Carbon materials obtained from carbide precursors (denoted as carbide-derived carbons, CDCs) received considerable attention in EDLC systems due to their precisely controllable and well-defined pore structure. CDCs show great promise as electrode materials and are highly suitable model substances for the investigation of fundamental mechanisms of EDLC operation. This chapter addresses the most important aspects of CDC synthesis and their use as advanced electrode materials in EDLCs. Besides the fundamental mechanisms of carbide-to-carbon transformation and the various accessible morphologies of these materials, current attempts to tune pore structure of CDCs from the micropore level, over mesopores to macropores and even external or inter-particular porosity are presented and discussed. The chapter provides an overview about the use of CDC materials as EDLC electrodes, and the influences of different parameters such as the carbon material and the device design are critically evaluated. Recent investigations on the electrosorption mechanisms in EDLCs based on CDC electrodes, which lead to important insights into the fundamental principles of these systems, are also part of this chapter. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.
view abstract 10.1002/9783527680054.ch15
- Structuring zeolite bodies for enhanced heat-transfer properties
Borchardt, L. and Michels, N.-L. and Nowak, T. and Mitchell, S. and Pérez-Ramírez, J.
Microporous and Mesoporous Materials 208 (2015)The predominantly insulating nature of zeolites, as many classes of porous catalysts, can severely impair heat transfer and hence their performance in industrial processes. Strategies developed to engineer the thermophysical properties of technical zeolites for fixed-bed applications comprise the use of conductive secondary phases as structured catalyst supports or as inert diluents. However, the impact of integrating conductive additives into composite zeolite bodies (pellets, extrudates, or granules) has not been widely explored. Here, using a transient hot-plate technique to decouple the distinct contributions of porosity, sample hydration, and temperature, we quantify the impact of metallic (copper), ceramic (silicon carbide, aluminum nitride, boron nitride), and carbonaceous (graphite, carbon nanotubes) phases on the thermal conductivity of shaped zeolites at the body and packed-bed scales. The decisive role of particle morphology, dominating over the intrinsic conductivity of an additive, is corroborated through the three-dimensional reconstruction of data acquired by focused ion beam-scanning electron microscopy and X-ray microtomography coupled with in-situ thermographic studies. In particular, the order-of-magnitude improvement evidenced on application of graphite sheets stems from the extended paths of low thermal resistance created in the millimeter-sized catalyst ensemble. Through the identification of structure-property relations, our approach provides new insights into the rational design of composite porous materials with enhanced heat-transfer properties. © 2015 Elsevier Inc.
view abstract 10.1016/j.micromeso.2015.01.028
- Trimodal hierarchical carbide-derived carbon monoliths from steam- and CO2-activated wood templates for high rate lithium sulfur batteries
Adam, M. and Strubel, P. and Borchardt, L. and Althues, H. and Dörfler, S. and Kaskel, S.
Journal of Materials Chemistry A 3 (2015)Hierarchically structured biomorphic carbide-derived carbon (CDC) materials are obtained by applying a combined activation- and CDC approach on abundantly available, renewable and cheap raw materials. For the synthesis of these materials we mimic nature by using wood structures as templates which are already optimized for mass transport during their long-term evolutional process. The impregnation of steam- or carbon dioxide-pre-activated wood templates with a polycarbosilane precursor and the subsequent halogen treatment yields a hierarchical material that exhibits longitudinally orientated macropores from the wood structure as well as well-defined and narrowly distributed micro- and meso-pores derived from the activation and CDC approach. These materials offer specific surface areas up to 1750 m2 g-1, micro-/meso-pore volumes up to 1.0 cm3 g-1 and macropore volumes of 1.2 cm3 g-1. This sophisticated hierarchical pore system ensures both efficient mass transfer and high specific surface area, ideal for mass transport limited applications, such as the lithium sulfur battery. Testing steam activated wood-CDCs as cathode materials for Li-S batteries reveals excellent performance, especially a highly stable discharge capacity and sulfur utilization. Stable capacities of over 580 mA h gsulfur-1 at current densities exceeding 20 mA cm-2 (2C) are possible using only very low amounts of electrolyte of 6.8 μL mgsulfur-1. © 2015 The Royal Society of Chemistry.
view abstract 10.1039/c5ta06782k
- A hard-templating route towards ordered mesoporous tungsten carbide and carbide-derived carbons
Borchardt, L. and Oschatz, M. and Graetz, S. and Lohe, M.R. and Rümmeli, M.H. and Kaskel, S.
Microporous and Mesoporous Materials 186 (2014)Ordered mesoporous tungsten carbide materials are synthesized via a nanocasting approach starting from hexagonal (SBA-15) and cubic (KIT-6) ordered silica templates. A tungsten chloride/sucrose precursor is converted into the desired ceramic by a thermal treatment in hydrogen and argon within the pores of the templates. The resulting materials show high BET surface areas and specific pore volumes of 431 m2/g and 0.53 cm3/g, respectively. They can be further converted to carbide-derived carbons (CDC) by metal atom extraction using hot chlorine gas. The ordered structure of the carbide matrix can be fully retained and the BET surface area and pore volume are noticeably enhanced to high values of 1246 m2/g and 1.63 cm3/g, respectively. © 2013 Elsevier Inc. All rights reserved.
view abstract 10.1016/j.micromeso.2013.12.009
- Controlling the growth of palladium aerogels with high-performance toward bioelectrocatalytic oxidation of glucose
Wen, D. and Herrmann, A.-K. and Borchardt, L. and Simon, F. and Liu, W. and Kaskel, S. and Eychmüller, A.
Journal of the American Chemical Society 136 (2014)We report the controllable synthesis of Pd aerogels with high surface area and porosity by destabilizing colloidal solutions of Pd nanoparticles with variable concentrations of calcium ions. Enzyme electrodes based on Pd aerogels co-immobilized with glucose oxidase show high activity toward glucose oxidation and are promising materials for applications in bioelectronics. © 2014 American Chemical Society.
view abstract 10.1021/ja412062e
- Evolution of porosity in carbide-derived carbon aerogels
Oschatz, M. and Nickel, W. and Thommes, M. and Cychosz, K.A. and Leistner, M. and Adam, M. and Mondin, G. and Strubel, P. and Borchardt, L. and Kaskel, S.
Journal of Materials Chemistry A 2 (2014)Carbide-derived carbon (CDC) aerogel monoliths with very high porosity are synthesized starting from polymeric precursors. Cross-linking by platinum-catalyzed hydrosilylation of polycarbosilanes followed by supercritical drying yields preceramic aerogels. After ceramic conversion and silicon extraction in hot chlorine gas, hierarchically porous carbon materials with specific surface areas as high as 2122 m2 g-1 and outstanding total pore volumes close to 9 cm3 g-1 are obtained. Their pore structure is controllable by the applied synthesis temperature as shown by combined nitrogen (-196 °C) and carbon dioxide (0 °C) measurements coupled with electron microscopic methods. The combination of large micropore volumes and the aerogel-type pore system leads to advanced adsorption properties due to a combination of large storage capacities and effective materials transport in comparison with purely microporous reference materials as shown by thermal response measurements. This journal is © the Partner Organisations 2014.
view abstract 10.1039/c4ta03401e
- Extraction of ACE-inhibiting dipeptides from protein hydrolysates using porous carbon materials
Hippauf, F. and Lunow, D. and Borchardt, L. and Henle, T. and Kaskel, S.
Carbon 77 (2014)This study reports on the extraction of strongly angiotensin-converting enzyme (ACE) inhibiting dipeptides from protein hydrolysates obtained by enzymatic proteolysis. Several dipeptides with different ACE inhibitory activities and hydrophobicities were investigated regarding to their adsorption affinity on commercially available activated carbon material Norit DLC Super 50. This porous carbon exhibits extremely high adsorption capacities for the strongest ACE inhibitor Ile-Trp (IC50 = 0.7 μM) of 726 mg/g as well as fast adsorption kinetics due to its micropore structure and small particle size. The filling of the pores was monitored by N2- physisorption revealing that complete pore filling occurred and Ile-Trp adsorption was only limited by the specific pore volume of Norit DLC Super 50, whereas less active peptides were adsorbed less efficient due to their higher hydrophobicity and did not impact Ile-Trp adsorption. After the adsorption, Ile-Trp was recovered by elution with ethanol. Three protein hydrolysates obtained by different enzyme combinations were mixed with activated carbon and the peptide adsorption was investigated by RP-HPLC. The amount of Trp-containing and ACE-inhibiting short chain peptides decreased selectively in contrast to more polar peptides, but the amount of adsorbed Ile-Trp is smaller than for single component adsorption. © 2014 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2014.05.021
- Hierarchical carbide-derived carbon foams with advanced mesostructure as a versatile electrochemical energy-storage material
Oschatz, M. and Borchardt, L. and Pinkert, K. and Thieme, S. and Lohe, M.R. and Hoffmann, C. and Benusch, M. and Wisser, F.M. and Ziegler, C. and Giebeler, L. and Rümmeli, M.H. and Eckert, J. and Eychmüller, A. and Kaskel, S.
Advanced Energy Materials 4 (2014)Highly porous carbide-derived carbon (CDC) mesofoams (DUT-70) are prepared by nanocasting of mesocellular silica foams with a polycarbosilane precursor. Ceramic conversion followed by silica removal and high-temperature chlorine treatment yields CDCs with a hierarchical micro-mesopore arrangement. This new type of polymer-based CDC is characterized by specific surface areas as high as 2700 m2 g-1, coupled with ultrahigh micro- and mesopore volumes up to 2.6 cm3 g-1. The relationship between synthesis conditions and the properties of the resulting carbon materials is described in detail, allowing precise control of the properties of DUT-70. Since the hierarchical pore system ensures both efficient mass transfer and high capacities, the novel CDC shows outstanding performance as an electrode material in electrochemical double-layer capacitors (EDLCs) with specific capacities above 240 F g-1 when measured in a symmetrical two-electrode configuration. Remarkable capacities of 175 F g-1 can be retained even at high current densities of 20 A g-1 as a result of the enhanced ion-transport pathways provided by the cellular mesostructure. Moreover, DUT-70 can be infiltrated with sulfur and host the active material in lithium-sulfur battery cathodes. Reversible capacities of 790 mAh g-1 are achieved at a current rate of C/10 after 100 cycles, which renders DUT-70 an ideal support material for electrochemical energy-storage applications. Hierarchical carbide-derived carbon (CDC) mesofoams (DUT-70) with extremely high specific surface areas and nanopore volumes are presented. DUT-70 shows outstanding specific capacities as electrode materials in electrochemical double-layer capacitors and as sulfur host in lithium-sulfur battery cathodes. This CDC is an advanced material for electrochemical energy storage, combining high capacities with efficient mass-transfer behavior. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/aenm.201300645
- Hydrogen production from catalytic decomposition of methane over ordered mesoporous carbons (CMK-3) and carbide-derived carbon (DUT-19)
Shilapuram, V. and Ozalp, N. and Oschatz, M. and Borchardt, L. and Kaskel, S.
Carbon 67 (2014)This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbidederived carbon (DUT-19) as catalysts. X-ray diffraction and N2 physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187 kJ/mol for CMK-3 and 196 kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition. © 2013 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2013.10.008
- Kroll-carbons based on silica and alumina templates as high-rate electrode materials in electrochemical double-layer capacitors
Oschatz, M. and Boukhalfa, S. and Nickel, W. and Lee, J.T. and Klosz, S. and Borchardt, L. and Eychmüller, A. and Yushin, G. and Kaskel, S.
Journal of Materials Chemistry A 2 (2014)Hierarchical Kroll-carbons (KCs) with combined micro- and mesopore systems are prepared from silica and alumina templates by a reductive carbochlorination reaction of fumed silica and alumina nanoparticles inside a dense carbon matrix. The resulting KCs offer specific surface areas close to 2000 m2 g-1 and total pore volumes exceeding 3 cm3 g-1, resulting from their hierarchical pore structure. High micropore volumes of 0.39 cm3 g-1 are achieved in alumina-based KCs due to the enhanced carbon etching reaction being mainly responsible for the evolution of porosity. Mesopore sizes are uniform and precisely controllable over a wide range by the template particle dimensions. The possibility of directly recycling the process exhaust gases for the template synthesis and the use of renewable carbohydrates as the carbon source lead to a scalable and efficient alternative to classical hard- and soft templating approaches for the production of mesoporous and hierarchical carbon materials. Silica- and alumina-based Kroll-carbons are versatile electrode materials in electrochemical double-layer capacitors (EDLCs). Specific capacitances of up to 135 F g-1 in an aqueous electrolyte (1 M sulfuric acid) and 174 F g-1 in ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) are achieved when measured in a symmetric cell configuration up to voltages of 0.6 and 2.5 V, respectively. 90% of the capacitance can be utilized at high current densities (20 A g -1) and room temperature rendering Kroll-carbons as attractive materials for EDLC electrodes resulting in high capacities and high rate performance due to the combined presence of micro- and mesopores. This journal is © the Partner Organisations 2014.
view abstract 10.1039/c3ta14815g
- Micro- and mesoporous carbide-derived carbon prepared by a sacrificial template method in high performance lithium sulfur battery cathodes
Oschatz, M. and Lee, J.T. and Kim, H. and Nickel, W. and Borchardt, L. and Cho, W.I. and Ziegler, C. and Kaskel, S. and Yushin, G.
Journal of Materials Chemistry A 2 (2014)Polymer-based carbide-derived carbons (CDCs) with combined micro- and mesopores are prepared by an advantageous sacrificial templating approach using poly(methylmethacrylate) (PMMA) spheres as the pore forming material. Resulting CDCs reveal uniform pore size and pore shape with a specific surface area of 2434 m2 g-1 and a total pore volume as high as 2.64 cm3 g-1. The bimodal CDC material is a highly attractive host structure for the active material in lithium-sulfur (Li-S) battery cathodes. It facilitates the utilization of high molarity electrolytes and therefore the cells exhibit good rate performance and stability. The cathodes in the 5 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte show the highest discharge capacities (up to 1404 mA h gs-1) and capacity retention (72% after 50 cycles at C/5). The unique network structure of the carbon host enables uniform distribution of sulfur through the conductive media and at the same time it facilitates rapid access for the electrolyte to the active material. This journal is © the Partner Organisations 2014.
view abstract 10.1039/c4ta03327b
- Multimetallic aerogels by template-free self-assembly of Au, Ag, Pt, and Pd nanoparticles
Herrmann, A.-K. and Formanek, P. and Borchardt, L. and Klose, M. and Giebeler, L. and Eckert, J. and Kaskel, S. and Gaponik, N. and Eychmüller, A.
Chemistry of Materials 26 (2014)Nanostructured, porous metals are of great interest for material scientists since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior, and size-enhanced catalytic reactivity. Here we present the formation of multimetallic porous three-dimensional networks by a template-free self-assembly process. Nanochains are formed by the controlled coalescence of Au, Ag, Pt, and Pd nanoparticles in aqueous media, and their interconnection and interpenetration leads to the formation of a self-supporting network. The resulting noble-metal-gels are transformed into solid aerogels by the supercritical drying technique. Compared to previously reported results, the technique is facilitated by exclusion of additional destabilizers. Moreover, temperature control is demonstrated as a powerful tool, allowing acceleration of the gelation process as well as improvement of its reproducibility and applicability. Electron microscopy shows the nanostructuring of the network and its high porosity. XRD and EDX STEM are used to investigate the alloying behavior of the bimetallic aerogels and prove the control of the alloying state by temperature induced phase modifications. Furthermore, the resulting multimetallic aerogels show an extremely low relative density (<0.2%) and a very high surface area (>50 m2/g) compared to porous noble metals obtained by other approaches. Electrically conductive thin films as well as hybrid materials with organic polymers are depicted to underline the processability of the materials, which is a key factor regarding handling of the fragile structures and integration into device architectures. Owing to their exceptional and tunable properties, multimetallic aerogels are very promising materials for applications in heterogeneous catalysis and electrocatalysis, hydrogen storage, and sensor systems but also in surface enhanced Raman spectroscopy (SERS) and the preparation of transparent conductive substrates. © 2013 American Chemical Society.
view abstract 10.1021/cm4033258
- Rediscovering zeolite mechanochemistry-A pathway beyond current synthesis and modification boundaries
Majano, G. and Borchardt, L. and Mitchell, S. and Valtchev, V. and Pérez-Ramírez, J.
Microporous and Mesoporous Materials 194 (2014)The search for new and improved methods to synthesize and modify zeolites remains a topic of central academic and industrial relevance. The current reliance on solvent-based methods imposes several drawbacks, including the need for subsequent workup steps and the copious generation of liquid waste. Providing a solvent-and process-efficient, but also a mechanistically-distinct route, mechanochemistry has been postulated as a scalable, one-step approach to overcome these limitations. Uniting essential studies in the field, this perspective explores the potential of mechanochemical methods to contribute to zeolite and zeotype material research. Particular emphasis is given to framework interactions associated with post-synthetic modifications. In addition to the archetypal crystal/particle size reduction, these include the introduction of functionalities by framework activation or ion exchange as well as the moderation of the type, density, and accessibility of active sites by controlled amorphization. The interesting prospects for zeolite catalysis are also discussed. We devise directions to construct a basic understanding of the underlying mechanisms in zeolite-related mechanochemistry, which we expect will broaden its applicability and facilitate the laboratory-to-industry transition. © 2014 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.micromeso.2014.04.006
- Role of surface functional groups in ordered mesoporous carbide-derived carbon/ionic liquid electrolyte double-layer capacitor interfaces
Pinkert, K. and Oschatz, M. and Borchardt, L. and Klose, M. and Zier, M. and Nickel, W. and Giebeler, L. and Oswald, S. and Kaskel, S. and Eckert, J.
ACS Applied Materials and Interfaces 6 (2014)Ordered mesoporous carbide-derived carbon (OM-CDC) with a specific surface area as high as 2900 m2 g-1 was used as a model system in a supercapacitor setup based on an ionic liquid (IL; 1-ethyl-3-methylimidazolium tetrafluoroborate) electrolyte. Our study systematically investigates the effect of surface functional groups on IL-based carbon supercapacitors. Oxygen and chlorine functionalization was achieved by air oxidation and chlorine treatment, respectively, to introduce well-defined levels of polarity. The latter was analyzed by means of water physisorption isotherms at 298 K, and the functionalization level was quantified with X-ray photoelectron spectroscopy. While oxygen functionalization leads to a decreased capacitance at higher power densities, surface chlorination significantly improves the rate capability. A high specific capacitance of up to 203 F g-1 was observed for a chlorinated OM-CDC sample with a drastically increased rate capability in a voltage range of ±3.4 V. © 2014 American Chemical Society.
view abstract 10.1021/am4055029
- Structural characterization of micro- and mesoporous carbon materials using in situ high pressure 129Xe NMR spectroscopy
Oschatz, M. and Hoffmann, H.C. and Pallmann, J. and Schaber, J. and Borchardt, L. and Nickel, W. and Senkovska, I. and Rico-Francés, S. and Silvestre-Albero, J. and Kaskel, S. and Brunner, E.
Chemistry of Materials 26 (2014)In situ high pressure 129Xe NMR spectroscopy in combination with volumetric adsorption measurements were used for the textural characterization of different carbon materials with well-defined porosity including microporous carbide-derived carbons, ordered mesoporous carbide-derived carbon, and ordered mesoporous CMK-3. Adsorption/desorption isotherms were measured also by NMR up to relative pressures close to p/p0 = 1 at 237 K. The 129Xe NMR chemical shift of xenon adsorbed in porous carbons is found to be correlated with the pore size in analogy to other materials such as zeolites. In addition, these measurements were performed loading the samples with n-nonane. Nonane molecules preferentially block the micropores. However, 129Xe NMR spectroscopy proves that the nonane also influences the mesopores, thus providing information about the pore system in hierarchically structured materials. © 2014 American Chemical Society.
view abstract 10.1021/cm501102y
- Tailoring porosity in carbon materials for supercapacitor applications
Borchardt, L. and Oschatz, M. and Kaskel, S.
Materials Horizons 1 (2014)Within the different available electrochemical energy storage systems, supercapacitors stand out due to their high power densities and ultra-long cycle life. Their key-components are the electrode materials where the charge accumulation takes place and therefore many different approaches for the synthesis of carbonaceous electrode structures with well-defined pore systems are available. This review focuses on different strategies for tailoring porous carbon materials from the micropore level, over mesopores to macropores and even external or inter-particular porosity. A wide range of materials such as activated carbons, templated carbons, carbide-derived carbons, carbon nanotubes, carbon aerogels, carbon onions, graphenes and carbon nanofibers are presented, always in relation to their pore structure and potential use in supercapacitor devices. © The Royal Society of Chemistry 2015.
view abstract 10.1039/c3mh00112a
- Thermogravimetric analysis of activated carbons, ordered mesoporous carbide-derived carbons, and their deactivation kinetics of catalytic methane decomposition
Shilapuram, V. and Ozalp, N. and Oschatz, M. and Borchardt, L. and Kaskel, S. and Lachance, R.
Industrial and Engineering Chemistry Research 53 (2014)This study presents the deactivation kinetics of methane decomposition for the activated carbons Fluka-05105 and Fluka-05120, ordered mesoporous carbon (CMK-3), and ordered mesoporous carbide-derived carbon (DUT-19). The experimental and thermodynamically predicted carbon deposition, the average and total hydrogen production, and the effect of flow rate on carbon formation rate of these catalysts were investigated. Results indicate that the experimental conditions chosen were within the reaction control regime. Catalytic activity was calculated via two different definitions present in literature: one in terms of carbon deposition rate and the other in terms of carbon mass deposited. Deactivation kinetics were obtained by fitting the experimental data by nonlinear regression analysis. Differences between the two methods in determining activity resulted in significant changes in the estimation of deactivation kinetics. The activity calculated based on the rate method results in the best fit of experimentally collected data. A deactivation order and methane concentration dependency of approximately 1.0 and 0.5 were determined for all the catalysts tested (Fluka-05105, Fluka-05120, CMK-3, and DUT-19). The activation energy of deactivation (Ed) was determined to be 192, 154, 166, and 181 kJ/mol for Fluka-05120, Fluka-05105, CMK-3, and DUT-19, respectively. DUT-19 was the best performing catalyst in terms of carbon formation rate, total carbon production, hydrogen production rate, average hydrogen production, and total hydrogen production. © 2013 American Chemical Society.
view abstract 10.1021/ie402195q
- A new route for the preparation of mesoporous carbon materials with high performance in lithium–sulphur battery cathodes
Oschatz, M. and Thieme, S. and Borchardt, L. and Lohe, M.R. and Biemelt, T. and Brückner, J. and Althues, H. and Kaskel, S.
Chemical Communications 49 (2013)A novel method for the preparation of highly mesoporous carbon materials (Kroll-Carbons; KCs) is described based on reactive carbochlorination etching of titania nanoparticles inside a dense carbon matrix leading to mesoporous carbons with precisely controllable porosity and high performance as cathode materials for lithium–sulphur (Li–S) batteries. © 2013 The Royal Society of Chemistry.
view abstract 10.1039/c3cc42841a
- Bimetallic aerogels: High-performance electrocatalysts for the oxygen reduction reaction
Liu, W. and Rodriguez, P. and Borchardt, L. and Foelske, A. and Yuan, J. and Herrmann, A.-K. and Geiger, D. and Zheng, Z. and Kaskel, S. and Gaponik, N. and Kötz, R. and Schmidt, T.J. and Eychmüller, A.
Angewandte Chemie - International Edition 52 (2013)Best of both worlds: PtxPdy, Pt, and Pd aerogels with high surface area and porosity can be synthesized in a controlled fashion by a straightforward and environmentally benign strategy. These materials, which are highly active and stable catalysts for the oxygen reduction reaction in PEFC cathodes, combine the high stability of extended surfaces with the high surface area of nanoparticles. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201303109
- Carbon dioxide activated carbide-derived carbon monoliths as high performance adsorbents
Oschatz, M. and Borchardt, L. and Senkovska, I. and Klein, N. and Leistner, M. and Kaskel, S.
Carbon 56 (2013)Carbide-derived carbon (CDC) monoliths (DUT-38) with a distinctive macropore network are physically activated using carbon dioxide as oxidizing agent. This procedure is carried out in a temperature range between 850 and 975 °C with durations ranging from 2 to 6 h. Resulting materials show significantly increased specific surface areas as high as 3100 m2/g and total (micro/meso) pore volumes of more than 1.9 cm3/g. The methane (214 mg/g at 80 bar/25 °C), hydrogen (55.6 mg/g at 40 bar/-196 °C), and n-butane (860 mg/g at 77 vol.%/25 °C) storage capacities of the activated CDCs are significantly higher as compared to the non-activated reference material. Moreover, carbon dioxide activation is a suitable method for the removal of metal chlorides and chlorine residuals adsorbed in the pores of CDC after high temperature chlorination. The activation does not influence the hydrophobic surface properties of the CDCs as determined by water adsorption experiments. The macropore network and the monolithic shape of the starting materials can be fully preserved during the activation procedure. n-Butane breakthrough studies demonstrate the materials applicability as an efficient hydrophobic filter material by combining excellent materials transport with some of the highest capacity values that have ever been reported for CDCs. © 2013 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2012.12.084
- Direct prediction of the desalination performance of porous carbon electrodes for capacitive deionization
Porada, S. and Borchardt, L. and Oschatz, M. and Bryjak, M. and Atchison, J.S. and Keesman, K.J. and Kaskel, S. and Biesheuvel, P.M. and Presser, V.
Energy and Environmental Science 6 (2013)Desalination by capacitive deionization (CDI) is an emerging technology for the energy- and cost-efficient removal of ions from water by electrosorption in charged porous carbon electrodes. A variety of carbon materials, including activated carbons, templated carbons, carbon aerogels, and carbon nanotubes, have been studied as electrode materials for CDI. Using carbide-derived carbons (CDCs) with precisely tailored pore size distributions (PSD) of micro- and mesopores, we studied experimentally and theoretically the effect of pore architecture on salt electrosorption capacity and salt removal rate. Of the reported CDC-materials, ordered mesoporous silicon carbide-derived carbon (OM SiC-CDC), with a bimodal distribution of pore sizes at 1 and 4 nm, shows the highest salt electrosorption capacity per unit mass, namely 15.0 mg of NaCl per 1 g of porous carbon in both electrodes at a cell voltage of 1.2 V (12.8 mg per 1 g of total electrode mass). We present a method to quantify the influence of each pore size increment on desalination performance in CDI by correlating the PSD with desalination performance. We obtain a high correlation when assuming the ion adsorption capacity to increase sharply for pore sizes below one nanometer, in line with previous observations for CDI and for electrical double layer capacitors, but in contrast to the commonly held view about CDI that mesopores are required to avoid electrical double layer overlap. To quantify the dynamics of CDI, we develop a two-dimensional porous electrode modified Donnan model. For two of the tested materials, both containing a fair degree of mesopores (while the total electrode porosity is ∼95 vol%), the model describes data for the accumulation rate of charge (current) and salt accumulation very well, and also accurately reproduces the effect of an increase in electrode thickness. However, for TiC-CDC with hardly any mesopores, and with a lower total porosity, the current is underestimated. Calculation results show that a material with higher electrode porosity is not necessarily responding faster, as more porosity also implies longer transport pathways across the electrode. Our work highlights that a direct prediction of CDI performance both for equilibrium and dynamics can be achieved based on the PSD and knowledge of the geometrical structure of the electrodes. © 2013 The Royal Society of Chemistry.
view abstract 10.1039/c3ee42209g
- Functionalised porous nanocomposites: A multidisciplinary approach to investigate designed structures for supercapacitor applications
Pinkert, K. and Giebeler, L. and Herklotz, M. and Oswald, S. and Thomas, J. and Meier, A. and Borchardt, L. and Kaskel, S. and Ehrenberg, H. and Eckert, J.
Journal of Materials Chemistry A 1 (2013)The rational design of nanocomposite structures with specific functions in energy storage applications is a key requisite to increase energy and power density in electrical storage systems. Nanoscale characterisation tools are essential to achieve controlled syntheses of such well-defined interface structures in order to reveal structure-property relationships in functional nanocomposites. In the following, we report on the synthesis of iron (hydr)oxide nanoparticles homogeneously embedded into the walls of the three dimensional carbon network of mesoporous carbon CMK-3 via a mild one-step redox functionalisation. Depth profile Auger electron spectroscopy (DP-AES) and energy filtered transmission electron microscopy (EF-TEM) are applied to analyse elemental distribution profiles and location of the active components. The combination of the two analytical techniques provides a highly resolved spatial distribution of transition metal (hydr)oxide nanoparticles inside the carbon network. Functionalised porous carbon nanocomposites were tested for supercapacitor applications and the highest energy density of an iron oxide carbon composite is demonstrated. The iron (hydr)oxide contributes with a pseudocapacitance of 357 F g-1 to the porous nanocomposite in a 6 M KOH electrolyte. An overall doubling of the specific capacitance of the active electrode material compared to the pristine CMK-3 is achieved. © The Royal Society of Chemistry 2013.
view abstract 10.1039/c3ta00118k
- High capacity micro-mesoporous carbon-sulfur nanocomposite cathodes with enhanced cycling stability prepared by a solvent-free procedure
Thieme, S. and Brückner, J. and Bauer, I. and Oschatz, M. and Borchardt, L. and Althues, H. and Kaskel, S.
Journal of Materials Chemistry A 1 (2013)The use of elemental sulfur as a cathode active material is challenging. Besides the complex electrochemical conversion mechanism there are negative side effects added to the system by application of solvent-based cathode preparation, such as chemical incompatibility caused by solvent contamination, sulfur evaporation and morphology change during drying as well as limited active material loading. Therefore we present a solvent-free, highly versatile pressing/thermal treatment method for the fast and reproducible production of mechanically stable and highly flexible freestanding carbon-sulfur composite cathode foils with tunable sulfur loading, high in-plane conductivity and enhanced cycling stability. Utilizing an optimized cathode composition consisting of sulfur, a porous carbon host material and a carbon nanotube conducting agent, a stable capacity >740 mA h g-1-S as well as high coulombic efficiency >96% was achieved over 160 cycles in our experiments at a moderate rate of C/10. Moreover, reversible cycling was possible up to a high rate of 1C due to the tuned carbon matrix properties as well as the highly conductive carbon nanotube percolation network. Thus not only a long-lasting electrical contact to insulating sulfur precipitates is provided but also the agglomeration of active material is restrained. To achieve even higher energy densities and improved corrosion resistance, the application of highly conductive freestanding cathode foils without a metallic current collector is a promising feature. © 2013 The Royal Society of Chemistry.
view abstract 10.1039/c3ta10641a
- Highly porous nitrogen-doped polyimine-based carbons with adjustable microstructures for CO2 capture
Wang, J. and Senkovska, I. and Oschatz, M. and Lohe, M.R. and Borchardt, L. and Heerwig, A. and Liu, Q. and Kaskel, S.
Journal of Materials Chemistry A 1 (2013)A series of highly porous nitrogen doped porous carbons (NPCs) have been successfully prepared using a novel porous polyimine as the precursor. The resulting NPCs have a high specific surface area of up to 3195 m2 g-1, high pore volume and micropore volume (up to 1.58 and 1.38 cm3 g-1, respectively), narrow micropore size distributions, and adjustable nitrogen (1.52-5.05 wt%) depending on the activation temperatures (600-750 °C). The CO2 uptakes of the NPCs prepared at higher temperatures (700-750 °C) are lower than those prepared at milder conditions (600-650 °C). At 1 bar, NPC-650 demonstrates the best CO2 capture performance and could efficiently adsorb CO2 molecules of 3.10 mmol g-1 (136 mg g-1) and 5.26 mmol g-1 (231.3 mg g-1), at 25 and 0 °C, respectively. The NPCs also show good a initial CO2/N2 adsorption selectivity of up to 23.4 and an adsorption ratio of CO2/N 2 (6.6) at 1 bar. Meanwhile, these NPCs exhibit a high stability and facile regeneration/recyclability without evident loss of the CO2 capture capacities. © 2013 The Royal Society of Chemistry.
view abstract 10.1039/c3ta11995e
- Imine-linked polymer-derived nitrogen-doped microporous carbons with excellent CO2 capture properties
Wang, J. and Senkovska, I. and Oschatz, M. and Lohe, M.R. and Borchardt, L. and Heerwig, A. and Liu, Q. and Kaskel, S.
ACS Applied Materials and Interfaces 5 (2013)A series of nitrogen-doped microporous carbons (NCs) was successfully prepared by direct pyrolysis of high-surface-area microporous imine-linked polymer (ILP, 744 m2/g) which was formed using commercial starting materials based on the Schiff base condensation under catalyst-free conditions. These NCs have moderate specific surface areas of up to 366 m2/g, pore volumes of 0.43 cm3/g, narrow micropore size distributions, and a high density of nitrogen functional groups (5.58-8.74%). The resulting NCs are highly suitable for CO2 capture adsorbents because of their microporous textural properties and large amount of Lewis basic sites. At 1 bar, NC-800 prepared by the pyrolysis of ILP at 800 C showed the highest CO 2 uptakes of 1.95 and 2.65 mmol/g at 25 and 0 C, respectively. The calculated adsorption capacity for CO2 per m2 (μmol of CO2/m2) of NC-800 is 7.41 μmol of CO2/m 2 at 1 bar and 25 C, the highest ever reported for porous carbon adsorbents. The isosteric heats of CO2 adsorption (Qst) for these NCs are as high as 49 kJ/mol at low CO2 surface coverage, and still ∼25 kJ/mol even at high CO2 uptake (2.0 mmol/g), respectively. Furthermore, these NCs also exhibit high stability, excellent adsorption selectivity for CO2 over N2, and easy regeneration and reuse without any evident loss of CO2 adsorption capacity. © 2013 American Chemical Society.
view abstract 10.1021/am400059t
- Interaction of electrolyte molecules with carbon materials of well-defined porosity: Characterization by solid-state NMR spectroscopy
Borchardt, L. and Oschatz, M. and Paasch, S. and Kaskel, S. and Brunner, E.
Physical Chemistry Chemical Physics 15 (2013)Electrochemical double-layer capacitors (EDLCs or supercapacitors) are of special potential interest with respect to energy storage. Nearly all EDLCs make use of porous carbons as electrode materials. Further tuning of their performance in EDLC applications requires a better understanding of their properties. In particular, the understanding of the interactions between carbon-based materials and electrolyte solutions is of fundamental interest with respect to future applications. Since the capacitance of carbon-based electrode materials is known to depend on the pore size, we have studied different porous carbon materials of well-defined, variable pore size loaded with 1 M TEABF 4 in acetonitrile or with pure acetonitrile using solid-state magic angle spinning (MAS) 1H, 11B, and 13C NMR spectroscopy. © the Owner Societies 2013.
view abstract 10.1039/c3cp52283k
- Mixed aerogels from Au and CdTe nanoparticles
Hendel, T. and Lesnyak, V. and Kühn, L. and Herrmann, A.-K. and Bigall, N.C. and Borchardt, L. and Kaskel, S. and Gaponik, N. and Eychmüller, A.
Advanced Functional Materials 23 (2013)Mixed metal-semiconductor nanocrystal aerogels are fabricated, which are light-emitting and highly porous macroscopic monoliths. Thiol-stabilized CdTe and Au nanoparticles from aqueous synthesis act as building blocks for the hybrid material. The Au colloids undergo a surface-modification to enhance the particle stability and achieve thiol functionalities. A photochemical treatment is applied for the gelation process which is found to be reversible by subsequent addition of thiol molecules. Via supercritical drying aerogels are formed. The variation of the initial CdTe to Au nanoparticle ratio permits a facile tuning of the content and the properties of the resulting aerogels. The obtained structures were characterized by means of optical spectroscopy, electron microscopy, elemental analysis, and nitrogen physisorption. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adfm.201201674
- Preparation of cubic ordered mesoporous silicon carbide monoliths by pressure assisted preceramic polymer nanocasting
Wang, J. and Oschatz, M. and Biemelt, T. and Lohe, M.R. and Borchardt, L. and Kaskel, S.
Microporous and Mesoporous Materials 168 (2013)Ordered mesoporous silicon carbide monoliths (OMSCMs) with three-dimensional (3D) bi-continuous cubic structure (Ia3d) have been successfully prepared using KIT-6 silica as the hard template and the commercial polycarbosilane (PCS-800) as the preceramic precursor. Tablet-like SiC/KIT-6 composite monoliths were formed via nanocasting of PCS-800 into the mesopores of KIT-6 silica by the wet impregnation, followed by pressing the PCS-800/KIT-6 composite powder with the addition of triblock copolymer P123 as a binder, and subsequent pyrolysis at 1073, 1273, or 1473 K in argon. The KIT-6 silica template was then dissolved in hydrogen fluoride (HF) solution to generate the silicon carbide (SiC) replicated monoliths with cubic ordered mesoporous structure. The OMSCMs demonstrated good macroscopic tablet-like appearances and no any cracks could be found in spite of the evident shrinkage. They were characterized by small-angle and wide-angle X-ray diffraction (XRD), nitrogen adsorption, Fourier-transform infrared (FT-IR), elemental analysis, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Nitrogen adsorption and small-angle XRD measurements showed that the OMSCMs had very high stability even after re-treatment at 1673 K under argon. And the transformation of amorphous into nano-crystalline state for SiC framework in the OMSCMs proceeded with the retention of the tablet-like morphology. © 2012 Elsevier Inc. All rights reserved.
view abstract 10.1016/j.micromeso.2012.09.037
- Sulfur-infiltrated micro- and mesoporous silicon carbide-derived carbon cathode for high-performance lithium sulfur batteries
Lee, J.T. and Zhao, Y. and Thieme, S. and Kim, H. and Oschatz, M. and Borchardt, L. and Magasinski, A. and Cho, W.-I. and Kaskel, S. and Yushin, G.
Advanced Materials 25 (2013)Novel nanostructured sulfur (S)-carbide derived carbon (CDC) composites with ordered mesopores and high S content are successfully prepared for lithium sulfur batteries. The tunable pore-size distribution and high pore volume of CDC allow for an excellent electrochemical performance of the composites at high current densities. A higher electrolyte molarity is found to enhance the capacity utilization dramatically and reduce S dissolution in S-CDC composite cathodes during cycling. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adma.201301579
- Textural characterization of micro- and mesoporous carbons using combined gas adsorption and n -nonane preadsorption
Oschatz, M. and Borchardt, L. and Rico-Francés, S. and Rodríguez-Reinoso, F. and Kaskel, S. and Silvestre-Albero, J.
Langmuir 29 (2013)Porous carbon and carbide materials with different structures were characterized using adsorption of nitrogen at 77.4 K before and after preadsorption of n-nonane. The selective blocking of the microporosity with n-nonane shows that ordered mesoporous silicon carbide material (OM-SiC) is almost exclusively mesoporous whereas the ordered mesoporous carbon CMK-3 contains a significant amount of micropores (∼25%). The insertion of micropores into OM-SiC using selective extraction of silicon by hot chlorine gas leads to the formation of ordered mesoporous carbide-derived carbon (OM-CDC) with a hierarchical pore structure and significantly higher micropore volume as compared to CMK-3, whereas a CDC material from a nonporous precursor is exclusively microporous. Volumes of narrow micropores, calculated by adsorption of carbon dioxide at 273 K, are in linear correlation with the volumes blocked by n-nonane. Argon adsorption measurements at 87.3 K allow for precise and reliable calculation of the pore size distribution of the materials using density functional theory (DFT) methods. © 2013 American Chemical Society.
view abstract 10.1021/la401206u
- Titanium carbide and carbide-derived carbon composite nanofibers by electrospinning of Ti-resin precursor
Martin, J.R. and Borchardt, L. and Oschatz, M. and Mondin, G. and Kaskel, S.
Chemie-Ingenieur-Technik 85 (2013)TiO2/C and TiC/C composite nanofibers were produced by electrospinning of resin/TiCl4 precursor solution. The resulting ceramic fiber webs were porous and showed surface areas as high as 523 m 2g-1. They were further converted to carbide-derived carbon (CDC) fibers under full retention of the fiber-like shape and flexibility. These CDC membranes showed a hierarchical pore structure and specific surface as high as 1378 m2g-1. Applications in the area of high temperature filtration, catalyst support and energy storage are conceivable. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/cite.201300057
- Twin polymerization at spherical hard templates: An approach to size-adjustable carbon hollow spheres with micro- or mesoporous shells
Böttger-Hiller, F. and Kempe, P. and Cox, G. and Panchenko, A. and Janssen, N. and Petzold, A. and Thurn-Albrecht, T. and Borchardt, L. and Rose, M. and Kaskel, S. and Georgi, C. and Lang, H. and Spange, S.
Angewandte Chemie - International Edition 52 (2013)Kitset hollow spheres: The combination of twin polymerization with hard templates makes hollow carbon spheres (HCSs) with tailored properties easily accessible. The thickness and pore texture of the HCS shells and also the diameter of the spherical cavity can be varied. The application potential of synthesized HCS is substantiated by an excellent cycling stability of lithium-sulfur batteries. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201209849
- Carbide-derived carbon monoliths with hierarchical pore architectures
Oschatz, M. and Borchardt, L. and Thommes, M. and Cychosz, K.A. and Senkovska, I. and Klein, N. and Frind, R. and Leistner, M. and Presser, V. and Gogotsi, Y. and Kaskel, S.
Angewandte Chemie - International Edition 51 (2012)Sierpinski carbon: Macroporous carbide-derived carbon monoliths (DUT-38) were synthesized starting from SiC-PolyHIPEs, resulting in a hierarchical micro-, meso-, and macroporous structure. The high specific surface area and high macropore volume renders PolyHIPE-CDC an excellent adsorbent combining high storage capacity with excellent adsorption rates in gas storage and air filtration. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201200024
- Complete and partial oxidation of methane on ceria/platinum silicon carbide nanocomposites
Frind, R. and Borchardt, L. and Kockrick, E. and Mammitzsch, L. and Petasch, U. and Herrmann, M. and Kaskel, S.
Catalysis Science and Technology 2 (2012)We have studied the catalytic activity of CeO 2/Pt-SiC composites in the total and partial oxidation as well as the dry reforming of methane. The composites were synthesized by an in situ functionalization strategy with variation in ceria and platinum contents and processing conditions. The impact of composition and pyrolysis temperature on the specific surface area and catalytic activity of the composite materials is studied. All catalysts have a high activity in the partial oxidation and dry reforming of methane close to the thermodynamic equilibrium composition. In the complete oxidation of methane, the T 10% was lowered by 443 K compared to the non-catalyzed reaction.
view abstract 10.1039/c1cy00311a
- Fungi-based porous carbons for CO 2 adsorption and separation
Wang, J. and Heerwig, A. and Lohe, M.R. and Oschatz, M. and Borchardt, L. and Kaskel, S.
Journal of Materials Chemistry 22 (2012)A series of porous carbons (PCs) with adjustable high surface areas and narrow micropore size distributions have been prepared by KOH activation of fungi-based carbon sources. The resulting PCs demonstrate both high CO 2 uptake (5.5 mmol g -1) and high CO 2/N 2 selectivity (27.3) at 273 K and 1 bar, implying their great potential as CO 2 capture sorbents. © 2012 The Royal Society of Chemistry.
view abstract 10.1039/c2jm32139d
- High-performance electrocatalysis on palladium aerogels
Liu, W. and Herrmann, A.-K. and Geiger, D. and Borchardt, L. and Simon, F. and Kaskel, S. and Gaponik, N. and Eychmüller, A.
Angewandte Chemie - International Edition 51 (2012)Nanostructures as catalysts: Pd aerogels modified with α-, β-, and γ-cyclodextrins can be obtained by the spontaneous self-assembly of in situ generated Pd nanoparticles. The Pd aerogels show excellent electrocatalytic activity for the oxidation of ethanol. The catalytic activity is believed to arise from the nonsupported nanometer-scale structure of the aerogel network and the interactions of ethanol with the cyclodextrin. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201108575
- Ordered mesoporous carbide-derived carbons prepared by soft templating
Borchardt, L. and Oschatz, M. and Lohe, M. and Presser, V. and Gogotsi, Y. and Kaskel, S.
Carbon 50 (2012)Free-standing films of ordered mesoporous silicon and titanium carbide-derived carbons have been synthesized using a novel soft templating approach without employing hydrofluoric acid. Tetraethyl orthosilicate or titanium citrate, alternatively, and a phenolic resin underwent an evaporation induced self-assembly yielding ordered mesoporous silicon carbide/carbon or titanium carbide/carbon composites. High temperature chlorine treatment transformed these materials conformally into carbide-derived carbons (CDC) while the ordered arrangement of mesopores was maintained. The corresponding hierarchical pore structures consist of narrowly distributed micro- and mesopores (distribution maxima at 1 and 5 nm, respectively) with a high surface area and pore volume of up to 1538 m 2/g and 2.53 cm 3/g, respectively. © 2012 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2012.04.006
- Preparation and application of cellular and nanoporous carbides
Borchardt, L. and Hoffmann, C. and Oschatz, M. and Mammitzsch, L. and Petasch, U. and Herrmann, M. and Kaskel, S.
Chemical Society Reviews 41 (2012)A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review. © 2012 The Royal Society of Chemistry.
view abstract 10.1039/c2cs15324f
- Synthesis, characterization, and hydrogen storage capacities of hierarchical porous carbide derived carbon monolith
Wang, J. and Oschatz, M. and Biemelt, T. and Borchardt, L. and Senkovska, I. and Lohe, M.R. and Kaskel, S.
Journal of Materials Chemistry 22 (2012)Hierarchical porous carbide-derived carbon monoliths (HPCDCM) were prepared by selective extraction of silicon from ordered mesoporous silicon carbide monoliths (OMSCM) through chlorination at high temperature. The OMSCM was firstly synthesized by pressure-assisted nanocasting procedure using KIT-6 silica as the hard template and polycarbosilane (PCS-800) as the preceramic precursor. The OMSCM showed cubic ordered mesoporous structure with specific surface area of over 600 m 2 g -1. After the chlorination, the resulting HPCDCM demonstrated very high specific surface area (2933 m 2 g -1), large pore volume (2.101 cm 3 g -1) with large volume of micropores (0.981 cm 3 g -1), and narrow dual pore size distributions (micropore: 0.9 nm, and mesopore: 3.1 nm). Macropores in the micron range were observed in the HPCDCM. The mesostructural ordering was not maintained in the HPCDCM and the volume of the HPCDCM had greatly shrunk, by 21.2% compared to that of the OMSCM, but the tablet-like appearance was well retained in the HPCDCM. At -196 °C, the HPCDCM shows good hydrogen uptakes of 2.4 wt% and 4.4 wt% at 1 bar and 36 bar, respectively. The calculated volumetric hydrogen storage capacity is 11.6 g L -1 at 36 bar. The gravimetric hydrogen uptake capacity of the HPCDCM is comparable to, or higher than, those of previously reported ordered mesoporous carbide-derived carbon (CDC) powder and microporous CDC powder. © The Royal Society of Chemistry 2012.
view abstract 10.1039/c2jm34472f
- Transition metal loaded silicon carbide-derived carbons with enhanced catalytic properties
Borchardt, L. and Hasché, F. and Lohe, M.R. and Oschatz, M. and Schmidt, F. and Kockrick, E. and Ziegler, C. and Lescouet, T. and Bachmatiuk, A. and Büchner, B. and Farrusseng, D. and Strasser, P. and Kaskel, S.
Carbon 50 (2012)Carbide-derived carbons (CDC) with incorporated transition metal nanoparticles (∼2.5 nm) were prepared using a microemulsion approach. Time-consuming post synthesis functionalization of the carbon support material can thus be avoided and nanoparticle sizes can be controlled by changing the microemulsion composition. This synthesis strategy is a technique for the preparation of highly porous carbon materials with a catalytically active component. In particular we investigated the integration of ruthenium, palladium, and platinum in a concentration ranging from 4.45 to 12 wt.%. It was found that the transition metal has a considerable influence on sorption properties of resulting nanoparticle-CDC composite materials. Depending on the used metal salt additive the surface area and the pore volume ranges from 1480 m 2/g and 1.25 cm 3/g for Pt to 2480 m 2/g and 2.0 cm 3/g for Ru doped carbons. Moreover, members of this material class show impressive properties as heterogeneous catalysts. The liquid phase oxidation of tetralin and the partial oxidation of methane were studied, and electrochemical applications were also investigated. Primarily Pt doped CDCs are highly active in the oxygen reduction reaction, which is of great importance in present day fuel cell research. © 2012 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2011.12.036
- 3D assembly of semiconductor and metal nanocrystals: Hybrid CdTe/Au structures with controlled content
Lesnyak, V. and Wolf, A. and Dubavik, A. and Borchardt, L. and Voitekhovich, S.V. and Gaponik, N. and Kaskel, S. and Eychmüller, A.
Journal of the American Chemical Society 133 (2011)A 3D metal ion assisted assembly of nanoparticles has been developed. The approach relies on the efficient complexation of cadmium ions and 5-mercaptomethyltetrazole employed as the stabilizer of both colloidal CdTe and Au nanoparticles. It enables in a facile way the formation of hybrid metal-semiconductor 3D structures with controllable and tunable composition in aqueous media. By means of critical point drying, these assemblies form highly porous aerogels. The hybrid architectures obtained are characterized by electron microscopy, nitrogen adsorption, and optical spectroscopy methods. © 2011 American Chemical Society.
view abstract 10.1021/ja202068s
- CeO2/Pt catalyst nanoparticle containing carbide-derived carbon composites by a new in situ functionalization strategy
Kockrick, E. and Borchardt, L. and Schrage, C. and Gaudillere, C. and Ziegler, C. and Freudenberg, T. and Farrusseng, D. and Eychmüller, A. and Kaskel, S.
Chemistry of Materials 23 (2011)A new class of CeO2/Pt nanostructures containing highly porous carbide-derived carbon composites was obtained for the first time using a polymer precursor strategy and subsequent ceramization. The catalytic transition metal compounds were incorporated into polymeric polycarbosilane structures using an inverse microemulsion method in precisely tunable nanoscale particle sizes. Porous ceramic and carbon composites were obtained by pyrolysis and subsequent chlorination processes. The adsorption properties of nonoxidic ceramic intermediates can be adjusted by the pyrolysis temperatures from mainly microporous to meso- and macroporous materials, respectively. These pore structures remain during the chlorination process confirmed by comparative nitrogen physisorption and small-angle X-ray scattering investigations. The specific surface areas significantly increase up to 1774 m2/g after selective silicon removal. In comparison to unsupported CeO2/Pt nanoparticle structures, the particle sizes and dispersion of the active metal compounds of composite structures remain during pyrolysis and chlorination process studied by electron microscopy methods. Ceramic and carbonaceous composites show catalytic activity and stability in selective methane oxidation. In contrast to the SiC composites, the CDC materials promote the formation of carbon monoxide and hydrogen in reforming reactions at higher temperatures, a conversion pathway important for the generation of synthetic fuels. © 2010 American Chemical Society.
view abstract 10.1021/cm102376b
- Ceria/silicon carbide core-shell materials prepared by miniemulsion technique
Borchardt, L. and Oschatz, M. and Frind, R. and Kockrick, E. and Lohe, M.R. and Hauser, C.P. and Weiss, C.K. and Landfester, K. and Büchner, B. and Kaskel, S.
Beilstein Journal of Nanotechnology 2 (2011)For the first time we present the synthesis of CeO2/Si(O)C core-shell particles prepared by the miniemulsion technique. The Si(O)C core was obtained by means of a polycarbosilane precursor (SMP10), which was subsequently functionalized with ceria and pyrolyzed to the ceramic. The size of these particles could easily be adjusted by varying the surfactants and the surfactant concentration, or by the addition of comonomers. Hence particle sizes ranged from 100 to 1000 nm, tunable by the preparation conditions. All materials were characterized by photon cross correlation spectroscopy, scanning electron microscopy and elemental mapping investigations. Furthermore, first catalytic tests were carried out by temperature programmed oxidation (TPO) of methane, and the activity of this material in lowering the onset temperature of methane combustion by 262 K was documented. © 2011 Borchardt et al.
view abstract 10.3762/bjnano.2.67
- Hierarchical micro- and mesoporous carbide-derived carbon as a high-performance electrode material in supercapacitors
Rose, M. and Korenblit, Y. and Kockrick, E. and Borchardt, L. and Oschatz, M. and Kaskel, S. and Yushin, G.
Small 7 (2011)Ordered mesoporous carbide-derived carbon (OM-CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of micropores. The micropores result in outstanding adsorption capacities and the well-defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temperature on the electrochemical performance of these materials in supercapacitors based on a 1 M aqueous solution of sulfuric acid and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are reported. Cyclic voltammetry shows the specific capacitance of the OM-CDC materials exceeds 200 F g-1 in the aqueous electrolyte and 185 F g-1 in the ionic liquid, when measured in a symmetric configuration in voltage ranges of up to 0.6 and 2 V, respectively. The ordered mesoporous channels in the produced OM-CDC materials serve as ion-highways and allow for very fast ionic transport into the bulk of the OM-CDC particles. At room temperature the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g-1 in ionic liquid and aqueous electrolytes, respectively. The supercapacitors based on 250-300 μm OM-CDC electrodes demonstrate an operating frequency of up to 7 Hz in aqueous electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM-CDC materials is unmatched by state-of-the art activated carbons and strictly microporous CDC materials. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/smll.201001898
- PEGylated hollow mesoporous silica nanoparticles as potential drug delivery vehicles
Zhu, Y. and Fang, Y. and Borchardt, L. and Kaskel, S.
Microporous and Mesoporous Materials 141 (2011)Herein we reported the PEGylated hollow mesoporous silica (HMS-PEG) nanoparticles as drug vehicles for drug delivery. Hollow mesoporous silica (HMS) nanoparticles with the diameter of ca. 100 nm were synthesized using the colloidal carbon spheres as templates, and HMS-PEG nanoparticles were successfully prepared by covalently grafting poly(oxyethylene)bis(amine) on amino-group modified HMS nanoparticles with p-phenylene diisothiocyanate (DITC) as a cross linker. HMS-PEG nanoparticles exhibited much better dispersity and stability in aqueous solution than HMS nanoparticles. In vitro cytotoxicity and cell uptake of HMS-PEG nanoparticles to Hela and NIH3T3 cells were evaluated. HMS-PEG nanoparticles have little in vitro cytotoxicity up to a concentration of 150 μg/ml, and the uptake amount of HMS-PEG nanoparticles is approximately two times than that of HMS nanoparticles in Hela and NIH3T3 cells. Doxorubicin hydrochloride (DOX), an anticancer drug, was loaded into HMS-PEG nanoparticles, and the DOX-loaded HMS-PEG nanoparticles had a sustained release property. Furthermore, the DOX-loaded HMS-PEG nanoparticles exhibited higher cytotoxicity than the DOX-loaded HMS nanoparticles against Hela and NIH3T3 cells. Therefore, the PEGylation of HMS nanoparticles is a promising strategy toward their potential application as drug delivery vehicles. © 2010 Elsevier Inc. All rights reserved.
view abstract 10.1016/j.micromeso.2010.11.013
- A cubic ordered, mesoporous carbide-derived carbon for gas and energy storage applications
Oschatz, M. and Kockrick, E. and Rose, M. and Borchardt, L. and Klein, N. and Senkovska, I. and Freudenberg, T. and Korenblit, Y. and Yushin, G. and Kaskel, S.
Carbon 48 (2010)A hierarchical and highly porous carbide-derived carbon (CDC) was obtained by nanocasting of pre-ceramic precursors into cubic ordered silica (KIT-6) and subsequent chlorination. Resulting CDC replica materials show high methane and n-butane uptake and excellent performance as electrode materials in supercapacitors. © 2010 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2010.06.058
- High-rate electrochemical capacitors based on ordered mesoporous silicon carbide-derived carbon
Korenblit, Y. and Rose, M. and Kockrick, E. and Borchardt, L. and Kvit, A. and Kaskel, S. and Yushin, G.
ACS Nano 4 (2010)Microporous carbons, produced by selective etching of metal carbides in a chlorine-containing environment, offer narrow distribution of micropores and one of the highest specific capacitances reported when used in electrical double layer capacitors (EDLC) with organic electrolytes. Previously, the small micropores in these carbons served as an impediment to ion transport and limited the power storage characteristics of EDLC. Here we demonstrate, for the first time, how the preparation and application of templated carbide-derived carbon (CDC) can overcome the present limitations and show the route for dramatic performance enhancement. The ordered mesoporous channels in the produced CDC serve as ion-highways and allow for very fast ionic transport into the bulk of the CDC particles. The enhanced transport led to 85% capacitance retention at current densities up to ∼20 A/g. The ordered mesopores in silicon carbide precursor also allow the produced CDC to exhibit a specific surface area up to 2430 m2/g and a specific capacitance up to 170 F/g when tested in 1 M tetraethylammonium tetrafluoroborate solution in acetonitrile, nearly doubling the previously reported values. © 2010 American Chemical Society.
view abstract 10.1021/nn901825y
- Ordered mesoporous boron carbide based materials via precursor nanocasting
Borchardt, L. and Kockrick, E. and Wollmann, P. and Kaskel, S. and Guron, M.M. and Sneddon, L.G. and Geiger, D.
Chemistry of Materials 22 (2010)Ordered mesoporous boron carbide materials with high specific surface areas up to 778 m2/g and hexagonal pore arrangement symmetries were obtained for the first time using a nanocasting strategy and the molecular bisdecaboranyl-hexane precursor for the infiltration into an ordered mesoporous silica template (SBA-15). Different preparation conditions were investigated, and it was found that by adjusting the precursor loading either nanorod structured replicas or tubular structured (CMK-5-like) materials were obtained. Changing the impregnation techniques, the solvents, and/or the pyrolysis temperatures allows tailoring of the properties of the hexagonal ordered mesoporous boron carbide replicas. The pore arrangement was altered to cubic ordered mesoporous boron carbide using KIT-6 silica matrix for nanocasting. © 2010 American Chemical Society.
view abstract 10.1021/cm100837r
- Ordered mesoporous carbide derived carbons for high pressure gas storage
Kockrick, E. and Schrage, C. and Borchardt, L. and Klein, N. and Rose, M. and Senkovska, I. and Kaskel, S.
Carbon 48 (2010)The design of advanced porous materials is crucial for the development of new energy storage systems for mobile applications. In the following a new class of highly porous carbon structures is applied in gas storage. Ordered mesoporous carbide derived carbons (OM-CDC) were synthesized by chlorination of mesostructured silicon carbide ceramics (OM-SiC). Resulting OM-CDC structures were characterized by nitrogen physisorption methods and small angle X-ray scattering demonstrating high specific surface areas and bimodal pore size distributions by varying the synthesis and chlorination conditions. The adsorption properties could be further enhanced by reductive hydrogen treatment. Storage capacities for mobile applications dependant on the synthesis conditions were investigated in high pressure hydrogen and methane adsorption with extraordinary high uptakes compared to micro- and mesoporous reference materials. In addition, the adsorption kinetics are studied in dynamic n-butane adsorption. © 2010 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.carbon.2010.01.004