Dr. Michael Felderhoff

Heterogeneous Catalysis
Max-Planck-Institut für Kohlenforschung


  • Effective thermal conductivity of dimagnesium iron hexahydride (Mg2FeH6) for heat storage applications
    Albert, R. and Wagner, C. and Urbanczyk, R. and Felderhoff, M.
    Applied Physics A: Materials Science and Processing 129 (2023)
    view abstract10.1007/s00339-022-06336-9
  • Synthesis, thermal stability, and hydrogen storage properties of poorly crystalline TiVFeCuNb multi-principal element alloy: Dedicated to the memory of Michel Latroche and his great contribution to the field of metal hydrides
    Balcerzak, M. and Ternieden, J. and Felderhoff, M.
    Journal of Alloys and Compounds 943 (2023)
    view abstract10.1016/j.jallcom.2023.169142
  • Hydride-based thermal energy storage
    Adams, M. and Buckley, C.E. and Busch, M. and Bunzel, R. and Felderhoff, M. and Heo, T.W. and Humphries, T.D. and Jensen, T.R. and Klug, J. and Klug, K.H. and Møller, K.T. and Paskevicius, M. and Peil, S. and Peinecke, K. and Sheppard, D.A. and Stuart, A.D. and Urbanczyk, R. and Wang, F. and Walker, G.S. and Wood, B.C. and Weiss, D. and Grant, D.M.
    Progress in Energy 4 (2022)
    view abstract10.1088/2516-1083/ac72ea
  • Activation of Molecular Hydrogen by Inter- and Intramolecular Al−N Lewis Pairs
    Bodach, A. and Nöthling, N. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2021 (2021)
    The field of frustrated Lewis pair chemistry offers many opportunities to activate molecular hydrogen, but Al−N systems have not been established yet. In this work, we describe several intermolecular classical Al−N Lewis pairs and an intramolecular ortho-ala-aminoarene for the activation of molecular hydrogen. Their ability was investigated using the isotope exchange reaction from HD to H2 and D2. The herein studied intermolecular Lewis pairs were based on alkylalanes and N-methyldiphenylamine, while the intramolecular Lewis pair was (o-TMP−C6H4)AlH2 ((2-(2,2,6,6-tetramethyl-piperidin-1-yl)phenyl)-aluminium dihydride). The activation of molecular hydrogen was carried out in toluene under mild conditions and monitored by 1H and 2H NMR spectroscopy. Furthermore, the Al−N interaction has been probed by 27Al NMR and crystallographic studies. Additionally, the crystal structure of pure AliBu3 was determined. These studies may attribute the pronounced reactivities of these Al−N compounds to elongated Al−N bond lengths. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstract10.1002/ejic.202001152
  • Amino−Organolithium Compounds and their Aggregation for the Synthesis of Amino−Organoaluminium Compounds
    Bodach, A. and Ortmeyer, J. and Herrmann, B. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2021 (2021)
    Here, we present a thorough structural study of small, easily accessible amino−organolithium compounds with bridging phenyl and naphthyl moieties. Their crystal structures most likely represent their aggregation as tetramers and dimers in both hydrocarbon and ethereal solvents. These amino−organolithium compounds were further used to generate their corresponding aluminium compounds as a model system. Their crystal structures are reported too. All structures are discussed with a focus on the different steric demands and bridging moieties. Additionally, the crystal structures of neophyllithium and decomposition products of some of the compounds mentioned above are reported. This study provides additional data for the future design and synthesis of amine stabilised organolithium and -aluminium compounds. © 2021 The Authors. European Journal of Inorganic Chemistry published by Wiley-VCH GmbH
    view abstract10.1002/ejic.202100224
  • Ammonia Synthesis and Mechanochemistry
    Felderhoff, M.
    Joule 5 (2021)
    Ammonia synthesis is one of the world's largest chemical processes and therefore also one of the world's largest CO2 emitters. New developments that operate under milder reaction conditions and environmentally friendly methods for supplying the feedstock for ammonia can significantly reduce these emissions. Mechanochemical processes have been in the focus of chemist for several years. Consequently, mechanochemical processes for the synthesis of ammonia are under development. © 2021 Elsevier Inc. Ammonia synthesis is one of the world's largest chemical processes and therefore also one of the world's largest CO2 emitters. New developments that operate under milder reaction conditions and environmentally friendly methods for supplying the feedstock for ammonia can significantly reduce these emissions. Mechanochemical processes have been in the focus of chemist for several years. Consequently, mechanochemical processes for the synthesis of ammonia are under development. © 2021 Elsevier Inc.
    view abstract10.1016/j.joule.2021.01.009
  • Mechanocatalytic Room-Temperature Synthesis of Ammonia from Its Elements Down to Atmospheric Pressure
    Reichle, S. and Felderhoff, M. and Schüth, F.
    Angewandte Chemie - International Edition (2021)
    Ammonia synthesis via the high-temperature and high-pressure Haber-Bosch process is one of the most important chemical processes in the world. In spite of numerous attempts over the last 100 years, continuous Haber-Bosch type ammonia synthesis at room-temperature had not been possible, yet. We report the development of a mechanocatalytic system operating continuously at room-temperature and at pressures down to 1 bar. With optimized experimental conditions, a cesium-promoted iron catalyst was shown to produce ammonia at concentrations of more than 0.2 vol. % for over 50 hours. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
    view abstract10.1002/anie.202112095
  • Mechanochemical synthesis and dehydrogenation properties of Yb(AlH4)3
    Cao, Z. and Felderhoff, M.
    International Journal of Hydrogen Energy 46 (2021)
    The facile synthesis of ytterbium tetrahydroaluminate Yb(AlH4)3 is conducted by a mechanochemical procedure under hydrogen atmosphere for the first time. Results show that the synthesized Yb(AlH4)3 remains as an amorphous state. The thermal decomposition of Yb(AlH4)3 goes through a four-stage pathway with several amorphous intermediate phases during the process. The first dehydrogenation step of Yb(AlH4)3 presents a relatively low apparent activation energy of 99.6 kJ mol−1, and ninety percent of the hydrogen from this stage can be liberated within 20 min at 160 °C. Rehydrogenation tests above 160 °C and 14 MPa hydrogen pressure demonstrate the unsuccessful rehydrogenations of the first decomposition step due to the formation of a thermodynamically more stable compound YbHCl. © 2021 Hydrogen Energy Publications LLC
    view abstract10.1016/j.ijhydene.2021.05.132
  • Mechanochemical Synthesis of Catalytic Materials
    Amrute, A.P. and De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry - A European Journal (2021)
    The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
    view abstract10.1002/chem.202004583
  • Mechanochemical Synthesis of Supported Bimetallic Catalysts
    De Bellis, J. and Felderhoff, M. and Schüth, F.
    Chemistry of Materials 33 (2021)
    In a previous publication, ball milling was introduced as an effective method for the preparation of supported metal catalysts, simply from the coarse powders of the metal and metal oxide support. In this follow-up study, we demonstrate that mixing multiple metal sources can result in supported alloyed nanoparticles, extending the field of application of the method to the synthesis of supported bimetallic catalysts. Ball milling Au and Pd or Au and Cu in a high-energy regime (shaker mill) indeed led to the formation of Au-Pd and Au-Cu nanoparticles, supported on MgO or yttria-stabilized zirconia (YSZ), which were explored as model systems. Powder X-ray diffraction and electron microscopy were the primary means to investigate as-synthesized materials. The catalytic performance in CO oxidation was also investigated to understand better how the synthetic method could affect the features of the final materials as catalysts. © 2021 The Authors. Published by American Chemical Society.
    view abstract10.1021/acs.chemmater.0c04134
  • Mg-Based System for H2 Sorption from CH4/H2 Gas Mixture
    Woeste, A.-L. and Balcerzak, M. and Urbanczyk, R. and Felderhoff, M.
    Energy Technology 9 (2021)
    Magnesium is considered as a potential material for the separation of hydrogen from different gas streams (CH4/H2, syngas, natural gas, etc.). Herein, an elemental mixture of Mg and Ni (5 wt%) is used for selective absorption of hydrogen from a CH4/H2 (90:10) mixture at 350 °C. The performed studies (X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and gas chromatography) show that analyzed material absorbs 4.5 wt% of hydrogen from CH4/H2 gas mixture and can be successfully applied for H2 separation. The proposed material may also be a promising system to capture hydrogen transported through natural gas networks. © 2021 The Authors. Energy Technology published by Wiley-VCH GmbH
    view abstract10.1002/ente.202001079
  • Review and outlook on high-entropy alloys for hydrogen storage
    Marques, F. and Balcerzak, M. and Winkelmann, F. and Zepon, G. and Felderhoff, M.
    Energy and Environmental Science 14 (2021)
    Recently, a new class of alloys, namely, high-entropy alloys (HEAs), started to be investigated for hydrogen storage as they can form metal hydrides. Considering that the properties of metal hydrides are greatly influenced by the type of phase formed, and chemical composition, HEAs (with their vastness of compositions) present a high potential for developing promising materials for this application. A crucial aspect in assessing the potential of these alloys is the effective compositional design and synthesis. Here, we evaluate the methods used for obtaining HEAs for hydrogen storage and, based on the most advanced discussions of phase formation and stability in HEAs, we expose some strategies for a better assessment of the vast compositional field. Moreover, we present and discuss the first attempts to model the hydrogenation properties of HEAs using thermodynamics and data science. The development of these kinds of predictive tools is paramount for exploring HEAs' potential for hydrogen storage. To date, the most promising HEA compositions can be classified into three classes: body-centered cubic HEAs, lightweight HEAs, and intermetallic HEAs. © 2021 The Royal Society of Chemistry.
    view abstract10.1039/d1ee01543e
  • Synthesis and Effective Thermal Conductivity Measurements of Hollow Mesoporous SiO2 Spheres for Heat-Insulating Applications
    Winkelmann, F. and Albert, R. and Felderhoff, M.
    Energy Technology 9 (2021)
    Mesoporous silica hollow spheres are an excellent model system to investigate the thermal conductivity for an efficient heat-insulating material with respect to its geometry. Four different monodisperse silica hollow spheres are synthesized via a three-step synthesis consisting of emulsifier-free emulsion polymerization, modified Stöber condensation process, and subsequent calcination. In this approach, cetyltrimethylammonium bromide (CTAB) is used as a structure directing component to produce a highly porous silica shell. The systematic investigations of the effective thermal conductivity (ETC) allow distinguishing the respective conduction pathways, such as solid conduction and gas conduction. The carried out thermal conductivity measurements reveal for all four samples promising low ETC values of ≈36 mW m−1 K−1 at 1013 mbar and 35 °C. In vacuum (0.03 mbar) all four samples showed, independent of shell thickness and inner diameter, a comparable reduced ETC of about 10 mW m−1 K−1. The comparison with previous studies on unstructured silica hollow spheres indicates that the solid state conductivity within the bulk is more dependent on the contact strengths and the number of contacts than on the thermal conductivity within the silica material, as the scattering probability of phonons is not influenced by an increased density of defects. © 2021 The Authors. Energy Technology published by Wiley-VCH GmbH
    view abstract10.1002/ente.202001048
  • Cycle Stability of the Effective Thermal Conductivity of Nickel-Activated Magnesium Hydride Powder under Operating Conditions
    Albert, R. and Wagner, C. and Urbanczyk, R. and Felderhoff, M.
    Energy Technology 8 (2020)
    Herein, the transient plane source (TPS) method is used to investigate the effective thermal conductivity (ETC) of nickel-activated magnesium hydride powder (MgH2 with 4 mass% Ni) under operating conditions at temperatures up to 400 °C and a hydrogen pressure up to 25 bar. MgH2 together with Ni can be used as heat storage material and is synthesized by mixing of the respective metal powders with subsequent temperature-controlled hydrogenation and dehydrogenation cycles under hydrogen gas pressure. Running a hydrogenation and dehydrogenation cycle test of nickel-activated magnesium hydride for more than 450 cycles shows a tremendous enhancement of the ETC. It can be shown that the ETC value of the MgH2 powder under hydrogen atmosphere depends on the sample temperature, the applied gas pressure, and the cycle number. The maximum ETC of dehydrogenated nickel-activated magnesium hydrides is above 8 W m−1 K−1 at 15 bar, 400 °C, and after 201 cycles. An investigation by electron microscopy shows a percolated network of dehydrogenated magnesium hydride particles which is formed by sintering during the dehydrogenation steps and which is responsible for the enhanced thermal conductivity. © 2020 The Authors. Published by Wiley-VCH GmbH
    view abstract10.1002/ente.202000356
  • Group 13-derived radicals from α-diimines: Via hydro-and carboalumination reactions
    Bodach, A. and Bamford, K.L. and Longobardi, L.E. and Felderhoff, M. and Stephan, D.W.
    Dalton Transactions 49 (2020)
    The mechanochemical synthesis of tertiary and secondary alanes AlR3 (R = Np 1 or Mes 2; HAlR2 R = Np 3 or Mes 4) is described. These species are reacted with several α-diimines to give a series of aluminium-derived radicals of the form [(diimine)AlR2] (6-11). EPR and several crystallographic studies are reported. These species are thought to form via hydro-or carboalumination and subsequent elimination reactions. This view is supported by the structural data for minor products C12H7(NHDipp)(NDipp)AliBu25 and C13H8(C(iBu)N(m-Xy)(NH(m-Xy)))AliBu212. In addition, the characterization of (C6F5)2B(OC(C6F5)OC12H8) indicates that such a carboboration pathway also provides access to related boron-derived radicals. © The Royal Society of Chemistry.
    view abstract10.1039/d0dt02498h
  • Low temperature dehydrogenation properties of ammonia borane within carbon nanotube arrays: a synergistic effect of nanoconfinement and alane
    Cao, Z. and Ouyang, L. and Felderhoff, M. and Zhu, M.
    RSC Advances 10 (2020)
    Ammonia borane (AB, NH3BH3) is considered as one of the most promising hydrogen storage materials for proton exchange membrane fuel cells due to its high theoretical hydrogen capacity under moderate temperatures. Unfortunately, its on-board application is hampered by the sluggish kinetics, volatile byproducts and harsh conditions for reversibility. In this work, AB and AlH3were simultaneously infiltrated into a carbon nanotube array (CMK-5) to combine the synergistic effect of alane with nanoconfinement for improving the dehydrogenation properties of AB. Results showed that the transformation from AB to DADB started at room temperature, which promoted AB to release 9.4 wt% H2within 10 min at a low temperature of 95 °C. Moreover, the entire suppression of all harmful byproducts was observed. © The Royal Society of Chemistry 2020.
    view abstract10.1039/d0ra02283g
  • Materials for hydrogen-based energy storage – past, recent progress and future outlook
    Hirscher, M. and Yartys, V.A. and Baricco, M. and Bellosta von Colbe, J. and Blanchard, D. and Bowman, R.C., Jr. and Broom, D.P. and Buckley, C.E. and Chang, F. and Chen, P. and Cho, Y.W. and Crivello, J.-C. and Cuevas, F. and David, W.I.F. and de Jongh, P.E. and Denys, R.V. and Dornheim, M. and Felderhoff, M. and Filinchuk, Y. and Froudakis, G.E. and Grant, D.M. and Gray, E.M. and Hauback, B.C. and He, T. and Humphries, T.D. and Jensen, T.R. and Kim, S. and Kojima, Y. and Latroche, M. and Li, H.-W. and Lototskyy, M.V. and Makepeace, J.W. and Møller, K.T. and Naheed, L. and Ngene, P. and Noréus, D. and Nygård, M.M. and Orimo, S.-I. and Paskevicius, M. and Pasquini, L. and Ravnsbæk, D.B. and Veronica Sofianos, M. and Udovic, T.J. and Vegge, T. and Walker, G.S. and Webb, C.J. and Weidenthaler, C. and Zlotea, C.
    Journal of Alloys and Compounds 827 (2020)
    Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, “Hydrogen-based Energy Storage” of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage. © 2020 The Authors
    view abstract10.1016/j.jallcom.2019.153548
  • Mg-containing multi-principal element alloys for hydrogen storage: A study of the MgTiNbCr0.5Mn0.5Ni0.5 and Mg0.68TiNbNi0.55 compositions
    Marques, F. and Pinto, H.C. and Figueroa, S.J.A. and Winkelmann, F. and Felderhoff, M. and Botta, W.J. and Zepon, G.
    International Journal of Hydrogen Energy 45 (2020)
    Recently, there has been growing interest in multi-principal element alloys for hydrogen storage. However, most of the papers published so far report compositions based only on transition metal elements, which limit the gravimetric storage capacities due to their densities. Since Mg is a low-density element promising for hydrogen storage, the study of Mg-containing multi-principal element compositions is opportune. In the present work, we report for the first time the structural characterization and hydrogen storage properties of the A2B type MgTiNbCr0.5Mn0.5Ni0.5 alloy and its derivative Mg0.68TiNbNi0.55 alloy. These Mg-containing multi-principal element alloys form major BCC phase (W-type, Im3¯m) and major FCC hydride (MH2 with CaF2-type structure) when synthesized by mechanical alloying (MA) and reactive milling (RM), respectively. Hydrogen is desorbed from both RM samples in two steps, with some overlap, from different hydrides formed during synthesis. The microstructure of the Mg0.68TiNbNi0.55 composition is more homogeneous (less secondary phases), but both alloys present a total gravimetric capacity of around 1.6 wt% H2. © 2020 Hydrogen Energy Publications LLC
    view abstract10.1016/j.ijhydene.2020.05.069
  • The direct and reversible hydrogenation of activated aluminium supported by piperidine
    Sandig-Predzymirska, L. and Ortmeyer, J. and Wagler, J. and Brendler, E. and Habermann, F. and Anders, M. and Felderhoff, M. and Mertens, F.
    Dalton Transactions 49 (2020)
    The reversible hydrogenation of aminoalanes employing activated aluminium and piperidine has been explored. A selection of transition metal (TM) compounds have been investigated as additives for producing TM-activated aluminium (TM = Ti, Zr, Hf and Y). The effect of these additives on the activation of aluminium with respect to hydrogenation of an aluminium/piperidinoalane system has been studied. It has been shown that Ti, Zr and Hf can efficiently promote the activation of aluminium for its hydrogenation. The experiments performed showed that the TM activity for the piperidinoalane formation decreases in the order Zr > Hf > Ti > Y. Using multinuclear NMR spectroscopy, the reversibility of this piperidinoalane-based hydrogenation system has been evidenced, demonstrating a potential pathway for hydrogen storage in aminoalanes. The syntheses of piperidinoalanes as well as their structural and spectroscopic characterisation are described. Single-crystal X-ray diffraction analyses of [pip2AlH]2 and [pip3Al]2 (pip = 1-piperidinyl, C5H10N) revealed dimers containing a central [AlN]2 unit. This journal is © The Royal Society of Chemistry.
    view abstract10.1039/d0dt03175e
  • Direct Hydrogenation of Aluminum via Stabilization with Triethylenediamine: A Mechanochemical Approach to Synthesize the Triethylenediamine ⋅ AlH 3 Adduct
    Ortmeyer, J. and Bodach, A. and Sandig-Predzymirska, L. and Zibrowius, B. and Mertens, F. and Felderhoff, M.
    ChemPhysChem 20 (2019)
    Two approaches for the synthesis of the triethylenediamine (TEDA) ⋅ AlH 3 adduct have been discovered. Both, the mechanochemical procedure and the wet chemical method lead to crystalline products. Starting from metallic Al powder and TEDA, ball milling under a pressure of 100 bar H 2 facilitates a direct hydrogenation of aluminum with conversions up to 90 %. Structure determination from X-ray powder diffraction data revealed an 1-D-coordination polymer of the type [TEDA−AlH 3 ] n . Furthermore, solid-state NMR techniques have been applied to analyze composition and structure of the products. Due to the polymeric arrangement, an enhanced stability of the material occurred which was investigated by thermal analysis showing a decomposition located above 200 °C. Overall, the stabilization of AlH 3 by TEDA holds promise for hydrogen storage applications. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cphc.201801093
  • Future perspectives of thermal energy storage with metal hydrides
    Manickam, K. and Mistry, P. and Walker, G. and Grant, D. and Buckley, C.E. and Humphries, T.D. and Paskevicius, M. and Jensen, T. and Albert, R. and Peinecke, K. and Felderhoff, M.
    International Journal of Hydrogen Energy 44 (2019)
    Thermochemical energy storage materials have advantage of much higher energy densities compared to latent or sensible heat storage materials. Metal hydrides show good reversibility and cycling stability combined with high enthalpies. They can be used for short and long-term heat storage applications and can increase the overall flexibility and efficiency of solar thermal energy production. Metal hydrides with working temperatures less than 500 °C were in the focus of research and development over the last years. For the new generation of solar thermal energy plants new hydrides materials with working temperatures above 600 °C must be developed and characterized. In addition to thorough research on new metal hydrides, the construction and engineering of heat storage systems at these high temperatures are challenging. Corrosion problems, hydrogen embrittlement and selection of heat transfer fluids are significant topics for future research activities. © 2018 Hydrogen Energy Publications LLC
    view abstract10.1016/j.ijhydene.2018.12.011
  • Magnesium based materials for hydrogen based energy storage: Past, present and future
    Yartys, V.A. and Lototskyy, M.V. and Akiba, E. and Albert, R. and Antonov, V.E. and Ares, J.R. and Baricco, M. and Bourgeois, N. and Buckley, C.E. and Bellosta von Colbe, J.M. and Crivello, J.-C. and Cuevas, F. and Denys, R.V. and Dornheim, M. and Felderhoff, M. and Grant, D.M. and Hauback, B.C. and Humphries, T.D. and Jacob, I. and Jensen, T.R. and de Jongh, P.E. and Joubert, J.-M. and Kuzovnikov, M.A. and Latroche, M. and Paskevicius, M. and Pasquini, L. and Popilevsky, L. and Skripnyuk, V.M. and Rabkin, E. and Sofianos, M.V. and Stuart, A. and Walker, G. and Wang, H. and Webb, C.J. and Zhu, M.
    International Journal of Hydrogen Energy 44 (2019)
    Magnesium hydride owns the largest share of publications on solid materials for hydrogen storage. The “Magnesium group” of international experts contributing to IEA Task 32 “Hydrogen Based Energy Storage” recently published two review papers presenting the activities of the group focused on magnesium hydride based materials and on Mg based compounds for hydrogen and energy storage. This review article not only overviews the latest activities on both fundamental aspects of Mg-based hydrides and their applications, but also presents a historic overview on the topic and outlines projected future developments. Particular attention is paid to the theoretical and experimental studies of Mg-H system at extreme pressures, kinetics and thermodynamics of the systems based on MgH 2 , nanostructuring, new Mg-based compounds and novel composites, and catalysis in the Mg based H storage systems. Finally, thermal energy storage and upscaled H storage systems accommodating MgH 2 are presented. © 2019 The Authors
    view abstract10.1016/j.ijhydene.2018.12.212
  • Milling Down to Nanometers: A General Process for the Direct Dry Synthesis of Supported Metal Catalysts
    Schreyer, H. and Eckert, R. and Immohr, S. and de Bellis, J. and Felderhoff, M. and Schüth, F.
    Angewandte Chemie - International Edition 58 (2019)
    Supported catalysts are among the most important classes of catalysts. They are typically prepared by wet-chemical methods, such as impregnation or co-precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of a support oxide leads in many cases to supported catalysts with particles in the nanometer size range. Various supports, including TiO2, Al2O3, Fe2O3, and Co3O4, and different metals, such as Au, Pt, Ag, Cu, and Ni, were studied, and for each of the supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts. The method thus provides a simple and cost-effective alternative to the conventionally used impregnation methods. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201903545
  • On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4
    Zibrowius, B. and Felderhoff, M.
    Physical Chemistry Chemical Physics 21 (2019)
    Potassium aluminium tetrahydride KAlH4 of high phase purity (space group Pnma (62)) was synthesized via a mechanochemical route. The thus obtained material was studied by 27Al and 39K MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T = 295 K were derived (27Al: δiso = (107.6 ± 0.2) ppm, CQ = (1.29 ± 0.02) MHz and η = 0.64 ± 0.02; 39K: δiso = (6.1 ± 0.2) ppm, CQ = (0.562 ± 0.005) MHz and η = 0.74 ± 0.02). The straightforward NMR spectroscopic approach applied here should also work for other complex aluminium hydrides and for many other materials containing half-integer nuclei experiencing small to medium-sized quadrupole couplings. © 2019 the Owner Societies.
    view abstract10.1039/c9cp01059a
  • Realizing facile regeneration of spent NaBH4 with Mg-Al alloy
    Zhong, H. and Ouyang, L. and Zeng, M. and Liu, J. and Wang, H. and Shao, H. and Felderhoff, M. and Zhu, M.
    Journal of Materials Chemistry A 7 (2019)
    The regeneration of sodium borohydride (NaBH4) is crucial to form a closed cycle after it either supplies hydrogen energy via a hydrolysis process or provides energy through electron transfer at the anode of direct borohydride fuel cells (DBFCs). In both of these cases, the spent fuels are NaB(OH)4 from NaBO2 aqueous solution. However, the current regeneration process from (NaB(OH)4)·xH2O to form NaBH4 by reduction reaction and calcination at high temperature with metal hydrides as reducing agents is very expensive. In this work, we developed a simple regeneration process via ball milling with Mg-Al alloys as the reducing agent for NaB(OH)4 under an argon atmosphere. Under optimized conditions, a high yield of about 72% of NaBH4 could be obtained. Mechanistic study showed that all the hydrogen atoms from NaB(OH)4 remain in NaBH4 and no additional hydrogen sources are needed for the reduction process. The inexpensive Mg-Al alloy works as a reducing agent transforming the H+ to H- in NaBH4. This approach demonstrates a ∼20-fold cost reduction compared with the method using metal hydrides. This opens the door to the commercial implementation of simple ball milling processes for the regeneration of spent NaBH4 from NaB(OH)4 with cheap reducing agents. © The Royal Society of Chemistry.
    view abstract10.1039/c9ta00769e
  • Thermal conductivity measurements of magnesium hydride powder beds under operating conditions for heat storage applications
    Albert, R. and Urbanczyk, R. and Felderhoff, M.
    International Journal of Hydrogen Energy 44 (2019)
    One of the major issues of the change in energy politics is the storage of renewable energy in order to facilitate a continuous energy supply to the grid. An efficient way to store energy (heat) is provided by the usage of Thermochemical Energy Storage (TES) in metal hydrides. Energy is stored in dehydrogenated metal hydrides and can be released by hydrogenation for consumption. One prominent candidate for high temperature (400 °C) heat storage is magnesium hydride. It is a well-known and investigated material which shows high cycling stability over hundreds of cycles. It is an abundant material, non-toxic and easy to prepare in bigger scales. One of the major drawbacks for heat storage applications is the low heat transfer capability of packed beds of magnesium hydrides. In this work we present results of effective thermal conductivity (ETC) which were measured under hydrogen pressure up to 25 bar and temperatures up to 410 °C in order to meet the operating conditions of magnesium hydride as a thermochemical heat storage material. We could show that the effective thermal conductivity of a magnesium hydride – hydrogen system at 410 °C and 25 bar hydrogen increases by 10% from 1.0 W m−1 K−1 to 1.1 W m−1 K−1 after 18 discharging and charging cycles. In dehydrogenated magnesium hydride this increase of the thermal conductivity was found to be at 50% from 1.20 W m−1 K−1 to 1.80 W m−1 K−1 at 21 bar hydrogen. These data are very important for the design and construction of heat storage tanks based on high temperature metal hydrides in the future. © 2019 Hydrogen Energy Publications LLC
    view abstract10.1016/j.ijhydene.2019.01.218
  • Mechanochemical synthesis and effect of various additives on the hydrogen absorption–desorption behavior of Na3AlH6
    Peinecke, K. and Meggouh, M. and Felderhoff, M.
    Journal of Materials Science 53 (2018)
    Sodium aluminum hydride has been extensively investigated for hydrogen storage applications whereas its intermediate decomposition compound Na3AlH6 received much less attention, despite having a lower dissociation pressure and a reasonable hydrogen storage capacity of 3.0 wt%. In this work, Na3AlH6 is synthesized through ball milling, starting from NaAlH4 and 2 NaH in the presence of TiCl3 catalyst precursor, and evaluated on its hydrogen sorption properties and cycle stability. Further addition of 8 mol% Al and 8 mol% activated carbon (AC) and their effect on both the hydrogen sorption properties and cycle stability have been investigated. In order to explore whether the introduction of the Al and AC additives would be more beneficial (in terms of hydrogen sorption behavior and cycle stability) after the Na3AlH6 synthesis or during its synthesis, pre-synthesized Na3AlH6-based measurements were also included in this work. TiCl3-catalyzed NaAlH4 + 2 NaH sample showed a stable reversible hydrogen storage capacity of 1.7 wt%, which was further increased to 2.1 wt% with the addition of Al-powder and activated carbon AC. © 2018, The Author(s).
    view abstract10.1007/s10853-018-2279-3
  • Special Issue: Application of Hydrogen Storage Materials, Carriers, and Processes
    Müller, K. and Felderhoff, M.
    Energy Technology 6 (2018)
    view abstract10.1002/ente.201800106
  • Study of an industrially oriented Mg content control technology during annealing process for the LaMg(Ni–Al)3.5 hydrogen storage alloy
    Tai, S. and Jie, H. and De, M. and Tongzao, L. and Ying, W. and Fangming, X. and Felderhoff, M. and Zhu, M. and Wang, H. and Renheng, T.
    International Journal of Hydrogen Energy 43 (2018)
    In this paper, we propose a novel and industrial feasible method for the high temperature annealing process of Mg-contained hydrogen storage alloys. To keep the Mg content in the alloy constant during manufacturing at high temperatures, the annealing process is carried out in a sealed container together with an external Mg vapor-producing source. The closed environment reduces the volume for the forming of Mg vapor pressure during the annealing process and excludes the influence from the “Cold Zone” areas of the furnace. External Mg metal, which is also loaded in the container with the alloy, plays an important role in providing the Mg source for the forming of the Mg vapor. This reduces the required Mg amounts from the alloy to produce saturated Mg vapor pressure during the annealing process. Our experimental results show that alloys annealed by this novel method have better electrical discharge properties and cyclic stability compared to alloys prepared by traditional annealing method used by most of hydrogen storage alloy manufacturers. This method could help to reduce the alloy production costs by making the phases’ ratio and performance change of the alloy more controllable during the production of this kind of hydrogen storage alloys. © 2018
    view abstract10.1016/j.ijhydene.2018.07.086
  • Synthesis, crystal structure analysis and decomposition of RbALH44
    Weidenthaler, C. and Felderhoff, M. and Bernert, T. and Sørby, M.H. and Hauback, B.C. and Krech, D.
    Crystals 8 (2018)
    RbAlH44, a member of the complex metal aluminum hydride family, can be synthesized phase pure by different synthesis routes. Synthesis from the metals by a mechanochemical reaction requires the presence of a catalyst, but also emphasizes the reversibility of hydrogenation. The structure refinement of neutron diffraction data confirms that RbAlD44 is isostructural to KAlD44. The decomposition proceeds via two distinct processes at temperatures above 275 °C. However, the structures formed during decomposition seem to be different from the compounds formed during hydrogen release of early alkali metal aluminum hydrides. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/cryst8020103
  • Development of a heat storage demonstration unit on the basis of Mg2FeH6 as heat storage material and molten salt as heat transfer media
    Urbanczyk, R. and Peinecke, K. and Peil, S. and Felderhoff, M.
    International Journal of Hydrogen Energy 42 (2017)
    The development and preliminary tests of a 5 kg Mg2FeH6 heat storage system which is useable for short and long-term storage applications at temperatures around 500 °C are described. The heat transfer for the heat storage process (dehydrogenation of the hydride Mg2FeH6) and heat release (hydrogenation of the hydride precursor 2Mg-Fe) is done by the flow of molten salt in appropriate heat exchangers serving as heat source or heat sink. The construction of the tube bundle reactor as a heat storage tank is presented. 1.6 kWh of heat could be released and 1.5 kWh of heat could be stored during the first experimental tests. Difficulties, which occured during the preliminary tests, are described. © 2017 Hydrogen Energy Publications LLC
    view abstract10.1016/j.ijhydene.2017.02.160
  • Enhancing the Regeneration Process of Consumed NaBH4 for Hydrogen Storage
    Ouyang, L. and Chen, W. and Liu, J. and Felderhoff, M. and Wang, H. and Zhu, M.
    Advanced Energy Materials (2017)
    Sodium borohydride (NaBH4) is regarded as an excellent hydrogen-generated material, but its irreversibility of hydrolysis and high cost of regeneration restrict its large-scale application. In this study a convenient and economical method for NaBH4 regeneration is developed for the first time without hydrides used as starting materials for the reduction process. The real hydrolysis by-products (NaBO2·2H2O and NaBO2·4H2O), instead of dehydrated sodium metaborate (NaBO2), are applied for the regeneration of NaBH4 with Mg at room temperature and atmospheric pressure. Therefore, the troublesome heat-wasting process to obtain NaBO2 using a drying procedure at over 350 °C from NaBO2·xH2O is omitted. Moreover, the highest regeneration yields of NaBH4 are achieved to date with 68.55% and 64.06% from reaction with NaBO2·2H2O and NaBO2·4H2O, respectively. The cost of NaBH4 regeneration shows a 34-fold reduction compared to the previous study that uses MgH2 as the reduction agent, where H2 is obtained from a separate process. Furthermore, the regeneration mechanism of NaBH4 is clarified and the intermediate compound, NaBH3(OH), is successfully observed for the first time during the regeneration process. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/aenm.201700299
  • Facile synthesis of anhydrous Li2B12H12 with high purity by solvent-free method
    He, L. and Shao, H. and Felderhoff, M. and Li, H.-W. and Li, X. and Zhu, Q. and Zhang, D. and Wu, D. and Fu, Y. and Deng, Y. and Lu, Z.
    Inorganica Chimica Acta 464 (2017)
    This work is aimed to synthesize anhydrous Li2B12H12 with high purity via solvent-free reaction between solid state reagents LiBH4 and B10H14. The reaction is conducted respectively in open system and sealed system for comparison. It is observed to experience three thermodynamic steps: (1) melting of B10H14 at 103 °C, (2) phase transition of LiBH4 at 118 °C and (3) Li2B12H12 formation at 135 °C. With appropriate heat treatment at 180 °C for 2 h, Li2B12H12 with purity high as 93% is obtained in open system of 2LiBH4 + 1.4B10H14 with excess B10H14. Sealed system reacting at approximate even optimized conditions is unavailable to produce such high purity of Li2B12H12. Chemical equilibrium confines the sufficient interaction between LiBH4 and B10H14 in sealed system but it does not do in open system. © 2017 Elsevier B.V.
    view abstract10.1016/j.ica.2017.05.025
  • Preferential Carbon Monoxide Oxidation over Copper-Based Catalysts under In Situ Ball Milling
    Eckert, R. and Felderhoff, M. and Schüth, F.
    Angewandte Chemie - International Edition 56 (2017)
    In situ ball milling of solid catalysts is a promising yet almost unexplored concept for boosting catalytic performance. The continuous preferential oxidation of CO (CO-PROX) under in situ ball milling of Cu-based catalysts such as Cu/Cr2O3 is presented. At temperatures as low as −40 °C, considerable activity and more than 95 % selectivity were achieved. A negative apparent activation energy was observed, which is attributed to the mechanically induced generation and subsequent thermal healing of short-lived surface defects. In situ ball milling at sub-zero temperatures resulted in an increase of the CO oxidation rate by roughly 4 orders of magnitude. This drastic and highly selective enhancement of CO oxidation showcases the potential of in situ ball milling in heterogeneous catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/anie.201610501
  • Reversible hydrogen storage in yttrium aluminum hydride
    Cao, Z. and Ouyang, L. and Wang, H. and Liu, J. and Felderhoff, M. and Zhu, M.
    Journal of Materials Chemistry A 5 (2017)
    Reversible hydrogen storage has been found in transition metal alanates, Y(AlH4)3, for the first time. An amount of 3.4 wt% H2 can be released at 140 °C from the first dehydrogenation step of Y(AlH4)3, and 75% of it is reversible at 145 °C and 100 bar H2, which holds promise for low-temperature applications. © 2017 The Royal Society of Chemistry.
    view abstract10.1039/c6ta10928d
  • Demonstration of Mg2FeH6 as heat storage material at temperatures up to 550 °C
    Urbanczyk, R. and Meggouh, M. and Moury, R. and Peinecke, K. and Peil, S. and Felderhoff, M.
    Applied Physics A: Materials Science and Processing 122 (2016)
    The storage of heat at high temperatures, which can be used to generate electricity after sunset in concentrating solar power plants, is one of the most challenging technologies. The use of metal hydride could be one possibility to solve the problem. During the endothermic heat storage process, the metal hydride is decomposed releasing hydrogen, which then can be stored. During the exothermic reaction of the metal with the hydrogen gas, the stored heat is then released. Previous research had shown that Mg and Fe powders can be used at temperatures up to 550 °C for heat storage and shows excellent cycle stability over hundreds of cycles without any degradation. Here, we describe the results of testing of a tube storage tank that contained 211 g of Mg and Fe powders in 2:1 ratio. Twenty-three dehydrogenations (storage) and 23 hydrogenations (heat release) in the temperature range between of 395 and 515 °C and pressure range between 1.5 and 8.6 MPa were done. During the dehydrogenation, 0.41–0.42 kWhth kg−1 of heat based on material 2 Mg/Fe can be stored in the tank. After testing, mainly Mg2FeH6 was observed and small amounts of MgH2 and Fe metal can be detected in the hydride samples. This means that the heat storage capacity of the system could be further increased if only Mg2FeH6 is produced during subsequent cycles. © 2016, The Author(s).
    view abstract10.1007/s00339-016-9811-6
  • Design and operation of an aluminium alloy tank using doped Na3AlH6 in kg scale for hydrogen storage
    Urbanczyk, R. and Peinecke, K. and Meggouh, M. and Minne, P. and Peil, S. and Bathen, D. and Felderhoff, M.
    Journal of Power Sources 324 (2016)
    In this publication the authors present an aluminium alloy tank for hydrogen storage using 1921 g of Na3AlH6 doped with 4 mol% of TiCl3 and 8 mol% of activated carbon. The tank and the heat exchangers are manufactured by extrusion moulding of Al-Mg-Si based alloys. EN AW 6082 T6 alloy is used for the tank and a specifically developed alloy with a composition similar to EN AW 6060 T6 is used for the heat exchangers. The three heat exchangers have a corrugated profile to enhance the surface area for heat transfer. The doped complex hydride Na3AlH6 is densified to a powder density of 0.62 g cm−3. The hydrogenation experiments are carried out at 2.5 MPa. During one of the dehydrogenation experiments approximately 38 g of hydrogen is released, accounting for gravimetric hydrogen density of 2.0 mass-%. With this tank 15 hydrogenation and 16 dehydrogenation tests are carried out. © 2016 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2016.05.102
  • Development of Zr-Fe-V alloys for hybrid hydrogen storage system
    Cao, Z. and Ouyang, L. and Wang, H. and Liu, J. and Sun, L. and Felderhoff, M. and Zhu, M.
    International Journal of Hydrogen Energy 41 (2016)
    The combination of unstable hydrogen storage materials with a high pressure tank provides a potential solution to on-board hydrogen storage system for fuel cell vehicles. However, none of the available solid-state materials can fulfill all the requirements. In this work, Zr-Fe-V-based alloys were systematically investigated for the possible use in such kind of hybrid storage devices. Among these alloys studied here, the composition (Zr0.7Ti0.3)1.04Fe1.8V0.2 shows the best overall properties with a reversible hydrogen capacity of 1.51 wt%, and a hydrogen desorption pressure of 11.2 atm at 0 °C. Besides, this alloy also shows excellent stability without obvious capacity loss even after 200 hydrogen absorption/desorption cycles. Calculated results show that the gravimetric density of the hybrid storage system combining a 35 MPa high pressure tank with (Zr0.7Ti0.3)1.04Fe1.8V0.2 alloy is 1.95 wt% when the volumetric density reaches 40 kg/m3. © 2016 Hydrogen Energy Publications LLC.
    view abstract10.1016/j.ijhydene.2016.04.083
  • Metal hydrides for concentrating solar thermal power energy storage
    Sheppard, D.A. and Paskevicius, M. and Humphries, T.D. and Felderhoff, M. and Capurso, G. and Bellosta von Colbe, J. and Dornheim, M. and Klassen, T. and Ward, P.A. and Teprovich, J.A., Jr. and Corgnale, C. and Zidan, R. and Grant, D.M. and Buckley, C.E.
    Applied Physics A: Materials Science and Processing 122 (2016)
    The development of alternative methods for thermal energy storage is important for improving the efficiency and decreasing the cost of concentrating solar thermal power. We focus on the underlying technology that allows metal hydrides to function as thermal energy storage (TES) systems and highlight the current state-of-the-art materials that can operate at temperatures as low as room temperature and as high as 1100 °C. The potential of metal hydrides for thermal storage is explored, while current knowledge gaps about hydride properties, such as hydride thermodynamics, intrinsic kinetics and cyclic stability, are identified. The engineering challenges associated with utilising metal hydrides for high-temperature TES are also addressed. © 2016, Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s00339-016-9825-0
  • Mg-based compounds for hydrogen and energy storage
    Crivello, J.-C. and Denys, R.V. and Dornheim, M. and Felderhoff, M. and Grant, D.M. and Huot, J. and Jensen, T.R. and de Jongh, P. and Latroche, M. and Walker, G.S. and Webb, C.J. and Yartys, V.A.
    Applied Physics A: Materials Science and Processing 122 (2016)
    Magnesium-based alloys attract significant interest as cost-efficient hydrogen storage materials allowing the combination of high gravimetric storage capacity of hydrogen with fast rates of hydrogen uptake and release and pronounced destabilization of the metal–hydrogen bonding in comparison with binary Mg–H systems. In this review, various groups of magnesium compounds are considered, including (1) RE–Mg–Ni hydrides (RE = La, Pr, Nd); (2) Mg alloys with p-elements (X = Si, Ge, Sn, and Al); and (3) magnesium alloys with d-elements (Ti, Fe, Co, Ni, Cu, Zn, Pd). The hydrogenation–disproportionation–desorption–recombination process in the Mg-based alloys (LaMg12, LaMg11Ni) and unusually high-pressure hydrides synthesized at pressures exceeding 100 MPa (MgNi2H3) and stabilized by Ni–H bonding are also discussed. The paper reviews interrelations between the properties of the Mg-based hydrides and p–T conditions of the metal–hydrogen interactions, chemical composition of the initial alloys, their crystal structures, and microstructural state. © 2016, Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s00339-016-9601-1
  • Molecular structure of diethylaminoalane in the solid state: An X-ray powder diffraction, DFT calculation and Raman spectroscopy study
    Bernert, T. and Ley, M.B. and Ruiz-Fuertes, J. and Fischer, M. and Felderhoff, M. and Weidenthaler, C.
    Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 72 (2016)
    The crystal structure of diethylaminoalane, [H2Al - N(C2H5)2]2, was determined by X-ray powder diffraction in conjunction with DFT calculations. Diethylaminoalane crystallizes in the monoclinic space group P21/c with a = 7.4020 (2), b = 12.9663 (3), c = 7.2878 (2) Å and β = 90.660 (2)° at 293 K. The crystal structure was confirmed by DFT calculations and Raman spectroscopy. The molecular structure of diethylaminoalane consists of dimers of [H2Al - N(CH2CH3)2] in which an Al2N2 four-membered ring is formed by a center of inversion. Such an arrangement of the aminoalane moieties in the crystal structure is well known for this class of compound, as shown by the comparison with ethylmethylaminoalane and diisopropylaminoalane.The crystal structure of diethylaminoalane, [H2Al - N(C2H5)2]2, was determined by X-ray powder diffraction, geometry optimization by density functional theory (DFT) and Raman spectroscopy. The DFT calculations were validated by calculating the ground state structures of two known aminoalanes while the Raman spectrum of diethylaminoalane was measured and compared to the simulated ones. Furthermore, the crystal structure of diethylaminoalane is compared with chemically and structurally similar compounds. © International Union of Crystallography, 2016.
    view abstract10.1107/S2052520616000093
  • The plastic crystalline A15 phase of dimethylaminoalane, [N(CH3)2-AlH2]3
    Ley, M.B. and Bernert, T. and Ruiz-Fuertes, J. and Goddard, R. and Farès, C. and Weidenthaler, C. and Felderhoff, M.
    Chemical Communications 52 (2016)
    A plastic crystalline phase of dimethylaminoalane has been discovered at T > 332 K. The phase transitions solid-plastic phase-liquid are fully reversible. The plastic crystalline phase exhibits a cubic unit cell, space group Pm3n, in which the dimethylaminoalane molecules rotate and adopt a structural arrangement reminiscent of the A15 phase. © 2016 The Royal Society of Chemistry.
    view abstract10.1039/c6cc06166d
  • An in situ powder diffraction cell for high-pressure hydrogenation experiments using laboratory X-ray diffractometers
    Moury, R. and Hauschild, K. and Kersten, W. and Ternieden, J. and Felderhoff, M. and Weidenthaler, C.
    Journal of Applied Crystallography 48 (2015)
    An in situ diffraction cell is presented which has been designed and constructed for in-house powder diffraction experiments under high gas pressures up to 30MPa. For a proof of principle, the in situ cell has been tested for several hydrogenation experiments under elevated pressures and temperatures. LaNi5 was chosen as an example for hydrogenation, applying simultaneously 5.5MPaH2 pressure at a temperature of 423K. For testing the high-pressure-temperature suitability of the in situ cell, pressure-temperature experiments up to 14MPa at 373K were performed, studying the rehydrogenation of NaH and Al to NaAlH4. The experimental setup enables recording of in situ X-ray diffraction data on laboratory instruments with short data acquisition times at elevated hydrogen pressures and temperatures. © 2015 International Union of Crystallography.
    view abstract10.1107/S1600576714025692
  • Crystal Structure Relation between Tetragonal and Orthorhombic CsAlD4: DFT and Time-of-Flight Neutron Powder Diffraction Studies
    Bernert, T. and Krech, D. and Kockelmann, W. and Felderhoff, M. and Frankcombe, T.J. and Weidenthaler, C.
    European Journal of Inorganic Chemistry 2015 (2015)
    The crystal structures of orthorhombic and tetragonal CsAlD4 were refined from time-of-flight neutron powder diffraction data starting from atomic positions predicted from DFT calculations. The earlier proposed crystal structure of orthorhombic CsAlH4 is confirmed. For tetragonal CsAlH4, DFT calculations predicted a crystal structure in I41/amd as potential minimum structure, while from neutron diffraction studies of CsAlD4 best refinement is obtained for a disordered structure in the space group I41/a, with a = 5.67231(9) Å, c = 14.2823(5) Å. While the caesium atoms are located on the Wyckoff position 4b and aluminium at Wyckoff position 4a, there are two distinct deuterium positions at the Wyckoff position 16f with occupancies of 50 % each. From this structure, the previously reported phase transition between the orthorhombic and tetragonal polymorphs could be explained. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/ejic.201500841
  • Development of hydrogen storage tank systems based on complex metal hydrides
    Ley, M.B. and Meggouh, M. and Moury, R. and Peinecke, K. and Felderhoff, M.
    Materials 8 (2015)
    This review describes recent research in the development of tank systems based on complex metal hydrides for thermolysis and hydrolysis. Commercial applications using complex metal hydrides are limited, especially for thermolysis-based systems where so far only demonstration projects have been performed. Hydrolysis-based systems find their way in space, naval, military and defense applications due to their compatibility with proton exchange membrane (PEM) fuel cells. Tank design, modeling, and development for thermolysis and hydrolysis systems as well as commercial applications of hydrolysis systems are described in more detail in this review. For thermolysis, mostly sodium aluminum hydride containing tanks were developed, and only a few examples with nitrides, ammonia borane and alane. For hydrolysis, sodium borohydride was the preferred material whereas ammonia borane found less popularity. Recycling of the sodium borohydride spent fuel remains an important part for their commercial viability. © 2015 by the authors.
    view abstract10.3390/ma8095280
  • Fluorescence X-ray absorption study of ScCl3-doped sodium alanate
    Léon, A. and Finck, N. and Rothe, J. and Felderhoff, M. and Fichtner, M.
    Journal of Physical Chemistry C 119 (2015)
    X-ray absorption spectroscopy measurements at the Sc K edge (E = 4492 eV) of metallic Sc, ScCl<inf>3</inf>, and ScCl<inf>3</inf>-doped NaAlH<inf>4</inf> are presented. After the doping process, a reduction of ScCl<inf>3</inf> occurs, but not to the metallic Sc(0) state. A complete reduction of Sc is observed after eight absorption/desorption cycles under hydrogen. After eight cycles, formation of a structure is observed where Sc is surrounded in the first shell by 13 Al atoms at an interatomic distance of 2.85 ± 0.02 Å. A comparative study based on XAS analysis between ScCl<inf>3</inf>, TiCl<inf>3</inf>, and CeCl<inf>3</inf> used as precursor in the doping reaction of sodium alanate indicates that other factors in addition to the reduction of the precursor to the metallic state are relevant for the hydrogen release and uptake reaction kinetics. ScCl<inf>3</inf> and TiCl<inf>3</inf> exhibit a similar behavior with the formation of intermetallic compounds, while CeCl<inf>3</inf> is stable under comparable experimental conditions. The formation of an intermetallic entity over the cycles is correlated to the observed decrease in the storage capacity. © 2015 American Chemical Society.
    view abstract10.1021/acs.jpcc.5b00727
  • Kinetics enhancement, reaction pathway change, and mechanism clarification in LiBH4 with Ti-catalyzed nanocrystalline MgH2 composite
    Shao, H. and Felderhoff, M. and Weidenthaler, C.
    Journal of Physical Chemistry C 119 (2015)
    A composite of 2LiBH4 + nano-MgH2* (Ti-catalyzed) shows significantly enhanced desorption kinetics compared to a conventional mixture of 2LiBH4 + MgH2. The desorption mechanism was studied in the temperature range between 304 and 383 °C and under different pressure conditions. Desorption temperatures are 50-70 °C lower compared to conventional 2LiBH4 + MgH2 mixtures. During the hydrogen release from a mixture of 2LiBH4 + nano-MgH2* at a hydrogen back-pressure of 0.4 MPa, MgB2 is formed and three different plateaus of equilibrium were detected. The reaction pathway is changed at 360 °C for the 2LiBH4 + MgH2 system when the nano-MgH2* is used. © 2015 American Chemical Society.
    view abstract10.1021/jp511479d
  • Aluminium alloy based hydrogen storage tank operated with sodium aluminium hexahydride Na3AlH6
    Urbanczyk, R. and Peinecke, K. and Felderhoff, M. and Hauschild, K. and Kersten, W. and Peil, S. and Bathen, D.
    International Journal of Hydrogen Energy 39 (2014)
    Here we present the development of an aluminium alloy based hydrogen storage tank, charged with Ti-doped sodium aluminium hexahydride Na3AlH6. This hydride has a theoretical hydrogen storage capacity of 3 mass-% and can be operated at lower pressure compared to sodium alanate NaAlH4. The tank was made of aluminium alloy EN AW 6082 T6. The heat transfer was realised through an oil flow in a bayonet heat exchanger, manufactured by extrusion moulding from aluminium alloy EN AW 6060 T6. Na3AlH6 is prepared from 4 mol-% TiCl3 doped sodium aluminium tetrahydride NaAlH4 by addition of two moles of sodium hydride NaH in ball milling process. The hydrogen storage tank was filled with 213 g of doped Na3AlH6 in dehydrogenated state. Maximum of 3.6 g (1.7 mass-% of the hydride mass) of hydrogen was released from the hydride at approximately 450 K and the same hydrogen mass was consumed at 2.5 MPa hydrogenation pressure. 45 cycle tests (rehydrogenation and dehydrogenation) were carried out without any failure of the tank or its components. Operation of the tank under real conditions indicated the possibility for applications with stationary HT-PEM fuel cell systems. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.ijhydene.2014.08.101
  • Beneficial effects of stoichiometry and nanostructure for a LiBH 4-MgH2 hydrogen storage system
    Hu, J. and Witter, R. and Shao, H. and Felderhoff, M. and Fichtner, M.
    Journal of Materials Chemistry A 2 (2014)
    The hydrogen storage system [MgH2-2LiBH4] shows attractive properties such as favorable thermodynamics, high hydrogen capacity and reversibility. However, there exists an incubation period that amounts up to 10 hours in the dehydrogenation steps, which restricts this system as a practical material. In this study, the influences of stoichiometry and the nanoscale MgH2 were investigated for the system. Considerably shortened incubation times were achieved with deficit amounts of LiBH 4 or by using nanoscale MgH2. In addition, the application of nanoscale MgH2 prevented or suppressed the formation of [B 12H12]2- in the dehydrogenation, which is otherwise an issue concerning the re-cyclability. © The Royal Society of Chemistry.
    view abstract10.1039/c3ta13775a
  • On the preparation and structure of caesium aluminium tetrahydride
    Krech, D. and Zibrowius, B. and Weidenthaler, C. and Felderhoff, M.
    European Journal of Inorganic Chemistry 2014 (2014)
    A new tetragonal phase of CsAlH4 was observed after the precipitation of CsAlH4 from a diglyme solution with an inert solvent. This new phase and the previously described orthorhombic phase were characterized by a combination of Xray powder diffraction analysis and 27Al and 133Cs solid-state NMR spectroscopy. The transformation of the tetragonal CsAlH4 phase into the orthorhombic CsAlH4 phase can be induced by thermal treatment, whereas the opposite process can be stimulated by mechanical treatment. The phase transformation processes are almost completely reversible and can be performed several times without any observable decomposition of CsAlH4. The structure of the tetragonal CsAlH4 phase (space group I41/a) was solved from X-ray powder diffraction data, and the lattice parameters were determined to be a = 5.6732(4) and c = 14.2795(11) A. © 2014 Wiley-VCH Verlag GmbH & Co.
    view abstract10.1002/ejic.201402629
  • An orders-of-magnitude increase in the rate of the solid-catalyzed co oxidation by in situ ball milling
    Immohr, S. and Felderhoff, M. and Weidenthaler, C. and Schüth, F.
    Angewandte Chemie - International Edition 52 (2013)
    Shaken, not stirred: CO oxidation was carried out continuously in a shaker ball mill. During milling, the reaction rate increases dramatically, but drops rapidly to zero when the mill is stopped. Compared to a conventional experiment in a plug-flow reactor, the rate of a ball-mill reaction catalyzed by Cr 2O3 is three orders of magnitude higher at room temperature and one order of magnitude higher at 100°C. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/anie.201305992
  • Thermochemical heat storage for high temperature applications-A review
    Felderhoff, M. and Urbanczyk, R. and Peil, S.
    Green 3 (2013)
    Heat storage for high temperature applications can be performed by several heat storage techniques. Very promising heat storage methods are based on thermochemical gas solid reactions. Most known systems are metal oxide/steam (metal hydroxides), carbon dioxide (metal carbonates), and metal/hydrogen (metal hydrides) systems. These heat storage materials posses high ravimetric and volumetric heat storage densities and because of separation of the reaction products and their storage in different locations heat losses can be avoided. The reported volumetric heat storage densities are 615, 1340 and 1513 [kWh m-3] for calcium hydroxide Ca(OH)2, calcium carbonate CaCO3 and magnesium iron hydride Mg2FeH6 respectively. Additional demands for gas storage decrease the heat storage density, but metal hydride systems can use available hydrogen storage possibilities for example caverns, pipelines and chemical plants.
    view abstract10.1515/green-2013-0011
  • Functional materials for hydrogen storage
    Felderhoff, M.
    Functional Materials for Sustainable Energy Applications (2012)
    Hydrogen is the lightest and most abundant element in the universe. The overall amount of hydrogen on Earth is around 0.74. wt%; it is mostly bound in water and carbon-based materials. The future challenges of a hydrogen-based energy economy include the production, distribution and safe storage of hydrogen. Of these, one of the most important is the safe storage of hydrogen for use by consumers in electronic devices, automotive applications or heating and burning processes. A simple technical- or chemical-based solution, which fulfills all the requirements in terms of size, weight and safety for these different applications, is not yet in sight. Therefore, a number of possible solutions for the storage of hydrogen in a solid state are currently being researched. © 2012 Woodhead Publishing Limited All rights reserved.
    view abstract10.1533/9780857096371.2.217
  • Synthesis, crystal structures, and hydrogen-storage properties of Eu(AlH 4) 2 and Sr(AlH 4) 2 and of their decomposition intermediates, EuAlH 5 and SrAlH 5
    Pommerin, A. and Wosylus, A. and Felderhoff, M. and Schüth, F. and Weidenthaler, C.
    Inorganic Chemistry 51 (2012)
    Complex Eu(AlH 4) 2 and Sr(AlH 4) 2 hydrides have been prepared by a mechanochemical metathesis reaction from NaAlH 4 and europium or strontium chlorides. The crystal structures were solved from powder X-ray diffraction data in combination with solid-state 27Al NMR spectroscopy. The thermolysis pathway was analyzed in detail, allowing identification of new intermediate EuAlH 5/SrAlH 5 compounds. Rehydrogenation experiments indicate that the second decomposition step is reversible. © 2012 American Chemical Society.
    view abstract10.1021/ic202492v
  • Formation of Al2H7 - anions - Indirect evidence of volatile AlH3 on sodium alanate using solid-state NMR spectroscopy
    Felderhoff, M. and Zibrowius, B.
    Physical Chemistry Chemical Physics 13 (2011)
    After more than a decade of intense research on NaAlH4 doped with transition metals as hydrogen storage material, the actual mechanism of the decomposition and rehydrogenation reaction is still unclear. Early on, monomeric AlH3 was named as a possible transport shuttle for aluminium, but never observed experimentally. Here we report for the first time the trapping of volatile AlH3 produced during the decomposition of undoped NaAlH4 by an adduct of sodium alanate and crown ether. The resulting Al2H7 - anion was identified by solid-state 27Al NMR spectroscopy. Based on this indirect evidence of volatile alane, we present a simple description of the processes occurring during the reversible dehydrogenation of NaAlH4. © 2011 the Owner Societies.
    view abstract10.1039/c1cp21877h
  • Formation of Al2H7- anions - Indirect evidence of volatile AlH3 on sodium alanate using solid-state NMR spectroscopy
    Felderhoff, M. and Zibrowius, B.
    Physical Chemistry Chemical Physics 13 (2011)
    After more than a decade of intense research on NaAlH4 doped with transition metals as hydrogen storage material, the actual mechanism of the decomposition and rehydrogenation reaction is still unclear. Early on, monomeric AlH3 was named as a possible transport shuttle for aluminium, but never observed experimentally. Here we report for the first time the trapping of volatile AlH3 produced during the decomposition of undoped NaAlH4 by an adduct of sodium alanate and crown ether. The resulting Al2H7- anion was identified by solid-state 27Al NMR spectroscopy. Based on this indirect evidence of volatile alane, we present a simple description of the processes occurring during the reversible dehydrogenation of NaAlH4. © 2011 the Owner Societies.
    view abstract10.1039/c1cp21877h
  • HT-PEM fuel cell system with integrated complex metal hydride storage tank
    Urbanczyk, R. and Peil, S. and Bathen, D. and Heßke, C. and Burfeind, J. and Hauschild, K. and Felderhoff, M. and Schüth, F.
    Fuel Cells 11 (2011)
    A hydrogen storage tank based on the metal hydride sodium alanate is coupled with a high temperature PEM fuel cell (HT-PEM). The waste heat of the fuel cell is used for desorbing hydrogen from the storage tank that in return feeds the fuel cell. ZBT has developed the HT-PEM fuel cell, Max-Planck-Institut für Kohlenforschung the sodium alanate, and IUTA the hydrogen storage tank. During the experiments of the system the fuel cell was operated by load cycling from 165 up to 240 W. Approximately 60 g of hydrogen were delivered from the tank, which was charged with 2676.8 g of sodium alanate doped with 4 mol.% of TiCl 3. This amount of hydrogen was desorbed in 3 h and generated a cumulated electrical energy of 660 Wh. In the first cycle 81.5 g of hydrogen were supplied during 3.69 h to the HT-PEM fuel cell, which was operated nearly constant at 260 W. In the latter case the cumulated electrical energy was 941 Wh. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/fuce.201100012
  • Hydrogen storage properties of nanostructured MgH2/TiH 2 composite prepared by ball milling under high hydrogen pressure
    Shao, H. and Felderhoff, M. and Schüth, F.
    International Journal of Hydrogen Energy 36 (2011)
    Nanostructured MgH2/0.1TiH2 composite was synthesized directly from Mg and Ti metal by ball milling under an initial hydrogen pressure of 30 MPa. The synthesized composite shows interesting hydrogen storage properties. The desorption temperature is more than 100 °C lower compared to commercial MgH2 from TG-DSC measurements. After desorption, the composite sample absorbs hydrogen at 100 °C to a capacity of 4 mass% in 4 h and may even absorb hydrogen at 40 °C. The improved properties are due to the catalyst and nanostructure introduced during high pressure ball milling. From the PCI results at 269, 280, 289 and 301 °C, the enthalpy change and entropy change during the desorption can be determined according to the van't Hoff equation. The values for the MgH2/0.1TiH2 nano-composite system are 77.4 kJ mol-1 H2 and 137.5 J K-1 mol-1 H2, respectively. These values are in agreement with those obtained for a commercial MgH2 system measured under the same conditions. Nanostructure and catalyst may greatly improve the kinetics, but do not change the thermodynamics of the materials. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.ijhydene.2011.05.180
  • Nanostructured Ti-catalyzed MgH2 for hydrogen storage
    Shao, H. and Felderhoff, M. and Schüth, F. and Weidenthaler, C.
    Nanotechnology 22 (2011)
    Nanocrystalline Ti-catalyzed MgH2 can be prepared by a homogeneously catalyzed synthesis method. Comprehensive characterization of this sample and measurements of hydrogen storage properties are discussed and compared to a commercial MgH2 sample. The catalyzed MgH2 nanocrystalline sample consists of two MgH2 phases-a tetrahedral β-MgH2 phase and an orthorhombic high-pressure modification γ-MgH2. Transmission electron microscopy was used for the observation of the morphology of the samples and to confirm the nanostructure. N2 adsorption measurement shows a BET surface area of 108m 2g-1 of the nanostructured material. This sample exhibits a hydrogen desorption temperature more than 130 °C lower compared to commercial MgH2. After desorption, the catalyzed nanocrystalline sample absorbs hydrogen 40 times faster than commercial MgH2 at 300 °C. Both the Ti catalyst and the nanocrystalline structure with correspondingly high surface area are thought to play important roles in the improvement of hydrogen storage properties. The desorption enthalpy and entropy values of the catalyzed MgH2 nanocrystalline sample are 77.7kJmol-1H2 and 138.3JK-1mol -1H2, respectively. Thermodynamic properties do not change with the nanostructure. © 2011 IOP Publishing Ltd.
    view abstract10.1088/0957-4484/22/23/235401
  • Solid-state hydrogen storage for mobile applications: Quo Vadis?
    Weidenthaler, C. and Felderhoff, M.
    Energy and Environmental Science 4 (2011)
    In times of severe shortage of fossil fuels new strategies have to be developed to assure future mobility. Fuel cell driven automotives with hydrogen as an energy carrier is one alternative discussed for the substitution of gasoline in the long term. Both the generation as well as the storage of hydrogen are technical challenges which have to be solved before hydrogen technology can be a real alternative for mobile applications. This perspective paper highlights the state-of-the art in the field of hydrogen storage, especially in solids, including the technical limitations. New potential research fields are discussed which may contribute to future energy supply in niche applications. © 2011 The Royal Society of Chemistry.
    view abstract10.1039/c0ee00771d
  • Complex Hydrides
    Weidenthaler, C. and Felderhoff, M.
    Handbook of Hydrogen Storage: New Materials for Future Energy Storage (2010)
    view abstract10.1002/9783527629800.ch5
  • Direct synthesis of pure complex aluminium hydrides by cryomilling
    Pommerin, A. and Weidenthaler, C. and Schüth, F. and Felderhoff, M.
    Scripta Materialia 62 (2010)
    Simple mechanochemical procedures can be used for the solid-state preparation of stable complex aluminium hydrides as hydrogen storage materials. For the synthesis of unstable complex hydrides, cryomilling at temperatures at which product decomposition does not take place under milling conditions appears to be a viable method. To probe the potential of cryomilling for the synthesis of complex aluminium hydrides, the reactions of different alkaline hydrides with AlH3 were tested under these conditions. © 2009 Acta Materialia Inc.
    view abstract10.1016/j.scriptamat.2009.12.041
  • Influence of the ball milling conditions on the preparation of rare earth aluminum hydrides
    Pommerin, A. and Felderhoff, M. and Schüth, F. and Weidenthaler, C.
    Scripta Materialia 63 (2010)
    The ball milling conditions in the preparation of rare earth aluminum hydrides from NaAlH4 and rare earth chlorides have a significant influence on product formation. Defined milling times and appropriate rotational speeds are required to obtain the desired products. It has been shown that starting directly from Na3AlH6 does not lead to the formation of REAlH6. Starting from rare earth iodides instead of chlorides allows dissolution of the alkali metal iodide formed and, therewith, the preparation of salt-free rare earth aluminum hydrides. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.scriptamat.2010.08.020

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