Prof. Dr. Angelika Beate Heinzel

Energy Technology
University of Duisburg-Essen


  • Investigation of the effect of carbon post- vs pre-coated metallic bipolar plates for PEMFCs – start-up and shut-down
    Müller, M.-V. and Giorgio, M. and Hausmann, P. and Kinlechner, L. and Heinzel, A. and Schwämmlein, J.
    International Journal of Hydrogen Energy 47 (2022)
    In this work, the influence of increased potentials during the start-up/shut-down process on metallic bipolar plates (316L) with the coating system Cr/a-C based on graphite-like carbon is investigated. In comparison to commonly applied post-coated bipolar plates, a new low-cost manufacturing process based on pre-coated metal sheets for bipolar plates was evaluated. By developing a vehicle near start-up/shut-down cycle, a relative humidity of 140% and anode residence time of 0.94 s show the greatest damage potential of the cycle variations. After 2000 start-up/shut-down cycles, pre-coated metallic bipolar plates show no increased voltage loss compared to conventional coatings. Nevertheless, the resistances increase for Cr/a-C post- and pre-coating at the H2 outlet. This correlates with an increased surface roughness of the bipolar plate but otherwise only minor surface changes can be observed. The coating variation has no effect on the extent of catalyst coated membrane thinning or increased content of metal ions. © 2021 Hydrogen Energy Publications LLC
    view abstract10.1016/j.ijhydene.2021.12.179
  • Techno-economic system analysis of an offshore energy hub with an outlook on electrofuel applications
    Thommessen, C. and Otto, M. and Nigbur, F. and Roes, J. and Heinzel, A.
    Smart Energy 3 (2021)
    The integration of cross-sectoral energy hubs into large-scale wind farms opens up existing structures to new applications and contributes to achieving renewable energy systems and climate protection targets. The offshore energy hub concept consists in establishing an artificially constructed energy conversion and distribution hub that addresses two energy-related markets by power supply to public grids and by potentially enabling the conversion of renewable electricity into hydrogen or ammonia and supplying it ashore. Hence, the energy hub concept enables smart integration of offshore wind power into gas grids. Power generation on demand from stored green gas is able to cover residual power loads at low carbon intensity. Electrofuel production provides also the opportunity to export renewable fuels for sectors with traditionally high greenhouse gas emissions, e.g., agriculture or transportation. In this contribution an energy hub system in the North Sea is modeled and simulated to determine production quantities and efficiencies of electricity, hydrogen and ammonia. When comparing the efficiencies of production, storage, and transport values of 45.1–65% for hydrogen and values of 52–52.3% for ammonia were determined. Re-conversion to electricity with fuel cells of both hydrogen and ammonia is less efficient and cost worthly than their use in electrofuel applications. Because of emerging and potential cost reductions a sensitivity analysis is performed where lower capital costs (50%) lead to cost reductions in hydrogen (42–45%) and ammonia production (40–42%). Results show that energy hubs can become sustainable pillars in future energy systems through improving cost-competitiveness of wind power. © 2021 The Authors
    view abstract10.1016/j.segy.2021.100027
  • Investigation and equalisation of the flow distribution in a fuel cell stack
    Bürkle, F. and Moyon, F. and Feierabend, L. and Wartmann, J. and Heinzel, A. and Czarske, J. and Büttner, L.
    Journal of Power Sources 448 (2020)
    The possibility to use fuel cells as an electrical power source makes them interesting for a wide range of applications. In this work, computational fluid dynamics (CFD) simulations and optical measurements are performed to predict the flow distribution in a flow setup resembling the parallel flow circuits in fuel cell stacks. For the first time it is shown that by an adaptation of the port sizes in the inlet manifold to the individual fuel cells, the average global deviation between the flow rates can be reduced from 10.1% to 4.0% by means of a model experiment. The measurements are performed with a high resolution laser Doppler velocity profile sensor (LD-PS) specifically developed for measurements in small-scale channels, in this work 4×1 mm2, allowing for a spatial resolution below 2 μm and relative velocity uncertainties below 0.1%, helping to resolve installation effects possibly occurring in fuel cells to improve their efficiency. The presented results can be used by manufacturers to increase the efficiency of their fuel cell stacks. © 2019 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2019.227546
  • Thermal post treatment of highly filled compounds for fuel cells
    Kayser, A. and Grundler, M. and Heinzel, A.
    AIP Conference Proceedings 2289 (2020)
    Functionalized polymers in general are claiming more and more novel applications; for example they can function as a metal replacement. Especially the E&E- market or the so-called "green technologies" require highly engineered polymers for many new needs such as a high level of thermal or electrical conductivity in polymers. To functionalize an intrinsic isolating polymer high loadings of conductive fillers, like graphite, carbon blacks, CNTs, metals and/or others, are necessary. For fuel cell application filler contents of more than 80 wt% in a thermoplastic polymer are needed. The mixtures, so-called compounds, exhibit a significantly different behavior in processing and in their properties compared to neat polymer. Especially viscosity sensitive processing techniques such as injection molding are often limiting the amount of filler that is applicable and therefore also limiting achievable conductivity. A low resistivity is critical for the use in fuel cells. At ZBT a new thermal post treatment technique was developed that can decrease resistivity of injection molded bipolar plates significantly. Reduction of resistivity ranged up to 76%. The influence of filler content, particle size, morphology, time and temperature of treatment were investigated extensively and the mechanism behind the temperature treatment was studied in detail. Using DSC and XRD method the change in crystallinity was found to be the driving factor suggesting that percolation in filled compounds is not only based upon degree of filling but also crystallinity of polymer. Furthermore temperature treatment showed great promise for implementation in future injection molding process of highly conductive compounds as even short times of thermal post treatment lead to a significant effect. © 2020 American Institute of Physics Inc.. All rights reserved.
    view abstract10.1063/5.0028718
  • Effect of the cyclic freeze-Thaw exposure on the performance of PEM fuel cells
    Gorelkov, S. and Palecki, S. and Heinzel, A.
    2019 European Space Power Conference, ESPC 2019 (2019)
    In this study, the behaviour of Polymer-Electrolyte Membrane (PEM) single cells with different types of MEA systems have been studied under thermal cycling with respect to structural and electrochemical changes. The cells have been insulated and exposed to repeated freeze-Thaw cycles with a minimum temperature of-40°C inside an environmental chamber. To some extent, great differences between the degrees of damage could be found for the various types of MEA systems (e.g. catalyst coated membrane (CCM), catalyst coated substrate (CCS)). © 2019 IEEE.
    view abstract10.1109/ESPC.2019.8932015
  • Membrane Fuel Cells [Membranbrennstoffzellen]
    Heinzel, A. and Beckhaus, P. and Karstedt, J.
    Chemie-Ingenieur-Technik 91 (2019)
    With the development of polymer membranes suitable as proton-conducting electrolytes, membrane fuel cells are now successfully applied in various areas. Depending on the application, the service life, the power density or other system aspects are optimized. Common to all applications is the requirement to reduce costs, which, however, plays a decisive role especially in passenger cars. The development of the membrane fuel cell has now reached a high technical level, but political flanking measures are still required to launch it on the market. This applies both to the hydrogen infrastructure for fuel cell vehicles and to the promotion of fuel cell-based combined heat and power generation. © 2019, Wiley-VCH Verlag. All rights reserved.
    view abstract10.1002/cite.201800194
  • Micro Alkaline Fuel Cell supported by MEMS-based Backbone
    Pilaski, M. and Sun, S.-H. and Dura, G. and Wartmann, J. and Letzkus, F. and Heinzel, A.
    Journal of Physics: Conference Series 1407 (2019)
    This work presents the application of nitride membranes produced with Si-MEMS-technology as a platform to build up new membrane-electrode assemblies (MEA) for alkaline fuel cells. Active alkaline fuel cell MEAs were combined by integrating hydroxide permeable electrolyte into micro-channels of 1 μm diameter in 5 to 10 μm thick MEMS-based membranes. A platinum catalyst was sprayed onto the surface and an electric conductive layer was applied on top. Taking advance of the small form factor these fuel cells can be applied in small devices with low energy demand. © Published under licence by IOP Publishing Ltd.
    view abstract10.1088/1742-6596/1407/1/012006
  • Significance of Cogeneration for Germany's Future Energy Supply
    Thommessen, C. and Witte, N. and Nigbur, F. and Roes, J. and Heinzel, A. and Verheyen, O.M.
    Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019 (2019)
    The continuous expansion of renewable energy sources leads to changes in supply systems. More flexibility is necessary since the degree of dependency on volatile renewables increases. This new paradigm affects the runtime of conventional plants and a characteristic change of the residual load, which must be covered by controllable systems. State-of-the-art studies resolve the future flexibility challenge non-congruent because of their given viewing point. The contribution of this paper is an analysis on the sense of cogeneration plants as flexible supply option in Germany's urban energy systems. Results show that cogeneration operation is eligible to cover major fluctuations of the residual load and to avoid many issues, which arise from increasing decentral renewable power generation and relate to all sectors electricity, heat, gas, and mobility. © 2019 IEEE.
    view abstract10.1109/ISGTEurope.2019.8905477
  • Assessment of available thermal capacity of district heating systems for increased medium-and short-term flexibility of multi-modal power systems
    Hinker, J. and Kippelt, S. and Myrzik, J.M.A. and Witte, N. and Heinzel, A.
    2017 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2017 - Proceedings 2018-January (2018)
    In theory, district heating systems (DHS) offer an opportunity to increase the flexibility of combined heat-and-power (CHP) plants by working as short- and medium-term thermal storage. Using this capacity, it is possible to dispatch CHP units more flexibly and thus offer, e.g., operating reserve for the electric grid without any additional investments in thermal storages. State-of-the-art optimization studies use this flexibility, but do not show the lever for further tweaks. This work's contribution is to analyze the actual extent of flexibility and the reasons for current limitations in detail. To this end, a model of the propagation of temperature fronts is suggested and applied, and the general applicability of pre-charging a DHS is proved by simulation. A thorough study of design and operation parameter changes is then conducted. Results show that some system variables (e.g., the thermal demand) must be forecast precisely to determine the absorbable thermal power, and that a smart design of system parameters (e.g., supply temperatures) can increase the flexibility. © 2017 IEEE.
    view abstract10.1109/ISGTEurope.2017.8260129
  • Development of a centrifugal fan with increased part-load efficiency for fuel cell applications
    Burgmann, S. and Fischer, T. and Rudersdorf, M. and Roos, A. and Heinzel, A. and Seume, J.
    Renewable Energy 116 (2018)
    Centrifugal fans are suitable for the air supply of fuel cells because of their relatively high efficiency and low power consumption. Fuel cells are operated over a broad range of current densities, which is proportional to the air mass flow rate, i.e., the air supply system needs to provide high efficiencies over a wide range of mass flow. To achieve this target, a centrifugal fan equipped with a diffuser and volute with variable cross-sectional area is developed based on numerical simulations (CFD), laser-optical flow measurements (PIV) and performance measurements of the centrifugal fan. The geometrical variability is achieved by a movable backplate of the diffuser and the volute. The variable cross-sectional area of the diffuser and volute allows maintaining high efficiencies and pressure ratios for operating points at off-design. A small diffuser width is suitable for low mass flow rates, and a large diffuser width for high mass flow rates. Thus, efficiency of the centrifugal fan can be increased at part-load operation by up to 7.1% points by appropriately adjusting the diffuser width. As a result the parasitic power consumption of the air supply system is reduced and hence the overall efficiency of the fuel cell system increases. © 2017 Elsevier Ltd
    view abstract10.1016/j.renene.2017.09.075
  • Effects, Damage Characteristics and Recovery Potential of Traffic-induced Nitric Oxide Emissions in PEM Fuel Cells under Variable Operating Conditions
    Misz, U. and Talke, A. and Heinzel, A. and Beckhaus, P.
    Fuel Cells 18 (2018)
    Understanding of the influence of traffic-related nitrogen oxides on proton exchange membrane (PEM) fuel cells is essential to improve life time and durability of fuel cell vehicles. In a 3-year work, both the damaging mechanisms and the influence of NOx on PEM fuel cells under real environmental and operating conditions became more comprehensible. It could be shown that even a low concentration level of 150 ppb NOx, which is often exceeded in traffic areas, causes considerable power losses. Furthermore, NO leads to significantly faster voltage drops compared to NO2, so typical NO peaks during rush hour traffic can reduce the fuel cell power. The concentration profile also has an influence on the degradation. The impact of NOx peaks is more negative compared to continuous NOx dosing when charging the fuel cell with the same total amount of NOx. It is possible to recover the fuel cell but it takes several hours depending on operating conditions and prior contamination level. To increase the recovery process the fuel cell has to be operated at a cathode potential below 0.3 V to reduce NOx and detach the contaminant from the platinum catalyst. A negative effect is the formation of NH4 +, which is suspected to decompose the membrane in long term perspective. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/fuce.201700214
  • How the colloid chemistry of precursor electrocatalyst dispersions is related to the polymer electrolyte membrane fuel cell performance
    Bredol, M. and Szydło, A. and Radev, I. and Philippi, W. and Bartholomäus, R. and Peinecke, V. and Heinzel, A.
    Journal of Power Sources 402 (2018)
    Polymer electrolyte membrane fuel cells (PEMFCs) operating at low temperature (60–80 °C, up to 110 °C) are mostly limited in their performance by the kinetics of the oxygen reduction reaction (ORR), leading to high loadings of platinum (Pt) in the cathode. Pt catalysts are without alternative in numerous industrial applications, and since Pt resources are limited, the associated high costs for low temperature fuel cells are hindering among other factors their commercialization. In order to increase the fraction of electrocatalytically available Pt towards ORR, this work is devoted to the factors responsible for the microstructure of the PEMFC cathodes. Typically, the active layers are coated by processes like spraying, doctor blading, printing etc. Therefore, the final structure actually is strongly dependent on the coating process and the physicochemical properties of the catalyst dispersions used. Selecting commercially available electrocatalysts from Johnson-Matthey and Tanaka as active material and ultrasonically assisted spraying as the coating method, systematic variations of the surface chemistry of the catalyst particles and their influence on catalyst layer morphology and therefore electrical and electrochemical properties of resulting membrane electrode assemblies (MEA) have been investigated. It could be shown, that the colloid–chemical properties of the catalyst dispersions have a profound influence not only on the microstructure of the MEAs but also on the performance under operating conditions. © 2018 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2018.09.005
  • Influence of nitrogen compounds on PEMFC: A comparative study
    Talke, A. and Misz, U. and Konrad, G. and Heinzel, A.
    Journal of the Electrochemical Society 165 (2018)
    Cyclic voltammetry, electrochemical impedance spectroscopy and current distribution measurements are employed at single cells and a fuel cell stack to reveal the differences and interrelations of ammonia, nitrogen oxide and nitrogen dioxide. It is shown that both nitrogen oxides are adsorbed at the catalyst as NO. The adsorption of NO2 is weaker and therefore leads to a lower and slower degradation. Moreover, all gases cause inhomogeneous stress of the MEA, which can lead to an accelerated degradation of the fuel cell. NH3 shows a combined reaction by partly being adsorbed as a nitric oxide and partly reacting with the perfluorosulfonic acid groups of the ionomer. © The Author(s) 2018. Published by ECS.
    view abstract10.1149/2.0181806jes
  • Influence of urban air on proton exchange membrane fuel cell vehicles – Long term effects of air contaminants in an authentic driving cycle
    Talke, A. and Misz, U. and Konrad, G. and Heinzel, A. and Klemp, D. and Wegener, R.
    Journal of Power Sources 400 (2018)
    Traffic related air pollutants cause power losses and decrease the lifetime of proton exchange membrane fuel cell (PEMFC). The relevance of this influence for vehicles is not exactly known due to a lack of studies under realistic conditions. Therefore, the present study aims at a better understanding. For the first time ever the influence of selected air pollutants on automobile fuel cell short stacks with different platinum loadings and a realistic driving cycle is examined. The driving cycle used, is an existing course near the city of Stuttgart, Germany. The experiments were accompanied with online measurements of relevant contaminant concentrations on the course. Furthermore, tests with a semi-dynamic profile have been executed for more than 1500 h and show an irreversible damage of the PEMFC by nitrogen oxides. With respect to the present results, spontaneous power losses of about 5% and over 10% in special situations by the nitrogen oxides can be expected for fuel cell vehicles in urban areas. NH3 will lead to a spontaneous power loss of less than 3%, but causes a progressive irreversible damage. Together the tests reveal that air pollutants have a significant negative influence on fuel cell vehicles in urban areas. © 2018 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2018.08.063
  • Investigation of Carbon Nanofiber-supported Electrocatalysts with Ultra-low Platinum Loading for the Use in PEM Fuel Cells
    Podleschny, P. and Rost, U. and Muntean, R. and Marginean, G. and Heinzel, A. and Peinecke, V. and Radev, I. and Muhler, M. and Brodmann, M.
    Fuel Cells 18 (2018)
    The present study aims to investigate gas diffusion electrodes with ultra-low platinum loading and increased durability, prepared by pulsed electrodeposition process, applicable for polymer electrolyte membrane fuel cells (PEMFC). Testing was performed both, in situ in a PEMFC test bench while prepared GDEs were compared to anodes and cathodes with commercially available catalysts by Johnson Matthey (JM), as well as ex situ regarding electrochemical properties and catalyst layer structure. High and stable performance of developed electrodes was achieved, while the Pt catalyst loading of investigated anodes and cathodes was reduced to 10 µgPt cm−2. The catalyst deposition was achieved via pulsed electrodeposition process from H2PtCl6-containing electrolyte on an oxygen plasma-pretreated corrosion-stable carbon nanofiber (CNF) support. In situ performance tests show a similar operation behavior of the compared anodes, while activation losses of investigated cathodes are high due to the limited amount of catalyst material. However, Pt/CNF_c cathodes show significantly higher power densities than cathodes prepared with JM catalyst. Membrane electrode assemblies containing developed Pt/CNF_a anodes with 10 µgPt cm−2 reached a power density of 0.525 W cm−2 at a cell potential of 0.65 V, which was similar to anodes with commercially available HiSPEC 2000 catalysts by JM. Accelerated stress tests (AST) revealed that Pt/CNF_a anodes preserve their performance, whereas the commercial catalyst degraded severely. Cyclic voltammetry (CV) indicated a high electrochemical active surface area of Pt/CNF_a anodes. Moreover, the electrode characteristics, analyzed via electrochemical impedance spectroscopy after AST, showed marginal anode degradation. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/fuce.201700220
  • Proton Exchange Membrane Water Electrolysis Modeling for System Simulation and Degradation Analysis
    Gößling, S. and Stypka, S. and Bahr, M. and Oberschachtsiek, B. and Heinzel, A.
    Chemie-Ingenieur-Technik 90 (2018)
    This paper presents a numeric model for proton exchange membrane electrolysis, which describes the current-voltage dependency. Besides physical constants and parameters characterizing material properties, it also contains parameters that cannot be measured ex situ, e.g., charge transfer coefficients and exchange current densities. To determine these parameters, the model includes an automated parameter calibration procedure that is able to find the best parameter combinations. An exemplary integration of the model in MATLAB/Simulink is presented, including a validation with dynamic measurement data. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cite.201800041
  • Testing Field for PEM, Alkaline and Solid Oxide Electrolysis Technology
    Stypka, S. and Oberschachtsiek, B. and Radev, I. and Heinzel, A.
    Chemie-Ingenieur-Technik 90 (2018)
    To test commercially available water electrolysis systems under dynamic (close-to-real) operation a test area with three different electrolyzers is build up, covering the significant technologies alkaline water electrolysis, proton exchange membrane water electrolysis, and high temperature steam electrolysis using solid oxide electrolysis cells. The hydrogen outputs of the systems are in the range between 5 to 10 Nm3 h−1 hydrogen at delivery pressures between 10 and 35 bar. Additional balance of plant is installed to demonstrate and evaluate the utilization of hydrogen for different applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/cite.201800039
  • Alkaline fuel cell with nitride membrane
    Sun, S.-H. and Pilaski, M. and Wartmann, J. and Letzkus, F. and Funke, B. and Dura, G. and Heinzel, A.
    Proceedings of SPIE - The International Society for Optical Engineering 10246 (2017)
    The aim of this work is to fabricate patterned nitride membranes with Si-MEMS-technology as a platform to build up new membrane-electrode-assemblies (MEA) for alkaline fuel cell applications. Two 6-inch wafer processes based on chemical vapor deposition (CVD) were developed for the fabrication of separated nitride membranes with a nitride thickness up to 1 μm. The mechanical stability of the perforated nitride membrane has been adjusted in both processes either by embedding of subsequent ion implantation step or by optimizing the deposition process parameters. A nearly 100% yield of separated membranes of each deposition process was achieved with layer thickness from 150 nm to 1 μm and micro-channel pattern width of 1μm at a pitch of 3 μm. The process for membrane coating with electrolyte materials could be verified to build up MEA. Uniform membrane coating with channel filling was achieved after the optimization of speed controlled dip-coating method and the selection of dimethylsulfoxide (DMSO) as electrolyte solvent. Finally, silver as conductive material was defined for printing a conductive layer onto the MEA by Ink-Technology. With the established IR-thermography setup, characterizations of MEAs in terms of catalytic conversion were performed successfully. The results of this work show promise for build up a platform on wafer-level for high throughput experiments. © 2017 SPIE.
    view abstract10.1117/12.2265689
  • Frost induced damages within porous materials - from concrete technology to fuel cells technique
    Palecki, S. and Gorelkov, S. and Wartmann, J. and Heinzel, A.
    Journal of Power Sources 372 (2017)
    Porous media like concrete or layers of membrane electrode assemblies (MEA) within fuel cells are affected by a cyclic frost exposure due to different damage mechanisms which could lead to essential degradation of the material. In general, frost damages can only occur in case of a specific material moisture content. In fuel cells, residual water is generally available after shut down inside the membrane i.e. the gas diffusion layer (GDL). During subsequent freezing, this could cause various damage phenomena such as frost heaves and delamination effects of the membrane electrode assembly, which depends on the location of pore water and on the pore structure itself. Porous materials possess a pore structure that could range over several orders of magnitudes with different properties and freezing behaviour of the pore water. Latter can be divided into macroscopic, structured and pre-structured water, influenced by surface interactions. Therefore below 0 °C different water modifications can coexist in a wide temperature range, so that during frost exposure a high amount of unfrozen and moveable water inside the pore system is still available. This induces transport mechanisms and shrinkage effects. The physical basics are similar for porous media. While the freezing behaviour of concrete has been studied over decades of years, in order to enhance the durability, the know-how about the influence of a frost attack on fuel cell systems is not fully understood to date. On the basis of frost damage models for concrete structures, an approach to describe the impact of cyclic freezing and thawing on membrane electrode assemblies has been developed within this research work. Major aim is beyond a better understanding of the frost induced mechanisms, the standardization of a suitable test procedure for the assessment of different MEA materials under such kind of attack. Within this contribution first results will be introduced. © 2017 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2017.10.065
  • Micrometer-sized nano-structured silicon/carbon composites for lithium-ion battery anodes synthesized based on a three-step Hansen solubility parameter (HSP) concept
    Sehlleier, Y.H. and Dobrowolny, S. and Xiao, L. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Journal of Industrial and Engineering Chemistry 52 (2017)
    The processing towards Si/C composites, components and synthesis parameters were selected based on the concept of Hansen solubility parameters (HSP). Si/polymer composites were generated through modified bulk polymerization and subsequent pyrolysis transformed the polymer into the desired porous carbon matrix. Coulombic efficiencies (CE) in excess of 76% after the first cycle and 99.95% after solid electrolyte interphase (SEI) formation have been achieved. A notably high specific delithiation capacity of around 1600 mAh/g with an extremely stable cycling performance even after 400 cycles is obtained. This scalable and economical synthesis approach is readily applicable to the commercial production of anode materials. © 2017 The Korean Society of Industrial and Engineering Chemistry
    view abstract10.1016/j.jiec.2017.04.001
  • Novel Si-CNT/polyaniline nanocomposites as Lithium-ion battery anodes for improved cycling performance
    Xiao, L. and Sehlleier, Y.H. and Dobrowolny, S. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Materials Today: Proceedings 4 (2017)
    A novel nanocomposite consisting of gas-phased produced Si nanoparticles, carbon nanotubes (CNTs), and polyaniline (PANi) is developed as an anode material (Si-CNT/PANi) for lithium-ion batteries. This nanocomposite integrates the merits from its three components, where Si nanoparticles provide high capacity, CNTs act as an electrically conductive and mechanically flexible network, and PANi coating further enhances the electrical conductivity and protects the silicon structure. An anode made of this nanocomposite shows a high reversible capacity of 2430 mAh/g with good capacity retention over 500 cycles compared to pristine Si. The Si-CNT/PANi nanocomposite also demonstrated a high Coulombic efficiency and improved rate-capabilities. © 2017 Elsevier Ltd.
    view abstract10.1016/j.matpr.2017.09.197
  • Reforming results of a novel radial reactor for a solid oxide fuel cell system with anode off-gas recirculation
    Bosch, T. and Carré, M. and Heinzel, A. and Steffen, M. and Lapicque, F.
    Journal of Power Sources 371 (2017)
    A novel reactor of a natural gas (NG) fueled, 1 kW net power solid oxide fuel cell (SOFC) system with anode off-gas recirculation (AOGR) is experimentally investigated. The reactor operates as pre-reformer, is of the type radial reactor with centrifugal z-flow, has the shape of a hollow cylinder with a volume of approximately 1 L and is equipped with two different precious metal wire-mesh catalyst packages as well as with an internal electric heater. Reforming investigations of the reactor are done stand-alone but as if the reactor would operate within the total SOFC system with AOGR. For the tests presented here it is assumed that the SOFC system runs on pure CH4 instead of NG. The manuscript focuses on the various phases of reactor operation during the startup process of the SOFC system. Startup process reforming experiments cover reactor operation points at which it runs on an oxygen to carbon ratio at the reactor inlet (ϕRI) of 1.2 with air supplied, up to a ϕRI of 2.4 without air supplied. As confirmed by a Monte Carlo simulation, most of the measured outlet gas concentrations are in or close to equilibrium. © 2017 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2017.10.025
  • Analysis of liquid water formation in polymer electrolyte membrane (PEM) fuel cell flow fields with a dry cathode supply
    Gößling, S. and Klages, M. and Haußmann, J. and Beckhaus, P. and Messerschmidt, M. and Arlt, T. and Kardjilov, N. and Manke, I. and Scholta, J. and Heinzel, A.
    Journal of Power Sources 306 (2016)
    PEM fuel cells can be operated within a wide range of different operating conditions. In this paper, the special case of operating a PEM fuel cell with a dry cathode supply and without external humidification of the cathode, is considered. A deeper understanding of the water management in the cells is essential for choosing the optimal operation strategy for a specific system. In this study a theoretical model is presented which aims to predict the location in the flow field at which liquid water forms at the cathode. It is validated with neutron images of a PEM fuel cell visualizing the locations at which liquid water forms in the fuel cell flow field channels. It is shown that the inclusion of the GDL diffusion resistance in the model is essential to describe the liquid water formation process inside the fuel cell. Good agreement of model predictions and measurement results has been achieved. While the model has been developed and validated especially for the operation with a dry cathode supply, the model is also applicable to fuel cells with a humidified cathode stream. © 2015 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.jpowsour.2015.12.060
  • High-yield and scalable synthesis of a Silicon/Aminosilane-functionalized Carbon NanoTubes/Carbon (Si/A-CNT/C) composite as a high-capacity anode for lithium-ion batteries
    Sehlleier, Y.H. and Dobrowolny, S. and Plümel, I. and Xiao, L. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Journal of Applied Electrochemistry 46 (2016)
    In this study, we present a novel anode architecture for high-performance lithium-ion batteries based on a Silicon/3-aminosilane-functionalized CNT/Carbon (Si/A-CNT/C) composite. A high-yield, low-cost approach has been developed to stabilize and support silicon as an active anode material. Silicon (Si) nanoparticles synthesized in a hot-wall reactor and aminosilane-functionalized carbon nanotubes (A-CNT) were dispersed in styrene and divinylbenzene (DVB) and subsequently polymerized forming a porous Si/A-CNT/C composite. Transmission electron microscopy showed that this method enables the interconnection and a uniform encapsulation of Si nanoparticles within a porous carbon matrix especially using aminosilane-functionalized CNT (A-CNT). Electrochemical characterization shows that this material can deliver a delithiation capacity of 2293 mAh g−1 with a capacity retention of more than 90 % after 200 cycles at lithiation and delithiation rate of 0.5 C. We conclude that the porous Si/A-CNT/C composite material can accommodate sufficient space for Si volume expansion and extraction and improve the electronic and ionic conduction. Excellent electrochemical performance during repeated cycling can thus be achieved. © 2015, Springer Science+Business Media Dordrecht.
    view abstract10.1007/s10800-015-0897-x
  • Investigation of the flow field inside the manifold of a real operated fuel cell stack using optical measurements and Computational Fluid Mechanics
    Schmieder, F. and Kinaci, M. E. and Wartmann, J. and Konig, J. and Buttner, L. and Czarske, J. and Burgmann, S. and Heinzel, A.
    Journal of Power Sources 304 (2016)
    The versatility of fuel cells enables a wide range of applications. Usually fuel cells are combined to stacks such that the reactant supply of the single cells is achieved via a pipe branching system, the manifold. The overall performance significantly depends on cell flow rates which are related to the fluidic interaction of the manifold and the cells. Computational Fluid Dynamics (CFD) simulations, which are often used to find a suitable design, lack experimental flow data for validation of the numerical results. To enable flow measurements within the small geometries of the manifold and to provide reliable velocity information inside a real fuel cell stack, a low-coherence Laser Doppler Anemometer (LDA) is applied, which uses multi-mode laser light to achieve a spatial resolution of <100 mu m. The use of fluorescent particles and backward scatter mode make the sensor highly suitable for the application in small manifold geometries like in fuel cell stacks. Sensor and measurement technique are validated in simplified stack models and the applicability to air flows is demonstrated. Finally, for the first time, velocity profiles with high spatial resolution inside an operated fuel cell stack are presented, which serve as benchmark for CFD to find an optimal geometry. (C) 2015 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.jpowsour.2015.11.010
  • Polymer compounds with high thermal conductivity
    Grundler, M. and Derieth, T. and Heinzel, A.
    AIP Conference Proceedings 1779 (2016)
    The thermal conductivity of commercially available thermally conductive polymer-compounds is usually between 1 W/mK and 20 W/mK what means that they are already 10 to 100 times higher than the conventional unfilled polymer. During the development at ZBT the values for thermal conductivity of polymer-compounds could be increased to more than 30 W/mK. In order to achieve such conductivities, the compound materials generally consist of a polymer, which functions as a binding matrix, and a high content (up to 80 wt.%) of conductive filler material. In various series of investigations the thermal conductivity but also the mechanical properties and the processing by extrusion and injection molding of the highly filled materials were evaluated. An orientation of filler particles by injection molding could be observed. Images by scanning-electron-microscopy of injection molded samples showed a structure of anisotropic layers which has a significant influence on the values of thermal conductivity. That's why a differentiation of "through-plane" and "tin-plane" thermal conductivity is highly recommended. © 2016 Author(s).
    view abstract10.1063/1.4965485
  • Power Management Optimization of a Fuel Cell/Battery/Supercapacitor Hybrid System for Transit Bus Applications
    Odeim, F. and Roes, J. and Heinzel, A.
    IEEE Transactions on Vehicular Technology 65 (2016)
    In this paper, the optimization of a power management strategy of a fuel cell/battery/supercapacitor hybrid vehicular system is investigated, both offline and in real time. Two offline optimization algorithms, namely, dynamic programming and Pontryagin's minimum principle, are first compared. The offline optimum is used as a benchmark when designing a real-time strategy, which is an inevitable step since the offline optimum is not real-time capable and is oriented only toward minimizing hydrogen consumption, which may result in the unnecessary overloading of the battery. The design and optimization of the real-time strategy makes use of a multiobjective genetic algorithm while taking into account, apart from hydrogen consumption, other important factors, such as the slow dynamics of the fuel cell system and minimizing the battery power burden. As a result, the real-time strategy is found to consume slightly more hydrogen than the offline optimum; however, it dramatically improves system durability. © 2016 IEEE.
    view abstract10.1109/TVT.2015.2456232
  • Sensitivity Analyses on the Impact of Air Contaminants on Automotive Fuel Cells
    Misz, U. and Talke, A. and Heinzel, A. and Konrad, G.
    Fuel Cells 16 (2016)
    It is known that traffic related air contaminants cause power loss, decreasing lifetime or a complete failure of proton exchange membrane fuel cell (PEMFC). Therefore, the present study aims for a better understanding and the development of a data basis for further decisions in dealing with air contaminants for automobile applications. The first section provides an overview of scientific literature about the influence of important air contaminants on proton exchange membrane fuel cells (PEMFC). The second section describes an extensive study of air contaminants at possible automotive operating conditions using a full factorial matrix test. The specific variation of temperature, cell potential and harmful gas concentration resulted in 27 operating points for each used air contaminant. The gases NO, NO2, SO2, NH3, toluene and ethane were used. The results indicate significant degradation but as well the possibility of regeneration. The degradation caused by different harmful gases is both, dependent on temperature and potential. Furthermore, a clear difference of the influence of NO and NO2 at low concentrations could be shown. The experiments give an overview of the cathode harming potential of relevant air contaminants. Hence, the work provides a basis for the development of cathode air filter and regeneration techniques for automotive applications. Copyright © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/fuce.201500159
  • Development of a simulation-software for a hydrogen production process on a solar tower
    Säck, J.-P. and Roeb, M. and Sattler, C. and Pitz-Paal, R. and Heinzel, A.
    Solar Energy 112 (2015)
    A simulation and control model for a two-step thermo-chemical water splitting cycle using metal oxids for the generation of hydrogen with a solar tower system as heat source has been developed. The simulation and control model consists of three main parts, the simulation of the solar flux distribution on the receiver, of the temperatures in the driven reactor modules and the produced hydrogen in the metal oxide.The results of the three parts of the simulation model have been evaluated by comparing and validating them with experimental data from the Hydrosol 100kWth pilot plant at the Plataforma Solar de Almería (PSA) in Spain.With the overall model of the hydrogen production plant that was created, an evaluation of the two-step thermochemical cycle process in combination with a solar tower system was performed. The model was used to perform parametric studies for the development of the plant and the operation strategies. For this purpose, a provision in the overall model was integrated. The simulation helps to reduce the frequency of using the flux measurement system and can be used for the heliostat field control, in particular for the temperature control in the solar chemical reactor modules. Because of these promising results the overall system model is being extended to enable a use as a control model with controller for the temperature control of the two core reactions in the process.The central control variable of the process control was the operating temperatures for the hydrogen production and the regeneration of the two modules. The process control with its PI controller turned out suitable to compensate diurnal changes of solar input power as well as certain statistical fluctuation due to cloud passage. At the same time the limits of the operability and controllability of the process became clear in terms of the minimum of solar power needed and maximum acceptable gradients.With this experience an operating strategy, the basic parameters of the system in operation, especially the starting up and shutdown procedures, regular operation and the response to disturbances were selected and optimized. With this operation/control strategy such a complex system can be operated in the future on a commercial scale automatically. The obtained results can also be adapted for other solar chemical processes. © 2014 Elsevier Ltd.
    view abstract10.1016/j.solener.2014.11.026
  • Energy storage technologies as options to a secure energy supply
    Ausfelder, F. and Beilmann, C. and Bertau, M. and Bräuninger, S. and Heinzel, A. and Hoer, R. and Koch, W. and Mahlendorf, F. and Metzelthin, A. and Peuckert, M. and Plass, L. and Räuchle, K. and Reuter, M. and Schaub, G. and Schiebahn, S. and Schwab, E. and Schüth, F. and Stolten, D. and Teßmer, G. and Wagemann, K. and Ziegahn, K.-F.
    Chemie-Ingenieur-Technik 87 (2015)
    The current energy system is subject to a profound change: A system, designed to cater to energy needs by supplying fossil fuels is now expected to shift to integrate ever larger amounts of renewable energies to achieve overall a more sustainable energy supply. The challenges arising from this paradigm change are currently most obvious in the area of electric power supply. However, it affects the entire energy system, albeit with different effects. Within the energy system, various independent grids fulfill the function to transport and distribute energy or energy carriers in order to address spatially different energy supply and demand situations. Temporal variations are currently addressed by just-in-time production of the required energy form. However, renewable energy sources generally supply their energy independently from any specific energy demand. Their contribution to the overall energy system is expected to increase significantly. Energy storage technologies also represent an option to compensate for a temporal difference in energy supply and demand. Energy storage systems have the ability for a controlled take-up of a certain amount of energy, storing this energy within a storage media on a relevant timescale and a controlled redispatch of the energy after a certain time delay. Energy storage systems can also be constructed as process chains by combinations of unit operations, each covering different aspects of those functions. Large-scale mechanical storage options for electrical power are currently almost exclusively pumped hydro storage. These systems might be complemented in the future by compressed-air storage and maybe liquid-air facilities. There are several electrochemical storage technologies currently under investigation for their suitability as large scale electrical energy storage in various stages of research, development, and demonstration. Thermal energy storage technologies are based on a large variety of storage principles: Sensible heat, latent heat (based on phase transitions), adsorption/desorption processes or on chemical reactions. The latter can be a route to permanent and loss-free storage of heat. Chemical energy storage systems are based on the energy contained within the chemical bonds of the respective storage molecules. These storage molecules can act as energy carriers. Equally well, these compounds can enter various industrial value chains in energy-intensive industrial sectors and are therefore in direct economic competition with established (fossil) supply routes for these compounds. Water electrolysis, producing hydrogen and oxygen, is and will be the key technology for the foreseeable future. Hydrogen can be transformed by various processes to other energy carriers of interest. These transformations make the stored energy accessible by different sectors of the energy system and/or as raw materials for energy-intensive industrial processes. Some functions of energy storage systems can be taken over by industrial processes. Within the overall energy system, chemical energy storage technologies open up opportunities to link, connect and interweave the various energy streams and sectors. While chemical energy storage offers a route for a stronger integration of renewable energy outside the power sector, it also creates new opportunities for increased flexibility, novel synergies and additional optimization. Several examples of specific energy utilization are discussed and evaluated with respect to energy storage applications. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
    view abstract10.1002/cite.201400183
  • Enhanced stability of multilayer graphene-supported catalysts for polymer electrolyte membrane fuel cell cathodes
    Marinkas, A. and Hempelmann, R. and Heinzel, A. and Peinecke, V. and Radev, I. and Natter, H.
    Journal of Power Sources 295 (2015)
    Abstract One of the biggest challenges in the field of polymer electrolyte membrane fuel cells (PEMFC) is to enhance the lifetime and the long-term stability of PEMFC electrodes, especially of cathodes, furthermore, to reduce their platinum loading, which could lead to a cost reduction for efficient PEMFCs. These demands could be achieved with a new catalyst support architecture consisting of a composite of carbon structures with significant different morphologies. A highly porous cathode catalyst support layer is prepared by addition of various carbon types (carbon black particles, multi-walled carbon nanotubes (MWCNT)) to multilayer graphene (MLG). The reported optimized cathodes shows extremely high durability and similar performance to commercial standard cathodes but with 89% lower Pt loading. The accelerated aging protocol (AAP) on the membrane electrode assemblies (MEA) shows that the presence of MLG increases drastically the durability and the Pt-extended electrochemical surface area (ECSA). In fact, after the AAP slightly enhanced performance can be observed for the MLG-containing cathodes instead of a performance loss, which is typical for the commercial carbon-based cathodes. Furthermore, the presence of MLG drastically decreases the ECSA loss rate. The MLG-containing cathodes show up to 6.8 times higher mass-normalized Pt-extended ECSA compared to the commercial standard systems. © 2015 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2015.06.126
  • Influence of carbon content, particle size, and partial manganese substitution on the electrochemical performance of LiFexMn1-xPO4/carbon composites
    Hamid, N.A. and Wennig, S. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Ionics 21 (2015)
    LiFePO<inf>4</inf>/C and LiFe<inf>x</inf>Mn<inf>1-x</inf>PO<inf>4</inf>/C (x = 0.7) nanocomposites were successfully synthesized via scalable spray-flame synthesis followed by solid-state reaction. A solution of iron (III) acetylacetonate and tributyl phosphate in toluene was used to produce amorphous, nanosized FePO<inf>4</inf>⋅H<inf>2</inf>O in a spray-flame reactor which was then milled with Li<inf>2</inf>CO<inf>3</inf> and glucose to produce a LiFePO<inf>4</inf>/C composite material in a solid-state reaction. The influence of calcination temperature and carbon content on the properties of the resulting material was investigated using specific surface area measurements (BET), X-ray diffraction (XRD), electron microscopy, and electrochemical characterization. The impact of manganese addition on the electrochemical behavior was analyzed using cyclic voltammetry (CV) and constant-current (CC) measurements. XRD shows that the combination of gas-phase synthesis and subsequent solid-state reaction yields highly pure LiFePO<inf>4</inf>/C. BET measurement revealed that the particle size of LiFePO<inf>4</inf> in the composite depends on the amount of glucose. A discharge capacity of more than 140 mAh/g at C/20 is achieved for LiFePO<inf>4</inf>/C with a carbon content of 6 wt%. This material supports high charge as well as discharge rates delivering more than 60 mAh/g at 16 C and sustains good cycle stability providing 115 mAh/g at 1 C. The energy density of the olivine increases about 10 % by substituting 30 mol% of iron by manganese while preserving the electrochemical performance of pure LiFePO<inf>4</inf>/C. © 2015, Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s11581-015-1366-6
  • Photothermally induced bromination of carbon/polymer bipolar plate materials for fuel cell applications
    Schade, M. and Franzka, S. and Cappuccio, F. and Peinecke, V. and Heinzel, A. and Hartmann, N.
    Applied Surface Science 336 (2015)
    A facile photothermal procedure for direct functionalization of carbon/polymer bipolar plate materials is demonstrated. Through irradiation with a microfocused beam of an Ar+-laser at λ = 514 nm in gaseous bromine and distinct laser powers and pulse lengths local bromination of the carbon/polymer material takes place. At a 1/e spot diameter of 2.1 μm, functionalized surface areas with diameters down to 5 μm are fabricated. In complementary experiments large-area bromination is investigated using an ordinary tungsten lamp. For characterization contact angle goniometry, X-ray photoelectron spectroscopy and electron microscopy in conjunction with labeling techniques are employed. After irradiation bromine groups can easily be substituted by other chemical functionalities, e.g. azide and amine groups. This provides a facile approach in order to fabricate surface patterns and gradient structures with varying wetting characteristics. Mechanistic aspects and prospects of photothermal routines in micropatterning of carbon/polymer materials are discussed. © 2014 Published by Elsevier B.V.
    view abstract10.1016/j.apsusc.2014.09.161
  • Power management optimization of an experimental fuel cell/battery/supercapacitor hybrid system
    Odeim, F. and Roes, J. and Heinzel, A.
    Energies 8 (2015)
    In this paper, an experimental fuel cell/battery/supercapacitor hybrid system is investigated in terms of modeling and power management design and optimization. The power management strategy is designed based on the role that should be played by each component of the hybrid power source. The supercapacitor is responsible for the peak power demands. The battery assists the supercapacitor in fulfilling the transient power demand by controlling its state-of-energy, whereas the fuel cell system, with its slow dynamics, controls the state-of-charge of the battery. The parameters of the power management strategy are optimized by a genetic algorithm and Pareto front analysis in a framework of multi-objective optimization, taking into account the hydrogen consumption, the battery loading and the acceleration performance. The optimization results are validated on a test bench composed of a fuel cell system (1.2 kW, 26 V), lithium polymer battery (30 Ah, 37 V), and a supercapacitor (167 F, 48 V).
    view abstract10.3390/en8076302
  • Si-CNT/rGO Nanoheterostructures as High-Performance Lithium-Ion-Battery Anodes
    Xiao, L. and Sehlleier, Y.H. and Dobrowolny, S. and Orthner, H. and Mahlendorf, F. and Heinzel, A. and Schulz, C. and Wiggers, H.
    ChemElectroChem 2 (2015)
    A robust and electrochemically stable 3D nanoheterostructure consisting of Si nanoparticles (NPs), carbon nanotubes (CNTs) and reduced graphene oxide (rGO) is developed as an anode material (Si-CNT/rGO) for lithium-ion batteries (LIBs). It integrates the benefits from its three building blocks of Si NPs, CNTs, and rGO; Si NPs offer high capacity, CNTs act as a mechanical, electrically conductive support to connect Si NPs, and highly electrically conductive and flexible rGO provides a robust matrix with enough void space to accommodate the volume changes of Si NPs upon lithiation/delithiation and to simultaneously assure good electric contact. The composite material shows a high reversible capacity of 1665mAhg-1 with good capacity retention of 88.6% over 500 cycles when cycled at 0.5C, that is, a 0.02% capacity decay per cycle. The high-power capability is demonstrated at 10C (16.2Ag-1) where 755mAhg-1 are delivered, thus indicating promising characteristics of this material for high-performance LIBs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/celc.201500323
  • Silicon/carbon nano-composite based anodes for advanced lithium-ion batteries
    Dobrowolny, S. and Mahlendorf, F. and Heinzel, A.
    ECS Transactions 66 (2015)
    In this study, the investigation of high capacity and high efficiency graphene coated silicon composite (Si/C composite) based electrodes prepared by using a wet chemical manufacturing process is presented. The active material provides a capacity of >2000 mAh g-1 with a coulombic efficiency >99% for more than 500 cycles. The focus is set to the investigation of the electrode structure during cycling progression by using galvanostatic cycling, electrochemical impedance spectroscopy, scanning electron microscopy, confocal microscopy and the measurement of the coating adhesion strength. Results show the applicability of improved Si/C composite electrodes for future lithium-ion batteries, both in half cells as well as in full cells in combination with a commercially available cathode material. © The Electrochemical Society.
    view abstract10.1149/06609.0029ecst
  • The influence of different pre-treatments of current collectors and variation of the binders on the performance of Li4Ti5O12 anodes for lithium ion batteries
    Wennig, S. and Langklotz, U. and Prinz, G.M. and Schmidt, A. and Oberschachtsiek, B. and Lorke, A. and Heinzel, A.
    Journal of Applied Electrochemistry 45 (2015)
    In order to optimize the electron transfer between the Li<inf>4</inf>Ti<inf>5</inf>O<inf>12</inf>-based active mass and the current collector, the surface of aluminum foil was modified either by alkaline etching or by a carbon coating. The as-modified aluminum foils were coated with an active mass of Li<inf>4</inf>Ti<inf>5</inf>O<inf>12</inf> mixed with polyvinylidene fluoride, sodium carboxymethyl cellulose, or polyacrylic acid as binders. Untreated aluminum and copper foils served as reference current collectors. The corrosion reactions of aluminum foil with the applied binder solutions were studied and the electrode structure has been analyzed, depending on the binder. Finally, the electrochemical performance of the prepared electrodes was investigated. Based on these measurements, conclusions concerning the electrical contact between the different current collectors and the active masses were drawn. The energy density of the Li<inf>4</inf>Ti<inf>5</inf>O<inf>12</inf> electrodes cast on carbon-coated aluminum foils was significantly increased, compared to the corresponding electrodes with a copper current collector. © 2015, Springer Science+Business Media Dordrecht.
    view abstract10.1007/s10800-015-0878-0
  • Chemical functionalization of carbon/polymer bipolar plate materials via oxygen plasma activation and subsequent silanization
    Schade, M. and Franzka, S. and Schröter, A. and Cappuccio, F. and Gajda, M. and Peinecke, V. and Heinzel, A. and Hartmann, N.
    Surface and Coatings Technology 240 (2014)
    A simple coating routine in order to tune the wettability of carbon/polymer bipolar plate materials is presented. Standard carbon/polypropylene composite materials as used for commercial bipolar plates for polymer-electrolyte-membrane fuel cell application are chemically modified via oxygen plasma activation and subsequent silanization using distinct precursor molecules including perfluorodecyltrichlorosilane and aminopropyltrimethoxysilane. For characterization of the samples contact angle measurements, infrared and Auger electron spectroscopy and scanning electron and atomic force microscopy are employed. Spectroscopic data provides direct evidence for successful functionalization of the substrates. Microscopic data reveals the inherent roughness of the micro-/nanostructured substrate surfaces. Depending on the particular silane precursor, the coating procedure yields hydrophilic and hydrophobic surfaces with static water contact angles ranging from 55° to 160°. The wettability of these substrates remains unchanged upon storage in clean air over a period of one year and more. Prospects of the coating procedure targeting the optimization of the water management in fuel cell applications are discussed. © 2013.
    view abstract10.1016/j.surfcoat.2013.12.037
  • Design and demonstration of an ethanol fuel processor for HT-PEM fuel cell applications
    Gardemann, U. and Steffen, M. and Heinzel, A.
    International Journal of Hydrogen Energy 39 (2014)
    This work describes the development of a compact ethanol fuel processor for small scale high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) systems with 200-500 W electrical power output. Promising markets for reformer fuel cell systems based on ethanol are mobile or portable leisure and security power supply applications as well as small scale stationary off grid power supply and backup power. Main components of the fuel processor to be developed were the reformer reactor, the shift converter, a catalytic burner and heat exchangers. Development focused in particular on the homogeneous evaporation of the liquid reactants ethanol and water for the reformer and burner and on the development of an efficient and autarkic start-up method, respectively. Theoretical as well as experimental work has been carried out for all main components separately including for example catalyst screening and evaporator performance tests in a first project period. Afterwards all components have been assembled to a complete fuel processor which has been qualified with various operation parameter set-ups. A theoretically defined basic operation point could practically be confirmed. The overall start-up time to receive reformate gas with appropriate quality to feed an HT-PEMFC (xCO < 2%) takes around 30 min. At steady state operation the hydrogen power output is around 900 W with H2 and CO fractions of 41.2% and 1.5%, respectively. © 2014 Hydrogen Energy Publications, LLC.
    view abstract10.1016/j.ijhydene.2014.05.027
  • Development of thin palladium membranes supported on large porous 310L tubes for a steam reformer operated with gas-to-liquid fuel
    Straczewski, G. and Völler-Blumenroth, J. and Beyer, H. and Pfeifer, P. and Steffen, M. and Felden, I. and Heinzel, A. and Wessling, M. and Dittmeyer, R.
    Chemical Engineering and Processing: Process Intensification 81 (2014)
    Palladium membranes were prepared on large tubes (80mm diameter and 150mm length) of porous stainless steel supports (PSS) using a modified electroless plating technique. The morphology of the palladium layer was found to be depending on the container material of the coating apparatus. The use of PMMA resulted in compact palladium layers with smooth surfaces whereas PTFE led to inhomogeneous palladium coating with rough surface. Two different ceramic materials and coating methods were used to prepare an intermediate layer needed to prevent intermetallic diffusion between the palladium and the support at elevated temperatures. Wet powder spraying of TiO2 followed by sintering resulted in a smoother surface than atmospheric plasma spraying of YSZ, thus allowing for a thinner palladium coating. Pd/TiO2/PSS membranes showed about 4 times higher hydrogen permeances than Pd/YSZ/PSS membranes as a consequence of higher palladium thickness and lower porosity of the ceramic intermediate layer. The selectivity against nitrogen was comparable for both membranes. However, the YSZ intermediate layer showed better stability at elevated temperatures. Two membrane tubes were applied in the membrane reformer, which produced hydrogen successfully from a gas-to-liquid (GtL) fuel. © 2014 Elsevier B.V.
    view abstract10.1016/j.cep.2014.04.002
  • Evaluation of hydrogen crossover through fuel cell membranes
    Schoemaker, M. and Misz, U. and Beckhaus, P. and Heinzel, A.
    Fuel Cells 14 (2014)
    Gas crossover is an unavoidable phenomenon in proton exchange fuel cell membranes. Nitrogen and oxygen from the cathode pass through the membrane to the anode, while hydrogen crosses from the anode to the cathode. The hydrogen crossover leads to a reduction in efficiency due to parasitic hydrogen consumption and mixed potentials on the cathode electrode. Furthermore it causes degradation effects and pinhole formation. Hence the hydrogen crossover represents a fundamental factor for the lifetime of a fuel cell and quantification of the crossover is a key factor for membrane qualification. In this article two in situ electrochemical techniques to evaluate the hydrogen crossover are described, cyclic voltammetry and potential step method. Both methods and the achieved results are compared to each other. Finally the potential step method is applied to evaluate the hydrogen crossover as a function of the anode pressure and the hydrogen permeability coefficients are determined. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/fuce.201300215
  • Laser Patterning of Silanized Carbon/Polymer Bipolar Plates with Tailored Wettability for Fuel Cell Applications
    Schade, M. and Franzka, S. and Schröter, A. and Cappuccio, F. and Peinecke, V. and Heinzel, A. and Hartmann, N.
    Laser Surface Modification and Adhesion (2014)
    Laser processing provides a powerful means to locally remove silane-based coatings and fabricate patterns with laterally varying wettability. Previous work predominantly focused on silane-based organic monolayers on flat substrate materials such as silicon wafers and quartz glass. In this chapter a simple laserassisted routine for patterning of silanized carbon/polymer bipolar plate materials is presented. Standard carbon/polypropylene composite materials as used for commercial bipolar plates for proton-exchange-membrane fuel cell applications can be chemically modifi ed via oxygen plasma activation and subsequent silanization using different precursor molecules including perfluorodecyltrichlorosilane and aminopropyltrimethoxysilane. Subsequently, laser ablation allows one to remove the coating. Additionally, substrate ablation occurs leaving a rough surface behind. For characterization of the samples contact angle measurements, infrared and Auger electron spectroscopy, scanning electron microscopy and profi lometry are employed. Spectroscopic data provide direct evidence for successful functionalization of the substrates. Microscopic and profi lometric data reveal the inherent roughness of the micro-/nanostructured substrate surfaces. Depending on the particular silane precursor, the coating procedure yields hydrophilic and hydrophobic surfaces with static water contact angles ranging from 55° to 160°. Laser ablation yields surfaces with static water contact angles of 135±5°. Hence, surface patterns with strongly varying wettability characteristics can be created. Combining silanization and laser processing provides a means to tailor the surface wettability in the channel structures of bipolar plates. Prospects of this approach for the optimization of the water management in fuel cell applications are discussed. © 2015 by Scrivener Publishing LLC. All rights reserved.
    view abstract10.1002/9781118831670.ch7
  • Power management optimization of fuel cell/battery hybrid vehicles with experimental validation
    Odeim, F. and Roes, J. and Wülbeck, L. and Heinzel, A.
    Journal of Power Sources 252 (2014)
    Fuel cell hybrid vehicles offer a high-efficiency and low-emission substitute for their internal combustion engine counterparts. The hybridization significantly improves the fuel economy of the vehicle; however, exploiting the hybridization requires a well-designed power management strategy that optimally shares the power demand between the power sources. This paper deals with the optimization of power management strategy of a fuel cell/battery hybrid vehicle, both off-line and in real-time. A new formulation of the optimization problem for the real-time strategy is presented. The new approach allows the optimization of the controller over a set of driving cycles at once, which improves the robustness of the designed strategy. The real-time optimization is applied to two forms of real-time controllers: a PI controller based on Pontryagin's Minimum Principle with three parameters and a fuzzy controller with ten parameters. The results show that the PI controller can outperform the fuzzy controller, even though it has fewer parameters. The real-time controllers are designed by simulation and then validated by experiment. © 2013 Published by Elsevier Inc.
    view abstract10.1016/j.jpowsour.2013.12.012
  • Graphene as catalyst support: The influences of carbon additives and catalyst preparation methods on the performance of PEM fuel cells
    Marinkas, A. and Arena, F. and Mitzel, J. and Prinz, G.M. and Heinzel, A. and Peinecke, V. and Natter, H.
    Carbon 58 (2013)
    The reduction of the platinum amount for efficient PEM (polymer electrolyte membrane) fuel cells was achieved by the use of graphene/carbon composites as catalyst support. The influences of the carbon support type and also of the catalyst preparation method on the fuel cell performance were investigated with electrochemical, spectroscopic and microscopic techniques. Using pure graphene supports the final catalyst layer consists of a dense and well orientated roof tile structure which causes strong mass transport limitations for fuels and products. Thus the catalysts efficiency and finally the fuel cell performance were reduced. The addition of different carbon additives like carbon black particles or multi-walled carbon nanotubes (MWCNT) destroys this structure and forms a porous layer which is very efficient for the mass transport. The network structure of the catalyst layer and therefore the performance depends on the amount and on the morphology of the carbon additives. Due to optimizing these parameters the platinum amount could be reduced by 37% compared to a commercial standard system. © 2013 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.carbon.2013.02.043
  • Sectional electrochemical impedance analysis of a high temperature polymer electrolyte membrane fuel cell with three types of flow-fields
    Siegel, C. and Buder, I. and Heinzel, A.
    Electrochimica Acta 112 (2013)
    This work reports sectional electrochemical impedance (EIS) measurements of a high temperature polymer electrolyte membrane (HTPEM) fuel cell. These measurements were taken using a high temperature stable polybenzimidazole membrane electrode assembly (MEA) doped with phosphoric acid (PBI/H 3PO4). Three different types of flow-fields (namely, a six channel parallel serpentine flow-field, a parallel straight flow-field, and a mixed-type flow-field) were analyzed in gas counter-flow and co-flow configuration under selected operating conditions. The current density distribution was also measured, and the results were presented to highlight the dominant factors that lead to inhomogeneous distributions. The results showed that the distribution mainly depended on the availability of oxygen, overlapped by the fluid-flow distribution. The situation changed once a carbon monoxide (CO) enriched gas was used at the anode side. In this case, the current density distribution decreased close to the cathode inlet and increased near the anode inlet. At high CO concentrations, the highest current densities were found close to the anode inlet. Sectional EIS measurements supported these observed trends and confirmed that the segments close to the anode inlet had a lower charge transfer resistance with a higher charge transfer resistance at segments closer to the anode outlet. © 2013 Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.electacta.2013.08.142
  • Development of a system model for a hydrogen production process on a solar tower
    Säck, J.-P. and Roeb, M. and Sattler, C. and Pitz-Paal, R. and Heinzel, A.
    Solar Energy 86 (2012)
    An attractive path to the production of hydrogen from water is a two-step thermo chemical cycle powered by concentrated sunlight from a solar tower system. In the first process step the redox system, a ferrite coated on a monolithic honeycomb absorber, is present in its reduced form while the concentrated solar energy hits the ceramic absorber. When water vapour is fed to the honeycomb at 800. °C, oxygen is abstracted from the water molecules, bond in the redox system and hydrogen is produced. When the metal oxide system is completely oxidised it is heated up for regeneration at 1100-1200. °C in an oxygen-lean atmosphere. Under those conditions and in the second process step, oxygen is set free from the redox system, so the metal oxide is being reduced and after completion of the reaction again capable for water splitting. Since the overall process consists of two core reaction steps, which need to be carried out sequentially in a reactor unit at two different temperature steps, a special process and plant concept had to be developed enabling the continuous supply of product regardless of the alternating nature of the solar reactor operation. The challenge of the process control is to keep the two core reaction temperatures constant and to ensure regular temperature switches after completion of the individual process steps, independent of the weather conditions, like DNI fluctuation, clouds and wind speed. Also start-up, the fast switching after completion of half-cycles and the shutdown must be controlled. State of the art is the manual switching of heliostats to fulfil those control tasks. This paper describes the development and use of a system model of this process. The model consists of three main parts: the simulation of the solar flux distribution at the receiver aperture, the simulation of the temperatures in the reactor modules and the simulation of the hydrogen generation. It can be used for the analysis of the operational behaviour. The model is intended to be used in the future for the control of the whole process. © 2011 Elsevier Ltd.
    view abstract10.1016/j.solener.2011.09.010
  • Dynamic PEMFC model as a base for a state classifier and controller
    Gößling, S. and Beckhaus, P. and Heinzel, A.
    Energy Procedia 28 (2012)
    Online state classification of PEM fuel cell systems is a challenging task. While electrochemical impedance spectroscopy (EIS), the measurement of the 1 kHz impedance, cyclic voltammetry, and the polarisation curve are the state-of-the-art in laboratory testing, it is hardly possible to install these analytic methods in application-oriented fuel cell systems. The necessary technical equipment is expensive, and hybridisation would be essential to create artificial operating conditions necessary during the measurement. A more economic solution for online state classification is the integration of a real-time model-based state classifier. A model, operating in parallel to the fuel cell, is able to provide extra information about the fuel cell such as the humidity of the membrane, which is not measurable in situ. On the other hand, online comparison of measurement data with the theoretical calculation allows us to detect malfunction of components. Based on a detailed model and a complex classification database, including error states of the system, it is possible to classify the state of a fuel cell or detect system errors. The voltage drift between classical physical models and a real fuel cell caused by irreversible degradation (platinum diversion, membrane thinning, carbon corrosion) and reversible degradation (contamination) is not yet completely understood, and therefore modelling so far remains imprecise. To avoid the misinterpretation caused by these constantly growing differences between the model and the reality, the described modelling approach has been focused on dynamic fuel cell reactions. Dynamic step responses of the fuel cell for abruptly changing operation conditions are being simulated in real time. The changing operation conditions may result from a real load cycle or, as for theses analyses, by forced stoichiometric steps. The comparison of the real and the simulated step responses is the basis for the state classifier and the controller to react. A conclusion of the series of measurement is shown, the model and its parameters are presented, and the opportunities of the state classifier and controller are discussed in this paper. © 2012 Published by Elsevier Ltd.
    view abstract10.1016/j.egypro.2012.08.045
  • High-capacity cathodes for lithium-ion batteries from nanostructured LiFePO 4 synthesized by highly-flexible and scalable flame spray pyrolysis
    Hamid, N.A. and Wennig, S. and Hardt, S. and Heinzel, A. and Schulz, C. and Wiggers, H.
    Journal of Power Sources 216 (2012)
    Olivine, LiFePO 4 is a promising cathode material for lithium-ion batteries due to its low cost, environmental acceptability and high stability. Its low electric conductivity prevented it for a long time from being used in large-scale applications. Decreasing its particle size along with carbon coating significantly improves electronic conductivity and lithium diffusion. With respect to the controlled formation of very small particles with large specific surface, gas-phase synthesis opens an economic and flexible route towards high-quality battery materials. Amorphous FePO 4 was synthesized as precursor material for LiFePO 4 by flame spray pyrolysis of a solution of iron acetylacetonate and tributyl phosphate in toluene. The pristine FePO 4 with a specific surface from 126-218 m 2 g -1 was post-processed to LiFePO 4/C composite material via a solid-state reaction using Li 2CO 3 and glucose. The final olivine LiFePO 4/C particles still showed a large specific surface of 24 m 2 g -1 and were characterized using X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectrocopy (XPS) and elemental analysis. Electrochemical investigations of the final LiFePO 4/C composites show reversible capacities of more than 145 mAh g -1 (about 115 mAh g -1 with respect to the total coating mass). The material supports high drain rates at 16 C while delivering 40 mAh g -1 and causes excellent cycle stability. © 2012 Elsevier B.V.
    view abstract10.1016/j.jpowsour.2012.05.047
  • Highly integrated steam reforming fuel processor with condensing burner technology for maximised electrical efficiency of CHP-PEMFC systems
    Pasdag, O. and Kvasnicka, A. and Steffen, M. and Heinzel, A.
    Energy Procedia 28 (2012)
    Compact fuel processors using natural gas, LPG and biogas for μCHP fuel cell systems have been developed at ZBT for over 10 years. The technology, based on steam reforming, includes a reformer and a WGS reactor, a water evaporator, heat exchangers and a fuel/anodic offgas burner integrated in an insulated housing. For coupling with a LT-PEMFC today an external preferential oxidation or methanation is added. A HT-PEMFC can be coupled directly to the fuel processor at a temperature level of 160°C. It is discussed that HT-PEMFC systems can exceed the electrical efficiency of LT-PEMFC systems up to five percentage points because of the integration of high quality heat from the fuel cell cooling cycle. In process simulations with AspenPlus® this efficiency advantage could be confirmed. But further investigations concerning heat integration showed for both systems the advantage of using the condensation enthalpy of the flue gas provided by the system burner. This gain in energy offers the opportunity to realise burner operation only with anodic offgas, without additional fuel firing. This study shows the use of condensing burner technology in the fuel processor in comparison of integrating HT-PEMFC heat and/or the use of conventional low-temperature burner technology. For comparison the system boundaries and efficiencies were clearly determined. Heat sources and sinks were identified and quantified along the process chain of steam reforming. A pinch analysis illustrates the requirement of additional heat flows concerning their power and temperature levels. © 2012 Published by Elsevier Ltd.
    view abstract10.1016/j.egypro.2012.08.040
  • Investigation of the effect of CO2 bubbles and slugs on the performance of a DMFC by means of laser-optical flow measurements
    Burgmann, S. and Blank, M. and Wartmann, J. and Heinzel, A.
    Fuel Cells 2012 Science & Technology - a Grove Fuel Cell Event 28 (2012)
    A single-channel DMFC is constructed that allows for flow measurements at the anode side as well as detailed time-resolved cell-voltage measurement. The coherence between flow and bubble clogging and slug movement can be investigated without parasitic effects like flow shortcuts through the gas diffusion layer (GDL) between neighbouring channels, as in serpentine or parallel-channel configurations. Optical access is granted to the anode side by a transparent foil, which is necessary for the application of the laser-optical velocity measurement technique (microparticle image velocimetry, mu PIV). Small fluorescent particles are added to the fluid, which are illuminated by a laser. The particle movement can be optically detected using a microscope, and transferred to a planar velocity field. Hence, the appearance and evolution of CO2 bubbles can be qualitatively and quantitatively investigated. The analysis of the velocity structure around a CO2 bubble or a moving slug allows a deeper understanding of the coherence of fluid motion, channel blockage, and cell performance. In addition to the flow analysis, a time-resolved measurement of the cell voltage is performed. The results clearly indicate that the cell power increases when huge bubbles reduce the free cross-section area of the channel. Methanol is forced into the GDL, i.e. methanol is continuously convected to the catalyst layer and is oxidised to CO2. Hence, the fuel consumption increases and the cell performance rises. When the huge bubble is released from the GDL and forms a moving slug, the moving slug effectively cleans the channel from CO2 bubbles on its way downstream. Since the channel cross-section is not severely diminished by the bubbles at this stage, the methanol flow is no longer forced into the GDL. The remaining amount of methanol in the GDL is oxidised. The cell power decreases until enough CO2 is produced to eventually form bubbles again that significantly reduce the free cross-section of the channel, and the process starts again. (C) 2012 Published by Elsevier Ltd.
    view abstract10.1016/j.egypro.2012.08.043
  • Membrane fuel cells - Options for bipolar plate materials and production technology
    Heinzel, A. and Kühnemann, L. and Derieth, T. and Grundler, M. and Grimm, T. and Kouachi, M.
    ECS Transactions 50 (2012)
    Polymer electrolyte membrane fuel cells PEMFC are the type of fuel cell with the broadest range of possible applications, ranging from power supply to electric drives to small scale grid independent power sources and residential CHP units. The technology has been intensively developed for more than two decades and the remaining R&D tasks focus on life time improvement and cost reduction. The following paper will give results on bipolar plate development for PEMFC. © The Electrochemical Society.
    view abstract10.1149/05002.0025ecst
  • Development of a near-dead-ended fuel cell stack operation in an automotive drive system
    Dehn, S. and Woehr, M. and Heinzel, A.
    2011 IEEE Vehicle Power and Propulsion Conference, VPPC 2011 (2011)
    During the past decade several important development steps, such as the 700 bar hydrogen storage or the freeze start capability, have brought fuel cell electric vehicles close to market introduction. Further drive system cost reduction by e.g. simplification of the fuel cell system architecture are intended for future fuel cell vehicle generations. Removing the anode recirculation loop and operating the fuel cell stack in the so-called near-dead-ended1 mode is one promising concept. Key experiments focussed on the fuel cell stack's anode side under vehicular load conditions and temperature levels have been performed successfully while maintaining fuel consumption constraints. The impact of cathode operating conditions on the liquid water accumulation and hydrogen concentration on the anode side has been investigated by simulation in order to optimize the operation of this lean anode concept. © 2011 IEEE.
    view abstract10.1109/VPPC.2011.6043028
  • Locally resolved measurements in a segmented HTPEM fuel cell with straight flow-fields
    Siegel, C. and Bandlamudi, G. and Filusch, F. and Heinzel, A.
    Fuel Cells 11 (2011)
    Significant advances have been reported in building and testing of high-temperature polymer electrolyte membrane (HTPEM) fuel cells and stacks during recent years. Quantity distribution measurement techniques (e.g. current density, temperature and electrochemical impedance spectroscopy (EIS)) using segmented cells are commonly used to characterise low-temperature PEM (LTPEM) fuel cells. Performing these measurements at higher temperatures is more difficult and a relatively new process. For this study, a fully operational segmented HTPEM fuel cell using a straight flow-field configuration was designed, constructed and tested. The cathode side bipolar half-plate consisted of 36 exchangeable segments, whereas, the anode side bipolar half-plate was not segmented. The cell was operated at various operating temperatures with various anode gas compositions and air (no backpressure). In addition to the experimental results, a simple computational fluid dynamics model based on COMSOL Multiphysics® 3.5a was used to support the observed behaviour during segmented measurements. The computational domain consisted of the cathode side gas channels and the porous media. All of the boundary conditions and gas properties were defined in a manner similar to the experimental investigations. Some of the theoretical results were compared to the experimental results and conclusions were drawn. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/fuce.201000101
  • Materials for membrane fuel cells
    Heinzel, A.
    Chemie-Ingenieur-Technik 83 (2011)
    Fuel cells as electrochemical conversion devices are nowadays ready for use thanks to targeted material development. For membrane fuel cells, the most important materials are the ionic conducting polymer electrolyte, the noble metal nanostructured electrocatalyst and its corrosion resistant carbon carrier material, the gas diffusion layer with its highly sophisticated pore system, as well as suitable construction materials for bipolar plates, which make a mass production possible. The progress of the past years has led to fuel cells with high specific power density, good durability and also with robust operational behavior. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/cite.201100070
  • Pollutant emissions of burners for steam reformers for residential power supply
    Gardemann, U. and Roes, J. and Heinzel, A.
    International Journal of Hydrogen Energy 36 (2011)
    The cogeneration of heat and power by means of a fuel cell based CHP unit is a promising option for efficient residential power supply. For most applications natural gas is used as fuel. One main component of such a CHP unit is a fuel processor in order to generate hydrogen from the natural gas with hydrogen thermal power output of about 6 kW. Usually the steam reforming process is used for hydrogen production. In order to meet the heat demand of the endothermic steam reforming process the fuel processor is equipped with a burner, which has to work with natural gas during start up phase and mainly with the low calorific anodic off gas of the fuel cell stack during normal operation. The presented work is focused on aspects of the main pollutant emissions (carbon monoxide and nitrogen oxide) of burners integrated into the reformer. Experimental investigations of two different burners, which were developed and adapted to the steam reformer requirements, in a real fuel processor environment show, that it is possible to operate both burner concepts with high and low calorific gases with very low pollutant emissions in order to compete with emissions of current heating boilers, which are in the range of 15 mg kWh-1 for CO and of 20 mg kWh-1 for NOx by adjusting suitable excess air ratios in the range of 1.2-1.4. But it is also demonstrated, that the efficiency of the fuel processor is influenced by the excess air ratio. An increase of the air ratio from 1.05 to 1.45 leads to an decrease of the efficiency from 80% to 76%. This results in a conflict of objectives between low pollutant emissions and high system efficiencies. The choice of a suitable burner concept and the definition of a suitable operation strategy can be based on the presented results. Additionally, aspects like fuel processor geometry, flame monitoring, pressure drop in the burner feed gas line as well as in the flue gas duct, investment costs and safety items have also to be considered for the burner selection. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.ijhydene.2011.01.066
  • Solid-phase temperature measurements in a HTPEM fuel cell
    Siegel, C. and Bandlamudi, G. and Heinzel, A.
    International Journal of Hydrogen Energy 36 (2011)
    Segmented temperature measurements were performed to better understand the thermal behaviour and thermal interactions between the fluid-(gas)-phase and solid-phase temperature within a working high temperature polymer electrolyte membrane (HTPEM) fuel cell. Three types of flow-fields were studied, and the influence of temperature for no-load and load operating conditions was investigated. Tests were performed under various operating conditions, and the results demonstrate the utility of segmented temperature measurements. A significant difference in the temperature distribution was observed when the HTPEM fuel cell was operated with pure hydrogen and with hydrogen containing carbon monoxide. The findings may lead to improved HTPEM fuel cells and future middle temperature polymer electrolyte membrane (MTPEM) fuel cell designs. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.ijhydene.2011.07.027
  • Systematic characterization of a PBI/H3PO4 sol-gel membrane - Modeling and simulation
    Siegel, C. and Bandlamudi, G. and Heinzel, A.
    Journal of Power Sources 196 (2011)
    This work presents a three-dimensional, steady-state, non-isothermal model of a high-temperature polymer-electrolyte-membrane fuel cell (HTPEMFC) using a phosphoric acid-doped polybenzimidazole (PBI/H3PO4) sol-gel membrane. The model accounts for the gold-plated copper current collector plates, the bipolar plates, all gas flow channels (flow-field), the gas diffusion layers, the reaction layers, and the membrane. Electrochemical reactions are modeled using an agglomerate approach and include the gas diffusivity and the gas solubility. The conductivity of the membrane is modeled using the Arrhenius equation to describe the temperature dependence. Finite elements are used to discretize all computational subdomains, and a commercially available code is used to solve the problem. The predicted values are compared to typical operating conditions, and a good agreement is found. The current density, the solid- and fluid-(gas)-phase temperatures and other quantities are analyzed throughout the computational subdomains. It was observed that the Arrhenius approach is valid in a certain temperature range and may overpredict the PBI/H3PO4 sol-gel membrane conductivity at higher solid-phase temperatures. Moreover, it is shown how the fluid-(gas)-phase temperature influences the solid-phase temperature and the current density distribution. Concrete values are deduced from the simulations and discussed according to experimental test. © 2010 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.jpowsour.2010.11.028
  • Fluid Flow and Electrochemical Performance in Miniaturized HT-PEMFCs
    Bandlamudi, G. and Siegel, C. and Van der Schoot, N. and Heinzel, A.
    Fuel Cell Seminar 2009 26 (2010)
    In the current work, three types of flow field structures were analysed: i) Fluid flow patterns such as uniformity in gas distribution in various channels of these flow fields were studied using particle image velocimetry (PIV) technique, ii) Pressure drop across each flow field structure was measured using standard anemometers, iii) Impedance of 3 single cells built with these three types of flow fields, each with a commercially available Celtec-P 1000 based membrane electrode assembly (MEA) was examined, to ensure, adequate contact between various cell components using electrochemical impedance spectroscopy (EIS) technique, iv) 3D-computational fluid dynamics (CFD) simulations were performed using a commercially available software to ascertain oxidant distribution in these flow fields. Finally, v) Experiments were performed in a test stand with these three types of single cells, (with hydrogen and air as reactant gases) to gauge each cell's overall performance. The active area of each cell was 27.6 cm(2). High temperature stable graphite compound based bipolar plates (FU 4369) from Schunk Kohlenstofftechnik GmbH, Germany were used in each cell.
    view abstract10.1149/1.3428976
  • Materials for fuel-cell technologies
    Steele, B.C.H. and Heinzel, A.
    Materials for Sustainable Energy: A Collection of Peer-Reviewed Research and Review Articles from Nature Publishing Group (2010)
    Fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel-cell technology can gain a significant share of the electrical power market, important issues have to be addressed. These issues include optimal choice of fuel, and the development of alternative materials in the fuel-cell stack. Present fuel-cell prototypes often use materials selected more than 25 years ago. Commercialization aspects, including cost and durability, have revealed inadequacies in some of these materials. Here we summarize recent progress in the search and development of innovative alternative materials. © 2011 Nature Publishing Group, a division of Macmillan Publishers Limited and published by World Scientific Publishing Co. under licence. All rights reserved.
    view abstract10.1142/9789814317665_0031
  • PBIÕH3PO4 gel based polymer electrolyte membrane fuel cells under the influence of reformates
    Bandlamudi, G.C. and Saborni, M. and Beckhaus, P. and Mahlendorf, F. and Heinzel, A.
    Journal of Fuel Cell Science and Technology 7 (2010)
    High temperature polymer electrolyte membrane fuel cells (HT PEMFCs) offer tremendous flexibility when used as energy converters in stationary as well as mobile power devices. Coupling HT PEMFC stacks with fuel processors that use liquid as well as gaseous fuels to generate hydrogen rich gas is a promising prospect, which paves the way for a possible hydrogen economy. The current paper deals with the performance aspects of a 150 Wel HT PEMFC stack, which potentially could be coupled to (i) a natural gas reformer, (ii) a propane reformer, or (iii) a methanol reformer. A 12 cell HT PEMFC stack with a total active area of about 600 cm2 was operated in a test rack, and the results show that HT PEMFCs are principally suited for operation with reformates. Copyright © 2010 by ASME.
    view abstract10.1115/1.3119054
  • batteries

  • electrochemistry

  • fuel cells

  • hydrogen generation

  • hydrogen storage

  • lithium-ion batteries

  • membrane fuel cells

  • surfaces

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