aLawrence Berkeley National Laboratory, Berkeley, California 94720, USA bLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USA cUnited Technologies Research Center, East Hartford, Connecticut 06118, USA dSchool of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom eChemical and Biomolecular Engineering Department, University of California, Berkeley, California 94720, USA fFuel Cell Research and Development, General Motors, Pontiac, Michigan 48340, USA gBallard Power Systems, Burnaby, British Columbia V5J 5J8, Canada hFuel Cell Research Centre, Queens University, Kingston, Ontario K7L 3N6, Canada iDepartment of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA jDepartment of Mechanical Aerospace and Biomedical Engineering, University of Tennessee at Knoxville, Knoxville, Tennessee 37996, USA kDepartment of Mechanical Engineering Technology, SUNY Alfred State College, Alfred, New York 14802, USA lDepartment of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G, Canada

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A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

The cost of polymer electrolyte fuel cell (PEFC) components is crucial to the commercial viability of the technology. Proton exchange membranes fabricated via the method of radiation grafting offer a cost-competitive option, because starting materials are inexpensive commodity products and the preparation procedure is based on established industrial processes. Radiation grafted membranes have been used with commercial success in membrane separation technology. This review focuses on the application of radiation grafted membranes in fuel cells, in particular the identification of fuel cell relevant membrane properties, aspects of membrane electrode assembly (MEA) fabrication, electrochemical performance and durability obtained in cell or stack tests, and investigation of failure modes and post mortem analysis. The application in hydrogen and methanol fuelled cells is treated separately. Optimized styrene / crosslinker grafted and sulfonated membranes show performance comparable to perfluorinated membranes. Some properties, such as methanol permeability, can be tailored to be superior. Durability of several thousand hours at practical operating conditions has been demonstrated. Alternative styrene derived monomers with higher chemical stability offer the prospect of enhanced durability or higher operating temperature.

Radiation Grafted Membranes for Polymer Electrolyte Fuel Cells

Fuel cell technology is one of the key emerging technologies that is currently attracting tremendous effort with the aim to provide alternative environmentally friendly and efficient power sources. The worldwide move away from conventional fossil fuel combustion power generation technologies is driving much of this important research. The replacement of a liquid electrolyte by PEM in such systems has eliminated the corrosion problems and conferred on the system additional advantages such as simplicity of construction, compactness, and quick self-starting at ambient temperatures. The successful performance of these kinds of fuel cell systems depends critically on the role played by the PEM. The second category involves the formation of acid-base complexes that provide a viable alternative for membranes that can maintain high conductivity at elevated temperatures without suffering from dehydration effects.

Radiation-grafted membranes for polymer electrolyte fuel cells: current trends and future directions.

Recent trends and developments in polymer electrolyte membrane fuel cell modelling

The development of proton-exchange membranes for fuel cells has generated global interest in order to have a potential source of power for stationary and portable applications. The membrane is the heart of a fuel cell and the performance of a fuel cell depends largely on the physico-chemical nature of the membrane and its stability in the hostile environment of hydrogen and oxygen at elevated temperatures. Efforts are being made to develop membranes that are similar to commercial Nafion

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Radiation Grafted Membranes

The commercial success of the polymer electrolyte fuel cell (PEFC) will to a large extent be determined by the nature, properties, functionality, and cost of the electrochemical sub-components used in the membrane electrode assembly (MEA). Materials research activities in Switzerland for the PEFC are being pursued at the Paul Scherrer Institut (Villigen AG) and the Swiss Federal Institute of Technology in Lausanne with different objectives. The radiation grafted proton exchange membrane developed at the Paul Scherrer Institut (PSI) has been brought to a near-product-like quality level with encouraging performance close to state-of-the-art materials and a life-time of several thousand hours. Furthermore, the membrane shows low methanol crossover in the direct methanol fuel cell. In addition, polyarylene block copolymer membranes have been investigated as an option for fluorine-free membranes. The electrocatalysis of Pt in acidic solution and in contact with a solid electrolyte, the development of new methanol oxidation and oxygen reduction catalysts, and co-sputtering of Pt and carbon as an alternative method for catalyst preparation are areas of fundamental research. More applied research is performed in the characterization of commercial electrodes in single cells, using standard as well as advanced diagnostic tools developed in-house. This article gives an overview over the research and development projects in Switzerland related to materials and components for the PEFC.

Materials for polymer electrolyte fuel cells

Fundamental and phenomenological models for cells, stacks, and complete systems of PEFC and SOFC are reviewed and their predictive power is assessed by comparing model simulations against experiments. Computationally efficient models suited for engineering design include the (1+1) dimensionality approach, which decouples the membrane in-plane and through-plane processes, and the volume-averaged-method (VAM) that considers only the lumped effect of pre-selected system components. The former model was shown to capture the measured lateral current density inhomogeneities in a PEFC and the latter was used for the optimization of commercial SOFC systems. State Space Modeling (SSM) was used to identify the main reaction pathways in SOFC and, in conjunction with the implementation of geometrically well- defined electrodes, has opened a new direction for the understanding of electrochemical reactions. Furthermore, SSM has advanced the understanding of the COpoisoning- induced anode impedance in PEFC. Detailed numerical models such as the Lattice Boltzmann (LB) method for transport in porous media and the full 3-D Computational Fluid Dynamics (CFD) Navier-Stokes simulations are addressed. These models contain all components of the relevant physics and they can improve the understanding of the related phenomena, a necessary condition for the development of both appropriate simplified models as well as reliable technologies. Within the LB framework, a technique for the characterization and computer- reconstruction of the porous electrode structure was developed using advanced pattern recognition algorithms. In CFD modeling, 3-D simulations were used to investigate SOFC with internal methane steam reforming and have exemplified the significance of porous and novel fractal channel distributors for the fuel and oxidant delivery, as well as for the cooling of PEFC. As importantly, the novel concept has been put forth of functionally designed, fractal-shaped fuel cells, showing promise of significant performance improvements over the conventional rectangular shaped units. Thermo-economic modeling for the optimization of PEFC is finally addressed. Keywords: Multidimensional simulations of fuel cells · Porous electrode structure characterization · State-space modeling of electrochemical reactions · Thermo-economic optimization

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Fuel Cell Modeling and Simulations

Polymer electrolyte and solid oxide are the two fuel cell types (PEFC, SOFC) under development in Switzerland. The very distinct operating temperatures of 80 °C (PEFC) and 800–950 °C (SOFC) impose fundamentally different requirements upon the nature of the fuel; normally purified H2 for the former (CO trace) and usually synthesis gas for the latter (H2, CO as main constituents). Apart from stored hydrogen, the most relevant fuels are primary hydrocarbons (natural gas, biogas, liquids,…), that then need processing (chemical conversion, cleaning) up to a level compatible with the fuel cell catalysts. These processes are briefly reviewed. Fuel compositions with an emphasis on impurities are given. Two application examples from Swiss RD are presented: gasoline conversion to high purity H2 for PEFC and contaminated biogas processing for SOFC. Keywords: Biogas · Fuel impurities · Fuel processing · Partial oxidation · Reforming

Faegheh Hajbolouri

Papers

Materials for polymer electrolyte fuel cells

Fuel Cell Modeling and Simulations

Fuels for Fuel Cells : Requirements and Fuel Processing

Link-up of a bench-scale “shift-less” gasoline fuel processor to a polymer electrolyte fuel cell