This book covers a significant number of R&D projects, performed mostly after 2000, devoted to the understanding and prevention of performance degradation processes in polymer electrolyte fuel cells (PEFCs). The extent and severity of performance degradation processes in PEFCs were recognized rather gradually. Indeed, the recognition overlapped with a significant number of industrial dem- strations of fuel cell powered vehicles, which would suggest a degree of technology maturity beyond the resaolution of fundamental failure mechanisms. An intriguing question, therefore, is why has there been this apparent delay in addressing fun- mental performance stability requirements. The apparent answer is that testing of the power system under fully realistic operation conditions was one prerequisite for revealing the nature and extent of some key modes of PEFC stack failure. Such modes of failure were not exposed to a similar degree, or not at all, in earlier tests of PEFC stacks which were not performed under fully relevant conditions, parti- larly such tests which did not include multiple onoff and/or high powerlow power cycles typical for transportation and mobile power applications of PEFCs. Long-term testing of PEFCs reported in the early 1990s by both Los Alamos National Laboratory and Ballard Power was performed under conditions of c- stant cell voltage, typically near the maximum power point of the PEFC.

Stack Components.- Dissolution and Stabilization of Platinum in Oxygen Cathodes.- Carbon-Support Requirements for Highly Durable Fuel Cell Operation.- Chemical Degradation of Perfluorinated Sulfonic Acid Membranes.- Chemical Degradation: Correlations Between Electrolyzer and Fuel Cell Findings.- Improvement of Membrane and Membrane Electrode Assembly Durability.- Durability of Radiation-Grafted Fuel Cell Membranes.- Durability Aspects of Gas-Diffusion and Microporous Layers.- High-Temperature Polymer Electrolyte Fuel Cells: Durability Insights.- Direct Methanol Fuel Cell Durability.- Influence of Metallic Bipolar Plates on the Durability of Polymer Electrolyte Fuel Cells.- Durability of Graphite Composite Bipolar Plates.- Gaskets: Important Durability Issues.- Cells and Stack Operation.- Air Impurities.- Impurity Effects on Electrode Reactions in Fuel Cells.- Performance and Durability of a Polymer Electrolyte Fuel Cell Operating with Reformate: Effects of CO, CO2, and Other Trace Impurities.- Subfreezing Phenomena in Polymer Electrolyte Fuel Cells.- Application of Accelerated Testing and Statistical Lifetime Modeling to Membrane Electrode Assembly Development.- Operating Requirements for Durable Polymer-Electrolyte Fuel Cell Stacks.- Design Requirements for Bipolar Plates and Stack Hardware for Durable Operation.- Heterogeneous Cell Ageing in Polymer Electrolyte Fuel Cell Stacks.- System Perspectives.- Degradation Factors of Polymer Electrolyte Fuel Cells in Residential Cogeneration Systems.- Fuel Cell Stack Durability for Vehicle Application.- R&D Status.- Durability Targets for Stationary and Automotive Applications in Japan.