Effect of Temperature on Cold Start Characteristics of PEFC and the Freezing Mechanism

Abstract

Cold start characteristics of a polymer electrolyte fuel cell were investigated experimentally, and microscopic observations were conducted to clarify the freezing mechanism in the cell. The results shows that the freezing mechanisms are classified into two types: freezing in catalyst layer at very low temperature like -20°C, and freezing of supercooled water at the interface between cathode catalyst layer and micro porous layer at near 0°C like -10°C. The amount of produced water in each the processes is related to the initial wet condition of the membrane because there is a period of back diffusion of produced water into the membrane. It is also shown that the performance of a subsequent normal temperature operation at 30°C after the shutdown in the cold start is temporarily deteriorated after the freezing at -10°C, but not after the freezing at -20°C. The ice formed at the interface between the catalyst and the micro porous layers is estimated to cause the temporal deterioration, and the function of micro porous layer on the gas diffusion layer is also discussed.