Analysis of the Deterioration Phenomena on PEFC and Effect of Four-Layer Electrode Catalyst on the Cell Performance

A long-term operation test of PEFCs was conducted for single cells having an effective area of 25 cm2. The decay rate of the cell voltage was relatively large in the beginning, decreased to about 4 µV h−1 from 3000 to 6000 h, and about 7 µV h−1 in the later stage from 9000 to 12000 h. In order to clarify the cause of the voltage decay, materials composing membrane electrode assembly (MEA) were analyzed by disassembling a cell every 3000 h. After operation, changes of materials, such as particle size change of Pt-Co cathode catalyst, loss of ionomer layers on Pt-Co/C, decrease in thickness of the polymer electrolyte membrane, pore size changes of the cathode, were observed. Electrochemical active surface area of the electrode showed a decreasing tendency. Based on these results, we focused on the improvement of cathode, and developed a “four-layer electrode catalyst” which consisted of Pt-Co alloy particle, carbon support, ionomer and fluorocarbon resin. A test cell using this new type cathode exhibited better performances than a cell using conventional cathode in the durability test under low humidity or low temperature conditions.