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

Abstract

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.