Durability of a PEMFC Pt–Co cathode catalyst layer during voltage cycling tests under supersaturated humidity conditions

Abstract

We examined the durability of a carbon-supported Pt-based Co alloy catalyst (Pt–Co/C) during voltage cycling tests under supersaturated humidity conditions to simulate events such as flooding. The voltage cycling tests were conducted from 0.4V to 1V for up to 50,000 cycles using 100% relative humidity (RH) hydrogen as the anode gas and 189% RH nitrogen as the cathode gas. We performed cyclic voltammetry (CV) to evaluate the electrochemical surface area (ECSA) and investigated polarization properties to evaluate the activity of Pt–Co/C. The ECSA of Pt–Co/C decreased more slowly than that of a platinum catalyst (Pt/C) during tests (percentages of initial ECSA were 62% and 37% for Pt–Co/C and Pt/C, respectively), either because (1) initial Pt–Co/C was not dispersed unlike Pt/C, or (2) Pt/C exhibited stronger resistance to agglomeration than Pt–Co/C. We concluded that Pt–Co/C exhibited high oxygen reduction reaction (ORR) activity and durability during voltage cycling tests because the mass activity of Pt–Co/C was about twice that of Pt/C throughout the 50,000 cycles. Electrocatalytic specific activities of Pt–Co/C were constant and about twice those of Pt/C for 4000–50,000 cycles, indicating that alloying can increase intrinsic activity for up to 50,000 cycles.