Effect of Co 2+ on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

Abstract

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co 2+ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co 2+. Findings indicated that Co 2+ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence of Co 2+ was reduced, with ∼9% more H 2O 2 being produced. We speculate that the weakly adsorbed Co 2+ on Pt could react with the H 2O 2 intermediate and form a Co 2+–H 2O 2 intermediate, inhibiting the further reduction of H 2O 2 and thus resulting in more H 2O 2 production. The fuel cell performance drop observed in the presence of Co 2+ could be attributed to the reduction in overall electron transfer number and the increase in H 2O 2 production. Higher production could intensify the attack by H 2O 2 and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.