Effect of Co2+ 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 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 2 O 2 production. Higher production could intensify the attack by H 2 O 2 and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.Crown

PEM fuel cell cathode contamination in the presence of cobalt ion (Co2+)

“…This is in agreement with the trend in cell voltage losses measured at different temperatures (as presented in a later section of this paper). (It should be pointed out that the losses in EPSA during fuel cell contamination tests at all temperatures are significantly higher than the loss in EPSA of the RDE electrode used in our previous study [15], i.e. >25% vs. 6%; the much longer contamination time used during testing might be an explanation for the higher EPSA losses).…”

“…Co 2+ contamination caused the EPSA to decrease by more than 25%, with the decrease becoming more significant as fuel cell temperature was lowered, supporting our hypothesis that Co 2+ adsorption on the Pt surface blocks active sites that would otherwise be used for the ORR. Furthermore, this weak adsorption of Co 2+ on the Pt surface not only reduces the rate of the reaction kinetics but also changes the mechanism of the ORR, boosting the production of H 2 O 2 (as reported in our previous paper [15]). …”

“…Several factors associated with Co 2+ contamination may contribute to reduced mass transfer of O 2 for the ORR. As mentioned earlier, reduction in the overall electron transfer number can cause the mass transfer limiting current density to decrease [15]. If the ORR electron transfer number dropped from a four-electron to a two-electron pathway in the presence of Co 2+ , more H 2 O 2 would be produced in the cathode catalyst layer.…”

“…9 and 10, in the presence of Co 2+ the ORR charge transfer resistance can increase significantly, resulting in fuel cell performance degradation. As far as the kinetic effect is concerned, our previous publication [15] provided a detailed discussion of the effect of Co 2+ on the ORR, investigated using the rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques. Our study showed that Co 2+ weakly adsorbs on the Pt surface of the catalyst layer.…”

“…This problem, manifested as performance degradation, could be the result of Pt catalyst agglomeration and dissolution, catalyst carbon support corrosion, membrane degradation, and fuel cell contamination caused by feed stream and component impurities [2][3][4][5][6]. These impurities may be present in the fuel (e.g., CO, H 2 S, NH 3 , and hydrocarbons) [7][8][9][10] and/or in the air (e.g., NO x ,S O x ,C O x , and some volatile organic compounds [VOCs]) [11][12][13][14], and may originate from the fuel cell components and system (e.g., Fe 3+ ,Cu 2+ , and Cr 3+ ) or from the alloy catalysts (e.g., Co 2+ ,Ni 2+ , and Fe 3+ ) [15].…”