Transient Loss and Recovery of Platinum Fuel Cell Cathode Catalyst at High Voltage Efficiency Regimes

Abstract

The performance of oxygen reduction reaction (ORR) catalysts, typically evaluated by potential scanning techniques, fails to capture the significant activity decay occurring at longer time scales. To meet the 65% peak energy efficiency target, the continuous decay of Pt/C ORR catalyst, commonly referred to as “transient performance loss”, is studied at 0.8 V by chronoamperometry under membrane electrode assembly (MEA) testing conditions. Based on the results from the time-resolved cyclic voltammetry (CV), surface oxidation was identified as the primary cause of the transient loss. The reduction of surface oxide was observed to occur at 0.6 V, and the recovery of cathode performance can hence be achieved at equal or lower potentials. In addition, the effects of operating temperature and cathode humidity were also studied. The coverage of Pt surface oxides and the extent of the transient loss were both significantly reduced as temperature decreased. However, the benefit of a lower operating temperature came at the cost of slower recovery kinetics. In terms of the impact of humidity, the presence of liquid water was identified as the critical factor leading to a much more severe performance loss over time.

Platinum Surface Oxide and Oxygen Reduction Reaction Kinetics during Transient Fuel Cell Operation

“…In contrast to Pt oxide growth, the ORR activity decay rate has not been studied as intensively. 22,[50][51][52] Interestingly, the log(time) fit (solid lines) also agrees with the ORR activity data (open symbols) quite well. This observation supports the hypothesis that the ORR activity decay can be predominantly attributed to Pt oxide formation.…”