Kinetic Effects of Temperature on Fe–N–C Catalysts for 2e- and 4e-Oxygen Reduction Reactions

Abstract

Hydrogen peroxide (H2O2) formed via the two-electron oxygen reduction reaction (2e-ORR) on carbon-based platinum group metal-free (PGM-free) catalysts at elevated temperature can cause catalyst degradation in fuel cells. In this work, we studied the effects of temperature on the selectivity of iron- and nitrogen-doped carbon (Fe–N–C) catalyst for 2e- and 4e-ORR in acidic electrolyte using a high-temperature rotating-ring disk electrode. The results of individual-heating experiments showed that H2O2 yield increased slightly with the increase of temperature. In the meantime, the results of sequential heating/cooling experiments suggested that prolonged high-temperature exposure at ORR polarization conditions can lead to catalyst degradation and higher selectivity for 2e-ORR. The temperature effects on the selectivity of Fe–N–C catalyst for 2e- and 4e-ORR was further explained with a kinetic model describing the competitive reactions and the thermodynamics of the system, which suggested that the increase of H2O2 yield with temperature in the individual-heating experiment was due to the promoted 2e-ORR pathway instead of catalyst degradation.