Enhancing oxygen reduction reaction performance in acidic media via bimetal Fe and Cr synergistic effects

Currently, it is a great challenge to improve the stability of Fe-based oxygen reduction reaction (ORR) catalysts in acidic medium, because the Fenton reaction between Fe-based catalyst and H2O2 will reduce the stability of the catalyst. In this study, Fe, Cr and nitrogen-doped carbon (FeCr-N-C) was synthesized via co-impregnation of biomass walnut shells with metal precursor solutions. The FeCr-N-C catalyst has an onset potential of 0.88 V vs. RHE and outperforms the Fe-N-C catalyst in acidic media. Moreover, FeCr-N-C shows negligible activity decay (ΔE1/2 = 14 mV) in 0.1 M HClO4 after 20 000 cycles. The experimental results proved that the bimetal synergism can produce low yield of H2O2 (<2%), which might attribute to variations of local electronic structure. The reactive oxygen species of the catalyst were analyzed by Ultraviolet-visible (UV-Vis) absorption spectra. It was proved that the presence of bimetal inhibited the Fenton reaction between Fe2+/Fe3+ and H2O2, and further improved the stability of the catalysts. Hence, this study proposes an efficient strategy to facilitate the practical application of Fe-based catalysts in acidic media.