Revealing the Role of the Metal in Non-Precious-Metal Catalysts for Oxygen Reduction via Selective Removal of Fe

Abstract

Non-precious-metal catalysts have been investigated as alternatives to Pt-based oxygen reduction reaction catalysts for more than 50 years. While the incorporation of a metal is known to be necessary to generate a catalyst with high activity, the exact role of the metal is still not well-understood. In this work, we prepare an active oxygen reduction reaction catalyst containing Fe and then selectively remove the Fe from the catalyst while preserving the carbon and nitrogen species. By comparing the oxygen reduction reaction activity of the catalyst before and after treatment, we show that in the absence of Fe the carbon and nitrogen sites in the catalyst exhibit a larger overpotential and lower selectivity for the 4e– reduction of oxygen in both acidic and alkaline conditions. These findings reveal the direct involvement of the metal in the active site of non-precious-metal catalysts and provide important guidance for future catalyst improvements.