Identification of the Highly Active Co–N₄ Coordination Motif for Selective Oxygen Reduction to Hydrogen Peroxide

Abstract

Electrosynthesis of hydrogen peroxide (H₂O₂) through oxygen reduction reaction (ORR) is an environment-friendly and sustainable route for obtaining a fundamental product in the chemical industry. Co-N₄ single-atom catalysts (SAC) have sparkled attention for being highly active in both 2e^- ORR, leading to H₂O₂ and 4e^- ORR, in which H₂O is the main product. However, there is still a lack of fundamental insights into the structure-function relationship between CoN₄ and the ORR mechanism over this family of catalysts. Here, by combining theoretical simulation and experiments, we unveil that pyrrole-type CoN₄ (Co-N SAC_Dp) is mainly responsible for the 2e^- ORR, while pyridine-type CoN₄ catalyzes the 4e^- ORR. Indeed, Co-N SAC_Dp exhibits a remarkable H₂O₂ selectivity of 94% and a superb H₂O₂ yield of 2032 mg for 90 h in a flow cell, outperforming most reported catalysts in acid media. Theoretical analysis and experimental investigations confirm that Co-N SAC_Dp─with weakening O₂/HOO* interaction─boosts the H₂O₂ production.