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 SACDp) is mainly responsible for the 2e– ORR, while pyridine-type CoN4 catalyzes the 4e– ORR. Indeed, Co–N SACDp 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 SACDp—with weakening O2/HOO* interaction—boosts the H2O2 production.