Elucidation and modulation of active sites in holey graphene electrocatalysts for H2O2 production

Abstract

Selective electrochemical oxygen reduction (ORR) toward a two-electron (2e(-)) pathway is an eco-friendly alternative method for H2O2 synthesis to replace the energy-intensive anthraquinone oxidation process. Carbon-based electrocatalysts (CBEs) show great potential for practical H2O2 synthesis. However, their complex structures make it challenging to determine the nature of active sites and to precisely control them. Herein, we show that precise modulation of the chemistry and structures of holey graphene with edge sites enriched by oxygen-containing functional groups can facilitate 2e(-) ORR. These combined functionalities could improve ORR performance under various pH conditions, for example, resulting in an average of 95% H2O2 selectivity, similar to 97% Faraday efficiency, high productivity of 2360 mol kg(cat)(-1) h(-1) in alkaline media. Density functional theory calculations on the oxygen functional groups at the edge sites revealed the most active site for 2e(-) ORR is a synergy between ether (C-O-C) and carbonyl (C=O) functional groups with nearly zero overpotential.