Understanding the high activity of mildly reduced graphene oxide electrocatalysts in oxygen reduction to hydrogen peroxide

Abstract

The direct electrochemical synthesis of hydrogen peroxide (H₂O₂) would provide an attractive alternative to the traditional anthraquinone oxidation process for continuous on-site applications. Its industrial viability depends greatly on developing cost-effective catalysts with high activity and selectivity. Recent experiments have demonstrated that mildly reduced graphene oxide (mrGO) electrocatalysts exhibit highly selective and stable H₂O₂ formation activity [e.g., H. W. Kim, M. B. Ross, N. Kornienko, L. Zhang, J. Guo, P. Yang and B. D. McCloskey, Nat. Catal., 2018, 1, 282–290]. However, the identification of active site structures for this catalytic process on mrGO is doubtful. Herein, by means of first-principles calculations, we examine the H₂O₂ formation activities of the active site structures proposed in experiments and find that their activities are actually very low. Then, we systematically investigate the H₂O₂ formation activities of different oxygen functional group structures on mrGO based on experimental observations, and discover two types of oxygen functional group structures (2EP and 1ET + 1EP) that have comparable or even lower overpotentials (<0.10 V) for H₂O₂ formation compared with the state-of-the-art PtHg₄ electrocatalyst. Our theoretical results reveal that the graphene edge and the synergetic effects between different oxygen functional groups are essential for the superior performance of mrGO for H₂O₂ production. This work not only provides a feasible explanation of the cause of high H₂O₂ formation activity of mrGO but also offers a guide for the design, synthesis, and mechanistic investigation of advanced carbon-based electrocatalysts for effective H₂O₂ production.