Atomically Dispersed Co/Mo Sites Anchored on Mesoporous Carbon Hollow Spheres for Highly Selective Oxygen Reduction to Hydrogen Peroxide in Acidic Media.

Abstract

Two-electron oxygen reduction reaction (2e^- ORR) in acidic media is a promising route for the decentralized and on-site hydrogen peroxide (H₂O₂) generation. Nevertheless, strong interaction between active sites and ^*OOH intermediates usually induces the O─O bond cleavage to convert 2e^- pathway into the sluggish 4e^- ORR. Therefore, it is highly necessary to optimize the electronic structure of 2e^- ORR electrocatalysts for the regulation of adsorption energy. Herein, we propose the utilization of atomically dispersed Co/Mo sites anchored on mesoporous carbon hollow spheres (Co/Mo-MCHS) via a template-engaged strategy for highly selective ORR to H₂O₂ in acid. Benefitting from the electron-donating effect of Mo atoms, an enriched electron density around the Co center for Co/Mo-MCHS is observed, resulting in optimal adsorption of the key ^*OOH intermediates to approach the apex of 2e^- ORR volcano plot. Moreover, the introduction of Mo species simultaneously suppresses the electroreduction of as-obtained H₂O₂ on Co sites. As a consequence, Co/Mo-MCHS delivers a high H₂O₂ selectivity of 90-95% in acid. The flow cell based on the Co/Mo-MCHS catalyst achieves a remarkable H₂O₂ yield of 2102 mg for 150 h. Moreover, this strategy can be extended to other early transition metal elements with similar electronic modifier effects.