Selective oxygen electroreduction to hydrogen peroxide in acidic media: The superiority of single-atom catalysts

Two-electron oxygen reduction reaction (2e-ORR) provides an environmentally friendly direction for the on-site production of hydrogen peroxide (H2O2). Central to this technology is the exploitation of efficient, economical, and safe 2e-ORR electrocatalysts. This overview starts with the fundamental chemistry of ORR to highlight the decisive role of adsorbing intermediates on the reaction pathway and activity, followed by a comprehensive survey of the tuning strategies to favor 2e-ORR on traditional precious metals. The latest achievements in designing efficient and selective precious-metal-based single-atom catalysts (SACs) and metal-nitrogen-carbon (M-N-x/C) catalysts, from the aspects of material synthesis, theoretical calculations, and mass transport promotion, are systematically summarized. Brief introductions on the evaluation metrics for 2e-ORR catalysts and the primary reactor designs for cathodic H2O2 synthesis are also included. We conclude this review with an outlook on the challenges and direction of efforts to advance electrocatalytic 2e-ORR into realistic H2O2 production.