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.