Transition Metal Oxides/Chalcogenides for Electrochemical Oxygen Reduction into Hydrogen Peroxides

Electrochemical oxygen reduction reaction via the two-electron pathway (2e-ORR) is becoming a promising and sustainable approach to producing hydrogen peroxide (H2O2) without significant carbon footprints. To achieve better performance, most of the recent progress and investigations have focused on developing novel carbon-based electrocatalysts. Nevertheless, the sophisticated preparations, decreased selectivity and undefined active sites of carbon-based catalysts have been generally acknowledged and criticized. To this end, transition metal oxides and chalcogenides have increasingly emerged for 2e-ORR, due to their catalytic stability and tunable microstructure. Here, the development of metal oxides and chalcogenides for O2-to-H2O2 conversion is prospectively reviewed. By summarizing previous theoretical and experimental efforts, their diversity and outstanding catalytic activity are firstly provided. Meanwhile, the topological and chemical factors influencing 2e-ORR selectivity of the metal oxides/chalcogenides are systematically elucidated, including morphology, phase structures, doping and defects engineering. Thus, emphasizing the influence on the binding of ORR intermediates, the active sites and the underlying mechanism is highlighted. Finally, future opportunities and challenges in designing metal oxides/chalcogenides-based catalysts for H2O2 electro-synthesis are outlined. The present review provides insights and fundamentals of metal oxides/chalcogenides as 2e-ORR catalysts, promoting their practical application in the energy-related industry.