Electrosynthesis of hydrogen peroxide via two-electron oxygen reduction reaction: A critical review focus on hydrophilicity/hydrophobicity of carbonaceous electrode

The electrochemical production of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (ORR) is an attractive decentralized alternative to the present industry dominant anthraquinone process. The catalyst/electrode is the crucial component of the system because it strongly influences the overall cost. Except for optimizing carbonaceous catalysts by increasing their intrinsic activity and selectivity, a growing number of studies have considered methods to obtain high catalytic efficiency from the perspective of liquid/gas wettability on the electrode surface. In this context, researchers with conflict standpoints all successfully fabricated catalysts/ electrodes with improved H2O2 production by regulating the hydrophilicity/ hydrophobicity/amphiphilicity. In this review, the basic parameter of material wettability and mechanism of three-phase interface are introduced. The debate on the role of material hydrophilicity/hydrophobicity toward ORR are summarized and discussed. A variety of strategies including development of novel catalysis materials and use of physical/chemical treatments on electrodes for the purpose of increasing H2O2 yield are presented. Finally, the challenges we are still facing and perspectives on future directions are proposed.