Hydrogen peroxide generation from O₂ electroreduction for environmental remediation: A state-of-the-art review

The electrochemical production of hydrogen peroxide (H₂O₂) by 2-electron oxygen reduction reaction (ORR) is an attractive alternative to the present complex anthraquinone process. The objective of this paper is to provide a state-of-the-arts review of the most important aspects of this process. First, recent advances in H₂O₂ production are reviewed and the advantages of H₂O₂ electrogeneration via 2-electron ORR are highlighted. Second, the selectivity of the ORR pathway towards H₂O₂ formation as well as the development process of H₂O₂ production are presented. The cathode characteristics are the decisive factors of H₂O₂ production. Thus the focus is shifted to the introduction of commonly used carbon cathodes and their modification methods, including the introduction of other active carbon materials, hetero-atoms doping (i.e., O, N, F, B, and P) and decoration with metal oxides. Cathode stability is evaluated due to its significance for long-term application. Effects of various operational parameters, such as electrode potential/current density, supporting electrolyte, electrolyte pH, temperature, dissolved oxygen, and current mode on H₂O₂ production are then discussed. Additionally, the environmental application of electrogenerated H₂O₂ on aqueous and gaseous contaminants removal, including dyes, pesticides, herbicides, phenolic compounds, drugs, VOCs, SO₂, NO, and Hg⁰, are described. Finally, a brief conclusion about the recent progress achieved in H₂O₂ electrogeneration via 2-electron ORR and an outlook on future research challenges are proposed.