Innovative strategies on electrocatalysts for H2O2 synthesis by water oxidation: from basics to environmental applications

Abstract

Electrochemical synthesis of hydrogen peroxide (H₂O₂) has been widely considered as an alternative to anthraquinone process due to its safety, feasibility and affordability. The two-electron water oxidation reaction (2e⁻ WOR) usually possesses superior potential for electrochemical H₂O₂ generation than the two-electron oxygen reduction reaction (2e⁻ ORR), because the former can avoid the low concentration and poor mass transfer of O₂ and can provide sufficient oxygen element supply. However, the 2e⁻ WOR faces the challenge of competition between 4e⁻ WOR (selectivity), low efficiency and H₂O₂ decomposition. Also, the mechanisms and the key parameters influencing the 2e⁻ WOR are not clear. In this review, we will focus on how to improve the selectivity and activity of 2e⁻ WOR, how to avoid and evaluate the decomposition of H₂O₂, and what will influence the mechanisms for 2e⁻ WOR. The basics of H₂O₂ synthesis by water oxidation are systematically overviewed, including thermodynamics, fundamental evaluation parameters, theoretical calculations, decomposition of H₂O₂, the influence of electrolyte and electrochemical reactors on 2e⁻ WOR. Most importantly, various innovative strategies on electrocatalysts are summarized, mainly involved in morphology and facet regulation, structure optimization, doping engineering, defect introduction, surface modification, dual-active-site strategy, reaction condition optimization of electrodes, and construction of dual two-channel pathway. The approaches for inhibiting H₂O₂ decomposition are reviewed, such as the addition of H₂O₂ stabilizer and bubble shielding method. Afterward, the environmental applications of H₂O₂ in disinfection and pollutant degradation are firstly reviewed. Finally, future challenges and opportunities towards H₂O₂ by 2e⁻ WOR are presented, which can inspire us for future development of 2e⁻ WOR.