N-doped carbon-based catalysts in situ generation hydrogen peroxide via 2-electron oxygen reduction reaction for degradation of organic contaminants in heterogeneous electro-Fenton process: A mini review

Heterogeneous electrochemical advanced oxidation processes (EAOPs), especial in situ catalytic production of hydrogen peroxide (H2O2) via 2-electron oxygen reduction reaction (ORR), has gained increasing attention owing to its safety, efficiency and cost-effectiveness. This review aims to provide a concise summary on the recent development of N-doped carbon-based catalysts as cathode for the improvement of ORR activity, the selectivity of H2O2 and the yield of hydroxyl radical (·OH). The methods of nitrogen doped in carbon-based catalysts, which are dominated by single nitrogen form and coexisting with multiple nitrogen forms, are introduced in this manuscript. The effects and mechanisms of different nitrogen forms on 2-electron ORR and ·OH are discussed in detail, and the synergistic effect of N co-doping with other heteroatoms (F/P/S/O) on ORR is analyzed. Finally, research directions on enhancing ORR activity and the yield of H2O2 and ·OH are put forward from four aspects: preparation methods, mechanism analysis, coupling effects and density functional theory (DFT) calculation.