Heteroatom Loading of Nanodiamonds Modulates the Coupled Electrocatalytic Production of H ₂ O ₂ by Oxygen Reduction and Water Oxidation

The synthesis of H₂O₂ via two-electron oxygen reduction (2e^- ORR) and two-electron water oxidation (2e^- WOR) has attracted attention due to its simplicity, energy efficiency, and sustainability. However, the electrochemical conversion of H₂O to H₂O₂ often suffers from limited selectivity at high current densities. Herein, we propose oxygen-doped nanodiamonds (O-ND) for 2e^- ORR to investigate the combined effects of heteroatom doping and the advantageous sp³ conformation on catalytic activity. We comprehensively characterized the configuration, doping, and crystal growth of O─ND using various techniques. The oxygen-doped sp³ diamond structure exhibited high catalytic activity for 2e^- ORR, with Faradaic efficiency (FE) increasing from 71% in pristine ND to 87.1% and an average FE of 80%. We also synthesized copper-doped nanodiamond composite catalysts (Cu-OND) with high 2e^- WOR activity, achieving 2e^- WOR FE of 78.2%. The complete battery system, after coupling O-ND (cathode) with Cu-OND (anode), demonstrates outstanding performance at 1.8 V, with the combined FE of cathode and anode reaching 161.1%. This result surpasses most currently reported values. Density functional theory (DFT) calculations revealed that the maximum dynamic active sites of the coupled reaction catalyst are derived from the local charge regulation effect of O-doped sp³C and the heterojunction structure of Cu-doped OND.