Achieving Free‐Electron Transfer Reversal and dz2‐Orbital Occupancy Modulation on Core‐shell NiS@Au Cocatalysts for Highly Selective H2O2 Photosynthesis

Spontaneous free‐electron migration usually occurs on the interface between host photocatalysts and cocatalysts, but the influences of the charge transfer direction on the two‐electron oxygen reduction reaction (2e‐‐ORR) of cocatalysts have not been taken seriously. Herein, an innovative electron‐transfer reversal is proposed to direct the free‐electron transfer in a way that enables highly selective 2e‐‐ORR on Au cocatalysts. To this end, metallic Au nanoparticles are originally loaded on NiS particles to fabricate novel core‐shell NiS@Au cocatalysts on g‐C3N4 surface by a directional photodeposition procedure. XAS spectra and DFT calculations disclose that the intergrated NiS induces a reversed free‐electron transfer from Au nanoparticles to NiS core, thus essentially modulating dz2‐orbital occupancy of Au atoms to enhance O2 adsorption and stabilize key *OOH intermediates, endowing core‐shell NiS@Au cocatalysts with a highly selective 2e‐‐ORR process for efficient H2O2 evolution. Consequently, the optimized g‐C3N4/NiS@Au photocatalyst achieves a remarkably promoted H2O2‐production rate of 264.82 μmol/h/50 mg in the air environment, possessing a high apparent quantum efficiency of 8.07% under visible light. This work provides novel insights on purposefully steering free‐electron transfer direction to engineer dz2‐orbital occupancy, offering a feasible approach for designing highly active photocatalysts and beyond.