Achieving Free‐Electron Transfer Reversal and <i>dz</i> ^<i>2</i> ‐Orbital Occupancy Modulation on Core‐shell NiS@Au Cocatalysts for Highly Selective H ₂ O ₂ 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.