Tuning Ni-O orbital interactions to steer oxygen activation for enhanced hydrogen peroxide photosynthesis

Nickel-based co-catalysts are attractive candidates for H₂O₂ photosynthesis via the two-electron oxygen reduction reaction (2e^- ORR). However, inherently strong O₂ adsorption and overactivation at Ni sites promote undesired O-O bond cleavage, compromising both selectivity and activity. Here, we introduce an orbital-level modulation strategy that tailors O₂ activation at Ni centers by tuning the Ni 3d-O 2p interactions through atomic ligand regulation. Specifically, incorporation of electronegative phosphorus ligands into Ni-decorated poly(triazine imide) (Ni/PTI) reconfigures the Ni 3d orbital distribution, constructing Ni₂P/PTI that suppresses excessive O₂ activation and reverses the H₂O₂ decomposition observed in Ni/PTI. This strategy achieves a 4.7-fold enhancement in H₂O₂ production under visible light in pure water. Mechanistically, phosphorus-mediated electronic tuning diminishes Ni 3 d_yz orbital contributions to O₂ π* antibonding orbitals, thereby preventing O-O bond cleavage and stabilizing key intermediates. Concurrently, phosphorus-induced Ni coordination adjustment promotes *OOH protonation and inhibits H₂O₂ decomposition, jointly reinforcing 2e^- ORR selectivity and efficiency. These findings establish atomic ligand-driven orbital modulation as a powerful principle for steering O₂ activation on Ni-based co-catalysts, offering a blueprint for designing transition-metal sites with optimized electronic structures and coordination environments for efficient H₂O₂ photosynthesis.