Coordination-Deficient Ni Sites Strengthen Orbital Coupling for Enhanced Photocatalytic H 2 O 2 Production

Photocatalytic H 2 O 2 synthesis presents a promising alternative to the energy-intensive anthraquinone process. However, carbon nitride-based photocatalysts suffer from limited H 2 O 2 production due to weak O 2 binding and inefficient formation of *OOH intermediates at the active sites. Here, we demonstrate that engineering coordination-deficient Ni sites in carbon nitride significantly enhances photocatalytic H 2 O 2 production through the systematic reduction of Ni coordination from fully coordinated Ni–N4 to coordination-deficient Ni–N2. Density functional theory calculations reveal that the coordination-deficient Ni–N2 sites exhibit upshifted d-orbital centers and strengthened Ni 3d–O 2p orbital coupling. This electronic modification transforms O 2 adsorption from Pauling-type to Griffiths-type configuration, facilitating *OOH intermediate stabilization. Guided by these insights, we synthesized a series of Ni sites with a tunable coordination deficiency through an intercalation–exfoliation strategy. The optimal Ni–N2 catalyst achieves a H 2 O 2 production rate of 240.23 μmol g –1 h –1, representing a 6.07-fold enhancement over pristine carbon nitride, with 94.15% H 2 O 2 retention efficiency. Femtosecond transient absorption spectroscopy reveals ultrafast electron injection into Ni d-orbital trap states on the picosecond time scale, creating long-lived excited states essential for O 2 activation. In situ spectroscopic studies confirm the preferential *OOH formation on the Ni–N2 sites, validating the direct two-electron pathway.