Modulating electronic structure of g-C3N4 hosted Co-N4 active sites by axial phosphorus coordination for efficient overall H2O2 photosynthesis from oxygen and water

Abstract

Single-atom catalysts are promising for H₂O₂ photosynthesis from O₂ and H₂O, but their efficiency is still limited by the ill-defined electronic structure. In this study, Co single-atoms with unique four planar N-coordination and one axial P-coordination (Co-N₄P₁) are decorated on the lateral edges of nanorod-like crystalline g-C₃N₄ (CCN) photocatalysts. Significantly, the electronic structures of central Co as active sites for O₂ reduction reaction (ORR) and planar N-coordinator as active sites for H₂O oxidation reaction (WOR) in Co-N₄P₁ can be well regulated by the synergetic effects of introducing axial P-coordinator, in contrast to the decorated Co single-atoms with only four planar N-coordination (Co-N₄). Specifically, directional photoelectron accumulation at central Co active sites, induced by an introduced midgap level in Co-N₄P₁, mediates the ORR active sites from 4e^–-ORR-selective terminal –NH₂ sites to 2e^–-ORR-selective Co sites, moreover, an elevated d-band center of Co 3d orbital strengthens ORR intermediate *OOH adsorption, thus jointly facilitating a highly selective and active 2e^–-ORR pathway to H₂O₂ photosynthesis. Simultaneously, a downshifted p-band center of N 2p orbital in Co-N₄P₁ weakens WOR intermediate *OH adsorption, thus enabling a preferable 2e^–-WOR pathway toward H₂O₂ photosynthesis. Subsequently, Co-N₄P₁ exhibits exceptional H₂O₂ photosynthesis efficiency, reaching 295.6 μmol g^–1 h^–1 with a remarkable solar-to-chemical conversion efficiency of 0.32 %, which is 15 times that of Co-N₄ (19.2 μmol g^–1 h^–1) and 10 times higher than CCN (27.6 μmol g^–1 h^–1). This electronic structure modulation on single-atom catalysts offers a promising strategy for boosting the activity and selectivity of H₂O₂ photosynthesis.