Electronic Configurations Modulated by Heterometallic Orbital Interactions of Spinel Cocatalysts in Covalent Organic Framework-Based Dyads for Photocatalytic Hydrogen Evolution

Metal sulfides are promising cocatalysts in covalent organic framework (COF)-based photocatalytic systems. It is of paramount importance to fine-tune the electronic configurations of these cocatalysts for enhancing the efficiency of photocatalytic hydrogen evolution. Herein, we report a strategy aimed at regulating heterometallic electron configuration of the cocatalysts to construct noble-metal-free photocatalytic systems, which is achieved by combining spinel sulfides (NiCo 2 S 4 ) with the ketoenamine-linked COFs (TpPa). In NiCo 2 S 4, the 3d orbital electrons of tetrahedral Ni sites (Ni Td ) and octahedral Co sites (Co Oh ) interact with the p orbital electrons of sulfur. Such interactions result in strong d–p orbital hybridization that triggers the electron migration from Ni Td to Co Oh sites, which improves the electron delocalization and facilitates the formation of hydrogen intermediates, thereby significantly boosting the kinetics of the photocatalytic hydrogen evolution reaction. The hydrogen evolution rate in the NiCo 2 S 4 /TpPa system is as high as 9160 μmol g –1 h –1, which outperforms that of Ni 3 S 4 /TpPa (700 μmol g –1 h –1 ), Co 3 S 4 /TpPa (2511 μmol g –1 h –1 ), and even Pt-loaded TpPa (5548 μmol g –1 h –1 ). This work presents a rational and effective approach to develop noble-metal-free, COFs-based photocatalytic systems for ameliorating hydrogen evolution performance.