The Electronic Microenvironments of Cocatalysts Monitored by <i>d–d</i> Orbital Coupling for Boosting Covalent Organic Framework‐Based Photocatalytic Hydrogen Evolution

Covalent organic frameworks (COFs)-based dyads are promising photocatalysts for the conversion of solar energy into green hydrogen, it is crucial and challenging to expedite the migration and utilization of charge carriers for realizing high hydrogen evolution efficiency. Herein, one new strategy is reported to modulate electronic microenvironments of cocatalysts by combining ketoenamine-linked COFs with Fe_1-xCo_xS. The strong d-d orbital coupling interactions between Fe and Co are validated to promote directional migration of the photogenerated electrons from COFs to the active sites of cocatalysts and the activation of water molecules, thus significantly improving photocatalytic kinetics. The hydrogen evolution rate in the optimized Fe_0.5Co_0.5S/TpPa-1 is as high as 13.49 mmol g^-1 h^-1, which surpasses those in homometallic counterpart FeS/TpPa-1 (1.32 mmol g^-1 h^-1) and CoS/TpPa-1 (0.96 mmol g^-1 h^-1), and is even higher than those in Pt-loaded TpPa-1 (7.11 mmol g^-1 h^-1). This work provides a rational approach to construct noble-metal-free COFs-based photocatalytic systems for ameliorating hydrogen evolution performance.