Modulating Electron‐Transfer via Covalent Assembly Polyoxometalate with Photosensitizer for Efficient H ₂ Evolution and Tandem Hydrogenation

Photocatalytic hydrogen evolution efficiency is critically dependent on electron transfer between photosensitizers (PSs) and catalysts. Herein, covalent assembly of Ir-PSs with Co₇ polyoxometalate was achieved via Schiff-base condensation to adjust electron transfer pathways, the resulting Ir-2@Co₇ assembly exhibits a turnover number of 2280 for H₂ evolution, ∼18 and ∼253 times higher than that of its physically mixture and Ir-1@Co₇, respectively. Moreover, the generated H₂ can drive tandem styrene hydrogenation under ambient conditions, achieving 99.9% ethylbenzene yield. Spectroscopic and thermodynamic analyses reveal that covalent linkage switches dominant quenching mechanism from reductive to oxidative, and dramatically enhances electron quenching rate constant by over two orders of magnitude from 2.54 × 10⁹ M^-1 s^-1 in physical-mixed system to 5.87 × 10¹¹ M^-1 s^-1 in the assembly. This work highlights the key role of covalent integration in promoting electron transfer, providing a general design principle for developing high-performance H₂ evolution and tandem hydrogenation systems.