Regulating Cocatalyst Spin‐Electronic Structures for Achieving Solar‐To‐H ₂ of 7.32% in Photothermal‐Catalytic H ₂ O Overall Splitting

Abstract Precise regulation of intrinsic electronic structure of cocatalyst functional material for triggering photocatalyst activity at ultrafast‐spatiotemporal atomic levels is crucial to liberate photocatalytic efficiency. Herein, gradient spin‐state Ni ₂ P as cocatalyst simultaneously including spin‐electronic configurations of tetra‐ (Ni ²⁺ ─(P) ₄ ) and penta‐coordination (Ni ^δ+ –(P) ₅ ) is designed for amplifying In ₂ S ₃ polarization by spin‐orbit coupling. So photo‐generated e ⁻ and h ⁺ from the In ₂ S ₃ photocatalyst vectorially transfer to Ni 2 p and In 3 d as redox active sites with charge density enhanced to ≈9.48 and 8.52 folds and long lifetime up to 289% (180.39 ns). Observably, energetic chemical adsorption and activation for *H and *OH at Ni 2 p and In 3 d are completed through electron nimble transfer into the corresponding orbits, performing an activation energy for H ₂ O splitting down to ≈59%. Also, the gradient spin‐polarized photocatalytic system with the two regulated electronic structures of Ni ₂ P as cocatalyst presents a remarkable productivity for solar energy conversion into H ₂ of 7.32% at 75 °C under AM 1.5 G irradiation through *OH dehydrogenation and *H coupling paths, ranking in one of the best H ₂ ‐generation catalysts for photocatalytic H ₂ O overall splitting. This research first paves a novel path to completely unlock photocatalytic efficiency through regulating spin‐electronic structures of cocatalysts.