Tailoring Antibonding‐Orbital Occupancy State of Selenium in Se‐Enriched ReSe2+x Cocatalyst for Exceptional H2 Evolution of TiO2 Photocatalyst

Abstract Electron density regulation of active sites can realize an optimal hydrogen‐binding strength, whereas the underlying regulation mechanism is still indistinct. Herein, a new concept of antibonding‐orbital occupancy state is first proposed to unveil the fundamental influence mechanism of electron density on the SeH ads bond strength for achieving first‐rank adsorption energy toward atomic hydrogen by constructing Se‐enriched surrounding to form electron‐deficient Se (2‐δ)‐ active sites in ReSe 2+ x nanodots. To this end, the Se‐rich ReSe 2+ x nanodots (0.3–1 nm) can be dexterously fabricated onto the TiO 2 to prepare Se‐rich ReSe 2+ x /TiO 2 by an ingenious one‐step photosynthesis route. In a surprise, a large number of visual H 2 bubbles are continuously produced on the resultant ReSe 2+ x /TiO 2 (0.7 wt.%) with an ultrahigh rate of 12 490.4 µmol h −1 g −1 and an apparent quantum efficiency of 60.0%, which is 5.0 times higher than that of traditional ReSe 2 /TiO 2 , even comparable with benchmark Pt/TiO 2 (0.7 wt.%). In situ/ex situ XPS characterizations coupled with density functional theory (DFT) calculations corroborate that a Se‐enriched environment can induce the formation of electron‐deficient Se (2‐δ)− and then reduce its antibonding‐orbital occupancy state, thus increasing the stability of H 1s‐p antibonding and accordingly reinforcing the SeH ads bonds. This holistic study identifies the dominant role of antibonding‐orbital occupancy states in the optimization of hydrogen‐binding energy.