Tailoring Antibonding-Orbital Occupancy State of Selenium in Se-Enriched ReSe2+x Cocatalyst for Exceptional H-2 Evolution of TiO2 Photocatalyst

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-delta)- active sites in ReSe2+x nanodots. To this end, the Se-rich ReSe2+x nanodots (0.3-1 nm) can be dexterously fabricated onto the TiO2 to prepare Se-rich ReSe2+x/TiO2 by an ingenious one-step photosynthesis route. In a surprise, a large number of visual H-2 bubbles are continuously produced on the resultant ReSe2+x/TiO2(0.7 wt.%) with an ultrahigh rate of 12 490.4 mu mol h(-1) g(-1) and an apparent quantum efficiency of 60.0%, which is 5.0 times higher than that of traditional ReSe2/TiO2, even comparable with benchmark Pt/TiO2(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-delta)- 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.