Increasing unsaturated Se number and facilitating atomic hydrogen adsorption of WSe2+x nanodots for improving photocatalytic H2 production of TiO2

Cost-effective 2D metal-selenides are verified to be potential cocatalyst candidates for photocatalytic H-2 evolution. However, their cocatalytic activities are limited by the scarce number of unsaturated Se atoms and their weak bonding with adsorbed hydrogen atoms (Se-H-ads). Herein, a versatile tactic of unsaturated selenium-enrichment regulation is developed, which can not only increase the active Se number, but also reinforce the weak Se-H-ads bonds via constructing electron-poor Se(2-delta)- active sites by the rational design of unsaturated Se-enriched WSe2+x amorphous nanodots (expressed as WSe2+x). To this end, the Se-enriched WSe2+x nanodots are skillfully deposited on the TiO2 surface by a complexation-photodeposition strategy, including the initial formation of stable [W(SeU)(n)](5+) complex-precursors and their following in situ photoreduction process. The resultant Se-enriched WSe2+x nanodots (0.5-1 nm) possess numerous unsaturated Se atoms (45.8%) because of their amorphous structure and unsaturated Se-enriched character, which is much higher than that of crystalline WSe2 (8.6%) and amorphous WSe2 (25.0%). H-2-evolution experiments display that the Se-enriched WSe2+x/TiO2 (3 wt%) realizes a maximal photoactivity of 3770.8 mu mol h(-1) g(-1) (AQE = 18.1%), which is 4.5 and 2.4 times larger than that of crystalline WSe2/TiO2 and amorphous WSe2/TiO2, respectively. Based on in situ/ex situ XPS and DFT results, an electron-poor Se(2-delta)--mediated hydrogen-generation mechanism is proposed, namely, the enriched selenium sites can induce the production of numerous electron-poor Se(2-delta)-, which can facilitate the adsorption of H-ads for fast H-2 formation via reinforcing the weak Se-H-ads bonds. This work highlights the significance of active-site enrichment to optimize the H-2-evolution process of cocatalysts.

Automated summary

This study develops a strategy to regulate unsaturated selenium enrichment, which enhances the catalytic activity of co-catalysts by constructing WSe2+x amorphous nanodots with unsaturated selenium atoms. The Se-enriched WSe2+x/TiO2 exhibits superior photocatalytic activity for hydrogen evolution.