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

Abstract

Cost-effective 2D metal-selenides are verified to be potential cocatalyst candidates for photocatalytic H₂ 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−δ)− active sites by the rational design of unsaturated Se-enriched WSe_2+x amorphous nanodots (expressed as WSe_2+x). To this end, the Se-enriched WSe_2+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 WSe_2+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%). H₂-evolution experiments display that the Se-enriched WSe_2+x/TiO₂ (3 wt%) realizes a maximal photoactivity of 3770.8 μmol 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−δ)−-mediated hydrogen-generation mechanism is proposed, namely, the enriched selenium sites can induce the production of numerous electron-poor Se^(2−δ)−, which can facilitate the adsorption of H_ads for fast H₂ formation via reinforcing the weak Se–H_ads bonds. This work highlights the significance of active-site enrichment to optimize the H₂-evolution process of cocatalysts.