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–Hads). 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–Hads bonds via constructing electron-poor Se(2−δ)− 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%). H2-evolution experiments display that the Se-enriched WSe2+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 Hads for fast H2 formation via reinforcing the weak Se–Hads bonds. This work highlights the significance of active-site enrichment to optimize the H2-evolution process of cocatalysts.