Simultaneously Optimizing the Number and Efficiency of Active Se Sites in Se‐Rich a‐MoSex Nanodot Cocatalysts for Efficient Photocatalytic H2 Evolution

MoSe 2 as a cost‐effective cocatalyst is of huge interest for photocatalytic water splitting. However, the H 2 ‐production activity of the bulk MoSe 2 is still unsatisfactory because its interfacial H 2 ‐generation rate is dominantly hindered by its insufficient and low‐efficiency Se sites. Herein, Se‐rich amorphous MoSe x nanodots ( a ‐MoSe x ) as a novel H 2 ‐evolution cocatalyst are fabricated onto TiO 2 via a lactic acid‐induced hydrolysis pathway. The as‐synthesized a ‐MoSe x cocatalyst displays an ultrasmall and amorphous structure, especially Se‐rich property, which distinctly maximizes the number of active Se sites and optimizes H 2 ‐production efficiency of Se atoms. Ultimately, the optimized a ‐MoSe x /TiO 2 (1 mL) photocatalyst delivers a superior H 2 ‐evolution rate of 86.28 μmol h −1 , which is about 76.4‐ and 2.5‐fold of the pure TiO 2 and the crystalline MoSe 2 modified‐TiO 2 samples, respectively. Combined with the experimental investigations and density functional theory (DFT) calculations, the Se‐rich amorphous MoSe x nanodots can not only effectively promote the photoexcited charge separation, but also achieve the simultaneous optimization of the number and H 2 ‐evolution efficiency of active Se sites, thus actually improving photocatalytic H 2 ‐production activity of TiO 2 . This work offers a new paradigm to simultaneously optimizing the number and efficiency of active Se sites for interfacial H 2 evolution, which delivers an inspiration on constructing highly efficient cocatalysts for solar‐energy conversion.