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

MoSe₂ as a cost‐effective cocatalyst is of huge interest for photocatalytic water splitting. However, the H₂‐production activity of the bulk MoSe₂ is still unsatisfactory because its interfacial H₂‐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 H₂‐evolution cocatalyst are fabricated onto TiO₂ 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 H₂‐production efficiency of Se atoms. Ultimately, the optimized a‐MoSe_x/TiO₂(1 mL) photocatalyst delivers a superior H₂‐evolution rate of 86.28 μmol h⁻¹, which is about 76.4‐ and 2.5‐fold of the pure TiO₂ and the crystalline MoSe₂ modified‐TiO₂ 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 H₂‐evolution efficiency of active Se sites, thus actually improving photocatalytic H₂‐production activity of TiO₂. This work offers a new paradigm to simultaneously optimizing the number and efficiency of active Se sites for interfacial H₂ evolution, which delivers an inspiration on constructing highly efficient cocatalysts for solar‐energy conversion.