Composition-dependent activity of Mn-doping NiS₂ nanosheets for boosting photocatalytic H₂ evolution

Two-dimensional transition metal disulfides are excellent photocatalytic materials, which can be significantly improved by optimizing the composition and structure. Herein, Mn-doping NiS₂ of (Ni_1-xMn_x)-S with various Ni/Mn molar ratios is proposed via a facile and low-cost solvothermal method. The optimal (Ni_4/6Mn_2/6)-S exhibits pinecone-like morphology composed of tiny nanosheets with enlarged active sites, which facilitates the separation of photoinduced electrons and holes, improves the electron transfer ability and conductivity, and enlarges the active sites compared with pure NiS₂ and MnS. Also, the negative shift of the conduction band derived from Mott-Schottky plots and the empirical formula provides a high thermodynamic driving force for hydrogen catalytic reaction. (Ni_4/6Mn_2/6)-S performs an ultrahigh hydrogen evolution rate of 24.86 mmol g^-1 h^-1 under UV-visible light irradiation, which is 1.5 times higher than pure NiS₂ (16.92 mmol g^-1 h^-1) and 2.3 times higher than pure MnS (10.69 mmol g^-1 h^-1). The outstanding repeatability of 86.7% retention and apparent quantum yield of 46.9% are also achieved. Therefore, this work offers a novel bimetallic sulfide of (Ni_1-xMn_x)-S to improve the conversion efficiency of solar energy to chemical energy for photocatalytic hydrogen production.