Double Type-II Heterojunction MnS/Mn–Cd–S/Ni-Polyoxometalate for Improving Visible-Light-Driven H₂ Production

Element doping and collaboration with other cocatalysts are two vital strategies to improve the photoelectrochemical properties and overcome the drawbacks of CdS for better photocatalytic performance. In this work, a series of manganese cadmium sulfides (Mn_xCd_1–xS) were obtained by a solvothermal method. When x is equal to or greater than 0.3, Mn_xCd_1–xS is composed of Mn–Cd–S sosoloid and MnS. Among all these Mn_xCd_1–xS products, the Mn_0.5Cd_0.5S sample showed the best photocatalytic hydrogen production (5.99 mmol g^–1 h^–1). To further elevate the hydrogen production rate of Mn_0.5Cd_0.5S, four kinds of Ni-POMs were coupled with it as cocatalysts, and all these composite photocatalysts displayed enhanced performance. The highest efficiency was observed for 15-Ni₄–Mn_0.5Cd_0.5S, which is up to 36.58 mmol g^–1 h^–1. Various characterizations indicated that Ni₄P₂W₁₈, Mn–Cd–S sosoloid and MnS in the 15-Ni₄–Mn_0.5Cd_0.5S composite form a double type-II heterojunction, which facilitates the separation and transfer of photogenerated carriers.