First-Principles Study on the Photocatalytic Performance of Janus MoSTe/XSe 2 (X = Mo, W) van Der Waals Heterojunctions for Water Splitting

Reasonable design of heterojunctions provides an effective way to improve the photocatalytic water splitting efficiency of monolayers, especially the design of a direct Z -scheme heterojunction. In this paper, based on the first-principles calculations, monolayers of Janus MoSTe and XSe 2 (X = S, Se) are used to construct direct Z -scheme heterojunctions, and their stabilities, light absorption properties, and photocatalytic efficiencies are studied. The results show that all heterojunctions exhibit a typical Z-type charge transfer paradigm at the interface, which can effectively retain the photogenerated electron–hole pairs with a high redox capacity. Moreover, heterojunctions between XSe 2 and S-surface MoSTe monolayers exhibit good photocatalytic performance in acidic and neutral solutions, as well as under the adjustment of uniaxial strain. As photocatalysts, their solar-to-hydrogen efficiencies are 10.50% for MoSTe–MoSe 2 and 10.94% for MoSTe-WSe 2, respectively. These theoretical predictions provide valuable guidance for the development of new two-dimensional photocatalysts for water splitting.