Ultrahigh Carrier Mobility and Enhanced Photocatalytic Activity in 2D GaSe/ZrTeS4 Heterostructures for Solar Water Splitting: A DFT Study

Photocatalytic water splitting offers a sustainable pathway for producing green hydrogen. Recently, two-dimensional (2D) heterostructures have shown promise in enhancing photocatalytic efficiency. In this study, we employ density functional theory (DFT) to investigate the GaSe/ZrTeS₄ van der Waals heterostructure. Calculations using the HSE06 functional reveal a direct bandgap of 1.70 eV and a type-II band alignment, which facilitates efficient separation of photogenerated electron–hole pairs. Optical analysis shows strong absorption in the visible-light region, which is critical for solar energy utilization. Band alignment indicates favorable redox potentials for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Under light illumination, Gibbs free energy analysis suggests that HER can proceed spontaneously on the ZrTeS₄ side. In contrast, the OER on the GaSe side requires an external potential of 1.15 V under acidic conditions; however, under alkaline conditions, the reaction becomes thermodynamically favorable without bias. The heterostructure also exhibits ultrahigh carrier mobilities of 2513.71 cm² V^–1 s^–1 for electrons and 7396.81 cm² V^–1 s^–1 for holes. Furthermore, the calculated solar-to-hydrogen (STH) efficiency reaches a remarkably high value of 40%, which remains unchanged across acidic, neutral, and alkaline environments, suggesting that GaSe/ZrTeS₄ is a potential 2D heterostructure for overall water splitting.