A direct Z-scheme GeS/GeSe van der Waals heterojunction as a promising photocatalyst with high optical absorption, solar-to-hydrogen efficiency and catalytic activity for overall water splitting: First-principles prediction

Seeking an efficient photocatalyst is the key to solve the problem of energy shortage and environmental pollution. We construct a GeS/GeSe heterojunction and explore its structural stability, electronic property, charge transfer, optical property and solar-to-hydrogen energy conversion efficiency by first-principles calculations. The results show that the GeS/ GeSe heterojunction has high thermal and kinetic stability and is a direct Z-scheme pho-tocatalyst with a smaller indirect band gap (1.73 eV) than two monolayers GeS (3.28 eV) and GeSe (3.00 eV), which can not only avoid the backward reaction and light-shielding effect caused by the carrier transfer mediators in traditional and all-solid-state Z-scheme pho-tocatalysts, but also increase the light-harvesting ability, suppress recombination of the photoexcited charge carriers, promote surface catalytic reaction by preserving the strong redox capacity of photoexcited charge carriers with respect to the traditional type-II and p-n heterojunction photocatalyst. The charge transfer analysis shows that the electron accumulates on the GeS side and the hole accumulates on the GeSe side, forming a built-in electric field from GeSe to GeS, which can effectively restrain the recombination of pho-togenerated carriers. Besides, its band edge positions support overall water splitting re-actions in acid and alkaline environments. The optical absorption of the heterojunction is higher than that of its monolayer materials and the solar-to-hydrogen energy conversion efficiency reaches up to 31.21%, which effectively improves the absorption and utilization rate of solar energy. We have good reasons to believe that the GeS/GeSe heterojunction provides an effective strategy for the research and development of efficient photocatalysts.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.