Layerwise replacement method to achieve high solar-to-hydrogen efficiency for photocatalytic water splitting: a first principles study†

Atomically layered stacking (ALS) two-dimensional (2D) materials, owing to their superior electrical properties and flexible tunability in addition to the advantages of traditional 2D materials, have garnered widespread attention in recent years. However, when used as photocatalysts for overall water splitting (OWS), many of them face challenges like low Solar-to-Hydrogen (STH) efficiency and insufficient driving force for photoinduced redox reactions. Here, using Al₂X₃ (X = S, Se) as samples, we demonstrate the potential of the Layerwise Replacement Method (LRM) in reducing the materials' bandgap, improving their light absorption performance, and boosting the STH efficiency. As anticipated, the Al₂S₂Se-t and Al₂TeSe₂-m monolayers demonstrate STH efficiencies exceeding 20%, surpassing the performance of the majority of reported photocatalysts. Additionally, under light excitation, the OER reaction on the Al₂S₂Se-t monolayer is exothermic, while on the Al₂TeSe₂-m monolayer, the OER energy barrier is reduced to 0.431 eV. Notably, on both materials, the HER energy barriers are approaching 0 eV. The improvement of these properties is primarily ascribed to the modulation of the materials' bandgap via the LRM, and secondarily to the reconstruction of the vertically intrinsic electric field (IEF). Our work not only offers a fresh perspective for the precise manipulation of atomically layered stacked 2D materials but also provides a rational strategy for designing novel and outstanding photocatalysts.