"Edge/Basal Plane Half-Reaction Separation" Mechanism of Two-Dimensional Materials for Photocatalytic Water Splitting

Two-dimensional (2D) materials are long considered as potential candidates for photocatalytic water splitting, but their applications are limited by high electron-hole recombination probability, low solar-to-hydrogen (STH) efficiencies, or "catalyst poisoning" issues. Herein, we propose an "edge/basal plane half-reaction separation" mechanism of 2D photocatalysts for water splitting with superior photocatalytic efficiency. As a proof-of-concept, we design a group of stable and potentially exfoliable 2D rhodium chalcogenide halide (RhXY, X = S, Se, Te; Y = Cl, Br, I) photocatalysts with band gap values from 1.93 to 2.71 eV and suitable band edges. The half-reactions for photocatalytic water splitting, i.e., hydrogen/ oxygen evolution reaction (HER/OER), prefer to happen on the edge and basal planes of RhXY, respectively, and RhSCl, RhSeCl, and RhSeBr can also trigger HER and OER simultaneously without sacrificial reagents or cocatalysts. This work paves the way for the rational design of 2D photocatalysts with spatially separated half-reactions.