Heteroatom P filling activates intrinsic S atomic sites of few-layered ZnIn2S4via modulation of H adsorption kinetics for sacrificial agent-free photocatalytic hydrogen evolution from pure water and seawater

Abstract

The rational engineering of photocatalytic active sites on an atomic scale with regulated H adsorption energy and accelerated reaction kinetics has been pivotal to realize photocatalytic H₂ evolution reactions (HERs) without sacrificial reagents. Although hydrogen evolution from pure water splitting is at the forefront of solar H₂ research, photocatalytic seawater splitting is more in line with the notion of sustainable development owing to the limited resources of freshwater. Herein, we report for the first time an H adsorption kinetics-oriented design of two-dimensional (2D) hexagonal ZnIn₂S₄ (ZIS) atomic layers via heteroatom P doping (ZIS-P) for the modulation of intrinsic S active sites to achieve sacrificial agent-free photocatalytic HERs using both pure water and seawater. Atomic insights from density functional theory (DFT) calculations reveal that non-metal P dopants with different valence electrons and electronegativity than substituted S3 atoms in ZIS give rise to the formation of a new hybridized level with a moderately filled state near the valence band maximum (VBM) and impart redistribution of electron density within the coordination, hence triggering the activation of neighboring S2 atoms. Thus, ZIS-P with tailored S2 atomic sites and fine-tuned electronic structure endows a diminishment in H adsorption–desorption barriers and enables energetically favorable HERs. In particular, the optimal ZIS-P sample demonstrated visible light-driven photocatalytic water splitting without any sacrificial reagents, resulting in H₂ evolution rates of 1.68 μmol h⁻¹ (pure water) and 1.54 μmol h⁻¹ (simulated seawater), respectively. This work presents an approach to engineer the inert active sites, thus alleviating the strength of H adsorption free energy and enhance the HER kinetics.