Effect of Metal Site Mobility of Single-Atom Catalyst on Photocatalytic Water Oxidation

Abstract

Understanding the impact of catalytic site diffusion on photocatalytic performance is crucial to the rational design of water oxidation photocatalysts. In this study, we combined ab initio nonadiabatic molecular dynamics (NAMD) with density functional theory (DFT) calculations to investigate single-atom transition metals (Ni, Pd) loaded on HfS₂ and their diffusion effects on photocatalytic water oxidation. Transition state calculations indicated that the barriers (0.58 eV) enable the diffusion possibility between the most stable H_S site and the metastable H_Hf site for Pd/1T-HfS₂. Moreover, electronic structure simulations reveal distinct properties of Pd/1T-HfS₂:Pd adsorption at the H_Hf site generate a deep defect state (∼0.5 eV above the valence band maximum (VBM)), while adsorption at the H_S site introduces a shallow defect state near the VBM (∼0.2 eV above the VBM). Compared to that of pristine 1T-HfS₂ (6.2 ns), the electron-hole recombination time extends to 7 ns for Pd(H_S)/1T-HfS₂ but decreases to 1.7 ns for Pd(H_Hf)/1T-HfS₂, driven by the position of the Pd-induced defect states. Thermodynamically, the catalytic properties of Pd(H_S)/1T-HfS₂ and Pd(H_Hf)/1T-HfS₂ show a pronounced difference, approximately 0.08 V in limiting potential. Generally, this study enhances understanding of dynamic photocatalytic properties in single-atom catalysts.