Boosting Hydrogen Evolution on MoS₂ via Ion Irradiation: Synergistic Effect of Vacancy and Substitution

Ion irradiation is a powerful tool for tailoring the properties of materials. It has been recently demonstrated to be effective in enhancing the catalytic activity of two-dimensional (2D) transition metal dichalcogenides toward the hydrogen evolution reaction (HER), but the fundamental mechanism remains elusive. Here, by using first-principles calculations, ab initio molecular dynamics (AIMD) and Monte Carlo simulations, we investigate the atomic structure and catalytic activity of 2D MoS₂ under F irradiation. By systematically calculating the Gibbs free energy of hydrogen adsorption (ΔG_H) on MoS₂ with various point defects, we reveal that sulfur vacancies (V_S) and substitutional fluorine atoms (F_S) are catalytically active sites, while other defects (e.g., interstitial atoms and adsorbed species) are chemically inert. Based on this, the optimal irradiation parameters are successfully identified with an incident ion energy range of 80-3000 eV and a fluence of 3 × 10¹⁴ ions/cm², which can maximize the formation of V_S and F_S while suppressing other defects. Surprisingly, with the obtained atomic structure of irradiated MoS₂, we find that the combined defects involving both V_S and F_S exhibit even smaller ΔG_H (∼-0.01 eV) compared to individual V_S and F_S (∼-0.06 eV), demonstrating their synergistic role in boosting HER. This work not only sheds light on the irradiation-enhanced catalytic performance of MoS₂ for water splitting but also provides crucial guidance for tuning the physicochemical properties of 2D materials/devices via defect engineering.