H<sub>2</sub> Regulates the Sulfur Vacancy of Mo-Doped\nWS<sub>2</sub> for Electrochemical Hydrogen Evolution Reaction

The\ndevelopment of efficient and economical nonprecious metal electrocatalysts\nis crucial for advancing the industrialization of the hydrogen evolution\nreaction (HER) in water electrolysis. WS<sub>2</sub> has become a\nhotspot in HER research due to its unique physicochemical properties\nand potential applications. In this work, a series of Mo-WS<sub>2</sub>-n (n = 0, 0.3, 0.5 and 1.0, representing H<sub>2</sub> pressure)\nsamples with abundant sulfur vacancies were prepared by utilizing\nH<sub>2</sub> as the structure directing agent (SDA). Among them,\nthe Mo-WS<sub>2</sub>-0.5 sample possessing abundant sulfur vacancies\ndemonstrated best acidic HER performance by displaying an overpotential\nof 146 mV at 10 mA cm<sup>–2</sup> and the Tafel slope of 46.8\nmV dec<sup>–1</sup>, which is superior to most reported WS<sub>2</sub>-based electrocatalysts. Furthermore, Mo-WS<sub>2</sub>-0.5\nexhibits good stability, proving its potential in practical applications.\nDuring the synthesis process, H<sub>2</sub> can effectively remove\nS atoms from WS<sub>2</sub> to create sulfur vacancies. Theoretical\ncalculations unravel that both Mo doping and sulfur vacancies can\nsignificantly reduce the Gibbs free energy of hydrogen atom adsorption\n(Δ<i>G</i><sub>H</sub>) of WS<sub>2</sub>. This study\nnot only offers new insights into understanding the effects of metal\ndoping and sulfur vacancies in WS<sub>2</sub> on acidic HER, but also\nprovides a practical approach for designing low-cost and high-performance\nnon-noble metal electrocatalysts.