S-Vacancy Defect and Transition-Metal Atom Doping to Trigger Hydrogen Evolution of Two-Dimensional MoS₂

Two-dimensional (2D) MoS2 is commonly used as an anode catalyst for electrochemical water splitting. However, the limited active edge sites of 2D MoS2 have hindered its electrochemical performance in electrochemical water splitting. Here, experimental outcomes and density functional theory (DFT) calculations demonstrate that the catalytic performance of inert 2D MoS2 surfaces can be triggered by doping transition-metal atoms and introducing S-vacancies. In this work, the catalytic activity of different metal-doped (Cu, Mn, and Nb) 2D MoS2 with S-vacancies shows a great difference among tested MoS2-based samples. Characterizations verify the existence of dopant ions and S-vacancies. In particular, the Cu-doped electrocatalyst exhibits a low overpotential of 197 mV at 10 mA cm–2 in an acidic solution and superior stability of less than 10 mV increase in overpotential after 12 h of continuous hydrogen production process, proving that Cu doping and introduced S-vacancies can benefit the electrochemical performance. Moreover, DFT calculations reveal that S-vacancies and the further introduction of different metal ions can alter the adsorption behavior of H atoms by changing the d-band center of the in-plane Mo site neighboring the doped heteroatom atoms and S-vacancy sites, which explains well the superior performance of Cu-doped 2D MoS2.