The Interplay of Dy Doping and Sulfur Vacancies in MoS₂ for an Efficient Hydrogen Evolution Reaction

A comprehensive understanding of rare-earth-doped MoS₂ is essential for the rational design of catalysts with increasing active sites to improve hydrogen evolution reaction (HER) performance. In this work, we synthesized Dy-doped MoS₂ (MoS₂/Dy) via a citrate-assisted hydrothermal method with varying Dy loadings. Citrate plays a vital role in stabilizing Dy ions in a solution mixture and preventing their precipitation. The successful formation of 2H-phase MoS₂ and its morphology were confirmed by X-ray diffraction (XRD) and electron microscopy analyses. The Dy-induced alteration in the electronic structure of MoS₂ and the local chemical environment of Dy were also elucidated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Upon variation of Dy doping, a decrease in the Mo:S ratio was observed with the presence of sulfur vacancies, which further enriches the exposure of the active sites. Among all synthesized catalysts, MoS₂ with the optimum Dy loading (7 wt %) exhibits the superior electrocatalytic performance in 0.5 M H₂SO₄, delivering a low overpotential of 202 mV at a current density of 10 mA cm^-2 and a favorable Tafel slope of 53.9 mV dec^-1. The MoS₂/Dy catalyst also demonstrates excellent durability, maintaining stable HER performance over 36 h without significant degradation. Moreover, density functional theory (DFT) calculations suggest that hydrogen adsorption near the sulfur vacancy and Dy atom provides the optimum value of -0.30 eV for HER. These results highlight the synergistic relation of Dy doping and sulfur vacancies in enhancing the electrocatalytic activity of MoS₂, positioning it as a promising candidate for sustainable hydrogen production in acid media.