Activating S-inert sites on ReS₂ basal plane via Mo doping to boost electrochemical hydrogen evolution reaction

Two-dimensional (2D) rhenium disulfide (ReS₂) is a promising material for electrocatalytic hydrogen evolution reaction (HER) due to its distorted 1T' phase crystal structure, unique Re–Re metal bonding, and weak interlayer coupling. However, the catalytic activity of ReS₂ is predominantly concentrated at the edge sulfur (S) site, whereas the basal plane S atoms with a large specific surface area are catalytically inert, which seriously degrades its overall performance. To address this issue, we employ a doping strategy by introducing molybdenum (Mo) atoms into centimeter-scale continuous monolayers of ReS₂ via low-pressure chemical vapor deposition (LPCVD). Experimental and density functional theory (DFT) results demonstrate that Mo atoms can act as electron donors that transfer valence electrons to surrounding S atoms, activating the inert S atoms. Additionally, the incorporation of Mo doping exerts an activating influence on the otherwise inert basal-plane S sites by modulating the p-band center of adjacent S atoms. Consequently, this doping strategy provides more HER active sites, thereby enhancing the adsorption capacity of hydrogen atoms. The above effects can be further quantified by studying the Gibbs free energy of hydrogen adsorption (ΔG_H∗). The results indicate that ΔG_H∗ values on different S sites including S₁, S_2, S₃, S_4, S_5, and S₆ decrease from 1.4689, 1.6855, 1.6845, 1.9141, 1.8246, and 1.8052 eV for ReS₂ to − 0.0842, 0.1796, 0.1409, 0.7616, 0.5162, and 0.5078 eV for Re_xMo_1-xS₂, respectively. Thus, Mo doping not only activates the native inert in-plane S sites but also enhances the adsorption capability for hydrogen atoms, making Re_xMo_1-xS₂ an efficient HER electrocatalyst. This work clearly reveals the effects of Mo doping on the electrochemical performance of ReS₂, thus providing a robust architecture for designing transition metal dichalcogenides-based catalysts in the future.