Controlled growth of vertical 3D MoS_2(1−x)Se_2x nanosheets for an efficient and stable hydrogen evolution reaction

Layered transition metal dichalcogenides (TMDs) are considered as promising hydrogen evolution reaction (HER) candidates due to their exposed active sites at edges and superior electron mobility along sheets, however their inert basal planes and non-ohmic contact with current collectors greatly hamper their application in HER reactions. Exposing active sites, accelerating charge transfer, and manipulating hydrogen adsorption free energy close to thermoneutral are significant to favor the HER process. Herein, component-controllable 3D MoS_2(1−x)Se_2x alloy nanosheets with a vertically oriented architecture were successfully grown on conductive carbon cloth substrates through a CVD technique. The bigger radius of Se can cause a slight distortion and bring about a polarized electric field in the basal planes, resulting in favorable bond breaking of adsorbed molecules. Among all tested catalysts, Mo(S_0.53Se_0.47)₂ alloy nanosheets exhibit the lowest Tafel slope (55.5 mV dec⁻¹), smallest overpotential (183 mV) at 10 mA cm⁻², and highest conductivity. The Mo(S_0.53Se_0.47)₂ alloy maintains its activity after 2000 cycles. Density functional theory calculations manifest adjustment of hydrogen adsorption free-energies and vacancy formation energies in MoS_2(1−x)Se_2x alloy nanosheets. S and Se vacancies serve as a crucial factor for HER performance. The 3D exposed active sites, adjusted hydrogen adsorption free energy, vacancy formation energies, and ohmic contact with carbon cloth are found to be responsible for the enhanced HER performance.