Phase selective hydrothermal synthesis of 1T MoS2 and Janus 1T MoSSe for the hydrogen evolution reaction

Abstract

Octahedral 1T-MoS₂, a transition metal dichalcogenide (TMD), is a promising and cost-effective alternative to Pt for the electrochemical hydrogen evolution reaction (HER) compared to its hexagonal 2H phase. However, the metastable nature of 1T-MoS₂ makes its synthesis challenging. Janus TMDs, such as MoSSe, with their intrinsic structural asymmetry, are emerging as efficient HER catalysts, and their 1T phase demonstrates improved stability. This study compares hydrothermally synthesized 1T-MoS₂ and solvothermally grown 1T-MoSSe with commercially available 2H-MoS₂ for the HER. Janus 1T-MoSSe exhibits superior performance with an overpotential of 87.8 mV at a current density of 10 mA cm⁻², a Tafel slope of 148 mV decade⁻¹, and an enhanced long-term stability of 10 000 cycles over 5 hours. Its low electrochemical impedance of 21 Ω indicates efficient charge transfer. Density functional theory (DFT) calculations validate the Janus material as the best catalyst with a hydrogen adsorption free energy (ΔG_H) of 0.46 eV. Bader charge analysis reveals the lowest charge on the Se atom in the MoSeS Janus material. The upshifted p-band center in Janus materials, compared to their pristine counterpart, optimizes the S/Se–H bond strength, enhancing hydrogen adsorption. This work highlights how structural engineering of TMDs into Janus structures can optimize their HER performance, providing a route for cost-effective and efficient hydrogen production technologies.