Boosted Hydrogen Evolution via Molten Salt Synthesis of Vacancy-Rich MoS_xSe_2-x Electrocatalysts

MoS_xSe_2-x emerges as a potent alternative to Pt-based electrodes in the electrochemical hydrogen evolution reaction (HER), although its practical application is hindered by suboptimal synthetic methods. Herein, a KSCN molten salt strategy is introduced, enabling the straightforward synthesis of MoS_xSe_2-x at a modest temperature of 320 °C through a one-step heating process involving Se powder and Na₂MoO₄ in a muffle furnace. It is elucidated that MoO₄^2- facilitates the decomposition of KSCN to S^2-, which subsequently activates Se powder, culminating in the formation of the Se_xS^2- polyanion. This polyanion then interacts with MoO₄^2-, yielding MoS_xSe_2-x characterized by a profusion of anion vacancies. This is attributed to the introduction of Se heteroatoms, causing lattice distortion and the substantial steric hindrance of Se_xS^2-, limiting crystal growth. Theoretical analyses indicate that the presence of Se atoms and anion vacancies collaboratively modulates the electronic structure of MoS_xSe_2-x. This results in a minimized band gap of 0.88 eV and an almost zero ΔG_H* of 0.09 eV in the optimized MoS_1.5Se_0.5. Consequently, MoS_1.5Se_0.5 exhibits remarkable HER performance, characterized by a low η₁₀ of 103 mV and a minimal Tafel slope of 33 mV dec^-1, alongside robust stability. This research not only unveils a potent electrocatalyst for HER but also introduces a simplified synthesis strategy for transition metal selenosulfides, broadening their applicability across various domains.