Boosted Hydrogen Evolution via Molten Salt Synthesis of Vacancy-Rich MoSxSe2–x Electrocatalysts

MoSxSe2–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 MoSxSe2–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 MoO42– facilitates the decomposition of KSCN to S2–, which subsequently activates Se powder, culminating in the formation of the SexS2– polyanion. This polyanion then interacts with MoO42–, yielding MoSxSe2–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 SexS2–, limiting crystal growth. Theoretical analyses indicate that the presence of Se atoms and anion vacancies collaboratively modulates the electronic structure of MoSxSe2–x. This results in a minimized band gap of 0.88 eV and an almost zero ΔGH* of 0.09 eV in the optimized MoS1.5Se0.5. Consequently, MoS1.5Se0.5 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.