1D Mo _<i>n</i> S _<i>n</i> Nanowires for Sustainable Hydrogen Evolution: Size and Fermi-Level Driven Catalysis

Transition-metal chalcogenide nanowires are promising noble-metal-free catalysts. Their catalytic properties remain underexplored for size and electronic structure tuning. The Mo6S6 nanowire shows well-documented environmental stability. Their structural analogs (MonSn, n = 6–11) lack systematic study. First-principles calculations reveal size-dependent hydrogen evolution reaction (HER) performance in the MonSn nanowires, comparable to platinum. The Mo6S6 nanowire exhibits a hydrogen adsorption free energy of −0.16 eV, similar to Pt(111) at −0.17 eV. The Mo8S8 nanowire, a semiconductor, shows unexpected HER activity despite its larger diameter. Electronic structure analysis indicates hydrogen adsorption triggers a semiconductor-to-metal transition. Strong Mo_4d–H_1s orbital coupling enables dynamic charge redistribution and interfacial conductivity. This metastability overcomes diameter-dependent activity limitations. HER performance in 1D chalcogenides depends on two factors: nanowire diameter affects active-site accessibility, and metal–adsorbate orbital hybridization drives electronic restructuring. The Mo8S8 nanowire combines Pt-competitive activity, ambient stability, and scalable synthesis potential. These findings redefine design principles for low-dimensional HER electrocatalysts. They connect quantum confinement effects with orbital-level reactivity modulation. The results provide a universal strategy for tuning low-dimensional HER catalysts. This approach has implications for transition-metal-based energy conversion systems.