Light-driven hydrogen evolution reactivity of molecular thio-oxomolybdate catalysts

Abstract

Heterogeneous molybdenum sulfides are widely used noble metal-free hydrogen evolution reaction (HER) catalysts. Thiomolybdates, their molecular analogues have been developed as viable minimal models to study reactivity at the molecular level. Here, we explore the light-driven HER reactivity and stability of the mixed thio-oxo-molybdate prototype [Mo₂O₂S₆]²⁻ in homogeneous solution. In combination with the photosensitizer [Ru(bpy)₃]²⁺, [Mo₂O₂S₆]²⁻ shows promising HER performance (turnover number TON > 500), as well as strong reactivity dependence on the reaction conditions. Mechanistic experimental studies combined with density functional theory computations reveal complex speciation of the catalyst in solution, as well as light-induced and light-independent reaction pathways for catalyst and photosensitizer which are in line with disulfide-for-solvent ligand exchange reactions. These structure–reactivity insights outline design rules for more robust, solvent-tolerant thiomolybdate HER catalysts.