Stiboviologens-Decorated Sb ₄ O ₆ Clusters for Electrocatalytic Proton Reduction via Coupled Electron Sponge and Proton Engine

Antimony (Sb)-based materials show great promise for hydrogen evolution reaction (HER) catalysis owing to their unique electronic structures and efficient proton-electron transfer capabilities. However, despite their potential, the molecular-level development of Sb-based catalysts has been hindered by significant synthetic challenges, particularly the difficulty in constructing well-defined molecular architectures, such as Sb-porphyrins or clusters. Herein, we report a new synthetic strategy to access two novel stiboviologens-decorated Sb₄O₆ clusters (<b>SbVO-Me</b> and <b>SbVO-Ph</b>) via directed oxidative coupling of stiboviologens. <b>SbVO-Me</b> and <b>SbVO-Ph</b> exhibit excellent redox activity, multielectron transfer capacity, and robust electrochromic behavior. DFT calculations and electrostatic potential mapping analyses reveal a cooperative electron-proton management mechanism: the viologen moiety acts as an "electron sponge," mediating charge accumulation and delivery, while the tetraantimony hexaoxide (Sb₄O₆) core serves as a "proton engine" to accelerate proton transport. In homogeneous acidic HER catalysis, the system achieves an overpotential of 535 mV with a Faradaic efficiency of 74.5%. Upon immobilization, the heterogeneous system delivers enhanced activity with a reduced overpotential of 182 mV. Mechanistic investigations support a cooperative catalytic pathway involving the viologens and Sb centers. This study introduces stiboviologens as a new class of main-group molecular catalysts, expanding the design landscape for viologen-based redox systems and offering new opportunities in proton-coupled electrocatalysis.