Disordered Ru-O6 Octahedrons for Efficient and Selective Electro-oxidation of Sulfide to Sulfoxide via Boosted Surface Oxygen Kinetics.

Abstract

Sulfoxides are essential intermediates for the production of various chemicals and pharmaceuticals, typically synthesized via direct sulfide oxidation. While current methods generally require harsh conditions and/or hazardous oxidants, electrochemical conversion from sulfide to sulfoxide promises ideal selectivity, sustainability, and energy efficiency while uniquely utilizing water as the green oxygen source. However, achieving efficient electro-organic conversion has been challenging due to sluggish surface oxygenating kinetics under nonaqueous conditions. Here we report the development of a novel amorphous ruthenium oxide catalyst characterized by disorderly connected regular/irregular Ru-O₆ octahedra. This unique surface structure significantly boosts the surface water oxidation kinetics in nonaqueous media, enabling a universal electro-oxidation approach for efficient sulfide-to-sulfoxide conversion. Superior performance was achieved under mild conditions (e.g., 99% selectivity, 98% yield, and 95% Faradaic efficiency for methyl phenyl sulfide to methyl phenyl sulfoxide), and this approach applies to a broad scope of sulfide substrates and pharmaceuticals. Scalable productions (12.95 g, 88% FE) under high current densities (>100 mA/cm²) further demonstrate the practical values of this electrocatalytic synthetic methodology. Mechanistic and theoretical investigations elucidate the critical role of disorderly arranged Ru-O octahedral units in enhancing the distributions of bonding orbitals and electronic coupling near the Fermi level, leading to boosted kinetics of surface water oxidation (*OH → *O) and subsequent sulfide oxidation (*O + MPS → *MPSO), which follow an adsorbate evolution mechanism-mediated Eley-Rideal reaction (AEM-ER) pathway. Our results highlight the unique and effective role of atomic disorder in overcoming common kinetic limitations during catalyst optimization, which enables ideal direct selective electro-oxidation of organics in nonaqueous media.