A paired electrolysis for hydroxymethanesulfonate synthesis using sulfide waste as the sulfur source

Electrochemical C–S bond construction represents an attractive route to produce valuable organosulfur compounds, yet current approaches suffer from low reaction efficiency and rely on sulfites (SO 3 2− ) as the sulfur source. Here we report a paired electrolysis for hydroxymethanesulfonate synthesis from widespread industrial-waste sulfides (HS − ). Specifically, HS − is oxidized to SO 3 2− by in-situ generated H 2 O 2 at cathode, and methanol is oxidized to formaldehyde at anode, with following C–S coupling to form hydroxymethanesulfonate. By matching HS − concentration with current density and strengthening convective mass transfer between intermediates, we achieve efficient hydroxymethanesulfonate production with Faradaic efficiency of 102.8% and productivity of 282 μmol h −1 in a membrane-free H-cell under optimized conditions (50 mA cm −2 , 0.05 M HS − , stirring in anodic chamber). By constructing a flow reactor, this paired electrolysis enables conversion of HS − -contaminated wastewater (from <10 ppm to 3000 ppm) with Faradaic efficiencies exceeding 100%, while tolerating coexisting anions and heavy metals in real effluents. It also converts waste H 2 S gas with >87% conversion and >74% hydroxymethanesulfonate selectivity over 102 hours of stable operation, demonstrating more cost-effective economics to both industrial and previous electrochemical methods.