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 (SO₃^2-) as the sulfur source. Here we report a paired electrolysis for hydroxymethanesulfonate synthesis from widespread industrial-waste sulfides (HS^-). Specifically, HS^- is oxidized to SO₃^2- by in-situ generated H₂O₂ 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 H₂S 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.