Sustainable Electrosynthesis of Hydroxymethanesulfonate from CO2 and Sulfite

Abstract

Organosulfur compounds play essential roles across the chemical, pharmaceutical, and energy sectors, yet conventional C-S bond formation typically relies on fossil-derived feedstocks and hazardous sulfur reagents, posing serious environmental and safety concerns. Here, we report an efficient and sustainable electrocatalytic C-S coupling strategy that enables the direct synthesis of hydroxymethanesulfonate (HMS) as the sole C-S product from CO2 and sulfite under ambient conditions. Using a molecular cobalt phthalocyanine supported on carbon nanotubes (CoPc/CNT) as the catalyst, HMS was obtained as the sole C-S coupling product, with a faradaic efficiency (FE) of 25.7% and a partial current density of -4.9 mA cm-2. Ab initio molecular dynamics simulations, combined with experimental studies, suggested that HMS formation proceeds via the electroreduction of CO2 to formaldehyde (HCHO), followed by its desorption and the subsequent selective chemical coupling with SO32-. Moreover, alkali metal cations were found to regulate the key *CO2→*CO→*CH2O transformations, with Na+ delivering optimal coupling efficiency due to its moderate hydration energy. Stable production of HMS was achieved over 5 h using a modified H-type cell, accompanied by effective separation of the electrolysis products (MeOH and HMS) and electrolyte from the solution. This work establishes a green and selective platform for electrocatalytic C-S bond formation from low-value feedstocks and provides new insights into carbon-heteroatom bond formation under sustainable conditions.