Electrolysis of Sulfur Waste to Capture and Store CO2

Water electrolysis can accelerate CO ₂ storage by rock weathering through the concerted formation of acid and base, where the acid drives silicate mineral dissolution and the base facilitates CO ₂ mineralization. However, the rare demonstration of electrolytic CO ₂ mineralization at current densities greater than 100 mA cm ^–2 requires a high operating voltage of >4 V. In this study, we demonstrate a continuous flow electrochemical reactor capable of mineralizing CO ₂ , but at a much lower voltage of 2 V. We achieved this result by coupling the capture and mineralization of CO ₂ with the oxidation of sulfurous waste in the form of sulfite. The lower voltage is a consequence of sulfite being oxidized at a significantly lower potential (–0.108 V vs. SHE) than water (1.23 V vs. SHE). The “sulfite electrolyzer” was designed to dissociate concentrated silicate mineral slurries (e.g., 30 g L ^–1 Mg ₂ SiO ₄ ) using a robust polyaniline-coated cation exchange membrane. We then performed integrated CO ₂ capture and mineralization using the sulfite electrolyzer. We achieved an energy intensity of 5.4 MWh ton ^–1 CO ₂ , and show a pathway for this technology to achieve a price below $100 per ton of stored CO ₂ . Our study demonstrates that waste feedstocks can be used to drive electrolytic capture and storage of CO ₂ at low voltages.