Fully-integrated electrochemical system that captures CO2 from flue gas to produce value-added chemicals at ambient conditions

Abstract

Stabilizing atmospheric CO₂ calls for a significant reduction in anthropogenic CO₂ emissions. There have been extensive efforts to develop individual technologies for CO₂ capture and CO₂ utilization (or reduction) to curb CO₂ emissions efficiently. However, for rapid and economically viable reduction of atmospheric CO₂, it is necessary to develop integrated technologies that capture and reduce CO₂ to value-added products and fuels in a closed carbon cycle. Here, we report a systematic protocol to develop and individually evaluate electrochemical CO₂ capture and electrochemical CO₂ reduction processes and demonstrate a functional, fully integrated, continuous process for CO₂ capture from simulated flue gas and its reduction to value-added products and fuels. For CO₂ capture, we integrated a migration-assisted moisture-gradient (MAMG) CO₂ capture process, where gaseous CO₂ is captured as HCO₃⁻ in a CO_2-binding organic liquid, transported under an electric field across an anion exchange membrane to an aqueous solution, and converted to dissolved CO₂ in the presence of water-abundant environment by equilibration between HCO₃⁻, CO_2(aq), and CO₃²⁻. For CO₂ reduction, we develop an electrochemical cell configuration for a CO₂-free extraction of CO₂ reduction gaseous products such as CO, CH₄, and C₂H₄ on a Cu mesh catalyst. Efficient integration of the CO₂ capture and CO₂ reduction processes is realized based on pH-driven operating lines where the rate of CO₂ capture equals the rate of CO₂ reduction. We demonstrate the successful integration of these continuous CO₂ captures and reduction processes to value-added products by operating the MAMG CO₂ capture unit at a current of 600 mA and the CO₂ reduction unit at a current density of 200 mA cm⁻² resulting in 40% faradaic efficiency (FE) towards C₂H₄ and CO₂RR FE of >57% for a simulated flue gas feed.