Electrochemically induced direct air capture via a redox-mediated aqueous flow system incorporating a solid proton–electron carrier

Direct air capture (DAC) plays a crucial role in mitigating climate change. Compared to conventional thermochemical DAC methods, electrochemically induced CO2 capture and release using redox-active sorbents is particularly attractive due to the significantly reduced energy consumption as it operates under ambient conditions. However, the limited availability of redox- active sorbents that are both oxygen-tolerant and highly water-soluble across a broad pH range (4– 14) has long hindered the development of such electrochemical DAC systems. Herein, we report electrochemically induced DAC using a redox-mediated aqueous flow system that incorporates a solid proton–electron carrier (SPEC) undergoing a proton-coupled electron transfer process. The new design physically isolates the oxygen-sensitive SPEC from air while allowing the oxygen- tolerant aqueous alkaline solution to capture ambient CO2, overcoming the oxygen sensitivity issue commonly associated with redox sorbents. Furthermore, the incorporation of SPEC theoretically enhances the volumetric CO2 capture capacity by up to an order of magnitude. In a 21-day, seven- cycle of continuous DAC experiment, the system consistently demonstrated an average CO2 capture capacity of 38.6 mL with a Coulombic efficiency of 100%. Moreover, the CO2 capture capacity was increased fourfold by utilizing more of capacity from SPEC without altering the electrolyte volume or composition. The highest CO2/e molar ratio was 0.54 and the lowest energy consumption for CO2 release and sorbent regeneration was 175.8 kJ mol-1 . The energy cost is anticipated to be halved when a redox mediator and a SPEC share the same redox potential, and their chemical redox reactions are driven by the Nernstian potential difference.