A porous solid electrolyte interface enables efficient electroreduction of captured carbon to CO

Direct electrochemical conversion of captured carbon species offers a route to avoid the energy-intensive steps of thermal CO 2 release, compression and transport in conventional carbon capture and utilization. In proton exchange membrane (PEM) reactors, however, the acidic cathode environment promotes hydrogen evolution and limits CO 2 regeneration from (bi)carbonate capture media, resulting in low carbon utilization and high energy demand. Here we show a modular PEM–porous solid electrolyte (PSE) reactor for direct conversion of (bi)carbonate to CO. Using a transparent cell with in situ visualization, we reveal that the PSE regulates proton transport, reduces local proton reduction, limits bubble accumulation and facilitates CO 2 transport to the cathode. The PEM–PSE reactor achieves a CO Faradaic efficiency of 90% at 200 mA cm −2 , a carbon efficiency of 84%, and an energy consumption of ~26.0 GJ t −1 CO. It operates at current densities up to 800 mA cm −2 , reaching a CO rate of ~8.0 mmol h −1 cm −2 . These results highlight the regulation of proton and gas transport in the electrochemical conversion of captured carbon.