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 CO2 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 CO2 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 CO2 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. Turning captured carbon dioxide into useful chemicals can save energy, but combining capture and conversion is difficult. Here, the authors report a membrane reactor converts bicarbonate solutions directly into carbon monoxide with high carbon efficiency and lower energy use.