Gas Retention in Porous Cathodes Governs Bicarbonate Electrolysis Performance

Abstract Bicarbonate electrolysis offers a direct route for converting captured CO2 into high-value chemicals without energy-intensive CO2 regeneration and compression. However, multiphase transport within liquid-fed porous cathodes remains poorly understood. We found carbon paper and carbon cloth yielded drastically different performance, and further analysis revealed gas retention, i.e., localized and temporary entrapment of internally generated gas within the pore network, as an important transport limitation. Flow pulse and recovery experiments under galvanostatic operations showed largely reversible performance losses, while operando X-ray imaging directly visualized gas retention. Gas retention intensifies with denser electrodes, lower catholyte flow rates, and higher current densities. Guided by these observations, an interdigitated flow field was employed to enhance through-plane convection and gas removal, increasing the maximum formate partial current density to 304 mA cm–2 and enabling 120 h of stable operation. These findings establish gas management as a critical design criterion for bicarbonate electrolyzers.