Enhancing Local CO₂ Concentration via Covalent Interaction for the Conversion of Carbonate to CO

Carbonate solution is the product of air capture, and the direct electrolysis of this solution, instead of CO₂ gas, could serve as a more energy-efficient route to achieve a zero-carbon cycle. Recent studies have demonstrated that integrating a bipolar membrane can achieve the in situ generation of CO₂ and combine carbonate electrolysis directly. In this study, we show that a cation exchange membrane (CEM) can achieve similar results in in situ carbonate conversion, with a lower overpotential compared to the commercial bipolar membrane in a membrane electrode assembly electrolyzer. Furthermore, we demonstrate that the insertion of a porous interfacial layer (IFL) between the Ag-based cathode catalyst layer and the CEM can retain the in situ generated CO₂ and improve the conversion of CO₂ to CO. Additionally, we adopted a chemically modified IFL by grafting CO₂-adsorbing silanes, which substantially improved the reaction rate for the reduction of CO₂ to CO at 200 mA/cm². The cell with this enhanced reaction rate was stable for 25 h, generating the highest Faradaic efficiency (FE) of 42% while maintaining a cell voltage of −3.72 V. This study highlights the importance of interfacial chemistry in the cathode compartment, which can suppress the parasitic hydrogen evolution reaction (HER) and convert CO₂ to CO efficiently.