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.