Overcoming voltage issue in bicarbonate electrolysis: dual mass-transfer pathways for CO₂ and ions

The direct electrolysis of CO₂-captured liquid, such as bicarbonate, offers economic advantages by eliminating the CO₂ regeneration step. However, high cell voltages remain a major barrier. Herein, we propose a new strategy to build dual mass-transfer pathways for CO₂ and ions using a carbon and anion exchange ionomer (AEI) to reduce cell voltages while achieving sufficient Faradaic efficiency (FE) for the CO₂ reduction reaction. By optimizing the interposer materials and ratio of carbon, Ag, and AEI, sufficient FE_CO (57 %) and low cell voltages (3.17 V) were achieved at 100 mA cm⁻². The formation of dual mass-transfer pathways in bicarbonate electrolysis was confirmed through in situ/operando visualization studies. To ensure stability, we recommend the generation of dual mass-transfer pathways using chemically and physically stable materials. Our work provides an understanding of the mass transfer in bicarbonate electrolysis and a direction for overcoming the voltage issue.