CO₂ Electrolysis with Bipolar Membranes in Forward Bias: Diagnosing Intrinsic Issues and Engineering Solutions

The efficient electrochemical reduction of CO2 is a promising approach for mitigating carbon emissions and producing valuable chemicals. Bipolar membranes (BPMs) in forward bias have garnered attention due to their ability to facilitate CO2 reduction by decoupling the pH environments of the cathode and anode. However, their application is currently hindered by challenges such as low stability and poor performance, which limit their practical viability. This study investigates the intrinsic problems of BPM-based CO2 electrolysis and proposes targeted solutions to enhance device performance and durability. To diagnose these issues, in situ X-ray imaging techniques were employed to visualize operational dynamics within the BPM. Key challenges identified include bubble formation at the bipolar junction, damage to the anode catalyst layer, and excessive swelling of the membrane layers (Figure 1). These phenomena degraded the system's mechanical integrity and electrochemical efficiency. To address these issues, a microporous alkaline layer joining the solid cation exchange membrane was introduced to mitigate bubble accumulation and reduce over-swelling, enabling more efficient CO2 and water removal from the junction. Additionally, overvoltage at the membrane junction was reduced by placing a catalyst directly at the bipolar junction. This design increased the water and CO2 recombination kinetics at the junction, improving the overall cell performance. The proposed modifications yielded significant improvements in BPM electrolysis performance. These findings highlight the importance of designing tailored mesostructured interface systems to overcome the limitations of BPMs in forward bias and pave the way for more robust and efficient CO2 electrolysis systems. Figure 1