Investigating Gas Diffusion Electrode Flooding in CO₂ Electrolysis With an Operando Water Trap System: The Role of (Bi)carbonate Salt Precipitation

The electrochemical reduction of CO 2 (CO 2 electrolysis) is a promising technology for not only reducing CO 2 emissions, but also contributing to a circular carbon economy. However, industrial feasibility has not been achieved yet, as flooding of the gas diffusion electrode (GDE) limits the long-term stability of CO 2 electrolysis. Although (bi)carbonate salt precipitation is often considered to be one of the main factors accelerating GDE flooding, direct evidence of this effect is still lacking and further investigations are needed. In this study, we address this gap by employing an operando water trap to quantify GDE flooding in a time-resolved manner. The results demonstrate a direct correlation between salt precipitation and GDE flooding, as (bi)carbonate catholytes show increased GDE flooding rates. Additionally, the bicarbonate anion (HCO 3 − ) was identified as the harmful species, independent of the catholyte’s pH. However, GDE flooding still occurs even when bicarbonate formation is mitigated, albeit at a much slower rate, indicating the need to investigate additional contributing factors.