The practical application of electrochemical carbon dioxide reduction reaction (CO2RR) technology remains hindered by poor stability, primarily owing to bicarbonate salt formation at the cathode, which blocks reactant CO2 mass flow. Here, using operando characterization tools, we tracked the salt formation process and quantified salt precipitation under varying device operational conditions, elucidating a potential mechanism and optimizing anolyte conditions for long-term (>1,000 h) operation CO2RR to CO under >100 mA cm–2. Liquid droplets carrying cations and (bi)carbonate ions were observed to migrate from the catalyst/membrane interface towards the backside of the gas diffusion electrode, driven by interfacial gas evolution and CO2 flow. These droplets eventually dried, forming bicarbonate salt precipitates that blocked the gas flow channels. On the basis of this observation, we applied a hydrophobic parylene coating to the cathode gas flow channel surface, facilitating the removal of the droplets and extending stability from ~100 h to over 500 h under 200 mA cm–2.
