Now, Haotian Wang, Xiaonan Shan and co-workers have revealed the formation and migration mechanism of precipitating species, specifically (bi)carbonate salts, using operando Raman and optical microscopy integrated with a customized CO2RR MEA electrolyzer. Their findings indicate that small droplets containing crossover cations and carbonate ions form at the catalyst/AEM interface. These droplets subsequently react with flowing CO2 to generate bicarbonate droplets. The migration of bicarbonate droplets occurs through gas evolution and convection at the catalyst/AEM interface, where H2 and CO are produced, as well as through CO2 gas flow to the gas diffusion electrode (GDE) backside and the gas flow channel of the endplate. Ultimately, these droplets evaporate leading to the precipitation of bicarbonate salts.
These findings lay the groundwork for the development of device-level strategies to mitigate salt precipitation in electrolyzers and enhance CO2RR stability. Notably, reducing the anolyte concentration from 0.1 M KHCO3 to 0.01 M enables CO2RR operation for at least 1,000 hours with a CO Faradaic efficiency (FE) >90% at a current density >100 mA cm–2. Additionally, the application of a hydrophobic parylene coating on the surface of the cathode gas flow channel prolongs the stability of the CO2RR to CO (with FE >90%) at a current density above 200 mA cm–2 from 100 hours to 500 hours.
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