Hidden parameters for electrochemical carbon dioxide reduction in zero-gap electrolyzers

The electrochemical reduction of CO2 from flue gas or direct air capture to relevant syngas mixtures is a promising route toward mitigation of environmental pollution and production of bulk chemicals and fuels. Among the different cell types, gas-fed zero-gap electrolyzers are promising as energy-efficient and scalable devices. We herein investigate the influence of operational parameters related to cathode water management, such as cell orientation, gas humidification, and cathode compression onto CO2R. By a stepwise optimization of our not yet fully optimized electrolyzer, stability could be improved by a factor of 3 up to 10 h at 3 V and 300 mA cm-2. Faradic efficiency for CO after 2 h of electrolysis was increased from 14% to over 60%. Controlling the water management is a key parameter as high water input leads to flooding of the electrodes, whereas lower values decrease the performance of the anion exchange membrane and reduce catalyst wetting.