Press it, Heat it, Twist it

The electrochemical reduction of excess CO2 to relevant syngas mixtures is a promising route towards mitigation of environmental pollution and production of bulk chemicals and fuels. Among the different cell types, gas-fed zero-gap electrolyzers have already shown great promise as energy efficient and scalable devices towards the reduction of CO2. Although catalysts, membranes and electrodes for CO2R are heavily investigated, we herein focus on crucial but rarely studied operational parameters, such as cell orientation, gas humidification and electrode compression. By step-wise optimization we improved the stability and selectivity of our electrolyzer by a factor of three generating our targeted syngas composition of 2:1 (H2:CO) at 300 mA cm‑2 and ca. 3 V for 10 h, simultaneously providing a guideline for crucial parameters in zero-gap electrolysis for CO2R. Controlling the water management is a key parameter as high humidification values lead to flooding of the electrodes, whereas lower values decrease the performance of the anion exchange membrane and reduce catalyst wetting.