Squeezing Gas Diffusion Electrodes in Zero-Gap CO ₂ Electrolyzers─Enough Is Enough

Recent scientific advancements indicate that the electrochemical reduction of carbon dioxide to carbon monoxide (CO2RR) is approaching industrial viability. Beyond scientific achievements, technology scale-up requires a full understanding of how certain cell components are to be used for long-term optimal performance and of what other challenges are posed by the larger sizes. Here, we investigated in detail how varying the compression ratio of the cathode gas diffusion electrode affects the electrochemical performance, using three fundamentally different carbon-based cathode supports. Electrochemical impedance spectroscopy and microtomography measurements are presented to explain the observed changes in the electrolysis performance, while the cathodes were gradually compressed to below 40% of their original thickness. The optimal compression range depends on the properties of the gas diffusion layer. Notably, a more than 100 μm wide optimal compression range is found for the thick ELAT1400W gas diffusion layer (i.e., a compression to 60-85% of its original thickness), which is further confirmed in 100-h-long experiments.