In operando investigations of oscillatory water and carbonate effects in MEA-based CO₂ electrolysis devices

Membrane electrode assembly (MEA) CO₂ electrolyzers are a promising approach toward producing carbon-neutral chemicals; however, they often have stability issues related to flooding of the gas diffusion electrode (GDE). Thus, there is an urgent need to comprehend water management in these devices and to engineer electrodes that allow both stable and efficient electrocatalytic performance. Here, we investigated the possible causes of suppression in the CO₂ reduction reaction (CO₂RR) selectivity on Cu via in operando X-ray diffraction (XRD) analysis. The in operando XRD allowed us to monitor electrolyte evolution and bicarbonate formation in the GDE, while in-line gas chromatograph and mass spectrometer allowed us to correlate those changes to the cathode and anode product distribution during CO₂ electrolysis (CO₂E). We found direct evidence for salt precipitation in the cathode GDEs, which causes electrolyte build-up and an increase in hydrogen evolution reaction (HER). We also observed that the increase in HER is related to a drop in cell potential, at least partially caused by a shift in ion transport through the membrane from carbonates to more conductive hydroxide ions. Thus, this work suggests that proper ion management is an important key to enhanced durability throughout the device.