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

Membrane electrode assembly (MEA) CO2 electrolysis (CO2E) is a promising route towards 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 water and bicarbonate formation in the GDE, while in-line gas and mass chromatographs allowed us to correlate those changes to the cathode and anode product distribution during CO2E. We found direct evidence for salt precipitation in the cathode GDEs, which causes water build-up and an increase in hydrogen evolution reaction (HER). We also observed that the increase in HER is related to a drop in total cell potential, caused by a shift in ion transport through the membrane from carbonates to more conductive hydroxide ions. Our results reported here also do not show any substantial catalyst-induced effects on CO2RR. Thus this work suggests proper ion management is an important key to enhanced durability throughout the device.