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CO2 electrolysis is a promising technology for a renewable feedstock of carbon-based chemicals. Membrane Electrode Assembly (MEA)-based CO2 electrolysers have been demonstrated to run at commercially relevant current densities. However, the MEA approach can suffer from an unstable production of targeted products, mainly caused by an increase in hydrogen production often within a few hours of operation. We conducted operando measurements in a custom-made electrochemical cell (with an electrode area of 64 mm2) using a high-energy synchrotron X-ray source to study CO2 electrolysis over Cu-based gas diffusion electrodes (GDEs). A series of experiments have been performed between 100 to 250 mA cm−2, showing a change in product distribution as a function of time. Expectedly, this is caused by an increase in water content in the GDE (also called as flooding of GDE) rather than any change of the catalyst itself, e.g. slow depletion of subsurface oxygen. Interestingly, we found that while the increase in water content is causing a gradual degradation of the performance, salt precipitation also had a major influence on water management as well. By having an in-line GC attached to the cell, we could monitor both cathodic and anodic performance as a function of time and relate this to variations in water content throughout the device. Variations in cations played a substantial role in modifying the hydration properties of the device adding an additional effect cations have beyond their role in catalysis. The insights generated from this work will allow future researchers to engineer devices that can maintain proper water management and thus entail long term stability. |
