Visualisation and quantification of flooding phenomena in gas diffusion electrodes (GDEs) used for electrochemical CO2 reduction: A combined EDX/ICP–MS approach

The most promising strategy to up-scale the electrochemical CO2 reduction reaction (ec-CO2RR) is based on the use of gas diffusion electrodes (GDEs) that allow current densities close to the range of 1 A/cm2 to be reached. At such high current densities, however, the flooding of the GDE cathode is often observed in CO2 electrolysers. Flooding hinders the access of CO2 to the catalyst, and by thus leaving space for (unwanted) hydrogen evolution, it usually leads to a decrease of the observable Faradaic efficiency of CO2 reduction products. To avoid flooding as much as possible has thus become one of the most important aims of to-date ec-CO2RR engineering, and robust analytical methods that can quantitatively assess flooding are now in demand. As flooding is very closely related to the formation of carbonate salts within the GDE structure, in this paper we use alkali (in particular, potassium) carbonates as a tracer of flooding. We present a novel analytical approach —based on the combination of cross-sectional energy-dispersive X-ray (EDX) mapping and inductively coupled plasma mass spectrometry (ICP--MS) analysis— that can not only visualise, but can also quantitatively describe the electrolysis time dependent flooding in GDEs, leading to a better understanding of electrolyser malfunctions.