The iR-corrected Tafel plots (Figure ) almost overlap in the kinetic region, confirming the representative nature of the ME-cell for studying the activity of the catalyst materials. Above 0.1 A cm -2 , the iR-corrected voltage (Ecell,iR corr.) of the ME-cell started to deviate from linear behaviour. This deviation may be explained by different mass transport properties arising from the different cell designs, for example, the lack of a flow field in the ME-cell. However, the difference in performance between the ME-cell and the LE-cell was minimal, which is rare for cells designed for imaging purposes. Additionally, the two cells were compared in the catalyst coated substrate (CCS) configuration (details are provided in Section S1.1 in the Supporting Information (SI)). These additional tests used CCS cut from the same materials for both cells and were performed to, firstly, eliminate any possible discrepancies related to the preparation of two different-sized CCMs and, secondly, ensure cell geometry was the only differentiating factor. As shown in Figure in the SI, performance of the two cells configured with CCS were found to be quite comparable and consistent with the findings from the CCM comparison.