The ME-cell was imaged using lab-based μ-CT in both the pristine and post-testing (degraded) states; the resulting cross-sectional images are provided in Figure and Figure , respectively. The CCM configuration was important for this study, rather than using a CCS, as it was not only representative of commercial electrolysers, but also particularly useful for tracking membrane thickness by μ-CT. By adhering the catalyst layer (containing highly attenuating dense elements, Pt, Ni and Fe) directly to the membrane, it was clearly outlined enabling accurate thickness measurements to be made (Figure ). One notable change between the pristine and degraded CCMs was loss of the Pt catalyst as highlighted by the yellow arrows in Figure . This change may explain the overall increase in Ecell,iR corr. seen in Figure . The more marked change was the 53 ± 3% decrease in membrane thickness after electrochemical testing (Figure ). The poly(aryl ether) backbone of Fumasep® FAA-3 is known to be susceptible to aryl ether cleavage under high pH conditions leading to thinning of the membrane. The through-plane ionic conductivity of the membrane (σmemb) was calculated using Equation 1 as outlined in the methodology (Section 4.4). The initial σmemb of Fumasep® FAA-3 was calculated using the initial HFR value for the ME-cell from Figure (129 mΩ cm 2 ), Rel for the ME-cell (20 mΩ cm 2 ) and tmemb from the lab-based μ-CT shown in Figure (76 μm) to be 69.1 ± 1.8 mS cm -1 in 1 M KOH at ambient temperature. This value was in good agreement with the value of 68.3 mS cm -1 at 40 °C in water measured by Khalid et al. To account for the 53% decrease in tmemb and the 25 mΩ cm 2 increase in the HFR (red plot in Figure ) measured for the ME-cell after electrochemical testing, the σmemb was calculated to be 26.3 ± 1.2 mS cm -1 , a 62% decrease. This suggests that the membrane was losing both ion conduction capacity and bulk thickness, the former due to loss of quaternary ammonium functional groups and the latter because of cleavage of the ether linkages in the polymer backbone. This finding is in agreement with previous ex-situ studies which found Fumasep® FAA-3 lost both conductivity and thickness when exposed to KOH due to hydroxyl attack and Hoffman elimination. The results obtained from lab-based μ-CT analysis demonstrate the successful implementation of the ME-cell for studying ionomer degradation in AEM electrolysers using μ-CT in a laboratory environment. Considering the limited availability of synchrotron sources, the ME-cell offers significant practicality for conducting in-situ electrolyser studies without requiring access to a synchrotron facility particularly if temporal resolution is not critical. For PEMWE, which can be stable for thousands of hours, a scan time of a few hours may not pose an issue. The ME-cell may be configured with Pt coated Ti instead of steel components to operate as a PEMWE. The capability to image an assembled electrolyser cell is essential for studying effects only observed when the CCM is wetted and under compression, and when the catalyst layer is undisturbed by cell disassembly -conditions impossible to achieve in typical post-mortem analyses.