Operando experiments require a test fixture that meets the requirements of both the system being investigated and the complementary technique. There is often a trade-off between how representative the system under investigation is and the ease of implementing the operando method. For this study the test fixture was designed to balance the performance of the electrolyser with the spatial resolution of the μ-CT. The quality and utility of information produced in μ-CT studies depends on the field of view (FOV) and spatial resolution. In general, FOV is reduced when spatial resolution is increased to ensure each volumetric pixel (voxel) is measured with higher statistical significance. Beamline I13-2 at Diamond Light Source provided a spatial resolution ranging from 0.325 μm with a 0.83 × 0.7 mm FOV to 3.6 μm with a 14 × 9.6 mm FOV. The cell therefore needed to be small to enable high resolution μ-CT, maintaining the entire active area within the 4.2 × 3.5 mm FOV (typical for the 2× objective lens setup at I13-2), while also being able to operate as a representative electrolyser. To that end, the ME-cell pictured in Figure was designed to have a 0.14 cm 2 active area for imaging the entire cell with 1.625 μm pixel size at I13-2. To ensure representative electrolyser performance the ME-cell design was based on a typical 5 cm 2 laboratory-electrolyser-cell (LE-cell) used in our research group.