To comprehend the Nernst-Planck equation within the framework of MEA devices, XRF is employed to investigate the motion of Cs + ions. Accordingly, the Cs + intensity for 0.1 M CsHCO3 (shown in Figure ) under different applied conditions as a function of MEA depth (i.e., at different MEA layers) for several continuous scans is reinterpreted in Figure (corresponding H2O signals are shown in Figure ). The Cs(x) is described by the through-plane distance across the MEA depth and the Cs(t) is reflected by the signal difference from continuous scans. Specifically, the AEM positioned between the anode and cathode adds complexity to the understanding of Cs + movement within the system. In this context, the convective term is negligible since there is no substantial convection in the scan direction, and the flow field channels are parallel to the incident X-ray beam.