Figure 8.

Operating principles and underlying physics of ED. (a) The feed flows through a stack of channels separated by alternating CEMs and AEMs, across which a current is applied. These channels are filled with spacer material that physically separates the membranes, promotes turbulent mixing, and inhibits ICP and the formation of laminar boundary layers near the membranes.^349,350 The concentration profiles of the ions exhibit axial growth of boundary layers of depletion and enrichment in the diluate and concentrate channels, respectively. Adapted with permission from ref (346). Copyright 1968 Elsevier. (b) Ion fluxes near a CEM and the associated convection–diffusion boundary layers, which become more strongly depleted with increasing current until the diffusion limit is reached. (c) The current–voltage relationship reaches a plateau at the limiting current, while overlimiting current, which results in an extended zone of ion depletion, is observed at higher voltages.