  We demonstrate the role of selectivity variation in the structure of the
non-equilibrium extended space-charge using 1D analytic and 2D numerical
Poisson-Nernst-Planck models for the electro- diffusive transport of a
symmetric electrolyte. This provides a deeper understanding of the underly- ing
mechanism behind a previously-observed maximum in the resistance-voltage curve
for a shallow micro-nanochannel interface device [Schiffbauer, Liel, Leibowitz,
Park, and Yossifon, submitted to Phys. Rev. E.]. The current study helps to
establish a connection between parameters such as the geometry and nanochannel
surface-charge and the control of selectivity and resistance in the
over-limiting current regime.
