A polymer-based strategy for regulating electroconvective instability and ion transport at ion-selective membranes

Effective management of electroconvective instability (ECI) is essential for controlling ion transport in electrochemical systems, including electrodialysis and energy conversion devices. While shear flow is known to suppress ECI via vortex confinement (“shear sheltering”), the role of fluid properties, particularly viscoelasticity, presents an open question. This paper introduces a control strategy that synergistically integrates shear flow with polymer-induced viscoelasticity to modulate ECI dynamics and ion transport. By conducting direct numerical simulations of the coupled Poisson–Nernst–Planck, Navier–Stokes, and Oldroyd–B constitutive equations, we illustrate that polymer elasticity, as quantified by the Weissenberg number ( Wi ), can fundamentally regulate ECI behavior. In contrast to the stabilizing effect of shear in Newtonian fluids, viscoelasticity disrupts shear sheltering. Spectral analysis reveals distinct transition routes: from steady flow to elastic chaos at low voltages ( ϕ  < 28, Wi  > 0.01) and from ECI to elastic dominance in the overlimiting regime ( ϕ  > 30), marked by a distinctive power spectral density decay ( f ⁻⁴ in viscoelastic cases vs. f ⁻⁸ in Newtonian fluid). This breakdown of shear sheltering arises from the competition between elastic stresses and Coulomb forces within the extended space charge layer, resulting in notable modulation of kinetic energy and ion transport. Furthermore, we map the system response across a broad parameter space, shear strength U _HP and viscosity ratio β , identifying regions of ion transport enhancement and suppression. Collectively, this work positions viscoelastic modulation of shear sheltering as a novel and tunable strategy for controlling stability–transport coupling, offering key insights for the optimization of electromembrane processes in microfluidics and electrochemical engineering.