Electrohydrodynamic ion regulation in soft-coated nanochannels: A comparative assessment of geometry effects on desalination performance

• Reverse-conical nanochannels maximize ion rejection via strong field focusing and enhanced Donnan exclusion. • Soft-layer charge density critically tunes the rejection–flux tradeoff across all tested electrolytes. • Ion hydration and mobility govern selectivity trends, making NaCl the most sensitive to PEL charge. • Pressure and voltage modulate electrohydrodynamics, shifting transport from surface-dominated to bulk-conductive. • Coupled PNP–NS simulations reveal reverse-conical geometry as the optimal design for high-efficiency desalination. Meeting the growing demand for high-quality freshwater requires membrane systems that can provide strong ion discrimination while sustaining adequate water transport. This work presents a comprehensive, systematic numerical investigation comparing three distinct integrated nanochannel arrays—a uniform array of cylindrical channel (Type 1), an array of forward-tapered cone (Type 2), and an array of reverse-tapered cone (Type 3)—specifically within soft-coated nanochannels featuring a negatively charged polyelectrolyte layer. Our approach uniquely analyzes the electrohydrodynamic ion regulation by evaluating these architectures using a fully coupled Poisson–Nernst–Planck and Navier–Stokes framework for three monovalent electrolytes (NaCl, KCl, and KNO 3 ) under a wide range of operating conditions. The simulations show that geometric confinement substantially alters electrohydrodynamic interactions inside the channels. The reverse-tapered design demonstrates the strongest ion-exclusion capability, reducing NaCl concentration by more than 99%, whereas the cylindrical and forward-tapered structures achieve approximately 87% and 95% rejection, respectively. The same geometry also produces a favorable balance between ion blocking and hydraulic throughput, delivering a pure-water flux of 41.8 L·m⁻²·h⁻¹ compared to 38.0 L·m⁻²·h⁻¹ for the forward-tapered channel under identical conditions. Analysis of ionic conductance and selectivity further reveals that the reverse-tapered configuration enhances electrostatic focusing, suppresses co-ion leakage, and yields higher selectivity ( S ) and lower conductance ( G ) than the other two geometries. These findings demonstrate that optimizing both the shape of the nanochannel and the charge characteristics of the soft layer provides a robust pathway for designing next-generation nanofluidic membranes with high desalination efficiency and competitive water permeability.