A geometry optimization framework for enhancement of ionic current rectification.

Ionic current rectification (ICR) is central to nanofluidics and iontronics, yet current nanopore designs often rely on parametric scans of predefined geometries, which limits their performance. This work presents a geometry optimization framework to inversely design charged nanoslits for the maximization of ICR. Treating the electrolyte-electrode interface as a continuous design variable governed by the steady-state Poisson-Nernst-Planck system, a shape gradient flow algorithm is developed to optimize the geometry. Within this framework, shape calculus is employed to perform sensitivity analysis, deriving expressions supported on the moving boundary. Without relying on predefined templates, optimization achieves higher rectification ratios than standard linear conical nanoslits. Thorough investigation reveals that the algorithm autonomously generates highly asymmetric geometries. Three representative optimized structures featuring local sharpened constrictions, entropic funnels, and asymmetric wavy interfaces are identified and analyzed. These emergent geometric features effectively amplify the local electric field, inducing extreme ion concentration polarization and electro-migration-dominated transport. This physics-driven geometry optimization framework offers a robust and systematic tool for designing next-generation, high-performance iontronic devices.