Non-ideal ion transport in moderately concentrated KCl solutions: Decoupling bulk and interfacial dynamics through impedance spectroscopy and equivalent circuit modeling

Abstract

This study investigates the concentration-dependent electrical and dynamic properties of KCl solutions (0.1–0.3 M) to elucidate ion transport mechanisms and validate classical electrolyte theory. Using AC conductivity analysis, we observed enhanced ionic conductivity with increasing concentration, evidenced by broadening Nyquist semicircles and rising CC plateaus, while equivalent circuit modeling decoupled bulk and interfacial processes, revealing decreasing resistances and shifting CPE parameters. Key results include a linear increase in conductivity (4.1–15.2 mS/cm) and opposing relaxation time trends (bulk τ₁ decreasing, interfacial τ₂ increasing), highlighting the interplay between ion mobility and electrode effects. The Debye screening length followed κ⁻¹ ∝ c⁻¹/² (A = 0.3036), confirming theoretical predictions, while derived ionic mobilities (4.25–5.25 × 10⁻⁸ m²/V·s) and diffusivities (1.09–1.35 × 10⁻⁹ m²/s) captured non-ideal behavior at moderate concentrations. This work provides a robust experimental framework linking macroscopic measurements to microscopic ion dynamics, offering insights for optimizing electrochemical systems.