Research on the Diffusion Impedance Model in Nanopipette for Localized Electrochemical Impedance Spectroscopy

Localized electrochemical impedance spectroscopy (LEIS) is a powerful technique for probing complex electrochemical processes and demonstrates significant potential for practical applications. The nanopipette-based LEIS method offers enhanced spatial resolution, establishing it as a promising new approach in impedance spectroscopy. However, nonideal Warburg diffusion of ions within the nanopipette introduces considerable errors in equivalent circuit decoupling of interfacial electrochemical reaction kinetics. To address this issue, a diffusion model was developed by incorporating a correction factor into the Warburg equation to account for nonlinear ion diffusion. In addition, a finite element-based numerical model was constructed to simulate ion transport within the nanopipette under different solution conditions and geometrical configurations. Comparative analysis between the numerical simulations and the proposed analytical model validates the robustness and applicability of the latter across diverse conditions. Finally, the experimental impedance spectroscopy data were fitted using the proposed model with fitting errors within 2% in the diffusion-dominated frequency range, confirming the model accuracy. This work provides a more accurate description of diffusion impedance, thereby advancing the use of nanopipette-based LEIS for high-precision characterization of localized interfacial electrochemical kinetics.