We study the impedance spectra for the leaky membrane model, which governs ion diffusion and electromigration in a porous medium with a fixed background charge, coupled with Butler-Volmer kinetics for describing electrochemical reactions that occur at the electrodes flanking the porous medium. Copper electrodeposition and electrodissolution is used as a prototypical example of Butler-Volmer reaction kinetics. For a negatively charged porous medium, because the leaky membrane model predicts overlimiting current that is carried by surface conduction, we focus on analyzing impedance spectra generated at overlimiting currents and high overpotentials. We show that when the porous medium is sufficiently negatively charged such that the charge transfer resistance is larger than or comparable with the bulk electrolyte impedance, the impedance spectrum in the Nyquist plot shifts leftwards as the applied steady state current increases. On the other hand, if the porous medium is neutral, positively charged or weakly negatively charged, the impedance spectrum shifts rightwards. Next, we perform nonlinear least squares fitting on experimental data to demonstrate that model predictions agree well with the data, thus providing a physical interpretation of the experimental impedance spectra and removing the need to fit them to ad hoc equivalent circuits.

Impedance analysis for leaky membrane model with Butler-Volmer reaction kinetics in charged porous media

256th National Meeting (2018)

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