On experimental determination of cell constants for interdigitated electrodes

The discrepancy reported in the literature between interdigitated electrode cell constants obtained from experiment and those obtained from numerical simulation is attributed, in part, to geometry-induced frequency dispersion. The frequency dispersion associated with the interdigitated electrode geometry yields a complex ohmic impedance with real asymptotic limits for ohmic resistance at high and low frequencies. The determination of cell constants from impedance measurements performed on gold interdigitated electrodes in aqueous KCl solutions of differing electrolyte resistivity is shown to be confounded by the presence of a surface film and by extrapolated values that fell between the high- and low-frequency ohmic resistances. A method is presented to ensure that impedance measurements performed in aqueous KCl solutions of differing concentration yields the low-frequency ohmic resistance, from which a well-defined cell constant is obtained that agrees with numerical simulations. The experimental results are supported by finite-element simulations that accounted for the presence of a film. (C) 2020 Elsevier Ltd. All rights reserved.