Electrode-electrolyte interface impedance: Experiments and model

Abstract

The impedance of the junction between a solid or aqueous electrolyte and a metal electrode at which no charge transfer processes occur (blocking contacts) follows closely the constant phase angle form, Z = A(j omega)-n, over a wide frequency range, where A is a constant, and the frequency exponent n is typically in the range of 0.7 to 0.95. Several models have been proposed in which the magnitude of the frequency exponent n is related by a simple expression to the fractal dimension d of the rough electrode surface. But experiments with aqueous H2SO4 and roughened platinum and silicon electrodes show that there is no simple relationship, if any at all, between n and d when d is determined from the analysis of one dimensional surface profiles. Moreover, n is not a simple function of the average roughness of the electrode. In order to gain some insight into the effect of electrode topography and the interface impedance, a model for the response of the interface to a constant voltage pulse was constructed. This model is based on the idea that, following a pulse, locally concentrated regions of ions accumulate rapidly at the tips of large protrusions on the electrode surface which screens deeper regions of the electrode from the field driven flux of mobile ions. After this rapid charging, ions are able to reach the deeper, screened regions of the electrode by diffusion, and it is this diffusive process that gives rise to the observed t1-n dependence of the charge collected. Computer simulations, similar to the diffusion limited aggregation model, using measured profiles as fixed (non-growing) clusters, gave exponents n in good agreement with experiment.

CMOS microelectrode array for the monitoring of electrogenic cells

“…Additionally, it is interesting to note that n, often termed the frequency dispersion coefficient, does not vary with surface roughness, as has been historically assumed (De Levie, 1965). The effect of the surface roughness on impedance has been the focus of intense research efforts and has resulted in many models such as the well known pore model of de Levie, models based on surface inhomogeneities leading to a distribution of relaxation times (Brug et al, 1984), and more recently in fractal geometry-based models (Nyikos and Pajkossy, 1985;Bates and Chu, 1992). The authors concur with the work of Pajkossy, where in the frequency range investigated the capacitance dispersion is attributed to adsorption effects (Pajkossy, 1994).…”

Local Impedance Spectroscopy: A Potential Tool to Characterize the Evolution of Emulsions and Foams

“…The sinusoidal current i(t) is injected into the sample through two electrical contacts and the resulting voltage drop u(t) is measured between the same two contacts. The two-electrode method works properly if the impedance of the electrode-electrolyte interface is much lower than the impedance of the sample since the measured impedance is the sum of both terms [14]. Above approximately 1,000 Hz the electrode-electrolyte interface impedance is dominated by the electrolyte resistance, where we can readily use the bipolar method above 1,000 Hz.…”

Testing miniaturized electrodes for impedance measurements within the β-dispersion – a practical approach

“…As seen in Fig.3, the double layer thickness is less than a nanometer for electrolytes with physiological salt concentration (140 mM), but can reach more than a micrometer for distilled water (0.1 M). The electrode impedance varies greatly with respect to the electrode potential as seen by cyclic voltammetry (Fig.4) [55]. Theoretically, the entire electrode impedance can be calculated [56].…”

“…With the conductivity , D can be estimated for aqueous 1:1 electrolytes by c RT D A charged surface of the electrode will influence the impedance as well but also the electrode potential especially for small potential differences between the electrode and the electrolyte. The surface potential is the -potential which equals the voltage drop across the Gouy-Chapman layer [55]. Since this layer is built up by weak electrostatic forces, a flow of the medium contacting the electrode will disturb this layer.…”