6533b855fe1ef96bd12b1497

RESEARCH PRODUCT

Electrochemical impedance spectroscopy of conductor-insulator composite electrodes: properties in the blocking and diffusive regimes

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Abstract The electrochemical response of graphite + high-density polyethylene composite electrodes as a function of the conductivity load was investigated. Percolation theory was used in order to explain the electrochemical behaviour of this type of composite electrode. In the blocking regime the electrochemical impedance of this electrode material behaved as R 0 + q · ( ω j) − η , where R 0 represents the uncompensated resistance of the cell. Its value depended on the graphite volume proportion ( ν ) with a power law R 0 ∞ ( ν — ν c ) − t with a critical exponent t = 3.2 ± 0.1 which is close to the mean field value, t = 3. With potassium chloride concentrations greater than 0.7 M, the uncompensated resistance, R 0 , coincided practically with the bulk resistivity of the solid. The electrochemical response of potassium ferricyanide was analyzed using a generalized Randles equivalent circuit where the double layer capacity and the Warburg impedance were substituted by two independent CPEs, respectively. In this diffusive regime and in the blocking regime, the values of the constants and exponents of the constant phase elements were interpreted on the basis of a surface model of composite electrodes and its disorder.