Electrochemical impedance spectroscopy study of the oxygen evolution reaction on a gas-evolving anode composed of lead dioxide microfibers

Abstract

The oxygen evolution reaction (OER) during the electrolysis of electrolyte-free water on a gas-evolving anode composed of lead dioxide microfibers (MF-β-PbO2) was studied in a solid polymer electrolyte cell using the electrochemical impedance spectroscopy (EIS) technique. EIS spectra were recorded as a function of the overpotential for the OER. Impedance spectra characterized by two time constants distributed in the low and high frequency domains indicated that both the charge transfer and adsorption of reaction intermediates affect the electrode kinetics. In addition, it was verified that morphological aspects do not comprise the main cause for the time constant observed in the high frequency domain. In trying to interpret the EIS findings, a transfer function was derived for the electrode mechanism of Pavlov and Monahov in order to permit the evaluation of the adsorption pseudocapacitance, the double-layer capacitance and the charge transfer and adsorption resistances. It was verified that the adsorption pseudocapacitance is potential-dependent while the double-layer capacitance is almost potential-independent. It was also verified that the adsorption resistance decreases exponentially upon increasing the overpotential, exhibiting Tafel-like behavior. The apparent charge transfer coefficient, the exchange current density and the kinetic rate constant were evaluated from the impedance data.