Characterisation of the electrochemical redox behaviour of Pt electrodes by potentiodynamic electrochemical impedance spectroscopy

Multi-frequency ac responses of Pt in aqueous solutions of sulphuric and perchloric acids have been characterised in cycles of Pt oxide anodic formation and cathodic reduction as functions of electrode potential, using the two orders frequency range below 1 kHz, where the double layer responded jointly with Faradaic processes. The potentiodynamic impedance spectra were fitted to an equivalent circuit, which contained double-layer capacitance in parallel with charge transfer resistance, R, and constant phase element (CPE). Double-layer capacitance has shown minima (20–25 μF cm−2 in 0.5 M H2SO4 and 25–35 μF cm−2 in 1 M HClO4) in the double-layer region and more than twofold increase in the platinum oxidation region. R −1 and CPE have shown maxima in the regions of platinum oxidation and reduction. Potentiodynamic curves of raw impedance data were also self-descriptive in monitoring platinum oxidation and reduction in both solutions and in presence of chloride.