Towards supercapacitors: Cyclic voltammetry and fast Fourier transform electrochemical impedance spectroscopy based evaluation of polypyrrole electrochemically deposited on the pencil graphite electrode

Abstract

A pencil graphite electrode was used for electrochemical synthesis of polypyrrole in an aqueous solution. Two key features of the polymerization were investigated: 1) the pH of the aqueous solution and 2) number of potential pulses for obtaining the polymer on the electrode. The pH values of the aqueous solutions were as follows: pH 1.0, pH 3.0 and pH 7.0. The number of potential pulses during electrochemical polymerization varied from 1 to 15. The obtained polymer further was analyzed by applying cyclic voltammetry and fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS). The main focus was addressed to the changes in the polypyrrole capacitance during its aging in the period up to 34 days. FFT-EIS-based analysis of polymer aging has shown that polypyrrole synthesized at low pH tends to possess better longevity in comparison to the polypyrrole synthesized at neutral pHs. Also it was observed that the Ppy layer degrades faster while being stored in a phosphate buffer solution than being stored in an air. This tendency was observed practically for all combinations of pHs. The plausible cause of the degradation might be based on oxygen dissolved in the aqueous medium. Fast Fourier transform electrochemical impedance spectroscopy data enabled us to draw the conclusion that the polymer layer grows thicker if during electrochemical polymerization higher number of potential pulses is applied. In addition, the increase of charge transfer resistance is observed when the thickness of the layer is increasing.