Negative capacitance for polyaniline: an analysis via electrochemical impedance spectroscopy

Polyaniline (PANI) films were electrodeposited on Pt electrode by cyclic voltammetry using an anodic switching potential of 0.90 V, which favored benzoquinone (BQ) as side product. The redox interactions between BQ and PANI were analyzed through electrochemical impedance spectroscopy (EIS). PANI films of different thickness were subjected to different applied potentials and impedance spectra were recorded. PANI films were found to show negative capacitance (inductive loop) in the potential range of 0.50–0.70 V. A redox mechanism involving the role of BQ to impart negative capacitance to PANI is given and supported by the results from X-ray photoelectron spectroscopy (XPS). An equivalent circuit including an inductor element (L) is found to fit perfectly with data from EIS. The effect of thickness of PANI on L-value is elucidated and discussed.