Estimation of Equilibrium Capacitance of Polyaniline Films Using Step Voltammetry

Abstract

© The Author(s) 2015. The equilibrium charge storage characteristic of polyaniline films has been determined using step voltammetry technique. The step coulogram (plot of charge stored versus potential) consists of five distinct regions, which correspond to the different energy bands exhibited by the film, in keeping with Raman and ESR spectroscopy data. The coulogram is piecewise linear, with constant capacitance in each band. Effect of the type and concentration of the acid on the equilibrium capacitances of the bands has been studied. The polaron band has the highest capacitance, followed by the bipolaron band and then the polaron lattice band. The charge stored at a given potential is found to be proportional to film mass. The film needs to be polarized to a threshold charge before faradaic charging begins. This faradaic threshold is independent of the type and concentration of the acids. The step coulogram is compared with the sweep coulogram obtained from linear sweep voltammetry. At low sweep rates, the sweep coulogram also exhibits five distinct bands. However, with increase in the sweep rate, the bands progressively reduce in number. The capacitance of the polaron band decreases linearly with square root of sweep rate and attains the equilibrium capacitance at zero sweep rate.