Continuous fast Fourier transform admittance voltammetry as a new approach for studying the change in morphology of polyaniline for supercapacitors application
In this study, continuous fast Fourier transform admittance voltammetry (CFFTAV) was used to study and characterize the surface morphology of polyaniline (PANI) on glassy carbon (GC) electrodes. Four polymer films with various thicknesses (0.5 μm to 11 μm) were synthesized by an electrochemical method. A new modified square wave voltammetry (SWV) method based on application of a discrete Fast Fourier Formation (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window was used. Moreover, the electrode response could be calculated by measuring the changes in SW voltammogram (or admittance). Results showed that by using the CFFTAV method, changes in the porosity of PANI and the behavior of PANI formation in H2SO4 solution were investigated more quantitatively than when using scanning electron microscopy (SEM), cyclic voltammetry (CV), charge–discharge (CD) and impedance spectroscopy (EIS) methods. By monitoring the electrode response, the kinetics for reaching steady state condition was studied. It was found that with the increasing thickness of polymer film from 0.5 μm to 11 μm, the accessible porosity decreased by up to three times. Furthermore, dimensions of nanochannels in the polymer film decreased with increasing the thickness. Moreover, maximum potential for ion insertion increased from 324 mV to 365 mV. Capability of electrodes for use as supercapacitor materials was tested by CV, CD and EIS, and the calculated capacity of electrodes was equal to 620 F g−1 and 247 F g−1 for thinnest and thickest polymer films respectively.