A study of charge density distribution and enhanced electrochemical properties of zinc cobaltite/polyaniline nanocomposite for supercapacitor application

Abstract

Solution combustion method was used to synthesize ZnCo2O4 nanoparticles. Then, physical blending method was used to prepare ZnCo2O4/polyaniline (PANI) composite. The crystallite sizes of the ZnCo2O4 and ZnCo2O4/PANI composites prepared were 17.16 nm and 25.46 nm, respectively, as calculated by XRD studies. The density of nanoparticles, cell parameters, and unit cell volume were calculated by Rietveld refinement technique. The cell volume and lattice constant obtained from the Rietveld method were in good agreement with those of Scherer’s method. Functional groups of the samples were further studied using FTIR. Maximum entropy method (MEM) was employed to study the chemical bonding and electron density distribution of the nanoparticles. The electrochemical properties of the pure and composite materials varied due to the changes in the electron density distribution and chemical bonding. The W–H method and size–strain plot method were used to determine the crystallite size and strain. The results obtained through these methods were in accordance with those of Scherer’s method. The morphological observations made through SEM revealed that the change in morphology of the nanomaterial has enhanced the electrochemical properties of the composite. The shape and size of the pure and nanocomposite observed by SEM and XRD were further confirmed by HR-TEM images. Selected area electron diffraction pattern of HR-TEM images was used to further confirm the crystalline nature of ZnCo2O4 and ZnCo2O4/PANI nanoparticles as examined by XRD. The CV and chronopotentiometry studies were used to study the electrochemical behavior of the samples. The specific capacitance values of pure and composite as obtained from CV study were 711 F/g and 867 F/g, respectively, at the applied current density of 0.5 A/g. Good capacitance retention of 98.9% was achieved for the nanocomposite up to 1000 cycles at a high current density of 4 A/g. The investigation by electrochemical impedance spectrum study also revealed that the nanocomposite exhibited low resistance compared with that of pure. The symmetrical capacitor was assembled by fabricating it with ZnCo2O4/PANI as the electrodes. The high specific capacitance and enhanced efficiency have been achieved due to the presence of PANI in the nanocomposite.