Biochar-ZnO/polyaniline composite in energy storage application: Synthesis, characterization and electrochemical analysis

Carbon materials displaying electrical double layer capacitance are widely used in the electrochemical energy storage devices. To enhance the electrochemical performance, compositing carbon with transition metal oxides and conducting polymers have been very much appreciated. A novel and effective approach to prepare a high energy density and high specific capacitance composite electrode material from a biomass is presented in the work. Pyrolysis of biomass at 500 oC in the nitrogen atmosphere yielded a biochar (BC) with well-developed porosity, surface functionality and suitable morphological characteristics. Anchoring ZnO nanoparticles on BC and subsequently coating it with a conducting polymeric material, polyaniline (PANI) obtained the hierarchical BC-ZnO/PANI composite. Both BC-ZnO and BC-ZnO/PANI composites have been characterized by FTIR, UV-Visible, XRD, SEM and TEM studies. The characteristic signals at 2θ values 18.5°, 28.4°, 24.0° and 31.4° in XRD correspond to wurtzite structure of ZnO nanoparticles. ZnO rod like structural morphology was confirmed by SEM analysis. The maximum specific capacitance was found to be 110.0 F/g for BC-ZnO and 198.0 F/g for BC-ZnO/PANI. The ternary composite displayed low solution resistance and charge transfer resistance as evident from the Nyquist plots. The results proved that PANI coating is a promising methodology in the fabrication of electrode materials for energy storage applications.