Spinel based nanostructured materials for asymmetric supercapacitor application

Abstract

The present thesis investigate the performance of spinel based mixed metal oxide for supercapacitor applications. Here in cobalt based spinel nanostructures viz NiCo2O4, MnCo2O4 and ZnCo2O4 were analyzed for their energy storage capability. NiCo2O4 nanorods were prepared by a hydrothermal method using urea as the structure directing agent. The nanorods were characterized using various material characterization techniques and the electrochemical performance was analyzed. The voltammetric studies indicated pseudocapacitance behavior of NiCo2O4 and the charge storage performance was evaluated using galvanostatic charge discharge (GCD) studies. The GCD studies revealed a capacitance of 227 F/g at a current density of 0.25 A/g. However upon introducing NiO as the secondary phase the supercapacitor showed an enhancement with specific capacitance of 490 F/g. The increment was attributed to the presence of secondary phase in the material. Further an asymmetric supercapacitor based on activated carbon as negative electrode and NiCo2O4-NiO as positive electrode was fabricated. The device showed a capacitance of 127 F/g and good cyclic stability over 2000 charge discharge cycles. Similarly, MnCo2O4 with nanorods morphology was prepared using hydrothermal method and the electrochemical studies were carried out as above. The electrode showed a capacitance of 187.5 F/g and 76 F/g in three and two electrode configuration respectively. The cell showed 88% capacitance retention after 5000 cycles. The pseudocapacitance nature of the electrode was studied using impedance spectroscopy. The deviation of the phase angle confirms the pseudocapacitance contribution of the electrode. Further ZnCo2O4 nanohexagons were prepared using a double hydroxide mediated synthesis and identical studies were performed as above. The electrochemical studies showed a specific capacitance of 194 F/g in three electrode and 35 F/g in two electrode configuration respectively. The electrode showed retention of 89% capacitance after 2000 charge-discharge cyc