The electrochemical performance of various NiCo₂O₄ nanostructures in hybrid supercapacitors: Investigating the impact of crystalline defects

Binary metal oxides exhibit a compelling combination of features that make them highly attractive electrode materials for supercapacitors. Herein, a facile hydrothermal method is employed for the preparation of defectrich hierarchical nanostructured NiCo2O4 with various morphologies, including urchin-like nanostructure, nanoflowers, and 2D nanosheets; and their electrochemical performances as electrodes for hybrid supercapacitor are studies. Notably, the supercapacitor based on the urchin-like nanostructure with high oxygen vacancies delivers a high gravimetric energy density of 45.2 Wh/kg at the power density of 750 W/kg, maintaining remarkable cycling stability. The electrode exhibits specific capacitance of 423.9 and 292.0 F/g at the current density of 1.5 and 7.5 A/g, respectively, with high capacitive retention of approximate to 94 % after 1500 cycles. Crystalline defects identified in nanostructured NiCo2O4 are suggested to significantly contribute to the high ionic/electrical conductivity and the electrochemical stability of the electrodes.