Abstract
Binder free nanostructured NiCo2O4 were grown using a facile hydrothermal technique. X-ray diffraction patterns confirmed the phase purity of NiCo2O4. The surface morphology and microstructure of the NiCo2O4 analyzed by scanning electron microscopy (SEM) showed flower-like morphology composed of needle-like structures. The potential application of binder free NiCo2O4 as an electrode for supercapacitor devices was investigated using electrochemical methods. The cyclic voltammograms of NiCo2O4 electrode using alkaline aqueous electrolytes showed the presence of redox peaks suggesting pseudocapacitance behavior. Quasi-solid state supercapacitor device fabricated by sandwiching two NiCo2O4 electrodes and separating them by ion transporting layer. The performance of the device was tested using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The device showed excellent flexibility and cyclic stability. The temperature dependent charge storage capacity was measured for their variable temperature applications. Specific capacitance of the device was enhanced by ~150% on raising the temperature from 20 to 60 °C. Hence, the results suggest that NiCo2O4 grown under these conditions could be a suitable material for high performance supercapacitor devices that can be operated at variable temperatures.
Highlights
NiCo2O4 is a ternary oxide material containing mixed valence metals and allows multiple electrochemical processes[30]
Advancing our interest on this material for supercapacitor applications, we report a facile hydrothermal method to grow flower-like morphology consisting needle-like structures
Binder free electrodes decorated with nanocrystals of NiCo2O4 on nickel foam were prepared following a facile hydrothermal method
Summary
Growing nanocrystalline form of NiCo2O4 directly on the conducting surface, the performance of supercapacitor devices can be augmented[31] By effecting this growth on conductive substrates, each nanostructured metal oxide gets its own electric contact with the substrate and participates in the electrochemical reactions more efficiently. Huang et al have fabricated electrodes using a facile electrodeposition of cobalt and nickel double hydroxide nanosheets on porous NiCo2O4 nanowires grown on carbon fiber paper[32] These materials showed very good cycling stability with a high capacitance of ∼ 1.64 F/cm[2] at 2 mA/cm[2]. The electrochemical testing revealed a very high a specific capacitance of 1078 F/g at a discharge current of 1 mA with very good cyclic stability These excellent capacitive performances were attributed to the hierarchical porous nanosheet like structures of NiCo2O4-GO. The specific capacitance of NiCo2O4 based supercapacitor device at different temperatures is estimated to be increasing linearly on raising the temperature
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