Chemically Deposited NiCo2O4 Thin Films for High-Performance Supercapacitors

Abstract

Changes in climatic conditions resulting from the consumption of fossil fuels and their limited availability have affected the global ecology and economy. The shift towards a more sustainable energy economy has illustrated the need for the development of low cost and environmentally friendly energy storage systems. Supercapacitors, also known as ultracapacitors or electrochemical capacitors, warrant broad important applications in electric vehicles and mobile power sources due to the unique combination of their properties, such as rapid charge–discharge behavior and higher specific power density than batteries and fuel cells while possessing higher energy densities than conventional double layer capacitors. NiCo2O4-based materials have been intensively investigated for pseudocapacitors due to their high theoretical specific capacitance, good chemical and thermal stability, natural abundance, environmental benignity and low cost. In the present work, Nickel cobalt oxide (NiCo2O4) thin films have been systematically prepared using spray pyrolysis method for its application in supercapacitors. Briefly, we prepared two different aqueous solutions of 0.1 M nickel chloride and cobalt chloride by dissolving in de-ionized water (DIW), respectively. In the spray pyrolysis process, aqueous solutions of nickel and cobalt precursor mixed with volume ratio 1:2 were sprayed over the FTO substrates maintained at various temperatures in the form of mist using air-blast spray pyrolysis unit. The sprayed mist undergoes thermal decomposition to form the NiCo2O4 thin films. The electrochemical performance of the NiCo2O4 thin film was measured in a 2M KOH electrolyte with potential window 0 to 0.5 V. Galvanostatic charge– discharge (GCD) studies were also carried out. The field-emission scanning electron microscopy (FE-SEM) image shown in Fig. 1, reveal that compact and uniform thin films of cubic nickel cobaltite with particle size 10-20 nm has been obtained by the oxidation of Ni and Co precursors. Moreover, it is observed that nanostructured NiCo2O4 thin film deposited at 350 0C exhibit the best charge storage property with high specific capacitance of 752 F g−1 and excellent cycle stability over 1000 cycles. The high specific capacitance, remarkable rate capability and excellent cycling stability of the composites mean that they show promise for application in supercapacitors. Figure 1