Carbonaceous nickel oxide nano-composites: As electrode materials in electrochemical capacitor applications

• Solution based microwave process is used to synthesize nano-composites of NiO.
• Adducted metal organic complex is used as a single source precursor for synthesis of carbonaceous nano-composites.
• By tuning the nature of solvents in the reaction medium it is possible to obtain either NiO/C or Ni/NiO/C composite.
• These composites show superior performance as electrode material for supercapacitor applications.
• Nano-composite such as Ni/NiO/C show enhanced capacitive behavior for its better conductivity because of C and Ni.

Carbonaceous nickel oxide powder samples have been synthesized from an adducted nickel β-ketoester complex used as a “single source precursor” through a solution-based microwave-assisted chemical route. Comprehensive analysis of the resulting powder material has been carried out using various characterization techniques. These analysis reveal that, depending on the solvent used, either NiO/C or Ni/NiO/C composites are formed, wherein Ni and/or NiO nanocrystals are enveloped in amorphous carbon. As the components emerge from the same molecular source, the composites are homogeneous on a fine scale, making them promising electrode materials for supercapacitors. Electrochemical capacitive behavior of these oxide composites is studied in a three-electrode configuration. With a specific capacitance of 113 F g−1, Ni/NiO/C is superior to NiO/C as capacitor electrode material, in 0.1 M Na2SO4 electrolyte. This is confirmed by impedance measurements, which show that charge-transfer resistance and equivalent series resistance are lower in Ni/NiO/C than in NiO/C, presumably because of the presence of metallic nickel in the former. The cyclic voltammograms are nearly rectangular and the electrodes display excellent cyclability in different electrolytes: Na2SO4, KOH and Ca(NO3)2·4H2O. Specific capacitance as high as 143 F g−1 is measured in Ca(NO3)2·4H2O electrolyte.

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