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

摘要

Carbonaceous nickel oxide powder samples have been synthesized from an adducted nickel P-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 Na_2SO_4 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: Na_2SO4, KOH and Ca(NO_3)_2·4H_2O. Spe-cific capacitance as high as 143 F g~(-1) is measured in Ca(NO_3)_2·4H_2O electrolyte.