Preparation and capacitive properties of cobalt–nickel oxides/carbon nanotube composites

In this paper, nickel–cobalt oxides/carbon nanotube (CNT) composites were prepared by adding and thermally decomposing nickel and cobalt nitrates directly onto the surface of carbon nanotube/graphite electrode to form nickel and cobalt oxides. Carbon nanotubes used in this paper were grown directly on graphite substrate by chemical vapor deposition technique. The capacitive behavior of nickel–cobalt oxides/CNT electrode was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1 M KOH aqueous solutions. The results show that nickel–cobalt oxides/CNT composite electrode has excellent charge–discharge cycle stability (0.2% and 3.6% losses of the specific capacitance are found at the 1000th and 2000th charge–discharge cycles, respectively) and good charge–discharge properties at high currrent density. Additionally, the effect of Ni/Co molar ratio on specific capacitance of the composite electrode was investigated and the highest specific capacitance (569 F g−1 at 10 mA cm−2) is obtained at Ni/Co molar ratio = 1:1.