Synthesis and electrochemical investigations of Ni_1-xO thin films and Ni_1-xO on three-dimensional carbon substrates for electrochemical capacitors

Nickel oxide/carbon nanotube (Ni_1-xO/CNT) film nanocomposite electrodes for electrochemical capacitors were prepared by electrochemically precipitating nickel hydroxide onto a CNT film substrate and heating it in air at 300°C. For comparison, nickel oxide thin film and nickel oxide/carbon paper (Ni_1-xO/C paper) electrodes were also prepared via electrochemical route. The nickel oxide layers (∼5 nm thickness) in the Ni_1-xO/CNT film electrode were coated uniformly on the surface of the individual CNTs, constructing a 3D nanoporous network structure through the entire thickness of the film. In comparison to the thin film and Ni_1-xO/C paper electrodes, the Ni_1-xO/CNT film electrode showed a very high specific capacitance of ∼ 1000 F g^-1with a high rate capability in 1 M KOH. The Ni_1-xO/CNT film electrode also showed a good cycle life during 100 cycles in 1 M KOH. The high specific capacitance and good power characteristics of the Ni_1-xO/CNT nanocomposite electrode can be attributed to the construction of an electrode with a very thin film of electroactive materials with a nanometer thickness on a CNT film substrate with a 3D nanoporous network structure.