Nickel hydroxide-impregnated and -coated carbon nanotubes using an easily manipulated solvothermal route for supercapacitors

Coaxial β-Ni(OH)2 nanoparticle-impregnated and -coated CNT composites were fabricated via a facile and controllable solvothermal strategy. By reacting Ni(NO3)2 with NaOH before ethanolthermal treatment the β-Ni(OH)2 nanoparticles with diameters of several nanometers are densely packed on the surfaces of CNTs. Using ammonia hydroxide as precipitator and water/ethanol mixture as solvent the cavity of CNTs can be fully filled with the β-Ni(OH)2 nanoparticles with diameters of ~3 nm. The key mechanism for the formation of the two different Ni(OH)2/CNT composite structures lies in the different solvents and precipitation sequences. Both types of Ni(OH)2/CNT composites exhibit enhanced specific capacitances compared with blank Ni(OH)2 and the acidic CNTs. By loading 5 wt% of CNTs, the capacitance of Ni(OH)2-impregnated composite is 65% higher than that of pure Ni(OH)2 nanoparticles due to the enhanced electrical conductivity and unique cavity confined structure. These results imply that the CNT-confined structures are promising candidates for high performance supercapacitor.