Band-gap shrinked NiO@Co3O4 nanotubes as high-performance supercapacitor electrodes

Abstract

Novel band-gap shrinked NiO@Co3O4 nanotube arrays on Ni foam have been fabricated via a two-step synthesis route. Hexagonal NiO nanotube arrays are obtained by electrodeposition of Ni nanoparticles onto ZnO nanoprisms followed by selective dissolution of ZnO. The inside and outside surfaces of the NiO nanotubes are homogeneously covered with Co3O4 nanosheets via hydrothermal treatment, which enlarges the surface area and accelerates electron transferring. Benefiting from the hierarchically hollow structure and the synergistic effects, the obtained NiO@Co3O4 nanotube arrays deliver a superior specific capacitance of 1769.2 F/g at 1 A/g and outstanding cycling stability (87.5% capacitance retention after 10,000 cycles at 20 A/g). Density functional theory calculations reveal that the disappearance of the band-gap of the NiO@Co3O4 composite is one intrinsic reason that the conductivity and the capacitive charge storage performance are enhanced significantly. The as-prepared NiO@Co3O4 nanotube arrays are highly promising electrodes for high-performance supercapacitors.