Surfactant dependent self-organization of Co3O4 nanowires on Ni foam for high performance supercapacitors: from nanowire microspheres to nanowire paddy fields.

Different surfactants were used in a typical hydrothermal process for controlling the morphology of the Co3O4 nanowire superstructure on Ni foam. It is easy for the Co3O4 nanowires to self-organize into nanowire microspheres on Ni foam in the absence of surfactants. And the nanowire microspheres gradually unfold into nanowire paddy fields with the addition of nonionic, cationic and anionic surfactants, respectively. The results of BET and electrochemical measurements show that the specific surface area and capacitance first decrease and then increase with the change in the Co3O4 superstructure morphology. Among these electrodes, the Co3O4 electrode with paddy like nanowires shows an outstanding specific capacitance of 1217.4 F g(-1) and areal specific capacitance as high as 6087 mF cm(-2) at 0.7 A g(-1) with high mass loading (5 mg cm(-2)), good power capability (showing a high specific capacitance of 835.1 F g(-1) (4176 mF cm(-2)) at 5 A g(-1)), excellent cycling stability and high columbic efficiency (∼100%). This exceptional performance is benefited from the almost monodispersed nanowire morphology and high specific surface area (121.4 m(2) g(-1)). At the same time, the asymmetric supercapacitor, employing the Co3O4 electrode with paddy-like nanowires as the positive electrode and the activated carbon electrode as the negative electrode, was successfully assembled. It shows a high specific energy and good long-term electrochemical stability. All these impressive results demonstrate that the Co3O4 electrode with paddy-like nanowires is promising for practical applications in supercapacitors.