Facile fabrication of hierarchical film composed of Co(OH) 2 @Carbon nanotube core/sheath nanocables and its capacitive performance.

A hierarchical film composed of Co(OH) 2 @carbon nanotube (CNT) core/sheath nanocables (CCNF) was generated via a simple and rapid electrophoretic deposition method. It is found that the Co(OH) 2 sheath was uniformly anchored on the surface of conductive CNT core. The Co(OH) 2 sheath, with a thickness of ∼20 nm, was composed of numerous very tiny nanoparticles. Such a unique nanostructure endows the CCNF with a high surface area of 126 m 2 g -1 and a hierarchical porosity, resulting in a large accessible surface area for redox activity. As expected, the CCNF exhibits high specific capacitance and excellent rate performance. Its specific capacitance reached 1215 F g -1 under a low current density of 1 A g -1 and was maintained at 832 F g -1 when the current density was increased 20 times to 20 A g -1 . A high capacitance retention of 99.3% was achieved after 10 000 cycles at 1 A g -1 . Such intriguing capacitive behavior is attributed to the synergistic effect of the CNT core and the Co(OH) 2 sheath.