Ultrathin β-Ni(OH)₂ Nanoplates Vertically Grown on Nickel-Coated Carbon Nanotubes as High-Performance Pseudocapacitor Electrode Materials

Various metal hydroxides/oxides grown on conductive substrates such as nickel foam have been reported and studied as supercapacitor electrode materials. However, the capacitances of these electrodes are extremely limited because of the low content of active materials grown on the limited surface of nickel foam. To achieve high capacitance, we use nickel-coated carbon nanotubes (Ni-CNTs) as the conductive substrate for the growth of β-Ni(OH)2. By a facile chemical method, ultrathin β-Ni(OH)2 nanoplates are vertically grown on the surface of Ni-CNTs. The density, thickness, and content of β-Ni(OH)2 can be easily controlled by modulating the ratio of NiCl2·6H2O to Ni-CNTs. This hierarchical nanostructure can provide remarkable synergistic effects: facilitate electron and ion transport and accelerate the reversible redox reactions. As-prepared Ni-CNTs@β-Ni(OH)2 composites exhibit high specific capacitances (∼1807 F g(-1) at 2 A g(-1), based on the mass of β-Ni(OH)2; ∼1283 F g(-1) at 2 A g(-1), based on the mass of composite), good rate capabilities, and excellent cycling stabilities. This strategy has potential for large-scale production and can be applied to the preparation of other hierarchical nanostructured metal hydroxide/oxide composites.