Concave Ni(OH) Nanocube Synthesis and Its Application in High-Performance Hybrid Capacitors.

The controlled synthesis of hollow structure transition metal compounds has long been a very interesting and significant research topic in the energy storage and conversion fields. Herein, an ultrasound-assisted chemical etching strategy is proposed for fabricating concave Ni(OH) nanocubes. The morphology and composition evolution of the concave Ni(OH) nanocubes suggest a possible formation mechanism. The as-synthesized Ni(OH) nanostructures used as supercapacitor electrode materials exhibit high specific capacitance (1624 F g at 2 A g) and excellent cycling stability (77% retention after 4000 cycles) due to their large specific surface area and open pathway. In addition, the corresponding hybrid capacitor (Ni(OH)//graphene) demonstrates high energy density (42.9 Wh kg at a power density of 800 W kg) and long cycle life (78% retention after 4000 cycles at 5 A g). This work offers a simple and economic approach for obtaining concave Ni(OH) nanocubes for energy storage and conversion.