Concave Ni(OH) 2 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) 2 nanocubes. The morphology and composition evolution of the concave Ni(OH) 2 nanocubes suggest a possible formation mechanism. The as-synthesized Ni(OH) 2 nanostructures used as supercapacitor electrode materials exhibit high specific capacitance (1624 F g -1 at 2 A g -1 ) 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) 2 //graphene) demonstrates high energy density (42.9 Wh kg -1 at a power density of 800 W kg -1 ) and long cycle life (78% retention after 4000 cycles at 5 A g -1 ). This work offers a simple and economic approach for obtaining concave Ni(OH) 2 nanocubes for energy storage and conversion.