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.