Hierarchical NiCo2O4@NiCo2O4 Core/Shell Nanoflake Arrays as High-Performance Supercapacitor Materials

Hierarchical NiCo2O4@NiCo2O4 core/shell nanoflake arrays on nickel foam for high-performance supercapacitors are fabricated by a two-step solution-based method which involves in hydrothermal process and chemical bath deposition. Compared with the bare NiCo2O4 nanoflake arrays, the core/shell electrode displays better pseudocapacitive behaviors in 2 M KOH, which exhibits high areal specific capacitances of 1.55 F cm–2 at 2 mA cm–2 and 1.16 F cm–2 at 40 mA cm–2 before activation as well as excellent cycling stability. The specific capacitance can achieve a maximum of 2.20 F cm–2 at a current density of 5 mA cm–2, which can still retain 2.17 F cm–2 (98.6% retention) after 4000 cycles. The enhanced pseudocapacitive performances are mainly attributed to its unique core/shell structure, which provides fast ion and electron transfer, a large number of active sites, and good strain accommodation.