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.