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

Abstract

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