Metal–Organic Framework Templated 3D Hierarchical ZnCo₂O₄@Ni(OH)₂ Core–Shell Nanosheet Arrays for High‐Performance Supercapacitors

Abstract

Designing core-shell electrode materials with desired components and architectures is a promising strategy for boosting electrochemical performance. Here, three-dimensional hierarchical ZnCo₂ O₄ @Ni(OH)₂ core-shell nanosheet arrays have been successfully fabricated on a Ni foam substrate, in which the porous ZnCo₂ O₄ nanosheet "core" as the conductive scaffold was synthesized by a metal-organic framework (MOF)-templated method, and the ultrathin Ni(OH)₂ nanoflakes "shell" with rich active sites were grafted on the ZnCo₂ O₄ nanosheet through a hydrothermal treatment. When directly used as a free-standing electrode for supercapacitor, these hierarchical ZnCo₂ O₄ @Ni(OH)₂ core-shell nanosheet arrays exhibited a high capacitance of 3063.2 mF cm^-2 (1021.1 F g^-1 ) at the current density of 1 mA cm^-2 . This electrode significantly outperformed individual Ni(OH)₂ or ZnCo₂ O₄ nanosheet arrays, benefiting from the robust core-shell arrays on Ni foam with good electrical conductivity and abundant active sites, as well as the synergetic effect between MOF-derived porous ZnCo₂ O₄ "core" and the ultrathin Ni(OH)₂ "shell". Moreover, the assembled ZnCo₂ O₄ @Ni(OH)₂ //activated-carbon asymmetric supercapacitor displayed excellent energy and power densities (maximum of 40.0 Wh kg^-1 and 8.02 kW kg^-1 ) and superior cycling stability of 98.4 % retention with 91.2 % coulombic efficiency over 5 000 cycles at 10 A g^-1 .