Metal-Organic Framework Templated 3D Hierarchical ZnCo2 O4 @Ni(OH)2 Core-Shell Nanosheet Arrays for High-Performance Supercapacitors.

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 .