ZIF-67-derived NiCo2O4@Co2P/Ni2P honeycomb nanosheets on carbon cloth for high-performance asymmetric supercapacitors

Abstract

Metal–organic framework (MOF)-derived transition metal oxides and transition metal phosphides have great application potential as electrode materials for supercapacitors, owing to their excellent redox activity and high conductivity. However, their electrochemical performances are limited by the stability of the nanostructures. Herein, hierarchical porous honeycomb nanosheets (NiCo₂O₄@Co₂P/Ni₂P-CC), for the first time, were prepared on carbon cloth by using ZIF-67 as a sacrificial template via in situ growth-etching and an ion exchange-carbonization-phosphorization method. Benefiting from its unique structure with hierarchical pores, a large specific surface area, transition metal oxide and transition metal phosphide, when employed as an electrode material in an asymmetric supercapacitor, the NiCo₂O₄@Co₂P/Ni₂P-CC nanosheets deliver an outstanding areal capacitance of 2881.88 mF cm^−a at 2 mA cm^−t, which is far superior to NiCo₂O₄-CC (1458.45 mF cm^−C at 2 mA cm^−t). An asymmetric supercapacitor was successfully assembled using NiCo₂O₄@Co₂P/Ni₂P-CC as a positive electrode and activated carbon/carbon cloth (AC/CC) as a negative electrode, exhibiting a maximum volumetric energy density of 2.53 mW h cm⁻ at a volumetric power density of 22.77 mW cm^−c, and excellent cycling stability (87.6% after 10 000 cycles). In this work, MOF-derived NiCo₂O₄@Co₂P/Ni₂P-CC nanosheets are used as an ideal electrode material, providing a reference for the rational design and preparation of electrode materials for asymmetric supercapacitors.