Hierarchical NiCo2O4@NiCo2O4 Nanoflake Arrays Supported on Ni Foam as High-performance Electrodes for Supercapacitors

A facile strategy for the stepwise preparation of a NiCo2O4 nanosheet array on a nickel foam skeleton was developed by a hydrothermal-calcination method. Under optimum process conditions, the NiCo2O4@NiCo2O4 materials supported on NiCo2O4 nanoflakes displayed different performances than bare NiCo2O4 nanosheet arrays according to experimental characterization and electrochemical studies and were grown in situ on nickel foam. The NiCo2O4 nanoflake material, used as the electrode of the supercapacitor, exhibited a multilevel mesoporous nanostructure that had a narrow pore size (3.18 nm) and wide pore size (6.22 nm). In addition, the specific surface area (SSA, 1.84 m(2)g(-1)) and average pore size (13 nm) were acquired by calculations, and this material showed a relatively high specific capacitance (Cs, 840 Fg(-1)) when the current density was 1Ag(-1), and a rate capability of 86.67% from 1 to 15 Ag-1 and the capacitance could maintain 93% of the initial value after 5000 charge-discharge cycles. The NiCo2O4@NiCo2O4 nanostructures provided effective electron pathways and a relatively large electroactive surface area, and narrow pore sizes were observed at 2.46 nm and 3.48 nm, while a wide pore size was observed at 5.53 nm. The SSA was improved to 8.64 m(2)g(-1), and the average pore diameter was distributed at 11 nm. Accordingly, a remarkable electrochemical performance demonstrated that the Cs of 1036 Fg(-1) was obtained at a current density of 1 Ag-1, and the rate capability reached 69.59% as the current density increased from 1 to 15 Ag-1.Excellent capacitance retention was retained at 92.5% after 5000 cycles, while the coulombic efficiency was maintained at 100%.

Automated summary

A facile hydrothermal-calcination method was used to prepare NiCo2O4 nanosheet array on a nickel foam skeleton, exhibiting remarkable electrochemical performance with high specific surface area and capacitance retention.