Hierarchical Core-Shell Nanosheet Arrays with MnO2 Grown on Mesoporous CoFe2O4 Support for High-Performance Asymmetric Supercapacitors

We demonstrated the design and fabrication of unique core-shell CoFe2O4@MnO2 nanosheets arrays (NSAs) on nickel foam via a facile and scalable method. The CoFe2O4 nanosheets (NSs) grown on the nickel foam acted as a porous skeleton with large surface areas for the growth of MnO2 NSs, achieving the enhancement of both the electrical and the ionic conductivities. Ultrathin MnO2 NSs were found vertically grown on the CoFe2O4 NSs in a core-shell nanoarchitecture. Its thickness can be controlled by retention times during the hydrothermal process. The obtained CoFe2O4@MnO2 NSAs electrode achieved a highly enhanced areal capacitance of 3.59 F cm−2 at a current density of 2 mA cm−2. An aqueous asymmetric supercapacitor (ASC) device was assembled using CoFe2O4@MnO2 NSAs as its positive electrode and the activated carbon (AC) as its negative electrode. The as-assembled ASC device can be operated in a voltage region of 1.6 V and exhibited a specific capacitance of 103.86 F g−1 at 5 mA cm−2. Its energy density and power density were as high as 37 W h kg−1 at 470 W kg−1 and 4800 W kg−1 at 15.3 W h kg−1, respectively. These remarkable electrochemical properties suggested that such CoFe2O4@MnO2 NSAs nanoarchitecture could be one of a potential candidates for the next generation energy storage devices with higher energy density delivery.