Monodisperse nickel/cobalt oxide composite hollow spheres with mesoporous shell for hybrid supercapacitor: A facile fabrication and excellent electrochemical performance

Abstract A flow atomization method that is suitable for commercial preparation was employed to fabricate the monodisperse nickel/cobalt oxide composite (NCOC) hollow spheres by means of silica as the template. The prepared hollow spheres present a spinel NCOC and mesoporous shell structure with a specific surface area of 343 m 2 g -1 and a mean pore size of 2.5 nm. The monodisperse NCOC hollow-sphere electrode exhibits a maximum specific capacity of 175 mAh g −1 at 1 A g −1 and delivers a 92.5% capacity retention after 50,000 cycles, suggesting superior long cycle stability. A hybrid supercapacitor with a total mass of 5 mg cm -2 has been assembled using monodisperse NCOC hollow spheres as positive electrode and nitrogen-doped mesoporous carbon derived from the pyrolysis of polypyrrole as negative electrode material. This device can be operated in a potential region of 0–1.5 V, displays a high energy density of 38.5 Wh kg −1 at a power density of 750.8 W kg −1 , and remains at 22.9 Wh kg −1 at 21.4 kW kg −1 . The long-term cyclic life up to 20,000 cycles with 9.5% capacitance loss also meets the growing demand for mass-produced energy-related devices.