Ali A. Ensafi, Seyyed Ebrahim Moosavifard, B. Rezaei and Saeid Kamari Kaverlavani

Engineering complex hollow nanostructures of mixed transition metal oxides is necessary to respond to the
increasing progress of modern electronics. As an interesting spinel mixed metal oxide, for the first time, we
engineer onion-like nanoporous CuCo2O4 hollow spheres (ON-CCO) with a high surface area of 63 m2 g
1
and more than six thin shells. It is derived from bimetal–organic frameworks for high-performance
asymmetric supercapacitors. The ON-CCO electrode exhibits excellent electrochemical performance
including high reversibility, fast kinetics, low internal resistance, and an ultrahigh specific capacitance of
1700 F g
1 with an excellent rate capability of 68% after increasing the current density by a factor of 50.
Furthermore, the as-prepared ON-CCO//AC asymmetric supercapacitor delivers significant performance
consisting of excellent cycle life (only 8.8% loss after 10 000 charge/discharge cycles), a maximum
energy density of 48.75 W h kg
1 and a power density of up to 37.5 kW kg
1, which is superior to
conventional supercapacitors and can compete with Ni–MH batteries. This remarkable performance
attributed to the unique structural properties of the ON-CCO electrode holds great promise for the
next-generation of high-performance portable electronics and electric vehicles.