Synthesis of hollow NiCo2O4 nanospheres with large specific surface area for asymmetric supercapacitors.

Hollow micro-/nanostructured electrode materials with high active surface area are highly desirable for achieving outstanding electrochemical properties. Herein, we report the successful synthesis of hierarchical hollow NiCo2O4 nanospheres with high surface area as electrode materials for supercapacitors. Electrochemical measurements prove that such electrode materials exhibit excellent electrochemical behavior with a specific capacitance reaching 1229 F/g at 1 A/g, remarkable rate performance (∼83.6% retention from 1 to 25 A/g) and good cycling performance (86.3% after 3000 cycles). Furthermore, the asymmetric supercapacitor is fabricated with hollow NiCo2O4 nanospheres electrode and activated carbon (AC) electrode as the positive and negative, respectively. This device exhibits a maximum energy density of 21.5 W h/kg, excellent cycling performance and coulombic efficiency. The results show that hollow NiCo2O4 nanosphere electrode is a promising electrode material for the future application in high performance supercapacitors.