An electrochemical exploration of hollow NiCo2O4 submicrospheres and its capacitive performances

Mesoporous NiCo2O4 hollow submicrospheres have been prepared through a facile and scalable soft template method utilizing a reflux route. The as-obtained mesoporous NiCo2O4 hollow submicrosphere electrode exhibits high specific capacitance of 987 F g(-1) at 1 A g(-1), superior capacity retention rate of 79.4 and 62.8% at 20 and 50 A g(-1), and remarkable cycling stability with almost no capacity loss at 5 A g(-1) over 5000 cycles. The superior electrochemical performances can be attributed to the unique mesoporous hollow structure with a large specific surface area (189.7 m(2) g(-1)) and superior pore-size distribution (3-5 nm). To further demonstrate its practical application, an asymmetric supercapacitor based on the mesoporous NiCo2O4 hollow submicrospheres as the positive electrode and activated carbon as the negative electrode is fabricated, which manifests high energy density of 27.2 Wh kg(-1) at the power density of 102 W kg(-1) or high power density of 8.16 kW kg(-1) at the energy density of 10.9 Wh kg(-1) and exceptional long-term cycling stability with 108.1% of the initial capacity retention at 3 A g(-1) over 10000 cycles. These impressive results render this NiCo2O4 hollow submicrospheres promising as one of the most attractive candidates for supercapacitors in practical applications. (C) 2015 Elsevier B.V. All rights reserved.