Facilely synthesized porous NiCo2O4 flowerlike nanostructure for high-rate supercapacitors

We have developed a facile and scalable method to grow porous NiCo2O4 nanostructure. The conductivity is measured by a linear sweep voltammetry, which indicates that the conductivity of the NiCo2O4 sample is at least two orders of magnitude higher than those of NiO and Co3O4 samples. The conductive NiCo2O4 hybrid electrode delivers an enhanced specific capacitance of 658 F g(-1) at 1 A g(-1) compared to NiO and Co3O4. Excellent rate capability, 78% specific capacitance retention for a 20-time current density increase and 77% specific capacitance retention for a 50-time scan rate rise, is achieved. The NiCo2O4 sample demonstrates ultralong cycling lifespan, no observable degradation is found for the total cycle numbers as high as 10000 cycles. Furthermore, the excellent capacitive performance of porous NiCo2O4 electrode is also evaluated by a two-electrode asymmetric supercapacitor device. The asymmetric supercapacitor device delivers a 64% rate property for the current density increase 20 times. Remarkably, the asymmetric supercapacitor device also shows ultrahigh long-term stability, 93.5% of specific capacitance can still be retained after 10,000 cycles cycling. These excellent capacitive performances indicate the as-fabricated porous NiCo2O4 flowerlike nanostructure a promising electrode materials for supercapacitors. (C) 2013 Elsevier B.V. All rights reserved.