An Asymmetric Supercapacitor with Mesoporous NiCo2O4 Nanorod/Graphene Composite and N-Doped Graphene Electrodes

In the present work, mesoporous NiCo2O4 nanorod/graphene oxide (NiCo2O4/GO) composite was prepared by a facile and cost-effective hydrothermal method and meanwhile, N-doped graphene (N-G) was fabricated also by a hydrothermal synthesis process. NiCo2O4/GO composite and N-G were used as positive and negative electrodes for the supercapacitor, respectively, which all displayed excellent electrochemical performances. The NiCo2O4/GO composite electrode exhibited a high specific capacitance of 709.7 F g−1 at a current density of 1 A g−1 and excellent rate capability as well as good cycling performance with 84.7% capacitance retention at 6 A g−1 after 3000 cycles. A high-voltage asymmetric supercapacitor (ASC) was successfully fabricated using NiCo2O4/GO composite and N-G as the positive and negative electrodes, respectively, in 1 M KOH aqueous electrolyte. The ASC delivered a high energy density of 34.4 Wh kg−1 at a power density of 800 W kg−1 and still maintained 28 Wh kg−1 at a power density of 8000 W kg−1. Furthermore, this ASC showed excellent cycling stability with 94.3% specific capacitance retained at 5 A g−1 after 5000 cycles. The impressive results can be ascribed to the positive synergistic effects of the two electrodes. Evidently, our work provides useful information for assembling high-performance supercapacitor devices.