Construction of 3D hierarchical porous NiCo2O4/graphene hydrogel/Ni foam electrode for high-performance supercapacitor

We report the utilization of three-dimensional graphene hydrogel embedded with Ni foam as a high-surface-area support and one-step electrodeposition of NiCo2O4 nanoflakes on the support for use as supercapacitor electrode, with dramatic improvements in the accessible electrode surface area and loading amount of pseudocapacitive material being achieved. The constructed NiCo2O4/graphene hydrogel/Ni foam ternary composite electrode possesses a hierarchical open-porous structure scaling from macropores to mesopores, which synergistically provides continuous electron path, commodious ion channel and large electrolyte-electrode interface, thus benefiting the improvement of overall energy storage properties of the supercapacitor electrode. Accordingly, the as-prepared electrode exhibits exceptional high capacitance of 3.84 F cm−2 at 2 mA cm−2 and excellent rate capability with 71.6% retention at 50 mA cm−2. Moreover, the assembled asymmetric supercapacitor using NiCo2O4/graphene hydrogel/Ni foam as positive electrode and graphene hydrogel/Ni foam as negative electrode renders a maximum energy density and power density of 65 Wh kg−1 and 18.9 kW kg−1, respectively, and a striking cycling stability with 92% capacitance retention after 5000 charge-discharge cycles. These desirable results suggest a great potential of hierarchical porous NiCo2O4/graphene hydrogel/Ni foam electrode for the high-performance supercapacitor application.