Microwave synthesis of three dimensional N-doped graphene self-supporting networks coated with Zinc/Nickel oxide nanocrystals for supercapacitor electrode applications

A hybrid of zinc/nickel oxide nanoparticles supported on nitrogen doped three-dimensional graphene networks (ZnO/NiO/3DNG) have been designed through a simple microwave process assisted tube furnace thermal treatment. Well dispersed coupled zinc/nickel oxides nanoparticles with sizes of 10–20 nm are homogeneously anchored on 3DNG hybrid structure. As electrode active material of supercapacitors, the ZnO/NiO/3DNG nanocomposites exhibits an ultrahigh specific capacitance of 1839.4 F g⁻¹ at a current density of l A g⁻¹ in 6.0 M KOH solution, the EIS analysis of the electrode after 6000th cycle at 10 A g⁻¹ remained about 93%, displayed that the fitting values of inner resistance and faradic charge transfer resistance of the electrode are low and electrode activity don’t change too much after cycling. Furthermore, the ZnO/NiO/3DNG composites exhibits the maximum energy density of 35.32 Wh kg⁻¹ with the power density 139.72 W kg⁻¹ at high current density of 10 A g⁻¹ in the two-electrode system. The outstanding performance originates from the flexible three dimensional N-doped unique structural, which play important roles in stabilizing ZnO and NiO.