Urchin-like porous NiCo2O4 nanostructure: Morphology control using porous reduced graphene oxide nanosheets for high performance flexible transparent energy storage devices

In this work, the incorporation of porous reduced graphene oxide (RGO) as support for nickel cobaltite and its strong influence on a structural directing agent is studied. It was found in experimental results that the RGO nanosheets, especially the porous carbon network would be favorable to serve as the nucleation sites for the growth of NiCo2O4 nanorods. Importantly, the epoxy groups present in the porous RGO attract an aggregated NiCo2O4 nanoparticle to form aggregated nanorod-like morphology through dangling bonds. The specific capacity of the NiCo2O4/RGO hybrid (606.6 C g-1 at 1 A g-1) is two times superior than that of NiCo2O4 (282.6 C g-1) and the high-rate performance for NiCo2O4/RGO hybrid is 3.5 times better than that of NiCo2O4. An asymmetric supercapacitor constructed with NiCo2O4/RGO (positive electrode) and activate carbon (negative electrode) delivered a maximum energy density of 49.6 W h kg-1 and long cycle life. In addition, a flexible transparent supercapacitor device assembled with the NiCo2O4/RGO hybrid electrode achieved a large areal capacity (5.27 mC cm-2 at 75.5% transparency), high energy density (1.17 mW h cm-2) and outstanding mechanical flexibility.