Graphene quantum dots encapsulated tremella-like NiCo2O4 for advanced asymmetric supercapacitors

A tremella-like NiCo2O4@graphene quantum dots (GQDs) composite is prepared where the tremella-like NiCo2O4 is homogeneously encapsulated by GQDs. Herein, the GQDs based on p-conjugated core with abundant edge sites, make NiCo2O4 favorable for advanced electric energy storage (EES). In terms of the synergistic effect between the conductive GQDs and tremella-like NiCo2O4, the as prepared NiCo2O4@GQDs composite exhibits an excellent specific capacitance of 1242 F g(-1) at 30 A g(-1) in 2.0M KOH electrolytes, much higher than that of pristine NiCo2O4 (790 F g(-1) at 30 A g(-1)). Also, it manifests outstanding cycle stability (99% capacitance retention after 4000 cycles). Furthermore, an asymmetric supercapacitor (ASC) is assembled by pairing NiCo2O4@GQDs composite as positive electrode and activated carbon (AC) as negative electrode (NiCo2O4@GQDs//AC), and its specific energy density is as high as 38 Wh kg(-1) at a power density of 800 W kg(-1). (c) 2019 Elsevier Ltd. All rights reserved.