Role of N doping on the electrochemical performances of ZnCo2O4 quantum dots/reduced graphene oxide composite nanosheets

It's demonstrated that carbon nanostructures, such as graphene, coupled with quantum dots (QDs) of active materials, can usually exhibit greatly enhanced electrochemical performances. However, the depositions of QDs on graphene nanosheets are often affected by the change in spatial electric field distribution induced by the formed defects. In this work, the effects of N doping on the deposition of ZnCo2O4 QDs on reduced graphene oxide nanosheets and on the electrochemical properties of the resultant electrodes have been explored in details. Results showed that ZnCo2O4 QDs decorated on nitrogen-doped graphene (NG) are around 4.3 +/- 0.9 nm in diameters and well-dispersed on the surface. This morphology is mainly due to the introduced defect sites by N doping, which can not only induce the nucleation of ZnCo2O4 QDs, but also limit their excessive growth to some extent. On the other hand, the doped N atoms could further supply a large amount of electroactive sites for energy storage. Series of tests indicated that the as obtained ZnCo2O4/NG hybrids as a battery-type electrode for hybrid supercapacitor can deliver high specific capacity (301.8 C g(-1) at 1 A g(-1)), excellent rate capability (84.5% remaining at 30 A g(-1)), as well as outstanding cycle performance (89.1% after 5000 cycles). Furthermore, the assembled ZnCo2O4/NG//activated carbon hybrid devices can output their maximum energy density of 28.3 Wh kg(-1) at 0.5 kW kg(-1) and retain 53.4% at high power density of 9.9 kW kg(-1). (C) 2017 Elsevier B.V. All rights reserved.