3D V2O5/graphene foam composite for electrochemical supercapacitor applications

N.M. Ndiaye, B.D. Ngom, N. Manyala
University of Pretoria,
South Africa

Keywords: graphene, vanadium pentoxide, asymmetric, supercapacitors

Summary:

Recently, graphene-based materials can be considered as an ideal candidate for energy storage due to their outstanding properties including a high theoretical specific surface area, good electrical conductivity and thermal stability [1]. The combination of metal oxide and graphene can improve the electrochemical performance of a composite electrode due to the high conductivity of the graphene and the hight specific capacity of the metal oxide [2]. This is also an efficient strategy for supercapacitors. Li et al, reported the synthesis of Rodlike V2O5 nanocrystals on reduced graphene oxide by solvothermal method and an annealing process for supercapacitors. The V2O5/reduced graphene oxide nanocomposites improved the performance electrochemical of V2O5 [3]. Recently, Hoa et al, reported in situ growth of flower-like V2O5 arrays on graphene@nickel foam as high-performance electrode for supercapacitors applications. They deposited V2O5 on the NF/G electrode by hydrothermal method to synthesis the NF/G/V2O5 composite. The NF/G/V2O5 composite exhibited an excellent performance electrochemical for supercapacitors. [4]. This work reports a new approach to synthesis a 3D V2O5/graphene foam composite by hydrothermal method and a freeze-drying process. The graphene foam was prepared by natural method prepared by chemical vapor deposition (CVD) [5]. The time-dependent evolution of orthorhombic 3D V2O5 ranging from 5 h to 25 h and its electrochemical performance for supercapacitor applications were also synthesized. The 3D V2O5 synthesized at 20h (denoted 3D V2O5-20h) was found to be optimal growth time for orthorhombic vanadium pentoxide V2O5 nanosheets due to the highest current response, highest discharge time which also shows its better charge storage capability. To enhance the electrochemical performance of as-prepared 3D V2O5, different masses of graphene foam (50-200 mg) were added into the 3D V2O5. The V2O5-20 h with 150mg GF mass loading composite (denoted 3D V2O5/150mg-GF) showed highest current response and a specific capacity than the others composites. This excellent performance of V2O5/150mg-GF composite could be attributed to the good quantity of graphene foam successfully introduced between the V2O5 nanosheets which ensure an excellent ion and electron transport. The electrochemical performance of as-prepared 3D V2O5/150mg GF composite was also evaluated in two-electrode asymmetric cell device where 3D V2O5/150mg GF composite electrode was a positive electrode and PANI grafted with iron (C-FP) as negative electrode. The V2O5/GF//C-FP asymmetric supercapacitor performed at a high cell voltage of 1.6 V in 6 M KOH electrolyte. The asymmetric supercapacitor exhibited a specific capacity of 41 mA h g-1 and an energy density of 39 W h kg−1 for a corresponding power density of 947 kW kg−1 at a current density of 1 A g-1. The supercapacitor also showed an excellent stability that included a good coulombic efficiency of 99% up to 10000 cycles