Study On The Synthesis And Properties Of Supercapacitors Based On 3D Structured Graphene Electrodes

Graphene-based supercapacitors demonstrate high potential for replacing the traditional energy storage system because of their high specific power capability, fast charge/discharge processes and long cycle life. However, the intrinsic properties and the theoretical limitation in specific capacitance of pure graphene-based electrodes restrict their practical applications in high performance areas. In this paper, 3D hybrid structured electrodes, graphene surface modification and the combination with faraday capacitor electrode materials were introduced into vertically oriented few-layer graphene(VFG) to investigate the probable method for improving the performance of graphene-based supercapacitors.The preparation technology of the 3D VFG-nanocup hybrid structured electrodes was proposed using VFG grown in situ on alveolate Pt film with high-density nanocups, which was called “one-step” method. The nanocup structure was generated by pre thermal annealing at 800℃. This unique structured material could achieve a larger specific surface area through increasing the density of as-grown VFG, which nearly doubled that of the electrode purely based on planar substrate. Moreover, the 3D hybrid structure could optimize the transmission and storage of charges, which contributed to the enhancement of the electrochemistry performance. The research indicated that the 3D VFG-nanocup hybrid structured electrodes exhibited high specific capacitance(up to 1052 μF/cm2) and power density(4.88 × 10-4 Wh/m2), which tripled that of VFG-plane.The morphology and surface status of as-grown VFG were optimized through the regulation of the gas flow rate ratios to achieve improved wettability, and the relationship between them was studied. The results suggested that VFG with suitable density and morphology could ensure the balance of perfect wettability and high electrochemistry performance. Besides, relatively high level of defects in the outside wall of VFG might lead to better wettability. Based on this theory, bilateral rotary etching with Ar plasma was conducted to the as-grown VFG as surface treatment, which introduced intrinsic defects to the surface of VFG and improved the smoothness of the top edges, thus achieved better wettability. The results indicated that the contact angle decreased dramatically after bilateral rotary etching treatment, and the specific capacitance rose up to more than 1000 μF/cm2.In order to combine the advantages of the electric double-layer capacitors(EDLCs) and pseudocapacitors to obtain high performance hybrid electrodes, electrochemical deposition was used to fabricate Mn O2 with distinct morphologies on VFG. The results suggested that the Mn O2/VFG hybrid electrode with a needle-like structure could take advantage of both Mn O2 and VFG in the energy storage, electrical properties and morphology. Therefore, it exhibited higher performance with the specific capacitance up to 11833 μF/cm2, which was twice higher than that of the Mn O2/VFG hybrid electrodes with a flocculent-like structure and nearly ten times higher when compared with the original untreated samples.