Study On Preparation And Electrochemical Performance Of Graphene/Manganese Dioxide Composites

The composite electro-deposition method was used to prepare graphene/nickel?G/Ni?composite coatings on substrates of nickel foam,and then manganese dioxide?MnO₂?was prepared by anode electro-deposition to obtain MnO₂/G/Ni composites materials applied on supercapacitors.The surface morphology of G/Ni composite coating,the distribution of graphene,and the morphology of MnO₂ were characterized by scanning electron microscopy?FSEM?,Raman spectroscopy,and X-ray photoelectron spectroscopy?XPS?.The effect on electrochemical performance by different states of G/Ni composite coatings and different morphology of MnO₂ were measured by cycle voltammetry?CV?,galvanostatic charge-discharge?GCD?and electrochemical impedance spectra?EIS?.The main results of this research are as follows:The G/Ni composite interlayer was obtained by composite electrodeposition.With the same charge in the electric field,the distribution of graphene in the G/Ni composite coating was more and more uneven with the increase of the electric current;The different morphology of MnO₂ was deposited on different G/Ni composite interlayer at 20 mA.MnO₂ with different morphologies?i.e.,uniform linear,small spherical and Large ball?can be fabricated on the different G/Ni composite interlayer deposited by 0.04 A,0.08 A and 0.12 A;Compared with pure MnO₂ electrode,the specific capacity of Mn O₂ composite electrode with G/Ni composite interlayer greatly was improved.Under the condition of 20 mA constant current to obtain MnO₂,G/Ni was deposited on nickel foam with 0.04A,900s process.The specific capacity of the MnO₂/G/Ni nanocomposite electrode is 219.3 F·g^-1 at a scanning speed of 0.4 A·g^-1.When the scanning speed is increased to 6.4 A·g^-1,the specific capacity is reduced to115.2 F·g^-1,the capacity retention rate is 52.53%.Compared with the pure MnO₂electrode,the specific capacity of the composite electrode with the intermediate layer increased by 83.59%,and the capacity retention rate was also higher;with the G/Ni composite electro-deposition current Increasing,the weaker the effect on specific capacity of MnO₂/G/Ni nanocomposite electrodes,MnO₂ at 20 mA constant current deposition conditions,The specific capacity is 172.8 F·g^-1 at 0.4 A·g^-1 scanning speed with the deposition of G/Ni composite interlayer at 0.12 A.The deposition current of MnO₂ increases,the specific capacity increases,When the process of G/Ni composite interlayer is 0.04A,900s,the specific capacity reaches an extreme value when deposition current of Mn O₂ is 80 mA.The specific capacity of MnO₂/G/Ni nanocomposite electrode is 257.95 F·g^-1 at the scanning speed of 0.4 A·g^-1under the condition of 80 mA.When the scanning speed is increased to 6.4 A·g^-1,the specific capacity is reduced to 160F·g^-1,and the capacity retention rate is 62.03%.The specific capacity retention rate of the composite electrode is 97.37%after 2000 cycles,which is higher than that of pure MnO₂ electrodes is 90.78%.After the first composite deposition of MnO₂/G/Ni,the second composite deposition is continued.As the deposition quality increased,the specific capacitance of the composite electrode is reduced to 159.2 F·g^-1 at a scan rate of 0.4 A·g^-1.The specific capacity retention rate dropped to 32.82%at a high 6.4 A·g^-1 current scanning rate.