| With the improvement of our life, the demand for energy is increasing faster, and thenon-renewable resources are drying up, what’s more, the energy crisis will break outinevitably. The development and utilization of the new energy is an effective way to solve theenergy crisis and the energy storage plays an impotent role in this solution. As efficientenvironmental protection energy storage component, the supercapacitor is becoming a hotspot of research in recent years.The supercapacitor is an efficient energy storage element with high specific capacity andpower. The performance of supercapacitor depends on the electrode materials. We areinterested in developing electrode materials which have high-performances, environmentallyfriendly nature and low fabrication cost. However, most of the presented electrode materialshave many disadvantages such as high cost of production and poor performances. For thisreason, microwave-hydrothermal method was used to research the preparation of nano-MnO2which is as an electrode component in energy storage device. Besides, the characterizationand the capacitive performances of the samples were studied.Various morphologies (such as rose-like microflowers, hollow tubular and rodlike) ofMnO2have been successfully synthesized through microwave-hydrothermal processing usingKMnO4as raw material. The δ-MnO2with rose-like microflower particles composed of plateparticles morphology was prepared firstly. As holding time went on, the plate particles curledinto hollow tube and dropped from flowers globular particles. The MnO2continuedcrystallizing in the hollow tube and the tube became α-MnO2with rod with square sectionmorphology. The electrode was prepared by smearing the mash which was obtained bymixing MnO2powders, PEG4000as binder and carbon dust which was used as conductiveagent. Next, the capacitive performances of the electrode were tested. The results show thatthe value of specific capacitance is199.65F/g at a scan rate of5mV/s for the sample whichwas obtained at125℃for1h. But with the scan rate increasing, specific capacitance decaysquickly, the specific capacitance maitains only16%of the original value when the scan rateincreases to50mV/s. The specific capacitance of the one-dimensional tubular sample which was obtained at125℃for2h is163.99F/g at a scan rate of5mV/s. There is still45%of theoriginal specific capacitance at50mV/s.The composite electrode materials of activated carbon fiber cloth and nano-MnO2wereprepared by microwave-hydrothermal processing. Different morphologies of samples wereobtained at different temperatures, holding time and concentration of KMnO4. Theelectrochemical performances of different samples were tested. The results show that thesample whose morphology is similar to the lawn particles gathered into a thickness of about100~200nm loading layer is prepared at70℃for1h from0.005mol/L KMnO4and ACFC.The δ-MnO2is grass leaf-like and the thickness of the leaf is10nm with4.5mg/cm2in loading.The specific capacitance of the sample which was obtained at70℃for0.25h is57.08F/g at ascan rate of5mV/s, and the internal resistance of the sample is small.The graphene oxide was reduced by microwave irradiating on the solution containedurea. Graphene with high transparency and integrity was obtained by0.90g urea and0.25mg/ml GO at95℃for150min. The composites of GO and MnO2were prepared bymicrowave hydrothermal method. To prepare the electrode, the composites were used asactive materials, carbon nano-tubes were used as conductive additive and PEG4000was usedas binder, after they were mixed, coated them on the surface of the unordered carbon fiberpaper. The electrochemical properties of the electrode were tested by electrochemicalworkstation. The results show that the specific capacitance is up to281F/g at a scan rate of5mV/s. The specific capacitance decays with the increasing of scan rate. When the scan rate isup to50mV/s, the specific capacitance still maintains40.6%of the original value, and it is114F/g. |
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