Preparation Of An Modified Rice Husk Carbon Materials And The Influence Of The Electrochemical Performance Of Supercapacitor

The supercapacitor is a new energy storage element with the characteristics of batteries and ordinary capacitor.However,the energy density of supercapacitor is much lower than traditional battery.According to the equationE?28?1/2CU²,there are two effective ways to improve the energy density of supercapacitors.One is to improve the working voltage and the other is to increase the specific capacitance of the electrode material.Based on above analysis,the work focuses on the research and development of high specific capacitance carbon materials and carbon/metallic oxide composites.The following three aspects have been studied in the thesis.1.Owing to the advantages of low cost and friendly environment,activated carbons from biomass materials have gained much more attention for being used as the materials for EDLCs.In this paper,rice husk,a kind of agricultural waste from grain,is applied to prepare activated carbons by carbonization and activation with ZnCl₂,and rice husk carbon are used as electrode material for supercapacitor.The pore structure,morphology and chemistry structural of carbons are characterized by using scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray diffraction?XRD?and the results of N₂ adsorption-desorption isotherms indicate the specific surface area of rice husk activated carbon ranging from 527 m²/g to 980 m²/g as the mass ratio of zinc chloride and activated carbon increased from 1:1 to 5:1.In SEM,it can be observed that there exist a large number of mesoporous with a size of about 50 nm.From the spectrum of XRD,with the rising proportion of zinc chloride activation agent,graphite crystallite formed gradually,when the proportion is 4:1,the maximum graphite contents.In a three-electrode,a high specific capacitance of 165 F·g^-11 was observed at the current density of 1 A·g^-11 and the cyclic voltammetry curve was closed to the rectangle,which suggests an ideal electrochemical property.The energy density of supercapacitor electrodes prepared from RC-4 has a good stability which is maintained 86.7%after2000 charge/discharge cycles.The excellent electrochemical performance of the rice husk activated carbon is attributed to the appropriate pore structure and the internal rich microcrystalline graphite.2.In order to improve the electrochemical behavior of carbon materials,carbon materials is modified by lead.The sample of rice husk carbon?RC?was prepared by ZnCl₂-activation.And on this basis,the rice husk-based activated carbon doped with lead?L-RC?was obtained by combination of impregnation and calcination method.The porosity of RC and L-RC was characterized by nitrogen adsorption isotherms at 77 K,XRD and TEM measurement.After doping lead,the specific surface area decreases from 988 m²/g to 847 m²/g.In TEM,two different morphologies of lead element is well-distributed in rice husk actived carbon.One was in the form of lead oxide particle distribution around 15 nm in husk activated carbon,another part was distributed on the surface of rice husk activated carbon by quantum dots which is similar to the film structure of the lead element on the surface of the rice husk activated carbon.To investigate the electrochemical properties of L-RC,L-RC was tested as an electrode in an aqueous electrolyte of 1.28 g·mL^-1H₂SO₄.Compared to RC,L-RC exhibits significant improvement in terms of specific capacitance up to 305F·g^-1 at the current density of 1 A·g^-1.More interesting,the potential window is distinctly expanded 47%at a voltagescan rate of 10 mV·s^-1.The excellent electrochemical performance of the composite electrode was owing to the synergistic effect of both the activated carbon porous structure and the Pb element modification of rice husk activated carbon.3.Rice husk actived carbon modified by nitric acid creates oxygen-containing functional groups,which may provide anchor sites between the activated carbon and manganese dioxide?MnO₂?nanorods.MnO₂ nanorods were synthesized in the surface of activated carbon in fluid phase method.The morphology and structure of MnO₂/oxidized activated carbon?MnO₂-n/RC?were characterized by SEM and XRD.The results indicated that the MnO₂ nanorods in the composite were dispersed homogeneously on the nitric acid treated activated carbon surface with the width of50-60 nm.The specific capacitance of the MnO₂-2/RC composite formed with a mass ratio of MnO₂:RC with 2:1 showed the best electrochemical performance among the MnO₂-2/RC composite electrodes fabricated,the specific capacitance of the MnO₂-2/RC composite was 256.9 F·g^-1 in 2 mol·L^-1 Na₂SO₄ solution with a scan rate of 10 mV·s^-1.The composite electrode exhibited a loss of less than 20%in the specific capacitance after 2000 cycles,indicating good electrochemical stability.Owing to the synergistic effect of both the activated carbon porous structure and the pseudo-Faradaic reactions of the MnO₂ nanorods,the composite electrode performance excellent in electrochemical test.