Preparation Of Grapnene/Biocarbon Composites And Their Electrochemical Performances

Electrochemical capacitor (EC), as a new energy storage device with long working lifeand high power density, has potential applications in the fields of electric vehicle and mobile,etc. Recently, the study on EC is mainly focused on the properties of its electrode materials. Inthis paper, biocarbons were prepared from rice husk with NaOH pretreatment, activated byH3PO4, pre-oxidized and pre-carbonized at200oC. Biocarbons were characterized by N2adsorption technique, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanelectron microscopy (SEM), transmission electron microscopy(TEM). To improve theelectrochemical properties of biocarbon, graphene oxide was added to make graphene/carbonmicrospheres (GO/CMS) composites. Meanwhile, the graphene/biocarbons composites wereprepared according to the preparation process of GO/CMS. The electrochemical performancewas evaluated by charge-discharge at constant current, cyclic voltammograms (CVs) andelectrochemical impedance spectrum (EIS). The main conclusions are as follow.NaOH pretreatment on rice husk at high temperature can increase the total pore volumeand specific surface area of obtained biocarbons. Both the total pore volume and specificsurface area of biocarbon go through a maximum with the increase of H3PO4/rice husk ratio.The specific capacitance of electrodes shows the same trend as the total volume and specificsurface area. The total volume and specific surface area also increase with the increasingpre-oxidation temperature. The optimum performance of biocarbons is obtained when thepre-oxidation temperature is200oC, and H3PO4/rice husk ratio is2:1from rice husk withNaOH pretreatment. The total volume and specific surface area reach1.30cm3.g-1and2009m2.g-1, and the percentage of mesoporous and macroporous volume to total volume is91.9%.The corresponding electrode exhibites good electrochemical performance, and its specificcapacitance is175.6F.g-1at50mA.g-1. The total volume of activated carbon microspheres (ACMSs) goes through a maximumwith the increasing ratio of H3PO4/starch. The total volume of GO/ACMS goes through amaximum with the increasing composited temperature and composited time. The specificcapacitance of ACMSs has the same change trend with the pore volume. The effect ofgraphene oxide concentration on the pore volume is negligible. The optimum performance isobtained when composited temperature is160oC, composited time is6h, and graphene oxideconcentration is1mg.mL-1while H3PO4/starch ratio is2:1. The corresponding electrode hasbetter electrochemical performance. The electrochemical performance of GO/ACMS has beenimproved greatly. The specific capacitance of GO/ACMS is286.1F.g-1, much higher than thatof ACMS.The introduction of graphene does not increase the electrochemical performance ofbiocarbon from rice husk. The specific capacitance of graphene/biocarbon from rice huskequals to the series specific capacitance of biocarbon electrode from rice husk andgraphene/ACMS electrode.