Preparation Of Carbon-based Composite Materials And Their Electrochemical Energy-storage Properties

Supercapacitor is one kind of electrochemical energy-storage devices, which hasbeen rapidly developed over the past decades. Owing to their environment-amity,economical cost for their production, and fast, high current charging and dischargingproperties, supercapacitor has attracted ever-increasing interest and attention. Carbonmaterials are typical materials for electric double layer EDL supercapacitor, whichstores energy via charging its EDLs. Because of their abundant raw materials,economical price, large specific surface area, and controlled pore size, porous carbonmaterials have become, by far, one of the most commercialized materials forsupercapacitor. However, if carbon materials store energy only via EDL energy-storageprinciple, their specific capacitance is not high enough to meet the requirements ofsome practical applications, and this severely limits their wide applications. In order toimprove the electrochemical energy-storage properties of porous carbon-basedsupercapacitor, this thesis aims to enhance the specific capacitance of carbon materialsby taking advantage of different strategies, and the main contents are outlined asfollows:1. Taking advantage of the high surface area and high conductivity of grapheneoxide (GO), reduced graphene oxide (rGO) was used to modify nitrogen-containedcarbon materials and their electrochemical properties were examined. rGO-modified,Nitrogen-contained carbon materials, C-rGOx(x=0,0.05，and0.25, where x representthe mass amount in gram of GO added into the reaction system, were prepared byhydrothermally polymerized melamine (M) and formaldehyde (F) in GO aqueousdispersion, followed by pyrolyzing the MF resin in N2atmosphere. Scanning electronmicroscopy SEM, transmission electron microscopy TEM, nitrogen adsorption anddesorption were used to characterize the morphology and pore structure of the preparedcarbon materials. It is indicated that at the guidance of the large surface area and theabundant surface oxygenated groups (e.g. carbonyl, carboxyl, hydroxy, and epoxy ofGO, M and F polymerized around the GO surface and generated nano-flaky organicpolymer. This, following pyrolysis of the organic polymer, not only generated aconductive rGO layer on the surface of the obtained carbon materials, but alsoendowed them with highly proportional mesopores. Electrochemical experimentsindicated that C-rGO0.25demonstrated a capacitance of as high as202F·g-1at a current of1A·g-1in6mol·L-1KOH electrolyte, their conductivity were also greatly improved.Therefore, the as prepared rGO-modified, nitrogen-contained carbon materials havegreat potential to be used as high performance materials for electrochemicalsupercapacitor.2. Chemical stripping of disordered mesoporous carbon and in-situ reduction ofKMnO4to prepare MnO2-carbon nanocomposites with improved electrochemicalproperties. Disordered mesoporous carbon materials were prepared by polymerizingresorcinol and formaldehyde in the presence of poly(propyleneoxide)-block-poly(ethylene oxide)-block-poly(propylene oxide) triblock copolymer F127, followed by pyrolysis of the polymerized products. It is found that themesoporous carbon materials can be stripped into flower-like product, meanwhile theirsurface-bound KMnO4can be in-situ reduced into MnO2by the carbon. As a result,nanocomposites of MnO2and disordered mesoporous carbon materials were obtained.The MnO2-modified MnO2-C nanocomposites showed a capacitance of218.7F·g-1at acurrent of1A·g-1in2mol·L-1Li2SO4electrolyte. In contrast, the parent disorderedmesoporous carbon materials showed only a capacitance of34F·g-1measured underthe same conditions. These experimental results showed that the total capacitance ofthe MnO2-C nanocomposites contained both pseudocapacitance contributed by theMnO2and EDL capacitance contributed by the mesoporous carbon materials andshowed much better energy-storage properties. Therefore, MnO2modification is aneffective method to improve the capacitance of carbon materials.