Preparation of Carbon Aerogel and Research on Its Structure with Double-layer Capacitance Performance
|Title||Preparation of Carbon Aerogel and Research on Its Structure with Double-layer Capacitance Performance|
In this thesis, the carbon aerogels were prepared from the sol-gel polymerization of resorcinol and formaldehyde by employing Hexamethylenetetramine (HMTA) as both a catalyst and cross-linking reagent, ethanol were used as solvent, followed by ambient drying and carbonization. The effect of R/H ratio, R/S ratio, F/R ratio, polymerization temperature and carbonization heating rate on the carbonization yield coefficient, specific surface area and pore size distribution was studied, respectively. Base on these, the technologic methods of controlling structures and properties of these carbon aerogels were established. In addition, the activated carbon aerogels were prepared by using phosphoric acid as activating agent to adjust pore structure. The influences of phosphoric acid on pore size distribution and electrochemical capacitance were studied preliminary. All kinds of prepared carbon aerogels were used for electrode materials of EDLC, their charge-discharge performance, cyclic voltammetry and AC impedance in 30wt% KOH, 1mol/L LBC305 and DLC307 electrolyte were investigated. The relations between EDLC’s performances and specific surface area, pore structure of carbon aerogels were also discussed.Studies show that carbon aerogels preparation by different technology have an effect on their specific surface area and pore size distribution. HMTA works in sol-gel not noly as a basic catalyst but also as a cross-linking reagent. The crosslinked action can increased network density of the aerogel, raise framework strength, reduce capillary tension and decrease the network collapse by ambient drying.The specific surface area of carbon aerogels decreased with raising of R/H ratio, by controlling use of HMTA, the specific surface area will reach 685.9 m2/g. The pore size and mesoporous increase with raising of R/S ratio. The specific surface area raised at first then declined with increasing F/R ratio. The effect of mesoporous were obvious control by the polymerization temperature, when its lower there are more micropore, the mesoporous increase with the raising of polymerization temperature. The specific surface area decreased with raising of carbonization heating rate. Carbonization yield coefficient preparation by different technology are about 50%.The specific capacitance of carbon aerogels related with the distribution of specific surface area and pore size distribution. The highest specific capacitance of 176F/g in 30wt% KOH could be reached, at R/H ratio of 50, R/S of 0.1 g/ml, F/R ratio of 2.0, polymerization temperature of 80â„ƒ, carbonization temperature of 900â„ƒand carbonization heating rate of 2â„ƒ/min. The specific capacitance of carbon aerogels increases gradually with increasing of the specific surface area, but the relationship between them is not linear dependence, it concerned with the distribution of internal pore structure. The results showed that specific capacitance is not high when the rate of mesoporous too low or too high, only the microporous and mesoporous distribution reasonable of carbon aerogels show higher specific capacitance.The carbon aerogels which used as the electrode materials of EDLC have good electrochemical performances. The cyclic voltammetry curves are similar to rectangle and obviously symmetrical without the peak of Faraday. The AC impedance spectrums are composed of three following portions: half circular arc in the high frequency domain, bias of 45Â°in the middle frequency range and have an rake ratio straight line in the lowest frequency domain. The behavior of electrochemistry of the carbon aerogels correlate with its micro-structures, the suitable mesoporous will improve the migration rate of electrolyte ion in the carbon aerogels as electrode, to form double layer capacitors rapidly.Carbon aerogels used for electrode materials of EDLC have good charging and discharging performance and cycle properties. Not only slow charge-discharge in small current density with long time but also can charging and discharging rapid in big electricity with short time.The specific surface area, total pore volume and micropore volume of Carbon aerogels increase efficient with phosphoric acid as activating agent, but mesoporous volume and average pore size decreased. Increased microporous specific surface area contribute from collapse of mesoporous. The specific capacitance of activated carbon aerogels in the organic electrolyte increases significant after phosphoric acid activation, and the specific capacitance decrease a lot when in big current density. The type of organic electrolyte to the influence of specific capacitance of activated carbon aerogels are much fewer.
|Subject||Carbon aerogels, Electric double-layer capacitor, electrochemical performance, pore structure, preparation,|
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