Preparation And Performance Of Carbon Aerogels For Supercapacitors

The supercapacitor, also known as double-layer capacitor or ultracapacitor, differs froma regular capacitor and batteries in that it has a very high capacitance，quick charge/discharge rate and long circle lifetime，etc. A capacitor stores energy by means of a staticcharge as opposed to an electrochemical reaction. Applying a voltage differential on thepositive and negative plates charges the capacitor. Prepare electrode materials is one of thekey techniques for development of supercpacitors. The most common electrode material iscarbon materials such as carbon aerogels, activated carbon, activated darbon fiber andcarbonnanotubes, etc. Carbon aerogels（CAs） is an ideal supercapacitor electrode materialdue to their sufficient specific surface area, good conductivity and stable physicochemicalproperties. In this article，in order to improve carbon aerogels’ electrochemical performance,we prepared active carbon aerogels（ACAs） with high surface area by CO₂activationtechnology and modified carbon aerogels by nitrogen-doped, in addition, in order to predigestpreparation technology of carbon aerogels, we prepared carbon aerogels with P123-doped byconventional trying, and then their electrochemical performances were tested in6mol·L^-1KOH solution. The main conclusions and results are summarized as follows:1. Activation of the carbon aerogels with high surface area was prepared by CO₂activation technology for improve structure property of carbon aerogels. Characterized bynitrogen adsorption, CAs have a surface area of739m²·g^-1and improved primely afteractivation, then the ACAs was activated in CO₂at temperature of950℃for10hour have thehighest surface area of4068m²·g^-1. However, its’ specific capacitance lower than the ACAsactivated at950℃for8hour with surface area only3165m²·g^-1which is up to327F·g^-1,andindicate that the specific capacitances of carbon aerogels is not only depend on specificsurface area, but also determined by it’s ratio of mesopore volume and conductivity, etc.2. In order to improve specific capacitance of carbon material, instead of increasing thespecific surface area and adjusting poresize distribution, one could also utilizes foreign atomsor surface functionlization to achieve this aim. In this paper, nitrogen-doped carbonaerogels（NCAs） were synthesized from Melamine （M）, Resorcinol（R） and Formaldehyde （F）by sol-gel, supercritical drying and carbonization process. Meanwhile, their electrochemicalperformances of the NCAs were tested in6mol·L^-1KOH solution, and the results indicatedthat their electrochemical performances were greatly improved after N-doping with thehighest specific capacitance reaching176F·g^-1.3. Complex operation, high cost and dangerous were disadvantages of the supercriticaldrying, to avoid this process we prepared organic aerogel with surfactant P123doping by conventional drying, so whole shape and lesser shrinkage organic aerogels was successfullyprepared and then was pyrolyzed to carbon aerogels（PCAs）. CO₂activation technics areinvestigated to adjust pore structure of carbon aerogels（APCAs） prepared by conventionaldrying. Analysis shows that there is strong interaction between P123and RF, and P123wasdisappears after carbonization. Characterized by nitrogen adsorption, PCAs prepared byconventional drying have a surface area of572m²·g^-1, and the APCAs activated at950℃for4hour have the highest surface area of3544m²·g^-1. Besides, their electrochemicalperformances were tested in6mol·L^-1KOH solution, and the results indicated that thespecific capacitance of PCAs was153F·g^-1, and the APCAs activated at950℃for4hourhave the highest specific capacitance of261F·g^-1.