Carbon Xerogel Preparation And Its Electrochemical Performance In Ionic Liquid

Supercapacitor, as a new energy storage device, is characterized by high power and long-life. However, the energy density of supercapacitor is still low. It is efficient to obtain maximum energy density by increasing electrode capacitance and widening maximum operating voltage. The use of ionic liquid electrolyte is one of the promising strategies to widen the electrochemical stability windows of supercapacitor. Carbon xerogels with high and tunable mesoporosity as the electrode seem to be suitable for IL-based supercapacitors because relatively large ionic sizes and high viscosity of IL need more mesoporosity to move ions easily. In this work, a series of carbon xerogels with different pore structures were prepared using different methods, and its the electrochemical performance in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte by cyclic voltammetry (CV) and AC impedance was investigated, and to explore the relation between double layer capacitance and porous structure of carbon xerogels. The main work is shown as follows:A series of carbon xerogels with different ratio of micropore surface to mesopore surface area were prepared with resorcinol (R) and formaldehyde (F) by two methods. One is synthesized using silica sol as the template with different mass percentage of SiO2 to the total mass of R and F. Another method is synthesized with different molar ratio of R to Na2CO3. The capacitance was determined by CV method. The results show that the ratio of capacitance to mesopore surface areas has a linear relation with the ratio of micropore to mesopore surface area in the range of micropore/mesopore surface ratio from 0.2 to 2.0. The capacitance per unit micropore surface area and the capacitance per unit mesopore surface area were obtained from the linear relation.A series of carbon xerogels with different pore size distribution are prepared using R and F as carbon precursor, adding cetyltrimethylamonium bromide (cationic surfactant), selecting water or ethanol solution as solvent. The microstructure of carbon xerogels was studied by IR, SEM and nitrogen adsorption. The electrochemical behavior was characterized by CV and AC impedance. It was found that the mesopore material with a BET surface area of 549 cm2 g"1 shows better electrochemical performance than the micropore material with a BET surface area of 515 cm2 g-1. And the role of surfactant in the process is discussed.