Vashchynskyi V. Electrochemical and Sorption Properties of Activated Carbon Obtained from Plant Materials

The methods of obtaining high-porous carbon material are developed and tested, the mechanisms of influence of carbonization temperature, presence in activating reagents of structural-morphological, adsorption and electrochemical properties of porous carbon materials are analyzed. It is established that the carbonization temperature increase of plant materials results in the reduction of porosity of carbon. It is also shown that the morphology and specific surface of the synthesized material depend on the ratio C/KOH during chemical activation in the temperature range 850-920 °C. It is found that the optimal conditions for obtaining the porous carbon material with pore sizes of 2-6 nm and specific surface S = 1300-1600 m2/g is carbonization of plant material at temperatures between 250 and 350 °C and KOH chemical activation with different ratios of C/KOH in the temperature range 850-920 °C. It is determined that sorption properties of the porous carbon material are defined by set of thermal and chemical reactions of activation: with increase in processing temperature of carbon material the development of its porous structure slows down and, therefore, sorption properties of materials are reduced. The synthesized porous carbon materials was firstly used as an electrode material of electrochemical capacitors with aqueous solution of electrolyte (KOH) and maximum values of specific capacity of 190 F/g at an optimal correlation KOH/activated carbon = 1:1 are reached. It was found that increasing of the KOH percentage during chemical activation leads to a decrease of specific capacity of porous carbon material and an increase of internal resistance of electrochemical capacitors. It is proved that one of the major factors determining capacity properties of the studied electrochemical capacitors is the electrical conductivity of the electrolyte. For non-aqueous electrolytes (1M solution of tetraethylammoniu tetrafluoroborate in acetonitrile) maximum specific capacity of 65 F/g is obtained at an optimal correlation C/KOH = 1:2. For electrochemical system porous carbon material/KI specific capacity within the limits of 155- 75 F/g at a charging current of 50 mA is provided.