Effect of chemical species in alkali agents on pore structure at activated carbon of rice husks

Abstract

To understand effect of chemical reactions of the activation process on pore structures, the activated carbon materials were fabricated by two types of chemical agent for the activation process from rice husk ashes. NaOH and Na₂CO₃ were used as a chemical agent. And their pore structure and hydrogen storage ability were estimated on temperature range from 77 to 298 K. The porous carbon activated by NaOH involved pores of 0.6, 1.1 and 1.5 nm diameter. The pore sizes in porous carbon activated by Na₂CO₃ were 0.6 and 1.5 nm in diameter. These results indicated that pore structures could be controlled by chemical agents on the activation. The hydrogen storage ability of the porous carbon material activated by NaOH was the same as that activated by Na₂CO₃ and the value was about 0.5 wt.% at 298 K. With a decrease in temperature, hydrogen storage ability was increased, and the difference of the maximum amount of stored hydrogen on these two porous carbon materials was made larger. The hydrogen storage ability at 77 K porous carbons activated by NaOH and Na₂CO₃ indicated 3.7 and that for Na₂CO₃ was 2.1 wt.%. From pore size distributions and temperature dependence, it was suggested that the size of pore for the hydrogen storage changed from 0.6 nm to both 0.6 and 1.1 nm with decreasing temperature.