The pore size distribution of CNT was measured by a gas adsorption analyzer (Micromeritics 3Flex). 0.011g of CNT powder was used as received without further treatment for the experiment. The nitrogen adsorption and desorption isotherms were measured at 77 K. The sample was degassed at 80℃ for 12 hours before the measurement. The CNT pore size distribution was calculated from nitrogen absorption data based on the NLDFT model.