Clarification of Gas Adsorption Properties of Carbon Nanotubes and Their Application to Hydrogen Storage

点击翻译按钮获取中文摘要

Gas adsorption properties of carbon soot containing single-wall carbon nanotubes (SWNTs) with different diameters and different concentrations were investigated by adsorption isotherms and thermal desorption mass spectrometry. Followings are the main achievement of the present study.1. Preparation of SWNTs with different diametersSWNTs were produced by carbon arc discharge in helium gas. Average diameter of SWNTs, ranging from 1.2 nm to 2.3 nm, was controlled by the concentration of sulfur additives. Yield of SWNTs in the raw product (soot) decreased from 20% to 1% with the increase of diameters.2. Isotherms of nitrogen and hydrogen measured by volumetric methodNitrogen and hydrogen isotherms of raw SWNT samples were measured in a pressure range from 0 to 400 Pa. The specific surface area of micropores changed from 90 to 53 m^2/g with the decrease of SWNT concentration in the raw soot, but the outer surface area did not change appreciably. The hydrogen uptake (0.56 to 0.50 wt%) seemingly depends on the micropore surface area, but the dependence was not prominent.3. Isotherm of hydrogen measured by gravimetric methodHydrogen isotherm of SWNTs with average diameter of 1.28 nm was measured at pressures less than 50 Torr. Hydrogen uptake at 77 K was 2.7 wt% for SWNTs with closed caps and 5 wt% for of SWNTs with broken caps. At room temperature, these values decreased to 0.3 wt% and 0.7 wt%, respectively.4. Thermal desorption mass spectrometryAfter exposing raw SWNT samples to hydrogen at 140K for 10 min, thermal desorption of hydrogen from the samples was measured at a rate of 4℃/min. A desorption peak was observed at 170 K. No desorption peak around 290 K, which was reported previously, was not observed.