Single-Walled Carbon Nanotubes with High Hydrogen Capacity

Abstract

SWCNTs (Single-Walled Carbon Nanotubes) were fabricated by means of a torch arc method and a conventional arc method with graphite rods containing 4.2mol% of Ni and 1.0mol% of Y employed as anodes.A necessary condition for SWCNTs to sorb significant amounts of hydrogen would be high G/D ratios, that is, the intensity ratios of Raman G band peaks to D band peaks must exceed 10. When this condition was satisfied, hydrogen capacities of most SWCNTs increased with specific surface areas. However, such SWCNTs that did not contain sufficient amounts of Y on surfaces tended to show lower capacities than expected from specific surface areas.An arbitrary lot of SWCNTs that satisfied the high G/D ratio condition sorbed 6.6wt% of hydrogen at 295K under 3.1MPa, while their hydrogen capacity under 100kPa was as less as 0.12wt%.Novel blue shifts of G band and breathing mode peaks were observed by in situ Raman spectrometry under hydrogen. These shifts were completely reversible and would be practically used to detect hydrogen sorption on SWCNTs. The intensity ratios of breathing mode peaks to G band also varied with hydrogen pressure probably owing to hydrogen sorption.