Hydrogen sorption properties of arc generated single-wall carbon nanotubes

Abstract

Studies regarding the possible use of single-wall carbon nanotubes (SWNTs) as a hydrogen storage material have attracted considerable interest in the last years. However, a large discrepancy in the results reported by different scientific groups is evident, and many of the recent studies do not confirm superior H2 adsorbing properties of SWNTs compared to more conventional carbon materials. Nevertheless, synthesis of SWNTs with different diameters and a development of techniques for purification and opening can contribute to the improvement of their H storage efficiency. In the present work, SWNTs were produced by arc evaporation of graphite electrodes with the use of two different catalysts, 3Co/Ni and YNi2. A three-step purification technique allowed enrichment of the samples with SWNTs reaching a level of purity exceeding 75%. In carefully performed sorption experiments on purified samples, reversible storage capacity of 2.4 wt.% H2 was observed at cryogenic temperatures below −150°C and at a pressure of 25 bar H2. Thermal desorption studies revealed the presence of weakly bonded physisorbed hydrogen (90%) and chemically bonded hydrogen (10%). The latter was released at temperatures above 450°C as a result of breaking of the covalent C–H bonds.