Single-wall carbon nanotubes and hydrogen storage

Since shortly after their discovery, single-wall carbon nanotubes (SWCN) were proposed as a promising material for hydrogen storage. This was based mainly on the low atomic weight of carbon (12 a.u.) and to the large specific surface area of this material. In fact, the theoretical surface of a graphene sheet, considering both sides, is 2704 m2/g and this figure was not expected to change too much for single wall carbon nanotubes. By assuming that each graphite hexagon could adsorb a hydrogen molecule, it is easy to derive a theoretical weight capacity of 7.7%. Preliminary measurements on these materials were very promising and substantially confirmed such an order of magnitude. However, further experiments turned out much less optimistic. Today, carbon nanotubes are still considered a very interesting material for hydrogen storage technology and, even though it is achieved that their measured features do not match the original expectations, they are still studied for the intrinsic interest bound to their topology. In the following, we will review the main experimental techniques and results that were obtained in the study of SWCN samples oriented towards hydrogen storage applications.