Hydrogen is a promising alternative to fossil fuels, but the main problem is to encourage its development by finding efficient means of storing it. An international team, co-ordinated by CSIC researcher Javier Bermejo, assigned to the University of the Basque Country (UPV/EHU), has shown the efficacy of carbon nanohorns as storage units for H2, opening thus ways to possible practical applications. The prestigious Physical Review of Letters journal, one of the most important in the field of physics, has published the article on this research (Phys. Rev. Lett. 98, 215503 (2007), June).
Although hydrogen provides a density of energy lower than that of petroleum derivatives, it does provide sufficient energy to propel a wide range of passenger vehicles and, in fact, hydrogen-driven prototype vehicles have been built since 1966 (GM Electrovan). Given the well-known increasing scarcity of petroleum oil, the employment of hydrogen provides a second advantage: its use as an energy source does not produce greenhouse gases, but water vapour.
The main problem currently in encouraging the use of hydrogen as a source of energy is finding efficacious means for its storage. In some cases, the costs arising from the manufacture of safe containers of compressed gas or for the handling of a cryogenic liquid such as liquid hydrogen limits the employment of this technology in practice. As an alternative to hydrogen storage in the mentioned gas or liquid phases, adsorbents are sought to which hydrogen is fixed without it reacting chemically and which will enable the storage of up to 6 kg of H2 within a reasonable refuelling time (about 3 minutes).
The research carried out by the international team co-ordinated by Javier Bermejo analysed the possibilities, as an adsorbent, of a new, dhalia-like carbonaceous structure, observed for the first time in 1999. This structure is made up of nanotubular aggregates with a closed horn form at the end. The dimensions of the whole are in the order of 0.1 micrometers. This flower-like structure has a very high specific surface area, enabling the adsorption of a significant quantity of gas.
In concrete, the research focused on measuring the mobility of the gas at various temperatures and certain details about the interaction between the H2 and the nanohorns, employing neutron spectroscopy to this end and undertaken at the ISIS spalation neutron source in the United Kingdom. The most remarkable result was being able to determine that hydrogen binds to the nanohorn with a firmness hitherto unknown with other nanostructures and, nevertheless, can still be freed for its use under controlled conditions. Moreover, the union of the carbonaceous structure is stable at a temperature to at least 80 kelvin (-193.15ºC), which opens new possibilities for its employment in practical applications.