Variously functionalised activated carbons for H2 storage

One of the main limitations for the development of hydrogen fuelled vehicles is the difficulty arising from its storage. The main requirements for an on-board storage device are light weight, small size, safety, high volumetric and gravimetric efficiency and quick loading and unloading [1]. Among the possibly suitable materials, some of which very exotic, activated carbons (ACs) fulfill many of these requirements. They have a very high specific surface area, from hundreds to thousands square meters, a microporous structure and sound interaction with H2. However, reported data limit to ca. 2 wt% of H2 [2] their storage capacity at room temperature, a value insufficient to fulfill the DoE objectives. The amount of stored H2 may be rather easily increased by proper functionalization, e.g. by treatment of the samples under reactive atmosphere or by doping the ACs with metals. In fact, the affinity of metallic nanoparticles for hydrogen and the spillover phenomenon appreciably improve the storage ability. We report on the storage capacity for H2 by high surface area metal doped and undoped AC (ca. 3000 m2/g) under cryogenic conditions (273K up to 100 bar and 77K up to 20 bar). In particular, we tested both noble (Pt, Pd, Rh) and non noble (Ni, Cu) metals as dopants at different loading (0.5 and 2 wt%), deposing them through conventional impregnation methodology and chemical vapor deposition technique. The best results, i.e. ca. 6 wt% H2 stored at 77K, 20 bar, have been achieved with 0.5 wt% Cu/AC. However, this represents only a slight improvement with respect to the results obtained with the undoped AC. The real advantage of metal doping becomes evident for the tests at 273K, where Ni or Cu doping brings about a 5-fold increase of the H2 amount stored at 100 bar. References [1] N. Texier-Mandoki, J. Dentzer, T. Piquero, S. Saadallah, P. David, C. Vix-Guterl, Carbon 42 (2004) 2744. [2] L. Schlapbach, A Zuttel, Nature, 414 (2001) 353.