Hydrogen storage in a CaH2/LiBH4 destabilized metal hydride system

A study was done to determine if the destabilized hydride system, CaH2/LiBH4, would be suitable for hydrogen storage. When several additives, TiCl3, V2O5, TiF3 and TiO2 were ball milled with the CaH2/LiBH4 mixture, TGA analysis showed that all of the mixtures released hydrogen in the 400-450 degrees C range with the desorption temperatures being in the order TiF3 < TiO2 <= TiCl3 < V2O5. Kinetic modeling measurements showed that the reaction is controlled by diffusion. An attempt was also made to lower the reaction temperature by using CaNi5H4 as a destabilizing agent instead of CaH2. TGA analysis showed that the CaNi5H4 had virtually the same effect on the reaction temperature as CaH2 and the added weight of the nickel in CaNi5H4 reduced the overall weight percentage of hydrogen released from the system. In a further attempt to reduce the reaction temperature, a ternary system consisting of CaH2, LiBH4 and LiNH2 was tested for hydrogen desorption. TGA analyses showed that the ternary system released all of its hydrogen at a temperature that was about 100 degrees C lower than the CaH2/LiBH4 mixture. However, attempts to do pressure composition isotherm analyses and temperature programmed desorption measurements showed that the release of hydrogen from the ternary mixture occurs irreversibly. It is likely that the reaction products are very stable thus, preventing the reverse reaction from occurring. (C) 2008 Elsevier B.V. All rights reserved.