First principles investigations of complex hydrides AMH4 and A3MH6 (A = Li, Na, K, M = B, Al, Ga) as hydrogen storage systems

Using ab initio computations the stability of complex hydrides related to the alanates NaAlH4 and Na3AlH6 is investigated. We find that Li substitution for Na reduces the hydrogen affinity of these materials, while K increases it. Substitution on the Al site by B or Ga markedly reduces the stability of the intermediate Na3AlH6 compound. The results indicate that both the overall stability, and as a consequence the hydriding temperatures and rehydriding pressures, can be tailored by combined substitution on the Na and Al site of the complex hydride NaAlH4. This may lead to a larger amount of hydrogen being released in a narrower range of temperature and pressure. (C) 2003 Elsevier B.V All rights reserved.