Electronic and structural properties of sodium-aluminum hexahydride (Na3AlH6) formed during the decomposition reaction of sodium alanate (NaAlH4) and the effects of Ti catalyst were studied using super-cell approach and density-functional theory. The preferred site of Ti was determined by substituting it at both the Na and Al sites and comparing the respective formation energies. The least unfavorable site for Ti was found to be the Al site. To examine the role of Ti substitution on the desorption of H, the energy cost to remove a H atom from the vicinity of Ti was calculated and compared with that from the pure Na3AlH6. The improvement in dehydrogenation of Na3AlH6 was found to be due to the weakening the Al-H bond caused by Ti substitution. A study was also made of the role played by metal vacancies in H desorption. Although this desorption was exothermic, the energies required to create these vacancies were high.

Effect of Ti and Metal Vacancies on the Electronic Structure, Stability and Dehydrogenation of Na3AlH6 - Supercell Band-Structure Formalism and Gradient-Corrected Density-Functional Theory. S.Li, P.Jena, R.Ahuja: Physical Review B, 2006, 73[21], 214107 (7pp)