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
Electronic and structural properties of sodium-aluminum hexahydride (Na3AlH6) formed during the decomposition reaction of sodium alanate (NaAlH4) and the effects of Ti catalyst are studied using supercell approach and density-functional theory. The preferred site of Ti has been determined by substituting it at both the Na and Al sites and comparing the respective formation energies. The least unfavorable site for Ti is found to be the Al site. To examine the role of Ti substitution on the desorption of hydrogen, 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. We also studied the role of metal vacancies on hydrogen desorption. Although this desorption was exothermic, the energies to create these vacancies are high
