DFT study of crystal structure and electronic properties of metal-doped AlH3 polymorphs

AlH 3 has been considered for a long time as a hydrogen storage material with suitable gravimetric and volumetric density for practical applications. Among eight AlH 3 polymorphs observed so far, in this work we focus our attention on an investigation of the effects of various metal dopants in α- and β-AlH 3 , to perceive a way of enhancing them. Substitutional incorporation of the metal dopants (Li, Sc, Ti, Cu, Cr, Fe, Nb, Mo, Zn, or Zr) is considered, as well as interstitial doping with Li, Sc, Ti, Cu, and Zr. The density functional theory (DFT) (using GGA-PW91) approach is used to address the crystal structure, bonding, dopant stability, and changes in hydrogen desorption energy. In addition, the kinetics of hydrogen desorption is also considered for several interstitially doped cases, by calculating the stability of native point defects. Promising results are presented for Zr, Ti, and Sc – doped hydrides. Doped hydrides, here studied, are considered as n - or p -type semiconducting materials, enabling wider application overcoming hydrogen storage scope. • Electronic properties of metal-doped α- and β-AlH 3 by several 3 d metals are studied. • Bonds between dopant and H atoms are classified as polar covalent. • Chemical nature rather than crystal structure determines the stability of dopants. • The formation of the positively charged hydrogen vacancy is discussed. • Ti, Zr and Sc dopants lower activation energy for H desorption in AlH 3 .