(91c) DFT Study on Hydrogen Desorption From NaMgH3 (001) Surface

DFT Study on
Hydrogen Desorption from NaMgH₃ (001) Surface

Authors: Fernando Soto¹,
Daniela S. Mainardi²

¹Institute for
Micro-manufacturing, Louisiana Tech University

²Institute for
Micro-manufacturing, Chemical Engineering, Louisiana Tech University

NaMgH₃
is the only magnesium based ternary hydride with Na and it has attracted the
attention as a possible candidate for hydrogen storage material because it has
high gravimetric hydrogen density (6 %) and high volumetric hydrogen density
(88 kg/m₃). Hydrogen disassociation in this material occurs at
atmospheric pressure and almost 670 K, which is well above the operable range
for on board hydrogen storage applications and a major impediment for practical
applications. In this study, aiming to enhance the dehydrogenation process on transition
metal modified- NaMgH₃,(001) surface has been investigated by using
density functional theory calculations. For the surface calculations, three
types of models can be identified: Hydrogen desorption from the surface of the NaMgH₃
(H_surf), within the NaMgH₃ (H_bulk), and at the bulk/surface interface (H_bulk/surf).

We
propose that Hydrogen desorption process is facilitated inNaMgH₃ by
doping the material with Ti at the surface site and Zn as a co-dopant at the
bulk site. The dehydrogenation energy of the co-doped surface structure is low,
in comparison to the pristine model, Furthermore, when doped with transition
metals from the 3d and 4d block elements, the dissociation barrier can also be
lowered, in some cases with better results than Ti and Zn. Carbon doping was
found to be the most promising, based on the considerations of the activation
barrier, and dehydrogenation energy cost. Our results predict that these types of model structures are potential useful materials for
hydrogen storage application.