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.