(87a) A DFT Study of NaMgH3 (001) Surfaces : Lattice Dynamics

A DFT Study of NaMgH₃ (001) Surfaces : Lattice Dynamics

Authors: Fernando Soto¹, Daniela S. Mainardi²

¹Institute for Micro-manufacturing, Louisiana Tech University

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

            Complex metal hydrides have emerged as one of the most promising solid-state hydrogen storage materials[1] due to their high hydrogen volumetric and gravimetric storage capacities. Mg-based alloys such as NaMgH₃ are especially interesting because of their light weight[2] and hydrogen mobility[3]. However, a solid state material must meet a set of technical requirements regarding gravimetric and volumetric densities, operating temperature, delivery pressure, fueling time, cycle life, cost and safety that no system currently satisfies[4]. For this reason, efforts have been devoted to decrease the desorption temperature and enhance the kinetics of complex metal hydrides[5]. For instance, thermodynamics and kinetics have been improved by doping NaAlH₄ with transition-metals[6] [7]; however, the improvement in dehydrating and hydrating kinetics occurs at the expense of hydrogen content[8]. Thus, the search for optimal storage materials, catalytic additives and destabilization options remains open.

            In spite of considerable experimental and computational work[9-17], a complete understanding of the vibrational properties such as phonons and dispersion of the NaMgH₃ (001) surfaces is still lacking. The study of surface phonons provides valuable insight into the surface structure and other phenomena specific to the surface, which can differ from the bulk. A density functional theory study addressing these issues is important in order to achieve a deeper understanding of the relevant mechanisms that could facilitate hydrogen desorption in this material.

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