276350 Investigation of Phase Stability of Magnesium Alanate for Hydrogen Storage From First Principles

Tuesday, October 30, 2012: 3:15 PM
305 (Convention Center )
Dong-Hee Lim, Energy Resources Engineering, Stanford University, Stanford, CA, Tim Mueller, Materials Science and Engineering, Johns Hopkins University, Baltimore, MD and Jennifer Wilcox, Department of Energy Resources Engineering, Stanford University, Stanford, CA

Complex hydrides including alanates ([AlH4]) have recently gained attention as alternative hydrogen storage materials. Many of these materials have been known to release hydrogen upon contact with water; however, the hydrolysis reactions are highly irreversible, a process known as “one-pass” hydrogen storage. Nanostructuring and nanocatalysis have been accepted as promising methods to overcome the irreversible hydrogenation process. Thus, predicting which phases may be more stable as a function of nanoparticle size may contribute to nanostructuring complex hydrides for hydrogen storage applications. We have employed density functional theory (DFT) using the projector-augmented wave (PAW) method within the generalized gradient approximation (GGA) to calculate relatively smaller nanoparticles of magnesium alanate (Mg(AlH4)2) ranging from 1 to 2 nm. Based upon these results, cluster expansion and Monte Carlo simulation methods were developed to predict the phase stabilities of 2-10 nm Mg(AlH4)2 nanoparticles. Our calculations provide phase stability diagrams of Mg(AlH4)2 nanoparticles as a function of particle size and temperature. This study may help identify how the relative stability of different compounds (Mg(AlH4)2, MgH2, Al, and H2) evolves as a function of nanoparticle size and temperature, which will facilitate experimental studies to determine the thermodynamically favored reaction pathways for the hydrogenation/dehydrogenation processes of Mg(AlH4)2.

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