Surface and Particle-Size Effects on Hydrogen Desorption from Catalyst-Doped MgH2

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2012-01-01
Authors
Reich, J.
Wang, Lin-Lin
Johnson, Duane
Johnson, Duane
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Ames Laboratory
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Abstract

With their high capacity, light-metal hydrides like MgH2 remain under scrutiny as reversible H-storage materials, especially to develop control of H-desorption properties by decreasing size (ball-milling) and/or adding catalysts. By employing density functional theory and simulated annealing, we study initial H2 desorption from semi-infinite stepped rutile (110) surface and Mg31H62 nanoclusters, with(out) transition-metal catalyst dopants (Ti or Fe). While Mg31H62structures are disordered (amorphous), the semi-infinite surfaces and nanoclusters have similar single, double, and triple H-to-metal bond configurations that yield similar H-desorption energies. Hence, there is no size effect on desorption energetics with reduction in sample size, but dopants do reduce the H-desorption energy. All desorption energies are endothermic, in contrast to a recent report.

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Reprinted with permission from J. Phys. Chem. C, 2012, 116 (38), pp. 20315–20320, doi:10.1021/jp304059c. Copyright 2012 American Chemical Society.

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