First-principle studies of the formation and diffusion of hydrogen vacancies in magnesium hydride

Du, A. J., Smith, S. C., & Lu, G. Q. (2007) First-principle studies of the formation and diffusion of hydrogen vacancies in magnesium hydride. The Journal of Physical Chemistry Part C : Nanomaterials, Interfaces and Hard Matter, 111(23), pp. 8360-8365.

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Ab initio density functional theory (DFT) calculations are performed to study the formation and diffusion of hydrogen vacancies on MgH2(110) surface and in bulk. We find that the formation energies for a single H-vacancy increase slightly from the surface to deep layers. The energies for creating adjacent surface divancacies at two inplane sites and at an inplane and a bridge site are even smaller than that for the formation of a single H-vacancy, a fact that is attributed to the strong vacancy−vacancy interactions.

The diffusion of an H-vacancy from an in-plane site to a bridge site on the surface has the smallest activation barrier calculated at 0.15 eV and should be fast at room temperature. The activation barriers computed for H-vacancy diffusion from the surface into sublayers are all less than 0.70 eV, which is much smaller than the activation energy for desorption of hydrogen on the MgH2(110) surface (1.78−2.80 eV/H2). This suggests that surface desorption is more likely than vacancy diffusion to be rate determining, such that finding effective catalyst on the MgH2 surface to facilitate desorption will be very important for improving overall dehydrogenation performance.

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ID Code: 61156
Item Type: Journal Article
Refereed: Yes
Keywords: hydrogen, formation, diffusion, magnesium hydride
DOI: 10.1021/jp072191z
ISSN: 1932-7455
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2007 American Chemical Society
Deposited On: 08 Jul 2013 03:39
Last Modified: 29 Jul 2013 00:37

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