APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Abstract: Q6.00004 : Point-defect-mediated dehydrogenation of alane
1:03 PM–1:39 PM
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For the engineering of better hydrogen storage materials a
systematic understanding of their hydrogen sorption kinetics is
crucial. Theoretical studies on metal hydrides have indicated
that in many cases point defects control mass transport and hence
hydrogen uptake and release. Manipulating point-defect
concentrations thus allows control over hydrogen sorption
kinetics, opening up new engineering strategies. However, in some
cases the relevance of kinetic limitations due to point defects
is still under debate; kinetic inhibition of hydrogen sorption
has also been attributed to surface effects, e.g. oxide layers or
low recombination rates.
We present a systematic analysis of the dehydrogenation kinetics
of alane (AlH3), one of the prime candidate materials for
hydrogen storage. Using hybrid-density functional calculations we
determine the concentrations and mobilities of point defects and
their complexes. Kinetic Monte Carlo simulations are used to
describe the full dehydrogenation reaction. We show that under
dehydrogenation conditions charged hydrogen vacancy defects form
in the crystal, which have a strong tendency towards clustering.
The vacancy clusters denote local nuclei of Al phase, and the
growth of these nuclei eventually drives the AlH3/Al
transformation. However, the low concentration of vacancy defects
limits the transport of hydrogen across the bulk, and hence acts
as the rate-limiting part of the process. The dehydrogenation is
therefore essentially inactive at room temperature, explaining
why AlH3 is metastable for years, even though it is
thermodynamically unstable. Our derived activation energy and
dehydrogenation curves are in excellent agreement with the
experimental data, providing evidence for the relevance of bulk
point-defect kinetics.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.Q6.4