A TEM based study of the microstructure during room temperature and low temperature hydrogen storage cycling in MgH2 promoted by Nb–V

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DOIResolve DOI: http://doi.org/10.1016/j.actamat.2012.06.009
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TypeArticle
Journal titleActa Materialia
ISSN1359-6454
Volume60
Issue16
Pages56465661; # of pages: 16
SubjectHydrogen storage; Magnesium hydride; TEM; Microstructure; Catalyst
AbstractMagnesium hydride combined with a new bimetallic Nb–V catalyst displays remarkably rapid and stable low temperature (200 °C) hydrogen storage kinetics, even after 500 full volumetric absorption/desorption cycles. The system is also able to fairly rapidly absorb hydrogen at room temperature at a pressure of 1 bar. This unprecedented absorption behavior was demonstrated for 20 cycles. We employed extensive cryo-stage transmission electron microscopy (TEM) analysis on fully and partially sorbed materials to provide insight into the rapid Mg to MgH2 phase transformation. After extended cycling of what was initially a 1.5 μm thick fully dense alloy film, the sample structure becomes analogous to that of a weakly agglomerated nanocomposite powder. The cycled Mg–V–Nb structure consists of a dense distribution of catalytic Nb–V nanocrystallites covering the surfaces of larger Mg and MgH2 particles. The partially absorbed 20 °C and 200 °C microstructures both show this morphology. TEM results combined with Johnson–Mehl–Avrami-type kinetic analysis point to the surface catalyst distribution and stability against coarsening as being a key influence on the two-stage hydriding kinetics. Remarkably, the mean size of the Nb0.5V0.5H nanocrystallites stays essentially invariant throughout cycling; it is 3 nm after 45 cycles and 4 nm after 500 cycles. A mechanistic description is provided for the cycling-induced microstructural evolution in the ternary alloy as well as in the binary baselines.
Publication date
LanguageEnglish
AffiliationSecurity and Disruptive Technologies; National Research Council Canada
Peer reviewedYes
IdentifierS1359645412003710
NPARC number21268616
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Record identifierb2584010-fbe6-4fd1-834c-c0fa8f58f7ef
Record created2013-10-28
Record modified2016-05-09
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