Hydrogenation reaction of CaH2-CaB6-Mg mixture

Title
Hydrogenation reaction of CaH2-CaB6-Mg mixture
Authors
김윤영Daniel Reed이영수심재혁한흥남David Book조영환
Keywords
Hydrogen storage material; Complex metal hydride; Ca(BH4)2; MgH2; Hydrogenation; Ball milling; X-ray diffraction; Ca4Mg3H14; Calcium borohydride; Magnesium hydride
Issue Date
2010-03
Publisher
Journal of alloys and compounds
Citation
VOL 492, NO 1-2, 597-600
Abstract
Hydrogen desorption/absorption cycling properties of Ca(BH4)2 +MgH2 mixture having 9.1 wt% of theoretical hydrogen capacity have been investigated. The hydrogenation reaction sequence starting from the dehydrogenated product CaH2 + CaB6 +Mg was thoroughly followed using X-ray diffraction, and that can be summarized as (i) Mg+H2→MgH2, (ii) 4CaH2 +3MgH2→Ca4Mg3H14, (iii) Ca4Mg3H14 + 2CaB6 +20H2→6Ca(BH4)2 +3MgH2. The steps (i) and (ii) proceeded rather fast, and the total amount of reabsorbed hydrogen was governed by the step (iii). The kinetics of the step (iii) was critically affected by the temperature of dehydrogenation/hydrogenation reaction, which we mainly attributed to the microstructure of the dehydrogenated product such as particle size. We indirectly proved our hypothesis by showing that inserting high-energy ball-milling process during hydrogenation is more effective than simply increasing the reaction time. Optimal reversibility was achieved from the sample which was dehydrogenated at 673K and hydrogenated at 623 K.
URI
http://pubs.kist.re.kr/handle/201004/37198
ISSN
0925-8388
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KIST Publication > Article
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