Magnesium borohydride Mg(BH4)​2 is a promising hydrogen storage material as it releases high hydrogen amt. at mild desorption temps., but it is still limited by slow dehydrogenation kinetics and harsh conditions are required for rehydrogenation. Composites made of com. Mg(BH4)​2 and synthesized silica aerogel microparticles were prepd. by thermal treatment under 120 bar of hydrogen and 200°. As a result, the sorption properties of the hydride are improved: calorimetric measurements show that the decompn. temp. is reduced by 60°, and the typical 3-​steps decompn. mechanism of Mg(BH4)​2 changes to a single-​step mechanism at 220-​400°. The kinetics of the 1st dehydrogenation at 300° was two times faster in Mg(BH4)​2-​SiO2 composites than in the case of bulk γ-​Mg(BH4)​2. Addnl., the rehydrogenation of this material at comparatively moderate conditions of 390° and 110 bar of H2 is presented for the 1st time, achieving cyclability with a reversible release of hydrogen up to 6​% H2. Different amts. of hydrogen were exchanged depending on the working temp. (300° or 400°) and the presence or absence of silica aerogel. Silica aerogel influence the performance of Mg(BH4)​2, acting as an additive, which can result in different hydrogenation-​dehydrogenation routes in which different amts. and types of intermediates are formed, influencing the kinetics and reversibility.

Reversible hydrogen sorption in the composite made of magnesium borohydride and silica aerogel

GIRELLA, ALESSANDRO
Investigation
;
COFRANCESCO, PACIFICO
Investigation
;
MILANESE, CHIARA
Supervision
;
2016-01-01

Abstract

Magnesium borohydride Mg(BH4)​2 is a promising hydrogen storage material as it releases high hydrogen amt. at mild desorption temps., but it is still limited by slow dehydrogenation kinetics and harsh conditions are required for rehydrogenation. Composites made of com. Mg(BH4)​2 and synthesized silica aerogel microparticles were prepd. by thermal treatment under 120 bar of hydrogen and 200°. As a result, the sorption properties of the hydride are improved: calorimetric measurements show that the decompn. temp. is reduced by 60°, and the typical 3-​steps decompn. mechanism of Mg(BH4)​2 changes to a single-​step mechanism at 220-​400°. The kinetics of the 1st dehydrogenation at 300° was two times faster in Mg(BH4)​2-​SiO2 composites than in the case of bulk γ-​Mg(BH4)​2. Addnl., the rehydrogenation of this material at comparatively moderate conditions of 390° and 110 bar of H2 is presented for the 1st time, achieving cyclability with a reversible release of hydrogen up to 6​% H2. Different amts. of hydrogen were exchanged depending on the working temp. (300° or 400°) and the presence or absence of silica aerogel. Silica aerogel influence the performance of Mg(BH4)​2, acting as an additive, which can result in different hydrogenation-​dehydrogenation routes in which different amts. and types of intermediates are formed, influencing the kinetics and reversibility.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/1180911
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