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A Mechanistic Analysis of Phase Evolution and Hydrogen Storage Behavior in Nanocrystalline Mg(BH4)2 within Reduced Graphene Oxide
journal contribution
posted on 2020-01-17, 16:37 authored by Sohee Jeong, Tae Wook Heo, Julia Oktawiec, Rongpei Shi, ShinYoung Kang, James L. White, Andreas Schneemann, Edmond W. Zaia, Liwen F. Wan, Keith G. Ray, Yi-Sheng Liu, Vitalie Stavila, Jinghua Guo, Jeffrey R. Long, Brandon C. Wood, Jeffrey J. UrbanMagnesium
borohydride (Mg(BH4)2, abbreviated
here MBH) has received tremendous attention as a promising onboard
hydrogen storage medium due to its excellent gravimetric and volumetric
hydrogen storage capacities. While the polymorphs of MBHalpha
(α), beta (β), and gamma (γ)have distinct
properties, their synthetic homogeneity can be difficult to control,
mainly due to their structural complexity and similar thermodynamic
properties. Here, we describe an effective approach for obtaining
pure polymorphic phases of MBH nanomaterials within a reduced graphene
oxide support (abbreviated MBHg) under mild conditions (60–190
°C under mild vacuum, 2 Torr), starting from two distinct samples
initially dried under Ar and vacuum. Specifically, we selectively
synthesize the thermodynamically stable α phase and metastable
β phase from the γ-phase within the temperature range
of 150–180 °C. The relevant underlying phase evolution
mechanism is elucidated by theoretical thermodynamics and kinetic
nucleation modeling. The resulting MBHg composites exhibit structural
stability, resistance to oxidation, and partially reversible formation
of diverse [BH4]− species during de-
and rehydrogenation processes, rendering them intriguing candidates
for further optimization toward hydrogen storage applications.
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nucleation modelingα phasephase evolution mechanismpolymorphic phasesγ- phasehydrogen storage capacitiesonboard hydrogen storage mediumMgMechanistic Analysistemperature rangeMBH nanomaterialsBH 4Phase Evolutiongraphene oxide supportReduced Graphene Oxide Magnesium borohydridemetastable β phaserehydrogenation processesMBHg composites exhibitHydrogen Storage Behaviorhydrogen storage applications
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