Electrolyte-Assisted Hydrogen Storage Reactions

Vajo, John J.; Tan, Hongjin; Ahn, Channing C.; Addison, Dan; Hwang, Son‐Jong; White, J. L.; Wang, Yichen; Stavila, Vitalie; Graetz, Jason

doi:10.1021/acs.jpcc.8b08335

Cited by 8 publications

(14 citation statements)

References 36 publications

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“…Magnesium diboride (MgB 2 ) is a fascinating material, not only for its superconducting properties but also for its ability to store hydrogen in the form of magnesium borohydride [Mg(BH 4 ) 2 ]. − While Mg(BH 4 ) 2 has an exceptionally high hydrogen gravimetric capacity of 14.9%, once it releases hydrogen to form MgB 2 , it is challenging to rehydrogenate MgB 2 back to Mg(BH 4 ) 2 . As first observed by Severa et al and reviewed by Ray and co-workers, the complete conversion of MgB 2 to Mg(BH 4 ) 2 requires excessively high pressures (950 bar) and temperatures (400 °C).…”

Section: Introductionmentioning

confidence: 99%

Nanoscale Mg–B via Surfactant Ball Milling of MgB₂: Morphology, Composition, and Improved Hydrogen Storage Properties

et al. 2020

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Metal borides have attracted the attention of researchers due to their useful physical properties and unique ability to form high hydrogen-capacity metal borohydrides. We demonstrate improved hydrogen storage properties of a nanoscale Mg–B material made by surfactant ball milling MgB2 in a mixture of heptane, oleic acid, and oleylamine. Transmission electron microscopy data show that Mg–B nanoplatelets are produced with sizes ranging from 5 to 50 nm, which agglomerate upon ethanol washing to produce an agglomerated nanoscale Mg–B material of micron-sized particles with some surfactant still remaining. X-ray diffraction measurements reveal a two-component material where 32% of the solid is a strained crystalline solid maintaining the hexagonal structure with the remainder being amorphous. Fourier transform infrared shows that the oleate binds in a “bridge-bonding” fashion preferentially to magnesium rather than boron, which is confirmed by density functional theory calculations. The Mg–B nanoscale material is deficient in boron relative to bulk MgB2 with a Mg–B ratio of ∼1:0.75. The nanoscale MgB0.75 material has a disrupted B–B ring network as indicated by X-ray absorption measurements. Hydrogenation experiments at 700 bar and 280 °C show that it partially hydrogenates at temperatures 100 °C below the threshold for bulk MgB2 hydrogenation. In addition, upon heating to 200 °C, the H–H bond-breaking ability increases ∼10-fold according to hydrogen–deuterium exchange experiments due to desorption of oleate at the surface. This behavior would make the nanoscale Mg–B material useful as an additive where rapid H–H bond breaking is needed.

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Section: Introductionmentioning

confidence: 99%

Nanoscale Mg–B via Surfactant Ball Milling of MgB₂: Morphology, Composition, and Improved Hydrogen Storage Properties

et al. 2020

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“…For instance, chemical doping by secondary species with predominantly ionic interactions (e.g., alkali and alkaline earth metals) could facilitate changes in B and H bonding configurations at MgB 2 edges, particularly if these dopants segregate naturally to reactive edges, interfaces, and grain boundaries where the highest reactivity is likely to be found. This may relate to the recently reported kinetic enhancement of MgB 2 hydrogenation by addition of an electrolyte solution comprised of LiI/KI/CsI or LiBH 4 /KBH 4 …”

Section: Discussionmentioning

confidence: 72%

“…This may relate to the recently reported kinetic enhancement of MgB 2 hydrogenation by addition of an electrolyte solution comprised of LiI/KI/CsI or LiBH 4 /KBH 4 . 39 We can further speculate regarding the evolution of the MgB 2 edge-plane chemistry as the reaction proceeds. Although the B-terminated edge planes are generally more reactive, we find a thermodynamic driving force toward Mg-terminated edge planes.…”

Section: Discussionmentioning

confidence: 92%

Understanding Hydrogenation Chemistry at MgB₂Reactive Edges fromAb InitioMolecular Dynamics

Ray

Klebanoff

Stavila

et al. 2022

ACS Appl. Mater. Interfaces

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Solid-state hydrogen storage materials often operate via transient, multistep chemical reactions at complex interfaces that are difficult to capture. Here, we use direct ab initio molecular dynamics simulations at accelerated temperatures and hydrogen pressures to probe the hydrogenation chemistry of the candidate material MgB2 without a priori assumption of reaction pathways. Focusing on highly reactive (101̅0) edge planes where initial hydrogen attack is likely to occur, we track mechanistic steps toward the formation of hydrogen-saturated BH4 – units and key chemical intermediates, involving H2 dissociation, generation of functionalities and molecular complexes containing BH2 and BH3 motifs, and B–B bond breaking. The genesis of higher-order boron clustering is also observed. Different charge states and chemical environments at the B-rich and Mg-rich edge planes are found to produce different chemical pathways and preferred speciation, with implications for overall hydrogenation kinetics. The reaction processes rely on B–H bond polarization and fluctuations between ionic and covalent character, which are critically enabled by the presence of Mg2+ cations in the nearby interphase region. Our results provide guidance for devising kinetic improvement strategies for MgB2-based hydrogen storage materials, while also providing a template for exploring chemical pathways in other solid-state energy storage reactions.

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“…Then the desired amount (0.50 g) of this mixture was lightly mixed using a spatula with the lithium aluminum hydride mixture (0.51 g). Previous differential scanning calorimetry (DSC) measurements confirmed that eutectic melting occurred from the ground mixture during the initial heating at ~110 • C. [15].…”

Section: Methodsmentioning

confidence: 93%

“…It was recently demonstrated that the presence of a liquid electrolyte (under reaction conditions), in the form of a eutectic, significantly increases the dehydrogenation and rehydrogenation reaction rates in some hydrides [15]. It has been suggested that the electrolyte substantially increases the reaction interface area as well as transport of heavy ions.…”

Section: Introductionmentioning

confidence: 99%

Electrolyte-Assisted Hydrogen Cycling in Lithium and Sodium Alanates at Low Pressures and Temperatures

Graetz

Vajo

2020

Energies

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An investigation of electrolyte-assisted hydrogen storage reactions in complex aluminum hydrides (LiAlH4 and NaAlH4) reveals significantly reduced reaction times for hydrogen desorption and uptake in the presence of an electrolyte. LiAlH4 evolves ~7.8 wt% H2 over ~3 h in the presence of a Li-KBH4 eutectic at 130 °C compared to ~25 h for the same material without the electrolyte. Similarly, NaAlH4 exhibits 4.8 wt% H2 evolution over ~4 h in the presence of a diglyme electrolyte at 150 °C compared to 4.4 wt% in ~15 h for the same material without the electrolyte. These reduced reaction times are composed of two effects, an increase in reaction rates and a change in the reaction kinetics. While typical solid state dehydrogenation reactions exhibit kinetics with rates that continuously decrease with the extent of reaction, we find that the addition of an electrolyte results in rates that are relatively constant over the full desorption window. Fitting the kinetics to an Avrami-Erofe’ev model supports these observations. The desorption rate coefficients increase in the presence of an electrolyte, suggesting an increase in the velocities of the reactant-product interfaces. In addition, including an electrolyte increases the growth parameters, primarily for the second desorption steps, resulting in the observed relatively constant reaction rates. Similar effects occur upon hydrogen uptake in NaH/Al where the presence of an electrolyte enables hydrogenation under more practical low temperature (75 °C) and pressure (50 bar H2) conditions.

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Electrolyte-Assisted Hydrogen Storage Reactions

Cited by 8 publications

References 36 publications

Nanoscale Mg–B via Surfactant Ball Milling of MgB₂: Morphology, Composition, and Improved Hydrogen Storage Properties

Nanoscale Mg–B via Surfactant Ball Milling of MgB₂: Morphology, Composition, and Improved Hydrogen Storage Properties

Understanding Hydrogenation Chemistry at MgB₂Reactive Edges fromAb InitioMolecular Dynamics

Electrolyte-Assisted Hydrogen Cycling in Lithium and Sodium Alanates at Low Pressures and Temperatures

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Electrolyte-Assisted Hydrogen Storage Reactions

Cited by 8 publications

References 36 publications

Nanoscale Mg–B via Surfactant Ball Milling of MgB2: Morphology, Composition, and Improved Hydrogen Storage Properties

Nanoscale Mg–B via Surfactant Ball Milling of MgB2: Morphology, Composition, and Improved Hydrogen Storage Properties

Understanding Hydrogenation Chemistry at MgB2Reactive Edges fromAb InitioMolecular Dynamics

Electrolyte-Assisted Hydrogen Cycling in Lithium and Sodium Alanates at Low Pressures and Temperatures

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Product

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Nanoscale Mg–B via Surfactant Ball Milling of MgB₂: Morphology, Composition, and Improved Hydrogen Storage Properties

Nanoscale Mg–B via Surfactant Ball Milling of MgB₂: Morphology, Composition, and Improved Hydrogen Storage Properties

Understanding Hydrogenation Chemistry at MgB₂Reactive Edges fromAb InitioMolecular Dynamics