Class Of Hydrogen Storage Materials Research Articles

Electrochemical Hydrogen Pump Using CsH2PO4/SnO2 Composite Proton Conducting Membrane

Liquid organic hydrogen carriers (LOHCs) are molecular compounds that have potential to be a promising class of hydrogen storage materials. Upon thermal treatment and in the presence of catalysts, H2-rich LOHCs can give off H2 without phase change. One immediate example is methylcyclohexane (C7H14) (MCH) conversion to toluene (C7H8) (TOL). The rate of H2 production of LOHC’s dehydrogenation reaction is kinetically limited. Therefore, adequate catalysts can help boost kinetics. An alternative approach to overcome the kinetic limitation is to shift the dehydrogenation reaction by removing H2 in the product via either a chemical or electrochemical route. Here we show an electrochemical H2 pump concept to promote the dehydrogenation reaction of MCH to TOL by pumping out H2 from the product line. We selected the super-protonic conductor CsH2PO4 (CDP) as the electrolyte for the pump due to the operating temperature of the dehydrogenation reaction (250-350 oC). However, CDP would not be stable if there is an insufficient amount of H2O (<38%) in the working environment, irreversibly dehydrated into a low-conductivity phase. On the other hand, too much H2O in MCH stream would negatively affect the catalytic performance of MCH-to-TOL conversion. Therefore, it is critical to limit the H2O content in MCH stream without affecting H2 pump performance.Here, we report the use of SnO2 to stabilize the super-protonic conducting phase in CDP. SnO2 is a super-hydrophilic material. We first show the ionic conductivity stabilization over a broad H2O content to demonstrate the effectiveness of SnO2 in stabilizing CDP conductivity. We then show the performance of H2 pump based on the composite CDP-SnO2 protonic conductor. We also show materials characterization results including XRD, SEM and Raman to facilitate our understanding of the observed improvement and degradation. Overall, this study provides a supporting method to accelerate the production of green hydrogen with LOHCs.

Exploring microstructure variations and hydrogen storage characteristics in TiVNbCrNi high-entropy alloys with different Ni incorporation

In recent years, high-entropy alloys (HEAs), as a novel class of hydrogen storage materials, have been deemed highly promising due to their extensive compositional tunability and the unique high entropy effects. This study aims to enhance the comprehensive hydrogen storage performance of the TiVNbCr-based HEA by introducing Ni. The effects of Ni addition on the microstructural evolution of the alloy and its impact on activation properties, hydrogen absorption and desorption kinetics, thermodynamics, and cycling performance under the complex physicochemical environment of multiple principal elements was systematically investigated. The findings indicate that Ni addition shortens the activation incubation period of the alloy but more Ni reduces the intrinsic hydrogen absorption kinetics. In the Ti25V30Nb10Cr33Ni2 alloy, a high reversible hydrogen storage capacity of up to 2.2 wt% at room temperature was achieved, surpassing most of the currently reported body-centered cubic (BCC)-structured high-entropy hydrogen storage alloys. Furthermore, the influence of Ni on the alloy's hydrogen desorption kinetics and cycling hydrogenation performance was studied. Results from 110 cycles of testing reveal that the introduction of Ni-induced Laves phases can act to relax stress, thereby reducing strain accumulation during the hydrogen absorption and desorption cycling process. This could provide guidance for the design of high-entropy hydrogen storage alloys with extended cycling lifetimes.

A Theoretical Study on Au(I) Decorated Isomeric Triazine Complexes as a New Class of Hydrogen Storage Materials

A Theoretical Study on Au(I) Decorated Isomeric Triazine Complexes as a New Class of Hydrogen Storage Materials

Recent Development in Nanoconfined Hydrides for Energy Storage.

Hydrogen is the ultimate vector for a carbon-free, sustainable green-energy. While being the most promising candidate to serve this purpose, hydrogen inherits a series of characteristics making it particularly difficult to handle, store, transport and use in a safe manner. The researchers’ attention has thus shifted to storing hydrogen in its more manageable forms: the light metal hydrides and related derivatives (ammonia-borane, tetrahydridoborates/borohydrides, tetrahydridoaluminates/alanates or reactive hydride composites). Even then, the thermodynamic and kinetic behavior faces either too high energy barriers or sluggish kinetics (or both), and an efficient tool to overcome these issues is through nanoconfinement. Nanoconfined energy storage materials are the current state-of-the-art approach regarding hydrogen storage field, and the current review aims to summarize the most recent progress in this intriguing field. The latest reviews concerning H2 production and storage are discussed, and the shift from bulk to nanomaterials is described in the context of physical and chemical aspects of nanoconfinement effects in the obtained nanocomposites. The types of hosts used for hydrogen materials are divided in classes of substances, the mean of hydride inclusion in said hosts and the classes of hydrogen storage materials are presented with their most recent trends and future prospects.

(Invited) Hydrogen Materials Advanced Research Consortium R&D Activities

The Hydrogen Materials—Advanced Research Consortium (HyMARC) is a National Lab-led consortium working to advance and develop hydrogen storage materials that meet DOE targets for energy density, kinetics and cost for a wide range of applications. The goal of HyMARC is to enable a doubling of the hydrogen storage density compared with state-of-the-art compressed storage systems. DOE’s Hydrogen and Fuel Cell Technologies Office launched HyMARC in 2015, bringing together world-class National Lab capabilities in materials modelling, characterization and synthesis; and fostering collaboration with industry and academia to overcome R&D challenges in materials-based hydrogen storage. The consortium is led by teams at Sandia National Laboratories and the National Renewable Energy Laboratory and includes groups at Lawrence Livermore, Lawrence Berkeley, and Pacific Northwest National Laboratories. HyMARC is working to develop foundational understanding of phenomena governing thermodynamics and kinetics of hydrogen release and uptake in all classes of hydrogen storage materials, including metal hydrides, adsorbents, and hydrogen carriers. It seeks to accelerate materials development by addressing critical R&D gaps in hydrogen storage—leveraging recent advances in predictive multiscale modeling, machine learning, high-resolution in situ characterization, and novel materials synthesis techniques to realize their goal to enable twice the energy density for hydrogen storage in the coming years. This presentation will describe HyMARC’s ongoing R&D activities and past accomplishments which have pushed the bar forward for materials-based hydrogen storage.

Data-Driven Discovery and Synthesis of High Entropy Alloy Hydrides with Targeted Thermodynamic Stability

Solid-state hydrogen storage materials that are optimized for specific use cases could be a crucial facilitator of the hydrogen economy transition. Yet, the discovery of novel hydriding materials has historically been a manual process driven by chemical intuition or experimental trial and error. Data-driven materials’ discovery paradigms provide an alternative to traditional approaches, whereby machine/statistical learning (ML) models are used to efficiently screen materials for desired properties and significantly narrow the scope of expensive/time-consuming first-principles modeling and experimental validation. Here, we specifically focus on a relatively new class of hydrogen storage materials, high entropy alloy (HEA) hydrides, whose vast combinatorial composition space and local structural disorder necessitate a data-driven approach that does not rely on exact crystal structures to make property predictions. Our ML model quickly screens hydride stability within a large HEA space and permits down selection for laboratory validation based on not only targeted thermodynamic properties but also secondary criteria such as alloy phase stability and density. To experimentally verify our predictions, we performed targeted synthesis and characterization of several novel hydrides that demonstrate significant destabilization (70× increase in equilibrium pressure, 20 kJ/molH2 decrease in desorption enthalpy) relative to the benchmark HEA hydride, TiVZrNbHfHx. Ultimately, by providing a large composition space in which hydride thermodynamics can be continuously tuned over a wide range, this work will enable efficient material selection for various applications, especially in areas such as metal hydride-based hydrogen compressors, actuators, and heat pumps.

Syntheses of alkali-metal carbazolides for hydrogen storage

Metalorganic hydrides are a new class of hydrogen storage materials. Replacing the H of N–H or O–H functional groups using metal hydrides have been recently reported, which substantially improved the dehydrogenation properties of heteroaromatic organic hydrides by lowering their enthalpies of dehydrogenation (ΔHd), enabling dehydrogenation at much lower temperatures. Among the reported metalorganic hydrides, lithium carbazolide and sodium carbazolide appear to be the most attractive hydrogen storage/delivery material owing to its high hydrogen capacity (>6.0 wt%) and ideal ΔHd. Nevertheless, the interaction of carbazole and corresponding metal hydride to form metallo-carbazolide is a multistep process involving intensive ball milling and high temperature treatment, where the interaction was not investigated in detail. In this paper, both alkali metal hydrides and amides were employed to react with carbazole to synthesize corresponding carbazolides, aiming to broaden and optimize the synthetic method and understand the reaction mechanism. Our experimental results showed that around one equivalent of H2 or NH3 could be released from the reactions of carbazole and corresponding hydrides or amides, respectively. Instrumental spectroscopic analyses proved that metallo-carbazolides were successfully synthesized from all precursors. It is found that the alkali metal amides (i.e., LiNH2 and NaNH2) with stronger Lewis basicities as metal precursors could synthesize the metallo-carbazolides under milder conditions. Furthermore, quasi in situ nuclear magnetic resonance results revealed that alkali metal could replace H (H–N) gradually, donating more electrons to carbazole ring. Additionally, the solubilized alkali cation may unselectively interact with π-electron of aromatic systems of both carbazole molecules and carbazolide anions via electrostatic cation-π interactions.

(Invited) Atomistic Simulations of Hydrogen Storage Materials

Solid state hydrogen storage materials possess good volumetric and gravimetric hydrogen storage densities and can be more attractive hydrogen storage media for hydrogen fuel cell vehicles. However, the current hydrogen storage materials are limited by their slow hydrogen storing and releasing kinetics. Understanding thermodynamic and kinetic foundations that limit the current storage materials is critical for accelerated material improvement. To achieve this understanding, we have been developing and applying atomistic simulation tools to study various classes of hydrogen storage materials. Here we present three cases. First, we have developed a series of molecular dynamics methods to study diffusional phase transformation hydrides, such as PdHx. This allows us to analytically quantify bulk and interfacial diffusivities, surface and interfacial energies, surface segregation, lattice constants, Gibbs free energy, and elastic constants, all as a function of temperature and composition. We then implemented all these properties in phase field codes and directly simulated the hydrogenation and dehydrogenation of PdHx at the engineering scale. Second, we have developed a high-fidelity Mg-H bond order potential to study the structural phase transformation hydrides, such as MgH2. We demonstrate that this potential not only captures the property trends for a variety of selected phases, but also ensures direct molecular dynamics simulation of formation and decomposition of the crystalline MgH2 phase. This new capability, not demonstrated in the past, opens up opportunities to explore in great details mechanisms of hydrogenation and dehydrogenation processes. Finally, we discuss our recent progress on developing a Mg-B-H ternary potential that can be used in atomistic simulations to study thermodynamics and kinetics behaviour of complex metal hydrides based on magnesium and boron. Acknowledgement - Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. A portion of this work was performed under the auspices of Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The authors gratefully acknowledge research support through the Hydrogen Storage Materials—Advanced Research Consortium (HyMARC), from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract Numbers DE-AC04-94AL85000 and DE-AC52-07NA27344. The views expressed in the article do not necessarily represent the views of the U.S. Department of Energy or the United States Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

Mg@C60 nano-lamellae and its 12.50 wt% hydrogen storage capacity

The design and synthesis of new hydrogen storage materials with high capacity are the prerequisite for extensive hydrogen energy application which can be achieved by multi-site hydrogen storage. Herein, a Mg@C60 nano-lamellae structure with multiple hydrogen storage sites has been prepared through a simple ball-milling process in which Mg nanoparticles (∼5 nm) are homogeneously dispersed on C60 nano-lamellae. The as-obtained C60/Mg nano-lamellae displays an excess hydrogen uptake of 12.50 wt% at 45 bar, which is far higher than the theoretical value (7.60 wt%) of metal Mg and the US Department of Energy (DOE) target (5.50 wt%, 2020 year), also the experimental values reported by now. The enhanced hydrogen storage mainly comes from several storage sites: MgH2, Hx–C60 (CH chemical bonding), H2@C60 (the endohedral H2 in C60). Interestingly, the hybridization of Mg and C60 not only facilitate the dissociation of H2 molecules to form CH bonding with C60, but also promote the deformation of C60 and access H2 molecules into the cavity of C60. This work provides new insight into the underlying chemistry behind the high hydrogen storage capacities of a new class of hydrogen storage materials, fullerene/alkaline-earth metals nanocomposites.

Elucidating the Role of Temperature and Pressure to the Thermodynamic Stability of Charged Defects in Complex Metal-Hydrides: A Case Study of NaAlH4

Complex metal hydrides are one of the most technologically relevant classes of hydrogen storage materials because of their huge applications as clean energy alternatives. In this class of materials, hydrogen-related point defects have been shown to play a crucial role in catalyzed dehydrogenation. We investigate the effects of environment (viz. finite temperature, hydrogen partial pressure, and doping) to understand the thermodynamic stability of point defects as a function of various charge states at a realistic condition in a bulk complex metal-hydride, using NaAlH4 as an example. Our approach employs density-functional theory (DFT) combined with ab initio atomistic thermodynamics, where the free energy of formation due to vibration of phonons is duly considered under harmonic approximation. We show that to understand the thermodynamic stability of various defects and its self-diffusion, the contribution of environmental effect to the free energy of formation is absolutely indispensable. We further vali...

Gold-containing metal nanoparticles for catalytic hydrogen generation from liquid chemical hydrides

Liquid chemical hydrides, which store hydrogen in the form of chemical bonds, are considered one of the most promising classes of hydrogen storage materials. Their application depends heavily on the development of efficient catalytic systems. Gold-containing metal nanoparticles have exhibited excellent catalytic performance for hydrogen generation from liquid chemical hydrides. The present mini-review focuses on recent developments in hydrogen generation from liquid chemical hydrides using gold-nanoparticle and gold-containing heterometallic nanoparticle catalysts.

Stabilization of volatile Ti(BH4)3 by nano-confinement in a metal-organic framework.

Liquid complex hydrides are a new class of hydrogen storage materials with several advantages over solid hydrides, e.g. they are flexible in shape, they are a flowing fluid and their convective properties facilitate heat transport. The physical and chemical properties of a gaseous hydride change when the molecules are adsorbed on a material with a large specific surface area, due to the interaction of the adsorbate with the surface of the host material and the reduced number of collisions between the hydride molecules. In this paper we report the synthesis and stabilization of gaseous Ti(BH4)3. The compound was successfully stabilized through adsorption in nanocavities. Ti(BH4)3, upon synthesis in its pure form, spontaneously and rapidly decomposes into diborane and titanium hydride at room temperature in an inert gas, e.g. argon. Ti(BH4)3 adsorbed in the cavities of a metal organic framework is stable for several months at ambient temperature and remains stable up to 350 K under vacuum. The adsorbed Ti(BH4)3 reaches approximately twice the density of the gas phase. The specific surface area (BET, N2 adsorption) of the MOF decreased from 1200 m2 g-1 to 770 m2 g-1 upon Ti(BH4)3 adsorption.

Complex Hydrides Li&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;MH&amp;lt;sub&amp;gt;5&amp;lt;/sub&amp;gt; (M = B, Al) for Hydrogen Storage Application: Theoretical Study of Structure, Vibrational Spectra and Thermodynamic Properties

Gaseous lithium complex hydrides Li2MH5 (M = B, Al) have been studied using DFT/B3P86 and MP2 methods with 6-311++G(d,p) basis set. High content of hydrogen by these materials accord them with good candidacy as a class of hydrogen storage materials. The optimized geometrical parameters, vibrational spectra and thermodynamic properties of the hydrides and the subunits LiH, Li2H+, Li2H2, MH3, MH4−, and LiMH4 have been determined. For the LiBH4 the equilibrium configuration was tridentate of C3v symmetry. For LiAlH4 two isomeric forms, bidentate (C2v) and tridentate (C3v), were confirmed to exist, and C2v isomer was shown to dominate in saturated vapor. For complex hydrides Li2MH5, different structural forms were considered but only one asymmetric form (C1) appeared to be equilibrium. Several possible channels of dissociation of Li2MH5 were considered; the enthalpies and Gibbs free energies of the reactions were computed. The enthalpies of formation ∆fH(0) of the complex hydrides in gaseous phase were determined: 60 ± 10 kJmol1 (Li2BH5) and 33 ± 10 kJmol1 (Li2AlH5). Heterophase decomposition of the gaseous Li2MH5 with solid products LiH and B/Al and hydrogen gas release was shown to be spontaneous at ambient temperature. Production of hydrogen gas via gaseous decomposition is highly endothermic and achievable at elevated temperatures. The complexes Li2MH5 are therefore proposed to be useful hydrogen storage materials under appropriate conditions.

Borohydride hydrazinates: high hydrogen content materials for hydrogenstorage

A new class of hydrogen storage materials, borohydride hydrazinates, was successfully synthesized. In particular, the bidentate NH2NH2 coordinates with LiBH4 in molar ratios of 1:1 and 1:2 giving rise to a monoclinic LiBH4·NH2NH2 and orthorhombic LiBH4·2NH2NH2, respectively. Around 13.0 wt% H2 can be released from LiBH4·NH2NH2 at 140 °C in the presence of Fe–B catalysts.

Hydride-Induced Amplification of Performance and Binding Enthalpies in Chromium Hydrazide Gels for Kubas-Type Hydrogen Storage

Hydrogen is the ideal fuel because it contains the most energy per gram of any chemical substance and forms water as the only byproduct of consumption. However, storage still remains a formidable challenge because of the thermodynamic and kinetic issues encountered when binding hydrogen to a carrier. In this study, we demonstrate how the principal binding sites in a new class of hydrogen storage materials based on the Kubas interaction can be tuned by variation of the coordination sphere about the metal to dramatically increase the binding enthalpies and performance, while also avoiding the shortcomings of hydrides and physisorpion materials, which have dominated most research to date. This was accomplished through hydrogenation of chromium alkyl hydrazide gels, synthesized from bis(trimethylsilylmethyl) chromium and hydrazine, to form materials with low-coordinate Cr hydride centers as the principal H(2) binding sites, thus exploiting the fact that metal hydrides form stronger Kubas interactions than the corresponding metal alkyls. This led to up to a 6-fold increase in storage capacity at room temperature. The material with the highest capacity has an excess reversible storage of 3.23 wt % at 298 K and 170 bar without saturation, corresponding to 40.8 kg H(2)/m(3), comparable to the 2015 DOE system goal for volumetric density (40 kg/m(3)) at a safe operating pressure. These materials possess linear isotherms and enthalpies that rise on coverage, retain up to 100% of their adsorption capacities on warming from 77 to 298 K, and have no kinetic barrier to adsorption or desorption. In a practical system, these materials would use pressure instead of temperature as a toggle and can thus be used in compressed gas tanks, currently employed in the majority of hydrogen test vehicles, to dramatically increase the amount of hydrogen stored, and therefore range of any vehicle.

Design and Synthesis of Vanadium Hydrazide Gels for Kubas-Type Hydrogen Adsorption: A New Class of Hydrogen Storage Materials

In this paper we demonstrate that the Kubas interaction, a nondissociative form of weak hydrogen chemisorption with binding enthalpies in the ideal 20-30 kJ/mol range for room-temperature hydrogen storage, can be exploited in the design of a new class of hydrogen storage materials which avoid the shortcomings of hydrides and physisorpion materials. This was accomplished through the synthesis of novel vanadium hydrazide gels that use low-coordinate V centers as the principal Kubas H(2) binding sites with only a negligible contribution from physisorption. Materials were synthesized at vanadium-to-hydrazine ratios of 4:3, 1:1, 1:1.5, and 1:2 and characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption, elemental analysis, infrared spectroscopy, and electron paramagnetic resonance spectroscopy. The material with the highest capacity possesses an excess reversible storage of 4.04 wt % at 77 K and 85 bar, corresponding to a true volumetric adsorption of 80 kg H(2)/m(3) and an excess volumetric adsorption of 60.01 kg/m(3). These values are in the range of the ultimate U.S. Department of Energy goal for volumetric density (70 kg/m(3)) as well as the best physisorption material studied to date (49 kg H(2)/m(3) for MOF-177). This material also displays a surprisingly high volumetric density of 23.2 kg H(2)/m(3) at room temperature and 85 bar--roughly 3 times higher than that of compressed gas and approaching the DOE 2010 goal of 28 kg H(2)/m(3). These materials possess linear isotherms and enthalpies that rise on coverage and have little or no kinetic barrier to adsorption or desorption. In a practical system these materials would use pressure instead of temperature as a toggle and can thus be used in compressed gas tanks, currently employed in many hydrogen test vehicles, to dramatically increase the amount of hydrogen stored and therefore the range of any vehicle.

Solid-State High-Resolution1H-NMR Study for Ammonia Borane of Hydrogen Storage Material

In liquids NMR, <TEX>$^{1}H$</TEX> is the most widely observed nucleus, which is not the case in solids NMR. The reason is due to the strong homo-dipolar interactions between the hydrogen atoms which mask the useful chemical shift information. Therefore we must remove the strong homo-dipolar interactions in order to get structural information, which can be investigated by the isotropic chemical shift. There are two ways of obtaining it. One is the ultra-fast MAS of ca. 70 kHz spinning speed, which has become available only recently. The other way is devising a pulse sequence which can remove the strong homo-dipolar interaction. In the latter way, MAS with a moderate spinning rate of a few kHz, is enough to remove the chemical shift anisotropy. In this report, 1D-CRAMPS and 2D MASFSLG techniques are utilized and their results will be compared. This kind of highresolution <TEX>$^{1}H$</TEX> NMR for solids, should become a valuable analytical tool in the understanding and the developing of a new class of hydrogen storage materials. Here ammonium borane <TEX>$-NH_{3}BH_{3}$</TEX>, whose hydrogen content is high, is used as a sample.

High-pressure techniques for discovering and re-hydrogenation of metal hydride materials

This overview will highlight features of the main classes of hydrogen storage materials based on their crystal structures. High-pressure techniques have proven to be a useful approach to rapidly discover light-weight, high-capacity hydrogen storage materials in the solid state. Focus will be on three different materials systems; magnesium-based transition metal hydrides, alanates and borohydrides, their crystal structures and properties, prepared by high-pressure sintering, high-energy ball milling or in a cubic anvil.