An overview of reactive hydride composite (RHC) for solid-state hydrogen storage materials

Light-weight solid-state hydrogen storage materials characterized by neutron scattering

Interface effects in NaAlH4–carbon nanocomposites for hydrogen storage

UTRC lead the development of the Simulink Framework model that enables a comparison of different hydrogen storage systems on a common basis. The Simulink Framework model was disseminated on the www.HSECoE.org website that is hosted by NREL. UTRC contributed to a better understanding of the safety aspects of the proposed hydrogen storage systems. UTRC also participated in the Failure Mode and Effect Analysis of both the chemical- and the adsorbent-based hydrogen storage system during Phase 2 of the Hydrogen Storage Engineering Center of Excellence. UTRC designed a hydrogen storage system with a reversible metal hydride material in a compacted form for light-duty vehicles with a 5.6 kg H2 storage capacity, giving it a 300 miles range. It contains a heat exchanger that enables efficient cooling of the metal hydride material during hydrogen absorption in order to meet the 3.3 minute refueling time target. It has been shown through computation that the kinetics of hydrogen absorption of Ti-catalyzed NaAlH4 was ultimately limiting the rate of hydrogen absorption to 85% of the material capacity in 3.3 minutes. An inverse analysis was performed in order to determine the material property requirements in order for a metal hydride based hydrogen storage system to meet the DOE targets. Work on metal hydride storage systems was halted after the Phase 1 to Phase 2 review due to the lack of metal hydride materials with the required material properties. UTRC contributed to the design of a chemical hydrogen storage system by developing an adsorbent for removing the impurity ammonia from the hydrogen gas, by developing a system to meter the transport of Ammonia Borane (AB) powder to a thermolysis reactor, and by developing a gas-liquid-separator (GLS) for the separation of hydrogen gas from AB slurry in silicone oil. Stripping impurities from hydrogen gas is essential for a long life of the fuel cell system on board of a vehicle. Work on solid transport of AB was halted after the Phase 1 to Phase 2 review in favor of studying the slurry-form of AB as it appeared to be difficult to transport a solid form of AB through the thermolysis reactor. UTRC demonstrated the operation of a compact GLS in the laboratory at a scale that would be required for the actual automotive application. The GLS met the targets for weight and volume. UTRC also reported about the unresolved issue associated with the high vapor pressure of fluids that could be used for making a slurry-form of AB. Work on the GLS was halted after the Phase 2 to Phase 3 review as the off-board regeneration efficiency of the spent AB was below the DOE target of 60%. UTRC contributed to the design of an adsorbent-based hydrogen storage system through measurements of the thermal conductivity of a compacted form of Metal Organic Framework (MOF) number 5 and through the development and sizing of a particulate filter. Thermal conductivity is important for the design of the modular adsorbent tank insert (MATI), as developed by Oregon State University (OSU), in order to enable a rapid refueling process. Stringent hydrogen quality requirements can only be met with an efficient particulate filtration system. UTRC developed a method to size the particulate filter by taking into account the effect of the pressure drop on the hydrogen adsorption process in the tank. UTRC raised awareness about the potential use of materials-based H2 storage systems in applications outside the traditional light-duty vehicle market segment by presenting at several conferences about niche application opportunities in Unmanned Aerial Vehicles (UAV), Autonomous Underwater Vehicles (AUV), portable power and others.

Lumped parameter simulation of hydrogen storage and purification systems using metal hydrides

Application of machine learning to thermal management of solid-state hydrogen storage: A comprehensive review

Enhancing reversible hydrogen storage performance of 2LiBH ₄ –MgH ₂ via in‐situ building heterogeneous nucleation sites

The transportation demands in our growing hydrogen (H2) economy requires robust storage systems. The current commercially implemented technology in fuel cell cars relies on the well-established technology of hydrogen gas compressed to 350–700 bar, depending on the application. The compressed gas tanks in use today are bulky and cost intensive. To address this challenge, material-based storage is one of the long-term alternatives considered and constitutes the focus of this talk.Material-based storage is broadly defined as hydrogen bound to solid materials, with its binding strength varying from physisorption to porous materials, such as zeolites and metal organic frameworks, to chemisorption in (complex) metal hydrides. The ultimate targets set by the U.S. Department of Energy for this technology include a system gravimetric capacity of 6.5 wt% and volumetric capacity of 40 g/L at 100 bar, operating temperatures ranging between -40 C and +40 C and adsorption/desorption timescales of < 5 min. Storage in the form of physisorbed or chemisorbed hydrogen has guided the materials research, which metal-organic framework and (complex) metal hydrides being the most promising materials classes. A variety of these materials have met one or more of the targets, but it has remained elusive for a single material system to meet all these stringent requirements. Nano-encapsulation and low-concentration chemical additives have previously been employed separately to overcome such challenges. Functionalization via atomic layer deposition (ALD), however, offers unique characteristics that make it suitable for both, nano-encapsulation and “doping” with low-concentration additives. This deposition technique has sub-monolayer thickness control, is highly conformal in high-surface area materials and is self-limiting, i.e., once the gas-phase precursor reacts with the available surface sites, the surface reactions stop.In this presentation, we will showcase examples where ALD, more generally vapor-phase functionalization, on (complex) metal hydrides and organic frameworks has improved the material properties for H2 storage. In our first study, Al2O3 was deposited on magnesium borohydride, Mg(BH4)2, at room temperature using trimethylaluminum (TMA) and water. From our findings, encouraging initial results were obtained: the H2 desorption temperature was lowered by 60–120 ˚C, the desorbed gravimetric H2 capacity at temperatures < 250 ˚C was doubled, and the desorption kinetics increased by a factor of ~6 compared to uncoated Mg(BH4)2. However, hydrolysis reactions caused by residual surface -OH groups from the ALD water-pulse degraded the sample substantially. Through this study, the use of TMA was observed to be highly reactive with the Mg(BH4)2 surface species, leading to the strategy of exposing the sample only to TMA. The relative mole fraction of the vapor-phase additive can be precisely controlled with the number of TMA pulses and pulse duration. By tuning these parameters, we show in our second study that 10 pulses of TMA at ambient conditions were able to decrease the H2 desorption temperature by ~100 ˚C while retaining <95 % of its H2 capacity. We applied this approach with other additives such as BBr3, TiCl4 and tetrahydrofuran, and demonstrate that this unique approach opens the door to a new class of molecular additives and catalysts which cannot easily be introduced with conventional mechano-chemical or solvent-based techniques for (complex) metal-hydrides. In the case of metal organic frameworks, ALD is a promising technique to functionalize the pores with metal atoms or functional groups able to tune the gas selectivity and binding energy, for which ~15 kJ/mol has been established as the optimal value for H2 storage in sorbent materials.Vapor-phase techniques such as ALD have numerous benefits over other functionalization tools for H2 storage materials opening innumerable opportunities to the field. To exploit these opportunities, the current limitations on room temperature and water-less ALD processes needs to be overcome which will greatly expand the possibilities of encapsulation and incorporation of additives for organic frameworks and (complex) metal hydrides.

Unraveling the Potential of Solid-State Hydrogen Storage Materials: Insights from First Principle Calculations

Hydrogen (H2) possesses a number of chemical and physical properties that have allowed it to be used widely in the synthesis and processing of materials in research laboratories as well as in industrial manufacturing. These uses are in addition to the emerging use of hydrogen in power generation technology, including transportation, as discussed in Chapter 2. Except for situations such as in the petrochemical industry, in which hydrogen is utilized more or less immediately after its production from a hydrocarbon feedstock, most applications require that hydrogen be stored after its production by some method prior to its eventual endpoint usage. Many factors influence the physical state (i.e., gas, liquid, solid, or contained in a chemical substance) in which hydrogen will be stored and how it will be supplied for a specific application. In those situations where hydrogen has been a well-established commodity, the physi-cal state is well understood, and storage systems have been developed over the years. For example, hydrogen is often used as a reactant in laboratory research or in manufacturing. In these applications, compressed hydrogen gas is deployed in appropriate size cylinders at pressures up to about 200-300 bar. In addition, when hydrogen is used in a unique and critical capability (e.g., as a rocket propellant for launching spacecraft), thenCONTENTSIntroduction 65 Compressed Gas Hydrogen Storage 67 Cryogenic Hydrogen Storage Systems 69 On-Board Reversible Hydrogen Storage Materials and Systems 74Interstitial Metal Hydrides 74 Complex Metal Hydrides 77 Adsorption Materials 78Off-Board Reversible Hydrogen Storage Materials and Systems 80 Liquid Organic Hydrogen Carriers 81 Hydrolysis Reactions 81 Metal Hydrides and Ammonia Borane 84Concluding Remarks 84 Acknowledgments 85 References 85cryogenic liquid hydrogen (LH2) is used and stored in cryogenic containment vessels as part of the launch vehicle. On the other hand, whenever hydrogen is to be used in a role that would either replace existing technologies or serve a novel function, the current storage approaches generally must be heavily adapted, or new ones developed, to meet the different operating parameters and constraints. Chapter 1 describes the increasing concerns over the energetic, political, and environ-

Sandia National Laboratories has developed a vehicle-scale demonstration hydrogen storage system as part of a Work for Others project funded by General Motors. This Demonstration System was developed based on the properties and characteristics of sodium alanates which are complex metal hydrides. The technology resulting from this program was developed to enable heat and mass management during refueling and hydrogen delivery to an automotive system. During this program the Demonstration System was subjected to repeated hydriding and dehydriding cycles to enable comparison of the vehicle-scale system performance to small-scale sample data. This paper describes the experimental results of life-cycle studies of the Demonstration System. Two of the four hydrogen storage modules of the Demonstration System were used for this study. A well-controlled and repeatable sorption cycle was defined for the repeated cycling, which began after the system had already been cycled forty-one times. After the first nine repeated cycles, a significant hydrogen storage capacity loss was observed. It was suspected that the sodium alanates had been affected either morphologically or by contamination. The mechanisms leading to this initial degradation were investigated and results indicated that water and/or air contamination of the hydrogen supply may have lead to oxidation of the hydride and possibly kinetic deactivation. Subsequent cycles showed continued capacity loss indicating that the mechanism of degradation was gradual and transport or kinetically limited. A materials analysis was then conducted using established methods including treatment with carbon dioxide to react with sodium oxides that may have formed. The module tubes were sectioned to examine chemical composition and morphology as a function of axial position. The results will be discussed.

Complex metal hydrides are attracting much attention as a class of candidate materials for hydrogen storage. Lithium-based complex hydrides, including lithium aluminum hydrides (LiAlH4 and Li3AlH6), are among the most promising materials, owing to their high hydrogen contents. In the present work, we investigated the dehydrogenation/rehydrogenation reactions of a combined system of Li3AlH6 and Mg(NH2)2, which has a theoretical hydrogen capacity of 6.5 wt %. Thermogravimetric analysis of hydrogenated 2/3Al−Li2Mg(NH)2 (doped with 4 wt % TiCl3) indicated that a large amount of hydrogen (∼6.2 wt %) can be stored under 300 °C and 172 bar of hydrogen pressure. The FT-IR and NMR results showed that the reaction between Li3AlH6 and Mg(NH2)2 is reversible. Further, a short-cycle experiment has demonstrated that the new combined material system of alanates and amides can maintain its hydrogen storage capacity upon cycling of the dehydrogenation/rehydrogenation reactions.

The emergence of a Hydrogen Economy will require the development of new media capable of safely storing hydrogen in a compact and light weight package. Metal hydrides and complex hydrides, where hydrogen is chemically bonded to the metal atoms in the bulk, offer some hope of overcoming the challenges associated with hydrogen storage. The objective is to find a material with a high volumetric and gravimetric hydrogen density that can also meet the unique demands of a low temperature automotive fuel cell. Currently, there is considerable effort to develop new materials with tunable thermodynamic and kinetic properties. This tutorial review provides an overview of the different types of metal hydrides and complex hydrides being investigated for on-board (reversible) and off-board (non-reversible) hydrogen storage along with a few new approaches to improving the hydrogenation-dehydrogenation properties.

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;One of the most critical elements in engineering a hydrogen fuel cell vehicle is the design of the on-board hydrogen storage system. Because the current compressed-gas hydrogen storage technology has several key challenges, including cost, volume and capacity, materials-based storage technologies are being evaluated as an alternative approach. These materials-based hydrogen storage technologies include metal hydrides, chemical hydrides, and adsorbent materials, all of which have drawbacks of their own. To optimize the engineering of storage systems based on these materials, it is critical to understand the impacts these systems will have on the overall vehicle system performance and what trade-offs between the hydrogen storage systems and the vehicle systems might exist that allow these alternative storage approaches to be viable.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;To gain a better understanding of the interactions that exist between various materials-based hydrogen storage systems and the vehicle system as well as the engineering challenges that exist when integrating one of these systems with a vehicle, the National Renewable Energy Laboratory (NREL) developed a vehicle-level model designed to be sensitive to these issues. The Hydrogen Storage Simulation Model (HSSIM) was developed under the Hydrogen Storage Engineering Center of Excellence (HSECoE) as a specialized tool that could be used to assist in the design and engineering of materials-based hydrogen storage systems being considered by the HSECoE. This tool is designed to not only allow for understanding key trade-offs, but also to have a seamless integration with the HSECoE fuel cell and detailed hydrogen storage system models and to evaluate progress towards the U.S. Department of Energy's hydrogen storage technical targets. This model has been integrated with a fuel cell model developed by Ford Motor Company in a HSECoE common modeling framework developed by United Technologies Research Center and other HSECoE partners.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;This paper focuses on the development, structure, and validation of the vehicle model HSSIM and summarizes its integration within the framework. HSSIM and the framework are then used to obtain trade-offs for various specific materials-based storage system designs. This includes hydrogen storage sizing analyses, mass compounding analyses, range versus volume studies, and vehicle and component performance analyses, such as acceleration rates and fuel cell and energy storage interactions.&lt;/div&gt;&lt;/div&gt;

Advanced reactor concept for complex hydrides: Hydrogen desorption at fuel cell relevant boundary conditions

The kinetics of lightweight solid-state hydrogen storage materials: A review