Polymer-based composite containing nanostructured LaNi5 for hydrogen storage: Improved air stability and processability

Safe and effective methods for hydrogen storage are still required to expand its usage as an energy carrier. One approach to contribute to solving this issue is to develop a polymer-based composite. In this study, an acrylonitrile-EPDM(ethylene/propylene/diene)-styrene (AES) composite containing nanostructured LaNi₅ was produced by wet ball milling (WM) for hydrogen storage, aiming operation at room temperature. The samples were processed as a cylindrical filament for the analyses performed. Improved particle dispersion was obtained for WM-AES/LaNi₅, which correlates with increasing the hydrogen sorption capacity. The polymer was able to maintain the specimen integrity after 20 hydriding cycles, avoiding the LaNi₅ pulverization and the reduction of LaNi₅ crystallite size. The crystallite size was in the nanoscale, reaching nearly 8 nm for WM-AES/LaNi₅. Fewer cycles were required to stabilize the hydrogen capacity for the composites. The samples were exposed to ambient air for up to 17 h, and their absorption kinetics were evaluated. The time required to reach 80% of hydrogen capacity after being exposed for 17 h increased 16.7x and 2.5x for ball-milled LaNi₅ and WM-AES/LaNi₅, respectively. Therefore, it is shown that the polymer reduces the effects of air exposure on its absorption kinetics. This study shows a promising method to produce a moldable polymer composite for hydrogen storage operational at room temperature.     

A metal hydride–polymer composite for hydrogen storage applications

To address the issue of the breakdown into fine powders that occurs in the practical use of metal hydrides, the possibility of using a polymeric material as a matrix that contains the active metal particles was experimentally assessed. A ball milling approach in the tumbling mode was used to develop a metal hydride–polymer composite with a high metal to polymer weight ratio. The alloy powder was blended with the polymer and a coating of the metal particles was obtained. The composite was consolidated by hot pressing and the pellets were characterized in terms of their hydriding–dehydriding properties. The materials did not show significant losses in either loading capacity or kinetic properties. The polymeric matrix resulted as being stable under hydrogen cycling. Further, from SEM observation it was confirmed that the metal powders remained embedded in the polymeric matrix even after a number of cycles and that the overall dimensional integrity was retained.     

Fundamentals and recent advances in polymer composites with hydride-forming metals for hydrogen storage applications

Hydrogen has unique properties that make it a promising energy vector to replace fossil fuels. However, it is still required to develop safe and efficient storage methods before being widely implemented. Storing hydrogen in hydride-forming metals (HFM) is an approach that has been extensively studied in the last decades. But only recently the preparation of polymer composites with HFM have been explored. Air resistance, volumetric stability and processability are some of the HFM properties that could be improved by incorporating a polymer phase. This review presents the fundamentals concepts of gas transport in dense polymers, and the evolution and trends of incorporating HFM particles into a polymer matrix. The most recent findings are summarized and discussed. The potential improvement of the most relevant classes of HFM and the mechanisms of how different classes of polymers could be advantageously used are reported.     

Experimental studies on LaNi4.25Al0.75 alloy for hydrogen and thermal energy storage applications

Reversible exothermic and endothermic reactions between metals/alloys and hydrogen gas provide great opportunity to utilize various thermal energy sources such as waste heat, industrial exhaust, and solar thermal energy. Metal hydrides with favourable properties to operate at medium temperature heat (about 150 °C) are limited, and studies on hydrides in this temperature range are scarce. Hence, the present study aims at experimental investigations on LaNi_4.25Al_0.75 alloy in the temperature range of 150 °C–200 °C. A novel cartridge type of reactor is employed to investigate the hydrogen storage characteristics and thermal storage performance of this alloy. LaNi_4.25Al_0.75 is found to have a hydrogen storage capacity of about 1.20 wt% at 10 bar and 25 °C. In addition, it can store a total thermal energy of 285.7 ${\mathrm{k}\mathrm{J}.\mathrm{k}\mathrm{g}}_{\mathrm{M}\mathrm{H}}^{-1}$ and can deliver heat at an average rate of 287.5 ${\mathrm{W}.\mathrm{k}\mathrm{g}}_{\mathrm{M}\mathrm{H}}^{-1}$ at an efficiency of 64.1%.     

AB5/ABS composite material for hydrogen storage

AB5 metal hydride (MH) particles were polymer dispersed in order to entrap the micro and nanoparticles produced by repeated fragmentations of the metal phase during the hydrogen charging/discharging cycles. Acrylonitrile-butadiene-styrene copolymer (ABS) was selected as a matrix on the basis of its physical and chemical properties. AB5/ABS composite pellets were obtained by using a dry mechanical particle coating approach in a tumbling-mill apparatus and successive consolidation by uniaxial hot pressing. A number of characterization techniques were used to assess the morphological, chemical and structural properties of the composites. High pressure DSC measurements, conducted at different pressure values, were used to assess the H₂ absorption properties and profile the Van't Hoff plots of the material. The overall results indicated that the AB5/ABS composite well tolerated the hydriding effects on metal particles, with no losses in hydriding kinetics. The material characteristics were found to be compatible with its application in developing MH-based H₂ storage devices.     

Thermal design of a hydrogen storage system using La(Ce)Ni5

Hydrogen storage within a metal hydride involves exothermic and endothermic processes for hydrogen absorption and desorption, respectively. In addition, the thermal conductivity of the particulate metal hydride (i.e., powder) after repeated absorption processes is extremely low compared to its bulk phase. Low heat conduction through the metal hydride powder makes the hydrogen charging slow; thus, appropriate thermal management is necessary to achieve the fast charging time with the maximum energy density. In this work, we propose a thermal design of a portable hydrogen storage system made of a 300-mL vessel by balancing the internal and external thermal resistances. A copper-mesh structure is employed inside the vessel for enhancing the effective thermal conductivity of metal hydride powder (i.e., reducing the internal thermal resistance). On the other hand, a compact fan is used for enhancing the forced convection heat transfer from the vessel (i.e., reducing the external thermal resistance). Consequently, a copper-mesh structure sacrificing 4.3% of the internal vessel volume was manufactured by following the thermal design. In addition, the effect of the proposed thermal design was confirmed by actual hydrogen-charging experiments that showed 73.5% reduction of the charging time.     

Nanomaterials for on-board solid-state hydrogen storage applications

Hydrogen has the highest gravimetric density (energy density per unit mass) of any fuel. The combustion of hydrogen releases energy in the form of heat. When hydrogen reacts with oxygen in a fuel cell, the reaction releases energy in the form of electricity. Unlike hydrocarbon-based fuels, the generation of energy from either the combustion of hydrogen or the reaction of hydrogen with oxygen in a fuel cell is not accompanied by the emission of greenhouse gases. This makes hydrogen a promising solution to solve global warming issues. However, hydrogen has a low volumetric density (low energy density per unit volume) which makes storing or transporting hydrogen extremely difficult and expensive. To accelerate the utilization of hydrogen as an energy carrier, it is necessary to develop advanced hydrogen storage methods that have the potential to have a higher energy density.The hydrogen storage market is segmented by application into: (1) Stationary power: stored hydrogen is consumed for example in a fuel cell for use in backup power stations, refueling stations, power stations; (2) Portable power: hydrogen storage applications for electronic devices such as mobile phones, flash lights, and portable generators; and (3) Transportation: industries including automobiles, aerospace, unmanned aerial systems, and hydrogen tanks used throughout the hydrogen supply chain. The increasing development of light and heavy fuel cell vehicles is expected to drive the development of on-board solid-state hydrogen technologies.A large number of research groups worldwide for many years have been trying to develop materials having the right set of thermodynamic and kinetic properties, along with all of the physical properties (high gravimetric density, high volumetric density, etc.) to allow for low-pressure storage system in ambient conditions. However, to date, no material has been found that satisfies all the desired properties to be viably used in many applications. Even if we consider only three parameters namely gravimetric density, volumetric density, and system cost, no materials that can meet the ultimate targets of the U.S. Department of Energy (DOE) or the 2030 targets of the European Union's Fuel Cells and Hydrogen Joint Undertaking (FCH JU) and the New Energy and Industrial Technology Development Organization (NEDO) in Japan.The present article reviews advances in solid-state hydrogen storage technology and compares the opportunities and challenges of selected materials. The materials reviewed in this article have a wider spectrum than the materials reviewed in other existing articles, including carbon nanotubes (CNTs), metal–organic frameworks (MOFs), graphene, boron nitride (BN), fullerene, silicon, amorphous manganese hydride molecular sieve, and metal hydrides. Pioneering works, important breakthroughs, as well as the latest developments for promising materials are also reviewed.In addition, for the first time the targets set by several official regulatory agencies for solid-state hydrogen storage are summarized. Achievements in academic and industrial research are compared against these targets.The future prospects of promising materials are analyzed based on how its practical application can be implemented according to market needs.     

Correlative high-resolution imaging of hydrogen in Mg2Ni hydrogen storage thin films

Nanometer scale imaging of hydrogen in solid materials remains an important challenge for the characterization of advanced materials, such as semiconductors, high-strength metallic alloys, and hydrogen storage materials. Within this work, we demonstrate high-resolution imaging of hydrogen and deuterium within Mg₂Ni/Mg₂NiH₄ hydrogen storage thin films using an in-house developed secondary ion mass spectrometer (SIMS) system attached to a commercially available dual-beam focused ion beam - scanning electron microscope (FIB-SEM) instrument. We further demonstrate a novel approach to measure the size, shape, and distribution of the hydride phase in partially transformed films using laser scanning confocal microscopy (LSCM) to measure surface topography changes from the hydride phase volume expansion. Combining these techniques provides new insights on hydride nucleation and growth within the Mg₂NiH_x system. Finally, we demonstrate the efficacy of tracking deuterium as a hydrogen analog to reduce the background for SIMS imaging of hydrogen in high-vacuum chambers (∼10⁻⁶ mbar).     

Improvement of Mg–Al alloys for hydrogen storage applications

In the context of energy carrier, storage of hydrogen is one of the key challenges for research today. The group of Mg-based hydrides stands as a promising candidate for competitive hydrogen storage with high reversible hydrogen capacity.     

A hybrid method for hydrogen storage and generation from water

This communication describes a new hybrid method for storing hydrogen in solid inorganic hydride materials as well as producing it from water based on the reaction between LiOH/LiOH·H₂O and LiH. As a hydrogen storage method, the release and uptake of hydrogen in this method are accomplished via a series of simple reactions with good kinetics within a practically reasonable temperature range. The reversible hydrogen storage capacity of the material system is 6–8.8 wt.% at <350 °C. This capacity is one of the highest among all other metal hydrides known to date in the same temperature range. As a hydrogen production method, 100% of hydrogen generated by this method comes from water by its reaction with alkali metal oxides. This method is also an environmentally friendly alternative to the current commercial processes for hydrogen production. The preliminary thermodynamic calculation on energy required for complete regeneration shows that the current system is energetically favorable.     

Spray-dried composite microparticles of polyetherimide and LaNi5 as a versatile material for hydrogen storage applications

Despite promising results for the encapsulation of sensitive components, spray drying hasn't been properly explored to produce energy storage powders. This study produced polyetherimide/LaNi₅ (40/60 wt%) microparticles by spray drying for hydrogen storage and comprehensively characterize their morphological, thermal, and hydrogen sorption properties. First, the effects of spray drying parameters on microparticle size and morphology were evaluated by a 2³ full factorial design. Samples were collected from the collector flask and the cyclone wall, differing particularly in the LaNi₅ weight fraction. The microparticles had a wrinkled surface, but the polyetherimide matrix successfully encapsulated the LaNi₅ particles. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that the glass transition temperature (T_g) and the onset of polyetherimide thermal degradation are inversely related to the LaNi₅ fraction. The microparticles absorbed hydrogen without incubation time, reaching maximum capacity of 0.4 wt% and 0.3 wt% for the samples from the cyclone and the collector. The H₂ capacity reduced after the first cycle. Spray drying effectively produced elastic microparticles where the polymer phase anchors the LaNi₅ particles through the H₂ absorption cycles, maintaining a constant morphology and thus an improved dimensional stability.     

Development of hydrogen storage reactor using composite of metal hydride materials with ENG

Hydrogen is widely accepted as a promising energy carrier replacing fossil fuels. In this context hydrogen storage is one of the critical challenges in realizing hydrogen economy which relies on hydrogen as the commercial fuel. Due to very low volumetric energy density of pure hydrogen, it is highly compressed as a gas phase or liquified at extremely low temperature. However, chemically combined state in other materials has advantages in terms of storage conditions and associated safety concerns.The present study focuses on a development of a hydrogen storage applicable to special fuel cell (FC) mobilities such as forklift but not limited to. We adopts a solid-state storage method using metal hydride composite prepared by processing La_0.9Ce_0.1Ni₅ and extended natural graphite (ENG). The isothermal hydrogen absorption/desorption behavior of the composite is measured at 20–80 °C. The results suggest that around 10 bar is sufficient to store 1.2 wt% of hydrogen. A cylindrical reactor is manufactured and experiments are carried out with the fabricated hydrogen storage material by changing operation conditions. The results of satisfaction are obtained in terms of the amount of hydrogen storage (>83 standard liter) and the absorption time (~10 min) under relatively moderate conditions of temperature (~19 °C) and pressure (~11 bar).As for scaling-up, a reactor of 2.0 kWh is designed based on the experimental results. CFD analysis is performed based on the hottest operation conditions focusing on a cooling water flow. The flow pattern and the temperature distribution of the cooling water are expected to be adequate not deviating from the stable operating conditions. CFD would be further applied to optimize the incorporated modular reactors.     

Finite element-based simulation of a metal hydride-based hydrogen storage tank

In this paper, a novel 3D flexible tool for simulation of metal hydrides-based (LaNi₅) hydrogen storage tanks is presented. The model is Finite Element-Based and considers coupled heat and mass transfer resistance through a non-uniform pressure and temperature metal hydride reactor. The governing equations were implemented and solved using the COMSOL Multiphysics simulation environment. A cylindrical reactor with different cooling system designs was simulated. The shortest reactor fill time (15 min) was obtained for a cooling design configuration consisting of twelve inner cooling tubes and an external cooling jacket. Additional simulations demonstrated that an increase of the hydride thermal conductivity can further improve the reactor dynamic performance, provided that the absorbent bed is sufficiently permeable to hydrogen.     

Zinc substituted MgH2 - a potential material for hydrogen storage applications

The search for efficient materials for onboard hydrogen storage applications is an emerging research field. Using density functional calculations, we demonstrate Zn substituted MgH₂ as a potential material for hydrogen storage. We predicted the ground state crystal structure of ZnH₂ which is found to be Pna2₁ (orthorhombic) structure with meta-stable behavior. The structural phase stability and phase transition of Mg_1−xZn_xH₂ systems have been analyzed. The H site energy of Mg_1−xZn_xH₂ systems is calculated to understand the hydrogen desorption process. Our calculations suggest that Zn substitution reduces the stability of MgH₂, thereby it may reduce the decomposition temperature of MgH₂. The band structure and density of states calculations reveal that the Mg_1−xZn_xH₂ systems are insulators. The chemical bonding behavior of Mg_1−xZn_xH₂ systems is established as iono-covalent in nature. Moreover, Zn substitution in MgH₂ induces disproportionate MgH bonds which could also contribute the reduction in the decomposition temperature as well as H sorption kinetics.     

Active disturbance rejection control of metal hydride hydrogen storage

Metal hydride (MH) hydrogen storage is used in both mobile and stationary applications. MH tanks can connect directly to high-pressure electrolyzers for on-demand charging, saving compression costs. To prevent high hydrogen pressure during charging, hydrogen generation needs to be controlled with consideration for unknown disturbances and time-varying dynamics. This work presents a robust control system to determine the appropriate mass flow rate of hydrogen, which the water electrolyzer should produce, to maintain the gaseous hydrogen pressure in the tank for the hydriding reaction. A control-oriented model is developed for MH hydrogen storage for control system design purposes. A proportional-integral (PI) and an active disturbance rejection control (ADRC) feedback controllers are investigated, and their performance is compared. Simulation results show that both the PI and ADRC controllers can reject both noises from the output measurements and unknown disturbances associated with the heat exchanger. ADRC excels in eliminating disturbances produced by the input mass flow rate, maintaining the pressure of the tank at the charging pressure with little oscillations. Additionally, the parameters estimated by the ADRC's extended state observer was used to predict the state-of-charge (SOC) of the MH.     

A metal hydride system for a forklift: Feasibility study on on-board chemical storage of hydrogen using numerical simulation

This paper describes a technical feasibility study of on-board metal hydride storage systems. The main advantages of these systems would be that of being able to replace counterweights with the weight of the storage system and using the heat emissions of fuel cells for energy, making forklifts a perfect use case. The main challenge is designing a system that supplies the required energy for a sufficiently long period. A first draft was set up and analyzed to provide a forklift based on a fuel cell with hydrogen from HydralloyC5 or FeTiMn. The primary design parameter was the required amount of stored hydrogen, which should provide energy equal to the energy capacity of a battery in an electric vehicle. To account for highly dynamic system requirements, the reactor design was optimized such that the storage was charged in a short time. Additionally, we investigated a system in which a fixed amount of hydrogen energy was required. For this purpose, we used a validated simulation model for the design concepts of metal hydride storage systems. The model includes all relevant terms and parameters to describe processes inside the system's particular reactions and the thermal conduction due to heat exchangers. We introduce an embedded fuel cell model to calculate the demand for hydrogen for a given power level. The resulting calculations provide the required time for charging or a full charge depending on the tank's diameter and, therefore, the necessary number of tanks. We conclude that the desired hydrogen supply times are given for some of the use cases. Accordingly, the simulated results suggest that using a metal hydride system could be highly practical in forklifts.     

On-board and Off-board performance of hydrogen storage options for light-duty vehicles

Leading physical and materials-based hydrogen storage options are evaluated for their potential to meet the vehicular targets for gravimetric and volumetric capacity, cost, efficiency, durability and operability, fuel purity, and environmental health and safety. Our analyses show that hydrogen stored as a compressed gas at 350–700 bar in Type III or Type IV tanks cannot meet the near-term volumetric target of 28 g/L. The problems of dormancy and hydrogen loss with conventional liquid H₂ storage can be mitigated by deploying pressure-bearing insulated tanks. Alane (AlH₃) is an attractive hydrogen carrier if it can be prepared and used as a slurry with >50% solids loading and an appropriate volume-exchange tank is developed. Regenerating AlH₃ is a major problem, however, since it is metastable and it cannot be directly formed by reacting the spent Al with H₂. We have evaluated two sorption-based hydrogen storage systems, one using AX-21, a high surface-area superactivated carbon, and the other using MOF-177, a metal-organic framework material. Releasing hydrogen by hydrolysis of sodium borohydride presents difficult chemical, thermal and water management issues, and regenerating NaBH₄ by converting B–O bonds is energy intensive. We have evaluated the option of using organic liquid carriers, such as n-ethylcarbazole, which can be dehydrogenated thermolytically on-board a vehicle and rehydrogenated efficiently in a central plant by established methods and processes. While ammonia borane has a high hydrogen content, a solvent that keeps it in a liquid state needs to be found, and developing an AB regeneration scheme that is practical, economical and efficient remains a major challenge.