Hydride Hydrogen Research Articles

Optimization of tree-shaped fin structures towards enhanced absorption performance of metal hydride hydrogen storage device: A numerical study

Tree-shaped fins were introduced to improve the heat transfer of metal hydride reactor. A two-dimensional steady-state model was first applied to obtain the optimal geometric structures of tree-shaped fins using genetic algorithm with the constraint of fixed fin mass. Then, the hydrogen absorption performance of MH reactors with embedded radial fins and tree-shaped fins were numerically studied and compared using a multi-physical model. It was indicated that the hydrogen absorption time for 90% saturation for the reactor with optimized tree-shaped fins nearly decreases by 20.7% as compared with that for radial fins. The heat transfer and absorption performance of MH reactor were much sensitive to the length ratio of tree-shaped fins, which can be improved with increasing the length ratio. Besides, the performance of optimized tree-shaped fins reactor with variable angle ratio was only slightly better than that for fixing angle ratio at 1, indicating that the angle ratio of tree-shaped fins can be kept at 1 for simplifying the design. Moreover, the absorption performance of the reactor can be enhanced with increasing the maximum branch level of tree-shaped fins. Furthermore, it was shown that the optimized geometric structures of tree-shaped fins under different MHs thermal conductivities are nearly identical.

Droop based control strategy for balancing the level of hydrogen storage in direct current microgrid application

An adaptive droop control method based on level of stored hydrogen (LSH) is proposed in order to balance the LSH of each metal hydride (MH) hydrogen storage unit for DC microgrid application. In this methodology, the droop coefficient is inversely proportional to the nth order of the LSH in charging mode, whereas it is proportional to nth order of the LSH in discharging mode. The droop coefficient is modified according to the LSH of MH tanks and controls the power sharing between the FC generators using DC-DC converters. Simulation results confirm the effectiveness of the proposed control strategy. It is found that using the adaptive droop control method, fuel cell (in discharging mode) with higher LSH of MH tank delivers more power using DC-DC converter, while other fuel cell with lower LSH of MH tank provides less power. Load sharing speed between the fuel cell units can be adjusted by modifying the exponent n of LSH in droop control. This control strategy is very useful for the decentralized control of hydrogen storage based microgrid.

Modelling of metal hydride hydrogen compressors from thermodynamics of hydrogen – Metal interactions viewpoint: Part I. Assessment of the performance of metal hydride materials

This work presents a model to determine productivity and heat consumption of hydrogen compression utilising metal hydrides (MH) by using Pressure – Composition – Temperature (PCT) diagrams of the MH materials at defined operating conditions – temperatures and hydrogen pressures. The present Part I is focused on the analysis of hydrogen compression performances of several AB5- and AB2-type intermetallic alloys which, when operating between temperatures of 20 and 150 °C, provide H2 compression up to 500 atm, with a cycle productivity about 100 NL H2/kg MH and compression ratio of up to 10, at H2 suction pressure below 10–15 atm, or up to 5 at higher suction pressures.We show that calculated cycle productivities of hydrogen compression are related to the operating conditions and significantly vary for the different MH materials, even though showing similar trends in their changes. The cycle productivity of MH material increases with decrease of the cooling temperature, decrease of the discharge pressure, increase of the heating temperature and increase of the suction pressure. When hydrogen pressure approaches plateau pressures for H2 absorption at cooling or H2 desorption at heating, the changes of the cycle productivity become very pronounced. Particularly, the compression productivity becomes very sensitive to the P-T variations when the isotherms show presence of “flat” pressure plateaux which are characteristic for the ideal PCT diagrams of the MH. Thus, in the latter case, even minor changes in P-T result in a dramatic variation of the cycle productivity and when aiming at increased efficiency of the process, a strict P-T control is required.

Modelling of metal hydride hydrogen compressors from thermodynamics of hydrogen – Metal interactions viewpoint: Part II. Assessment of the performance of metal hydride compressors

Performance of the thermally-driven metal hydride hydrogen compressor (MHHC) is defined by (a) its H2 compression ratio and maximum output H2 pressure; (b) throughput productivity/average output flow rate; (c) specific thermal energy consumption which determines H2 compression efficiency. In earlier studies, the focus of the R&D efforts was on the optimisation of the design of the MH containers and heat and mass transfer in the MH storage and compression system aimed at shortening the time of the H2 compression cycle. This work considers an important but insufficiently studied aspect of the development of the industrial-scale thermally driven MHHC's – selection of the materials and optimisation of the materials performance. Further to the operation in the specified pressure/temperature ranges, materials selection should be based on the estimation of the productivity of the compression cycle, and specific heat consumption required for the H2 compression, which together determine the process efficiency.The current work presents a model to determine productivity and heat consumption for a single- and multi-stage MHHC's which is based on use of Pressure – Composition – Temperature (PCT) diagrams of the utilized metal hydrides at defined operating conditions – temperatures and hydrogen pressures – and main operational features of the MHHC (number of stages, amounts of the MH materials used, cycle time). In Part I of this work [Lototskyy, Yartys, et al., Int J Hydrogen Energy, DOI: 10.1016/j.ijhydene.2020.10.090], we showed that the calculated cycle productivities significantly vary for the different materials. Analysis of the system performance carried out in this work (Part II) shows that the throughput productivity and efficiency of a multi-stage MHHC also depends on the types and amounts of the used MH materials in the multi-stage compressor layout. This has been analysed for a number of the most practically important AB5 and Laves type AB2 hydrogen storage alloys integrated into the MHHC's.A comparison of experimentally measured performances of single-, two- and three-stage industrial-scale MHHC's developed by the authors earlier shows their satisfactory agreement with the modelling results thus demonstrating a high value of the presented method for the proper materials selection during development of the MHHC. As an important future development, the work presents a performance evaluation of a two-stage MHHC for H2 compression operating in the pressure range from 30 to 500 atm at operating temperatures between 20 and 150 °C.

Thermal management and power saving operations for improved energy efficiency within a renewable hydrogen energy system utilizing metal hydride hydrogen storage

To ensure the energy efficiency of renewable hydrogen energy systems, power conservation and thermal management are necessary. This study applies these principals to the operation of metal hydride tanks (MHTs) in a bench-scale hydrogen system, named Hydro Q-BiC™, comprising photovoltaic panels (20 kW), an electrolyzer (5 Nm3/h), MHTs containing a TiFe-based MH (40 Nm3), fuel cells (FC; 3.5 kW(power)/2.5 kW(heat)), and Li-ion batteries (20 kW/20 kWh). Here, we show that in a modified hydrogen production operation, with limited use of auxiliaries for cooling the MHTs, the power consumption of the MHTs was reduced by more than 99% compared to a typical operation. The thermal requirements for the MHTs were reduced by ceasing production in a pressurized state. During the hydrogen use operation, the power consumption was reduced to 1/4 and the FC heat output could be fully used; hence, the overall energy efficiency (power-to-hydrogen-to-power/heat) was as high as ~ 60% (43% for the typical operation).

Performance investigation of a multi-stage sorption hydrogen compressor

Among several thermodynamic applications of metal hydrides, sorption hydrogen compressor (SHC) is more attractive for real-time application due to ease of construction and operation. In the present study, a four-stage sorption hydrogen compressor is proposed with detailed working principle for the compression output of >500 bar pressure. By adopting the screening methodology, four metal hydrides, i.e. La0.9Ce0.1Ni5, Ti0.99Zr0.01V0.43Fe0.99Cr0.05Mn1.5, MmNi5 and TiCrMn are selected for stages – 1, 2, 3 and 4 respectively with the supply temperature of 298 K and discharge temperatures of 373 K. The performance of sorption hydrogen compressor is estimated through finite volume approach and thermodynamic simulation in terms of variations in metal hydride bed pressure, temperature, hydrogen transmission, compressor work and efficiency. The numerical model is validated with experimentally measured metal hydride bed temperature and hydrogen concentration for single-stage hydrogen compressor, which are observed to be in good agreement. The cycle time of multi-stage SHC is predicted to be ~100 min with the maximum compression ratio of 73 with an overall efficiency of 10.62% employing 0.5 kg of each alloy and supply pressure of 9.5 bar. It is also observed that the discharge temperature greatly influences system performance. The dynamic performance of the system is also estimated with the implementation of simulation generated property data and observed that the performance parameters increased with the progression of hydrogen transmission.

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.

Perspectives and challenges of hydrogen storage in solid-state hydrides

Hydrogen has been widely considered as a clean energy carrier that bridges the energy producers and energy consumers in an efficient and safe way for a sustainable society. Hydrogen can be stored in a gas, liquid and solid states and each method has its unique advantage. Though compressed hydrogen and liquefied hydrogen are mature technologies for industrial applications, appropriate measures are necessary to deal with the issues at high pressure up to around 100 MPa and low temperature at around 20 K. Distinct from those technologies, storing hydrogen in solid-state hydrides can realize a more compact and much safer approach that does not require high hydrogen pressure and cryogenic temperature. In this review, we will provide an overview of the major material groups that are capable of absorbing and desorbing hydrogen reversibly. The main features on hydrogen storage properties of each material group are summarized, together with the discussion of the key issues and the guidance of materials design, aiming at providing insights for new material development as well as industrial applications.

Formation of a Key Intermediate Complex Species in Catalytic Hydrolysis of NH3BH3 by Bimetal Clusters: Metal-Dihydride and Boron-Multihydroxy.

The hydrolysis of AB (AB, NH3BH3) with the help of transition metal catalysts has been identified as one of the promising strategies for the dehydrogenation in numerous experiments. Although great progress has been achieved in experiments, evaluation of the B-N bond cleavage channel as well as the hydrogen transfer channel has not been performed to gain a deep understanding of the kinetic route. Based on the density functional theory (DFT) calculation, we presented a clear mechanistic study on the hydrolytic reaction of AB by choosing the smallest NiCu cluster as a catalyst model. Two attacking types of water molecules were considered for the hydrolytic reaction of AB: stepwise and simultaneous adsorption on the catalyst. The Ni and Cu metal atoms play the distinctive roles in catalytic activity, i.e., Ni atom takes reactions for the H2O decomposition with the formation of [OH]− group whereas Cu atom takes reactions for the hydride transfer with the formation of metal-dihydride complex. The formation of Cu-dihydride and B-multihydroxy complex is the prerequisite for the effectively hydrolytic dehydrogenation of AB. By analyzing the maximum barrier height of the pathways which determines the kinetic rates, we found that the hydride hydrogen transferring rather than the N-B bond breaking is responsible to the experimentally measured activation energy barrier.

Application of Intermetallics (La,Ce)Ni5 in Hydrogen Energy Storage Systems

The hydrogen sorption characteristics of La1–xCexNi5 alloys (x = 0, 0.1, 0.2, 0.25, 0.5) were studied in the temperature range 298–363 K. The optimal compositions of intermetallic compounds were determined for use as hydrogen sorbents in reusable accumulators: compounds La0.9Ce0.1Ni5 and La0.8Ce0.2Ni5. Based on them, a metal hydride hydrogen accumulator was designed and manufactured and its technical and operational characteristics were found. The developed devices are proposed to be applied in electric energy storage systems using hydrogen as an energy carrier.

МЕТАЛОГІДРИДНИЙ АКУМУЛЯТОР-КОМПРЕСОР ВОДНЮ З АВТОМАТИЧНОЮ СИСТЕМОЮ УПРАВЛІННЯ ТА КОНТРОЛЮ

A project of metal hydride hydrogen compressor is presented, which can be used as an element of refueling complexes, hydrogen storage and compression systems. The capacity of the developed sample is 40 kg of hydrogen, the mass is 4,8 ton, and the maximum compression pressure is 15 MPa. The base metal hydride material on the basis of which this compressor battery model is developed is LaNi4.5Al0.5. the sorption capacity of hydrogen of which is determined experimentally, and is at least 1.38 % by weight. A feature of the developed compressor battery is the use of air cooling, the presence of an automatic monitoring and control system, I allow a number of operations to be performed in automatic mode, and the use of software, electrical and automatic protection against overpressure. Each accumulator-compressor is made in the form of a steel box in which six blocks (capsules) are placed. The block, respectively, is made in the form of a steel coaxial multilayer cylinder, on the outer side of which there is a heating element and a layer of thermal insulation. In the middle of the cylinder is a sealed capsule filled with metal hydride material. Capsules are interconnected with the collector through a piping system. Also, the piping system is equipped with an inlet valve connecting the volume formed with an external receiver. The battery-compressor is equipped with an external receiver, to which a hydrogen, vacuum, nutrient and consumable outline is connected. Each circuit is equipped with an electromagnetic valve, as well as measuring devices, which makes it possible to carry out automatic control of parameters and automatic control of the device in accordance with the operating mode. A list of equipment is presented, on the basis of which a system of automatic control and monitoring, a block diagram of the main operating modes, an interface of the developed software are developed. Depending on the mode chosen by the operator, the automatic control and monitoring system allows activation of metal hydride materials, purification of contaminants of harmful impurities, sorption and desorption of hydrogen.

Numerical simulation on the storage performance of a phase change materials based metal hydride hydrogen storage tank

In metal hydride (MH) hydrogen storage tanks, the integration of phase change materials (PCM) can store and release the reaction heat to promote the reaction process without an external heat source. In order to get a high-performance MH-PCM storage tank and understand the effect of mass ratio of PCM to MH on the storage performance, this research proposes a novel MH-PCM storage unit (PCM sandwiched between two layers of MH) stacked inside a cylindrical tank. A mathematical model is established to describe the heat and mass transfer in the process of hydrogen ab/desorption and heat storage/release. It is found that the PCM sandwiched structure has a larger heat transfer area than the surrounding structure, which improves the hydrogen absorption and desorption rate. For the MH-PCM unit, the mass ratio of PCM to MH affects the hydrogen ab/desorption rate. Varying the mass ratio of PCM to MH requires adjustments in the hydrogen absorption pressure for completely absorbing the hydrogen, which also impacts the amount of sensible and latent heat stored in the PCM. The results show that in order to fully absorb the hydrogen, the hydrogen absorption pressure must increase to compensate for reduced mass ratio of PCM to MH, and the ratio of sensible heat to latent heat storage increases.

Semiconductor-to-Metal-like Behavior of Si with Dopant Concentration—An Electrochemical Investigation and Illustration with Surface Hydride Formation and Hydrogen Evolution Reaction

n-type and p-type silicon of various dopant concentrations (1014 to 1019 cm–3) are electrochemically characterized in a 1% hydrogen fluoride (HF) electrolyte with voltammetry, electrochemical imped...

Metal hydride thermal management using phase change material in the context of a standalone solar-hydrogen system

In this paper, a model of a metal hydride thermal management using phase change material in the context of a standalone solar-hydrogen system is proposed and investigated. The HOMER software is used to simulate the optimal system architecture and yearly power profiles of the electrolyser and fuel cell stacks used in a case study of a remote household in southeast Australia. A dynamic theoretical model of a phase change material arrangement for thermal management of the metal hydride hydrogen storage unit is then built in MATLAB environment to study the performance behaviour of the hydrogen storage system in this context. Based on the case used for this study, it was found that approximately equivalent to ~12% of total energy content of the hydrogen generated by the electrolyser can be saved annually by replacing an external energy thermal management system with the proposed phase change material thermal management solution. It was also found that the conductivity of phase change materials must be improved to a minimum of 1.5 W/mK, in order to make this thermal management arrangement more practical.

Metal hydride hydrogen storage and compression systems for energy storage technologies

Along with a brief overview of literature data on energy storage technologies utilising hydrogen and metal hydrides, this article presents results of the related R&D activities carried out by the authors. The focus is put on proper selection of metal hydride materials on the basis of AB5- and AB2-type intermetallic compounds for hydrogen storage and compression applications, based on the analysis of PCT properties of the materials in systems with H2 gas. The article also presents features of integrated energy storage systems utilising metal hydride hydrogen storage and compression, as well as their metal hydride based components developed at IPCP and HySA Systems.

Design tool for estimating metal hydride storage system characteristics for light-duty hydrogen fuel cell vehicles

The U.S. Department of Energy (DOE) has developed the Framework model to simulate fuel cell-based light-duty vehicle operation for various hydrogen storage systems. This transient model simulates the performance of the storage system, fuel cell, and vehicle for comparison to DOE's Technical Targets using four drive cycles. Metal hydride hydrogen storage models have been developed for the Framework model. Despite the utility of this model, it requires that material researchers input system design specifications that cannot be easily estimated. To address this challenge, a design tool has been developed that allows researchers to directly enter physical and thermodynamic metal hydride properties into a simple sizing module that then estimates the systems parameters required to run the storage system model. This design tool can also be used as a standalone MS Excel model to estimate the storage system mass and volume outside of Framework and compare it to the DOE Technical Targets. This model will be explained and exercised with existing hydrogen storage materials.

Analysis of metal hydride storage on the basis of thermophysical properties and its application in microgrid

Present study focuses on the analysis of metal hydride hydrogen storage in renewable power generators-based microgrid (µG) system. The design of metal hydride storage unit requires parametric analysis on the basis of its thermophysical properties such as activation/deactivation energy, enthalpy of formation, equilibrium pressure, reaction kinetics and external thermal management system. This parametric analysis helps to assess suitability of the hydride storage with hydrogen generation (electrolyzer) and utilization (fuel cell) units in µG. Application of metal hydride in the µG creates a sophisticated system which requires careful analysis and operating strategy for achieving manifold benefits such as higher efficiency, durability of the components and self-sufficiency. In the present study, different hydrides are selected namely, LaNi5, TiCr1.6Mn0.2, hydroalloy C5 graphite and MgH2 for performance analysis on the basis of their thermophysical properties. The performance is evaluated in different operating modes aiming for higher efficiency, components durability and system self-sufficiency (minimum grid-dependency). A detailed mathematical modelling is performed in the MATLAB simulation tool for performance evaluation of overall µG system, which consists of 5 kW photovoltaic (PV), 1 kW fuel cell (FC), 5 L hydride storage and 0.6 kW electrolyzer. It was observed that the hydrogen charging and discharging processes in the hydride storage unit strongly depend on its thermophysical properties and hence require certain specific operating conditions for efficient working. Considering suitable discharging characteristics at low temperature and pressure, LaNi5and C5 hydroalloy can be suitable for transient operation with proton exchange membrane fuel cell application. Overall energy efficiency of up to ≈ 95.49% is achieved in such type of storage-based µG. Grid-dependency ratio (load demand met by grid power/total load demand) was found between 0.26 and 5.83% in different operating modes.

A radiation shielding sensitivity analysis based on metal hydrides multilayers

In order to shield neutron and gamma rays efficiently, a multilayer model is designed with metal hydrides and heavy metals and is analysed based on Monte Carlo simulations. In terms of shielding performance, the hydrogen in metal hydrides acts as a moderator to slow down the neutron energy and heavy metals are good for absorbing gamma rays. A simulation and calculational analysis are carried out with various parameters such as spectrum change, shield thickness, and number of multilayers. In addition, the rate of DPA (displacement per atom) is analysed to estimate both the lifetime and radiation resistance with the MCNP code. From lots of simulations, ZrH2 and W couples are the best candidate especially for shielding gamma rays, while TiH2 with W is good for neutron shielding. The concept of multilayer metal hydride such as TiH2 and ZrH2 coupled with W could be one of best combinations to shield both neutron and gamma-rays in many nuclear facilities such as nuclear reactor, fusion reactor and other applications.

Experimental behaviour of a three-stage metal hydride hydrogen compressor

A three-stage metal hydride hydrogen compressor (MHHC) system based in AB2-type alloys has been set-up. Every stage can be considered as a Sieverts-type apparatus. The MHHC system can work in the pressure and temperature ranges comprised from vacuum to 250 bar and from RT to 200 °C, respectively. An efficient thermal management system was set up for the operational ranges of temperature desired. It drops temperature shifts due to hydrogen expansion during stage coupling and hydrogen absorption/desorption in the alloys. Each reactor consists of a single and thin stainless-steel tube to maximize heat transfer. These were filled with similar amount of AB2 alloy. The MHHC system was able to produce a compression ratio as high as 84.7 for inlet and outlet hydrogen pressures of 1.44 and 122 bar for a temperature span of 23 °C – 120 °C.

Correlation between the Parameters of Gas-Phase and Electrochemical Hydrogenation Processes of Intermetallic Compounds

The main ways measuring the parameters that characterize processes of the gas-phase and electrochemical hydrogenation of intermetallic compounds—promising materials for metal hydride hydrogen tanks and chemical power sources—are listed and discussed. The general principles of the mathematical treatment of pertinent experimental data and ways of determining the effective diffusion coefficient of hydrogen in metal hydrides are described. It is shown that sorption/desorption isotherms can be constructed for metal−hydrogen systems on the basis of electrochemical measurements.