Metal Hydride Based Hydrogen Storage Research Articles

A new AB4-type single-phase superlattice compound for electrochemical hydrogen storage

Metal-hydride based hydrogen storage materials have recently been designed for rechargeable batteries where protons serve as charge carriers. However, the metal-hydride materials generally suffer from poor cycling stability during electrochemical hydrogen storage process. Herein, we report, for the first time, a new AB4-type single-phase La0.78Mg0.22Ni3.67Al0.10 metal-hydride superlattice compound with excellent electrochemical hydrogen storage properties. This metal-hydride compound is able to deliver a high discharge capacity of 393 mAh g−1, according to its hydrogen gas absorbability (1.50 wt%), and exhibit a superior rate capability of 180 mAh g−1 even at 1.8 A g−1. In addition, the compound retains its crystalline structure when subjects to electrochemical cycling and shows strong anti-oxidation ability in alkaline electrolyte, indicative of excellent cyclability. Our results demonstrate that the AB4-type superlattice structure metal-hydride can be a promising electrode material for hydrogen storage, and provide a new avenue for the applications of metal-hydride batteries.

Design of a large-scale metal hydride based hydrogen storage reactor: Simulation and heat transfer optimization

An optimized design for a 210 kg alloy, TiMn alloy based hydrogen storage system for stationary application is presented. A majority of the studies on metal hydride hydrogen systems reported in literature are based on system scale less than 10 kg, leaving questions on the design and performance of large-scale systems unanswered. On the basis of sensitivity to various design and operating parameters such as thermal conductivity, porosity, heat transfer coefficient etc., a comprehensive design methodology is suggested. Following a series of performance analyses, a multi-tubular shell and tube type storage system is selected for the present application which completes the absorption process in 900 s and the desorption process in 2000 s at a system gravimetric capacity of 0.7% which is a vast improvement over similar studies. The study also indicates that after fifty percent reaction completion, heat transfer ceases to be the major controlling factor in the reaction. This could help prevent over-designing systems on the basis of heat transfer, and ensure optimum system weight.

Numerical simulation of the effect of aluminum foam on sorption induced wall strain in vertical, metal hydride based hydrogen storage container

Low thermal conductivity of metal hydride alloys significantly affects the sorption performance of hydrogen storage devices. Upon hydrogenation they also exert significant stresses on the containers due to volume changes and thermal cycling. Aluminum foam has been widely accepted as a means to enhance heat transfer and thereby improve sorption performance of metal hydride storage devices. In addition to this, such foams can also serve to homogenize the container strains. In this study, numerical simulation of the wall strain development upon hydrogenation of a vertically aligned metal hydride storage device is performed. The device contains LaNi5 as the storage alloy embedded with aluminum foam. Role of aluminum foam on hydrogenation and consequent development of wall strains is studied. Effect of controlled spatial variation of foam density as a means for strain reduction is also investigated.

Optimization and comprehensive characterization of metal hydride based hydrogen storage systems using in-situ Neutron Radiography

For the storage of hydrogen, complex metal hydrides are considered as highly promising with respect to capacity, reversibility and safety. The optimization of corresponding storage tanks demands a precise and time-resolved investigation of the hydrogen distribution in scaled-up metal hydride beds. In this study it is shown that in situ fission Neutron Radiography provides unique insights into the spatial distribution of hydrogen even for scaled-up compacts and therewith enables a direct study of hydrogen storage tanks. A technique is introduced for the precise quantification of both time-resolved data and a priori material distribution, allowing inter alia for an optimization of compacts manufacturing process. For the first time, several macroscopic fields are combined which elucidates the great potential of Neutron Imaging for investigations of metal hydrides by going further than solely ’imaging’ the system: A combination of in-situ Neutron Radiography, IR-Thermography and thermodynamic quantities can reveal the interdependency of different driving forces for a scaled-up sodium alanate pellet by means of a multi-correlation analysis. A decisive and time-resolved, complex influence of material packing density is derived. The results of this study enable a variety of new investigation possibilities that provide essential information on the optimization of future hydrogen storage tanks.

System design and exergetic evaluation of a flexible integrated reforming combined cycle (IRCC) power plant system with carbon dioxide (CO2) capture and metal hydride based hydrogen storage

Natural gas combined cycle (NGCC) power plants with pre-combustion CO2 capture called, integrated reforming combined cycle (IRCC) power plants could be operated in a flexible and environment friendly manner by incorporating hydrogen storage. The current article presents a thermodynamic model evaluation of such a flexible large scale power plant system with co-production of hydrogen and subsequent hydrogen storage with metal hydrides (MH). A comparative analysis has been presented using steady state ASPEN Plus models for a Reference NGCC system, an IRCC system and a Flexible IRCC system with MH (MgH2) based hydrogen storage. In addition, a detailed exergy analysis indicating irreversibilities in the system has been presented. The system study indicates that such Flexible IRCC systems could be operated with a time based average (considering charging and discharging) electrical efficiency above 45% depending on the amount of hydrogen stored, appropriate heat integration and choice of the metal hydride. Exergy analysis indicates that such flexible systems could still be operated at a relatively high average net exergy efficiency (considering charging and discharging). Addition of MH based H2 storage in an IRCC system does not lead to significant electrical/exergy efficiency penalty. Carbon capture and storage is a larger source of efficiency penalty than the MH based H2 storage unit. The largest exergy destruction is observed in the gas turbine combustor and reformer units, providing additional scope for efficiency enhancement. With a larger share of renewable power in the total electrical power production expected in future, Flexible IRCC systems as presented in this article could be used as an efficient solution to address the large fluctuations in power supply and demand. Additional investigations are however encouraged further toward optimizing the choice of the metal hydride, detailed design of a single heat integrated system (including part load behavior) and economic assessments based on the heat and mass balances developed in this study.

Energetic evaluation of hydrogen storage in metal hydrides

Metal hydrides are considered as promising candidates for hydrogen storage as they exhibit higher energy densities than compressed gas storage storages. This study represents a theoretical thermodynamic analysis of metal hydride-based hydrogen storage systems, focusing mainly on the energy demand to operate the storage system and the resulting efficiency. The main energy demand occurs during hydrogen release. This energy demand is composed of three contributions: the heat required to heat the hydride up to desorption temperature, the heat of reaction and the work of compression to reach the targeted outlet pressure. A sensitivity analysis was performed to demonstrate the impact of several parameters, for example, heat of reaction and hydrogen uptake on the energy balance. The most influential parameter is the heat of reaction. The hydrogen uptake does not have a noticeable influence as long as it is not too low. Several possibilities to improve the efficiency of the storage system are discussed (heat integration and the application of a heat storage system). Heat integration can significantly improve the overall efficiency, whereas the application of a heat storage system does not seem realistic. Compared with other hydrogen storage technologies, metal hydrides can feature higher efficiencies than low-temperature hydrogen storage concepts, for example, liquefied or cryo-adsorbed hydrogen. The efficiencies of a metal hydride storage system are similar to those reached with a system based on liquid organic hydrogen carriers. Copyright © 2016 John Wiley & Sons, Ltd.

Robust economic model predictive control of a community micro-grid

In this paper we propose a novel economic robust predictive controller for periodic operation. The proposed controller joins dynamic and economic trajectory planning and robust predictive controller for tracking in a single layer taking into account bounded disturbances, algebraic constraints and periodic operation. We study the closed-loop system properties of the proposed controller and provide a design procedure that guarantees that the perturbed closed-loop system converges asymptotically to the optimal economic reachable periodic trajectory, constraint satisfaction and recursive feasibility. The proposed controller has been applied to control a cluster of interconnected micro-grids. Each nano-grid is connected to an electric utility and has a renewable energy source, a cluster of batteries and a metal hydride based hydrogen storage system. The cluster must satisfy a periodic energy demand while maximizing the profit of the energy sold to the electric utility taking into account time varying prices.

Numerical simulation of the parametric influence on the wall strain distribution of vertically placed metal hydride based hydrogen storage container

Metal hydride hydrogen storage alloys show significant thermal variations and dimensional non-homogeneity during their charge–discharge cycles. Pulverization, settling and agglomeration of these alloys and the consequent densification influence the rate of hydrogenation and wall strains on storage containers. In this study, numerical simulation of the wall strain distribution of a vertically placed hydrogen storage device is conducted with LaNi5 as the hydrogen storage alloy. The influence of salient parameters such as bed thickness, hydrogen supply pressure and coolant temperature on wall strains is studied with its already known effect on sorption performance. Effect of the densification of hydride particles during hydriding is also studied.

Thermal modeling of LmNi4.91Sn0.15 based solid state hydrogen storage device with embedded cooling tubes

A 2-D mathematical model is developed for predicting the minimum charging/discharging time of the metal hydride based hydrogen storage device by varying the number of cooling tubes embedded in it. This study is extended to 3-D mathematical model for predicting the hydriding and dehydriding characteristics of LmNi4.91Sn0.15 based hydrogen storage device with 60 embedded cooling tubes (ECT) using COMSOL Multiphysics 4.3. The performance of the hydrogen storage device during hydriding/dehydriding process is presented for different supply pressure (10–35 bar), hot fluid temperature (30–60 °C) and effective thermal conductivity of hydride bed (0.2–2.5 W/(m∙K)). It is observed that the rate of heat transfer and the hydriding and dehydriding rates are enhanced when the number of ECT is increased from 24 to 70. For the reactor with 60 ECT, the rate of hydrogen absorption is rapid for the supply pressure of 35 bar and hydride bed effective thermal conductivity of 2.5 W/(m∙K). The numerically predicted hydrogen storage capacity (wt%) and amount of hydrogen desorbed (wt%) are compared with experimental data and found a good accord between them.

Experimental study of metal hydride-based hydrogen storage tank at constant supply pressure

Metal hydride-based hydrogen storage tank is tested using 1 kg of AB5 alloy, namely LaNi5. The hydrogen tank is of annular cylindrical with inner and outer heat exchangers. The inner one is a finned spiral heat exchanger and the outer one is a conventional jacket. Performance (storage capacity and storage time) studies are carried out by varying the supply pressure and the cooling temperature of the hydride bed. At any given cooling temperature, hydrogen storage rate is found to increase with supply pressure. Cooling temperature is found to have a significant effect on hydrogen storage capacity at lower supply pressures.

Tests on LmNi4.91Sn0.15 based solid state hydrogen storage device with embedded cooling tubes – Part A: Absorption process

In Part A of this manuscript which consists of two parts, the experimental investigations pertaining to the absorption of hydrogen in an LmNi4.91Sn0.15 based solid state hydrogen storage device with embedded cooling tubes (ECT) are presented. Two metal hydride based hydrogen storage devices with 36 and 60 ECT filled with 2.75 kg of LmNi4.91Sn0.15 were fabricated. Performances of the hydrogen storage devices in terms of hydrogen absorption rate and amount of hydrogen absorbed are reported for different supply pressures (10–35 bar), absorption temperatures (20–30 °C) and cooling fluid flow rates (2.2–30 l/min). At any given absorption temperature, the rate of hydrogen absorption and the amount of hydrogen absorbed are found to increase with hydrogen supply pressure up to about 35 bar. At the supply condition of 35 bar hydrogen pressure and 30 °C absorption temperature, with oil as a heat transfer fluid at a flow rate of 3.2 l/min, the maximum amount of hydrogen absorbed are ≈1.18 wt% in 10 min for 36 ECT, and 8 min for 60 ECT. At the absorption condition of 25 bar supply pressure, 30 l/min water flow rate and 30 °C absorption temperature, the absorption time of the reactor with 60 ECT was reduced to 5 min.

Dynamic modeling and simulation of hydrogen supply capacity from a metal hydride tank

The current study presents a modeling of a LaNi5 metal hydride-based hydrogen storage tank to simulate and control the dynamic processes of hydrogen discharge from a metal hydride tank in various operating conditions. The metal hydride takes a partial volume in the tank and, therefore, hydrogen discharge through the exit of the tank was driven by two factors; one factor is compressibility of pressurized gaseous hydrogen in the tank, i.e. the pressure difference between the interior and the exit of the tank makes hydrogen released. The other factor is desorption of hydrogen from the metal hydride, which is subsequently released through the tank exit. The duration of a supposed full load supply is evaluated, which depends on the initial tank pressure, the circulation water temperature, and the metal hydride volume fraction in the tank. In the high pressure regime, the duration of full load supply is increased with increasing circulation water temperature while, in the low pressure regime where the initial amount of hydrogen absorbed in the metal hydride varies sensitively with the metal hydride temperature, the duration of full load supply is increased and then decreased with increasing circulation water temperature. PID control logic was implemented in the hydrogen supply system to simulate a representative scenario of hydrogen consumption demand for a fuel cell system. The demanded hydrogen consumption rate was controlled adequately by manipulating the discharge valve of the tank at a circulation water temperature not less than a certain limit, which is increased with an increase in the tank exit pressure.

Performance tests on metal hydride based hydrogen storage devices

In this manuscript, the performance tests on the metal hydride based hydrogen storage devices employing Mg + 30% MmNi5 and MmNi4.08Co0.2Mn0.62Al0.1 are presented. Hydrogen storage performances of Mg + 30% MmNi5 were investigated in the absorption and desorption temperatures ranges of 120–150 °C and 300–350 °C, respectively. The respective ranges for MmNi4.08Co0.2Mn0.62Al0.1 are 30–180 °C and 40–60 °C. For both the hydrides, supply pressures were varied from 10 to 30 bar. The maximum observed hydrogen storage capacities of Mg + 30% MmNi5 at 20 bar supply pressure and 150 °C absorption temperature and MmNi4.08Co0.2Mn0.62Al0.1 at 30 bar supply pressure, and 30 °C absorption temperature are 2.5 wt% and 1.2 wt%, respectively. For both the hydrides, the hydrogen storage capacities and the hydrogen absorption rates were found to increase with supply pressure. For a given supply pressure of 20 bar, the hydrogen storage capacity of Mg + 30% MmNi5 was found to increase from 1.94 wt% at 120 °C to 2.5 wt% at 150 °C absorption temperature. The effect of supply pressure on the hydrogen storage capacities of Mg + 30% MmNi5 at 150 °C absorption temperature and MmNi4.08Co0.2Mn0.62Al0.1 at 30 °C absorption temperature was limited to 20 bar and 30 bar, respectively.

Thermal modeling and performance analysis of industrial-scale metal hydride based hydrogen storage container

In this paper, a performance analysis of a metal hydride based hydrogen storage container with embedded cooling tubes during absorption of hydrogen is presented. A 2-D mathematical model in cylindrical coordinates is developed using the commercial software COMSOL Multiphysics 4.2. Numerical results obtained are found in good agreement with experimental data available in the literature. Different container geometries, depending upon the number and arrangement of cooling tubes inside the hydride bed, are considered to obtain an optimum geometry. For this optimum geometry, the effects of various operating parameters viz. supply pressure, cooling fluid temperature and overall heat transfer coefficient on the hydriding characteristics of MmNi4.6Al0.4 are presented. Industrial-scale hydrogen storage container with the capacity of about 150 kg of alloy mass is also modeled. In summary, this paper demonstrates the modeling and the selection of optimum geometry of a metal hydride based hydrogen storage container (MHHSC) based on minimum absorption time and easy manufacturing aspects.

Hydrogen storage systems based on hydride materials with enhanced thermal conductivity

The reaction of hydrogen gas with a metal to form a metal hydride is exothermic. If the heat released is not removed from the system, the resulting temperature rise of the hydride will reduce the hydrogen absorption rate. Hence, hydrogen storage systems based on hydride materials must include a way to remove the heat generated during the absorption process. The heat removal rate can be increased by (i) increasing the effective thermal conductivity of the metal hydride by mixing it with high-conductivity materials such as aluminum foam or graphite, (ii) optimizing the shape of the tank, and (iii) introducing an active cooling environment instead of relying on natural convection. This paper presents a parametric study of hydrogen storage efficiency that explores quantitatively the influence of these parameters. An axisymmetric mathematical model was formulated in Ansys Fluent 12.1 to evaluate the transient heat and mass transfer in a cylindrical metal hydride tank, and to predict the transient temperatures and mass of hydrogen stored as a function of the thermal conductivity of the enhanced hydride material, aspect ratio of the cylindrical tank, and thermal boundary conditions. The model was validated by comparing the transient temperature at selected locations within the storage tank with concurrent experiments conducted with LaNi 5 material. The parametric study revealed that the aspect ratio of the tank has a stronger influence when the effective thermal conductivity of the metal hydride bed is low or when the heat removal rate from the tank surface is high (active cooling). It was also found that for a hydrogen filling time of 3 min, adding 30% aluminum foam to the metal hydride maximizes hydrogen absorption under natural convection, whereas the addition of only 10% aluminum foam maximizes the hydrogen content under active cooling. For filling times beyond 3 min, the amount of aluminum foam required to maximize hydrogen content can be reduced for both natural convection and active cooling. This study should prove useful in the design of practical metal hydride-based hydrogen storage systems.

Acceptability envelope for metal hydride-based hydrogen storage systems

The design and evaluation of media-based hydrogen storage systems requires the use of detailed numerical models and experimental studies, with significant amount of time and monetary investment. Thus a scoping tool, referred to as the Acceptability Envelope, was developed to screen preliminary candidate media and storage vessel designs, identifying the range of chemical, physical and geometrical parameters for the coupled media and storage vessel system that allow it to meet performance targets. The model which underpins the analysis allows simplifying the storage system, thus resulting in one input-one output scheme, by grouping of selected quantities. Two cases have been analyzed and results are presented here. In the first application the DOE technical targets (Year 2010, Year 2015 and Ultimate) are used to determine the range of parameters required for the metal hydride media and storage vessel. In the second case the most promising metal hydrides available are compared, highlighting the potential of storage systems, utilizing them, to achieve 40% of the 2010 DOE technical target. Results show that systems based on Li–Mg media have the best potential to attain these performance targets.

Optimization of heat exchanger designs in metal hydride based hydrogen storage systems

Design of the heat exchanger in a metal hydride based hydrogen storage system influences the storage capacity, gravimetric hydrogen storage density, and refueling time for automotive on-board hydrogen storage systems. The choice of a storage bed design incorporating the heat exchanger and the corresponding geometrical design parameters is not obvious. A systematic study is presented to optimize the heat exchanger design using computational fluid dynamics (CFD) modeling. Three different shell and tube heat exchanger designs are chosen. In the first design, metal hydride is present in the shell and heat transfer fluid flows through straight parallel cooling tubes placed inside the bed. The cooling tubes are interconnected by conducting fins. In the second design, heat transfer fluid flows through helical tubes in the bed. The helical tube design permits use of a specific maximum distance between the metal hydride and the coolant for removing heat during refueling. In the third design, the metal hydride is present in the tubes and the fluid flows through the shell. An automated tool is generated using COMSOL-MATLAB integration to arrive at the optimal geometric parameters for each design type. Using sodium alanate as the reference storage material, the relative merits of each design are analyzed and a comparison of the gravimetric and volumetric hydrogen storage densities for the three designs is presented.

Numerical analysis of heat and mass transfer during absorption of hydrogen in metal hydride based hydrogen storage tanks

In this paper, hydriding in a cylindrical metal hydride hydrogen storage tank containing HWT5800 (Ti 0.98Zr 0.02V 0.43Fe 0.09Cr 0.05Mn 1.5) is numerically studied with a two-dimensional mathematical model. The heat and mass transfer of this model is computed by finite difference method. The effects of supply pressure, cooling fluid temperature, overall heat transfer coefficient and height to the radius ratio of the tank (H/R) on the hydriding in the hydrogen storage tank are studied. It is found that hydride formation initially takes place uniformly all over the bed and hydriding processes take place at a slower rate at the core region. Supply pressure, cooling fluid temperature and overall heat transfer coefficient play significant roles during the absorption of hydrogen. At the H/R = 2 both maximum bed temperature and the average bed temperature are the highest, and the hydride bed takes the longest time to saturate.

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 (LaNi 5) 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.

Numerical analysis and performance assessment of metal hydride-based hydrogen storage systems

This paper presents a detailed analysis of low-temperature, metal hydride-based hydrogen storage systems by means of a lumped model previously developed by the authors. In the first part of this study the model is applied to simulate experimental systems described in the literature, where the absorption and desorption of hydrogen under constant-pressure conditions are studied. The numerically evaluated time evolution of several key parameters (such as hydrogen mass flow, temperature and pressure) is reported and its accordance with experimental results available in the literature is discussed, in order to identify the model's strengths and limitations and its validity range, and to offer analytical insight into the behavior of the storage system as different operating parameters are varied. The model is then used as a tool to predict the performance of metal hydride hydrogen storage devices operating in FC-based energy systems. This is accomplished by analyzing the storage system response to a constant flow condition, i.e. when the FC operates under a constant external load.