Metal Hydride Hydrogen Compressor Research Articles

Development of a high-pressure 700 bar metal hydride hydrogen compressor

HySA Systems and TF Design have recently developed a single-stage prototype high-pressure metal hydride hydrogen compressor (MHHC) which is able to compress hydrogen from 100 to >700 bar at the working temperatures from 20 to 150 °C, with estimated productivity about 1 Nm3/h. The MHHC comprises of two 2 m-long fibre-wound high-pressure MH containers developed by the authors earlier and assembled in two modules operating in a mode of a cyclic lower-pressure H2 absorption (on cooling) and high-pressure H2 desorption (on heating). The containers operate using a self-developed multicomponent C14 Laves type Ti–based AB2 intermetallic alloy. The article considers phase-structural and hydrogen sorption properties of the utilized metal hydride material, hydrogen compression performances of the metal hydride container, as well as layout and the expected performance characteristics of the compressor assembly.

Development of Ti-Zr-Mn based AB2 type metal hydrides alloys for an 865 bar two-stage hydrogen compressor

This study reports the development of a new Ti-Zr-Mn-based AB2 type hydrogen storage alloys for a two-stage metal hydride hydrogen compressor (MHHC). The hydrogen storage alloys are designed to compress hydrogen from 35 to 865 bar within a temperature difference of 115 °C. High-pressure PCT measurements up to 700 bar were carried out to test the performance of the alloys. The alloys' hysteresis and the plateau slope were reduced by optimizing the composition. The introduction of fugacity correction into the Van't hoff equation reduces the deviation between calculation and actual pressure to 24 bar at a pressure above 350 bar. A precise relation between the Ti/Zr ratio and the desorption pressure is described and helps make a correct design of the alloy composition. The designed alloy shows looses less than 1% of the capacity over 3000 full cycles. The desorption plateau pressure of the alloy is constant within 92% during the whole cycling process. A 2 stages compressor working with two types of alloys offers compression with a temperature range between -20 and 95 °C for the refueling hydrogen vehicles up to 865 bar.

Analytical and experimental evaluation of LaNi5-xMx, where M = Fe, Mn, and Al hydrides for hydrogen compression applications

Metal Hydride Hydrogen Compressors (MHHC) will play a vital role in the hydrogen economy in the coming times. Developing a more efficient and optimized MHHC requires revisiting the existing materials and selecting the best-suited material. The current work compares LaNi5-xMx, where M = Fe, Mn, and Al hydrides, through a thermodynamic evaluation of the compressor's performance. The operating conditions have been chosen as 20 to 40 °C for absorption and 80 to 140 °C for desorption to provide a baseline for comparing the materials. The performance parameters include thermal efficiency, pressure ratio, and throughput (i.e. mass of hydrogen delivered per 100 g of hydride (wt.%)). The Pressure Concentration Isotherms (PCIs) are taken from the published literature, and the equilibrium pressures at the desired temperature conditions are calculated from the van't Hoff equation. LaNi4.8Al0.2 gives good performance throughout the studied temperature and pressure range. The throughput of LaNi4.8Al0.2 drops from 1.4 wt.% to around 1 wt.% at high absorption temperatures. A separate experimental study of LaNi4.8Al0.2 is documented where it is used in a prototype of MHHC, and its performance parameters are compared with the thermodynamic analysis. The reaction kinetics, throughput, pressure ratio, and efficiency are reported. A pressure ratio of 4.2 is achieved with an efficiency of 5.2 % at 3 bar supply pressure, and absorption and desorption temperatures of 30 and 140 °C, respectively.

Performance improvement of metal hydride hydrogen compressors using electromagnetic induction heating

While there are some hydrogen refueling stations (HRS) functioning in different parts of the world, their use is not widespread enough, primarily due to their expensive cost. Hydrogen compression is a main contributor to the capital and operation costs of the HRS. By improving H2 compression technology, it is possible to optimize the infrastructure for refueling with hydrogen in terms of cost and performance. The use of metal hydride hydrogen compressors (MHHCs), which have the potential to be inexpensive and have the ability to use waste heat and renewable energy sources for the H2 compression, is a promising solution to overcome this issue. The duration of the H2 compression cycle is nevertheless a serious challenge due to the metal hydride (MH) bed's low heat conductivity. As a heating technique to improve the performance of MHHCs, electromagnetic induction (EMI) is examined numerically for the first time in this work. The dynamic behavior of a two-stage MHHC with each MH reactor having an external heat exchanger and being ringed by a copper coil traversed by an alternating current is described by a two-dimensional mathematical model, which was established and successfully verified by the reference data. Numerical simulations were performed with the help of this model, and the findings showed that the EMI heating method is faster than the heat transfer fluid (HTF) heating technique. For instance, at a delivery temperature of 373 K and a supply pressure of 20 bar, it is possible to produce 106 NL H2 per kilogram of HPMH at a pressure of 97 bar with a 74 % shorter compression time than with the HTF heating technique.

Development of a metal hydride hydrogen compressor with high-pressure hydrogen storage alloys

Single- and double-stage metal hydride hydrogen compressors (MHHC) were developed using two series of metal hydrides of AB5-based La0.5Ce0.5Ni5-xAlx (x = 0, 0.1, 0.2) alloys and AB2-based Ti1-yZryMn0.8Cr1.2 (y = 0.05, 0.1, 0.2) alloys. In single-stage mode, La0.5Ce0.5Ni5 and Ti0.9Zr0.1Mn0.8Cr1.2 alloys could produce hydrogen pressures of 117 atm and 132 atm, respectively, at 100 °C. When the temperature was raised to 140 °C, both alloys could produce hydrogen pressures of 200 atm. The Ti0.9Zr0.1Mn0.8Cr1.2 alloy exhibited higher hydrogen discharging pressure and faster kinetics than those of the La0.5Ce0.5Ni5 alloy. A pair of alloys were used for a double-stage MHHC (first stage: Ti0.9Zr0.1Mn0.8Cr1.2; second stage: Ti0.95Zr0.05Mn0.8Cr1.2). The initial hydrogen pressure of 50 atm increased to 245 atm when the working temperature was raised from 25 °C to 100 °C, which provides an opportunity for designing a compact and simple MHHC.

Improved hydrogen ab-/desorption performance of Ti–Cr based alloys via dual-effect of oxide reduction and element substitution by minor Al additive

Hysteresis of hydrogen storage alloys essentially hinders the compressibility and operation efficiency of metal hydride hydrogen compressors. In this work, minor Al additive was added into Ti–Cr based hydrogen compression alloys through induction levitation melting, and the apparent hysteresis was successfully ameliorated. The XRD and SEM results indicate homogeneous element distribution of a main C14 Laves phase of Ti0.96Zr0.06Cr1.0Mn0.6Fe0.4Alx (x = 0, 0.01, 0.02, 0.04, 0.08) alloys, and vanishing of a minor oxide phase in case the Al additive is introduced. As Al stoichiometry increases in the alloys, the hydrogenation plateau decreases obviously but the dehydrogenation plateau hardly changes. Meanwhile, the hydrogen capacity ascends initially but descends slightly. Additionally, no severe performance degradation is induced. The mechanism for overall performance improvement can be concluded as dual functions of Al additive: one can be oxide reduction of other elements during melting determined by XPS and ICP, and the other can be partial Al substitution for the B-side elements, leading to relieved deformation energy surrounding the vacant Al-containing interstitials. As to hydrogenation kinetics, the alloys exhibit accelerated hydrogenation rate with increased Al stoichiometry due to decreased activation energy and hydrogenation plateau. Furthermore, the first-principles calculation results indicate random Al substitution for the B-side atoms, and anisotropic expansion of the unit cell can be attributed to Al substitution at 6h sites. This work reveals a simple and effective way to enhance hydrogen storage performance of Ti–Cr based alloys.

Laves phase double substitution alloy design and device filling modification for Ti-based metal hydride hydrogen compressors

The ambition of carbon neutrality has become a common pursuit for researchers worldwide, and hydrogen as a green and clean energy carrier is expected to contribute to this achievement. Since hydrogen fuel cell vehicles require a high input hydrogen pressure, compressors in hydrogen refueling stations are thus indispensable for the large-scale application of hydrogen energy. Compared to conventional mechanical hydrogen compressors, metal hydride based hydrogen compressors have the advantages of high security and low cost, providing a viable solution for hydrogen refueling station development. Herein, two series of Ti0.95Zr0.07Cr1.3-xMnxFe0.4 (x = 0.2, 0.3, 0.4, 0.6) and Ti0.95Zr0.07Cr1.0Mn0.6Fe0.4-yCuy (y = 0.1, 0.15, 0.2, 0.3) alloys were designed to achieve 8–22 MPa hydrogen compression in water bath at 283–353 K. All the as-prepared alloys exhibit the single hexagonal C14 Laves phase structure. In particular, the double substitution of Cr and Fe by Cu and Mn elements in Ti–Zr–Cr–Mn–Fe alloy can enlarge its hydrogen storage capacity without varying the equilibrium pressure. For instance, Ti0.95Zr0.07Cr1.0Mn0.6Fe0.25Cu0.15 alloy has a hydrogenation plateau pressure of 6.16 MPa at 283 K and a dehydrogenation plateau pressure of 24.23 MPa at 353 K, with the max hydrogen capacity of 1.72 wt%. Furthermore, the relative high density molding method of metal hydride bed with 20 g of alloy powder was developed. The binder epoxy resin and the thermal conductor flake graphite were selected and added into the alloys to form metal hydride compacts (MHCs). The structural stability of modified MHCs can be enhanced due to the formation of a three-dimensional grid structure, with a higher resistance to pulverization and degradation. The improved thermal conductivity involving a filling compact strategy can significantly shorten hydrogenation reaction time by 50% and lower the abrupt temperature of metal hydride bed by 20 K with excellent stability over 100 cycles, and provide new insights of the development of safe and efficient hydride hydrogen compressor.

Development and optimization of a two-stage metal hydride hydrogen compressor with AB2-type alloys

This study reports the development of a two-stage metal hydride hydrogen compressor (MHHC) capable of compressing hydrogen from 1 to 30 MPa through a temperature change between 20 and 150 °C. AB2-type hydrogen storage alloys in the C14 Laves phase are employed, where A = Ti and Zr and B = Cr, Mn, and V. The pressure transfer conditions between the two stages are investigated, and the composition of the AB2 alloys is optimized accordingly: the Mn content x in Ti0.8Zr0.2Cr1.9−xMnxV0.1 and the Zr content y in Ti1−yZryCr1.2Mn0.8, for the 1st and the 2nd stage materials, respectively. A laboratory-scale two-stage compressor is fabricated and operated using the selected alloys, whereby hydrogen is successfully compressed to 30 MPa. The compression capacity is analyzed to estimate the useable capacity of the materials. The results of this study can serve as a guide for the design and evaluation of multistage MHHCs.

A self-sustaining renewable energy driven hydrogen refuelling system utilising a metal hydride-based compressor

The transition towards carbon-free transportation is only possible by the adoption of renewable energy alternatives. Hydrogen-based transportation is an attractive option considering the availability of the required refuelling infrastructure. A well-established network of hydrogen refuelling infrastructure is important for the widespread commercialization of fuel-cell electric vehicles. The most expensive H2 refuelling components originate from hydrogen compression. Due to their ability to run on solar thermal energy, a metal hydride hydrogen compressor is used in this study. In this communication, the aim is to present a study on solar thermal based hydrogen compressors for a hydrogen refuelling station. An analytical study is presented on the energy assessment of a metal hydride compressor by considering three candidate pairs of metal hydrides (Pair 1: Ti0.95Zr0.05Cr0.8Mn0.8V0.2Ni0.2/Ti0.8Zr0.2Cr0.95Fe0.95V0.1; Pair 2: TiCr1.55Mn0.2Fe0.2/Ti0.9Zr0.1Mn1.4Cr0.35V0.2Fe0.05, Pair 3: La0.35Ce0.45Ca0.2Ni4.95Al0.05/Ti0.8Zr0.2Cr0.95Fe0.95V0.1) to achieve refuelling pressure of 700 bar. The variation in thermal efficiency of the compressor and thermal energy requirements with changes in heat source temperature, supply pressure and heat losses are presented. Furthermore, the economics of three pairs of alloys for high-pressure compression is compared. It was found that Ti0.95Zr0.05Cr0.8Mn0.8V0.2Ni0.2/Ti0.8Zr0.2Cr0.95Fe0.95V0.1 pair has the maximum compressor efficiency of 7.2% at supply pressure and heat source temperature of 25 bar and 150 °C, respectively. In addition, the study revealed that heat losses from the reactor could reduce efficiency by around 12.5%. The economic study revealed that the Ti0.95Zr0.05Cr0.8Mn0.8V0.2Ni0.2/Ti0.8Zr0.2Cr0.95Fe0.95V0.1 pair has the least cost for hydrogen compression among the other chosen pairs.

A dynamic model for predicting the absorption and desorption behaviors of metal hydride systems and its implementation for screening of alloys for metal hydride hydrogen compressor

The goal of the current study is to develop a dynamic model for forecasting the absorption and desorption behavior of metal hydride hydrogen system. The accuracy of the developed dynamic model is verified with the actual model. The effect of reactor diameter (10–25 mm), hydrogen supply pressure (5–20 bar) and desorption temperature (40–70 °C) on the accuracy of the temperature profile predicted by the dynamic model as compared to the actual model is investigated. The results showed that the percentage deviation of the dynamic model with actual model increase with the reactor diameter. The dynamic model predicted the average bed temperature during absorption with a maximum deviation of 4.32% (14 K) for a reactor of 25 mm diameter compared to the actual model. A maximum deviation of only 2.11% (6.32 K) was observed for the same reactor during desorption at 323 K. Further, the percentage deviation increases with the supply pressure and desorption temperature. Overall, it is observed that the slower the absorption/desorption, the better is the prediction accuracy of the dynamic model. On the other hand, the dynamic model is over 300 times faster than the actual, which saves computational time and cost. Furthermore, the dynamic model is extended for studying the coupled reactor system of a dual-stage metal hydride hydrogen compressor. Four alloy pairs are compared in terms of compression ratio, the amount of energy lost due to hysteresis, average hydrogen discharge rate, and isentropic efficiency. The comparison results suggested that an appropriate combination of AB5-AB2 type alloy is suitable for higher delivery plateau pressure, lower energy loss due to hysteresis, and a reasonable compression ratio.

Performance enhancement of metal hydride hydrogen compressors using a novel operating procedure

The H2 refueling infrastructure's capital and operating expenses are mostly driven by the cost of hydrogen compression. To effectively address this issue, thermally driven H2 compression using metal hydrides (MH) may be used. For industrial customers who have the required infrastructure, such as H2 pipelines, low-grade heat sources, etc., metal hydride hydrogen compressors (MHHC) are particularly promising. However, the H2 compression cycle time issue is brought on by the poor thermal conductivity of the MH's powder. In the present study, a novel MHHC operating procedure is examined numerically. This procedure offers two possible options: The first is referred to as a “Multiple-Cycle Simultaneous Procedure’ (MCSiP for short), as the MH beds' sensible cooling (or sensible heating) and hydrogen's absorption (or desorption) processes start simultaneously and the final pressure is reached after a number of sub-cycles of compression. The second one, dubbed the ”Multiple-Cycle Sequential Procedure“ (MCSeP for short), is similar to the MCSiP mode except that the MH beds' sensible cooling (or sensible heating) as well as the hydrogen's absorption (or desorption) start out sequentially. To evaluate the impact of this procedure on the compressor’s performance, a theoretical model was established and effectively validated by comparison with experimental results reported in the literature. The simulation findings show that the suggested procedure compresses more hydrogen mass at high pressure and is faster than the other operating methods. For instance, 140 NL H2 at a pressure of 110 bar can be obtained with a 70% reduction in compression time compared to the commonly used operating mode utilizing 1.0 kg of MmNi4.6Al0.4 as low pressure MH and 0.832 kg of Ti0.99Zr0.01V0.43Fe0.099Cr0.05Mn1.5 as high pressure MH and operating conditions of 20 bar supply pressure, 293 K absorption temperature, and 373 K desorption temperature.

Hydrogen Compression Materials with Output Hydrogen Pressure in a Wide Range of Pressures Using a Low-Potential Heat-Transfer Agent

In order to meet the demand of metal hydride–hydrogen compressors (MHHC) and their hydrogen compression materials for high-pressure hydrogen filling in a hydrogen energy field, four kinds of hydrogen storage alloys with low-grade heat source (<373 K) heating outputs and different hydrogen pressures (up to 80 MPa) were developed as hydrogen compression materials. The preliminary compositions of the hydrogen storage alloys were determined by using a statistical model and research experience. The rare earth series AB5 and Ti/Zr base AB2 hydrogen storage alloys were prepared using a high-temperature melting method. The composition, structure, and hydrogenation/dehydrogenation plateau characteristics of the alloys were tested by an inductively coupled plasma mass spectrometer (ICP-MAS), X-ray diffractometer (XRD), and pressure–composition isothermal (PCT) tester. The median output pressures of the four-stage hydrogen storage alloys at 363 K were 8.90 MPa, 25.04 MPa, 42.97 MPa, and 84.73 MPa, respectively, which met the requirements of the 20 MPa, 35 MPa, and 70 MPa high-pressure hydrogen injections for the MHHCs. In fact, due to the tilted pressure plateau of the PCT curve, the synergy between the adjacent two alloys still needed to be adjusted.

Alloy selection for dual stage metal-hydride hydrogen compressor: Using a thermodynamic model to identify metal-hydride pairs

Metal-hydrides offer a potentially competitive method for compressing hydrogen, particularly where waste heat is available. Metal hydrides are metal alloys or intermetallic compounds that react reversibly with H2. They readily absorb low-pressure H2 at low temperature, and then release H2 at a higher pressure when the temperature is raised. The high pressure H2 is released at a pressure above that expected from standard press-temperature relations. The absorption and desorption pressures of the hydrides are determined by their thermodynamic properties (enthalpy and entropy). To achieve compression ratios above about 10, more than one stage of compression is typically required. The challenge is to find alloy pairs that can work together effectively to achieve the desired compression from the heating/cooling available. Previously, a thermodynamic model has been proposed for identifying suitable metal hydrides that can be paired together to achieve a desired compression. This paper describes methods used previously in the literature to select alloy pairs, and applies the current method to an example selection of 33 hydrides with potential for hydrogen compression. The example application aims to find pairs that can compress a H2 stream from 10 to 350 bar using a temperature range of 30–150 °C, however the theory could readily be adapted to different compression ratios and temperature ranges. For the specific example evaluated none of the potential pairs were able to meet the compression target, however, modification of the parameters (heating/cooling availability) or alloy properties could resolve this issue.

Low-cost vanadium-free Ti–Zr–Cr–Mn–Fe based alloys for metal hydride hydrogen compressor under mild conditions

Hydrogen is the ideal green fuel and carbon-neutral energy carrier alternative to nonrenewable fuel sources. The high construction cost of hydrogen refueling stations has become one of the limitations to the further promotion and application of hydrogen energy. To realize 8–22 MPa hydrogen compression under mild conditions, the low cost Ti0.95Zr0.07Cr1.7-xMn0.3Fex (x = 0–0.5) alloys were designed and prepared by magnetic levitation melting in this work. The effect of Fe on Cr substitution on the microstructure and hydrogen storage properties of the alloy has been systematically investigated. With the increase of Fe substitution for Cr, all the alloys maintain a single C14 Laves phase, the thermodynamic plateau curve broadens and rises, while the hydrogen storage capacity diminishes slightly. For a better description of the thermodynamic properties of alloys at high temperatures as the function of temperature, a non-linear Van't Hoff fitting is introduced with satisfactory prediction. On account of significant Fe substitution for Cr, the unit cell shrinks and the interstitial size of alloy decreases, an optimal alloying constituent, Ti0.95Zr0.07Cr1.3Mn0.3Fe0.4, has been proposed and experimentally proved for the first time. This alloy exhibits the best overall performances and the plateau pressure is respectively 5.74 MPa for hydrogenation at 283 K and 25.97 MPa for dehydrogenation at 353 K without apparent hysteresis phenomenon. The hydrogen storage capacity is 1.59 wt% within 3 min and dehydrogenation enthalpy is 21.20 kJ/mol H2. This study provides a comprehensive insight into the low-cost hydrogen storage alloy design and application on quick response and high cycle stability metal hydride hydrogen compressors.

Reactor design and numerical study on metal hydride based finned reactor configurations for hydrogen compression application

The present study is focussed on the design and development of a single stage metal hydride hydrogen compressor. A 0.5 kg alloy mass capacity reactor is designed to withstand 100 bar at 120 °C. The Von Misses equivalent stress is calculated for the designed reactor and it is found to have a design margin of 11.4%. The reactor has an excellent weight ratio of 2.22. To enhance the thermal performance of the reactor, extended surfaces are incorporated. A numerical model is developed to compare the performance of three different fin configurations namely longitudinal fins, transverse fins and spiral fins. Longitudinal fins are found to provide better thermal enhancement during initial period of absorption half cycle. However, transverse fins showed better performance in the desorption case. Nevertheless, as the time progresses all the fin configurations showed similar performance under different operating temperatures. Further, hydrogen discharge rate is studied at various discharge pressure to understand the requirements while coupling with an empty cylinder or fuel cell. The study revealed that a 0.5 kg reactor can discharge hydrogen at the rate of 2.27 lpm for 2000 s when discharged to fill a cylinder up to 10 bar. The compression rate of the developed compressor is found to be 136 l/h at 10 bar discharge pressure and 373 K heat source temperature. The isentropic efficiency of the compressor is found to be 11.5%.

Development of (Ti–Zr)1.02(Cr–Mn–Fe)2-Based Alloys toward Excellent Hydrogen Compression Performance in Water-Bath Environments

Three series of alloys, Ti0.92Zr0.10Cr1.7–xMn0.3Fex (x = 0.2–0.4), Ti0.92Zr0.10Cr1.6–yMnyFe0.4 (y = 0.1–0.7), and Ti0.92+zZr0.10–zCr1.3Mn0.3Fe0.4 (z = 0, 0.015, 0.04), were prepared by induction levitation melting for a metal hydride hydrogen compressor from 8 to 20 MPa at water-bath temperature, with investigation on their crystal structural characteristics and hydrogen storage properties. The results show that a single C14-Laves phase with homogeneous element distribution exists in all of the alloys. The hydrogen ab-/desorption plateau of the alloys is increased as the Fe, Mn, or Ti content increases due to decrement of the interstitial site radius originated from the respective atomic size. The hydrogen storage capacity of the alloys also correlates negatively with the hydrogen affinity of interstitial sites due to the influence of the element electronegativity. In a comprehensive consideration of the hydrogen storage performance for application, the Ti0.935Zr0.085Cr1.3Mn0.3Fe0.4 alloy shows saturated hydrogenation under 8 MPa at 293 K and dehydrogenation around 24.91 MPa pressure at 363 K with a hydrogen capacity of 1.74 wt %, as well as excellent cycling performance and mere hysteresis. The Ti0.92Zr0.10Cr1.0Mn0.6Fe0.4 alloy is another promising candidate with a remarkable hydrogen capacity of 1.86 wt % at 283 K and a dehydrogenation pressure of 27.94 MPa at 363 K, together with a satisfactory cycling durability. This study can guide the compositional design of AB2-type hydrogen storage alloys for hydrogen compression application.

Calculation of Two-Stage Metal Hydride Hydrogen Compressors Using a Model of Intermetallic Compound–Hydrogen Phase Equilibria

Calculation of Two-Stage Metal Hydride Hydrogen Compressors Using a Model of Intermetallic Compound–Hydrogen Phase Equilibria

Thermodynamic analysis of a metal hydride hydrogen compressor with aluminium substituted LaNi5 hydrides

The operating conditions of a Metal Hydride Hydrogen Compressor (MHHC) is often dictated by the hydride used to build it. This research focuses on finding the appropriate operating conditions for MHHC to get the ideal throughput and efficiency using aluminium based hydrides. For this, hydrogen absorption and desorption characteristics of LaNi5-xAlx (where x is 0, 0.2 and 0.4) hydrides were studied for estimating the suitability of these materials for developing hydrogen compressor. From the Pressure Concentration Isotherms (PCIs) and van't Hoff plot, an estimate of the reversible hydrogen weight percent attainable, equilibrium pressure and absorption and desorption temperature range were collected and the effect of aluminium concentration on these properties was studied. Further thermodynamic analysis was made by calculating the performance parameters like thermal efficiency, isentropic work required, theoretical heat supplied and pressure ratio by varying the operating conditions like supply pressure (3–5 bar), absorption temperatures (20–40 °C), and desorption temperature (80–140 °C). It is observed that the higher aluminium content in the hydride allows the hydrogen compressor to be operated at a lower supply pressure. Whereas lower aluminium content in hydrides give higher thermal efficiency and discharge pressure for a particular desorption temperature, while requiring a higher supply pressure to perform efficiently. The maximum thermal efficiency within the studied operating conditions was found to be 0.24 for LaNi5 at 3 bar supply pressure, 30 °C absorption and 140 °C desorption temperature with a pressure ratio of 8.97.

Influence of element substitution on structural stability and hydrogen storage performance: A theoretical and experimental study on TiCr2-xMnx alloy

AB2-type alloys have been widely used for metal hydride hydrogen compressors and hydrogen storage systems. The crystal structure and hydrogen storage properties mostly rely on their composition and atomic distribution. Thus, revealing the relationship between structure and properties can lead to the design of alloys with optimized properties for hydrogen storage application. Here, the structure stability, bonding energy, thermodynamic and kinetic properties of TiCr2-xMnx (x = 0, 0.25, 0.5, 0.75, 1) alloy/hydride have been firstly investigated by combining density functional theory calculation and experiment. It demonstrates that Mn-doped TiCr2 alloy has a stable C14 phase, and Mn can optionally substitute for Cr sites. Additionally, with increase of Mn content, the desorption plateau increases and the ΔH value decreases. In particular, the ΔH values of TiCr2-xMnx hydrides are consistent with the heat released when H atoms occupy the interstitial interstices. Finally, the hydrogen absorption kinetics simulation shows that Mn is unfavorable to the hydrogen absorption kinetics, in which TiCrMn is 124 s longer than TiCr2 when 90% hydrogen-absorption capacity is reached. The relationship between calculations and experiments presents here can be used as a reference for subsequent screening of alloying elements with high melting point and cost for metal hydride system.

Pilot autonomous hybrid hydrogen refueling station utilizing a metal hydride compressor covering local transportation needs

The need for decreasing carbon emissions in the transportation sector in order to meet the targets of the European Union by 2030, inevitably leads to the large scale adoption of cleaner alternatives. Hydrogen fueled vehicles could possibly provide one such alternative, if we could assume that the necessary infrastructure would be widely available throughout Europe. Already, the European Union has committed to the construction of a significant number of Hydrogen Refueling Stations (HRS) by year 2025 and in view of that, there is a need of developing suitable configurations for the production, compression, storage and dispensing of green hydrogen to hydrogen fueled vehicles. This work presents an autonomous hybrid system which produces green hydrogen by PV- powered water electrolysis (PEM), which is subsequently compressed by a novel metal hydride hydrogen compressor to pressures up to 200 bar. This pilot HRS will meet the daily demand of 2 scooters and a golf cart which have been transformed, in order for their electric motor to be powered by a hydrogen fuel cell instead of a battery. An important element of the work which is presented, revolves around the integration of the metal hydride compressor with the rest of the system, and how this integration won’t hinder its functionality. The complete system design and layout is presented, while the results from the system operation could give a good idea regarding the optimal system sizing for similar large scale applications.