The EU Horizon2020 RISE project 778,307 "Hydrogen fuelled utility and their support systems utilising metal hydrides" (HYDRIDE4MOBILITY) worked on the commercialization of hydrogen powered forklifts using metal hydride (MH) based hydrogen stores. The project consortium joined forces of 9 academic and industrial partners from 4 countries. The work program included a) Development of the materials for hydrogen storage and compression; b) Theoretical modelling and optimisation of the materials performance and system integration; c) Advanced fibre reinforced composite cylinder systems for H-2 storage and compression; d) System validation. Materials development was focused on i) Zr/Ti-based Laves type high entropy alloys; ii) Mg-rich composite materials; iii) REMNiSn intermetallics; iv) Mg based materials for the hydrolysis process; v) Cost-efficient alloys. For the optimized AB(2 +/- x) alloys the Zr/Ti content was optimized at A = Zr78-88Ti12-22 while B=Ni10Mn5.83VFe. These alloys provided a) Low hysteresis of hydrogen absorption-desorption; b) Excellent kinetics of charge and discharge; c) Tailored thermodynamics; d) Long cycle life. Zr0.85Ti0.15TM2 alloy provided a reversible H storage and electrochemical capacity of 1.6 wt% H and 450 mAh/g. The tanks development targeted: i) High efficiency of heat and hydrogen exchange; ii) Reduction of the weight and increasing the working H-2 pressure; iii) Modelling, testing and optimizing the H-2 stores with fast performance. The system for power generation was validated at the Implats plant in a fuel cell powered forklift with on-board MH hydrogen storage and on-site H-2 refuelling. The outcome on the HYDRIDE4MOBILITY project (2017-2024) (http://hydride4mobility.fesb.unist.hr) was presented in 58 publications.

Advancing of hydrogen and metal hydride energy technologies requires purposeful development of efficient hydrogen storage materials, particularly, tuning their composition towards optimization of hydrogen sorption properties suitable for the end-use applications. This study employed linear regression modelling to analyze hydrogen storage properties of low-, medium- and high-entropy alloys with BCC, C14- and C15-AB2 and AB5 structures found in the literature (>350 entries in total) and to make predictions based on the model further validated by additional reference data and results of own experiments. It was found that the applied model gives a good qualitative correspondence with the reference data on hydrogen sorption capacity and thermodynamics of hydrogen interaction with the alloys but has a limiting predicting capacity allowing only rough quantitative estimations. It was also concluded that the unit cell volume, valence electron concentration, and, to a lesser extent, electronegativity mismatch, exhibit strong effects on the hydrogen sorption properties of the studied alloys while the influence of other factors including the mixing entropy is much less pronounced.

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 degrees C, with estimated productivity about 1 Nm(3)/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 H-2 absorption (on cooling) and high-pressure H-2 desorption (on heating). The containers operate using a self-developed multicomponent C14 Laves type Ti-based AB(2) 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.

A first-principles method based on the density functional theory (DFT) was employed in conjunction with quasi-harmonic Debye model to investigate the structural, elastic, and thermodynamic properties of a series of AB2-based Laves phases alloys and their hydrides. Simulation results revealed that the studied materials possess the Laves phase structure with lattice parameters comparable to experimental findings. For the first time, to the best of our knowledge, mixing entropy determined using Debye model was used to classify alloys into (Low- Medium-High Entropy Alloys) LEA, MEA and HEA categories rather than the commonly used ideal solution model, which is often inaccurate and ignores the impact of temperature. Lattice analyses of the alloy materials indicated that cell volume increases with the addition of elements, while the enthalpy of hydride formation indicates that hydrogen absorption in these alloys is exothermic and that the 3.00 H/F.U configuration is energetically stable. The alloys and their hydrides are metallic with no band gap at the Fermi level. The thermodynamic properties were studied using the quasi-harmonic Debye model and it was found that Bulk modulus decreases with increasing volume, and the hydrides possess lower bulk modulus compared to their metallic counterparts. Moreover, Debye temperature decreases with the gradual addition of elements, indicating weaker chemical bonds in ternary and other alloys. All hydrides have lower Debye temperature than their parent alloy materials. Finally, The alloys are classified into low-, medium-, and high-entropy alloys based on mixing entropy calculated using the Debye model. TiMn2 is classified as a low-entropy alloy, ZrMn2, Ti0.5Zr0.5Mn2, and Ti0.5Zr0.5MnFe as medium-entropy alloys, and Ti0.5Zr0.5(MnCr)2, Ti0.5Zr0.5Mn2/3Fe2/3Cr2/3, and Ti0.5Zr0.5Mn0.5Fe0.5Cr0.5Ni0.5 as high-entropy alloys.

The development of compact, safe, and efficient methods for storing hydrogen is one of the key problems of hydrogen energy. Currently used technologies for storing hydrogen in the form of compressed gas or cryogenic liquid require significant capital investments and maintenance costs for compressor and cryogenic equipment, are characterized by high energy costs, and their implementation requires special safety measures as well as the use of hydrogen-neutral structural materials. A promising way to solve these problems for medium-scale storage systems is the use of metal hydrides, which provide the simplest, most compact, and safe hydrogen storage compared to traditional methods. However, the high cost of hydride-forming materials hinders the implementation of this approach. The use of alloys based on the TiFe intermetallic compound would reduce the costs of metal hydride hydrogen storage by more than five times. This circumstance is the reason for the growing interest of specialists in the field of hydrogen energy technologies in hydrogen-storage materials based on titanium-iron alloys. Although hydrogen systems with the TiFe intermetallic compound and its derivatives have been studied for more than 50 years, the search for ways to increase the resistance of their hydrogen sorption characteristics to poisoning by oxygen-containing impurities in the gas and solid phases has become particularly relevant in recent years. This article provides an overview of research and development aimed at obtaining, studying the properties, and using titanium-iron alloys with improved hydrogen sorption characteristics. An analysis of the data presented in the scientific literature is presented, and approaches to the development of highly efficient hydride-forming materials based on the TiFe intermetallic compound and hydrogen-storage systems based on them are formulated.

This article presents experimental results on the preparation and characterisation of a multi-component AB(2)-type intermetallic hydrogen storage alloy (A = Ti0.85Zr0.15, B = Mn1.22Ni0.22Cr0.2V0.3Fe0.06). The alloy samples were prepared by induction melting using Y2O3-lined alumo-silica and graphite crucibles. The characterisation results were compared with the ones for the reference sample of the same composition prepared by arc melting. It has been shown that the induction-melted samples exhibit reduced hydrogen sorption capacities and sloping plateaux on the pressure composition isotherms (PCI's). The origin of the observed effects has been shown to be in the inhomogeneity of the induction-melted alloys and their contamination due to crucible-melt interaction, particularly pronounced for the alloy melted in the alumo-silica crucible; this alloy was additionally characterised by the decrease of Zr/Ti ratio and, in turn, higher plateau pressures of the PCI's.

Metal hydride (MH) hydrogen storage and compression systems with near-atmospheric H2 suction pressure are necessary for the utilization of the low-pressure H2 produced by solid oxide electrolyzers or released as a byproduct of chemical industries. Such systems should provide reasonably high productivity in the modes of both charge (H2 absorption at PL ≤ 1 atm) and discharge (H2 desorption at PH = 2–5 atm), which implies the provision of H2 equilibrium pressures Peq < PL at the available cooling temperature (TL = 15–20 °C) and, at the same time, Peq > PH when heated to TH = 90–150 °C. This work presents results of the development of such systems based on AB5-type intermetallics characterized by Peq of 0.1–0.3 atm and 3–8 atm for H2 absorption at TL = 15 °C and H2 desorption at TH = 100 °C, respectively. The MH powders mixed with 1 wt.% of Ni-doped graphene-like material or expanded natural graphite for the improvement of H2 charge dynamics were loaded in a cylindrical container equipped with internal and external heat exchangers. The developed units with a capacity of about 1 Nm3 H2 were shown to exhibit H2 flow rates above 10 NL/min during H2 charge at ≤1 atm when cooled to ≤20 °C with cold water and H2 release at a pressure above 2 and 5 atm when heated to 90 and 120 °C with hot water and steam, respectively.

Hydrolysis of light metals and hydrides can potentially be used for the generation of hydrogen on-board fuel cell vehicles, or, alternatively, for refilling their fuel tanks with H2 generated and pressurised without compressor on site, at near-ambient conditions. Implementation of this approach requires solution of several problems, including the possibility of controlling H2 release and avoiding thermal runaway. We have solved this problem by developing the apparatus for the controlled generation of pressurised H2 using hydrolysis of Mg or MgH2 in organic acid solutions. The development is based on the results of experimental studies of MgH2 hydrolysis in dilute aqueous solutions of acetic, citric, and oxalic acids. It was shown that the hydrogen yield approaches 100% with a fast hydrolysis rate when the molar ratio acid/MgH2 exceeds 0.9, 2.0, and 2.7 for the citric, oxalic, and acetic acids, respectively. In doing so, the pH of the reaction solutions after hydrolysis corresponds to 4.53, 2.11, and 4.28, accordingly, testifying to the buffer nature of the solutions “citric acid/magnesium citrate” and “acetic acid/magnesium acetate”. We also overview testing results of the developed apparatus where the process rate is effectively controlled by the control of the acid concentration in the hydrolysis reactor.

Thermal batteries utilizing metal hydride pairs are gaining tremendous research appeal for their applications in thermochemical energy storage. The pair consisting of a high-temperature metal hydride (HTMH: Mg-based hydride) and a low-temperature metal hydride (LTMH: AB2 type hydride) is attractive due to its relatively high energy storage density and medium energy storage efficiency. The energy storage efficiency can be significantly increased by improving the heat discharging performance of the thermal battery. In this study, we experimentally explore the heat releasing performance of an MgH2/(TiZr)(MnFeCr)2-based thermal battery. More specifically, the effects of LTMH bed heat transfer conditions on the heat discharging performance were briefly discussed. These heat transfer conditions include natural convection, forced convection, and resistive heating. The results showed that when operating the LTMH bed under active heat transfer conditions (forced convection or resistive heating), the thermochemical energy storage density varies between 1500 and 1820 kJ/ kg-Mg with relatively high-temperature lift (heat upgrade) between 47 and 55 degrees C. On the other side, the thermal battery discharges heat at a relatively high specific power, ca. 100-225 W/kg-Mg, which can be a benefit for heat-to-work conversion applications using organic or steam Rankine cycles.

Hydrolysis of MgH2 has a high theoretical hydrogen yield (15.2%) and is very attractive for onsite hydrogen production. However, the low solubility of Mg(OH)2 causes sluggish kinetics and incomplete utilization of MgH2. In this paper, we solve this problem by using organic acids (acetic, citric and oxalic) and nanoscale graphene-like carbon. The organic acid solution significantly increases the yield and rate of H2 generation due to its acidic nature. The hydrogen yield approaches 100% with a fast hydrolysis rate when the molar ratio Acid/MgH2 exceeds 0.9, 2.0 and 2.7 for the citric, oxalic and acetic acid, respectively. In doing so, pH of the reaction solutions after hydrolysis corresponds to 4.53, 2.11 and 4.28, accordingly, testifying about buffer nature of the solutions “citric acid / magnesium citrate” and “acetic acid / magnesium acetate”. The addition of graphene-like material (GLM) also significantly increases the yield and rate of H2 generation due to the decrease of particle size and increase of defects in the material, as well as due to stabilising the MgH2 nanoparticles and preventing their agglomeration. Additionally, GLM encapsulates the MgH2 particles thus suppressing the formation of MgO and, in turn, promoting achievement of the maximum hydrogen yield. In addition, this work presents layout and operation features of the developed apparatus for the controlled generation of pressurised hydrogen using hydrolysis of Mg or MgH2 in acidic solutions, as well as its testing results for the hydrolysis of Mg and MgH2 in the solution of citric acid.

High entropy alloys (HEAs) formed by multi-principal elements show promising hydrogen storage performance. However, many aspects of their behaviours remain poorly understood. Properties of the HEAs are related to their chemical composition and the nature of their constituent elements, including electronegativity, atomic radii, and valence electron concentration (VEC). Unfortunately, many of the related studies do not adopt unambiguous meaning of these fundamental properties, consequently causing uncertainties. The present review quoting 177 reference publications, aims at clarification of these features by performing systematic analysis of the available experimental data for the multi-component hydrogen storage alloys crystallizing as BCC solid solutions and Laves phase intermetallics. The correlations between the hydrogen sorption performance and the composition-related features including atomic size mismatch, VEC and, most importantly, mixing entropy and enthalpy, have been analysed. We show that VEC plays the most significant role in tuning the hydrogen storage performance of the HEAs. At the same time, no clear correlations of the hydrogen sorption capacity or the enthalpy of hydride formation with other key properties of the HEAs were observed. The correlations were however established when simultaneously accounting the effects of several HEA properties on their hydrogen sorption performance. Based on our observations, we conclude that hydrogen storage performance of the medium-and high-entropy alloys is rather similar, and thus hydride-forming HEAs might be considered as a group of conventional hydrogen storage alloys rather than their separate class.

Hydrogen absorption performances of LaNi5 alloy are sensitive to the surface reactions with poisonous gases, such as oxygen, readily forming oxides/hydroxides. In this study, we report the studies on the hydrogen absorption behaviour of AB5-type hydrogen storage alloys, formed by LaNi(5–x)Snx (X = 0.2) followed by electroless Pd deposition. The uncoated and Pd-coated materials were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), atomic absorption spectroscopy (AAS), X-ray diffraction (XRD) and Brunauer–Emmet–Teller. XRD analyses indicated that both LaNi5 and LaNi4.8Sn0.2 alloys crystallize in CaCu5-type crystal structure, while SEM analysis and particle size distribution histograms showed increment in particle size upon Sn incorporation. Palladium particles on the surface of the materials were detected by AAS and EDS analyses. Furthermore, substitution of a small fraction of Ni by Sn leads to an increase in hydrogen absorption capacity even without activation. Moreover, a decrease in hydrogen absorption rate was observed for LaNi4.8Sn0.2 alloy and this was related to an increment in the crystalline unit cell volume. Kinetic curves of Pd-coated alloys show superior absorption kinetics compared to their uncoated counterparts due to high affinity of Pd for hydrogen.

MgH2-based hydrogen storage materials are promising candidates for solid-state hydrogen storage allowing efficient thermal management in energy systems integrating metal hydride hydrogen store with a solid oxide fuel cell (SOFC) providing dissipated heat at temperatures between 400 and 600 degrees C. Recently, we have shown that graphite-modified composite of TiH2 and MgH2 prepared by high-energy reactive ball milling in hydrogen (HRBM), demonstrates a high reversible gravimetric H storage capacity exceeding 5 wt % H, fast hydrogenation/dehydrogenation kinetics and excellent cycle stabidlity. In present study, 0.9 MgH2 + 0.1 TiH2 + 5 wt %C nanocomposite with a maximum hydrogen storage capacity of 6.3 wt% H was prepared by HRBM preceded by a short homogenizing premilling in inert gas. 300 g of the composite was loaded into a storage tank accommodating an air-heated stainless steel metal hydride (MH) container equipped with transversal internal (copper) and external (aluminium) fins. Tests of the tank were carried out in a temperature range from 150 degrees C (H-2 absorption) to 370 degrees C (H-2 desorption) and showed its ability to deliver up to 185 NL H-2 corresponding to a reversible H storage capacity of the MH material of appr. 5 wt% H. No significant deterioration of the reversible H storage capacity was observed during 20 heating/cooling H-2 discharge/charge cycles. It was found that H-2 desorption performance can be tailored by selecting appropriate thermal management conditions and an optimal operational regime has been proposed. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The goal of the EU Horizon 2020 RISE project 778307 “Hydrogen fuelled utility vehicles and their support systems utilising metal hydrides” (HYDRIDE4MOBILITY), is in addressing critical issues towards a commercial implementation of hydrogen powered forklifts using metal hydride (MH) based hydrogen storage and PEM fuel cells, together with the systems for their refuelling at industrial customers facilities. For these applications, high specific weight of the metallic hydrides has an added value, as it allows counterbalancing of a vehicle with no extra cost. Improving the rates of H2 charge/discharge in MH on the materials and system level, simplification of the design and reducing the system cost, together with improvement of the efficiency of system “MH store-FC”, is in the focus of this work as a joint effort of consortium uniting academic teams and industrial partners from two EU and associated countries Member States (Norway, Germany, Croatia), and two partner countries (South Africa and Indonesia).The work within the project is focused on the validation of various efficient and cost-competitive solutions including (i) advanced MH materials for hydrogen storage and compression, (ii) advanced MH containers characterised by improved charge-discharge dynamic performance and ability to be mass produced, (iii) integrated hydrogen storage and compression/refuelling systems which are developed and tested together with PEM fuel cells during the collaborative efforts of the consortium.This article gives an overview of HYDRIDE4MOBILITY project focused on the results generated during its first phase (2017–2019).

The deterioration of hydrogen charging performances resulting from the surface chemical action of electrophilic gases such as CO2 is one of the prevailing drawbacks of TiMn1.52 materials. In this study, we report the effect of autocatalytic Pd deposition on the morphology, structure, and hydrogenation kinetics of TiMn1.52 alloy. Both the uncoated and Pd-coated materials were characterized using scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). XRD analyses indicated that TiMn1.52 alloy contains C14-type Laves phase without any second phase, while the SEM images, together with a particle size distribution histogram, showed a smooth non-porous surface with irregular-shaped particles ranging in size from 1 to 8 µm. The XRD pattern of Pd-coated alloy revealed that C14-type Laves phase was still maintained upon Pd deposition. This was further supported by calculated crystallite size of 29 nm for both materials. Furthermore, a Sieverts-type apparatus was used to study the kinetics of the alloys after pre-exposure to air and upon vacuum heating at 300 °C. The Pd-coated AB2 alloy exhibited good coating quality as confirmed by EDS with enhanced hydrogen absorption kinetics, even without activation. This is attributed to improved surface tolerance and a hydrogen spillover mechanism, facilitated by Pd nanoparticles. Vacuum heating at 300 °C resulted in removal of surface barriers and showed improved hydrogen absorption performances for both coated and uncoated alloys.

A multi component AB(2) type hydrogen storage intermetallic alloy (A = Ti0.85Zr0.15, B-2 = Mn1.22Ni0.22Cr0.2V0.3Fe0.06; was investigated in this work. The intermetallic specified above was modified by oxygen to yield the composition AB(2)O(0.05). The oxygen was introduced by adding TiO2 to the charge, with corresponding decrease of the Ti amount, followed by arc melting and annealing at the same conditions as for the oxygen free AB(2)-type alloy. The addition of oxygen to the alloy did not change much the PCT properties; the only difference was that the plateau pressure for the oxygen-modified alloy increased slightly. Both alloys have shown to be excellent candidates for H-2 storage, particularly for utility vehicles, due to their relatively high reversible H-2 storage capacity (1.6 wt%) and low plateau pressure at room temperature (<5 bar). The addition of oxygen improved hydrogen absorption kinetics in the AB(2) alloy allowing it to immediately absorb H-2 without activation while for the non-modified sample an incubation period (30 min) was observed at the same conditions. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen compression is a main contributor in the capital and operation costs of the H-2 refuelling infrastructure. The use of metal hydrides (MH) for thermally-driven H-2 compression can provide efficient solution to mitigate this challenge. MH compressors are particularly promising for industrial customers who possess necessary infrastructure including pipeline H-2, sources of low-grade heat, etc. Here we present the details about layout of the H-2 refuelling station and its operation at Impala Platinum refineries in Springs, South Africa, since its start-up in September 2015. The station provides H-2 dispensing at the pressure up to 185 bar and uses pipeline H-2 (P = 50-60 bar) available at the customer site. H-2 compression to P = 200 bar with productivity up to 13 Nm(3)/h is provided by the integrated 1-stage MH H-2 compressor which uses steam (T similar to 140 degrees C) for the heating and circulating water (T similar to 20 degrees C) for the cooling; both steam and water are also available from the customer infrastructure. The station also includes H-2 dispenser, buffer tank (standard gas cylinder pack), and control block on the basis of Siemens Program Logic Controller (PLC) which provides fully automated system operation. Switching H-2 and steam/water flows is carried out with the help of remotely controlled, pneumatically actuated valves and auxiliary check valves. Additionally, at P = 200 bar the control block switches the system into standby mode when MH compression modules are cooled down and their gas manifolds are connected to the H-2 supply line. The H-2 dispensing is independent on the compressor operation and takes from 6 to 15 min. The refuelling station complies with South African safety regulations for operation in a fire and explosion hazardous environment. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

This review highlights the state of art progress in crucible designs which have been identified as showing potential for induction melting three groups of titanium alloys based on the systems; Ti–Al, Ti–Ni, as well as multicomponent Ti-based hydrogen storage alloys. Several important parameters for crucible design, including; crucible-melt interactions, thermodynamic stability, and, thermal shock resistance of different crucibles will be discussed. Based on the findings of the review, the selection criteria for identifying crucibles for melting titanium alloys were outlined and several specific promising solutions were suggested.

The "low-temperature" intermetallic hydrides with hydrogen storage capacities below 2 wt % can provide compact H-2 storage simultaneously serving as a ballast. Thus, their low weight capacity, which is usually considered as a major disadvantage to their use in vehicular H-2 storage applications, is an advantage for the heavy duty utility vehicles. Here, we present new engineering solutions of a MH hydrogen storage tank for fuel cell utility vehicles which combines compactness, adjustable high weight, as well as good dynamics of hydrogen charge/discharge. The tank is an assembly of several MH cassettes each comprising several MH containers made of stainless steel tube with embedded (pressed-in) perforated copper fins and filled with a powder of a composite MH material which contains AB(2) - and AB(5)-type hydride forming alloys and expanded natural graphite. The assembly of the MH containers staggered together with heating/cooling tubes in the cassette is encased in molten lead followed by the solidification of the latter. The tank can provide >2 h long H-2 supply to the fuel cell stack operated at 11 kWe (H-2 flow rate of 120 NIJmin). The refuelling time of the MH tank (T = 15-20 degrees C, P(H-2) = 100-150 bar) is about 15-20 min. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hydride-forming alloys are currently considered reliable and suitable hydrogen storage materials because of their relatively high volumetric densities, and reversible H-2 absorption/desorption kinetics, with high storage capacity. Nonetheless, their practical use is obstructed by several factors, including deterioration and slow hydrogen absorption/desorption kinetics resulting from the surface chemical action of gas impurities. Lately, common strategies, such as spark plasma sintering, mechanical alloying, melt spinning, surface modification and alloying with other elements have been exploited, in order to overcome kinetic barriers. Through these techniques, improvements in hydriding kinetics has been achieved, however, it is still far from that required in practical application. In this review, we provide a critical overview on the effect of mechanical alloying of various metal hydrides (MHs), ranging from binary hydrides (CaH2, MgH2, etc) to ternary hydrides (examples being Ti-Mn-N and Ca-La-Mg-based systems), that are used in solid-state hydrogen storage, while we also deliver comparative study on how the aforementioned alloy preparation techniques affect H-2 absorption/desorption kinetics of different MHs. Comparisons have been made on the resultant material phases attained by mechanical alloying with those of melt spinning and spark plasma sintering techniques. The reaction mechanism, surface modification techniques and hydrogen storage properties of these various MHs were discussed in detail. We also discussed the remaining challenges and proposed some suggestions to the emerging research of MHs. Based on the findings obtained in this review, the combination of two or more compatible techniques, e.g., synthesis of metal alloy materials through mechanical alloying followed by surface modification (metal deposition, metal-metal co-deposition or fluorination), may provide better hydriding kinetics.