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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.

Fuel cell-battery hybrid systems for thepowertrain, which have the advantage of emission-free power generation and adapt to material transport and emission reduction, are investigated. Based on the characteristics of thefuel cell systemand the characteristics of the electric forklift truck powertrain system, this work defines the design principle of the control strategy to improve overall performance and economy. A simulation platform for fuel cell and electric vehicles has been established. The optimal performance of thefuel cell stackand the battery capacity were defined for the specific application. An energy control strategy was defined for different operating cycles and operating conditions. Model validation involved comparing simulation results with experimental data obtained during VDI60 test protocol. The main parameters that influence the forklift performance were defined and evaluated, such asenergy loss, fuel cell operating conditions and different battery charging cycles. The optimal size of the fuel cell stack of 11kW and the battery of 10 Ah was determined for the specific load profile with the proposed control strategy. The results obtained in this work forms the basis for an in-depth study of the energy management of fuel cell battery drive trains for forklift trucks.

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 °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 stability. 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 pre-milling 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 °C (H2 absorption) to 370 °C (H2 desorption) and showed its ability to deliver up to 185 NL H2 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 H2 discharge/charge cycles. It was found that H2 desorption performance can be tailored by selecting appropriate thermal management conditions and an optimal operational regime has been proposed.

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.

This paper presents the investigation of a two dimensional coupled model of heat and mass transfer in a mixture of AB2 – AB5 metal hydride (MH) systems of a cylindrical configuration during hydrogen sorption using COMSOL 5.3a commercial software. The parametric study on the sorption process has been studied with variation of heat transfer coefficient (HTC), and activation energy (AE) to understand the effects they have on the reaction kinetics of the sorption process. The simulation results demonstrate the importance of mutual dependence between the temperature propagation in the body of metal hydride, the absorbed concentration of the hydrogen gas, and the gas pressure for the absorption of hydrogen gas in metal hydrides. The decrease in the activation energy is found to have significant effect on the dynamic performances of hydrogen absorption in the MH reactors with an increased amount of hydrogen conversion, whilst the variation of heat transfer coefficient displayed insignificant change in hydrogen conversion. The simulated results show good agreement with the experimental results obtained from HYSA Systems and were implemented for use in the STILL RX60-30L electric forklift fuel cell applications designed by HYSA Systems in the University of the Western Cape.

The kinetics of the hydrogenation of magnesium composites with graphene-like material (GLM) on which nickel particles are deposited (Ni/GLM) and dehydrogenation of MgH2+Ni/GLM composites is studied. The mechanism of the reactions is revealed using the obtained results and the mathematical processing of curves with the Avrami–Erofeev equation. It is found that Ni/GLM considerably accelerates the hydrogenation of Mg and the decomposition of MgH2 in the composite. The hydrogen-accumulating Mg+Ni/GLM composite is shown to have cyclic stability with rapid and virtually complete reversible hydrogenation.

Fuel cell powered forklifts have several advantages over the battery powered ones. They possess higher productivity by eliminating time consuming battery swap and can be refueled in 5-10 minutes. Fuel cell powered forklifts maintain constant power throughout entire shift as there is no voltage drop as compared to battery powered ones. In this work, we present a prototype fuel cell power module for 3-tonne electric forklift developed by HySA Systems and integrated by Hot Platinum (Pty) Ltd, South Africa. The BoP was designed around Ballard 9SSL/75 Cell FC stack, and its main components included: air supply, H2 storage and supply, the closed circuit liquid stack cooling / MH heating, and power conditioning and control subsystems. The MH tank has dimensions of 704 mm (W) x 970 mm (D) x 270 mm (H), weight ~1200 kg and combines functions of H2 storage and vehicle ballast thus adding flexibility to the layout of the BoP components within strict space constrains of the application. The power module provided stable operation of the forklift during 60 complete cycles of the VDI60 test carried out at ambient temperature of 27 °C. Load energy consumption at 60 VDI cycles/hour was 9.564 kWh/h compared to 7.5 kWh/h claimed by forklift manufacturer.

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM, Industrial and public interest in hydrogen technologies has risen strongly recently, as hydrogen is the ideal means for medium to long term energy storage, transport and usage in combination with renewable and green energy supply. In a future energy system, the production, storage and usage of green hydrogen is a key technology. Hydrogen is and will in future be even more used for industrial production processes as a reduction agent or for the production of synthetic hydrocarbons, especially in the chemical industry and in refineries. Under certain conditions material based systems for hydrogen storage and compression offer advantages over the classical systems based on gaseous or liquid hydrogen. This includes in particular lower maintenance costs, higher reliability and safety. Hydrogen storage is possible at pressures and temperatures much closer to ambient conditions. Hydrogen compression is possible without any moving parts and only by using waste heat. In this paper, we summarize the newest developments of hydrogen carriers for storage and compression and in addition, give an overview of the different research activities in this field

In present study nanocomposites of Graphene Like Material (GLM) and nickel containing 5–60 wt % Ni were prepared by a co-reduction of graphite oxide and Ni2+ ions. These nanocomposites served as effective catalysts of hydrogenation-dehydrogenation of magnesium based materials and showed a high stability on cycling. Composites of magnesium hydride with Ni/GLM were prepared by high-energy ball milling in hydrogen. The microstructures and phase compositions of the studied materials were characterized by XRD, SEM and TEM showing that Ni nanoparticles have size of 2–5 nm and are uniformly distributed in the composites. The kinetic curves of hydrogen absorption and desorption by the composites were measured using a Sievert's type laboratory setup and were analyzed using the Avraami – Erofeev approach. The re-hydrogenation rate constants and the Avraami exponents fitting the kinetic equations for the Mg/MgH2+Ni/GLM composites show significant changes as compared to the Mg/MgH2 prepared at the same conditions and this difference has been assigned to the changes in the mechanism of nucleation and growth and alteration of the rate-limiting steps of the hydrogenation reaction. The composites of Mg with Ni/GLM have a high reversible hydrogen capacity exceeding 6.5 wt % H and also show high rates of hydrogen absorption and desorption and thus belong to the promising hydrogen storage materials.

We describe a metal hydride (MH) hydrogen storage tank for light fuel cell vehicle application developed at HySA Systems. A multi-component AB2-type hydrogen storage alloy was produced by vacuum induction melting (10 kg per a load) at our industrial-scale facility. The MH alloy has acceptable H sorption performance, including reversible H storage capacity up to ∼170 NL/kg (1.5 wt% H). The cassette-type MH tank was made up of 2 cylindrical aluminium canisters with transversal internal copper fins and external aluminium fins for improving the heat exchange between the heating medium and the MH tank. Heat supply and removal was provided from the outside using air at T = 15–25 °C. The MH tank was tested at the conditions of natural or forced (velocity ∼2 m/s) air convection. The tests included H2 charge of the tank at P = 15–40 bar and its discharge at P = 1 bar. The tank in the H2 discharge mode was also tested together with open cathode low-temperature proton exchange membrane fuel cell (LT PEMFC).

Ball milling of magnesium hydride with germanium additives in argon for up to 10 h was shown to result in the formation of nanocomposites of α- and γ-modifications of MgH2 together with individual Ge phase. When the as milled samples are heated-up, Ge interacts with MgH2 to form Mg2Ge at T = 350–400 °C; the phase transformation overlaps with MgH2 decomposition and Mg2Ge phase remains in the material after its re-hydrogenation at T = 300 °C and P(H2)∼15 bar. The ball milled Ge-MgH2 nanocomposites were found to be characterised by an improved hydrogen release via hydrolysis in organic acid solutions as compared to pure MgH2 prepared and tested at the same conditions. It was found that the composite containing 5 wt% of Ge and ball milled for 5 h showed the best hydrogen generation performance, with total hydrogen release exceeding 1.55 NL/g (yield close to 100%) in one minute.

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 AB2type hydrogen storage intermetallic alloy (A=Ti0.85Zr0.15, B2=Mn1.22Ni0.22Cr0.2V0.3Fe0.06; was investigated in this work. The intermetallic specified above was modified by oxygen to yield the composition AB2O0.05. The oxygen was introduced by adding TiO2to the charge, with corresponding decrease of the Ti amount, followed by arc melting and annealing at the same conditions as for the oxygen free AB2-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 H2storage, particularly for utility vehicles, due to their relatively high reversible H2storage capacity (1.6wt%) and low plateau pressure at room temperature (2alloy allowing it to immediately absorb H2without activation while for the non-modified sample an incubation period (30min) was observed at the same conditions.

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.

This work presents a hybrid model for the simulation of heat and mass transfer in metal hydride (MH) reactors. The model combines “lumped” approach based on mass and energy conservation for the gas phase with detailed consideration of the heat and mass exchange processes in the solid. The developed calculation procedure was realised numerically and integrated in a combined model of a two-stage MH hydrogen compressor (MHHC). Experimental validation based on the data available in the literature, the results of testing two types of MH reactors for H2 compression, as well as a small-scale two-stage MHHC, demonstrated the qualitative and quantitative agreement of calculated and experimentally measured dependencies.

In energy systems, multi-generation including co-generation and tri-generation has gained tremendous interest in the recent years as an effective way of waste heat recovery. Solid oxide fuel cells are efficient power plants that not only generate electricity with high energy efficiency but also produce high quality waste heat that can be further used for hot and chilled water production. In this work, we present a concept of combined cooling, heating and power (CCHP) energy system which uses solar power as a primary energy source and utilizes a reversible solid oxide fuel cell (R-SOFC) for producing hydrogen and generating electricity in the electrolyser (SOEC) and fuel cell (SOFC) modes, respectively. The system uses “high temperature” metal hydride (MH) for storage of both hydrogen and heat, as well as “low temperature” MH's for the additional heat management, including hot water supply, residential heating during winter time, or cooling/air conditioning during summer time. The work presents evaluation of energy balances of the system components, as well as heat-and-mass transfer modelling of MH beds in metal hydride hydrogen and heat storage system (MHHS; MgH2), MH hydrogen compressor (MHHC; AB5; A = La + Mm, B Ni + Co + Al + Mn) and MH heat pump (MHHP; AB2; A = Ti + Zr, B Mn + Cr + Ni + Fe). A case study of a 3 kWe R-SOFC is analysed and discussed. The results showed that the energy efficiencies are 69.4 and 72.4% in electrolyser and fuel cell modes, respectively. The round-trip COP's of metal hydride heat management system (MHHC + MHHP) are close to 40% for both heating and cooling outputs. Moreover, the tri-generation leads to an improvement of 36% in round-trip energy efficiency as compared to that of a stand-alone R-SOFC.

This work presents results of the experimental studies (XRD, SEM, PCT) of hydride forming intermetallides used in the first (LaNi5) and the second (La0.5Ce0.5Ni5) stages of industrial-scale metal hydride hydrogen compressor providing H2 compression from 3.5 to 150 atm with the productivity about 10 Nm3/h. During the operation, both materials underwent 18,180 hydrogenation/dehydrogenation (h/d) cycles which included H2 absorption at the pressure of 3.5 atm (LaNi5) and 35–38 atm (La0.5Ce0.5Ni5) at T = 15–20 °C followed by H2 desorption at the pressure of 35–38 atm (LaNi5) and 150 atm (La0.5Ce0.5Ni5) at T = 150–160 °C. It was found that the observed ∼30% drop of the productivity of the compressor by the end of its operation is associated with a degradation of the first stage hydride material (LaNi5) under conditions specified above. The cycling resulted in the appearance of Ni and LaH2+x phases in addition to the parent intermetallide. In turn, the cycled LaNi5 exhibited more than 20% lower hydrogen storage capacity than the alloy at the beginning of the cycling; the cycling was also found to result in a noticeable sloping of initially flat plateau. Conversely, the degradation effects in La0.5Ce0.5Ni5 were found to be much less pronounced, in spite of the higher operating H2 pressures. The observed effect was associated with the decrease of thermodynamic driving force (TDF) of AB5 disproportionation in H2 when substituting La with Ce.

This work provides an overview of R&D activities at South African Institute for Advanced Materials Chemistry (SAIAMC) on metal hydride hydrogen compression technology with a focus on engineering solutions for industrial-scale applications. A summary of layout features, as well as test / operation results are presented for industrial-scale prototypes of: (i) 1-stage H2 compressor for refueling station (50–200 bar, up to 13 Nm3/h), and (ii) 3-stage H2 compressor (3–200 bar, up to 5 Nm3/h). The developed systems provide hydrogen compression utilizing low-grade steam (T=120–140 °C) and cooling water (T=15–25 °C) available at sites of industrial customers.

In this work, we report about development of computer model of hydrogen Thermal Desorption Spectra (TDS) using a combination of modified Kissinger approach and combined form of differential kinetic equation. For an individual TDS peak, the developed model allows to adequately fit the experimental TDS data using up to 6 parameters, including the activation energy of desorption and the pre-exponent factor. The fitting procedure also allows visualizing the reaction model function using the experimental TDS data. The model was verified for the nanostructured magnesium hydride prepared by high-energy ball milling of magnesium in hydrogen, including its composites with carbon and titanium.

Mg-based materials have become the cornerstone of hydrogen storage applications and have shown recently promises in thermal energy storage applications. However, synthesis of some materials including Mg2FeH6 ternary hydride poses a number of challenges. In spite a variety of reports on various synthesis routes yielding Mg2FeH6, none of them produces a 100% pure Mg2FeH6. In this communication, we have attempted to synthesize Mg2FeH6 by high energy reactive ball milling (HERBM) performed in hydrogen gas. Prior to the ball milling, the starting stoichiometric 2:1 mixture of the initial materials Mg+Fe was heat treated through a judicious temperature program. It was found that the yield of Mg2FeH6 is related to the conditions of heat treatment, time and temperature, and the milling parameters such as ball to powder mass ratio (BPR) and rotation speed of the planetary mill. Moreover, it was found that the synthesis took place in less than 5 hours of milling with a maximum yield of Mg2FeH6 of 84 wt%, which is a noticeable improvement as compared to the reference data.

This paper reviews state-of-the art developments in hydrogen energy systems which integrate fuel cells with metal hydride-based hydrogen storage. The 187 reference papers included in this review provide an overview of all major publications in the field, as well as recent work by several of the authors of the review. The review contains four parts. The first part gives an overview of the existing types of fuel cells and outlines the potential of using metal hydride stores as a source of hydrogen fuel. The second part of the review considers the suitability and optimisation of different metal hydrides based on their energy efficient thermal integration with fuel cells. The performances of metal hydrides are considered from the viewpoint of the reversible heat driven interaction of the metal hydrides with gaseous H2. Efficiencies of hydrogen and heat exchange in hydrogen stores to control H2 charge/discharge flow rates are the focus of the third section of the review and are considered together with metal hydride – fuel cell system integration issues and the corresponding engineering solutions. Finally, the last section of the review describes specific hydrogen- fuelled systems presented in the available reference data.

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. Keywords: Titanium alloys, Induction melting, Crucible, Chemical stability, Thermal shock resistance

The present work was focused on the studies of the effect of variation of stoichiometric composition of Ti–Zr based AB2±x Laves phase alloys by changing the ratio between A (Ti + Zr) and B (Mn + V + Fe + Ni) components belonging to both hypo-stoichiometric (AB1.90, AB1.95) and over-stoichiometric (AB2.08) alloys further to the stoichiometric AB2.0 composition to optimize their hydrogen storage behaviours and performances as the alloy anodes of nickel metal hydride batteries. AB2-xLa0.03 Laves type alloys (A = Ti0.15Zr0.85; B = Mn0.64–0.69V0.11–0.119Fe0.11–0.119Ni1.097–1.184; x = 0, 0.05 and 0.1) were arc melted and then homogenized by annealing. The studies involved probing of the phase-structural composition by X-Ray diffraction (XRD), together with studies of the microstructural state, hydrogen absorption–desorption and thermodynamic characteristics of gas–solid reactions and electrochemical charge-discharge performance, further to the impedance spectroscopy characterization. The alloys were probed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and XRD. These studies concluded that the alloys contained the main C15 FCC Laves type AB2 intermetallic co-existing with a secondary C14 hexagonal Laves phase and a small amount of LaNi intermetallic. The gaseous H storage capacity and electrochemical performances were found to be closely dependent on the stoichiometric compositions of the alloys. High discharge capacities approaching 500 mAh/g were achieved for the AB1.95 alloy. At 500 mA/g current density, the discharge capacity was maintained as high as 80%, with very low capacity retention after 500 cycles. The alloy which had the highest capacity retention after 500 cycles was found to be AB2.0 alloy. Furthermore, AB2.0 alloy showed an excellent cyclic stability together with a high hydrogen diffusion coefficient. Studies of hydrogen diffusion coefficients showed that annealing enhanced the H diffusion rates allowing advanced performance at high discharge current densities. This has been related to a higher content of C15 Laves compound which allows to reach a higher H mobility in contrast with higher storage capacity observed for the C14 Laves type polymorph.

International Symposium On Materials for Energy Storage & Conversion, Akyaka, Mugla / Turkey, September 11-13, 2019 (oral); mESC-IS2019, Abstracts, p. 127

The use of fuel cells (FC) in heavy duty utility vehicles, including material handling units / forklifts or underground mining vehicles, has a number of advantages over similar battery-driven vehicles including: constant power during the entire shift, and shorter refuelling time as compared to the time to recharge the battery. Most of vehicular FC power systems demonstrated so far have utilised compressed H2 stored in gas cylinders at pressures up to 350 bar. This solution, however, results in too light weight of the FC power modules for the utility vehicles which require additional ballast for a proper counterbalancing to provide vehicle stability. In the undeground applications, the use of pressurised hydrogen (> 20 bar) is not acceptable at all for the safety reasons. A promising alternative is the application of metal hydrides (MH) for the on-board hydrogen storage [1]. The “low-temperature” intermetallic hydrides with hydrogen storage capacities below 2 wt% can provide compact H2 storage simultaneously serving as a ballast. Thus, their low weight capacity, which is usually considered as a major disadvantage to their use in vehicular H2 storage applications, is an advantage for the heavy duty utility vehicles [2]. Here, we present new engineering solutions [3, 4] of a MH hydrogen storage tank for FC 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 cassette comprises 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 AB2- and AB5-type hydride forming alloys and expanded natural graphite. H2 input / output pipelines are ended by gas filters inside the MH containers and connected to a common gas manifold from the opposite side. The assembly of the MH containers staggered together with heating / cooling tubes is encased in molten lead followed by the solidification of the latter. During lead encasing, the inner space of the MH containers is evacuated providing initial activation of the MH material. After cooling down, the MH cassette is filled with pressurised H2 for the initial H2 charge which starts immediately and completes in about 1.5 hours. One MH cassette comprising of five 51.3x800 mm MH containers (each filled with ~3 kg of the MH material) has hydrogen storage capacity about 2.5 Nm3 H2. When heated with a running water to T=40– 50 °C (typical coolant temperature during the operation of a PEMFC stack), the cassette can release more than 60% of this maximum amount at the H2 flow rate of 25 NL/min that corresponds to 1 hour long full load operation of 2.5 kWe stack at 50% efficiency. Furthermore, at the heating temperature about 40 °C and H2 output flow rate of 15 NL/min (equivalent to the stack power of 1.38 kWe at the same efficiency) the H2 release remains stable during >2 hours providing utilisation of ~80% of the stored H2. References [1] M.V. Lototskyy, et al, . Progr. Natur. Sci., 27 (2017) 3-20 [2] M.V. Lototskyy, et al, . J. Power Sources, 316 (2016) 239-250 [3] M.V.Lototskyy, et. al, Patent application WO 2015/189758 A1 [4] M.V.Lototskyy, et. al, Patent application UK 1806840.3 (2018)

Hydrogen storage nanocomposites prepared by high energy reactive ball milling of magnesium and vanadium alloys in hydrogen (HRBM) are characterised by exceptionally fast hydrogenation rates and a significantly decreased hydride decomposition temperature. Replacement of vanadium in these materials with vanadium-rich Ferrovanadium (FeV, V80Fe20) is very cost efficient and is suggested as a durable way towards large scale applications of Mg-based hydrogen storage materials. The current work presents the results of the experimental study of Mg–(FeV) hydrogen storage nanocomposites prepared by HRBM of Mg powder and FeV (0–50 mol.%). The additives of FeV were shown to improve hydrogen sorption performance of Mg including facilitation of the hydrogenation during the HRBM and improvements of the dehydrogenation/re-hydrogenation kinetics. The improvements resemble the behaviour of pure vanadium metal, and the Mg–(FeV) nanocomposites exhibited a good stability of the hydrogen sorption performance during hydrogen absorption – desorption cycling at T = 350 °C caused by a stability of the cycling performance of the nanostructured FeV acting as a catalyst. Further improvement of the cycle stability including the increase of the reversible hydrogen storage capacity and acceleration of H2 absorption kinetics during the cycling was observed for the composites containing carbon additives (activated carbon, graphite or multi-walled carbon nanotubes; 5 wt%), with the best performance achieved for activated carbon.

In this paper, the solution of the Lacher model describing the relationship between the Pressure – Composition, and Temperature (PCT diagrams) of AB5 type metal-hydrides (LaNi4.8Sn0.2, LmNi4.91Sn0.15, LaNi4.5Al0.5) for hydrogen storage using C ++ platform, with the help of a numerical method of nonlinear equation, Newton-Raphson method is presented. This study focuses on the development of a C ++ code to describe the iteration of Newton-Raphson for application in Hydrogen to Metal-Hydride systems.

This paper describes a Portable Polymer Electrolyte Membrane Fuel Cell (PEMFC) System developed at HySA Systems, UWC. The system has a rated maximum output power of 130 W at 240 VAC and 5 VDC USB output port. Hydrogen is supplied to the PEMFC using Metal Hydride (MH) on the basis of a multi-component AB2 – type hydrogen storage alloy (A=Ti,Zr; B=Mn,Fe,Cr,Ni; Ti:Zr=0.55:0.45). The stainless steel MH canister with external aluminium fins was developed in-house. The heat transfer performance was optimized by utilizing external fins and compacting thermal expanded graphite (TEG) with the MH powder to form pellets. The MH canister has a maximum hydrogen storage capacity of 90 NL H2. It is well-known that the endothermic desorption of H2 from MH results in the significant cooling, which decrease H2 supply flow rate. To overcome this problem and improve the dynamic performance, the MH canister was placed in front of the fuel cell exhaust to utilise the waste heat generated by PEMFC. By utilisation of the PEMFC waste heat in combination with external fins and MH / TEG compacts, the MH canister allowed for >40 minutes-long stable operation at the stack power of 130 W (225 W/kg(MH)) with the utilisation of >90% of the stored H2. Figure 1 illustrates the MH storage unit integrated with 200 W PEMFC stack, Figure 2 shows the rated power of the PEMFC and temperature of the MH canister at different loads connected to the system. Figure 1

A novel hydrogen storage system for a RX60-30L 3-tonne electric forklift (STILL), equipped with a GenDrive 1600-80A fuel cell power module (Plug Power) has been developed. The system combines a compressed H2 composite cylinder (CGH2) and a liquid-heated-cooled metal hydride (MH) extension tank which is thermally integrated with a power module. The MH extension tank comprises a MH bed formed according to an advanced solution to provide easy activation of the MH material and fast H2 charge/discharge. The system has the same hydrogen storage capacity (∼19 Nm3 H2 or 1.7 kg) as the separate CGH2 tank charged at P = 350 bar, but at a lower H2 charge pressure (≤185 bar). A 15 min cycle refuelling provides the forklift with full-load operation (according to VDI-60 protocol) during >3 h, or 2 to 4 working shifts in a real industrial environment. The work also presents a hydrogen refuelling station (dispensing pressure up to 185 bar) with integrated MH compressor which has been developed for forklift refuelling.

We present test results of a commercial 3-tonne electric forklift (STILL) equipped with a commercial fuel cell power module (Plug Power) and a MH hydrogen storage tank (HySA Systems and TF Design). The tests included: (i) performance evaluation of “hybrid” hydrogen storage system during refuelling at low (

An advanced, eco-efficient “waste plus waste to hydrogen” method was developed for hydrogen generation and the simultaneous treatment of two types of waste generated from magnesium and brewery-based industries via hydrolysis. The hydrolysis of Mg scraps was carried out using brewery wastewater and the reaction was accelerated with acetic acid (aa) at different concentrations (0, 12, 18, 24 and 30 wt% aa). The concentration of pollutants such as cyclortisiloxane-hexamethyle (C6H18O3Si3), which are persistent in conventional wastewater treatment, was successfully reduced. After the hydrolysis of the wastewater, 62.4% of chemical oxygen demand (COD) reduction and the complete colour removal were observed. The highest hydrogen generation, about 0.99 NL/min (>60% H2 yield in 5 min), was observed in the presence of 30 wt% aa concentration in the hydrolysis reaction. This study proposes an eco-efficient hydrogen generation and waste treatment method as it simultaneously degrades pollutants and produces hydrogen utilizing Mg scrap waste and brewery wastewater without additional energy consumption.

In this paper optimal battery capacity and fuel cell stack power were calculated for the specific application of the fuel cell powered forklift. Optimal energy strategy has been defined for different operation cycles and working conditions. Numerical model of the specific fuel cell powered forklift has been designed and validated together with available experimental results. Simulations results where validated with the experimental data. The most important parameters on the forklift performance have been defined and evaluated, such as: energy lost, battery load cycles etc. The main research outcome of the herein presented study is the novel control strategy for optimization of the PEM FC-Battery hybrid system in real environment/conditions.

Heat storage systems based on 2 tanks thermochemical heat storage are gaining momentum for their utilization in solar power plants or industrial waste heat recovery, since they can efficiently store heat for. However, their performance is generally limited by reactor configuration, design and optimization on the one hand and most importantly on the selection of appropriate thermochemical materials [1]. Metal hydrides, although at the early stage of research and development (in heat storage applications), can offer several advantages over other thermochemical materials (salt hydrates, metal hydroxides, oxide and carbonates) such as high energy storage density and power density. In this study, we present a system that combines latent heat and thermochemical heat storage based on two-tank metal hydrides. The systems consists of two metal hydrides tanks coupled (See Figure 1). During the heat charging the high temperature metal hydride (HTMH) desorbs hydrogen which in turn is stored in the low temperature metal hydride (LTMH). In the meantime, the heat generated from hydrogen absorption in the LTMH tank is stored as latent heat in a phase change material (PCM) jacket surrounding the LTMH tank, to be reused during the heat discharging. For simulations of this heat storage system, a metal hydrides pair based on Mg2NiH4 (HTMH)- LaNi5 (LTMH) and Rubitherm RT(Tm) based on commercial phase change materials are selected for discussion. The results of the simulation shows that the performance indicators such as energy density, power density and storage efficiency is a function of the properties of the selected phase change material, more specifically the melting temperature, Tm and the range of transition temperature.

Hydride-forming alloys are currently considered reliable and suitable hydrogen storage materials because of their relatively high volumetric densities, and reversible H2 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 H2 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.

This work summarises the results of development and long-term testing of two prototype models of industrial-scale metal-hydride thermal sorption hydrogen compressors, TSC1-3.5/150 (up to 11 Nm3 h−1; water cooling/steam heating) and TSC2-3.5/150 (up to 15 Nm3 h−1; heating and cooling by circulating oil). Both compressors have a two-stage layout utilising LaNi5 for the stage 1 and La0.5Ce0.5Ni5 for stage 2, thus providing hydrogen compression from 0.35 to 15 MPa at a cooling temperature of about 20 °C and a heating temperature between 150 °C and 160 °C. The compressors were operating for one year each and exhibited a satisfactory performance. The results of this work can be used in various medium-to-large scale hydrogen compression applications, including renewable energy systems.

A new semi-empirical model of phase equilibria of hydride forming metals and alloys with hydrogen gas (PCT diagrams) has been developed. Within the model, pressure – composition isotherms (PCI’s) for hydrogen absorption and desorption are presented as pseudo-convolutions of one core function, or “ideal” PCI built according to Lacher model, or model of Van der Waals lattice gas, with two modified asymmetric pseudo Voight distribution functions. The median of the absorption distribution is shifted from the one of the desorption distribution towards higher pressures, by the value related to a minimum of a hysteresis free energy (assumed to be constant) and an excessive chemical potential of hydrogen in over-saturated α-solid solution. The model allows to simultaneously fit both H2 absorption and desorption datasets and adequately simulates the features of experimental PCT diagrams in wide temperature range including (i) presence of several plateau segments, (ii) hysteresis including its disappearance when approaching to critical temperature, (iii) shape of transitions between α-, (α + β)- and β-regions, and (iv) flat or sloping plateaux including temperature and concentration dependencies of the plateau slope. The article also presents a demonstration software (macro-enabled Excel workbook with an ActiveX calculation module) for the fitting of experimental PCT datasets verified on the systems H2 – LaNi5–xSnx, H2 – TiFe and H2 – bcc-V(Ti,M); M = Zr,Ni.

A 3D numerical heat-and-mass transfer model was used for the comparison of H2 uptake performances of powdered cylindrical MH beds comprising MmNi4.6Al0.4 hydrogen storage material. The considered options of heat exchange between the MH and a heat transfer fluid included internal cooling using straight (I) or helically coiled (II) tubing, as well as external cooling of the MH bed without (III) and with (IV) transversal fins. The dynamic performances of these layouts were compared based on the numerical simulation. The effect of heat transfer coefficient was also analysed.

An experimental study was undertaken on the preparation, by High Energy Reactive Ball Milling in Hydrogen (HRBM), of hydrogen storage materials on the basis of Mg mixed with FeTiO 3 , and their further characterisation (SEM, TEM, XRD, volumetric H 2 absorption studies, TDS). It was shown that the addition of ⩾5 wt.% of FeTiO 3 dramatically improves H absorption in Mg and reduces the temperature of further H desorption. Subsequent addition of carbon, including Graphite (G), Activated Carbon (AC) and Multi-Wall Carbon Nanotubes (MWCNT) results in some slowing of the H absorption down but significantly improves re-hydrogenation performances of the material, which in time is able to re-absorb about 5 wt.% H in less than 5–7 min (15 bar H 2 /250 °C). These improvements were associated with the reduction of FeTiO 3 to yield nanoparticles of Fe and TiFe(Hx).

This paper describes the layout and presents the results of the testing of a novel prototype “distributed hybrid” hydrogen storage and supply system that has the potential to be used for Low Temperature Proton Exchange Membrane Fuel Cell (LT-PEMFC) applications. The system consists of individual Metal Hydride (MH) and Compressed Gas (CGH2) tanks with common gas manifold, and a thermal management system where heat exchanger of the liquid heated-cooled MH tank is integrated with the cooling system of the LT-PEMFC BoP. The MH tank is filled with a medium-stability AB 2 -type MH material (H 2 equilibrium pressure of about 10 bar at room temperature). This innovative solution allows for (i) an increase in hydrogen storage capacity of the whole gas storage system and the reduction of H 2 charge pressure; (ii) shorter charging times in the refuelling mode and smoother peaks of H 2 consumption during its supply to the fuel cell stack; (iii) the use of standard parts with simple layout and lower costs; and (iv) adding flexibility in the layout and placement of the components of the hydrogen storage and supply system.

Evaluation of the performances of hydrogen storage systems accommodating solid H storage materials should include characteristics on their reversible hydrogen storage capacity, operating pressures and temperatures, packing densities, and heat effects of hydrogen uptake and release. We have conducted a performance evaluation of the systems accumulating 5 kg of hydrogen in a containment of cylindrical geometry filled with a solid H storage material including such hydrides and reactive hydride composites as AlH 3 , MgH 2 , “low-temperature” (inter)metallic hydrides, NaAlH 4 , Na 3 AlH 6 , LiBH 4 + MgH 2 , and MOFs. The analysis yielded gravimetric and volumetric H storage capacities, and energy efficiencies of hydrogen stores. We conclude that the weight efficiency of hydrogen stores, apart from the gravimetric H storage capacity of the material, is greatly affected by its packing density, and by the pressure–temperature conditions which determine type and dimensions of the containment. The materials with low heat effects of H exchange, operating close to the ambient conditions, should be targeted in the course of the development of new hydrogen stores as offering the best energy efficiency of their operation.

This short review highlights and discusses the recent developments and thermal management issues related to metal hydride (MH) systems for hydrogen storage, hydrogen compression and heat management (refrigeration, pump and upgrade, etc.). Special attention is paid to aligning the system features with the requirements of the specific application. The considered system features include the MH material, the MH bed on the basis of its corresponding MH container, as well as the layout of the integrated system.

Thermo-chemical energy storage based on metal hydrides has gained tremendous interest in solar heat storage applications such as concentrated solar power systems (CSP) and parabolic troughs. In such systems, two metal hydride beds are connected and operating in an alternative way as energy storage or hydrogen storage. However, the selection of metal hydrides is essential for a smooth operation of these CSP systems in terms of energy storage efficiency and density. In this study, thermal energy storage systems using metal hydrides are modeled and analyzed in detail using first law of thermodynamics. For these purpose, four conventional metal hydrides are selected namely LaNi5, Mg, Mg2Ni and Mg2FeH6. The comparison of performance is made in terms of volumetric energy storage and energy storage efficiency. The effects of operating conditions (temperature, hydrogen pressure and heat transfer fluid mass flow rates) and reactor design on the aforementioned performance metrics are studied and discussed in detail. The preliminary results showed that Mg-based hydrides store energy ranging from 1.3 to 2.4 GJ m−3 while the energy storage can be as low as 30% due to their slow intrinsic kinetics. On the other hand, coupling Mg-based hydrides with LaNi5 allow us to recover heat at a useful temperature above 330 K with low energy density ca.500 MJ m−3 provided suitable operating conditions are selected. The results of this study will be helpful to screen out all potentially viable hydrides materials for heat storage applications.