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Metal hydrides can store hydrogen at low pressures and with high volumetric capacity. For the possible application as storage medium in hydrogen stand-alone power systems, large metal hydride hydrogen storage units are usually required. A reliable and verified kinetic correlation is an important tool in the designing process of a larger storage unit. This paper describes kinetic investigation of a AB5-type alloy and its corresponding hydride, with the purpose of finding a semi-empirical correlation suitable for use in heat and mass transfer modelling and engineering design of metal hydride storage units. [Copyright &y& Elsevier]

Rare earth (RE) metals form two stoichiometric hydrides, REH 2 and REH 3 , and for the yttrium group of RE transformation of a FCC (REH 2) into an HCP (REH 3) lattice takes place during the second step of hydrogenation REH 2 + ½ H 2 → REH 3. Earlier studies of the hydrogen desorption properties of the rare earth hydrides were limited to Y and RE = La, Ce, Pr, Nd, Sm, Gd, Tb and Er. The present work is focused on the studies of the kinetics and mechanism of hydrogen desorption from trihydrides of heavy rare earths, DyH 3 , HoH 3, and ErH 3. The Thermal Desorption Spectroscopy (TDS) studies were performed at pressures below 1 × 10−5 mbar during linear heating from room temperature to 1173 K at different heating rates ranging from 1 to 5.5 K/min. Hydrogen desorption traces show the presence of two main events with the low-temperature peak appearing below 573 K, while the second peak is positioned at 1083–1159 K, with the peak temperatures gradually increasing following the rise of the heating rate. Fitting of the peak temperatures in the TDS spectra using the Kissinger method yielded activation energies of hydrogen desorption for both hydrogen desorption events. For DyH 3 and ErH 3 , the shapes of the TDS spectra appear to be well described by a phase-stuctural transformation following a model of nucleation and growth, while for HoH 3 the dehydrogenation mechanism includes a phase boundary reaction. This applied model of phase-structural transformations shows differences in dimensionality and rate-limiting steps as related to the studied compound and the desorption events, REH 3 → REH 2 or REH 2 → RE. Typical hydrogen desorption from rare earth (RE) hydrides shown by the TDS experiment using various heating rates. Image 1 • TDS traces show two events of H 2 desorption, γ−RΕΗ 3-y.→β-REH 2+x and β− RΕΗ 2+x →α-RE. • Activation energies of hydrogen desorption from REH 3 change as follows DyH 3 HoH 2 >DyH 2. • Kinetics of phase transformations on H 2 desorption follows the nucleation and growth model. [ABSTRACT FROM AUTHOR]

Magnesium hydride is a promising material for hydrogen generation via hydrolysis owing to high hydrogen storage capacity, mild reaction conditions, and low cost of magnesium metal. Unfortunately, the hydrolysis reaction of MgH2 is rapidly hindered due to the formation of a passive Mg(OH)2 layer. Various additives can be used to improve the efficiency of the reaction. The present study examines the influence of 5 wt.% EDTA and TiC–2TiB2 additives on the hydrolysis of the nanostructured MgH2 and compares it with the hydrolysis performance of pure MgH2 and MgH2 + 5 wt.% AlCl3 for the first time. MgH2 was synthesized by high-energy ball milling of Mg powder in hydrogen gas, while MgH2-based nanocomposites were prepared either by mixing the obtained MgH2 with 5 wt.% of additives or by milling Mg with 5 wt.% of additive in hydrogen. The synthesized MgH2 is nanosized, containing a mixture of β-MgH2 and high-pressure γ-modification of MgH2. The hydrogen generation performance in terms of MgH2 conversion rate and hydrogen yield was determined volumetrically. It was found that the MgH2 + 5 wt.% EDTA composite displays the lowest reactivity among the tested materials, probably due to the interaction of MgH2 with EDTA during the ball milling. Pure MgH2 and MgH2 + 5 wt.% (TiC–2TiB2) composite demonstrate almost twice as better hydrolysis performance, which is, however, still quite far from application requirements. The maximum hydrogen yield of 557 mL/g MgH2 and conversion rate of 30.3% was observed for MgH2 + 5 wt.% AlCl3 composition after 10 min of hydrolysis, which can be attributed to the destabilization of the Mg(OH)2 layer by chlorine ions. [ABSTRACT FROM AUTHOR]

In present work we have developed a theoretical model for the description of the electrochemical discharge process in the metal hydride anodes of the metal hydride batteries at various current densities. The model is based on the description of the assembly of the spherically shaped metal hydride particles where the process of electrochemical discharge is fit using a shrinking core model, with a shell of the H storage alloy growing inside the particle by decreasing volume of the internal metal hydride core. The model accounts results of the D.O.S. calculations for La 2 MgNi 9 intermetallic alloy and has been tested for this metal hydride anode material having an electrochemical discharge capacity of 400 mAh/g and hydrogen storage capacity of 13 at.H/f.u. La 2 MgNi 9 . It allows to quantitatively describe kinetic behaviors of the electrode at various applied current densities and to estimate the diffusion coefficient for hydrogen and equilibrium content of H in the solid solution domain of hydrogen in La 2 MgNi 9 . This model has a general applicability and can be used for the optimization of the materials and the electrodes of the metal hydride rechargeable batteries at high current densities. [ABSTRACT FROM AUTHOR]

Ni-Co bimetallic nanoparticles (NPs) have been synthesized via reduction of Ni and Co hydroxides by hydrazine in water / ethylene glycol solutions. It was found that the particle size and polydispersity of the obtained chemically homogeneous NPs decrease with a decreasing to 50 at.% content of Ni in the reaction mixture. A different trend was observed for Ni 25 Co 75 and was related to the formation of Ni- and Co-rich particles. Ni-Co-NPs were tested as catalysts of hydrolysis of alkaline solutions of NaBH 4 , with the highest rate of hydrogen generation observed for Ni 50 Co 50. Zero-order kinetics of hydrogen evolution process was observed for all studied systems. Based on the data of the kinetic studies, we conclude that the rate of the hydrolysis process (a) increased with increasing NaBH 4 concentration in the range 0.1 – 1 mol/L; (b) decreased by 25% with increasing pH of the solution from 9 to 14. Studies of the temperature dependence of the rates of the hydrolysis process showed that the activation energy of the reaction decreased to 26 kJ/mol with decreasing contents of NaBH 4 and catalysts. Based on a comparison of the values of activation energy of hydrolysis reaction and the enthalpy of activation of viscous flow of initial NaBH 4 solution and the solution obtained after the hydrolysis, a diffusion-controlled reaction mechanism was proposed. • Bimetallic Ni-Co nanoparticles were synthesized and used as catalysts of NaBH 4 hydrolysis. • Ni 50 Co 50 nanoparticles showed the best catalytic activity. • Zero-order kinetics of hydrogen generation was observed. • Hydrolysis of NaBH 4 catalyzed by Ni 50 Co 50 showed a low sensitivity to pH. • Activation energy of NaBH 4 hydrolysis can be decreased to 26 kJ/mol. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of quenching rate and Ti/V ratio on the phase-structural composition. [•] Grain size refinement in the rapidly solidified Ti–V alloys. [•] Hydrogen storage properties of rapidly solidified binary Ti–V. [•] Mechanism of phase transformations in the hydrides of the RS Ti–V alloys. [ABSTRACT FROM AUTHOR]

Abstract: Time-resolved studies uncovered kinetics and mechanism of Mg–hydrogen interactions during High energy reactive ball milling in hydrogen (HRBM) in presence of various types of carbon, including graphite (G), activated carbon (AC), multi-wall carbon nanotubes (MWCNT), expandable (EG) and thermally-expanded (TEG) graphite. Introduction of carbon significantly changes the hydrogenation behaviour, which becomes strongly dependent on the nature and amount of carbon additive. For the materials containing 1wt.% AC or TEG, and 5wt.% MWCNT, the hydrogenation becomes superior to that for the individual magnesium and finishes within 1h. Analysis of the data indicates that carbon acts as a carrier of the “activated” hydrogen by a mechanism of spill-over. For Mg–G the hydrogenation starts from an incubation period and proceeds slower. An increase in the content of EG and TEG above 1wt.% results in the deterioration of the hydrogenation kinetics. The effect of carbon additives has roots in their destruction during the HRBM to form graphene layers encapsulating the MgH2 nanoparticles and preventing the grain growth. This results in an increase of absorption–desorption cycle stability and a decrease of the MgH2 crystallite size in the re-hydrogenated Mg–C hybrid materials (40–125nm) as compared to Mg alone (180nm). [Copyright &y& Elsevier]

Abstract: In this work we utilized the melt spinning process to prepare a nanostructured Ti0.8V0.2 alloy for hydrogen storage applications. The alloy ribbons were solidified from the melt using two different wheel spinner velocities, 1000 and 3000rpm. LOM, and SEM were utilized to examine the microstructures of the ribbons and their corresponding hydrides. Hydrogen absorption and desorption experiments were performed using a TDS setup. Arc melted Ti0.8V0.2 and rapidly solidified (RS) materials (RS1000 and RS3000) formed FCC dihydrides with lattice parameters ranging from 4.4198 to 4.4338Å. RS resulted in a dramatic decrease of the grain size, down to smaller than 200nm for the hydrogenated Ti0.8V0.2 RS3000 alloy. The thermal stability of the hydrides was strongly affected by the RS solidification rate. For the hydride of Ti0.8V0.2 RS3000, a significant decrease in the thermal stability was observed, so the peak of hydrogen desorption was shifted to much lower temperatures, by ∼80°C, as compared to the hydrogenated as cast alloy. [Copyright &y& Elsevier]

Abstract: This paper summarises collaborative activities of South African and Norwegian groups in the development and characterisation of the advanced hydride-forming materials obtained by surface modification of AB5-type substrate by fluorination and/or electroless deposition of single- or mixed-metal coatings on the basis of palladium. The surface modification was shown to significantly improve activation performance and poisoning tolerance of the hydride-forming materials. In particular, hydrogen absorption rate, after long-term pre-exposure to air, was shown to be increased by ∼100 times for the surface-modified materials, as compared to the unmodified alloy. It was shown that the surface modification route significantly influenced surface morphology and rate of hydrogenation. Finally, feasibility of application of the surface-modified hydride-forming materials for efficient hydrogen separation from gas mixtures containing CO2 and CO has been demonstrated. The approach undertaken has the potential in tailoring of new classes of highly efficient and robust composite H storage materials for hydrogen separation and purification. [Copyright &y& Elsevier]

Abstract: Aluminum hydride (AlH3) and its associated compounds make up a fascinating class of materials that have motivated considerable scientific and technological research over the past 50 years. Due primarily to its high energy density, AlH3 has become a promising hydrogen and energy storage material that has been used (or proposed for use) as a rocket fuel, explosive, reducing agent and as a hydrogen source for portable fuel cells. This review covers the past, present and future research on aluminum hydride and includes the latest research developments on the synthesis of α-AlH3 and the other polymorphs (e.g., microcrystallization reaction, batch and continuous methods), crystallographic structures, thermodynamics and kinetics (e.g., as a function of crystallite size, catalysts and surface coatings), high-pressure hydrogenation experiments and possible regeneration routes. [Copyright &y& Elsevier]

Abstract: Reactive ball milling in hydrogen was applied to synthesize nanocrystalline Mg- and Mg8Mm20Ni-based hydrides with crystallite size below 10nm. These hydrides were studied by in situ synchrotron X-ray diffraction performed at the Swiss–Norwegian Beam Lines of the European Synchrotron Radiation Facility, Grenoble. Characterization of the phase-structural and microstructural state of the constituents during the reversible processes of synthesis and decomposition of the hydrides upon application of hydrogen pressure or vacuum at temperatures 20–350°C and kinetics of hydrogen uptake was performed. Details of the mechanism of the phase-structural transformations were provided by high time resolution of the synchrotron X-ray diffraction data, high sensitivity in determining formation of the phase constituents, excellent accuracy in yielding the crystallographic characteristics and in probing the microstructural evolution of the constituents formed. [Copyright &y& Elsevier]

Abstract: The non-hydrogenated and hydrogenated microstructure and hydrogen storage properties of a melt-spun Mg–10Ni–2Mm (at.%) alloy have been studied. By increasing the solidification rate, the kinetics of the H-absorption/desorption reactions of the melt-spun ribbons was greatly improved, probably due to fast hydrogen diffusion in considerably amounts of nano-sized grains. RS processing resulted in the formation of the high-temperature cubic modification of Mg2NiH4 and the solid solution hydride phase Mg2NiH0.3 due to incomplete hydrogenation of Mg2Ni. A maximum hydrogen storage capacity of 5.1wt.% H was obtained. The samples that were solidified at the highest solidification rate, displayed the narrowest desorption temperature range (during vacuum TDS) due to a high uniformity of the nano-sized particle distribution. [Copyright &y& Elsevier]

Abstract: A pre-treatment technique was developed to facilitate electroless deposition of palladium layers on the surface of metal hydride-forming alloys for increasing hydrogen absorption kinetics. The technique involved functionalization of the oxidized surface of the alloys by deposition of assembled layers derived from γ-aminopropyltriethoxysilane. This results in the formation of a surface assembly of adhesive functional groups for the immobilization of palladium as a unique catalyst for hydrogen sorption. The layers of γ-aminopropyltriethoxysilane aided immobilization of Pd nuclei, in the activation procedure of electroless deposition, by increasing the chemical adhesion. Pd electroless deposition on rare-earth metal hydride-forming alloys, without γ-aminopropyltriethoxysilane pre-treatment, facilitated the deposition of Pd agglomerates, whereas the use of γ-aminopropyltriethoxysilane pre-treatment facilitated the deposition of continuous Pd layers on the surface of the alloy resulting in dramatic improvements in hydrogen sorption performances, including faster kinetics of hydrogenation of the non-activated material under mild conditions, compared to that observed for non-activated unmodified starting materials and materials surface modified by Pd electroless deposition without the additional γ-aminopropyltriethoxysilane pre-treatment step. The attractiveness of aminosilane pre-treatment for improvement of hydrogen sorption properties of rare earth–nickel-based AB5 alloys, and the influence of the differences in surface structure between deposited Pd agglomerates and layers was demonstrated. [Copyright &y& Elsevier]

Abstract: Microstructure and hydrogen storage properties of a melt-spun Mg–10Ni–2Mm (at.%) alloy were studied in comparison with those of a conventionally prepared ball-milled one. The kinetics of H-absorption/desorption was improved through melt-spinning by obtaining nanograins in an amorphous matrix. The melt-spun ribbon alloy and the 2h ball-milled alloy reached a maximum hydrogen storage capacity of ∼4.2wt.% in 141min and ∼3.2wt.% in 210min, respectively. Vacuum temperature desorption spectroscopy (TDS) (heating rate 5°C/min) of the melt-spun alloy showed narrower desorption temperature range (220–330°C), displaying a sharp joint peak at ∼286°C than the 2h ball-milled one (250–425°C) with a broad peak around ∼310°C. The species of hydrides were closely related to the microstructure. TEM micrographs and a sharp TDS peak demonstrated that the grains remained nano-sized in the melt-spun ribbons even after heating up to 350°C during cycles. [Copyright &y& Elsevier]

Abstract: Kinetics of H uptake/release in Mg can be improved by alloying with Ni and RE, as well as by reducing the grain size of the Mg alloy. Both these approaches were applied in the present work for the alloy 72wt.% Mg–20wt.% Ni–8wt.% Mm (ternary eutectic Mg–Mg2Ni–MmMg12). The alloy was processed by the equal channel angular pressing (ECAP) technique. In ECAP the sample is subjected to heavy plastic strain by pressing it through a die with an angle of 90°. ECAP treatment resulted in a fine microstructure compared to the rather heterogeneous as-cast material. Hydrogenated and non-hydrogenated samples were investigated using SEM and XRD. Hydrogenation properties were studied by TDS and PCT. Hydrogenated samples consist of MgH2, Mg2NiH4 and MmH2+x and exhibit a maximum H-storage capacity of ∼5.5wt.%. To initiate the first hydrogenation, the alloy needs to be activated at ∼300°C. However, already after one hydrogenation cycle its H-absorption becomes quite fast: 4.5wt.% H is absorbed in just 15min. Vacuum TDS (heating rate 0.5°C/min) shows that desorption starts at low temperature, ∼135°C, with a peak at ∼210°C. The alloy was also subjected to high energy ball milling (HEBM) in Ar or H2 to yield further refinement of the microstructure. ∼1wt.% Nb2O5 was added to facilitate H exchange. The H sorption characteristics of the alloy treated by ECAP and HEBM have been compared with the ones for the as-cast material. [Copyright &y& Elsevier]

Abstract: Desorption of hydrogen from the powders of metal hydrides (MH) is affected by several interplaying processes including hydrogen desorption from and recombination on the metal surface, diffusion within the bulk metal and different hydride phases, and decomposition of the hydride phase. In present work, possible mechanisms of hydrogen release from the MH are proposed and discussed. Analytical models are developed which cover common distributed and confluent cases. The models adequately fit the experimental data of the thermal desorption spectroscopy and barometric thermocycling studies. Rate constants of the reactions of hydrogen release from the MH are evaluated on the basis of the fitting of the experimental data by the proposed models. These data are of significant importance in the assessments of suitability of the MH in particular applications. [Copyright &y& Elsevier]

Abstract: The Pressure–Composition–Temperature (P–C–T) relationships in the NdNiIn-based Cu- and Al-containing Nd(Ni1−x Cu x )(In1−y Al y )–H systems were measured volumetrically in the temperature range of 298–348 K. The P–C–T diagrams show clear plateaux regions indicating a formation of two hydride phases, - ( 0.6 at. H/f.u.) and - (1.3–1.5 at. H/f.u.) hydrides. The -hydride is rather stable and does not decompose at hydrogen pressures above 10−3 MPa within the applied range of temperatures. The substitutions cause significant modifications of the P–C–T diagrams. These changes proceed differently for the Cu- and Al-containing systems. The relative partial molar thermodynamic properties for the studied system are:  kJ (molH)−1,  J ( for NdNiIn–H;  kJ (molH)−1,  J ( for NdNi0.98Cu0.02In–H;  kJ (molH)−1,  J ( for NdNiIn0.95Al0.05–H systems. [Copyright &y& Elsevier]

Abstract: An average Ce-valence state () of two types of Ce-containing intermetallic compounds, equiatomic CeNiX ( Al, Ga, Sn) and CeM3 ( Ni, Co, Mn), and their hydrides was estimated from X-ray absorption spectroscopy (XAS) and analysed in parallel with hydrogen-induced volume changes on hydrogenation. The largest valence states in the initial compounds were found in CeM3(v=3.32−3.36) followed by CeNiAl1−x Ga x (). This contrasts to CeNiSn, which is close to a pure trivalent state (). On hydrogenation, a conversion from mixed-valent CeNiAl1−x Ga x , , 1, to pure hydrides takes place ( / %). In CeNiSnD z (, 1.8, , 8.0%) the changes in the valence state towards are very small. The situation for the CeM3-hydrides is complex. For CeNi3D2.8, CeNi2.75Mn0.25D3.4 and CeCo3D3.4 ( /) where rather similar electronic properties can be expected, a decrease in the contribution of for CeNi3D3 and CeNi2.75Mn0.25D3.4 ( and 3.12, respectively) contrasts to the behaviour of CeCo3D3.4 where the hydrogen induced valence change is very small (). [Copyright &y& Elsevier]

Abstract: The crystal structure of NdNiInD1.2 contains D–D pairs with the shortest known separation of 1.56 Å. This work was aimed on studies of the factors influencing the formation and the length of such a pair. We have studied the NdNiIn-based alloys, in which Ni or In are partially substituted by the chemically related elements, Cu or Al, respectively. Three equiatomic intermetallics, NdNiIn, NdCuIn and NdNiAl, are isostructural and crystallise with the ZrNiAl type of structure. In the NdNi1−x Cu x In (; 0.02; 0.05; 0.25; 0.50; 0.75 and 1.00) quaternary system a complete solid solubility range has been found. In contrast, in the Al-containing NdNiIn1−x Al x alloys the range of a solid solution is limited to the region NdNiIn–NdNiIn0.75Al0.25. The substitutions result in regular changes in V, a, c and of the hexagonal unit cells. Small substitutions by Cu and Al () do not lead to significant changes in H content and types of the crystal structures formed (PND data). However, a decrease in the stability of the hydrides is observed. In NdNi1−x Cu x In, Cu has a strong preference for the occupation of the CuIn6 trigonal prisms. An increase of the Cu content is accompanied by a decrease of the D/Nd(Ni1−x Cu x )In ratio and a distinct growth of the distance between Ni(Cu) and D (from 1.51 to 1.84 Å). pairing is very sensitive to the content of both Al and Cu. When the level of substitution exceeds , H pairing becomes unstable and H atoms favour other types of ordering in the metal sublattice. [Copyright &y& Elsevier]

Abstract: The Pressure–Composition–Temperature (P–C–T) relations for the LaNiIn, LaNi0.95Cu0.05In and LaNiIn0.98Al0.02–H systems were measured by a volumetric Sieverts’ method at 398–423K. All isotherms show plateau pressure regions indicating equilibria between two hydride phases. The replacements of Ni by Cu and In by Al affect the P–C–T diagrams, stability of the hydrides, homogeneity regions of the hydrides formed, slope of the isotherms and critical temperatures of the β–γ transition. In addition, the Cu-doping induces a significant hysteresis between the hydrogen absorption and desorption processes. The relative partial molar thermodynamic properties for the studied systems are: ΔH H =−34.6±2.1kJ(molH)−1, ΔS H =−70.7±3.6J(K·molH)−1 for LaNiIn–H; ΔH H =−34.1±0.5kJ(molH)−1, ΔS H =−74.9±1.0J(K·molH)−1 for LaNi0.95Cu0.05In–H; ΔH H =−33.2±0.8kJ(molH)−1, ΔS H =−68.3±1.2J(K·molH)−1 for LaNiIn0.98Al0.02–H. [Copyright &y& Elsevier]

The present work is focused on the studies of structure, hydrogen storage and electrochemical properties of the La 3-x Mg x Ni 9 (x = 1.0, 1.1 and 1.2) alloys as active materials of negative electrodes in the Nickel-Metal Hydride (Ni/MH) batteries. A change of Mg content affects properties of the studied alloys such as the phase homogeneity, hydrogen storage and electrochemical capacities, cycle stability, and high-rate discharge performance. X-ray diffraction study shows that Mg substitution for La and annealing of the La 3-x Mg x Ni 9 alloys promotes the formation of more homogeneous materials, with a predominant formation of the target AB 3 PuNi 3 structure type intermetallics. The electrodes prepared from the annealed alloys show the maximum discharge capacities of ∼400 mAh g−1 at discharge current density of ∼60 mA/g. The high rate discharge-abilities (HRD) at the discharge current density of 350 mA g−1 keep high values of the remaining reversible discharge capacities, ∼86, 85 and 80%, for the La 2 MgNi 9 , La 1·9 Mg 1·1 Ni 9 and La 1·8 Mg 1·2 Ni 9 alloy electrodes, respectively. After 200 cycles with 100% depth of discharge (DOD), the La 1·9 Mg 1·1 Ni 9 alloy electrode exhibits a very good cycling stability with its discharge capacity remaining at a level of ∼64% of its initial capacity. • La 3-x Mg x Ni 9 (x = 1.0; 1.1; 1.2) alloys crystallize with PuNi 3 type trigonal structures. • Increase of Mg content results in a gradual contraction of the unit cells. • The as cast alloys showed presence of 6 different types of intermetallics. • Annealing leads to the predominant formation of the 1:3 and 2:7 intermetallics. • Maximum discharge capacity of the anodes reaches 400 mAh/g. [ABSTRACT FROM AUTHOR]

Hydrogen diffusion in the La 1.5 Nd 0.5 MgNi 9 battery electrode material has been studied using low amplitude potentiostatic experiments. Complex diffusion behavior is examined in frames of electroanalytical models proposed for the lithium intercalation materials. Hydrogen diffusion coefficient D H changes with hydrogen content in the metal hydride anode electrode and has a maximum of ca. 2 × 10 −11 cm 2 /s at ca. 85% of discharge. Such a behavior differs from the trends known for the transport in lithium battery materials, but qualitatively agrees with the data for the highly concentrated β-PdH x . [ABSTRACT FROM AUTHOR]

Abstract: A hexagonal CaCu5-type La0.5Ce0.5Ni4Co intermetallic alloy was studied as H storage material in as cast condition using PCT and in situ Synchrotron XRD studies performed between 263 and 353K. A significant shrinking of the unit cells takes place on a substitution of La with Ce. SR XRD showed the formation of two hexagonal hydrides, a γ-trihydride La0.5Ce0.5Ni4CoH3, and a saturated β-hexahydride La0.5Ce0.5Ni4CoH∼6. In addition, an α-H solid solution was experimentally observed. Hysteresis of hydrogen absorption and desorption between the flat single plateaus isotherms measured during the PCT measurements was rather small, with no indication of the formation of the thermodynamically stable γ-(La,Ce)(Ni,Co)5H3. The SR XRD revealed that (a) the relative abundance of the γ-hydride is higher during the desorption compared to the absorption; its relative amount reaches 50wt.% in maximum; (b) anisotropic strains in all constituent phases during both hydrogen absorption and desorption are not developed; (c) the pressure of the formation of the γ-phase was found to be strongly temperature-dependent. The formation of large amounts of metastable γ-(La,Ce)(Ni,Co)5H3 hydride in quasiequilibrium experimental conditions applied during the SR XRD experiments and during reaching the thermodynamic equilibrium between the constituent phases can be responsible for the reduced hysteresis of the PCT isotherms and absence of noticeable anisotropic strains in the constituent phases. [Copyright &y& Elsevier]

Abstract: Hydrogen storage performance of the TiFe-based materials suffers from difficulties with hydrogenation and sensitivity towards impurities in hydrogen gas reducing hydrogen uptake rates and decreasing the cycle stability. In present work the surface modification of the sintered Ti1.1Fe0.9O x and arc-melted TiFe was performed using autocatalytic deposition of the Pd-based catalytic layers in order to achieve improvement of the H storage characteristics. Pd deposition proved to be efficient in significant facilitation of the hydrogenation ability of the materials at moderate H2 pressures and room temperature, even after their long exposure to air. Activation performance of the sintered Ti1.1Fe0.9O x is superior than that for the arc-melted TiFe. This effect was associated with the presence of the oxygen-containing suboxide Ti4Fe2O1−x in the sintered sample acting as a hydrogen transfer catalyst. γ-Aminopropyltriethoxysilane pre-functionalization and subsequent Pd–P autocatalytic deposition onto the sintered Ti1.1Fe0.9O x intermetallic substrate resulted in a better hydrogenation kinetics compared to the samples prepared by the conventional Pd deposition. [Copyright &y& Elsevier]

Abstract: The microstructural evolution of as-quenched ribbons and ball-milled hydrides of the Mg–10Ni–2Mm alloy was studied by TEM. These studies showed a refinement of the microstructures during the applied processing and a nucleation of MmMg12 intermetallic at the grain boundaries of Mg and Mg2Ni. The interface between MmMg12 and Mg2Ni is semi-coherent, with an ordered repetition of the consistent atomic arrangements. The kinetics of H-absorption/desorption is improved due to the fast hydrogen diffusion in the nanograins, thus, providing paths for H-exchange. TEM studies showed (a) stability of the nano-sized grains in the ball-milled Cu-1000 (the surface velocity of the copper wheel: 1000rpm) sample that underwent cycling of hydrogen desorption and absorption during heating to 350°C; (b) formation of MmH3−x hydride from MmMg12 and its preferential location at grain boundaries of MgH2. Clearly, MmH3−x and Mg2NiH4 act as nucleation centres to initiate the formation of MgH2, thus, promoting hydrogen absorption by the Mg alloys. Pressure–composition–temperature diagrams show the presence of two plateaux, Mg–MgH2 and Mg2Ni–Mg2NiH4. The MgH2 plateau showed no hysteresis and practically no slope, while the plateau for Mg2NiH4 exhibited both a pronounced hysteresis and a slope, particularly for the nanocrystalline sample. The maximum hydrogen storage capacity of the nanocrystalline sample was higher than that of the microcrystalline one. [Copyright &y& Elsevier]