Reversible Hydrogen Absorption Research Articles

Influence of oxygen introduced in TiFe-based hydride forming alloy on its morphology, structural and hydrogen sorption properties

Hydrogen sorption performances of TiFe are very sensitive to the preparation conditions, especially ones which result in contamination of the material with oxygen. In this paper the effect of oxygen introduction (≤1 wt.%) on phase composition of TiFe alloy was investigated. It was observed that the increase of oxygen content in the alloy results in the decrease of the abundance of the main TiFe phase, together with the increase in the abundance of the mixed suboxide, Ti 4 Fe 2 O 1− x . The observed effect was quantified in terms of the balance of the reaction of TiFe with oxygen to yield Ti 4 Fe 2 O 1− x and TiFe 2 . In addition, a comparison of hydrogen sorption performances of arc-melted TiFe(O) and sintered Ti 1.1 Fe 0.9 O x was carried out. It was shown that the introduction of oxygen improves activation performances of the TiFe based material, but decreases its reversible hydrogen absorption capacity because of: (i) decrease of fraction of TiFe intermetallide in the material interacting with oxygen to yield Ti 4 Fe 2 O 1− x and TiFe 2 ; (ii) formation of stable hydrides on the basis of Ti 4 Fe 2 O 1− x mixed suboxide and titanium hydride, if titanium is taken in the excess; and (iii) destabilisation of both β-TiFeH and, especially, γ-TiFeH 2 . The observed features should be taken into account in industrial-scale processes for the manufacturing of TiFe to assure a good quality of the final product which may contain oxygen, but in the amount below 0.2 wt.%. ► Effect of oxygen introduction (up to 1 wt.%) into TiFe alloy was studied. ► Mixed suboxide, Ti 4 Fe 2 O 1− x , is formed even at 0.1 wt.% O. ► The effect quantified from balance of reaction TiFe + O = Ti 4 Fe 2 O 1− x + TiFe 2 . ► TiFe(O) has better activation performances than oxygen-free TiFe. ► O introduction decreases reversible H capacity.

Fully reversible hydrogen absorption and desorption reactions with Sc(Al 1− xMg x), x=0.0, 0.15, 0.20

The hydrogen storage properties of Sc(Al 1− x Mg x ), x=0.0, 0.15, 0.20, have been studied by X-ray powder diffraction, thermal desorption spectroscopy, pressure-composition-isotherms and scanning electron microscopy techniques. Hydrogen is absorbed from the gas phase at 70 kPa and 400 °C under the formation of ScH 2 and aluminium with magnesium in solid solution. The reaction is fully reversible in vacuum at 500 °C and shows the hydrogenation–disproportionation–desorption-recombination (HDDR) behaviour. The activation energy of desorption was determined by the Kissinger method to 185 kJ/mol. The material is stable up to at least six absorption–desorption cycles and there is no change in particle size during cycling.

Engineering the Mg–Mg2Ni eutectic transformation to produce improved hydrogen storage alloys

Abstract The technique of trace element doping to modify the solidification mechanism of faceted/non-faceted eutectics has been applied to the Mg–Mg 2 Ni alloy system. It is demonstrated that the micro- and nano-structure of cast hypoeutectic Mg–Mg 2 Ni alloys can be varied by trace additions of Na, Ca or Eu to the liquid prior to solidification. As a result, the reversible hydrogen absorption capability was in excess of 90% of the theoretical value of 6.8 wt.% under the absorption parameters of 350 °C and 1 MPa for 24 min and subsequent desorption at 0.2 MPa for 24 min after activation. The hydrogen absorption kinetics have been dramatically improved under realistic industrial conditions, and show no sign of reduced capacity over 200 cycles. This processing route results in a non-pyrophoric material that may be produced in large quantities at comparatively low cost.

Prediction of enthalpy of formation and Gibbs energy change in pseudo-binary (Ti–Zr)(Fe–Cr)2 and pseudo-ternary (Ti–Zr)(Fe–Cr)2-H system using extended Miedema model

The thermodynamic model proposed by Miedema is capable of predicting the enthalpy of formation (ΔH) and relative stability of phases in binary but not in ternary or multi-component systems. While developing nanocrystalline binary/ternary metal hydrides for compressor-driven reversible heating–cooling applications, it is necessary to identify appropriate alloy compositions with suitable hydrogen storage capacity and reversible hydrogen absorption–desorption capability. Accordingly, a suitable modification of the Miedema model is proposed in the present study for calculating ΔH of AB2 type of pseudo-binary (Ti–Zr)(Fe–Cr)2 and pseudo-ternary (Ti–Zr)(Fe–Cr)2-H alloys. Subsequently, Gibbs energy (ΔG) of the possible phases is estimated to predict relative phase stability/equilibrium in a given system. It is shown that grain size or interfacial energy contribution exerts a significant influence on ΔG and relative stability of the phases beyond a critical value/limit. Finally, the predicted phase equilibrium from this model-based calculation is validated by suitable comparison with relevant experimental data reported in the literature.

In situ SR-XRD studies of hydrogen absorption–desorption in LaNi 4.7Sn 0.3

Phase-structural transformations during hydride formation and decomposition in the advanced hydrogen storage alloy LaNi 4.7Sn 0.3, are studied by in situ synchrotron X-ray powder diffraction (SR-XRD). A specially designed cell for in situ studies in H 2-atmosphere is attached to a metal hydride hydrogen storage unit developed at IFE providing hydrogen gas at convenient pressures. The studied sample is kept in a quartz glass capillary. Temperature cycling between RT and 100 ° C at H 2 pressures of 2–3 bar was employed to LaNi 4.70Sn 0.30H°∼6 which resulted in a reversible hydrogen absorption–desorption process. Both a large temperature-dependent homogeneity range of the β -hydride and a small hysteresis in the formation-decomposition of the β -hydride have been revealed.

High hydrogen storage capacity of nanosized magnesium synthesized by high energy ball-milling

To prepare nanosized magnesium which reversibly absorbs hydrogen with high capacity even under mild conditions, high energy ball-milling of Mg or MgH 2 with benzene or cyclohexane as additives have been studied. In ball-milling of Mg or MgH 2, the use of the organic additives is very crucial in determining the characteristics of the resulting nanosized magnesium. Benzene and cyclohexane served to maintain the high-degree dispersion of nanostructured magnesium with small crystallite sizes (9–10 nm) and high surface areas (24–25 m 2 g −1). The behavior of hydrogen absorption by the magnesium was extensively evaluated by differential scanning calorimetry (DSC) measurements and volumetric techniques. The nanosized magnesium prepared by ball-milling of MgH 2 with benzene showed reversible DSC traces for hydriding/dehydriding under 0.1 MPa hydrogen pressure. Moreover, 1 at.% Al-doped or 2.9 at.% Ni-doped nanosized samples obtained by milling of MgH 2 with solutions of Al(C 2H 5) 3 or Ni(C 5H 5) 2 in benzene showed satisfying hydrogen absorption rates, respectively. The reversible hydrogen absorption by the 1 at.% Al-doped sample approximately reached a maximal capacity of 7.3 wt.% even at a 0.1 MPa H 2 atmosphere.

Highly Effective Li2O/Li3N with Ultrafast Kinetics for H2 Storage

The refueling time and safe hydrogen storage are critical factors in the development of a hydrogen economy for transportation. The finding of a fast and high-capacity H 2 storage material represents a worldwide challenge. The short-term target of the U.S. Department of Energy for a hydrogen storage material is a 4.5 wt% reversible hydrogen capacity. In this paper, we report that reversible 5 wt% H 2 can be reached in only 3 min even at the relatively low temperature of 180 °C by a Li 2 O/Li 3 N solid material. Furthermore, this material has excellent stability because successive cycles of absorption-desorption did not decrease the reversible hydrogen capacity and absorption rate.

Applications of microwave reflectance methods to the study of p-Si in fluoride solutions

The principles and applications of microwave reflectivity measurements in semiconductor electrochemistry are reviewed and illustrated by theoretical calculations and experimental examples. The microwave response of the illuminated p-Si ∣ NH 4F junction has been studied under depletion conditions and related to the calculated concentration profiles of electrons and holes. Time- and frequency-resolved measurements have been used to follow the interfacial transfer of photogenerated electrons to protons in solution. The rate constant for interfacial electron transfer is very small, probably reflecting the absence of low energy sites for stabilisation of the intermediate, in the two-electron reduction of H + to H 2. The time dependent measurements provide evidence for reversible hydrogen absorption into the surface region of the silicon. Potential modulated microwave reflectivity has been used to study the behaviour of p-type silicon in fluoride solutions under depletion and accumulation conditions in the dark. Under depletion conditions, the time-resolved and periodic microwave responses are related to the changes in the width of the space charge region (SCR), and the sensitivity factor that relates the normalised reflectivity changes to changes in carrier concentrations can be obtained by comparison of the microwave response with the potential dependent space charge capacitance. Under accumulation conditions, dissolution of the p-Si occurs, resulting in porous silicon formation or electropolishing depending on the applied potential. In this case, the microwave response gives information about the potential distribution across the Si ∣ (oxide) ∣ solution system.

Europium palladium hydrides.

The first fully structurally characterized ternary europium palladium hydrides (deuterides) are reported. The most Eu rich compound is Eu(2)PdD(4). Its beta-K(2)SO(4) type structure (space group Pnma, a = 749.47(1) pm, b = 543.34(1) pm, c = 947.91(1) pm, Z = 4) contains tetrahedral 18-electron [PdD(4)](4)(-) complex anions and divalent Eu cations. The compound is presumably nonmetallic and shows paramagnetic behavior (mu(eff) = 8.0(2) mu(B)) with ferromagnetic ordering at T(C) = 15.1(4) K. A metallic compound at intermediate Eu content is EuPdD(3). It crystallizes with the cubic perovskite structure (space group Pm3m, a = 380.01(2) pm, Z = 1) in which palladium is octahedrally surrounded by fully occupied deuterium sites. Metallic hydrides at low Eu content form by reversible hydrogen absorption of intermetallic EuPd(2) (Fd3m, a = 775.91(1) pm, Z = 8). Depending on the experimental conditions at least three phases with distinctly different hydrogen contents x exist: EuPd(2)H(x) ( approximately )(0.1) (a = 777.02(2) pm, Z = 8, T = 298 K, p(H(2)) = 590 kPa), EuPd(2)H(x) ( approximately )(1.5) (a = 794.47(5) pm, Z = 8, T = 298 K, p(H(2)) = 590 kPa), and EuPd(2)H(x) ( approximately )(2.1) (a = 802.1(1) pm, Z = 8, T = 350 K, p(H(2)) = 610 kPa). All crystallize with cubic Laves phase derivative structures and have presumably disordered hydrogen distributions.

The intrinsic degradation behavior of (V0.53Ti0.47)0.925Fe0.075 alloy during temperature-induced hydrogen absorption-desorption cycling

Abstract The intrinsic degradation behavior of an (V 0.53 Ti 0.47 ) 0.925 Fe 0.075 alloy having a BCC structure and two plateau regions (the low and high plateau region) has been investigated using P–C isotherm measurements, thermal desorption analysis, XRD and TEM analysis during temperature-induced hydrogen absorption–desorption cycling (thermal cycling). After 400 thermal cycles between room temperature and 600°C under 10 atm H 2 , the total reversible hydrogen absorption capacity decreases by about 40%. In the low plateau region the reversible hydrogen absorption capacity decreases by about 24% after 400 cycles. The majority of the capacity loss takes place during the first 243 cycles. In the high plateau region, however the reversible hydrogen absorption capacity decreases by about 16% gradually with cycling. From the result of the thermal desorption analysis, it is found that the peak obtained at high temperature corresponds to the desorption of hydrogen of the low plateau region which shifts to lower temperatures and the peak area decreases after 223 cycles and then the area is maintained without any clear change up to 400 cycles. The low temperature peak corresponds to desorption of hydrogen from the high plateau; this does not shift but its peak area decreases gradually with cycles. From P–C isotherm measurements it is also found that the degradation behavior at each plateau region is different. In addition, XRD analysis shows that the crystal structure of the de-hydrided sample changes from BCC to BCT after degradation; the hydrided sample maintains FCC structure although the peaks are broadened after degradation. From the result of a static isothermal hydrogenation treatment, it is found that the change of crystal structure from BCC to BCT is caused only by temperature effects. The result of TEM analysis shows that peak broadening is caused by the formation of an amorphous phase in the FCC matrix.

Improvement of the thermodynamical and electrochemical properties of multicomponent Laves phase hydrides by thermal annealing

The reversible hydrogen absorption and desorption behaviour of Zr1−xTixNi1/0.9Mn0.5/0.6Cr0.4V0.1 with xTi=0.1, 0.3, 0.4, 0.6 was investigated in solid/gas and electrochemical experiments at room temperature. One aspect of this work was to study the thermodynamical properties (Vol./AB2; Peq(plateau); Capmax) of the different samples depending on their Ti content. Another aspect was the analysis of the influence of the annealing treatment on the metallurgical properties and finally the hydrogen absorption/desorption properties of the different samples in solid–gas and electrochemical media. Zr0.7Ti0.3Ni0.9Mn0.6Cr0.4V0.1, for example, shows an increase in the maximum electrochemical discharge capacity by more than 30% to 355 mAhg−1 after appropriate annealing treatment.

Structural characterization and reversible hydrogen absorption properties of Mg 2Ni rich nanocomposite materials synthesized by mechanical alloying

Starting from a mixture of Mg and Ni with an atomic ration of 2:1 and using a planetary ball mill, we have successfully elaborated a Mg 2Ni rich nanocomposite material formed by the Mg 2Ni phase, some residual Ni and an amorphous phase. The synthesis of this composite proceeded at milling intensities 10 and 7, corresponding respectively to 10 and 3.5 W g −1 shock power, respectively after 4 and 18 h. The best hydrogen absorption capacity reported, 3.53 wt % (3.75 H/mole), is for the composite synthesized at 3.5 W g −1 shock power and 24 h mechanical alloying time. These mechanical alloying time and hydrogen absorption capacity are better than those reported up today [18, 3].

Reversible and irreversible hydrogen absorption in Ni 67 − xCu xZr 33 glasses monitored by in situ resistivity measurements

The process of hydrogen absorption and desorption are investigated in Ni 67 − x Cu x Zr 33 glassy alloys by in situ resistivity measurements. The cyclic charging and discharging process has been monitored by conventional DC method using a computer-controlled system, exposing the samples to hydrogen of 6 MPa pressure at 293, 328 and 373 K, respectively. Normalized resistivities as a function of charging and discharging times are compared for the first and repeated cycles. Separate samples, taken from specific points of cycling, were investigated by transmission electron microscopy (TEM) measurements. Hydrogen content (H/M ratio) was determined by weight measurements, and checked by gas chromatography, which is combined with an appropriate vacuum extraction and heating technique of the samples. A gradual hydrogen-induced phase separation could be detected on the samples by scanning transmission electron microscopy (STEM) with increasing number of the cycling.

Hydrogenation behaviour and structure of R 5Fe 2B 6 (R=Ce, Pr, Nd, Sm, Gd and Tb) borides

The hydrogenation behaviour and structural characteristics of the R 5Fe 2B 6 (R=Ce, Pr, Nd, Sm, Gd and Tb) borides have been studied in the present work. Hydride formation is accompanied by an anisotropic expansion of the initial trigonal unit cells (Pr 5Co 2B 6 type crystal structure) in the [001] direction only. Heating in hydrogen of the Pr and Nd containing borides results in their disproportionation and the formation of the R-hydride and two compounds, namely R 1.1Fe 4B 4 and R 2B 5. Recombination to form the initial (Pr,Nd) 5Fe 2B 6 borides is observed on vacuum heating of this three phase mixture. The disappearance of additional phases present in the cast material, demonstrates another example of the successful use of the hydrogenation–disproportionation–desorption and recombination process for the homogenisation of a rare earth containing alloy. Under the same conditions, reversible hydrogen absorption–desorption takes place in the case of the corresponding Sm, Gd and Tb compounds indicating an increase of the thermodynamic stability of the borides with increasing atomic number of the R-component. Hydrogen absorption–desorption properties were characterised by means of temperature–pressure analysis and hydrogen differential thermal analysis. An increase in the thermal stability of the R 5Fe 2B 6H x -hydrides with increasing atomic number of the R-component is consistent with the insertion of the hydrogen atoms into the structural slabs consisting of the rare earth atoms only.

無水フッ化水素で表面改質したＬａＮｉ５−ｘＡｌｘ（ｘ＝０，０．３）の水素化・脱水素化特性に及ぼすＣＯの影響

Hydrogen storage alloys exhibit reversible high-rate hydrogen absorption and desorption reactions. The hydrogen storage density of the alloys is higher than that liquid H2. The exposure of the alloys to impurity gases such as O2, CO, CO2, and H2O readily reduces reactivity with H2 gas. In this study, the surface of LaNi5-xAlx alloy was treated using anhydrous hydrogen fluoride to examine the effect of CO on fluorinated alloy H2 reactivity. This HF treatment effectively reduced alloy surface poisoning by CO. Compared with the initial transfer, the HF-treated alloy still exhibited 80% hydrogen transfer after 100-cycle hydriding-dehydriding reactions in a H2 gas including 1000ppm CO, while the transfer became zero for untreated alloy after five hydriding-dehydriding cycles. AES analysis of HF-treated samples showed that the HF treatment induced the surface segregation of Ni and F atoms where almost no La atoms was detected. The concentration of La atoms was found to increase with depth, in which a mixed region of La, Ni, Al, F, and O atoms was formed. This fluorinated surface layer seems to function both to prevent surface CO poisoning and to act as a catalyst.

Reversible hydrogen absorption in neutron generating tubes

The operation of neutron generating tubes is presented. The real system is described. Some aspects of reversible absorption of hydrogen isotope by metals are analyzed. A model describing decisive phenomena and letting us to avoid undesirable situations is proposed. Analogies with other chemical systems are pointed out.

The intrinsic degradation behaviour of the Laves phase alloy Zr 0.9Ti 0.1Cr 0.9Fe 1.1 upon temperature-induced hydrogen absorption-desorption cycling

The intrinsic degradation behaviour of the Zr-based Laves phase alloy Zr 0.9Ti 0.1Cr 0.9Fe 1.1 upon temperature-induced hydrogen absorption-desorption cycling is investigated by pressure-composition isotherm measurements, X-ray diffractometry and thermal analysis on the degraded samples. After 7000 thermal cycles between room temperature and 270 °C the reversible hydrogen absorption capacity decreases by about 15%. As the cycling temperature and/or applied hydrogen pressure increase, the degradation phenomenon becomes more severe. The cause of the intrinsic degradation is found to be a stable crystalline hydride phase with a higher Cr content than the original matrix. Under severe cycling conditions it is observed that transformation to an amorphous phase is also a possible reason for the degradation. These structural modifications are strongly activated by the internal accumulation of elastic strain due to the repetitive hydrogenation treatments and the applied thermal energy. It is suggested that the corresponding mechanism is related to the motion of Cr and Fe atoms.

Hydrogen absorption by M5X3 phase ZrAl compounds

Abstract The hydrogen absorption of the M5X3 phase ZrAl compounds was studied. The compounds exist in two forms: a high temperature phase with D8m W5Si3 structure and a Nowotny phase of D88 Mn5Si3 structure stabilized by the presence of oxygen. Zr5Al3 with the D8m structure absorbs hydrogen at room temperature and at a hydrogen pressure below 1 atm. The hydride Zr5Al3H8 is formed at a hydrogen pressure of 1 atm. More than two hydrogen atoms can be desorbed on temperature cycling up to 200 °C. The structure of the hydride was determined by powder diffraction to be monoclinic ( a = 11.072 A , b = 11.072 A , c = 5.890 A , β = 90.57°, body centred). Zr5Al3 forms the hexagonal D88 Zr5Al3O1−x structure when oxygen is present. A hexagonal supercell with an a axis 3 1 2 times larger than that of the parent D88 structure appears for an oxygen content above Zr5Al3O0.1. Unlike previously studied D88 structures, such as Y5Si3 and Ho5Si3, which are poisoned for hydrogen absorption when oxygen is included, this oxygenstabilized D88 system still exhibits significant reversible hydrogen absorption. That this structure retains its hydrogen absorption capacity is not consistent with previous assumptions that the hydrogen and oxygen exclusively occupy the characteristic metal octahedral columns.

THE INFLUENCE OF Si ON PHASE RELATION AND HYDROGEN ABSORPTION PROPERTIES OF LaNi5

In this work, the phase relations of LaNi5-xSix(x≤1.25) have been studied by means of X-ray powder diffraction method and DTA method, and the hydrogen absorption properties of the samples have been measured using gas-gathering method. The α-phase (LaNi5) and the new discovered ternary compound LaNi4Si (β) forms a eutectic system. The eutectic reactionis α+β(?)1170℃/ L. The eutectic point is at x=0.96. In the single phase area of a-phase, the lattice parameter a de-creases and c increases with the substitution of Si, The ternary compound LaNi4Si belongs to orthorhqmbic system with lattice parameters a = 8.382?, b = 5.210?, c = 3.989?. The measured density is 7.59 g/cm3. There are two formula unit per unit cell. Possible space groups are D2h5,C2v2,C2v4. The hydrogen quantities absorbed by the La1-ySiyNi5 samples decrease rapidly with Si content increasing. The absorbed hydrogen quantities of La-Ni5-xSix samples vary slowly with the Si content and the plateau pressures decrease. The formation free energy of LaNi4.8Si0.2H6.5 is 475 cal/mol H2. Si substitution increased the stability of hydrides. The new compound LaNi4Si has reversible hydrogen absorption and desorption properties with formation of hydride LaNi4SiH3.6.

Hydrogen absorption in various zirconium- and hafnium-based intermetallic compounds

The interaction with hydrogen gas of sixteen intermetallics containing zirconium or hafnium at a concentration of at least 50 at.% was studied. It was found that reversible hydrogen absorption involving the formation of a ternary hydride occurred for all the hafnium compounds and for the zirconium compounds of 50 at.% Zr composition. For all compounds of higher zirconium content hydrogen absorption was found to be irreversible because of the formation of the binary hydride ZrH 2. Lattice parameters are given for the intermetallic compounds of hafnium before and after charging with hydrogen gas.