Hydrogen Desorption Plateau Pressure Research Articles

Effect of Mn substitution on plateau pressure regulation of the Ti0.92Zr0.1Cr1.6−xMnxFe0.4 alloys for primary hydrogen compressor

The Ti0.92Zr0.1Cr1.6−xMnxFe0.4 (x = 0.15, 0.3, 0.45, 0.6 at%) alloys were synthesized by vacuum electric arc furnace. The effect of Mn substitution on plateau pressure regulation of these alloys was investigated for the primary hydrogen compressor. With increasing Mn content, the hydrogen absorption/desorption plateau pressures of the Ti0.92Zr0.1Cr1.6−xMnxFe0.4 (x = 0.15, 0.3,0.45,0.6 at%) alloys increased, the plateau slope factor decreased, meanwhile, both enthalpy and entropy change values decreased. The Ti0.92Zr0.1Cr1.0Mn0.6Fe0.4 alloy had the best comprehensive performance. Based on the pressure composition isotherms measurement, the plateau pressure and hydrogen storage capacity were obtained at 298–363 K. The hydrogen absorption/desorption curves of the Ti0.92Zr0.1Cr1.0Mn0.6Fe0.4 alloy at 353 and 363 K were firstly tested by experiment method. At 298 K, the hydrogen absorption plateau pressure and maximum capacity were 7.82 MPa and 1.79 wt%. At 363 K, the hydrogen desorption plateau pressure and maximum capacity were 27.21 MPa and 1.54 wt%. Hydrogen pressure from 8 MPa to 25 MPa was successfully obtained at 298–363 K, satisfying operating temperature and pressure requirements for the primary hydrogen compression materials.

Effect of Fe and Al on hydrogen storage properties of 75 V-Ti-Cr alloys

V-based hydrogen storage alloys are considered promising materials with high hydrogen capacity under ambient conditions. 75 V-Ti-15Cr alloys with different Fe and Al addition (1–3 at%) have been investigated. All the alloys are confirmed to show body-centered tetragonal (BCT) structure after dehydrogenated at room temperature. The PCT tests manifest that the hydrogen storage capacity decreases and desorption plateau pressure rises with the content of Fe or Al. The relationship between the hydrogen storage property and lattice parameters of BCT phase is discussed. Also, the relationship between hydrogen capacity and electron density is analyzed. Among the studied alloys, the 75 V-Ti-15Cr-1Al-1Fe alloy shows optimal hydrogen storage capacity (2.26 wt%) and plateau pressure (0.5 MPa) at room temperature. Cycle test proves that the optimized 75 V-Ti-15Cr-1Al-1Fe alloy possesses excellent durability and the retention rate of hydrogen capacity can achieve 97% after 100 cycles. The slight capacity attenuation possibly results from the derivation of lattice defects and small contraction of the hydrogen absorption phases.

High‐pressure hydrogen storage properties of Ti x Cr 1 − y Fe y Mn 1.0 alloys

TixCr1 − yFeyMn1.0 (x = 1.02, 1.05, 1.1, 0.05 ≤ y ≤ 0.25) alloys were prepared by plasma arc melting and annealing at 1273 K for 2 hours. The XRD results show that the main phase of all alloys is the C14 type Laves phase, and a little secondary phase exists in a mixture of the binary alloy phase. The lattice parameters increase with Ti super-stoichiometry ratio increasing, whereas smaller lattice parameters emerge with increasing Fe stoichiometry content. Additionally, as the Ti super-stoichiometry ratio decreases, the pressure-composition-temperature measurements indicated that hydrogen absorption and desorption plateau pressures of TixCr0.9Fe0.1Mn1.0 (x = 1.1, 1.05, 1.02) alloys increase from 3.15, 0.67, to 5.94, 1.13 MPa at 233 K, respectively. On the other hand, with the Fe content increasing in Ti1.05Cr1 − yFeyMn1.0 (0.1 ≤ y ≤ 0.25) alloys from 0.1 to 0.25, the hydrogen desorption plateau pressures increased from 1.41 to 2.46 MPa at 243 K. The hydrogen desorption plateau slopes reduce to 0.2 with Ti super-stoichiometry ratio decreasing to 1.02, but the alloys are very difficult to activate for hydrogen absorption and cannot activate when the Fe substituting for Cr exceeds 0.2. The maximum hydrogen storage capacities were more than 1.85 wt% at 201 K. The reversible hydrogen storage capacities can remain more than 1.55 wt% at 271 K. The enthalpy and entropy for all hydride dehydrogenation are in the range of 21.0 to 25.5 kJ/mol H2 and 116 to 122 J mol−1 K−1, respectively. Our results suggest that Ti1.05Cr0.75Fe0.25Mn1.0 alloy with low enthalpy holds great promise for a high hydrogen pressure hybrid tank in a hydrogen refueling station (45 MPa at 333 K), and the other alloys of low cost may be used for a potable hybrid tank due to high dissociation pressure at 243 K and high volumetric density exceeding 40 kg/m3.

Model for hydrogen desorption plateau pressure of AB2 type-Tix(CrFeMn)2 alloys

The semi-empirical model for predicting the hydrogen desorption enthalpy and plateau pressure of AB2 type-Tix(CrFeMn)2 Alloys is established by MATLAB soft in the method of linear-interaction. Through the significance testing analysis, it indicates that the factor order of the influence on the hydrogen desorption plateau pressure is T>δ2 > Z/R>(Δn)2/3 >(ΔX)2. Due to its negative and positive coefficients, the effects of (ΔX)2, δ2, (Δn)2/3 on the desorption plateau pressure and enthalpy are negative, and Z/R effect is positive. The relative error of ΔH was less than 3.7% in the choose database which is more accuracy than previous model of AB2. The calculated desorption plateau pressures by the model are agreed with our experimental data very good in the most experiment. The difference of ΔH calculated by the model and fitting experimental data were not more than 4 kJ/(mol H2). The model can be used to save cost and development time through predicting the hydrogen desorption plateau pressure of different composition alloys.

Enhanced cycling stability and high rate dischargeability of A2B7-type La–Mg–Ni-based alloys by in-situ formed (La,Mg)5Ni19 superlattice phase

In this work, various amounts of (La,Mg)5Ni19 phase is successfully produced in a A2B7-type La0.75Mg0.25Ni3.5 alloy by zone heating the as-cast alloy at the peritectic reaction temperature of the (La,Mg)5Ni19 phase (1203 K) for different durations. The formation process, electrochemical effects and functioning mechanism of the (La,Mg)5Ni19 phase are studied. The as-cast alloy contains (La,Mg)2Ni7 and LaNi5 main phases, and (La,Mg)5Ni19 minor phase. During zone heating, the peritectic reaction between the LaNi5 solid phase and the melted (La,Mg)2Ni7 liquid phase occurs, forming (La,Mg)5Ni19 phase. Thus the (La,Mg)5Ni19 phase abundance increases from 9.8 wt% (as-cast) to 46.2 wt% (heated for 24 h). The hydrogen desorption plateau pressure of the alloys increases with increasing (La,Mg)5Ni19 phase abundance, contributing to fast hydrogen desorption and large current dischargeability. In addition, the (La,Mg)5Ni19 phase network in the alloy matrix has a good structural stability against repeated hydrogen absorption/desorption, keeping the alloy from serious lattice destruction and crystal defects. Moreover, the discrete expansion/contraction between the LaNi5 phase and the superlattice phases during cycling decreases with the consumption of the LaNi5 phase, which relives the alloys' pulverization, and thus enhancing the oxidation resistance. Thereby, the cycling stability of the alloy electrodes of the 150th cycle increases from 65.4% (9.8 wt% (La,Mg)5Ni19 phase) to 80.4% (46.2 wt% (La,Mg)5Ni19 phase).

Effects of alloying elements (Al, Mn, Ru) on desorption plateau pressures of vanadium hydrides: An experimental and first-principles study

Vanadium-based alloys are promising for the reversible and compact storage of renewable hydrogen. To improve the hydrogen desorption plateau pressure of vanadium hydrides, V–3A binary alloys of V97Al3, V97Mn3, and V97Ru3 were prepared by vacuum arc melting. Hydrogen absorption and desorption properties of the newly prepared V–3A alloys were studied, and compared to vanadium hydrides, by pressure-composition-temperature measurements and first-principles calculations. Among the studied materials, V–3Ru showed the highest hydrogen desorption plateau pressures between T = 373 and 433 K. During hydrogen loading, V–3Ru also reached the highest hydrogen to metal ratio between the alloys. Meanwhile, V–3Ru was also the alloy with the highest hardness. Findings of hydrogen absorption and desorption measurements were supported with DFT calculations of hydride formation energies. The calculated DOS, ELF and atomic charges were used to study the effects of alloying on the electronic properties of hydrides. The bonding interactions in vanadium dihydrides were influenced the most through Al alloying, whereas V–3Mn and V–3Ru hydrides showed comparable electronic properties.

Study on the hydrogen storage property of (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05

The hydrogen storage of (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05 <x < 1.2, 0.2 <y < 0.6) alloys, prepared by Ar plasma arc melting, were investigated by X-ray diffraction, pressure-composition- temperature (PCT). The results indicated that all (TiZr0.1)xCr1.7-yFeyMn0.3 (1.05 ≤x ≤ 1.2, 0.2 ≤y ≤ 0.6) alloys were determined as C14-type Laves phase, the cell parameters a, c and unit cell volume of (TiZr0.1)xCr1.1Fe0.6Mn0.3 (1.05 ≤x ≤ 1.2) alloys increased with increasing the (TiZr) super-stoichiometry from 1.05 to 1.2, and the value of a/c almost unchanged. The hydrogen absorption and desorption plateau pressure decreased from 5.6, 4.4–2.6, 2.2 MPa with the increase of (TiZr) super-stoichiometry from 1.05 to1.2 at 274 K respectively, and the hydrogen desorption plateau pressure decline was not obvious when the (TiZr) super-stoichiometry exceeded 1.15. The (TiZr0.1)1.1Cr1.1Fe0.6Mn0.3 alloy had the best comprehensive properties about the maximum and reversible hydrogen storage capacity was 1.79 and 1.45 wt% respectively. The cell parameters a, c and unit cell volume of (TiZr0.1)1.1Cr1.7-yFeyMn0.3(0.2 ≤y ≤ 0.6) alloys increased as the ratio of Fe/Cr content decreased. The hydrogenation and dehydrogenation plateau pressure decreased from 4.5, 3.4–1.0, 0.9 MPa respectively and the maximum hydrogen storage capacity increased from 1.79 to 2.0 wt% as the Fe content reduced from 0.6 to 0.2 at 274 K. The maximum and the reversible hydrogen storage capacity were about 2.0 and 1.65 wt% as the ratio of Fe/Cr was 0.13 (ie, (TiZr0.1)1.1Cr1.5Fe0.2Mn0.3 alloy), its relative molar enthalpy of dissociation hydrogen was 24.30 kJ/mol H2.

Self-Discharge Characteristic of La0.60Nd0.15Mg0.25Ni3.50 Alloy with Single-Phase Ce2Ni7-Type Super-Stacking Structure

Self-discharge performance is one of the key indexes of nickel-metal hydride batteries. In this work, single-phase Ce2Ni7-type La–Nd–Mg–Ni-based alloy with great application potential in long-term storage Ni/MH batteries are prepared by step-wise annealing. The as-cast alloy contains CaCu5-, Gd2Co7- and Ce5Co19-type phases. After annealed at 1248 K, CaCu5- and Ce5Co19-type phases disappear and a single-phase Gd2Co7-type structure is obtained. With the temperature increase, Gd2Co7-type structure begins to transform into Ce2Ni7-type structure. As annealed at 1323 K, the alloy shows a Ce2Ni7-type single-phase structure. The C60 (discharge capacity at 60 mA g−1) of Ce2Ni7-type electrode reaches 405 mAh g−1, and the C1900 is even high to 210 mAh g−1. The Ce2Ni7-type electrode also shows superior self-discharge properties and the charge retention rate for 1 d (CRT1d) is 96.5%. Moreover after 150 cycles, the CRT1d is even high to 97.7% and CRT7d is 81.5%. While those of the as-cast electrodes are only 79% and 36%, respectively. Electrochemical pressure-composition isotherms show that Ce2Ni7-type electrode has relatively lower hydrogen desorption plateau pressure, indicating more stable hydride and less reversible self-discharge. After 150 cycles, the plateau pressure gets even lower. Moreover Ce2Ni7-type electrode possesses smaller corrosion current density, indicating minor oxidation/corrosion degree.

Self-discharge characteristic and mechanism of single-phase PuNi3-, Gd2Co7-, and Pr5Co19-type Nd–Mg–Ni-based alloys

To decrease the self-discharge rate of the nickel metal hydride batteries, the self-discharge characteristic and mechanism of single-phase PuNi3-, Gd2Co7-, and Pr5Co19-type Nd–Mg–Ni-based alloys are studied from the perspective of structure in this work. It is found that the self-discharge rate of the alloy electrodes gradually increases with a rising [NdNi5]/[NdMgNi4] subunit ratio. The factors resulting in reversible and irreversible self-discharge are analyzed by electrochemical pressure-composition isotherms, Tafel and SEM measurements. Electrochemical P-C isotherms show that with the increasing [NdNi5]/[NdMgNi4] subunit ratio, the hydrogen desorption plateau pressure sharply elevates, leading to less stability of the corresponding hydride and more reversible self-discharge of the alloys; whereas, corrosion current density of the three alloy electrodes gradually decreases and SEM shows that the amount of hydroxide accumulating on the alloy surface diminishes, indicating the oxidation/corrosion degree alleviates and less irreversible self-discharge with the higher [NdNi5]/[NdMgNi4] ratio. By calculating the proportion of reversible and irreversible self-discharge in total capacity loss, we find that the reversible self-discharge is nearly more than 90% for the three single-phase alloys, while irreversible self-discharge is less than 10%, which illustrates that reversible self-discharge is the dominate factor in self-discharge of Nd–Mg–Ni-based alloys in this study.

Effect of rare earth doping on the hydrogen storage performance of Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage application

In order to improve the activation behavior of Ti1.02Cr1.1Mn0.3Fe0.6 alloy with high hydrogen desorption pressure for hybrid hydrogen storage vessel application, the rare earth (RE) doped Ti1.02Cr1.1Mn0.3Fe0.6RE0.03 (RE = La, Ce, Ho) alloys were prepared by induction levitation melting. The effect of rare earth doping on the microstructures and hydrogen storage properties was also investigated systematically. The results show that Ti1.02Cr1.1Mn0.3Fe0.6 alloy displays a single C14 Laves phase, and there is a secondary phase of rare earth oxide in the RE doped alloys. The RE doping strategy can expand the unit cell volume of C14 Laves main phase. After RE doping, the activation behavior of the Ti1.02Cr1.1Mn0.3Fe0.6RE0.03 alloy is obviously improved and the hydrogen storage capacity is increased, while the hydrogen desorption plateau pressure is decreased. Moreover, the RE-free alloy can hardly absorb hydrogen at room temperature under 34–43 MPa hydrogen pressure, but all RE-doped alloys can absorb hydrogen to saturation under the same condition. The decline of pressure plateau is inversely proportional to the atomic number of RE. Among the studied alloys, the Ti1.02Cr1.1Mn0.3Fe0.6La0.03 alloy shows the best overall properties and can be fully activated at room temperature. Its hydrogen absorption pressure is 39.31 MPa and 51.27 MPa under 298 K and 318 K, respectively. Its hydrogen storage capacity is up to 1.715 wt% and the dissociation enthalpy is 16.63 kJ/mol H2 with a desorption plateau slope of 0.098.

Influence of annealing treatment on the microstructure and hydrogen storage performance of Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage application

The as-cast Ti1.02Cr1.1Mn0.3Fe0.6 alloy for hybrid hydrogen storage vessel application was annealed at different temperatures (873K, 973K, 1123K, 1173K) for 2h, and annealed at 1123K for different time (2, 5, 8h) respectively, and their microstructure and hydrogen storage properties were investigated systematically. The results show that the as-cast alloy has a single C14 Laves phase, and all annealed alloys consist of a C14 Laves main phase and a secondary phase. After annealing at different temperatures for 2h, the hydrogen absorption pressure at 298K decreases, however, the maximum hydrogen storage capacity and desorption pressures at 318K decrease slightly too. As the annealing time extends, the hydrogen absorption plateau pressure at 298K and hydrogen desorption plateau pressure at 318K increase, and the hydrogen desorption capacity increases first and then decreases, which reaches the highest desorption capacity of 1.721wt.% at the annealing time of 5h. Among the studied alloys, the alloy annealed at 1123K for 5h has the best overall properties for hybrid hydrogen storage application, its hydrogen absorption plateau at 298K is 29.09MPa, its hydrogen desorption plateau pressure at 318K is 45.12MPa, its hydrogen storage capacity is 1.721wt.% and its dissociation enthalpy (ΔHd) is 17.78kJ/mol H2.

Effects of Stoichiometric Ratio on the Microstructure and Electrochemical Properties of Ml&lt;sub&gt;0.96&lt;/sub&gt;Mg&lt;sub&gt;0.04&lt;/sub&gt;(Ni&lt;sub&gt;0.846&lt;/sub&gt;Co&lt;sub&gt;0.014&lt;/sub&gt;Mn&lt;sub&gt;0.08&lt;/sub&gt;Al&lt;sub&gt;0.06&lt;/sub&gt;)&lt;sub&gt;x&lt;/sub&gt; (x=5.0-5.3) Alloys

The as-cast Ml0.96Mg0.04(Ni0.846Co0.014Mn0.08Al0.06)x (x=5.0, 5.1, 5.2, 5.3) hydrogen storage alloys were prepared by vacuum induction melting method under argon atmosphere. Crystal structure, hydrogen absorption, desorption properties and electrochemical properties were investigated by means of XRD, SEM, EDS, PCT (Pressure Composition isotherms) and tri-electrode tests. The XRD and SEM results showed that the alloy were consisted of CaCu5-type phase as the main phase and (Al, Mn)(Ni, Co)2-type phase as the secondary phase. The content of the second phase increased as the stoichiometric ratio increased. PCT results indicated that the amount of hydrogen absorption decreased, while the hydrogen-desorption plateau pressure increased as the stoichiometric ratio increased. The electrochemical test results exhibited that the alloys had excellent activation performance at the second cycle, and the maximum capacity of the alloys were 341.2 mAh/g, 336.5 mAh/g, 333.6 mAh/g, 330.3 mAh/g as the stoichiometric x=5.0, 5.1, 5.2, 5.3, respectively. In addition, the cycle life increased slightly as the stoichiometric ratio increased. ML0.96Mg0.04(Ni0.846Co0.014Mn0.08Al0.06)5.0 had the best performance due to the combine action of trace Mg and stoichiometric ratio.

Preparation of TiFe based alloys melted by CaO crucible and its hydrogen storage properties

The carbon contamination of alloys prepared by the electro graphite crucible is impossible to avoid due to the inherit reaction between the melt and the crucible. In this study, the TiFe-based alloy is prepared by VIM process using CaO crucible as well as the electro graphite crucible. The samples are examined by means of Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Energy Dispersive Spectrometer (EDS), and the PCT curves are also measured. It is resulted that, the oxygen content of alloys melted by CaO crucible is almost equal to the one melted by graphite crucible and without the carbon contamination, meanwhile the carbon content of alloys obtained by the electro graphite crucible is 1860ppm, which exceeds the tolerance of the commercial alloy (1000ppm). The microstructure of the alloy melted by CaO crucible is dendrite, while it is composed of the equiaxed crystal with the lamellar structure and the spherical TiC particles distributed along grain boundaries or within the grain when melted by the graphite crucible; the interfacial reaction of the electro graphite crucible with TiFe alloy melt is serious and the interaction layer is formed up to 200μm in thickness, the carbon in TiFe-based alloys forms TiC. The hydrogen desorption plateau pressure of alloys melted by CaO crucible is (0.11–0.4)×105Pa, and that by the graphite crucible is (0.6–1)×105Pa. This may imply that the CaO crucible may be the promising candidate for melting the high performance TiFe based hydrogen storage alloys.

Effect of Cu content on structure, hydrogen storage properties and electrode performance of LaNi4.1-x Co0.6Mn0.3Cu x alloys

The effect of Cu content on structure, hydrogen storage, and electrochemical properties of LaNi4.1-x Co0.6Mn0.3Cu x alloys has been investigated. For sample, A, B, C, and D are used to represent alloys (x = 0, 0.15, 0.3, and 0.45), respectively. The results indicate that the four alloys are all single-phase alloy with LaNi5 phase of CaCu5 hexagonal structure, the hydrogen storage capacities of the alloy are about 1.49 wt% (A), 1.48 wt% (B), 1.43 wt% (C), and 1.25 wt% (D) at 303 K. With the increase of Cu content (x) from A to D, hydrogen desorption plateau pressure and pressure hysteresis decrease. Alloy electrode A shows better activation property and higher capacity (334.44 mAh/g). The addition of Cu improves the cyclic stability of the alloy electrodes when x = 0 ~ 0.45. However, their self-discharge properties and high-rate dischargeability (HRD) decrease with the increase of x. Further, electrochemical kinetics and electrochemical impedance spectroscopy (EIS) analysis show that the reaction of alloy electrode is controlled by charge transfer step, and the adding of Cu benefits the electrode properties in alkaline solution.

Influence of Ti super-stoichiometry on the hydrogen storage properties of Ti1+xCr1.2Mn0.2Fe0.6 (x=0–0.1) alloys for hybrid hydrogen storage application

Abstract Ti1+xCr1.2Mn0.2Fe0.6 (x = 0, 0.02, 0.05, 0.1) alloys with high hydrogen desorption plateau pressures for hybrid hydrogen storage vessel application were prepared by induction levitation melting, as well as the effect of Ti super-stoichiometry on the crystallographic characteristics and hydrogen storage properties were systematically investigated. The results show that all of the alloys were determined as a single phase of C14-type Laves structure, the unit cell volume expands with increasing Ti content. Compared with the stoichiometric TiCr1.2Mn0.2Fe0.6 alloy, the titanium super-stoichiometric Ti1+xCr1.2Mn0.2Fe0.6 (x = 0.02, 0.05, 0.1) alloys have larger hydrogen storage capacities and lower hydrogen desorption plateau pressures. Among the studied alloys, Ti1.02Cr1.2Mn0.2Fe0.6 has the best overall properties for hybrid hydrogen storage application, its hydrogen desorption plateau pressure at 318 K is 37.69 MPa, its hydrogen storage capacity is 1.61 wt.% and its dissociation enthalpy (ΔHd) is 16.67 kJ/mol H2.

Development of Ti–Cr–Mn–Fe based alloys with high hydrogen desorption pressures for hybrid hydrogen storage vessel application

Three series of Ti–Cr–Mn–Fe based alloys with high hydrogen desorption plateau pressures for hybrid hydrogen storage vessel application were prepared by induction levitation melting, as well as their crystallographic characteristics and hydrogen storage properties were investigated. The results show that all of the alloys were determined as a single phase of C14-type Laves structure. As the Fe content in the TiCr1.9−xMn0.1Fex (x = 0.4–0.6) alloys increases, the hydrogen absorption and desorption plateau pressures increase, and the hydrogen storage capacity and plateau slope factor decrease respectively. The same trends are observed when increasing the Mn content in the TiCr1.4−yMnyFe0.6 (y = 0.1–0.3) alloys, except for the plateau slope factor. Compared with the stoichiometric TiCr1.1Mn0.3Fe0.6 alloy, the titanium super-stoichiometric Ti1+zCr1.1Mn0.3Fe0.6 (z = 0.02, 0.04) alloys have larger hydrogen storage capacities and lower hydrogen desorption plateau pressures. Among the studied alloys, Ti1.02Cr1.1Mn0.3Fe0.6 has the best overall properties for hybrid hydrogen storage application. Its hydrogen desorption pressure at 318 K is 41.28 MPa, its hydrogen storage capacity is 1.78 wt.% and its dissociation enthalpy (ΔHd) is 16.24 kJ/mol H2.

The influence of Co content on LaNi3.2-xMn03Cox (x=0.2∼0.8) Alloy Hydrogen Storage and Electrochemical Properties

The cold crucible levitation melting prepared LaNi3.2-xMn03Cox (x = 0.2 ∼ 0.8) series alloys, the system of Co substitution of Ni on the alloy structure, hydrogen storage performance and electrochemical properties. XRD analysis showed that the cast alloy by the La2Ni7 phase, LaNi5 phase and LaNi3 phase composition; PCT test shows that with the Co substitution increases, the amount of the cast alloy of hydrogen first increased and then decreased, alloy hydrogen absorption and desorption plateau pressure changed little . Electrochemical tests show that as x increases the maximum discharge capacity of alloy electrodes decreases, the maximum discharge capacity Cmax by the x = 0.2 when 320.5mAh / g decreased to x = 0.8 when 286.6mAh / g, but the cycle stability significantly improved after 60 charge-discharge cycles, the alloy electrode capacity retention rate (S60) by the x = 0.2 and gradually increased to 72.9% when x = 0.8 at 84.9%.

Influence of Fe content on the microstructure and hydrogen storage properties of Ti 16Zr 5Cr 22V 57−xFe x ( x = 2–8) alloys

The influence of Fe content on the microstructure and hydrogen storage properties of Ti 16Zr 5Cr 22V 57−xFe x ( x = 2–8) alloys was investigated systematically. The results show that all alloys consist of a BCC main phase and a small amount of C14 Laves secondary phase. The crystal lattice parameters of the BCC main phase in the alloys decrease with the increase of the Fe content. Under moderate conditions, all the alloys have good activation behaviors and hydriding/dehydriding kinetics. As the x increases, the hydrogen desorption plateau pressure of the alloys increases consequently. Among the studied alloys, Ti 16Zr 5Cr 22V 55Fe 2 alloy has suitable hydrogen desorption plateau pressures indicated by the middle value of pressure range. (0.1–1 MPa) at 298 K and the best overall hydrogen storage properties.

Influence of Cu addition on structure and hydrogen desorption characteristics of Ti 0.16Zr 0.05Cr 0.22V 0.57 alloy

Hydrogen storage characteristics of Cu-substituted (Ti 0.16Zr 0.05Cr 0.22V 0.57) 1− x Cu x ( x = 0.0, 0.03, 0.05, 0.07, 0.10) alloy compositions were investigated. Alloy compositions were prepared by arc-melting in a water-cooled Cu mould in argon atmosphere. Phase analysis was carried out using Rietveld refinement. X-ray diffraction and transmission electron microscopy results show these alloys retain the parent BCC structure. It was observed that with increasing Cu content, the lattice parameter decreases. Increase in hydrogen desorption plateau pressure and shortening of the plateau region was observed for Cu-substituted alloys. Differential thermal analysis (DTA) show residual hydrogen in the Cu-substituted alloys released at lower temperatures.

Structure, morphology and hydrogen storage properties of composites prepared by ball milling [formula omitted] with La–Mg-based alloy

Hydrogen storage alloy composites Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 - x wt % La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 ( x = 0 , 5 , 10 ) were prepared by ball milling method. Their structures, morphologies and the hydrogen storage characteristics were intensively studied in the present work. It was found that the bulk of composites maintained the hexagonal C14 Laves phase structure after ball milling with additional La–Mg-based alloy for two hours. Scanning electron microscopy (SEM) observations revealed that the average size of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 and La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 particles were reduced to several hundred nanometers after ball milling process. Energy dispersive X-ray spectrometer (EDS) patterns of the composites showed that the La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 phase was uniformly distributed on the surface of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 . The hydrogen absorption–desorption characteristics of the composites were improved with increasing dispersivity of the La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 alloy particles. Pressure–composition–temperature (PCT) measurements revealed that the pressure plateau and the hysteresis decreased with increasing x. Among these composites, the sample of x = 10 exhibited more significant hydrogen storage performances. Its hydrogen absorption and desorption plateau pressure were 0.547 and 0.302 MPa, respectively, which were much lower than those of the Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 alloy. Moreover, it took only 200 and 2500 s to reach the constant pressure for the hydrogen absorption and desorption reaction. These improvements can be attributed to the preferable dispersivity of La–Mg-based alloy particles and also the formation of micro-crack after ball milling. Both factors synergetically facilitate the diffusion of hydrogen atoms in the composites and accelerate the dissociation of hydrogen molecules and recombination of hydrogen atoms on the surface of composites during the hydrogen absorption–desorption process.