Hydrogen storage alloy with high storage capacity

Abstract

Disclosed herein a hydrogen storage alloy represented by the general formula: Tix-0.02VyCrzCe0.02; wherein 0.1≦x≦0.5, 0.1≦y≦0.5 and 0.2≦z≦0.5 and x+y+z≦0.98, said hydrogen storage alloy having a body-centered cubic structure. This hydrogen storage alloy is adapted to achieve maximum hydrogen storage of 4.14 wt% at 298K under the hydrogen pressure of 0 bar and showed 2.13 wt% after 1500 absorption-desorption cycles. The alloy also showed fast hydrogen kinetics, where it reached 90% of maximum capacity within 40 secs.

Description

[0001] TITLE: HYDROGEN STORAGE ALLOY WITH HIGH STORAGE CAPACITY

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a hydrogen storage alloy that showed high capacity and exceptional cycle life characteristics by improving the conventional V-based hydrogen storage alloy of a body-centered cubic structure, and its synthesis method thereof.

[0004] BACKGROUND OF THE INVENTION

[0005] Hydrogen has been recognized as an ideal fuel for the future. It has a high energy density means more energy per unit of weight, thus making hydrogen a better fuel for a greater range of performance for stationary, vehicle, and other applications. The search for the development of an efficient hydrogen storage medium is crucial for the hydrogen economy. Metal hydrides have been investigated as a solid-state hydrogen storage medium due to their ability to store hydrogen safely and reversibly in practical conditions. The safety, higher volumetric storage capacity and better reversibility are the major advantages of metal hydride -based storage over other storage mediums. Besides, metal hydride-based systems can have several applications and these can be used for hydrogen purification, nonmechanical compression, thermal energy storage, heat pumps and, vehicular applications. Body-centered cubic (BCC) based solid solution alloys have higher hydrogen storage capacity than other intermetallic alloys but show slow kinetics and require extensive activation treatment for several cycles before they can react with hydrogen at appreciable rates. To overcome these drawbacks, many approaches are taken by various groups, including heat treatment at high temperatures [Lee SM, Perng TP. Effect of the second phase on the initiation of hydrogenation ofTiFel-xMx (M = Cr,Mn) alloys. Int J Hydrogen Energy 1994; 19: 259-63. https: / / doi.org / 10.1016 / 0360-3199(94)90095-7; Tamura Tominaga Y, Matsumoto K, Fuda Kuriiwa T, Kamegawa A, et al. Protium absorption properties of Ti-V-Cr-Mn alloys with a b.c.c. structure. J Alloys Compd 2002;330- 332:522-5. https: / / doi.org / 10.1016 / S0925-8388(01 )01544-4. mechanical deformation such as high pressure torsion, ball milling [Huot J, Cuevas F, Deledda S, Edalati K, Filinchuk Y, Grosdidier T, et al. Mechanochemistry of metal hydrides: Recent advances. Materials (Basel) 2019;12. https: / / doi.org / 10.3390 / mal2172778], however these techniques are difficult to implement when large scale materials synthesis and processing are to be done and are not economical to scale up. In vanadium-based BCC solid solution alloys the alloying of other metal with atomic radius at least 5% lesser than solvent metal, results in better activation of the alloys [Akiba E, Iba H. Hydrogen absorption by Laves phase related BCC solid solution. Intermetallic s 1998;6:461-70. https: / / doi.org / 10. JO J 6 / 50966-9795(97)00088-5], Ti-V-Cr, a vanadium-based BCC solid solution alloy has been explored at different ratios of Ti, V, and Cr to improve the rate of first hydrogenation and overall hydrogen storage capacity. Laves phase-related BCC solid solution alloys [Akiba E, Okada M. Metallic hydrides III: Body-centered-cubic solid-solution alloys. MRS Bull 2002;27:699- 703. https: / / doi.org / 10.1557 / mrs2002.225] have shown improved activation properties due to the presence of BCC / C14 interface, which allows hydrogen to diffuse easily. However, the laves structure is a compact structure as compared with the BCC structure, and hence its presence reduces the maximum hydrogen storage capacity [Akiba E, Iba H. Hydrogen absorption by Laves phase related BCC solid solution. Intermetallics 1998;6:461-70. https: / / doi.org / 10.1016 / S0966- 9795(97)00088-5; Mouri T, Iba H. Hydrogen-absorbing alloys with a large capacity for a new energy carrier. Mater Sci Eng A 2002; 329-331:346-50. https : / / doi. org / 10.1016 / S0921 -5093(01 )01597-0] .

[0006] A large number of studies are reported to show the effect of the addition or substitution of one ofthe elements Ti, V or Cr, in Ti-V-Cr alloy with other metals, to improve the overall hydrogen storage properties. Although the Zr, Ni addition [Kamble A, Sharma P, Huot J. Effect of addition of Zr, Ni, and Zr-Ni alloy on the hydrogen absorption of Body Centred Cubic 52Ti-12V-36Cr alloy. Int J Hydrogen Energy 2018;43:7424-9. https: / / doi.Org / 10.1016 / j.ijhydene.2018.02.106] improve the first kinetics, still the incubation period was observed in the alloys.

[0007] Reference is made to JPH08104941 A. In this document, the inventors have claimed a hydrogen storage alloy of Cr of 20 to 30 at% and 5 to 15 at % Fe and V with a 0.1 to 1 at% of S with a body-centered cubic structure. The activation of these alloys was performed at 500 °C for 2 hours. And, the maximum hydrogen storage capacity reported is 1.7 wt%. However, this alloy shows a lower hydrogen storage capacity with a higher activation temperature.

[0008] Further reference is made to JP2003226925A. In this patent, the inventor discussed an alloy with formulae Ti (ioo-ab)CraXb where 40<Cr (at%) <60 and X= Ru, Rh, Os, Ir which show hydrogen storage capacity of a maximum 2.5 wt%. Before hydrogenation, all the alloys are preheated at temperature ranges of 1300 to 1450 °C for a predetermined time to achieve a homogenous alloy composition. At the same time, some alloy compositions were heated at 500 °C for 6 hours. However, this alloy shows a lower hydrogen storage capacity and require high temperature heat treatment to achieve homogeneity and activation of alloys.

[0009] Further, reference is made to JP2007534837A. In this work, an alloy with a constituent element of 8.0 to 45 atomic percent titanium, 5.0 to 75 atomic percent vanadium, and 10 to 65 atomic percent chromium is disclosed. Other elements of 0 to 16 atomic percent are introduced such that nickel, manganese, molybdenum, aluminium, iron, silicon, magnesium, ruthenium, and cobalt. This alloy showed a body-centered cubic structure. Before any further hydrogenation studies, the alloy was annealed at temperatures ranging from 1350 °C to 1450 °C for 5 min and then quenched. Then further, oxidized layers are removed by etching or mechanical grinding. This implies that alloys require a lot of heat treatment and mechanical before the first hydrogenation. The alloys show a maximum of high hydrogen storage capacity of 4 wt% with a reversible hydrogen storage capacity of 3.0 wt%. However, the operating hydrogenation temperature are 90 °C to 110 °C. This method involves annealing or high temperature heat treatment such as 1300 °C to 1500 °C which increases the overall production cost due to achieving and maintaining such high temperatures leads to high energy consumption, which makes it economically impractical.

[0010] Further reference is made to US6048644A. This document discloses the invention of an electrode for alkaline storage batteries, that uses hydrogen storage alloy as active material. A hydrogen storage alloy electrode comprising particles of the hydrogen storage alloy is represented by the general formula Vi-x-y-zTixM'yLnz. wherein Ln is at least one element selected from La and Ce or a mixture of rare earth elements, M' represents at least one element selected from the group consisting of Cr, Mn, Fe, Co, Nb, Mo, Cu and Zr, wherein 0.2^x^0.4, 0.005 said alloy having a body-centered cubic structure, and wherein said particles are nickel-free. The alloys have their surface disposed with Ni diffusive layer by one of the following methods. One where 10 wt% nickel powder is added into the alloy particles and mix them in a motor, followed by ball milling or heat treating. The other method involves treating of the alloy particle with 2% of hydrofluoric acid, then immerse them in an electroless nickel plating bath for 30 minutes at 50 °C, followed by heat treatment for 10 wt % nickel adherence. According to references [I. P. Jain, et al “Effect of Zr, Ni and ZryNiio alloy on hydrogen storage characteristics of TiFe alloy”, Int. J. Hydrogen Energy. 40 (2015) 16921-16927. https: / / doi.Org / 10.1016 / j.ijhydene.2015.06.007], [A. Kamble, et al, “Effect of addition of Zr, Ni, and Zr-Ni alloy on the hydrogen absorption of Body Centred Cubic 52Ti-12V-36Cr alloy”, Int. J. Hydrogen Energy. 43 (2018) 7424-7429. https: / / doi.Org / 10.1016 / j.ijhydene.2018.02.106] even a minimal amount of Ni can profoundly influence hydrogen storage performance. Thus, alloys with the inclusion of Ni cannot be directly compared to alloy compositions with the absence of Ni element. Also, the highest hydrogen storage capacity reported in this document is limited to 1.9 H / M. Further reference is made to a non-patent literature “ Catalytic Influence of Various Cerium Precursors on the Hydrogen Sorption Properties of NaAlHf" authored by Jianjiang Hu, Shuhua Ren, Raiker Witter, Maximilian Fichtner; (https: / / doi.org / 10.1002 / aenm.201100724). This article teaches that sodium alanate (NaAlH4) is one of the metal complex hydrides most often investigated for use as a hydrogen-storage material. The properties of NaAlH4 doped with CcCIs differ from materials with other dopants, with faster sorption kinetics and a more stable capacity. In this paper, various precursors of Ce are applied to investigate their catalytic effects on the sorption performance of this material. The re-hydrogenation is found to be completed in approximately 10 min. Although all the Ce precursors investigated in this work result in reversible hydrogen storage materials, desorption kinetics are enhanced upon formation of cerium aluminide (CeAU) in the composites. While the use of CeAh instead of CeCh can increase the hydrogen capacity by bypassing the formation of the ineffective NaCl, the highest capacity of 4.9 wt% — close to the theoretical value — is obtained from NaAlEh doped directly with metallic cerium. However, in NaAlH4, a complex hydride, hydrogen forms chemical bonds with the compound, and with binding energy of >100 kJ / mol, in this hydrogen is already present in the compound, and hydrogen can be dehydrogenated / released at higher temperatures but putting back the hydrogen in the compound is always challenging with complex hydrides. In contrast, intermetallic compounds trap hydrogen in interstitial sites, forming metallic bonds with a binding energy range of 50-100 kJ / mol that are weaker than chemical bonds. As a result, the mechanisms governing hydrogen interaction with complex hydride (NaAlH4) during hydriding and dehydriding are distinctly dissimilar than in case of solid solution alloys. Complex hydrides involve multi-step absorption and desorption processes with various intermediates compounds. Consequently, the effect of Ce in NaAlH4 differs significantly from its impact in solid solutions alloys. Thus, there remain a need for a hydrogen storage alloy having high hydrogen storage capacity with easier activation, for storing hydrogen at ambient conditions, which can be scalable with economical viable process of synthesize and activation for hydrogen storage applications.

[0011] SUMMARY OF THE INVENTION

[0012] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key / critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0013] The main objective of the invention is to overcome the drawbacks of prior art.

[0014] Another objective of present invention is to provide a hydrogen storage material comprising Ti substituted with Ce, in small amount to see the presence of another phase.

[0015] Thus, present invention represents the substitution of Ti with Ce in TiVCr BCC alloy to study the effect of the presence of Ce / CeC phase and BCC phase on the activation, kinetics, thermodynamics and hydrogen storage capacity of the alloy.

[0016] One aspect of the present invention relates to a hydrogen storage alloy represented by the general formula:

[0017] T ix-0.02 VyCrzCeo.o2 ; wherein said hydrogen storage alloy having a body-centered cubic structure. Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

[0018] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0019] The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 illustrates XRD pattern for Ti0.14V0.50Cr0.34Ce0.02 (V rich alloy), Ti0.36V0.i6Cr0.46Ce0.02 (Cr rich alloy), Tio.4sVo.i6Cro.34Ceo.o2 (Ti rich alloy), Tio.46Vo.26Cro.26 Ceo.02 (Main composition).

[0021] Figure 2 illustrates Back Scattering Electron (BSE) SEM micrographs of (a) Ti0.14V0.50Cr0.34 Ceo.02 (V rich alloy), (b) Ti0.36V0.i6Cr0.46Ce0.02 (Cr rich alloy), (c) Tio.4sVo.i6Cro.34 Ceo.02 (Ti rich alloy), (d) Tio.46Vo.26Cro.26 Ceo.02 (Main composition).

[0022] Figure 3 illustrates elemental mapping of Ti0.46V0.26Cr0.26Ce0.02 (Main composition) alloy.

[0023] Figure 4 illustrates first hydrogenation of as cast Ti0.14V0.50Cr0.34 Ceo.02 (V rich alloy), Tio.36Vo.i6Cro.46Ceo.o2(Cr rich alloy), Tio.4sVo.i6Cro.34Ceo.o2(Ti rich alloy), and Tio.4sVo.25Cro.25 Ceo.02 (Main composition) alloys.

[0024] Figure 5 illustrates First hydrogenation kinetics at 298 K for the Ti0.46V0.26Cr0.26Ce0.02 (Main Composition)

[0025] Figure 6 illustrates PCI plot for H2 absorption and desorption for Ti0.46V0.26Cr0.26Ce0.02 alloy at 303 K, 323 K and 343 K (Main Composition). Figure 7 illustrates Van't hoff plot for H2 (a) Absorption (b) Desorption for Ti0.46V0.26Cr0.26Ce0.02 alloy (Main Composition).

[0026] Figure 8 illustrates cyclic study for hydrogen for 100 cycle for Ti0.46V0.26Cr0.26Ce0.02 alloy (Main Composition).

[0027] Figure 9 illustrates PCT in between 1500 cycle in the pressure of 3 to 60 bar at 298 K for Ti0.46V0.26Cr0.26Ce0.02 alloy (Main Composition).

[0028] Figure 10 illustrates powder XRD pattern of hydride sample after 10 cycle for Ti0.46V0.26Cr0.26Ce0.02 alloy (Main Composition).

[0029] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

[0030] DETAILED DESCRIPTION OF THE INVENTION

[0031] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary implementations of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0032] Features that are described and / or illustrated with respect to one implementation may be used in the same way or in a similar way in one or more other implementations and / or in combination with or instead of the features of the other implementations. Present invention relates to a hydrogen storage alloy represented by the general formula:

[0033] T ix-0.02 VyCrzCeo.o2 ; said hydrogen storage alloy having a body-centered cubic structure.

[0034] In an embodiment of present invention, said hydrogen storage alloy is Tio.46Vo.26Cro.26 Ceo.02

[0035] In another embodiment, said hydrogen storage alloy is adapted to achieve maximum hydrogen storage of 4.14 wt% at 298 K under the hydrogen pressure of 40 bar.

[0036] In a further embodiment, said hydrogen storage alloy is prepared in vacuum arc melting furnace.

[0037] In yet another embodiment, said hydrogen storage alloy is adapted to absorb 90% of maximum hydrogen storage capacity within 40 sec.

[0038] In another embodiment of present invention, there is provided a synthesis method of a hydrogen storage alloy represented by the general formula Tix-o.o2VyCrzCeo.o2; wherein said hydrogen storage alloy having a body-centered cubic structure; comprising: a. weighing 10-50 at% of metallic Ti, 10-50 at% of metallic V, 20-50 at% of metallic Cr and 2 at% of Ce in such a way that their total weight become 100% and placing in a copper hearth within the electric arc melting furnace chamber; b. generating an electric arc by using a tungsten rod an anode, and the copper hearth below the samples as a cathode and heating the sample material in the crucible hereby melting the sample; c. gradually reducing the power fed to the electrode and allowing the material to cool and solidify in the crucible in a pellet form; d. repeating step (b) 5 times and after each melting pellet is turn over, to achieve a homogeneous alloy composition.

[0039] For the Main composition performed after 1500 hydrogen absorption and desorption cycle, the reversible hydrogen storage capacity is 2.13 wt%

[0040] Experimental Details:

[0041] Pure metallic elements: Vanadium (metal basis, >99.70 %), Chromium (metal basis, >99.99 %), Titanium (sponge, >99.95 %), and Cerium (ingot, 99.80%) were purchased from Alfa Aesar and used as starting raw material. All the materials were taken to the desired stoichiometric ratio for the alloy of Tix-o.o2VyCrzCeo.o2, where in x ranges from 10 atomic percent to 50 atomic percent, y from 10 atomic percent to 50 atomic percent, and z from 20 to 50 atomic percent alloy.

[0042] Table 1 Notation of different alloy composition

[0043] All these alloys are synthesized in the water cooled hearth for the synthesis using vacuum arc melting. The sample was turned over after each melting and re-melted five times to ensure the homogeneity of the ingot. The prepared ingot was crushed using hardened steel mortar and pestle in the open atmosphere. It was then divided into two parts for structure and morphology characterization and measurement of hydrogen storage characteristics. The part of the ingot was molded in epoxy resin and was prepared for morphological studies. The sample preparation for SEM- EDS involves the polishing of the sample mold using Silicon carbide sheets with grit sizes ranging from 100-2500 mesh, followed by fine polishing using colloidal silica (MetSil40) solution. Micro structure was investigated by a scanning electron microscope (SEM), FEG Zeiss SEM Gemini 300, equipped with energy dispersive spectrometer (EDS) at an operating voltage of 15 keV. The surface morphology, internal structure and composition distribution of the alloy was analyzed at different magnification and positions using point mapping and color mapping. These images then further analyzed using ImageJ software to calculate the area fraction of phases present. To study the crystal pattern of the diffraction pattern was recorded by the X-ray diffraction (XRD) technique using Rigaku Japan, smart lab, using Cu Ka radiation (k=1.5406 A) operated at 40 kV voltage and 30 mA current. The data was recorded at a 29 ranges of 20°-100° with step size of 0.01. Phase identification were performed by High score plus.

[0044] Hydrogen storage properties were measured by volumetric Sievert’s apparatus- IMI Hiden Isochema hydrogen sorption analyzer, UK. Sample ingot was crushed into fine powder using a hardened steel mortar and pestle. Approx. 800 mg of the sample has been loaded into gold plated stainless steel reactor attached to the Sievert’s apparatus of known volume. The system first undergoes a leak test using argon at 80 bar and followed by piconometry of the sample. The volume occupied by the sample in the reaction chamber was calibrated and considered during calculation. The complete system was degassed by heating at 623 K for 2 hours under vacuum pressure (10-8 bar). Hydrogen with purity (>99.999 %) was then injected into the reaction chamber.

[0045] The static first hydrogenation or activation was observed under an initial hydrogen pressure of 40 bar for 15 hours. The drop in pressure over time gives the wt. % H of hydrogen absorbed. Thermodynamic properties were determined through the acquisition of Pressure-Composition-Isotherm (PCI) curves at three different temperatures: 303, 323, and 343 K within the pressure range 0.001 < PH2= <60 bar. The cyclic hydrogen absorption studies were performed at the home made Sievert’s apparatus hydrogenation at T= 303 K and PH2= 40 bar and before each hydrogenation cycle the sample undergoes desorption at T= 623 K PH2= 0.01 bar for 2 hours.

[0046] The main composition underwent continuous 1500 cycle was performed in volumetric Sievert’s apparatus- IMI Hiden Isochema, where absorption of hydrogen was performed at 40 bar for 20 min followed by desorption at 10’8bar for 10 min. Several PCI were performed at different interval at pressure range of 3 bar to 60 bar at 298 K. Before PCI measurement the sample was heated to 623 K for 2 hour under vacuum.

[0047] Results and discussion

[0048] The X-ray diffraction pattern of the alloy is shown in Figure 1. The pattern shows four major diffractions of BCC phase (space group: I m -3 m, 229) with minor peaks of CeCh (space group: F m -3 m, 225). Additionally, the diffraction peaks of pure Ce were also observed at 29 = 31° and 36° with space group F m -3 m, 225, which can be attributed to the excessive Ce in the sample. As it can be predicated by peak intensity, the phase fraction of BCC is the highest, followed by the CeOi peak. But a slight shift in the XRD pattern is observed which still can be experimental error in height adjustment parameter. Also this can lattice expansion or contraction can be reason for shift.

[0049] The surface morphology of all the alloys was studied using FE-SEM. The homogeneity and elemental mapping of the polished sample at different magnifications and morphological locations.

[0050] The micro structure represented in Figure 2 shows multiphase alloys. There are two major phases namely: grey phase and bright phase. In backscattered electron microscopy heavier elements looks brighter comparison to lighter elements. The bright phase is assumed to be Cerium which is further confirmed by EDS analysis. The chemical composition of grey and white phase can be identified by EDS. Multiple scan were done at different locations on the surface for each sample. The area selected and the phase composition of grey and bright phase can be seen in the Table 3 and Table 4, respectively. The Cr rich alloy show another minor phase as dark grey phase, which was not observed in XRD. It’s chemical composition is mentioned in Table 5. The results of SEM and EDS confirms the results from XRD of the formation of two phase, grey and bright phase.

[0051] The bulk composition of all the alloys are analyzed by EDS and are mentioned in Table 2. As during the preparation method, there is a chance of loss of material, the overall composition of the surface is also identified by EDS analysis. It is also important to note here that the calculation of composition is done by the randomly chosen view, thus composition can slightly vary.

[0052] Table 2 Elemental abundances as measured by EDS Table 3 Chemical composition of Grey phase

[0053] Table 4 Chemical composition of Bright phase

[0054] Table 5 Chemical composition of dark grey phase

[0055] Figure 3 shows elemental mapping for Ti0.46V0.26Cr0.26Ce0.02 compositions. ImageJ was usedto identify the area fraction of the bright phase. The area of the bright phase and grey phase is calculated and found to be 3.9 %, and 96.1 % respectively.

[0056] Figure 3 also shows the color mapping of the elements of the alloy, where the brightness of the color present indicates the presence of the elements. The mapping of elements shows a uniform distribution of individual elements throughout the matrix. The Ti, V, Cr are present in the grey phase while Ce segregates and form the white precipitate. The elemental mapping confirms these results as shown above, including the overall atomic percentage of alloy, grey phase, and bright phase.

[0057] For first hydrogenation, the alloy was pre-heated at 623 K for two hours under a dynamic vacuum, and hydrogen was pressurized into the system under a pressure of 40 bar. The first hydrogenation absorption kinetics was recorded at room temperature for 15 hours for complete saturation and shown in Figure 4. As observed in Figure 4, Main composition absorbs a maximum hydrogen storage capacity of 4.14 wt% followed by Ti rich alloy and Cr rich alloy with a capacity of 3.4 wt.% and 2.9 wt.% respectively. V rich alloy absorb 2.3 wt.% hydrogen. The high hydrogen storage capacity of the Ti rich alloys can be attributed to the ability of Ti to form stable hydride. This is the reason main composition showed almost double hydrogen storage capacity than V rich. Vanadium hydrides are reported to form two type of hydrides: monohydride and dihydride. Mono hydride phase stable at room temperature, while di hydride is very unstable. This is why vanadium-rich BCC alloys show two plateau during PCI measurement. In this study, no annealing, mechanical, or high temperature heat treatment (> 1273 K) was done, which may be the reason for low capacity than other alloys. Table 6 showed the tgo% (time to absorb 90% of the maximum capacity). V rich alloy, Cr rich alloy, Ti rich alloy and main composition alloy take 540, 510, 600, and 40 s respectively to reach 90 % of the total capacity. As explained earlier the tendency of Ti to form strong bong with hydrogen leads to increase kinetics of hydrogen absorption.

[0058] Table 6 First hydrogenation properties of all the alloys

[0059] The time required for 90% hydrogen uptake for the main composition that is Ti0.46V0.26Cr0.26Ce0.02 alloy is 40 secs, which is the fastest kinetics reported for BCC solid solution alloys with no incubation period observed. The storage capacity s 4.14 wt.% is also the highest ever reported capacity with the novel composition and not reported anywhere so far.

[0060] Thermodynamics

[0061] The hydrogen pressure concentration Isotherm (PCI) curves were recorded at the temperature range of 303, 323 and 343 K of the Ti0.46V0.26Cr0.26Ce0.02 (main composition) alloy. As it can be shown in Figure 6, sloping plateau and hysterics were observed. The hydrogen absorption / desorption plateau is shows sloping behavior, and shows ambiguous plateau pressure. Equilibrium pressure is calculated by fixing the capacity points at at 2.19 and 2.40 wt. % for absorption and desorption, respectively. The desorption PCI curves show partial desorption, which indicates that the applied temperature and pressure conditions were not sufficient for the complete desorption of the alloy.

[0062] Table 7 Thermodynamic parameter of the alloy

[0063] Hysteresis, defined as the difference in the gap between absorption and desorption plateau and it is considered to be important parameter for practical application. Hysteresis = In (Pa / Pd), where Paand Pd are equilibrium pressure for absorption and desorption respectively. The increase in absorption and desorption equilibrium pressure and plateau slope is observed with increase in temperature. The hydrogen absorption capacity decreases with an increase in temperature. Thermodynamic parameters such as the enthalpy and entropy of hydrogenation and dehydrogenation were calculated using Van’t hoff equation as given below: where Peqstands for equilibrium pressure, T is the absolute temperature, R is the gas constant, Po is a reference pressure usually taken as 1 bar. A plot of In Peqvs. 1000 / T is known as van’t hoff plot and is shown in Figure 7 (a) and (b) for absorption and desorption, respectively. Enthalpy and entropy can be calculated from slope and intercept of the plot. The enthalpy of the Ti0.46V0.26Cr0.26Ce0.02 is found to be 64 and 107 kJ / mol H2 for absorption and desorption. Cycle Life

[0064] The cycle stability of the alloy studied in the homemade sievert’s apparatus is shown in Figure 8. After first hydrogenation, the following hydrogen absorption cycle showed a sudden reduction in the hydrogen storage capacity, this is due to the formation of stable hydride during first hydrogenation that require a higher temperature than the applied conditions to desorb the alloy completely. Further hydrogenation cyclic studies were performed and a slight but continuous decrease in the hydrogen storage capacity of the alloy was observed. The repeated absorption and desorption of hydrogen can lead to a reduction in crystallite size of the alloy, that may be the reason behind the continuous reduction in capacity during cycling. A slight variation in the hydrogen storage capacity can be related to the change in the temperature of the environment.

[0065] Cyclic PCI

[0066] A total of 1500 continuous cycles were performed on Ti0.46V0.26Cr0.26Ce0.02 alloys, as illustrated in Figure 9. Pressure composition was recorded during intervals between cycles at the 50th, 100th, 500th, 750th, 1000th, and 1500thcycles to investigate the deterioration of capacity and PCI measurement within the cycle. The maximum hydrogen storage capacity observed after 1500 cycles is 2.13 wt%. To the best of our knowledge, this represents the highest reversible capacity recorded after 1500 cycles for V-based BCC solid solution alloys.

[0067] Hydride XRD

[0068] To study the change in crystal structure of the alloy, the sample was taken out of the reaction chamber in the hydride form after 10 cycle and recorded the XRD pattern. The XRD results showed that the main phase BCC is completely converted into FCC after hydrogenation and the dual peak of FCC phase is clearly visible at 29 value of 35.9° and 41.6°. In addition, a small amount of Ti hydride phase is also detected with a space group of Fm-3m, 225. Whereas the XRD peak of CeCh shows no change after hydrogen sorption, indicating the CeCh does not participate in the hydrogen absorption. Also, all of the diffraction peaks are broader as compared in as cast showing that after the sorption cycles, the crystallite size reduces due to repetitive absorption and desorption of hydrogen effect the crystal parameter of the sample.

Claims

CLAIMS:

1. A hydrogen storage alloy represented by the general formula:T ix-0.02 VyCrzCeo.o2 ;said hydrogen storage alloy having a body-centered cubic structure.

2. The hydrogen storage alloy as claimed in claim 1, wherein said hydrogen storage alloy is Tio.46Vo.26Cro.26 Ceo.02.

3. The hydrogen storage alloy as claimed in claim 2, wherein said hydrogen storage alloy is adapted to achieve maximum hydrogen storage of 4.14 wt% at 298 K under the hydrogen pressure of 40 bar.

4. The hydrogen storage alloy as claimed in claim 2, wherein said hydrogen storage alloy is prepared in vacuum arc melting furnace.

5. The hydrogen storage alloy as claimed in claim 2, wherein said hydrogen storage alloy is adapted to absorb 90% of maximum hydrogen storage capacity within 40 sec.

6. The hydrogen storage alloy as claimed in claim 2, wherein the reversible hydrogen storage capacity of said alloy is 2.13 wt% after performing 1500 hydrogen absorption and desorption cycle.

7. A synthesis method of a hydrogen storage alloy represented by the general formula Tix-o.o2VyCrzCeo.o2; wherein 0.1^x^0.5, 0.1^y^0.5 and 0.2^z^0.5 and x+y+z^0.98, said hydrogen storage alloy having a body-centered cubic structure; comprising: a. weighing 10-50 at% of metallic Ti, 10-50 at% of metallic V, 20-50 at% of metallic Cr and 2 at% of Ce in such a way that their total weight become 100% and placing in a copper hearth within the electric arc melting furnace chamber;b. generating an electric arc by using a tungsten rod an anode, and the copper hearth below the samples as a cathode and heating the sample material in the crucible thereby melting the sample; c. gradually reducing the power fed to the electrode and allowing the material to cool and solidify in the crucible; d. repeating step (b) 3-5 times to achieve a homogeneous alloy composition.

8. The method as claimed in claim 7, wherein the alloy material undergoes activation treatment at 350 °C for 2 hours under a vacuum of 10’8bar in the Sievert’s apparatus.

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