CN1248637A - Ferro-titanium base hydrogen storage alloy - Google Patents

Abstract

A titanium-iron-based hydrogen storage alloy, characterized in that the chemical formula of the alloy is Ti _1+x Fe+y wt%M, wherein 0<x<0.3;0<y<8; M is Mm, Ml, La, One of the metals such as Ce, Pr, Nd, Sm, Li, Mg and Ca. The alloy of the present invention is a TiFe-based alloy with a non-TiFe stoichiometric ratio, without special activation treatment like TiFe, and can be hydrogenated once at room temperature and under a hydrogen pressure of 4.0 MPa, with a hydrogen storage capacity of more than 1.7 wt%. Due to the advantages of large hydrogen storage capacity, light weight, low cost and convenient operation, it is especially suitable for application in mobile or portable hydrogen storage devices such as hydrogen purifiers and hydrogen fuel tanks.

Description

TiFe-based hydrogen storage alloy

The invention relates to a metal-based alloy, in particular to a non-stoichiometric titanium-iron-based hydrogen storage alloy.

Due to resource and environmental issues, it will be an inevitable trend in the future development of the energy field that humans will gradually shift from fossil fuels to renewable energy such as solar energy and hydrogen energy. Hydrogen storage materials are both energy storage materials and functional materials. In addition to being used in the storage and transportation of hydrogen, they are also broadened to hydrogen purification and compression, electrochemistry (secondary batteries), energy conversion (heat storage, refrigeration, air conditioning, heating, etc.) , heat engine, etc.) and chemical catalysis and other fields. In particular, hydrogen storage materials have the characteristics of safety, flexibility and effectiveness when used as hydrogen energy storage and transportation carriers, and have broad prospects for the application of the current rapid development of zero-emission hydrogen fuel cells and hydrogen fuel tanks for hydrogen-burning vehicles.

So far, the hydrogen storage materials with practical application value are mainly some alloys that can reversibly absorb and desorb hydrogen at room temperature, such as AB ₅ -type rare earth alloys and AB-type and AB _2- type titanium alloys. If it is a hydrogen storage alloy used for hydrogen storage and transportation or as a hydrogen fuel tank, it should not only be able to absorb and release hydrogen at room temperature, but also have basic properties such as high hydrogen storage capacity, suitable balance pressure, and easy activation. TiFe alloy is a typical representative of AB type hydrogen storage alloy. TiFe alloy reacts with hydrogen to form TiFeH _1.04 hydride (β phase) and TiFeH _1.95 hydride (γ phase), and two platforms appear on the PCT curve, β phase and γ phase correspond to the low pressure platform and high pressure platform on the curve, respectively. The γ-phase with high hydrogen storage capacity is obtained when the hydrogen pressure is continuously increased after the formation of the β-phase. TiFeH _1.95 refers to the maximum saturated hydride at 0°C and 6.5MPa. The hydrogen storage capacity deduced from this formula is 1.8wt%, which is significantly higher than the 1.4wt% of common rare earth (AB ₅ type) alloys. In addition to the advantage of high hydrogen storage capacity, the decomposition pressure of TiFe alloy hydride is several atmospheres. Fe and Ti are abundant in nature and cheap, which is conducive to industrial-scale application.

However, TiFe alloys also have some fatal shortcomings as hydrogen storage materials, the most important of which is that it is difficult to activate, and alloys that have not been activated cannot perform reversible hydrogen absorption and desorption operations at room temperature. According to the document [1] (Inorganic Chemistry, Vol.13, No.1, 1974, P 218-223) the TiFe activation process reported is as follows: TiFe alloy is broken into particles and then put into the reactor to seal, exhaust, and heat the reactor To 400 ~ 450 ° C, continue to exhaust while heating, then fill the reactor with hydrogen to 0.7MPa, exhaust after half an hour and slowly cool to room temperature, and then fill with hydrogen to 6.5MPa, such as TiFe alloy within 15 minutes If the hydrogen absorption is still not possible, repeat the above-mentioned activation operation until it is completely activated. Practice has shown that the above-mentioned activation treatment method usually needs to be repeated many times before hydrogen absorption can start, and the maximum hydrogen absorption capacity can only be reached after more than ten hydrogen absorption and desorption cycles, which is labor-intensive and time-consuming and increases manufacturing costs.

So far, the main method to improve the activation performance of TiFe alloy is through alloying, such as Cr, Mn, Zr, Ni, Co, Nb, Al, V and other transition metal elements to partially replace Ti or Fe in TiFe alloy, and the composition is based on TiFe. based ternary or multicomponent alloys. Among them, the TiFe _1-x Mn _x (x=0.1～0.3) alloy with Mn as the replacement element has the best performance (see document [2] J.of the Less-Common Met., 134, 1987, P 275-286 ), although this stoichiometrically designed ternary alloy system can be activated at room temperature and under a hydrogen pressure of 4-5 MPa, the maximum hydrogen storage capacity is less than 1.6wt%, which is much lower than that of TiFe binary alloys. This document also proposes another series of Ti _1-x FeMn _x (x=0.1-0.3) alloys in which Ti is partially replaced by Mn, but its hydrogen storage capacity is too much reduced (less than 1 wt%), and has no practical application value. Another method proposed to improve the activation performance of TiFe alloys is to allow excessive Ti content in TiFe alloys to form non-stoichiometric alloys, such as Ti _1+x Fe (x=0.1, 0.2, 0.3, 0.4 and 0.5) (see literature [3] J. of Alloys and Compounds, 177, 1991, P 107-118). Studies have shown that this method can improve the activation performance of the alloy. The higher the x content, the greater the activation effect. However, the higher the x, the more Ti deviates from the stoichiometry, and the more β-Ti phases appear in the alloy structure. After hydrogenation The more hydrides that do not desorb hydrogen at normal temperature are formed, the greater the reduction in hydrogen storage capacity. According to literature [1], when the composition is 49.2wt% Ti and 50.5wt% Fe (equivalent to the chemical formula Ti _1.14 Fe), the solid solution hydrogen capacity without desorbing hydrogen accounts for about 15% of the saturated hydrogen storage capacity (on the PCT curve) and when Ti is further increased to a composition of 63.2wt% Ti and 36.7wt% Fe (equivalent to the chemical formula Ti ₂ Fe), the amount of solid solution hydrogen that does not desorb accounts for 56%, and the hydrogen storage capacity is comparable to that of the original TiFe binary alloy The gap is too big. Document [4] (J.of the Less-Common Met., 108,1985, P 313-325) proposes that another method to improve the activation performance of TiFe alloy is to add 4.5wt% mixed rare earth metals (Mm ), which constitutes TiFe+4.5wt%Mm alloy. It is believed that this new alloy can be fully activated after three hydrogen absorption and desorption operations at room temperature (27.1°C) and 6.0 MPa. The hydrogen storage capacity calculated according to the PCT curve of the alloy provided in the literature is about 1.56wt%, which is obviously much lower than that of typical TiFe alloys.

The object of the present invention is to provide a titanium-iron-based hydrogen storage alloy without special activation treatment, the hydrogen storage capacity of the alloy can maintain the level of the original TiFe binary alloy, and can be hydrogenated once at room temperature and at a lower hydrogen pressure. It has the advantages of large hydrogen storage capacity, light weight, and low cost, so it is especially suitable for applications in mobile or portable hydrogen storage devices such as hydrogen purifiers and hydrogen fuel tanks.

A titanium-iron-based hydrogen storage alloy, characterized in that the chemical formula of the hydrogen storage alloy is Ti _1+x Fe+y wt% M, where 0<x<0.3;0<y<8; M is cerium-rich mixed rare earth Metal Mm or lanthanum-rich mixed rare earth metal Ml, or one of metals such as La, Ce, Pr, Nd, Sm, Li, Mg and Ca. In the alloy system of the present invention, the titanium content exceeds the stoichiometric ratio range of Ti in typical TiFe alloys, and a certain percentage of metal elements (M) is added. This type of metal elements (M) is neither solid-soluble in Ti nor solid Soluble in Fe (of course not solid soluble in TiFe), but it is easy to absorb hydrogen to form hydride. The alloy of the present invention does not need to carry out the activation treatment process like TiFe, and it will start to absorb hydrogen after the incubation period of only a few minutes or more than ten minutes when it is first contacted with hydrogen at room temperature (such as 25 ° C) and 4.0 MPa hydrogen pressure, and The hydrogen absorption saturation can be reached within tens of minutes, and then the application of hydrogen absorption and desorption can be performed. Studies have shown that the alloy of the present invention is not a single TiFe phase structure, but a small amount of hydrogen-absorbing metal element (M) particles embedded with a small amount of hydrogen-absorbing metal elements (M) in the alloy of the present invention because Ti is stoichiometrically added. The network eutectic structure composed of TiFe phase is shown in Figure 1. Since both β-Ti and hydrogen-absorbing metal element (M) particles react with hydrogen prior to the TiFe phase, and form hydrides and undergo volume expansion, resulting in a large number of microcracks in the alloy and a TiFe phase with a clean surface, the hydrogen It is easy to reach the clean TiFe surface through these microcracks, so that TiFe is easy to hydrogenate. Through the optimized proportioning of the alloy components of the present invention, not only the problem of activation at room temperature is solved, but also the hydrides that do not desorb hydrogen are reduced to the minimum, and the hydrogen storage capacity at 4.0 MPa has reached more than 1.7 wt% (close to that at 6.0 MPa). The highest level of TiFe alloy), the hydrogen absorption equilibrium pressure at room temperature is within 1.0MPa.

Compared with the prior art, the alloy of the present invention has the following advantages: (1) compared with TiFe alloy, no special activation treatment is required, and it is convenient to use and low in cost; (2) the hydrogen absorption pressure to reach the saturated hydrogen storage capacity (1.7wt%) is 4.0MPa, which is lower than TiFe’s 6.0MPa; (3) The alloy composition not only makes Ti overstoichiometric but also adds hydrogen-absorbing elements, and the hydrogen storage capacity reaches more than 1.7wt%, which is higher than that of TiFe _1-x Mn _x system, Various titanium-iron-based hydrogen storage alloys such as Ti _1+x Fe system and TiFe+4.5wt%Mm.

Fig. 1 is the metallographic microstructure of the alloy whose chemical formula is Ti _1.2 Fe+6.0wt% Mm (200×)

Figure 2 is the PCT curve of the alloy with the chemical formula Ti _1.2 Fe+6.0wt%Mm at different temperatures, the abscissa is the hydrogen storage capacity (H/M), and the ordinate is the hydrogen absorption and desorption equilibrium pressure (MPa)

Example 1:

In the general formula of the alloy of the present invention, x=0.2; y=6.0 and M=Mm are selected, and the chemical formula is _Ti1.2Fe +6.0wt%Mm alloy. First calculate the Ti and Fe addition amount (wt%) required according to the Ti _1.2 Fe chemical formula, and then calculate the 6.0wt% Mm addition amount (wt%) of the Ti _1.2 Fe addition amount. Among the raw materials, Fe is industrial pure iron with a purity ≥ 99.5%; Ti is titanium metal with a purity ≥ 99%; the total content of rare earth elements in the mixed rare earth metal Mm is ≥ 99%, and Ce ≥ 40%. The above raw materials are cleaned and dried, weighed according to the calculated addition amount, placed in a non-consumable electric arc furnace, evacuated to 0.13Pa, then smelted under the protection of 0.05MPa argon, and solidified in a water-cooled mold cool down. In order to make the composition uniform, it needs to be smelted twice. Take out the alloy ingot and break it into small pieces and put it into the reactor (such as hydrogen storage, hydrogen fuel tank or other hydride container), then evacuate the reactor to 1.3Pa and then introduce hydrogen with a purity of ≥99.9% to a hydrogen pressure of 4.0MPa After an incubation period of several minutes to more than ten minutes, the alloy begins to absorb hydrogen, and after several hours to more than ten hours, the hydrogen absorption is saturated, and then it can be put into use. The PCT curves of the alloy at different temperatures are shown in Figure 2, which reflects the hydrogen storage properties of the alloy at various temperatures, such as the hydrogen storage capacity and the equilibrium pressure of hydrogen absorption and desorption. The actual measurement results show that the hydrogen storage capacity reaches 1.73wt% or 194ml/g.

Example 2:

Preferably, the chemical formula in the alloy of the present invention is Ti _1.2 Fe+3.0wt%Ca alloy. As in Example 1, the amount of addition of each metal was calculated according to the chemical formula. Among the raw materials, Fe and Ti are the same as in Example 1; Ca is block metal calcium with a purity of 99%. After cleaning and drying the raw materials, weigh them according to the amount added, place them in the graphite crucible of the vacuum induction furnace, and after evacuating to <0.13Pa vacuum, carry out melting under the protection of 0.05MPa argon gas, and pour into metal Cool the ingot mold to room temperature under vacuum and take it out. The first hydrogenation operation process of the alloy is the same as in Example 1. The alloy does not require special activation treatment, and it is easy to absorb hydrogen when it comes into contact with hydrogen for the first time. The saturated hydride formed is Ti _1.2 Fe(+3.0wt%Ca)H _2.0 , and the measured hydrogen storage capacity reaches 1.7wt% or 190ml/g.

Claims (1)

1. A titanium-iron-based hydrogen storage alloy, characterized in that: the chemical formula of the hydrogen storage alloy is Ti1 _+xFe +ywt%M, where 0<x<0.3;0<y<8; M is cerium-rich misch metal Mm or lanthanum-rich misch metal Ml, or one of metals such as La, Ce, Pr, Nd, Sm, Li, Mg and Ca.

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