Hydrogen absorption and release method

Abstract

To provide a hydrogen storage alloy capable of increasing the effective hydrogen storage capacity within a hydrogen pressure range from 0.1 MPa(abs) to 1.1 MPa(abs) inclusive, and a hydrogen storage method and a hydrogen release method using the alloy.SOLUTION: A hydrogen storage alloy absorbs hydrogen at a temperature of 40°C or less and a hydrogen pressure of 1.1 MPa (abs) or less, and releases hydrogen at a temperature of 50°C or more and a hydrogen pressure from 0.1 MPa (abs) to 1.1 MPa (abs) inclusive. The hydrogen storage alloy has a composition represented by the general formula TiFexMnyNbz (0.761≤x≤0.837, 0.101≤y≤0.205, and 0.008≤z≤0.091).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a hydrogen storage alloy and a hydrogen storage using the same. Release method Thereof.

Background Art

[0002] When hydrogen is utilized for carbon dioxide reduction, it is conceivable to store hydrogen in various forms such as liquid hydrogen and high-pressure gas. As one means of storing hydrogen, a hydrogen storage alloy that can take in hydrogen and store hydrogen at a volume density higher than that of liquid hydrogen can be mentioned. A method of safely storing hydrogen using a hydrogen storage alloy has been considered and adopted in various places for a long time. As a hydrogen storage alloy, for example, a titanium-iron-vanadium hydrogen storage ternary alloy is known (see, for example, Patent Document 1). In addition, Patent Documents 2 and 3 describe a titanium-based hydrogen storage alloy represented by the general formula Ti 1+k Fe 1-l Mn l A m (where 0 ≦ k ≦ 0.3, 0 < l ≦ 0.3, 0 < m ≦  0.1, and A is an element composed of at least one of niobium and rare earth elements).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the hydrogen storage ternary alloy described in Patent Document 1 does not have a sufficient effective hydrogen storage capacity to absorb and release hydrogen within the hydrogen pressure range of 0.1 MPa (abs) to 1.1 MPa (abs), and a hydrogen storage alloy with a higher effective hydrogen storage capacity has been desired. Note that abs refers to absolute pressure. Patent Document 2 also includes an example in which Ti 1.1 Fe 0.8 Mn 0.2 Nb 0.05 and TiFe 0.8 Mn 0.2 Nb 0.05 However, Patent Document 3 does not disclose an example in which Fe, Mn, and Nb are combined to form a hydrogen storage alloy of approximately 1 mol. Furthermore, Patent Document 3 does not disclose an example in which a hydrogen storage alloy containing Nb is used.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a hydrogen storage alloy that can increase the effective hydrogen storage capacity within a hydrogen pressure range of 0.1 MPa (abs) or more and 1.1 MPa (abs) or less, and a hydrogen storage method and a hydrogen release method using the same. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a hydrogen storage alloy that stores hydrogen at a temperature of 40°C or less and a hydrogen pressure of 1.1 MPa (abs) or less, and releases hydrogen at a temperature of 50°C or more and a hydrogen pressure of 0.1 MPa (abs) to 1.1 MPa (abs), and has the general formula TiFe x Mn y Nb z It is characterized by having a composition expressed by (0.761≦x≦0.837, 0.101≦y≦0.205, 0.008≦z≦0.091).

[0007] According to the hydrogen storage alloy of the present invention, by containing a very small amount of Nb, the effective hydrogen storage capacity can be improved compared to hydrogen storage alloys that do not contain Nb, both in summer and outside of summer, within the hydrogen pressure range of 0.1 MPa (abs) or more and 1.1 MPa (abs) or less. [Effects of the Invention]

[0008] According to the present invention, the effective hydrogen storage capacity can be increased within the hydrogen pressure range of 0.1 MPa (abs) to 1.1 MPa (abs). [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of the hydrogen storage alloy of Example 1. FIG. [Figure 2] 1 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of the hydrogen storage alloy of Example 2. FIG. [Figure 3] FIG. 10 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of the hydrogen storage alloy of Example 3. [Figure 4] FIG. 10 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of the hydrogen storage alloy of Example 4. [Figure 5] FIG. 10 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of the hydrogen storage alloy of Example 5. [Figure 6] FIG. 10 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of the hydrogen storage alloy of Example 6. [Figure 7] FIG. 1 is a graph showing PCT characteristics (hydrogen absorption and desorption characteristics) of a hydrogen storage alloy of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a hydrogen storage alloy according to an embodiment of the present invention and a hydrogen storage method and a hydrogen release method using the same will be described. It should be noted that the present embodiment is specifically described to allow a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0011] [Hydrogen storage alloy] The hydrogen storage alloy according to this embodiment is a hydrogen storage alloy that absorbs hydrogen at a temperature of 40°C or less and a hydrogen pressure of 1.1 MPa (abs) or less, and desorbs hydrogen at a temperature of 50°C or more and a hydrogen pressure of 0.1 MPa (abs) or more and 1.1 MPa (abs) or less, and has the general formula TiFe x Mn y Nb z The hydrogen storage alloy according to this embodiment has a composition expressed as (0.761≦x≦0.837, 0.101≦y≦0.205, 0.008≦z≦0.091). In other words, the hydrogen storage alloy according to this embodiment is a quaternary alloy consisting of titanium (Ti), iron (Fe), manganese (Mn), and niobium (Nb). In the hydrogen storage alloy according to this embodiment, when the number of titanium atoms is taken as 1, the ratio of the number of iron atoms to the number of titanium atoms is 0.761 or more and 0.837 or less, the ratio of the number of manganese atoms is 0.101 or more and 0.205 or less, and the ratio of the number of niobium atoms is 0.008 or more and 0.091 or less. Furthermore, when the number of titanium atoms is taken as 1, the hydrogen storage alloy according to this embodiment preferably has the ratio of the number of iron atoms to the number of titanium atoms of 0.779 or more and 0.828 or less, the ratio of the number of manganese atoms of 0.159 or more and 0.170 or less, and the ratio of the number of niobium atoms of 0.008 or more and 0.037 or less.

[0012] TiFe x Mn y Nb z In quaternary alloys, as the ratio of the number of manganese atoms approaches 0 or the ratio of the number of iron atoms approaches 1, TiFe x Mn y Nb z The initial activation of the quaternary alloy becomes difficult. Also, as the ratio of the number of iron atoms decreases and the ratio of the number of manganese atoms increases, TiFe x Mn y Nb z The hydrogen storage and release pressures of the quaternary alloy are reduced.

[0013] When the ratio of the number of niobium atoms to the number of titanium atoms is less than 0.008, the effect of increasing the effective hydrogen storage capacity is hardly observed. When the ratio of the number of niobium atoms to the number of titanium atoms is more than 0.091, the number of undissolved niobium atoms increases, and TiFex Mn y Nb z A niobium-rich phase is formed in the quaternary alloy, which deviates from the composition of the intermetallic compound required for hydrogen storage, and therefore the effect of increasing the niobium atoms cannot be expected.

[0014] The hydrogen storage alloy according to this embodiment can store hydrogen at temperatures of 40°C or less and hydrogen pressures of 1.1 MPa (abs) or less. At temperatures of 40°C or less, the alloy temperature can be controlled throughout the year by heat exchange with the outside air. At hydrogen pressures of 1.1 MPa (abs) or less, the alloy is exempt from the High-Pressure Gas Safety Act.

[0015] The hydrogen storage alloy according to this embodiment can release hydrogen at a temperature of 50°C or higher and a hydrogen pressure of 0.1 MPa (abs) to 1.1 MPa (abs). At temperatures of 50°C or higher, the hydrogen storage alloy can be heated by the thermal output from a fuel cell, and the temperature of the alloy can be controlled by the fuel cell to which it is applied. At hydrogen pressures of 0.1 MPa (abs) to 1.1 MPa (abs), the alloy is exempt from the High Pressure Gas Safety Act.

[0016] According to the hydrogen storage alloy of this embodiment, the effective hydrogen storage capacity can be increased within the hydrogen pressure range of 0.1 MPa (abs) to 1 MPa (abs).

[0017] The method for producing the hydrogen storage alloy according to this embodiment is not particularly limited, and the following method, for example, can be used. Alloy raw materials such as titanium, iron, manganese, and niobium are heated and melted in an arc melting furnace or a high-frequency melting furnace to produce a molten alloy so that the desired composition of the hydrogen storage alloy is achieved. The molten alloy is then poured into a mold and cooled naturally or in a water-cooled copper mold to produce an alloy ingot. The alloy ingot is then heat-treated as desired. The heat-treated alloy ingot is then coarsely crushed and then finely crushed.

[0018] [Hydrogen absorption method] In the hydrogen storage method according to this embodiment, hydrogen is stored using the hydrogen storage alloy of the above embodiment at a temperature of 40° C. or less and a hydrogen pressure of 1.1 MPa (abs) or less.

[0019] According to the hydrogen absorption method of this embodiment, hydrogen can be absorbed at a temperature of 40° C. or less and a hydrogen pressure of 1.1 MPa (abs) or less, which can be controlled by heat exchange with the outside air in summer.

[0020] [Hydrogen release method] In the hydrogen releasing method according to this embodiment, the hydrogen storage alloy of the above embodiment is used to release hydrogen at a temperature of 50° C. or higher and a hydrogen pressure of 0.1 MPa (abs) to 1.1 MPa (abs).

[0021] According to the hydrogen releasing method of this embodiment, hydrogen can be released at a temperature of 50° C. or higher and a hydrogen pressure of 0.1 MPa (abs) to 1.1 MPa (abs), which can be controlled by a fuel cell. [Example]

[0022] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. It should be noted that Examples 1, 2, and 5 are reference examples.

[0023] [Example 1] Atomic ratio of TiFe 0.794 Mn 0.190 Nb 0.009 The raw material metals were melted by high-frequency melting to obtain an alloy ingot having the composition shown in Table 1. Specifically, the raw material metals were heat-treated in an argon atmosphere at a temperature of 1000°C to 1200°C for 24 hours to 96 hours to obtain the alloy ingot. The alloy ingot was then coarsely crushed and further finely crushed to produce TiFe alloys with an average particle size of 0.5 mm. 0.794 Mn 0.190 Nb 0.009 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis using an energy dispersive X-ray spectrometer (EDS, product name: OCTANE-PRO, manufactured by Ametec Co., Ltd. (Edax Division)). The elemental analysis of the hydrogen storage alloy was carried out five times by changing the measurement position (field of view), and the average value was calculated. The results are shown in Table 1. As shown in Table 1, TiFe 0.794 Mn 0.190 Nb 0.190 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were evaluated in accordance with JIS H7201:2007, "Method for measuring pressure-composition isotherms (PCT curves) of hydrogen storage alloys." The hydrogen temperature during hydrogen absorption was set to 20°C, a temperature that can be controlled by heat exchange with outside air in non-summer, and 40°C, a temperature that can be controlled by heat exchange with outside air in summer. The hydrogen temperature during hydrogen desorption was set to 50°C, a temperature that can be controlled by a fuel cell. The hydrogen pressure during hydrogen absorption and desorption was set to 0.1 MPa (abs) or more and 1.1 MPa (abs) or less. The results are shown in Figure 1.

[0024] [Table 1]

[0025] [Example 2] Atomic ratio of TiFe 0.793 Mn 0.183 Nb 0.018 The same procedure as in Example 1 was repeated except that the composition was changed to 0.793 Mn 0.183 Nb 0.018 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis in the same manner as in Example 1. The results are shown in Table 2. As shown in Table 2, TiFe 0.793 Mn 0.183 Nb 0.018 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were also evaluated. The results are shown in Figure 2.

[0026] [Table 2]

[0027] [Example 3] Atomic ratio of TiFe 0.809 Mn 0.166 Nb 0.036 The same procedure as in Example 1 was repeated except that the composition was changed to 0.809 Mn 0.166 Nb 0.036 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis in the same manner as in Example 1. The results are shown in Table 3. As shown in Table 3, TiFe 0.809 Mn 0.166 Nb 0.036 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were also evaluated. The results are shown in Figure 3.

[0028] [Table 3]

[0029] [Example 4] Atomic ratio of TiFe 0.821 Mn 0.141 Nb 0.054 The same procedure as in Example 1 was repeated except that the composition was changed to 0.821 Mn 0.141 Nb 0.054 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis in the same manner as in Example 1. The results are shown in Table 4. As shown in Table 4, TiFe 0.821 Mn 0.141 Nb 0.054 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were also evaluated. The results are shown in Figure 4.

[0030] [Table 4]

[0031] [Example 5] Atomic ratio of TiFe 0.785 Mn 0.124 Nb 0.070 The same procedure as in Example 1 was repeated except that the composition was changed to 0.785 Mn 0.124 Nb 0.070 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis in the same manner as in Example 1. The results are shown in Table 5. As shown in Table 5, TiFe 0.785 Mn 0.124 Nb 0.070 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were also evaluated. The results are shown in Figure 5.

[0032] [Table 5]

[0033] [Example 6] Atomic ratio of TiFe 0.822 Mn 0.104 Nb 0.081 The same procedure as in Example 1 was repeated except that the composition was changed to 0.822 Mn 0.104 Nb 0.081 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis in the same manner as in Example 1. The results are shown in Table 6. As shown in Table 6, TiFe 0.822 Mn 0.104 Nb 0.081 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were also evaluated. The results are shown in Figure 6.

[0034] [Table 6]

[0035] [Comparative Example] Atomic ratio of TiFe 0.804 Mn 0.218 The same procedure as in Example 1 was repeated except that the composition was changed to 0.804 Mn 0.218 A hydrogen storage alloy having the composition shown below was obtained. The obtained hydrogen storage alloy was subjected to elemental analysis in the same manner as in Example 1. The results are shown in Table 7. As shown in Table 7, TiFe 0.804 Mn 0.218 It was confirmed that this was obtained. The PCT characteristics (hydrogen absorption and desorption characteristics) of the obtained hydrogen storage alloy were also evaluated. The results are shown in Figure 7.

[0036] [Table 7]

[0037] The results shown in Figures 1 to 7 are summarized in Tables 8 and 9. Table 8 shows the hydrogen absorption rates (storage rates) of the hydrogen storage alloys of Examples 1 to 6 and the Comparative Example, assuming a time other than summer. Table 9 shows the hydrogen absorption rates (storage rates) of the hydrogen storage alloys of Examples 1 to 6 and the Comparative Example, assuming a time other than summer. The hydrogen absorption rates (storage rates) are shown in "H / M," which is the number of hydrogen atoms per metal atom (Nb, Mn, Fe, Ti in Examples 1 to 6, and Mn, Fe, Ti in the Comparative Example). Under the High Pressure Gas Safety Act, it is desirable to operate the hydrogen storage alloys so that the pressure does not exceed 1.1 MPa (abs), which is the limit for high pressure gas applications. However, in actual operation, it is necessary to operate the hydrogen storage alloys so that the pressure does not exceed 1 MPa (abs) in consideration of the safety factor. Therefore, the hydrogen absorption rate (storage rate) of the hydrogen storage alloys of Examples 1 to 6 and the Comparative Example was evaluated at hydrogen pressures up to 1 MPa (abs). Hydrogen can be absorbed up to 1 MPa (abs) on the absorption curves at 20°C and 40°C, but heating (from the absorption curve on line α (the line perpendicular to the horizontal axis) in the figure to the desorption curve at 50°C) makes it unusable if the pressure exceeds 1 MPa (abs). Therefore, if the 1 MPa (abs) line on the vertical axis is extended horizontally and hydrogen absorption at 20°C and hydrogen desorption at 50°C are assumed in a non-summer environment, the upper limit of usability is the point where it first intersects with the absorption curve at 20°C or the desorption curve at 50°C (the point where it intersects with line α in the figure). Furthermore, if the 1 MPa (abs) line is extended horizontally and hydrogen absorption at 40°C and hydrogen desorption at 50°C are assumed in summer, the upper limit of usability is the point where it first intersects with the absorption curve at 40°C or the desorption curve at 50°C (the point where it intersects with line β (the line perpendicular to the horizontal axis) in the figure). On the other hand, since there is no problem with starting hydrogen absorption at pressures below 0.1 MPa (abs), the lower limit of usable hydrogen release is the 0.1 MPa (abs) point on the release curve at a temperature of 50°C (the point where it intersects with line segment γ (the line segment perpendicular to the horizontal axis) in the figure). Note that 0.1 MPa (abs), the lower limit of hydrogen pressure during hydrogen release, is atmospheric pressure. Therefore, in the case of assuming a season other than summer and in the case of assuming summer, the usable portion of the hydrogen storage alloy is between the respective upper and lower usable limits.

[0038] [Table 8]

[0039] [Table 9]

[0040] From the results in Table 8, it was confirmed that, assuming seasons other than summer, the hydrogen storage alloys of Examples 1 to 6 had hydrogen storage capacities that were 13.7% or more higher than the hydrogen storage alloy of the comparative example. From the results in Table 9, it was confirmed that, assuming summer, the hydrogen storage rate of the hydrogen storage alloys of Examples 1 to 6 was 12.1% or more higher than that of the hydrogen storage alloy of the comparative example. From the above results, it was found that the hydrogen storage alloys of Examples 1 to 6, which contain a very small amount of Nb, have a higher hydrogen storage rate than the hydrogen storage alloy of the comparative example, which does not contain Nb, both in summer and outside of summer.

Claims

[Claim 1] a step of absorbing hydrogen using a hydrogen storage alloy at a temperature of 40°C or less and a hydrogen pressure of 1.1 MPa (abs) or less; and releasing hydrogen using the hydrogen storage alloy at a temperature of 50°C or higher and a hydrogen pressure of 0.1 MPa (abs) to 1.1 MPa (abs), The hydrogen storage alloy absorbs hydrogen at a temperature of 40° C. or less and a hydrogen pressure of 1.1 MPa (abs) or less, and releases hydrogen at a temperature of 50° C. or more and a hydrogen pressure of 0.1 MPa (abs) to 1.1 MPa (abs), and has the general formula TiFe ｘ Mn ｙ Nb ｚ A method for absorbing and releasing hydrogen, characterized in that the composition is expressed by (0.809≦x≦0.822, 0.104≦y≦0.166, 0.036≦z≦0.081).

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