Hydrogen separation filter

Abstract

To provide a hydrogen separation membrane having high hydrogen selectivity.SOLUTION: A hydrogen separation filter includes: a foil of a first metal; a lattice expansion layer formed on the foil and made of a second metal; and a hydrogen dissociation layer formed on the lattice expansion layer and made of a third metal. The first metal is selected from a group consisting of Pd, V, Ta, Nb and alloys thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a hydrogen separation filter. [Background technology]

[0002] A known method for purifying hydrogen is membrane separation using a metal membrane. Patent document 1 describes a hydrogen separation membrane obtained by forming a palladium-silver film on both sides of a pure palladium plate by sputtering. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-109146 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] There is a need for hydrogen separation membranes with higher hydrogen selectivity. This disclosure provides a hydrogen separation membrane with higher hydrogen selectivity. [Means for solving the problem]

[0005] The forms of this disclosure include the following: [Aspect 1] The first metal foil, A lattice expansion layer made of a second metal formed on the foil, A hydrogen dissociation layer made of a third metal is formed on the lattice expansion layer, Includes, The first metal is selected from the group consisting of Pd, V, Ta, Nb, and alloys thereof. The second metal is selected from the group consisting of Ag, Au, Al, Pt, and alloys thereof, and the third metal is Pd, or The second metal is selected from the group consisting of Nb, W, Mo, and alloys thereof, and the third metal is V, or The second metal is selected from the group consisting of Nb, W, Mo, V, and alloys thereof, and the third metal is Ta, or The second metal is selected from the group consisting of Mg, Y, Zr, Cd, Gd, Tb, Dy, Ho, Er, Hf, Sc, and alloys thereof, and the third metal is Ti, or A hydrogen separation filter in which the second metal is selected from the group consisting of Eu, Li, Na, K, Rb, Cs, Ba, and alloys thereof, and the third metal is Nb. [Aspect 2] The hydrogen separation filter according to embodiment 1, wherein the first metal is V. [Aspect 3] The hydrogen separation filter according to embodiment 1 or 2, wherein the third metal is Pd. [Aspect 4] A hydrogen separation filter according to any one of embodiments 1 to 3, wherein the second metal is Ag. [Aspect 5] Lattice constant a of a bulk metal having the same composition and crystal structure as the third metal described above. 3b The hydrogen separation filter according to any one of embodiments 1 to 4, wherein the lattice constant a3 of the third metal in the hydrogen dissociation layer, obtained from the interplanar spacing of crystal planes perpendicular to the interface between the lattice expansion layer and the hydrogen dissociation layer, satisfies the following formula (1). a 3b <a3(1) [Effects of the Invention]

[0006] The hydrogen separation membrane of this disclosure has high hydrogen selectivity. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic cross-sectional view of a hydrogen separation filter according to an embodiment. [Modes for carrying out the invention]

[0008] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, the same members or members having the same functions are denoted by the same reference numerals, and repeated descriptions may be omitted. For convenience of explanation, the dimensional ratios and shapes of each member in the drawings may be exaggerated and may be different from the actual dimensional ratios and shapes. In addition, in the present application, the numerical range represented by using the symbol "~" includes the numerical values described before and after the symbol "~" as the lower limit value and the upper limit value, respectively. The upper limit value and the lower limit value of the numerical range disclosed in the present application can be used alone or in any combination.

[0009] In the present application, "including ~" and "containing ~" mean that additional components may be included, and include "consisting of ~" and "essentially consisting of ~". "Essentially consisting of ~" means that additional components that do not substantially have an adverse effect may be included. "Consisting of ~" means including only the described materials, but does not exclude including inevitable impurities.

[0010] In the present application, "vertical" includes not only exact vertical but also substantial vertical, and "parallel" includes not only exact parallel but also substantial parallel. In addition, in the present application, "on ~" includes both "directly on ~" and "indirectly on ~" unless otherwise specified in the context.

[0011] The hydrogen separation filter 1 according to the embodiment shown in FIG. 1 includes a foil 20, a lattice expansion layer 40 formed on the foil 20, and a hydrogen dissociation layer 60 formed on the lattice expansion layer 40.

[0012] The hydrogen separation filter 1 shown in FIG. 1 selectively separates hydrogen as follows. On the surface 64 of the hydrogen dissociation layer 60, hydrogen molecules are dissociatively adsorbed to generate hydrogen atoms. The hydrogen atoms diffuse through the hydrogen dissociation layer 60, the lattice expansion layer 40, and the foil 20. On the surface 22 of the foil 20, the hydrogen atoms recombine to form hydrogen molecules and leave the hydrogen separation filter 1. In this way, the hydrogen separation filter 1 selectively separates hydrogen.

[0013] The foil 20 is a foil of a first metal. The first metal is a metal through which hydrogen can diffuse. Specifically, the first metal is selected from the group consisting of Pd, V, Ta, Nb, and alloys thereof. In particular, the first metal may be V. V is inexpensive and has a large hydrogen diffusion coefficient.

[0014] The lattice expansion layer 40 is made of a second metal. The hydrogen dissociation layer 60 is made of a third metal.

[0015] The third metal is selected from the group consisting of Pd, V, Ta, Ti, and Nb. In particular, the third metal may be Pd. Pd has particularly high hydrogen dissociation performance.

[0016] The second metal has the same crystal structure as the third metal. Also, the second metal in the lattice expansion layer 40 may have the same crystal orientation as the third metal in the hydrogen dissociation layer 60.

[0017] A bulk metal having the same composition and the same crystal structure as the second metal (hereinafter, appropriately referred to as "second bulk metal") has a lattice constant a 2b A bulk metal having the same composition and the same crystal structure as the third metal (hereinafter, appropriately referred to as "third bulk metal") has a lattice constant a 3b The lattice constant a 2b and the lattice constant a 3b may satisfy the following formula (2). 1.03a 3b ≦ a 2b ≦ 1.15a 3b (2)

[0018] In addition, when the second metal and the third metal have a crystal structure other than a cubic crystal structure, the lattice constants of the same crystal axes of the second bulk metal and the third bulk metal may satisfy formula (2). Here, the bulk metal means a self-standing metal in a completely relaxed state, that is, not supported by other members. By the second metal and the third metal having the same crystal structure and a composition satisfying formula (2), the lattice constant a3 of the third metal in the hydrogen dissociation layer 60 can be made larger than the lattice constant a 3b of the third bulk metal.

[0019] For example, if the third metal is Pd having a face-centered cubic (fcc) structure, the second metal may be selected from the group consisting of Ag, Al, Au, Pt, and their alloys, all of which have an fcc structure. In particular, the second metal may be Ag, which is relatively inexpensive and chemically stable. If the third metal is V having a body-centered cubic (bcc) structure, the second metal may be selected from the group consisting of Nb, W, Mo, and their alloys, all of which have a bcc structure. If the third metal is Ta having a bcc structure, the second metal may be selected from the group consisting of Nb, W, Mo, V, and their alloys, all of which have a bcc structure. If the third metal is Ti having a hexagonal close-packed (hcp) structure, the second metal may be selected from the group consisting of Mg, Y, Zr, Cd, Gd, Tb, Dy, Ho, Er, Hf, Sc, and their alloys, all of which have an hcp structure. If the third metal is Nb having a bcc structure, the second metal may be selected from the group consisting of Eu, Li, Na, K, Rb, Cs, Ba, and alloys thereof, all having a bcc structure. The lattice constants of these metals in their relaxed states are shown in Table 1.

[0020] [Table 1]

[0021] The lattice constant a3 of the third metal in the hydrogen dissociation layer 60 may satisfy the following equation (1). a 3b <a3(1)

[0022] The lattice constant a3 of the third metal may satisfy the following equation (3). 1.01a 3b ≤ a3 ≤ 1.05a 3b (3)

[0023] The lattice constant a3 of the third metal may satisfy the following equation (4). 1.02a 3b ≤ a3 ≤ 1.03a 3b (4)

[0024] Here, the lattice constant a3 of the third metal is determined from the interplanar spacing of crystal planes perpendicular to the interface 62 between the lattice expansion layer 40 and the hydrogen dissociation layer 60. Specifically, an electron diffraction pattern of the third metal is obtained using a transmission electron microscope (TEM), the interplanar spacing of crystal planes perpendicular to the interface 62 between the lattice expansion layer 40 and the hydrogen dissociation layer 60 is determined based on the electron diffraction pattern, and the lattice constant a3 of the third metal is determined using the value of the interplanar spacing. Equation (1) above indicates that the crystal lattice of the third metal in the hydrogen dissociation layer 60 is expanded at least in a direction parallel to the interface 62 compared to a completely relaxed state. The crystal lattice of the third metal in the hydrogen dissociation layer 60 may also be expanded in a direction perpendicular to the interface 62. Due to the expansion of the crystal lattice in the hydrogen dissociation layer 60, the hydrogen diffusion coefficient of the hydrogen dissociation layer 60 becomes larger. As a result, the hydrogen separation filter 1 can have high hydrogen selectivity. For example, if the third metal is Pd, the Pd crystal lattice expands, changing the hydrogen diffusion pathway from octahedral sites to tetrahedral sites, which in turn makes it easier for hydrogen to diffuse due to quantum effects of the atomic nucleus.

[0025] An example of a manufacturing method for the hydrogen separation filter 1 according to this embodiment will be described. First, the surface of the foil 20 is cleaned by ion etching. Next, a second metal is deposited on the foil 20 by sputtering to form a lattice expansion layer 40. Next, a third metal is deposited on the lattice expansion layer 40 to form a hydrogen dissociation layer 60. In this way, the hydrogen separation filter 1 according to this embodiment is obtained.

[0026] The present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Examples]

[0027] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0028] (1) Fabrication of a hydrogen separation filter Example 1 A 0.1 mm thick vanadium foil (V foil) was placed in the deposition chamber of a sputtering apparatus equipped with a pure Ag target and a pure Pd target. The surface of the V foil was cleaned by Ar ion etching. An Ag layer was formed on the V foil by sputtering. Next, a Pd layer was formed on the Ag layer by sputtering. In this way, a hydrogen separation filter (hereinafter simply referred to as "filter") was fabricated.

[0029] Comparative Example 1 A 0.1 mm thick V-foil was placed in the deposition chamber of a sputtering apparatus equipped with an AgPd alloy target. The surface of the V-foil was cleaned by Ar ion etching. An AgPd alloy layer was formed on the V-foil by sputtering. A filter was thus fabricated.

[0030] (2) Measurement of lattice constant The electron diffraction pattern of the Pd layer of the filter in Example 1 was obtained using a TEM. Based on the electron diffraction pattern, the interplanar spacing of the crystal planes perpendicular to the interface between the Pd layer and the Ag layer was determined. The lattice constant of the Pd layer was calculated using this interplanar spacing value. Lattice constant a pd The lattice constant a of fully relaxed Pd is pdb This was approximately 1.026 times (0.38898 nm).

[0031] (3) Evaluation of hydrogen separation performance In accordance with JIS K7126:2006 (Plastics and sheets - Gas permeability test methods - Part 1: Differential pressure method), the hydrogen gas permeability and nitrogen gas permeability (unit: mol·m³) of the filters of Example 1 and Comparative Example 1 were determined by gas chromatography. -2 ·s -1 ·Pa -1 The following measurements were taken: The ratio of hydrogen gas permeability to nitrogen gas permeability of the filter in Example 1 (i.e., hydrogen gas permeability / nitrogen gas permeability; hereinafter simply referred to as the "permeability ratio") was 12 times that of the filter in Comparative Example 1. This demonstrated that the filter in Example 1 could separate hydrogen with significantly higher selectivity than the filter in Comparative Example 1. [Explanation of Symbols]

[0032] 1: Hydrogen separation filter, 20: Foil, 40: Lattice expansion layer, 60: Hydrogen dissociation layer, 62: Interface between the lattice expansion layer and the hydrogen dissociation layer, 64: Surface of the hydrogen dissociation layer

Claims

1. The first metal foil, A lattice expansion layer made of a second metal formed on the foil, A hydrogen dissociation layer made of a third metal is formed directly on the lattice expansion layer, Includes, The first metal is selected from the group consisting of Pd, V, Ta, Nb, and alloys thereof. The second metal is selected from the group consisting of Ag, Au, Al, Pt, and alloys thereof, and the third metal is Pd, or The second metal is selected from the group consisting of Nb, W, Mo, and alloys thereof, and the third metal is V, or The second metal is selected from the group consisting of Nb, W, Mo, V, and alloys thereof, and the third metal is Ta, or The second metal is selected from the group consisting of Mg, Y, Zr, Cd, Gd, Tb, Dy, Ho, Er, Hf, Sc, and alloys thereof, and the third metal is Ti, or the second metal is selected from the group consisting of Eu, Li, Na, K, Rb, Cs, Ba, and alloys thereof, and the third metal is Nb. The lattice constant a3b of a bulk metal having the same composition and crystal structure as the third metal, and the lattice constant a3 of the third metal in the hydrogen dissociation layer, wherein the lattice constant a3 obtained from the interplanar spacing of crystal planes perpendicular to the interface between the lattice expansion layer and the hydrogen dissociation layer, are given by the following formula (1): a 3b <a 3 (1) A hydrogen separation filter that satisfies the requirements.

2. The hydrogen separation filter according to claim 1, wherein the first metal is V.

3. The hydrogen separation filter according to claim 1, wherein the third metal is Pd.

4. The hydrogen separation filter according to claim 1, wherein the second metal is Ag.

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