JP2009185308A - HYDROGEN SEPARATING THIN FILM BY SIMULTANEOUS PLATING OF Pd-Ag, AND ITS MANUFACTURING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen separating thin film, wherein palladium and silver are uniformly film-deposited so as to have a predetermined composition by the electroless plating on a surface of a non-conductive base material, and rapidly alloyed by heating at ≤600°C when manufacturing a dense palladium-silver alloy film which is used for the hydrogen separating thin film. <P>SOLUTION: A method is provided for film-depositing palladium and silver at the predetermined composition ratio uniformly in the depth direction by controlling the deposition rate of both elements by continuously adding silver-containing aqueous solution at the predetermined flow rate in a process of performing the plating by immersing a porous base material with seed cores stuck thereto in a plating bath containing palladium and silver. The hydrogen separating thin film is manufactured by the method. A method is also provided for manufacturing the alloy film of palladium and silver to be used for the hydrogen separating film wherein palladium and silver are uniformly deposited on the surface of the non-conductive base material so as to have a predetermined composition by the electroless plating. The hydrogen separating thin film is manufactured by the method. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a hydrogen separation thin film made of a palladium / silver alloy for allowing hydrogen to pass through quickly and selectively to separate hydrogen efficiently, and palladium (Pd) and silver (Ag) by electroless plating. In particular, the present invention relates to a method for producing a thin film for hydrogen separation by uniformly depositing Pd and an Ag-containing plating solution at a constant rate. By controlling the deposition and uniformly electrolessly plating Pd and Ag, originally, Pd and Ag having different deposition rates due to the difference in oxidation-reduction potential are simultaneously deposited while maintaining a constant composition ratio. The present invention relates to a method for producing a thin film for hydrogen separation, and a thin film for hydrogen separation produced by the method. The present invention simply provides an alloy thin film having a uniform Pd / Ag composition in a short time by mild heating while maintaining the composition ratio of Pd and Ag having different deposition rates depending on the oxidation-reduction potential. Is.

  Securing hydrogen as a clean energy source is an extremely important issue from the perspective of responding to the coming “hydrogen society”. Among the hydrogen separation technologies, the membrane separation technology is expected as an excellent separation method that can continuously separate hydrogen by using the hydrogen partial pressure inside and outside the membrane as a driving force and that consumes less energy. The most important technical problem in the hydrogen membrane separation method is to provide a separation membrane material that selectively permeates hydrogen in a large amount and has excellent durability. From this point of view, various hydrogen permselective membranes have been developed with the aim of high-efficiency separation of hydrogen.

  Among these, the palladium thin film, in particular, has excellent hydrogen selective permeability and high hydrogen permeation amount per unit area due to a unique permeation mechanism in which hydrogen molecules dissociate atomically and permeate through a dense membrane. Has been the focus of attention. However, while the palladium thin film has excellent transmission performance, it has a critical temperature. Below the critical pressure, the transition of the crystal phase from the α phase to the β phase occurs, and as a result, defects and pinholes are liable to occur, so the operating temperature and the hydrogen pressure range in hydrogen separation have been limited.

  Such hydrogen embrittlement due to the phase transition is alleviated by alloying with palladium and other metals, especially silver, improving the mechanical strength and increasing the hydrogen permeation rate. Thus, various methods for producing alloy films of palladium and other metals that have achieved high transmittance and long life have been studied (see Non-Patent Document 1).

  Among various metal thin film formation methods, the electroless plating method can be performed under mild conditions, does not require special equipment, does not require an external power supply, does not choose the size and shape of the sample, and at one time It is a simple method with excellent features such as being capable of plating a large number of samples, and it can be plated on non-conductive materials such as plastics and ceramics. Is actively used (see Non-Patent Document 2).

  When plating a non-conductive material, it is necessary to plant a metal seed nucleus in advance on the surface of the substrate. However, in electroless plating, since palladium exhibits catalytic activity for the oxidation reaction of the reducing agent, Palladium is frequently used as the core metal. As a method of forming a composite film of palladium and silver by electroless plating, the surface of the substrate on which palladium seed nuclei are deposited is first plated with palladium, and further silver is deposited by electrolytic plating to form an alloy. There is.

  That is, after plating palladium on the surface of the substrate, the plating solution is changed to a solution containing silver, silver is deposited by ordinary electrolytic plating, and finally the deposited Pd and Ag layers are alloyed by heat treatment. There is known a method of converting to a non-patent document 3 (for example, see Non-Patent Document 3). However, this method is complicated in operation and has two layers of metal, so that atomic diffusion between different metals is slow, and an alloy thin film having a uniform composition is formed at a high temperature of 800 ° C. or more for a long time. Need.

  Therefore, by simultaneously plating two kinds of metals to form a thin film in which both metals are mixed and deposited, atomic diffusion between the metals becomes easy, and a uniform alloy film can be formed in a short time under mild heat treatment conditions. It is considered possible. Under such assumptions, a method of simultaneously electrolessly plating palladium and silver by changing the mixing ratio of metal ions in the plating solution and controlling the type and concentration of the chelating reagent for stabilization has been attempted. (For example, refer nonpatent literatures 4 and 5.). In addition, a method for forming a silver alloy film is known in which a metal nobler than silver is precipitated by displacement plating from a mixed aqueous solution of silver and Pd or Pt, Au, and Rh (see Patent Document 1).

  However, since these conventional methods are plated using a mixed solution of palladium and silver, there is a problem that silver that is easily reduced is preferentially precipitated. From this, 1) metal of the deposited film It is difficult to accurately control the composition, 2) composition unevenness is likely to occur, 3) when the silver concentration is high, silver preferentially forms a plating film, and the progress of plating is hindered, etc. As a result, it is not easy to obtain an alloy film having a uniform composition. In particular, since silver is likely to precipitate preferentially, palladium having a catalytic effect for promoting plating is easily concealed, and as a result, formation of a plating film is hindered. Thus, the conventional method can be used to form a plating film with controlled deposition so that palladium and silver have a precisely uniform composition ratio in the depth (thickness) direction of the film. The fact was that it was not.

JP 2000-212763 A S. N. Pagliieri, J. et al. D. Way, Separation and Purification Methods, 31, p. 20, p. 2002 Edited by Glenn Mallory, Juan Hajdu, Electroplating, American Surface Treatment Association, 421, 1990 K. Hou, R.A. Hughes, J. et al. Membrane Science, 214, 43, 2003 Y. S. Cheng, K.M. L. Yeung, J. et al. Membrane Science, 158, 127, 1999 J. et al. Shu, B .; P. A. Grandjean, E .; Ghali, S .; Kaliaguine, J. et al. MembraneScience, 77, 181, 1993

  Under such circumstances, the present inventors have developed a new hydrogen separation thin film and a method for producing the same, which are capable of solving the problems of the conventional methods in view of the prior art. As a result of intensive research as a target, in the method of producing an alloy thin film of palladium and silver by electroless plating, the deposition rate of both elements is controlled by gradually supplying silver that is easy to precipitate, thereby reducing the depth of the film. The present inventors have succeeded in forming a uniform plating film of palladium and silver having a constant composition ratio in the thickness (thickness) direction, and completed the present invention.

  The present invention relates to an alloy film of palladium and silver used as a thin film for hydrogen separation, in which palladium and silver are uniformly deposited with a constant composition on the surface of a non-conductive substrate by electroless plating. The object is to provide a thin film for separation. In addition, the present invention controls the deposition rate of both elements by adding a silver-containing aqueous solution continuously to a plating bath containing palladium and silver at a constant flow rate and gradually supplying silver that is easy to precipitate. The object of the present invention is to provide a method for producing a uniform plating film of palladium and silver having a constant composition ratio with respect to the depth direction (relative thickness) of the film.

The present invention for solving the above-described problems comprises the following technical means.
(1) A hydrogen separation thin film comprising a plating film prepared by simultaneously depositing palladium and silver on the surface of a porous support by electroless plating, wherein the composition ratio of both elements of palladium and silver in the film is A thin film for hydrogen separation characterized by maintaining a constant ratio with respect to the thickness direction (relative thickness) of the plating film.
(2) The thin film for hydrogen separation according to (1), wherein the composition ratio of palladium to silver in the plating film maintains a constant ratio within a range of ± 20% with palladium.
(3) The thin film for hydrogen separation according to (1) or (2), wherein the ratio of palladium to silver in the plating film is in the range of 1 to 30% by weight.
(4) The thin film for hydrogen separation according to any one of (1) to (3), wherein a thickness of the plating film is 0.1 μm or more and 10 μm or less.
(5) The thin film for hydrogen separation according to any one of (1) to (4), wherein the plating film is alloyed by heat treatment after film formation.
(6) A method for producing a thin film for hydrogen separation comprising a plating film in which palladium and silver are simultaneously deposited by electroless plating on the surface of a porous support, comprising a chelating reagent that stabilizes palladium and silver Into the initial plating solution containing palladium and silver, a solution containing silver is continuously injected at a predetermined rate, and both elements are constant in the thickness direction (relative thickness) of the plating film. A method for producing a thin film for hydrogen separation, characterized by depositing simultaneously while maintaining a composition ratio.
(7) The method for producing a thin film for hydrogen separation according to (6), wherein the solution containing silver contains a chelating reagent.
(8) The solution containing silver is continuously injected at a rate such that the composition ratio of palladium to silver in the plating film is a constant ratio within a range of ± 20% with palladium. A method for producing a thin film for hydrogen separation as described in 6) or (7).
(9) The hydrogen separation thin film according to any one of (6) to (8), wherein a hydrogen separation thin film having a ratio of palladium to silver in the plating film in the range of 1 to 30% by weight is produced. Manufacturing method.
(10) The method for producing a hydrogen separation thin film according to any one of (6) to (9), wherein a hydrogen separation thin film having a thickness of the plating film of 0.1 μm to 10 μm is produced.
(11) The method for producing a thin film for hydrogen separation according to any one of (6) to (10), wherein the plating film is alloyed by heat treatment at an alloying temperature of 600 ° C. or less after the film formation.
(12) The method for producing a thin film for hydrogen separation according to any one of (6) to (11), wherein the total concentration of palladium and silver used as the initial plating solution is in the range of 2 mM to 20 mM.
(13) The method for producing a thin film for hydrogen separation according to any one of (6) to (12), wherein the concentration of silver to be continuously injected and added is in the range of 1 mM to 10 mM.
(14) From the above (6) to (13), the addition rate of the solution containing silver to be continuously injected and added per 100 cm ^{2 of the} plated coating area is 0.2 to 1.0 ml per minute. The method for producing a thin film for hydrogen separation according to any one of the above.
(15) From the above (6), the amount of silver up to one third of the total amount of silver injected into the initial plating solution is coexisted with palladium, and the remaining amount of silver is continuously injected and added. The method for producing a thin film for hydrogen separation as described in any one of 14).

Next, the present invention will be described in more detail.
The present invention is a hydrogen separation thin film comprising a plating film prepared by simultaneously depositing palladium and silver on the surface of a porous support by electroless plating, the composition ratio of both elements of palladium and silver in the film Is characterized by maintaining a constant ratio with respect to the thickness direction (relative thickness) of the plating film. In the present invention, the composition ratio of palladium to silver in the plating film is maintained at a constant ratio within a range of ± 20% with palladium, and the ratio of palladium to silver in the plating film is 1 to 30. It is a preferred embodiment that it is in the range of% by weight and the thickness of the plating film is 0.1 μm or more and 10 μm or less.

  Furthermore, the present invention is a method for producing a hydrogen separation thin film comprising a plating film in which palladium and silver are simultaneously deposited by electroless plating on the surface of a porous support, and stabilizes palladium and silver and these. A silver-containing solution is continuously injected at a predetermined rate into a palladium / silver mixed initial plating solution containing a chelating reagent, and both elements are in the thickness direction (relative thickness) of the plating film. In addition, it is characterized in that precipitation is performed simultaneously while maintaining a constant composition ratio.

  The above-mentioned problem of the present invention is to prepare two solutions of palladium and silver-containing plating aqueous solution and silver-containing silver-containing plating aqueous solution in the method of performing electroless plating, and to add palladium and silver-containing plating aqueous solution to a certain concentration of silver It was found that the solution can be solved by continuously adding and supplying the aqueous solution at a predetermined flow rate. That is, in the present invention, a palladium seed nucleus is activated on the surface of a porous support (porous substrate) having an appropriate shape such as a tube or a plate, and then a complexing agent and a reducing agent are added. The deposition rate of palladium and silver is controlled by performing electroless plating while continuously injecting a silver-containing solution containing a complexing agent at a predetermined flow rate into the mixed plating aqueous solution of palladium and silver. It is important to deposit both elements at a uniform composition ratio.

  In the method of the present invention, the porous material of the porous support used as the base material for forming the film is not particularly limited as long as it is a porous material, but from the viewpoint of heat resistance, preferably a ceramic or a metal is used. . Examples of ceramics include alumina, silica, zirconia, and oxide ceramics such as zirconia stabilized by the addition of yttria or ceria. Examples of the metal include porous stainless steel and alloys. Examples of the form of the porous substrate include a tube shape and a plate shape, and these are used as a support for a hydrogen permeable membrane or a reaction membrane.

  In plating on non-conductive materials such as ceramics, palladium that is both conductive and catalytic is indispensable as a seed nucleus. When plating palladium and silver simultaneously, it is important to deposit and distribute fine seed nuclei of metallic palladium uniformly. This is achieved by a known method (for example, see Non-Patent Document 2) in which the palladium complex is uniformly held on the surface of the porous substrate and then reduced using, for example, tin chloride or hydrazine.

  In the method of the present invention, first, extremely fine seed nuclei made of metallic palladium, usually 20 nanometers or less, are uniformly deposited and distributed on the surface of the non-conductive porous substrate. For this purpose, it is preferable to use a method in which the palladium complex is uniformly held on the surface of the non-conductive porous substrate and then reduced. As a method for retaining the palladium complex on the surface of the base material, after impregnating or adsorbing palladium on a nonconductive porous base material, preferably a nonconductive porous ceramic base material such as alumina, A method of drying is preferred.

Preferred examples of the palladium compound in the palladium-containing solution include palladium acetate, palladium chloride, [PdCl ₄ ] ²⁻ , [Pd (acac) ₂ ] (acac = acetylacetonate ion). The solvent is not particularly limited as long as it easily dissolves the palladium compound, but in the case of complex ions having a charge such as [PdCl ₄ ] ²⁻ , a polar solvent such as water, , [Pd (acac) ₂ ], and neutral complexes such as palladium acetate include organic solvents such as acetonitrile and chloroform.

  The concentration of the palladium complex is preferably in the range of 0.1 to 5% by mass in terms of palladium. After immersing the ceramic base material in the palladium complex solution, the ceramic base material is taken out and dried, whereby the solvent is evaporated and removed, and the palladium complex is held on the substrate.

  The reducing method is not particularly limited, but as the reducing agent, it is preferable to use an aqueous solution of a compound having an aldehyde group such as glucose or formic acid, a borohydride compound, or hydrazine. Hydrazine is particularly advantageous in that it has a strong reducing power and the reaction product is only nitrogen and can be excluded from the system.

  In this way, by holding the palladium complex on the porous substrate and repeating the reduction treatment, very fine palladium fine particles uniformly distributed on the surface of the non-conductive porous substrate are formed as seed nuclei. . In order to generate a uniform and high-density seed nucleus, it is desirable to repeat this operation at least twice. In the present invention, the fact that the composition ratio of both elements of palladium and silver maintains a constant ratio with respect to the depth (thickness) direction (relative thickness) of the film is completely in the depth direction of the film. It does not mean that it is constant, but it means that a substantially constant ratio is maintained.

  In the method of the present invention, the porous substrate obtained by uniformly distributing the very fine seed nuclei thus obtained on the surface is immersed in a mixed plating solution of palladium and silver containing a complexing agent, Electroless plating is performed while adding the silver-containing solution at a predetermined rate. The silver content to be precipitated is controlled by the silver concentration and the addition rate. This mixed plating solution usually contains a palladium salt, a silver salt, a complexing agent that dissolves them stably, and a reducing agent.

  Examples of the palladium salt used in the mixed plating solution include palladium acetate, palladium chloride, palladium sulfate and the like, and examples of the silver salt include silver nitrate, silver sulfate and silver acetate. As a complexing agent, a combination of ammonia and a chelating agent, particularly a combination of ammonia and EDTA is preferable. Examples of chelating agents include EDTA, NTA (nitrilotriacetic acid), and aliphatic oxyacids such as citric acid and tartaric acid.

  The palladium concentration in the plating solution is usually 0.002 to 0.02M, preferably 0.05 to 0.01M. Silver is usually used in a proportion of 1 to 30% by weight, preferably 5 to 25% by weight with respect to palladium, and up to one third of this amount is mixed with a palladium solution to form an initial plating solution, The remaining two thirds are used for the silver solution that is continuously supplied during the plating process.

The total concentration of palladium and silver used as the initial plating solution is usually 0.002 to 0.02M. The complexing agent is usually selected to have a concentration of EDTA of 0.05 to 0.1 M and ammonia of 5 to 10 M, and the solvent is usually water. Pd ²⁺ and Ag ⁺ have different redox potentials, so the easiness of precipitation of both elements differs. However, by continuously supplying a silver solution during the plating process, the deposition amount ratio of both metals is kept constant. It is possible to achieve uniform simultaneous plating.

  The temperature of the plating solution at the time of electroless plating is usually in the range of room temperature to 90 ° C., but 40 to 80 from the viewpoint of maintaining a reaction rate of a certain level and reducing ammonia transpiration and chemical decomposition. The range of 50 ° C to 70 ° C is preferable. Although the plating time depends on the plating solution temperature and film thickness, 90% palladium and silver in the plating solution are deposited in 3 to 5 hours, and both are almost quantitatively deposited in 5 to 8 hours. During the plating operation, it is desirable to sufficiently stir in order to prevent unevenness in the concentration of the plating solution.

When the solution containing silver is continuously injected into the palladium / silver mixed plating solution, it is preferably performed at a substantially constant rate. Specifically, the addition rate of the silver solution to be added per 100 cm ^{2 of} the plated coating area is usually 0.001 to 0.02M, preferably 0.005 to 0.01M. It is preferably 0.2 to 1.0 ml per minute.

  Thereby, palladium and silver can be made to precipitate by a fixed composition ratio by supplementing the silver component consumed by precipitation. Further, in order to stabilize the plating solution, the solution containing silver used for injection is preferably stabilized by a chelating reagent. By performing film formation under the above conditions, a plated film in which palladium and silver are uniformly deposited with a constant composition can be produced.

  The plating film obtained by uniformly depositing palladium and silver obtained by the present invention in a uniform composition is precipitating by mixing both elements in advance, so that alloying is rapid, and in a known method, for example, in an electric furnace Alloying is easily achieved by heating at about 600 ° C., and a hydrogen separation membrane made of a palladium / silver alloy having a uniform composition ratio in the depth (thickness) direction of the membrane is obtained. In order to perform alloying under such mild heat treatment conditions, it is preferable that the change in the composition ratio of palladium in the hydrogen separation membrane in the film thickness direction is within a range of ± 20%.

  The thickness of the hydrogen separation membrane is preferably 0.1 to 10 μm. If the thickness of the hydrogen separation membrane is less than 0.1 μm, defects may easily occur in the hydrogen separation membrane, and if it exceeds 10 μm, the hydrogen permeation rate through the hydrogen separation membrane decreases and the separation efficiency decreases. Sometimes. The ratio of palladium to silver is preferably in the range of 1 to 30% by weight. By setting it as such a composition range, hydrogen embrittlement can be suppressed, suppressing the fall of a hydrogen permeation rate.

  In the method of the present invention, a non-conductive porous ceramic base material is impregnated with a palladium complex solution and dried. After the palladium complex is uniformly held on the surface of the base material, the base material is reduced and the base material is reduced. The palladium seed nuclei are uniformly deposited and distributed on the surface of the substrate, and then immersed in a mixed plating solution of palladium and silver containing ammonia and EDTA as a complexing agent. Electroless plating is preferably performed while adding at a constant flow rate. As the reducing agent used in this case, for example, hydrazine is preferable.

  The characteristics of the electroless plating process in the method of the present invention are 1) using a mixed plating solution of palladium and silver as an initial plating solution, and 2) continuously adding a silver solution in the plating process. As the initial plating solution, it is preferable to use a complexing agent in which a mixed solution of palladium and silver, ammonia and EDTA are combined. At this time, the total concentration of palladium and silver used as the plating solution is preferably in the range of 2 mM to 20 mM. Further, it is preferable to use twice as much silver as the initial plating solution as the amount of silver to be added.

Furthermore, when the content ratio of palladium salt (Pd / Ag) is 10 to 100% by weight and the silver content ratio is 10% or more, the ammonia concentration is 4M and the EDTA concentration is 0.1M or more. It is preferable that it is 4-10M and EDTA density | concentration is 0.1-0.2M. The concentration of silver to be added is preferably 0.01M or more. In the plating process, the addition rate of silver to be added is preferably 0.1 to 1.0 ml per minute when the plating area is 100 cm ² .

  Conventionally, it is known that a plating film is formed using a mixed solution of palladium and silver. However, since silver forms a plating film preferentially, the metal composition of the plating film can be accurately controlled. It was difficult, and compositional irregularities were likely to occur, and it was difficult to produce a plating film having a uniform composition. On the other hand, the present invention continuously adds and supplies a silver-containing plating solution at a constant rate to an initial plating solution containing palladium and silver, thereby providing palladium and silver at a constant composition ratio. Thus, it is possible to form a plating film by depositing uniformly, thereby producing and providing a thin film for hydrogen separation that can be suitably used as a thin film for hydrogen separation.

The present invention has the following effects.
(1) According to the method of the present invention, a composite film in which palladium and silver are uniformly deposited with a constant composition in the depth (thickness) direction of the film by electroless plating is formed on the surface of the porous substrate. Can do.
(2) The composite film is a process in which a porous base material is immersed in a mixed plating solution of palladium and silver, and in the process of plating, the concentration of the complexing agent and the reducing agent is controlled, and the aqueous silver solution is continuously supplied at a constant flow rate. It can produce by adding.
(3) According to the present invention, a thin film having a substantially uniform Pd and Ag composition in the depth (thickness) direction of the film is formed, and a Pd / Ag alloy thin film for hydrogen separation having a substantially uniform composition by mild and short-time heat treatment Can be made and provided.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited at all by the following examples.

(Production Example 1)
As a membrane substrate, an α-alumina porous tube (inner diameter 8.5 mm, outer diameter 10 mm, porous portion 80 mm) was used, and the tube was immersed in 30 ml of a 0.6% chloroform solution of palladium acetate for 15 minutes. This was air-dried and then immersed in a 0.2M aqueous ammonia solution containing 2M hydrazine for 15 seconds to deposit palladium seed nuclei on the surface of the porous tube. The tube whose surface turned black due to the precipitation of fine palladium particles was washed with water and dried at 110 ° C. This operation was repeated 5 times.

(Production Example 2)
Yttria-stabilized zirconia (YSZ) (inner diameter: 10 mm, outer diameter: 11 mm, porous portion: 110 mm) was used as a membrane substrate, and the tube was immersed in 30 ml of a 0.6% chloroform solution of palladium acetate for 15 minutes. This was air-dried and then immersed in a 0.2M aqueous ammonia solution containing 2M hydrazine for 15 seconds to deposit palladium seed nuclei on the surface of the porous tube. The tube whose surface turned black due to the precipitation of fine palladium particles was washed with water and dried at 110 ° C. This operation was repeated 5 times.

In this example, a Pd ₂₀ Ag ₈₀ (weight ratio) film was formed by electroless plating using the alumina tube having an outer diameter of 10 mm described in Production Example 1 as a base material. As an initial plating solution, 160 ml of a solution containing 0.012 M palladium, 0.15 M EDTA, 4 M ammonia is mixed with 15 ml of a solution containing 0.01 M silver, 0.15 M EDTA, 5 M ammonia, After heating to ° C, 3.2 ml of 1M hydrazine was added, stirred well and warmed to 65 ° C.

  In this, the alumina tube provided with the palladium nuclide prepared in Production Example 1 was immersed, and after 40 minutes, a mixed solution of 0.01 M silver, 0.15 M EDTA, 5 M ammonia was added 0.16 ml per minute. The addition was continued for 4 hours at a flow rate. The total amount of silver solution added was 35 ml. A small amount of plating solution was sampled in a timely manner to measure the concentration of palladium and silver. When 38 ml (4 hours) of the silver mixed solution was added, the plating was finished, and the tube was taken out and washed thoroughly with water.

  As a result, a thin film containing palladium in a weight ratio of 80% and silver in a weight ratio of 20% was formed. FIG. 1 shows the deposition ratio / plating time of palladium and silver. It is recognized that both elements are deposited at a constant composition ratio as time passes. FIG. 2 shows the precipitation ratios of palladium and silver in the depth (relative thickness) direction of the film. ○ represents palladium, and ● represents silver. It can be seen that the concentration distribution of palladium and silver in the depth direction of the film is fairly constant by the continuous injection method according to the present invention. FIG. 3 shows an electron micrograph of the tube cross section and a state in which both elements are uniformly distributed according to the distribution state of palladium and silver.

In this example, a film of Pd ₈₄ Ag _{16 was formed} using yttria-stabilized zirconia (YSZ) having an outer diameter of 10 mm described in Production Example 2 as a base material. Initial plating solution obtained by mixing 250 ml of a solution containing 0.012M palladium, 0.15M EDTA, 4M ammonia, and 15 mM hydrazine with 22 ml of a solution containing 0.01M silver, 0.15M EDTA, and 5M ammonia. The mixture was warmed to 60 ° C. and 4.5 ml of 1M hydrazine was added. Into this, the YSZ tube provided with the palladium nuclide prepared in Production Example 2 was immersed, and after 30 minutes, a mixed solution of 0.01 M silver, 15 M EDTA, and 5 M ammonia was added at a flow rate of 0.17 ml per minute. For 4 hours continuously.

  The total amount of silver solution added was 40 ml. A small amount of plating solution was sampled in a timely manner to measure the concentration of palladium and silver. When 40 ml (4 hours) of the silver mixed solution was added, the plating was finished, and the tube was taken out and washed thoroughly with water. As a result, a thin film containing 84% by weight of palladium and 16% by weight of silver was formed. FIG. 4 shows the precipitation ratios of palladium and silver in the film depth (relative thickness) direction. ○ represents palladium, and ● represents silver. It can be seen that the concentration distribution of palladium and silver in the depth direction of the film is fairly constant by the continuous injection method according to the present invention.

In this example, a film of Pd ₈₁ Ag ₁₉ (weight ratio) was formed by electroless plating using yttria-stabilized zirconia (YSZ) described in Production Example 2 as a base material. Stir the initial plating solution, which is a mixture of 0.012M palladium, 0.15M EDTA, 4M ammonia in 250ml and 0.01M silver, 0.15M EDTA, 5M ammonia in 22ml solution. The mixture was heated to 60 ° C. and 4.5 ml of 1M hydrazine was added. Into this, the tube provided with the palladium nuclide prepared in Production Example 1 was immersed, and after 30 minutes, a mixed solution of 0.01 M silver, 15 M EDTA, and 5 M ammonia was added at a flow rate of 0.2 ml per minute. Added continuously over time.

  The total amount of silver solution added was 60 ml. A small amount of plating solution was sampled in a timely manner to measure the concentration of palladium and silver. When 60 ml (5 hours) of the silver mixed solution was added, the plating was finished, and the tube was taken out and washed thoroughly with water. As a result, a thin film containing 72% by weight of palladium and 28% by weight of silver was formed. FIG. 5 shows the precipitation ratios of palladium and silver in the depth direction (relative thickness) of the film. ○ represents palladium, and ● represents silver.

The Pd ₈₀ Ag ₂₀ (weight ratio) -coated porous alumina tube produced by the electroless plating method described in Example 1 was heated at 600 ° C. in a hydrogen atmosphere to perform alloying. The alloying process was monitored by X-ray diffraction. The palladium and silver peaks observed before heating approached with heating for an hour and changed to a new diffraction peak for the alloy after 2 hours of heating. FIG. 6 shows an X-ray diffraction pattern. The solid line shows the diffraction peak before heating, the dotted line shows the diffraction peak after 1 hour, and the broken line shows the diffraction peak after 2 hours.

An yttria-stabilized zirconia (YSZ) tube coated with a Pd ₈₁ Ag ₁₉ film prepared by simultaneous electroless plating of Pd and Ag described in Example 3 above, and a hydrogen separation membrane obtained by heating and alloying this tube according to Example 4 The hydrogen permeation test was conducted using That is, a tube with one end closed was fixed to a cylinder having a gas inlet and an outlet and installed in an annular electric furnace. At 300 ° C., hydrogen was sent under pressure from the outside of the tube. The gas that permeated through the membrane was measured with a soap film flow meter while changing the hydrogen pressure. FIG. 7 shows the results of plotting the hydrogen permeation rate as the y-axis and the difference in gas pressure inside and outside the membrane as the x-axis.

(Comparative Example 1)
For comparison, the same alumina tube as in Example 1 was used as a base material, and both elements were coated from a mixed plating solution of palladium and silver without using the continuous addition method of the present invention. 206 ml of a plating solution containing 8 mM palladium, 2 mM silver, 4 M ammonia, 0.15 M EDTA, and 15 mM hydrazine was heated to 60 ° C., and the palladium nuclide prepared in Production Example 1 was given therein. The alumina tube was immersed and plated for 8 hours. Thereby, a thin film containing palladium in a weight ratio of 80% and silver in a weight ratio of 20% was formed. FIG. 8 shows the precipitation ratios of palladium and silver in the film depth (relative thickness) direction. ○ represents palladium, and ● represents silver. It can be seen that the composition of Pd and Ag in the depth direction of the film is not constant by not using the continuous addition method of the present invention.

  As described above in detail, the present invention relates to a thin film for hydrogen separation by simultaneous plating of Pd—Ag and a method for producing the same. According to the present invention, hydrogen can be rapidly and selectively permeated to form hydrogen. It is possible to provide a hydrogen separation thin film made of a palladium / silver alloy and a method for manufacturing the same. By the method of the present invention, a Pd / Ag-containing thin film for hydrogen separation having a constant Pd and Ag composition in the depth (relative thickness) direction of the membrane can be produced. The present invention relates to a hydrogen separation membrane comprising a composite membrane in which palladium and silver are deposited on the surface of a porous substrate by electroless plating with a constant composition in the depth (relative film thickness) direction of the membrane, and production thereof Useful as a method.

Example 1 shows the percentage of metal plated relative to the total amount of metal added when plating palladium and silver simultaneously. ○ represents palladium, and ● represents silver. The fraction of palladium and silver in the depth direction of the metal thin film formed by Example 1 is shown. ○ represents palladium, and ● represents silver. The electron micrograph of a tube cross section and the distribution state of palladium and silver by EDX analysis are shown. The fraction of palladium and silver in the depth direction of the metal thin film formed by Example 2 is shown. ○ represents palladium, and ● represents silver. The fraction of palladium and silver in the depth direction of the metal thin film formed by Example 3 is shown. ○ represents palladium, and ● represents silver. The X-ray-diffraction pattern of the thin film in the heating alloying process shown in Example 4 is shown. The solid line shows the diffraction peak before heating, the dotted line shows the diffraction peak after 1 hour, and the broken line shows the diffraction peak after 2 hours. Hydrogen permeation rate (▲) of the hydrogen separation membrane immediately after (before heating and alloying) produced by simultaneous electroless plating of Pd and Ag described in Example 3 and hydrogen of the hydrogen separation membrane heat-alloyed according to Example 4 Represents the transmission speed (●). The vertical axis represents the hydrogen permeation rate, and the horizontal axis represents the hydrogen differential pressure inside and outside the hydrogen separation membrane. The fraction of palladium and silver in the depth direction of the film of the thin film formed by the manufacturing method described in Comparative Example 1 is shown. ○ represents palladium, and ● represents silver.

Claims (15)

  A thin film for hydrogen separation comprising a plating film prepared by simultaneously depositing palladium and silver on the surface of a porous support by electroless plating, wherein the composition ratio of both elements of palladium and silver in the film is the plating film A thin film for hydrogen separation characterized by maintaining a constant ratio with respect to the thickness direction (relative thickness).   The thin film for hydrogen separation according to claim 1, wherein a composition ratio of palladium to silver in the plating film maintains a constant ratio within a range of ± 20% with palladium.   The thin film for hydrogen separation according to claim 1 or 2, wherein a ratio of palladium to silver in the plating film is in the range of 1 to 30% by weight.   The thin film for hydrogen separation according to any one of claims 1 to 3, wherein the plating film has a thickness of 0.1 µm or more and 10 µm or less.   The thin film for hydrogen separation according to any one of claims 1 to 4, wherein the plating film is alloyed by a heat treatment after the film formation.   A method for producing a thin film for hydrogen separation comprising a plating film in which palladium and silver are simultaneously deposited by electroless plating on the surface of a porous support, comprising palladium, silver and a chelating reagent that stabilizes the palladium, The silver-containing initial plating solution is continuously injected with a solution containing silver at a predetermined rate, so that both elements have a constant composition ratio in the thickness direction (relative thickness) of the plating film. A method for producing a thin film for hydrogen separation, wherein the film is deposited simultaneously while maintaining.   The method for producing a thin film for hydrogen separation according to claim 6, wherein the solution containing silver contains a chelating reagent.   The solution containing silver is continuously injected at a rate such that the composition ratio of palladium to silver in the plating film is a constant ratio within a range of ± 20% of palladium. A method for producing a thin film for hydrogen separation described in 1.   The method for producing a thin film for hydrogen separation according to any one of claims 6 to 8, wherein a hydrogen separation thin film having a ratio of palladium to silver in the plating film in the range of 1 to 30% by weight is produced.   The method for producing a hydrogen separation thin film according to any one of claims 6 to 9, wherein a hydrogen separation thin film having a thickness of the plating film of 0.1 µm to 10 µm is produced.   The method for producing a thin film for hydrogen separation according to any one of claims 6 to 10, wherein the plated film is alloyed by heat treatment at an alloying temperature of 600 ° C or lower after the film formation.   The method for producing a thin film for hydrogen separation according to any one of claims 6 to 11, wherein the total concentration of palladium and silver used as the initial plating solution is in the range of 2 mM to 20 mM.   The method for producing a thin film for hydrogen separation according to any one of claims 6 to 12, wherein the concentration of silver added by continuously injecting is in the range of 1 mM to 10 mM. The addition rate of the solution containing silver added by continuously injecting and adding per 100 cm ^{2 of the} plating coating area is 0.2 to 1.0 ml per minute. A method for producing a thin film for hydrogen separation described in 1.   The amount of silver up to 1/3 of the total amount of silver injected into the initial plating solution coexists with palladium, and the remaining amount of silver is continuously injected and added. A method for producing a thin film for hydrogen separation as described in the item.