JP5468432B2 - Method for producing thin film on metal powder sintered porous substrate - Google Patents

Description

  The present invention relates to a method for producing a thin film on a metal porous substrate, and more particularly to a production method applicable as a dense film forming method on a porous substrate for functional thin films including fuel cell members in general.

  In recent years, fuel cells have attracted attention as a clean energy source capable of high energy conversion and friendly to the global environment. The principle is to extract the energy of hydrogen and oxygen directly in the form of electrical energy not by fuel reaction but by electrochemical reaction. A fuel cell uses an ion conductive electrolyte membrane as an electrolyte. Porous electrodes are attached to both sides of the electrolyte membrane, and fuel gas such as hydrogen or hydrocarbon is supplied to one electrode (fuel electrode) using this electrolyte membrane as a partition. At the same time, air or oxygen gas is supplied to the other electrode (air electrode), and there are several types depending on the electrolyte membrane used and the operating temperature.

  At present, research and development of polymer fuel cells (PEFC) as fuel cells are mainly underway. However, since it has an operating temperature of about 100 ° C. and Pt which is a noble metal as an electrode catalyst, it is a fuel cell. This is a major limitation of cost reduction. If the operating temperature of the fuel cell can be increased to 200 ° C. or higher, an inexpensive material such as Fe or Ni can be used as an electrode catalyst, and the practical application of the fuel cell can be greatly promoted.

  On the other hand, in a solid oxide fuel cell (SOFC) whose operating temperature is as high as 800 to 1000 ° C., it is necessary to use a ceramic material for an electrode or the like, which is problematic in terms of cost and mechanical strength. Therefore, development of a fuel cell that operates in an intermediate temperature range of about 200 to 600 ° C. that can use an inexpensive metal material such as Fe or Ni, which is advantageous in terms of cost and mechanical strength, is demanded.

  A fuel cell using an oxide having proton conductivity as an electrolyte has been proposed as a fuel cell operating in an intermediate temperature range to solve such problems. However, the electrical conductivity of the proton conductor electrolyte is still not sufficient, and there is a problem that the power generation loss is large. In order to increase the power generation output density, it is important to improve the electrical conductivity of the electrolyte itself or to reduce the membrane resistance as much as possible by reducing the thickness of the electrolyte. However, since the electrolyte uses bulk ceramic, Conductivity is difficult.

  In addition, when the electrolyte itself is made thin (1 μm or less), the electrolyte needs to have an area of a certain size or more in order to ensure the function as a battery. Therefore, the member including the electrolyte membrane is broken by its own weight. No mechanical strength is required. Therefore, when a thin film having no strength is used as the electrolyte, a method of forming an electrolyte membrane on a support having mechanical strength is employed. For example, as disclosed in Japanese Patent Application Laid-Open No. 2006-253071 (Patent Document 1), a structure in which an electrolyte is thinned using a porous fuel electrode (ceramic) as a support, or Japanese Patent Application Laid-Open No. 2007-200663 (Patent). As disclosed in the literature 2), the porous fuel electrode (ceramic) is used as a support and the electrolyte is made into a thin film, or as disclosed in Japanese Patent Application Laid-Open No. 2004-273343 (patent document 3). There has been proposed a fuel cell system including a catalyst for causing a reaction with endotherm using a hydrocarbon compound on the anode side.

However, these have secured the strength by increasing the thickness of the ceramic material part of the anode or cathode as a support, and are resistant to mechanical properties, cost, electrical conductivity, and heat shock due to starting and stopping, and durable. There was a problem of being inferior. On the other hand, when a porous metal body having excellent mechanical properties, cost, and electrical conductivity is used as a support and an electrolyte membrane is formed thereon, the porous body is added to add the function of the electrolyte as a partition wall. It is necessary to form a dense film with no pinholes on it. However, although there is an example as described above for disposing a thin film on a ceramic support, a metal porous body has a larger pore diameter than a ceramic porous body. It was necessary to increase the film thickness, and it was difficult to achieve a thin film aimed by the present invention.
JP 2006-253071 A JP 2007-200633 A JP 2004-273343 A

  As described above, in order to improve the power generation output density of the fuel cell operating in the middle temperature range, it is important to improve the electrical conductivity of the electrolyte itself or reduce the membrane resistance as much as possible by reducing the thickness of the electrolyte. However, since the electrolyte uses bulk ceramic, it is difficult to increase the conductivity of the electrolyte itself, and there is a big problem in practical use and general use.

  In order to solve the above-described problems, the present inventors have intensively developed, and as a result, after the oxide thin film is formed by the polishing process and the CVD method and / or the PVD method according to the present invention, By implementing the liquid phase method, it becomes possible to more effectively seal or improve voids, defects, irregularities, etc. that remain without being completely sealed by the CVD method. The present invention provides a method for producing an intermediate temperature fuel cell having excellent power generation characteristics by enabling the formation of a high-quality and dense thin film.

The gist of the invention is that
(1) A metal characterized by forming a thin oxide film on a polished surface of a sintered metal powder porous substrate by a CVD method and / or a PVD method, and subsequently forming a film by a liquid phase method A method for producing a thin film on a powder sintered porous substrate.
(2) A method for producing a thin film on a metal powder sintered porous substrate, wherein the liquid phase method described in (1) is a MOD method or a sol-gel method.

( 3 ) A metal powder sintered porous body characterized by adding a catalyst to a material to be deposited by any of the CVD method, liquid phase method, and PVD method described in (1) or (2) above A method for producing a thin film on a substrate.
( 4 ) A method for producing a thin film on a metal powder sintered porous substrate, wherein the method for producing a thin film according to any one of (1) to ( 3 ) is used for a fuel cell member.

  As described above, by performing the liquid phase method after the polishing process and the CVD method or PVD method according to the present invention, vacancies, defects, irregularities, etc. remaining without being completely sealed by the CVD method or PVD method, etc. Can be more effectively sealed or improved, and by forming a high-quality and dense thin film on the porous substrate, it is possible to improve the power generation characteristics of the fuel cell and further to the CVD method. In comparison, the application of the PVD method or the liquid phase method, which has a simple apparatus structure and a high film formation rate, has an extremely excellent effect of reducing the total film formation cost.

Hereinafter, the present invention will be described in detail.
In a fuel cell in which a cathode material is disposed between an anode and an electrolyte according to the present invention, and if necessary, an electrolyte and a support, the support is made of a sintered metal porous body, and particularly a stainless steel spherical material produced by a gas atomization method. The sintered metal porous body formed by sintering powder has both good high temperature corrosion resistance by stainless steel, good air permeability by gas atomized spherical powder and good mechanical properties due to high sintering density, and machining It is most suitable as a sintered compact base material for smoothing the surface by cold working or the like.

  A film is formed on the surface of the sintered metal porous body, the surface of which is smoothed by machining or cold working. A film is formed on the metal sintered porous body smoothed in this way by chemical vapor deposition (CVD) / or PVD. After film formation, defects such as vacancies existing in the film formed on the porous metal substrate are sealed by the liquid phase method, and uniform film formation becomes possible. Therefore, a film without defects such as pinholes and cracks can be obtained. Further, the application of the liquid phase method or the PVD method makes it possible to increase the overall film forming speed, thereby enabling cost reduction.

The CVD film forming method is as follows. As an example, a method for forming a Y-doped SrZrO ₃ (SZYO) oxide will be described. Sr (METHD) ₂ , Zr (METHD) ₄ , and Y (EDMDD) ₃ were used as Sr, Zr, and Y as film forming materials (METHD = C ₁₄ H ₂₅ O ₄ , EMDDD = C ₁₄ H ₂₅ O ₂ ligand). Each raw material was dissolved in an organic solvent (ethylcyclohexane: hereinafter referred to as ECH) so that the raw materials of Sr and Zr were 0.1 mol / L and the Y raw material was 0.01 mol / L. The supply amount of each raw material was controlled by a liquid mass flow controller. For example, the total flow rate of the raw material was set to 0.7 g / min and introduced into the raw material vaporizer. In the apparatus of the configuration according to the present invention, the mist-vaporization method was introduced for the material vaporization.

  The raw material solution is mist (mist) once by an ultrasonic vibrator, and vaporized without contacting the heater with a heated carrier gas. The specific surface area of the raw material solution is greatly increased by the mist formation. Therefore, the vaporization efficiency can be greatly improved. In this case, for example, nitrogen was used as the carrier gas, the flow rate was set to 300 sccm, and the temperature of the raw material vaporizer was set to 280 ° C. The pressure in the raw material vaporizer was about 23 Torr. The raw material thus vaporized is mixed with the reaction gas (oxygen) and then introduced into the deposition substrate. The oxygen supply amount at that time was set to 1000 sccm, for example. In addition, the film formation was carried out at a substrate temperature of 600 ° C., the film formation time was set to 30 minutes, and an SZYO oxide thin film of about 200 nm was obtained on the support.

  In addition, after film formation by the CVD method, defects such as vacancies existing in the CVD film formed on the metal porous substrate by the liquid phase method are sealed to enable uniform film formation. However, it is preferable to apply the MOD method or the sol-gel method as the liquid phase method. The MOD method uses, as a raw material, a MOD (Metal Organic Deposition) solution obtained by diluting an organic molecule containing a metal element such as an organometallic acid salt with an organic solvent. This is a method of obtaining a predetermined oxide thin film by coating the surface, and then heating, drying, pyrolyzing, and baking the coated material.

  The sol-gel method uses a sol-gel solution prepared by diluting a gel body obtained by hydrolyzing a metal alkoxide with an organic solvent to a viscosity suitable for coating as a raw material. The sol-gel method is spin-on or dipped like a MOD solution. In this method, the surface of the substrate is coated by a method or the like, and then the coating is heated, dried, pyrolyzed, and fired to obtain a predetermined oxide thin film. The film barrier properties of the film thus obtained were confirmed.

  FIG. 1 is a diagram showing an outline of a gas barrier property test apparatus for confirming the denseness of a film formation substrate. Using the apparatus shown in FIG. 1, He gas is flowed from the He tank 1 to the film formation surface 2 and the substrate 3 at a pressure of 0.2 MPa, gas detection is performed by cupoflex at the atmospheric outlet 4, and 0.1 MPa of He gas The presence or absence of gas permeability due to the differential pressure is confirmed. Reference numeral 5 denotes a pressure gauge. As a result of this confirmation, it was determined that the densified film had been formed without pinholes or cracks and had gas barrier properties, and other than that, it was determined that the densification was insufficient.

FIG. 2 is a schematic diagram of an example of a thin film fuel cell. As shown in FIG. 2, on a smoothed stainless porous body 6, if necessary, a catalyst 7, for example, a LaSrMnO ₃ (LSM) powder widely used as a cathode material for a solid oxide fuel cell is used. Is supported, applied, or formed into a film. An electrolyte film 8 made of a dense oxide thin film is formed on the smooth surface of the porous body 6, and an anode film 9 is formed on the electrolyte film 8. In this way, by arranging all the members excluding the porous body as a thin film, the conductivity calculated by the product of the conductivity and the thickness can be increased regardless of the conductivity of the material. The specific resistance is reduced, leading to an improvement in output characteristics as a fuel cell.

Further, a catalyst is added to a material to be deposited by any one of the CVD method, the liquid phase method, and the PVD method. As described above, LaSrMnO ₃ (LSM) powder, (La, Sr) (Co, Fe) O ₃ (LSCF) powder or the like is used as the catalyst, and this is used as a raw material for a solid electrolyte, such as a MOD liquid or a sol-gel liquid. By adding and applying to sinter, a region where the solid electrolyte and the catalyst are mixed can be formed. Further, by increasing the amount of LSM or LSCF to be added, conductivity can be expressed, and the solid electrolyte / catalyst mixed region can be used as an electrode as it is.

Hereinafter, the present invention will be specifically described by way of examples.
As a support, stainless steel (SUS316L) gas atomized powder was prepared (average particle size 12 μm), poured into a predetermined mold, heated at a sintering temperature of 1050 ° C., and a sintered porous body of φ25 × 1 mm was produced. Was subjected to wet emery polishing and buff polishing to prepare a smooth metal sintered porous body smoothed to a roughness Ra = 0.1 μm. Thereafter, a solid electrolyte (SZYO) having a thickness of about 0.4 mm was formed using a CVD method, and then about 0.15 mm of SZYO was deposited using a liquid phase method to seal the remaining vacancies, defects and irregularities. Furthermore, the same liquid phase process was repeated, and the case where 0.15 mm of double was deposited was also examined.

  As a comparative material, an unsmoothed stainless steel powder sintered porous body and a commercially available alumina porous support (φ25 mm × 1 mm, average pore diameter 0.5 μm) were prepared as sintered. On each substrate, SZYO, which is a proton conductive oxide, was formed as a solid electrolyte by a CVD method. Film formation was performed by a liquid supply MOCVD method, and film formation was performed at a film formation temperature of 600 ° C. for 30 minutes, and a 250 nm thin film was formed on a smooth porous body to produce a fuel cell. The film formation state has a film as a target concept based on a microphotograph, and has a fuel cell structure with a thin film arrangement. The obtained porous film was confirmed for gas barrier properties. The results are shown in Table 1.

表１に示すように、ＣＶＤ法による成膜直後では未平滑のステンレス鋼粉末焼結多孔体並びにルミナ製多孔質支持体に比べ、平滑化したステンレス鋼粉末焼結多孔体がより高いガスバリア性を持つことがわかる。しかし、この場合においても燃料電池として実用化するにはガスバリア性が不十分なため、この上にＳＺＹＯを液相法により成膜を行った。１回の液相法による堆積は約０．１５ｍｍであったが、ガスバリア性が改善されていることがわかる。さらに液相法による堆積を繰り返することにより、ガスバリア性が改善していることがわかる。

As shown in Table 1, the smoothed stainless steel powder sintered porous body has a higher gas barrier property immediately after film formation by the CVD method than the smooth stainless steel powder sintered porous body and Lumina porous support. I understand that I have it. However, even in this case, since the gas barrier property is insufficient for practical use as a fuel cell, a film of SZYO was formed thereon by a liquid phase method. Deposition by one liquid phase method was about 0.15 mm, but it can be seen that the gas barrier property is improved. Further, it can be seen that the gas barrier property is improved by repeating the deposition by the liquid phase method.

一般にＣＶＤ法の成膜速度は遅く０．４ｍｍのＳＺＹＯ薄膜の堆積には５〜６時間必要とするが、液相法によれば数十分程度であり、電解質膜の形成には液相法の使用が望ましい。しかし、液相法で形成する場合、多孔質体の空孔に原料液が多量にしみ込んでしまい、良好な薄膜の形成が困難である。また、表２に示すように、ＣＶＤに比べガスバリア性が良くないという問題がある。そこで、本発明によればＣＶＤ法で全ての電解質膜を形成するのではなく、液相法を併用することで成膜時間の大幅な短縮を図ることができるとともに、良好なガスバリア性を持つ薄膜を形成することができる。

In general, the deposition rate of the CVD method is slow, and it takes 5 to 6 hours to deposit a 0.4 mm SZYO thin film. However, according to the liquid phase method, it is about several tens of minutes. Is desirable. However, in the case of forming by a liquid phase method, a large amount of the raw material liquid penetrates into the pores of the porous body, and it is difficult to form a good thin film. Further, as shown in Table 2, there is a problem that gas barrier properties are not good as compared with CVD. Therefore, according to the present invention, not all the electrolyte membranes are formed by the CVD method, but the film formation time can be greatly shortened by using the liquid phase method together, and a thin film having good gas barrier properties. Can be formed.

In this embodiment, the CVD method is used for forming the electrolyte, and the film formation is performed by the liquid phase method. However, instead of the CVD method, a sputtering method or an AD (aerosol deposition) method with a high film formation rate can be used. The PVD method may be used, and even in this case, an improvement in gas barrier properties can be expected by film formation by an additional liquid phase method. Actually, when the gas barrier property of the solid electrolyte membrane formed on the stainless steel powder sintered porous body by the AD method was examined, the pressure reduction time was about 19 minutes despite the thick film thickness of about 40 mm. In order to reduce the operating temperature of the fuel cell, it is necessary to make the solid electrolyte membrane 1 mm or less, but it is difficult to develop a good gas barrier property only by the AD method. Therefore, it is considered that the present invention in which additional film formation is performed by the liquid phase method and sealing is performed effectively also in the AD method.

As described above, by carrying out the liquid phase method after the polishing process and the CVD method or PVD method according to the present invention, vacancies, defects, irregularities remaining without being completely sealed by the CVD method or PVD method. Etc. can be more effectively sealed or improved, and a high-quality and dense thin film can be formed on the porous substrate, thereby improving the power generation characteristics of the fuel cell, and the CVD method. Compared with, the application of the liquid phase method or PVD method, which has a simpler structure and faster film formation speed, is capable of reducing the total film formation cost. It becomes possible to provide a method for producing a thin film on a metal powder sintered porous substrate capable of improving desired functionality required for a member.

It is a figure which shows the outline of the gas barrier property test apparatus for confirming the denseness of the film-forming board | substrate. It is a schematic diagram of an example of a thin film fuel cell.

DESCRIPTION OF SYMBOLS 1 He tank 2 Film-forming surface 3 Porous board | substrate 4 Gas outlet 5 Pressure gauge 6 Stainless steel porous body 7 Catalyst 8 Electrolyte film | membrane consisting of oxide thin film 9 Anode film


Patent applicant Sanyo Special Steel Co., Ltd. and 1 other
Attorney: Attorney Shiina

Claims (4)

A metal powder characterized by depositing an oxide thin film on a polished surface of a sintered metal powder porous substrate by a CVD method and / or a PVD method and then depositing the oxide thin film on the surface by a liquid phase method A method for producing a thin film on a sintered porous substrate. A method for producing a thin film on a metal powder sintered porous substrate, wherein the liquid phase method according to claim 1 is a MOD method or a sol-gel method. A method for producing a thin film on a metal powder sintered porous substrate, comprising adding a catalyst to a material to be deposited by any one of the CVD method, liquid phase method, and PVD method according to claim 1 . A method for producing a thin film on a metal powder sintered porous substrate, wherein the method for producing a thin film according to any one of claims 1 to 3 is used for a fuel cell member.

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