JP2006054170A - Proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte, and electrochemical device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use a membrane even under an environment of mixed gas atmosphere containing CO<SB>2</SB>by overcoming fragility of AECeO<SB>3</SB>to CO<SB>2</SB>while maintaining proton conductivity of the AECeO<SB>3</SB>. <P>SOLUTION: This is composed of a composite membrane of a proton conductive oxide membrane 1 which has perovskite type oxide (ABO<SB>3</SB>) as the basic structure wherein barium (Ba) or strontium (Sr) is arranged at A site and rare-earth element cerium (Ce) at B site, and through which a proton (H+) is enabled to pass, and from which only hydrogen is separable in a gas 3 containing CO<SB>2</SB>, and a hydrogen permeable membrane 2 through which the proton (H+) is enabled to pass, and from which only hydrogen is separable in the gas 3 containing CO<SB>2</SB>. In a state that compound interfaces of these both membranes are continuously joined together, the hydrogen permeable membrane 2 is formed on the surface of at least the gas side of the proton conductive oxide membrane 1, and the composite membranes 1, 2 are furthermore supported by a porous support S. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte and an electrochemical device using the same. More specifically, the present invention relates to a method for avoiding fragility of a proton conductive oxide electrolyte in a gas containing CO ₂ .

In the Central Research Institute of Electric Power Company, the applicant of the present invention, four existing fuel cells (PAFC (phosphoric acid fuel cell), MCFC (molten carbonate fuel cell), SOFC (solid oxide fuel cell)) and PEFC have been developed so far. (Solid polymer fuel cells)) is being analyzed by the same evaluation method, and research on clarifying the generalized relationship between the output voltage and the operating temperature of the fuel cell continues. In addition, if a fuel cell that operates in the middle temperature range of about 250 to 500 ° C using a proton (H ⁺ ) transfer type electrolyte (that is, a proton that can move in the electrolyte) can be developed by researching such a fuel cell It has been shown that there is a possibility that the fuel cell is superior in terms of performance and material as compared with existing fuel cells (see Patent Document 1). The proton transfer electrolyte here may be a molten salt or an aqueous electrolyte. However, these electrolytes cannot be applied to fuel cells because they are chemically unstable in the middle temperature range of about 250 ° C to 500 ° C, or other ions may be involved in the electrode reaction. .

  On the other hand, as another specific example of the proton transfer electrolyte, for example, Patent Document 2 in which “a method for separating hydrogen from hydrocarbon reformed gas using a high-temperature proton conductor” is described in Proton Conductive Oxide (Proton conductive oxide solid electrolyte) is disclosed (see Patent Document 2). Since this oxide has a proton conductive function, this proton conductive oxide has a technology for electrochemically separating hydrogen in a gas (for example, natural gas reformed gas), and various electric It is considered or expected to be applied to technology related to chemical devices (see Patent Document 2).

As an example of the above proton conductive oxide solid electrolyte, there is an oxide AECeO ₃ (where AE is Ba or Sr) having a perovskite structure typified by SrCeO ₃ . As shown in FIG. 35, AECeO ₃ is known to exhibit good proton conductivity in a medium and high temperature region in a hydrogen stream and still exhibit high conductivity. For this reason, when these oxides are applied to an electrolyte of an electrochemical device (for example, a fuel cell, a hydrogen sensor, or a hydrogen pump) using only hydrogen, it is considered that high performance is exhibited.

For example, the proton-conducting SrCeO ₃ film 101 shown in FIG. 36 is provided in a gas flow path mixed with hydrogen, carbon dioxide, or the like, such as the reformed gas 102 in the figure, and functions as a hydrogen permeable film. In this case, an external voltage 106 is applied between the electrode 104 on the primary side (in this case, the reformed gas 102 side) and the electrode 105 on the secondary side (in this case, the hydrogen 103 side after separation). The applied voltage becomes the driving force (driving force) of proton H ⁺ . When such a proton conductive SrCeO ₃ membrane (hydrogen permeable membrane) 101 is used, it is possible to set and supply various secondary hydrogen pressures while fixing the primary pressure. There are advantages. In addition, since it is possible to pressurize while using the reformed gas 102 at normal pressure, there is an advantage that a boosting device for storing hydrogen and an installation space therefor are unnecessary.

JP 2004-119077 A JP 2003-2610 A

However, usually, the gas to be subjected to hydrogen separation (the reformed gas 102 in the above example) is almost always a mixed gas containing other gases such as CO ₂ . When an oxide (AECeO ₃ ) having a perovskite structure such as the SrCeO ₃ film 101 described above is applied to an electrolyte of an electrochemical device, a specific problem occurs.

That is, the oxide AECeO ₃ when exposed to an atmosphere containing CO ₂
AECeO ₃ + CO ₂ → AECO ₃ + CeO ₂
As such, it reacts with CO ₂ and easily decomposes. For this reason, as shown in Patent Document 1, for example, when this oxide AECeO ₃ is applied to an electrolyte of an electrochemical device (for example, a hydrogen pump) through which a gas containing CO ₂ flows, Patent Document 1 is used at the initial stage. Although the initial performance as described above is exhibited, there is a problem in that it cannot be used for a long time, that is, it is vulnerable to CO ₂ in such a mixed gas (for example, the first Summary of 27th Battery Discussion Meeting (3B10, p226-227)).

Accordingly, the present invention provides such prior art view of the problems had, while maintaining proton conductivity of AECeO _3, under a gas atmosphere containing CO ₂ to overcome the vulnerability to CO ₂ of the AECeO ₃ However, it is an object of the present invention to provide a proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte that can be used, and an electrochemical device using the same.

  In order to achieve this object, the present inventor conducted various studies and experiments. The process and outline of such examination and experiment will be described below.

First, the present inventor examined another conventional hydrogen separation method (see FIG. 37). A hydrogen permeable membrane (Pd metal membrane, etc., indicated by reference numeral 201 in the figure) used for hydrogen separation is a hybrid gas (in the figure, such as reformed gas) such as H ₂ (hydrogen) or CO ₂ (carbon dioxide). , Indicated by reference numeral 202), and can be transmitted in a state where hydrogen molecules are separated (that is, in the state of protons (H ⁺ ) and electrons (e ⁻ )). It is possible to separate hydrogen from the reformed gas (see FIG. 37, hydrogen after separation is indicated by reference numeral 203). The advantage of such a hydrogen separation method is that it does not require an amount of power for hydrogen separation. Therefore, the driving force (driving force) is only the hydrogen partial pressure difference. However, in order to perform efficient separation, a very high hydrogen partial pressure difference is required (that is, a high partial pressure difference is required between the pressure High P _H2 and the pressure Low P _H2 shown in FIG. 37). Accordingly, the pressure on the primary side (reformed gas side) and the secondary side (separated hydrogen side) are fixed in accordance with the target hydrogen pressure, so a storage booster is required. . In addition, there is a disadvantage in that normal pressure reformed gas cannot be used.

The hydrogen separation method (see FIG. 37) using a hydrogen permeable membrane (such as a Pd metal membrane) examined here has advantages and disadvantages as described above. These advantages and disadvantages are related to oxides having a perovskite structure. Compared with the advantages and disadvantages of the hydrogen separation method using (AECeO ₃ ), it can be seen that the two are interchanged with each other (that is, the point where one is an advantage is the other is the disadvantage). Therefore, as a result of intensive studies to solve the above problems while paying attention to such a relationship, the present inventor has made a proton conductive oxide (AECeO ₃ ) and a hydrogen permeable membrane (for example, Pd metal) into a composite membrane. When using an electrolyte, only hydrogen (specifically in the form of protons) permeates the Pd membrane and reaches the AECeO ₃ membrane, so the vulnerability of AECeO ₃ to CO ₂ can be overcome and even in a gas environment containing CO ₂ It has been found that it can be used as an electrolyte for usable electrochemical devices, and it has been found that the use of this electrolyte can solve the above problems even in a gas environment containing CO ₂ .

The present invention is based on such knowledge, and the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 1 arranges barium (Ba) or strontium (Sr) at the A site. The base structure is a perovskite oxide (ABO ₃ ) with rare earth element cerium (Ce) distributed at the B site, allowing protons (H ⁺ ) to pass through and separating only hydrogen from a gas containing CO _2. Consisting of a composite membrane of a proton conductive oxide membrane and a hydrogen permeable membrane that allows protons (H ⁺ ) to pass through and separates only hydrogen from a gas containing CO ₂ In this state, a hydrogen permeable film is formed on at least the gas side surface of the proton conductive oxide film, and the composite film is supported by the porous support.

The present invention is characterized in that a new composite membrane electrolyte structure suitable for hydrogen separation is constructed based on the above-described knowledge. In other words, the AECeO ₃ 's vulnerability to CO ₂ is maintained while maintaining the proton conductivity of the AECeO ₃ by adopting a composite membrane structure in which the proton conductive oxide membrane and the hydrogen permeable membrane complement each other's disadvantages. Overcoming this, it is possible to use even in a gas atmosphere environment containing CO ₂ . In other words, this composite membrane electrolyte is a state in which another membrane is interposed between the ceramic (AECeO ₃ ) and the reformed gas. In other words, the hydrogen permeable protection is provided on the surface of the ceramic (AECeO ₃ ). A film-like element is formed, and such a composite film structure prevents ceramic decomposition by CO ₂ .

Also, in this composite membrane electrolyte structure, when hydrogen moves from one solid phase to another, it does not move as a hydrogen element or hydrogen molecule, but exhibits a phenomenon in which it moves continuously as a proton. (See FIG. 1). In this case, the hydrogen permeable membrane (eg, Pd membrane) selectively permeates only hydrogen (H ₂ ) and does not permeate other molecules (N ₂ , CO, CO _2, etc.). The permeable membrane can be regarded as a proton-electron mixed conductor (see FIG. 1). Therefore, this hydrogen permeable membrane serves as an electrode and an electrolyte. If the hydrogen permeable membrane is regarded as a part of the proton conductive oxide film as the protective film, hydrogen (H ₂ ) is the only gas that contacts (or passes) the proton conductive oxide film.

  Moreover, in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention, a composite membrane comprising a proton conductive oxide membrane and a hydrogen permeable membrane is supported by a porous support. The porous support in this case does not affect the function of the composite membrane for separating hydrogen from the gas. In short, since the porous support is a porous body, it should be excellent in gas diffusibility to such an extent that hydrogen does not inhibit this reaction when entering the membrane as protons from the hydrogen permeable membrane. Moreover, since this porous support serves as a base material that strongly supports the composite membrane, the composite membrane (proton conductive oxide membrane and hydrogen permeable membrane) itself has the strength required for the base material. It is enough even if not. In other words, since it is not necessary to ensure a predetermined strength with the composite membrane itself, each of the proton conductive oxide film and the hydrogen permeable membrane constituting the composite membrane can be thinned to a necessary and sufficient thickness. There is an advantage that the degree of freedom of design is expanded. Further, it is advantageous in terms of cost by making the proton conductive oxide film and the hydrogen permeable film thinner.

Further, in the invention described in claim 2, the proton conductive oxide film in the proton conductive oxide film-hydrogen permeable membrane composite membrane electrolyte described in claim 1 is a part of rare earth element cerium (Ce). The structure is substituted with another low-valent rare earth element different from the cerium (Ce ⁴⁺ ). By substituting with a low valence element, for example, when Ce ⁴⁺ → Yb ³⁺ , the electrical neutrality in the crystal lattice is broken, and in order to compensate for this, 1/2 oxygen in the lattice is lost. Then, the electrical neutrality in the lattice is maintained. In this manner, oxide ion vacancies can be intentionally generated (doping), and proton generation is further promoted.

  The invention according to claim 3 is characterized in that the other rare earth elements in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 1 or 2 are ytterbium (Yb), yttrium (Y), It is one kind of rare earth element selected from the group consisting of Sium (Dy), Gadolinium (Gd), Samarium (Sm) and Neodymium (Nd).

  According to a fourth aspect of the present invention, the hydrogen permeable membrane in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of the first to third aspects is a metal or alloy exhibiting hydrogen permeability. There is. Among metals or alloys, those showing hydrogen permeability are applied to the hydrogen permeable membrane in the present invention.

  The invention according to claim 5 is the metal or alloy showing hydrogen permeability in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 4, wherein palladium (Pd), niobium (Nb), One or more selected from the group consisting of tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni), or silver and silver (Ag) These alloys are used as components.

  According to a sixth aspect of the present invention, the metal or alloy exhibiting hydrogen permeability in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the fourth or fifth aspect is palladium (Pd), niobium (Nb ), Tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni), or one or two or more thereof and silver ( It is formed by an electroless plating method using an alloy of Ag) as a component.

  The invention according to claim 7 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of claims 1 to 6, wherein the porous support is formed on the gas side surface of the composite membrane. It is formed.

  The invention according to claim 8 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 7, wherein a porous cathode is formed on the surface opposite to the gas side of the composite membrane. That is.

  The invention according to claim 9 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 8, wherein the porous cathode has at least a perovskite structure. And any one of silver (Ag).

The invention according to claim 10 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 7, wherein protons (H ⁺ ) are present on the surface of the composite membrane opposite to the gas side. Another hydrogen permeable membrane that can pass is formed.

  The invention according to claim 11 is that the other hydrogen permeable membrane in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 10 is a metal or alloy exhibiting hydrogen permeability. is there.

  The invention according to claim 12 is characterized in that the metal or alloy showing hydrogen permeability constituting another hydrogen permeable membrane in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 11 is palladium ( One or more selected from the group consisting of Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni) Or an alloy of them and silver (Ag).

  The invention according to claim 13 is a metal or an alloy exhibiting hydrogen permeability constituting another hydrogen permeable membrane in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 11 or 12. One or two selected from the group consisting of palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni) It is characterized by being formed by an electroless plating method using at least a seed or an alloy of silver and silver (Ag) as a component.

  The invention according to claim 14 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of claims 1 to 6, wherein the porous support is a gas side of the composite membrane. It is a porous cathode formed on the opposite surface.

  The invention according to claim 15 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of claims 1 to 6, wherein the composite membrane is porous on the surface opposite to the gas side. A porous cathode is formed, and a porous support is formed on the surface of the porous cathode.

The invention according to claim 16 is the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of claims 1 to 6, wherein the proton on the surface opposite to the gas side of the composite membrane. Another hydrogen permeable membrane through which (H ⁺ ) can pass is formed, and a porous support is formed on the surface of the other hydrogen permeable membrane.

  An invention according to claim 17 is an electrochemical device using the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of claims 1 to 16, comprising a fuel cell, a hydrogen sensor It is applied to any of hydrogen pumps, water vapor sensors and exhaust gas purification devices.

This electrochemical device can be applied to a hydrogen sensor capable of quantifying the hydrogen concentration in a mixed gas containing at least H ₂ and CO ₂ as described in claim 18.

The electrochemical device can also be applied to a hydrogen pump that can separate only hydrogen from a mixed gas containing at least H ₂ and CO ₂ as described in claim 19.

Furthermore, as described in claim 20, the electrochemical device can be applied to a water vapor sensor capable of determining a water vapor concentration from a mixed gas containing at least water vapor and CO ₂ .

Furthermore, as described in claim 21, the electrochemical device can be applied to an exhaust gas purification device for removing NOx from exhaust gas containing at least water vapor, CO ₂ and NOx.

Here, the concept of the metal / oxide composite membrane type electrolyte will be described below, and then the examination content on overcoming the vulnerability of AECeO ₃ to CO ₂ will be described, whereby the proton conductivity according to the present invention will be described. The contents of the oxide membrane-hydrogen permeable membrane composite membrane type electrolyte will be described in more detail. In the following, "1. Perovskite type proton conductor oxide", "2. Hydrogen permeable membrane", "3. Fuel cell using hydrogen permeable membrane and proton conductive oxide", and "4. Metal The fuel cell using the oxide composite membrane electrolyte will be described in the order of items.

1. Perovskite-type proton conductor oxide In order to solve the problems of the prior art, the present inventor first examined an oxide AECeO ₃ having a perovskite structure. For example, a fuel cell that operates in an intermediate temperature range requires an electrolyte having a high proton conductivity in the intermediate temperature range, and in order to sufficiently operate as a fuel cell, the following electrode reactions of Formulas 1 and 2 are performed. It needs to proceed smoothly.

  However, in general, an electrolyte having a high proton conductivity in a low temperature region has a problem of lacking chemical stability because a decomposition reaction proceeds in a middle temperature region. Moreover, even if it exists stably in the middle temperature range, there is no electrolyte that actually exhibits the fuel cell reaction as represented by the chemical formulas 1 and 2 described above.

On the other hand, a perovskite-type structure-based oxide (AECeO ₃ ) having a high proton conductivity such as SrCeO ₃ and BaCeO ₃ as shown in FIG. In addition, the oxide having the perovskite structure (ABO ₃ ) as described above increases the conduction by holes (p-type electronic conductivity) as the oxygen partial pressure increases in a high temperature atmosphere without any hydrogen source. It is known to do. In this case, since the conductivity is proportional to the quarter power of the oxygen partial pressure, it is considered to be in lattice defect equilibrium involving oxide ion vacancies.

  When such an oxide is exposed to an atmosphere containing a hydrogen source such as hydrogen gas or water vapor, proton conductivity is exhibited. This means that these oxides take in hydrogen from the hydrogen source in the atmosphere and hydrogen is present in the form of protons. FIG. 2 schematically shows the relationship between lattice defects of such an oxide and proton generation. In FIG. 2, (a) is the stoichiometric composition, (b) is the proton or hole conduction mechanism in wet oxygen, (c) is the hole electron conduction mechanism in dry oxygen, and (d) is in hydrogen. The proton conduction mechanism is shown. Note that the square (□) in FIG. 2 represents oxide ion vacancies. Here, lattice defects do not directly generate protons. First, oxygen and vacancies in the atmosphere generate holes (h) according to the defect reaction equation (see the equation in the figure), and when hydrogen is introduced into the equilibrium, holes and hydrogen react. Proton is generated. That is, proton conductivity does not appear unless a large number of oxide ion vacancies exist. However, since the conductivity is proportional to the proton concentration and mobility, just because the oxide ion vacancy concentration is high (= proton concentration is high) does not mean that the conductivity is high. High conductivity can be obtained only when both high concentration and mobility are obtained.

Many studies so far have confirmed that the base oxide alone does not exhibit proton conductivity, and that doping of the B site with a trivalent cation is essential for the development of proton conductivity. For example, when a part of Ce ⁴⁺ of the B site cation of SrCeO ₃ is substituted and dissolved with Yb ³⁺ , oxide neutral vacancies are generated in the crystal because the electrical neutral condition is satisfied.

  These vacancies are in an equilibrium relationship shown in Chemical Formula 4 with holes (indicated by symbol h with a right shoulder on the right shoulder) and atmospheric oxygen at high temperature. Therefore, only the p-type electron conductivity is exhibited in an atmosphere without a hydrogen source. On the other hand, when a hydrogen source, for example, water vapor is introduced into the atmosphere, the equilibrium relationship shown in Chemical Formulas 5 and 6 is established between the water vapor molecules and holes or oxide ion vacancies together with Chemical Formula 4, and hydrogen is oxidized. Proton conductivity is expressed by being taken into the product.

Here, K ₁ , K ₂ , and K ₃ are equilibrium constants in the chemical formulas 4 to 6, respectively. Since chemical formula 4, chemical formula 5 and chemical formula 6 are not independent of each other and are related by chemical formula 7, two of these chemical formulas can be used to express an equilibrium relationship.

However, the perovskite oxide (AECeO ₃ ), which has alkaline earth metal at the A site and Ce at the B site, has proton conductivity, but when CO ₂ is present in the atmosphere, the chemical formula can be expressed by thermodynamic equilibrium. As shown in FIG. 8, the chemical stability is lacking as it is easily decomposed into CeO ₂ and ACO ₃ . For this reason, attention must be paid to CO ₂ in the atmosphere in order to use SrCeO ₃ or BaCeO ₃ for electrochemical devices.

Further, in order to use SrCeO ₃ or BaCeO ₃ as an electrolyte even in an atmosphere containing CO ₂ , it is necessary to shield the electrolyte membrane surface from CO ₂ in the atmosphere.

2. Hydrogen Permeation Membrane A phenomenon in which hydrogen permeates a metal membrane as a proton has been found in a palladium (Pd) membrane. The hydrogen permeation mechanism of Pd and its alloy film is qualitatively considered to be a mechanism through which hydrogen permeates according to the principle shown in FIG. When a hydrogen partial pressure difference occurs on both sides of the Pd film having hydrogen permeability, hydrogen molecules on the high hydrogen partial pressure side dissociate on the metal surface and become hydrogen atoms (see FIG. 3). Hydrogen atoms are deprived of electrons by Pd and become protons, and diffuse in the metal as protons due to the concentration gradient. The diffused protons recombine with free electrons on the low hydrogen partial pressure side to become hydrogen atoms, and these hydrogen atoms associate to become molecules due to the catalytic ability of Pd, and finally released as hydrogen molecules to the low hydrogen partial pressure side. . Thus, the metal Pd film can be regarded as a kind of mixed conductor that conducts protons and electrons. The present inventor decided to utilize such a remarkable function particularly in the Pd film. Since the Pd film alone may cause hydrogen embrittlement, an alloy of Pd and Ag is more preferable.

3. Fuel cell using hydrogen permeable membrane and proton conductive oxide If the metal Pd with hydrogen permeability described in “2. About hydrogen permeable membrane” can be placed between AECeO ₃ and gas atmosphere, CO ₂ will be It is considered that AECeO ₃ can be used even in a gas environment. This is because, as shown in FIG. 4, H ₂ permeates the Pd film from the CO ₂ -containing gas (for example, reformed gas) side, so that only H ₂ is used as the fuel gas on the oxide (AECeO ₃ ) film side. Because it becomes available as

However, when such a double membrane structure (double structure consisting of a Pd film and an AECeO ₃ film) was constructed (see FIG. 4), it was found that there were the following points. That is, first, hydrogen partial pressure may be extremely increased by hydrogen that has permeated through the Pd film, and Ce ⁴⁺ in the oxide may be easily reduced to Ce ³⁺ . On the other hand, for example, it was considered that the addition of water vapor at about room temperature saturation slightly reduced the hydrogen partial pressure due to the equilibrium with water vapor, thereby preventing Ce ^{4+ from} being reduced. However, in this case, water vapor is inhibited by the Pd film and does not reach the oxide film. Secondly, for example, thickening the Pd film greatly affects the cost, so it is necessary to reduce the film thickness to some extent. However, it was considered that the thinning of the hydrogen permeable film such as Pd metal alone has a problem in strength.

4). Fuel Cell Using Metal / Oxide Composite Membrane Type Electrolyte As a result of various examinations and experiments, in applying both the proton conductive oxide membrane and the hydrogen permeable membrane as described above to a fuel cell, for example, FIG. The metal / oxide composite membrane type electrolyte as shown in FIG. 1, that is, it was desirable to make the composite in a state where the metal Pd film and the oxide AECeO ₃ film were superposed (see FIG. 5). ). Thus, by joining and compounding a metal (Pd) film and an oxide (AECeO ₃ ) film, the oxide (AECeO ₃ ) can be protected from a gas environment containing CO ₂ . Here, in comparison with the “fuel cell using a hydrogen permeable membrane and proton conductive ceramics” shown in FIG. 4, the electrolyte shown in FIG. 5 has a series of bulk (in this case, Pd membrane → AECeO ₃ membrane). This is characterized in that protons can pass directly and continuously through the Pd membrane → AECeO ₃ membrane. In this case, since no electron transfer (electrode reaction) occurs at the interface between the Pd film and the oxide (AECeO ₃ ) film, the oxide (AECeO ₃ ) is not reduced by the generated H or H ₂ . In other words, it is possible to overcome the vulnerability to CO ₂ while maintaining proton conductivity.

As described above, in order to create an ideal interface by joining a metal (Pd) film and an oxide (AECeO ₃ ) film, coating by the following method can be considered.

First, as a method for forming a metal (Pd) film on an oxide (AECeO ₃ ) film, the following methods may be mentioned.
(1) Chemical: Electroless plating method, electrolytic plating method, MOD method, CVD method, slurry coating method, spin coating method, dip method
(2) Physical… PVD method {sputtering, vapor deposition, MBE (Molecular Beam Epitaxy) method, plasma spraying method, plasma spraying method}
Among the above, the electroless plating method is capable of producing a dense thin film uniformly, and is a preferable method for improving the continuous bondability of the composite interface between the oxide (AECeO ₃ ) film and the metal (Pd) film. . In addition, a dense thin film can also be produced by plasma spraying and plasma spraying. In the present invention, since it is necessary to combine a dense film, the plasma spraying method and the plasma spray method, which are easy to form an automatic film, are suitable for forming a composite film if industrial production is targeted. It is.

Examples of a method for forming a thin oxide (AECeO ₃ ) film on the porous support include the following methods.
(1) Chemical… Slurry coating method, spin coating method, dipping method
(2) Physical… PVD method {sputtering, vapor deposition, MBE (Molecular Beam Epitaxy) method, plasma spraying method, plasma spraying method}
By adopting the above method, it is possible to reduce the thickness of the oxide (AECeO ₃ ) film. Furthermore, an oxide (AECeO ₃ ) thin film is formed on the porous support, and further a metal (Pd ) The cost is reduced by forming a thin film.

Here, Pd or Pd-Ag alloy was examined as an example, but from the hydrogen permeation form as described above, as a composite film, a metal other than Pd that permeates hydrogen (for example, niobium (Nb), tantalum ( Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni), etc.) films, alloy films composed of two or more of these elements, or oxides (for example, It is considered that the same effect can be obtained when a film of SrZrO ₃ , BaZrO ₃ ) or the like is applied. In particular, when a metal film or an alloy film is used, there is an advantage that an electrode is unnecessary because the metal film or the alloy film itself can be regarded as a proton-electron mixed conductor.

  In addition, since a Pd film is used, it is necessary to reduce the thickness to some extent in terms of cost. However, regarding the point that the reduction of the thickness of a hydrogen permeable membrane such as a Pd film alone is problematic in terms of strength, the following is considered. It was. In other words, we first tried to thicken the Pd film itself and make the Pd film itself function as a base material, but it was not practical in view of cost (the amount of Pd used exceeds the practical level) It was considered. In this case, it was considered that the base material (support) is made of a material that does not affect hydrogen permeation rather than ensuring the strength with the composite membrane itself. Specifically, it was considered that a structure in which a composite membrane composed of a proton conductive oxide membrane and a hydrogen permeable membrane is supported by a porous support is suitable. The porous support in this case does not affect the function of the composite membrane for separating hydrogen from the gas. In addition, since the porous support serves as a base material that strongly supports the composite membrane, it is not necessary to secure a predetermined strength with the composite membrane itself. Each of the material film and the hydrogen permeable film can be thinned to a necessary and sufficient thickness.

  As described above, the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to the present invention can exhibit a unique effect as an electrolyte in a fuel cell. Not limited to. As shown in Example 1 below, the results of experiments by the inventors are suitable for electrochemical devices such as hydrogen sensors, hydrogen pumps, and water vapor sensors. Furthermore, as described below, it is also very suitable as an electrolyte in an exhaust gas purifying electrochemical device.

  That is, the present inventor examined the possibility of applying the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention in addition to the hydrogen sensor, hydrogen pump, and water vapor sensor. As an example, specifically, detailed examination was made on the application of the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte as an electrochemical device for exhaust gas purification. The background is as follows.

That is, conventionally, as a method for removing nitrogen oxide (NOx) contained in the exhaust gas of an internal combustion engine such as an automobile, a catalytic reduction method using a catalyst supporting a noble metal as an active component has been used. That is, a catalyst in which a noble metal such as platinum or rhodium is supported on a carrier such as alumina having a large specific surface area is used as a catalyst for purifying automobile exhaust gas. Furthermore, the nitrogen oxides contained in the exhaust gas of various plants, such as boiler (NOx) is, NH ₃ uncatalyzed denitration method by addition, is converted into N ₂ and O ₂ by the selective catalytic reduction method using NH ₃ with a catalyst Has been detoxified. However, this conventional method for removing nitrogen oxide has the following problems (1) and (2).

(1) Problems with catalysts for automobile exhaust gas purification Catalysts carrying noble metals for automobile exhaust gas purification have low precious metal reserves and high prices, and precious metals have large price fluctuations and are secured stably. There is a difficult problem. Recent automobiles tend to shift to combustion in the lean burn region. As a result, NOx tends to increase with incomplete combustion, and the NOx removal rate can be improved without increasing the amount of precious metal supported. Technology development that can As another decomposition method of nitrogen oxides, there is a reduction method using ammonia. This method is excellent in that no precious metal is required, but it requires equipment for supplying ammonia, like an automobile. When there is not enough space, it is difficult to mount a device such as a cylinder for supplying ammonia in an automobile.

(2) Problems with the reduction method using ammonia in various plants such as boilers When applying the NOx ammonia reduction method to various plants such as boilers, unreacted ammonia reacts with SOx contained slightly in the exhaust gas. However, it produces ammonium sulfate and adheres to the low temperature part of the heat exchanger, which is the heat recovery device of the boiler, and the pressure loss of the heat exchanger increases over time. It is.

  In view of the above problems, the present inventors have found that the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention has a specific effect when applied to an exhaust gas purification electrochemical device. It came. That is, the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention basically generates protons from water vapor in the atmosphere by the defect equilibrium represented by the chemical formulas 4 to 7, based on the operating principle of the hydrogen pump. Captures and produces hydrogen on the cathode side. The produced hydrogen reduces NOx based on the following chemical formulas 9 and 10. Furthermore, since this NOx reduction reaction can be controlled by the amount of current applied to the device, finer NOx reduction can be realized by feedback control using a NOx sensor.

  For example, water vapor exists in the exhaust gas of an automobile, and the temperature of the exhaust gas purifying catalyst during traveling reaches several hundred degrees. Under such circumstances, an automobile exhaust gas purification electrochemical device decomposes water vapor in exhaust gas, supplies hydrogen, which is a reducing agent of NOx, into the exhaust gas, and converts NOx based on chemical formulas 9 and 10 Decompose.

  In addition, since many of the exhaust gases in various plants such as the boilers mentioned above contain water vapor, the non-catalytic denitration with ammonia in these various plants or the selective catalytic reduction of ammonia with NOx using the catalyst is also performed in the high temperature part of the boiler. By disposing the electrochemical device for purifying exhaust gas according to the invention, hydrogen can be supplied into the exhaust gas, and ammonia as a reducing agent can be reduced.

As described above, according to the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte of claim 1, the proton conductivity of AECeO ₃ is maintained, but the vulnerability of AECeO ₃ to CO ₂ is overcome. It can be used even in a mixed gas atmosphere containing CO ₂ .

Further, in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 2, a part of the rare earth element cerium (Ce) is made of another low valence rare earth element different from the cerium (Ce ⁴⁺ ). those that were replaced, the proton conductivity of AECeO ₃ can overcome vulnerability to CO ₂ of AECeO ₃ while maintaining. By substituting with a low valence element, for example, when Ce ⁴⁺ → Yb ³⁺ , the electrical neutrality in the crystal lattice is broken, and in order to compensate for this, 1/2 oxygen in the lattice is lost. Then, the electrical neutrality in the lattice is maintained. In this manner, oxide ion vacancies can be intentionally generated (doping), and proton generation is further promoted. The other rare earth elements are ytterbium (Yb), yttrium (Y), dysprosium (Dy), gadolinium (Gd), samarium (Sm), neodymium (Nd) as described in claim 3. One kind of rare earth element selected from the group can be used.

5. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 4, wherein the hydrogen permeable membrane is a metal or an alloy. Since the metal membrane itself can be regarded as a proton-electron mixed conductor, the fuel electrode There is an advantage that it becomes unnecessary. In this case, the metal or alloy exhibiting hydrogen permeability is palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr) as described in claim 5. One or two or more selected from the group consisting of copper (Cu) and nickel (Ni), or an alloy thereof with silver (Ag) can be used. In addition, as described in claim 7, by depositing these metals or alloys on the surface of the proton conductive oxide film by an electroless plating method, a denser and more uniform film can be formed. As a result, the continuous bonding property of the composite interface in the composite oxide membrane-hydrogen permeable membrane composite electrolyte is improved, and the anode overvoltage can be reduced while overcoming the vulnerability of AECeO ₃ to CO ₂ .

  According to the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte of claim 7, wherein the porous support is formed on the gas side surface of the composite membrane, hydrogen such as Pd without interfering with hydrogen permeation. Since it is possible to reduce the thickness of the permeable membrane alone, it is possible to set a film thickness suitable for various electrochemical devices. The same applies to the case where the porous cathode is formed on the surface opposite to the gas side of the composite membrane as in the eighth aspect. Furthermore, the cathode overvoltage can be reduced by including silver (Ag) in the porous cathode as described in claim 9.

11. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane type according to claim 10, wherein another hydrogen permeable membrane capable of allowing protons (H ⁺ ) to pass through is formed on the surface opposite to the gas side of the composite membrane. The electrolyte is in a state in which protective films are formed on both sides of the proton conductive oxide film. Therefore, even if CO ₂ is contained in the gas flowing on the cathode side (oxidant gas), the gas atmosphere environment containing CO ₂ overcomes the vulnerability of proton conductive oxide film (AECeO ₃ ) to CO ₂ It can also be used below. 12. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 11, wherein the other hydrogen permeable membrane is a metal or an alloy, so that the metal membrane itself can be regarded as a proton-electron mixed conductor. There is an advantage that becomes unnecessary. In this case, the metal or alloy exhibiting hydrogen permeability is palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr) as described in claim 11. One or two or more selected from the group consisting of copper (Cu) and nickel (Ni), or an alloy of these with silver (Ag) can be used. As described in claim 13, by depositing these metals or alloys on the surface of the proton conductive oxide film by an electroless plating method, a denser and more uniform film can be formed. Can improve the continuous bondability of the composite interface in the porous oxide membrane-hydrogen permeable membrane composite membrane electrolyte and overcome the vulnerability of AECeO ₃ to CO ₂

  15. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to claim 14, wherein the porous support is a porous cathode formed on the surface opposite to the gas side of the composite membrane. Also functions as a base material and supports the composite membrane in strength. Accordingly, even in this case, it is possible to reduce the thickness of a single hydrogen permeable film such as Pd without interfering with hydrogen permeation, so that it is possible to set a film thickness suitable for various electrochemical devices.

  16. The proton conductive oxide membrane-hydrogen permeable membrane according to claim 15, wherein a porous cathode is formed on the surface opposite to the gas side of the composite membrane, and further a porous support is formed on the surface of the porous cathode. Even with the composite membrane type electrolyte, it is possible to reduce the thickness of a hydrogen permeable membrane such as Pd alone without interfering with hydrogen permeation, so that it is possible to set a film thickness suitable for various electrochemical devices.

Further, another hydrogen permeable membrane through which protons (H ⁺ ) can pass is formed on the surface opposite to the gas side of the composite membrane, and a porous support is formed on the surface of the other hydrogen permeable membrane. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 16 is in a state in which protective films are formed on both sides of the proton conductive oxide membrane. Therefore, also contain CO ₂ in the gas (oxidant gas) flowing in the cathode side, the proton conductive oxide film (AECeO ₃₎ gas atmosphere environment containing CO ₂ to overcome the vulnerability to CO ₂ of It can also be used below.

Further, according to the invention of claim 17, in various devices such as a fuel device, the proton conductivity of AECeO ₃ is maintained, but the vulnerability of AECeO ₃ to CO ₂ is overcome and the mixed gas atmosphere environment containing CO ₂ is maintained. Can be used. For example, the present invention can be applied to a hydrogen sensor as in claim 18, applied to a hydrogen pump as in claim 19, or applied to a water vapor sensor as in claim 20. Alternatively, the present invention can be applied to an exhaust gas purifying device as in the twenty-first aspect.

  Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention has hydrogen permeability or proton (H ⁺ ) permeability capable of separating hydrogen from a gas 3 containing CO ₂ as shown in FIG. a electrolyte, and protons (H ⁺⁾ proton conductive oxide film 1 can pass through the proton (H ⁺⁾ is a composite film of a hydrogen permeable membrane 2 can pass, the interface of both membranes The hydrogen permeable membrane 2 is formed on the surface of at least the gas 3 side of the proton conductive oxide film 1 in a continuously bonded state.

The proton conductive oxide film 1 has a basic structure of perovskite oxide (ABO ₃ ) in which barium (Ba) or strontium (Sr) is arranged at the A site and rare earth element cerium (Ce) is arranged at the B site. Can be adopted.

  As the A-site element, it is more preferable to employ barium (Ba) from the viewpoint of reducing electrolyte resistance.

  In addition, in order to generate oxide ion vacancies to express proton conductivity, cerium (Ce) at the B site is ytterbium (Yb), yttrium (Y), dysprosium (Dy), gadolinium (Gd). It is preferable to partially substitute with one kind of rare earth element selected from the group consisting of samarium (Sm) and neodymium (Nd), but is not limited to these elements and is different from cerium (Ce) It is also possible to employ other low-valent rare earth elements.

  Note that the solid electrolyte such as the proton conductive oxide film of the present invention has higher electrolyte resistance as the sinterability decreases. From such a viewpoint, it is preferable to improve the sinterability. Examples of the technique for increasing the sinterability include, but are not limited to, increasing the sintering temperature and increasing the molding load during final molding. The degree of sintering is preferably 90% or more, more preferably 95% or more.

The hydrogen permeable membrane 2 is a membrane through which protons (H ⁺ ) can pass and only hydrogen can be separated from a gas containing CO _2. Palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum ( One or more selected from the group consisting of La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni), or an alloy of these and silver (Ag) However, the present invention is not limited to these, and any material that can pass protons (H ⁺ ) and can separate only hydrogen from a gas containing CO ₂ is not limited to metals or alloys, but is oxidized. It is also possible to employ materials such as objects. It is more preferable to alloy with Ag which has an effect of suppressing hydrogen embrittlement.

  Here, when a metal or alloy membrane is employed as the hydrogen permeable membrane, the membrane itself can be regarded as a proton-electron mixed conductor and thus acts as an electrode. Therefore, it is preferable to employ a metal or alloy film from the viewpoint of eliminating the need for a fuel electrode. When materials such as oxides are used, a fuel electrode may be used in combination, and when the hydrogen permeable membrane using a metal or alloy film is thin, it does not work well as an electrode. That's fine.

  The fuel electrode is preferably made of a material that allows fuel gas to pass therethrough and acts as an electrode. For example, a porous metal, an electrode formed in a lattice shape, or an electrode having a plurality of holes for allowing gas to pass therethrough may be employed. it can. When the hydrogen permeable membrane is an oxide membrane, the oxide membrane is disposed on the gas side, and the fuel electrode may be used in contact with the proton conductive oxide. When the hydrogen permeable membrane is a metal or alloy, the fuel electrode may be used in contact with the proton conductive oxide, or the hydrogen permeable membrane may be contacted with the proton conductive oxide and The fuel electrode may be brought into contact with the hydrogen permeable membrane.

  Next, the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention is characterized in that the composite interface is continuously joined in order to reduce the anode overvoltage.

  The continuous bonding of the composite interface is achieved by forming a dense hydrogen permeable membrane using a proton conductive oxide film as a base material, or by forming a dense proton conductive oxide film using a hydrogen permeable film as a base material. Achieved. In the present invention, a dense hydrogen permeable membrane is formed using a proton conductive oxide film as a base material.

  An example of a method for forming a dense film is a paste method. In this case, since the particle diameter of the paste material is large, the adhesiveness with the base material is improved and the anode overvoltage can be reduced by applying a high temperature treatment after applying the paste to the substrate.

Examples of the paste include one of palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), and nickel (Ni). Alternatively, it is preferable to form a film showing good hydrogen permeability by including particles of two or more elements.
It is more preferable to include silver (Ag) that has an effect of suppressing hydrogen embrittlement.

  Moreover, when using a paste method, it is preferable to add metal resinate to a paste agent and to improve adhesiveness with a base material. As a result, it is possible to prevent the film formed by the paste method from peeling off from the substrate.

  The metal resinate is a metal resinate, and a fine metal is generated by burning the resin during the heat treatment as compared with the case where the metal containing no metal resinate is directly heat-treated. This fine metal bites into the ceramic microscopically, that is, it is blended in anticipation of an anchoring effect on the ceramic, and examples thereof include, but are not limited to, terpineol sulfide Pd.

When a paste containing a metal resinate is applied to the substrate and then heat treatment is performed, pores (holes) are generated. The pores, will be passed through the CO _2, it is not preferable because that would expose the proton conductive oxide film of the fragile present invention CO ₂ relative to CO _2. Therefore, in order to fill the pores, it is preferable to further coat a paste containing no metal resinate and heat-treat the paste at a temperature higher than the heat treatment temperature to make the hydrogen permeable film more dense.

  The case where a Pd—Ag alloy film is formed will be described below as an example. First, a paste containing a metal resinate is applied to a substrate, and the binder contained in the paste is burned off at about 200 ° C. Next, heat treatment is performed. An infinite number of pores are generated at a heat treatment temperature of about 900 ° C., and the number of pores decreases as the heat treatment temperature is raised. However, above 1300 ° C, Pd-Ag begins to sinter and the pore diameter increases. Therefore, if the heat treatment temperature is x, 900 ° C. <x <1300 ° C. may be satisfied, but 1100 ° C. <x <1300 ° C. is preferable, and x≈1200 ° C. is most preferable.

  Even when heat treatment is performed at 1200 ° C., which is the most preferable heat treatment temperature, pores are generated. Therefore, in order to fill the pores, the paste is repeatedly applied. Here, as the paste for performing the overcoating, a paste not containing a metal resinate that is less likely to generate pores is preferable. When this is heat-treated at a temperature of about 1300 ° C., which is higher than the temperature at which the first film is heat-treated, the pores are burned out and a dense film can be formed.

  Next, as a preferable means for forming a denser film and improving the continuous bonding state of the composite interface, physical deposition method (PVD method), chemical deposition method (CVD method), discharge polymerization method Sol-gel method, electroplating method, electroless plating method, screen method, etc., but from the viewpoint of cost, film formation simplicity and film formation uniformity, it is most preferable to employ the electroless plating method. .

  Here, although the proton conductive oxide film has proton conductivity, it does not have electronic conductivity, and thus is difficult to be plated. Therefore, it is necessary to impart an activity to the plating reaction to the substrate before performing the electroless plating treatment. As a method of applying electroless plating to a non-conductive substrate, a two-component method (sensitization-activation method), which is a typical pretreatment for the activation of a catalyst by a wet method, is adopted, and the substrate is activated for the plating reaction. The pretreatment for catalyst activation to be imparted may be performed, but it is not limited to this method as long as the activity for the plating reaction can be imparted.

  Here, in adopting the electroless plating method, it is necessary to prepare a plating bath in order to form a film on the proton conductive oxide film. In the plating bath, palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni), silver (Ag ) And the like, the constituent components of the target hydrogen permeable membrane are plated, and the film can be formed.

As an example, a method for forming a Pd—Ag alloy by an electroless plating method will be described. The proton conductive oxide film is used as a substrate to impart activity to the plating reaction. Specifically, the substrate is alternately immersed in each of the SnCl ₂ hydrochloric acid solution and the PdCl ₂ hydrochloric acid solution to generate Pd nuclei. Next, a Pd plating bath is immersed in an alkaline solution containing [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O so that the plating reaction is activated. Pd nucleus is used as a catalyst to surround Pd. Precipitate. Next, the substrate on which Pd is deposited is immersed in a solution containing [Pd (NH ₃ ) ₄ ] Cl ₂ and AgNO ₃ as an Ag plating bath to precipitate Ag. Finally, a Pd—Ag dense alloy film that is continuously bonded very well to the proton conductive oxide film 1 can be obtained by heat treatment in an N ₂ atmosphere.

  Next, it is preferable to reduce the thickness of the proton conductive oxide film from the viewpoint of cost reduction. Examples of the method for forming a proton conductive oxide thin film include a slurry coating method, a spin coating method, a dip method, and a physical deposition method (PVD method). However, if a thin film can be formed, it is limited to these methods. It is not something. In view of cost problems, the proton conductive oxide film should have a thickness of 50 μm or less, more preferably 35 μm or less, and even more preferably 20 μm or less. However, if the proton conductive oxide film is thinned so far, it becomes difficult to have an electrolyte self-supporting structure, and therefore a porous support structure is preferable. Specifically, a proton conductive oxide thin film is formed on the porous support, and further a hydrogen permeable thin film is formed. This makes it possible to produce a low-cost electrochemical device.

  In view of cost, a suitable thickness of the hydrogen permeable membrane is 1 μm or less, more preferably 0.5 μm or less, and further preferably 0.1 μm or less.

  As described above, the most preferable combination of the electrolyte in which the proton conductive oxide film 1 and the hydrogen permeable film 2 are combined is as follows. That is, as the proton conductive oxide film 1, the A site is barium (Ba), and the B site cerium (Ce) is ytterbium (Yb), yttrium (Y), dysprosium (Dy), gadolinium (Gd), samarium. Pd (Pd), niobium (Nb) formed by electroless plating as the hydrogen permeable membrane 2 using a material partially substituted with one kind of rare earth element selected from the group consisting of (Sm) and neodymium (Nd) One or more selected from the group consisting of tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu) and nickel (Ni), or silver (Ag) It is most preferable to use a film containing an alloy of) as a component.

As described above, in the electrolyte in which the proton conductive oxide film 1 and the hydrogen permeable film 2 are combined, only hydrogen (specifically in the form of protons) passes through the Pd film and reaches the AECeO ₃ film. Therefore, the vulnerability of AECeO ₃ to CO ₂ can be overcome, and it can be used as an electrolyte for an electrochemical device that can be used even in an environment of gas 3 containing CO ₂ . Such a proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte is suitable for application to an electrochemical device. For example, an exhaust gas containing water vapor and NOx such as automobile exhaust gas is purified. Therefore, it can be applied as an exhaust gas purification device. In such a case, the NOx can be decomposed by decomposing water vapor in the exhaust gas and supplying the NOx reducing agent hydrogen to the exhaust gas.

  Furthermore, it is preferable to use silver (Ag) as the cathode electrode in the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte. Conventionally, platinum (Pt), which is a high-cost material, has been used as the cathode electrode, but using silver (Ag) rather than platinum (Pt) can reduce costs and reduce cathode overvoltage. preferable. Examples of the silver (Ag) film forming method include, but are not limited to, a paste method.

The porous cathode is preferably an electron-oxide ion mixed conductive oxide having a perovskite structure or a cermet of silver (Ag) and an electron-oxide ion mixed conductive oxide having a perovskite structure. Even in this case, the cost can be reduced as compared with platinum (Pt). Examples of the electron-oxide ion mixed conductive oxide having a perovskite structure include LaMnO ₃ and SrMnO _3, but are not limited thereto. In order to bring these into good contact with the proton conductive oxide film, heat treatment is performed while pressing the proton-conductive oxide film with the electron-oxide ion mixed conductive oxide, or these films are simply bonded to each other. However, it is not limited to these methods.

  In addition to the above-described preferred example, silver (Ag) as a cathode electrode, an electron-oxide ion mixed conductive oxide having a perovskite structure, or an electron-oxide ion mixed conductive oxide having a perovskite structure and silver (Ag) By using cermet, the structure is extremely excellent as an electrochemical device.

  In addition, the composite film in the present embodiment is strongly supported by the porous support S, and thus can be thinned. The porous support S is made of, for example, porous Ni. A specific form in the case where the composite membrane is supported by the porous support S will be described below (see FIGS. 30 to 34).

First, the porous support S is formed on the surface of the composite membrane on the anode gas (gas containing CO ₂ ) side (see FIG. 30). A porous cathode (indicated by reference numeral 4 in FIGS. 30 to 34) is formed on the surface of the composite membrane opposite to the anode gas side (see FIG. 30). Incidentally, although the thickness of the porous cathode 4 in this embodiment is 40 μm, this is only an example and is not limited to this thickness. In the present embodiment, the porous support S and the porous cathode 4 are provided separately (see FIG. 30), but the porous cathode 4 itself may be provided with a function as a porous support. It is possible (see FIG. 32). As the porous support S, one having a maximum of 0.002 to 3 μm, preferably 0.004 to 0.5 μm can be appropriately selected and used without hindering gas diffusion. Specifically, for example, a Ni—YSZ cermet porous body or a Ni—Al ₂ O ₃ cermet porous body having pores of 0.1 to 0.5 μm can be exemplified. Thereby, since the hydrogen permeable membrane (for example, Pd metal) 2 can be thinned, it is possible to set a film thickness suitable for various electrochemical devices. When the temperature is 600 ° C. or lower, the porous support S provided on the anode side is made of metal Ni or Ni alloy, and the porous support S provided on the cathode side is made of SUS material such as SUS316L or SUS310S. It becomes possible.

In addition, the porous support S is formed on the surface of the composite membrane on the anode gas (gas containing CO ₂ ) side, and proton (H ⁺ ) can pass on the surface opposite to the anode gas. Another hydrogen permeable membrane 2 ′ can be formed (see FIG. 31). The porous support S makes it possible to reduce the thickness of the hydrogen permeable membrane (for example, Pd metal) 2, 2 ′ without hindering hydrogen permeation. Further, even when the gas (oxidant gas) 5 flowing on the cathode side contains CO ₂ , the hydrogen permeable membrane 2 ′ covering the proton conductive oxide film 1 is formed of the proton conductive oxide film 1. Overcoming vulnerability to CO ₂

  As shown in FIG. 32, the porous cathode 4 formed on the surface opposite to the anode gas side of the composite membrane can also function as the porous support S (see FIG. 32). In this case, since the porous cathode 4 also functions as a substrate and strongly supports the composite membrane, the hydrogen permeable membrane 2 such as Pd can be thinned without interfering with hydrogen permeation.

  As shown in FIG. 33, the porous cathode 4 may be formed on the surface of the composite membrane opposite to the anode gas side, and the porous support S may be further formed on the cathode side surface of the porous cathode 4. Yes (see FIG. 33). Also in this case, it becomes possible to reduce the thickness of a hydrogen permeable film such as Pd alone without hindering hydrogen permeation.

As shown in FIG. 34, another hydrogen permeable membrane 2 ′ through which protons (H ⁺ ) can pass is formed on the surface opposite to the anode gas side of the composite membrane, and further, the cathode side of this hydrogen permeable membrane 2 ′. A porous support S can also be formed on the surface (see FIG. 34). In this case, a protective film is formed on both surfaces of the proton conductive oxide film 1. Therefore, even if CO ₂ is contained in the gas (oxidant gas) 5 flowing on the cathode side, the gas containing CO ₂ by overcoming the vulnerability of the proton conductive oxide film (AECeO ₃ ) 1 to CO ₂ is overcome. It can be used even in an atmospheric environment.

  The above is a preferred embodiment of the present invention. However, what has been described here is merely an example of the preferred embodiment, and the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. is there. For example, the present invention is not limited to the exhaust gas purification device described above, and is suitable for application to electrochemical devices such as fuel cells, hydrogen sensors, hydrogen pumps, and water vapor sensors.

  In this specification, “proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte” is mainly described. However, the “composite membrane type” referred to here is a case where they are physically bonded. And chemically bonded together are conceivable. If it is considered to be a chemical junction, an intermediate product exists between the two membranes, which may become a high resistance layer for proton transfer, while the intermediate product becomes a high proton conductive layer. There is also a possibility. In consideration of the above, in the case of chemical bonding, it is a condition that there is no proton transfer high resistance layer.

In addition, when the present invention is applied to, for example, an electrochemical device for exhaust gas purification, the Pd / SCO composite film described below (SCO is SrCe _0.95 Yb _0.05 O _3-a , hereinafter simply referred to as SCO). ) Is preferably a Pd / SCO / Pd electrolyte membrane having a structure in which both sides are covered with a Pd thin film. When an electrochemical device is used in exhaust gas, both the anode and cathode are exposed to the exhaust gas, so that the cathode side is also covered with a Pd electrolyte membrane to prevent this side from reacting with CO ₂ and decomposing. it can.

Next, the concept of the metal / oxide composite membrane type electrolyte will be described first, while showing the concrete contents of the experiments and examinations actually performed as examples below, and then the AECeO _{3 according to} the present invention with respect to CO ₂ We will explain the contents of the experiment to confirm the overcoming of the vulnerability.

[Example 1]
In order to verify the effectiveness of the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to the present invention, the present inventor formed a Pd / AECeO ₃ composite membrane and used a fuel containing CO ₂ The possibility of power generation with batteries was confirmed. This is mainly a verification of “overcoming vulnerability to CO ₂ ” and “cell structure of electrochemical device”, as well as examination of application to various electrochemical devices such as hydrogen sensors, hydrogen pumps, and fuel cells. It is.

In this example, the interface (solid / solid interface) between the solid phase metal (Pd) and the solid phase oxide (AECeO ₃ ) is continuous, and this solid / solid interface is defined as the solid phase. It was kept in mind that the bonding state was the same as the interface with the liquid phase (solid / liquid interface). Although there is no difference between the two at the macro level, there is a large gap when compared at the micro level. More specifically, when a liquid phase is used as the electrolyte, protons move continuously at the solid / liquid interface. On the other hand, at the solid / solid interface, a discontinuous surface occurs as shown in FIG.
-The micro space generated at the interface becomes an electrochemical resistance and the performance is deteriorated.-The interface becomes an extreme reducing atmosphere, and the oxide may be reduced and the material may be deteriorated. In other words, continuous conduction of protons is particularly important at the solid / solid interface, and it is necessary to realize a bonding state similar to that at the solid / liquid interface. Incidentally, the metal / Pd film is required as a container to hold the liquid at the solid / liquid interface, while the difference is that the metal / Pd film covers the CO ₂ resistance of the ceramic at the solid / solid interface. is there.

Below,
(1) Preparation of metal / oxide composite membrane type electrolyte (2) Confirmation of CO ₂ resistance of composite membrane by CO ₂ atmosphere continuous exposure test (3) Proton conductivity of Pd / SCO composite membrane (4) Pd / SCO composite The fuel cell power generation using a membrane is divided into items, and the description will be made along this item.

(1) Fabrication of metal / oxide composite membrane type electrolyte (1.1) Examination of hydrogen permeable membrane 2 Most metal materials having the hydrogen permeable ability required as the hydrogen permeable membrane 2 cause self-collapse in a hydrogen atmosphere. It is known. These metals have a property of absorbing a large amount of hydrogen in accordance with the pressure and temperature of hydrogen and causing phase transformation. In the phase transformation, the metal lattice is expanded, strain is generated in the metal, and plastic deformation (hydrogen embrittlement) occurs. As the hydrogen permeable membrane 2, a Pd membrane which is attracting attention is no exception, and the lifetime of the membrane due to hydrogen embrittlement becomes a problem. However, Pd is said to relax phase transformation when Ag interacts with hydrogen atoms in a state where Ag is substitutional solid solution and alloyed. In addition, when a proper amount of Ag is dissolved, the diffusion coefficient of hydrogen decreases, but the solubility of hydrogen increases and the hydrogen permeation coefficient increases due to alloying. For this reason, in recent years, research on hydrogen separation membranes using Pd—Ag alloy membranes has been actively conducted in fields that require high-purity hydrogen such as fuel cells and semiconductor industries. Therefore, the present inventor paid attention to the Pd—Ag alloy as an oxide composite material.

(1.2) Paste composition In this example, a Pd-Ag alloy film was produced by a paste method. The Pd-Ag paste is prepared by kneading an appropriate amount of Pd and Ag metal powder, solvent (α terpineol), binder (ethylcellulose, and metal resinate: terpineol sulfide Pd) in anticipation of an anchor effect with oxides. Produced. The metal resinate is a metal resinate, and the resin burns during the heat treatment to generate fine Pd metal as compared with the case of directly heat-treating Pd not containing the metal resinate. This fine Pd metal bites into the ceramic microscopically, that is, it is blended in anticipation of an anchor effect on the ceramic. The Pd / Ag mixing ratio (wt%) was prepared by using Pd / Ag = 77/23, which is reported to have the best hydrogen permeability, and a paste containing a metal resinate (AR) and a paste containing no metal resinate ( AN) was produced.

(1.3) Film Formation on Alumina Substrate In order to determine the heat treatment temperature, Pd-Ag film formation was tried on the alumina substrate. Apply paste (AR) to alumina substrate, burn out the binder in air at 200 ° C in an atmospheric furnace, and then anneal at 900, 1000, 1100, 1200, 1300 ° C for 1 hour to increase the heat treatment temperature. Compared. The result is shown in FIG. At 900 ° C, innumerable holes were formed on the film surface, but the number gradually decreased with increasing annealing temperature. However, when the temperature exceeded 1300 ° C, the hole diameter increased. This means that Pd-Ag has started to sinter. When a paste (AN) to which no metal resinate was added was used, peeling of the film was observed at 1200 ° C. or lower. When the paste added with the metal resinate was used, no peeling of the film occurred, and it was confirmed that the metal resinate has an anchor effect. Furthermore, when heat treatment was performed at 1300 ° C. using a paste (AN) to which no metal resinate was added, there was no peeling and the number of pores did not increase as much as AR.

  In AR, the number of pores was the smallest at a heat treatment temperature of 1200 ° C., but pores were still observed and the film was not completely dense. Therefore, to fill the remaining pores and heat treatment at a higher temperature to make the film denser, compared to the paste (AR) to which the metal resinate is added even if heat-treated at 1300 ° C on the above-mentioned film formed. Then, a paste (AN) not added with a metal resinate with a small amount of pores was repeatedly applied and annealed at 1300 ° C. FIG. 7 shows the result. Most pores disappeared by the overcoating process. From the above, after applying the paste (AR) added with the metal resinate on the alumina substrate and heat-treating at 1200 ° C. to form the Pd-Ag film, the paste (AN) without adding the metal resinate was applied on the Pd-Ag film. It was judged that the film forming method in which the film was overcoated and heat-treated at 1300 ° C. was preferable as the film forming condition.

(1.4) Film formation on SrCeO ₃ substrate Next, an attempt was made to form a Pd film on the AECeO ₃ substrate. As the AECeO ₃ substrate, a dense body having a diameter of 16.8 mm, a thickness of 1.0 μm, and a relative density of 95% or more among SrCe _0.95 Yb _0.05 O _3-a (SCO) manufactured by TYK was easily selected. As the film forming conditions, the film forming conditions on the alumina described in the previous section (1.3) were used. The results are shown in FIG. Also on the SCO substrate, the same deposition conditions as the alumina substrate, that is, the paste (AR) added with the metal resinate was applied on the SCO substrate and heat treated at 1200 ° C. to form the Pd-Ag film, and then the metal resinate was added. It was confirmed that it was possible to form a dense film in which most pores disappeared by repeatedly applying the paste (AN) not added to the Pd-Ag film and heat-treating it at 1300 ° C.

(1.5) Adhesion of Pd / SCO composite film
In order to confirm the adhesion between the Pd-Ag film and the SCO substrate, the sample cross section was mirror finished and the cross section was observed with an optical microscope (observation magnification × 500). The results are shown in FIG. The Pd-Ag film was very well adhered to the SCO substrate, and it was confirmed that the Pd film was not peeled off in the scratch test. Furthermore, it was confirmed that the SCO substrate was a dense film having a relative density of about 95% or more but contained closed pores. On the other hand, it was confirmed that the Pd film had almost no pores and was formed as a very dense film. The film thickness was about 65 μm.

(1.6) Cross-sectional observation of composite film by EPMA Elemental analysis of the film was performed by EPMA (Electron Probe MicroAnalyzer: JEOL, JXA-8900R). A characteristic X-ray image of Pd, Ag, Ce, and Sr by EPMA is shown in FIG. Diffusion of each film component element was not confirmed, and it was found that the formed film was physically well adhered and compounded without chemical diffusion. Moreover, it can be said that the fact that there is no mutual diffusion in the heat treatment at a high temperature of 1300 ° C. shows that there is no chemical reaction between the Pd—Ag phase and the SCO phase. Therefore, it is considered that the Pd / SCO composite film is composited while maintaining the physical properties of the Pd-Ag film and the SCO substrate. Furthermore, although the Pd-Ag film was Pd particles and Ag particles in the initial stage of paste preparation, it was confirmed that they were uniformly alloyed without uneven distribution of Pd and Ag elements.

  Next, the Pd-Ag film composition was analyzed by EDX analysis. FIG. 11 shows the result of composition correction based on actual measurement values of EDX measurement (Energy Dispersive X-ray Analysis) using a standard sample. While the charged composition was Pd / Ag = 77/23, the composition after the film formation was Pd / Ag = 84.9 / 15.1, indicating that the Ag component was considerably reduced. This is considered to be greatly affected by the annealing temperature. The Pd-Ag binary phase diagram is shown in FIG. It is known that Pd and Ag have the same cubic crystal structure and form a complete solid solution. The melting point of Ag (962 ° C.) is considerably lower than that of Pd (about 1555 ° C.), and it is considered that the Ag particles first dissolve first during the annealing process. From the results of EPMA, the diffusion of Ag into the SCO film was not confirmed, but in the Pd-Ag film, the Pd element is uniformly distributed, but the Ag element is slightly from the surface to the SCO film interface. Concentration distribution was confirmed. This is because the dissolved Ag particles evaporate as the temperature rises from the film surface, so the Ag concentration slightly decreases toward the surface side, and it is thought that the concentration distribution of Ag that eventually alloyed with Pd was generated. The total amount of Ag is also considered to have decreased.

(2) To confirm the CO ₂ resistance resistance to CO ₂ confirmation fabricated composite membrane of the composite membrane by CO ₂ atmosphere continuous exposure test was carried out continuous exposure tests in CO ₂ atmosphere.

(2.1) Experimental method There are two types of samples used for the test (SCO substrate, Pd / SCO composite film substrate). The Pd / SCO substrate was subjected to the film formation conditions in (1.1) to (1.6) described above, that is, the paste (AR) added with a metal resinate was applied to the entire SCO substrate and heat-treated at 1200 ° C. After forming the Ag film, a paste (AN) to which no metal resinate was added was overcoated on the Pd-Ag film and heat-treated at 1300 ° C. to eliminate the exposed surface of the SCO phase. Both samples were placed on an alumina felt and set in a tubular furnace. The CO ₂ resistance test was performed in a CO ₂ atmosphere after evacuating the tube furnace. The CO ₂ exposure time was 10 hours, and the temperature was constant at 650 ° C.

(2.2) Surface composition analysis of composite film by XRD
The XRD analysis results after the CO ₂ exposure test are shown in FIG. The Pd / SCO plate was peeled off from the Pd film on the surface to analyze the SCO layer. Compared with the peak of the SCO substrate before the heat treatment, the peak of the SCO substrate after the CO ₂ exposure almost showed diffraction peaks attributed to CeO ₂ and SrCO ₃ , and it was confirmed that the SCO phase was completely decomposed. On the other hand, the Pd / SCO substrate showed a diffraction peak almost exclusively attributed to the SCO phase, and it was clarified that the vulnerability to the CO ₂ of the SCO phase was overcome by combining with the Pd film.

(3) Proton conductivity of Pd / SCO composite membrane (3.1) Experimental method
In order to confirm the proton conductivity of the Pd / SCO composite membrane, (1) from the electromotive force obtained by the hydrogen concentration cell method, it is determined whether or not the conductive species are ions, and (2) the electrochemical nature of hydrogen. Proton was directly identified as a conductive species by the transmission method. Below, the two types of measurement methods will be described.

(3.1.1) Hydrogen concentration cell method When a hydrogen activity difference (concentration difference) occurs on both sides of the proton conductor, an electromotive force corresponding to the activity difference is shown. FIG. 14 shows the operating principle of a hydrogen concentration cell using the difference in concentration of hydrogen. Proton conductive solid is used as an electrolyte partition, and porous electrodes are attached to both sides to form two electrode chambers. When a high hydrogen partial pressure gas is introduced into one and a low hydrogen partial pressure gas is introduced into the other, a high hydrogen content is obtained. An electromotive force is generated with the pressure side as the negative electrode. The battery configuration at this time is expressed as Formula (Chemical Formula) 11, and an electrode reaction like Chemical Formulas 12 and 13 is about to occur between the negative electrode (anode) and the positive electrode (cathode). A derived electromotive force E (V) is generated.

Where R is the gas constant (8.314 JK ⁻¹ mol ⁻¹ ), T is the absolute temperature (K), F is the Faraday constant (96485 Cmol ⁻¹ ), P _H2 (1) and P _H2 (2) are the anode and The hydrogen partial pressure at the cathode. If one hydrogen partial pressure (for example, P _H2 (1)) is fixed in the chemical formula 14, the electromotive force is the logarithm of the other hydrogen partial pressure (in this case, P _H2 (2)), as shown in FIG. In contrast, a linear relationship is established. Further, the value obtained by dividing the measured electromotive force E by the theoretical electromotive force E ₀ obtained from the chemical formula 14 can be regarded as the ion transport number under the condition. In addition, when a hydrogen activity difference (concentration difference) occurs on both sides of the proton conductor, it is possible to apply this to a hydrogen sensor by utilizing an electromotive force corresponding to the activity difference. is there.

(3.1.2) Electrochemical Permeation Method of Hydrogen FIG. 16 shows the operating principle of the electrochemical permeation method (hydrogen pump) of hydrogen. Using a proton conductive solid as a partition wall, a hydrogen source is introduced into one side, and an inert gas such as argon is introduced into the other side. When a direct current is applied with the argon side as a cathode, if it is a proton conductor, an electrode reaction as shown in chemical formulas 12 and 13 occurs at each pole. In this case, since ions other than protons cannot pass through the partition wall, only hydrogen can permeate (pump). Thus, since the hydrogen pump forcibly permeates hydrogen using an electrochemical reaction, the proton conductivity of the supplied electrolyte can be directly confirmed. Further, after calculating the hydrogen permeation rate from the hydrogen concentration obtained from the cathode outlet gas analysis, the proton transport number (proportion of protons in all conductive species) is compared with the theoretical hydrogen permeation rate calculated from Faraday's law. ) Can be calculated.

(3.2) Hydrogen concentration cell using Pd / SCO composite membrane As shown in FIGS. 17 and 18, the produced electrolyte membrane was SrCe _0.95 Yb _0.05 O _3-a (thickness 1 mm, φ16.8 mm) substrate 5 In addition, a Pd—Ag film 6 (φ13 mm, thickness 65 μm) is formed on one side. On the other hand, a platinum paste was applied in a circular shape (φ12 mm) at the center, and baked in air at 900 ° C. for 30 minutes, and used as a porous electrode Pt7 (φ12 mm). An outline of the apparatus used in the experiment is shown in FIG. A sample in which a platinum net was attached to the electrode portions on both sides as a current collector was pressed from above and below with a φ17 × 13 mm alumina tube through a Pyrex (registered trademark) glass ring. Each gas chamber was heated to 1000 ° C. to soften Pyrex (registered trademark) glass to gas tight (in a state where the gas seal was completely effective). Both the anode 6 and the cathode 7 were confirmed to be gas tight by using a membrane flow meter and having no difference in the flow rate at the inlet and outlet. Thereafter, air was introduced for about 30 minutes to stabilize the state of the electrode, and then the experiment was started by switching to a predetermined gas. In FIG. 19, the gas flow rate is set by MFC 8, the target gas is supplied to each of the anode 6 and the cathode 7 via the humidifier 9, and the anode exhaust gas 10 and the cathode exhaust gas 11 are discharged. Here, reference numeral 5 represents an electrolyte. The cathode exhaust gas 11 is arranged so that the exhaust gas composition can be measured by the micro gas chromatography device 13. The reaction temperature is adjusted by the electric furnace 12. The gas was introduced at a flow rate of 100 ml / min. The electromotive force generated between the anode 6 and the cathode 7 was measured using an electrometer (HE-106 manufactured by Hokuto Denko). As the gas, 100% H ₂ humidified at room temperature (3%) is introduced into the Pd film side that becomes the anode 6, and 1, 5, 10, 20, 50, and 100% H ₂ are Ar-based for the cathode 7, respectively. It was introduced as a mixed gas. Before the measurement, it was confirmed that the cathode inlet gas had a target gas composition by using micro gas chromatography (M-200, manufactured by HP, molecular sieve column: MS-20).

  FIG. 20 shows the results of measuring the electromotive force in each gas composition at 650, 750, 850, and 950 ° C. Within the measurement condition range, it almost coincided with the theoretical value calculated from the Nernst equation (Chemical formula 14). From this result, it was confirmed that the conductive species of the Pd / SCO composite film are ions.

(3.3) Hydrogen permeation experiment using Pd / SCO composite membrane In the hydrogen concentration cell method, it is possible to determine whether or not the conductive species is an ion, but whether the proton is conductive or not directly. It cannot be judged. Therefore, a direct current was applied between the anode and the cathode, and it was directly confirmed whether or not hydrogen was generated on the cathode side (hydrogen pump). In the case described above, hydrogen was bubbled on the Pd-Ag film side and argon on the other side of the Pd / SCO composite film (see FIGS. 17 and 18), both were bubbled at room temperature, humidified, and circulated at 100 ml / min. . As the apparatus, the above-described experimental apparatus (see FIG. 19) was used. A solar current potentiogalvanostat SI1286 was used for DC energization, and a constant current was passed between the anode and cathode. At that time, the amount of generated hydrogen was quantified at the cathode outlet using micro gas chromatography (HP-M-200, molecular sieve column: MS-20). Measurements were performed at 650, 750, 850, and 950 ° C.

FIG. 21 shows the hydrogen generation rate with respect to the energization current. The broken line is the theoretical hydrogen generation rate (ml / min) calculated according to Faraday's law. At 650 ° C., the hydrogen generation rate was almost the theoretical value, and the Pd / SCO composite membrane was found to be a proton conductor having a proton transport number t _{H +} very close to 1. However, as the temperature increased, the hydrogen generation rate decreased from the broken line at high current. At a low current, the proton transport number is approximately 1, but at a high current, there are charge carriers other than protons. With respect to this point, it has been reported that when the amount of current is increased, water vapor in the cathode is decomposed and oxide ion conductivity is expressed as shown in chemical formula 15 (S. Hmajima, H. Matsumoto, H. Iwahara). , Proceedings of the 26th Solid State Ionics Conference P154, 2000). According to this report, at high currents, proton transport numbers may decrease and current efficiency may decrease.

  Therefore, it is considered that the Pd / SCO composite membrane has a proton conductive function similar to that of the SCO membrane. From the above, it has been clarified that the SCO membrane has a proton conductive function similar to that of SCO without degrading the proton conductive function by being combined with Pd.

(4) Fuel cell power generation using Pd / SCO composite membrane (4.1) Power generation principle of fuel cell The principle of a hydrogen-oxygen fuel cell using a proton conductor will be described. The operating principle is shown in FIG. Consider the combustion reaction of hydrogen and oxygen as shown in chemical formula 16.

The combustion reaction of hydrogen is an oxidation reaction of hydrogen with oxygen, and usually releases thermal energy. From the standpoint of oxygen, this combustion reaction is a reduction reaction of oxygen by combustion. Thus, thermal energy is released when both reactions occur in the same field. Therefore, for example, as shown in FIG. 22, if a reduction reaction can be performed using hydrogen as an anode active material and oxygen as a positive electrode (cathode) active material via a proton conductive electrolyte, combustion of hydrogen can be performed. The chemical energy of the reaction can be directly converted into electric energy based on the same principle as that of a dry battery (Chemical Formulas 17 and 18).

  In this case, the electromotive force E between the electrodes is generated as a potential difference between the anode from which electrons are released by the oxidation reaction of hydrogen and the cathode from which electrons are insufficient by the reduction reaction of oxygen. In the case of a hydrogen-oxygen fuel cell, the electromotive force E can be expressed by the following equation.

Here, K represents the equilibrium constant of Chemical Formula 16, p _i represents each gas partial pressure, subscripts a and c represent the anode and cathode, respectively, R, F and T represent the gas constant, Faraday constant and absolute temperature, respectively.

(4.2) Experimental Method FIG. 23 shows the apparatus configuration used in the experiment. The basic configuration of FIG. 23 is the same as that of FIG. 19 except that the gas that can be supplied to the anode side is O ₂ instead of H ₂ . As the electrolyte, the same sample as in (3.2) (see FIGS. 17 and 18) was used. The sample electrolyte was sandwiched between alumina tubes with electrolyte partition walls, the Pd-Ag film side as an anode, and the porous platinum side as a cathode. Wet hydrogen or hydrogen and carbon dioxide wet mixed gas saturated at room temperature as the fuel gas was passed through the anode, and wet oxygen saturated at room temperature as the oxidant gas 5 was flowed through the cathode at 100 ml / min. By configuring the fuel cell in this way, an electromotive force calculated from the Nernst equation (Chemical Formula 19) is generated. The generated terminal voltage was measured using an electrometer (HE-106 manufactured by Hokuto Denko). A solartron potentiogalvanostat SI1286 as an external load device was connected between the anode and the cathode to confirm the power generation performance.

(4.3) Characteristics of Fuel Cell Using Pd / SCO Composite Membrane FIG. 24 shows the electromotive force of the hydrogen-oxygen fuel cell at measurement temperatures of 650, 750, 850, and 950 ° C. At the same time, the theoretical electromotive force calculated from the Nernst equation (chemical formula 19) is shown in FIG. The electromotive force showed a value close to the theoretical electromotive force at 650 ° C. Prior to the test, it was confirmed that there was no gas tight and no cross leak, so the ratio between the measured value of electromotive force and the theoretical value was the ion transport number (actual value / theoretical value): t _ion (0 <t _ion In contrast, the electron transport number (in this case, hole conduction) is represented as t _h (= 1−t _ion ). FIG. 25 shows t _ion and t _h calculated from the electromotive force. The t _ion was 0.88 at 950 ° C., but became 0.99 at 650 ° C. As a result, it was found that the Pd / SCO composite membrane produced this time functions as a pure proton conductor having a proton transport number of 1 under the fuel cell atmosphere conditions lower than 650 ° C.

  Next, we actually took out the current and tried to generate electricity. The results are shown in FIG. It showed stable voltage and current during power generation, and it was found that fuel cell power generation is possible using the composite membrane type electrolyte of the Pd-Ag film and SCO film according to the present invention.

(4.4) Long-term power generation characteristics using fuel gas containing CO ₂ Up to the previous section (4.3), we confirmed the possibility of power generation using Pd / SCO composite membranes. It is to confirm the possibility of power generation under anode gas conditions containing CO ₂ . In response to this, as described below, when introducing an anode gas containing CO ₂ , it was decided that the Pd membrane would not cause any deterioration of the SCO membrane due to CO _{2 and} that fuel cell power generation could be performed stably.

FIG. 27 shows a change with time in voltage during power generation when a mixed gas of CO ₂ and H ₂ is introduced into the anode. The voltage decreased for a while in the initial stage and then became constant and stable. In addition, when a continuous load test was conducted, it was confirmed that the power generation was stable for at least the same 10 days as the CO ₂ exposure test. From the above results, the metal / oxide composite membrane electrolyte (Pd / SCO) that can maintain proton conductivity and overcome the vulnerability to CO _{2 according} to the present invention is a fuel cell that uses fuel containing CO _2. It became clear that it was applicable.

[Example 2]
In Example 1, the possibility of power generation when a Pd / SCO membrane was used as an electrolyte of a fuel cell was examined and verified as theoretically. However, in order to actually apply as an electrolyte of a fuel cell, various studies must be made at the operating temperature. Therefore, as Example 2, the metal / oxide composite membrane type electrolyte was further examined from the viewpoint of performance and the material cost of the electrolyte with respect to the medium temperature fuel cell using the metal / oxide composite membrane type electrolyte.

The fuel cell power generation test was performed in the same procedure as in [Example 1]. In Example 2, BaCe _0.8 Y _0.2 O _3-a (hereinafter referred to as BCO) having higher conductivity than SCO and leading to cost reduction was also examined. In the produced composite membrane type electrolyte, a Pd—Ag alloy film (φ13 mm, thickness 65 mm) is formed in a circular shape at the center of one side of the SCO or BCO substrate. On the other hand, a platinum paste was applied in a circular shape (φ13 mm) at the center, and baked in air at 900 ° C. for 30 minutes, and used as a porous electrode.

FIG. 39 shows current-voltage characteristics in the middle temperature range (500 to 600 ° C.) when SCO and BCO are used as the electrolyte. The power generation test temperature was 600 ° C. for the Pd / SCO composite membrane and 500 and 600 ° C. for the Pd / BCO composite membrane. From the current-voltage characteristics at 600 ° C, the short-circuit current density was doubled by using BCO with high proton conductivity. In addition, the battery performance at 500 ° C for Pd / BCO has improved to about two thirds of the battery performance level at 600 ° C for Pd / SCO. However, even in the Pd / BCO cell, since the short-circuit current density is about 7 mAcm ⁻² , further performance improvement is expected. Next, we analyzed the factors that govern the performance of the BCO cell, and conducted experiments to extract issues for performance improvement using the following method.

  First, current-voltage characteristics and overvoltage characteristics were evaluated. By evaluating these, the voltage drop factor during power generation of the BCO cell can be separated into electrolyte resistance, anode reaction resistance, and cathode reaction resistance. Therefore, from this result, it is possible to grasp how much the battery performance is reduced by which factor (component). The overvoltage characteristics were measured by a current interruption (current interruption) method with a reference electrode 16 provided. As shown in FIG. 38, the reference electrode 15 was produced by applying a Pt paste to the side surface of the electrolyte 14, drying it, and baking it at 900 ° C. A platinum wire of φ0.3 mm was wound from above and attached to the platinum lead wire 16. Reference numeral 19 denotes an anode electrode, and a cathode electrode is formed on the opposite surface through the electrolyte 14. A current collecting net 17 is arranged on the cathode electrode side and the anode electrode side, and these are sandwiched between glass packings 18 (the current collecting net 17 and the glass packing 18 on the anode electrode side are not shown).

Here, the current interruption method will be described. An electrochemical cell composed of an electrode and an electrolyte is shown in FIG. 40 as a simplified electrical equivalent circuit. At high temperatures, the conductance of the capacitor component of the electrolyte is considered to be negligibly small (C _b = 0), and for an electrolyte it is usually represented only by ohmic resistance (R _b ). The electrode-electrolyte interface is represented by a parallel circuit composed of an electrode reaction resistance _Re and a double layer capacitance _Cdl . The current interruption method is a method in which an actual battery is charged with an electric double layer with a pulse current having a cycle of about several milliseconds and an overvoltage is obtained from a transient curve observed thereafter. FIG. 41B shows the device configuration. Specifically, using a function generator 20 (NF circuit block WF1256) and potentio galvanostat 23 (SolarTron SI1286), the pulse current is 2 msec / cycle between the cathode and anode of the measurement cell 24 and an off pulse width of 0.1 msec. Apply. At this time, the change in potential between each electrode and the reference electrode was measured using an electrometer 22 after being synchronized using a digital oscilloscope 21. In this case, as shown in FIG. 41 (a), when the current is interrupted, it changes abruptly by the potential corresponding to the ohmic resistance (FIG. 41, iR _b drop). Next, the electric charge charged in C _dl is discharged through a resistance (electrode reaction resistance R _e ) in parallel with the capacitance, and the corresponding potential changes transiently. By measuring the potential before and after blocking the potential difference in this way, it is possible to determine the overvoltage (h = iR _e ).

  During the test, in order to confirm whether the electrolyte has deteriorated over time, a 1 kHz, 5 mV AC signal was input between the cell terminals by the AC method, and the impedance was monitored as the electrolyte resistance.

The current-voltage characteristics of the fuel cell at 500 ° C. are shown in FIG. Further, in FIG. 42, the breakdown of the voltage drop caused by taking out the current was obtained from the overvoltage due to the BCO film (electrolyte overvoltage), the overvoltage due to the Pd film (anode overvoltage), and the overvoltage due to the porous Pt (cathode overvoltage). The anode overvoltage was the smallest, followed by the cathode overvoltage and the electrolyte overvoltage in this order, and the short-circuit current density was 7 mA / cm ² or less at 500 ° C. Therefore, by overhauling each battery member from the material and the production method, an attempt was made to reduce overvoltage and improve performance.

(1) Overvoltage reduction by electrolyte densification The electrolyte overvoltage is proportional to the electrolyte resistance. Therefore, the electrolyte resistance of the initial BCO was obtained from the electrolyte overvoltage in FIG. 42 and shown in FIG. It was found that the electrolyte resistance of the initial BCO was considerably larger than the electrolyte resistance converted from the conductivity of BCO at 500 ° C. shown in FIG. The reasons for this are (1) reaction deterioration of the electrolyte and (2) poor sinterability of the electrolyte. As for the cause of 1, the BCO surface after the test has been subjected to X-ray diffraction analysis so far, but only the BCO single-phase peak has been obtained. For this reason, it is considered that most of the overvoltage is caused by the sinterability of the electrolyte of 2. A solid electrolyte such as BCO exhibits an electrolyte resistance converted from electrical conductivity if the degree of sintering is 95% or more. Conversely, as the degree of sintering decreases, the electrolyte resistance increases. In BCO, the theoretical electrolyte resistance converted from the conductivity should be about 6Ω at 500 ° C, but the electrolyte resistance measured during this test was about 80Ω at 500 ° C. In addition to the net resistance of the electrolyte, the electrolyte resistance includes contact resistance with the current collecting net and lead wire resistance. However, since it is unlikely that the contact resistance and the lead wire resistance are several tens of Ω or more, it can be seen that most of 80 Ω is caused by the electrolyte resistance. In other words, it was found that the initial BCO has poor sinterability and needs to be densified. Therefore, the BCO sintering process was reviewed. Specifically, when the molding load was increased in the final molding before the sintering heat treatment, it was found that the sintered body of the same weight decreased in volume by about 8% and became dense. This densified BCO sample was used for the test, and the results of comparing the initial BCO electrolyte resistance, the improved BCO electrolyte resistance, and the BCO electrolyte resistance converted from the BCO conductivity as physical properties are shown in FIG. . The electrolyte resistance of the initial BCO was about 20 times larger than the electrolyte resistance calculated from the BCO conductivity, which was a factor in performance degradation. However, this time, by densifying the BCO electrolyte, the electrolyte resistance could be reduced to about 1/7 compared to the initial BCO electrolyte resistance. Since the density of the electrolyte affects the performance of the electrochemical device, it was expected that more preferable electrochemical device performance can be obtained by setting the degree of sintering to 95% or more.

(2) Low overvoltage by reviewing Pd film formation method (2.1) Examination of Pd film formation method As mentioned above, reduction of anode overvoltage was also cited as an issue. Hereinafter, a method for reducing the anode overvoltage was examined from the viewpoint of the denseness of the film and the adhesion to the electrolyte.

  In order to further improve the adhesion of the film to the substrate and form a dense film, it is necessary to raise the film formation temperature sufficiently. However, since the Pd paste film is an alloy film with Ag as described above in Example 1, the processing temperature cannot be increased. Therefore, it was considered that the same effect as increasing the processing temperature can be obtained by making the starting particles constituting the membrane fine. From this point of view, an electroless plating method having good adhesion to the substrate and a high possibility of forming a uniform dense film was studied.

(2.2) Formation of dense Pd alloy film by electroless plating method In order to perform electroless plating on non-conductive substrates such as ceramics, plastics, glass, etc., catalytic activation that gives the substrate activity against the plating reaction It is known that pretreatment is necessary. Further, it is known that the treatment at this time changes the distribution and activity of catalyst nuclei formed on the substrate surface, and deposits plating films having different surface forms and physical properties. Here, electroless plating was performed using a two-component method (sensitization-activation method), which is a typical pretreatment for catalyst activation by a wet method. The two-component method activation pretreatment is generally represented by the following reaction formula.
Pd ²⁺ + Sn ²⁺ = Pd + Sn ⁴
Hereafter, the electroless plating method performed here is demonstrated based on the electroless-plating flowchart shown in FIG.
As a preparatory stage, the substrate was washed with acetone and replaced with alcohol, followed by drying. As then the catalyst activation pretreatment (two-liquid method), SnCl ₂ HCl solution an solution, a PdCl ₂ solution of hydrochloric acid as a two-part, repeated 10 times immersed alternately into one-pack and two-pack, to precipitate Pd nuclei It was. Next, electroless plating bath containing [Pd (NH ₃ ) ₄ ] Cl ₂ · H ₂ O, EDTA · 2Na, NH ₃ (28% aqueous solution), H ₂ NNH ₂ · H ₂ O, and ammonia / alkaline The Pd nucleus was immersed for 1 hour to deposit Pd around the Pd nucleus as a catalyst to form a thin film of Pd. This was washed with distilled water, and was added to a solution containing [Pd (NH ₃ ) ₄ ] Cl ₂ , AgNO ₃ , EDTA · 2Na, NH ₃ (28% aqueous solution), H ₂ NNH ₂ · H ₂ O for 1 hour. Immersion was performed to deposit silver on the palladium thin film to form a silver thin film. Further, this was washed with distilled water and subjected to heat treatment at 850 ° C. for 10 hours in a N ₂ gas stream to obtain a dense Pd alloy film.

(2.3) Cross-sectional observation of Pd alloy film by EPMA Al ₂ O ₃ was selected as the electroless plating substrate, and the properties of the plating film were confirmed. The cross-sectional analysis of the Pd alloy dense film plated on the substrate was performed by EPMA (Electron Probe MicroAnalyzer: JEOL, JXA-8900R). A characteristic X-ray image of Pd, Ag, Al by EPMA is shown in FIG. In the figure, (a) is a characteristic X-ray image of Pd, (b) is Ag, and (c) is a characteristic X-ray image of Al. It was observed that Pd and Ag were well diffused and alloyed. On the other hand, no diffusion of Al element from the substrate toward the Pd film was confirmed.
Next, Pd alloy film composition was analyzed by EDX (Energy Dispersive X-ray) analysis attached to EPMA. Table 2 shows the result of quantifying the composition ratio (wt%) by EDX at each part of the membrane using Pd and Ag standard samples. The composition ratio averaged to Pd / Ag = 76.6 / 23.4, and good results were obtained. From the above, it was confirmed that by selecting the electroless plating method, it was possible to alloy the target composition uniformly without uneven distribution of Pd and Ag elements.

(2.4) Anode overvoltage when electroless plating is applied
The anode overvoltage was compared using a composite membrane type electrolyte with a Pd alloy dense film formed on BCO by electroless plating and a composite membrane type electrolyte using the paste method. The measurement method used was a current interruption method. The result of measuring the anode overvoltage at 500 ° C. is shown in FIG. It was confirmed that the anode overvoltage can be further reduced in the Pd alloy dense film using the electroless plating method compared with the Pd alloy dense film produced by the paste method. Therefore, it was suggested that the Pd alloy dense film formed by the electroless plating method is more closely adhered to the BCO than the Pd alloy dense film prepared by the paste method and is a dense film.

  Here, the anode reaction of the composite membrane type electrolyte was considered as follows. 1 Diffusion and adsorption of hydrogen on dense film, 2 Dissociation of hydrogen molecule into hydrogen atom, 3 Dissolution of hydrogen atom into Pd dense film, 4 Diffusion of hydrogen, 5 Ionization of hydrogen to proton at Pd / BCO interface, 6 Proton dissolution in BCO. The factors that increase the anode overvoltage were discussed below. The processes 1 to 4 are considered to depend on the physical properties of the Pd alloy film, and it is considered that there is no difference depending on the film forming method. However, processes 5 and 6 depend on the superiority or inferiority of the film adhesion. From these viewpoints, it was suggested that the Pd alloy dense film formed by the electroless plating method was more firmly adhered to the BCO than the Pd alloy dense film prepared by the paste method.

(3) Cathode overvoltage reduction by reviewing the cathode material The porous Pt that has been used as a cathode material so far, as shown in the temperature dependence of the overvoltage shown in FIG. Cathode overvoltage has increased considerably. Also, Pt itself is an expensive material and is not considered suitable as a cathode for future medium temperature fuel cells. Therefore, the cathode material was examined.

  In the middle temperature range, a cathode material that exhibits electrode activity and is inexpensive must be selected. Recently, good cathode activity in a medium temperature region has been shown in a cathode using inexpensive Ag. Pt is about 3,000 yen / g, whereas Ag is about 26 yen / g (26,000 yen / kg), which is superior in cost. Therefore, in this study, we compared overvoltages at 500 ° C using Ag as the cathode target material and Pt and Pd as the comparative cathode materials. Since Pd can be used as an anode material in an intermediate temperature range, it was selected to confirm whether it can be applied to the cathode. The overvoltage comparison results are shown in FIG. Each paste was applied and dried, and Pt and Pd were baked at 900 ° C., and Ag was baked at 800 ° C. because the melting point was as low as 962 ° C. From FIG. 48, it became clear that the cathode overvoltage can be greatly reduced by applying a porous Ag cathode. On the other hand, Pd showed the same cathode overvoltage as Pt.

  An SEM photograph of the cathode surface after the test is shown in FIG. In the figure, (a) is Pd, (b) is Pt, and (c) is the result of SEM observation of the Ag cathode surface. The surface morphology of Ag was observed as Ag aggregated compared to Pt and Pd. In general, in a porous electrode, the overvoltage increases as the area of the three-phase (gas-electrode-electrolyte) interface where the electrode reaction occurs, but FIG. 48 shows the result that the overvoltage decreases in contrast to the above. Regarding this result, it is suggested that the characteristic of Ag which is not in Pt and Pd is that oxygen permeability is involved in the electrode reaction. From the above, the possibility as a cathode material in the middle temperature range of Ag was shown.

(4) Improvement of battery performance by cells with performance improvement measures Densification of electrolyte, review of Pd film formation method, and change of cathode material can reduce overvoltage and improve cell performance. FIG. 50 shows the result of applying a power generation test at 500 ° C. by reconfiguring a single cell. As a result of selecting an electroless Pd alloy plating dense film + BCO film + porous Ag cathode, the maximum power density was 0.037 Wcm ^-2 even at 500 ° C, and Pd / SrCeO ₃ cell using the Pd paste method of Example 1 We succeeded in improving the battery performance by about 15 times.

Next, the battery performance that can be reached in the medium temperature fuel cell was estimated, and the battery performance level was examined. The battery performance of the intermediate temperature fuel cell was estimated as follows. Since the electrolyte resistance, anode and cathode reaction resistance can be obtained from the electrical conductivity of BCO and the overvoltage characteristics of the Pd dense film and Ag porous cathode, the battery output density, that is, the battery performance can be estimated. As a trial calculation condition, in a hydrogen-oxygen fuel cell, an operating temperature of 500 ° C. and an electrolyte thinning were successfully established. A BCO film thickness of 20 mm was set, an electroless Pd alloy plating dense thin film was used for the anode, and porous Ag was used for the cathode. After calculating the total resistance, the output density characteristics were estimated from the current-voltage characteristics. The trial calculation results are shown in FIG. The results so far are also shown in the figure for comparison. The estimated performance at 500 ° C is comparable to the current high-temperature SOFC performance (power density at 0.22 Wcm ^-2 , 300 mAcm ^-2 , 0.74 V) when electroless Pd alloy plated dense thin film + BCO thin film + porous Ag cathode is selected. 0.24 Wcm ^-2 (BaCeO ₃ film thickness 20mm, 300mAcm ^-2 power density) was estimated, and it was shown that the battery performance level was comparable to high temperature SOFC.
[Example 3]
Up to this point, the possibility of power generation when using Pd / SCO membranes and Pd / BCO membranes as fuel cell electrolytes has been investigated and verified theoretically. Therefore, further consideration was given below from the viewpoint of material cost, and the possibility as a fuel cell was estimated.

The comparison target was SOFC. In the cost estimation, we compared BCO, which has higher conductivity than SCO and leads to cost reduction. The composite membrane electrolyte according to the present invention has a merit that an anode material is not required because a metal part also has an anode function by compounding a metal and an oxide electrolyte. On the other hand, the applied palladium (Pd) alloy membrane shows high hydrogen permselectivity and has the potential to be used for the production of high-purity hydrogen necessary for semiconductor production, but metal Pd is extremely expensive like gold and platinum. This metal is a major obstacle to practical use. As materials for the hydrogen permeable membrane 2, there are currently active developments of inexpensive metal film materials to replace them, and among them, Zr-Ni, V-Ni, Nb-Ni, etc. are inexpensive. Attention has been focused on new alloy materials. The hydrogen permeability of these permeable membranes is one order of magnitude less than that of Pd membranes (10 ^-7 mol / (m ² · s · Pa)). It's a fraction of the cost. Therefore, in order to aim for practical use, it is considered essential to reduce the amount of Pd used as much as possible or to develop an inexpensive hydrogen permeable membrane 2.

  Actually, the film thickness of the metal / oxide composite membrane type electrolyte was estimated from the viewpoint of material cost. The following formula 1 was used for the trial calculation formula. Moreover, the value of Table 3 was used for the material unit price and the density.

First, the cost for electrolyte (YSZ) + anode (Ni-YSZ) in SOFC was estimated. The trial calculation performance was performed at 0.74 V at 300 mA / cm ² with an electrolyte thickness of 40 μm and an anode thickness of 100 μm (see Table 3 for results). The raw material cost per kW of SOFC (electrolyte + anode) using YSZ was about 1,785 yen. It is necessary to consider the total costs required for manufacturing in total for the actual estimated cost. Taking the flat-plate SOFC estimated on a monthly basis as an example, it is approximately 68,000 yen / kW. The cost of the electrolyte + anode was estimated to be about 11,000 yen / kW. Next, the cost of Pd-BCO was estimated based on the raw material cost of YSZ. In Pd-BCO, since the cost of Pd is extremely high, the optimum Pd film thickness and BCO film thickness were obtained by using the Pd film thickness as a parameter and comparing it with the raw material cost of YSZ. Note that the BCO film thickness is the same as the YSZ film thickness order because the current SOFC electrolyte film thickness is several tens of μm, and it is considered difficult to produce an electrolyte film thickness of 10 μm or less from the viewpoint of the manufacturing method. The results are shown in FIG. From FIG. 28, when the Pd film thickness is thicker than 0.1 μm, it seems difficult to put it to practical use in terms of cost. Even if the Pd film thickness is 0.1 μm or less, it is considered that if the BCO film thickness is greater than 20 μm, it will be higher than YSZ. The Pd film thickness can be reduced to 0.1 μm using the currently supported Pd hydrogen permeable film 2 film formation technology using the support film method. As a target, it is estimated that the BCO film thickness is preferably 20 μm or less in terms of cost.

  As described above, since the Pd / BCO electrolyte membrane is the thickest and has a thickness of about 20 μm, the structure cannot be kept mechanically with the electrolyte self-supporting membrane type. Therefore, a porous body support membrane type structure with a cathode or an anode is desirable. The porous body support membrane type structure is a structure that can be used in a sensor. In the case of an electromotive force type sensor that does not pass an electric current, there is no voltage drop due to ohmic cross, so that an electrolyte membrane self-supporting structure can be adopted. For other devices, it is necessary to make the electrolyte as thin as possible to energize. For this reason, since the strength of the electrolyte itself is insufficient, a porous body support membrane type structure is desirable.

  In the above, the future development target specifications of the metal / oxide composite membrane type electrolyte were calculated from the viewpoint of raw material costs. The electrolyte is preferably changed from SCO to BCO with high conductivity so that the film thickness is 20 μm or less and the Pd film thickness is 0.1 μm or less.

It is the schematic which showed simply the structure of the proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte which concerns on this invention. The defect structure and proton generation of AECe _1-x M _x O _3-a are compared with (a) stoichiometric composition (Stoichiometry), (b) in wet oxygen, (c) in dry oxygen, (d) It is the figure shown roughly about each in hydrogen. It is the figure which showed the principle of hydrogen permeation in a Pd film. It is a figure which shows the structure of the fuel cell using a hydrogen permeable membrane and proton conductive ceramics. It is a figure which shows the structure of the fuel cell using a metal / oxide composite membrane type electrolyte. For the paste containing metal resinate (AR) and the paste not containing metal resinate (AN), the Pd film formed on the alumina plate at each temperature (900 ° C, 1000 ° C, 1100 ° C, 1200 ° C, 1300 ° C) It is an image which shows a mode. (A) AR 900 ° C in air, (b) AR 1000 ° C in air, (c) AR 1100 ° C in air, (d) AR 1200 ° C in air, (e) AR 1300 ° C in air, (f) AN 1300 ℃ in air. It is an image which shows the mode of the Pd film | membrane densely formed on the alumina by two heat processing. It is an image which shows the mode of the Pd film densely formed on the SCO substrate by two heat treatments. It is an optical micrograph (x500) of a sample cross section. It is a figure which shows the characteristic X-ray image of each element by EPMA of a sample cross section. It is a graph which shows the correction | amendment content of the EDX actual value using a reference material. It is a binary phase diagram of Pd-Ag. It is a graph showing the comparison results of SrCeO ₃ phases before and after the exposure test as seen from the XRD analysis results. It is a figure which shows the principle of the hydrogen concentration battery using a proton conductor. It is a graph which shows the schematic relationship between the hydrogen partial pressure and an electromotive force in a hydrogen concentration battery. It is a figure which shows the principle of the hydrogen pump using a proton conductor. It is a top view of the composite membrane type electrolyte membrane produced in the present Example. It is a side view of the composite membrane type electrolyte membrane produced in the present Example. It is the apparatus schematic of a hydrogen concentration cell method. It is a graph which shows the relationship (actual battle: theoretical value) of the electromotive force and hydrogen partial pressure of a hydrogen concentration battery. It is a graph which shows the hydrogen generation rate with respect to an electric current. It is a figure which shows the principle of the hydrogen oxygen fuel cell using a proton conductor. It is the schematic of the apparatus used for the fuel cell experiment. It is a graph which shows the electromotive force of the fuel cell in each temperature. It is a graph which shows the temperature dependence of the proton transport number in the fuel cell atmosphere of Pd / SCO calculated | required from the electromotive force. It is a graph which shows the current-voltage characteristic of the fuel cell using a Pd / SCO film | membrane. 3 is a graph showing a change with time of voltage during discharge in a fuel cell using a fuel containing CO ₂ . It is a graph which shows Pd film thickness dependence of Pd-BCO film | membrane material cost. It is a figure which shows the mode of joining in a solid / liquid interface, and the mode of joining in a solid / solid interface. 1 is a diagram showing an embodiment of the present invention, and shows a composite membrane electrolyte in which a porous support is formed on the surface of the composite membrane on the anode gas (CO ₂ -containing gas) side. FIG. 2 is a diagram showing an embodiment of the present invention, in which a porous support is formed on the surface of the composite membrane on the anode gas (gas containing CO ₂ ) side, and protons are formed on the surface opposite to the anode gas. Another hydrogen permeable membrane through which (H ⁺ ) can pass is formed. 1 is a diagram showing an embodiment of the present invention, in which a porous cathode formed on a surface opposite to an anode gas side of a composite membrane is made to function as a porous support. 1 is a diagram showing an embodiment of the present invention, in which a porous cathode is formed on the surface of the composite membrane opposite to the anode gas side, and a porous support is formed on the cathode side surface of the porous cathode. It is. FIG. 5 is a diagram showing an embodiment of the present invention, in which another hydrogen permeable membrane capable of allowing protons (H ⁺ ) to pass is formed on the surface opposite to the anode gas side of the composite membrane, and further, the cathode side of the hydrogen permeable membrane A porous support is formed on the surface. It is a graph which shows the proton conductivity in hydrogen of various perovskite type oxides. SrCeO is a diagram showing the concept of a conventional hydrogen separation method using a ₃ membrane. It is a figure which shows the concept of the conventional hydrogen separation method using a Pd membrane. It is a figure which shows the setting state of a single cell. It is a figure which shows the current-voltage characteristic in the medium temperature range (500-600 degreeC) at the time of using SCO and BCO for electrolyte. It is a figure which shows the electrical equivalent circuit of the electrochemical cell which consists of an electrode and electrolyte. R _b : electrolyte resistance, R _e : reaction resistance, C _b : electrolyte capacitor capacity, C _dl : double layer capacity. It is a figure shown about the current interruption (current interruption) method. (A) is a waveform observed with an oscilloscope, (b) is a schematic diagram of the apparatus of the current interruption (current interruption) method. It is a figure which shows the electric current-voltage characteristic of the fuel cell in 500 degreeC. In the figure, OCV represents an open circuit voltage. It is a figure which shows the result of having compared the electrolyte resistance of BCO converted from the electrolyte resistance by initial stage BCO, the electrolyte resistance of BCO after improvement, and the electrical conductivity of BCO as a physical-property value. It is a flowchart of an electroless-plating process. The Al ₂ O ₃ the cross section of the Pd alloy dense film plated on a substrate which is a result of analysis by EPMA, illustrates Pd, Ag, a characteristic X-ray image of al. (A) is a characteristic X-ray image of Pd, (b) is Ag, and (c) is a characteristic X-ray image of Al. The results of measurement of anode overvoltage at 500 ° C by current interruption method using composite membrane type electrolyte with Pd alloy dense film by electroless plating on BCO and composite membrane type electrolyte using paste method are shown. FIG. It is a figure which shows the temperature dependence of overvoltage when using porous Pt as a cathode material. It is a figure which shows the comparison result of the overvoltage when Ag, Pt, and Pd are used as a cathode material. It is a figure which shows the SEM observation result of Ag, Pt, and a Pd cathode surface. (A) is Pd, (b) is Pt, (c) is an SEM observation result of the Ag cathode surface. It is a figure showing the result of conducting a power generation test at 500 ° C by reconfiguring a single cell by applying an improvement measure to reduce overvoltage by densifying the electrolyte, reviewing the Pd film formation method, and changing the cathode material . FIG. 5 is a diagram showing the results of trial calculation of output density characteristics from current-voltage characteristics after selecting the electroless Pd alloy plated dense thin film for the anode and porous Ag for the cathode and calculating the total resistance.

Explanation of symbols

1 SrCeO ₃ film (proton conductive oxide film)
2 Pd membrane (hydrogen permeable membrane)
3 Oxidant gas (gas containing CO ₂ )
S porous support

Claims (21)

Perovskite oxide (ABO ₃ ) with barium (Ba) or strontium (Sr) at the A site and rare earth element cerium (Ce) at the B site is the basic structure, allowing protons (H ⁺ ) to pass through. and only separable proton conductive oxide film hydrogen from gas containing CO ₂ there, and the protons (H ⁺⁾ are separable only hydrogen from gas containing and CO ₂ can pass through a hydrogen-permeable membrane The hydrogen permeable membrane is formed on at least the gas side surface of the proton conductive oxide film in a state where the composite interface between these two membranes is continuously joined, and the composite membrane is porous. A proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte supported by a porous support. The proton conductive oxide film has a structure in which a part of the rare earth element cerium (Ce) is substituted with another low-valent rare earth element different from the cerium (Ce ⁴⁺ ). The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 1.   The other rare earth element is one kind of rare earth element selected from the group consisting of ytterbium (Yb), yttrium (Y), dysprosium (Dy), gadolinium (Gd), samarium (Sm), and neodymium (Nd). The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 2.   The proton conductive oxide membrane-hydrogen permeable membrane composite membrane type electrolyte according to any one of claims 1 to 3, wherein the hydrogen permeable membrane is a metal or an alloy exhibiting hydrogen permeability.   The metal or alloy exhibiting hydrogen permeability is palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni) 5. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 4, comprising one or more selected from the group consisting of, or an alloy thereof with silver (Ag).   The metal or alloy exhibiting hydrogen permeability is palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper (Cu), nickel (Ni) 6. The proton conductivity according to claim 4 or 5, wherein the proton conductivity is formed by electroless plating using one or more selected from the group consisting of, or an alloy of silver and silver (Ag) as a component. Oxide membrane-hydrogen permeable membrane composite membrane electrolyte.   The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to any one of claims 1 to 6, wherein a porous support is formed on the gas side surface of the composite membrane. .   8. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 7, wherein a porous cathode is formed on a surface of the composite membrane opposite to the gas side.   9. The proton conductive oxidation according to claim 8, wherein the porous cathode contains at least one of an electron-oxide ion mixed conductive oxide having a perovskite structure and silver (Ag). Material membrane-hydrogen permeable membrane composite membrane type electrolyte. 8. The proton conductive oxidation according to claim 7, wherein another hydrogen permeable membrane through which the proton (H ⁺ ) can pass is formed on a surface opposite to the gas side of the composite membrane. 9. Material membrane-hydrogen permeable membrane composite membrane type electrolyte.   The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to claim 10, wherein the another hydrogen permeable membrane is a metal or an alloy exhibiting hydrogen permeability.   The metal or alloy showing hydrogen permeability constituting the another hydrogen permeable membrane is palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper The proton conductive oxide film-hydrogen permeation according to claim 11, comprising one or more selected from the group consisting of (Cu) and nickel (Ni), or an alloy thereof with silver (Ag). Membrane composite membrane electrolyte.   The metal or alloy showing hydrogen permeability constituting the another hydrogen permeable membrane is palladium (Pd), niobium (Nb), tantalum (Ta), lanthanum (La), titanium (Ti), zirconium (Zr), copper 12. It is formed by electroless plating using one or more selected from the group consisting of (Cu) and nickel (Ni), or an alloy of these and silver (Ag) as a component. Alternatively, a proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to 12,   The proton conductive oxidation according to any one of claims 1 to 6, wherein the porous support is a porous cathode formed on a surface of the composite membrane opposite to the gas side. Material membrane-hydrogen permeable membrane composite membrane type electrolyte.   The porous cathode is formed on the surface of the composite membrane opposite to the gas side, and the porous support is formed on the surface of the porous cathode. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to any one of the above. Another hydrogen permeable membrane through which the proton (H ⁺ ) can pass is formed on the surface of the composite membrane opposite to the gas side, and the porous support is formed on the surface of the other hydrogen permeable membrane. The proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to any one of claims 1 to 6, wherein the electrolyte is a membrane electrolyte.   An electrochemical device using the proton conductive oxide membrane-hydrogen permeable membrane composite membrane electrolyte according to any one of claims 1 to 16, comprising a fuel cell, a hydrogen sensor, a hydrogen pump, a water vapor sensor, and exhaust gas purification An electrochemical device that is applied to any one of the devices. The electrochemical device according to claim 17, wherein the electrochemical device is applied as a hydrogen sensor capable of quantifying a hydrogen concentration in a mixed gas containing at least H ₂ and CO ₂ . The electrochemical device according to claim 17, wherein the electrochemical device is applied as a hydrogen pump capable of separating only hydrogen from a mixed gas containing at least H ₂ and CO ₂ . An electrochemical device according to claim 17, characterized in that it is applied as steam sensor capable quantify water vapor concentration from a mixed gas containing at least steam and CO _2. 18. The electrochemical device according to claim 17, which is applied as an exhaust gas purification device for removing NOx from exhaust gas containing at least water vapor, CO ₂ and NOx.