JP2010244867A - Method for manufacturing electrochemical cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain sufficient joining strength and conductivity by firing in an oxidizing atmosphere in an electrochemical cell of a type of joining an internal fuel electrode and a conductive plate with a conductive joining material. <P>SOLUTION: The cell includes: a fuel electrode 9 provided with a gas passage for flowing a fuel gas and made of a porous ceramic; a solid electrolyte membrane 6 covering an outer surface 9a of the fuel electrode; a dense conductive plate 12 provided in an outer surface side of the solid electrolyte membrane 6, electrically connected to an air electrode and the fuel electrode 9 in contact with an oxidizing gas, and exposed to the outer surface side of the solid electrolyte membrane 6; and a joining material 17 provided between the conductive plate 12 and the fuel electrode 9. The joining material 17 is generated by interposing a mixture between the conductive plate 12 and the fuel electrode 9, and firing the mixture at a temperature of 800 to 1,000°C in an oxidizing atmosphere, the mixture including: a metal oxide powder of 10 to 55 vol%, which is not decomposed by a reducing atmosphere; and a metal powder of 90 to 45 vol%, which has an average particle diameter of 10 μm or below. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrochemical cell such as a solid oxide fuel cell.

  In Patent Document 1, a fuel flow path is formed inside, for example, a fuel electrode of a ceramic electrochemical cell, and a solid electrolyte membrane and an air electrode membrane are formed on the fuel electrode. A gas supply hole and a gas discharge hole are provided in the cell itself, and a plurality of cells are directly stacked to form a stack. In forming the stack, the gas supply passages are formed by connecting the gas supply holes of adjacent cells, and the gas discharge passages are formed by connecting the gas discharge holes of the cells. However, in this structure, since the fuel electrode itself is not exposed to the outer surface of the cell, it is difficult to electrically connect adjacent cells. Therefore, an opening is provided in the solid electrolyte membrane, and the surface of the fuel electrode is exposed therefrom and protrudes to the outer surface of the cell. This protruding portion is used as an electrical connection pad. However, details of the fuel electrode and the connection pad are not described.

On the other hand, in Patent Document 2, a metal plating layer is provided on an air electrode, a paste made of nickel particles and a solvent is applied on the metal plating layer, and fired in a reducing atmosphere at 900 to 1100 ° C., whereby the air electrode is made of nickel felt. It is joined to.
In addition, the present applicant disclosed in Patent Document 3 that a porous bonding material is formed by sintering a mixture of platinum, nickel, zirconia, or the like between an internal fuel electrode and a conductive plate.

WO 2007/029860 A1 Patent No. 3652195 Japanese Patent Application No. 2008-81539

  In the structure as described in Patent Document 1, the inventor sinters a mixture of a metal oxide such as nickel oxide and zirconia in an air atmosphere when generating a bonding material between the fuel electrode and the conductive plate. We considered making it. However, as a result, it was found that at the firing temperature of 1000 ° C. or lower, the sintering of the bonding material particles did not proceed, the bonding strength between the bonding material and the fuel electrode interface did not appear, and the electrical resistance was high. If this is fired at 1200 ° C. or higher, a strong bonding strength is exhibited at the interface between the bonding material and the fuel electrode. However, for example, when stainless steel is used for the conductive plate, an oxide film is rapidly formed at a firing temperature of 1200 ° C. or higher, and thus the resistance of the joined body is rapidly increased. In addition, when a lanthanum chromite oxide is used for the conductive plate, if it is fired at 1200 ° C. or higher, a reaction product is generated at the interface between the bonding material and the conductive plate, and the resistance of the bonded body rapidly increases. It was.

On the other hand, for example, in Patent Document 2, as a bonding material, paste is fired in a reducing atmosphere at 900 to 1100 ° C. made of nickel particles and a solvent. However, firing in a reducing atmosphere causes decomposition of the air electrode exposed to the outside in a cell as described in Patent Document 1, so it is necessary to fire in an oxidizing atmosphere, and the bonding material described in Patent Document 2 is applied. Can not. Further, since the bonding material is made of pure nickel metal material, the greater the coating amount of the bonding material, the shrinkage amount at the time of firing becomes large, assembly for interfacial peeling is likely to occur, the coating amount of the bonding material 1 mm ² It was necessary to join at a very thin joining material thickness of 0.08 to 0.15 mg per unit and a joining material thickness of 8.9 to 17 μm. In the cell stack manufacturing process of Patent Document 1, with such a thin bonding material thickness, in consideration of the irregularities on the cell surface, bonding can be performed only in a very narrow region.

  An object of the present invention is to obtain sufficient bonding strength and conductivity by firing in an oxidizing atmosphere in an electrochemical cell of a type in which an internal fuel electrode and a conductive plate are bonded with a conductive bonding material. It is to be.

The present invention
A fuel electrode made of porous ceramic in which a gas flow path for flowing fuel gas is formed,
A solid electrolyte membrane covering the outer surface of the fuel electrode;
An air electrode that is provided on the outer surface side of the solid electrolyte membrane and is in contact with the oxidizing gas,
An electrochemical cell comprising a dense conductive plate that is electrically connected to the fuel electrode and exposed on the outer surface side of the solid electrolyte membrane, and a bonding material provided between the conductive plate and the fuel electrode When manufacturing
A mixture of 10 to 55% by volume of metal oxide powder that does not decompose in a reducing atmosphere and 90 to 45% by volume of metal powder having an average particle size of 10 μm or less is interposed between the conductive plate and the fuel electrode, and 800 under an oxidizing atmosphere. The bonding material is produced by firing at a temperature of from 1000C to 1000C.

  According to the present invention, in an electrochemical cell of a type in which the internal fuel electrode and the conductive plate are joined with the conductive joining material, sufficient joining strength and conductivity can be obtained by firing in an oxidizing atmosphere.

  That is, by using sintering between metal particles with the driving force of surface oxidation of metal particles in an oxidizing atmosphere, the joined body can be firmly fired at a firing temperature of 1000 ° C. or less even in a reducing atmosphere. Realized that. In addition, by including a material that does not decompose even in a reducing atmosphere as a framework material in the bonding material, it is possible to suppress the firing shrinkage of the bonding material that occurs during metal particle sintering, and the reduction shrinkage that occurs when the bonding material is reduced. In addition, it was possible to obtain good interfacial conductivity by suppressing peeling of the bonded body interface.

  Moreover, by making the particle size of the metal particles as fine as 10 μm or less, a stronger sintered strength of the joined body can be obtained.

  Furthermore, by setting it as the above compounding quantity, there is no peeling in the joining interface of a joined body, and the electrical resistance of a junction part can be kept low over a long period of time.

It is a perspective view which decomposes | disassembles and shows the electrochemical cell 1 which can apply this invention. (A) is sectional drawing which cut | disconnected the cell 1 of FIG. 1 along the IIa-IIa line, (b) is sectional drawing which cut | disconnected the cell 1 of FIG. 1 along the IIb-IIb line. . It is sectional drawing which cut the cell 1 of FIG. 1 along the III-III line. (A) is sectional drawing which shows the exposed part 11 of the fuel electrode 9 from the solid electrolyte membrane 6, (b) makes the electroconductive joining material 17 produce | generate between the electrically conductive plate 12 and the solid electrolyte membrane 9. FIG. It is sectional drawing which shows the state.

Hereinafter, the present invention will be described in more detail with reference to the drawings as appropriate.
As shown in FIGS. 1 to 3, a gas flow path 8 for flowing a reducing gas is formed inside the fuel electrode 9. The fuel electrode 9 has a flat plate shape, and the solid electrolyte membrane 6 is provided so as to cover both main surfaces and side surfaces of the fuel electrode 9. Air electrodes 2A, 2B, or 2C are formed on the solid electrolyte membrane 6 on both main surfaces, respectively, and are exposed on the surface of the cell. Further, a conductive plate 3 that is electrically connected to the inner fuel electrode 9 is exposed on the surface of the cell 1. Adjacent cells are electrically connected using this conductive plate 3.

  Through holes 4 and 5 are formed in the electrochemical cell 1. During operation of the electrochemical cell, reducing gas is supplied from the through hole 5. This gas flows in the flow path 8 as indicated by arrows A, B, and C, and flows out from the through hole 4. During this time, it contributes to the electrochemical reaction.

  Here, in order to electrically connect the conductive plate 12 to the fuel electrode 9, for example, as shown in FIG. 4A, the solid electrolyte 6 is opened on the surface 9 a of the fuel electrode 9 to form the exposed portion 11. . Then, a connecting material is accommodated between the conductive plate 12 and the fuel electrode 9, and the periphery thereof is sealed with a sealing material 13. In this state, heat treatment is performed to form the conductive bonding layer 17. 12a is a joint surface of the conductive plate, and 12b is a connection surface to the outside.

  Here, although the material of the conductive plate is not limited, there are noble metals such as platinum, nickel-based alloys such as nickel, inconel and nichrome, iron-based alloys such as stainless steel, and conductive ceramics such as lanthanum chromite.

  The material of the sealing member is not particularly limited, but it needs to have oxidation resistance and reduction resistance at the operating temperature of the electrochemical cell. Specifically, glass mainly composed of silica, crystallized glass, metal brazing and the like can be exemplified. Also, compression seals such as O-rings, C-rings, E-rings, metal jacket gaskets, and mica gaskets can be exemplified.

  In the present invention, a mixture of reduction-resistant metal oxide powder 10 to 55% by volume and metal powder 90 to 45% by volume having an average particle size of 10 μm or less is interposed between the conductive plate and the fuel electrode, and an oxidizing atmosphere. A joining material is produced | generated by baking at 800 to 1000 degreeC under.

The reduction-resistant metal oxide powder forms a skeleton after sintering. This material is a material that does not decompose even in a reducing atmosphere such as an operating temperature of 800 ° C. and a fuel utilization rate of 10% (oxygen partial pressure of 6.8 × 10 ¹⁸ atm) as the operating conditions of the solid oxide fuel cell. Specific examples include zirconia, ceria, alumina, titania, and magnesia.
Further, it is desirable that the bonding material is an inexpensive material and does not generate an interface product with the fuel electrode material. Therefore, the material is preferably zirconia, ceria, or alumina used as the fuel electrode material.

The metal powder is preferably a heat-resistant metal such as nickel, cobalt or iron, an alloy, or a noble metal such as platinum or palladium.
Furthermore, it is desirable that the bonding material is an inexpensive material and does not generate an interface product with the fuel electrode material. Therefore, the material is preferably nickel used as a fuel electrode material.

  The average particle diameter of the metal oxide powder is not particularly limited, but is preferably 10 μm or less from the viewpoint of bonding strength and conductivity between the conductive plate and the fuel electrode. There is no particular lower limit, but when the average particle size is reduced, the specific surface area of the mixed powder increases, and when the mixed powder is made into a paste, it is necessary to add a large amount of binder and solvent, so that the drying shrinkage of the paste increases. There is a fear. In this respect, 0.1 μm or more is preferable.

  By setting the average particle size of the metal powder to 10 μm or less, the bonding strength between the fuel electrode and the conductive plate is remarkably improved and the electric resistance is lowered. There is no particular lower limit on the average particle size, but if the average particle size is decreased, the specific surface area of the mixed powder increases, and when the mixed powder is made into a paste, it is necessary to add a large amount of binder and solvent. There is a risk of shrinkage. In this respect, 0.1 μm or more is preferable.

  In the present invention, a mixture of reduction-resistant metal oxide powder 10 to 55% by volume and metal powder 90 to 45% by volume having an average particle size of 10 μm or less is used. However, the total of the volume of the reduction-resistant metal oxide powder and the volume of the metal powder is 100% by volume.

  By setting the ratio of the reduction-resistant metal oxide powder in the mixture to 10% by volume or more, it is possible to prevent interfacial peeling at the bonded portion and to prevent an increase in resistance value over time. In addition, by setting the ratio of the reduction-resistant metal oxide powder in the mixture to 55% by volume or less, it is possible to prevent the resistance value of the joint portion from increasing over time.

  The mixture is preferably made into a paste by mixing a solvent and a binder. Examples of such solvents include ethanol, butanol, terpineol, acetone, xylene, toluene, and butyl carbitol acetate. Examples of such a binder include methyl cellulose, ethyl cellulose, polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

  In the present invention, the bonding material is generated by baking the mixture at 800 ° C. to 1000 ° C. in an oxidizing atmosphere. Here, the oxidizing atmosphere only needs to contain oxygen, but examples include air (atmosphere), diluted air, oxygen, and diluted oxygen. Further, by setting the firing temperature to 800 ° C. to 1000 ° C., the strength and conductivity of the joint portion are increased.

  The porosity of the bonding material is usually 50% or more. However, since the porosity of the bonding material is proportional to the resistance generated at the conductive plate / fuel electrode junction, the porosity of the bonding material is preferably 40% or less.

  In the present invention, the electrochemical cell is preferably plate-shaped. However, it is not limited to a flat plate shape, and may be a curved plate or a circular arc plate. In addition, each corner of the cell is preferably R-shaped.

The oxidizing gas is not particularly limited as long as it is a gas that can supply oxygen ions to the solid electrolyte membrane, and examples thereof include air, diluted air, oxygen, and diluted oxygen. Examples of the reducing gas include H ₂ , CO, CH ₄ and a mixed gas thereof.

The electrochemical cell targeted by the present invention means a general cell for causing an electrochemical reaction. For example, the electrochemical cell can be used as an oxygen pump or a high temperature steam electrolysis cell. The high-temperature steam electrolysis cell can be used for a hydrogen production apparatus and a steam removal apparatus. Moreover, an electrochemical cell can be used as a decomposition cell for NOx and SOx. This decomposition cell can be used as a purification device for exhaust gas from automobiles and power generation devices. In this case, oxygen in the exhaust gas is removed through the solid electrolyte membrane, and NOx is electrolyzed and decomposed into N ₂ and O ₂ ^−, and oxygen generated by this decomposition can also be removed. Moreover, with this process, water vapor in the exhaust gas is electrolysis produced hydrogen and oxygen, the hydrogen reduces NOx into N _2. In a preferred embodiment, the electrochemical cell is a solid oxide fuel cell.

  The material of the air electrode is preferably a perovskite complex oxide containing lanthanum, more preferably lanthanum manganite or lanthanum cobaltite, and even more preferably lanthanum manganite. Lanthanum cobaltite and lanthanum manganite may be doped with strontium, calcium, chromium, cobalt (in the case of lanthanum manganite), iron, nickel, aluminum or the like.

  As the material for the fuel electrode, nickel-magnesia alumina spinel, nickel-nickel alumina spinel, nickel-zirconia, platinum-cerium oxide, ruthenium-zirconia, and the like are preferable.

  In the present invention, the fuel electrode is covered with the solid electrolyte membrane, thereby maintaining the airtightness between the oxidizing gas and the reducing gas. The material of the solid electrolyte is not particularly limited, and any oxygen ion conductor can be used. For example, it may be yttria stabilized zirconia or yttria partially stabilized zirconia, and in the case of a NOx decomposition cell, cerium oxide is also preferable.

(Experiment 1)
A solid oxide fuel cell described with reference to FIGS. First, the cell 1 shown in FIGS. 1-3 was produced as follows.
(Preparation of molded body for fuel electrode 9)
An organic binder and water were added to the nickel oxide powder and 3 mol% yttria-stabilized zirconia powder and wet-mixed in a ball mill, and the mixture was dried and granulated. This granulated powder was press-molded using a mold to produce two molded bodies for the fuel electrode 9. After press-molding the same material as the molded body for the fuel electrode, a flow path forming member was formed by a punching press. A flow path forming member was sandwiched between the two molded articles for the fuel electrode and joined by pressing to obtain a molded article for the fuel electrode 9.

(Formation of solid electrolyte membrane)
A paste was prepared from 3 mol% yttria-stabilized zirconia powder, and the solid electrolyte membrane 6 was applied to the surface of the molded body for the fuel electrode 9 by dipping and dried in a drying furnace. At this time, however, the exposed portion 11 of the solid electrolyte membrane 9 was formed.

(Sintering and air electrode formation)
The obtained molded product was fired at 1400 ° C. for 2 hours to obtain a sintered body. Air electrodes 2A, 2B, and 2C were screen-printed on both surfaces of the sintered body and fired at 1200 ° C. for 1 hour to obtain a unit cell 1 of a solid oxide fuel cell.

  The obtained cell has a flat plate shape with a length of 150 mm, a width of 150 mm, and a thickness of 2 mm. The thickness of the solid electrolyte membrane 6 was 5 μm.

  Next, nickel oxide powder having an average particle diameter shown in Table 1 or metallic nickel powder having an average particle diameter shown in Table 1 and 3 mol% yttria-stabilized zirconia powder having an average particle diameter of 1 μm were mixed. The volume ratio of both was mixed at 75:25 as metallic nickel powder (in the case of nickel oxide powder, calculated by the volume of nickel in the powder): 3 mol% yttria stabilized zirconia powder. A solvent was added to the mixed powder to prepare a paste. Using this paste, a stainless steel conductive plate and a fuel electrode were joined. The joined body was dried and then fired in air at 800 ° C. for 1 hour. In order to evaluate the adhesion of these connectors, a tensile test was performed.

  As shown in Table 1, when the mixture of nickel oxide powder and zirconia powder was sintered, it was not bonded at the interface between the bonding material and the fuel electrode, and the bonding strength was not expressed. However, when a mixture of metallic nickel powder having an average particle size of 10 μm or less and zirconia powder was sintered, a bonding strength of 7 to 10 MPa was developed.

(Experiment 2)
A cell was produced in the same manner as in Experiment 1. Next, metallic nickel powder having an average particle diameter of 1 μm and ceria powder having an average particle diameter of 1 μm were mixed at a volume ratio of nickel and ceria of 75:25, and a solvent was added to prepare a paste. Using this, a joined body was produced in the same manner as in Experiment 1. In order to evaluate the adhesion of these connectors, a tensile test was performed. As a result, a bonding strength of 11 MPa was obtained.

(Experiment 3)
A cell was produced in the same manner as in Experiment 1. Subsequently, metallic nickel powder having an average particle diameter of 1 μm and 3 mol% yttria-stabilized zirconia powder having an average particle diameter of 1 μm were mixed at a blending ratio shown in Table 2, and a solvent was added to the obtained mixed powder to prepare a paste. . Using this, the stainless steel conductive plate and the fuel electrode were joined. After drying this bonded body, it was fired in air at 800 ° C. for 1 hour, and then subjected to reduction treatment in a hydrogen atmosphere at 800 ° C. for 1 hour.

  Then, the resistance temporal change in the hydrogen humidified atmosphere of this joined body was measured and evaluated after the initial value and 100 hours had elapsed. After the measurement, the peeling state of the bonded interface was confirmed by observing the cross section of the bonded structure. Moreover, the dimensional fluctuation | variation of the joining paste which performed the said heat processing was measured, and the shrinkage amount of the joining paste was confirmed.

  As a result, as shown in Table 2, when the zirconia compounding amount of the bonding material is less than 10% by volume, the shrinkage amount of the bonding material is large, peeling occurs at the bonded body interface, and the resistance of the bonded body increases. . If the zirconia content in the bonding material exceeds 55% by volume, although there is no separation at the bonded body interface, the nickel particles in the vicinity of the bonded material / fuel electrode interface and the nickel on the fuel electrode side agglomerate, and the bonded body interface The conductive path was cut off, and the resistance increased.

  DESCRIPTION OF SYMBOLS 1 Electrochemical cell 2A, 2B, 2C Air electrode 3 Conductive part 4, 5 Through-hole 6 Solid electrolyte membrane 6a Surface of solid electrolyte membrane 8 Fuel gas flow path 9 Fuel electrode 9a Joint surface of fuel electrode 9 12 Conductive plate 12a Conductivity Bonding surface 12b Connecting surface 13 Sealing material 17 Bonding material

Claims (3)

A fuel electrode made of porous ceramic in which a gas flow path for flowing fuel gas is formed,
A solid electrolyte membrane covering the outer surface of the fuel electrode;
An air electrode that is provided on the outer surface side of the solid electrolyte membrane and is in contact with the oxidizing gas,
A dense conductive plate that is electrically connected to the fuel electrode and exposed on the outer surface side of the solid electrolyte membrane; and a bonding material provided between the conductive plate and the fuel electrode. When manufacturing an electrochemical cell
A mixture of reduction-resistant metal oxide powder 10 to 55% by volume and metal powder 90 to 45% by volume with an average particle size of 10 μm or less is interposed between the conductive plate and the fuel electrode, and in an oxidizing atmosphere. A method for producing an electrochemical cell, wherein the bonding material is produced by firing at 800 ° C. to 1000 ° C.   2. The method according to claim 1, wherein the metal oxide powder is zirconia, ceria or alumina.   3. The method according to claim 1, wherein the metal powder is nickel.

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