JP2006040762A - Fuel battery cell supporting body, fuel battery cell, and fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel battery cell supporting body capable of effectively restraining crack and exfoliation of a solid electrolyte by restraining reduction swelling. <P>SOLUTION: The supporting body contains iron group metal (M) and/or an oxide of the iron group metal (M), an oxide of rare earth containing at least one kind of rare earth element, and a compound containing Mg, which has gas permeability and conductivity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell support, a fuel cell, and a fuel cell that contain an iron group metal and / or an oxide of an iron group metal and are gas permeable and conductive.

  In recent years, various fuel cells in which a stack of fuel cells is accommodated in a storage container have been proposed as next-generation energy.

  FIG. 3 shows a cell stack of a conventional solid oxide fuel cell. This cell stack arranges a plurality of fuel cells 1 in an aligned manner, and one adjacent fuel cell 1a and the other fuel cell 1b. A current collecting member 5 made of metal felt is interposed between the fuel electrode 7 of one fuel cell 1a and an oxygen electrode (air electrode) 11 of the other fuel cell 1b. It had been.

  In the fuel cell 1 (1a, 1b), a solid electrolyte 9 and an oxygen electrode 11 made of conductive ceramics are sequentially provided on the outer peripheral surface of a fuel electrode 7 made of a cylindrical cermet (the inside becomes a fuel gas passage). An interconnector 13 is provided on the surface of the fuel electrode 7 that is configured and is not covered with the solid electrolyte 9 or the oxygen electrode 11. As apparent from FIG. 3, the interconnector 13 is electrically connected to the fuel electrode 7 so as not to be connected to the oxygen electrode 11.

  The interconnector 13 is formed of a conductive ceramic that is not easily altered by an oxygen-containing gas such as fuel gas and air. The conductive ceramic is formed between the fuel gas flowing inside the fuel electrode 7 and the outside of the oxygen electrode 11. It must be dense to shut off the flowing oxygen-containing gas.

  The current collecting member 5 provided between the adjacent fuel cells 1a, 1b is electrically connected to the fuel electrode 7 of one fuel cell 1a via the interconnector 13, and the other fuel cell. It is connected to the oxygen electrode 11 of the cell 1b, so that adjacent fuel cells are connected in series.

  The fuel cell is configured by accommodating a cell stack having the above structure in a storage container, and a fuel gas (hydrogen) is allowed to flow inside the fuel electrode 7 and an air (oxygen) is allowed to flow to the oxygen electrode 11 at about 1000 ° C. It generates electricity.

In the fuel cell constituting the fuel cell described above, generally, the fuel electrode 7 is formed of Ni and ZrO ₂ (YSZ) containing Y ₂ O ₃ , and the solid electrolyte 9 contains Y ₂ O ₃ . is formed from ZrO 2 _(YSZ) for the oxygen electrode 11 is composed of a perovskite-type composite oxide of lanthanum manganate system. Conventionally, a fuel electrode material made of NiO—MgO solid solution and YSZ is also known (see, for example, Patent Documents 1 and 2).

  As a method for manufacturing such a fuel battery cell, a so-called co-sintering method in which the fuel electrode 7 and the solid electrolyte 9 are formed by simultaneous firing is known. This co-sintering method is a very simple process and has a small number of manufacturing steps, and is advantageous in improving the yield during manufacturing of cells and reducing costs.

However, although the solid electrolyte 9 is formed of Y ₂ O ₃ containing ZrO ₂ having a thermal expansion coefficient of 10.8 × 10 ⁻⁶ / ° C., the fuel electrode 7 supporting the solid electrolyte 9 has a thermal expansion. Since Ni has a coefficient of 16.3 × 10 ⁻⁶ / ° C., which is significantly larger than YSZ, there is a difference in thermal expansion between the solid electrolyte 9 and the fuel electrode 7 supporting the same during simultaneous firing. Largely, there were problems such as generation of cracks in the fuel electrode 7 and peeling of the solid electrolyte 9.

In order to solve this problem, the applicant of the present invention has provided a fuel electrode, a support substrate in which a rare earth oxide (Y ₂ O ₃ , Yb ₂ O _3, etc.) having a lower thermal expansion coefficient than ZrO ₂ and Ni are combined. A fuel cell in which a solid electrolyte and an oxygen electrode layer are formed has been developed (see Patent Document 3).

According to the fuel cell described above, the thermal expansion coefficient of the support substrate can be brought close to the thermal expansion coefficient of the solid electrolyte, thereby suppressing cracking at the fuel electrode and simultaneous separation of the solid electrolyte from the fuel electrode. it can.
JP 04-33266 A Japanese Patent Laid-Open No. 06-1111829 JP 2004-152585 A

  However, when power is generated after co-firing, or when the iron group metal oxide in the fuel electrode or the support substrate is reduced, fuel gas (hydrogen) is supplied into the fuel gas passage formed in the support substrate. Therefore, the inside of the support substrate is exposed to a reducing atmosphere, but when the support substrate is first exposed to the reducing atmosphere, the support substrate expands (hereinafter abbreviated as reducing expansion) and cracks occur in the solid electrolyte. In some cases, peeling occurred.

  An object of this invention is to provide the support body for fuel cells which can suppress the crack and peeling of a solid electrolyte effectively by suppression of reductive expansion.

  When the present inventors reduce iron group metal oxides such as NiO to become metals such as Ni, the crystallographically the volume should shrink, but in the supporting substrate including this, the first is mainly the first. It was found experimentally that volume expansion occurs during reduction. As one of the causes, although not clear, temporary expansion due to the generation of water vapor in Ni due to the difference in the diffusion rate of hydrogen and oxygen during reduction can be considered. And as a result of examining the additive element which controls the precipitation form of Ni in order to suppress reductive expansion, it discovered that Mg was effective and came to this invention.

  That is, the support for a fuel cell according to the present invention includes an iron group metal (M) and / or an iron group metal (M) oxide (of the iron group metal (M) and iron group metal (M) oxides. At least one kind), a rare earth oxide containing at least one rare earth element, and a Mg-containing compound, and is characterized by being gas permeable and conductive.

  In the present invention, the support that occupies most of the volume of the cell is composed of rare earth oxide and iron group metal and / or oxide and Mg-containing compound. It becomes possible to suppress. In particular, during the initial reduction of the support, it can be hardly expanded or slightly contracted, and when the fuel cell is constructed, it is effective for cracking and peeling of the fuel electrode layer and the solid electrolyte layer. Can be suppressed.

  That is, for example, MgO is dissolved in NiO to become (Ni, Mg) O during firing in a support substrate or in a high-temperature oxidizing atmosphere, and becomes a plurality of points on the surface in a high-temperature reducing atmosphere such as power generation. From this, metal Ni is precipitated to become (Ni, Mg) O having a high Mg concentration. On the other hand, in such a precipitation form of metal Ni, a large number of grain boundaries of metal Ni are formed on the surface of (Ni, Mg) O, and the diffusion rate of oxygen is increased, so that water vapor is not easily generated in Ni. As a result, it is considered that reductive expansion can be suppressed.

  In addition, the fuel cell support according to the present invention is characterized in that the Mg / (Mg + M) ratio is 0.1 to 20 mol%. In such a fuel cell support, reductive expansion can be effectively suppressed.

Furthermore, in the support for a fuel cell according to the present invention, the rare earth oxide is Y ₂ O ₃ and / or Yb ₂ O ₃ (Y ₂ O ₃ , Yb ₂ O ₃ , Y ₂ O ₃ and Yb ₂ O). ₃ ). Further, the iron group metal is Ni. Thereby, an inexpensive support for a fuel cell can be provided.

  The fuel cell according to the present invention includes the support for a fuel cell having a fuel gas passage formed therein, a fuel electrode layer formed on the support, and the support so as to cover the fuel electrode layer. It is characterized by comprising a solid electrolyte layer formed above and an oxygen electrode provided on the solid electrolyte layer so as to face the fuel electrode layer. In such a fuel cell, since the reduction expansion in the support for the fuel cell can be suppressed, it becomes possible to effectively suppress cracks and separation in the fuel electrode and the solid electrolyte due to the reduction expansion after the simultaneous firing. .

  In addition, the Mg-containing compound in the support causes a solid solution and reaction with the iron group metal or its oxide, but the thermal expansion coefficient is hardly changed. Therefore, by controlling the content ratio of the rare earth oxide, The thermal expansion coefficient can be brought close to the thermal expansion coefficient of the solid electrolyte layer or the fuel electrode layer, and the generation and separation of cracks due to the difference in thermal expansion during simultaneous firing can be effectively suppressed.

  The fuel cell of the present invention is characterized in that a plurality of the above-mentioned fuel cells are accommodated in a storage container. In such a fuel cell, since the crack and breakage of the fuel cell can be suppressed, long-term reliability can be improved.

  In the support for a fuel cell according to the present invention, the thermal expansion coefficient of the support can be brought close to the thermal expansion coefficient of the solid electrolyte layer or the fuel electrode layer, and cracking or peeling due to the difference in thermal expansion during simultaneous firing can be achieved. Can be effectively suppressed, and at the same time, reductive expansion can be effectively suppressed by adding an appropriate amount of Mg component, and cracks and peeling in the fuel electrode and the solid electrolyte can be effectively suppressed.

  In addition, any iron group metal or oxide thereof constituting the support is less likely to diffuse into the solid electrolyte. Therefore, even when the support and the solid electrolyte layer are co-fired, adverse effects on the ionic conductivity and the like of the solid electrolyte layer can be avoided. Rare earth elements are originally contained in solid electrolytes as stabilizers, and their influence on ionic conductivity is negligible even when diffused. Further, the Mg component may diffuse at the time of co-firing, but if it is a small amount, there is almost no influence on the ionic conductivity or the like even if it is dissolved in the solid electrolyte layer.

  In FIG. 1 showing a cross section of the fuel cell of the present invention, the fuel cell indicated by 30 as a whole has a hollow flat plate shape, a flat cross section, and an elliptical columnar support substrate (support) as a whole. 31 is provided. Inside the support substrate 31, a plurality of fuel gas passages 31 a are formed penetrating in the length direction at appropriate intervals. The fuel cell 30 is provided with various members on the support substrate 31. It has a structure. A plurality of such fuel cells 30 are connected to each other in series by a current collecting member 40 as shown in FIG. 2, thereby forming a cell stack constituting the fuel cell.

  As understood from the shape shown in FIG. 1, the support substrate 31 includes a flat portion A and arc-shaped portions B at both ends of the flat portion A. Both surfaces of the flat portion A are formed substantially parallel to each other, and a fuel electrode layer 32 is provided so as to cover one surface of the flat portion A and the arc-shaped portions B on both sides. A dense solid electrolyte layer 33 is laminated so as to cover, and an oxygen electrode 34 is laminated on one surface of the flat portion A so as to face the fuel electrode layer 32 on the solid electrolyte layer 33. Has been.

  An interconnector 35 is formed on the other surface of the flat portion A where the fuel electrode layer 32 and the solid electrode layer 33 are not stacked. As is clear from FIG. 1, the fuel electrode layer 32 and the solid electrolyte layer 33 extend to both sides of the interconnector 35 and are configured so that the surface of the support substrate 31 is not exposed to the outside.

  In the fuel cell having the above structure, the portion of the fuel electrode layer 32 facing the oxygen electrode 34 operates as a fuel electrode to generate electric power. That is, an oxygen-containing gas such as air is allowed to flow outside the oxygen electrode 34, and a fuel gas (hydrogen) is allowed to flow through the gas passage 31a in the support substrate 31 and heated to a predetermined operating temperature. Electricity is generated by generating an electrode reaction of the formula (1) and generating an electrode reaction of the following formula (2), for example, in the portion of the fuel electrode layer 32 that becomes the fuel electrode.

Oxygen electrode: 1 / 2O ₂ + 2e ⁻ → O ²⁻ (solid electrolyte) (1)
Fuel electrode: O ²⁻ (solid electrolyte) + H ₂ → H ₂ O + 2e ⁻ (2)
The current generated by the power generation is collected through the interconnector 35 attached to the support substrate 31.

(Support substrate 31)
In the fuel cell 30 having the above-described structure, the support substrate 31 is gas permeable so as to allow the fuel gas to permeate to the fuel electrode, and conductive for collecting current via the interconnector 35. It is required that the solid electrolyte is free from cracks and peeling due to a difference in thermal expansion during simultaneous firing. While satisfying such a requirement, the volume of the support substrate 31 during the first reduction is mainly satisfied. The support substrate 31 is composed of an iron group metal component, a rare earth oxide, and an Mg component for the purpose of suppressing cracks such as solid electrolyte caused by expansion.

  The iron group metal component is for imparting conductivity to the support substrate 31 and may be a single iron group metal, or an iron group metal oxide, an iron group metal alloy or an alloy oxide. May be. The iron group metals include iron, nickel, and cobalt. In the present invention, any of them can be used, but Ni and / or NiO is changed to iron group because it is inexpensive and stable in fuel gas. It is preferable to contain as a component.

The rare earth oxide component is used to approximate the thermal expansion coefficient of the support substrate 31 to the stabilized zirconia or lanthanum gallate perovskite composition forming the solid electrolyte layer 33, and the like. In order to maintain conductivity and prevent diffusion to the solid electrolyte layer 33, etc., at least one selected from the group consisting of Y, Lu, Yb, Tm, Er, Ho, Dy, Gd, Sm, Pr in particular. The rare earth element-containing oxide is used in combination with the iron group component. Specific examples of such rare earth oxides include Y ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , Tm ₂ O ₃ , Er ₂ O ₃ , Ho ₂ O ₃ , Dy ₂ O ₃ , Gd ₂ O. ₃ , Sm ₂ O ₃ , Pr ₂ O ₃ can be exemplified, and Y ₂ O ₃ and Yb ₂ O ₃ are preferable in that they are particularly inexpensive. In particular, the iron group component described above is contained in the support substrate 31 in an amount of 35 to 65% by volume in terms of approximating the thermal expansion coefficient of the support substrate 31 to that of a solid electrolyte material such as stabilized zirconia. Is preferably contained in the support substrate 31 in an amount of 35 to 65% by volume.

  In the present invention, it is preferable that the Mg component is contained in the support substrate 31 in an amount of 0.1 to 20 mol% in terms of Mg / (Mg + M) ratio, particularly for the purpose of suppressing the reduction expansion. In particular, it is desirable that the content be 1 to 10 mol%, more preferably 5 to 10 mol%. The Mg component is present in the support substrate as a compound that is dissolved and reacted with the Mg-containing oxide and / or the iron group metal oxide. For example, it exists as (Ni, Mg) O as a compound of MgO, MgO and NiO.

  The support substrate 31 may contain other metal components and oxide components as long as required characteristics are not impaired.

  Since the support substrate 31 as described above needs to have fuel gas permeability, it is usually preferable that the open porosity is 30% or more, particularly 35 to 50%. Further, the conductivity of the support substrate 31 is preferably 300 S / cm or more, and particularly preferably 440 S / cm or more. The linear expansion coefficient of the support substrate 31 during the reduction is desirably 0.01 to −0.05, and the support substrate 31 may be slightly contracted.

  Further, the length of the flat portion A of the support substrate 31 is normally 15 to 35 mm, the length of the arc-shaped portion B (the length of the arc) is about 3 to 8 mm, and the thickness of the support substrate 31 is (flat portion). The present invention can be suitably used when the distance between both surfaces of A is about 2.5 to 5 mm.

(Fuel electrode layer 32)
In the present invention, the fuel electrode layer 32 causes the electrode reaction of the above-described formula (2), and is formed of a known porous conductive ceramic. For example, it is formed from ZrO ₂ in which a rare earth element is dissolved, and Ni and / or NiO. As ZrO ₂ (stabilized zirconia) in which the rare earth element is dissolved, the same one used for forming the solid electrolyte layer 33 described below is preferably used.

  The stabilized zirconia content in the fuel electrode layer 32 is preferably in the range of 35 to 65% by volume, and the Ni or NiO content is preferably 65 to 35% by volume. Further, the open porosity of the fuel electrode layer 32 is preferably 15% or more, particularly preferably in the range of 20 to 40%, and the thickness is preferably 1 to 30 μm. For example, if the thickness of the fuel electrode layer 32 is too thin, the performance may be deteriorated, and if it is too thick, there is a risk of peeling due to a difference in thermal expansion between the solid electrolyte layer 33 and the fuel electrode layer 32. .

  Further, in the example of FIG. 1, the fuel electrode layer 32 extends to both sides of the interconnector 35, but it is sufficient that the fuel electrode is formed at a position facing the oxygen electrode 34. For example, the fuel electrode layer 32 may be formed only in the flat portion A on the side where the oxygen electrode 34 is provided. Furthermore, the fuel electrode layer 32 can be formed over the entire circumference of the support substrate 31. In the present invention, it is preferable that the entire solid electrolyte layer 33 is formed on the fuel electrode layer 32 in order to increase the bonding strength between the solid electrolyte layer 33 and the support substrate 31.

(Solid electrolyte layer 33)
The solid electrolyte layer 33 provided on the fuel electrode layer 32 is generally formed of a dense ceramic called ZrO ₂ (usually stabilized zirconia) in which 3 to 15 mol% of a rare earth element is dissolved. . Examples of rare earth elements include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, but they are inexpensive. From the point, Y and Yb are desirable.

  The stabilized zirconia ceramics forming the solid electrolyte layer 33 is desirably a dense material having a relative density (according to Archimedes method) of 93% or more, particularly 95% or more from the viewpoint of preventing gas permeation. It is desirable that the thickness is 10 to 100 μm. The solid electrolyte layer 3 may be composed of a lanthanum gallate perovskite type composition in addition to the stabilized zirconia.

(Oxygen electrode 34)
The oxygen electrode 34 is formed of a conductive ceramic made of a so-called ABO ₃ type perovskite oxide. As such a perovskite oxide, at least one of transition metal perovskite oxides, particularly LaMnO ₃ oxides, LaFeO ₃ oxides, and LaCoO ₃ oxides having La at the A site is preferable. LaFeO ₃ -based oxides are particularly suitable because they have high electrical conductivity at an operating temperature of about 1000 ° C. In the perovskite oxide, Sr and the like may exist together with La at the A site, and Co and Mn may exist together with Fe at the B site.

  The oxygen electrode 34 must have gas permeability. Therefore, the conductive ceramic (perovskite oxide) forming the oxygen electrode 34 has an open porosity of 20% or more, particularly 30 to 50. It is desirable to be in the range of%.

  The thickness of the oxygen electrode 34 is preferably 30 to 100 μm from the viewpoint of current collection.

(Interconnector 35)
The interconnector 35 provided on the support substrate 31 at the position facing the oxygen electrode 34 is made of conductive ceramics, but is in contact with the fuel gas (hydrogen) and the oxygen-containing gas. It is necessary to have oxidation resistance. For this reason, lanthanum chromite perovskite oxides (LaCrO ₃ oxides) are generally used as the conductive ceramics. Further, in order to prevent leakage of the fuel gas passing through the inside of the support substrate 31 and the oxygen-containing gas passing through the outside of the support substrate 31, such conductive ceramics must be dense, for example, 93% or more, particularly 95%. It is preferable to have the above relative density.

  The interconnector 35 is desirably 10 to 200 μm from the viewpoint of preventing gas leakage and electrical resistance. That is, if the thickness is smaller than this range, gas leakage is likely to occur, and if the thickness is larger than this range, the electric resistance is large, and the current collecting function may be reduced due to a potential drop. .

Further, as is clear from FIG. 1, in order to prevent gas leakage, a dense solid electrolyte layer 33 is in close contact with both sides of the interconnector 35. _A bonding layer (not shown) made of ₂ O ₃ or the like can be provided between both side surfaces of the interconnector 35 and the solid electrolyte layer 33.

  A P-type semiconductor layer 39 is preferably provided on the outer surface (upper surface) of the interconnector 35. By connecting the current collecting member 40 to the interconnector 35 via the P-type semiconductor layer 39, the contact between the two becomes an ohmic contact, the potential drop can be reduced, and the deterioration of the current collecting performance can be effectively avoided. Thus, for example, the current from the oxygen electrode 34 of one fuel cell 30 can be efficiently transmitted to the support substrate 31 of the other fuel cell 30. As such a P-type semiconductor, a transition metal perovskite oxide can be exemplified.

Specifically, those having higher electronic conductivity than LaCrO ₃ oxides constituting the interconnector 35, for example, LaMnO ₃ oxides and LaFeO ₃ oxides in which Mn, Fe, Co, etc. exist at the B site P-type semiconductor ceramics made of at least one of LaCoO ₃ -based oxides can be used. In general, the thickness of the P-type semiconductor layer 39 is preferably in the range of 30 to 100 μm.

  The interconnector 35 can also be provided directly on the flat portion A of the support substrate 31 on the side where the solid electrolyte layer 33 is not provided. The fuel electrode layer 32 is also provided in this portion, and this fuel electrode layer 32 is provided. An interconnector 35 can also be provided on the top. That is, the fuel electrode layer 32 can be provided over the entire circumference of the support substrate 31, and the interconnector 35 can be provided on the fuel electrode layer 32. That is, when the interconnector 35 is provided on the support substrate 31 via the fuel electrode layer 32, it is advantageous in that the potential drop at the interface between the support substrate 31 and the interconnector 35 can be suppressed. is there.

(Manufacture of fuel cells)
The fuel battery cell having the above structure is manufactured as follows.

First, an iron group metal such as Ni or its oxide powder, a rare earth oxide powder such as Y ₂ O ₃ , an Mg-containing compound powder such as MgO, an organic binder, and a solvent are mixed to prepare a slurry. A support substrate molded body is prepared and dried by extrusion molding using this slurry, and dried.

  Next, a fuel electrode layer forming material (Ni or NiO powder and stabilized zirconia powder), an organic binder, and a solvent are mixed to prepare a slurry, and a sheet for the fuel electrode layer is prepared using this slurry. Further, instead of producing a sheet for the fuel electrode layer, a paste in which the fuel electrode forming material is dispersed in a solvent is applied to a predetermined position of the formed support substrate and dried, and then the fuel electrode layer is formed. A coating layer may be formed.

  Furthermore, a stabilized zirconia powder, an organic binder, and a solvent are mixed to prepare a slurry, and a solid electrolyte layer sheet is prepared using this slurry.

  The support substrate molded body, the fuel electrode sheet, and the solid electrolyte layer sheet formed as described above are laminated so as to have a layer structure as shown in FIG. 1, for example, and dried. In this case, when the coating layer for the fuel electrode layer is formed on the surface of the support substrate molded body, only the solid electrolyte layer sheet may be laminated on the support substrate molded body and dried.

Thereafter, the interconnector material (e.g., LaCrO ₃ based oxide powder), an organic binder and a solvent were mixed to prepare a slurry, to produce the interconnector sheet.

  This interconnector sheet is further laminated at a predetermined position of the laminate obtained above to produce a firing laminate.

Next, the above laminate for firing is subjected to a binder removal treatment, and co-fired at 1300 to 1600 ° C. in an oxygen-containing atmosphere, and an oxygen electrode forming material (for example, LaFeO ₃₎ is placed at a predetermined position of the obtained sintered body. And paste containing a P-type semiconductor layer forming material (for example, LaFeO ₃ -based oxide powder) and a solvent by dipping or the like, if necessary. The fuel cell 30 of the present invention having the structure shown in FIG. 1 can be manufactured by baking.

  When Ni is used for forming the fuel electrode layer 32, Ni is oxidized to NiO by firing in an oxygen-containing atmosphere. If necessary, it is returned to Ni by reduction treatment. be able to. Further, since it is exposed to a reducing atmosphere during power generation, it is also reduced to Ni at this time.

  Further, the Mg-containing compound in the support substrate 31 dissolves and reacts with NiO, but Ni can be precipitated and impart conductivity by performing a reduction treatment as necessary. Further, since Ni is exposed to a reducing atmosphere during power generation, Ni is also deposited at this time. The volume expansion during the first reduction can be suppressed by generating a Mg-containing compound such as (Ni, Mg) O during firing.

In the fuel cell of the present invention, a fuel electrode is formed on a support substrate formed using an iron group metal such as Ni or an oxide thereof, a specific rare earth oxide such as Y ₂ O ₃ , and an Mg-containing compound. By providing a layer, a solid electrolyte layer, and an oxygen electrode, it is possible to effectively avoid inconveniences such as peeling of the solid electrolyte layer and occurrence of cracks during simultaneous firing due to thermal expansion differences, and at the same time, mainly the support substrate during the first reduction. Since volume expansion can be suppressed, a practical fuel cell can be produced at low cost and in high yield by simultaneous firing according to the present invention.

  In addition, Mg element present in the support substrate may diffuse into the solid electrolyte layer at the time of co-firing, but if it is small, it may adversely affect the ionic conductivity of the solid electrolyte or the conductivity of the oxygen side electrode. There is no.

(Cell stack)
As shown in FIG. 2, the cell stack includes a plurality of the fuel cells 30 described above, and a metal felt and / or between one fuel cell 30 and the other fuel cell 30 adjacent in the vertical direction. A current collecting member 40 made of a metal plate is interposed, and both are connected in series with each other. That is, the support substrate 31 of one fuel cell 30 is electrically connected to the oxygen electrode 34 of the other fuel cell 30 via the interconnector 35, the P-type semiconductor layer 39, and the current collecting member 40. . Such cell stacks are arranged side by side as shown in FIG. 2, and adjacent cell stacks are connected in series by a conductive member 42.

  The fuel cell of the present invention is configured by accommodating the cell stack of FIG. 2 in a storage container. The storage container is provided with an introduction pipe for introducing a fuel gas such as hydrogen into the fuel battery cell 30 from the outside, and an introduction pipe for introducing an oxygen-containing gas such as air into the external space of the fuel battery cell 30. The fuel cell is heated to a predetermined temperature (for example, 600 to 900 ° C.) to generate electric power, and the used fuel gas and oxygen-containing gas are discharged out of the storage container.

  In addition, this invention is not limited to the said form, A various change is possible in the range which does not change the summary of invention. For example, the shape of the support substrate 31 can be a cylindrical shape, and an intermediate layer having appropriate conductivity can be formed between the oxygen electrode 34 and the solid electrolyte layer 33.

NiO powder having an average particle size of 0.5 μm and Y ₂ O ₃ powder (average particle size is 0.6 to 0.9 μm), after firing, NiO is 48 vol% in terms of Ni, and Y ₂ O ₃ is 52 vol. % Were mixed (Sample No. 1).

Next, MgO powder (average particle size 0.5 μm) was externally added to 100 parts by mass of the mixed powder of NiO and Y ₂ O ₃ so as to have a mass part shown in Table 1, and mixed ( Sample No. 2-8). Sample No. 7 and 8 used Yb ₂ O ₃ instead of Y ₂ O ₃ . Table 1 also shows the molar ratio of Mg / (Mg + Ni), which is the ratio of Mg (mol) to the total amount (mol) of Mg and Ni.

  A slurry for a support substrate formed by mixing a pore agent, an organic binder (polyvinyl alcohol), and water (solvent) into the above mixed powder is extruded into a rectangular parallelepiped shape, dried, and treated to remove the binder. Firing was performed at 1500 ° C. in the air.

The obtained sintered body was processed into a height of 3 mm, a width of 4 mm, and a length of 40 mm, and subjected to a reduction treatment at 850 ° C. for 16 hours in a reducing atmosphere at an oxygen partial pressure of about 10 ⁻¹⁹ Pa. Measure the length in the direction, and subtract the length before reduction from the length after reduction as the elongation in the longitudinal direction (Elongation in the longitudinal direction) / (Length in the longitudinal direction before reduction) ). Furthermore, the conductivity was measured by a 4-terminal method at 1000 ° C. in a reducing atmosphere at an oxygen partial pressure of about 10 ⁻¹⁹ Pa. The results are shown in Table 1.

  As understood from the results in Table 1, it can be seen that the expansion in the reducing atmosphere can be suppressed by adding the MgO powder. Further, as the amount of MgO increases, the expansion turns to the minus (shrinkage) side and the conductivity of the support substrate decreases, but the Mg / (Mg + Ni) ratio is within the range of 0.3 to 19.6 mol%. If it exists, it turns out that the fall of electrical conductivity is small.

  Each sample powder used in Example 1 was extruded in the same manner as in Example 1 to produce a flat support substrate molded body, which was dried.

Next, for forming a fuel electrode layer using a slurry obtained by mixing ZrO ₂ (YSZ) powder containing 8 mol% Y ₂ O ₃ , NiO powder, organic binder (acrylic resin), and solvent (toluene). A sheet was prepared, and a sheet for a solid electrolyte layer was prepared using a slurry in which the YSZ powder, an organic binder (acrylic resin), and a solvent made of toluene were mixed, and these sheets were laminated.

  The laminated sheet was wound around the support substrate molded body so that both ends thereof were separated from each other with a predetermined interval (see FIG. 1), and dried.

On the other hand, an interconnector sheet was prepared using a slurry in which an LaCrO ₃ oxide powder having an average particle diameter of 2 μm, an organic binder (acrylic resin), and a solvent (toluene) was mixed. A laminated sheet for sintering was prepared by laminating on the exposed portion of the support substrate molded body in the sheet, and comprising a support substrate molded body, a fuel electrode layer sheet, and a solid electrolyte layer sheet.

  Next, the laminated sheet for sintering was subjected to binder removal treatment, and co-fired at 1500 ° C. in the air.

The obtained sintered body was immersed in a paste made of La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ powder having an average particle diameter of 2 μm and a solvent (normal paraffin), and sintered. A coating layer for oxygen electrode is provided on the surface of the solid electrolyte layer formed on the body, and at the same time, the paste is applied to the outer surface of the interconnector formed on the sintered body, and a coating layer for P-type semiconductor is provided, Baking was performed at 1150 ° C. to produce fuel cells as shown in FIG. 1 (Sample Nos. 9 to 16).

  In the fabricated fuel cell, the length of the flat portion A of the support substrate is 26 mm, the length of the arc-shaped portion B is 3.5 mm, the thickness is 2.8 mm, the thickness of the fuel electrode layer is 10 μm, and the thickness of the solid electrolyte layer is The thickness of 40 μm, the thickness of the oxygen electrode was 50 μm, the thickness of the interconnector was 50 μm, and the thickness of the P-type semiconductor layer was 50 μm.

  The cross section of the solid electrolyte layer of the obtained fuel cell is analyzed by EPMA to confirm the diffusing element from the support substrate, and hydrogen gas is allowed to flow in the gas passage of the support substrate, and the outside of the fuel cell (oxygen electrode) The outer surface of the fuel cell is allowed to flow at 850 ° C. for 100 hours and cooled, and then the inside of the fuel cell is pressurized and soaked in water, observed for gas leaks, cracks in the support substrate, solid electrolyte layer, The separation of the solid electrolyte layer and the fuel electrode layer from the support substrate was observed.

The power generation performance per fuel cell after 100 hours at 850 ° C. was measured and listed in Table 2.

As understood from the results in Table 2, the fuel cell sample Nos. In Nos. 10 to 16, cracks in the fuel electrode layer and the solid electrolyte layer, and separation of the solid electrolyte layer and the fuel electrode layer from the support substrate were not observed. Further, no diffusing element was observed, and the power generation performance was as good as 0.30 W / cm ² or more.

  On the other hand, Sample No. 1 has a large linear expansion coefficient of 0.16%. In No. 9, the support substrate expanded and cracks occurred in the fuel electrode layer and the solid electrolyte layer.

It is a cross-sectional view showing a hollow flat fuel cell. It is a cross-sectional view which shows the cell stack formed of the some fuel cell of FIG. It is a cross-sectional view showing a cell stack composed of cylindrical fuel cells.

Explanation of symbols

31 ... support substrate 31a ... fuel gas passage 32 ... fuel electrode 33 ... solid electrolyte 34 ... oxygen electrode 35 ... interconnector 40 ... current collecting member

Claims (6)

It contains an oxide of iron group metal (M) and / or iron group metal (M), a rare earth oxide containing at least one rare earth element, and an Mg-containing compound, and is gas permeable and conductive. A support for a fuel cell, comprising: The fuel cell support according to claim 1, wherein the Mg / (Mg + M) ratio is 0.1 to 20 mol%. Rare earth _oxides, Y 2 _{O 3} and / or claim 1 or 2 fuel cell support according to characterized in that the _Yb 2 _{O 3.} The support for a fuel cell according to any one of claims 1 to 3, wherein the iron group metal (M) is Ni. The fuel cell support according to any one of claims 1 to 4, wherein a fuel gas passage is formed therein, a fuel electrode layer formed on the support, and a fuel electrode layer so as to cover the fuel electrode layer A fuel cell comprising: a solid electrolyte layer formed on the support; and an oxygen electrode provided on the solid electrolyte layer so as to face the fuel electrode layer. 6. A fuel cell comprising a plurality of the fuel cells according to claim 5 housed in a housing container.

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