JP2008226653A - Fuel cell and fuel cell stack, and fuel cell - Google Patents

Abstract

The present invention provides a fuel cell having improved durability by preventing a component contained in an oxygen-side electrode from diffusing into a solid electrolyte, a fuel cell stack using the same, and a fuel cell.
An intermediate layer and an oxygen side electrode containing Sr are sequentially provided on one surface of a solid electrolyte, and a fuel is provided on the other surface of the solid electrolyte facing the oxygen side electrode. In the fuel battery cell 10 including the side electrode 7, the intermediate layer 4 has a surface layer region 4a on the solid electrolyte 9 side formed more densely than the other region 4b, so that the power generation performance of the fuel cell 10 is deteriorated. Can be suppressed.
[Selection] Figure 1

Description

  The present invention provides a fuel cell in which an intermediate layer and an oxygen-side electrode are sequentially provided on one surface of a solid electrolyte, and a fuel-side electrode is provided on the other surface facing the oxygen-side electrode of the solid electrolyte. And a fuel cell stack, and a fuel cell.

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

  FIG. 3 shows a conventional solid oxide fuel cell stack, in which a plurality of fuel cells 21 (21a, 21b) are aligned and assembled, and one fuel cell 21a and the other A current collecting member 25 made of metal felt is interposed between the fuel cell 21b and the fuel side electrode 27 of one fuel cell 21a and the oxygen side electrode 23 of the other fuel cell 21b are electrically connected. Configured.

  The fuel cell 21 (21a, 21b) is configured by sequentially providing a solid electrolyte 29 and an oxygen-side electrode 23 made of conductive ceramics on the outer peripheral surface of a fuel-side electrode 27 made of a cylindrical metal, The interconnector 22 is provided on the fuel side electrode 27 exposed from the solid electrolyte 29 and the oxygen side electrode 23 so as not to be connected to the oxygen side electrode 23, and is electrically connected to the fuel side electrode 27.

  Since the interconnector 22 reliably shuts off the fuel gas flowing inside the fuel side electrode 27 and the oxygen-containing gas flowing outside the oxygen-side electrode 23, the interconnector 22 is dense and hardly deteriorates by the fuel gas and the oxygen-containing gas. It is made of conductive ceramics.

  The electrical connection between one fuel cell 21a and the other fuel cell 21b is made by connecting the fuel side electrode 27 of one fuel cell 21a to the interconnector 22 and the current collecting member 25 provided on the fuel side electrode 27. And is connected to the oxygen side electrode 23 of the other fuel battery cell 21b.

  The fuel cell is configured by housing the fuel cell stack in a storage container. The fuel (hydrogen) is allowed to flow inside the fuel side electrode 27, and the air (oxygen) is allowed to flow to the oxygen side electrode 23. It generates electricity.

In such a fuel cell 21, in general, the fuel side electrode 27 is made of ZrO ₂ (YSZ) containing Ni and Y ₂ O ₃ , and the solid electrolyte 29 is ZrO ₂ (YSZ containing Y ₂ O _3). The oxygen side electrode 23 is made of a LaMnO ₃ composite oxide in which Sr coexists.

  Recently, a production method in which a solid electrolyte and an oxygen side electrode are simultaneously fired has also been proposed. However, when the solid electrolyte and the oxygen-side electrode are co-fired, Sr contained in the oxygen-side electrode diffuses into the solid electrolyte, and a reaction layer having a high electric resistance is formed at the interface. There was a problem of causing the performance degradation.

  Therefore, a fuel cell having an intermediate layer formed between the solid electrolyte and the oxygen side electrode for the purpose of preventing performance deterioration of the fuel cell in simultaneous firing of the solid electrolyte and the oxygen side electrode, and a method for producing the same Has been proposed (see, for example, Patent Document 1 and Patent Document 2).

In addition, in order to provide a solid electrolyte fuel cell with excellent heat cycle durability and sufficient power generation performance, a solid electrolyte layer, a reaction preventing layer, a mixed layer, and an air electrode layer are sequentially laminated on the surface of the fuel electrode substrate. In addition, a solid electrolyte fuel cell has been proposed in which the mixed layer contains materials for a reaction preventing layer and an air electrode layer (see, for example, Patent Document 3).
JP 2003-288914 A JP 2004-63226 A JP 2005-327637 A

  However, when an intermediate layer consisting of one layer is formed between the solid electrolyte and the oxygen side electrode, it is difficult to completely suppress the diffusion of Sr contained in the oxygen side electrode into the solid electrolyte. When power generation is performed, there is a problem that Sr diffused into the solid electrolyte (contained in the solid electrolyte) reacts with the solid electrolyte component, and the power generation performance of the fuel cell deteriorates due to a high resistance reaction product. there were.

  Also, in the fuel cell in which the solid electrolyte is first fired and then the intermediate layer is baked, when the solid electrolyte and the intermediate layer have insufficient adhesion, and the power generation of the fuel cell is performed for a long time, the solid electrolyte and There was also a problem that peeling occurred between the intermediate layer and the power generation performance of the fuel cell deteriorated.

  Furthermore, as disclosed in Patent Document 3, in order to prevent the separation between the solid electrolyte layer and the oxygen electrode side electrode, a reaction preventing layer is provided on the surface of the solid electrolyte layer, and the component of the oxygen side electrode is provided on the surface of the reaction preventing layer. Even when a mixed layer containing oxygen is provided, the component of the oxygen side electrode and the component of the oxygen side electrode contained in the mixed layer are transferred into the solid electrolyte when power generation of the fuel cell is performed for a long time. It diffused to form a high-resistance reaction product, and there was a problem that the power generation performance of the fuel cell deteriorated.

  Therefore, the present invention prevents Sr contained in the oxygen-side electrode from being included (diffused) in the solid electrolyte, prevents formation of a high-resistance reaction product in the solid electrolyte, It is an object of the present invention to provide a fuel cell that suppresses deterioration of power generation performance, a fuel cell stack using the fuel cell, and a fuel cell.

  The fuel cell according to the present invention includes an intermediate layer and an oxygen-side electrode containing Sr in order on one surface of the solid electrolyte, and on the other surface facing the oxygen-side electrode of the solid electrolyte. A fuel cell including a fuel-side electrode, wherein the intermediate layer has a surface layer region on the solid electrolyte side formed more densely than other regions.

  In such a fuel cell, by providing an intermediate layer between the solid electrolyte and the oxygen side electrode, Sr contained in the oxygen side electrode can be prevented from diffusing into the solid electrolyte. Accordingly, it is possible to prevent the solid electrolyte component and Sr from forming a high-resistance reaction product in the solid electrolyte, and it is possible to prevent deterioration of the power generation performance of the fuel cell in long-time power generation.

  Here, since the surface layer region on the solid electrolyte side of the intermediate layer is formed more densely than the other regions, Sr contained in the oxygen side electrode permeates the other region of the intermediate layer and enters the surface layer region. Even when it is diffused, it is possible to prevent Sr from diffusing into the solid electrolyte. This is probably because Sr causes grain boundary diffusion, although no clear factor is known. As a result, it is possible to prevent the formation of a reaction product of Sr and the solid electrolyte in the solid electrolyte, so that deterioration of the power generation performance of the fuel cell can be suppressed, and the fuel cell in long-time power generation It is possible to suppress the deterioration of the power generation performance.

  In the fuel cell of the present invention, the intermediate layer includes a first layer that forms a surface region, and a second layer that forms another region, and the first layer, the solid electrolyte, Is preferably formed by co-firing.

  In such a fuel cell, the solid electrolyte and the first layer are formed by co-firing with the solid electrolyte and the first layer forming the surface layer region of the intermediate layer. It can suppress that an electrolyte and a 1st layer peel. Thereby, since it can suppress that a solid electrolyte and a 1st layer peel, degradation of the power generation performance of the fuel cell in long-time power generation can be suppressed.

  In the fuel battery cell of the present invention, it is preferable that the first layer has a thickness of 1 to 10 μm and the second layer has a thickness of 5 to 20 μm.

  In such a fuel cell, when the thickness of the first layer of the intermediate layer is 1 to 10 μm, Sr contained in the oxygen side electrode can be prevented from diffusing into the solid electrolyte.

  On the other hand, by setting the thickness of the second layer of the intermediate layer to 5 to 20 μm, it is possible to reduce the amount of the second layer of Sr that is contained in the oxygen-side electrode through long-term continuous operation. Thereby, Sr contained in the oxygen-side electrode can be prevented from diffusing into the solid electrolyte, the deterioration of the power generation performance of the fuel cell in long-time power generation can be suppressed, and the long-term reliability is excellent. It can be set as a fuel cell.

  In the fuel cell of the present invention, it is preferable that the first layer and the second layer contain the same rare earth element (except Sr).

  In such a fuel cell, the first layer and the second layer of the intermediate layer contain the same rare earth element, thereby improving the bonding strength between the first layer and the second layer. be able to. Therefore, separation of the first layer and the second layer can be suppressed, deterioration of the power generation performance of the fuel cell in long-time power generation can be suppressed, and fuel cell excellent in long-term reliability It can be.

  The fuel cell stack of the present invention is characterized in that a plurality of the fuel cells described above are electrically connected in series.

  In such a fuel cell stack, since long-term power generation is configured by electrically connecting a plurality of fuel cells that suppress deterioration of power generation performance during long-term power generation and have excellent long-term reliability. It can be set as the fuel cell stack excellent in.

  The fuel cell of the present invention is characterized in that the fuel cell stack is stored in a storage container.

  Such a fuel cell is characterized in that a fuel cell stack having excellent long-term reliability is stored in a storage container, so that a fuel cell having excellent long-term reliability can be obtained.

  The fuel cell according to the present invention includes an intermediate layer and an oxygen-side electrode layer containing Sr on the surface of one side of the solid electrolyte in order, and the surface layer region on the solid electrolyte side of the intermediate layer is denser than the other regions. Therefore, it is possible to provide a fuel cell having excellent long-term reliability, in which deterioration of power generation performance during long-time power generation is suppressed. Furthermore, it is possible to provide a fuel cell stack having excellent long-term reliability and a fuel cell having excellent long-term reliability, which are configured using the fuel cell of the present invention.

  Fig.1 (a) shows the cross section of the hollow flat fuel cell 10, (b) is a perspective view of (a). In both drawings, each configuration of the fuel cell 10 is partially enlarged. FIG. 2 is an enlarged cross-sectional view of a part of the fuel battery cell 10 according to the present invention that is involved in power generation.

  The fuel battery cell 10 includes a conductive support substrate 3 having a flat cross section and an elliptical column shape as a whole. Inside the conductive support substrate 3, a plurality of fuel gas passages 5 are formed in the longitudinal direction at appropriate intervals, and the fuel cell 10 is provided with various members on the conductive support substrate 3. It has a structure.

  As understood from the shape shown in FIG. 1, the conductive support substrate 3 includes a flat portion n and arc-shaped portions m at both ends of the flat portion n. Both surfaces of the flat portion n are formed substantially in parallel with each other, and a fuel side electrode 7 is provided so as to cover one surface (lower surface) of the flat portion n and the arc-shaped portions m on both sides. A dense solid electrolyte 9 is laminated so as to cover the electrode 7. On the solid electrolyte 9, the oxygen side electrode 1 containing Sr is laminated so as to face the fuel side electrode 7 with the intermediate layer 4 interposed therebetween. Further, the interconnector 2 is formed on the surface of the other flat portion n where the fuel side electrode 7 and the solid electrolyte 9 are not laminated. As is clear from FIG. 1, the fuel side electrode 7 and the solid electrolyte 9 extend to both sides of the interconnector 2 and are configured so that the surface of the conductive support substrate 3 is not exposed to the outside.

  Here, in the fuel cell 10, the portion of the fuel side electrode 7 facing the oxygen side electrode 1 functions as a fuel side electrode to generate electric power. That is, power is generated by flowing an oxygen-containing gas such as air outside the oxygen side electrode 1 and flowing a fuel gas (hydrogen) through the gas passage 5 in the conductive support substrate 3 and heating it to a predetermined operating temperature. The current generated by the power generation is collected via the interconnector 2 attached to the conductive support substrate 3.

In the present invention, the solid electrolyte 9 provided on the outer surface of the conductive support substrate 3 is a densely composed of partially stabilized or stabilized ZrO ₂ containing 3 to 15 mol% of rare earth elements such as Y, Sc and Yb. It is preferable to use high quality ceramics. As the rare earth element, Y is preferable because it is inexpensive. Further, the solid electrolyte 9 is desirably a dense material having a relative density (according to Archimedes method) of 93% or more, particularly 95% or more in terms of preventing gas permeation, and a thickness of 5 to 50 μm. It is preferable.

In the present invention, the oxygen-side electrode 1 is preferably formed from a conductive ceramic made of a so-called ABO ₃ type perovskite oxide. Such a perovskite oxide is preferably a transition metal perovskite oxide, particularly at least one of a LaMnO ₃ oxide, a LaFeO ₃ oxide, and a LaCoO ₃ oxide in which Sr and La coexist at the A site. 600 From the viewpoint of high electrical conductivity at an operating temperature of about ˜1000 ° C., LaCoO ₃ -based oxides are particularly preferable. In the perovskite oxide, Fe and Mn may be present together with Co at the B site.

  In addition, the oxygen side electrode 1 needs to have gas permeability. Therefore, the conductive ceramic (perovskite oxide) forming the oxygen side electrode 1 has an open porosity of 20% or more, particularly 30 to 50%. It is preferable that it exists in the range. Furthermore, the thickness of the oxygen-side electrode 1 is preferably 30 to 100 μm from the viewpoint of current collection.

  In the present invention, the intermediate layer 4 is provided on the surface of the solid electrolyte 9. Here, in the intermediate layer 4, the surface layer region (indicated by 4a in the figure) on the solid electrolyte 9 side is formed more densely than the other region (indicated by 4b in the figure). Thereby, even when Sr contained in the oxygen-side electrode 1 diffuses to the solid electrolyte 9 side due to long-time power generation of the fuel cell 10, Sr diffuses into the solid electrolyte 9 by the intermediate layer 4. Can be prevented. Further, even when Sr permeates the other region 4 b of the intermediate layer 4, the dense surface layer region 4 a of the intermediate layer 4 can prevent Sr from being diffused, and Sr can enter the solid electrolyte 9. It can be prevented from spreading. This is probably because Sr causes grain boundary diffusion, although no clear factor is known. Thereby, in the solid electrolyte 9, it is possible to prevent the formation of a reaction layer having a high electrical resistance due to the reaction between the components of the solid electrolyte 9 and Sr contained in the oxygen-side electrode 1. Deterioration can be suppressed, and deterioration of the power generation performance of the fuel cell 10 during long-time power generation can be suppressed.

  The surface layer region 4a of the intermediate layer 4 and the other region 4b of the intermediate layer can be formed with the surface layer region as the first layer 4a and the other region as the second layer 4b. In this case, the second layer 4b only needs to have a lower density than the first layer 4a, and may be formed of a plurality of layers. Therefore, for example, the second layer 4b may be formed from two layers, and the intermediate layer 4 may be formed from three layers as a whole, or may be formed as a larger number of layers.

  When the intermediate layer 4 is formed from the first layer 4a and the second layer 4b, the first layer 4a and the second layer 4b contain, for example, the same rare earth element (except Sr) It is preferable to form so as to. Thereby, the thermal expansion coefficients of the first layer 4a and the second layer 4b can be brought close to each other, and the bonding strength between the first layer 4a and the second layer 4b can be improved. The reason why Sr is excluded here is to effectively prevent Sr from being contained in the solid electrolyte 9 due to long-term power generation.

Such an identical rare earth element includes, for example, Ce. In particular, when the first layer 4a and the second layer 4b are produced, the raw material powder may be, for example, the following formula (1): (CeO ₂ ) _1-x (REO _1.5 ) _x
In the formula (1), RE is preferably at least one of Sm, Y, Yb, and Gd, and x preferably has a composition represented by a number satisfying 0 <x ≦ 0.3. . Here, examples of the rare earth element RE other than Ce include Sm, Y, Yb, and Gd, and these rare earth elements can be appropriately selected and used. As a result, when the first layer 4a and the second layer 4b are formed of the raw material powder containing at least one kind of the same rare earth element, the thermal expansion coefficients of the first layer 4a and the second layer 4b are reduced. can do. Thereby, for example, since the thermal expansion coefficient of the solid electrolyte 9 containing Zr can be brought close to, the occurrence of cracks and peeling due to the difference in thermal expansion can be suppressed. The first layer 4a and the second layer 4b can also be made from the same composition.

Furthermore, the first layer 4a and the second layer 4b are preferably, for example, CeO ₂ in which Sm or Gd is dissolved, and the raw material powder is represented by the following formula (2) :( CeO ₂ ) _{1- x} (SmO _1.5 ) _x
(3): (CeO ₂ ) _1-x (GdO _1.5 ) _x
In the formulas (2) and (3), x preferably has a composition represented by a number satisfying 0 <x ≦ 0.3. Furthermore, from the viewpoint of reducing electrical resistance, it is preferable that 10 to 20 mol% of _{SmO 1.5} or _{GdO 1.5} consists of CeO ₂ was dissolved. In addition, in order to heighten the effect which suppresses formation of the reaction product of the component of the solid electrolyte 9 and Sr in this raw material powder, you may contain the oxide of another rare earth element.

  Then, an oxygen layer electrode containing the intermediate layer 4 (first layer 4a, second layer 4b) and Sr is formed in this order on the surface of one side of the solid electrolyte 9, so that it is contained in the oxygen electrode 1 Sr that is contained (diffused) in the solid electrolyte 9 can be prevented, deterioration of the performance of the fuel cell 10 can be suppressed, and the deterioration of the power generation performance of the fuel cell 10 during long-time power generation can be suppressed. Can be suppressed. Note that the fact that Sr is not contained in the solid electrolyte 9 means that Sr cannot be confirmed in the solid electrolyte 9 when surface analysis is performed using, for example, EPMA (X-ray microanalyzer).

  Furthermore, it is preferable that the solid electrolyte 9 and the first layer 4a are formed by simultaneous firing, and the second layer 4b and the oxygen side electrode 1 are sequentially formed on the first layer 4a. That is, the second layer 4b is preferably formed in a separate step after the solid electrolyte 9 and the first layer 4a are formed by simultaneous firing.

  Although such a manufacturing method will be described later, since the solid electrolyte 9 and the first layer 4a are formed by simultaneous firing at a high temperature, the bonding between the solid electrolyte 9 and the first layer 4a is strengthened. In addition, the first layer 4a can be made dense.

  Further, the second layer 4b can be formed on the surface of the first layer 4a in a step different from the simultaneous firing, so that the density is lower than that of the first layer 4a. . Therefore, for example, when the oxygen side electrode 1 is formed after the second layer 4b is formed, the second layer 4b and the oxygen side electrode 1 can improve the bonding strength by the anchor effect. it can. Thereby, it can suppress that the 2nd layer 4b and the oxygen side electrode 1 peel, and can suppress degradation of the electric power generation performance of the fuel cell 10 in long-time electric power generation.

  Here, in the case where the second layer 4b is composed of a plurality of layers, it is preferable that the layer bonded to the oxygen-side electrode 1 be bonded by the anchor effect, and the other layers constituting the second layer 4b. These layers can be formed by appropriately adjusting, for example, by forming each layer in order as appropriate and then separately forming a layer bonded to the oxygen-side electrode 1.

  Note that the second layer 4b only needs to have a lower density than the first layer 4a, and Sr, which is a component of the oxygen side electrode 1, is not included in the solid electrolyte 9 (diffuses). It is not intended to limit the densification of the second layer 4b. However, it is preferable to make the second layer 4b by adjusting as appropriate so that the second layer 4b and the oxygen-side electrode 1 can be firmly bonded by the anchor effect.

  By densifying the second layer 4b, Sr contained in the oxygen-side electrode 1 can be further prevented (suppressed) from diffusing to the solid electrolyte 9 side. In densifying the second layer 4b, the heat treatment temperature and heat treatment time of the second layer 4b are appropriately changed in accordance with the grain size of the raw material to be the second layer 4b, so that the second layer 4b 4b can be densified.

  Since the second layer 4b preferably has a lower density than the first layer 4a, for example, at a temperature lower than the firing temperature at the time of simultaneous firing of the first layer 4a and the solid electrolyte 9. It is preferable to perform heat treatment (firing). Specifically, for example, it is preferably formed by heat treatment at a temperature 200 ° C. or lower than the firing temperature at the time of simultaneous firing. As such a specific temperature, for example, the second layer 4b is preferably formed at 1100 to 1300 ° C. Thereby, the second layer 4a can be made denser than the first layer 4a, and the bonding strength with the oxygen-side electrode 1 can be improved.

  In the fuel cell of the present invention, the thickness of the first layer 4a is preferably 1 to 10 μm, and the thickness of the second layer 4b is preferably 5 to 20 μm.

  By setting the thickness of the first layer 4 a to 1 to 10 μm, it is possible to effectively prevent Sr contained in the oxygen-side electrode 1 from diffusing into the solid electrolyte 9. In addition, it is possible to prevent the solid electrolyte 9 and the first layer 4a from being peeled off during simultaneous sintering.

  Furthermore, by setting the thickness of the second layer 4b to 5 to 20 μm, it is possible to reduce the amount of the Sr second layer 4b that is contained in the oxygen-side electrode 1 through long-term continuous operation. Thereby, Sr contained in the oxygen-side electrode 1 can be prevented from diffusing into the solid electrolyte, the deterioration of the power generation performance of the fuel cell 10 during long-time power generation can be suppressed, and long-term reliability can be achieved. It can be set as the outstanding fuel battery cell.

  When the thickness of the second layer 4b is 20 μm or more, the first layer 4a and the second layer 4b may be peeled off due to a difference in thermal expansion from the first layer 4a. Attention is required.

  Below, the other member which comprises the fuel cell 10 of this invention is demonstrated.

  Since the conductive support substrate 3 is required to be gas permeable to allow the fuel gas to permeate to the fuel side electrode 7 and to be conductive to collect current via the interconnector 2, For example, it is preferably formed of an iron group metal component and a specific rare earth oxide.

  Examples of the iron group metal component include an iron group metal element, an iron group metal oxide, an iron group metal alloy or an alloy oxide, and the like. More specifically, for example, the iron group metals include iron, nickel, and cobalt. In the present invention, any of them can be used, but since it is inexpensive and stable in fuel gas, It is preferable to contain Ni and / or NiO as a group component.

The rare earth oxide component is used to bring the coefficient of thermal expansion of the conductive support substrate 3 close to the coefficient of thermal expansion of the solid electrolyte 9, and Y, Lu, Yb, Tm, Er, Ho, Dy, A rare earth oxide containing at least one element selected from the group consisting of Gd, Sm, and Pr 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, there is almost no solid solution and reaction with the iron group metal oxide, and the thermal expansion coefficient is almost the same as that of the solid electrolyte 9. and from the point that it is _{inexpensive, Y 2 O 3, Yb 2} O 3 it is preferred.

  Further, in the present invention, iron group metal component: rare earth oxide component = 35: 65 or more in that the good conductivity of the conductive support substrate 3 is maintained and the thermal expansion coefficient is approximated to that of the solid electrolyte 9. It is preferably present in a volume ratio of 65:35. The conductive support substrate 3 may contain other metal components and oxide components as long as required characteristics are not impaired.

  Further, since the conductive support substrate 3 is required 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 conductive support substrate 3 is preferably 300 S / cm or more, and particularly preferably 440 S / cm or more.

  Specific dimensions of the conductive support substrate 3 include a length 15 to 35 mm of the flat portion n, a length (arc length) 2 to 8 mm of the arc-shaped portion m, and a thickness (flat) of the conductive support substrate 3. The distance between both surfaces of the part n) can be 1.5 to 5 mm.

In the present invention, the fuel-side electrode 7 causes an electrode reaction, and is preferably formed from a known porous conductive ceramic. For example, it is formed from ZrO _{2 in which a} rare earth element is dissolved or CeO ₂ in which a rare earth element is dissolved, and Ni and / or NiO.

The content of ZrO ₂ in which the rare earth element is dissolved in the fuel side electrode 7 or CeO ₂ in which the rare earth element is dissolved is preferably in the range of 35 to 65% by volume, and the Ni or NiO content is 65%. It is preferable that it is thru | or 35 volume%. Further, the open porosity of the fuel side electrode 7 is preferably 15% or more, particularly preferably in the range of 20 to 40%, and the thickness thereof is preferably 1 to 30 μm. For example, if the thickness of the fuel side electrode 7 is too thin, the performance may be deteriorated. If the thickness is too thick, there is a possibility that separation due to a difference in thermal expansion occurs between the solid electrolyte 9 and the fuel side electrode 7.

  Further, in the example of FIG. 1, the fuel side electrode 7 extends to both sides of the interconnector 2, but the fuel side electrode 7 only has to be formed at a position facing the oxygen side electrode 1. Therefore, for example, the fuel side electrode 7 may be formed only in the flat portion n on the side where the oxygen side electrode 1 is provided. In addition, the interconnector 2 can be provided directly on the flat portion n of the conductive support substrate 3 on the side where the solid electrolyte 9 is not provided. In this case, the interconnector 2 is provided between the interconnector 2 and the conductive support substrate 3. Can be suppressed.

  Further, a layer 8 having a composition similar to that of the fuel side electrode 7 is provided between the interconnector 2 and the conductive support substrate 3 in order to reduce a difference in thermal expansion coefficient between the interconnector 2 and the conductive support substrate 3. May be formed. FIG. 1 shows a state in which a layer 8 having a composition similar to that of the fuel-side electrode 7 is formed between the interconnector 2 and the conductive support substrate 3.

The interconnector 2 provided on the conductive support substrate 3 through the layer 8 having a similar composition to the fuel side electrode 7 at a position facing the oxygen side electrode 1 is made of conductive ceramics. Although it is preferable to have contact with the fuel gas (hydrogen) and the oxygen-containing gas, it is necessary to have reduction resistance and oxidation resistance. For this reason, lanthanum chromite-based perovskite oxides (LaCrO ₃ -based oxides) are generally used as conductive ceramics having reduction resistance and oxidation resistance. Further, in order to prevent leakage of the fuel gas passing through the inside of the conductive support substrate 3 and the oxygen-containing gas passing through the outside of the conductive support substrate 3, such conductive ceramics must be dense, for example 93% or more In particular, it is preferable to have a relative density of 95% or more.

  The thickness of the interconnector 2 is preferably 10 to 200 μm from the viewpoint of preventing gas leakage and electrical resistance. If the thickness is smaller than this range, gas leakage is liable to occur. If the thickness is larger than this range, the electric resistance is large, and the current collecting function may be lowered due to a potential drop.

  Moreover, it is preferable to provide the P-type semiconductor 6 on the outer surface (upper surface) of the interconnector 2. By connecting the current collecting member to the interconnector 2 via the P-type semiconductor 6, the contact between the two becomes an ohmic contact, the potential drop is reduced, and the deterioration of the current collecting performance can be effectively avoided. .

As such a P-type semiconductor 6, a transition metal perovskite-type oxide can be exemplified. Specifically, those having higher electron conductivity than LaCrO ₃ oxides constituting the interconnector 2, 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 6 is preferably in the range of 30 to 100 μm.

  The manufacturing method of the fuel cell 10 of the present invention described above will be described. In the description, the case where the second layer 4b is formed as one layer is shown.

First, a clay is prepared by mixing an iron group metal such as Ni or its oxide powder, a rare earth oxide powder such as Y ₂ O ₃ , an organic binder, and a solvent, and using this clay A conductive support substrate 3 molded body is prepared by extrusion molding and dried. As the conductive support substrate 3 molded body, a calcined body obtained by calcining the conductive support substrate 3 molded body at 900 to 1000 ° C. for 2 to 6 hours may be used.

Next, for example, ZrO ₂ (YSZ) raw material in which NiO and Y ₂ O ₃ are dissolved is weighed and mixed according to a predetermined composition. Thereafter, an organic binder and a solvent are mixed with the mixed powder to prepare a slurry for the fuel side electrode 7.

Further, a slurry obtained by adding toluene, a binder, a commercially available dispersant, etc. to a ZrO ₂ powder in which a rare earth element is solid-solubilized is molded into a thickness of 7 to 75 μm by a method such as a doctor blade. A solid electrolyte 9 compact is produced. The fuel-side electrode 7 slurry is applied on the obtained sheet-like solid electrolyte 9 molded body to form a fuel-side electrode 7 molded body, and the surface on the fuel-side electrode 7 molded body side is formed on the conductive support substrate 3 molded body. Laminate to. The slurry for the fuel side electrode 7 is applied to a predetermined position of the conductive support substrate 3 molded body and dried, and the solid electrolyte 9 molded body coated with the slurry for the fuel side electrode 7 is laminated on the conductive support substrate 3 molded body. You may do it.

Subsequently, for example, CeO ₂ powder in which SmO _1.5 is dissolved is heat-treated at 800 to 900 ° C. for 2 to 6 hours, and then wet pulverized to adjust the aggregation degree to 5 to 35, and the intermediate layer 4 Adjust raw material powder for the molded body. The wet crushing is desirably ball milled for 10 to 20 hours using a solvent. The same applies to the case where the intermediate layer 4 is formed of CeO ₂ powder in which GdO _1.5 is dissolved.

  In the present invention, toluene as a solvent is added to the raw material powder of the intermediate layer 4 molded body whose coagulation degree is adjusted to produce a slurry for the intermediate layer 4, and this slurry is applied onto the solid electrolyte 9 molded body. The coating film of the 1st layer 4a is formed, and the 1st layer 4a molded object is produced. Alternatively, a sheet-like first layer 4a molded body may be produced and laminated on the solid electrolyte 9 molded body.

Subsequently, a material for the interconnector 2 (for example, LaCrO ₃ -based oxide powder), an organic binder and a solvent are mixed to prepare a slurry, a sheet for the interconnector 2 is produced, and a solid electrolyte 9 molded body is formed. No conductive support substrate 3 is laminated on the exposed surface of the molded body.

  Next, the above-mentioned laminated molded body is subjected to binder removal treatment and co-fired at 1400 to 1600 ° C. for 2 to 6 hours in an oxygen-containing atmosphere.

  Thereafter, the intermediate layer slurry is applied to the surface of the formed first layer 4a sintered body to produce a second layer 4b molded body and sintered. In the present invention, when the second layer 4b compact is sintered, it is preferably 200 ° C. or more lower than the temperature at the time of simultaneous firing of the solid electrolyte 9 and the first layer 4a, for example, 1100 ° C. to 1300 ° C. It is preferable to carry out with.

  When the second layer 4b is formed from a plurality of layers, the second layer 4b can be manufactured by appropriately adjusting the manufacturing method, for example, sequentially sintering each layer constituting the second layer 4b.

  Here, in densifying the second layer 4b, the sintering time can be appropriately adjusted depending on the particle size, sintering temperature, and the like of the intermediate layer raw material. It is also possible to densify the second layer 4b by sintering the second layer 4b and the first layer 4a and fixing them, followed by further baking. In this case, it is preferable to appropriately adjust the baking temperature and baking time so that the second layer 4b and the oxygen-side electrode 1 can be firmly bonded. The sintering time for fixing the second layer 4b and the first layer 4a can be 2 to 6 hours.

  Moreover, the solid electrolyte 9 molded body of the present invention is a concept including the solid electrolyte 9 calcined body, and the intermediate layer 4 molded body may be laminated on the solid electrolyte 9 calcined body.

Further, a slurry containing a material for the oxygen side electrode 1 (for example, LaCoO ₃ oxide powder), a solvent, and a pore increasing agent is applied on the intermediate layer 4 by dipping or the like. Further, if necessary, a slurry containing a material for P-type semiconductor layer 6 (for example, LaCoO ₃ oxide powder) and a solvent is applied by dipping or the like to a predetermined position of the interconnector 2 at 1000 to 1300 ° C., By baking for 2 to 6 hours, the fuel cell 10 of the present invention having the structure shown in FIG. 1 can be manufactured. In addition, it is preferable that the fuel cell 10 thereafter causes hydrogen gas to flow therein to perform reduction treatment of the conductive support substrate 3 and the fuel side electrode 7. In that case, it is preferable to perform a reduction process at 750-1000 degreeC for 5 to 20 hours, for example.

  That is, when the fuel cell 10 of the present invention is manufactured, the first layer 4a and the second layer 4b are manufactured by separate processes, and after the second layer 4b is baked, the oxygen side electrode 1 is baked. For this reason, the second layer 4b does not contain the component of the oxygen-side electrode 1. Thereby, it can suppress that the component contained in the oxygen side electrode 1 diffuses to the solid electrolyte 9 side immediately after production of the fuel cell 10.

  Further, the fuel cell stack of the present invention is fixed to the manifold in a state where a plurality of the fuel cells 10 produced as described above are arranged upright and arranged between the fuel cells 10. The member is bonded to the oxygen-side electrode 1 of one fuel cell 10 by a conductive adhesive such as conductive ceramic, and is bonded to the P-type semiconductor layer 6 of the other adjacent fuel cell 10 by a conductive adhesive. As a result, the plurality of fuel cells 10 are electrically connected directly to each other to form a fuel cell stack.

  The fuel cell stack of the present invention can be a fuel cell stack having excellent long-term reliability by electrically connecting a plurality of the fuel cells 10 produced as described above.

  Furthermore, the fuel cell of the present invention has the fuel cell stack stacked in a storage container, and a fuel gas introduction pipe for supplying fuel gas such as city gas and an air introduction pipe for supplying air to the storage container. It is constituted by arranging.

The fuel cell of the present invention is characterized in that the fuel cell stack is housed in a storage container, and therefore, a fuel cell excellent in long-term reliability, which prevents deterioration in power generation performance during long-time power generation, can do. At that time, a plurality of fuel cell stacks can be connected and stored in the storage container.

  An example in which the second intermediate layer 4b is formed as one layer is shown below.

First, NiO powder having an average particle diameter of 0.5 μm and Y ₂ O ₃ powder having an average particle diameter of 0.9 μm are calcined and reduced, so that the volume ratio is 48% by volume for Ni and 52% by volume for Y ₂ O _3. Then, the kneaded material prepared with an organic binder and a solvent was molded by an extrusion molding method, dried and degreased to prepare a conductive support substrate 3 molded body. Sample No. In No. 1, the volume ratio of the Y ₂ O ₃ powder after calcination-reduction was 45% by volume for Ni and 55% by volume for Y ₂ O ₃ .

Next, a slurry for the fuel-side electrode 7 in which a NiO powder having an average particle size of 0.5 μm, a ZrO ₂ powder in which Y ₂ O ₃ is solid-solved, an organic binder, and a solvent is mixed is prepared. The coating layer for the fuel side electrode 7 was formed by coating and drying by screen printing. Next, using a slurry obtained by mixing ZrO ₂ powder (solid electrolyte 9 raw material powder) having a particle diameter of 0.8 μm by solid micro-track method in which 8 mol% of yttrium was dissolved, an organic binder and a solvent, A sheet for solid electrolyte 9 having a thickness of 30 μm was produced by a blade method. The sheet for the solid electrolyte 9 was attached on the coating layer of the fuel side electrode 7 and dried. Sample No. In No. 3, the particle size of the ZrO ₂ powder was 1.0 μm. In No. 4, the thickness of the solid electrolyte 9 sheet was 40 μm.

  Subsequently, the laminated molded body in which the molded bodies were laminated as described above was calcined at 1000 ° C. for 3 hours.

Next, a complex oxide containing 85 mol% of CeO ₂ and 15 mol% of any of other oxides of rare earth elements (SmO _1.5 , YO _1.5 , YbO _1.5 , GdO _1.5 ), Using isopropyl alcohol (IPA) as a solvent, pulverizing with a vibration mill or ball mill, calcining at 900 ° C. for 4 hours, pulverizing again with a ball mill, adjusting the degree of aggregation of ceramic particles, Layer 4 raw material powder was obtained. The slurry of the intermediate layer 4 produced by adding and mixing an acrylic binder and toluene to this powder was applied by screen printing on the solid electrolyte 9 calcined body of the obtained laminated calcined body, A molded body of the first layer 4a was produced. Sample No. In No. 5, the oxide of another rare earth element was 10 mol%, and sample No. In No. 6, the oxide of another rare earth element was set to 20 mol%. In No. 7, the calcining temperature was 850 ° C.

Subsequently, the LaCrO ₃ type oxide, to prepare a slurry for the interconnector 2 by mixing an organic binder and a solvent, which, solid electrolyte exposed conductive calcined body is not formed support substrate 3 calcined body on And co-fired at 1510 ° C. for 3 hours in the air.

  Next, the slurry of the intermediate layer 4 is applied to the surface of the formed first layer 4a sintered body by a screen printing method to form a second layer 4b film. Time sintering was performed.

  In Table 1, No. 12-No. In No. 15, the first layer 4a was not formed but was fired simultaneously, and only the second layer 4b was sintered. No. No. 16 did not form the second layer 4b.

Next, a mixed liquid composed 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 isopropyl alcohol is prepared and sprayed on the surface of the intermediate layer of the laminated sintered body. This was applied to form an oxygen-side electrode 1 molded body, and baked at 1100 ° C. for 4 hours to form the oxygen-side electrode 1. Thus, the fuel battery cell 10 shown in FIG. 1 was produced.

  The size of the produced fuel cell 10 is 25 mm × 200 mm, the thickness of the conductive support substrate 3 (distance between nn) is 2 mm, the open porosity is 35%, and the thickness of the fuel side electrode 7 is 10 μm. The open porosity was 24%, the thickness of the oxygen-side electrode 1 was 50 μm, the open porosity was 40%, and the relative density was 97%.

  Next, hydrogen gas was allowed to flow inside the fuel cell 10 and the conductive support substrate 3 and the fuel side electrode 7 were subjected to reduction treatment at 850 ° C. for 10 hours.

  The obtained fuel cell 10 was subjected to surface analysis by EPMA (X-ray microanalyzer) for the diffusion of Sr contained in the oxygen-side electrode into the solid electrolyte 9 and listed in Table 1 as the presence or absence of Sr.

  Here, the presence / absence of Sr was determined to be absent when Sr was not found in the solid electrolyte 9, and was determined as being possible when Sr was observed.

Subsequently, the fuel gas is circulated through the fuel gas passage 5 of the obtained fuel battery cell 10, the oxygen-containing gas is circulated outside the fuel battery cell 10, and the fuel battery cell 10 is 750 ° C. using an electric furnace. The power generation performance of the fuel cell was confirmed by performing a power generation test for 3 hours. Thereafter, power generation was performed for 1000 hours under conditions of a fuel utilization rate of 75% and a current density of 0.6 A / cm ² . At that time, the value at 0 hours of power generation was used as the initial voltage, the voltage after 1000 hours was measured, the change from the initial voltage was determined as the deterioration rate, and the deterioration rate of power generation performance was determined. Regarding evaluation of power generation performance deterioration, the deterioration rate is less than 0.5%, the deterioration rate is 0.5-1%, the deterioration rate is 1-3%, and the deterioration rate is 1-3%. Table 1 shows the results of the evaluation, assuming that the deterioration rate is 3 to 5% in many cases and the deterioration rate is 5% or more.

Further, the density of the first layer 4a and the second layer 4b of each fuel cell 10 after the power generation test was observed with a scanning electron microscope (SEM).

  From the results of Table 1, the first layer 4a and the second layer 4b have the same composition, the first layer 4a and the solid electrolyte 9 are co-fired, and the second layer 4b is determined from the temperature during co-firing. When sintered at a temperature as low as 200 ° C. or more (Sample Nos. 1-3, No20, No.21), the solid electrolyte 9 does not contain Sr, and the result is that the power generation performance is very little deteriorated. Indicated. In addition, up to a thickness of 5 to 20 μm of the second layer 4b (sample Nos. 4 to 6 and Nos. 17 to 19), the solid electrolyte 9 does not contain Sr, and the power generation performance is hardly deteriorated. The result was shown.

  Furthermore, when the thickness of each of the first layer 4a and the second layer 4b is increased or decreased (sample Nos. 7 to 9), Sr is not contained in the solid electrolyte 9, and the power generation performance The result showed that there was considerably little deterioration.

  On the other hand, even when the first layer 4a is fired at the same time, when the second layer 4b is sintered at 1400 ° C. or higher (No. 10, No. 11), the solid electrolyte 9 contains Sr. Although it was not, it was sintered at almost the same temperature as the co-firing of the solid electrolyte 9 and the first layer 4a or at a low temperature of about 100 ° C., so that the power generation performance was hardly deteriorated. It was.

  Furthermore, when there is no first layer 4a and the second layer 4b is retrofitted to the sintered body (sample Nos. 12 to 15), or when the second layer 4b is not formed (sample No. 16). Showed that the power generation performance deterioration rate was severe.

  On the other hand, the first layer 4a and the second layer 4b are samples (sample No.) in which the same rare earth element is Ce and the other rare earth elements are different in composition in the first layer 4a and the second layer 4b. 22 to 33), when the second layer 4b was baked at 1400 ° C. or higher (sample Nos. 27 and 33), Sr was not contained in the solid electrolyte 9, but the solid electrolyte 9 and the second layer 4b Since the sintering was performed at substantially the same temperature as that at the time of co-firing with the first layer 4a or at a temperature as low as about 100 ° C., the results showed that the power generation performance was hardly deteriorated. In the other samples, Sr was not contained in the solid electrolyte 9, and the results showed that the power generation performance was very little deteriorated.

  In addition, as a result of comparing the density of the first layer 4a and the second layer 4b, in all the fuel cells 10 in which the first layer 4a and the second layer 4b are formed, the density of the first layer 4a is high. The degree of density was higher than the degree of density of the second layer 4b.

The fuel cell of this invention is shown, (a) is a cross-sectional view, (b) is a perspective view of (a). FIG. 3 is an enlarged cross-sectional view showing a part of a part engaged in power generation of the fuel cell according to the present invention. It is a cross-sectional view which shows the cell stack which consists of the conventional fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Oxygen side electrode 2 ... Interconnector 3 ... Conductive support substrate 4a ... 1st layer 4b ... 2nd layer 5 ... Fuel gas passage 7 ... Fuel side electrode 9 ... Solid electrolyte 10 ... Fuel battery cells

Claims (6)

A fuel cell comprising an intermediate layer and an oxygen-side electrode containing Sr in order on one surface of the solid electrolyte, and a fuel-side electrode on the other surface of the solid electrolyte facing the oxygen-side electrode The intermediate layer has a surface layer region on the solid electrolyte side formed more densely than other regions. The intermediate layer has a first layer that forms a surface layer region and a second layer that forms another region, and the first layer and the solid electrolyte are formed by simultaneous firing. The fuel cell according to claim 1. 3. The fuel cell according to claim 2, wherein the thickness of the first layer is 1 to 10 μm, and the thickness of the second layer is 5 to 20 μm. 4. The fuel cell according to claim 2, wherein the first layer and the second layer contain the same rare earth element (excluding Sr). 5. A fuel cell stack comprising a plurality of the fuel cells according to any one of claims 1 to 4 electrically connected in series. 6. A fuel cell comprising the fuel cell stack according to claim 5 housed in a housing container.

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