JP5588888B2 - Fuel cell stack and fuel cell - Google Patents

Description

  The present invention relates to a fuel cell stack and a fuel cell using a solid electrolyte as an electrolyte.

  A fuel cell is a converter that generates electric energy by supplying a reactant (fuel) and an oxidant (air or oxygen) into the cell. As the structure of the fuel cell, a single cell in which the fuel electrode layer is arranged on one side of the solid electrolyte layer and the air electrode layer is arranged on the other side is stacked by stacking them through a separator, and this fuel cell stack is further stacked. A fuel cell is known.

  In the fuel cell stack and the fuel cell, a gas flow path for flowing fuel gas is formed on one side of the separator, and a gas flow path for flowing oxidant gas is formed on the other side of the separator. In many cases (see FIG. 8 of Patent Document 1). In addition, as described in Patent Document 2, a technique for forming a gas flow path inside the air electrode layer has also been proposed.

  Conventionally, ceramics have been used as the separator material. In recent years, attempts have been made to use metal materials from the viewpoints of practicality and economy.

JP-A-5-159790 (FIG. 8) JP-A-9-50812

  In the fuel cell stack, one side of the separator is exposed to a reducing atmosphere, and the other side is exposed to an oxidizing atmosphere. In the case of a metal separator using a metal material as a separator material, there is a problem that deterioration due to oxidation is likely to occur. On the other hand, the ceramic separator is excellent in oxidation resistance, but has higher electric resistance than the metal separator. Therefore, there is a problem that a voltage drop is large when a current generated by power generation is taken out.

  The present invention has been made in view of such a problem, and a problem to be solved by the present invention is a fuel capable of suppressing deterioration due to oxidation of a metal separator and reducing a voltage drop. It is to provide a battery stack.

  The present invention provides a single cell comprising a solid electrolyte layer, a fuel electrode layer provided on one side of the solid electrolyte layer, and an air electrode layer provided on the other side of the solid electrolyte layer, and a metal separator. A plurality of stacked fuel cell stacks, wherein the air electrode layer is disposed in contact with the solid electrolyte layer and a surface of the porous layer in contact with the metal separator side The fuel cell stack has a dense layer. (Claim 1)

  As described above, the fuel cell stack of the present invention includes a porous layer in which the air electrode layer is disposed in contact with the solid electrolyte layer, and a dense layer in which the porous layer is disposed in contact with the surface on the metal separator side. And have. Therefore, the oxidant gas supplied to the porous layer of the air electrode layer is gas-sealed by the dense layer, and the oxidant gas can be prevented from contacting the metal separator. Thereby, deterioration due to oxidation of the metal separator can be suppressed. Therefore, high reliability of the stack can be achieved.

Moreover, since the oxidant gas is gas-sealed by the dense layer as described above, a metal separator can be used as a separator, and oxidation resistance does not need to be considered so much. Thus, it becomes possible to use a metal separator made of various metal materials having low electrical resistance. Thereby, compared with the case where the separator made from ceramics is used, the voltage drop at the time of taking out the electric current which arose by electric power generation can be made small. Therefore, high performance of the stack can be achieved.
As described above, according to the present invention, deterioration due to oxidation of the metal separator can be suppressed, and the voltage drop can be reduced.

FIG. 2 is an explanatory diagram schematically showing a configuration of a fuel cell stack in Example 1. It is explanatory drawing which shows the single cell of a fuel cell stack in Example 1 with the flow of gas. FIG. 10 is an explanatory view showing a modification of the air electrode layer of the fuel cell stack in Example 2. FIG. 10 is an explanatory view showing a modification of the air electrode layer of the fuel cell stack in Example 3. FIG. 10 is an explanatory view showing a modification of the air electrode layer of the fuel cell stack in Example 4.

  In the fuel cell stack of the present invention, examples of the solid electrolyte constituting the solid electrolyte layer include solid oxide ceramics such as zirconia and ceria based solid solutions in which oxides such as yttria and scandia are solid solution, and fluorine based hydrocarbons. Examples thereof include a solid polymer electrolyte in which an electrolyte group such as a sulfonic acid group is introduced into a polymer such as ionic conductive glass such as phosphate glass. The solid electrolyte constituting the solid electrolyte layer is preferably a solid electrolyte exhibiting oxygen ion conductivity, and more preferably a zirconia-based solid oxide ceramic. A solid oxide fuel cell (hereinafter referred to as “SOFC”) stack using a solid oxide layer as a solid electrolyte layer has a high battery operating temperature, and deterioration due to oxidation of a metal separator tends to be a problem. For this reason, the effect of the present invention is great. However, the present invention is not limited to the SOFC stack.

  The fuel cell stack may have a flat plate structure or a cylindrical structure. Preferably, it is a flat plate type that is relatively easy to stack. Further, the unit cell may have any power generation main element of the fuel electrode layer, the solid electrolyte layer, and the air electrode layer function as a support. A thing other than the power generation main element can also be provided as a separate support. Examples of the material constituting the fuel electrode layer include, in the case of an SOFC stack, metallic nickel, nickel oxide, and cermet of these and zirconia-based solid oxide ceramics such as yttria-stabilized zirconia. .

  Here, the air electrode has a porous layer and a dense layer. In the present invention, the porosity of the porous layer is not particularly limited as long as the porous layer can pass the oxidant gas flowing through the air electrode layer. The porosity distribution may be uniform or different in the thickness direction. It can be determined in consideration of the diffusibility of the oxidant gas, the manufacturability of the air electrode layer, and the like. The porous layer can be composed of one layer or two or more layers.

  On the other hand, in the present invention, “dense” in the dense layer means that the gas permeability of the oxidant gas flowing in the air electrode layer is negligibly small. The dense layer can be composed of one layer or two or more layers. Preferably, it is comprised from 1 layer. This is because the thickness of the single cell is reduced, and the stack can be easily downsized. As a material constituting the porous layer and the dense layer, for example, in the case of SOFC stack, a perovskite type having conductivity such as lanthanum-manganese oxide, lanthanum-cobalt oxide, lanthanum-iron oxide, etc. An oxide etc. can be illustrated.

  In the air electrode layer, the thickness of the porous layer and the thickness of the dense layer are not particularly limited. It can be set in consideration of the diffusibility of the oxidant gas, the ease of forming the gas flow path, the gas sealability and the like. Preferably, the dense layer has a thickness in the range of 0.05 to 0.5 times, more preferably in the range of 0.1 to 0.2 times the thickness of the porous layer. This is because there is a good balance between gas sealing properties and diffusibility of oxidizing gas. As for the thickness of a porous layer, 100-1000 micrometers is preferable, More preferably, it is 200-500 micrometers. On the other hand, the thickness of the dense layer is preferably 10 to 100 μm, more preferably 20 to 50 μm.

  In the case of an SOFC stack, the air electrode layer can be manufactured, for example, by laminating a layered porous layer forming material containing a porosifying agent and a layered dense layer forming material and firing the layered porous layer forming material. Moreover, it can also manufacture by extruding and baking a porous layer forming material and a dense layer forming material.

In the fuel cell stack, the air electrode layer preferably has a gas flow path for flowing an oxidant gas at a boundary between the porous layer and the dense layer.
In this case, it becomes easy to control the oxidant gas flowing in the surface direction of the porous layer. Therefore, it can contribute to the performance improvement of the stack. The gas channel may be formed on the porous layer side with the boundary interposed therebetween, or may be formed on the dense layer side with the boundary interposed therebetween. It can also be formed across the porous layer and the dense layer across the boundary. Preferably, the gas flow path is formed on the porous layer side with the boundary interposed therebetween. This is because the oxidant gas can be supplied using not only the gas flow path but also the porous portion where the gas flow path is not formed, and the diffusibility of the oxidant gas is excellent.

Moreover, it is preferable that the said gas flow path is comprised from the space enclosed by the several groove part formed in the porous layer, and the surface of a dense layer (Claim 3).
In this case, the area where the porous layer and the oxidant gas are in contact with each other increases. Therefore, the oxidant gas easily diffuses into the porous layer. In addition, the thickness of the dense layer not involved in gas diffusion can be reduced, and the thickness of the porous layer can be increased accordingly. Therefore, compared with the case where it has the air electrode layer of the same thickness, the diffusibility of oxidizing gas improves and is advantageous.

The dense layer preferably further covers the side surface of the porous layer.
In this case, the oxidant gas is gas-sealed by the dense layer not only on the plane of the porous layer but also on the side surfaces of the porous layer. Therefore, it is easy to suppress contact between the oxidant gas and the metal separator, and it is easy to suppress deterioration due to oxidation of the metal separator. Therefore, it becomes easy to achieve high reliability of the stack.

  The dense layer may cover part of the side surface of the porous layer, or may cover all of the side surface of the porous layer except for a portion that becomes a gas flow path. The latter is preferred. This is because the smaller the side exposure of the porous layer, the better the gas sealability of the oxidant gas supplied to the porous layer, which is more advantageous in suppressing deterioration due to oxidation of the metal separator.

  The metal separator is made of a metal material. The above “metal” is meant to include alloys in addition to pure metals. Although the said metal separator may be comprised from the metal material containing Cr, it is preferable to be comprised from the metal material which does not contain Cr (Claim 5). The “metal material not containing Cr” includes a metal material containing Cr as an inevitable impurity.

Here, in the case of a conventional fuel cell stack using a metallic separator containing Cr, the protective coating Cr ₂ O ₃ formed on the separator surface is oxidized and CrO ₃ (g) is evaporated, which is condensed in the air electrode. Cr poisoning may occur. Cr poisoning increases the electrical resistance between cells and reduces battery performance. However, in the fuel cell stack of the present invention, since the oxidant gas is gas-sealed by the dense layer, the oxidant gas is difficult to contact the metal separator, and deterioration due to oxidation of the metal separator can be suppressed. Therefore, even when a metal separator containing Cr is used, it can be said that the structure is hardly affected by Cr poisoning. Further, when the metal separator is made of a metal material not containing Cr, it is easy to avoid the influence of Cr poisoning in combination with the air electrode layer having a dense layer. Therefore, there is no possibility that the electrical resistance between cells increases due to Cr poisoning, which can contribute to higher performance of the stack. In particular, a solid oxide fuel cell using solid oxide ceramics as a solid electrolyte has a large effect because it has a relatively high operating temperature and a strong oxidizing atmosphere.

  Examples of the metal material containing Cr include stainless steel and Cr-based alloys. Examples of the stainless steel include ferritic stainless steels such as SUS430, SUS434, and SUS405, martensitic stainless steels such as SUS403, SUS410, and SUS431, and austenitic stainless steels such as SUS201, SUS301, and SUS305. On the other hand, examples of the metal material not containing Cr include Ni-based alloys, Cu-based alloys, and Fe-based alloys. Among these, Ni-based alloys are preferable from the viewpoint of excellent heat resistance. Ni-based alloys include Ni-Fe-Co alloys, Ni-Cu alloys, Ni-Mo alloys, and the like. Of these Ni-based alloys, Ni—Fe—Co alloys are preferable from the viewpoint of strength, thermal expansion, and the like.

In the fuel cell stack, the single cell has a thermal expansion coefficient of 9.5 to 14.5 × 10 ⁻⁶ / K, and the metal separator has a thermal expansion coefficient of 9.5 to 14.5. It is preferable to be in the range of × 10 ⁻⁶ / K. It is because it becomes easy to prevent peeling of the joint part between components due to thermal strain. More preferably, the thermal expansion coefficient of the single cell is in the range of 10 to 12 × 10 ⁻⁶ / K, and the thermal expansion coefficient of the metal separator is in the range of 10 to 12 × 10 ⁻⁶ / K. Good.

The fuel cell of the present invention has the fuel cell stack described above (claim 6).
Therefore, it is possible to increase the voltage while suppressing a decrease in output due to deterioration due to oxidation of the metal separator. The fuel cell stack can be stacked.

Example 1
A fuel cell stack and a fuel cell according to an embodiment of the present invention will be described with reference to FIGS.
The fuel cell stack 1 of this example is a flat type stack, and as shown in FIG. 1, four single cells 2 are stacked via metal separators 3 arranged between the cells. The unit cell 2 includes a solid electrolyte layer 21, a fuel electrode layer 22 provided on one surface of the solid electrolyte layer 21, and an air electrode layer 23 provided on the other surface of the solid electrolyte layer 21. For the solid electrolyte layer 21, yttria stabilized zirconia (thickness: 10 μm) was used. For the fuel electrode layer 22, cermet (thickness: 500 μm) of nickel oxide and yttria stabilized zirconia was used.

The air electrode layer 23 includes a porous layer 231 and a dense layer 232. The porous layer 231 is disposed in contact with the solid electrolyte layer 21. On the other hand, the dense layer 232 is disposed in contact with the surface of the porous layer 231 on the metal separator 3 side. Both the porous layer 231 and the dense layer 232 were formed of the same material (La _0.8 Sr _0.2 MnO ₃ ). However, the porous layer 231 was made porous to such an extent that air as an oxidant gas was vented (porosity was about 30% to 50%). On the other hand, the dense layer 232 was densified to such an extent that air as an oxidant gas was not substantially permeated. The thickness of the porous layer 231 was 300 μm, and the thickness of the dense layer 232 was 50 μm.

  The air electrode layer 23 has a gas flow path 233 through which an oxidant gas flows at the boundary B between the porous layer 231 and the dense layer 232. Specifically, the gas channel 233 is formed of a plurality of channel groups. The plurality of flow path groups includes a space 233 b surrounded by a plurality of grooves 233 a formed in the porous layer 231 and the surface of the dense layer 232. One end portions of these flow path groups communicate with one side end face of the porous layer 231. Further, the other end portion of the flow path group communicates with a side end surface at a position facing one side end surface of the porous layer 231. The groove width was 2000 μm, the groove depth was 200 μm, and the pitch of the grooves was 2000 μm.

The air electrode layer 23 was coated with a paste containing La _0.8 Sr _0.2 MnO ₃ powder, a porosifying agent and a binder, and after forming a flow path pattern with the binder, La _0.8 The slurry containing Sr _0.2 MnO ₃ powder and a binder was applied and fired. At this time, a screen printing method was used for the coating.

  The metal separator 3 disposed between the cells is made of flat stainless steel (SUS430). The thickness of the metal separator 3 was 1 mm. The metal separator 3 has a gas flow path 31 through which hydrogen gas as fuel gas flows on the surface on the fuel electrode layer 22 side. The surface on the air electrode layer 23 side is a flat surface. This is because in this example, the gas flow path 233 through which the oxidant gas flows is formed in the air electrode layer 23.

  As shown in FIG. 1, the fuel cell stack 1 of this example includes a metal separator 11 outside the cell, a current collector 12, a seal member 13, and a pair of insulations in addition to the single cell 2 and the metal separator 3 between the cells. A body 14, a pair of fixing members 15, a gas supply manifold 16, a gas exhaust manifold 17, and the like.

  The metal separator 11 outside the cell is laminated and disposed above the uppermost unit cell 2 (on the air electrode layer 23 side). The metal separator 11 outside the cell is made of the same material as the metal separator 3 between the cells. However, the gas separator is not formed on both sides of the metal separator 11 outside the cell. This is because it is not necessary to supply fuel gas to the fuel electrode layer 22 of the single cell 2.

  The current collector 12 is disposed between the single cell 2 and the metal separator 3, and between the single cell 2 and the metal separator 11. Ni felt was used for the current collector 12 arranged between the fuel electrode layer 22 side of the single cell 2 and the metal separator 3. In addition, Ni mesh or the like can be applied. On the other hand, a ferrite Cr alloy was used for the current collector 12 disposed between the air electrode layer 23 side of the single cell 2 and the metal separators 3 and 11. In addition, a conductive contact material such as a silver-based paste can be applied.

  The seal member 13 is provided on the side end surface of the single cell 2. In this example, the portion other than the gas flow path 233 on the side end face of the single cell 2 was sealed with a glass sealing material.

  The pair of insulators 14 is formed in a plate shape from alumina. The pair of insulators 14 are stacked outside the single cells 2 at both ends stacked via the metal separator 3. A pair of fixing members 15 are laminated on the outside of the pair of insulators 14. The fuel cell stack 1 has four through holes (not shown) penetrating the stack 1 in a direction perpendicular to the stacking direction from one fixing member 15 to the other fixing member 15 so as not to affect power generation. ing. Bolts (not shown) as fastening members are inserted into these through holes, and nuts (not shown) which are mating fastening members are attached to the ends of the bolts. The fuel cell stack 1 is sandwiched between the pair of fixing members 15 by the fastening force of these fastening members.

  The gas supply manifold 16 is provided on one side end face of the single cell 2. The gas supply manifold 16 has a fuel gas supply passage 161 for supplying hydrogen as a fuel gas (arrow F) to the metal separator 3 and an air as an oxidant gas (arrow A) supplied to the air electrode layer 23 therein. And an oxidant gas supply path 162 for performing the operation. The fuel gas supply passage 161 and the oxidant gas supply passage 162 communicate with each other between the gas supply manifolds 16 arranged in a stacked manner. The upstream end of the fuel gas supply path 161 is connected to a gas supply system (not shown). On the other hand, the upstream end of the oxidant gas supply path 162 is connected to an air supply system (not shown).

  The gas exhaust manifold 17 is provided on the other side end surface of the single cell 2. The gas exhaust manifold 17 includes a fuel gas exhaust passage 171 that exhausts fuel gas that has not been used for power generation to the outside of the stack 1 and an oxidant that exhausts oxidant gas that has not been used for power generation to the outside of the stack 1. And a gas exhaust passage 172. The fuel gas exhaust passage 171 and the oxidant gas exhaust passage 172 communicate with each other between the stacked gas exhaust manifolds 17. The downstream end of the fuel gas exhaust path 171 is connected to a fuel gas exhaust system (not shown). On the other hand, the downstream end of the oxidant gas exhaust path 172 is connected to an oxidant gas exhaust system (not shown).

  The fuel cell stack 1 can be operated as follows. Hydrogen gas (fuel gas) is supplied from the upstream end (In) of the fuel gas supply path 161 of the gas supply manifold 16. The hydrogen gas flows through the fuel gas supply path 161 and reaches the metal separator 3 disposed on the fuel electrode layer 22 side of each unit cell 2. The hydrogen gas that has reached the metal separator 3 flows through the gas flow path 31 in the metal separator 3 and is supplied to the fuel electrode layer 22 of each unit cell 2. On the other hand, air (oxidant gas) is supplied from the upstream end (In) of the oxidant gas supply path 162 of the gas exhaust manifold 17. The air flows through the oxidant gas supply path 162 and is supplied to the porous layer 231 side of the air electrode layer 23 of each single cell 2.

  The hydrogen gas and air supplied to each single cell 2 are consumed for battery reaction. On the other hand, the hydrogen gas not subjected to the cell reaction flows through the fuel gas exhaust passage 171 in the gas exhaust manifold 17 and is exhausted from the downstream end (Out) of the fuel gas exhaust passage 171. On the other hand, the air that has not been subjected to the battery reaction flows through the oxidant gas exhaust passage 172 in the gas exhaust manifold 17 and is exhausted from the downstream end (Out) of the oxidant gas exhaust passage 172.

  As described above, the fuel cell stack 1 can generate an electromotive force between the fuel electrode layer 22 and the air electrode layer 23 of each unit cell 2, and can function as a power generator. On the fuel electrode layer 22 side, the electric power generated by the power generation is disposed below the fuel cell stack 1 via the current collector 12 disposed between the fuel electrode layer 22 and the metal separator 3. Is taken out at the end of the fuel electrode layer 22 side. On the other hand, on the air electrode layer 23 side, the air electrode of the single cell 2 disposed above the fuel cell stack 1 via the current collector 12 disposed between the air electrode layer 23 and the metal separator 3. It is taken out at the end on the layer 23 side. The electric power of the entire fuel cell stack 1 is taken out between both ends of the stack. In addition, the fuel cell stack 1 of this example can be suitably operated at a temperature of 600 to 900 ° C.

  According to this example described above, air as an oxidant gas supplied to the porous layer 231 of the air electrode layer 23 is gas-sealed by the dense layer 232, and the air is prevented from coming into contact with the metal separator 3. be able to. Thereby, the deterioration by the oxidation of the metal separator 3 can be suppressed. Therefore, high reliability of the stack 1 can be achieved.

  Further, since air is gas-sealed by the dense layer 232, a metal separator can be used as a separator, and oxidation resistance does not need to be considered so much, so the degree of freedom in selecting a metal material constituting the metal separator 3 It becomes possible to use the metal separator 3 comprised from various metal materials with low electrical resistance. Thereby, compared with the case where the separator made from ceramics is used, the voltage drop at the time of taking out the electric current which arose by electric power generation can be made small.

  Next, the fuel cell (module) of this example will be described. The fuel cell (not shown) of this example has the fuel cell stack 1 of this example described above. Specifically, in the fuel cell of this example, three fuel cell stacks 1 are arranged in a stack, and the fuel cell stacks 1 are connected in series.

  According to the fuel cell of this example, it is possible to increase the voltage while suppressing a decrease in output due to deterioration due to oxidation of the metal separator 3. In this example, three fuel cell stacks 1 are stacked and arranged. However, the present invention is not limited to this, and a plurality of fuel cell stacks 1 can be stacked in consideration of a required voltage value.

(Example 2)
In this example, as shown in FIG. 3, the structure of the air electrode layer 23 of the single cell 2 in the fuel cell stack 1 of Example 1 is changed.
In the fuel cell stack 1 of this example, as shown in FIG. 3, the dense layer 232 covers the side surface of the porous layer 231. Specifically, the dense layer 232 has a pair of extending portions 232a facing the planar edge. The pair of extending portions 232a cover two opposing side surfaces that do not intersect the flow path of the oxidant gas air among the four side surfaces of the porous layer 231 formed in a square shape when viewed from the stacking direction. To do. In this example, the porous layer 231 is formed smaller than the solid electrolyte layer 21 by the thickness of the extended portion 232a. That is, the extending portion 232 a is disposed on the inner side than the solid electrolyte layer 21. Others are the same as in the first embodiment.

  When configured in this way, air is gas-sealed by the dense layer 232 not only on the plane of the porous layer 231 but also on the side surfaces of the porous layer 231. Therefore, it becomes easy to suppress the contact between the air, which is the oxidant gas, and the metal separator 3, and it becomes easy to suppress deterioration of the metal separator 3 due to oxidation. Furthermore, since the extending portion 232a is disposed on the inner side of the solid electrolyte layer 21, the extending portion 232a and the fuel electrode layer 22 are easily separated from each other, and the risk of leakage is easily avoided. The other functions and effects are the same as those of the first embodiment.

(Example 3)
In this example, as shown in FIG. 4, the structure of the air electrode layer 23 of the single cell 2 in the fuel cell stack 1 of Example 1 is changed.
In the fuel cell stack 1 of this example, the air electrode layer 23 has a gas flow path 234 through which air as an oxidant gas flows at the boundary B between the porous layer 231 and the dense layer 232 as shown in FIG. doing. However, the gas flow path 234 is formed on the dense layer 232 side across the boundary B. Others are the same as in the first embodiment.

  Even in such a configuration, the dense layer 232 can gas-seal the air as the oxidant gas. Therefore, contact between air and the metal separator 3 is suppressed, and deterioration of the metal separator 3 due to oxidation can be suppressed. The other functions and effects are the same as those of the first embodiment.

Example 4
In this example, as shown in FIG. 5, the structure of the air electrode layer 23 of the single cell 2 in the fuel cell stack 1 of Example 1 is changed.
In the fuel cell stack 1 of this example, the air electrode layer 23 has a gas flow path 235 for flowing air as an oxidant gas at the boundary B between the porous layer 231 and the dense layer 232 as shown in FIG. doing. However, the gas flow path 235 is formed across the porous layer 231 and the dense layer 232 across the boundary B. Others are the same as in the first embodiment.

  Even in such a configuration, the dense layer 232 can gas-seal the air as the oxidant gas. Therefore, contact between air and the metal separator 3 is suppressed, and deterioration of the metal separator 3 due to oxidation can be suppressed. The other functions and effects are the same as those of the first embodiment.

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Single cell 21 Solid electrolyte layer 22 Fuel electrode layer 23 Air electrode layer 231 Porous layer 232 Dense layer 232a Extension part B Boundary 233 Gas flow path 233a Groove part 233b Space 234 Gas flow path 235 Gas flow path 3 (Between cells) Metal separator 31 Gas flow path 11 (Outside cell) Metal separator 12 Current collector 13 Seal member 14 Insulator 15 Fixed member 16 Gas supply manifold 161 Fuel gas supply path 162 Oxidant gas supply path 17 Gas exhaust manifold 171 Fuel gas exhaust passage 172 Oxidant gas exhaust passage

Claims (6)

A plurality of single cells each including a solid electrolyte layer, a fuel electrode layer provided on one surface of the solid electrolyte layer, and an air electrode layer provided on the other surface of the solid electrolyte layer are stacked via a metal separator. A fuel cell stack comprising:
The air electrode layer has a porous layer disposed in contact with the solid electrolyte layer, and a dense layer disposed in contact with a surface of the porous layer on the metal separator side. Battery stack.   2. The fuel cell stack according to claim 1, wherein the air electrode layer has a gas flow path for flowing an oxidant gas at a boundary between the porous layer and the dense layer. 3.   3. The fuel cell stack according to claim 2, wherein the gas flow path is configured by a space surrounded by a plurality of grooves formed in the porous layer and a surface of the dense layer. Fuel cell stack.   The fuel cell stack according to any one of claims 1 to 3, wherein the dense layer further covers a side surface of the porous layer.   The fuel cell stack according to any one of claims 1 to 4, wherein the metal separator is made of a metal material not containing Cr.   A fuel cell comprising the fuel cell stack according to claim 1.

Images