JP6924568B2 - Current collector and solid oxide fuel cell cell unit - Google Patents

Description

The present invention relates to a current collector used in a solid oxide fuel cell cell unit.

One of the fuel cells is a solid oxide fuel cell (hereinafter also referred to as "SOFC") in which a solid oxide is used as a solid electrolyte. A solid oxide fuel cell uses an oxide ion conductive solid electrolyte as an electrolyte, has electrodes on both sides thereof, supplies fuel gas to one side, and oxidant gas (air, oxygen, etc.) on the other side. ) Is supplied, and power is generated by the reaction between these fuel gases and the oxidant gas.

The solid oxide fuel cell takes out the electromotive force generated by power generation to the outside and uses this electric power. A current collector is used when taking out to the outside. This current collecting member is provided between adjacent fuel cell cells and is a member that electrically connects the fuel cell cells to each other.

It is known that an alloy containing chromium (Cr) is used as the base material of the current collector member. The substrate because it contains chromium, is oxidized by oxygen contained in the atmosphere, Cr ₂ O ₃ layer is formed on the surface.

The current collector member is exposed to a high temperature environment during the operation of the fuel cell. It is known that this causes the chromium contained in the base material to diffuse, and the air electrode is poisoned with chromium. In order to prevent this, it is known to form a protective layer on the surface of the base material.

Patent Document 1 describes that a protective layer is formed by an electrodeposition coating method after electropolishing the surface of a base material of an alloy or oxide containing chromium. It is described that by electropolishing the base material, the smoothness of the base material can be maintained and uneven coating of the coating film can be suppressed, so that it is possible to form a protective layer in which cracks and peeling are unlikely to occur. There is.

Patent Document 2 describes a method of manufacturing an interconnector by forming a coating film containing cobalt oxide as a main component on a base material containing stainless steel as a main component. It is described that the surface roughness (Ra) is reduced to 1.2 μm or less by electropolishing the base material.

JP 2015-011958 Japanese Unexamined Patent Publication No. 2011-192546

Until now, it has been considered that uneven thickness of the protective layer can be suppressed by making the surface roughness of the base material uniform. However, when forming a protective layer having a certain thickness, it is difficult to suppress uneven thickness of the protective layer only by making the surface roughness of the base material uniform. That is, it was found that even if the surface roughness of the base material is made uniform, cracks and peeling occur when coating unevenness occurs on the protective layer.

Therefore, an object of the present invention is to suppress the occurrence of uneven thickness and cracks in the current collector member in which the protective layer is formed on the surface of the base material.

The current collecting member according to the present invention includes a metal base material containing chromium, a Cr ₂ O ₃ layer formed on the surface of the metal base material, and a protective layer formed on the surface of the _{Cr 2} O _{3 layer.} , a current collecting member having a surface roughness Ra ₁ of the metal substrate, the surface roughness Ra ₂ of the Cr ₂ O ₃ layer, the relationship between the surface roughness Ra ₃ of the protective layer, Ra a ₁ ≦ Ra ₃ ≦ Ra _2, wherein the protective layer thickness d ₃ is 1μm or more state, and are less 23 .mu.m, Cr ₂ O ₃ layer thickness d ₂ is 0.05μm or more, Ru der below 2.2 .mu.m.

Further, the solid oxide fuel cell unit according to the present invention includes a fuel electrode, a solid electrolyte, and an air electrode, and the above-mentioned current collecting member is electrically connected to the air electrode.

It is sectional drawing which shows one aspect of the current collecting member by this invention. It is a schematic diagram which shows one aspect of the cross section of the solid oxide fuel cell according to this invention. It is a partial cross-sectional view which shows the fuel cell unit by this invention. It is a perspective view which shows the fuel cell cell stack by this invention.

Definition The shape of the fuel cell according to the present invention is not limited, and may be, for example, a cylindrical shape, a plate shape, or a hollow plate shape having a plurality of gas flow paths formed therein. Further, the inner electrode may be formed on the surface of the support.

Current collector member In the present invention, the current collector member is a metal base material containing chromium, a Cr ₂ O ₃ layer formed on the surface of the metal base material, and a protection formed on the surface of the _{Cr 2} O _{3 layer.} a current collecting member having a layer, and a surface roughness Ra ₁ of the metal substrate, the surface roughness Ra ₂ of the Cr ₂ O ₃ layer, the relationship between the surface roughness Ra ₃ of the protective layer , Ra ₁ ≤ Ra ₃ ≤ Ra ₂ , and the thickness d _{3 of the} protective layer is 1 μm or more. As a result, it is possible to suppress the occurrence of uneven thickness in the protective layer and to produce a current collecting member without cracks or peeling.

An example of the current collecting member 10 used in the present invention is shown in FIG. In FIG. 1, 1 is a metal base material, 2 is a Cr ₂ O ₃ layer, and 3 is a protective layer. _{A Cr 2} O ₃ layer 2 and a protective layer 3 are formed on the surface of the metal base material 1 in this order.

Metal Substrate In the present invention, the metal substrate 1 contains chromium (Cr) and iron (Fe). The metal base material 1 preferably contains 20 mol% or more of chromium. Further, it is preferable that iron is contained in an amount of 70 mol% or more.

In the present invention, in addition to chromium and iron, the metal substrate 1 includes nickel (Ni), tungsten (W), manganese (Mn), aluminum (Al), silicon (Si), niobium (Nb), and titanium (Ti). , Zirconium (Zr), copper (Cu) and the like may be contained.

In the present invention, the metal base material 1 is preferably ferritic stainless steel or austenite stainless steel. As a result, by heat-treating the metal base material 1, _{an oxide film containing Cr 2} O ₃ as a main component can be formed on the surface, so that iron contained in the metal base material 1 can be prevented from being oxidized. More preferably, the metal base material 1 is a ferritic stainless steel. As a result, the difference in thermal expansion from other members constituting the fuel cell can be reduced, and cracks generated due to the difference in thermal expansion during operation of the fuel cell can be suppressed.

In the present invention, the surface roughness Ra ₁ of the metal substrate 1 is preferably 0.9 μm or less. More preferably, the surface roughness Ra ₁ is 0.6 μm or less. As a result, a dense Cr ₂ O ₃ layer 2 can be formed on the surface of the metal base material 1, and the oxidation resistance of the metal base material 1 can be improved.

In the present invention, the surface roughness means the arithmetic mean roughness (Ra) and can be calculated by the following method.

A protective layer 3, a Cr ₂ O ₃ layer 2, and a metal base material 1 are cut out from the current collecting member 10, and the resin-filled material is polished and then observed using an SEM (Scanning Electron Microscope). The arithmetic mean roughness Ra is calculated from the SEM image taken at 100 to 1000 times by a method based on JISB0601: 1994. The surface roughness Ra ₁ of the metal substrate is calculated using the contour curve tracing the interface between the metal substrate and the Cr ₂ O ₃ layer or voids (pores).

Cr ₂ O ₃ layer In the present invention, Cr ₂ O ₃ layer 2 contains Cr ₂ O ₃ (chromium oxide) as a main component. The main component means that the Cr ₂ O ₃ layer 2 contains 90 mol% or more. Cr ₂ O ₃ layer 2, in addition to the _Cr 2 _{O 3,} tungsten (W), manganese (Mn), aluminum (Al), silicon (Si), niobium (Nb), titanium (Ti), zirconium (Zr) , Copper (Cu) and the like may be contained.

In the present invention, the Cr ₂ O ₃ layer 2 is formed on the surface of the metal base material 1. That is, it is formed between the metal base material 1 and the protective layer 3.

In the present invention, the film thickness d _{2 of the Cr 2} O ₃ layer 2 is preferably 0.05 μm or more and 2.2 μm or less, and more preferably 0.1 μm or more and 1.8 μm or less. Even more preferably, it is 0.4 μm or more and 1.6 μm or less. As a result, _{chromium diffuses from the Cr 2} O ₃ layer 2 to the protective layer 3, so that adhesion can be obtained and peeling of the protective layer 3 can be prevented. Further, _{it is possible to suppress the resistance of the Cr 2} O ₃ layer 2 from becoming too large, and to suppress a decrease in the power generation output of the fuel cell.

The film thickness d ₂ of the Cr ₂ O ₃ layer 2 can be obtained by the following method.

The current collecting member 10 is cut out so as to include the protective layer 3, the Cr ₂ O ₃ layer 2, and the metal base material 1, and the resin-filled material is polished. Then, using an SEM (Scanning Electron Microscope), an image is taken at 1000 to 10000 times to obtain an SEM image. From the obtained SEM image, _{the shortest distance from the surface of the Cr 2} O ₃ layer 2 to the metal substrate 1 was measured at 3 points, and the average value was taken as the film thickness d _{2 of the Cr 2} O _{3 layer 2.} ..

In the present invention, the surface roughness Ra _{2 of the Cr 2} O ₃ layer 2 is preferably 1.5 μm or less. More preferably, it is 1.4 μm or less. Even more preferably, it is 1.2 μm or less. As a result, it is possible to suppress the occurrence of uneven thickness of the protective layer 3 and to form the protective layer 3 without cracks on the surface of _{the Cr 2} O _{3 layer 2.} Furthermore, peeling of the protective layer 3 can be suppressed.

In the present invention, the surface roughness Ra _{2 of the Cr 2} O ₃ layer 2 can be calculated by the following method.

A protective layer 3, a Cr ₂ O ₃ layer 2, and a metal base material 1 are cut out from the current collecting member 10, and the resin-filled material is polished and then observed using an SEM (Scanning Electron Microscope). The arithmetic mean roughness Ra is calculated from the SEM image taken at 100 to 1000 times by a method based on JISB0601: 1994. The surface roughness of the _Cr 2 _{O 3} layer 2 Ra ₂ is calculated from the outline curve tracing the interface between the _Cr 2 _{O 3} layer 2 and the protective layer 3 or voids (pores).

Protective layer In the present invention, the protective layer 3 is _{formed on the surface of the Cr 2} O ₃ layer 2 and constitutes the outermost surface of the current collector member 10.

In the present invention, the film thickness d ₃ of the protective layer 3 is 1 μm or more. Further, it is preferably 1 μm or more and 23 μm or less, and more preferably 1 μm or more and 10 μm or less. As a result, it is possible to prevent the _{Cr 2} O _{3 layer 2 from being exposed.} Further, it is possible to prevent cracks from being formed when the protective layer 3 is formed, and to suppress the evaporation of chromium from the _{Cr 2} O _{3 layer 2.}

The film thickness d ₃ of the protective layer 3 can be obtained by the following method.

A protective layer 3, a Cr ₂ O ₃ layer 2, and a metal base material 1 are cut out from the current collecting member, and the resin-filled material is polished and then observed using an SEM (Scanning Electron Microscope). An SEM image is obtained by taking a picture at 100 to 1000 times. From the obtained image, the shortest distance from the surface of the protective layer 3 to Cr ₂ O ₃ layer 2 was measured three points, and the thickness d ₃ of the protective layer 3 that averaged value.

In the present invention, the protective layer 3 is represented by the chemical formula AB ₂ O ₄ (however, at least one metal element selected from A: Mn and Cu, and at least one metal element selected from B: Co and Mn). It is preferable to contain a transition metal oxide having a spinel-type crystal structure as a main component. It is more preferable that the protective layer 3 contains MnCo ₂ O _{4 as a main component.} This makes it possible to suppress the evaporation of chromium from the _{Cr 2} O _{3 layer 2.} The main component means that the protective layer 3 contains 90 mol% or more.

In the present invention, the protective layer 3 preferably has a surface roughness Ra ₃ of 1 μm or less. More preferably, Ra ₃ is 0.9 μm or less. This makes it possible to form the protective layer 3 without cracks.

In the present invention, the surface roughness Ra ₃ of the protective layer 3 can be calculated by the following method.

Using a laser microscope (for example, Olympus OLS4000), the surface of the protective layer 3 of the produced current collecting member 10 is photographed at a magnification of 100 to 1000 to obtain a profile. From this profile, the arithmetic mean roughness Ra is calculated by a method based on JISB0601: 1994.

In the present invention, the surface roughness Ra ₃ of the surface roughness Ra ₂ and the protective layer 3 of the surface roughness Ra ₁ and _Cr 2 _{O 3} layer 2 of the metal substrate 1 satisfies Ra ₁ ≦ Ra ₃ ≦ Ra _2. Preferably, Ra ₁ <Ra ₃ <Ra ₂ . As a result, it is possible to make the surface of the metal base material 1 uniform while also making the surface of the protective layer 3 which is the outermost surface of the current collecting member 10 uniform. Therefore, it is possible to suppress the occurrence of uneven thickness of the protective layer 3. From the above, it is possible to suppress the occurrence of cracks due to thermal stress caused by the difference in the coefficient of thermal expansion between the layers of the current collector members during the operation of the fuel cell. In particular, since the surface of the protective layer 3 is uniform, it is possible to prevent cracks from occurring on the surface of the protective layer 3.

Air electrode In the present invention, the air electrode is not particularly limited as long as it can form a fuel cell, and examples thereof include perovskite-type oxides.

Specific perovskite-type oxides include La _1-x Sr _x CoO ₃ (where x = 0.1 to 0.3) and LaCo _1-x Ni _x O ₃ (where x = 0.1 to 0). .6) lanthanum cobalt oxides, such as, (La, Sr) FeO ₃ system and (La, Sr) CoO3 lanthanum cobalt ferrite-based oxide is a solid solution of _{(La 1-m Sr m Co} 1-n Fe n O ₃ (where 0.05 <m <0.50, 0 ≦ n ≦ 1)), samarium cobalt-based oxide containing samarium and cobalt (Sm _0.5 Sr _0.5 CoO ₃ ) and the like can be mentioned. Preferred is lanthanum strontium cobaltite ferrite (LSCF).

In the present invention, the air electrode may be a single layer or a plurality of layers. As an example of a multi-layered air electrode, for example, La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ is provided as an air electrode catalyst layer on a solid electrolyte, and a fuel cell cell is provided. Examples thereof include a configuration in which _{La 0.6} Sr _0.4 Co _0.8 Fe _0.2 O ₃ is provided as an air electrode on the outermost surface layer.

Fuel electrode In the present invention, the fuel electrode is not particularly limited as long as it can form a fuel cell, and examples thereof include NiO / zirconium-containing oxide and NiO / cerium-containing oxide. Here, the NiO / zirconium-containing oxide means a mixture of NiO and a zirconium-containing oxide uniformly in a predetermined ratio. Further, the NiO / cerium-containing oxide means a mixture of NiO and cerium-containing oxide uniformly in a predetermined ratio. Examples of the zirconium-containing oxide of the NiO / zirconium-containing oxide include a zirconium-containing oxide doped with one or more of _{CaO, Y 2} O ₃ , and Sc ₂ O _3. Further, as the cerium-containing oxide of the NiO / cerium-containing oxide, the general formula Ce1-yLnyO2 (where Ln is La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Any one or a combination of two or more of Lu, Sc, and Y, and 0.05 ≦ y ≦ 0.50) and the like can be mentioned. Since NiO is reduced to Ni in a fuel atmosphere, the above-mentioned mixture becomes a Ni / zirconium-containing oxide or a Ni / cerium-containing oxide, respectively.

In the present invention, the fuel electrode may be a single layer or a multi-layer. Examples of a multi-layer fuel electrode include a fuel electrode having a Ni / YSZ (yttria-stabilized zirconia) layer on the side facing the support, or a Ni / GDC (Gd ₂ O _{3) on the side facing the solid electrolyte.} -CeO ₂ ) A fuel electrode having a layer (which functions as a fuel electrode catalyst layer), and a fuel electrode having both of these layers can be mentioned.

Solid Electrolyte In the present invention, the solid electrolyte is not particularly limited as long as it can form a fuel cell, and for example, a lanthanum gallate oxide and one or more of Y, Ca, and Sc as a solid solution species are used. Examples include solid-dissolved stabilized zirconia. The solid electrolyte is preferably a lanthanum gallate-based oxide Sr and Mg-doped, more preferably the general formula _La in _{1-a Sr a Ga 1-} b-c Mg b Co c O 3 ( where, 0 It is a lanthanum gallate-based oxide (LSGM) represented by 0.05 ≦ a ≦ 0.3, 0 <b <0.3, 0 ≦ c ≦ 0.15). _{According to one preferred embodiment of the present invention, a cerium oxide (Ce 1-x} La _x O ₂ (where 0) in which La is dissolved in ceria as a reaction suppressing layer between the solid electrolyte and the fuel electrode is used. .3 <x <0.5)) may be provided. The reaction suppression layer is preferably Ce _0.6 La _0.4 O ₂ .

In the present invention, the solid electrolyte may be a single layer or a multi-layer. As an example of the case where the solid electrolyte is a multi-layer, for example, there is a configuration in which a reaction suppression layer such as _{Ce 0.6} La _0.4 O _{2 is provided between the fuel electrode and the solid electrolyte composed of LSGM.}

Fuel cell cell FIG. 2 is a schematic view showing an aspect of a cross section of the solid oxide fuel cell of the present invention, and shows a type in which an inner electrode is used as a fuel electrode. The solid oxide fuel cell 210 in the present invention includes, for example, a porous support 201, a (first / second) fuel pole 202, a (first / second) solid electrolyte 203, and (first / second). ) It is composed of an air electrode 204 and a current collecting layer 205. Here, (first / second) means "a single layer or two or more layers, and in the case of two layers, it has a first layer and a second layer". In the solid oxide fuel cell of the present invention, the preferable thickness of each layer is 0.5 to 2 mm for the porous support, 10 to 200 μm for the fuel electrode, 0 to 30 μm for the fuel electrode catalyst layer, and the reaction suppression layer. The size is 0 to 20 μm, the solid electrolyte is 5 to 60 μm, the air electrode catalyst layer is 0 to 50 μm, and the air electrode is 10 to 200 μm.

FIG. 3 is a partial cross-sectional view showing the fuel cell unit according to the present invention. As shown in the figure, the fuel cell unit 16 includes a fuel cell 84 and inner electrode terminals 86 connected to the vertical ends of the fuel cell 84, respectively. The fuel cell 84 is a tubular structure extending in the vertical direction, and has an inner electrode layer 90, an outer electrode layer 92, and an inner electrode on a cylindrical porous support 91 forming a fuel gas flow path 88 inside. It comprises a solid electrolyte 94 between the layer 90 and the outer electrode layer 92.

Since the inner electrode terminals 86 attached to the upper end side and the lower end side of the fuel cell 84 have the same structure, the inner electrode terminals 86 attached to the upper end side will be specifically described here. The upper 90a of the inner electrode layer 90 includes a solid electrolyte 94, an outer peripheral surface 90b exposed to the outer electrode layer 92, and an upper end surface 90c. The inner electrode terminal 86 is connected to the outer peripheral surface 90b of the inner electrode layer 90 via a conductive sealing material 96, and further comes into direct contact with the upper end surface 90c of the inner electrode layer 90 to contact the inner electrode layer 90. It is electrically connected. At the center of the inner electrode terminal 86, a fuel gas flow path 98 communicating with the fuel gas flow path 88 of the inner electrode layer 90 is formed.

The inner electrode terminals 86 are provided so as to surround the upper and lower ends of the fuel cell 84, respectively, and function as a current collecting member for extracting the electric power generated by the fuel cell 84 from the fuel cell 84.

In the present invention, the current collecting member 10 of the present invention can be used as the inner electrode terminal 86. In the figure, the inner electrode terminals 86 are provided at both ends of the fuel cell 84, but the current collecting member 10 of the present invention is provided as the inner electrode terminals 86 on the upper end side or the lower end side to collect current from one end. You may do so.

Method for Manufacturing Solid Oxide Fuel Cell Cell Unit The solid oxide fuel cell unit 16 according to the present invention can be appropriately manufactured according to a known method. The preferred production method is as follows.

In the present invention, the current collecting member 10 is preferably manufactured by the following method.

First, the surface treatment of the prepared metal base material 1 is performed. Examples of the surface treatment include mechanical polishing, chemical polishing, electrolytic polishing, acid cleaning, and immobilization treatment. Of these, electrolytic polishing is preferable. This makes it possible to smooth the surface by eliminating the unevenness on the surface of the metal base material and to form a _{dense Cr 2} O _{3 layer on the surface of the metal base material.}

Then, the metal substrate 1 subjected to surface treatment subjected to a heat treatment of 500 ° C. to 900 ° C. in air to form a _Cr 2 _{O 3} layer 2.

Next, a coating liquid for forming the protective layer 3 is applied to the surface of _{the Cr 2} O _{3 layer 2.}

The coating liquid for forming the protective layer 3 is a chemical formula AB ₂ O ₄ (however, at least one metal element selected from A: Mn and Cu, and at least one metal selected from B: Co and Mn). It can be obtained by mixing a powder of a transition metal oxide having a spinel-type crystal structure represented by (element), a solvent, and a binder. Necessary materials can be appropriately added to the coating liquid depending on the purpose.

The coating can be preferably carried out by a slurry coating method for coating a slurry liquid, a tape casting method, a doctor blade method, a transfer method or the like. A printing method can also be used, and a screen printing method, an inkjet method, or the like can be used. Of these, it is preferable to use the slurry coating method because it has few defects and can form a uniform film thickness even in a complicated shape.

Next, the protective layer 3 is formed by performing a heat treatment at 700 ° C. to 900 ° C. in the atmosphere. From the above, the current collecting member 10 can be obtained.

For the air electrode, solid electrolyte and fuel electrode, a slurry is prepared by adding a molding aid such as a solvent (water, alcohol, etc.), a dispersant, a binder, etc. to each raw material powder, coated with the slurry, dried, and then dried. It can be obtained by firing (1100 ° C. or higher and lower than 1400 ° C.). The coating can be preferably performed by a slurry coating method for coating a slurry liquid, a tape casting method, a doctor blade method, a transfer method or the like. A printing method can also be used, and a screen printing method, an inkjet method, or the like can be used.

The firing may be performed each time each electrode and the solid electrolyte are formed, but it is also possible to perform "co-firing" in which a plurality of layers are fired at once. Further, the firing is preferably performed in an oxidizing atmosphere so that the solid electrolyte is not denatured due to diffusion of the dopant or the like. More preferably, firing is performed in an atmosphere having an oxygen concentration of 20% by mass or more and 30% by mass or less using a mixed gas of air and oxygen.

According to a preferred embodiment of the present invention, when a fuel electrode is used for the inner electrode and an air electrode is used for the outer electrode, the fuel electrode and the solid electrolyte are co-fired, and then the air electrode is formed at a temperature lower than that of co-firing. Bake.

A silver paste is applied to the inner surface of the produced current collector member 10, and the end portion of the fuel cell is inserted inside the silver paste. Then, the solid oxide fuel cell unit 16 can be manufactured by firing in the atmosphere at 700 to 900 ° C.

Solid Oxide Fuel Cell Cell Stack According to the present invention, there is provided a solid oxide fuel cell cell stack including the solid oxide fuel cell cell unit according to the present invention. FIG. 4 is a perspective view showing a solid oxide fuel cell stack. As shown in FIG. 4, the fuel cell stack 14 includes 16 fuel cell units 16, and the lower end side and the upper end side of the fuel cell unit 16 are made of ceramic lower support plates (shown, respectively). It is supported by the upper support plate 100. A through hole through which the inner electrode terminal 86 can pass is formed in each of the lower support plate and the upper support plate 100.

Further, a current collector 102 and an external terminal 104 are attached to the fuel cell unit 16. The current collector 102 is electrically connected to the fuel electrode connection portion 102a that is electrically connected to the inner electrode terminal 86 attached to the inner electrode 90 that is the fuel electrode, and the entire outer peripheral surface of the outer electrode 92 that is the air electrode. It is integrally formed with the air electrode connecting portion 102b which is connected to the air electrode. The air electrode connecting portion 102b is formed of a vertical portion 102c extending in the vertical direction on the surface of the outer electrode 92 and a large number of horizontal portions 102d extending in the horizontal direction from the vertical portion 102c along the surface of the outer electrode 92. There is. Further, the fuel electrode connecting portion 102a extends linearly from the vertical portion of the air electrode connecting portion 102b toward the inner electrode terminal 86 located in the vertical direction of the fuel cell unit 16 diagonally upward or diagonally downward. ing.

Further, a silver thin film is formed on the entire outer surface of the outer electrode layer 92 (air electrode) of each fuel cell unit 16 as an electrode on the air electrode side. When the air electrode connecting portion 102b comes into contact with the surface of the thin film, the current collector 102 is electrically connected to the entire air electrode.

Further, the inner electrode terminals 86 at the upper end and the lower end of the two fuel cell units 16 located at the ends of the fuel cell stack 14 (the back side and the front side of the left end in FIG. 4) are external terminals, respectively. 104 is connected. These external terminals 104 are connected to the external terminals 104 (not shown) of the fuel cell unit 16 at the end of the adjacent fuel cell stack 14, and as described above, of the 160 fuel cell units 16. All are connected in series.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Preparation of current collector member A current collector member was produced by the following method.

A metal having the composition shown in Table 1 was used as the metal base material. This metal substrate was subjected to electrolytic polishing as a surface treatment for 1 to 100 seconds. The metal substrate was subjected to a surface treatment was heat-treated for 1 to 10 hours at 500 to 900 ° C. in the air to form a _Cr 2 _{O 3} layer.

Next, a coating liquid for forming a protective layer was applied to the surface of _{the Cr 2} O _{3 layer.} The coating liquid was a mixture of MnCo ₂ O ₄ powder, a solvent, and a binder. This coating liquid was _{applied to the surface of the Cr 2} O ₃ layer by a slurry coating method, dried in a dryer, cooled at room temperature, and then fired at 850 ° C. for 2 hours to form a protective layer. From the above, each sample was obtained.

The surface roughness Ra ₁ of the metal substrate was controlled by changing the electrolytic polishing time. The roughness Ra ₂ and the thickness d ₂ of the Cr ₂ O ₃ layer were controlled by changing the temperature and time of the heat treatment. The roughness Ra ₃ and the thickness d ₃ of the protective layer were controlled by changing the concentration of the coating liquid for forming the protective layer and the coating weight.

The surface roughness and thickness of the obtained sample were determined by the following methods. The results are shown in Table 2.

Surface Roughness of Metal Substrate Ra ₁ and Cr ₂ O ₃ Layer Roughness Ra ₂
Protective layer from each sample, Cr ₂ O ₃ layer, cut to include a metal substrate, after polishing the those buried resin, was observed with SEM. The arithmetic mean roughness Ra was calculated from the SEM image taken at 100 to 1000 times by a method based on JISB0601: 1994. The surface roughness Ra ₁ of the metal substrate was calculated using the contour curve tracing the interface between the metal substrate and the Cr ₂ O ₃ layer or voids (pores). Surface roughness of the Cr ₂ O ₃ layer Ra ₂ was calculated from the outline curve tracing the interface between the _Cr 2 _{O 3} layer and the protective layer or voids (pores).

Protective layer roughness Ra ₃
Using a laser microscope (for example, Olympus OLS4000), the surface of the protective layer of the prepared sample was photographed at a magnification of 100 to 1000 to obtain a profile. The arithmetic mean roughness Ra was calculated from this profile by a method based on JISB0601: 1994, and this was designated as the roughness Ra ₃ of the protective layer.

Cr ₂ O ₃ layer thickness d ₂ and protective layer thickness d ₃
Protective layer from each sample, Cr ₂ O ₃ layer, cut to include a metal substrate, after polishing the those buried resin, was observed with SEM (Scanning Electron Microscope). The image was taken at 100 to 1000 times to obtain an SEM image. Cr ₂ O ₃ layer thickness _{d 2} of, from the obtained SEM image was measured three points the shortest distance from the surface of the _Cr 2 _{O 3} layer to the metal substrate, those taking the average value _Cr 2 O _three layers 2 thickness was _{d 2.} The film thickness d _{3 of the} protective layer is obtained by measuring the shortest distance from the surface of the protective layer to the Cr ₂ O ₃ layer 2 at three points from the obtained image and taking an average value to _{obtain the film thickness d 3 of the protective layer.} And said.

(evaluation)
The surface of the protective layer, which is the surface of the prepared current collector, was observed with a stereomicroscope at a magnification of 10 to evaluate the presence or _{absence of surface cracks and the presence or absence of exposure of the Cr 2} O _{3 layer.} The results are shown in Table 2.
・ Surface cracks: No cracks: No cracks ・ Cr ₂ O ₃ layer exposed: No exposed parts: No exposed parts

1 Metal substrate 2 Cr ₂ O ₃ layer 3 Protective layer 10 Current collecting member 14 Solid oxide fuel cell cell stack 16 Solid oxide fuel cell cell unit 84 Fuel cell cell 86 Inner electrode terminal 88 Fuel gas flow path 90 Inside Electrode layer 91 Support 92 Outer electrode layer 94 Solid electrolyte

Claims (6)

With a metal substrate containing chromium,
And Cr ₂ O ₃ layer was made form the surface of the metal substrate,
A current collector having a protective layer formed on the surface of the Cr ₂ O _{3 layer.}
Wherein a surface roughness Ra ₁ of the metal substrate, the surface roughness Ra ₂ of the Cr ₂ O ₃ layer, the relationship between the surface roughness Ra ₃ of the protective layer is a _{Ra 1 ≦ Ra 3 ≦ Ra 2} ,
The thickness d _{3 of the} protective layer is 1 μm or more and 23 μm or less.
A _{current collector having a Cr 2} O ₃ layer thickness d ₂ of 0.05 μm or more and 2.2 μm or less. The current collector according to claim 1, wherein the surface roughness Ra _{3 of the protective layer is 1 μm or less.} The current collector according to claim 1 or 2, wherein the surface roughness Ra _{1 of the metal base material is 0.9 μm or less.} The protective layer is _{a spinel represented by the chemical formula AB 2} O ₄ (however, at least one metal element selected from A: Mn and Cu, and at least one metal element selected from B: Co and Mn). The current collecting member according to any one of claims 1 to 3, which contains a transition metal oxide having a type crystal structure as a main component. The current collecting member according to any one of claims 1 to 4, wherein the protective layer contains MnCo ₂ O _4. It has a fuel electrode, a solid electrolyte, and an air electrode.
A solid oxide fuel cell cell unit in which the current collecting member according to any one of claims 1 to 5 is electrically connected to the air electrode.

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