Current collecting structure for electrochemical reaction cell stack, electrochemical reaction cell stack, and method for manufacturing current collecting structure for electrochemical reaction cell stack

Abstract

To improve the durability of an electrochemical reaction cell stack.SOLUTION: A current collecting structure for an electrochemical reaction cell stack includes a Cr-containing member formed from an alloy containing Cr, and a Ni member that is formed from Ni and joined to the Cr-containing member. The current collecting structure for an electrochemical reaction cell stack is characterized in that, when a heat treatment at 900°C for 100 hours is performed in a reducing gas atmosphere containing water vapor, the Cr concentration inside the Ni member located near a joint portion where the Cr-containing member and the Ni member are joined to each other is 1 atm% or more.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The technology disclosed in this specification relates to a current collector structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a method for manufacturing a current collector structure for an electrochemical reaction cell stack.

Background Art

[0002] As one of fuel cells that generate electricity by utilizing the electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") is known. SOFC is generally used in the form of a fuel cell stack. The fuel cell stack includes a single cell and a current collector structure for a fuel cell stack (hereinafter also simply referred to as a "current collector structure"). The current collector structure is electrically connected to the single cell and collects the electric power generated in the single cell.

[0003] Conventionally, a current collector structure has been disclosed that includes an interconnector (Cr-containing member) formed of a ferritic stainless steel, which is an alloy containing Cr, and a fuel electrode side current collector (Ni-made member) formed of Ni, the fuel electrode side current collector being joined to the interconnector (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The conductivity between the Cr-containing member and the Ni member in the current collector structure affects the resistance value of the fuel cell stack. Also, the conductivity between the Cr-containing member and the Ni member is affected by the bondability between the Cr-containing member and the Ni member. Specifically, when the bonding between the Cr-containing member and the Ni member is insufficient, during the operation of the fuel cell stack, Cr contained in the Cr-containing member does not sufficiently diffuse into the interior of the Ni member, and instead, it forms a relatively low-conductivity oxide film at the interface between the Cr-containing member and the Ni member. As a result, the conductivity between the Cr-containing member and the Ni member decreases, which in turn causes an increase in the resistance value of the fuel cell stack, leading to the problem of a decrease in the durability performance of the fuel cell stack.

[0006] Note that such a problem is a common problem also in a current collector structure used in an electrolysis cell stack, which is a form of an electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen by utilizing electrolysis of water. In this specification, a fuel cell single cell and an electrolysis single cell are collectively referred to as an electrochemical reaction single cell, and a fuel cell stack and an electrolysis cell stack are collectively referred to as an electrochemical reaction cell stack. Also, such a problem is not limited to SOFC and SOEC, but is a common problem also in other types of electrochemical reaction cell stacks.

[0007] This specification discloses a technology capable of solving the above-described problems.

Means for Solving the Problems

[0008] The technology disclosed in this specification can be realized, for example, in the following forms.

[0009] (1) The current collecting structure for an electrochemical reaction cell stack disclosed in this specification includes a Cr-containing member formed from an alloy containing Cr, and a Ni member formed from Ni, the Ni member being joined to the Cr-containing member. Regarding the current collecting structure for the electrochemical reaction cell stack, when heat treatment is performed at 900°C for 100 hours in a reducing gas atmosphere containing water vapor, the Cr concentration inside the Ni member located near the joint where the Cr-containing member and the Ni member are joined is 1 atm% or more.

[0010] According to this current collecting structure for an electrochemical reaction cell stack, during the operation of the electrochemical reaction cell stack, Cr contained in the Cr-containing member is sufficiently diffused into the interior of the Ni member, so that the adhesion at the interface between the Cr-containing member and the Ni member is improved and the formation of an oxide film is suppressed. Therefore, a decrease in conductivity between the Cr-containing member and the Ni member can be suppressed, and consequently an increase in the resistance value of the electrochemical reaction cell stack can be suppressed, and the durability performance of the electrochemical reaction cell stack can be improved.

[0011] (2) In the current collector structure for the electrochemical reaction cell stack, when the direction in which the Ni member and the Cr-containing member are arranged via the joint portion is defined as the first direction, the Ni member may be configured such that a porous layer having a higher porosity than the central portion in the first direction of the Ni member exists on the joint portion side rather than the central portion. According to this configuration, since a porous layer having a higher porosity than the central portion exists on the joint portion side rather than the central portion of the Ni member in the first direction, when, for example, the joining process between the Cr-containing member and the Ni member is performed in a high-temperature environment during the manufacture of the electrochemical reaction cell stack, the stress caused by the thermal expansion difference between the Cr-containing member and the Ni member can be alleviated. As a result, the peeling of the joint portion between the Cr-containing member and the Ni member is suppressed, the adhesion between the Cr-containing member and the Ni member is improved, and the Cr contained in the Cr-containing member is sufficiently diffused into the interior of the Ni member, so that the formation of the oxide film at the interface between the Cr-containing member and the Ni member is suppressed. Therefore, the decrease in conductivity between the Cr-containing member and the Ni member is suppressed, and consequently, the increase in the resistance value of the electrochemical reaction cell stack is suppressed, and the durability performance of the electrochemical reaction cell stack can be more effectively improved.

[0012] (3) In the current collector structure for the electrochemical reaction cell stack, the thickness of the porous layer in the first direction may be configured to be 5 μm or less. According to this configuration, since a porous layer having a thickness of 5 μm or less in the first direction exists in the Ni member, it is possible to suppress the peeling of the joint portion between the Cr-containing member and the Ni member during the manufacture of the electrochemical reaction cell stack and to suppress the intrusion of oxygen into the joint portion during the operation of the electrochemical reaction cell stack. Therefore, the formation of the oxide film at the interface between the Cr-containing member and the Ni member is suppressed, the decrease in conductivity between the Cr-containing member and the Ni member is suppressed, and consequently, the increase in the resistance value of the electrochemical reaction cell stack is suppressed, and the durability performance of the electrochemical reaction cell stack can be more effectively improved.

[0013] (4) In the current collector structure for the electrochemical reaction cell stack, the Ni member may be formed of a foil with a thickness of 30 μm or more, or a mesh with a wire diameter of 60 μm or more. According to this configuration, during the operation of the electrochemical reaction cell stack, inside the Ni member, Cr diffused from the Cr-containing member reacts with oxygen dissociated from H2O contained in the gas inside the electrochemical reaction cell stack, generating an internal oxidation layer (for example, a layer containing Cr2O3) inside the Ni member. At this time, when the internal oxidation layer grows on each of the surface on the joint side and the surface on the side opposite to the joint in the first direction, if the thickness of the Ni member is thin, since the distance between the surfaces is short, the internal oxidation layers formed on each surface side may connect, blocking the conduction path inside the Ni member. According to this configuration, the Ni member is formed of a foil with a thickness of 30 μm or more, or a mesh with a wire diameter of 60 μm or more. As a result, the distance between the surfaces becomes relatively long, suppressing the blocking of the conduction path. Therefore, a decrease in conductivity between the Cr-containing member and the Ni member can be suppressed, and consequently, an increase in the resistance value of the electrochemical reaction cell stack can be suppressed, more effectively improving the durability performance of the electrochemical reaction cell stack.

[0014] (5) In the current collector structure for the electrochemical reaction cell stack, the surface of the Cr-containing member joined to the Ni member may have a ten-point average roughness defined in JIS B 0601 of 10 μm or less.

[0015] When manufacturing an electrochemical reaction cell stack, when joining a Cr-containing member and a Ni member, for example, the volume expansion when Ni is oxidized to NiO is utilized to form NiO in the gap between the Cr-containing member and the Ni member, thereby improving the adhesion between the Cr-containing member and the Ni member. Thereafter, when further performing a reduction treatment from NiO to Ni with higher conductivity, a porous layer is formed on the Ni member due to the volume shrinkage accompanying the conversion from NiO to Ni. At this time, when the porous layer is thick, oxygen easily enters the joint during the operation of the electrochemical reaction cell stack, an oxide film is generated at the interface between the Cr-containing member and the Ni member, leading to an increase in the resistance value. According to this configuration, the surface of the Cr-containing member that joins with the Ni member has a ten-point average roughness defined by JIS B 0601 of 10 μm or less. Thereby, since the gap between the Cr-containing member and the Ni member does not become excessively large, the thickness of the porous layer formed on the Ni member can be suppressed, and the intrusion of oxygen into the joint during the operation of the electrochemical reaction cell stack can be suppressed. Therefore, the generation of the oxide film at the interface between the Cr-containing member and the Ni member is suppressed, the decrease in conductivity between the Cr-containing member and the Ni member is suppressed, and thus the increase in the resistance value of the electrochemical reaction cell stack is suppressed, and the durability performance of the electrochemical reaction cell stack can be more effectively improved.

[0016] (6) The electrochemical reaction cell stack disclosed in this specification includes the current collecting structure for an electrochemical reaction cell stack described in (1) and a single cell electrically connected to the current collecting structure for an electrochemical reaction cell stack.

[0017] According to this electrochemical reaction cell stack, during operation, Cr contained in the Cr-containing member in the current collecting structure for an electrochemical reaction cell stack is sufficiently diffused into the interior of the Ni member, so that the adhesion at the interface between the Cr-containing member and the Ni member is improved and the generation of the oxide film is suppressed. Therefore, the decrease in conductivity between the Cr-containing member and the Ni member is suppressed, and thus the increase in the resistance value of the electrochemical reaction cell stack is suppressed, and the durability performance of the electrochemical reaction cell stack can be improved.

[0018] (7) The manufacturing method of the current collector structure for an electrochemical reaction cell stack disclosed in this specification is a manufacturing method of a current collector structure for an electrochemical reaction cell stack including a Cr-containing member formed from an alloy containing Cr and a Ni member formed from Ni, the Ni member being joined to the Cr-containing member, and includes a joining step of pressure-joining the Cr-containing member and the Ni member under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO.

[0019] According to the manufacturing method of the current collector structure for this electrochemical reaction cell stack, by utilizing the volume expansion when Ni is oxidized to NiO during the joining step, NiO is formed in the gap between the Cr-containing member and the Ni member, thereby improving the adhesion between the Cr-containing member and the Ni member and suppressing the formation of an oxide film at the interface. Therefore, it is possible to suppress a decrease in conductivity between the Cr-containing member and the Ni member, and consequently suppress an increase in the resistance value of the electrochemical reaction cell stack, and improve the durability performance of the electrochemical reaction cell stack.

[0020] (8) In the manufacturing method of the current collector structure for the electrochemical reaction cell stack described above, further, after the joining step, in a reducing gas atmosphere, a reducing step of heating the Cr-containing member and the Ni member at a temperature of 800 °C or higher while pressurizing the Cr-containing member and the Ni member in a first direction in which the Cr-containing member and the Ni member are arranged may be provided. According to this configuration, by applying pressure, it is possible to suppress a decrease in the adhesion between the Cr-containing member and the Ni member due to the volume contraction accompanying the reduction of NiO to Ni in the reducing step, and perform a reduction treatment of NiO to Ni having higher conductivity. Further, since NiO is reduced to Ni at a temperature of 800 °C or higher, NiO can be reliably reduced. Therefore, an increase in the resistance value of the electrochemical reaction cell stack can be suppressed, and the durability performance of the electrochemical reaction cell stack can be more effectively improved.

[0021] Note that the technology disclosed in this specification can be implemented in various forms, for example, in the form of a current collector structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a method for manufacturing a current collector structure for an electrochemical reaction cell stack, etc.

Brief Description of Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0023] A. First Embodiment: A-1. Configuration of Fuel Cell Stack 10: FIG. 1 is a perspective view showing the external configuration of the fuel cell stack 10 in the first embodiment, FIG. 2 is an explanatory view showing the XZ cross-sectional configuration of the fuel cell stack 10 at the position II-II in FIG. 1, FIG. 3 is an explanatory view showing the XZ cross-sectional configuration of the fuel cell stack 10 at the position III-III in FIG. 1, and FIG. 4 is an explanatory view showing the YZ cross-sectional configuration of the fuel cell stack 10 at the position IV-IV in FIG. 1. In each figure, XYZ axes orthogonal to each other for specifying directions are shown. In this specification, for convenience, the Z-axis direction is referred to as the vertical direction, the positive Z-axis direction is referred to as the upward direction, and the negative Z-axis direction is referred to as the downward direction. However, the fuel cell stack 10 may actually be installed in a direction different from such an orientation. Also, the "thickness" of each member in this specification means the length of each member in the vertical direction unless otherwise specified. The fuel cell stack 10 is an example of an electrochemical reaction cell stack. The Z-axis direction is an example of the first direction.

[0024] (Overall Configuration of Fuel Cell Stack 10) As shown in FIGS. 1 to 4, the fuel cell stack 10 includes a power generation block 100, a terminal separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating portion 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating portion 220, the terminal separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have substantially the same-sized rectangular outer shapes and are arranged to overlap in this order in a predetermined arrangement direction (vertical direction).

[0025] As shown in FIGS. 1 and 4, the fuel cell stack 10 has bolt holes BH penetrating from the first end plate 210 to the second end plate 270 near each of the four corners. Bolts B are inserted into each bolt hole BH. Nuts N are screwed onto both ends of each bolt B. These bolts B and nuts N integrally fasten the members from the first end plate 210 to the second end plate 270. As shown in FIGS. 2 to 4, the first plate 232 is supported by the terminal separator 230, and the four gas passage members 280 are connected to the second end plate 270.

[0026] As shown in FIGS. 2 to 4, the power generation block 100 is composed of a plurality (seven in this embodiment) of power generation units 100U arranged side by side in a predetermined arrangement direction (vertical direction).

[0027] (The first end plate 210) The first end plate 210 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel, for example. As shown in FIGS. 1 to 4, the first end plate 210 includes a rectangular frame-shaped flat portion 211 having a through hole 212 near the center, an outer convex portion 213 and an inner convex portion 214 protruding in a direction opposite to the insulating portion 220 (upward in FIG. 2) from the flat portion 211. The flat portion 211 has holes forming the bolt holes BH described above. The outer convex portion 213 protrudes from the outer peripheral edge of the flat portion 211. The outer convex portion 213 is formed over the entire outer periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner peripheral edge of the flat portion 211. The inner convex portion 214 is formed over the entire inner periphery of the flat portion 211.

[0028] (The insulating portion 220) The insulating part 220 is a rectangular frame-shaped member having a through-hole near the center, and is formed of, for example, an insulating material. As shown in FIG. 2, the insulating part 220 is sandwiched between the first end plate 210 and the terminal separator 230, thereby ensuring the insulation between the first end plate 210 and the terminal separator 230.

[0029] (Terminal separator 230) As shown in FIGS. 2 to 4, the terminal separator 230 is a rectangular frame-shaped member having a through-hole 231 near the center, and is formed of, for example, metal.

[0030] (First plate 232) The first plate 232 is a rectangular flat plate-shaped member and is formed of a conductive material such as stainless steel. As shown in FIGS. 2 to 4, the first plate 232 is joined to the peripheral portion of the through-hole 231 in the terminal separator 230 by, for example, welding. The terminal separator 230 and the first plate 232 partition the power generation block 100 from the external space of the fuel cell stack 10.

[0031] The first plate 232 is connected to an interconnector 190 (described later) provided in a power generation unit 100U arranged at one end (the upper end in FIG. 2) of a plurality of power generation units 100U constituting the power generation block 100 through a connection member having the same structure as the fuel electrode current collecting member 144 (described later), whereby the power generation unit 100U and the first plate 232 are electrically connected.

[0032] (First terminal plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through hole 241 near the center, and is formed of a conductive material such as ferrite stainless steel that forms an alumina oxide film on the surface, for example. The first terminal plate 240 is electrically connected to a power generation unit 100U arranged at one end (the upper end in FIG. 2) of a plurality of power generation units 100U that make up the power generation block 100 via the first plate 232 and the end separator 230. One end portion (the right end portion in FIG. 2) of the first terminal plate 240 protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0033] (The second terminal plate 250) The second terminal plate 250 is a rectangular plate-shaped member and is formed of a conductive material such as ferrite stainless steel that forms an alumina oxide film on the surface, for example. The second terminal plate 250 is electrically connected to a power generation unit 100U arranged at the other end (the lower end in FIG. 2) of a plurality of power generation units 100U that make up the power generation block 100. One end portion (the right end portion in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0034] (The second plate 260) The second plate 260 is a rectangular flat plate-shaped member and is formed of an insulating material, for example. The peripheral portion of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring the insulation between the second terminal plate 250 and the second end plate 270.

[0035] (The second end plate 270) The second end plate 270 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel, for example. The second end plate 270 includes a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the planar portion 271 in a direction opposite to the second terminal plate 250 (downward in FIG. 2). The planar portion 271 has holes that constitute the bolt holes BH described above. The outer convex portion 273 protrudes from the outer peripheral edge of the planar portion 271. The outer convex portion 273 is formed over the entire circumference of the outer peripheral portion of the planar portion 271. The inner convex portion 274 protrudes from the inner peripheral edge of the planar portion 271. The inner convex portion 274 is formed over the entire circumference of the inner peripheral portion of the planar portion 271.

[0036] (Manifolds 311, 312, 321, 322) As shown in FIGS. 1, 2, and 3, the fuel cell stack 10 has four holes penetrating from the power generation block 100 to the second end plate 270. The four holes are an oxidant gas supply manifold 311, an oxidant gas discharge manifold 312, a fuel gas supply manifold 321, and a fuel gas discharge manifold 322, respectively.

[0037] As shown in FIG. 2, the oxidant gas supply manifold 311 is a gas flow path that supplies the oxidant gas OG introduced from the outside of the fuel cell stack 10 to an air chamber 313 (described later) of each power generation unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges the oxidant off-gas OOG discharged from the air chamber 313 of each power generation unit 100U to the outside of the fuel cell stack 10. As the oxidant gas OG, for example, air is used. The oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312 are arranged on opposite sides of each other with the air chamber 313 interposed therebetween.

[0038] As shown in FIG. 3, the fuel gas supply manifold 321 is a gas flow path that supplies the fuel gas FG introduced from the outside of the fuel cell stack 10 to the fuel chamber 323 (described later) of each power generation unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges the fuel off-gas FOG discharged from the fuel chamber 323 of each power generation unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, a hydrogen-rich gas obtained by reforming city gas is used. The fuel gas supply manifold 321 and the fuel gas discharge manifold 322 are arranged on opposite sides of each other with the fuel chamber 323 interposed therebetween.

[0039] (Gas passage member 280) As shown in FIGS. 1 to 3, each of the four gas passage members 280 includes a main body portion 281 and a flange portion 282. A gas through-hole 283 penetrating in the vertical direction is formed in the main body portion 281. The flange portion 282 is provided so as to project outward from the other end (the lower end in FIG. 2) of the main body portion 281. The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into the respective bolt holes 284. One end (the upper end in FIGS. 2 and 3) of the main body portion 281 provided in the four gas passage members 280 is joined to the second end plate 270 by, for example, welding, and the gas through-holes 283 communicate with the manifolds 311, 312, 321, and 322, respectively. Gas pipes for supplying or discharging gas are connected to each main body portion 281 (not shown).

[0040] (Overall configuration of the power generation unit 100U) FIG. 5 is an explanatory diagram showing an XZ cross-sectional configuration of two adjacent power generation units 100U at the same position as the cross-section shown in FIG. 2. FIG. 6 is an explanatory diagram showing an XZ cross-sectional configuration of two adjacent power generation units 100U at the same position as the cross-section shown in FIG. 3. As shown in FIGS. 5 and 6, the power generation unit 100U includes a single cell 110, a separator for single cell 120, an air electrode frame 130, a fuel electrode frame 140, a current collecting structure 160, and two separators 180 for IC. One separator 180 for IC, the air electrode frame 130, the separator for single cell 120, the fuel electrode frame 140, and the other separator 180 for IC are arranged to overlap in this order.

[0041] (Single cell 110) The single cell 110 includes an electrolyte layer 112, an air electrode 114, a fuel electrode 116, and a reaction prevention layer 118. As shown in FIGS. 5 and 6, the air electrode 114, the reaction prevention layer 118, the electrolyte layer 112, and the fuel electrode 116 are arranged to overlap in this order. The single cell 110 of the present embodiment is a fuel electrode support type single cell in which other layers (electrolyte layer 112, air electrode 114, reaction prevention layer 118) constituting the single cell 110 are supported by the fuel electrode 116. The single cell 110 is supported by the separator for single cell 120.

[0042] The electrolyte layer 112 is a rectangular flat plate-like member, and has one surface (the upper surface in FIGS. 5 and 6) where the air electrode 114 is disposed, and the other surface (the lower surface in FIGS. 5 and 6) where the fuel electrode 116 is disposed and which is parallel to one surface. The electrolyte layer 112 is a layer containing a solid oxide (for example, YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular outer shape smaller than that of the electrolyte layer 112, and contains, for example, a perovskite-type oxide (for example, LSCF (lanthanum strontium cobalt ferrite)). The fuel electrode 116 is a layer having a rectangular outer shape substantially the same size as that of the electrolyte layer 112, and contains, for example, Ni (nickel), a cermet composed of Ni and ceramic particles, a Ni-based alloy, or the like. The reaction prevention layer 118 is a layer having a rectangular outer shape substantially the same size as that of the air electrode 114, and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has a function of suppressing the reaction of an element (for example, Sr) diffused from the air electrode 114 with an element (for example, Zr) contained in the electrolyte layer 112 to generate a high-resistance substance (for example, SrZrO3).

[0043] (Separator 120 for single cell) As shown in FIGS. 5 and 6, the separator 120 for single cell is a rectangular frame-like member having a substantially rectangular through-hole 121 near the center, and is formed of, for example, a metal. The peripheral portion of the through-hole 121 in the separator 120 for single cell is joined to the peripheral portion of one surface (the surface where the air electrode 114 is disposed: the upper surface in FIGS. 5 and 6) of the electrolyte layer 112 by a joining portion 124. The joining portion 124 is formed of, for example, a brazing material (Ag brazing material).

[0044] (Air electrode frame 130) As shown in FIGS. 5 and 6, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through-hole 131 near the center, and is formed of, for example, mica. The thickness of the air electrode frame 130 is preferably 0.5 mm or more and 5 mm or less. As shown in FIG. 5, the air electrode frame 130 has an oxidant gas supply communication passage 132 that communicates the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communication passage 133 that communicates the air chamber 313 and the oxidant gas discharge manifold 312.

[0045] (Fuel electrode frame 140) As shown in FIGS. 5 and 6, the fuel electrode frame 140 is a rectangular frame-shaped member having a substantially rectangular through-hole 141 near the center, and is formed of, for example, metal. As shown in FIG. 6, the fuel electrode frame 140 has a fuel gas supply communication passage 142 that communicates the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication passage 143 that communicates the fuel chamber 323 and the fuel gas discharge manifold 322.

[0046] (Separator 180 for IC) As shown in FIGS. 5 and 6, the separator 180 for IC is a rectangular frame-shaped member having a through-hole 181 near the center, and is formed of, for example, metal.

[0047] (Current collector structure 160) The current collector structure 160 is electrically connected to the single cell 110 and collects the electric power generated in the single cell 110. The current collector structure 160 includes an interconnector 190 and a fuel electrode current collecting member 144. The current collector structure 160 is an example of a current collector structure for an electrochemical reaction cell stack.

[0048] As shown in FIGS. 5 and 6, the interconnector 190 includes a flat plate portion 191 having a rectangular flat plate shape, a plurality of plate-shaped air electrode current collecting portions 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collecting portions 192 are formed of an alloy containing Fe and Cr (for example, ferritic stainless steel) and have conductivity. The coating layer 193 has conductivity and is disposed so as to cover the surface of the air electrode current collecting portion 192 and the surface of the flat plate portion 191 where the air electrode current collecting portion 192 is disposed. The flat plate portion 191 is joined to the peripheral edge portion of the through hole 181 in the separator 180 for IC, for example, by welding. The interconnector 190 is supported by the separator 180 for IC. The interconnector 190 is an example of a Cr-containing member.

[0049] The fuel electrode current collecting member 144 is a member that connects the interconnector 190 and the fuel electrode 116 and is formed of Ni. The fuel electrode current collecting member 144 is formed of a foil having a thickness in the vertical direction (the length of L1 shown in FIG. 8) of 30 μm or more. As shown in FIGS. 5 and 6, the fuel electrode current collecting member 144 includes an interconnector facing portion 146, an electrode facing portion 145 parallel to the interconnector facing portion 146, and a connecting portion 147 that connects the electrode facing portion 145 and the interconnector facing portion 146, and has a U shape as a whole. The electrode facing portion 145 is joined to the fuel electrode 116, and the interconnector facing portion 146 is joined to the flat plate portion 191 of the interconnector 190. The fuel electrode current collecting member 144 is disposed between the single cell 110 and the interconnector 190. In this specification, "formed of Ni" means a configuration in which Ni occupies 90 wt% or more, and is not limited to a configuration formed only of Ni. The fuel electrode current collecting member 144 is an example of a Ni-made member.

[0050] As shown in FIGS. 5 and 6, the interconnector 190 is shared by two adjacent power generation units 100U. More specifically, as shown in FIGS. 5 and 6, the air electrode current collector 192 is joined to the air electrode 114 of the single cell 110 provided in one of the two adjacent power generation units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, and is thereby electrically connected to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of the single cell 110 provided in the other of the two adjacent power generation units 100U via the fuel electrode current collector member 144. Thereby, electrical continuity between two adjacent power generation units 100U is ensured.

[0051] However, as shown in FIG. 2, the power generation unit 100U located at the other end (the lower end in FIG. 2) among the plurality of power generation units 100U does not include the interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this power generation unit 100U is connected to the second terminal plate 250 via the fuel electrode current collector member 144.

[0052] A spacer 149 made of, for example, mica is disposed between the electrode facing portion 145 and the interconnector facing portion 146. Therefore, the fuel electrode current collector member 144 follows the deformation of the power generation unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnector 190 (or the second terminal plate 250) via the fuel electrode current collector member 144 is maintained well.

[0053] (Air chamber 313 and fuel chamber 323) As shown in FIGS. 5 and 6, the space partitioned by the single cell separator 120, the single cell 110, the air electrode frame 130, the IC separator 180, and the interconnector 190 faces the air electrode 114 and serves as an air chamber 313 through which the oxidant gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the external space over the entire circumference, seals the space between the single cell separator 120 and the IC separator 180, and serves to prevent gas from leaking out of the air chamber 313 to the external space.

[0054] Further, the space partitioned by the single-cell separator 120, the single cell 110, the fuel electrode frame 140, the IC separator 180, and the interconnector 190 faces the fuel electrode 116 and serves as a fuel chamber 323 through which the fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 over the entire circumference from the external space, seals the space between the single-cell separator 120 and the IC separator 180, and prevents gas from leaking out of the fuel chamber 323 into the external space.

[0055] The single-cell separator 120 partitions the air chamber 313 and the fuel chamber 323, suppressing gas leakage (cross leakage) from the air electrode 114 side to the fuel electrode 116 side or from the fuel electrode 116 side to the air electrode 114 side around the single cell 110. Also, the IC separator 180 and the interconnector 190 suppress gas leakage between adjacent power generation units 100U.

[0056] A-2. Operation of the fuel cell stack 10: As shown in FIGS. 2 and 5, the oxidant gas OG is supplied to the oxidant gas supply manifold 311 through a gas pipe (not shown) and a gas passage member 280, and is then supplied to the air chamber 313 through the oxidant gas supply communication flow path 132.

[0057] Also, as shown in FIGS. 3 and 6, the fuel gas FG is supplied to the fuel gas supply manifold 321 through a gas pipe (not shown) and a gas passage member 280, and is then supplied to the fuel chamber 323 through the fuel gas supply communication flow path 142.

[0058] When an oxidant gas OG is supplied to the air chamber 313 of each power generation unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power generation by the electrochemical reaction of the oxidant gas OG and the fuel gas FG is performed in the single cell 110. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent power generation units 100U, and electrical continuity between the two adjacent power generation units 100U is ensured by the interconnector 190. That is, the plurality of power generation units 100U included in the fuel cell stack 10 are electrically connected in series. Further, a second terminal plate 250 is electrically connected to the power generation unit 100U located at the other end (the lower end in FIG. 2) among the plurality of power generation units 100U, and a first terminal plate 240 is electrically connected to the power generation unit 100U located at one end (the upper end in FIG. 2). Thereby, the electrical energy generated in each power generation unit 100U is taken out from the terminal plates 240 and 250 that function as output terminals of the fuel cell stack 10. Since the SOFC generates power at a relatively high temperature (for example, 700°C to 1000°C), after startup, the fuel cell stack 10 may be heated by a heater (not shown) until it reaches a state where the high temperature can be maintained by the heat generated by power generation.

[0059] As shown in FIGS. 2 and 5, the oxidant off-gas OOG discharged from the air chamber 313 of each power generation unit 100U to the oxidant gas discharge manifold 312 through the oxidant gas discharge communication flow path 133 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body portion 281. Further, as shown in FIGS. 3 and 6, the fuel off-gas FOG discharged from the fuel chamber 323 of each power generation unit 100U to the fuel gas discharge manifold 322 through the fuel gas discharge communication flow path 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body portion 281.

[0060] A-3. Detailed Configuration of the Current Collector Structure 160: Figs. 7 and 8 are XZ cross-sectional views showing the detailed configuration of the current collector structure 160 of the first embodiment. Fig. 7 shows an enlarged view of the X1 portion in Fig. 6. Fig. 8 shows an enlarged view of the X2 portion in Fig. 7. The fuel electrode current collector member 144 and the interconnector 190 are arranged in the vertical direction. Further, as shown in Fig. 8, the surface 191S of the flat plate portion 191 of the interconnector 190 and the surface 144S of the fuel electrode current collector member 144 face each other in the vertical direction. In the current collector structure 160, a joint portion CP where the interconnector 190 and the fuel electrode current collector member 144 are joined to each other is formed by joining the surface 191S and the surface 144S to each other. Specifically, the joint portion CP means a portion where the interconnector 190 and the fuel electrode current collector member 144 are physically in contact, and when observing a cross-section perpendicular to the XY plane with an SEM (for example, VE-9800 manufactured by Keyence, the same applies hereinafter), it means a portion where there is no interval of 1 μm or more between the interconnector 190 and the fuel electrode current collector member 144.

[0061] The current collector structure 160 is configured such that when heat-treated at 900°C for 100 hours in a reducing gas atmosphere containing water vapor (for example, H2O / H2 = 1 and H2 / N2 = 0.1 as the volume flow rate of the gas), the Cr concentration inside the fuel electrode current collector member 144 located in the vicinity of the joint portion CP becomes 1 atm% or more. That is, it can be said that the current collector structure 160 is configured such that during the operation of the fuel cell stack 10, Cr contained in the interconnector 190 diffuses into the inside of the fuel electrode current collector member 144. As a result, during the operation of the fuel cell stack 10, an internal oxidation layer IN containing Cr oxide (for example, Cr2O3) is formed inside the fuel electrode current collector member 144 located in the vicinity of the joint portion CP (see Fig. 8).

[0062] FIG. 9 is an explanatory diagram showing an outline of a method for measuring the Cr concentration of the current collector structure 160. In this specification, the "vicinity of the joint CP" means a portion sandwiched between a position 6 μm away from the surface 144S and a position 12 μm away from the surface 144S in the fuel electrode current collector member 144. The measurement of the Cr concentration is carried out by cutting a cross-section orthogonal to the XY plane and including the joint CP after the above heat treatment, and performing SEM / EDX analysis on the periphery of the joint CP. That is, as shown in FIG. 9, for each 6-μm square region sandwiched between a position 6 μm away from the joint CP in the direction of the fuel electrode current collector member 144 and a position 12 μm away from the joint CP, the Cr concentration (atm%) is determined by dividing the content of Cr by the total content of Cr, Ni, and Fe, thereby determining the Cr concentration in the vicinity of the joint CP. Note that the configuration in which "the Cr concentration inside the fuel electrode current collector member 144 located in the vicinity of the joint CP is 1 atm% or more" means a configuration in which the Cr concentration in at least one of the 6-μm square regions in an arbitrary cross-section including the joint CP in the fuel cell stack 10 is 1 atm% or more. In other words, the Cr concentration in the vicinity of the joint CP before the above heat treatment is less than 1 atm%.

[0063] In the fuel electrode current collector member 144, there is a porous layer PL with a higher porosity than the central portion in the vertical direction (i.e., the position of the center line CL that virtually bisects the fuel electrode current collector member 144 in the vertical direction) on the joint CP side. The porosity of the porous layer PL can be measured by observing a cross-section orthogonal to the XY plane with an SEM, and is preferably 1% or more and 50% or less, more preferably 5% or more and 30% or less. Also, the thickness of the porous layer PL in the vertical direction is preferably 5 μm or less. Further, the porous layer PL preferably exists at the peripheral edge of the joint CP.

[0064] Further, the surface 191S of the flat plate portion 191 in the interconnector 190 is suppressed to a predetermined roughness or less. More specifically, the surface 191S has a ten-point average roughness defined by JIS B 0601 of 10 μm or less. The roughness of the surface 191S can be measured, for example, as follows. That is, a section including the joint portion CP between the interconnector 190 and the fuel electrode current collector member 144 is cut out from the fuel cell stack 10, and a contour curve of the surface 191S is obtained from an image magnified 500 times by SEM of a cross section orthogonal to the XY plane, and the ten-point average roughness Rz is obtained in accordance with JIS B 0601.

[0065] A-4. Method for manufacturing the current collector structure 160: FIG. 10 is a flowchart showing a method for manufacturing the current collector structure 160. FIG. 11 is an explanatory diagram schematically showing an interface between the interconnector 190 and the fuel electrode current collector member 144 in the manufacturing process of the current collector structure 160. The method for manufacturing the current collector structure 160 is, for example, as follows.

[0066] First, the interconnector 190 and the fuel electrode current collector member 144 are prepared by a known method (S11).

[0067] Next, the interconnector 190 and the fuel electrode current collector member 144 are pressure-bonded (S12). Specifically, the interconnector 190 and the fuel electrode current collector member 144 are pressure-bonded under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO. The oxygen partial pressure at which Ni is oxidized to NiO can be obtained, for example, from an Ellingham diagram. Also, as long as the oxygen partial pressure is equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO, the gas species is not particularly limited. S12 is an example of a bonding step.

[0068] As shown in FIG. 11(A), there is a gap SP at the interface between the interconnector 190 and the fuel electrode current collector member 144 before the step S12 is performed. On the other hand, as shown in FIG. 11(B), after the step S12 is performed, volume expansion occurs due to the oxidation of Ni contained in the fuel electrode current collector member 144 to NiO, and the gap SP is filled with the nickel oxide layer NOL. As a result, the adhesion between the interconnector 190 and the fuel electrode current collector member 144 is improved.

[0069] Next, the interconnector 190 and the fuel electrode current collector member 144 are heated while being pressurized (S13). Specifically, in a reducing gas atmosphere, the interconnector 190 and the fuel electrode current collector member 144 are heated at a temperature of 800° C. or higher while being pressurized in the vertical direction in which the interconnector 190 and the fuel electrode current collector member 144 are arranged. The heating temperature is preferably 800° C. or higher and 900° C. or lower. S13 is an example of a reduction process.

[0070] As shown in FIG. 11(C), after the step S13 is performed, the nickel oxide layer NOL changes to a porous layer PL. That is, volume shrinkage occurs due to the reduction of NiO in the nickel oxide layer NOL to Ni, and a porous portion is formed. In the step S13, since heating and pressurization are performed, the porous layer PL becomes a relatively dense layer. Further, since NiO is reduced to Ni having higher conductivity, the resistance value of the current collector structure 160 decreases.

[0071] A-5. Effects of this embodiment: As described above, the current collector structure 160 of this embodiment includes an interconnector 190 formed of an alloy containing Cr and a fuel electrode current collector member 144 formed of Ni, and the fuel electrode current collector member 144 joined to the interconnector 190. When the current collector structure 160 is subjected to a heat treatment at 900° C. for 100 hours in a reducing gas atmosphere containing water vapor, the Cr concentration inside the fuel electrode current collector member 144 located near the joint portion CP where the interconnector 190 and the fuel electrode current collector member 144 are joined is 1 atm% or more.

[0072] According to the current collector structure 160 of the present embodiment, during the operation of the fuel cell stack 10, Cr contained in the interconnector 190 is sufficiently diffused into the inside of the fuel electrode current collector member 144. Therefore, the adhesion at the interface between the interconnector 190 and the fuel electrode current collector member 144 is improved, and the formation of the oxide film is suppressed. As a result, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, and thus an increase in the resistance value of the fuel cell stack 10 is suppressed, and the durability performance of the fuel cell stack 10 can be improved.

[0073] Further, in the current collector structure 160 of the present embodiment, when the direction in which the fuel electrode current collector member 144 and the interconnector 190 are arranged via the joint portion CP is the vertical direction, in the fuel electrode current collector member 144, there is a porous layer PL having a higher porosity on the joint portion CP side than the central portion in the vertical direction of the fuel electrode current collector member 144. According to the current collector structure 160 of the present embodiment, since there is a porous layer PL having a higher porosity on the joint portion CP side than the central portion in the vertical direction of the fuel electrode current collector member 144, when, for example, the joining process of the interconnector 190 and the fuel electrode current collector member 144 is performed in a high-temperature environment during the manufacture of the fuel cell stack 10, the stress caused by the difference in thermal expansion between the interconnector 190 and the fuel electrode current collector member 144 can be relaxed. Thereby, the peeling of the joint portion CP between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, the adhesion between the interconnector 190 and the fuel electrode current collector member 144 is improved, and Cr contained in the interconnector 190 is sufficiently diffused into the inside of the fuel electrode current collector member 144. Therefore, the formation of the oxide film at the interface between the interconnector 190 and the fuel electrode current collector member 144 is suppressed. As a result, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, and thus an increase in the resistance value of the fuel cell stack 10 is suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0074] Further, in the current collector structure 160 of the present embodiment, the thickness of the porous layer PL in the vertical direction is 5 μm or less. According to the current collector structure 160 of the present embodiment, since the porous layer PL having a thickness of 5 μm or less in the vertical direction exists in the fuel electrode current collector member 144, peeling of the joint portion CP between the interconnector 190 and the fuel electrode current collector member 144 during the manufacture of the fuel cell stack 10 can be suppressed, and intrusion of oxygen into the joint portion CP during the operation of the fuel cell stack 10 can be suppressed. Therefore, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 can be suppressed, and thus an increase in the resistance value of the fuel cell stack 10 can be suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0075] Further, in the current collector structure 160 of the present embodiment, the fuel electrode current collector member 144 is formed of a foil having a thickness of 30 μm or more. During the operation of the fuel cell stack 10, inside the fuel electrode current collector member 144, internal oxidation layer IN is generated inside the fuel electrode current collector member 144 by the reaction between Cr diffused from the interconnector 190 and oxygen dissociated from H2O contained in the gas in the fuel cell stack 10. At this time, when the internal oxidation layer IN grows on each of the surface on the joint portion CP side and the surface on the side opposite to the joint portion CP in the vertical direction, if the thickness of the fuel electrode current collector member 144 is small, the distance between the surfaces is short, so the internal oxidation layers IN formed on each surface side are connected, and the conduction path from the interconnector 190 to the fuel electrode 116 may be blocked inside the fuel electrode current collector member 144. According to the current collector structure 160 of the present embodiment, the fuel electrode current collector member 144 is formed of a foil having a thickness of 30 μm or more. Thereby, the distance between the surfaces becomes relatively long, and blocking of the conduction path is suppressed. Therefore, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 can be suppressed, and thus an increase in the resistance value of the fuel cell stack 10 can be suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0076] In addition, in the current collector structure 160 of the present embodiment, the surface 191S of the interconnector 190 that is joined to the fuel electrode current collector member 144 has a ten-point average roughness defined in JIS B 0601 of 10 μm or less.

[0077] During the manufacture of the fuel cell stack 10, when joining the interconnector 190 and the fuel electrode current collector member 144, for example, when Ni is oxidized to NiO, the volume expansion is utilized to form NiO in the gap SP between the interconnector 190 and the fuel electrode current collector member 144, thereby improving the adhesion between the interconnector 190 and the fuel electrode current collector member 144. Subsequently, when further performing a reduction treatment from NiO to Ni with higher conductivity, a porous layer PL is formed on the fuel electrode current collector member 144 due to the volume contraction accompanying the conversion from NiO to Ni. At this time, if the porous layer PL is thick, oxygen easily penetrates into the joint portion CP during the operation of the fuel cell stack 10, an oxide film is generated at the interface between the interconnector 190 and the fuel electrode current collector member 144, leading to an increase in the resistance value. According to the current collector structure 160 of the present embodiment, the surface 191S of the interconnector 190 that is joined to the fuel electrode current collector member 144 has a ten-point average roughness defined in JIS B 0601 of 10 μm or less. As a result, the gap SP between the interconnector 190 and the fuel electrode current collector member 144 does not become excessively large, so that the thickness of the porous layer PL formed on the fuel electrode current collector member 144 can be suppressed, and the intrusion of oxygen into the joint portion CP during the operation of the fuel cell stack 10 can be suppressed. Therefore, the generation of the oxide film at the interface between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, the decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, and thus the increase in the resistance value of the fuel cell stack 10 is suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0078] In addition, the fuel cell stack 10 of the present embodiment includes a current collector structure 160 and a single cell 110 electrically connected to the current collector structure 160.

[0079] According to the fuel cell stack 10 of the present embodiment, during operation, Cr contained in the interconnector 190 in the current collector structure 160 is sufficiently diffused into the interior of the fuel electrode current collector member 144. Therefore, the adhesion at the interface between the interconnector 190 and the fuel electrode current collector member 144 is improved, and the formation of the oxide film is suppressed. As a result, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 can be suppressed, and thus an increase in the resistance value of the fuel cell stack 10 can be suppressed, and the durability performance of the fuel cell stack 10 can be improved.

[0080] Further, the manufacturing method of the current collector structure 160 of the present embodiment includes a joining step S12 of joining the interconnector 190 and the fuel electrode current collector member 144 under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO.

[0081] According to the manufacturing method of the current collector structure 160 of the present embodiment, by utilizing the volume expansion when Ni is oxidized to NiO during the joining step S12, NiO is formed in the gap SP between the interconnector 190 and the fuel electrode current collector member 144, thereby improving the adhesion between the interconnector 190 and the fuel electrode current collector member 144 and suppressing the formation of the oxide film. As a result, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144 can be suppressed, and thus an increase in the resistance value of the fuel cell stack 10 can be suppressed, and the durability performance of the fuel cell stack 10 can be improved.

[0082] In addition, in the manufacturing method of the current collector structure 160 of the present embodiment, further, after the joining step S12, in a reducing gas atmosphere, a reduction step S13 is provided in which the interconnector 190 and the fuel electrode current collector member 144 are heated at a temperature of 800 °C or higher while being pressed in the vertical direction in which the interconnector 190 and the fuel electrode current collector member 144 are aligned. According to the manufacturing method of the current collector structure 160 of the present embodiment, by applying pressure, it is possible to suppress a decrease in the adhesion between the interconnector 190 and the fuel electrode current collector member 144 due to volume shrinkage accompanying the reduction of NiO to Ni in the reduction step S13, while performing a reduction treatment from NiO to Ni having higher conductivity. In addition, since NiO is reduced to Ni at a temperature of 800 °C or higher, NiO can be surely reduced. Therefore, an increase in the resistance value of the fuel cell stack 10 can be suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0083] A-6. Performance Evaluation: Next, the performance evaluation of the present embodiment will be described. A plurality of samples of the fuel cell stack 10 each including a current collector structure 160 having different physical properties were prepared, and performance evaluation was performed using the plurality of samples. Tables 1 to 3 show the performance evaluation results.

[0084] (Preparation of Evaluation Samples) The current collector structure 160 was fabricated by the method described in the above "A-4. Manufacturing Method of Current Collector Structure 160". Specifically, the members constituting the fuel cell stack 10 were laminated, and the joining step S12 and the reduction step S13 were carried out in a state where the members from the first end plate 210 to the second end plate 270 were fastened by bolts B and nuts N. At that time, by changing the configuration of the fuel electrode current collector member 144, the conditions of the joining step S12, and the conditions of the reduction step S13, current collector structures 160 having different physical properties were fabricated. Then, samples of the fuel cell stack 10 each including a current collector structure 160 having different physical properties were prepared by a known method, and the following performance evaluation was performed.

[0085] (Performance Evaluation - Cr Concentration after Heat Treatment) From the fuel cell stack 10 fabricated by the above method, a portion including the interconnector 190 and the fuel electrode current collector member 144 was cut out and heat-treated at 900 °C for 100 hours in a reducing gas atmosphere containing water vapor (H2O / H2 = 1, H2 / N2 = 0.1). After the heat treatment, it was cut along a cross-section orthogonal to the XY plane and including the joint portion CP, and the Cr concentration of each sample of the fuel cell stack 10 was measured by the method described above.

[0086] (Performance Evaluation - Stack Deterioration Rate) Regarding the fuel cell stack 10 fabricated by the above method, the operation was started at 700 °C, and the potential V I at the start of operation was measured. Then, continuous operation was performed for 10,000 hours at a temperature of 700 °C, and the potential V E after 10,000 hours from the start of operation was measured. Using the following formula, the stack deterioration rate of each sample of the fuel cell stack 10 due to continuous operation was calculated. Stack deterioration rate (%) = 100 × (V I - V E ) / V I

[0087] (Performance Evaluation Results) Table 1 is a table showing the performance evaluation results.

Table 1

[0088] In Table 1 and the subsequent tables, the configurations of the fuel electrode current collector member 144 and the interconnector 190 of each sample, the conditions of the joining process S12, the conditions of the reduction process S13, and the performance evaluation results are shown. Among the descriptions in each table, "flowing gas" indicates the type of gas supplied to the fuel chamber 323 through the fuel gas supply manifold 321 or the fuel gas discharge manifold 322 when performing the joining process S12. Also, "Cr concentration after heat treatment" indicates the average value of the Cr concentrations of each 6-μm square region sandwiched between the positions 6 μm and 12 μm away from the joint portion CP in the direction of the fuel electrode current collector member 144 when measuring the Cr concentration at an arbitrary cross-section including the joint portion CP.

[0089] Table 1 shows Samples S1 to S3. Among Samples S1 to S3, the Cr concentration after heat treatment of Sample S1 was relatively low, while the Cr concentrations after heat treatment of Samples S2 and S3 were relatively high. Also, the stack degradation rate of Sample S1 was relatively high, while the stack degradation rates of Samples S2 and S3 were relatively low. From the above, it was confirmed that the Cr concentration after heat treatment and the stack degradation rate were correlated, and the higher the Cr concentration after heat treatment, the lower the stack degradation rate (that is, the higher the durability performance of the fuel cell stack 10).

[0090] Furthermore, among Samples S1 to S3, Sample S1 did not have the porous layer PL, while Samples S2 and S3 had the porous layer PL. From this, it was confirmed that the presence or absence of the porous layer PL and the stack degradation rate were correlated, and the samples having the porous layer PL had a low stack degradation rate. That is, by having the porous layer PL, the adhesion between the interconnector 190 and the fuel electrode current collector member 144 was improved, and as a result of sufficient diffusion of Cr of the interconnector 190 into the fuel electrode current collector member 144, it was considered that the stack degradation rate was suppressed.

[0091] Also, it is considered that the presence or absence of the porous layer PL is due to the conditions of the joining step S12. That is, for Sample S1, it is considered that the porous layer PL was not formed as a result of the relatively low oxygen partial pressure in the joining step S12, so that Ni of the fuel electrode current collector member 144 was not oxidized to NiO, and for Samples S2 and 3, it is considered that the porous layer PL was formed as a result of the relatively high oxygen partial pressure in the joining step S12, so that Ni of the fuel electrode current collector member 144 was oxidized to NiO.

[0092] Table 2 is a table showing the performance evaluation results.

Table 2

[0093] Table 2 shows Samples S4 and S5. For Sample S4, the thickness of the porous layer PL of the fuel electrode current collector member 144 is greater than 5 μm, while for Sample S5, the thickness of the porous layer PL of the fuel electrode current collector member 144 is 5 μm or less. Also, the stack degradation rate of Sample S4 was relatively high, and the stack degradation rate of Sample S5 was relatively low. From this, it was confirmed that there is a correlation between the thickness of the porous layer PL and the stack degradation rate, and that the stack degradation rate becomes lower when the porous layer PL is 5 μm or less.

[0094] Also, the thickness of the porous layer PL is considered to be due to the conditions of the reduction step S13. That is, for Sample S4, it is considered that the porous layer PL was not densified because the reduction temperature in the reduction step S13 was lower than 800°C, and for Sample S5, it is considered that the porous layer PL was densified because the reduction temperature in the reduction step S13 was 800°C or higher.

[0095] Table 3 is a table showing the performance evaluation results.

Table 3

[0096] Table 3 shows Samples S6 to S8. The shape of the fuel electrode current collector member 144 of Sample S6 is a foil with a thickness less than 30 μm, the shape of the fuel electrode current collector member 144 of Sample S7 is a foil with a thickness of 30 μm or more, and the shape of the fuel electrode current collector member 144 of Sample S8 is a mesh with a wire diameter of the mesh of 60 μm or more. Also, the stack degradation rate of Sample S6 was relatively high, and the stack degradation rates of Samples S7 and S8 were relatively low. From the above, it was confirmed that there is a correlation between the thickness of the fuel electrode current collector member 144 and the stack degradation rate, and that the thicker the fuel electrode current collector member 144, the lower the stack degradation rate. Regarding the configuration where the fuel electrode current collector member 144 is a mesh, it will be described in detail later.

[0097] B. Second Embodiment: FIG. 12 is an XZ cross-sectional view showing the detailed configuration of the current collector structure 160a of the second embodiment. Hereinafter, among the configurations of the fuel cell stack 10 of the second embodiment, for the configurations that are the same as those of the fuel cell stack 10 of the first embodiment described above, the description thereof will be appropriately omitted by attaching the same reference numerals.

[0098] The current collector structure 160a of the second embodiment is different from the current collector structure 160 of the first embodiment in the configuration of the fuel electrode current collector member. Specifically, in the current collector structure 160a of the second embodiment, the fuel electrode current collector member 144a is formed of a mesh. The fuel electrode current collector member 144a is composed of a plurality of wire rods made of Ni, and the wire rods extending in the X-axis direction and the wire rods extending in the Y-axis direction form a mesh structure. The fuel electrode current collector member 144a has a wire diameter (the length of L2 shown in FIG. 12) of 60 μm or more.

[0099] As described above, in the current collector structure 160a of the second embodiment, the fuel electrode current collector member 144a is formed of a mesh with a wire diameter of 60 μm or more. During the operation of the fuel cell stack 10, inside the fuel electrode current collector member 144a, Cr diffused from the interconnector 190 reacts with oxygen dissociated from H2O contained in the gas in the fuel cell stack 10, thereby generating an internal oxidation layer IN inside the fuel electrode current collector member 144a. At this time, when the internal oxidation layer IN grows on each of the surface on the joint portion CP side and the surface on the side opposite to the vertical joint portion CP, if the thickness of the fuel electrode current collector member 144a is small, the distance between the surfaces is short, so the internal oxidation layers IN formed on each surface side are connected, and the conduction path inside the fuel electrode current collector member 144a may be blocked. According to the current collector structure 160a of the present embodiment, the fuel electrode current collector member 144a is formed of a mesh with a wire diameter of 60 μm or more. As a result, the distance between the surfaces becomes relatively long, and the interruption of the conduction path is suppressed. Therefore, a decrease in conductivity between the interconnector 190 and the fuel electrode current collector member 144a can be suppressed, and thus an increase in the resistance value of the fuel cell stack 10 can be suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0100] C. Modification example: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the gist thereof. For example, the following modifications are also possible.

[0101] The configurations of the fuel cell stack 10 and the power generation unit 100U in the above-described embodiments are merely examples, and can be variously modified. For example, the number of single cells 110 (the number of power generation units 100U) included in the fuel cell stack 10 in the above-described embodiments is merely an example, and the number of single cells 110 is appropriately determined according to the output voltage required for the fuel cell stack 10.

[0102] The materials constituting each member in the above-described embodiments are merely illustrative, and each member may be constituted by other materials.

[0103] In the above-described embodiment, the porous layer PL exists in the current collector structure 160, but the current collector structure does not necessarily have to have a porous layer. Also, in the above-described embodiment, the thickness of the porous layer PL is 5 μm or less, but the porous layer may be thicker than 5 μm.

[0104] In the first embodiment, the fuel electrode current collector member 144 is formed of a foil having a thickness of 30 μm or more, and in the second embodiment, the fuel electrode current collector member 144a is formed of a mesh having a wire diameter of 60 μm or more. However, the shape of the Ni-made member is not limited to these, and its thickness is also not limited to these.

[0105] In the above-described embodiment, the ten-point average roughness of the surface 191S is 10 μm or less for the fuel cell stack, but the roughness of the surface of the Ni-made member joined to the Cr-containing member is not limited to this.

[0106] The manufacturing method of the current collector structure is not limited to the above-described embodiment.

[0107] The fuel cell stack 10 of the above embodiment is a co-flow type SOFC, but the technology disclosed in this specification is also applicable to a counter-flow type SOFC or a cross-flow type SOFC.

[0108] In the above embodiment, the single cell 110 is a fuel electrode supported type single cell, but it may be other types of single cells such as an electrolyte supported type or a metal supported type.

[0109] In the current collector structure 160 of the above embodiment, the interconnect 190 is taken as an example of a Cr-containing member, but the Cr-containing member is not limited to this. For example, when the first plate 232 in the above embodiment contains Cr, the first plate 232 can also be taken as an example of a Cr-containing member. When the metal support in a metal supported type single cell contains Cr, the metal support can also be taken as an example of a Cr-containing member. Similarly, in the current collector structure 160 of the above embodiment, the fuel electrode current collector member 144 is taken as an example of a Ni-made member, but the Ni-made member is not limited to this.

[0110] In the above embodiment, the fuel cell stack 10 is configured to include a plurality of flat plate type single cells 110, but the present invention is similarly applicable to a fuel cell stack including a plurality of single cells of other types (for example, cylindrical type, flat cylindrical type, etc.).

[0111] In the above embodiment, the electrochemical reaction cell stack is a cell stack used for a solid oxide type fuel cell (SOFC), but the above configuration is also applicable to a cell stack used for other types of fuel cells such as a polymer electrolyte fuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a molten carbonate fuel cell (MCFC), or an electrolysis cell stack including an electrolysis cell unit, which is a constituent unit of a solid oxide electrolysis cell (SOEC), as a single cell.

Explanation of Reference Numerals

[0112] 10: Fuel cell stack 100: Power generation block 100U: Power generation unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120: Separator for single cell 121: Through hole 124: Joint 130: Air electrode frame 131: Through hole 132: Oxidant gas supply communication flow path 133: Oxidant gas discharge communication flow path 140: Fuel electrode frame 141: Through hole 142: Fuel gas supply communication flow path 143: Fuel gas discharge communication flow path 144, 144a: Fuel electrode current collector member 144S: Surface 145: Electrode facing part 146: Interconnector facing part 147: Connecting part 149: Spacer 160, 160a: Current collection structure 180: Separator for IC 181: Through hole 190: Interconnector 191: Flat plate part 191S: Surface 192: Air electrode current collection part 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Plane part 212: Through hole 213: Outer convex part 214: Inner convex part 220: Insulating part 230: Terminal separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Plane part 272: Through hole 273: Outer convex part 274: Inner convex part 280: Gas passage member 281: Body part 282: Flange part 283: Gas through hole 284: Bolt hole 311: Oxidant gas supply manifold 312: Oxidant gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber B: Bolt BH: Bolt hole N: Nut FG: Fuel gas FOG: Fuel off-gas OG: Oxidant gas OOG: Oxidant off-gas CP: Joint IN: Internal oxide layer PL: Porous layer CL: Center line SP: Gap NOL: Nickel oxide layer

Claims

1. A Cr-containing member formed from an alloy containing Cr, and A Ni member formed from Ni, the Ni member being joined to the Cr-containing member, In a current collector structure for an electrochemical reaction cell stack comprising: When the current collector structure for the electrochemical reaction cell stack is heat-treated at 900 °C for 100 hours in a reducing gas atmosphere containing water vapor, the Cr concentration inside the Ni member located near the joint where the Cr-containing member and the Ni member are joined is 1 atm% or more. A current collector structure for an electrochemical reaction cell stack, characterized by this.

2. In the current collector structure for an electrochemical reaction cell stack according to Claim 1, When the direction in which the Ni member and the Cr-containing member are aligned through the joint is defined as the first direction, in the Ni member, there is a porous layer with a higher porosity than the central part in the first direction of the Ni member on the joint side of the central part. A current collector structure for an electrochemical reaction cell stack, characterized by this.

3. In the current collector structure for an electrochemical reaction cell stack according to Claim 2, The thickness of the porous layer in the first direction is 5 μm or less. A current collector structure for an electrochemical reaction cell stack, characterized by this.

4. In the current collector structure for an electrochemical reaction cell stack according to Claim 1, The Ni member is formed of a foil with a thickness of 30 μm or more, or a mesh with a wire diameter of 60 μm or more. A current collector structure for an electrochemical reaction cell stack, characterized by this.

5. In the current collector structure for an electrochemical reaction cell stack according to Claim 2, The surface of the Cr-containing member joined to the Ni member has a ten-point average roughness defined by JIS B 0601 of 10 μm or less. A current collector structure for an electrochemical reaction cell stack, characterized by this.

6. An electrochemical reaction cell stack comprising the current collector structure for an electrochemical reaction cell stack according to Claim 1 and a single cell electrically connected to the current collector structure for the electrochemical reaction cell stack. An electrochemical reaction cell stack, characterized by this.

7. A Cr-containing member formed from an alloy containing Cr, and A Ni member formed from Ni, the Ni member being joined to the Cr-containing member, In a method for manufacturing a current collector structure for an electrochemical reaction cell stack comprising: A joining step of pressure-joining the Cr-containing member and the Ni member under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO is provided. A method for manufacturing a current collecting structure for an electrochemical reaction cell stack, characterized by the above.

8. In the method for manufacturing a current collecting structure for an electrochemical reaction cell stack according to Claim 7, further, After the joining step, a reduction step of heating the Cr-containing member and the Ni member at a temperature of 800°C or higher while applying pressure in a first direction in which the Cr-containing member and the Ni member are aligned in a reducing gas atmosphere is provided. A method for manufacturing a current collecting structure for an electrochemical reaction cell stack, characterized by the above.

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