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 collecting structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a method for manufacturing a current collecting structure for an electrochemical reaction cell stack. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs") are known as one type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack. A fuel cell stack includes a single cell and a current collecting structure for a fuel cell stack (hereinafter simply referred to as a "current collecting structure"). The current collecting structure is electrically connected to the single cell and collects the electricity generated by the single cell.

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

[0004] [Patent Document 1] Patent No. 6773472 Summary of the Invention [Problem to be solved by the invention]

[0005] The electrical conductivity between the Cr-containing member and the Ni member in the current collecting structure affects the resistance of the fuel cell stack. Furthermore, the electrical conductivity between the Cr-containing member and the Ni member is affected by the bonding strength between the Cr-containing member and the Ni member. Specifically, if the bonding strength between the Cr-containing member and the Ni member is insufficient, the Cr contained in the Cr-containing member will not sufficiently diffuse into the Ni member during operation of the fuel cell stack, and an oxide film with relatively low electrical conductivity will form at the interface between the Cr-containing member and the Ni member. This reduces the electrical conductivity between the Cr-containing member and the Ni member, which in turn increases the resistance of the fuel cell stack and reduces the durability of the fuel cell stack.

[0006] Note that such issues are also common to current collecting structures used in electrolysis cell stacks, which are a type of electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen by electrolysis of water. In this specification, a single fuel cell cell and a single electrolysis cell are collectively referred to as a single electrochemical reaction cell, and a fuel cell stack and an electrolysis cell stack are collectively referred to as an electrochemical reaction cell stack. Furthermore, such issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

[0007] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

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

[0009] (1) A 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. When the current collecting structure for an electrochemical reaction cell stack 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 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, the Cr contained in the Cr-containing member is sufficiently diffused into the Ni member during operation of the electrochemical reaction cell stack, improving the adhesion at the interface between the Cr-containing member and the Ni member and suppressing the formation of an oxide film, thereby suppressing a decrease in the conductivity between the Cr-containing member and the Ni member, thereby suppressing an increase in the resistance value of the electrochemical reaction cell stack, and improving the durability of the electrochemical reaction cell stack.

[0011] (2) In the current collecting structure for an electrochemical reaction cell stack, when the direction in which the Ni member and the Cr-containing member are aligned via the joint is defined as a first direction, the Ni member may have a porous layer with a higher porosity than the central portion thereof, located closer to the joint than the central portion in the first direction. According to this configuration, the porous layer with a higher porosity than the central portion is located closer to the joint than the central portion in the first direction. Therefore, when, for example, the Cr-containing member and the Ni member are joined in a high-temperature environment during the manufacture of an electrochemical reaction cell stack, stress caused by the difference in thermal expansion between the Cr-containing member and the Ni member can be alleviated. This suppresses peeling at the joint between the Cr-containing member and the Ni member, improves adhesion between the Cr-containing member and the Ni member, and allows the Cr contained in the Cr-containing member to be sufficiently diffused into the Ni member, thereby suppressing the formation of an oxide film at the interface between the Cr-containing member and the Ni member. This suppresses a decrease in conductivity between the Cr-containing member and the Ni member, thereby suppressing an increase in the resistance value of the electrochemical reaction cell stack and more effectively improving the durability of the electrochemical reaction cell stack.

[0012] (3) In the current collecting structure for an electrochemical reaction cell stack, the thickness of the porous layer in the first direction may be 5 μm or less. According to this configuration, the Ni member has a porous layer with a thickness of 5 μm or less in the first direction. This prevents peeling at the joint between the Cr-containing member and the Ni member during the manufacture of the electrochemical reaction cell stack, while also preventing oxygen from penetrating into the joint during operation of the electrochemical reaction cell stack. This prevents the formation of an oxide film at the interface between the Cr-containing member and the Ni member, thereby preventing a decrease in conductivity between the Cr-containing member and the Ni member and ultimately preventing an increase in the resistance value of the electrochemical reaction cell stack, thereby more effectively improving the durability of the electrochemical reaction cell stack.

[0013] (4) In the current collecting structure for an electrochemical reaction cell stack, the Ni member may be formed of a foil having a thickness of 30 μm or more or a mesh having a wire diameter of 60 μm or more. According to this configuration, during operation of the electrochemical reaction cell stack, Cr diffused from the Cr-containing member reacts with oxygen dissociated from HO contained in the gas in the electrochemical reaction cell stack inside the Ni member, forming an internal oxidation layer (e.g., a layer containing CrO) inside the Ni member. When this occurs, if the internal oxidation layers grow on the surface on the joint side and the surface opposite the joint in the first direction, if the Ni member is thin, the distance between the surfaces is short, and the internal oxidation layers formed on the surfaces may connect, blocking the internal conduction path within the Ni member. According to this configuration, the Ni member is formed of a foil having a thickness of 30 μm or more or a mesh having a wire diameter of 60 μm or more. This relatively long distance between the surfaces prevents the conduction path from being blocked. This suppresses a decrease in conductivity between the Cr-containing member and the Ni member, thereby suppressing an increase in the resistance value of the electrochemical reaction cell stack and more effectively improving the durability of the electrochemical reaction cell stack.

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

[0015] During the manufacture of an electrochemical reaction cell stack, when joining a Cr-containing member and a Ni member, the volume expansion that occurs when Ni is oxidized to NiO can be utilized to form NiO in the gap between the Cr-containing member and the Ni member, thereby improving the adhesion between the two. If a further reduction process is subsequently performed to convert NiO into Ni, which has higher conductivity, a porous layer is formed in the Ni member due to the volume shrinkage that accompanies the conversion of NiO to Ni. If the porous layer is thick, oxygen can easily penetrate the joint during operation of the electrochemical reaction cell stack, forming an oxide film at the interface between the Cr-containing member and the Ni member, resulting in an increase in resistance. According to this configuration, the surface of the Cr-containing member that is joined to the Ni member has a ten-point average roughness of 10 μm or less as defined by JIS B 0601. This prevents the gap between the Cr-containing member and the Ni member from becoming excessively large, thereby reducing the thickness of the porous layer formed in the Ni member and suppressing oxygen penetration into the joint during operation of the electrochemical reaction cell stack. This suppresses the formation of an oxide film at the interface between the Cr-containing member and the Ni member, suppresses a decrease in conductivity between the Cr-containing member and the Ni member, and ultimately suppresses an increase in the resistance value of the electrochemical reaction cell stack, thereby more effectively improving the durability performance of the electrochemical reaction cell stack.

[0016] (6) The electrochemical reaction cell stack disclosed in this specification comprises a current collecting structure for an electrochemical reaction cell stack as 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, the Cr contained in the Cr-containing member in the current collecting structure for the electrochemical reaction cell stack is sufficiently diffused into the Ni member during operation, improving the adhesion at the interface between the Cr-containing member and the Ni member and suppressing the formation of an oxide film, thereby suppressing a decrease in the conductivity between the Cr-containing member and the Ni member, thereby suppressing an increase in the resistance value of the electrochemical reaction cell stack, and improving the durability of the electrochemical reaction cell stack.

[0018] (7) The present specification discloses a method for manufacturing a current collecting structure for an electrochemical reaction cell stack, which 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, 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 this method for manufacturing a current collecting structure for an electrochemical reaction cell stack, the volume expansion that occurs when Ni is oxidized to NiO during the joining process 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 and suppressing the formation of an oxide film at the interface, thereby suppressing a decrease in the conductivity between the Cr-containing member and the Ni member, and ultimately suppressing an increase in the resistance value of the electrochemical reaction cell stack and improving the durability of the electrochemical reaction cell stack.

[0020] (8) The above-described method for manufacturing a current collecting structure for an electrochemical reaction cell stack may further include a reduction step, after the joining step, in which the Cr-containing member and the Ni member are heated at a temperature of 800°C or higher under a reducing gas atmosphere while applying pressure to them in a first direction in which the Cr-containing member and the Ni member are aligned. According to this configuration, applying pressure can reduce NiO to Ni, which has higher electrical conductivity, while suppressing a decrease in adhesion between the Cr-containing member and the Ni member due to volumetric shrinkage associated with the reduction of NiO to Ni in the reduction step. Furthermore, since NiO is reduced to Ni at a temperature of 800°C or higher, the NiO can be reliably reduced. This suppresses an increase in the resistance value of the electrochemical reaction cell stack and more effectively improves the durability of the electrochemical reaction cell stack.

[0021] The technology disclosed in this specification can be realized in various forms, such as a current collecting structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a method for manufacturing a current collecting structure for an electrochemical reaction cell stack. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack 10 according to a first embodiment; [Figure 2] FIG. 2 is an explanatory diagram showing the XZ cross-sectional configuration of the fuel cell stack 10 taken along the line II-II in FIG. 1. [Figure 3] FIG. 3 is an explanatory diagram showing the XZ cross-sectional configuration of the fuel cell stack 10 taken along the line III-III in FIG. 1. [Figure 4] FIG. 4 is an explanatory diagram showing the YZ cross-sectional configuration of the fuel cell stack 10 taken along the line IV-IV in FIG. [Figure 5] FIG. 3 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generating units 100U at the same position as the cross-section shown in FIG. 2. [Figure 6] FIG. 4 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generating units 100U at the same position as the cross-section shown in FIG. 3. [Figure 7] FIG. 1 is an XZ cross-sectional view showing a detailed configuration of a current collecting structure 160 according to a first embodiment. [Figure 8] FIG. 1 is an XZ cross-sectional view showing a detailed configuration of a current collecting structure 160 according to a first embodiment. [Figure 9] An explanatory diagram showing an outline of a method for measuring the Cr concentration of the current collecting structure 160. [Figure 10] Flowchart showing a method for manufacturing a current collecting structure 160 [Figure 11] FIG. 10 is an explanatory diagram schematically illustrating the interface between the interconnector 190 and the anode current collecting member 144 during the manufacturing process of the current collecting structure 160. [Figure 12] FIG. 10 is an XZ cross-sectional view showing a detailed configuration of a current collecting structure 160a according to a second embodiment. DETAILED DESCRIPTION OF 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 a fuel cell stack 10 according to a first embodiment. FIG. 2 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 10 taken along line II-II in FIG. 1 . FIG. 3 is an explanatory diagram showing an XZ cross-sectional configuration of the fuel cell stack 10 taken along line III-III in FIG. 1 . FIG. 4 is an explanatory diagram showing a YZ cross-sectional configuration of the fuel cell stack 10 taken along line IV-IV in FIG. 1 . Each figure shows mutually orthogonal X, Y, and Z axes for identifying directions. For convenience, the Z-axis direction is referred to as the up-down direction, the positive Z-axis direction as the up-down direction, and the negative Z-axis direction as the down-down direction in this specification. However, the fuel cell stack 10 may actually be installed in a different orientation. Furthermore, unless otherwise specified, the "thickness" of each component in this specification refers to the vertical length of each component. The fuel cell stack 10 is an example of an electrochemical reaction cell stack. The Z-axis direction is an example of a first direction.

[0024] (Overall configuration of fuel cell stack 10) 1 to 4, the fuel cell stack 10 includes a power generation block 100, an end separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating section 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating section 220, the end 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 rectangular outer shapes of approximately the same size and are arranged in a stacked manner 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 near each of the four corners, penetrating from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. A nut N is screwed onto both ends of each bolt B. These bolts B and nuts N fasten the members from the first end plate 210 to the second end plate 270 together. 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 made up of a plurality of (seven in this embodiment) power generation units 100U arranged side by side in a predetermined arrangement direction (vertical direction).

[0027] (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. As shown in FIGS. 1 to 4 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is formed around the entire outer periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is formed around the entire inner periphery of the flat portion 211.

[0028] (insulating part 220) Insulating section 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of, for example, an insulating material. As shown in Figure 2, insulating section 220 is sandwiched between first end plate 210 and end separator 230, thereby ensuring insulation between first end plate 210 and end 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 made of, for example, metal.

[0030] (First Plate 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 to 4, the first plate 232 is joined, for example, by welding, to the peripheral portion of the through-hole 231 in the terminal separator 230. The terminal separator 230 and the first plate 232 separate 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 Figure 2) of the multiple power generation units 100U that make up the power generation block 100, via a connecting member having the same structure as the anode current collecting member 144 (described later), thereby electrically connecting the power generation unit 100U and the first plate 232.

[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 made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. The first terminal plate 240 is electrically connected to the power generating unit 100U located at one end (the upper end in FIG. 2) of the multiple power generating units 100U that make up the power generating block 100, via a first plate 232 and a terminal separator 230. One end (the right end in FIG. 2) of the first terminal plate 240 protrudes laterally from the power generating block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0033] (2nd terminal plate 250) The second terminal plate 250 is a rectangular plate-shaped member made of a conductive material such as ferritic stainless steel that has an alumina oxide coating on its surface. The second terminal plate 250 is electrically connected to the power generating unit 100U that is located at the other end (the lower end in FIG. 2) of the multiple power generating units 100U that make up the power generating block 100. One end (the right end in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generating block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

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

[0035] (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. The second end plate 270 has a rectangular, frame-like flat 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 flat portion 271 in the direction opposite to the second terminal plate 250 (downward in FIG. 2). The flat portion 271 has holes that form the bolt holes BH described above. The outer convex portion 273 protrudes from the outer periphery of the flat portion 271. The outer convex portion 273 is formed around the entire outer periphery of the flat portion 271. The inner convex portion 274 protrudes from the inner periphery of the flat portion 271. The inner convex portion 274 is formed around the entire inner periphery of the flat portion 271.

[0036] (Manifolds 311, 312, 321, 322) 1, 2, and 3, the fuel cell stack 10 has four holes that penetrate 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] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies the oxidant gas OG introduced from outside the fuel cell stack 10 to an air chamber 313 (described later) of each power generating 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 generating unit 100U to the outside of the fuel cell stack 10. For example, air is used as the oxidant gas OG. The oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312 are arranged on opposite sides of the air chamber 313.

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

[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. The main body portion 281 has a gas through hole 283 that penetrates in the vertical direction. The flange portion 282 is provided so as to protrude 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. A bolt (not shown) for connecting the fuel cell stack 10 to an external device is inserted into each bolt hole 284. One end (the upper end in FIGS. 2 and 3 ) of the main body portion 281 included in each of the four gas passage members 280 is joined to the second end plate 270 by, for example, welding, and the gas through hole 283 communicates with the manifolds 311, 312, 321, and 322, respectively. A gas pipe (not shown) for supplying or discharging gas is connected to each of the main body portions 281.

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

[0041] (single cell 110) The unit cell 110 includes an electrolyte layer 112, an air electrode 114, an anode 116, and a reaction prevention layer 118. As shown in Figures 5 and 6, the air electrode 114, the reaction prevention layer 118, the electrolyte layer 112, and the anode 116 are stacked in this order. The unit cell 110 of this embodiment is an anode-supported unit cell in which the anode 116 supports the other layers (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) that make up the unit cell 110. The unit cell 110 is supported by a unit cell separator 120.

[0042] The electrolyte layer 112 is a rectangular, flat member having one surface (the upper surface in FIGS. 5 and 6 ) on which the air electrode 114 is disposed and another surface (the lower surface in FIGS. 5 and 6 ) parallel to the first surface on which the anode 116 is disposed. The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The cathode 114 is a layer having a rectangular shape smaller than that of the electrolyte layer 112 and containing, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)). The anode 116 is a layer having a rectangular shape and approximately the same size as the electrolyte layer 112 and containing, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, or the like. The reaction prevention layer 118 is a layer having a rectangular shape and approximately the same size as the air electrode 114 and containing, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of preventing elements (e.g., Sr) diffused from the air electrode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

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

[0044] (Air electrode frame 130) 5 and 6, the air electrode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made 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 communicating channel 132 that connects the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communicating channel 133 that connects the air chamber 313 and the oxidant gas discharge manifold 312.

[0045] (fuel electrode frame 140) 5 and 6, the anode frame 140 is a rectangular frame-like member having a substantially rectangular through-hole 141 near the center, and is made of, for example, metal. As shown in Fig. 6, the anode frame 140 has a fuel gas supply communication channel 142 that connects the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication channel 143 that connects the fuel chamber 323 and the fuel gas discharge manifold 322.

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

[0047] (current collecting structure 160) The current collecting structure 160 is electrically connected to the unit cell 110 and collects the electricity generated in the unit cell 110. The current collecting structure 160 includes an interconnector 190 and an anode current collecting member 144. The current collecting structure 160 is an example of a current collecting structure for an electrochemical reaction cell stack.

[0048] As shown in FIGS. 5 and 6 , the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 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 collector 192 are formed of an alloy containing Fe and Cr (e.g., ferritic stainless steel) and are electrically conductive. The coating layer 193 is electrically conductive and is disposed so as to cover the surface of the air electrode current collector 192 and the surface of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding. The interconnector 190 is supported by the IC separator 180. The interconnector 190 is an example of a Cr-containing member.

[0049] The anode current collecting member 144 is a member that connects the interconnector 190 and the anode 116 and is made of Ni. The anode current collecting member 144 is formed of foil having a thickness in the vertical direction (the length L1 shown in FIG. 8) of 30 μm or more. As shown in FIGS. 5 and 6 , the anode current collecting member 144 has 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 is U-shaped overall. The electrode facing portion 145 is joined to the anode 116, and the interconnector facing portion 146 is joined to a flat portion 191 of the interconnector 190. The anode current collecting member 144 is disposed between the unit cell 110 and the interconnector 190. Note that in this specification, "made of Ni" means a configuration in which Ni accounts for 90 wt % or more, and is not limited to a configuration made only of Ni. The anode current collecting member 144 is an example of a member made of Ni.

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

[0051] However, as shown in Figure 2, the power generating unit 100U located at the other end (the lower end in Figure 2) of the multiple power generating units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 included in this power generating unit 100U is connected to the second terminal plate 250 via the fuel electrode current collecting 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. This allows the anode current collecting member 144 to follow deformation of the power generating unit 100U due to temperature cycles and reactant gas pressure fluctuations, and good electrical connection is maintained between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144.

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

[0054] 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 forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the entire periphery of the fuel chamber 323 from the external space, and seals the gap between the single cell separator 120 and the IC separator 180, thereby preventing gas from leaking from the fuel chamber 323 to the external space.

[0055] The single cell separator 120 separates the air chamber 313 and the fuel chamber 323, thereby preventing 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. In addition, the IC separator 180 and the interconnector 190 prevent gas leakage between adjacent power generating units 100U.

[0056] A-2. Operation of fuel cell stack 10: As shown in Figures 2 and 5, the oxidizing gas OG is supplied to the oxidizing gas supply manifold 311 via a gas pipe (not shown) and a gas passage member 280, and is supplied to the air chamber 313 via the oxidizing gas supply communicating passage 132.

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

[0058] When an oxidant gas OG is supplied to the air chamber 313 of each power generating unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power is generated in the unit cell 110 by an electrochemical reaction between the oxidant gas OG and the fuel gas FG. This power generation reaction is exothermic. As described above, the interconnector 190 is shared by two adjacent power generating units 100U, and the interconnector 190 ensures electrical continuity between the two adjacent power generating units 100U. In other words, the multiple power generating units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, a second terminal plate 250 is electrically connected to the power generating unit 100U located at the other end (the lower end in FIG. 2 ) of the multiple power generating units 100U, and a first terminal plate 240 is electrically connected to the power generating unit 100U located at one end (the upper end in FIG. 2 ). As a result, electrical energy generated in each power generating unit 100U is extracted from the terminal plates 240, 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (e.g., 700°C to 1000°C), after startup, the fuel cell stack 10 may be heated by a heater (not shown) until the high temperature can be maintained using the heat generated by power generation.

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

[0060] A-3. Detailed configuration of current collecting structure 160: 7 and 8 are XZ cross-sectional views showing the detailed configuration of the current collecting structure 160 of the first embodiment. FIG. 7 shows an enlarged view of the X1 portion of FIG. 6. FIG. 8 shows an enlarged view of the X2 portion of FIG. 7. The anode current collecting member 144 and the interconnector 190 are aligned in the vertical direction. As shown in FIG. 8, a surface 191S of a flat plate portion 191 of the interconnector 190 and a surface 144S of the anode current collecting member 144 face each other in the vertical direction. In the current collecting structure 160, the surfaces 191S and 144S are joined to each other to form a joint CP at which the interconnector 190 and the anode current collecting member 144 are joined to each other. Specifically, the joint CP refers to the portion where the interconnector 190 and the anode current collecting member 144 are in physical contact with each other, and refers to the portion where there is no gap of 1 μm or more between the interconnector 190 and the anode current collecting member 144 when a cross section perpendicular to the XY plane is observed using an SEM (for example, a Keyence VE-9800; the same applies below).

[0061] The current collecting structure 160 is configured so that, when heat-treated at 900°C for 100 hours in a reducing gas atmosphere containing water vapor (for example, gas volume flow rates of HO / H=1 and H / N=0.1), the Cr concentration inside the anode current collecting member 144 located near the joint CP is 1 atm% or higher. In other words, the current collecting structure 160 is configured so that the Cr contained in the interconnector 190 diffuses into the anode current collecting member 144 during operation of the fuel cell stack 10. As a result, an internal oxidation layer IN containing Cr oxide (for example, CrO) is formed inside the anode current collecting member 144 located near the joint CP during operation of the fuel cell stack 10 (see FIG. 8).

[0062] FIG. 9 is an explanatory diagram outlining a method for measuring the Cr concentration of the current collecting structure 160. In this specification, "the vicinity of the joint CP" refers to a portion of the anode current collecting member 144 sandwiched between positions 6 μm and 12 μm away from the surface 144S. The Cr concentration is measured by cutting the anode current collecting member 144 at a cross section perpendicular to the XY plane, including the joint CP, and performing SEM / EDX analysis on the periphery of the joint CP. That is, as shown in FIG. 9, the Cr content of each 6 μm square region sandwiched between positions 6 μm and 12 μm away from the joint CP in the direction of the anode current collecting member 144 is divided by the total content of Cr, Ni, and Fe to determine the Cr concentration (atm %), thereby determining the Cr concentration near the joint CP. The phrase "the Cr concentration inside the anode current collecting member 144 located near the joint CP is 1 atm% or more" means that the Cr concentration is 1 atm% or more in at least one region among each 6 μm square region in any cross section including the joint CP in the fuel cell stack 10. In other words, the Cr concentration near the joint CP before the heat treatment is less than 1 atm%.

[0063] The anode current collecting member 144 has a porous layer PL located closer to the joint CP than the vertical center of the anode current collecting member 144 (i.e., the position of the center line CL that vertically bisects the anode current collecting member 144). The porosity of the porous layer PL can be measured by observing a cross section perpendicular to the XY plane using an SEM, and is preferably 1% to 50%, more preferably 5% to 30%. The vertical thickness of the porous layer PL is preferably 5 μm or less. The porous layer PL is preferably located on the periphery of the joint CP.

[0064] Furthermore, surface 191S of flat plate portion 191 of interconnector 190 is kept below a predetermined roughness. More specifically, surface 191S has a ten-point average roughness of 10 μm or less as defined in JIS B 0601. The roughness of surface 191S can be measured, for example, as follows: A sample is cut out from fuel cell stack 10 so as to include joint portion CP between interconnector 190 and anode current collecting member 144, and a profile curve of surface 191S is obtained from an image of a cross section perpendicular to the XY plane magnified 500 times by SEM, and the ten-point average roughness Rz is obtained in accordance with JIS B 0601.

[0065] A-4. Method for manufacturing current collecting structure 160: Fig. 10 is a flowchart showing a method for manufacturing the current collecting structure 160. Fig. 11 is an explanatory diagram schematically showing the interface between the interconnector 190 and the anode current collecting member 144 during the manufacturing process of the current collecting structure 160. The current collecting structure 160 can be manufactured, for example, as follows.

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

[0067] Next, the interconnector 190 and the anode current collecting member 144 are pressure-bonded together (S12). Specifically, the interconnector 190 and the anode current collecting member 144 are pressure-bonded together 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 determined, for example, from an Ellingham diagram. The type of gas is not particularly limited as long as the oxygen partial pressure is equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO. S12 is an example of a bonding process.

[0068] 11(A), before step S12 is performed, a gap SP exists at the interface between interconnector 190 and anode current collecting member 144. On the other hand, after step S12 is performed, as shown in Fig. 11(B), Ni contained in anode current collecting member 144 is oxidized to NiO, causing volume expansion, and the gap SP is filled with a nickel oxide layer NOL. This improves the adhesion between interconnector 190 and anode current collecting member 144.

[0069] Next, interconnector 190 and anode current collecting member 144 are heated while being pressurized (S13). Specifically, in a reducing gas atmosphere, interconnector 190 and anode current collecting member 144 are heated at a temperature of 800°C or higher while being pressurized in the vertical direction in which interconnector 190 and anode current collecting 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 step.

[0070] As shown in FIG. 11(C), after step S13, the nickel oxide layer NOL changes into a porous layer PL. That is, volume shrinkage occurs due to the reduction of NiO in the nickel oxide layer NOL to Ni, resulting in the formation of porous portions. In step S13, heating and pressure are applied, so the porous layer PL becomes a relatively dense layer. Furthermore, the resistance value of the current collecting structure 160 decreases as NiO is reduced to Ni, which has higher conductivity.

[0071] A-5. Advantages of this embodiment: As described above, the current collecting structure 160 of this embodiment includes an interconnector 190 made of an alloy containing Cr, and an anode current collecting member 144 made of Ni, which is joined to the interconnector 190. When the current collecting 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 anode current collecting member 144 located near the joint CP where the interconnector 190 and the anode current collecting member 144 are joined is 1 atm% or more.

[0072] According to the current collecting structure 160 of this embodiment, the Cr contained in the interconnector 190 is sufficiently diffused into the anode current collecting member 144 during operation of the fuel cell stack 10, thereby improving the adhesion at the interface between the interconnector 190 and the anode current collecting member 144 and suppressing the formation of an oxide film. This suppresses a decrease in the conductivity between the interconnector 190 and the anode current collecting member 144, thereby suppressing an increase in the resistance value of the fuel cell stack 10 and improving the durability of the fuel cell stack 10.

[0073] Furthermore, in the current collecting structure 160 of the present embodiment, when the direction in which the anode current collecting member 144 and the interconnector 190 are aligned with each other via the joint CP is defined as the vertical direction, the anode current collecting member 144 has a porous layer PL with a higher porosity than the central portion on the joint CP side of the vertical center of the anode current collecting member 144. According to the current collecting structure 160 of the present embodiment, the porous layer PL with a higher porosity than the central portion is present on the joint CP side of the vertical center of the anode current collecting member 144. Therefore, when, for example, joining process of the interconnector 190 and the anode current collecting member 144 is performed in a high-temperature environment during production of the fuel cell stack 10, stress caused by the difference in thermal expansion between the interconnector 190 and the anode current collecting member 144 can be alleviated. This suppresses peeling at joint CP between interconnector 190 and anode current collecting member 144, improves adhesion between interconnector 190 and anode current collecting member 144, and the Cr contained in interconnector 190 is sufficiently diffused into the inside of anode current collecting member 144, thereby suppressing the formation of an oxide film at the interface between interconnector 190 and anode current collecting member 144. This suppresses a decrease in conductivity between interconnector 190 and anode current collecting member 144, thereby suppressing an increase in the resistance value of fuel cell stack 10 and more effectively improving the durability performance of fuel cell stack 10.

[0074] Furthermore, in the current collecting structure 160 of this embodiment, the porous layer PL has a vertical thickness of 5 μm or less. According to the current collecting structure 160 of this embodiment, the anode current collecting member 144 has a porous layer PL with a vertical thickness of 5 μm or less. Therefore, peeling of the joint CP between the interconnector 190 and the anode current collecting member 144 during the manufacture of the fuel cell stack 10 can be suppressed, and oxygen can be suppressed from entering the joint CP during operation of the fuel cell stack 10. This suppresses a decrease in conductivity between the interconnector 190 and the anode current collecting member 144, thereby suppressing an increase in the resistance value of the fuel cell stack 10 and more effectively improving the durability of the fuel cell stack 10.

[0075] In the current collecting structure 160 of this embodiment, the anode current collecting member 144 is formed of a foil having a thickness of 30 μm or more. During operation of the fuel cell stack 10, Cr diffused from the interconnector 190 reacts with oxygen dissociated from HO contained in the gas in the fuel cell stack 10 inside the anode current collecting member 144, thereby forming an internal oxide layer IN inside the anode current collecting member 144. When the internal oxide layers IN grow on the surface on the joint CP side and on the surface on the vertical opposite side from the joint CP, if the thickness of the anode current collecting member 144 is thin, the distance between the surfaces is short, and the internal oxide layers IN formed on the surfaces may be connected to each other, thereby blocking the conduction path from the interconnector 190 to the anode 116 inside the anode current collecting member 144. In the current collecting structure 160 of this embodiment, the anode current collecting member 144 is formed of a foil having a thickness of 30 μm or more. This makes the distance between the surfaces relatively long, preventing the conduction path from being interrupted, thereby preventing a decrease in conductivity between the interconnector 190 and the anode current collecting member 144, and thus preventing an increase in the resistance value of the fuel cell stack 10, thereby more effectively improving the durability of the fuel cell stack 10.

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

[0077] During the manufacture of the fuel cell stack 10, when the interconnector 190 and the anode current collecting member 144 are joined, for example, volume expansion that occurs when Ni is oxidized to NiO may be utilized to form NiO in the gap SP between the interconnector 190 and the anode current collecting member 144, thereby improving the adhesion between the interconnector 190 and the anode current collecting member 144. If a reduction process is subsequently performed to convert NiO to Ni, which has higher conductivity, volume contraction accompanying the conversion of NiO to Ni causes a porous layer PL to be formed in the anode current collecting member 144. If the porous layer PL is thick, oxygen may easily penetrate into the joint CP during operation of the fuel cell stack 10, forming an oxide film at the interface between the interconnector 190 and the anode current collecting member 144 and resulting in an increase in resistance. According to the current collecting structure 160 of this embodiment, the surface 191S of the interconnector 190 that is joined to the anode current collecting member 144 has a ten-point average roughness of 10 μm or less as defined by JIS B 0601. This prevents the gap SP between the interconnector 190 and the anode current collecting member 144 from becoming excessively large, thereby suppressing the thickness of the porous layer PL formed in the anode current collecting member 144 and inhibiting the intrusion of oxygen into the joint CP during operation of the fuel cell stack 10. This prevents the formation of an oxide film at the interface between the interconnector 190 and the anode current collecting member 144, inhibits a decrease in conductivity between the interconnector 190 and the anode current collecting member 144, and ultimately inhibits an increase in the resistance value of the fuel cell stack 10, making it possible to more effectively improve the durability of the fuel cell stack 10.

[0078] The fuel cell stack 10 of this embodiment also includes a current collecting structure 160 and a single cell 110 electrically connected to the current collecting structure 160.

[0079] According to the fuel cell stack 10 of this embodiment, during operation, Cr contained in the interconnector 190 of the current collecting structure 160 is sufficiently diffused into the inside of the anode current collecting member 144, thereby improving the adhesion at the interface between the interconnector 190 and the anode current collecting member 144 and suppressing the formation of an oxide film. This suppresses a decrease in the conductivity between the interconnector 190 and the anode current collecting member 144, thereby suppressing an increase in the resistance value of the fuel cell stack 10 and improving the durability of the fuel cell stack 10.

[0080] The manufacturing method of the current collecting structure 160 of this embodiment also includes a bonding step S12 in which the interconnector 190 and the anode current collecting member 144 are pressure-bonded together 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 collecting structure 160 of the present embodiment, by utilizing the volume expansion that occurs when Ni is oxidized to NiO during the joining step S12, NiO is formed in the gap SP between the interconnector 190 and the anode current collecting member 144, thereby improving the adhesion between the interconnector 190 and the anode current collecting member 144 and suppressing the formation of an oxide film. This suppresses a decrease in the conductivity between the interconnector 190 and the anode current collecting member 144, thereby suppressing an increase in the resistance value of the fuel cell stack 10 and improving the durability of the fuel cell stack 10.

[0082] Furthermore, the manufacturing method of the current collecting structure 160 of this embodiment further includes, after the joining step S12, a reduction step S13 in which the interconnector 190 and the anode current collecting member 144 are heated at a temperature of 800°C or higher while applying pressure to them in a reducing gas atmosphere in the vertical direction in which the interconnector 190 and the anode current collecting member 144 are arranged. According to the manufacturing method of the current collecting structure 160 of this embodiment, by applying pressure, it is possible to reduce NiO to Ni, which has higher conductivity, while suppressing a decrease in adhesion between the interconnector 190 and the anode current collecting member 144 due to volumetric shrinkage accompanying the reduction of NiO to Ni in the reduction step S13. Furthermore, because NiO is reduced to Ni at a temperature of 800°C or higher, the NiO can be reliably reduced. This suppresses an increase in the resistance value of the fuel cell stack 10, and more effectively improves the durability of the fuel cell stack 10.

[0083] A-6. Performance evaluation: Next, performance evaluation of this embodiment will be described. Multiple samples of the fuel cell stack 10, each including a current collecting structure 160 with various different physical properties, were fabricated, and performance evaluation was carried out using these multiple samples. Tables 1 to 3 show the performance evaluation results.

[0084] (Preparation of evaluation samples) The current collecting structure 160 was fabricated using the method described above in "A-4. Manufacturing method of current collecting structure 160." Specifically, the components constituting the fuel cell stack 10 were stacked, and the components from the first end plate 210 to the second end plate 270 were fastened together using bolts B and nuts N, and then the joining step S12 and the reduction step S13 were carried out. By varying the configuration of the anode current collecting member 144, the conditions for the joining step S12, and the conditions for the reduction step S13, current collecting structures 160 with various different physical properties were fabricated. Samples of fuel cell stacks 10 each including a current collecting structure 160 with various different physical properties were then fabricated using a known method, and the following performance evaluations were performed.

[0085] (Performance evaluation - Cr concentration after heat treatment) A portion including the interconnector 190 and the anode current collecting member 144 was cut out from the fuel cell stack 10 fabricated by the above method and subjected to a heat treatment at 900°C for 100 hours in a reducing gas atmosphere containing water vapor (HO / H=1, H / N=0.1). After the heat treatment, the sample was cut at a cross section perpendicular to the XY plane and including the joint CP, and the Cr concentration of each sample of the fuel cell stack 10 was measured by the above method.

[0086] (Performance evaluation - stack deterioration rate) The fuel cell stack 10 manufactured by the above method was started to operate at 700°C, and the potential V I After that, the temperature is kept at 700°C and the voltage V is measured after 10,000 hours of continuous operation. E The stack deterioration rate due to continuous operation of each sample of the fuel cell stack 10 was calculated using the following formula. Stack deterioration rate (%) = 100 × (V I -V E ) / V I

[0087] (Performance evaluation results) Table 1 shows the performance evaluation results. [Table 1]

[0088] Table 1 and the following tables show the configuration of anode current collecting member 144 and interconnector 190 for each sample, the conditions for joining step S12, the conditions for reducing step S13, and the performance evaluation results. In each table, "flowing gas" refers to the type of gas supplied to fuel chamber 323 via fuel gas supply manifold 321 or fuel gas discharge manifold 322 during joining step S12. Furthermore, "Cr concentration after heat treatment" refers to the average Cr concentration in each 6-μm square region sandwiched between a position 6 μm and a position 12 μm away from joint CP in the direction of anode current collecting member 144, when the Cr concentration was measured at an arbitrary cross section including joint CP.

[0089] Table 1 shows samples S1 to S3. Of 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. Furthermore, the stack deterioration rate of sample S1 was relatively high, while the stack deterioration rates of samples S2 and S3 were relatively low. From the above, it was confirmed that there is a correlation between the Cr concentration after heat treatment and the stack deterioration rate, and that the higher the Cr concentration after heat treatment, the lower the stack deterioration rate (i.e., the higher the durability performance of the fuel cell stack 10).

[0090] Furthermore, among samples S1 to S3, sample S1 does not have a porous layer PL, while samples S2 and S3 have a porous layer PL. This confirms that the presence or absence of a porous layer PL correlates with the stack deterioration rate, and that samples having a porous layer PL have a low stack deterioration rate. In other words, it is believed that the presence of porous layer PL improves the adhesion between interconnector 190 and anode current collecting member 144, and as a result, Cr in interconnector 190 is sufficiently diffused inside anode current collecting member 144, thereby suppressing the stack deterioration rate.

[0091] The presence or absence of the porous layer PL is considered to be due to the conditions of the joining step S12. That is, in sample S1, the relatively low oxygen partial pressure in the joining step S12 is considered to have prevented the Ni of the anode current collecting member 144 from being oxidized to NiO, and as a result, the porous layer PL was not formed. In samples S2 and S3, the relatively high oxygen partial pressure in the joining step S12 is considered to have prevented the Ni of the anode current collecting member 144 from being oxidized to NiO, and as a result, the porous layer PL was formed.

[0092] Table 2 shows the performance evaluation results. [Table 2]

[0093] Table 2 shows samples S4 and S5. Sample S4 had a porous layer PL of the anode current collecting member 144 with a thickness of greater than 5 μm, whereas sample S5 had a porous layer PL of the anode current collecting member 144 with a thickness of 5 μm or less. The stack deterioration rate of sample S4 was relatively high, while the stack deterioration rate of sample S5 was relatively low. This confirmed that the thickness of the porous layer PL correlates with the stack deterioration rate, and that a porous layer PL of 5 μm or less reduces the stack deterioration rate.

[0094] The thickness of the porous layer PL is considered to be due to the conditions of the reduction step S13. That is, in sample S4, the reduction temperature in the reduction step S13 was lower than 800°C, which is considered to have prevented the porous layer PL from being densified, whereas in sample S5, the reduction temperature in the reduction step S13 was 800°C or higher, which is considered to have prevented the porous layer PL from being densified.

[0095] Table 3 shows the performance evaluation results. [Table 3]

[0096] Table 3 shows samples S6 to S8. The anode current collecting member 144 of sample S6 was foil-shaped and had a thickness of less than 30 μm. The anode current collecting member 144 of sample S7 was foil-shaped and had a thickness of 30 μm or more. The anode current collecting member 144 of sample S8 was mesh-shaped and had a wire diameter of 60 μm or more. The stack deterioration rate of sample S6 was relatively high, while the stack deterioration rates of samples S7 and S8 were relatively low. From the above, it was confirmed that the thickness of the anode current collecting member 144 correlates with the stack deterioration rate, and that the thicker the anode current collecting member 144, the lower the stack deterioration rate. The configuration in which the anode current collecting member 144 is mesh will be described in detail later.

[0097] B. Second embodiment: 12 is an XZ cross-sectional view showing the detailed configuration of the current collecting structure 160a of the second embodiment. In the following, among the configuration of the fuel cell stack 10 of the second embodiment, the same configuration as that of the fuel cell stack 10 of the first embodiment described above will be denoted by the same reference numerals and the description thereof will be omitted as appropriate.

[0098] The current collecting structure 160a of the second embodiment differs from the current collecting structure 160 of the first embodiment in the configuration of the anode current collecting member. Specifically, in the current collecting structure 160a of the second embodiment, the anode current collecting member 144a is configured as a mesh. The anode current collecting member 144a is configured of multiple wires made of Ni, and wires extending in the X-axis direction and wires extending in the Y-axis direction form a mesh structure. The anode current collecting member 144a has a wire diameter (length L2 shown in FIG. 12) of 60 μm or more.

[0099] As described above, in the current collecting structure 160a of the second embodiment, the anode current collecting member 144a is formed of a mesh having a wire diameter of 60 μm or more. During operation of the fuel cell stack 10, Cr diffused from the interconnector 190 reacts with oxygen dissociated from HO contained in the gas in the fuel cell stack 10 inside the anode current collecting member 144a, forming an internal oxide layer IN inside the anode current collecting member 144a. When the internal oxide layers IN grow on the surface on the joint CP side and on the surface opposite the joint CP in the vertical direction, if the thickness of the anode current collecting member 144a is thin, the distance between the surfaces is short, and the internal oxide layers IN formed on the respective surfaces may be connected, blocking the electrical path inside the anode current collecting member 144a. According to the current collecting structure 160a of the present embodiment, the anode current collecting member 144a is formed of a mesh having a wire diameter of 60 μm or more. This makes the distance between the surfaces relatively long, preventing the conduction path from being interrupted, thereby preventing a decrease in conductivity between the interconnector 190 and the anode current collecting member 144a, and thus preventing an increase in the resistance of the fuel cell stack 10, thereby more effectively improving the durability of the fuel cell stack 10.

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

[0101] The configurations of the fuel cell stack 10 and the power generating units 100U in the above embodiment are merely examples and can be modified in various ways. For example, the number of unit cells 110 included in the fuel cell stack 10 in the above embodiment (the number of power generating units 100U) is merely an example, and the number of unit cells 110 is determined appropriately depending on the output voltage required for the fuel cell stack 10.

[0102] The materials constituting each member in the above embodiment are merely examples, and each member may be made of other materials.

[0103] In the above embodiment, the current collecting structure 160 has a porous layer PL, but the current collecting structure does not necessarily have to have a porous layer. Also, in the above 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 collecting member 144 is formed from a foil having a thickness of 30 μm or more, and in the second embodiment, the fuel electrode current collecting member 144a is formed from a mesh having a wire diameter of 60 μm or more, but the shape of the Ni member is not limited to these, and its thickness is not limited to these either.

[0105] In the above embodiment, the ten-point mean roughness of the surface 191S is 10 μm or less, but the roughness of the surface of the Cr-containing member to be joined to the Ni member is not limited to this.

[0106] The method for manufacturing the current collecting structure is not limited to the above 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 counter-flow type SOFCs and cross-flow type SOFCs.

[0108] In the above embodiment, the unit cell 110 is an anode-supported unit cell, but it may be another type of unit cell such as an electrolyte-supported type or a metal-supported type.

[0109] In the current collecting structure 160 of the above embodiment, the interconnector 190 is an example of a Cr-containing member, but the Cr-containing member is not limited thereto. For example, if the first plate 232 in the above embodiment contains Cr, the first plate 232 can also be an example of a Cr-containing member, and if the metal support in a metal-supported unit cell contains Cr, the metal support can also be an example of a Cr-containing member. Similarly, in the current collecting structure 160 of the above embodiment, the anode current collecting member 144 is an example of a Ni member, but the Ni member is not limited thereto.

[0110] In the above embodiment, the fuel cell stack 10 is configured to have a plurality of flat-type unit cells 110, but the present invention is equally applicable to fuel cell stacks that have a plurality of unit cells of other types (e.g., cylindrical, flat cylindrical, etc.).

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

[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: single cell separator 121: through hole 124: joint portion 130: air electrode frame 131: through hole 132: oxidant gas supply communication channel 133: oxidant gas discharge communication channel 140: fuel electrode frame 141: through hole 142: fuel gas supply communication channel 143: fuel gas discharge communication channel 144, 144a: fuel electrode current collecting member 144S: surface 145: electrode facing portion 146: interconnector facing portion 147: connecting portion 149: spacer 160, 160a: current collecting structure 180: IC separator 181: through hole 190: Interconnector 191: Flat plate portion 191S: Surface 192: Air electrode current collecting portion 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat portion 212: Through hole 213: Outer convex portion 214: Inner convex portion 220: Insulating portion 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: Flat portion 272: Through hole 273: Outer convex portion 274: Inner convex portion 280: Gas passage member 281: Main body portion 282: Flange portion 283: Gas through hole 284: Bolt hole 311: Oxidant gas supply manifold 312: Oxidizer gas exhaust manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas exhaust manifold 323: Fuel chamber B: Bolt BH: Bolt hole N: Nut FG: Fuel gas FOG: Fuel off-gas OG: Oxidizer gas OOG: Oxidizer off-gas CP: Joint IN: Inner 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; a Ni member formed from Ni and joined to the Cr-containing member; A current collecting structure for an electrochemical reaction cell stack, comprising: When the current collecting structure for an electrochemical reaction cell stack 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 Ni member located in the vicinity of the joint where the Cr-containing member and the Ni member are joined is 1 atm% or more. A current collecting structure for an electrochemical reaction cell stack, comprising:

2. The current collecting structure for an electrochemical reaction cell stack according to claim 1, When a direction in which the Ni member and the Cr-containing member are aligned with each other through the joint is defined as a first direction, the Ni member has a porous layer that is closer to the joint than a center portion of the Ni member in the first direction, and the porous layer has a higher porosity than the center portion. A current collecting structure for an electrochemical reaction cell stack, comprising:

3. The current collecting 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 collecting structure for an electrochemical reaction cell stack, comprising:

4. The current collecting structure for an electrochemical reaction cell stack according to claim 1, The Ni member is formed of a foil having a thickness of 30 μm or more, or a mesh having a wire diameter of 60 μm or more. A current collecting structure for an electrochemical reaction cell stack, comprising:

5. The current collecting structure for an electrochemical reaction cell stack according to claim 2, The surface of the Cr-containing member to be joined to the Ni member has a ten-point average roughness of 10 μm or less as defined in JIS B 0601. A current collecting structure for an electrochemical reaction cell stack, comprising:

6. A current collecting structure for an electrochemical reaction cell stack according to claim 1, and a unit cell electrically connected to the current collecting structure for an electrochemical reaction cell stack. An electrochemical reaction cell stack comprising:

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

8. The method for producing a current collecting structure for an electrochemical reaction cell stack according to claim 7, further comprising: a reduction step of heating the Cr-containing member and the Ni-made member at a temperature of 800°C or higher while applying pressure to them in a first direction in which the Cr-containing member and the Ni-made member are aligned under a reducing gas atmosphere after the joining step; A method for manufacturing a current collecting structure for an electrochemical reaction cell stack, comprising:

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