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 conductive member joined to the Cr-containing member. With respect to a joint portion of the Cr-containing member and the conductive member, the proportion of a portion where the thickness of an oxide film on the surface of the Cr-containing member is 0.1 μm or less or a metal joint portion where no oxide film exists is equal to 0.0005% 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. SOFCs are 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 that is an alloy containing Cr, and a fuel electrode side current collector (conductive member) joined to the interconnector. An oxidation-resistant film (oxide film) is formed on the surface of the interconnector on the side facing the fuel electrode side current collector (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 conductive 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 conductive member is affected by the bondability between the Cr-containing member and the conductive member. Specifically, in the current collector structure, during the operation of the fuel cell stack, the adhesion between the Cr-containing member and the conductive member is improved by the mutual diffusion of metals between the Cr-containing member and the conductive member. However, when an oxide film exists on the interface between the Cr-containing member and the conductive member to a certain extent or more, the diffusion path of the metal becomes narrow, the mutual diffusion of the metals becomes insufficient, and as a result, the adhesion between the Cr-containing member and the conductive member decreases, and the oxide film on the interface between the Cr-containing member and the conductive member further grows. Therefore, there is a problem that the conductivity between the Cr-containing member and the conductive member decreases, which in turn causes an increase in the resistance value of the fuel cell stack and 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 electrolytic cell stack which is a form of an electrolytic cell (hereinafter referred to as "SOEC") that generates hydrogen by utilizing electrolysis of water. In this specification, a fuel cell single cell and an electrolytic single cell are collectively referred to as an electrochemical reaction single cell, and a fuel cell stack and an electrolytic 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 of an alloy containing Cr, and a conductive member joined to the Cr-containing member. Among the joints where the Cr-containing member and the conductive member are joined, the proportion occupied by the metal joint, which is a portion where the thickness of the oxide film on the surface of the Cr-containing member is 0.1 μm or less, or a portion where the oxide film does not exist, is 0.0005% or more.

[0010] According to this current collecting structure for an electrochemical reaction cell stack, among the joints where the Cr-containing member and the conductive member are joined, the proportion occupied by the metal joint is 0.0005% or more. As a result, during the operation of the electrochemical reaction cell stack, the metal diffuses sufficiently between the Cr-containing member and the conductive member, thereby improving the adhesion between the Cr-containing member and the conductive member. Therefore, it is possible to suppress a decrease in conductivity between the Cr-containing member and the conductive member, and thus suppress an increase in the resistance value of the electrochemical reaction cell stack, and improve the durability performance of the electrochemical reaction cell stack.

[0011] (2) In the above current collecting structure for an electrochemical reaction cell stack, the conductive member may be configured to be formed of at least one of Ni, a Ni-Cr alloy, or stainless steel. According to this configuration, compared with a current collecting structure for an electrochemical reaction cell stack including a conductive member containing Ti or Al as a main component, for example, the generation of highly resistive reaction products (for example, NiTiO3 or Al2O3) during the operation of the electrochemical reaction cell stack is suppressed. Therefore, it is possible to suppress a decrease in conductivity between the Cr-containing member and the conductive member, and thus suppress an increase in the resistance value of the electrochemical reaction cell stack, and more effectively improve the durability performance of the electrochemical reaction cell stack.

[0012] (3) In the current collector structure for the electrochemical reaction cell stack, when the direction in which the conductive member and the Cr-containing member are arranged via the joint portion is defined as the first direction, the conductive member may be configured such that a porous layer having a higher porosity than the central portion in the first direction of the conductive 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 in the first direction of the conductive member, when, for example, the joining process between the Cr-containing member and the conductive 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 conductive member can be alleviated. As a result, the peeling of the joint portion between the Cr-containing member and the conductive member is suppressed, and the adhesion between the Cr-containing member and the conductive member is improved by sufficient mutual diffusion of the metal between the Cr-containing member and the conductive member. Therefore, a decrease in the conductivity between the Cr-containing member and the conductive 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 more effectively improved.

[0013] (4) 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 conductive member, it is possible to suppress the peeling of the joint portion between the Cr-containing member and the conductive 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 growth of the oxide film at the interface between the Cr-containing member and the conductive member is suppressed, a decrease in the conductivity between the Cr-containing member and the conductive member is suppressed, and consequently, an 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.

[0014] (5) The electrochemical reaction cell stack disclosed in this specification includes the current collector structure for the electrochemical reaction cell stack described in (1) and a single cell electrically connected to the current collector structure for the electrochemical reaction cell stack.

[0015] According to this electrochemical reaction cell stack, during operation, metals diffuse sufficiently between the Cr-containing member and the conductive member, thereby improving the adhesion between the Cr-containing member and the conductive member. Therefore, a decrease in conductivity between the Cr-containing member and the conductive member can be suppressed, and thus 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.

[0016] (6) The manufacturing method of the current collector structure for an electrochemical reaction cell stack disclosed in this specification is the manufacturing method of the current collector structure for an electrochemical reaction cell stack described in (1), and includes a joining step of joining the conductive member and the Cr-containing member under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which the metal contained in the conductive member is oxidized.

[0017] According to the manufacturing method of this current collector structure for an electrochemical reaction cell stack, during the joining step, the metal contained in the conductive member becomes a metal oxide and expands in volume, and a metal oxide is formed in the gap between the Cr-containing member and the conductive member, thereby improving the adhesion between the Cr-containing member and the conductive member. Therefore, a decrease in conductivity between the Cr-containing member and the conductive member can be suppressed, and thus 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.

[0018] Note that the technology disclosed in this specification can be realized in various forms, for example, in the forms of a current collector structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a manufacturing method of a current collector structure for an electrochemical reaction cell stack.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0020] A. Embodiment: A-1. Configuration of the fuel cell stack 10: FIG. 1 is a perspective view showing the external configuration of the fuel cell stack 10, FIG. 2 is an explanatory drawing showing the XZ cross-sectional configuration of the fuel cell stack 10 at the position of II-II in FIG. 1, FIG. 3 is an explanatory drawing showing the XZ cross-sectional configuration of the fuel cell stack 10 at the position of III-III in FIG. 1, and FIG. 4 is an explanatory drawing showing the YZ cross-sectional configuration of the fuel cell stack 10 at the position of 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.

[0021] (Overall Structure 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).

[0022] As shown in FIGS. 1 and 4, the fuel cell stack 10 has bolt holes BH that penetrate 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.

[0023] 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).

[0024] (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, and an outer convex portion 213 and an inner convex portion 214 that protrude in a direction opposite to the insulating portion 220 (upward in FIG. 2) from the flat portion 211. The flat portion 211 has holes that constitute 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 circumference of the outer peripheral portion 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 circumference of the inner peripheral portion of the flat portion 211.

[0025] (Insulating portion 220) The insulating portion 220 is a rectangular frame-shaped member having a through hole near the center, and is formed of an insulating material, for example. As shown in FIG. 2, the insulating portion 220 is sandwiched between the first end plate 210 and the end separator 230, thereby ensuring insulation between the first end plate 210 and the end separator 230.

[0026] (End separator 230) As shown in FIGS. 2 to 4, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near the center, and is formed of metal, for example.

[0027] (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, for example. As shown in FIGS. 2 to 4, the first plate 232 is joined to the peripheral edge portion of the through hole 231 in the end separator 230 by welding, for example. The end separator 230 and the first plate 232 partition the power generation block 100 from the external space of the fuel cell stack 10.

[0028] 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 via a connection member having the same structure as the fuel electrode current collector member 144 described later. Thus, the power generation unit 100U and the first plate 232 are electrically connected.

[0029] (The 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 constituting 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 projects laterally from the power generation block 100, and this projecting portion functions as the positive output terminal of the fuel cell stack 10.

[0030] (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 constituting the power generation block 100. One end portion (the right end portion in FIG. 2) of the second terminal plate 250 projects laterally from the power generation block 100, and this projecting portion functions as the negative output terminal of the fuel cell stack 10.

[0031] (The second plate 260) The second plate 260 is a rectangular flat plate-like member and is formed of, for example, an insulating material. 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.

[0032] (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, for example, a conductive material such as stainless steel. The second end plate 270 includes a rectangular frame-shaped 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 a direction opposite to the second terminal plate 250 (downward in FIG. 2). The flat 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 flat portion 271. The outer convex portion 273 is formed over the entire outer periphery of the flat portion 271. The inner convex portion 274 protrudes from the inner peripheral edge of the flat portion 271. The inner convex portion 274 is formed over the entire inner periphery of the flat portion 271.

[0033] (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.

[0034] As shown in FIG. 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 the air chamber 313 (described below) 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 therebetween.

[0035] As shown in FIG. 3, the fuel gas supply manifold 321 is a gas flow path that supplies the fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chamber 323 (described below) 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 therebetween.

[0036] (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 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 provided in the four gas passage members 280 is joined to the second end plate 270, for example, by welding, and the gas through-holes 283 communicate with the manifolds 311, 312, 321, and 322, respectively. A gas pipe for supplying or discharging gas is connected to each main body portion 281 (not shown).

[0037] (Overall Configuration of 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 for IC 180. One separator for IC 180, the air electrode frame 130, the separator for single cell 120, the fuel electrode frame 140, and the other separator for IC 180 are arranged to overlap in this order.

[0038] (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.

[0039] The electrolyte layer 112 is a rectangular flat plate member, having one surface (the upper surface in FIGS. 5 and 6) where the air electrode 114 is disposed, and the other surface parallel to one surface (the lower surface in FIGS. 5 and 6) where the fuel electrode 116 is disposed. 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).

[0040] (Separator 120 for single cell) As shown in FIGS. 5 and 6, the separator 120 for single cell is a rectangular frame 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).

[0041] (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 flow path 132 that communicates the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communication flow path 133 that communicates the air chamber 313 and the oxidant gas discharge manifold 312.

[0042] (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 flow path 142 that communicates the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication flow path 143 that communicates the fuel chamber 323 and the fuel gas discharge manifold 322.

[0043] (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.

[0044] (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.

[0045] 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-like 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 arranged 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 arranged. The flat plate portion 191 is joined to the peripheral portion 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.

[0046] The fuel electrode current collecting member 144 is a member that connects the interconnector 190 and the fuel electrode 116 and is formed of at least one of Ni, a Ni-Cr alloy, or stainless steel. 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 arranged between the single cell 110 and the interconnector 190. The fuel electrode current collecting member 144 is an example of a conductive member.

[0047] 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 through 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 through the fuel electrode current collector member 144. Thereby, electrical continuity between two adjacent power generation units 100U is ensured.

[0048] 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 through the fuel electrode current collector member 144.

[0049] 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) through the fuel electrode current collector member 144 is maintained well.

[0050] (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 plays a role of preventing gas from leaking out of the air chamber 313 into the external space.

[0051] Further, the space defined 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.

[0052] 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. Further, the IC separator 180 and the interconnector 190 suppress gas leakage between adjacent power generation units 100U.

[0053] 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.

[0054] 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.

[0055] 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. Note that since the SOFC generates power at a relatively high temperature (for example, 700° C. to 1000° C.), the fuel cell stack 10 may be heated by a heater (not shown) until the high temperature can be maintained by the heat generated by power generation after startup.

[0056] 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 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.

[0057] A-3. Detailed Configuration of the Current Collection Structure 160: Figs. 7 and 8 are XZ cross-sectional views showing the detailed configuration of the current collector structure 160. 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 side by side in the vertical direction. Further, as shown in Fig. 8, the surface 191S of the flat plate portion 191 in 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 gap of 1 μm or more between the interconnector 190 and the fuel electrode current collector member 144. Further, an oxide film 194 is formed on a part of the interconnector 190, and the oxide film 194 constitutes a part of the surface 191S. The oxide film 194 mainly contains, for example, Cr2O3.

[0058] The current collector structure 160 further includes a metal joint portion MP. The metal joint portion MP means a portion of the joint portion CP between the interconnector 190 and the fuel electrode current collector member 144 where the oxide film 194 on the surface 191S of the interconnector 190 is extremely thin or the oxide film 194 does not exist. More specifically, the metal joint portion MP means a portion of the joint portion CP where the thickness of the oxide film 194 on the surface 191S is 0.1 μm or less or the oxide film 194 does not exist. In the current collector structure 160, the ratio occupied by the metal joint portion MP in the joint portion CP is 0.0005%. In consideration of the time required for manufacturing the current collector structure 160 and the ease of controlling the manufacturing conditions of the current collector structure 160, the ratio occupied by the metal joint portion MP in the joint portion CP is preferably 5% or less.

[0059] In the fuel electrode current collector member 144, a porous layer PL having a higher porosity than the central portion in the vertical direction in the fuel electrode current collector member 144 (that is, the position of the center line CL that virtually bisects the fuel electrode current collector member 144 in the vertical direction) exists on the joint portion CP side rather than the central portion. 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. Further, 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 portion CP.

[0060] A-4. Method for manufacturing the current collector structure 160: FIG. 9 is a flowchart showing a method for manufacturing the current collector structure 160. FIG. 10 is an explanatory diagram schematically showing the 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 as follows, for example.

[0061] First, the interconnector 190 and the fuel electrode current collector member 144 are prepared by a known method (S11).

[0062] 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 the metal (for example, Ni) contained in the fuel electrode current collector member 144 is oxidized. The oxygen partial pressure at which the metal contained in the fuel electrode current collector member 144 is oxidized can be obtained from, for example, an Ellingham diagram. Further, as long as the oxygen partial pressure is equal to or higher than the oxygen partial pressure at which the metal contained in the fuel electrode current collector member 144 is oxidized, the gas species are not particularly limited. S12 is an example of a bonding step.

[0063] As shown in Fig. 10(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. 10(B), after the step S12 is performed, volume expansion occurs due to oxidation of the metal contained in the fuel electrode current collector member 144, and the gap SP is filled with the metal oxide layer MOL. As a result, the adhesion between the interconnector 190 and the fuel electrode current collector member 144 is improved.

[0064] 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 step.

[0065] As shown in Fig. 10(C), after the step S13 is performed, the metal oxide layer MOL changes to a porous layer PL. That is, volume shrinkage occurs due to reduction of the metal oxide in the metal oxide layer MOL, 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. In addition, since the metal oxide is reduced to a metal with higher conductivity, the resistance value of the current collector structure 160 decreases.

[0066] 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 joined to the interconnector 190. Among the joint portions CP where the interconnector 190 and the fuel electrode current collector member 144 are joined, the ratio occupied by the metal joint portion MP, which is a portion where the thickness of the oxide film 194 on the surface of the interconnector 190 is 0.1 μm or less or a portion where no oxide film exists, is 0.0005% or more.

[0067] According to the current collector structure 160 of the present embodiment, among the joint portions CP where the interconnector 190 and the fuel electrode current collector member 144 are joined, the ratio occupied by the metal joint portion MP is 0.0005% or more. Thereby, during the operation of the fuel cell stack 10, the metal diffuses sufficiently between the interconnector 190 and the fuel electrode current collector member 144, improving the adhesion between the interconnector 190 and the fuel electrode current collector member 144. Therefore, a decrease in the 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, improving the durability performance of the fuel cell stack 10.

[0068] Further, in the current collector structure 160 of the present embodiment, the fuel electrode current collector member 144 is formed of at least one of Ni, Ni-Cr alloy, or stainless steel. According to the current collector structure 160 of the present embodiment, compared with a current collector structure including a fuel electrode current collector member containing Ti or Al as a main component, for example, the generation of high-resistance reaction products (for example, NiTiO3 or Al2O3) during the operation of the fuel cell stack 10 is suppressed. Therefore, a decrease in the 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, more effectively improving the durability performance of the fuel cell stack 10.

[0069] Also, 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 defined as the vertical direction, a porous layer PL having a porosity higher than that at the central portion in the vertical direction of the fuel electrode current collector member 144 exists on the joint portion CP side rather than the central portion of the fuel electrode current collector member 144. According to the current collector structure 160 of the present embodiment, since the porous layer PL having a porosity higher than that at the central portion in the vertical direction exists on the joint portion CP side rather than the central portion of the fuel electrode current collector member 144 in the vertical direction, when, for example, the joining process between 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 alleviated. As a result, the peeling of the joint portion CP between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, and the adhesion between the interconnector 190 and the fuel electrode current collector member 144 is improved by sufficient mutual diffusion of the metal between the interconnector 190 and the fuel electrode current collector member 144. Therefore, a decrease in the 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.

[0070] Also, 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 on the fuel electrode current collector member 144, it is possible to suppress the 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 and to suppress the intrusion of oxygen into the joint portion CP during the operation of the fuel cell stack 10. Therefore, the growth of the oxide film 194 at the interface between the interconnector 190 and the fuel electrode current collector member 144 is suppressed, a decrease in the 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 can be suppressed, and the durability performance of the fuel cell stack 10 can be more effectively improved.

[0071] Further, 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.

[0072] According to the fuel cell stack 10 of the present embodiment, during operation, the adhesion between the interconnector 190 and the fuel electrode current collector member 144 is improved by sufficient mutual diffusion of metals between the interconnector 190 and the fuel electrode current collector member 144. 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 improved.

[0073] Further, the manufacturing method of the current collector structure 160 of the present embodiment includes a joining step S12 of joining the fuel electrode current collector member 144 and the interconnector 190 under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which the metal contained in the fuel electrode current collector member 144 is oxidized.

[0074] According to the manufacturing method of the current collector structure 160 of the present embodiment, during the joining step S12, the metal contained in the fuel electrode current collector member 144 becomes a metal oxide and expands in volume, and a metal oxide 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. 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 improved.

[0075] 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.

[0076] (Fabrication of Evaluation Samples) The current collector structure 160 was fabricated by the method described in the above "A-4. Method for Manufacturing the Current Collector Structure 160". 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 with various physical properties were fabricated. Specifically, the members that would become the fuel cell stack 10 were laminated, and the joining step S12 and the reduction step S13 were carried out with the members from the first end plate 210 to the second end plate 270 fastened by bolts B and nuts N. Then, samples of the fuel cell stack 10 each having a current collector structure 160 with different physical properties were fabricated by known methods, and the following performance evaluations were conducted.

[0077] (Performance Evaluation - Ratio of Metal Joint MP) 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. The cut-out portion was cut along a cross-section including the joint portion CP, and observation of an image magnified 1000 times by SEM was performed. At this time, an observation field was selected where the length of the contour line of the joint portion CP was 80% or more with respect to the length of the contour line of the surface 191S of the interconnector 190. Next, elemental mapping by EPMA was performed within the selected observation field to identify the oxide film 194 present at the interface between the interconnector 190 and the fuel electrode current collector member 144. Specifically, for example, in view of the fact that the oxide film 194 mainly composed of Cr2O3 has a higher Cr concentration than the interconnector 190 formed from ferritic stainless steel, a portion constituting the surface 191S of the interconnector 190 and having a higher Cr concentration than the Cr concentration at the center of the interconnector 190 (that is, the position where the interconnector 190 is virtually bisected in the vertical direction) was identified as the oxide film 194. Among the joint portion CP, a portion where the thickness of the oxide film 194 identified by the above method was 0.1 μm or less was defined as the metal joint portion MP. Further, the lengths of the contour lines of the joint portion CP and the metal joint portion MP were measured, and the ratio of the length of the contour line of the metal joint portion MP to the length of the contour line of the joint portion CP was defined as the ratio (%) of the metal joint portion MP.

[0078] (Performance Evaluation - Stack Deterioration Rate) For the fuel cell stack 10 fabricated by the above method, the operation is started at 700 °C, and the potential V at the start of operation I is measured. Thereafter, continuous operation is performed for 10,000 hours at a temperature of 700 °C, and the potential V E is measured when 10,000 hours have elapsed since the start of operation. Using the following formula, the stack degradation rate due to continuous operation of each sample of the fuel cell stack 10 was calculated. Stack degradation rate (%) = 100×(V I - V E ) / V I

[0079] (Performance evaluation results) Table 1 is a table showing the performance evaluation results.

Table 1

[0080] In Table 1 and the tables hereinafter, the configurations of the fuel electrode current collector member 144 and the interconnector 190 of each sample, the conditions of the joining step S12, the conditions of the reduction step S13, and the performance evaluation results are shown. Among the descriptions in each table, "flowing gas" indicates the gas species supplied to the fuel chamber 323 via the fuel gas supply manifold 321 or the fuel gas discharge manifold 322 when performing the joining step S12. Also, "ten-point average roughness" means the roughness of the surface 191S of the interconnector 190. The measurement of the ten-point average roughness can be performed by cutting out from each sample so as to include the joint portion CP between the interconnector 190 and the fuel electrode current collector member 144, obtaining the contour curve of the surface 191S from an image magnified 500 times by SEM of a cross section orthogonal to the XY plane, and obtaining the ten-point average roughness Rz in accordance with JIS B 0601. Also, although the description is omitted in the table, the thickness of the fuel electrode current collector member 144 of each sample is 50 μm.

[0081] Table 1 shows Samples S1 to S3. Among Samples S1 to S3, the ratio of the metal joint MP in Sample S1 was less than 0.0005%, and the ratios of the metal joint MP in Samples S2 and S3 were 0.0005% or more. Also, the stack degradation rate of Sample S1 was relatively high, and the stack degradation rates of Samples S2 and S3 were relatively low. From the above, it was confirmed that the ratio of the metal joint MP and the stack degradation rate were correlated, and in the configuration where the ratio of the metal joint MP was 0.0005% or more, the stack degradation rate was low (that is, the durability performance of the fuel cell stack 10 was high).

[0082] Furthermore, among Samples S1 to S3, Sample S1 did not have the porous layer PL, and 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 mutual diffusion of metals between the interconnector 190 and the fuel electrode current collector member 144, it was considered that the stack degradation rate was suppressed.

[0083] Also, the presence or absence of the porous layer PL is considered to be 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 the metal contained in the fuel electrode current collector member 144 was not converted into a metal oxide, and for Samples S2 and S3, 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 the metal contained in the fuel electrode current collector member 144 was converted into a metal oxide.

[0084] Table 2 is a table showing the performance evaluation results.

Table 2

[0085] Table 2 shows Samples S4 to S6. 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 Samples S5 and S6, 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 rates of Samples S5 and S6 were 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 low when the porous layer PL is 5 μm or less.

[0086] 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 Samples S5 and S6, it is considered that the porous layer PL was densified because the reduction temperature in the reduction step S13 was 800°C or higher.

[0087] Table 3 is a table showing the performance evaluation results.

Table 3

[0088] Table 3 shows Samples S7 to S9. Comparing Sample S7 and Sample S8, Sample S8 has a higher reduction temperature in the reduction step S13 and a higher ratio of the metal joint portion MP. From this, it was confirmed that the higher the reduction temperature in the reduction step S13, the higher the ratio of the metal joint portion MP. Also, comparing Sample S8 and Sample S9, Sample S9 has a lower ten-point average roughness value of the surface 191S of the interconnector 190 and a higher ratio of the metal joint portion MP. From this, it was confirmed that the lower the ten-point average roughness value of the surface 191S of the interconnector 190, the higher the ratio of the metal joint portion MP.

[0089] B. Modified 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.

[0090] 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 included in the fuel cell stack 10 in the above-described embodiments (the number of power generation units 100U) is merely an example, and the number of single cells 110 can be appropriately determined according to the output voltage required for the fuel cell stack 10.

[0091] The materials constituting each member in the above-described embodiments are merely illustrative, and each member may be constituted by other materials. For example, in the above-described embodiment, the fuel electrode current collecting member 144 is formed of at least one of Ni, Ni-Cr alloy, or stainless steel, but the materials of the current collecting member are not limited thereto.

[0092] In the above-described embodiment, the porous layer PL exists in the current collecting structure 160, but the current collecting structure does not necessarily have to have a porous layer. Further, 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.

[0093] The manufacturing method of the current collecting structure is not limited to the above-described embodiment.

[0094] In the above-described embodiment, the oxide film 194 is formed on a part of the surface 191S of the interconnector 190, but the oxide film does not have to be formed on the surface of the Cr-containing member.

[0095] The fuel cell stack 10 of the above-described 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.

[0096] In the above-described embodiment, the single cell 110 is a fuel electrode-supported single cell, but it may be other types of single cells such as an electrolyte-supported type or a metal-supported type.

[0097] In the current collector structure 160 of the above-described embodiment, the interconnector 190 is taken as an example of a Cr-containing member, but the Cr-containing member is not limited thereto. For example, when the first plate 232 in the above-described embodiment contains Cr, the first plate 232 can also be taken as an example of a Cr-containing member, and when the metal support in a metal-supported 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-described embodiment, the fuel electrode current collector member 144 is taken as an example of a conductive member, but the conductive member is not limited thereto.

[0098] In the above-described embodiment, the fuel cell stack 10 is configured to include a plurality of flat 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.).

[0099] In the above-described embodiment, the electrochemical reaction cell stack is a cell stack used for a solid oxide 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 fuel cell (PAFC), and 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.

Description of Reference Numerals

[0100] 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: Fuel electrode current collecting member 144S: Surface 145: Electrode facing part 146: Interconnector facing part 147: Connecting part 149: Spacer 160: Current collecting structure 180: Separator for IC 181: Through hole 190: Interconnector 191: Flat plate part 191S: Surface 192: Air electrode current collecting part 193: Coating layer 194: Oxide film 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 MP: Metal joint PL: Porous layer CL: Center line SP: Gap MOL: Metal oxide layer

Claims

1. A Cr-containing member formed from an alloy containing Cr, A conductive member joined to the Cr-containing member, In a current collector structure for an electrochemical reaction cell stack comprising: Among the joints where the Cr-containing member and the conductive member are joined, the proportion occupied by the metal joint, which is a portion where the thickness of the oxide film on the surface of the Cr-containing member is 0.1 μm or less or a portion where the oxide film does not exist, is 0.0005% or more. A current collector structure for an electrochemical reaction cell stack, characterized by the above.

2. In the current collector structure for an electrochemical reaction cell stack according to Claim 1, The conductive member is formed of at least one of Ni, a Ni-Cr alloy, or stainless steel. A current collector structure for an electrochemical reaction cell stack, characterized by the above.

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

4. In the current collector structure for an electrochemical reaction cell stack according to Claim 3, 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 the above.

5. 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 an electrochemical reaction cell stack. An electrochemical reaction cell stack, characterized by the above.

6. In the method for manufacturing a current collector structure for an electrochemical reaction cell stack according to Claim 1, The method includes a joining step of joining the conductive member and the Cr-containing member under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which the metal contained in the conductive member is oxidized. A method for manufacturing a current collector structure for an electrochemical reaction cell stack, characterized by the above.

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