JP7801377B2 - Current collecting structure for electrochemical reaction cell stack, electrochemical reaction cell stack, and method for manufacturing current collecting structure for electrochemical reaction cell stack - Google Patents

Description

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.

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

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

Patent No. 6773472

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 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 fuel cell stack operation, and will instead form an oxide film with relatively low electrical conductivity 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 causes an increase in the resistance of the fuel cell stack and reduces the durability of the fuel cell stack.

Note that these issues are also common to current collecting structures used in electrolysis cell stacks, which are a form of electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen using the electrolysis of water. In this specification, single fuel cell cells and single electrolysis cells are collectively referred to as single electrochemical reaction cells, and fuel cell stacks and electrolysis cell stacks are collectively referred to as electrochemical reaction cell stacks. Furthermore, these issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

This specification discloses technology that can solve the above-mentioned problems.

The technology disclosed in this specification can be realized, for example, in the following forms:

(1) The current collecting structure for an electrochemical reaction cell stack disclosed in this specification comprises 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.

With 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 adhesion at the interface between the Cr-containing member and the Ni member and suppressing the formation of an oxide film. This prevents 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 improving the durability of the electrochemical reaction cell stack.

(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, located closer to the joint than the central portion in the first direction. According to this configuration, a 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 sufficiently diffuses the Cr contained in the Cr-containing member 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 prevents a decrease in conductivity between the Cr-containing member and the Ni member, thereby preventing an increase in the resistance value of the electrochemical reaction cell stack and more effectively improving the durability of the electrochemical reaction cell stack.

(3) In the above-described 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 component 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 component and the Ni component 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 component and the Ni component, preventing a decrease in conductivity between the Cr-containing component and the Ni component, thereby preventing an increase in the resistance value of the electrochemical reaction cell stack and more effectively improving the durability of the electrochemical reaction cell stack.

(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 H ₂ O contained in the gas in the electrochemical reaction cell stack inside the Ni member, thereby forming an internal oxidation layer (e.g., a layer containing Cr ₂ O ₃ ) 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 each surface may connect, blocking the internal conduction path of 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 makes the distance between the surfaces relatively long, preventing the conduction path from being interrupted, thereby preventing a decrease in conductivity between the Cr-containing member and the Ni member, and thus 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.

(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 of 10 μm or less as defined in JIS B 0601.

During the manufacture of an electrochemical reaction cell stack, when joining a Cr-containing member and a Ni-based 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-based member, thereby improving adhesion between the two. If a further reduction process is subsequently performed to convert NiO into more conductive Ni, a porous layer is formed in the Ni-based 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-based member, resulting in increased resistance. According to this configuration, the surface of the Cr-containing member that joins the Ni-based 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 the intrusion of oxygen 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, suppressing a decrease in 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, more effectively improving the durability of the electrochemical reaction cell stack.

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

With this electrochemical reaction cell stack, during operation, 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, improving adhesion at the interface between the Cr-containing member and the Ni member and suppressing the formation of an oxide film. This prevents 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 improving the durability of the electrochemical reaction cell stack.

(7) The method for manufacturing a current collecting structure for an electrochemical reaction cell stack disclosed in this specification is a method for manufacturing a current collecting structure for an electrochemical reaction cell stack comprising 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 comprises 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.

This method for manufacturing a current collecting structure for an electrochemical reaction cell stack utilizes the volume expansion that occurs when Ni is oxidized to NiO during the bonding process to form NiO in the gap between the Cr-containing member and the Ni member, improving adhesion between the Cr-containing member and the Ni member and suppressing the formation of an oxide film at the interface. 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 improving the durability of the electrochemical reaction cell stack.

(8) The above-described method for manufacturing a current collecting structure for an electrochemical reaction cell stack may further include, after the joining step, a reduction step in which, in a reducing gas atmosphere, the Cr-containing member and the Ni member are heated at a temperature of 800°C or higher while being pressurized in a first direction in which the Cr-containing member and the Ni member are aligned. According to this configuration, by applying pressure, it is possible to reduce NiO to Ni with higher 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, because NiO is reduced to Ni at a temperature of 800°C or higher, 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.

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.

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 the XZ cross-sectional structure of the fuel cell stack 10 taken along the line II-II in FIG. 1. FIG. 2 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. FIG. 4 is an explanatory diagram showing the YZ cross-sectional structure of the fuel cell stack 10 taken along the line IV-IV in FIG. 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. 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. FIG. 1 is an XZ cross-sectional view showing a detailed configuration of a current collecting structure 160 according to a first embodiment. FIG. 1 is an XZ cross-sectional view showing a detailed configuration of a current collecting structure 160 according to a first embodiment. FIG. 1 is an explanatory diagram showing an outline of a method for measuring the Cr concentration of a current collecting structure 160. Flowchart showing the method of manufacturing the current collecting structure 160 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. FIG. 10 is an XZ cross-sectional view showing a detailed configuration of a current collecting structure 160a according to a second embodiment.

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 the 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 the 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 the 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. However, the fuel cell stack 10 may actually be installed in an orientation different from these. 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.

(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 one on top of the other in this order in a predetermined arrangement direction (vertical direction).

As shown in Figures 1 and 4, the fuel cell stack 10 has bolt holes BH near each of its 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 threaded 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 Figures 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.

As shown in Figures 2 to 4, the power generation block 100 is composed of multiple (seven in this embodiment) power generation units 100U arranged in a predetermined arrangement direction (vertical direction).

(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 planar 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 planar portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The planar portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the planar portion 211. The outer convex portion 213 is formed around the entire periphery of the outer periphery of the planar portion 211. The inner convex portion 214 protrudes from the inner periphery of the planar portion 211. The inner convex portion 214 is formed around the entire inner periphery of the planar portion 211.

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

(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.

(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 generating block 100 from the external space of the fuel cell stack 10.

The first plate 232 is connected to an interconnector 190 (described below) provided in the 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 below), thereby electrically connecting the power generation unit 100U and the first plate 232.

(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, which has an alumina oxide coating formed 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 a positive output terminal for the fuel cell stack 10.

(Second 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 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.

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

(Second end plate 270)
The second end plate 270 is formed by pressing (bending) a single plate-like member and is made of a conductive material such as stainless steel. The second end plate 270 includes a rectangular, frame-like planar portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the planar portion 271 in the direction opposite the second terminal plate 250 (downward in FIG. 2 ). The planar portion 271 has holes that form the bolt holes BH described above. The outer convex portion 273 protrudes from the outer periphery of the planar portion 271. The outer convex portion 273 is formed around the entire outer periphery of the planar portion 271. The inner convex portion 274 protrudes from the inner periphery of the planar portion 271. The inner convex portion 274 is formed around the entire inner periphery of the planar portion 271.

(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 correspond to 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.

As shown in FIG. 2, the oxidant gas supply manifold 311 is a gas flow path that supplies 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 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. Air, for example, 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.

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 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 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. 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.

(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 is formed in the main body portion 281, penetrating the main body portion 281 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 of each of the four gas passage members 280 is joined to the second end plate 270 by, for example, welding, and the gas through-holes 283 are connected to 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.

(Overall configuration of power generating unit 100U)
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, a cathode frame 130, an anode frame 140, a current collecting structure 160, and two IC separators 180. One IC separator 180, the cathode 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.

(Single cell 110)
The unit cell 110 includes an electrolyte layer 112, a cathode 114, an anode 116, and a reaction prevention layer 118. As shown in Figures 5 and 6, the cathode 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, cathode 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.

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 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 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 cathode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO ₃ ).

(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, brazing material (Ag brazing).

(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.

(Anode 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.

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

Current Collecting Structure 160
The current collecting structure 160 is electrically connected to the unit cell 110 and collects the power 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.

As shown in Figures 5 and 6, the interconnector 190 comprises a rectangular flat plate portion 191, multiple 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 collectors 192 are formed from 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 collectors 192 are 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.

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 from foil with a vertical thickness (length L1 shown in Figure 8) of 30 μm or more. As shown in Figures 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 connecting 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 the flat portion 191 of the interconnector 190. The anode current collecting member 144 is disposed between the single cell 110 and the interconnector 190. In this specification, "formed from 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 Ni member.

As shown in Figures 5 and 6, the interconnector 190 is shared by two adjacent power generating units 100U. More specifically, as shown in Figures 5 and 6, the cathode current collecting portion 192 is joined to the cathode 114 of the unit cell 110 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 electrically connecting to the cathode 114. The flat plate portion 191 is electrically connected to the anode 116 of the unit cell 110 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.

However, as shown in FIG. 2, the power generating unit 100U located at the other end (the lower end in FIG. 2) of the multiple power generating units 100U does not have an interconnector 190 on the anode 116 side. The anode 116 included in this power generating unit 100U is connected to the second terminal plate 250 via the anode current collecting member 144.

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, maintaining good electrical connection between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144.

(Air chamber 313 and fuel chamber 323)
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 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, thereby preventing gas from leaking from the air chamber 313 to the external space.

The space partitioned by the single cell separator 120, single cell 110, fuel electrode frame 140, IC separator 180, and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 separates the entire periphery of the fuel chamber 323 from the external space and seals the gap between the single cell separator 120 and IC separator 180, preventing gas from leaking from the fuel chamber 323 to the external space.

The single cell separator 120 separates the air chamber 313 and the fuel chamber 323, 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. The IC separator 180 and interconnector 190 also prevent gas leakage between adjacent power generation units 100U.

A-2. Operation of the 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 piping (not shown) and a gas passage member 280, and is supplied to the air chamber 313 via the oxidizing gas supply communication passage 132.

Also, as shown in Figures 3 and 6, 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.

When oxidant gas OG is supplied to the air chamber 313 of each power generating unit 100U and fuel gas FG is supplied to the fuel chamber 323, power is generated in the single cell 110 through 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, the power generating unit 100U located at the other end (the lower end in Figure 2) of the multiple power generating units 100U is electrically connected to a second terminal plate 250, and the power generating unit 100U located at one end (the upper end in Figure 2) is electrically connected to a first terminal plate 240. 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.

As shown in Figures 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 communication passage 133 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. As shown in Figures 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 communication passage 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

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 the 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, thereby forming a joint CP where the interconnector 190 and the anode current collecting member 144 are joined to each other. Specifically, the joint CP refers to a portion where the interconnector 190 and the anode current collecting member 144 are in physical contact with each other, and refers to a 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 with an SEM (for example, a VE-9800 manufactured by Keyence; the same applies hereinafter).

The current collecting structure 160 is configured so that when heat treatment is performed at 900°C for 100 hours in a reducing gas atmosphere containing water vapor (for example, _H2O / _H2 = 1, _H2 / _N2 = 0.1 as gas volume flow rates), the Cr concentration inside the anode current collecting member 144 located near the joint CP is 1 atm% or more. 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, _Cr2O3 ) is formed inside the anode current collecting member ₁₄₄ located near the joint CP during operation of the fuel cell stack 10 (see Figure 8).

Figure 9 is an explanatory diagram outlining a method for measuring the Cr concentration of the current collecting structure 160. In this specification, "vicinity of the joint CP" refers to the area between 6 μm and 12 μm away from the surface 144S of the anode current collecting member 144. 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, after the heat treatment, and performing SEM/EDX analysis on the area surrounding the joint CP. That is, as shown in Figure 9, for each 6 μm square region between 6 μm and 12 μm away from the joint CP in the direction toward the anode current collecting member 144, the Cr content 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. Note that a configuration in which "the Cr concentration inside the anode current collecting member 144 located near the joint CP is 1 atm% or higher" means a configuration in which the Cr concentration in at least one region of each 6 μm square region in any cross section of the fuel cell stack 10 that includes the joint CP is 1 atm% or higher. In other words, the Cr concentration near the joint CP before the heat treatment is less than 1 atm%.

The anode current collecting member 144 has a porous layer PL with a higher porosity than the center, 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% or more and 50% or less, and more preferably 5% or more and 30% or less. The vertical thickness of the porous layer PL is preferably 5 μm or less. The porous layer PL is preferably present on the periphery of the joint CP.

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

A-4. Method for manufacturing the 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.

First, prepare the interconnector 190 and the anode current collecting member 144 using a known method (S11).

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 greater 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. Furthermore, the type of gas is not particularly limited as long as it is under an oxygen partial pressure equal to or greater than the oxygen partial pressure at which Ni is oxidized to NiO. S12 is an example of a bonding process.

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

Next, the interconnector 190 and the anode current collecting member 144 are heated while being pressurized (S13). Specifically, in a reducing gas atmosphere, the interconnector 190 and the anode current collecting 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 anode current collecting member 144 are aligned. The heating temperature is preferably 800°C or higher and 900°C or lower. S13 is an example of a reduction process.

As shown in Figure 11(C), after step S13, the nickel oxide layer NOL changes into a porous layer PL. In other words, volume shrinkage occurs as the NiO in the nickel oxide layer NOL is reduced to Ni, resulting in the formation of porous portions. Because heating and pressure are applied in step S13, 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.

A-5. Effects of this embodiment:
As described above, current collecting structure 160 of the present embodiment includes interconnector 190 formed from an alloy containing Cr, and anode current collecting member 144 formed from Ni, which is joined to interconnector 190. When 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 anode current collecting member 144 located in the vicinity of joint CP where interconnector 190 and anode current collecting member 144 are joined is 1 atm% or more.

With the current collecting structure 160 of this embodiment, during operation of the fuel cell stack 10, the Cr contained in the interconnector 190 is sufficiently diffused into the interior of the anode current collecting member 144, improving 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 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.

Furthermore, in the current collecting structure 160 of this embodiment, when the direction in which the anode current collecting member 144 and the interconnector 190 are aligned 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 this embodiment, the porous layer PL with a higher porosity than the central portion is located on the joint CP side of the vertical center of the anode current collecting member 144. Therefore, when, for example, the joining process between the interconnector 190 and the anode current collecting member 144 is performed in a high-temperature environment during the manufacture 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 prevents peeling at the joint CP between the interconnector 190 and the anode current collecting member 144, improves adhesion between the interconnector 190 and the anode current collecting member 144, and allows the Cr contained in the interconnector 190 to be sufficiently diffused into the anode current collecting member 144, thereby preventing the formation of an oxide film at the interface between the interconnector 190 and the anode current collecting member 144. This prevents a decrease in conductivity between the interconnector 190 and the anode current collecting member 144, thereby preventing an increase in the resistance value of the fuel cell stack 10 and more effectively improving the durability of the fuel cell stack 10.

Furthermore, in the current collecting structure 160 of this embodiment, the vertical thickness of the porous layer PL is 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. This prevents peeling of the joint CP between the interconnector 190 and the anode current collecting member 144 during manufacturing of the fuel cell stack 10, while also preventing oxygen from penetrating into the joint CP during operation of the fuel cell stack 10. This prevents a decrease in conductivity between the interconnector 190 and the anode current collecting member 144, thereby preventing an increase in the resistance value of the fuel cell stack 10 and more effectively improving the durability of the fuel cell stack 10.

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 H ₂ O 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 layer IN grows 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 144 is thin, the distance between the surfaces is short, and the internal oxide layers IN formed on the surfaces may be connected, 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 of the fuel cell stack 10, thereby more effectively improving the durability of the fuel cell stack 10.

Furthermore, in 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.

During the manufacture of the fuel cell stack 10, when joining the interconnector 190 and the anode current collecting member 144, the 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 the more conductive Ni, the volume contraction that accompanies the conversion of NiO to Ni forms a porous layer PL in the anode current collecting member 144. If the porous layer PL is thick, oxygen may easily penetrate 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 joins with the anode current collecting member 144 has a ten-point average roughness of 10 μm or less as defined in JIS B 0601. This prevents the gap SP between the interconnector 190 and the anode current collecting member 144 from becoming excessively large, thereby reducing the thickness of the porous layer PL formed in the anode current collecting member 144 and preventing oxygen from penetrating 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, preventing a decrease in conductivity between the interconnector 190 and the anode current collecting member 144 and ultimately preventing an increase in the resistance of the fuel cell stack 10, thereby more effectively improving the durability of the fuel cell stack 10.

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.

In the fuel cell stack 10 of this embodiment, during operation, the Cr contained in the interconnector 190 of the current collecting structure 160 is sufficiently diffused into the interior of the anode current collecting member 144, improving 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 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.

The manufacturing method for 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 under an oxygen partial pressure equal to or higher than the oxygen partial pressure at which Ni is oxidized to NiO.

The manufacturing method for the current collecting structure 160 of this embodiment utilizes the volume expansion that occurs when Ni is oxidized to NiO during the bonding step S12 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 and suppressing the formation of an oxide film. 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 improving the durability of the fuel cell stack 10.

In addition, 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 aligned. 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 with higher conductivity while suppressing a decrease in adhesion between the interconnector 190 and the anode current collecting member 144 due to volumetric shrinkage associated with 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.

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 performed using these multiple samples. Tables 1 to 3 show the performance evaluation results.

(Preparation of evaluation samples)
The current collecting structure 160 was fabricated by the method described above in "A-4. Manufacturing method of the 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 the fuel cell stack 10 each including the current collecting structures 160 with various different physical properties were then fabricated by a known method, and the following performance evaluations were performed.

(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 ( _H2O / _H2 = 1, _H2 / _N2 = 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.

(Performance evaluation - stack deterioration rate)
The fuel cell stack 10 fabricated by the above method was started to operate at 700°C, and the potential _VI at the start of operation was measured. Subsequently, the stack was continuously operated for 10,000 hours at 700°C, and the potential _VE was measured 10,000 hours after the start of operation. The stack deterioration rate due to continuous operation of each sample of the fuel cell stack 10 was calculated using the following equation.
Stack deterioration rate (%) = 100 × (V _I - V _E ) / V _I

(Performance evaluation results)
Table 1 shows the performance evaluation results.

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

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).

Furthermore, of 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 that have a porous layer PL have a lower stack deterioration rate. In other words, it is believed that the presence of the porous layer PL improves the adhesion between the interconnector 190 and the anode current collecting member 144, and as a result, the Cr of the interconnector 190 is sufficiently diffused inside the anode current collecting member 144, thereby suppressing the stack deterioration rate.

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

Table 2 shows the performance evaluation results.

Table 2 shows samples S4 and S5. Sample S4 has a porous layer PL of the anode current collecting member 144 with a thickness greater than 5 μm, while sample S5 has a porous layer PL of the anode current collecting member 144 with a thickness of 5 μm or less. Furthermore, the stack deterioration rate of sample S4 was relatively high, while the stack deterioration rate of sample S5 was relatively low. This confirms that the thickness of the porous layer PL and the stack deterioration rate are correlated, and that a porous layer PL of 5 μm or less reduces the stack deterioration rate.

The thickness of the porous layer PL is also thought to be due to the conditions of the reduction step S13. That is, for sample S4, the reduction temperature in the reduction step S13 was lower than 800°C, which is thought to have prevented the porous layer PL from being densified. For sample S5, the reduction temperature in the reduction step S13 was 800°C or higher, which is thought to have caused the porous layer PL to be densified.

Table 3 shows the performance evaluation results.

Table 3 shows samples S6 to S8. The anode current collecting member 144 of sample S6 is foil-shaped and has a thickness of less than 30 μm. The anode current collecting member 144 of sample S7 is foil-shaped and has a thickness of 30 μm or more. The anode current collecting member 144 of sample S8 is mesh-shaped and has a wire diameter of 60 μm or more. Furthermore, 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 and the stack deterioration rate are correlated, 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.

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.

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 from multiple wires made of Ni, with wires extending in the X-axis direction and wires extending in the Y-axis direction forming a mesh-like structure. The anode current collecting member 144a has a wire diameter (length L2 shown in Figure 12) of 60 μm or more.

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 H ₂ O contained in the gas in the fuel cell stack 10 inside the anode current collecting member 144a, thereby forming an internal oxide layer IN inside the anode current collecting member 144a. When the internal oxide layer IN grows 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 surfaces may be connected, thereby interrupting the electrical conduction 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.

C. Variations:
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 spirit thereof, for example, the following modifications are also possible.

The configurations of the fuel cell stack 10 and power generation units 100U in the above embodiments are merely examples and can be modified in various ways. For example, the number of unit cells 110 (number of power generation units 100U) included in the fuel cell stack 10 in the above embodiments 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.

The materials used to make each component in the above embodiment are merely examples, and each component may be made of other materials.

In the above embodiment, the current collecting structure 160 includes a porous layer PL, but the current collecting structure does not necessarily need to include 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.

In the first embodiment, the anode current collecting member 144 is formed from a foil with a thickness of 30 μm or more, and in the second embodiment, the anode current collecting member 144a is formed from a mesh with a wire diameter of 60 μm or more, but the shape of the Ni member is not limited to these, and neither is its thickness.

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

The method for manufacturing the current collecting structure is not limited to the above embodiment.

The fuel cell stack 10 in the above embodiment is a coflow-type SOFC, but the technology disclosed in this specification can also be applied to counterflow-type SOFCs and crossflow-type SOFCs.

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

In the current collecting structure 160 of the above embodiment, the interconnector 190 is an example of a Cr-containing member, but Cr-containing members are not limited to this. 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 single 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 Ni members are not limited to this.

In the above embodiment, the fuel cell stack 10 is configured to include multiple flat-plate type unit cells 110, but the present invention is equally applicable to fuel cell stacks that include multiple unit cells of other types (e.g., cylindrical, flat cylindrical, etc.).

In the above embodiment, the electrochemical reaction cell stack was a cell stack used in a solid oxide fuel cell (SOFC), but the above configuration can also be applied to cell stacks used in other types of fuel cells, such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolysis cell stacks that include electrolysis cell units, which are the constituent elements of solid oxide electrolysis cells (SOECs), as single cells.

10: Fuel cell stack 100: Power generation block 100U: Power generation unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Anode 118: Reaction prevention layer 120: Single cell separator 121: Through hole 124: Joint 130: Air electrode frame 131: Through hole 132: Oxidant gas supply communication channel 133: Oxidant gas discharge communication channel 140: Anode frame 141: Through hole 142: Fuel gas supply communication channel 143: Fuel gas discharge communication channel 144, 144a: Anode current collecting member 144S: Surface 145: Electrode opposing portion 146: Interconnector opposing portion 147: Connection 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: Oxidant 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: Oxidant gas; OOG: Oxidant off-gas; CP: Joint; IN: Inner oxide layer; PL: Porous layer; CL: Center line; SP: Gap; NOL: Nickel oxide layer.

Claims (8)

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: 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: 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: 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: 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: 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: 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: 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: