Electrochemical reaction cell stack

Abstract

To reduce the occurrence of peeling of a seal member from a joining object member.SOLUTION: An electrochemical reaction cell stack includes a first member to be joined, a second member to be joined different from the first member to be joined, and a seal member that joins the first member to be joined and the second member to be joined, wherein the seal member includes a first glass seal that is joined to the first member to be joined and is made of glass, a second glass seal that is joined to the second member to be joined and is made of glass, and an intermediate seal that is disposed between the first glass seal and the second glass seal, the intermediate seal having pores, the maximum diameter of the pores is 20 μm or less.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The technology disclosed herein relates to electrochemical reaction cell stacks. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs"), which have an electrolyte layer containing solid oxide, 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, in which multiple constituent units (electrochemical reaction units) are arranged in a predetermined direction.

[0003] A sealing member is used to connect two structural units provided in a fuel cell stack. The sealing member may include a first sealing portion and second sealing portions laminated on both sides of the first sealing portion (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-170342 [Patent Document 2] Special Publication No. 2010-511996 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned SOFC, it is required to reduce the occurrence of peeling of the sealing member from the member to be joined.

[0006] These issues are also common to electrolysis cell stacks that include multiple electrolysis cell units, which are constituent elements of solid oxide electrolysis cells (hereinafter referred to as "SOECs") that generate hydrogen using the electrolysis reaction of water. Furthermore, these issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms. (1) The electrochemical reaction cell stack disclosed in this specification comprises a first member to be joined, a second member to be joined, and a sealing member that joins the first member to be joined and the second member to be joined, wherein the sealing member comprises a first glass seal made of glass that is joined to the first member to be joined, a second glass seal made of glass that is joined to the second member to be joined, and an intermediate seal that is disposed between the first glass seal and the second glass seal, wherein the intermediate seal has pores, and the maximum pore diameter of the intermediate seal is 20 μm or less.

[0008] According to the above configuration, the leakage current flowing through the sealing member can be reduced, thereby reducing the occurrence of peeling of the glass seal from the member to be joined.

[0009] (2) In the electrochemical reaction cell stack described in (1) above, the thickness of the intermediate seal may be greater than the thickness of the first glass seal and the thickness of the second glass seal.

[0010] According to the above configuration, the relatively large thickness of the intermediate seal results in a relatively large electrical resistance of the intermediate seal, which reduces leakage current flowing through the seal member and thus reduces the occurrence of peeling of the glass seal from the joining target component.

[0011] (3) In the electrochemical reaction cell stack described in (1) or (2) above, the intermediate seal may contain magnesium oxide as a main component.

[0012] According to the above configuration, the occurrence of peeling of the glass seal from the joining target component can be reduced.

[0013] The technology disclosed in this specification can be realized in various forms, for example, in the form of an electrochemical reaction cell stack and a manufacturing method thereof. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack according to an embodiment; [Figure 2] FIG. 2 is a cross-sectional view of the fuel cell stack according to the embodiment taken along line II-II in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the fuel cell stack according to the embodiment taken along line III-III in FIG. 1. [Figure 4] 2 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, taken along the same line as in FIG. 1; [Figure 5] 3 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, taken along the same line as line III-III in FIG. 1; [Figure 6] FIG. 3 is an enlarged partial cross-sectional view showing the area within the frame F1 in FIG. 2; [Figure 7] FIG. 7 is an enlarged partial cross-sectional view showing the area within the frame F2 in FIG. 6; [Figure 8] 8 is a cross-sectional view showing the fuel cell stack of the embodiment taken along line VIII-VIII in FIG. 6. [Figure 9] Schematic diagram showing the shape of an air bubble contained in the intermediate seal of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] A. Implementation: The embodiment will be described with reference to Figures 1 to 9. A fuel cell stack 10 (an example of an electrochemical reaction cell stack) of the present embodiment is used in a solid oxide fuel cell having an electrolyte layer 112 containing a solid oxide.

[0016] (Overall configuration of fuel cell stack 10) 1 to 3, 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 example of a second joining target member), an insulating section 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating section 220, the end separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have rectangular outer shapes of approximately the same size and are arranged in this order, stacked in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0017] As shown in Fig. 1, the fuel cell stack 10 has bolt holes BH near each of the four corners, penetrating from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. A nut N is screwed onto both ends of each bolt B. These bolts B and nuts N fasten the members from the first end plate 210 to the second end plate 270 together. As shown in Figs. 2 and 3, 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.

[0018] As shown in Figures 2 and 3, the power generation block 100 is composed of multiple (seven in this embodiment) electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction units 100U") arranged in a predetermined arrangement direction (vertical direction in Figure 2).

[0019] (Overall configuration of 100U electrochemical reaction units) 4 and 5, the electrochemical reaction unit 100U includes a single cell 110, a single cell separator 120, an air electrode frame 130, an anode frame 140, an anode current collecting member 144, two interconnectors 190, and two IC separators 180. One IC separator 180, the air electrode frame 130, the single cell separator 120, the anode frame 140, and the other IC separator 180 are stacked in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are supported by the two IC separators 180, and the anode current collecting member 144 is disposed between the single cell 110 and the interconnectors 190.

[0020] 4 and 5, the IC separator 180 and the interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Fig. 2, the reaction unit 100U located at one end (the lower end in Fig. 2) of the multiple reaction units 100U does not have the IC separator 180 and the interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 overlaps the fuel electrode frame 140.

[0021] (single cell 110) The unit cell 110 includes an electrolyte layer 112, a cathode 114, and an anode 116. As shown in Figures 4 and 5, the cathode 114, the electrolyte layer 112, and the anode 116 are stacked in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the cathode 114. 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.

[0022] The electrolyte layer 112 is a rectangular, flat member having one surface (the upper surface in FIGS. 4 and 5) on which the air electrode 114 is disposed and another surface (the lower surface in FIGS. 4 and 5) 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 substantially the same as that of 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 substantially the same as that of the air electrode 114 and containing, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of preventing elements (e.g., Sr) diffused from the air electrode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0023] (Single cell separator 120) As shown in FIGS. 4 and 5, the single cell separator 120 is a rectangular frame-shaped member having a substantially rectangular through-hole 121 near the center. The single cell separator 120 is electrically conductive and is made of a metal such as ferritic stainless steel. The thickness of the single cell separator 120 is, for example, 0.05 mm or more and 0.2 mm or less. The peripheral portion of the through-hole 121 in the single cell separator 120 is joined to the peripheral portion of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is disposed: the upper surface in FIGS. 4 and 5) by a joint 124. The joint 124 is made of, for example, a brazing material (Ag brazing).

[0024] (Air electrode frame 130) As shown in FIGS. 4 and 5, the cathode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made of, for example, insulating ceramics (mica, etc.).

[0025] (fuel electrode frame 140) 5, the fuel electrode frame 140 is a rectangular frame-like member having a substantially rectangular through-hole 141 near the center. The fuel electrode frame 140 is electrically conductive and is made of a metal such as ferritic stainless steel.

[0026] (IC separator 180) 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center. IC separator 180 is conductive and is made of a metal such as ferritic stainless steel. The thickness of IC separator 180 is, for example, 0.05 mm or more and 0.2 mm or less.

[0027] (Interconnector 190 and anode current collecting member 144) As shown in FIGS. 4 and 5 , the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collector 192 are electrically conductive and formed of a metal such as ferritic stainless steel. The coating layer 193 is electrically conductive and formed of a spinel-type oxide, for example. The coating layer 193 is disposed so as to cover the surface of the air electrode current collector 192 and the surface of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The flat plate portion 191 is joined to the periphery of the through-hole 181 in the IC separator 180, for example, by welding.

[0028] The anode current collecting member 144 is a member that connects the interconnector 190 and the anode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 4 and 5, the anode current collecting member 144 has an interconnector facing portion 146, an electrode facing portion 145 that is 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 an overall U-shape. The electrode facing portion 145 is in contact with the anode 116, and the interconnector facing portion 146 is in contact with a flat portion 191 of the interconnector 190.

[0029] As described above, the interconnector 190 is shared by two adjacent reaction units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collecting part 192 is joined to the air electrode 114 of the unit cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, and is thereby electrically connected to the air electrode 114. The flat plate part 191 is electrically connected to the anode 116 of the unit cell 110 provided in the other of the two adjacent reaction units 100U via an anode current collecting member 144. This ensures electrical continuity between the two adjacent reaction units 100U.

[0030] However, as described above, the reaction unit 100U located at one end (the lower end in FIG. 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 included in this reaction unit 100U is connected to the second terminal plate 250 via the fuel electrode current collecting member 144.

[0031] 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 reaction unit 100U due to temperature cycles and fluctuations in reactant gas pressure, and good electrical connection between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144 is maintained.

[0032] (Air chamber 313 and fuel chamber 323) 4 and 5, the space partitioned by the single cell separator 120, single cell 110, air electrode frame 130, IC separator 180, and interconnector 190 faces the air electrode 114 and serves as an air chamber 313 through which oxidant gas OG flows. The air electrode frame 130 partitions the entire periphery of the air chamber 313 from the external space and seals the gap between the single cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 to the external space.

[0033] The space partitioned by the single cell separator 120, the single cell 110, the fuel electrode frame 140, the IC separator 180, and the interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the entire periphery of the fuel chamber 323 from the external space, and seals the gap between the single cell separator 120 and the IC separator 180, thereby preventing gas from leaking from the fuel chamber 323 to the external space.

[0034] The single cell separator 120 separates the air chamber 313 and the fuel chamber 323, thereby preventing gas leakage (cross leakage) from the air electrode 114 side to the fuel electrode 116 side or from the fuel electrode 116 side to the air electrode 114 side around the single cell 110. In addition, the IC separator 180 and the interconnector 190 prevent gas leakage between adjacent reaction units 100U.

[0035] (First end plate 210) The first end plate 210 is formed by pressing (bending) a single plate-like member. The first end plate 210 is electrically conductive and is made of a metal such as ferritic stainless steel. The thickness of the first end plate 210 is, for example, 0.5 mm or more and 3 mm or less. As shown in FIGS. 1 to 3 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is disposed around the entire periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is arranged along the entire inner periphery of the flat portion 211 .

[0036] (insulating part 220) Insulating section 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of an insulating material. As shown in Figures 2 and 3, insulating section 220 is sandwiched between first end plate 210 and end separator 230, thereby ensuring insulation between first end plate 210 and end separator 230.

[0037] (Terminal separator 230) 2 and 3, terminal separator 230 is a rectangular frame-shaped member having a through-hole 231 near the center. Terminal separator 230 is conductive and is made of a metal such as ferritic stainless steel.

[0038] (First Plate 232) The first plate 232 is a rectangular, flat member. The first plate 232 is electrically conductive and is made of a metal such as ferritic stainless steel. As shown in FIGS. 2 and 3 , the first plate 232 is joined to the peripheral portion of the through-hole 231 in the terminal separator 230 by, for example, welding. The terminal separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0039] The first plate 232 is connected to an interconnector 190 provided in the reaction unit 100U arranged at the other end (the upper end in Figure 2) of the multiple reaction 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, thereby electrically connecting this reaction unit 100U and the first plate 232.

[0040] (First terminal plate 240) As shown in FIGS. 2 and 3, the first terminal plate 240 is a rectangular frame-shaped member having a through-hole 241 near the center. The first terminal plate 240 is formed of a metal such as ferritic stainless steel. The thickness of the first terminal plate 240 is, for example, 0.2 mm or more and 3 mm or less. The first terminal plate 240 is electrically connected to the reaction unit 100U arranged at the other end (the upper end in FIG. 2) of the multiple reaction units 100U that make up the power generation 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 generation block 100, and this protruding portion functions as a positive output terminal for the fuel cell stack 10.

[0041] (2nd terminal plate 250) The second terminal plate 250 is a rectangular, plate-shaped member. The second terminal plate 250 is electrically conductive and made of a metal such as ferritic stainless steel. The thickness of the second terminal plate 250 is, for example, 0.2 mm or more and 3 mm or less. As described above, the second terminal plate 250 is connected to the anode 116 of the reaction unit 100U located at one end (the lower end in FIG. 2) of the multiple reaction units 100U via the anode current collecting member 144, thereby electrically connecting the reaction unit 100U to the second terminal plate 250. One end (the right end in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0042] (Second plate 260) Second plate 260 is a rectangular, flat member made of an insulating material. As shown in Figures 2 and 3, the peripheral edge of second plate 260 is sandwiched between second terminal plate 250 and second end plate 270, thereby ensuring insulation between second terminal plate 250 and second end plate 270.

[0043] (Second end plate 270) The second end plate 270 is formed by pressing (bending) a single plate-like member. The second end plate 270 is formed of a metal such as ferritic stainless steel. The thickness of the second end plate 270 is, for example, 0.5 mm or more and 3 mm or less. As shown in FIGS. 2 and 3 , the second end plate 270 includes a rectangular, frame-like flat portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the flat portion 271 in the direction opposite to the second terminal plate 250 (downward in FIG. 2 ). The outer convex portion 273 protrudes from the outer periphery of the flat portion 271. The outer convex portion 273 is disposed around the entire periphery of the flat portion 271. The inner convex portion 274 protrudes from the inner periphery of the flat portion 271. The inner convex portion 274 is disposed around the entire inner periphery of the flat portion 271.

[0044] (Manifolds 311, 312, 321, 322) 1 to 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.

[0045] 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 of each reaction 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 reaction unit 100U to the outside of the fuel cell stack 10. As the oxidant gas OG, for example, air is used.

[0046] 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 chambers 323 of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges fuel off-gas FOG discharged from the fuel chambers 323 of each reaction 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.

[0047] The second terminal plate 250 has four manifold holes. The four manifold holes are holes that penetrate the second terminal plate 250 and are part of the manifolds 311, 312, 321, and 322, respectively. Of the four manifold holes provided in the second terminal plate 250, the manifold hole that forms part of the oxidant gas supply manifold 311 will be referred to as the "manifold hole 311H1" below (see FIG. 6).

[0048] Second end plate 270 has four manifold holes. The four manifold holes are holes that penetrate second end plate 270 and are part of four manifolds 311, 312, 321, and 322. Hereinafter, of the four manifold holes provided in second end plate 270, the manifold hole that forms part of oxidant gas supply manifold 311 will be referred to as "manifold hole 311H2" (see FIG. 6).

[0049] (Gas passage member 280) As shown in FIGS. 1 to 3, each of the four gas passage members 280 includes a main body portion 281 and a flange portion 282. The main body portion 281 is cylindrical with both ends open. The flange portion 282 is provided so as to protrude outward from one 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.

[0050] The second end plate 270 has four holding tube portions 275 for connecting the gas passage member 280. As shown in FIG. 6, one of the four holding tube portions 275 is a cylindrical portion extending from the edge of the manifold hole 311H2 toward the opposite side from the power generation block 100 (downward in FIG. 6). The other end (upper end in FIG. 6) of the main body portion 281 is joined to the holding tube portion 275 by, for example, welding. The internal space of the main body portion 281 is connected to the oxidizing gas supply manifold 311. A gas pipe (not shown) for supplying or discharging gas is connected to each main body portion 281. The other three holding tube portions 275 are disposed at positions corresponding to the manifolds 312, 321, and 322, respectively, and are similarly connected to the gas passage member 280.

[0051] (Joint structure between second terminal plate 250 and second end plate 270) The second end plate 270 is joined to the second terminal plate 250 via a stress relief member 400 (an example of a first joining target member) and a seal member 500. More specifically, on the flat portion 271, the peripheral portions of the four manifolds 311, 312, 321, and 322 are joined to the second terminal plate 250 via the stress relief member 400 and the seal member 500. Since the joining structures around the four manifolds 311, 312, 321, and 322 are identical to one another, the following describes the joining structure around the oxidant gas supply manifold 311, and omits a description of the other three.

[0052] 6, the second plate 260 has a seal receiving hole 261 at a position corresponding to the oxidizing gas supply manifold 311. The seal receiving hole 261 is a hole that penetrates the second plate 260 and is slightly larger than the manifold holes 311H1 and 311H2.

[0053] The stress relaxation member 400 is a thin, flat, elastically deformable member and has a manifold hole 311H3. The manifold hole 311H3 is a hole that penetrates the stress relaxation member 400 and is part of the oxidant gas supply manifold 311. The peripheral edge of the manifold hole 311H3 in the stress relaxation member 400 is sandwiched between the peripheral part of the seal receiving hole 261 in the second plate 260 and the peripheral part of the manifold hole 311H2 in the flat surface portion 271. The stress relaxation member 400 is joined to the flat surface portion 271 around the entire periphery of the manifold hole 311H3. The stress relaxation member 400 can be joined to the flat surface portion 271 by, for example, laser welding.

[0054] The seal member 500 is a member that joins the second terminal plate 250 and the stress relaxation member 400. The seal member 500 is disposed inside the seal accommodating hole 261. As shown in Fig. 7, the seal member 500 includes a first glass seal 510, a second glass seal 520, and an intermediate seal 530, which are disposed in this order.

[0055] The first glass seal 510 is an annular member having a first through-hole 511. The first glass seal 510 is made of glass. The first glass seal 510 may be made of SiO2-B2O3-MgO-based glass. One surface of the first glass seal 510 is bonded to the stress relaxation member 400, and the other surface is bonded to the intermediate seal 530.

[0056] The second glass seal 520 is an annular member having a second through hole 521. The second glass seal 520 is made of glass. The second glass seal 520 may be made of SiO2-B2O3-MgO-based glass. One surface of the second glass seal 520 is bonded to the second terminal plate 250, and the other surface is bonded to the intermediate seal 530.

[0057] The intermediate seal 530 is an annular member having a third through hole 531. The intermediate seal 530 may be formed of an insulating material such as insulating ceramics. The intermediate seal 530 may be ceramic containing magnesium oxide (MgO) or ceramic containing magnesium oxide as its main component. In this specification, "main component" means that the component is contained at 90% by volume or more. In this embodiment, the intermediate seal 530 contains magnesium oxide at 90% by volume or more and also contains a sintering aid (e.g., CaO, SiO2, Al2O3) and the like. The intermediate seal 530 is sandwiched between the first glass seal 510 and the second glass seal 520.

[0058] The first glass seal 510, the second glass seal 520, and the intermediate seal 530 overlap each other so that the first through hole 511, the second through hole 521, and the third through hole 531 are connected to each other. The three through holes 511, 521, and 531 are part of the oxidant gas supply manifold 311. One surface of the first glass seal 510 is bonded to the surface of the stress relaxation member 400 so as to surround the entire periphery of the manifold hole 311H3. The other surface of the first glass seal 510 is bonded to the surface of the intermediate seal 530 so as to surround the entire periphery of the third through hole 531. One surface of the second glass seal 520 is bonded to the surface of the second terminal plate 250 so as to surround the entire periphery of the manifold hole 311H1. The other surface of the second glass seal 520 is bonded to the other surface of the intermediate seal 530 so as to surround the edge of the third through-hole 531 over the entire periphery.

[0059] In this embodiment, the thickness T3 of the middle seal 530 is greater than the thickness T1 of the first glass seal 510 and greater than the thickness T2 of the second glass seal 520.

[0060] In this embodiment, the middle seal 530 is a porous member having a large number of pores 532. The maximum pore diameter of the middle seal 530 is 20 μm or less. The maximum pore diameter of the middle seal 530 is determined as follows. An SEM image is obtained by photographing an arbitrary cross section of the middle seal 530 using a scanning electron microscope (SEM) at a magnification of 500 times. The pore diameter of each pore 532 appearing in the obtained SEM image is measured. As shown in FIG. 9 , the pore diameter D of a certain pore 532 is the value of the maximum distance between two parallel lines when the outline of the pore 532 appearing in the SEM image is sandwiched between the two lines. The value of the pore diameter D of the pore 532 with the largest pore diameter among the pores 532 appearing in the SEM image is determined as the maximum pore diameter of the middle seal 530. In ceramics, pores are generally uniformly distributed, and it is unlikely that extremely large pores are locally distributed, so the maximum pore size may be determined using an SEM image of any cross section of the mid-seal 530. In this specification, the phrase "the maximum pore size is 20 μm or less" does not include cases where no pores are observed when the cross section of the mid-seal is imaged with an SEM.

[0061] (Method of manufacturing fuel cell stack 10) An example of a method for manufacturing the fuel cell stack 10 having the above configuration will be described below.

[0062] The intermediate seal 530 having a maximum pore diameter of 20 μm or less is produced as follows: The raw material powders of the intermediate seal 530 are weighed to obtain the desired composition. These raw material powders are wet-mixed to obtain a slurry. The obtained slurry is dried, granulated, and uniaxially pressed to form into the desired shape. The obtained molded body is degreased and then fired to obtain the intermediate seal 530. The size of the pores 532 contained in the intermediate seal 530 can be adjusted by adjusting the load during press molding.

[0063] The second plate 260 is placed on top of the second end plate 270, which has the stress relief member 400 bonded to its surface, and the first glass seal 510, intermediate seal 530, and second glass seal 520 are placed in this order inside the seal receiving hole 261. The second terminal plate 250 is placed on top of the second plate 260, and other components are then layered to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is heat-treated at a heat treatment temperature higher than the operating temperature. The heat treatment temperature is, for example, 850°C. This heat treatment bonds the second terminal plate 250 and intermediate seal 530 together via the first glass seal 510, and bonds the intermediate seal 530 and stress relief member 400 together via the second glass seal 520. In this manner, the fuel cell stack 10 is completed.

[0064] (Operation of fuel cell stack 10) 2 and 4, the oxidizing gas OG is supplied from the oxidizing gas supply manifold 311 to the air chamber 313 via the gas passage member 280. Also, as shown in FIGS. 3 and 5, the fuel gas FG is supplied from the fuel gas supply manifold 321 to the fuel chamber 323 via the gas passage member 280.

[0065] When an oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and the fuel gas FG. This power generation reaction is exothermic. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures electrical continuity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, a second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end in FIG. 2 ) of the multiple reaction units 100U, and a first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end in FIG. 2 ). As a result, electrical energy generated in each reaction 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.

[0066] 2 and 4, the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidant gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the inside of the main body 281. Also, as shown in FIGS. 3 and 5, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 is discharged to the outside of the fuel cell stack 10 through the inside of the main body 281.

[0067] When a voltage is applied during operation of the fuel cell stack 10, the first glass seal 510 may peel off from the stress relaxation member 400. Alternatively, the second glass seal 520 may peel off from the second terminal plate 250. The relationship between the second glass seal 520 and the second terminal plate 250 is similar to the relationship between the first glass seal 510 and the stress relaxation member 400. Therefore, the relationship between the first glass seal 510 and the stress relaxation member 400 will be described in detail below, and a description of the relationship between the second glass seal 520 and the second terminal plate 250 will be omitted.

[0068] The mechanism by which the first glass seal 510 peels off from the stress relaxation member 400 is believed to be as follows. The following describes a case in which stainless steel is used as the material for the stress relaxation member 400, but it is believed that a similar phenomenon would occur even if another material is used. Furthermore, the following describes a case in which the first terminal plate 240 is the positive output terminal and the second terminal plate 250 is the negative output terminal, but it is believed that a similar phenomenon would occur even if the first terminal plate 240 is the negative output terminal and the second terminal plate 250 is the positive output terminal.

[0069] An oxide film is generally formed on the surface of the stress relaxation member 400. During the heat treatment for bonding, the glass components contained in the first glass seal 510 diffuse into the oxide film, forming a reaction layer at the interface between the first glass seal 510 and the stress relaxation member 400, thereby bonding the first glass seal 510 and the stress relaxation member 400.

[0070] When a voltage is applied during operation of the fuel cell stack 10, the iron elements contained in the stress relaxation member 400 ionize, causing pitting corrosion on the surface of the stress relaxation member 400. Meanwhile, components contained in the glass ionize, and negative oxygen ions migrate toward the positive stress relaxation member 400. These oxygen ions react with iron ions to form iron oxide between the base material of the stress relaxation member 400 and the oxide film. Alternatively, some iron elements dissolve in the oxide film. As a result, the bonding strength at the interface between the stress relaxation member 400 and the first glass seal 510 decreases. Meanwhile, an oxide film is again formed on the surface of the stress relaxation member 400 where pitting corrosion occurred. This causes peeling between the base material of the stress relaxation member 400 and the oxide film, causing the first glass seal 510 to peel off from the stress relaxation member 400.

[0071] In the intermediate seal 530, the dielectric constant of the pores is generally lower than that of the ceramic. Therefore, when a voltage is applied to the ceramic, the voltage applied to the pores is higher than that of the surrounding ceramic, resulting in the pores being short-circuited. (However, the entire ceramic is not short-circuited.) The short-circuiting of the pores causes the movement of minute ions, resulting in a leakage current. If the pore diameter of the pores 532 contained in the intermediate seal 530 is too large, the leakage current flowing through the seal member 500, i.e., the movement of ions within the seal member 500, increases. If the maximum pore diameter of the intermediate seal 530 is 20 μm or less, the leakage current flowing through the seal member 500 can be reduced, and the occurrence of peeling of the first glass seal 510 from the stress relaxation member 400 can be reduced.

[0072] Furthermore, in this embodiment, the thickness T3 of the intermediate seal 530 is greater than the thickness T1 of the first glass seal 510 and greater than the thickness T2 of the second glass seal 520. The relatively large thickness T3 of the intermediate seal 530 results in a relatively large electrical resistance of the intermediate seal 530. This reduces the leakage current flowing through the seal member 500 and reduces the occurrence of peeling of the first glass seal 510 from the stress relief member 400.

[0073] (Action and effect) As described above, the fuel cell stack 10 of this embodiment includes the second terminal plate 250, the stress relaxation member 400, and the seal member 500. The seal member 500 is a member that joins the second terminal plate 250 and the stress relaxation member 400. The seal member 500 includes a first glass seal 510 made of glass that is joined to the second terminal plate 250, a second glass seal 520 that is also made of glass that is joined to the stress relaxation member 400, and an intermediate seal 530 that is disposed between the first glass seal 510 and the second glass seal 520. The intermediate seal 530 has pores 532. The maximum pore diameter of the intermediate seal 530 is 20 μm or less.

[0074] The above configuration reduces the leakage current flowing through the seal member 500. This reduces the occurrence of peeling of the first glass seal 510 from the stress relaxation member 400 and the second glass seal 520 from the second terminal plate 250.

[0075] The thickness T3 of the middle seal 530 is greater than the thickness T1 of the first glass seal 510 and the thickness T2 of the second glass seal 520.

[0076] According to the above configuration, the relatively large thickness T3 of the intermediate seal 530 results in a relatively large electrical resistance of the intermediate seal 530, thereby reducing the leakage current flowing through the seal member 500. This reduces the occurrence of peeling of the first glass seal 510 from the stress relaxation member 400 and the second glass seal 520 from the second terminal plate 250.

[0077] The intermediate seal 530 is primarily composed of magnesium oxide. This configuration reduces the likelihood of the first glass seal 510 peeling off from the stress relaxation member 400 and the second glass seal 520 peeling off from the second terminal plate 250.

[0078] B. Working Example Three types of seal material samples with different maximum pore sizes for the middle seal were prepared. For each sample, a voltage application test was conducted to measure the leakage current and evaluate durability.

[0079] A sealing member having the same configuration as the above embodiment and a maximum pore size of the intermediate seal of 10 μm was prepared. The sealing member was sandwiched between two circular stainless steel plates with a diameter of 20 mm and a thickness of 2 mm, and heat treatment was performed to bond the glass seal and the stainless steel plates, resulting in sample S1. Two samples S1 were prepared, and a voltage of 450 V was applied to each of them in an electric furnace at 700°C, using the two stainless steel plates as electrodes. The value of the current flowing at this time was measured and used as the leakage current value. Furthermore, after applying voltage for 500 hours, sample S1 was observed for the presence or absence of peeling of the glass seal from the stainless steel plates.

[0080] Two samples each of sample S2, in which the maximum pore size of the intermediate seal is 20 μm, and sample S3, in which the maximum pore size of the intermediate seal is 30 μm, were prepared and tested in the same manner.

[0081] Table 1 shows the leakage current, the average value of the leakage current, and whether or not the glass seal peeled off from the stainless steel plate for each sample.

[0082] [Table 1]

[0083] In sample S3, where the maximum pore size of the middle seal was 30 μm, the average leakage current was 180.5 μA. Peeling of the glass seal from the stainless steel plate was also observed. In sample S2, where the maximum pore size of the middle seal was 20 μm, the average leakage current was 28.5 μA, a significant reduction in leakage current compared to sample S3. Peeling of the glass seal from the stainless steel plate was not observed. In sample S3, where the maximum pore size of the middle seal was 10 μm, the average leakage current was 4.85 μA, a further reduction in leakage current compared to sample S2. Peeling of the glass seal from the stainless steel plate was not observed.

[0084] 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. (1) The first member to be joined may be a member different from the stress relaxation member 400. For example, the electrochemical reaction cell stack may not be provided with a stress relaxation member, and a sealing member may be joined to an end plate. Alternatively, the first member to be joined may be, for example, a unit cell, or may be a member (e.g., a separator) that is different from the unit cell among the members that make up the electrochemical reaction cell stack. Furthermore, the second member to be joined may be a member different from the second terminal plate 250, or may be any member that is different from the first member to be joined among the members that make up the electrochemical reaction cell stack. (2) The thickness of the intermediate seal may be smaller than the thickness of the first glass seal, may be smaller than the thickness of the second glass seal, or may be smaller than both the thickness of the first glass seal and the thickness of the second glass seal. (3) In the above embodiment, the fuel cell stack 10 includes a plurality of flat-type unit cells 110, but the electrochemical reaction cell stack may include other types of unit cells (e.g., cylindrical, flat cylindrical). (4) 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. [Explanation of symbols]

[0085] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction 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 140: Anode frame 141: Through hole 144: Anode current collecting member 145: Electrode opposing portion 146: Interconnector opposing portion 147: Connecting portion 149: Spacer 180: IC separator 181: Through hole 190: Interconnector 191: Flat portion 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: End separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate (second joining target member) 260: Second plate 261: Seal accommodating hole 270: Second end plate 271: Flat portion 272: Through hole 273: Outer convex portion 274: Inner convex portion 275: Holding cylinder portion 280: Gas passage member 281: Main body portion 282: Flange portion 284: Bolt hole 311: Oxidizer gas supply manifold 311H1, 311H2, 311H3: Manifold holes 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber 400: Stress relief member (first joining target member) 500: Sealing member 510: First glass seal 511: First through hole 520: Second glass seal 521: Second through hole 530: Intermediate seal 531: Third through hole 532: Air hole B: Bolt BH: Bolt hole D: Air hole diameter FG: Fuel gas FOG: Fuel off-gas N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas T1: Thickness of first glass seal 510 T2: Thickness of second glass seal 520 T3: Thickness of intermediate seal 530

Claims

1. a first member to be joined; A second member to be joined; a seal member that joins the first member to be joined and the second member to be joined, The sealing member is a first glass seal made of glass to be joined to the first joining target member; a second glass seal made of glass that is joined to the second joining target member; an intermediate seal disposed between the first glass seal and the second glass seal; The intermediate seal has pores, and the maximum pore size of the intermediate seal is 20 μm or less. Electrochemical reaction cell stack.

2. 2. The electrochemical reaction cell stack according to claim 1, the thickness of the intermediate seal is greater than the thickness of the first glass seal and the thickness of the second glass seal; Electrochemical reaction cell stack.

3. 3. The electrochemical reaction cell stack according to claim 1 or 2, The intermediate seal is made primarily of magnesium oxide. Electrochemical reaction cell stack.

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