Electrochemical reaction cell stack

Abstract

To reduce occurrence of a crack in a seal member.SOLUTION: An electrochemical reaction cell stack comprising a single cell including a fuel electrode, an electrolyte layer, and an air electrode comprises: a first joint target member which is the single cell or the other member which is different from the single cell in members constituting the electrochemical reaction cell stack; a second joint target member which is different from the first joint target member in the members constituting the electrochemical reaction cell stack; and a seal member which joins the first joint target member and the second joint target member. The seal member includes: a first glass seal, which is made of glass, to be joined to the first joint target member; a second glass seal, which is made of glass, to be joined to the second joint target member; and an intermediate seal which is disposed between the first glass seal and the second glass seal. A thermal expansion coefficient of the intermediate seal is larger than a thermal expansion coefficient of the first glass seal and a thermal expansion coefficient of the second glass seal.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. As the sealing member, a member including a first sealing portion and second sealing portions laminated on both sides of the first sealing portion is sometimes used (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 cracks in the sealing members.

[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 unit cell including a fuel electrode, an electrolyte layer, and an air electrode; a first joining target member which is a member different from the unit cell or one of the members constituting the electrochemical reaction cell stack; a second joining target member different from the first joining target member among the members constituting the electrochemical reaction cell stack; and a seal member joining the first joining target member and the second joining target member, wherein the seal member comprises a first glass seal made of glass joined to the first joining target member, a second glass seal made of glass joined to the second joining target member, and an intermediate seal disposed between the first glass seal and the second glass seal, and the thermal expansion coefficient of the intermediate seal is greater than the thermal expansion coefficient of the first glass seal and the thermal expansion coefficient of the second glass seal.

[0008] According to the above configuration, the occurrence of cracks in the glass seal can be reduced.

[0009] (2) Another electrochemical reaction cell stack disclosed in this specification comprises a unit cell including a fuel electrode, an electrolyte layer, and an air electrode, a first joining target member which is a member different from the unit cell or one of the members constituting the electrochemical reaction cell stack, a second joining target member different from the first joining target member among the members constituting the electrochemical reaction cell stack, and a sealing member joining the first joining target member and the second joining target member, wherein the sealing member comprises a first glass seal made of glass joined to the first joining target member, a second glass seal made of glass joined to the second joining target member, and an intermediate seal disposed between the first glass seal and the second glass seal, and satisfies the following (i) and (ii): (i) When the joint length between the first glass seal and the intermediate seal is L11 and the joint length between the first glass seal and the first joining target member is L12, the following formula (1) is satisfied. L11 <L12···(1) (ii) When the joining length between the second glass seal and the intermediate seal is L21 and the joining length between the second glass seal and the second joining target member is L22, the following formula (2) is satisfied. L21 <L22···(2)

[0010] According to the above configuration, the occurrence of cracks in the glass seal can be reduced.

[0011] (3) Another electrochemical reaction cell stack disclosed in this specification comprises a unit cell including a fuel electrode, an electrolyte layer, and an air electrode; a first joining target member which is a member different from the unit cell or one of the members constituting the electrochemical reaction cell stack; a second joining target member different from the first joining target member among the members constituting the electrochemical reaction cell stack; and a seal member joining the first joining target member and the second joining target member, wherein the seal member comprises a first glass seal made of glass joined to the first joining target member, a second glass seal made of glass joined to the second joining target member, and an intermediate seal disposed between the first glass seal and the second glass seal and containing magnesium oxide, wherein the proportion of magnesium oxide contained in the intermediate seal is greater than the proportion of magnesium oxide contained in the first glass seal and the proportion of magnesium oxide contained in the second glass seal.

[0012] According to the above configuration, the occurrence of cracks in the glass seal can be reduced.

[0013] (4) In the electrochemical reaction cell stack according to any one of (1) to (3) above, the intermediate seal may contain magnesium oxide as a main component.

[0014] This configuration effectively reduces the occurrence of cracks in the glass seal.

[0015] 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]

[0016] [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. DETAILED DESCRIPTION OF THE INVENTION

[0017] A. Implementation: The embodiment will be described with reference to Figures 1 to 8. 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.

[0018] (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).

[0019] 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.

[0020] 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).

[0021] (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.

[0022] 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.

[0023] (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.

[0024] 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 and approximately the same size as the electrolyte layer 112 and containing, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, or the like. The reaction prevention layer 118 is a layer having a rectangular shape and approximately the same size as the air electrode 114 and containing, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of preventing elements (e.g., Sr) diffused from the air electrode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0025] (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 plate thickness of the single cell separator 120 is relatively thin, for example, not less than 0.05 mm and not more than 0.2 mm. 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).

[0026] (Air electrode frame 130) 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.). The thickness of the cathode frame 130 is preferably 0.5 to 5 mm.

[0027] (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.

[0028] (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.

[0029] (Interconnector 190 and anode current collecting member 144) 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 collectors 192 are electrically conductive and formed of a metal such as ferritic stainless steel. The coating layer 193 is electrically conductive and is disposed so as to cover the surface of the air electrode current collector 192 and the surface of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] (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.

[0035] 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.

[0036] 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.

[0037] (First end plate 210) The first end plate 210 is a member formed by pressing (bending) a single plate-like member. The first end plate 210 is electrically conductive and is formed from a metal such as ferritic stainless steel. 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 disposed around the entire inner periphery of the flat portion 211.

[0038] (insulating part 220) Insulating section 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of, for example, an insulating material. As shown in Figure 2, insulating section 220 is sandwiched between first end plate 210 and end separator 230, thereby ensuring insulation between first end plate 210 and end separator 230.

[0039] (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.

[0040] (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.

[0041] 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.

[0042] (First terminal plate 240) 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 electrically conductive and is made of a metal such as ferritic stainless steel. 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.

[0043] (2nd terminal plate 250) The second terminal plate 250 is a rectangular, plate-shaped member. The second terminal plate 250 is electrically conductive and is made of a metal such as ferritic stainless steel. 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.

[0044] (Second plate 260) Second plate 260 is a rectangular, flat member made of, for example, an insulating material. The peripheral edge of second plate 260 is sandwiched between second terminal plate 250 and second end plate 270, thereby ensuring insulation between second terminal plate 250 and second end plate 270.

[0045] (Second end plate 270) The second end plate 270 is a member formed by pressing (bending) a single plate-shaped member. The second end plate 270 is electrically conductive and is formed from a metal such as ferritic stainless steel. The second end plate 270 includes a rectangular, frame-shaped flat portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the flat portion 271 in 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.

[0046] (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.

[0047] 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. For example, air is used as the oxidant gas OG. The oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312 are arranged on opposite sides of the air chamber 313.

[0048] 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 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 chamber 323 of each reaction 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.

[0049] 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).

[0050] 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).

[0051] (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.

[0052] 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). One end (the 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 of the main body portions 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.

[0053] (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.

[0054] 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.

[0055] 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 stress relaxation member 400 is sandwiched between the periphery of the seal receiving hole 261 in the second plate 260 and the periphery of the manifold hole 311H2 in the flat portion 271. The stress relaxation member 400 is joined to the flat portion 271 around the entire periphery of the manifold hole 311H3. The stress relaxation member 400 can be joined to the flat portion 271 by, for example, laser welding.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The intermediate seal 530 is an annular member having a third through hole 531. The intermediate seal 530 is formed of an insulating material such as ceramics. The intermediate seal 530 may be ceramics containing magnesium oxide (MgO) or ceramics containing magnesium oxide as a 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.

[0060] The coefficient of thermal expansion of the mid-seal 530 is greater than the coefficient of thermal expansion of the first glass seal 510 and greater than the coefficient of thermal expansion of the second glass seal 520 .

[0061] The magnitude of the thermal expansion coefficient depends on the amount of magnesium oxide contained in the intermediate seal 530 and the glass seals 510 and 520. Therefore, in order to make the thermal expansion coefficient of the intermediate seal 530 larger than that of the first glass seal 510, the percentage (volume %) of magnesium oxide contained in the intermediate seal 530 may be larger than that of the first glass seal 510. Furthermore, in order to make the thermal expansion coefficient of the intermediate seal 530 larger than that of the second glass seal 520, the percentage (volume %) of magnesium oxide contained in the intermediate seal 530 may be larger than that of the second glass seal 520. The percentage (volume %) of magnesium oxide can be confirmed by quantitative analysis using, for example, X-ray fluorescence analysis.

[0062] The coefficient of thermal expansion of the mid-seal 530 may also be greater than the coefficient of thermal expansion of the second terminal plate 250 and may also be greater than the coefficient of thermal expansion of the stress relief member 400 .

[0063] 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 oxidizing gas supply manifold 311.

[0064] 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 edge 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 edge 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 edge 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 entire periphery of the edge of the third through hole 531.

[0065] (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.

[0066] The second plate 260 is placed on top of the second end plate 270, which has the stress relaxation 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 relaxation member 400 together via the second glass seal 520.

[0067] Because the thermal expansion coefficient of the intermediate seal 530 is greater than that of the first glass seal 510, the intermediate seal 530 shrinks more than the first glass seal 510 during cooling after heat treatment. During this shrinkage, the portion of the first glass seal 510 that is in contact with the intermediate seal 530 is affected by the shrinkage of the intermediate seal 530 and shrinks more than other portions. Therefore, the following relationship holds between the intermediate seal 530 and the first glass seal 510:

[0068] A cross section of the seal member 500 is taken perpendicularly to the interface with the stress relaxation member 400. This cross section may include the contour lines of the first glass seal 510: a contour line defining the interface with the intermediate seal 530, a contour line defining the interface with the stress relaxation member 400, and two contour lines defining side surfaces connecting the interface with the intermediate seal 530 and the interface with the stress relaxation member 400. Hereinafter, this cross section will be referred to as the "first vertical cross section." An example of the first vertical cross section is shown in FIG. 7. In the first vertical cross section, when the bonding length between the first glass seal 510 and the intermediate seal 530 is L11 and the bonding length between the first glass seal 510 and the stress relaxation member 400 is L12, the following formula (1) is satisfied:

[0069] L11 <L12···(1)

[0070] The bonding length L11 is the length from one end E11 of the contour line of the first glass seal 510 that appears in the first vertical cross section, which defines the interface with the intermediate seal 530, to the other end E12 that abuts on one of the two contour lines that define the side surfaces. The bonding length L12 is the length from one end E13 of the contour line of the first glass seal 510 that appears in the first vertical cross section, which defines the interface with the stress relaxation member 400, to the other end E14 that abuts on the other.

[0071] Similarly, since the thermal expansion coefficient of the mid-seal 530 is greater than the thermal expansion coefficient of the second glass seal 520, the following relationship holds between the mid-seal 530 and the second glass seal 520:

[0072] A cross section of the seal member 500 is defined by cutting it perpendicularly to the interface with the second terminal plate 250. This cross section may include the contour lines of the second glass seal 520: a contour line defining the interface with the intermediate seal 530, a contour line defining the interface with the second terminal plate 250, and two contour lines defining side surfaces connecting the interface with the intermediate seal 530 and the interface with the second terminal plate 250. Hereinafter, this cross section will be referred to as a "second longitudinal cross section." The second longitudinal cross section may be the same as or different from the first longitudinal cross section. In this embodiment, a cross section identical to the first longitudinal cross section is shown in FIG. 7 as an example of the second longitudinal cross section. In the second longitudinal cross section, when the bonding length between the second glass seal 520 and the intermediate seal 530 is L21 and the bonding length between the second glass seal 520 and the second terminal plate 250 is L22, the following formula (2) is satisfied:

[0073] L21 <L22···(2)

[0074] The bonding length L21 is the length of the contour line of the second glass seal 520 that appears in the second vertical cross section, from one end E21 that contacts one of the two contour lines that define the side surfaces to the other end E22 that contacts the other of the two contour lines that define the side surfaces of the contour line that defines the interface with the second terminal plate 250. The bonding length L22 is the length of the contour line of the second glass seal 520 that appears in the second vertical cross section, from one end E23 that contacts one of the two contour lines that define the side surfaces to the other end E24 that contacts the other of the two contour lines that define the interface with the second terminal plate 250.

[0075] (Operation of fuel cell stack 10) As shown in FIGS. 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.

[0076] 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.

[0077] 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.

[0078] 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 internal space 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 via the fuel gas discharge communication channel is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0079] The fuel cell stack 10 reaches high temperatures during operation and returns to room temperature when operation is stopped. This causes stress in the gas passage member 280 due to expansion and contraction caused by temperature changes. In this embodiment, as described above, the thermal expansion coefficient of the intermediate seal 530 is greater than that of the first glass seal 510. Therefore, during cooling after heat treatment, the intermediate seal 530 contracts more than the first glass seal 510. This causes compressive stress in the first glass seal 510. The same applies to the second glass seal 520. Generally, glass is relatively weak against tensile stress but strong against compressive stress. Therefore, by maintaining a state in which compressive stress is generated in the glass seals 510 and 520, it is possible to reduce the occurrence of cracks in the seal member 500 due to stress generated in the gas passage member 280 being transmitted to the seal member 500. In particular, the gas passage member 280 is a member that is elongated in one direction and expands and contracts relatively greatly in the longitudinal direction. Therefore, relatively large stress is likely to be generated around the gas passage member 280. By applying the above-described configuration to the seal member 500 disposed near such a gas passage member 280, the occurrence of cracks can be effectively reduced.

[0080] (Action and effect) As described above, the fuel cell stack 10 of this embodiment includes a unit cell 110 including an anode 116, an electrolyte layer 112, and an cathode 114, a stress relief member 400, a second terminal plate 250, and a seal member 500. The seal member 500 is a member that joins the stress relief member 400 and the second terminal plate 250. The seal member 500 includes a first glass seal 510, a second glass seal 520, and an intermediate seal 530. The first glass seal 510 is made of glass and is joined to the second terminal plate 250. The second glass seal 520 is made of glass and is joined to the stress relief member 400. The intermediate seal 530 is disposed between the first glass seal 510 and the second glass seal 520. The thermal expansion coefficient of the intermediate seal 530 is greater than that of the first glass seal 510 and is also greater than that of the second glass seal 520.

[0081] The above fuel cell stack 10 satisfies the following (i) and (ii). (i) When the joint length between the first glass seal 510 and the intermediate seal 530 is L11 and the joint length between the first glass seal 510 and the stress relaxation member 400 is L12, the following formula (1) is satisfied. L11 <L12···(1) (ii) When the joint length between the second glass seal 520 and the intermediate seal 530 is L21 and the joint length between the second glass seal 520 and the second terminal plate 250 is L22, the following formula (2) is satisfied. L21 <L22···(2)

[0082] The proportion of magnesium oxide contained in the intermediate seal 530 is greater than the proportion of magnesium oxide contained in the first glass seal 510 and greater than the proportion of magnesium oxide contained in the second glass seal 520 .

[0083] According to the above configuration, the occurrence of cracks in the glass seals 510 and 520 can be reduced.

[0084] Magnesium oxide may be used as the main component of intermediate seal 530. This configuration effectively reduces the occurrence of cracks in glass seals 510 and 520.

[0085] B. 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, as long as it is a member that is different from the first member to be joined among the members that make up the electrochemical reaction cell stack. (2) 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). (3) 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]

[0086] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Reaction unit 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 tube 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 exhaust 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 B: Bolt BH: Bolt hole FG: Fuel gas FOG: Fuel off-gas L11, L12, L21, L22: Joint length N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas

Claims

1. An electrochemical reaction cell stack including a single cell including an anode, an electrolyte layer, and an cathode, a first joining target member which is a member different from the unit cell among the members constituting the unit cell or the electrochemical reaction cell stack; a second joining target member that is different from the first joining target member among the members that configure the electrochemical reaction cell stack; 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 coefficient of thermal expansion of the intermediate seal is greater than the coefficient of thermal expansion of the first glass seal and the coefficient of thermal expansion of the second glass seal; Electrochemical reaction cell stack.

2. An electrochemical reaction cell stack including a single cell including an anode, an electrolyte layer, and an cathode, a first joining target member which is a member different from the unit cell among the members constituting the unit cell or the electrochemical reaction cell stack; a second joining target member that is different from the first joining target member among the members that configure the electrochemical reaction cell stack; 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; Satisfy the following (i) and (ii): Electrochemical reaction cell stack. (i) When the joining length between the first glass seal and the intermediate seal is L11 and the joining length between the first glass seal and the first joining target member is L12, the following formula (1) is satisfied. L11<L12...(1) (ii) When the joining length between the second glass seal and the intermediate seal is L21 and the joining length between the second glass seal and the second joining target member is L22, the following formula (2) is satisfied. L21<L22...(2)

3. An electrochemical reaction cell stack including a single cell including an anode, an electrolyte layer, and an cathode, a first joining target member which is a member different from the unit cell among the members constituting the unit cell or the electrochemical reaction cell stack; a second joining target member that is different from the first joining target member among the members that configure the electrochemical reaction cell stack; 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 including magnesium oxide; a proportion of magnesium oxide contained in the intermediate seal is greater than a proportion of magnesium oxide contained in the first glass seal and a proportion of magnesium oxide contained in the second glass seal; Electrochemical reaction cell stack.

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

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