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 in the present specification relates to an electrochemical reaction cell stack.

Background Art

[0002] As one type of fuel cell that generates power using an electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") including an electrolyte layer containing a solid oxide is known. The SOFC is generally used in the form of a fuel cell stack in which a plurality of structural units (electrochemical reaction units) are arranged side by side in a predetermined direction.

[0003] A sealing member is used to connect two structural units provided in the fuel cell stack. As the sealing member, a member including a first seal portion and second seal portions laminated on both surfaces of the first seal portion may be used (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above SOFC, it is required to reduce the occurrence of cracks in the sealing member.

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

[0007] The technologies disclosed herein can be implemented, for example, in the following forms: (1) An electrochemical reaction cell stack disclosed herein comprises a single cell including a fuel electrode, an electrolyte layer, and an air electrode, the single cell or a first joining target member which is a different member from the single cell among the members constituting the electrochemical reaction cell stack, a second joining target member which is a different member from the first joining target member among the members constituting the electrochemical reaction cell stack, and a sealing member which joins the first joining target member and the second joining target member, wherein the sealing member comprises a first glass seal made of glass which is joined to the first joining target member, a second glass seal made of glass which is joined to the second joining target member, and an intermediate seal disposed between the first glass seal and the second glass seal, wherein 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.

[0008] The above configuration can reduce the occurrence of cracks in the glass seal.

[0009] (2) Other electrochemical reaction cell stacks disclosed herein include a single cell comprising a fuel electrode, an electrolyte layer, and an air electrode, wherein the single cell or a first joining target member which is a different member from the single cell among the members constituting the electrochemical reaction cell stack, a second joining target member which is a different member from the first joining target member among the members constituting the electrochemical reaction cell stack, and a sealing member which joins the first joining target member and the second joining target member, wherein the sealing member comprises a first glass seal made of glass which is joined to the first joining target member, a second glass seal made of glass which is joined to the second joining target member, and an intermediate seal which is disposed between the first glass seal and the second glass seal, and satisfies the following (i) and (ii). (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 member to be joined is L12, the following equation (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 member to be joined is L22, the following equation (2) is satisfied. L21 <L22···(2)

[0010] The above configuration can reduce the occurrence of cracks in the glass seal.

[0011] (3) Other electrochemical reaction cell stacks disclosed herein include a single cell comprising a fuel electrode, an electrolyte layer, and an air electrode, wherein the single cell or a first joining target member which is a different member from the single cell among the members constituting the electrochemical reaction cell stack, a second joining target member which is a different member from the first joining target member among the members constituting the electrochemical reaction cell stack, and a sealing member which joins the first joining target member and the second joining target member, wherein the sealing member comprises a first glass seal made of glass which is joined to the first joining target member, a second glass seal made of glass which is joined to the second joining target member, and an intermediate seal disposed between the first glass seal and the second glass seal which contains 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] The above configuration can reduce the occurrence of cracks in the glass seal.

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

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

[0015] The technologies disclosed herein can be implemented in various forms, for example, in the form of an electrochemical reaction cell stack and a method for producing the same. [Brief explanation of the drawing]

[0016] [Figure 1] Perspective view showing the external configuration of the fuel cell stack of the embodiment. [Figure 2] A cross-sectional view showing the fuel cell stack of the embodiment, cut along the line II-II in Figure 1. [Figure 3]Cross-sectional view of the fuel cell stack of the embodiment taken along line III-III in Figure 1 [Figure 4] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, taken at the same position as line II-II in Figure 1 [Figure 5] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, taken at the same position as line III-III in Figure 1 [Figure 6] Partial enlarged cross-sectional view showing the inside of frame F1 in Figure 2 in an enlarged manner [Figure 7] Partial enlarged cross-sectional view showing the inside of frame F2 in Figure 6 in an enlarged manner [Figure 8] Cross-sectional view of the fuel cell stack of the embodiment taken along line VIII-VIII in Figure 6 [Mode for Carrying Out the Invention]

[0017] A. Embodiment: The embodiment will be described with reference to Figure 1 to Figure 8. The fuel cell stack 10 of the present embodiment (an example of an electrochemical reaction cell stack) is used for a solid oxide fuel cell including an electrolyte layer 112 containing a solid oxide.

[0018] (Overall Configuration of Fuel Cell Stack 10) As shown in Figure 1 to Figure 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 member to be joined), an insulating portion 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating portion 220, the 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 substantially the same size, and are arranged to overlap in this order in a predetermined arrangement direction (the vertical direction in Figure 2).

[0019] As shown in Figure 1, the fuel cell stack 10 has bolt holes BH near each of its four corners, each extending from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. Nuts N are threaded onto both ends of each bolt B. These bolts B and nuts N fasten the components from the first end plate 210 to the second end plate 270 together. As shown in Figures 2 and 3, the first plate 232 is supported by the end 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 a plurality (seven in this embodiment) of electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction unit 100U") arranged in a predetermined arrangement direction (up and down direction in Figure 2).

[0021] (Overall composition of an electrochemical reaction unit of 100U) As shown in Figures 4 and 5, the electrochemical reaction unit 100U comprises a single cell 110, a single cell separator 120, an air electrode frame 130, a fuel electrode frame 140, a fuel electrode current collector 144, two interconnectors 190, and two IC separators 180. One IC separator 180, the air electrode frame 130, the single cell separator 120, the fuel electrode frame 140, and the other IC separator 180 are arranged in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are each supported by the two IC separators 180, and the fuel electrode current collector 144 is positioned between the single cell 110 and the interconnectors 190.

[0022] As shown in Figures 4 and 5, the IC separator 180 and interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Figure 2, one of the multiple reaction units 100U located at one end (the lower end in Figure 2) does not have an IC separator 180 and interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 is superimposed on the fuel electrode frame 140.

[0023] (Single cell 110) The single cell 110 comprises an electrolyte layer 112, an air electrode 114, and a fuel electrode 116. As shown in Figures 4 and 5, the air electrode 114, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the air electrode 114. The single cell 110 of this embodiment is a fuel electrode-supported single cell in which the other layers constituting the single cell 110 (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) are supported by the fuel electrode 116.

[0024] The electrolyte layer 112 is a rectangular, flat member having one side on which the air electrode 114 is located (the upper side in Figures 4 and 5) and another side parallel to the air electrode 116 (the lower side in Figures 4 and 5). The electrolyte layer 112 is a layer containing a solid oxide (for example, YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite-type oxide (for example, LSCF (lanthanum strontium cobalt iron oxide)). The fuel electrode 116 is a layer having a rectangular shape approximately the same size as the electrolyte layer 112 and contains, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, etc. The reaction prevention layer 118 is a layer having a rectangular shape approximately the same size as the air electrode 114 and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of elements (e.g., Sr) diffused from the air electrode 114 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 Figures 4 and 5, the single-cell separator 120 is a rectangular frame-shaped member having a roughly rectangular through-hole 121 near its center. The single-cell separator 120 is conductive and is made of a metal such as ferritic stainless steel. The thickness of the single-cell separator 120 is relatively thin, for example, 0.05 mm or more and 0.2 mm or less. The periphery of the through-hole 121 in the single-cell separator 120 is joined to the periphery of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is located: the upper surface in Figures 4 and 5) by a joint 124. The joint 124 is made of, for example, brazing material (Ag brazing).

[0026] (Air pole frame 130) As shown in Figures 4 and 5, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through-hole 131 near the center, and is formed of, for example, an insulating ceramic (such as mica). The thickness of the air electrode frame 130 is preferably 0.5-5 mm.

[0027] (Fuel pole frame 140) As shown in Figure 5, the fuel electrode frame 140 is a rectangular frame-shaped member having a roughly rectangular through-hole 141 near its center. The fuel electrode frame 140 is conductive and is made of a metal such as ferritic stainless steel.

[0028] (IC separator 180) As shown in Figures 4 and 5, the IC separator 180 is a rectangular frame-shaped member having a through hole 181 near the center. The IC separator 180 is conductive and is made of a metal such as ferritic stainless steel.

[0029] (Interconnector 190, and fuel electrode current collector 144) As shown in Figures 4 and 5, the interconnector 190 comprises 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 conductive and are made of a metal such as ferritic stainless steel. The coating layer 193 is conductive and is arranged to cover the surface of the air electrode current collectors 192 and the surface of the flat plate portion 191 on which the air electrode current collectors 192 are arranged. 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 fuel electrode current collector 144 is a member that connects the interconnector 190 and the fuel electrode 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 fuel electrode current collector 144 comprises an interconnector-facing portion 146, an electrode-facing portion 145 parallel to the interconnector-facing portion 146, and a connecting portion 147 connecting the electrode-facing portion 145 and the interconnector-facing portion 146, and is U-shaped overall. The electrode-facing portion 145 is in contact with the fuel electrode 116, and the interconnector-facing portion 146 is in contact with the flat plate 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 collector 192 is joined to the air electrode 114 of a single 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, thereby electrically connecting to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of a single cell 110 provided in the other of the two adjacent reaction units 100U via a fuel electrode current collector 144. This ensures electrical conductivity between the two adjacent reaction units 100U.

[0032] However, as described above, the reaction unit 100U located at one end (the lower end of Figure 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this reaction unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0033] A spacer 149, for example made of mica, is placed between the electrode facing portion 145 and the interconnect facing portion 146. As a result, the fuel electrode current collector 144 follows the deformation of the reaction unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnect 190 (or second terminal plate 250) via the fuel electrode current collector 144 is maintained well.

[0034] (Air chamber 313 and fuel chamber 323) As shown in Figures 4 and 5, the space partitioned by the single-cell separator 120 and single cell 110, the air electrode frame 130, the IC separator 180 and interconnector 190 faces the air electrode 114 and forms an air chamber 313 through which the oxidizer gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 into the outside space.

[0035] Furthermore, the space partitioned by the single-cell separator 120 and single cell 110, the fuel electrode frame 140, the IC separator 180 and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the fuel chamber 323 into the outside space.

[0036] The single-cell separator 120 separates the air chamber 313 from the fuel chamber 323, suppressing gas leakage (cross-leakage) from the air electrode 114 to the fuel electrode 116, or from the fuel electrode 116 to the air electrode 114, around the single-cell 110. In addition, the IC separator 180 and interconnector 190 suppress gas leakage between adjacent reaction units 100U.

[0037] (First end plate 210) The first end plate 210 is a member formed by press-forming (bending) a single plate-shaped member. The first end plate 210 is conductive and is made of a metal such as ferritic stainless steel. As shown in Figures 1-3, the first end plate 210 comprises a rectangular frame-shaped planar portion 211 having a through hole 212 near the center, and an outer projection 213 and an inner projection 214 that project from the planar portion 211 in the opposite direction to the insulating portion 220 (upwards in Figure 2). The planar portion 211 has holes that constitute the bolt holes BH described above. The outer projection 213 protrudes from the outer peripheral edge of the planar portion 211. The outer projection 213 is arranged around the entire circumference of the outer peripheral portion of the planar portion 211. The inner projection 214 protrudes from the inner peripheral edge of the planar portion 211. The inner projection 214 is arranged around the entire circumference of the inner peripheral portion of the planar portion 211.

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

[0039] (End separator 230) As shown in Figures 2 and 3, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near its center. The end separator 230 is conductive and is made of a metal such as ferritic stainless steel.

[0040] (Plate 1, No. 232) The first plate 232 is a rectangular, flat member. The first plate 232 is conductive and is made of a metal such as ferritic stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined to the peripheral portion of the through hole 231 in the end separator 230, for example, by welding. The end 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 on a reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via a connecting member with the same structure as the fuel electrode current collector 144. In this way, the reaction unit 100U and the first plate 232 are electrically connected.

[0042] (Terminal 1 Plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through hole 241 near its center. The first terminal plate 240 is 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 located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via the first plate 232 and the end separator 230. One end of the first terminal plate 240 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0043] (Terminal 2 Plate 250) The second terminal plate 250 is a rectangular plate-shaped member. The second terminal plate 250 is conductive and is made of a metal such as ferritic stainless steel. As described above, the second terminal plate 250 is connected to a fuel electrode 116 provided on a reaction unit 100U located at one end (the lower end in Figure 2) of the plurality of reaction units 100U via a fuel electrode current collector 144, thereby electrically connecting this reaction unit 100U and the second terminal plate 250. One end of the second terminal plate 250 (the right end in Figure 2) 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] (Plate 2, page 260) The second plate 260 is a rectangular, flat member, formed of, for example, an insulating material. The peripheral edge of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring insulation between the second terminal plate 250 and the second end plate 270.

[0045] (Second end plate 270) The second end plate 270 is a component formed by press-forming (bending) a single plate-shaped member. The second end plate 270 is conductive and is made of a metal such as ferritic stainless steel. The second end plate 270 comprises a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer projection 273 and an inner projection 274 that project from the planar portion 271 in the opposite direction from the second terminal plate 250 (downward in Figure 2). The outer projection 273 protrudes from the outer peripheral edge of the planar portion 271. The outer projection 273 is arranged around the entire circumference of the outer peripheral portion of the planar portion 271. The inner projection 274 protrudes from the inner peripheral edge of the planar portion 271. The inner projection 274 is arranged around the entire circumference of the inner peripheral portion of the planar portion 271.

[0046] (Manifolds 311, 312, 321, 322) As shown in Figures 1-3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are the oxidizer gas supply manifold 311, the oxidizer gas discharge manifold 312, the fuel gas supply manifold 321, and the fuel gas discharge manifold 322, respectively.

[0047] As shown in Figure 2, the oxidizer gas supply manifold 311 is a gas flow path that supplies oxidizer gas OG, introduced from outside the fuel cell stack 10, to the air chamber 313 of each reaction unit 100U. The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer 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 oxidizer gas OG. The oxidizer gas supply manifold 311 and the oxidizer gas discharge manifold 312 are located on opposite sides of the air chamber 313.

[0048] As shown in Figure 3, the fuel gas supply manifold 321 is a gas passage 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 passage 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 located 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 parts of manifolds 311, 312, 321, and 322, respectively. Hereinafter, of the four manifold holes provided in the second terminal plate 250, the manifold hole that forms part of the oxidizer gas supply manifold 311 will be referred to as "manifold hole 311H1" (see Figure 6).

[0050] The second end plate 270 has four manifold holes. Each of the four manifold holes is a hole that penetrates the second end plate 270 and is part of the four manifolds 311, 312, 321, and 322. Hereinafter, of the four manifold holes provided in the second end plate 270, the manifold hole that forms part of the oxidizer gas supply manifold 311 will be referred to as "manifold hole 311H2" (see Figure 6).

[0051] (Gas passage member 280) Each of the four gas passage members 280 comprises a main body portion 281 and a flange portion 282, as shown in Figures 1-3. The main body portion 281 is cylindrical with open ends. The flange portion 282 is provided so as to protrude outward from one end of the main body portion 281 (the lower end in Figure 2). The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into each bolt hole 284.

[0052] The second end plate 270 is provided with four retaining cylindrical portions 275 for connecting the gas passage member 280. As shown in Figure 6, one of the four retaining cylindrical portions 275 is a cylindrical portion extending from the edge of the manifold hole 311H2 toward the opposite side of the power generation block 100 (downward in Figure 6). One end of the main body portion 281 (upper end in Figure 6) is joined to the retaining cylindrical portion 275, for example, by welding. The internal space of the main body portion 281 is in communication with the oxidizer gas supply manifold 311. Gas piping (not shown) for gas supply or discharge is connected to each main body portion 281. The other three retaining cylindrical portions 275 are positioned corresponding to manifolds 312, 321, and 322, respectively, and are similarly connected to the gas passage member 280.

[0053] (Joining structure between the second terminal plate 250 and the second end plate 270) The second end plate 270 is joined to the second terminal plate 250 via a stress-relieving member 400 (an example of a first joining target member) and a sealing member 500. More specifically, in the planar section 271, the peripheral portions of the four manifolds 311, 312, 321, and 322 are each joined to the second terminal plate 250 via a stress-relieving member 400 and a sealing member 500. Since the joining structures around the four manifolds 311, 312, 321, and 322 are identical to each other, the joining structure around the oxidizer gas supply manifold 311 will be described below, and the other three will not be described.

[0054] As shown in Figure 6, the second plate 260 has a seal housing hole 261 at a position corresponding to the oxidizer gas supply manifold 311. The seal housing hole 261 is slightly larger than the manifold holes 311H1 and 311H2 and is a hole that penetrates the second plate 260.

[0055] The stress-relieving member 400 is a thin, flat, elastically deformable member having a manifold hole 311H3. The manifold hole 311H3 is a hole that penetrates the stress-relieving member 400 and is part of the oxidizer gas supply manifold 311. The peripheral edge of the stress-relieving member 400 is sandwiched between the peripheral portion of the seal housing hole 261 in the second plate 260 and the peripheral portion of the manifold hole 311H2 in the flat portion 271. The stress-relieving member 400 is joined to the flat portion 271 around the entire circumference of the manifold hole 311H3. The method of joining the stress-relieving member 400 to the flat portion 271 is, for example, laser welding.

[0056] The sealing member 500 is a member that joins the second terminal plate 250 and the stress relief member 400. The sealing member 500 is located inside the seal housing hole 261. As shown in Figure 7, the sealing member 500 comprises a first glass seal 510, a second glass seal 520, and an intermediate seal 530, which are arranged in 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 also be made of SiO2-B2O3-MgO glass. One side of the first glass seal 510 is joined to the stress relaxation member 400, and the other side is joined 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 also be made of SiO2-B2O3-MgO glass. One side of the second glass seal 520 is bonded to the second terminal plate 250, and the other side 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 a ceramic containing magnesium oxide (MgO), or a ceramic mainly composed of magnesium oxide. In this specification, "main component" means that the component is present in an amount of 90 volume or more. In this embodiment, the intermediate seal 530 contains 90 volume or more of magnesium oxide, and also contains sintering aids (e.g., CaO, SiO2, Al2O3), etc. The intermediate seal 530 is sandwiched between the first glass seal 510 and the second glass seal 520.

[0060] The thermal expansion coefficient of the intermediate seal 530 is greater than that of the first glass seal 510, and also greater than that of the second glass seal 520.

[0061] The magnitude of the thermal expansion coefficients of the intermediate seal 530 and the glass seals 510 and 520 is determined by the amount of magnesium oxide they contain. Therefore, in order to make the thermal expansion coefficient of the intermediate seal 530 greater than that of the first glass seal 510, the proportion (volume %) of magnesium oxide contained in the intermediate seal 530 may be greater than the proportion (volume %) of magnesium oxide contained in the first glass seal 510. Similarly, in order to make the thermal expansion coefficient of the intermediate seal 530 greater than that of the second glass seal 520, the proportion (volume %) of magnesium oxide contained in the intermediate seal 530 may be greater than the proportion (volume %) of magnesium oxide contained in the second glass seal 520. To confirm the proportion (volume %) of magnesium oxide, quantitative analysis can be performed, for example, by X-ray fluorescence analysis.

[0062] The thermal expansion coefficient of the intermediate seal 530 may be greater than that of the second terminal plate 250, and may also be greater than that of the stress relaxation member 400.

[0063] The first glass seal 510, the second glass seal 520, and the intermediate seal 530 overlap so that the first through-hole 511, the second through-hole 521, and the third through-hole 531 are aligned. The three through-holes 511, 521, and 531 are part of the oxidizer gas supply manifold 311.

[0064] One side of the first glass seal 510 is joined to the surface of the stress-relieving member 400 so as to surround the entire edge of the manifold hole 311H3. The other side of the first glass seal 510 is joined to the surface of the intermediate seal 530 so as to surround the entire edge of the third through hole 531. One side of the second glass seal 520 is joined to the surface of the second terminal plate 250 so as to surround the entire edge of the manifold hole 311H1. The other side of the second glass seal 520 is joined to the other surface of the intermediate seal 530 so as to surround the entire edge of the third through hole 531.

[0065] (Manufacturing method for fuel cell stack 10) An example of a manufacturing method for the fuel cell stack 10 with the above configuration is described below.

[0066] A second plate 260 is placed on top of a second end plate 270, which has a stress-relieving member 400 bonded to its surface. The first glass seal 510, intermediate seal 530, and second glass seal 520 are then stacked inside the seal housing hole 261 in this order. A second terminal plate 250 is placed on top of the second plate 260, and other components are further stacked to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is then heat-treated at a heat treatment temperature higher than the operating temperature. The heat treatment temperature is, for example, 850°C. Through this heat treatment, the second terminal plate 250 and the intermediate seal 530 are joined by the first glass seal 510, and the intermediate seal 530 and the stress-relieving member 400 are joined by 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 is set by cutting the sealing member 500 perpendicular to the interface with the stress-relieving member 400. This cross-section only needs to include, as 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-relieving member 400, and two contour lines defining the side surface connecting the interface with the intermediate seal 530 and the interface with the stress-relieving member 400. Hereinafter, this cross-section will be referred to as the "first longitudinal cross-section". An example of the first longitudinal cross-section is shown in Figure 7. In the first longitudinal cross-section, when the joining length between the first glass seal 510 and the intermediate seal 530 is L11 and the joining length between the first glass seal 510 and the stress-relieving member 400 is L12, the following equation (1) is satisfied.

[0069] L11 <L12···(1)

[0070] The joint length L11 is the length from one end E11, which touches one of the two contour lines defining the side surface of the contour line of the first glass seal 510 that defines the interface with the intermediate seal 530, to the other end E12, which touches the other contour line. The joint length L12 is the length from one end E13, which touches one of the two contour lines defining the side surface of the contour line of the first glass seal 510 that defines the interface with the stress relaxation member 400, to the other end E14, which touches the other contour line.

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

[0072] A cross-section is set by cutting the sealing member 500 perpendicular to the interface with the second terminal plate 250. This cross-section only needs to include 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 the side surface connecting the interface with the intermediate seal 530 and the interface with the second terminal plate 250, as the contour lines of the second glass seal 520. Hereinafter, this cross-section will be referred to as the "second longitudinal cross-section". The second longitudinal cross-section may be the same as the first longitudinal cross-section or may be different. In this embodiment, a cross-section identical to the first longitudinal cross-section is shown in Figure 7 as an example of the second longitudinal cross-section. In the second longitudinal cross-section, when the joining length between the second glass seal 520 and the intermediate seal 530 is L21 and the joining length between the second glass seal 520 and the second terminal plate 250 is L22, the following equation (2) is satisfied.

[0073] L21 <L22···(2)

[0074] The joint length L21 is the length from one end E21, which is in contact with one of the two contour lines defining the side surface of the contour line of the second glass seal 520 that defines the interface with the intermediate seal 530, to the other end E22, which is in contact with the other contour line. The joint length L22 is the length from one end E23, which is in contact with one of the two contour lines defining the side surface of the contour line of the second glass seal 520 that defines the interface with the second terminal plate 250, to the other end E24, which is in contact with the other contour line.

[0075] (Operation of fuel cell stack 10) As shown in Figures 2 and 4, the oxidizer gas OG is supplied from the oxidizer gas supply manifold 311 to the air chamber 313 via the gas passage member 280.

[0076] Furthermore, as shown in Figures 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 oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and fuel gas FG is supplied to the fuel chamber 323, electricity is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and fuel gas FG. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures conductivity 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, the second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end of Figure 2), and the first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end of Figure 2). As a result, the electrical energy generated in each reaction unit 100U is extracted from the terminal plates 240 and 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (for example, 700°C to 1000°C), the fuel cell stack 10 may be heated by a heater (not shown) after startup until the high temperature can be maintained by the heat generated by power generation.

[0078] As shown in Figures 2 and 4, the oxidizer off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidizer 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 Figures 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 becomes hot during operation and returns to room temperature when operation is stopped, so stress is generated 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 larger than that of the first glass seal 510, so when cooling after heat treatment, the intermediate seal 530 shrinks more than the first glass seal 510. As a result, compressive stress is generated 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 keeping the glass seals 510 and 520 in a state where compressive stress is generated, it is possible to reduce the occurrence of cracks in the seal member 500 caused by the stress generated in the gas passage member 280 being transmitted to the seal member 500. In particular, the gas passage member 280 is an elongated member in one direction and expands and contracts relatively large in the longitudinal direction, so relatively large stress is likely to be generated around the gas passage member 280. By applying the above configuration to the sealing member 500 located near the gas passage member 280, the occurrence of cracks can be effectively reduced.

[0080] (Effects and Benefits) As described above, the fuel cell stack 10 of this embodiment comprises a single cell 110 including a fuel electrode 116, an electrolyte layer 112, and an air electrode 114, a stress relaxation member 400, a second terminal plate 250, and a sealing member 500. The sealing member 500 is a member that joins the stress relaxation member 400 and the second terminal plate 250. The sealing member 500 comprises 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 relaxation 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 greater than that of the second glass seal 520.

[0081] The fuel cell stack 10 described above satisfies the following conditions (i) and (ii). (i) When the joining length between the first glass seal 510 and the intermediate seal 530 is L11, and the joining length between the first glass seal 510 and the stress relaxation member 400 is L12, the following equation (1) is satisfied. L11 <L12···(1) (ii) When the joining length between the second glass seal 520 and the intermediate seal 530 is L21, and the joining length between the second glass seal 520 and the second terminal plate 250 is L22, the following equation (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 also 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] The intermediate seal 530 may have magnesium oxide as its main component. With this configuration, the occurrence of cracks in the glass seals 510 and 520 can be effectively reduced.

[0085] B. Variations The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible. (1) The first member to be joined may be a different member from the stress relaxation member 400. For example, the electrochemical reaction cell stack may not have a stress relaxation member, and the sealing member may be joined to the end plate. Alternatively, the first member to be joined may be, for example, a single cell, or a different member (e.g., a separator) from the members constituting the electrochemical reaction cell stack. Furthermore, the second member to be joined may be a different member from the second terminal plate 250, or a different member from the first member to be joined from the members constituting the electrochemical reaction cell stack. (2) In the above embodiment, the fuel cell stack 10 was equipped with a plurality of flat-plate type single cells 110, but the electrochemical reaction cell stack may be equipped with other types of single cells (for example, 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 electrolytic cell stacks that have electrolytic cell units, which are constituent units of solid oxide electrolytic 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: Fuel electrode 118: Reaction prevention layer 120: Separator for single cell 121: Through hole 124: Joint 130: Air electrode frame 131: Through hole 140: Fuel electrode frame 141: Through hole 144: Fuel electrode current collector 145: Electrode opposing part 146: Interconnector opposing part 147: Connecting part 149: Spacer 180: Separator for IC 181: Through hole 190: Interconnector 191: Flat plate part 192: Air electrode current collector part 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat part 212: Through hole 213: Outer protrusion 214: Inner protrusion 220: Insulation part 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 housing hole 270: Second end plate 271: Flat part 272: Through hole 273: Outer protrusion 274: Inner protrusion 275: Retaining cylinder part 280: Gas passage member 281: Main body part 282: Flange part 284: Bolt hole 311: Oxidizer gas supply manifold 311H1, 311H2, 311H3: Manifold hole 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 joint target member) 500: Seal 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 comprising a single cell including a fuel electrode, an electrolyte layer, and an air electrode, The first member to be joined is the single cell, or a member other than the single cell among the members constituting the electrochemical reaction cell stack, Among the members constituting the electrochemical reaction cell stack, a second member to be joined is different from the first member to be joined, The device comprises a sealing member for joining the first member to be joined and the second member to be joined, The sealing member, A first glass seal made of glass is joined to the first member to be joined, A second glass seal made of glass is joined to the second member to be joined, The system comprises an intermediate seal disposed between the first glass seal and the second glass seal, The thermal expansion coefficient of the intermediate seal is greater than that of the first glass seal and the second glass seal. The interface between the first glass seal and the first member to be joined is planar, The interface between the second glass seal and the second member to be joined is planar. Electrochemical reaction cell stack.

2. An electrochemical reaction cell stack according to claim 1, The following conditions (i) and (ii) are met: 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 member to be joined 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 member to be joined is L22, the following equation (2) is satisfied. L21<L22...(2)

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