Seal structure and electrochemical reaction cell stack

Abstract

To reduce cracking of a glass seal part.SOLUTION: A seal structure comprises a first joined member, a second joined member, and a glass seal part which joins together the first joined member and the second joined member, wherein the glass seal part is made of crystallized glass, and has a standard deviation of 10% or less in crystallinity.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The technology disclosed herein relates to a seal structure and an electrochemical reaction cell stack. [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] BACKGROUND ART A cell stack is known that includes a metal member, an electrochemical cell, and a glass seal member (glass seal portion) that joins the metal member and the electrochemical cell (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-107593 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above cell stack, it is desired to reduce the occurrence of cracks in the glass seal portion.

[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 seal structure disclosed in this specification comprises a first member to be joined, a second member to be joined, and a glass seal portion that joins the first member to be joined and the second member to be joined, wherein the glass seal portion is made of crystallized glass, and the standard deviation of the crystallinity of the glass seal portion is 10% or less.

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

[0009] (2) In the seal structure described in (1) above, the standard deviation of the crystallinity of the glass seal portion may be 8.8% or less. With this configuration, the occurrence of cracks in the glass seal portion is further reduced.

[0010] (3) In the seal structure described in (1) above, the standard deviation of the crystallinity of the glass seal portion may be 6.7% or less. With this configuration, the occurrence of cracks in the glass seal portion is further reduced.

[0011] (4) In the seal structure according to any one of (1) to (3), the crystallinity of the glass seal portion may be 35% or more. This configuration further reduces the occurrence of cracks in the glass seal portion.

[0012] (5) In the seal structure according to any one of (1) to (3) above, the crystallinity of the glass seal portion may be 50% or more. This configuration further reduces the occurrence of cracks in the glass seal portion.

[0013] (6) In the seal structure according to any one of (1) to (5) above, the porosity of the glass seal portion may be 15% or less. With this configuration, the occurrence of cracks in the glass seal portion is further reduced.

[0014] (7) The present specification discloses an electrochemical reaction cell stack including a unit cell including the seal structure according to any one of (1) to (6) above, an anode, an electrolyte layer, and an cathode. This configuration 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] Micrograph of a cross section of a glass seal portion in an embodiment DETAILED DESCRIPTION OF THE INVENTION

[0017] A. Implementation: The embodiment will be described with reference to Figures 1 to 6. 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 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 a stacked manner in this order 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 example of a first member to be joined), an air electrode frame 130, an anode frame 140, an anode current collecting member 144, two interconnectors 190, two IC separators 180 (an example of a second member to be joined), and a glass seal portion 135. 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 substantially the same as that of the electrolyte layer 112 and containing, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, or the like. The reaction prevention layer 118 is a layer having a rectangular shape substantially the same as that of the air electrode 114 and containing, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of preventing elements (e.g., Sr) diffused from the air electrode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[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 thickness of the single cell separator 120 is, for example, 0.05 mm or more and 0.2 mm or less. The peripheral portion of the through-hole 121 in the single cell separator 120 is joined to the peripheral portion of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is disposed: the upper surface in FIGS. 4 and 5) by a joint 124. The joint 124 is made of, for example, a brazing material (Ag brazing).

[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, for example, 0.5 mm or more and 5 mm or less. The cathode frame 130 has two seal holes 132 arranged on both sides of the through-hole 131.

[0027] (Glass seal part 135) Each cathode frame 130 has two seal holes 132, each of which has a glass seal 135 disposed therein. The glass seal 135 is a cylindrical member with openings at both ends. The glass seal 135 is made of crystallized glass. More specifically, the glass seal 135 may be made of, for example, SiO2-B2O3-MgO-based glass. One end of the glass seal 135 is bonded to the single cell separator 120, and the other end is bonded to the IC separator 180. The single cell separator 120, the IC separator 180, and the glass seal 135 form a seal structure 400.

[0028] The standard deviation of the crystallinity of the glass seal portion 135 may be 10% or less, 8.8% or less, or 6.7% or less. The crystallinity of the glass seal portion 135 may be 35% or more, or 50% or more. The porosity of the glass seal portion 135 may be 15% or less.

[0029] The crystallinity, standard deviation of the crystallinity, and porosity of the glass seal portion 135 are determined as follows.

[0030] A cross section of the target glass seal portion 135 is imaged using a scanning electron microscope (SEM) at a magnification of 2000 times and an observation area of ​​50 μm × 40 μm to obtain an SEM image. In the obtained SEM image, crystals are shown in light gray, amorphous portions are shown in dark gray, and pores are shown in black, as shown in FIG.

[0031] The obtained SEM images are analyzed using image analysis software (e.g., ImageJ). In image analysis, first, a threshold is set between light gray and dark gray for the SEM images, and binarization is performed. In the binarized image, crystals are displayed in white, and amorphous and pores are displayed in black. The ratio Rw (%) of the area Aw of the white region in the observation area to the area A0 of the entire observation area in the binarized image is calculated using the following formula (1). Next, a threshold is set between dark gray and black for the SEM images, and binarization is performed. In the binarized image, crystals and amorphous regions are displayed in white, and pores are displayed in black. The ratio Ab of the area Ab of the black region in the observation area to the area A0 of the entire observation area in the binarized image is calculated using the following formula (2), and this is defined as the porosity Rp (%) of the observation area. From the calculated ratio Rw and porosity Rp, the crystallinity Rc (%) of the observation area is calculated using the following formula (3).

[0032] Rw = (Aw / A0) × 100 (1) Rp = (Ab / A0) × 100 (2) Rc={Rw / (100-Rp)}×100...(3)

[0033] The same process is performed for the other nine locations on the cross section of the target glass seal portion 135, and the crystallinity Rc and porosity Rp are calculated. The average value of the crystallinity Rc data from the ten locations is calculated and used as the crystallinity of that glass seal portion 135. The standard deviation of the crystallinity is calculated from the crystallinity Rc data from the ten locations and used as the standard deviation of the crystallinity of that glass seal portion 135. The average value of the porosity Rp data from the ten locations is calculated and used as the porosity of that glass seal portion 135.

[0034] (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.

[0035] (IC separator 180) 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center. IC separator 180 is conductive and is made of a metal such as ferritic stainless steel. The thickness of IC separator 180 is, for example, 0.05 mm or more and 0.2 mm or less.

[0036] (Interconnector 190 and anode current collecting member 144) As shown in FIGS. 4 and 5 , the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collector 192 are electrically conductive and formed of a metal such as ferritic stainless steel. The coating layer 193 is electrically conductive and formed of a spinel-type oxide, for example. The coating layer 193 is disposed so as to cover the surface of the air electrode current collector 192 and the surface of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The flat plate portion 191 is joined to the periphery of the through-hole 181 in the IC separator 180, for example, by welding.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] (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.

[0042] 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.

[0043] 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.

[0044] (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 formed of a metal such as ferritic stainless steel. The thickness of the first end plate 210 is, for example, 0.5 mm or more and 3 mm or less. As shown in FIGS. 1 to 3 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is disposed around the entire periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is arranged along the entire inner periphery of the flat portion 211 .

[0045] (insulating part 220) Insulating section 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of an insulating material. As shown in Figures 2 and 3, insulating section 220 is sandwiched between first end plate 210 and end separator 230, thereby ensuring insulation between first end plate 210 and end separator 230.

[0046] (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.

[0047] (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.

[0048] 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.

[0049] (First terminal plate 240) As shown in FIGS. 2 and 3, the first terminal plate 240 is a rectangular frame-shaped member having a through-hole 241 near the center. The first terminal plate 240 is electrically conductive and is formed of a metal such as ferritic stainless steel. The thickness of the first terminal plate 240 is, for example, 0.2 mm or more and 3 mm or less. The first terminal plate 240 is electrically connected to the reaction unit 100U arranged at the other end (the upper end in FIG. 2) of the multiple reaction units 100U that make up the power generation block 100 via a first plate 232 and a terminal separator 230. One end (the right end in FIG. 2) of the first terminal plate 240 protrudes laterally from the power generation block 100, and this protruding portion functions as a positive output terminal for the fuel cell stack 10.

[0050] (2nd terminal plate 250) The second terminal plate 250 is a rectangular, plate-shaped member. The second terminal plate 250 is electrically conductive and made of a metal such as ferritic stainless steel. The thickness of the second terminal plate 250 is, for example, 0.2 mm or more and 3 mm or less. As described above, the second terminal plate 250 is connected to the anode 116 of the reaction unit 100U located at one end (the lower end in FIG. 2) of the multiple reaction units 100U via the anode current collecting member 144, thereby electrically connecting the reaction unit 100U to the second terminal plate 250. One end (the right end in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0051] (Second plate 260) Second plate 260 is a rectangular, flat member made of an insulating material. As shown in Figures 2 and 3, the peripheral edge of second plate 260 is sandwiched between second terminal plate 250 and second end plate 270, thereby ensuring insulation between second terminal plate 250 and second end plate 270.

[0052] (Second end plate 270) The second end plate 270 is formed by pressing (bending) a single plate-like member. The second end plate 270 is formed of a metal such as ferritic stainless steel. The thickness of the second end plate 270 is, for example, 0.5 mm or more and 3 mm or less. As shown in FIGS. 2 and 3 , the second end plate 270 includes a rectangular, frame-like flat portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the flat portion 271 in the direction opposite to the second terminal plate 250 (downward in FIG. 2 ). The outer convex portion 273 protrudes from the outer periphery of the flat portion 271. The outer convex portion 273 is disposed around the entire periphery of the flat portion 271. The inner convex portion 274 protrudes from the inner periphery of the flat portion 271. The inner convex portion 274 is disposed around the entire inner periphery of the flat portion 271.

[0053] (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.

[0054] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies the oxidant gas OG introduced from outside the fuel cell stack 10 to the air chamber 313 of each reaction unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the outside of the fuel cell stack 10. As the oxidant gas OG, for example, air is used.

[0055] 3, the fuel gas supply manifold 321 is a gas flow path that supplies fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chambers 323 of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges fuel off-gas FOG discharged from the fuel chambers 323 of each reaction unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, a hydrogen-rich gas obtained by reforming city gas is used.

[0056] As shown in FIG. 5 , the fuel gas supply manifold 321 penetrates one of the two glass seals 135 disposed inside each cathode frame 130. In other words, the internal space of the glass seal 135 is part of the fuel gas supply manifold 321. Similarly, the fuel gas discharge manifold 322 penetrates the other of the two glass seals 135 disposed inside each cathode frame 130. In other words, the internal space of the glass seal 135 is part of the fuel gas discharge manifold 322. The glass seal 135 prevents leakage of fuel gas (FG) or fuel off-gas (FOG) from the fuel gas supply manifold 321 and the fuel gas discharge manifold 322 through the interface between the cathode frame 130 and the single cell separator 120 or the interface between the cathode frame 130 and the IC separator 180.

[0057] (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 and open at both ends. 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. The other end (the upper end in FIGS. 2 and 3) of the main body portion 281 included in each of the four gas passage members 280 is joined to the second end plate 270 by, for example, welding, and the internal space of the main body portion 281 is connected to the manifolds 311, 312, 321, and 322, respectively. A gas pipe for supplying or discharging gas is connected to each of the main body portions 281.

[0058] (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.

[0059] A glass raw material powder is press-molded, and the resulting molded body is calcined at a temperature equal to or lower than the crystallization temperature of the glass to obtain a glass calcined body.

[0060] The air electrode frame 130 is placed on the ferritic stainless steel single cell separator 120, and the resulting glass calcined body is placed inside each of the two seal holes 132. A ferritic stainless steel IC separator 180 is placed on the air electrode frame 130 to obtain a stack. The other components that make up the fuel cell stack 10 are then layered on the resulting stack, in order, to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is placed in a firing furnace and heat-treated at a heat treatment temperature that is higher than the operating temperature. The heat treatment temperature may be any temperature at which glass crystallization begins, for example, 800°C or higher. This heat treatment crystallizes the glass contained in the glass calcined body, forming a glass seal 135 made of crystallized glass. The glass seal 135 bonds adjacent single cell separators 120 and IC separators 180 together.

[0061] During this heat treatment, the standard deviation of the crystallinity of the glass seal portion 135 can be adjusted by adjusting the temperature program of the firing furnace or the arrangement of the fuel cell stack 10 within the firing furnace. More specifically, the temperature distribution within the glass calcined body can be made uniform by slowly increasing the temperature within the firing furnace or adjusting the distance between the heater provided in the firing furnace and the fuel cell stack 10. For example, the rate of temperature increase from the glass transition point to the glass crystallization temperature range can be adjusted to be slower than in other temperature ranges, thereby making the temperature distribution within the glass calcined body uniform as crystallization progresses. This allows glass crystallization to proceed uniformly within the glass calcined body, thereby reducing the standard deviation of the crystallinity of the resulting glass seal portion 135. Furthermore, the progress of crystallization can be controlled by adjusting the firing temperature and firing time, thereby adjusting the average crystallinity and porosity of the glass seal portion 135.

[0062] Furthermore, when preparing the glass calcined body, glass seed crystal particles may be added to the glass raw material powder and mixed uniformly, which allows crystallization to proceed uniformly within the glass calcined body during heat treatment, further reducing the standard deviation of the crystallinity of the glass seal portion 135.

[0063] (Operation of fuel cell stack 10) 2 and 4, the oxidizing gas OG is supplied from the oxidizing gas supply manifold 311 to the air chamber 313 via the gas passage member 280. Also, as shown in FIGS. 3 and 5, the fuel gas FG is supplied from the fuel gas supply manifold 321 to the fuel chamber 323 via the gas passage member 280.

[0064] 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.

[0065] 2 and 4, the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidant gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the inside of the main body 281. Also, as shown in FIGS. 3 and 5, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 is discharged to the outside of the fuel cell stack 10 through the inside of the main body 281.

[0066] The fuel cell stack 10 reaches high temperatures during operation and returns to room temperature when operation is stopped. This causes stress in the glass seal portion 135 due to the difference in thermal expansion coefficient between it and the components to which it is joined (in this embodiment, the single cell separator 120 and the IC separator 180). If the standard deviation of the crystallinity of the glass seal portion 135 is large, there will be localized areas within the glass seal portion 135 with extremely low crystallinity, i.e., areas with extremely low strength, which raises concerns about cracks occurring in these areas and reduced sealing performance. If the standard deviation of the glass seal portion 135 is 10% or less, there will be relatively few areas with extremely low crystallinity, reducing the occurrence of cracks.

[0067] (Action and effect) As described above, the fuel cell stack 10 of this embodiment includes the single cell separator 120, the IC separator 180, and the glass seal portion 135 that joins the single cell separator 120 and the IC separator 180. The glass seal portion 135 is made of crystallized glass, and the standard deviation of the crystallinity of the glass seal portion 135 is 10% or less. With this configuration, the occurrence of cracks in the glass seal portion 135 is reduced.

[0068] Furthermore, the crystallinity of the glass seal portion 135 is 35% or more. Additionally, the porosity of the glass seal portion 135 is 15% or less. With this configuration, the occurrence of cracks in the glass seal portion 135 is further reduced.

[0069] B. Working Example A number of fuel cell stack samples having the same configuration as the above embodiment but with different degrees of crystallinity in the glass seal portion were fabricated and subjected to a thermal cycle test to check for the occurrence of cracks.

[0070] The raw material powder of SiO2-B2O3-MgO-based glass was press-molded, and the resulting molded body was calcined at a temperature below the crystallization temperature of the glass to obtain a glass calcined body.

[0071] An air electrode frame was placed on a ferritic stainless steel single cell separator, and the resulting glass calcined body was placed inside each of the two seal holes. A ferritic stainless steel IC separator was placed on the air electrode frame. The other components that make up the fuel cell stack were then layered on top of the resulting laminate, in order, to assemble the fuel cell stack. The assembled fuel cell stack was placed in a firing furnace and heat-treated at 850°C. During this heat treatment, the temperature program of the firing furnace and the stack arrangement within the furnace were adjusted to obtain eight fuel cell stack samples S1-S8 with different crystallinity in the glass seal area.

[0072] Ten randomly selected points were cut out from the glass seal portion of one of the eight fuel cell stacks. Each of the cut-out portions was embedded in resin, and the cross section was mirror-polished to obtain ten test pieces. SEM images were taken of each test piece as described in the above embodiment, and image analysis was performed to determine the crystallinity Rc and porosity Rp. The average value and standard deviation of the crystallinity Rc data for the ten test pieces were calculated. The average value of the porosity Rp data for the ten test pieces was also used as the porosity of the glass seal portion of that fuel cell stack.

[0073] The average value and standard deviation of the crystallinity and the porosity were determined in the same manner for the other seven fuel cell stacks.

[0074] Each of the eight fuel cell stacks was placed in an electric furnace and subjected to a thermal cycle test, in which one cycle consisted of heating from 70°C to 700°C and then cooling back to 70°C. After 100, 200, and 300 cycles, the occurrence of cracks in the glass seal was observed.

[0075] Table 1 shows the average value and standard deviation of the crystallinity of each sample, the porosity data, and whether or not cracks occurred after the thermal cycle test.

[0076] [Table 1]

[0077] As shown in Table 1, in samples S1 and S2, where the standard deviation of the crystallinity in the glass seal exceeds 10%, cracks occurred after 100 thermal cycles. In contrast, in samples S3-8, where the standard deviation of the crystallinity in the glass seal is 10% or less, no cracks were observed after 100 thermal cycles. Furthermore, in samples S4 and S6-8, where the standard deviation of the crystallinity is 8.8% or less, no cracks were observed even after 200 thermal cycles, and in sample S6, where the standard deviation of the crystallinity is 6.7% or less, no cracks were observed even after 300 thermal cycles.

[0078] Comparing Sample S3 and Sample S5, which have similar standard deviations of crystallinity, we found that Sample S3, with an average crystallinity of 30%, developed cracks after 200 thermal cycles, whereas Sample S5, with an average crystallinity of 35%, did not develop cracks even after 200 thermal cycles. Furthermore, comparing Sample S4 and Sample S7, which have similar standard deviations of crystallinity, we found that Sample S4, with an average crystallinity of 30%, developed cracks after 300 thermal cycles, whereas Sample S7, with an average crystallinity of 50%, did not develop cracks even after 300 thermal cycles. These results suggest that, given similar standard deviations of crystallinity, a higher average crystallinity reduces cracking. This is likely because a higher crystallinity increases the overall strength of the glass seal.

[0079] Comparing sample S4 and sample S8, which have similar average crystallinity values ​​and standard deviations, cracks were observed in sample S4, which has a porosity of over 15%, after 300 thermal cycles, whereas no cracks were observed in sample S8, which has a porosity of 15%, even after 300 thermal cycles. These results suggest that, if the average crystallinity values ​​and standard deviations are similar, a lower porosity can reduce cracking. This is thought to be because the lower the porosity, the greater the strength of the entire glass seal.

[0080] C. Variations The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible. (1) The first member to be joined may be a member different from the unit cell separator 120. The first member to be joined may be, for example, a unit cell, or may be a member that constitutes the electrochemical reaction cell stack but is different from the unit cell. The second member to be joined may be a member different from the IC separator 180, or may be a member that constitutes the electrochemical reaction cell stack but is different from the first member to be joined. (2) In the method for manufacturing a seal structure, a glass paste may be used instead of the glass calcined body. The glass paste is prepared by, for example, mixing a glass raw material powder with a binder and a solvent. In this case, seed crystal particles may be uniformly mixed with the glass raw material powder. (3) In the above embodiment, the fuel cell stack 10 includes a plurality of flat-type unit cells 110, but the electrochemical reaction cell stack may include other types of unit cells (e.g., cylindrical, flat cylindrical). (4) The above configuration can also be applied to cell stacks used in other types of fuel cells, such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolysis cell stacks that include electrolysis cell units, which are the constituent elements of solid oxide electrolysis cells (SOECs), as single cells. [Explanation of symbols]

[0081] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Anode 118: Reaction prevention layer 120: Separator for single cell (first joining target member) 121: Through hole 124: Joint portion 130: Air electrode frame 131: Through hole 132: Seal hole 135: Glass seal portion 140: Anode frame 141: Through hole 144: Anode current collecting member 145: Electrode opposing portion 146: Interconnector opposing portion 147: Connection portion 149: Spacer 180: Separator for IC (second joining target member) 181: Through hole 190: Interconnector 191: Flat plate portion 192: Air electrode current collecting portion 193: Covering layer 196: Conductive bonding material 210: First end plate 211: Flat portion 212: Through hole 213: Outer convex portion 214: Inner convex portion 220: Insulating portion 230: Terminal separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Flat portion 272: Through hole 273: Outer convex portion 274: Inner convex portion 280: Gas passage member 281: Main body portion 282: Flange portion 284: Bolt hole 311: Oxidizer gas supply manifold 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber 400: Seal structure B: Bolt BH: Bolt hole FG: Fuel gas FOG: Fuel off-gas N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas

Claims

1. a first member to be joined; A second member to be joined; a glass seal portion that joins the first member to be joined and the second member to be joined, The glass seal is made of crystallized glass, The standard deviation of the crystallinity of the glass seal portion is 10% or less. Seal structure.

2. The seal structure according to claim 1, The standard deviation of the crystallinity of the glass seal portion is 8.8% or less. Seal structure.

3. The seal structure according to claim 1, The standard deviation of the crystallinity of the glass seal portion is 6.7% or less. Seal structure.

4. The seal structure according to claim 1, The crystallinity of the glass seal portion is 35% or more. Seal structure.

5. The seal structure according to claim 1, The crystallinity of the glass seal portion is 50% or more. Seal structure.

6. The seal structure according to claim 1, The porosity of the glass seal portion is 15% or less. Seal structure.

7. The seal structure according to claim 1 ; a single cell including an anode, an electrolyte layer, and an air cathode; Electrochemical reaction cell stack.

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