Seal structure and electrochemical reaction cell stack

Abstract

To reduce extension of a crack in a glass seal part.SOLUTION: The seal structure is provided with a first member to be joined, a second member to be joined, and a glass seal part interposed between the first member to be joined and the second member to be joined, wherein the glass seal part has a joining surface which is in contact with the first member to be joined, a non-joining surface which forms an angle with the joining surface and is not in contact with either the first member to be joined or the second member to be joined, and a surface region including the non-joining surface, the surface region contains rod-like particles, and the average orientation angle of the rod-like particles with respect to the non-joining surface is 45-90 °.SELECTED DRAWING: Figure 7

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 an electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack, in which multiple structural units (electrochemical reaction units) are arranged in a predetermined direction. A glass part (glass seal part) is used to connect two structural units provided in the fuel cell stack (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-107590 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above SOFC, there is a need to reduce the propagation of cracks that occur in the glass seal.

[0005] 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]

[0006] The technology disclosed in this specification can be realized, for example, in the following forms. (1) The seal structure disclosed in this specification includes a first member to be joined, a second member to be joined, and a glass seal portion interposed between the first member to be joined and the second member to be joined. The glass seal portion has a joining surface that contacts the first member to be joined, a non-joining surface that forms an angle with the joining surface and does not contact either the first member to be joined or the second member to be joined, and a surface region that includes the non-joining surface. The surface region includes rod-shaped particles. The rod-shaped particles have an average orientation angle of 45° or more and 90° or less with respect to the non-joining surface.

[0007] According to the above configuration, the propagation of cracks in the glass seal portion is reduced.

[0008] (2) In the seal structure described in (1) above, the rod-shaped particles may have an average aspect ratio of 3 or more.

[0009] This configuration further reduces the propagation of cracks in the glass seal portion.

[0010] (3) The electrochemical reaction cell stack disclosed in this specification includes the seal structure described in (1) or (2) above.

[0011] This configuration reduces the propagation of cracks in the glass seal portion.

[0012] 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]

[0013] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack according to an embodiment; [Figure 2] FIG. 2 is a cross-sectional view of the fuel cell stack according to the embodiment taken along line II-II in FIG. 1. [Figure 3]FIG. 3 is a cross-sectional view of the fuel cell stack according to the embodiment taken along line III-III in FIG. 1. [Figure 4] 2 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, taken along the same line as in FIG. 1; [Figure 5] 3 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment, taken along the same line as line III-III in FIG. 1; [Figure 6] FIG. 6 is an enlarged view of the area within frame F1 in FIG. 5. [Figure 7] Enlarged view of circle R1 in Figure 6 [Figure 8] FIG. 5 is an enlarged view of the area within frame F2 in FIG. [Figure 9] Enlarged view of circle R2 in Figure 8 DETAILED DESCRIPTION OF THE INVENTION

[0014] A. Implementation: The embodiment will be described with reference to Figures 1 to 9. A fuel cell stack 10 (an example of an electrochemical reaction cell stack) of the present embodiment is used in a solid oxide fuel cell having an electrolyte layer 112 containing a solid oxide.

[0015] (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 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).

[0016] 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.

[0017] 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).

[0018] (Overall configuration of 100U electrochemical reaction units) 4 and 5, the electrochemical reaction unit 100U includes a single cell 110, a single cell separator 120, an air electrode frame 130, an anode frame 140, an anode current collecting member 144, two interconnectors 190, two IC separators 180, a first glass seal 135, and a second glass seal 125. 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.

[0019] 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.

[0020] (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.

[0021] The electrolyte layer 112 is a rectangular, flat member having one surface (the upper surface in FIGS. 4 and 5) on which the air electrode 114 is disposed and another surface (the lower surface in FIGS. 4 and 5) parallel to the first surface on which the anode 116 is disposed. The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The cathode 114 is a layer having a rectangular shape smaller than that of the electrolyte layer 112 and containing, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)). The anode 116 is a layer having a rectangular shape and approximately the same size as the electrolyte layer 112 and containing, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, or the like. The reaction prevention layer 118 is a layer having a rectangular shape and approximately the same size as the air electrode 114 and containing, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of preventing elements (e.g., Sr) diffused from the air electrode 114 from reacting with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0022] (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).

[0023] (Second glass seal portion 125) The second glass seal 125 is disposed on the single cell 110 and covers the edge of the through-hole 121 and its surrounding area in the single-cell separator 120. The second glass seal 125 is made of, for example, SiO2-B2O3-MgO-based glass. The second glass seal 125 seals the gap between the single cell 110 and the single-cell separator 120, effectively 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.

[0024] (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 cathode frame 130 has two seal holes 132 arranged on both sides of the through-hole 131.

[0025] (First glass seal portion 135) Each cathode frame 130 has two seal holes 132, each of which has a first glass seal 135 disposed inside. The first glass seal 135 is a cylindrical member with openings on both ends. The first glass seal 135 is made of, for example, SiO2-B2O3-MgO-based glass. One end of the first glass seal 135 is bonded to the single cell separator 120, and the other end is bonded to the IC separator 180.

[0026] (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.

[0027] (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.

[0028] (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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] (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.

[0034] 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.

[0035] 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.

[0036] (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 .

[0037] (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.

[0038] (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.

[0039] (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.

[0040] 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.

[0041] (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.

[0042] (2nd terminal plate 250) The second terminal plate 250 is a rectangular, plate-shaped member. The second terminal plate 250 is electrically conductive and is made of a metal such as ferritic stainless steel. 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 provided in the reaction unit 100U arranged 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 and 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 a negative output terminal of the fuel cell stack 10.

[0043] (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.

[0044] (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.

[0045] (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.

[0046] 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.

[0047] 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.

[0048] As shown in FIG. 5 , the fuel gas supply manifold 321 penetrates one of the two first glass seals 135 disposed inside each cathode frame 130. That is, the internal space of the first glass seal 135 forms part of the fuel gas supply manifold 321. Similarly, the fuel gas discharge manifold 322 penetrates the other of the two first glass seals 135 disposed inside each cathode frame 130. That is, the internal space of the first glass seal 135 forms part of the fuel gas discharge manifold 322. The first 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.

[0049] (Gas passage member 280) As shown in FIGS. 1 to 3, each of the four gas passage members 280 includes a main body portion 281 and a flange portion 282. The main body portion 281 is cylindrical 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.

[0050] (Details of the first glass seal portion 135) As shown in Fig. 6, the first glass seal portion 135 is interposed between the unit cell separator 120 and the IC separator 180. One end of the first glass seal portion 135 is joined to the IC separator 180, and the other end is joined to the unit cell separator 120. The unit cell separator 120, the IC separator 180, and the first glass seal portion 135 form a seal structure 410. The IC separator 180 is an example of a first member to be joined, the unit cell separator 120 is an example of a second member to be joined, and the first glass seal portion 135 is an example of a glass seal portion.

[0051] The first glass seal portion 135 has a first bonding surface 135S1 (an example of a bonding surface), a second bonding surface 135S2, a first non-bonding surface 135S3 (an example of a non-bonding surface), and a second non-bonding surface 135S4 (an example of a non-bonding surface). The first bonding surface 135S1 is a surface that contacts the IC separator 180. The second bonding surface 135S2 is a surface that contacts the single cell separator 120. In this embodiment, the first bonding surface 135S1 and the second bonding surface 135S2 are parallel to each other. The first non-bonding surface 135S3 and the second non-bonding surface 135S4 extend at an angle from the first bonding surface 135S1 and are surfaces that do not contact either the single cell separator 120 or the IC separator 180. In this embodiment, the first non-bonding surface 135S3 is the outer peripheral surface of the first glass seal portion 135, and the second non-bonding surface 135S4 is the inner peripheral surface of the first glass seal portion 135. The non-bonding surfaces 135S3 and 135S4 are perpendicular to the first bonding surface 135S1 and the second bonding surface 135S2.

[0052] The first glass seal portion 135 has a first surface region As1 (an example of a surface region) including the first non-bonding surface 135S3 and a second surface region As2 (an example of a surface region) including the second non-bonding surface 135S4. The first surface region As1 and the second surface region As2 have substantially the same configuration, so the following will describe the first surface region As1 in detail, and will omit a description of the second surface region As2.

[0053] The first surface region As1 is a region extending from the first non-bonding surface 135S3 to a depth of 80 μm. As shown in FIG. 7, the first surface region As1 includes rod-shaped particles 136. The rod-shaped particles 136 are glass crystal particles and have a shape that is elongated in one direction. The rod-shaped particles 136 included in the first surface region As1 may have an average aspect ratio of 1.1 or more, and may also have an average aspect ratio of 3 or more. The rod-shaped particles 136 included in the first surface region As1 may have an average orientation angle with respect to the first non-bonding surface 135S3 that is 45° or more and 90° or less.

[0054] The average orientation angle and average aspect ratio of the rod-shaped particles 136 contained in the first surface region As1 are determined as follows. A cross section of the first glass seal portion 135 cut perpendicular to the first bonding surface 135S1 is photographed using a scanning electron microscope (SEM) so as to include the first non-bonding surface 135S3, thereby obtaining an SEM image. The first surface region As1 appearing in the obtained SEM image is divided into three equal parts along the first non-bonding surface 135S3, as shown in FIG. 6, to set three divided regions As11, As12, and As13. Ten rod-shaped particles 136 are randomly selected from each of the three divided regions As11, As12, and As13, for a total of 30 rod-shaped particles 136. The maximum Feret diameter Dmax and minimum Feret diameter Dmin are determined for each of the selected rod-shaped particles 136. As shown in FIG. 7, the maximum Feret diameter Dmax of a rod-shaped particle 136 is the maximum distance between two parallel lines when the outline of the rod-shaped particle 136 is sandwiched between the two lines in the SEM image. The minimum Feret diameter Dmin of a rod-shaped particle 136 is the minimum distance between two parallel lines when the outline of the rod-shaped particle 136 is sandwiched between the two parallel lines. The value (Dmax / Dmin) obtained by dividing the maximum Feret diameter Dmax by the minimum Feret diameter Dmin is the aspect ratio of the rod-shaped particle 136. When a line Lc parallel to the two parallel lines used to determine the minimum Feret diameter Dmin is set at the center of these two lines, the angle θ1 formed by the line Lc and the line representing the first non-bonding surface 135S3 in the SEM image is the orientation angle θ1 of the rod-shaped particle 136. The average aspect ratio is calculated from the aspect ratios of the 30 rod-shaped particles 136. The average orientation angle θ1 of the 30 rod-shaped particles 136 ...

[0055] The standard deviation of the crystallinity of the first glass seal portion 135 may be 10% or less, 8.8% or less, or 6.7% or less. With this configuration, there are relatively fewer areas with extremely low crystallinity, i.e., areas with extremely low strength, thereby reducing the occurrence of cracks. The crystallinity of the first glass seal portion 135 may be 35% or more, or 50% or more. With this configuration, the strength of the entire first glass seal portion 135 is improved, thereby reducing the occurrence of cracks. The porosity of the first glass seal portion 135 may be 30% or less, or 15% or less. With this configuration, the strength of the entire first glass seal portion 135 is improved, thereby reducing the occurrence of cracks.

[0056] The crystallinity, standard deviation of the crystallinity, and porosity of the first glass seal portion 135 are determined as follows.

[0057] A SEM image is obtained by capturing an image of one location on the cross section of the target first glass seal portion 135 using a scanning electron microscope (SEM) at a magnification of 2000x and an observation area of ​​50 μm × 40 μm. In the obtained SEM image, crystals are shown in light gray, amorphous regions are shown in dark gray, and pores are shown in black.

[0058] 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).

[0059] Rw = (Aw / A0) × 100 (1) Rp = (Ab / A0) × 100 (2) Rc={Rw / (100-Rp)}×100...(3)

[0060] The same process is performed for the other nine locations on the cross section of the target first 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 first 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 first 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 first glass seal portion 135.

[0061] (Details of the second glass seal portion 125) As shown in FIG. 8 , the second glass seal 125 is interposed between the unit cell 110 and the unit cell separator 120 to join them together. The second glass seal 125 is arranged in a frame shape on the surface of the electrolyte layer 112, along the edge of the through-hole 121 in the unit cell separator 120. The entire peripheral edge of the through-hole 121 is embedded in the second glass seal 125. The unit cell 110, the unit cell separator 120, and the second glass seal 125 form a seal structure 420. The unit cell 110 is an example of a first member to be joined, the unit cell separator 120 is an example of a second member to be joined, and the second glass seal 125 is an example of a glass seal.

[0062] The second glass seal portion 125 has a third bonding surface 125S1 (an example of a bonding surface) and a third non-bonding surface 125S2 (an example of a non-bonding surface). The third bonding surface 125S1 is a surface that contacts the electrolyte layer 112. The third non-bonding surface 125S2 extends at an angle from the third bonding surface 125S1 and is a surface that does not contact either the unit cell 110 or the unit cell separator 120.

[0063] The second glass seal portion 125 has a third surface region As3 (an example of a surface region) including the third non-bonding surface 125S2. The third surface region As3 is a region extending from the third non-bonding surface 125S2 to a depth of 80 μm. As shown in FIG. 9, the third surface region As3 includes rod-shaped particles 126. The rod-shaped particles 126 are glass crystal particles. The rod-shaped particles 126 are particles having a shape elongated in one direction, similar to the rod-shaped particles 136 included in the first glass seal portion 135. The average aspect ratio of the rod-shaped particles 126 may be 1.1 or more, and may be 3 or more. The average orientation angle of the rod-shaped particles 126 with respect to the third non-bonding surface 125S2 may be 45° or more and 90° or less.

[0064] The average orientation angle and average aspect ratio of the rod-shaped particles 126 are determined in the same manner as the average orientation angle and average aspect ratio of the rod-shaped particles 136 described above. As shown in FIG. 9 , in the second glass seal portion 125, the line representing the third non-bonding surface 125S2 that appears in the SEM image is not a straight line. In such a case, the orientation angle of the rod-shaped particle 126 may be determined as the angle θ2 formed by a straight line Lc parallel to the two parallel lines used to determine the minimum Feret diameter Dmin, which is set at the center of these two lines, and a tangent Lt to the line representing the third non-bonding surface 125S2 at the intersection P of the third non-bonding surface 125S2 and the straight line Lc.

[0065] Similar to the first glass seal member 135, the standard deviation of the crystallinity of the second glass seal member 125 may be 10% or less, 8.8% or less, or 6.7% or less. The crystallinity of the second glass seal member 125 may be 35% or more, or 50% or more. The porosity of the second glass seal member 125 may be 30% or less, or 15% or less. The crystallinity, standard deviation of the crystallinity, and porosity of the second glass seal member 125 are determined in the same manner as the first glass seal member 135.

[0066] (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.

[0067] 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 cylindrical calcined glass body.

[0068] A paste containing glass seed crystal particles is applied to the outer and inner surfaces of the obtained calcined glass body by screen printing. The seed crystal particles are rod-shaped particles. The seed crystal particles may contain, for example, at least one element selected from Ba, Ca, Mg, Al, La, Ti, Cr, Zr, Ce, and B, or at least one oxide of these elements. By reducing the size of the opening of the screen used for printing to the extent that the seed crystal particles can pass through, the orientation angle of the seed crystal particles relative to the application surface can approach 90°.

[0069] A glass paste is prepared by mixing glass raw material powder, a binder, and a solvent. The single cell 110 is stacked around the through-hole 121 in the single cell separator 120. The glass paste is applied to the electrolyte layer 112 by screen printing so that it overlaps with the edge of the through-hole 121. A paste containing glass seed crystal particles is then applied to the surface of the applied glass paste by screen printing. The paste containing seed crystal particles and the application method are the same as those for the glass calcined body described above.

[0070] The cathode frame 130 is placed on the single cell separator 120, and a glass calcined body coated with paste is placed inside each of the two seal holes 132. The IC separator 180 is placed on the cathode frame 130, and the other components constituting the fuel cell stack 10 are then layered in order to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is placed in a firing furnace and heated to the glass softening temperature to melt the glass calcined body and glass paste, followed by heat treatment at a heat treatment temperature higher than the operating temperature. The softening temperature may be equal to or higher than the temperature at which glass softening begins, e.g., 700°C. The heat treatment temperature may be equal to or higher than the temperature at which glass crystallization begins, e.g., 850°C. This heat treatment crystallizes the glass contained in the glass calcined body, forming a first glass seal portion 135. The first glass seal portion 135 bonds adjacent single cell separators 120 and IC separators 180 together. Furthermore, the glass contained in the glass paste crystallizes to form the second glass seal portion 125. The second glass seal portion 125 bonds the unit cell 110 and the unit cell separator 120. During the heat treatment, the seed crystal particles contained in the paste grow while maintaining their orientation angle at the time of application, becoming rod-shaped particles 126 and 136. Therefore, when applying the paste containing seed crystal particles, the average orientation angle of the rod-shaped particles 126 and 136 contained in the surface regions As1, As2, and As3 can be adjusted by adjusting the orientation angle of the seed crystal particles with respect to the application surface as described above. Furthermore, the longer the heat treatment time, the larger the aspect ratio of the rod-shaped particles 126 and 136.

[0071] (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.

[0072] 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.

[0073] 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.

[0074] The fuel cell stack 10 reaches high temperatures during operation and returns to room temperature when operation is stopped. Therefore, stress is generated in the first glass seal portion 135 due to the difference in thermal expansion coefficient between the first glass seal portion 135 and the components to which it is bonded (in this embodiment, the single cell separator 120 and the IC separator 180). This stress can cause cracks to form in the first glass seal portion 135. Cracks tend to extend from the edge 135C of the non-bonding surfaces 135S3 and 135S4, which contacts the first bonding surface 135S1, along the non-bonding surfaces 135S3 and 135S4. The closer the average orientation angle of the rod-shaped particles 136 contained in the surface regions As1 and As2 is to 90°, the more likely the rod-shaped particles 136 are to prevent cracks from extending along the non-bonding surfaces 135S3 and 135S4. Furthermore, the greater the aspect ratio of the rod-shaped particles 136, the more likely the rod-shaped particles 136 are to prevent cracks from extending. The same applies to the second glass seal portion 125.

[0075] (Action and effect) As described above, the fuel cell stack 10 of this embodiment includes an IC separator 180, a single cell separator 120, and a first glass seal member 135 interposed between the IC separator 180 and the single cell separator 120. The first glass seal member 135 has a first bonding surface 135S1 that contacts the IC separator 180, a first non-bonding surface 135S3 and a second non-bonding surface 135S4 that are angled relative to the first bonding surface 135S1 and do not contact either the IC separator 180 or the single cell separator 120, and surface regions As1 and As2 that include the non-bonding surfaces 135S3 and 135S4. The surface regions As1 and As2 include rod-shaped particles 136. The average orientation angle of the rod-shaped particles 136 relative to the non-bonding surfaces 135S3 and 135S4 is 45° or more and 90° or less.

[0076] The fuel cell stack 10 of this embodiment further includes a unit cell 110 and a second glass seal portion 125 interposed between the unit cell 110 and the unit cell separator 120. The second glass seal portion 125 has a third bonding surface 125S1 that contacts the unit cell 110, a third non-bonding surface 125S2 that is angled relative to the third bonding surface 125S1 and does not contact either the unit cell 110 or the unit cell separator 120, and a third surface region As3 that includes the third non-bonding surface 125S2. The third surface region As3 includes rod-shaped particles 126. The rod-shaped particles 126 have an average orientation angle of 45° or more and 90° or less with respect to the third non-bonding surface 125S2.

[0077] According to the above configuration, the propagation of cracks occurring in the first glass seal portion 135 and the second glass seal portion 125 is reduced.

[0078] In the fuel cell stack 10 of this embodiment, the rod-shaped particles 126, 136 have an average aspect ratio of at least 3. With this configuration, the propagation of cracks that occur in the first glass seal portion 135 and the second glass seal portion 125 is further reduced.

[0079] B. Working Example Several samples with different orientation angles and aspect ratios of rod-shaped particles in the glass seal were prepared and subjected to a thermal cycle test to evaluate the state of crack propagation.

[0080] (Sample S1) Glass raw material powder was press-molded, and the resulting cylindrical molded body was calcined at a temperature below the crystallization temperature of the glass to obtain a glass calcined body. A paste containing seed crystal particles was applied to the outer surface of the glass calcined body by screen printing. The orientation angle of the seed crystal particles relative to the outer surface was adjusted by adjusting the opening dimensions of the screen used. Next, two ferritic stainless steel metal plates were placed on each of the two end surfaces of the paste-applied glass calcined body to obtain a laminate. This laminate was placed in a firing furnace and heated at the softening temperature of the glass to melt the glass calcined body. The glass and metal plates were then bonded together by heat treatment for 10 hours at a temperature above the crystallization temperature of the glass. This resulted in sample S1, in which a glass seal portion was sandwiched between two metal plates.

[0081] The glass seal portion of Sample 1 was cut in a direction perpendicular to the end face (the bonded surface with the metal plate), and the cross section was imaged using an SEM at a magnification of 200x, including the outer peripheral surface (non-bonded surface). Using the obtained SEM image, the average orientation angle and average aspect ratio of the rod-like particles contained in the region from the non-bonded surface to a depth of 80 μm (first surface region) were determined using the method described in the above embodiment.

[0082] (Samples S2-S8) The size of the screen opening used when applying the paste containing seed crystal particles was changed so as to obtain the desired average orientation angle. In addition, the heat treatment time was changed as shown in Table 1. Samples S2-S8 were obtained in the same manner as Sample S1.

[0083] (Samples S9 and S10) The surface of the glass calcined body to which the paste containing seed crystal particles was applied was changed to the end surface of the glass calcined body, i.e., the joining surface to be joined with the metal plate. In addition, the heat treatment time was changed as shown in Table 1. Otherwise, samples S9 and S10 were obtained in the same manner as sample S1.

[0084] (Evaluation method) Each sample was placed in an electric furnace, and the temperature was increased from 100°C to 700°C and then decreased to 100°C, and this cycle was repeated 100 and 200 times. After 100 and 200 cycles, the presence or absence of crack propagation in the glass seal was observed. A sample in which no crack propagation was observed after 200 cycles was evaluated as ⊚, a sample in which no crack propagation was observed after 100 cycles but propagation was observed after 200 cycles was evaluated as ○, and a sample in which crack propagation was observed after 100 cycles was evaluated as ×.

[0085] Table 1 shows the data on the average orientation angle and average aspect ratio for each sample, as well as whether or not cracks propagated after the thermal cycle test.

[0086] [Table 1]

[0087] As shown in Table 1, crack propagation was observed after 100 cycles in samples S9 and S10, which had an average orientation angle of 30° or less. In contrast, no crack propagation was observed after 100 cycles in samples S1-S8, which all had an average orientation angle of 45° or more. In particular, no crack propagation was observed even after 200 cycles in samples S1, S2, S3, and S6, which had an average aspect ratio of 3 or more and an average orientation angle of 50° or more.

[0088] 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 IC separator 180 and the unit cell 110. The second member to be joined may be a member different from the unit cell separator 120, and may be any member that is different from the first member to be joined among the members that make up the electrochemical reaction cell stack. (2) In the first embodiment, the non-bonding surfaces 135S3 and 135S4 are perpendicular to the first bonding surface 135S1 and the second bonding surface 135S2. However, the non-bonding surfaces do not have to be perpendicular to the bonding surfaces. (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]

[0089] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction unit 110: Single cell (first bonding target member) 112: Electrolyte layer 114: Air electrode 116: Anode 118: Reaction prevention layer 120: Single cell separator (second bonding target member) 121: Through hole 124: Bonding portion 125: Second glass seal portion (glass seal portion) 125S1: Third bonding surface (bonding surface) 125S2: Third non-bonding surface (non-bonding surface) 126: Rod-shaped particle 130: Air electrode frame 131: Through hole 132: Seal hole 135: First glass seal portion (glass seal portion) 135C: Edge 135S1: First bonding surface (bonding surface) 135S2: Second bonding surface 135S3: First non-bonding surface (non-bonding surface) 135S4: Second non-bonding surface (non-bonding surface) 136: Rod-shaped particle 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: IC separator (first bonding target member) 181: Through hole 190: Interconnector 191: Flat plate portion 192: Air cathode current collecting portion 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat portion 212: Through hole 213: Outer convex portion 214: Inner convex portion 220: Insulating portion 230: Terminal separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Flat portion 272: Through hole 273: Outer convex portion 274: Inner convex portion 280: Gas passage member 281: Main body portion 282: Flange portion 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 410, 420: Seal structure As11, As12, As13: Divided region As1: First surface region (surface region) As2: Second surface region (surface region) As3: Third surface region (surface region) B: Bolt BH: Bolt hole Dmax: Maximum Feret diameter Dmin: Minimum Feret diameter FG: Fuel gas FOG: Fuel off-gas Lc: Straight line N: Nut OG: Oxidizer gas OOG: Oxidizer off-gasθ1, θ2: orientation angles

Claims

1. a first member to be joined; A second member to be joined; a glass seal portion interposed between the first member to be joined and the second member to be joined; Equipped with The glass seal portion is a joining surface in contact with the first joining target member; a non-joining surface that is angled with the joining surface and does not contact either the first member to be joined or the second member to be joined; a surface region including the non-bonding surface; the surface region comprises rod-shaped particles; the rod-shaped particles have an average orientation angle of 45° or more and 90° or less with respect to the non-bonding surfaces; Seal structure.

2. The seal structure according to claim 1, The rod-shaped particles have an average aspect ratio of 3 or more. Seal structure.

3. An electrochemical reaction cell stack comprising the seal structure according to claim 1 or 2.

Images