Electrochemical reaction cell stack

Abstract

To suppress the occurrence of cracks on a joint surface between a glass seal part and a metal member and the peeling of the glass seal part from the metal member.SOLUTION: A stack that causes an electrochemical reaction includes a single cell including a fuel electrode, an electrolyte layer, and an air electrode, a metal member made of a chromium-containing alloy and having an oxide film on a surface thereof, and a glass seal member that is interposed between the metal member and another member or between the metal member and the single cell and is in contact with the oxide film, wherein the oxide film contains at least one of the following components i) and ii): i) at least one of: a) TiO and Ti2O3; b) TiO2ii; at least one of: c) NbO and Nb2O3; and d) at least one of: NbO2 and Nb2O5 SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs") are known as one type of fuel cell that generates electricity by utilizing an electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack. Conventionally, a cell stack has been known that includes a plurality of fuel cell units, an alloy member made of an alloy material containing Cr (chromium), and a glass seal that joins the alloy member to the fuel cell units (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-107593 Summary of the Invention [Problem to be solved by the invention]

[0004] An oxide film containing Cr exists on the surface of alloy members containing Cr. The glass seal is in contact with this oxide film. When a high voltage is applied to the glass seal during cell stack operation, oxygen ions are extracted from the oxide film, which can reduce the oxide film. Furthermore, because the fuel gas supplied to the cell stack is a hydrogen-rich reducing gas, the alloy member is surrounded by a reducing atmosphere, which can reduce the oxide film. In such cases, there is a concern that cracks may occur in the oxide film or in the interface between the oxide film and the glass seal, or that the glass seal may peel off from the oxide film. This problem is particularly pronounced in pure hydrogen power generation, which uses hydrogen gas as fuel gas, because the alloy member is surrounded by a strongly reducing atmosphere.

[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.

[0006] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms. (1) The electrochemical reaction cell stack disclosed in this specification comprises a unit cell including a fuel electrode, an electrolyte layer, and a cathode; a metal member made of a chromium-containing alloy having an oxide film on its surface; and a glass seal portion interposed between the metal member and another member or between the metal member and the unit cell and in contact with the oxide film, wherein the oxide film contains at least one of the following components i) and ii): i) a) and b) below a) at least one of TiO and Ti2O3 b) TiO2 ii) c) and d) below. c) at least one of NbO and Nb2O3 d) at least one of NbO2 and Nb2O5

[0008] According to the above configuration, the occurrence of cracks at the joint surface between the glass seal and the metal member and the separation of the glass seal from the metal member are suppressed.

[0009] (2) In the electrochemical reaction cell stack described in (1) above, the oxide film may have a contact area that contacts the glass seal portion and a non-contact area that does not contact the glass seal portion, and at least one of the components i) and ii) may be included in a nearby area of ​​the non-contact area that is within a distance of 100 μm measured along the surface of the oxide film from the boundary position with the contact area.

[0010] This configuration effectively prevents cracks from occurring at the joint surface between the glass seal and the metal member, and prevents the glass seal from peeling off from the metal member.

[0011] (3) In the electrochemical reaction cell stack described in (2) above, the content of the components i) and ii) in the adjacent region in terms of TiO2 and NbO2 may be 0.1 mass % or more and 10 mass % or less.

[0012] This configuration effectively prevents cracks from occurring at the joint surface between the glass seal and the metal member, and prevents the glass seal from peeling off from the metal member.

[0013] (4) In the electrochemical reaction cell stack according to any one of (1) to (3) above, the glass seal may be made of SiO2-B2O3-MgO-based glass.

[0014] The thermal expansion coefficient of SiO2-B2O3-MgO glass is close to that of chromium-containing alloys. If the glass seal is made of SiO2-B2O3-MgO glass, cracks at the interface between the glass seal and the metal component and peeling of the glass seal from the metal component are effectively suppressed.

[0015] (5) Another electrochemical reaction cell stack disclosed in this specification comprises a unit cell including an anode, an electrolyte layer, and an cathode; a metal member made of a chromium-containing alloy having an oxide film on its surface; and a glass seal portion interposed between the metal member and another member or between the metal member and the unit cell and in contact with the oxide film, wherein the oxide film contains the following components e) and f): e) at least one of MO and M2O3 f) at least one of MO2 and M2O5 (where M is a transition metal element excluding chromium)

[0016] According to the above configuration, the occurrence of cracks at the joint surface between the glass seal and the metal member and the separation of the glass seal from the metal member are suppressed. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack according to a first embodiment; [Figure 2] FIG. 2 is a cross-sectional view showing the fuel cell stack of the first embodiment taken along line II-II in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view showing the fuel cell stack of the first 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 first embodiment, taken along the same line as line II-II in FIG. 1; [Figure 5] FIG. 3 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, taken along the same line as line III-III in FIG. 1; [Figure 6] Enlarged view of box F in Figure 5 [Figure 7] FIG. 10 is a partially enlarged cross-sectional view showing the periphery of a glass seal portion in a fuel cell stack according to a modified example; DETAILED DESCRIPTION OF THE INVENTION

[0018] A. Implementation: A-1. Configuration of fuel cell stack 10: The first embodiment 1 will be described with reference to Figures 1 to 6. A fuel cell stack 10 (an example of an electrochemical reaction cell stack) of this embodiment is used in a solid oxide fuel cell having an electrolyte layer 112 containing a solid oxide.

[0019] (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, four gas passage members 280, and a glass seal section 135. 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).

[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] 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.

[0022] (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 metal member), an air electrode frame 130, a glass seal portion 135, an anode frame 140, an anode current collecting member 144, two interconnectors 190, and two IC separators 180. One IC separator 180 (an example of another member), 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 each supported by the two IC separators 180, and the anode current collecting member 144 is disposed between the single cell 110 and the interconnector 190.

[0023] 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.

[0024] (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.

[0025] 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).

[0026] (Single cell separator 120) As shown in Figures 4 and 5, the single cell separator 120 is a rectangular frame-like member having a substantially rectangular through-hole 121 near the center, and is made of, for example, metal. The plate thickness of the single cell separator 120 is relatively thin, for example, not less than 0.05 mm and not more than 0.2 mm. The peripheral portion of the through-hole 121 in the single cell separator 120 is joined to the peripheral portion of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is disposed: the upper surface in Figures 4 and 5) with a sealant 124. The sealant 124 is made of, for example, a brazing material (Ag brazing).

[0027] (Air electrode frame 130) As shown in Figures 4 and 5, the cathode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made of, for example, insulating ceramics (mica, etc.). The thickness of the cathode frame 130 is preferably 0.5-5 mm. The cathode frame 130 has two seal holes 132 arranged on both sides of the through-hole 131.

[0028] (Glass seal part 135) Each cathode frame 130 has two seal holes 132, each of which has a glass seal 135 disposed inside. The glass seal 135 is a cylindrical member with openings on both ends and is made of crystallized 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.

[0029] (fuel electrode frame 140) As shown in FIG. 5, the fuel electrode frame 140 is a rectangular frame-like member having a substantially rectangular through-hole 141 near the center, and is made of, for example, metal.

[0030] (IC separator 180) As shown in FIGS. 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center, and is made of a metal such as ferritic stainless steel.

[0031] (Interconnector 190 and anode current collecting member 144) 4 and 5, the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-like air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are electrically conductive and made of a metal (e.g., ferritic stainless steel). The coating layer 193 is electrically conductive and is disposed so as to cover the surface of the air electrode current collector 192 and the surface of the flat plate portion 191 on which the air electrode current collector 192 is disposed. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] (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.

[0037] 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.

[0038] 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.

[0039] (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 stainless steel. As shown in FIGS. 1 to 3 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is formed around the entire outer 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 formed around the entire inner periphery of the flat portion 211.

[0040] (insulating part 220) Insulating portion 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of an insulating material such as crystallized glass or insulating ceramics such as mica or forsterite. As shown in Fig. 2, insulating portion 220 is sandwiched between first end plate 210 and terminal separator 230, thereby ensuring insulation between first end plate 210 and terminal separator 230.

[0041] (Terminal separator 230) As shown in FIGS. 2 and 3, the terminal separator 230 is a rectangular frame-shaped member having a through-hole 231 near the center, and is made of, for example, metal.

[0042] (First Plate 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined by welding, for example, to the periphery of the through-hole 231 in the terminal separator 230. The terminal separator 230 and the first plate 232 separate the power generating block 100 from the external space of the fuel cell stack 10.

[0043] The first plate 232 is connected to an interconnector 190 (described later) provided in a reaction unit 100U arranged at one 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 (described later), thereby electrically connecting this reaction unit 100U and the first plate 232.

[0044] (First terminal plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through-hole 241 near the center, and is made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. The first terminal plate 240 is electrically connected to the reaction unit 100U arranged at one 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.

[0045] (2nd terminal plate 250) The second terminal plate 250 is a rectangular plate-shaped member made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. The second terminal plate 250 is electrically connected to the reaction unit 100U that is arranged at the other end (the lower end in FIG. 2) of the multiple reaction units 100U that make up the power generation block 100. 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.

[0046] (Second plate 260) Second plate 260 is a rectangular, flat member made of, for example, an insulating material. The peripheral edge of second plate 260 is sandwiched between second terminal plate 250 and second end plate 270, thereby ensuring insulation between second terminal plate 250 and second end plate 270.

[0047] (Second end plate 270) The second end plate 270 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel. The second end plate 270 has 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 flat portion 271 has holes that form the bolt holes BH described above. The outer convex portion 273 protrudes from the outer periphery of the flat portion 271. The outer convex portion 273 is formed around the entire outer 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 formed around the entire inner periphery of the flat portion 271.

[0048] (Manifolds 311, 312, 321, 322) 1, 2, and 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are 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.

[0049] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies an oxidant gas OG introduced from outside the fuel cell stack 10 to an air chamber 313 (described later) of each reaction unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges an 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.

[0050] 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 a fuel chamber 323 (described later) of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, a hydrogen-rich gas obtained by reforming city gas is used.

[0051] 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. That is, the internal space of the 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 glass seals 135 disposed inside each cathode frame 130. That is, the internal space of the glass seal 135 forms 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.

[0052] (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 has a gas through hole 283 that penetrates in the vertical direction. The flange portion 282 is provided so as to protrude outward from the other 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. One 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 gas through hole 283 communicates with the manifolds 311, 312, 321, and 322, respectively. A gas pipe (not shown) for supplying or discharging gas is connected to each of the main body portions 281.

[0053] A-2. Operation of fuel cell stack 10: 2, the oxidizing gas OG is supplied to the air chamber 313 through the gas passage member 280 and the oxidizing gas supply manifold 311. Also, as shown in FIG. 3, the fuel gas FG is supplied to the fuel chamber 323 through the gas passage member 280 and the fuel gas supply manifold 321.

[0054] 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.

[0055] 2, the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidant gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in FIG. 3, 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 internal space of the main body 281.

[0056] A-3.Detailed composition of oxide film 122: In this embodiment, the single cell separator 120 is a ferritic stainless steel containing Ti (titanium), Al (aluminum) and Cr, and has an oxide film 122 on the surface, the main component of which is alumina (Al2O3) containing Cr.

[0057] 6, one end of the glass seal portion 135 is in contact with the single cell separator 120. The glass seal portion 135 is made of SiO2-B2O3-MgO-based glass and has a thermal expansion coefficient close to that of the single cell separator 120, which is made of a chromium-containing alloy.

[0058] The region of the oxide coating 122 that is in contact with the glass seal portion 135 is the contact region Ar1, and the region that is not in contact with the glass seal portion 135 is the non-contact region Ar2. Within the non-contact region Ar2, the region within a distance L of 100 μm measured along the surface of the oxide coating 122 from the boundary position with the contact region Ar1 is the proximity region Ar2n.

[0059] The oxide film 122 may contain at least one of the following components i) and ii). i) a) and b) below a) at least one of TiO and Ti2O3 b) TiO2 ii) c) and d) below. c) at least one of NbO and Nb2O3 d) at least one of NbO2 and Nb2O5

[0060] When a high voltage is applied to the glass seal portion 135 during operation of the fuel cell stack 10, oxygen ions are extracted from the oxide film 122, which may reduce the oxide film. When the oxide film 122 is reduced, the charge balance is disrupted due to a decrease in oxygen ions inside the oxide film 122, and the repulsion due to Coulomb force increases, causing the oxide film 122 to expand. This phenomenon is not limited to the oxide film 122 whose main component is alumina, but is common to all oxides.

[0061] When the oxide film 122 contains component i), i.e., titanium oxide, component a) serves to suppress the reduction of the oxide film 122. Titanium oxide is less easily reduced than oxides containing chromium, so as the amount of titanium oxide dissolved in the oxide film 122 increases, the reduction of the oxide film 122 as a whole is suppressed. In general, the ease of dissolution depends on the valence of the metal element contained in the dissolved substance, and substances containing elements with the same valence as the metal element contained in the substance constituting the oxide film 122 (the dissolved substance) are more likely to be dissolved. Since the valence of metal elements contained in the substances constituting the oxide film 122 is generally divalent or trivalent, divalent TiO and trivalent Ti2O3 are more likely to be dissolved than tetravalent TiO2. The inclusion of component a), which is relatively easily dissolved, in the oxide film 122 suppresses the reduction of the oxide film 122.

[0062] On the other hand, component b) improves the bonding strength of the single-cell separator 120 to the glass seal portion 135, and contributes to preventing peeling of the single-cell separator 120 from the glass seal portion 135. The reason why component b) contributes to improving bonding strength is not entirely clear, but it is speculated as follows. Because the glass and the oxide film are bonded by ionic bonds, it is thought that substances containing elements with a valence similar to that of Si contained in SiO2, which determines the structure of glass, bond more easily to glass. Because the valence of Si contained in SiO2 is tetravalent, tetravalent TiO2 bonds more easily to glass than divalent TiO or trivalent Ti2O3, and this is thought to contribute to improving bonding strength.

[0063] Therefore, when titanium oxide is dissolved in the oxide film 122, the oxide film 122 containing both component a) and component b) effectively prevents cracks from occurring at the joint surface between the glass seal portion 135 and the unit-cell separator 120 and prevents the glass seal portion 135 from peeling off from the unit-cell separator 120. It is particularly effective for the adjacent region Ar2n, which is likely to be the starting point for cracks and peeling, to contain both component a) and component b).

[0064] The same applies to the case where component ii) (i.e., niobium oxide) is dissolved in oxide coating 122. In other words, by including both component c) that is relatively easily dissolved in oxide coating 122 and component d) that contributes to improving the bonding strength, the occurrence of cracks at the bonding surface between glass seal portion 135 and unit cell separator 120 and peeling of glass seal portion 135 from unit cell separator 120 are effectively suppressed. It is particularly effective for the vicinity region Ar2n to include both component c) and component d).

[0065] The same applies to the case where an oxide of a transition metal element other than titanium oxide or niobium oxide is dissolved in the oxide film 122. In other words, the oxide film 122 may contain both the following components e) and f). When the oxide film 122 contains both component e), which is relatively easily dissolved, and component f), which contributes to improving the bonding strength, the occurrence of cracks at the bonding surface between the glass seal portion 135 and the single-cell separator 120 and peeling of the glass seal portion 135 from the single-cell separator 120 are effectively suppressed. e) at least one of MO and M2O3 f) at least one of MO2 and M2O5 (where M is a transition metal element excluding chromium)

[0066] The contents of components i) and ii) in the vicinity region Ar2n may be 0.1% by mass or more and 10% by mass or less. A content within this range can provide sufficient crack and peeling suppression. In this specification, the "contents of components i) and ii) in the vicinity region" refers to the mass ratio of components i) and ii) to the total mass of the inclusions contained in the vicinity region. Furthermore, when only one of components i) and ii) is contained in the vicinity region Ar2n, the content refers to the content of that component. When both components are contained, the content refers to the sum of the contents of components i) and ii). The content of component i) is calculated in terms of TiO2, i.e., calculated assuming that all Ti contained in the vicinity region Ar2n exists as TiO2. Similarly, the content of component ii) is calculated in terms of NbO2, i.e., calculated assuming that all Nb contained in the vicinity region Ar2n exists as NbO2.

[0067] A-4. Manufacturing method of fuel cell stack 10: An example of a method for manufacturing the fuel cell stack 10 having the above configuration will be described below.

[0068] When the oxide film 122 is to contain components a) and b), a plate made of an alloy containing Ti and Cr is prepared as the material for the single cell separator 120. This plate is heat-treated at 1000°C in the air, for example, to form the oxide film 122 on the surface. After the oxide film 122 is formed, the plate is processed as necessary to obtain the single cell separator 120.

[0069] This single cell separator 120 is stacked with other components to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is heat treated at a heat treatment temperature higher than the operating temperature to bond the glass seal portion 135 and the single cell separator 120. The heat treatment temperature is, for example, 800°C or higher. The dissolution of titanium oxide into the oxide film 122 progresses during the heat treatment as Ti contained in the alloy that is the material of the single cell separator 120 diffuses into the oxide film 122. The heat treatment is performed in a reducing atmosphere, that is, in an atmosphere where the oxygen partial pressure is lower than that of the atmosphere (for example, when the heat treatment temperature is 850°C, the 10 -25 ~10 -27 Alternatively, the fuel cell stack 10 after the heat treatment can be kept in a reducing atmosphere for a certain period of time, so that the oxide film 122 contains both the component a) and the component b).

[0070] When the oxide film 122 contains components c) and d), the fuel cell stack 10 can be manufactured using the same procedures as above, except that a plate made of an alloy containing Nb and Cr is prepared as the material for the unit cell separator 120. When the oxide film 122 contains components e) and f), the fuel cell stack 10 can be manufactured using the same procedures as above, except that a plate made of an alloy containing the desired transition metal M and Cr is prepared as the material for the unit cell separator 120.

[0071] A-5. Advantages of this embodiment: As described above, the fuel cell stack 10 of this embodiment comprises a single cell 110 including a fuel electrode 116, an electrolyte layer 112, and an air electrode 114, a single cell separator 120 made of a chromium-containing alloy having an oxide film 122 on its surface, and a glass seal portion 135 interposed between the single cell separator 120 and the IC separator 180 and in contact with the oxide film 122, wherein the oxide film 122 contains at least one of the following components i) and ii). i) a) and b) below a) at least one of TiO and Ti2O3 b) TiO2 ii) c) and d) below. c) at least one of NbO and Nb2O3 d) at least one of NbO2 and Nb2O5

[0072] According to the above configuration, the occurrence of cracks at the joint surface between the glass seal portion 135 and the unit cell separator 120 and the peeling of the glass seal portion 135 from the unit cell separator 120 are suppressed.

[0073] The oxide coating 122 has a contact area Ar1 that contacts the glass seal portion 135 and a non-contact area Ar2 that does not contact the glass seal portion 135, and at least one of components i) and ii) is contained in a proximity area Ar2n of the non-contact area Ar2, which is within a distance L of 100 μm measured along the surface of the oxide coating 122 from the boundary with the contact area Ar1. This configuration effectively prevents cracks from occurring at the joint surface between the glass seal portion 135 and the single-cell separator 120 and peeling of the glass seal portion 135 from the single-cell separator 120.

[0074] The content of components i) and ii) in the adjacent region Ar2n in terms of TiO2 and NbO2 is 0.1 mass% or more and 10 mass% or less. This configuration effectively prevents cracks from occurring at the joint surface between the glass seal portion 135 and the unit cell separator 120, and prevents the glass seal portion 135 from peeling off from the unit cell separator 120.

[0075] Glass seal 135 is made of SiO2-B2O3-MgO-based glass. The thermal expansion coefficient of SiO2-B2O3-MgO-based glass is close to that of chromium-containing alloys, which effectively prevents cracks from occurring at the joint surface between glass seal 135 and single-cell separator 120 and prevents glass seal 135 from peeling off from single-cell separator 120.

[0076] Furthermore, when the oxide coating 122 contains the following components e) and f), the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120 and the peeling of the glass seal portion 135 from the single-cell separator 120 are suppressed, just as when the oxide coating 122 contains component i) or component ii). e) at least one of MO and M2O3 f) at least one of MO2 and M2O5 (where M is a transition metal element excluding chromium)

[0077] A-6. Performance evaluation: A number of samples of metal members with different titanium oxide compositions in the oxide film were prepared, and a voltage application test was carried out to check for the occurrence of cracks and peeling.

[0078] 1. Creating a sample 1) Samples S1-S9 A metal member made of ferritic stainless steel containing Ti, Al, and Cr was heat-treated at 1000°C in an air atmosphere to form an oxide film on the surface, mainly composed of alumina with Cr solid solution. A glass seal made of SiO2-B2O3-MgO glass was sandwiched between two metal members with oxide films, and the glass seal and metal member were bonded by heat treatment at 850°C. The oxygen partial pressure during the heat treatment was set at 10 -25 ~10 -27 By adjusting the pressure to 1000 kJ / cm 2 atm, the titanium oxide composition in the oxide film was adjusted to be as shown in Table 1, and samples S1 to S9 were obtained.

[0079] 2) Samples S10-S18 A metal member made of ferritic stainless steel containing Ti and Cr was heat-treated at 1000°C in an air atmosphere to form an oxide film mainly composed of chromium oxide (Cr2O3) on the surface. A glass seal made of SiO2-B2O3-MgO glass was sandwiched between two metal members with oxide films formed, and the glass seal and metal member were bonded by heat treatment at 850°C. The oxygen partial pressure during the heat treatment was kept at 10 -25 ~10 -27By adjusting the pressure to 1000 kJ / cm 2 atm, the titanium oxide composition in the oxide film was adjusted to be as shown in Table 1, and samples S10 to S18 were obtained.

[0080] 3) Measurement of titanium oxide content Before being subjected to the voltage application test described in 2 below, sample S1 was fractured within the oxide film so that the fracture surface included both the contact and adjacent regions of the oxide film and was parallel to the interface between the glass and the oxide film. The fracture surface was measured using X-ray Photoelectron Spectroscopy (XPS) to determine the titanium oxide content in the oxide film. The XPS measurement was performed with a beam diameter of 100 μm and within a binding energy range of 452 eV to 468 eV. TiO-derived Ti2p 3 / 2 , Ti2p 1 / 2 The peaks of TiO2 are at 455 eV and 461 eV, respectively. 3 / 2 , Ti2p 1 / 2 The peaks of Ti2p are at 458 eV and 464 eV, respectively. 3 / 2 Peak area and Ti2p 1 / 2 Since the peak area ratio is 2:1, the TiO content is expressed as Ti2p 3 / 2 Peak area and Ti2p 1 / 2 The area ratio of the peaks was fixed at 2:1 and fitting was performed. 3 / 2 and Ti2p 1 / 2 The total peak area of ​​the TiO2 oxide film was used to calculate the TiO2 content. The TiO2 content was calculated in a similar manner. The molar ratio of TiO2 to TiO2 in the oxide film was calculated from the obtained TiO2 content and TiO2 content. In addition, the same fracture surface as that used for the XPS measurement was subjected to SEM / EDX analysis to calculate the titanium oxide content (mass%) in the oxide film in terms of TiO2.

[0081] For samples S2-S18, the ratio of the TiO and TiO2 contents in the oxide film and the titanium oxide content in the oxide film were determined using the same method.

[0082] 2. Voltage application test Samples S1-S18 obtained in 1 above were subjected to a voltage application test. The voltage application test was performed by placing each sample in an electric furnace at 700°C and applying a voltage of 5 V or 10 V for 10 hours. The voltage was applied by connecting a cord connected to an external power source to the metal member and other members. After the voltage application, each sample was cooled to room temperature and subjected to a tensile test to observe the presence or absence of cracks and peeling at the joint surface between the oxide coating of the metal member and the glass seal. Samples in which cracks or peeling were observed in the tensile test after application of a voltage of 5 V were evaluated as ×; samples in which no cracks or peeling were observed in the tensile test after application of a voltage of 5 V but cracks or peeling were observed in the tensile test after application of a voltage of 10 V were evaluated as ○; and samples in which no cracks or peeling were observed in the tensile test after application of a voltage of 5 V and 10 V were evaluated as ⊚.

[0083] [Table 1]

[0084] 3.Results As shown in Table 1, for samples S6 and S15, which contain TiO2 in the oxide film and do not contain TiO, peeling was observed between the oxide film and the glass seal in a tensile test after a voltage of 5V was applied. Reductive expansion of the oxide film due to the applied voltage was observed, and this is thought to have caused the peeling. For samples S9 and S18, which contain TiO2 in the oxide film but do not contain TiO, peeling was observed between the oxide film and the glass seal in a tensile test after a voltage of 5V was applied. This is thought to have been caused by poor adhesion between the metal member and the glass seal.

[0085] For the other samples containing both TiO2 and TiO as titanium oxides in the oxide film, no cracking or peeling was observed in the tensile test after application of a voltage of 5 V. Of these, for samples S2-S4, S7, S8, S11-S13, S16, and S17, which had a titanium oxide content of 0.1 mass % or more and 10 mass % or less, no cracking or peeling was observed in the tensile test after application of a voltage of 10 V.

[0086] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible. (1) In the above embodiment, the glass seal portion 135 is a component interposed between the single cell separator 120, which is a metal component, and the IC separator 180, which is another component. However, the glass seal portion may be a component interposed between, for example, the single cell separator, which is a metal component, and the single cell. (2) In the above embodiment, the metal member is the unit cell separator 120 and the other member is the IC separator 180. However, for example, the metal member may be an IC separator and the other member may be a unit cell separator. Alternatively, the metal member may be an IC separator and the other member may be an interconnector, or the metal member may be an interconnector and the other member may be an IC separator. (3) In the above embodiment, the fuel cell stack 10 is configured to include 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) In the above embodiment, at least one of components i) and ii) is contained in the adjacent region of the oxide film. However, at least one of components i) and ii) may be contained in a region of the oxide film other than the adjacent region. (5) For example, as shown in FIG. 7, when the glass seal portion 135 is bonded near a corner of the single cell separator 120B, the adjacent region Ar2nB may be a portion of the oxide coating 122B that is bent along the corner. (6) In the above embodiment, the electrochemical reaction cell stack is a cell stack used in a solid oxide fuel cell (SOFC). However, the above configuration is also applicable to cell stacks used in other types of fuel cells, such as a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), or a molten carbonate fuel cell (MCFC), or to an electrolysis cell stack having, as a single cell, an electrolysis cell unit, which is a constituent unit of a solid oxide electrolysis cell (SOEC). [Explanation of symbols]

[0087] 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, 120B: Separator for single cell (metal member) 121: Through hole 122, 122B: Oxide film 124: Sealing material 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: IC separator 181: Through hole 190: Interconnector 191: Flat plate portion 192: Air electrode current collecting portion 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat portion 212: Through hole 213: Outer convex portion 214: Inner convex portion 220: Insulating portion 230: 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 283: Gas through hole 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 Ar1: Contact area Ar2: Non-contact area Ar2n, Ar2nB: Adjacent area B: Bolt BH: Bolt hole FG: Fuel gas FOG: Fuel off-gas N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas

Claims

1. a single cell including an anode, an electrolyte layer, and an cathode; a metal member made of a chromium-containing alloy having an oxide film on its surface; a glass seal portion interposed between the metal member and another member or between the metal member and the unit cell and in contact with the oxide film; Equipped with The electrochemical reaction cell stack, wherein the oxide film contains at least one of the following components i) and ii): i) a) and b) below. a) TiO and Ti 2 O 3 At least one of b) Unclear 2 ii) c) and d) below. c) NbO and Nb 2 O 3 At least one of d) NbO 2 and Nb 2 O 5 At least one of

2. the oxide film has a contact area that contacts the glass seal portion and a non-contact area that does not contact the glass seal portion, at least one of the components i) and ii) is contained in a nearby region of the non-contact region, the distance of which is measured along the surface of the oxide coating from the boundary position with the contact region to within 100 μm; The electrochemical reaction cell stack according to claim 1 .

3. TiO of the components i) and ii) in the adjacent region ２ and NbO ２ The content in terms of carbon dioxide is 0.1% by mass or more and 10% by mass or less, The electrochemical reaction cell stack according to claim 2 .

4. The glass seal portion is made of SiO 2 -B 2 O 3 - made of MgO-based glass, The electrochemical reaction cell stack according to claim 1 or 2.

5. a single cell including an anode, an electrolyte layer, and an cathode; a metal member made of a chromium-containing alloy having an oxide film on its surface; a glass seal portion interposed between the metal member and another member or between the metal member and the unit cell and in contact with the oxide film; Equipped with An electrochemical reaction cell stack, wherein the oxide film comprises the following components e) and f): e) MO and M 2 O 3 At least one of f) MO 2 and M 2 O 5 At least one of (wherein M is a transition metal element other than chromium)

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