Electrochemical reaction cell stack

Abstract

To suppress the occurrence of cracks around an oxide film in an electrochemical reaction cell stack.SOLUTION: An electrochemical reaction cell stack includes a single cell, a metal member, an oxide film formed on a surface of the metal member and containing Ti, and an insulating member disposed between the single cell or a conductive member electrically connected to the single cell and the oxide film. When a TiO2 voltage is applied between the metallic member and the single cell or an electrically conductive member electrically connected to the single cell at 700 °C for 200 hours, an absolute difference between a TiO2 abundance ratio after the voltage application and a TiO2 abundance ratio before the voltage application is 0.3 or less, where the 20V abundance ratio is a value obtained by dividing a TiO2 content in the oxide film by a total value of a TiO content and the TiO2 content.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Solid oxide fuel cells (SOFCs) are known as one type of fuel cell that generates electricity using the electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of a fuel cell stack. Conventionally, a cell stack is known that comprises a plurality of fuel cell cells, a manifold made of an alloy material containing Cr, and a glass seal member that joins the fuel cell cells and the manifold (see, for example, Patent Document 1).

[0003] As described above, a fuel cell stack comprises a single cell, a metal member, and an insulating member. The fuel cell stack may further include an oxide film containing Ti formed on the surface of the metal member. In such a fuel cell stack, the insulating member is positioned between the single cell or a conductive member electrically connected to the single cell and the oxide film formed on the surface of the metal member. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-107593 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Because an insulating material is interposed between a single cell or a conductive material electrically connected to a single cell and the oxide film, a relatively large electric field is generated, for example, when a fuel cell stack generates electricity. At this time, if the current flowing through the single cell leaks into the Ti-containing oxide film through the insulating material, the ratio of TiO to TiO2 in the oxide film may change due to the change in the valence state of Ti. When the ratio of TiO to TiO2 changes, the volume of the oxide film changes, cracks may occur in the oxide film or at the interface between the oxide film and other materials, and ultimately the oxide film and other materials may delaminate.

[0006] Furthermore, these challenges are also common to electrolytic cell stacks, which are a form of electrolytic cell (hereinafter referred to as "SOEC") that uses the electrolysis reaction of water to produce hydrogen.In this specification, fuel cell single cells and electrolytic single cells are collectively referred to as single cells, and fuel cell stacks and electrolytic cell stacks are collectively referred to as electrochemical reaction cell stacks.In addition, these challenges are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

[0007] This specification discloses a technology capable of solving the above-mentioned problems. [Means for solving the problem]

[0008] The technologies disclosed herein can be implemented, for example, in the following forms:

[0009] (1) The electrochemical reaction cell stack disclosed herein comprises a single cell, a metal member, an oxide film containing Ti formed on the surface of the metal member, a conductive member electrically connected to the single cell or the single cell, and an insulating member disposed between the oxide film. When the TiO2 content in the oxide film is divided by the sum of the TiO content and the TiO2 content to obtain the TiO2 abundance ratio, when a voltage of 20V at 700°C is applied between the metal member and the single cell or the conductive member electrically connected to the single cell for 200 hours, the absolute difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.3 or less.

[0010] According to this electrochemical reaction cell stack, when a voltage of 20V is applied at 700°C for 200 hours, the absolute value of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.3 or less. In other words, by suppressing the conversion between TiO and TiO2, for example, the change in the volume of the oxide film due to the change in the ratio of TiO and TiO2 in the oxide film can be suppressed, and the occurrence of cracks in the oxide film or at the interface between the oxide film and other components can be suppressed.

[0011] (2) In the electrochemical reaction cell stack described above, the absolute value of the difference between the ratio of TiO2 after voltage application and the ratio of TiO2 before voltage application may be 0.1 or less. According to this configuration, the absolute value of the difference between the ratio of TiO2 after voltage application and the ratio of TiO2 before voltage application is 0.1 or less. That is, for example, by suppressing the conversion between TiO and TiO2, it is possible to suppress the change in the volume of the oxide film that occurs with changes in the ratio of TiO and TiO2 in the oxide film, and to more effectively suppress the occurrence of cracks in the oxide film or at the interface between the oxide film and other components.

[0012] (3) In the electrochemical reaction cell stack described above, the oxide film may contain at least one of Al and Cr. With this configuration, for example, when the metal member contains a metal such as Fe, the Al or Cr contained in the oxide film can suppress the oxidation of the metal in the metal member, and consequently suppress the oxidation of the metal member.

[0013] (4) In the electrochemical reaction cell stack described above, the metal member may be configured to contain 0.05% by mass or more of Ti. With this configuration, for example, when the metal member contains other metals such as Fe, the Ti contained in the metal member, which has a relatively high ionization tendency, can suppress the oxidation of the other metals in the metal member, and consequently suppress the oxidation of the metal member.

[0014] (5) In the electrochemical reaction cell stack described above, the insulating member may be made of crystallized glass. With this configuration, since the insulating member is made of crystallized glass, it is possible to ensure both insulation between the single cell or the conductive member electrically connected to the single cell and the oxide film, and bonding between the insulating member and the oxide film.

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

[0016] [Figure 1] Perspective view showing the external configuration of the fuel cell stack 10 in this embodiment. [Figure 2] This diagram shows the XZ cross-sectional configuration of the fuel cell stack 10 at position II-II in Figure 1. [Figure 3] This diagram shows the XZ cross-sectional configuration of the fuel cell stack 10 at position III-III in Figure 1. [Figure 4] Diagram illustrating the YZ cross-sectional configuration of the fuel cell stack 10 at position IV-IV in Figure 1. [Figure 5]Explanatory drawing showing the XZ cross-sectional configuration of two adjacent power generation units 100U at the same position as the cross-section shown in FIG. 2 [Figure 6] Explanatory drawing showing the XZ cross-sectional configuration of two adjacent power generation units 100U at the same position as the cross-section shown in FIG. 3 [Figure 7] Explanatory drawing showing an enlarged XZ cross-sectional configuration of the X1 portion of FIG. 6 [Figure 8] Explanatory drawing showing an enlarged XZ cross-sectional configuration of the X2 portion of FIG. 3 [Figure 9] Top view of the test piece [Figure 10] Cross-sectional view of the test piece at the position of X-X in FIG. 9

Mode for Carrying Out the Invention

[0017] A. Embodiment: A-1. Configuration of the fuel cell stack 10: FIG. 1 is a perspective view showing the external configuration of the fuel cell stack 10 in the present embodiment, FIG. 2 is an explanatory drawing showing the XZ cross-sectional configuration of the fuel cell stack 10 at the position of II-II in FIG. 1, FIG. 3 is an explanatory drawing showing the XZ cross-sectional configuration of the fuel cell stack 10 at the position of III-III in FIG. 1, and FIG. 4 is an explanatory drawing showing the YZ cross-sectional configuration of the fuel cell stack 10 at the position of IV-IV in FIG. 1. In each figure, XYZ axes orthogonal to each other for specifying directions are shown. In this specification, for convenience, the Z-axis direction is referred to as the vertical direction, the positive Z-axis direction is referred to as the upward direction, and the negative Z-axis direction is referred to as the downward direction. However, the fuel cell stack 10 may actually be installed in a direction different from such an orientation. The fuel cell stack 10 is an example of an electrochemical reaction cell stack in the claims.

[0018] (Overall configuration of the fuel cell stack 10) As shown in Figures 1 to 4, the fuel cell stack 10 comprises 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 roughly the same rectangular shape and are arranged in this order overlapping in a predetermined arrangement direction (vertical direction).

[0019] As shown in Figures 1 and 4, the fuel cell stack 10 has bolt holes BH near each of its four corners, each extending from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. Nuts N are threaded onto both ends of each bolt B. These bolts B and nuts N fasten the components from the first end plate 210 to the second end plate 270 together. As shown in Figures 2 to 4, the first plate 232 is supported by the end separator 230, and the four gas passage members 280 are connected to the second end plate 270.

[0020] As shown in Figures 2 to 4, the power generation block 100 is composed of a plurality (seven in this embodiment) of power generation units 100U arranged in a predetermined arrangement direction (vertical direction).

[0021] (First end plate 210) The first end plate 210 is a component formed by press-forming (bending) a single plate-shaped member. The first end plate 210 is made of a metal such as stainless steel and contains 0.05 mass% or more of Ti. An oxide film OM2 is formed on the surface of the first end plate 210, as will be described in detail later (see Figure 8). As shown in Figures 1 to 4, the first end plate 210 comprises a rectangular frame-shaped planar portion 211 having a through hole 212 near the center, and an outer projection 213 and an inner projection 214 that protrude from the planar portion 211 in the opposite direction to the insulating portion 220 (upwards in Figure 2). The planar portion 211 has holes that constitute the bolt holes BH described above. The outer projection 213 protrudes from the outer peripheral edge of the planar portion 211. The outer projection 213 is formed around the entire circumference of the outer peripheral portion of the planar portion 211. The inner projection 214 protrudes from the inner peripheral edge of the planar portion 211. The inner protrusion 214 is formed around the entire circumference of the inner part of the flat portion 211. The first end plate 210 is an example of a metal member in the claims.

[0022] (Insulation part 220) The insulating portion 220 is a rectangular frame-shaped member having a through hole near the center, and is formed of an insulating material such as crystallized glass, mica, forsterite, or other insulating ceramics. As shown in Figure 2, the insulating portion 220 is sandwiched between the first end plate 210 and the end separator 230, thereby ensuring insulation between the first end plate 210 and the end separator 230. The insulating portion 220 is an example of an insulating member within the scope of the claims.

[0023] (End separator 230) The end separator 230, as shown in Figures 2 to 4, is a rectangular frame-shaped member having a through hole 231 near the center, and is made of, for example, metal. The end separator 230 is an example of a conductive member in the claims.

[0024] (Plate 1, No. 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 to 4, the first plate 232 is joined to the peripheral portion of the through hole 231 in the end separator 230, for example, by welding. The end separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0025] The first plate 232 is connected to an interconnector 190, described later, provided on a power generation unit 100U located at one end (the upper end in Figure 2) of the multiple power generation units 100U that make up the power generation block 100, via a connecting member having the same structure as the fuel electrode current collector 144, described later. In this way, the power generation unit 100U and the first plate 232 are electrically connected.

[0026] (Terminal 1 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 film on its surface. The first terminal plate 240 is electrically connected to a power generation unit 100U located at one end (upper end in Figure 2) of the multiple power generation units 100U that make up the power generation block 100, via the first plate 232 and the end separator 230. One end of the first terminal plate 240 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0027] (Terminal 2 Plate 250) The second terminal plate 250 is a rectangular plate-shaped member, formed from a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. The second terminal plate 250 is electrically connected to the power generation unit 100U located at the other end (lower end in Figure 2) of the multiple power generation units 100U that make up the power generation block 100. One end of the second terminal plate 250 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0028] (Plate 2, page 260) The second plate 260 is a rectangular, flat member, formed of, for example, an insulating material. The peripheral edge of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring insulation between the second terminal plate 250 and the second end plate 270.

[0029] (Second end plate 270) The second end plate 270 is a member formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. The second end plate 270 comprises a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer projection 273 and an inner projection 274 projecting from the planar portion 271 in the opposite direction to the second terminal plate 250 (downward in Figure 2). The planar portion 271 has holes that constitute the bolt holes BH described above. The outer projection 273 protrudes from the outer peripheral edge of the planar portion 271. The outer projection 273 is formed around the entire circumference of the outer peripheral portion of the planar portion 271. The inner projection 274 protrudes from the inner peripheral edge of the planar portion 271. The inner projection 274 is formed around the entire circumference of the inner peripheral portion of the planar portion 271.

[0030] (Manifolds 311, 312, 321, 322) As shown in Figures 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 the oxidizer gas supply manifold 311, the oxidizer gas discharge manifold 312, the fuel gas supply manifold 321, and the fuel gas discharge manifold 322, respectively.

[0031] As shown in Figure 2, the oxidizer gas supply manifold 311 is a gas flow path that supplies oxidizer gas OG, introduced from outside the fuel cell stack 10, to the air chambers 313 of each power generation unit 100U (described later). The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer off-gas OOG, discharged from the air chambers 313 of each power generation unit 100U, to the outside of the fuel cell stack 10. For example, air is used as the oxidizer gas OG. The oxidizer gas supply manifold 311 and the oxidizer gas discharge manifold 312 are located on opposite sides of the air chamber 313.

[0032] As shown in Figure 3, the fuel gas supply manifold 321 is a gas passage that supplies fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chamber 323 of each power generation unit 100U, which will be described later. The fuel gas discharge manifold 322 is a gas passage that discharges fuel off-gas FOG discharged from the fuel chamber 323 of each power generation unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used. The fuel gas supply manifold 321 and the fuel gas discharge manifold 322 are located on opposite sides of the fuel chamber 323.

[0033] (Gas passage member 280) Each of the four gas passage members 280 comprises a main body portion 281 and a flange portion 282, as shown in Figures 1 to 3. The main body portion 281 has a gas through-hole 283 that penetrates vertically. The flange portion 282 is provided so as to protrude outward from the other end of the main body portion 281 (the lower end in Figure 2). The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into each bolt hole 284. One end of the main body portion 281 provided on the four gas passage members 280 (the upper end in Figures 2 and 3) is joined to the second end plate 270, for example by welding, and the gas through-holes 283 communicate with manifolds 311, 312, 321, and 322, respectively. Gas piping (not shown) for gas supply or discharge is connected to each main body portion 281.

[0034] (Overall configuration of a 100U power generation unit) Figure 5 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generation units 100U at the same position as the cross-section shown in Figure 2. Figure 6 is an explanatory diagram showing the XZ cross-sectional configuration of two adjacent power generation units 100U at the same position as the cross-section shown in Figure 3. As shown in Figures 5 and 6, the power generation unit 100U comprises a single cell 110, a single cell separator 120, an air electrode frame 130, a glass seal portion 135, a fuel electrode frame 140, a fuel electrode current collector 144, two interconnectors 190, and two IC separators 180. One IC separator 180, the air electrode frame 130, the single cell separator 120, the fuel electrode frame 140, and the other IC separator 180 are arranged in this order, overlapping each other. The single cell 110 is supported by the single cell separator 120, the interconnector 190 is supported by the IC separator 180, and the fuel electrode current collector 144 is positioned between the single cell 110 and the interconnector 190.

[0035] As shown in Figures 5 and 6, the IC separator 180 and interconnector 190 are shared by two adjacent power generation units 100U. However, as shown in Figure 2, the power generation unit 100U located at the other end (the lower end of Figure 2) of the multiple power generation units 100U does not have the IC separator 180 and interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 overlaps the fuel electrode frame 140.

[0036] (Single cell 110) The single cell 110 comprises an electrolyte layer 112, an air electrode 114, a fuel electrode 116, and a reaction prevention layer 118. As shown in Figures 5 and 6, the air electrode 114, the reaction prevention layer 118, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order. The single cell 110 of this embodiment is a fuel electrode-supported single cell in which the other layers constituting the single cell 110 (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) are supported by the fuel electrode 116.

[0037] The electrolyte layer 112 is a rectangular, flat member having one side on which the air electrode 114 is located (the upper side in Figures 5 and 6) and another side parallel to the air electrode 116 (the lower side in Figures 5 and 6). The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)). The fuel electrode 116 is a layer having a rectangular shape approximately the same size as the electrolyte layer 112 and contains, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, etc. The reaction prevention layer 118 is a layer having a rectangular shape approximately the same size as the air electrode 114 and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of elements (e.g., Sr) diffused from the air electrode 114 with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0038] (Single-cell separator 120) The single-cell separator 120, as shown in Figures 5 and 6, is a rectangular frame-shaped member having a substantially rectangular through-hole 121 near the center, and is made of, for example, metal. The thickness of the single-cell separator 120 is relatively thin, for example, 0.05 mm or more and 0.2 mm or less. The peripheral edge of the through-hole 121 in the single-cell separator 120 is joined to the peripheral edge of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is arranged: the upper surface in Figures 5 and 6) by a joint 124. The joint 124 is made of, for example, brazing material (Ag brazing). The single-cell separator 120 is an example of a conductive member in the claims.

[0039] (Air pole frame 130) As shown in Figures 5 and 6, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through-hole 131 near the center, and is formed of, for example, mica. The thickness of the air electrode frame 130 is preferably 0.5 mm or more and 5 mm or less. As shown in Figure 5, the air electrode frame 130 has an oxidant gas supply communication channel 132 that connects the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communication channel 133 that connects the air chamber 313 and the oxidant gas discharge manifold 312. The air electrode frame 130 is an example of an insulating member in the claims.

[0040] (Glass seal portion 135) The glass seal portion 135 is provided between the single-cell separator 120 and the IC separator 180, which are vertically opposed to each other with the air electrode frame 130 in between. The glass seal portion 135 is made of crystallized glass. The glass seal portion 135 is annular and is arranged to surround the fuel gas supply manifold 321 and the fuel gas discharge manifold 322, respectively. The glass seal portion 135 suppresses 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 air electrode frame 130 and the single-cell separator 120, and the interface between the air electrode frame 130 and the IC separator 180. The glass seal portion 135 is an example of an insulating member in the claims.

[0041] (Fuel pole frame 140) As shown in Figures 5 and 6, the fuel electrode frame 140 is a rectangular frame-shaped member having a substantially rectangular through hole 141 near the center, and is made of, for example, metal. As shown in Figure 6, the fuel electrode frame 140 has a fuel gas supply communication passage 142 that connects the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication passage 143 that connects the fuel chamber 323 and the fuel gas discharge manifold 322.

[0042] (IC separator 180) As shown in Figures 5 and 6, the IC separator 180 is a rectangular frame-shaped member having a through hole 181 near the center. The IC separator 180 is made of metal and contains 0.05 mass% or more of Ti. An oxide film OM1 is formed on the surface of the IC separator 180, as will be described in detail later (see Figure 7). The IC separator 180 is an example of a metal member in the claims.

[0043] (Interconnector 190, and fuel electrode current collector 144) As shown in Figures 5 and 6, the interconnector 190 comprises a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are conductive and made of metal (for example, ferritic stainless steel). The coating layer 193 is conductive and is arranged to cover the surface of the air electrode current collectors 192 and the surface of the flat plate portion 191 on which the air electrode current collectors 192 are arranged. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0044] The fuel electrode current collector 144 is a member that connects the interconnector 190 and the fuel electrode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 5 and 6, the fuel electrode current collector 144 comprises an interconnector-facing portion 146, an electrode-facing portion 145 parallel to the interconnector-facing portion 146, and a connecting portion 147 connecting the electrode-facing portion 145 and the interconnector-facing portion 146, and is U-shaped overall. The electrode-facing portion 145 is in contact with the fuel electrode 116, and the interconnector-facing portion 146 is in contact with the flat plate portion 191 of the interconnector 190.

[0045] As described above, the interconnector 190 is shared by two adjacent power generation units 100U. More specifically, as shown in Figures 5 and 6, the air electrode current collector 192 is joined to the air electrode 114 of a single cell 110 provided in one of the two adjacent power generation units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, thereby electrically connecting to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of a single cell 110 provided in the other of the two adjacent power generation units 100U via a fuel electrode current collector member 144. This ensures electrical conductivity between the two adjacent power generation units 100U.

[0046] However, as described above, the power generation unit 100U located at the other end (the lower end of Figure 2) among the multiple power generation units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this power generation unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0047] A spacer 149, for example made of mica, is placed between the electrode facing portion 145 and the interconnect facing portion 146. As a result, the fuel electrode current collector 144 follows the deformation of the power generation unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnect 190 (or second terminal plate 250) via the fuel electrode current collector 144 is maintained in good condition.

[0048] (Air chamber 313 and fuel chamber 323) As shown in Figures 5 and 6, the space partitioned by the single-cell separator 120 and single cell 110, the air electrode frame 130, the IC separator 180 and interconnector 190 faces the air electrode 114 and forms an air chamber 313 through which the oxidizer gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 into the outside space.

[0049] Furthermore, the space partitioned by the single-cell separator 120 and single cell 110, the fuel electrode frame 140, the IC separator 180 and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the fuel chamber 323 into the outside space.

[0050] The single-cell separator 120 separates the air chamber 313 from the fuel chamber 323, suppressing gas leakage (cross-leakage) from the air electrode 114 to the fuel electrode 116, or from the fuel electrode 116 to the air electrode 114, around the single cell 110. In addition, the IC separator 180 and interconnector 190 suppress gas leakage between adjacent power generation units 100U.

[0051] A-2. Operation of the fuel cell stack 10: As shown in Figures 2 and 5, the oxidizer gas OG is supplied to the oxidizer gas supply manifold 311 via gas piping (not shown) and gas passage member 280, and then supplied to the air chamber 313 via the oxidizer gas supply communication channel 132.

[0052] Furthermore, as shown in Figures 3 and 6, the fuel gas FG is supplied to the fuel gas supply manifold 321 via gas piping (not shown) and gas passage members 280, and then supplied to the fuel chamber 323 via the fuel gas supply communication channel 142.

[0053] When oxidant gas OG is supplied to the air chamber 313 of each power generation unit 100U and fuel gas FG is supplied to the fuel chamber 323, electricity is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and fuel gas FG. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent power generation units 100U, and the interconnector 190 ensures conductivity between the two adjacent power generation units 100U. In other words, the multiple power generation units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, the power generation unit 100U located at the other end (lower end in Figure 2) of the multiple power generation units 100U is electrically connected to the second terminal plate 250, and the power generation unit 100U located at the one end (upper end in Figure 2) is electrically connected to the first terminal plate 240. As a result, the electrical energy generated in each power generation unit 100U is extracted from the terminal plates 240 and 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (for example, 700°C to 1000°C), the fuel cell stack 10 may be heated by a heater (not shown) after startup until the high temperature can be maintained by the heat generated by power generation.

[0054] As shown in Figures 2 and 5, the oxidizer off-gas OOG discharged from the air chamber 313 of each power generation unit 100U to the oxidizer gas discharge manifold 312 via the oxidizer gas discharge communication channel 133 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in Figures 3 and 6, the fuel off-gas FOG discharged from the fuel chamber 323 of each power generation unit 100U to the fuel gas discharge manifold 322 via the fuel gas discharge communication channel 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0055] A-3. Detailed configuration around the oxide film OM: Figure 7 is an enlarged explanatory diagram showing the XZ cross-sectional configuration of part X1 in Figure 6. Figure 7 shows a part of the single-cell separator 120, a part of the air electrode frame 130, a part of the glass seal part 135, and a part of the IC separator 180.

[0056] An oxide film OM1 is formed on the surface of the IC separator 180. The air electrode frame 130 and the glass seal portion 135 are positioned between the single-cell separator 120, which is electrically connected to the single cell 110 via a joint portion 124, and the oxide film OM1. Due to this configuration, a relatively large electric field is generated around the oxide film OM1, for example, when the fuel cell stack 10 generates power. In addition, in configurations where the fuel cell stack 10 does not include a single-cell separator 120 (specifically, a configuration where a part of the single cell 110 extends to the outer edge of the power generation block 100), the air electrode frame 130 and the glass seal portion 135 may be directly connected to the single cell 110 and positioned between the single cell 110 and the oxide film OM1.

[0057] The oxide film OM1 contains, for example, 0.1% by mass or more (preferably 0.5% by mass or more) and 10% by mass or less of Ti. Specifically, the oxide film OM1 contains Ti oxides such as TiO and TiO2. In addition, the IC separator 180 of this embodiment contains at least one of Al and Cr in addition to Ti.

[0058] Figure 8 is an enlarged explanatory diagram showing the XZ cross-sectional configuration of part X2 in Figure 3. Figure 7 shows a part of the end separator 230, a part of the insulating part 220, and a part of the first end plate 210.

[0059] An oxide film OM2 is formed on the surface of the first end plate 210. The insulating portion 220 is positioned between the end separator 230, which is electrically connected to the single cell 110 via the interconnector 190, the fuel electrode current collector 144, and the first plate 232, and the oxide film OM2. Due to this configuration, an electric field is generated around the oxide film OM2, for example, when the fuel cell stack 10 generates electricity.

[0060] The oxide film OM2 contains Ti. Specifically, the oxide film OM2 contains Ti oxides such as TiO and TiO2. In addition, the first end plate 210 of this embodiment contains at least one of Al and Cr in addition to Ti.

[0061] In this embodiment, the fuel cell stack 10 is configured such that, when the ratio of TiO2 is defined as the number of moles of TiO2 in each of the oxide films OM1 and OM2 (hereinafter collectively referred to simply as "oxide film OM") divided by the sum of the number of moles of TiO and the number of moles of TiO2, and a voltage of 20V is applied to the fuel cell stack 10 at 700°C for 200 hours, the absolute value of the difference between the ratio of TiO2 after voltage application and the ratio of TiO2 before voltage application is 0.3 or less, preferably 0.1 or less. Means for achieving such a configuration include, for example, increasing the resistance values ​​of the insulating members, such as the glass seal portion 135, the air electrode frame 130, and the insulating portion 220. More specifically, this can be achieved by increasing the thickness of the insulating member, using a material with high volume resistivity (for example, alumina), or, if glass is used as the insulating member, by adjusting the content of transition metals contained in the glass or increasing the crystallinity of the glass.

[0062] A4. Effects of this embodiment: As described above, the fuel cell stack 10 of this embodiment comprises a single cell 110, a metal member (IC separator 180, first end plate 210), an oxide film OM containing Ti formed on the surface of the metal member, a conductive member (single cell separator 120, end separator 230) electrically connected to the single cell 110 or the single cell 110, and an insulating member (air electrode frame 130, glass seal portion 135, insulating portion 220) disposed between the oxide film OM and the metal member. When the TiO2 content in the oxide film OM is divided by the sum of the TiO content and the TiO2 content to obtain the TiO2 abundance ratio, when a voltage of 20V at 700°C is applied between the metal member and the single cell 110 or the conductive member electrically connected to the single cell 110 for 200 hours, the absolute value of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.3 or less.

[0063] According to the fuel cell stack 10 of this embodiment, when a voltage of 20V is applied at 700°C for 200 hours, the absolute value of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.3 or less. That is, for example, by suppressing the conversion between TiO and TiO2, it is possible to suppress the change in volume of the oxide film OM that accompanies changes in the ratio of TiO and TiO2 in the oxide film OM, and thereby suppress the occurrence of cracks in the oxide film OM or at the interface between the oxide film OM and other components.

[0064] Furthermore, in the fuel cell stack 10 of this embodiment, the absolute value of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.1 or less. According to the fuel cell stack 10 of this embodiment, the absolute value of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.1 or less. That is, for example, by suppressing the conversion between TiO and TiO2, it is possible to suppress the change in the volume of the oxide film OM that accompanies the change in the ratio of TiO and TiO2 in the oxide film OM, and to more effectively suppress the occurrence of cracks in the oxide film OM or at the interface between the oxide film OM and other components.

[0065] Furthermore, in the fuel cell stack 10 of this embodiment, the oxide film OM contains at least one of Al and Cr. According to the fuel cell stack 10 of this embodiment, for example, when a metal member contains a metal such as Fe, the Al or Cr contained in the oxide film OM can suppress the oxidation of the metal in the metal member, and consequently suppress the oxidation of the metal member.

[0066] Furthermore, in the fuel cell stack 10 of this embodiment, the metal component contains 0.05% by mass or more of Ti. According to the fuel cell stack 10 of this embodiment, for example, when the metal component contains other metals such as Fe, the Ti contained in the metal component, which has a relatively high ionization tendency, can suppress the oxidation of the other metals in the metal component, and consequently suppress the oxidation of the metal component itself.

[0067] Furthermore, in the fuel cell stack 10 of this embodiment, the glass seal portion 135 is made of crystallized glass. According to the fuel cell stack 10 of this embodiment, because the glass seal portion 135 is made of crystallized glass, it is possible to ensure both insulation between the single cell 110 and the oxide film OM, and bonding between the glass seal portion 135 and the oxide film OM.

[0068] A-5. Performance evaluation: Next, the performance evaluation of this embodiment will be described. For example, by adjusting the resistance value of the insulating material, several fuel cell stack 10 samples were prepared in which the absolute value of the difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application was different, and the crack resistance (resistance to cracks) was evaluated using these samples. Table 1 shows the performance evaluation results.

[0069] (Measurement of the absolute difference in the relative abundance of TiO2 in each sample) The absolute difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application was measured using a test piece simulating a fuel cell stack 10. Figure 9 shows a top view of the test piece, and Figure 10 shows a cross-sectional view of the test piece at position XX in Figure 9. The test piece consists of two metal members ME, an insulating member IM, two metal plates PL, two insulators IN, a bolt B, and two nuts N. Through holes are formed near the center of each of the metal members ME, insulating member IM, metal plates PL, and insulators IN.

[0070] The method for preparing the test piece will now be explained. First, an oxide film OM was formed on the surface of a metal member ME containing Ti by heat treatment at, for example, 1000°C. Next, one insulator IN, one metal plate PL, one metal member ME, one insulator IM, the other metal member ME, the other metal plate PL, and the other insulator IN were stacked in this order so that their through holes were in communication. A bolt B was inserted into the through hole, and all the members were fastened together using a nut N to prepare the test piece.

[0071] The test pieces fabricated by the above method were subjected to a voltage application test. The voltage application test was performed by placing the test pieces in an electric furnace at 700°C and applying a voltage of 20V for 200 hours. The voltage was applied by connecting a cord connected to an external power source to each of the two metal plates PL. One metal member ME corresponds to the end separator 230 and single cell separator 120 in the fuel cell stack 10, the other metal member ME corresponds to the first end plate 210 and IC separator 180 in the fuel cell stack 10, and the insulating member IM corresponds to the insulating part 220, air electrode frame 130, and glass seal part 135 in the fuel cell stack 10. The insulator IN does not correspond to any of the components in the fuel cell stack 10, but is used to insulate the metal plate PL and the nut N.

[0072] The measurement of the contents of TiO and TiO2 in the oxide film OM before voltage application was carried out by using, as a measurement sample, a part cut out from the test piece before the voltage application test. The measurement sample was broken within the layer of the oxide film OM in the test piece, and the fracture surface was subjected to measurement by the XPS method (X-ray photoelectron spectroscopy). Also, the measurement of the contents of TiO and TiO2 in the oxide film OM after voltage application was carried out by breaking the test piece after the voltage application test within the layer of the oxide film OM and subjecting the fracture surface to measurement by the XPS method. The measurement by the XPS method was carried out with a beam diameter of 100 μm within the range where the binding energy was 452 eV or more and 468 eV or less. Ti2p 3 / 2 , Ti2p 1 / 2 peaks were at 455 eV and 461 eV respectively, and Ti2p 3 / 2 , Ti2p 1 / 2 peaks of TiO2 were at 458 eV and 464 eV respectively. In principle, since the ratio of the Ti2p 3 / 2 peak area to the Ti2p 1 / 2 peak area is 2:1, the content of TiO was determined by fixing the ratio of the peak area of Ti2p 3 / 2 to the peak area of Ti2p 1 / 2 to be 2:1 and performing fitting, and using the total value of the fitted Ti2p 3 / 2 and Ti2p 1 / 2 peak areas. The content of TiO2 was determined in the same manner. From the obtained TiO content and TiO2 content, the abundance ratio of TiO2 was determined by the following formula (1). Abundance ratio of TiO2 = TiO2 content ÷ (TiO content + TiO2 content) ···(1) For each test piece, the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application was calculated to evaluate the characteristics of each test piece. In addition, the abundance ratio of TiO2 in the oxide film provided in an actual product (for example, the fuel cell stack 10) can be measured by taking out members corresponding to one metal member ME, the other metal member ME, and the insulating member IM and using the same method as the measurement method in the test piece.

[0073] (Evaluation of crack resistance) The crack resistance was evaluated using multiple fuel cell stacks 10 as samples, each with the same conditions as the test piece, such as the composition and thickness of the insulating material. The evaluation was performed by checking for the presence or absence of cracks in the oxide film OM or at the interface between the oxide film OM and other materials after heating the fuel cell stacks 10 under constant conditions. One heating cycle consisted of raising the temperature from 70°C to 700°C in 2 hours, holding at 700°C for 2 hours, and then cooling from 700°C to 70°C in 12 hours. First, the presence or absence of cracks was checked after performing the heating cycle 280 times for each fuel cell stack 10. Fuel cell stacks 10 that did not show cracks after 280 cycles were subjected to an additional 120 cycles (400 cycles in total) of heating before being checked for cracks again. The evaluation criteria were as follows: samples that developed cracks after 280 cycles were marked "Unacceptable" (×), samples that showed no cracks after 280 cycles but developed cracks after 400 cycles were marked "Acceptable" (△), and samples that showed no cracks after 400 cycles were marked "Good" (○). The presence or absence of cracks was determined by observation using a scanning electron microscope (SEM).

[0074] (Performance evaluation results) Table 1 shows the performance evaluation results. [Table 1]

[0075] Table 1 shows the evaluation of the crack resistance of each sample. The "absolute value of the difference in the abundance ratio of TiO2 before and after voltage application" in the table indicates the absolute value of the difference between the abundance ratio of TiO2 after voltage application and the abundance ratio of TiO2 before voltage application.

[0076] As shown in Table 1, the crack resistance evaluation for samples (S1, S2) where the absolute difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application was greater than 0.3 was all "×" (not good). Furthermore, the crack resistance evaluation for samples (S3-S5) where the absolute difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application was 0.3 or less but greater than 0.1 was all "△" (good). Additionally, the crack resistance evaluation for samples (S6-S8) where the absolute difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application was 0.1 or less was all "○" (good). From these results, it was confirmed that crack occurrence can be suppressed in a fuel cell stack 10 where the absolute difference between the TiO2 abundance ratio after voltage application and the TiO2 abundance ratio before voltage application is 0.3 or less, preferably 0.1 or less.

[0077] B. Variations: The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible.

[0078] The configuration of the fuel cell stack 10 and the power generation unit 100U in the above embodiment is merely an example and can be modified in various ways. For example, the number of single cells 110 (number of power generation units 100U) included in the fuel cell stack 10 in the above embodiment is merely an example, and the number of single cells 110 can be appropriately determined according to the output voltage required for the fuel cell stack 10.

[0079] The materials constituting each component in the above embodiment are merely examples, and each component may be made of other materials. For example, the glass seal portion 135 in the above embodiment is made of crystallized glass, but it may be made of other insulating materials such as mica or insulating ceramics, or it may contain multiple insulating materials.

[0080] In the above embodiment, no oxide film is formed on the conductive members (single-cell separator 120 and end separator 230), but an oxide film may be formed on the conductive members.

[0081] In the above embodiment, the single-cell separator 120 is used as an example of a conductive member and the IC separator 180 is used as an example of a metal member. However, the single-cell separator 120 may be used as an example of a metal member and the IC separator 180 may be used as an example of a conductive member.

[0082] In the above embodiment, the oxide film OM contains at least one of Al and Cr, but it does not necessarily have to contain at least one of Al and Cr.

[0083] In the above embodiment, the metal members (IC separator 180 and first end plate 210) contain 0.05% by mass or more of Ti, but they do not necessarily have to contain Ti.

[0084] Although the fuel cell stack 10 in the above embodiment is a co-flow type SOFC, the technologies disclosed herein are also applicable to counter-flow type SOFCs and cross-flow type SOFCs.

[0085] In the above embodiment, the single cell 110 is a fuel electrode-supported single cell, but it may be other types of single cells such as an electrolyte-supported or metal-supported type.

[0086] In the above embodiment, the fuel cell stack 10 is configured to have multiple flat-plate type single cells 110, but the present invention is similarly applicable to fuel cell stacks that have multiple single cells of other types (for example, cylindrical, flat cylindrical, etc.).

[0087] In the above embodiment, the electrochemical reaction cell stack was 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 polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolytic cell stacks that include electrolytic cell units, which are constituent units of solid oxide electrolytic cells (SOECs), as single cells. [Explanation of symbols]

[0088] 10: Fuel cell stack 100: Power generation block 100U: Power generation unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120: Separator for single cell 121: Through hole 124: Joint 130: Air electrode frame 131: Through hole 132: Oxidizer gas supply communication channel 133: Oxidizer gas discharge communication channel 135: Glass seal section 140: Fuel electrode frame 141: Through hole 142: Fuel gas supply communication channel 143: Fuel gas discharge communication channel 144: Fuel electrode current collector 145: Electrode opposing section 146: Interconnector opposing section 147: Connecting section 149: Spacer 180: Separator for IC 181: Through hole 190: Interconnector 191: Flat plate section 192: Air electrode current collector 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat section 212: Through hole 213: Outer protrusion 214: Inner protrusion 220: Insulation section 230: End 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 section 272: Through hole 273: Outer protrusion 274: Inner protrusion 280: Gas passage member 281: Main body section 282: Flange section 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 exhaust manifold 323: Fuel chamber B: Bolt BH: Bolt hole N: Nut FG: Fuel gas FOG: Fuel off-gas OG: Oxidizer gas OOG: Oxidizer off-gas OM1: Oxide film OM2: Oxide film

Claims

1. Single cell and, Metal components and An oxide film containing Ti is formed on the surface of the metal member, An insulating member disposed between the single cell or a conductive member electrically connected to the single cell and the oxide film, In an electrochemical reaction cell stack comprising, TiO in the oxide film ２ The content of TiO and TiO ２ The value obtained by dividing the total value of the content by the total value of TiO ２ When the ratio of TiO is such that a voltage of 20V at 700°C is applied for 200 hours between the metal member and the single cell or the conductive member electrically connected to the single cell, the TiO after voltage application ２ The relative abundance of the TiO before voltage application ２ The absolute value of the difference from the abundance ratio is 0.3 or less. An electrochemical reaction cell stack characterized by the following features.

2. In the electrochemical reaction cell stack according to claim 1, The TiO after voltage application ２ The relative abundance of the TiO before voltage application ２ The absolute value of the difference from the relative abundance is 0.1 or less. An electrochemical reaction cell stack characterized by the following features.

3. In the electrochemical reaction cell stack according to claim 1, The oxide film contains at least one of Al and Cr. An electrochemical reaction cell stack characterized by the following features.

4. In the electrochemical reaction cell stack according to claim 1, The aforementioned metal member contains 0.05% by mass or more of Ti. An electrochemical reaction cell stack characterized by the following features.

5. In the electrochemical reaction cell stack according to any one of claims 1 to 4, The insulating member is crystallized glass. An electrochemical reaction cell stack characterized by the following features.

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