Electrochemical reaction cell stack

Abstract

To suppress peeling between an oxide film and an insulating member in an electrochemical reaction cell stack.SOLUTION: An electrochemical reaction cell stack includes a unit cell, a first metal member, a first oxide film formed on a surface of the first metal member and mainly composed of a metal oxide containing a first metal element, and an insulating member disposed between the unit cell or a conductive member electrically connected to the unit cell and the first oxide film. The first oxide film contains a first specific element having a standard electrode potential whose absolute value is larger than that of the first metal element.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 cells (single cells), a manifold (first metal member) made of an alloy material containing Cr, and a glass seal member (insulating member) that joins the fuel cell cells and the manifold (see, for example, Patent Document 1).

[0003] The fuel cell stack may further include a first oxide film formed on the surface of the first metal member and containing a metal oxide containing the first metal element as a main component. In such a fuel cell stack, an insulating member is disposed between the unit cell or a conductive member electrically connected to the unit cell and the first oxide film formed on the surface of the first metal member. [Prior art documents] [Patent documents]

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

[0005] Because an insulating member is interposed between the first oxide film and a single cell or a conductive member electrically connected to the single cell, a relatively large electric field is generated, for example, when the fuel cell stack generates power. Voltages are applied to the conductive member, the first oxide film, and the insulating member, respectively, and at this time, an oxidation-reduction reaction of the first metal element may occur in the first oxide film. If an oxidation-reduction reaction of the first metal element occurs, the volume of the first oxide film changes, causing cracks at the interface between the first oxide film and the insulating member, which may eventually lead to peeling between the first oxide film and the insulating member.

[0006] Note that these issues are also common to electrolysis cell stacks, which are a type of electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen using the electrolysis reaction of water. In this specification, a single fuel cell cell and a single electrolysis cell are collectively referred to as a single cell, and a fuel cell stack and an electrolysis cell stack are collectively referred to as an electrochemical reaction cell stack. Furthermore, these issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

[0007] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0008] The technology disclosed in this specification can be realized, for example, in the following forms.

[0009] (1) The electrochemical reaction cell stack disclosed in this specification includes a unit cell, a first metal member, a first oxide film formed on the surface of the first metal member and mainly composed of a metal oxide containing a first metal element, and an insulating member disposed between the unit cell or a conductive member electrically connected to the unit cell and the first oxide film. The first oxide film contains a first specific element having a standard electrode potential whose absolute value is greater than that of the first metal element.

[0010] According to this electrochemical reaction cell stack, the first oxide film contains a first specific element that is less susceptible to oxidation and reduction than the first metal element, which is the main component, making the first oxide film as a whole less susceptible to oxidation and reduction. This improves the voltage resistance of the entire first oxide film and suppresses the occurrence of cracks at the interface between the first oxide film and the insulating member. Therefore, according to this electrochemical reaction cell stack, peeling between the first oxide film and the insulating member can be suppressed.

[0011] (2) In the electrochemical reaction cell stack described in (1) above, the insulating member may be made of glass. According to this configuration, since the insulating member is made of glass, it is possible to improve the gas sealing performance between the first oxide film and the insulating member while suppressing peeling between the first oxide film and the insulating member.

[0012] (3) The electrochemical reaction cell stack described in (1) above may further include the conductive member, the conductive member including a second metal member and a second oxide film formed on the surface of the second metal member and composed primarily of a metal oxide containing a second metal element, wherein the second oxide film may contain a second specific element having a standard electrode potential greater in absolute value than the second metal element. According to this configuration, the second oxide film contains the second specific element, which is less susceptible to oxidation-reduction than the second metal element, which is the main component, making the second oxide film less susceptible to oxidation-reduction. This improves the voltage resistance of the entire second oxide film and suppresses cracking at the interface between the second oxide film and the insulating member. Therefore, this electrochemical reaction cell stack can suppress peeling between the second oxide film and the insulating member.

[0013] (4) In the electrochemical reaction cell stack described in (1) above, the first metal element may be either Al or Cr. According to this configuration, by using either Al or Cr as the first metal element, oxidation of the first metal member can be suppressed when the electrochemical reaction cell stack is operated at high temperatures, and high reliability can be achieved.

[0014] (5) In the electrochemical reaction cell stack described in (3) above, the second metal element may be either Al or Cr. According to this configuration, by using either Al or Cr as the second metal element, oxidation of the second metal member can be suppressed when the electrochemical reaction cell stack is operated at high temperatures, and high reliability can be achieved.

[0015] (6) In the electrochemical reaction cell stack described in (1) above, the concentration of the first specific element in the first oxide film may be 2 mol% or more. With this configuration, the concentration of the first specific element in the first oxide film is 2 mol% or more, which more effectively suppresses peeling between the first oxide film and the insulating member.

[0016] (7) In the electrochemical reaction cell stack described in (1) above, the first oxide film may have a first portion that is a portion that overlaps with the insulating member in a first direction that is a direction in which the first oxide film and the insulating member are stacked, and a second portion that is a portion that does not overlap with the insulating member in the first direction and is a portion that is adjacent to the first portion in a second direction that intersects the first direction, and the first specific element may be located in at least one of the first portion and a portion of the second portion that is within 100 μm of a boundary with the first portion in the second direction. With this configuration, the first specific element is located in a portion of the first oxide film that is likely to be subjected to voltage, so that peeling between the first oxide film and the insulating member can be more effectively suppressed.

[0017] (8) In the electrochemical reaction cell stack according to any one of (1) to (7) above, the first oxide film may be mainly composed of alumina, and the first specific element may be at least one of Ba, Ca, La, Mg, and Sr. According to this configuration, since the first specific element is at least one of Ba, Ca, La, Mg, and Sr, the durability of the electrochemical reaction cell stack can be improved.

[0018] (9) In the electrochemical reaction cell stack according to any one of (1) to (7) above, the first oxide film may be mainly composed of chromia, and the first specific element may be at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn. According to this configuration, the first specific element is at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn, and therefore the durability of the electrochemical reaction cell stack can be improved.

[0019] The technology disclosed in this specification can be realized in various forms, for example, in the form of an electrochemical reaction cell stack and a manufacturing method thereof. [Brief explanation of the drawings]

[0020] [Figure 1] A perspective view showing the appearance of a fuel cell stack. [Figure 2] FIG. 2 is an explanatory diagram showing an XZ cross section of the fuel cell stack taken along the line II-II in FIG. 1; [Figure 3] FIG. 2 is an explanatory diagram showing an XZ cross section of the fuel cell stack taken along the line III-III in FIG. 1; [Figure 4] An explanatory diagram showing an XZ cross section of two adjacent power generating units at the same position as the cross section shown in Figure 2. [Figure 5] FIG. 4 is an explanatory diagram showing an XZ cross section of two adjacent power generating units at the same position as the cross section shown in FIG. 3. [Figure 6] An explanatory diagram showing an enlarged view of the X1 portion of FIG. 5. [Figure 7] An explanatory diagram showing an enlarged view of the X2 portion of FIG. 3. [Figure 8] Top view of the test piece [Figure 9] Cross-sectional view of the test piece at position IX-IX in Figure 8 DETAILED DESCRIPTION OF THE INVENTION

[0021] A. Implementation: (Configuration of fuel cell stack 10) FIG. 1 is a perspective view showing the appearance of a fuel cell stack 10, FIG. 2 is an explanatory diagram showing an XZ cross section of the fuel cell stack 10 taken along line II-II in FIG. 1, and FIG. 3 is an explanatory diagram showing an XZ cross section of the fuel cell stack 10 taken along line III-III in FIG. 1. Each figure shows mutually orthogonal X, Y, and Z axes for specifying directions. For convenience, the Z-axis direction will be referred to as the up-down direction, the positive Z-axis direction as the up-down direction, and the negative Z-axis direction as the down-down direction in this specification; however, the fuel cell stack 10 may actually be installed in an orientation different from these orientations. The fuel cell stack 10 is an example of an electrochemical reaction cell stack.

[0022] 1 to 3, the fuel cell stack 10 includes a power generation block 100, an end separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating section 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating section 220, the end separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have rectangular outer shapes of approximately the same size and are arranged in a stacked manner in this order in a predetermined arrangement direction (vertical direction).

[0023] 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. Four gas passage members 280 are connected to the second end plate 270.

[0024] As shown in FIGS. 2 and 3, the power generation block 100 is made up of a plurality of (seven in this embodiment) power generation units 100U arranged side by side in a predetermined arrangement direction (vertical direction).

[0025] The first end plate 210 is a member formed by pressing (bending) a single plate-like member. 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.

[0026] Insulating section 220 is a rectangular frame-shaped member with a through hole near the center, and is made of an insulating material. As shown in Figures 2 and 3, insulating section 220 is sandwiched between first end plate 210 and end separator 230, thereby ensuring insulation between first end plate 210 and end separator 230.

[0027] 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.

[0028] 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.

[0029] The first plate 232 is connected to an interconnector 190 (described later) provided in a power generation unit 100U arranged 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 anode current collecting member 144 (described later), thereby electrically connecting the power generation unit 100U and the first plate 232.

[0030] 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 power generating unit 100U located at one end (the upper end in FIG. 2) of the multiple power generating units 100U that make up the power generating 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 generating block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0031] The second terminal plate 250 is a rectangular plate-shaped member made of a conductive material such as ferritic stainless steel that has an alumina oxide coating on its surface. The second terminal plate 250 is electrically connected to the power generating unit 100U that is located at the other end (the lower end in FIG. 2) of the multiple power generating units 100U that make up the power generating block 100. One end (the right end in FIG. 2) of the second terminal plate 250 protrudes laterally from the power generating block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0032] 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.

[0033] 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. Second end plate 270 includes a rectangular, frame-like flat portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from flat portion 271 in the direction opposite second terminal plate 250 (downward in FIG. 2). Flat portion 271 has holes that form the bolt holes BH described above. Outer convex portion 273 protrudes from the outer periphery of flat portion 271. Outer convex portion 273 is formed around the entire outer periphery of flat portion 271. Inner convex portion 274 protrudes from the inner periphery of flat portion 271. Inner convex portion 274 is formed around the entire inner periphery of flat portion 271. As will be described in detail later, an oxide film 276 is formed on the surface of second end plate 270 (see FIG. 7). The second end plate 270 is an example of a first metal member in the claims. The oxide film 276 is an example of a first oxide film in the claims.

[0034] 1 to 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes 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.

[0035] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies the oxidant gas OG introduced from outside the fuel cell stack 10 to an air chamber 313 (described later) of each power generating unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges the oxidant off-gas OOG discharged from the air chamber 313 of each power generating unit 100U to the outside of the fuel cell stack 10. For example, air is used as the oxidant gas OG. The oxidant gas supply manifold 311 and the oxidant gas discharge manifold 312 are arranged on opposite sides of the air chamber 313.

[0036] As shown in Fig. 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 power generating 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 power generating unit 100U to the outside of the fuel cell stack 10. For example, hydrogen-rich gas obtained by reforming city gas is used as the fuel gas FG. The fuel gas supply manifold 321 and the fuel gas discharge manifold 322 are arranged on opposite sides of the fuel chamber 323.

[0037] The second end plate 270 is joined to the second terminal plate 250 via a glass seal portion 500. More specifically, peripheral portions of the four manifolds 311, 312, 321, and 322 on the flat surface portion 271 are each joined to the second terminal plate 250 via the glass seal portion 500. The glass seal portion 500 is an example of an insulating member in the claims. The second terminal plate 250 is an example of a conductive member in the claims.

[0038] 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 formed therethrough in the vertical direction. The flange portion 282 is provided so as to protrude outward from the other end (the lower end in FIGS. 2 and 3 ) 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 is connected to 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.

[0039] Fig. 4 is an explanatory diagram showing an XZ cross section of two adjacent power generating units 100U at the same position as the cross section shown in Fig. 2. Fig. 5 is an explanatory diagram showing an XZ cross section of two adjacent power generating units 100U at the same position as the cross section shown in Fig. 3. As shown in Figs. 4 and 5, the power generating unit 100U includes a single cell 110, a single cell separator 120, 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, the air electrode frame 130, the single cell separator 120, the anode frame 140, and the other IC separator 180 are arranged in this order, stacked one on top of the other.

[0040] The unit cell 110 includes an electrolyte layer 112, an air electrode 114, an anode 116, and a reaction prevention layer 118. As shown in Figures 4 and 5, the air electrode 114, the reaction prevention layer 118, the electrolyte layer 112, and the anode 116 are arranged in this order. 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, air electrode 114, and reaction prevention layer 118) that make up the unit cell 110. The unit cell 110 is supported by a unit cell separator 120.

[0041] 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).

[0042] 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 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 disposed: the upper surface in Figures 4 and 5) by a joint 124. The joint 124 is made of, for example, a brazing material (Ag brazing). The single cell separator 120 is an example of a conductive member within the scope of the claims.

[0043] 4 and 5, the air electrode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made of, for example, mica. As shown in Fig. 4, the air electrode frame 130 has an oxidant gas supply communicating channel 132 that connects the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communicating channel 133 that connects the air chamber 313 and the oxidant gas discharge manifold 312.

[0044] The glass seal 135 is provided between the single cell separator 120 and the IC separator 180, which face each other in the vertical direction with the cathode frame 130 sandwiched between them. The glass seal 135 is made of glass. The glass seal 135 is annular and is disposed so as to surround the fuel gas supply manifold 321 and 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. The glass seal 135 is an example of an insulating member as defined in the claims.

[0045] 4 and 5, the anode 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. As shown in Fig. 5, the anode frame 140 has a fuel gas supply communication channel 142 that connects the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication channel 143 that connects the fuel chamber 323 and the fuel gas discharge manifold 322.

[0046] As shown in Figures 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center, and is made of, for example, metal. As will be described in detail later, an oxide film 186 is formed on the surface of IC separator 180 (see Figure 6). IC separator 180 is an example of a first metal member in the claims. Oxide film 186 is an example of a first oxide film in the claims.

[0047] As shown in FIGS. 4 and 5 , the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are electrically conductive and formed 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. The interconnector 190 is supported by the IC separator 180.

[0048] The anode current collecting member 144 is a member that connects the interconnector 190 and the anode 116. The anode current collecting member 144 is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in FIGS. 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.

[0049] As shown in Figures 4 and 5, the interconnector 190 is shared by two adjacent power generating units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collecting portion 192 is joined to the air electrode 114 of the unit cell 110 provided in one of the two adjacent power generating units 100U via a conductive bonding material 196 formed, for example, of a spinel-type oxide. This electrically connects the air electrode current collecting portion 192 to the air electrode 114. The flat plate portion 191 is electrically connected to the anode 116 of the unit cell 110 provided in the other of the two adjacent power generating units 100U via an anode current collecting member 144. This ensures electrical continuity between the two adjacent power generating units 100U.

[0050] However, as shown in Figure 2, the power generating unit 100U located at the other end (the lower end in Figure 2) of the multiple power generating units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 included in this power generating unit 100U is connected to the second terminal plate 250 via the fuel electrode current collecting member 144.

[0051] 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 power generating unit 100U due to temperature cycles and reactant gas pressure fluctuations, and good electrical connection is maintained between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144.

[0052] 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.

[0053] 4 and 5, 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.

[0054] 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 power generating units 100U.

[0055] (Operation of fuel cell stack 10) As shown in Figures 2 and 4, the oxidizing gas OG is supplied to the oxidizing gas supply manifold 311 via a gas pipe (not shown) and a gas passage member 280, and is supplied to the air chamber 313 via the oxidizing gas supply communicating passage 132.

[0056] As shown in FIGS. 3 and 5, the fuel gas FG is supplied to the fuel gas supply manifold 321 via a gas pipe (not shown) and a gas passage member 280, and is supplied to the fuel chamber 323 via the fuel gas supply communication passage 142.

[0057] When an oxidant gas OG is supplied to the air chamber 313 of each power generating unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power is generated in the unit 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 power generating units 100U, and the interconnector 190 ensures electrical continuity between the two adjacent power generating units 100U. In other words, the multiple power generating 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 power generating unit 100U located at the other end (the lower end in FIG. 2 ) of the multiple power generating units 100U, and a first terminal plate 240 is electrically connected to the power generating unit 100U located at one end (the upper end in FIG. 2 ). As a result, electrical energy generated in each power generating 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.

[0058] 2 and 4, the oxidant off-gas OOG discharged from the air chamber 313 of each power generating unit 100U to the oxidant gas discharge manifold 312 via the oxidant gas discharge communicating passage 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 FIGS. 3 and 5, the fuel off-gas FOG discharged from the fuel chamber 323 of each power generating unit 100U to the fuel gas discharge manifold 322 via the fuel gas discharge communicating passage 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0059] (Detailed structure around oxide film 186) Fig. 6 is an explanatory diagram showing an enlarged view of part X1 in Fig. 5. Fig. 6 shows a part of the single cell separator 120, a part of the cathode frame 130, a part of the glass seal part 135, and a part of the IC separator 180.

[0060] An oxide film 186 is formed on the surface of the IC separator 180. The cathode frame 130 and the glass seal 135 are each disposed between the oxide film 186 and the unit cell separator 120, which is electrically connected to the unit cell 110 via the joint 124. Due to this configuration, a relatively large electric field is generated around the oxide film 186, for example, during power generation in the fuel cell stack 10. Note that in an embodiment in which the fuel cell stack 10 does not include the unit cell separator 120, such as an embodiment in which a portion of the unit cell 110 extends to the outer edge of the power generation block 100, the cathode frame 130 and the glass seal 135 may each be directly connected to the unit cell 110 and disposed between the unit cell 110 and the oxide film 186.

[0061] The oxide film 186 is mainly composed of a metal oxide containing a first metal element. The IC separator 180 is formed of a metal containing the first metal element. In this embodiment, the first metal element is either Al (aluminum) or Cr (chromium). When the first metal element is Al, the metal oxide containing the first metal element is alumina. When the first metal element is Cr, the metal oxide containing the first metal element is chromia.

[0062] The oxide film 186 includes a first specific element having a larger absolute value of standard electrode potential than the first metal element. More specifically, when the first metal element is Al and the oxide film 186 is mainly composed of alumina, the first specific element is, for example, at least one of Ba (barium), Ca (calcium), La (lanthanum), Mg (magnesium), and Sr (strontium). When the first metal element is Cr and the oxide film 186 is mainly composed of chromia, the first specific element is, for example, at least one of Al, Ba, Ca, La, Mg, Mn (manganese), Sr, Ti (titanium), and Zn (zinc). The concentration of the first specific element in the oxide film 186 is preferably 2 mol% or more, and more preferably 3 mol% or more.

[0063] As shown in FIG. 6 , the oxide film 186 has an overlapping portion 186d and a non-overlapping portion 186n. The overlapping portion 186d is a portion that overlaps with the glass seal portion 135 in the Z-axis direction, which is the direction in which the oxide film 186 and the glass seal portion 135 are stacked. The non-overlapping portion 186n is a portion that does not overlap with the glass seal portion 135 in the Z-axis direction and is a portion that is adjacent to the overlapping portion 186d in the Y-axis direction, which intersects with the Z-axis direction. In the oxide film 186, the first specific element is located in at least one of the overlapping portion 186d and a portion of the non-overlapping portion 186n that is within 100 μm in the Y-axis direction from the boundary with the overlapping portion 186d. The overlapping portion 186d is an example of a first portion. The non-overlapping portion 186n is an example of a second portion. The Z-axis direction is an example of a first direction. The Y-axis direction is an example of a second direction.

[0064] The single cell separator 120 also has a flat plate portion 125 and an oxide film 126. The flat plate portion 125 is a flat plate member made of metal. The oxide film 126 is a coating formed on the surface of the flat plate portion 125. Similar to the vicinity of the oxide film 186, a relatively large electric field is generated around the oxide film 126, for example, when the fuel cell stack 10 generates electricity. The flat plate portion 125 is an example of a second metal member. The oxide film 126 is an example of a second oxide film.

[0065] The oxide film 126 is mainly composed of a metal oxide containing a second metal element. The flat plate portion 125 is formed of a metal containing the second metal element. In this embodiment, the second metal element is either Al or Cr. When the second metal element is Al, the metal oxide containing the second metal element is alumina. When the second metal element is Cr, the metal oxide containing the second metal element is chromia.

[0066] The oxide film 126 includes a second specific element having a standard electrode potential with a larger absolute value than that of the second metal element. More specifically, when the second metal element is Al and the oxide film 126 is primarily composed of alumina, the second specific element is, for example, at least one of Ba, Ca, La, Mg, and Sr. When the second metal element is Cr and the oxide film 126 is primarily composed of chromia, the second specific element is, for example, at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn.

[0067] (Details of the oxide film 276) Fig. 7 is an explanatory diagram showing an enlarged view of part X2 in Fig. 3. Fig. 7 shows a part of the second end plate 270, a part of the second plate 260, a part of the glass seal portion 500, and a part of the second terminal plate 250.

[0068] An oxide film 276 is formed on the surface of the second end plate 270. The second plate 260 and the glass seal portion 500 are disposed between the oxide film 276 and the second terminal plate 250. Due to this configuration, a relatively large electric field is generated around the oxide film 276, for example, when the fuel cell stack 10 generates electricity.

[0069] The oxide film 276 is mainly composed of a metal oxide containing a first metal element. The second end plate 270 is formed of a metal containing the first metal element. In this embodiment, the first metal element is either Al or Cr. When the first metal element is Al, the metal oxide containing the first metal element is alumina. When the first metal element is Cr, the metal oxide containing the first metal element is chromia.

[0070] The oxide film 276 includes a first specific element having a standard electrode potential with a larger absolute value than that of the first metal element. More specifically, when the first metal element is Al and the oxide film 276 is primarily composed of alumina, the first specific element is, for example, at least one of Ba, Ca, La, Mg, and Sr. When the first metal element is Cr and the oxide film 276 is primarily composed of chromia, the first specific element is, for example, at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn. The concentration of the first specific element in the oxide film 276 is preferably 2 mol% or more, and more preferably 3 mol% or more.

[0071] As shown in FIG. 7 , the oxide film 276 has an overlapping portion 276d and a non-overlapping portion 276n. The overlapping portion 276d is a portion that overlaps with the glass seal portion 500 in the Z-axis direction, which is the direction in which the oxide film 276 and the glass seal portion 500 are stacked. The non-overlapping portion 276n is a portion that does not overlap with the glass seal portion 500 in the Z-axis direction and is a portion that is adjacent to the overlapping portion 276d in the Y-axis direction, which intersects with the Z-axis direction. In the oxide film 276, the first specific element is located in at least one of the overlapping portion 276d and a portion of the non-overlapping portion 276n that is within 100 μm in the Y-axis direction from the boundary with the overlapping portion 276d. The overlapping portion 276d is an example of a first portion. The non-overlapping portion 276n is an example of a second portion. The Z-axis direction is an example of a first direction. The Y-axis direction is an example of a second direction.

[0072] The second terminal plate 250 also has a flat plate portion 255 and an oxide film 256. The flat plate portion 255 is a flat plate member made of metal. The oxide film 256 is a coating formed on the surface of the flat plate portion 255. Similar to the vicinity of the oxide film 276, a relatively large electric field is generated around the oxide film 256, for example, when the fuel cell stack 10 generates electricity. The flat plate portion 255 is an example of a second metal member. The oxide film 256 is an example of a second oxide film.

[0073] The oxide film 256 is mainly composed of a metal oxide containing a second metal element. The flat plate portion 255 is formed of a metal containing the second metal element. In this embodiment, the second metal element is either Al or Cr. When the second metal element is Al, the metal oxide containing the second metal element is alumina. When the second metal element is Cr, the metal oxide containing the second metal element is chromia.

[0074] (Effects of this embodiment) As described above, the fuel cell stack 10 of this embodiment includes the unit cell 110, the first metal member (IC separator 180, second end plate 270), the first oxide film (oxide film 186, oxide film 276) formed on the surface of the first metal member and composed primarily of a metal oxide containing a first metal element, the unit cell 110 or a conductive member (single cell separator 120, second terminal plate 250) electrically connected to the unit cell 110, and an insulating member (glass seal portion 135, glass seal portion 500) disposed between the unit cell 110 and the first oxide film. The first oxide film contains a first specific element having a standard electrode potential with an absolute value greater than that of the first metal element.

[0075] According to the fuel cell stack 10 of this embodiment, the first oxide film contains the first specific element, which is less susceptible to oxidation-reduction than the first metal element, which is the main component, making the first oxide film as a whole less susceptible to oxidation-reduction reactions. This improves the voltage resistance of the entire first oxide film, and suppresses the occurrence of cracks at the interface between the first oxide film and the insulating member. Therefore, the fuel cell stack 10 can suppress peeling between the first oxide film and the insulating member.

[0076] Furthermore, in the fuel cell stack 10 of this embodiment, the insulating member is made of glass. According to the fuel cell stack 10 of this embodiment, since the insulating member is made of glass, it is possible to improve the gas sealing performance between the first oxide film and the insulating member while suppressing peeling between the first oxide film and the insulating member.

[0077] The fuel cell stack 10 of this embodiment further includes a conductive member (single cell separator 120, second terminal plate 250) having a second metal member (flat plate portion 125, flat plate portion 255) and a second oxide film (oxide film 126, oxide film 256) formed on the surface of the second metal member and composed primarily of a metal oxide containing a second metal element, the second oxide film containing a second specific element having a standard electrode potential with a larger absolute value than the second metal element. According to the fuel cell stack 10 of this embodiment, the second oxide film contains the second specific element that is less susceptible to oxidation-reduction than the second metal element that is the main component, making the second oxide film as a whole less susceptible to oxidation-reduction reactions. This improves the voltage resistance of the entire second oxide film and suppresses the occurrence of cracks at the interface between the second oxide film and the insulating member. Therefore, this electrochemical reaction cell stack can suppress peeling between the second oxide film and the insulating member.

[0078] Furthermore, in the fuel cell stack 10 of this embodiment, the first metal element is either Al or Cr. According to the fuel cell stack 10 of this embodiment, by using either Al or Cr as the first metal element, oxidation of the first metal member can be suppressed when the fuel cell stack 10 is operated at high temperatures, and high reliability can be achieved.

[0079] Furthermore, in the fuel cell stack 10 of this embodiment, the second metal element is either Al or Cr. According to the fuel cell stack 10 of this embodiment, by using either Al or Cr as the second metal element, oxidation of the second metal member can be suppressed when the fuel cell stack 10 is operated at high temperatures, and high reliability can be achieved.

[0080] In addition, in the fuel cell stack 10 of this embodiment, the concentration of the first specific element in the first oxide film is 2 mol % or more. According to the fuel cell stack 10 of this embodiment, since the concentration of the first specific element in the first oxide film is 2 mol % or more, peeling between the first oxide film and the insulating member can be more effectively suppressed.

[0081] In addition, in the fuel cell stack 10 of this embodiment, the first oxide film has a first portion (overlapping portion 186d, overlapping portion 276d) that overlaps with the insulating member in the Z-axis direction, which is the direction in which the first oxide film and the insulating member (glass seal portion 135, glass seal portion 500) are stacked, and a second portion (non-overlapping portion 186n, non-overlapping portion 276n) that does not overlap with the insulating member in the Z-axis direction and is adjacent to the first portion in the Y-axis direction that intersects the Z-axis direction, and the first specific element is located in at least one of the first portion and a portion of the second portion that is within 100 μm of the boundary with the first portion in the Y-axis direction. According to the fuel cell stack 10 of this embodiment, the first specific element is located in a portion of the first oxide film that is likely to be subjected to voltage, which more effectively suppresses peeling between the first oxide film and the insulating member.

[0082] In the fuel cell stack 10 of this embodiment, the first oxide film is mainly composed of alumina, and the first specified element is at least one of Ba, Ca, La, Mg, and Sr. According to the fuel cell stack 10 of this embodiment, since the first specified element is at least one of Ba, Ca, La, Mg, and Sr, corrosion of the first metal member is suppressed compared to when the first specified element contains, for example, Na, and the durability of the fuel cell stack 10 can be improved.

[0083] Furthermore, in the fuel cell stack 10 of this embodiment, the first oxide film is primarily composed of chromia, and the first specific element is at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn. According to the fuel cell stack 10 of this embodiment, since the first specific element is at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn, corrosion of the first metal member is suppressed compared to when the first specific element contains, for example, Na, and the durability of the fuel cell stack 10 can be improved.

[0084] In the fuel cell stack 10 of this embodiment, the concentration of the third specific element, which has a smaller absolute value of the standard electrode potential than the first metal element contained in the first oxide film, may be 10 mol% or less, or 2 mol% or less. By setting the concentration of the third specific element in the first oxide film to 10 mol% or less or 2 mol% or less, oxidation-reduction reactions are less likely to occur in the first oxide film as a whole, and the voltage resistance of the first oxide film as a whole is more effectively improved. When the first oxide film is mainly composed of alumina, the third specific element is, for example, at least one of Mn, Cr, Fe, Co, Ni, and Cu. When the first oxide film is mainly composed of chromia, the third specific element is, for example, at least one of Fe, Co, Ni, and Cu.

[0085] In addition, in the fuel cell stack 10 of this embodiment, the concentration of the fourth specific element, which has a smaller absolute value of the standard electrode potential than the second metal element contained in the second oxide film, may be 10 mol% or less, or 2 mol% or less. By setting the concentration of the fourth specific element in the second oxide film to 10 mol% or less or 2 mol% or less, oxidation-reduction reactions are less likely to occur in the second oxide film as a whole, and the voltage resistance of the second oxide film as a whole is more effectively improved. When the second oxide film is mainly composed of alumina, the fourth specific element is, for example, at least one of Mn, Cr, Fe, Co, Ni, and Cu. When the second oxide film is mainly composed of chromia, the fourth specific element is, for example, at least one of Fe, Co, Ni, and Cu.

[0086] (Performance evaluation) Next, a performance evaluation of this embodiment will be described. A plurality of fuel cell stack samples (SA1 to SA24) having different compositions of the first oxide film were fabricated, and performance evaluation was carried out using these samples.

[0087] The resistance to peeling between the first oxide film and the insulating member was evaluated using a test piece simulating a fuel cell stack 10. FIG. 8 shows a top view of the test piece, and FIG. 9 shows a cross-sectional view of the test piece taken along line IX-IX in FIG. 8. The test piece includes a first metal member ME1, a second metal member ME2, an insulating member IM, two metal plates PL, two insulators IN, a bolt B, and two nuts N. A first oxide film OM1 is formed on the surface of the first metal member ME1. The insulating member IM is made of glass. The first metal member ME1, the second metal member ME2, the insulating member IM, the metal plates PL, and the insulator IN each have a through-hole formed near the center.

[0088] In the above test piece, the first metal member ME1 corresponds to the second end plate 270 and IC separator 180 in the fuel cell stack 10, the second metal member ME2 corresponds to the second terminal plate 250 and single cell separator 120 in the fuel cell stack 10, and the insulating member IM corresponds to the glass seal portion 500 and glass seal portion 135 in the fuel cell stack 10. Furthermore, the insulator IN does not correspond to any of the members in the fuel cell stack 10, but is used to insulate the metal plate PL from the nut N.

[0089] First, a test piece was prepared. A metal oxide powder was applied to the surface of a first metal member ME1 containing either Al or Cr. Specifically, when the first metal member ME1 contained Al, a powder of at least one of La2O3, MgO, BaO, CaO, and Sr2O3 was applied. When the first metal member ME1 contained Cr, a powder of at least one of La2O3, MgO, BaO, CaO, Sr2O3, Al2O3, MnO, TiO, and ZnO was applied. Next, the first metal member ME1 coated with the metal oxide powder was heat-treated, for example, at 1000°C, to form a first oxide film OM1 on the surface of the first metal member ME1. Next, one insulator IN, one metal plate PL, first metal member ME1, insulating member IM, second metal member ME2, the other metal plate PL, and the other insulator IN were stacked in this order so that their through holes were connected, and bolts B were inserted into the through holes, and all the components were fastened together using nuts N. Next, a heat treatment was performed at a temperature above the softening temperature of the glass contained in the insulating member IM (for example, 850°C), and the first oxide film OM1 and the insulating member IM were joined to produce a test piece.

[0090] Next, the composition of the first oxide film OM1 in the test piece prepared by the above method was analyzed. First, the test piece prepared by the above method was embedded in resin and mirror-polished to reveal a cross section perpendicular to the interface between the first oxide film OM1 and the insulating member IM. The cross section revealed by mirror polishing was analyzed by energy dispersive X-ray spectroscopy (SEM / EDX) in a range of thickness (entire thickness of the first oxide film OM1) × width (5 μm) to analyze the composition of the first oxide film OM1. Note that the "thickness direction" refers to the direction perpendicular to the interface between the first oxide film OM1 and the insulating member IM, and the "width direction" refers to the direction along the interface between the first oxide film OM1 and the insulating member IM.

[0091] Next, the test piece prepared by the above method was subjected to a voltage application test. First, the test piece prepared by the above method was heated to 700°C in an air atmosphere, for example, by placing it in an electric furnace. After the temperature of the test piece reached 700°C, a predetermined voltage was applied for 10 hours. The voltage was applied by connecting cords connected to an external power source to each of the two metal plates PL. After that, the voltage application was stopped, the test piece was cooled to room temperature, and the bolts B, nuts N, insulators IN, and metal plates PL were removed. Then, a tensile test was performed in the direction of peeling the first metal member ME1 and the second metal member ME2 to check for delamination between the first oxide film OM1 and the insulating member IM.

[0092] The results of the performance evaluation are explained below. Table 1 shows the results of the performance evaluation.

[0093] [Table 1]

[0094] In the "Voltage application test" column in Table 1, samples in which no delamination between the first oxide film OM1 and the insulating member IM was confirmed in the tensile test are marked with an "O" and samples in which delamination between the first oxide film OM1 and the insulating member IM was confirmed in the tensile test are marked with an "X".

[0095] The first oxide film OM1 of each of samples SA1 to SA14 shown in Table 1 is primarily composed of alumina. Therefore, the primary component of the first oxide film OM1 of each of samples SA1 to SA14 shown in Table 1, excluding oxygen (element O), is Al. Furthermore, La, Mg, Ba, Ca, and Sr shown as components of the first oxide film OM1 are elements whose absolute values ​​of standard electrode potential are greater than Al. That is, in samples SA1 to SA14, La, Mg, Ba, Ca, and Sr correspond to the first specific elements.

[0096] Of the samples shown in Table 1, samples SA2 to SA14 contain the first specified element, while sample SA1 does not. Furthermore, in a voltage application test, samples SA2 to SA14 did not show delamination between the first oxide film OM1 and the insulating member IM when an applied voltage of at least 1.2 V was applied, while sample SA1 showed delamination between the first oxide film OM1 and the insulating member IM when an applied voltage of 1.2 V was applied. This confirms that the inclusion of the first specified element in the first oxide film suppresses delamination between the first oxide film and the insulating member.

[0097] Among the samples containing the first specific element, sample SA7 contained 1 mol% or more but less than 2 mol% of the first specific element, samples SA2 to SA6, and SA8 contained 2 mol% or more but less than 3 mol% of the first specific element, and samples SA9 to SA14 contained 3 mol% or more of the first specific element. Furthermore, in a voltage application test, sample SA7 exhibited delamination between the first oxide film OM1 and the insulating member IM when an applied voltage of 2.0 V was observed, samples SA2 to SA6, and SA8 exhibited delamination between the first oxide film OM1 and the insulating member IM when an applied voltage of 5.0 V was observed, and samples SA9 to SA14 did not exhibit delamination between the first oxide film OM1 and the insulating member IM at any applied voltage. This confirms that the concentration of the first specific element in the first oxide film is preferably 2 mol% or more, and more preferably 3 mol% or more.

[0098] Table 2 shows the performance evaluation results. [Table 2]

[0099] In the "Voltage application test" column in Table 2, samples in which no delamination between the first oxide film OM1 and the insulating member IM was confirmed in the tensile test are marked with an "O" and samples in which delamination between the first oxide film OM1 and the insulating member IM was confirmed in the tensile test are marked with an "X".

[0100] The first oxide film OM1 of each of samples SA15 to SA24 shown in Table 2 is primarily composed of chromia. Therefore, the primary component of the first oxide film OM1 of each of samples SA15 to SA24 shown in Table 2, excluding oxygen (element O), is Cr. Furthermore, Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn shown as components of the first oxide film OM1 are elements whose absolute values ​​of standard electrode potential are greater than that of Cr. That is, in samples SA15 to SA24, Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn correspond to the first specified elements.

[0101] Of the samples shown in Table 2, samples SA16 to SA24 contain the first specified element, while sample SA15 does not. Furthermore, in a voltage application test, samples SA16 to SA24 did not show delamination between the first oxide film OM1 and the insulating member IM when an applied voltage of 1.0 V was applied, while sample SA15 showed delamination between the first oxide film OM1 and the insulating member IM when an applied voltage of 1.0 V was applied. This confirms that the inclusion of the first specified element in the first oxide film suppresses delamination between the first oxide film and the insulating member.

[0102] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit thereof, for example, the following modifications are also possible.

[0103] The configurations of the fuel cell stack 10 and the power generation unit 100U in the above embodiment are merely examples and can be modified in various ways. For example, the number of unit cells (number of power generation units) included in the fuel cell stack is merely an example, and the number of unit cells is determined appropriately depending on the output voltage required for the fuel cell stack.

[0104] In the above embodiment, the first metal element contained in the first oxide film is either Al or Cr, but the first metal element may be a metal element other than Al or Cr. Also, in the above embodiment, the second metal element contained in the second oxide film is either Al or Cr, but the second metal element may be a metal element other than Al or Cr.

[0105] In the above embodiment, the insulating members (glass seal portion 135 and glass seal portion 500) are both formed of glass, but the insulating members may be formed of other insulating materials such as mica or insulating ceramics, or may be formed of multiple insulating materials.

[0106] In the above embodiment, the first specific element is located in at least one of the first portion in the first oxide film and the portion of the second portion that is within 100 μm of the boundary with the first portion in the Y-axis direction, but the first specific element may be contained in any position in the first oxide film.

[0107] The fuel cell stack 10 of the above embodiment is a co-flow type SOFC, but the technology disclosed in this specification is also applicable to counter-flow type SOFCs and cross-flow type SOFCs.

[0108] In the above embodiment, the unit cell 110 is an anode-supported unit cell, but it may be another type of unit cell such as an electrolyte-supported type or a metal-supported type.

[0109] In the above embodiment, the fuel cell stack 10 is configured to have a plurality of flat-type unit cells 110, but the technology disclosed in this specification is equally applicable to fuel cell stacks having a plurality of unit cells of other types (e.g., cylindrical, flat cylindrical, etc.).

[0110] In the above embodiment, the electrochemical reaction unit is a fuel cell power generation unit, which is a constituent unit of a solid oxide fuel cell (SOFC), but the present invention can also be applied to an electrolysis cell unit, which is a constituent unit of a solid oxide electrolysis cell (SOEC). [Explanation of symbols]

[0111] 10: Fuel cell stack 100: Power generation block 100U: Power generation unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Anode 118: Reaction prevention layer 120: Single cell separator 124: Joint portion 125: Flat plate portion 126: Oxide film 130: Air electrode frame 132: Oxidant gas supply communicating channel 133: Oxidant gas discharge communicating channel 135: Glass seal portion 140: Anode frame 142: Fuel gas supply communicating channel 143: Fuel gas discharge communicating channel 149: Spacer 180: IC separator 186: Oxide film 186d: Overlapping portion 186n: Non-overlapping portion 190: Interconnector 191: Flat plate portion 192: Air electrode current collecting portion 193: Coating layer 196: Conductive bonding material 210: First end plate 216: Oxide film 220: Insulation portion 230: End separator 232: First plate 240: First terminal plate 250: Second terminal plate 255: Flat plate portion 256: Oxide film 260: Second plate 270: Second end plate 276: Oxide film 276d: Overlapping portion 276n: Non-overlapping portion 280: Gas passage member 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 500: Glass seal portion B: Bolt BH: Bolt hole N: Nut FG: Fuel gas FOG: Fuel off-gas OG: Oxidizer gas OOG: Oxidizer off-gas

Claims

1. A single cell and a first metal member; a first oxide film formed on the surface of the first metal member and containing a metal oxide containing a first metal element as a main component; an insulating member disposed between the unit cell or a conductive member electrically connected to the unit cell and the first oxide film; An electrochemical reaction cell stack comprising: the first oxide film contains a first specific element having a standard electrode potential whose absolute value is greater than that of the first metal element; An electrochemical reaction cell stack comprising:

2. The electrochemical reaction cell stack according to claim 1, The insulating member is made of glass. An electrochemical reaction cell stack comprising:

3. The electrochemical reaction cell stack according to claim 1, further comprising: The conductive member, A second metal member; a second oxide film formed on a surface of the second metal member and containing a metal oxide containing a second metal element as a main component, the second oxide film contains a second specific element having a standard electrode potential whose absolute value is greater than that of the second metal element; An electrochemical reaction cell stack comprising:

4. The electrochemical reaction cell stack according to claim 1, The first metal element is either Al or Cr. An electrochemical reaction cell stack comprising:

5. The electrochemical reaction cell stack according to claim 3, the second metal element is either Al or Cr; An electrochemical reaction cell stack comprising:

6. The electrochemical reaction cell stack according to claim 1, the concentration of the first specific element in the first oxide film is 2 mol% or more; An electrochemical reaction cell stack comprising:

7. The electrochemical reaction cell stack according to claim 1, The first oxide film is a first portion that overlaps with the insulating member in a first direction that is a direction in which the first oxide film and the insulating member are stacked; a second portion that does not overlap with the insulating member in the first direction and is adjacent to the first portion in a second direction intersecting the first direction, the first specific element is located in at least one of the first portion and a portion of the second portion that is located within 100 μm of a boundary with the first portion in the second direction; An electrochemical reaction cell stack comprising:

8. The electrochemical reaction cell stack according to any one of claims 1 to 7, the first oxide film is mainly composed of alumina, The first specific element is at least one of Ba, Ca, La, Mg, and Sr. An electrochemical reaction cell stack comprising:

9. The electrochemical reaction cell stack according to any one of claims 1 to 7, the first oxide film is mainly composed of chromia, The first specific element is at least one of Al, Ba, Ca, La, Mg, Mn, Sr, Ti, and Zn. An electrochemical reaction cell stack comprising:

Images