Joining member and electrochemical reaction cell stack

Abstract

To suppress corrosion of a bonding part.SOLUTION: A bonding member includes: a first metal member containing a film-forming element; a second metal member bonded to the first metal member by welding, the second metal member not containing the film-forming element or containing the film-forming element, and having a concentration of the film-forming element lower than a concentration of the film-forming element contained in the first metal member. The bonding part between the first metal member and the second metal member includes a first melting part penetrating the first metal member and a second melting part extending from the first melting part to the inside of the second metal member. In a cross section including the first melting part and the second melting part, when a width of a first region adjacent to the second melting part in the first melting part is defined as a first bonding width W1 and a width of a second region adjacent to the first melting part in the second melting part is defined as a second bonding width W2, the following expression (1) is satisfied: W1>W2...(1).SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The technology disclosed in this specification relates to a joining member, an electrochemical reaction cell stack, and a method for manufacturing a joining member.

Background Art

[0002] As one type of fuel cell that generates electricity by utilizing an electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") including an electrolyte layer containing a solid oxide is known. The SOFC is used in the form of a fuel cell stack including a power generation block in which a plurality of constituent units (electrochemical reaction units) are arranged side by side in a predetermined direction. Two members provided in the fuel cell, for example, an interconnector that electrically connects two adjacent single cells and a frame that supports the interconnector, may be joined by welding (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Fuel cells are operated at 1000°C for high-temperature types and 700°C to 800°C for medium-temperature types. Due to use in such a high-temperature environment, there is a concern that the joints may corrode.

[0005] This problem is also a common problem in an electrolysis cell stack including a plurality of electrolysis cell units that are constituent units of a solid oxide electrolysis cell (hereinafter referred to as "SOEC") that generates hydrogen by utilizing an electrolysis reaction of water. Further, such a problem is not limited to SOFCs and SOECs, but is a common problem in other types of electrochemical reaction cell stacks.

[0006] This specification discloses a technology capable of solving the above-mentioned problems. [Means for solving the problem]

[0007] The technologies disclosed herein can be implemented, for example, in the following forms:

[0008] (1) The joining member disclosed herein is used in an electrochemical reaction cell stack comprising a single cell including a fuel electrode, an electrolyte layer, and an air electrode, and comprising: a first metal member containing a film-forming element that forms a passivation film; and a second metal member disposed on top of the first metal member and joined to the first metal member by welding, the second metal member not containing the film-forming element, or containing the film-forming element, wherein the concentration of the film-forming element is lower than the concentration of the film-forming element contained in the first metal member, and the joining member is used in an electrochemical reaction cell stack comprising a single cell including a fuel electrode, an electrolyte layer, and an air electrode. The joint member is configured such that the joint between the first metal member and the second metal member is composed of a first molten portion penetrating the first metal member and a second molten portion extending from the first molten portion into the interior of the second metal member, and in a cross-section including the first molten portion and the second molten portion, the width of the first region of the first molten portion adjacent to the second molten portion is defined as the first joint width W1, and the width of the second region of the second molten portion adjacent to the first molten portion is defined as the second joint width W2, thereby satisfying the following formula (1).

[0009] W1>W2···(1)

[0010] According to the above configuration, the concentration of film-forming elements in the joint can be sufficiently high, and corrosion of the joint can be effectively suppressed.

[0011] (2) In the joining member described in (1) above, the ratio of the first joining width W1 to the second joining width W2 may be 1.2 or more.

[0012] This configuration makes it possible to reliably increase the concentration of film-forming elements contained in the joint.

[0013] (3) The joining member described in (1) or (2) above may satisfy the following formula (2) when the depth of the second molten portion in the cross-section is defined as the joining depth D.

[0014] D×3 <W1···(2)

[0015] This configuration helps to suppress the adverse effects that an excessively thick second metal component can have on the electrochemical cell stack.

[0016] (4) In the joining member described in any one of (1) to (3) above, the thickness of the first metal member may be less than the thickness of the second metal member.

[0017] When the thickness of the first metal member, which contains a relatively large amount of film-forming elements, is smaller than the thickness of the second metal member, the film-forming elements do not diffuse sufficiently into the joint, which can easily lead to premature corrosion of the joint. The above configuration can be suitably applied to joint members with such a configuration.

[0018] (5) The electrochemical reaction cell stack disclosed herein comprises the joining member described in any one of (1) to (4) above.

[0019] According to the above configuration, the concentration of film-forming elements in the joint can be sufficiently high, and corrosion of the joint can be effectively suppressed.

[0020] (6) The manufacturing method of the joining member disclosed by this specification includes a first metal member containing a film-forming element for forming a passive film, and a second metal member disposed so as to overlap the first metal member and joined to the first metal member by welding, the second metal member not containing the film-forming element or containing the film-forming element and having a concentration of the film-forming element lower than the concentration of the film-forming element contained in the first metal member, and is a method for manufacturing a joining member used in an electrochemical reaction cell stack including a fuel electrode, an electrolyte layer, and an air electrode, including: a film-forming step of forming a passive film containing the film-forming element on the surface of one of the first metal member and the second metal member; a stacking step of stacking the other of the first metal member and the second metal member on the surface where the passive film is formed in the one member; and a welding step of welding the first metal member and the second metal member by irradiating a high-energy beam on an irradiation surface on the side opposite to the surface where the one member is disposed in the other member.

[0021] According to the above configuration, the concentration of the film-forming element contained in the joining portion can be made sufficiently high, and corrosion of the joining portion can be effectively suppressed.

[0022] Note that the technology disclosed in this specification can be realized in various forms, for example, in the form of an electrochemical reaction cell stack and its manufacturing method, etc.

Brief Description of the Drawings

[0023] [Figure 1] Perspective view showing the external configuration of the fuel cell stack of the first embodiment [Figure 2] Cross-sectional view showing the fuel cell stack of the first embodiment cut along line II-II of FIG. 1 [Figure 3] Cross-sectional view showing the fuel cell stack of the first embodiment cut along line III-III of FIG. 1 [Figure 4]Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, cut at the same position as the line II-II in FIG. 1 [Figure 5] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, cut at the same position as the line III-III in FIG. 1 [Figure 6] Partial enlarged cross-sectional view showing the step of forming a joint by irradiating a laser at a portion where an IC separator and an interconnector are overlapped in the embodiment [Figure 7] Chart explaining the method for determining the first joint width W1 and the second joint width W2 in the embodiment

Mode for Carrying Out the Invention

[0024] A. Embodiment: A-1. Configuration of the fuel cell stack 10: Embodiment 1 will be described with reference to FIGS. 1 to 7. The fuel cell stack 10 (an example of an electrochemical reaction cell stack) of the present embodiment is used for a solid oxide type fuel cell including an electrolyte layer 112 containing a solid oxide.

[0025] (Overall configuration of the fuel cell stack 10) As shown in FIGS. 1 to 3, the fuel cell stack 10 includes a power generation block 100 (an example of a reaction block), a terminal separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating portion 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating portion 220, the terminal 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 substantially the same-sized rectangular outer shapes and are arranged to overlap in this order in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0026] As shown in Figure 1, 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 and 3, 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.

[0027] As shown in Figures 2 and 3, the power generation block 100 is composed of a plurality (seven in this embodiment) of electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction unit 100U") arranged in a predetermined arrangement direction (up and down direction in Figure 2).

[0028] (Overall composition of an electrochemical reaction unit of 100U) As shown in Figures 4 and 5, the electrochemical reaction unit 100U comprises a single cell 110, a single cell separator 120, an air electrode frame 130, a fuel electrode frame 140, a fuel electrode current collector 144, two interconnectors 190 (an example of a second metal member), and two IC separators 180 (an example of a first metal member). 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. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are each supported by the two IC separators 180, and the fuel electrode current collector 144 is positioned between the single cell 110 and the interconnectors 190.

[0029] As shown in Figures 4 and 5, the IC separator 180 and interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Figure 2, one of the multiple reaction units 100U located at one end (the lower end in Figure 2) does not have an IC separator 180 and interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 is superimposed on the fuel electrode frame 140.

[0030] (Single cell 110) The single cell 110 comprises an electrolyte layer 112, an air electrode 114, and a fuel electrode 116. As shown in Figures 4 and 5, the air electrode 114, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the air electrode 114. 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.

[0031] 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 4 and 5) and another side parallel to the air electrode 116 (the lower side in Figures 4 and 5). The electrolyte layer 112 is a layer containing a solid oxide (for example, 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 (for example, 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).

[0032] (Single-cell separator 120) As shown in Figures 4 and 5, the single-cell separator 120 is a rectangular frame-shaped member having a roughly 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 periphery of the through-hole 121 in the single-cell separator 120 is joined to the periphery of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is located: the upper surface in Figures 4 and 5) by a sealing material 124. The sealing material 124 is made of, for example, brazing material (Ag brazing).

[0033] (Air pole frame 130) As shown in Figures 4 and 5, 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, an insulating ceramic (such as mica). The thickness of the air electrode frame 130 is preferably 0.5-5 mm.

[0034] (Fuel pole frame 140) As shown in Figure 5, the fuel electrode frame 140 is a rectangular frame-shaped member having a roughly rectangular through-hole 141 near the center, and is formed of, for example, metal.

[0035] (IC separator 180) As shown in Figures 4 and 5, 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 ferritic stainless steel containing aluminum, and as shown in Figure 6, it has a base material 182 and an oxide film 183 (an example of a passivation film) formed on the surface of the base material 182, with alumina as the main component.

[0036] (Interconnector 190, and fuel electrode current collector 144) As shown in Figures 4 and 5, the interconnector 190 comprises a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collector portions 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collector portions 192 are made of conductive, aluminum-free ferritic stainless steel. The coating layer 193 is conductive and is arranged to cover one surface of the flat plate portion 191 and the surface of the air electrode current collector portions 192.

[0037] The interconnector 190 has an outer shape that is slightly larger than the edge of the through hole 181 in the IC separator 180, and the flat plate portion 191 is positioned to overlap the peripheral edge of the through hole 181 in the IC separator 180. The interconnector 190 is joined to the IC separator 180 by welding.

[0038] 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 4 and 5, 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.

[0039] As described above, the interconnector 190 is shared by two adjacent reaction units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collector 192 is joined to the air electrode 114 of a single cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, 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 reaction units 100U via a fuel electrode current collector 144. This ensures electrical conductivity between the two adjacent reaction units 100U.

[0040] However, as described above, the reaction unit 100U located at one end (the lower end of Figure 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this reaction unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0041] 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 reaction 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 well.

[0042] (Air chamber 313 and fuel chamber 323) As shown in Figures 4 and 5, 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.

[0043] 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.

[0044] 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 reaction units 100U.

[0045] (First end plate 210) The first end plate 210 is a member formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. As shown in Figures 1-3, 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 project 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 projection 214 is formed around the entire circumference of the inner peripheral portion of the planar portion 211.

[0046] (Insulation part 220) The insulating portion 220 is a rectangular frame-shaped member having a through hole near the center, and is formed of, for example, an insulating material. 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.

[0047] (End separator 230) As shown in Figures 2 and 3, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near the center, and is made of, for example, metal.

[0048] (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 and 3, 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.

[0049] The first plate 232 is connected to an interconnector 190 provided on a reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via a connecting member with the same structure as the fuel electrode current collector 144. In this way, the reaction unit 100U and the first plate 232 are electrically connected.

[0050] (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 the reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute 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.

[0051] (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. As described above, the second terminal plate 250 is connected to a fuel electrode 116 provided on a reaction unit 100U located at one end (the lower end in Figure 2) of the plurality of reaction units 100U via a fuel electrode current collector 144, thereby electrically connecting this reaction unit 100U and the second terminal plate 250. One end of the second terminal plate 250 (the 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.

[0052] (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.

[0053] (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.

[0054] (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.

[0055] 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 chamber 313 of each reaction unit 100U. The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer off-gas OOG, discharged from the air chamber 313 of each reaction 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.

[0056] 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 reaction unit 100U. The fuel gas discharge manifold 322 is a gas passage that discharges fuel off-gas FOG, discharged from the fuel chamber 323 of each reaction unit 100U, to the outside of the fuel cell stack 10. 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 located on opposite sides of the fuel chamber 323.

[0057] (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 2 and 3. The main body portion 281 is cylindrical with open ends. The flange portion 282 is provided so as to protrude outward from one 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 internal space of the main body portion 281 communicates with the manifolds 311, 312, 321, and 322, respectively. Gas piping for gas supply or discharge is connected to each main body portion 281.

[0058] (Joint portion 400, and joint member 500) In this embodiment, the joining member 500 is an IC separator 180 and an interconnector 190 joined by welding. As shown in Figure 6, in the interconnector 190, the joining portion 194 joined to the IC separator 180 includes a flat plate portion 191 and a portion of the coating layer 193 that is located on the surface of the flat plate portion 191. The thickness T2 of the joining portion 194 is greater than the thickness T1 of the IC separator 180. The IC separator 180 has a first surface 180F1 (the lower surface of the lower oxide film 183 in Figure 6) that is in contact with the joining portion 194, and a second surface 180F2 (the upper surface of the upper oxide film 183 in Figure 6) that is located on the opposite side of the first surface 180F1 and parallel to the first surface 180F1. The thickness T1 of the IC separator 180 is expressed by the distance between the first surface 180F1 and the second surface 180F2. The joint portion 194 has a third surface 194F1 (upper surface in Figure 6) that is in contact with the IC separator 180, and a fourth surface 194F2 (lower surface of the coating layer 193 in Figure 6) that is on the opposite side of the third surface 194F1 and arranged parallel to the third surface 194F1. The thickness T2 of the joint portion 194 is expressed by the distance between the third surface 194F1 and the fourth surface 194F2. The thickness T1 of the IC separator 180 is, for example, 0.1 mm, and the thickness T2 of the joint portion 194 is, for example, 0.8 mm.

[0059] The joint 400 that joins the IC separator 180 and the interconnector 190 is formed by welding, which melts a portion of the IC separator 180 and a portion of the interconnector 190 together, and then allows them to cool and solidify. The joint 400 is located outside the through hole 181 and surrounds the through hole 181 around its entire circumference. As shown in Figure 6, the joint 400 includes a first molten portion 410 and a second molten portion 420.

[0060] The first molten portion 410 is the part of the joint 400 that penetrates the IC separator 180. On the exposed surface of the first molten portion 410 that is exposed from the second surface 180F2, an oxide film 430 (an example of a passivation film) mainly composed of alumina is formed. This oxide film 430 suppresses corrosion of the joint 400.

[0061] The second molten portion 420 is a portion of the joint portion 400 that is connected to the first molten portion 410 and extends into the interior of the joint portion 194. The second molten portion 420 does not penetrate the interconnector 190. In other words, the second molten portion 420 is not exposed from the fourth surface 194F2 of the joint portion 194.

[0062] The joint 400 is identified in elemental mapping analysis using EPMA (Electron Probe Micro Analyzer) as a region where the concentration of film-forming elements is higher than that of the base material. If the joint 400 contains two or more metal elements that can form a film, the metal element with the highest concentration on the outer surface of the oxide film 430 is designated as the "film-forming element." This is because the metal element with the highest concentration on the outer surface of the oxide film 430 plays a more important role in preventing corrosion. The metal element with the highest concentration on the outer surface of the oxide film 430 can be determined by elemental analysis (qualitative analysis) using EPMA. As described above, the IC separator 180 in this embodiment is made of ferritic stainless steel containing aluminum and contains Cr (chromium) and Al (aluminum) as metal elements that can form a film. Therefore, the joint 400 also contains Cr and Al as metal elements that can form a film. The oxide film 430 is primarily composed of alumina, with a higher concentration of Al closer to the outer surface and a higher concentration of Cr further away from the outer surface. Therefore, Al, the metal element with the highest concentration on the outer surface of the oxide film 430, becomes the film-forming element, and the joint 400 is identified in elemental mapping analysis as a region with a higher concentration of Al than its surroundings.

[0063] In a cross section of the joining member 500 that is perpendicular to the third surface 194F1 and includes the first molten portion 410 and the second molten portion 420 (hereinafter referred to as the "specific cross section"), when the width of the first region AR1 adjacent to the second molten portion 420 within the first molten portion 410 is defined as the first joining width W1, and the width of the second region AR2 adjacent to the first molten portion 410 within the second molten portion 420 is defined as the second joining width W2, the following equation (1) is satisfied.

[0064] W1>W2···(1)

[0065] The first joint width W1 and the second joint width W2 are determined as follows. First, elemental mapping analysis is performed on a specific cross section as described above, and the region where the Al concentration is higher than the surrounding area is identified as the joint 400. In the specific cross section, the line passing through the contact points P1 and P2 between the third surface 194F1 and the outer edge of the joint 400 is defined as the reference line RL. The line that is closer to the second surface 180F2 than the reference line RL and 100 μm away from the reference line RL is defined as the first virtual line L1. The line that is closer to the fourth surface 194F2 than the reference line RL and 100 μm away from the reference line RL is defined as the second virtual line L2. The first joint width W1 is represented by the maximum width of the first region AR1 located between the reference line RL and the first virtual line L1 in the first molten portion 410. The second joint width W2 is represented by the maximum width of the second region AR2 located between the reference line RL and the second virtual line L2 in the second molten portion 420. More specifically, the first joint width W1 is determined as follows: Multiple measurement lines are set parallel to the reference line RL and overlapping the first region AR1. Line analysis by EPMA is performed on each measurement line, and the concentration of the film-forming element is defined as C1, with the maximum value of the film-forming element concentration as Cwmax. Figure 7 shows an example chart of the film-forming element concentration C1 obtained by performing line analysis on the measurement line ML1 shown in Figure 6. The width of the section of the measurement line ML1 where C1 < 0.95 Cwmax is defined as the width of the first region War1 on that measurement line ML1. The maximum value among the multiple widths War1 of the first region obtained for multiple measurement lines is defined as the value of the first joint width W1. The second joint width W2 is determined as follows. Multiple measurement lines are set parallel to the reference line RL and overlapping the second region AR2. Line analysis by EPMA is performed on each measurement line, and the concentration of the film-forming element is defined as C2, and the minimum concentration of the film-forming element is defined as Cwmin. Figure 7 shows an example chart of the film-forming element concentration C2 obtained by performing line analysis on the measurement line ML2 shown in Figure 6. The width of the interval on the measurement line ML2 where C1 > 0.05 Cwmax is defined as the width War2 of the second region on that measurement line ML2. The maximum value among the multiple widths War2 of the second region obtained for multiple measurement lines is defined as the value of the second bonding width W2.In this embodiment, the interconnector 190, which is the second metal member, does not contain Al, which is a film-forming element. However, if the second metal member contains a film-forming element, the width of the section where C2 > 1.05 Cwmin may be used as the width War2 of the second region on the measurement line.

[0066] The ratio W1 / W2 of the first joint width to the second joint width W2 may be 1.2 or greater.

[0067] Furthermore, when the depth of the second molten portion 420 is defined as the joining depth D, the following equation (2) is satisfied.

[0068] D×3 <W1···(2)

[0069] The joint depth D is determined as follows: Multiple measurement lines are set perpendicular to the reference line RL and overlapping the second molten area 420. Line analysis by EPMA is performed on each measurement line, and the concentration of the film-forming element is defined as C3, and the minimum concentration of the film-forming element as Cdmin. The length of the section where C1 > 0.05 Cdmax is defined as the depth Dar2 of the second region on that measurement line. The maximum value among the multiple second region depths Dar2 obtained for multiple measurement lines is defined as the joint depth D. If the second metal member contains a film-forming element, the width of the section where C3 > 1.05 Cdmin may be used as the depth Dar2 of the second region on that measurement line.

[0070] (Method for manufacturing the joining member 500) The following describes an example of a method for manufacturing a joint member 500 by welding an IC separator 180 and an interconnector 190.

[0071] First, the IC separator 180 is heat-treated at a high temperature to form an oxide film 183 with a desired thickness on its surface (film formation step). Stainless steel, which is the material for the IC separator 180, generally has a passivation film on its surface, but in this embodiment, heat treatment is performed to obtain an oxide film 183 with sufficient thickness.

[0072] The interconnector 190 is placed on the first surface 180F1 of the IC separator 180 after the coating process (lamination process).

[0073] Next, the laser head LH of the welding apparatus is used to irradiate the second surface 180F2 (an example of the irradiation surface) of the IC separator 180 with a laser (an example of a high-energy beam) to weld the IC separator 180 and the interconnector 190 (welding process: see Figure 6). The parts of the IC separator 180 and interconnector 190 that are irradiated with the laser melt, and then cool and solidify to form the joint 400.

[0074] In the welding process, the heat generated by the laser irradiation is transmitted from the second surface 180F2, which is the irradiation surface, into the interior, causing the IC separator 180 and the interconnector 190 to partially melt. Therefore, by appropriately controlling the scanning speed of the laser head LH, the desired joint widths W1, W2 and joint depth D can be obtained. In addition, when welding two members, the focal position is generally set at the interface between the two members, but by adjusting the focal position to be inside the IC separator 180, the IC separator 180 can be melted over a wider area than the interconnector 190, and the first joint width W1 can be made larger than the second joint width W2.

[0075] Furthermore, an oxide film 183 is present on the surface of the IC separator 180. Generally, in metal components, the thermal conductivity of the passive film is lower than that of the base material. Therefore, the presence of the oxide film 183 suppresses the transfer of heat from the IC separator 180 to the interconnector 190. As a result, the IC separator 180 can be melted over a wider area than the interconnector 190, and the first joint width W1 can be made larger than the second joint width W2.

[0076] A joint 400 in which the first joint width W1 is greater than the second joint width W2 is formed by melting an IC separator 180 containing Al as a film-forming element over a wider area than the interconnector 190. In such a joint 400, the concentration of the film-forming element (Al) is higher compared to a joint in which the first joint width W1 is equal to or smaller than the second joint width W2.

[0077] A-2. Operation of the fuel cell stack 10: As shown in Figure 2, the oxidizer gas OG is supplied to the air chamber 313 through the gas passage member 280 and the oxidizer gas supply manifold 311. Also, as shown in Figure 3, the fuel gas FG is supplied to the fuel chamber 323 through the gas passage member 280 and the fuel gas supply manifold 321.

[0078] When oxidant gas OG is supplied to the air chamber 313 of each reaction 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 reaction units 100U, and the interconnector 190 ensures conductivity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, the second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end of Figure 2), and the first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end of Figure 2). As a result, the electrical energy generated in each reaction 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.

[0079] As shown in Figure 2, the oxidizer off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidizer gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in Figure 3, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0080] During operation of the fuel cell stack 10, the interior becomes hot, raising concerns about corrosion of the joint 400. In this embodiment, since the joint 400 contains Al as a film-forming element, an oxide film 430 is formed on the exposed surface of the joint 400, and this oxide film 430 suppresses corrosion of the joint 400. The interior of the fuel cell stack 10 is hot, and water vapor generated by the power generation reaction is present, so the components contained in the formed oxide film 430 gradually evaporate. As a result, the film-forming elements contained in the joint 400 come into contact with air, and a new oxide film 430 is formed. This process is repeated, and when the film-forming elements contained in the joint 400 are depleted, the oxide film 430 will no longer be formed, and corrosion of the joint 400 will occur. As described above, in this embodiment, the joint 400 has a first joint width W1 that is larger than the second joint width W2. Therefore, compared to a joint where the first joint width W1 is equal to or smaller than the second joint width W2, the concentration of the film-forming element (Al) is higher. As a result, the time until the film-forming element is depleted is relatively longer, and corrosion of the joint 400 is suppressed over a long period of time.

[0081] Furthermore, if the ratio of the first joint width W1 to the second joint width W2, W1 / W2, is 1.2 or greater, the concentration of film-forming elements in the joint 400 will be reliably increased, and corrosion of the joint 400 will be suppressed over a long period of time.

[0082] This configuration is particularly effective when the thickness T1 of the IC separator 180 containing the film-forming element is smaller than the thickness T2 of the bonding portion 194 that does not contain the film-forming element, that is, when the concentration of the film-forming element in the bonding portion 400 tends to be relatively low.

[0083] Furthermore, when the depth of the second molten portion 420 is defined as the joining depth D, the following equation (2) is satisfied.

[0084] D×3 <W1···(2)

[0085] With this configuration, by relatively reducing the size of the second molten portion 420 which does not contain film-forming elements, the concentration of film-forming elements in the joint portion 400 increases compared to the case where the second molten portion 420 is relatively large. In addition, the adverse effects on the fuel cell stack 10 caused by the thickness of the joint portion 194 becoming unnecessarily large are suppressed. Adverse effects include, for example, the increased consumption of gas required to heat the fuel cell stack 10 to a temperature sufficient to cause an electrochemical reaction during startup, which would result in the user having to pay higher gas bills.

[0086] A-3. Effects of this embodiment: As described above, the fuel cell stack 10 of this embodiment comprises a single cell 110 and a connecting member 500. The single cell 110 includes a fuel electrode 116, an electrolyte layer 112, and an air electrode 114. The connecting member 500 includes an IC separator 180 and an interconnector 190. The IC separator 180 includes a film-forming element that forms an oxide film 430. The interconnector 190 is a member that is arranged on top of the IC separator 180 and joined to the IC separator 180 by welding, and does not include a film-forming element. The joint 400 between the IC separator 180 and the interconnector 190 is composed of a first molten portion 410 that penetrates the IC separator 180 and a second molten portion 420 that extends from the first molten portion 410 into the interior of the interconnector 190. In a cross-section of a joining member 500 including a first molten portion 410 and a second molten portion 420, when the width of the first region AR1 adjacent to the second molten portion 420 within the first molten portion 410 is defined as the first joining width W1, and the width of the second region AR2 adjacent to the first molten portion 410 within the second molten portion 420 is defined as the second joining width W2, the following equation (1) is satisfied.

[0087] W1>W2···(1)

[0088] According to the above configuration, the concentration of film-forming elements in the joint 400 can be sufficiently high, and corrosion of the joint 400 can be effectively suppressed.

[0089] Furthermore, the ratio of the first joint width W1 to the second joint width W2 may be 1.2 or greater. With such a configuration, the concentration of film-forming elements contained in the joint 400 can be reliably increased.

[0090] Furthermore, in the above cross-section, when the depth of the second molten portion 420 is defined as the joining depth D, the following equation (2) is satisfied.

[0091] D×3 <W1···(2)

[0092] This configuration makes it possible to suppress the adverse effects that an excessively thick interconnector 190 would have on the fuel cell stack 10.

[0093] Furthermore, the thickness T1 of the IC separator 180 is smaller than the thickness T2 of the interconnector 190. When the thickness T1 of the IC separator 180, which contains a relatively large amount of film-forming elements, is smaller than the thickness T2 of the interconnector 190, the film-forming elements do not diffuse sufficiently into the joint 400, and the joint 400 is prone to premature corrosion. The above configuration can be suitably applied to a joint member 500 with such a configuration.

[0094] Furthermore, the manufacturing method of the joining member 500 of this embodiment includes a film forming step of forming an oxide film 183 containing a film-forming element on the surface of the IC separator 180; a lamination step of stacking the interconnector 190 on the first surface 180F1 of the IC separator 180 on which the oxide film 183 has been formed; and a welding step of welding the IC separator 180 and the interconnector 190 by irradiating a laser onto the second surface 180F2 of the interconnector 190 that is opposite to the first surface 180F1 on which the IC separator 180 is placed.

[0095] According to the above configuration, the concentration of film-forming elements in the joint 400 can be sufficiently high, and corrosion of the joint 400 can be effectively suppressed.

[0096] B. Variations (1) In the above embodiment, the film-forming element was aluminum, but the film-forming element can be any element that forms a passive film, for example, chromium. (2) In the above embodiment, the second metal member was a member that did not contain a film-forming element, but the second metal member may contain a film-forming element, and the concentration of the film-forming element contained in the second metal member may be lower than the concentration of the film-forming element contained in the first metal member. (3) In the above embodiment, the first metal member was an IC separator 180 and the second metal member was an interconnector 190. However, the combination of the first and second metal members is not limited to the above embodiment. For example, the first metal member may be an end separator 230 and the second metal member may be a first plate 232. The thickness of the end separator 230 may be, for example, 0.3 mm, and the thickness of the first plate 232 may be, for example, 1.5 mm. Alternatively, in the case of an electrochemical reaction cell stack comprising a metal-supported single cell supported by a metal support, the first metal member may be a single-cell separator and the second metal member may be a metal support. In particular, the configuration disclosed herein can be suitably applied to members disposed in an electrochemical reaction cell stack under high-temperature atmospheres, oxygen-rich atmospheres, or water vapor-rich atmospheres. (4) If the thickness of the first metal member differs depending on the location, “thickness of the first metal member” refers to the thickness of the part of the first metal member that is joined to the second metal member, that is, the thickness of the part where a joint formed by welding is located. The same applies to the thickness of the second metal member. (5) In the above embodiment, an oxide film 183 was formed on the IC separator 180 in the film formation process, but a passivation film may be formed on the surface of the second metal member in the film formation process. (6) In the above embodiments, laser welding was given as an example of a welding method, but any welding method applicable to the technology disclosed herein may be any method that involves irradiating the irradiation surface of the target members with some kind of high-energy radiation to melt and join the target members, such as arc welding or electron beam welding, in addition to laser welding. (7) In the above embodiment, the electrochemical reaction cell stack was a cell stack used in a solid oxide fuel cell (SOFC). However, the electrochemical reaction cell stack may be a cell stack used in other types of fuel cells such as polymer electrolyte fuel cells (PEFC), phosphoric acid fuel cells (PAFC), or molten carbonate fuel cells (MCFC), or an electrolytic cell stack that comprises electrolytic cell units, which are constituent units of a solid oxide electrolytic cell (SOEC), as single cells. [Explanation of symbols]

[0097] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120: Separator for single cell 121: Through hole 124: Sealing material 130: Air electrode frame 131: Through hole 140: Fuel electrode frame 141: Through hole 144: Fuel electrode current collector 145: Electrode opposing part 146: Interconnector opposing part 147: Connecting part 149: Spacer 180: Separator for IC (first metal component) 180F1: First surface 180F2: Second surface (irradiation surface) 181: Through hole 182: Base material 183: Oxide film (passivation film) 190: Interconnector (second metal component) 191: Flat plate section 192: Air electrode current collector section 193: Coating layer 194: Joint section 194F1: Third surface 194F2: Fourth surface 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 284: Bolt hole 311: Oxidizing gas supply manifold 312: Oxidizer gas exhaust manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas exhaust manifold 323: Fuel chamber 400: Joint 410: First molten area 420: Second molten area 430: Oxide film (passivation film) 500: Joining member AR1: First region AR2: Second region B: Bolt BH: Bolt hole D: Joint depth FG: Fuel gas FOG: Fuel off-gas L1: First imaginary line L2: Second imaginary line LH: Laser head N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas P1, P2: Contact points RL: Reference line T1: Thickness T2: Thickness W1: First joint width W2: Second joint width

Claims

1. A first metal member containing a film-forming element that forms a passivation film, A second metal member is arranged to overlap the first metal member and is joined to the first metal member by welding, A second metal member which does not contain the aforementioned film-forming element, or which contains the aforementioned film-forming element, and the concentration of the film-forming element is lower than the concentration of the film-forming element contained in the first metal member, Equipped with, A bonding member used in an electrochemical reaction cell stack comprising a single cell including a fuel electrode, an electrolyte layer, and an air electrode, The joint between the first metal member and the second metal member is A first molten portion that penetrates the first metal member, A second molten portion extending from the first molten portion into the interior of the second metal member, It is composed of, In a cross-section including the first molten portion and the second molten portion, The width of the first region adjacent to the second molten portion within the first molten portion is defined as the first joining width W1. When the width of the second region adjacent to the first molten portion of the second molten portion is defined as the second joining width W2, The following equation (1) is satisfied, There is a step at the boundary between the first molten portion and the second molten portion. Joining member. W1>W2...(1)

2. The ratio of the first joint width W1 to the second joint width W2 is 1.2 or more. The joining member according to claim 1.

3. In the cross-section, when the depth of the second molten portion is defined as the joining depth D, The following equation (2) is satisfied: The joining member according to claim 1 or claim 2. D×3<W1...(2)

4. The thickness of the first metal member is smaller than the thickness of the second metal member. The joining member according to claim 1 or claim 2.

5. An electrochemical reaction cell stack comprising the joining member according to claim 1 or claim 2.

Images