Bonding member, electrochemical reaction cell stack, and manufacturing method of the bonding member

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 the joining member. [Background technology]

[0002] Solid oxide fuel cells (hereinafter referred to as "SOFCs"), which have an electrolyte layer containing solid oxide, are known as one type of fuel cell that generates electricity using the electrochemical reaction between hydrogen and oxygen. SOFCs are used in the form of a fuel cell stack that includes a power generation block in which multiple structural units (electrochemical reaction units) are arranged in a predetermined direction. Two components included in a fuel cell, for example, an interconnector that electrically connects two adjacent unit cells and a frame that supports this interconnector, are sometimes joined by welding (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6100291 Summary of the Invention [Problem to be solved by the invention]

[0004] High-temperature fuel cells are operated at 1000°C, and medium-temperature fuel cells are operated at 700°C to 800°C. There are concerns that use in such high-temperature environments could cause corrosion of joints.

[0005] These issues are also common to electrolysis cell stacks that include multiple electrolysis cell units, which are constituent elements of solid oxide electrolysis cells (hereinafter referred to as "SOECs") that generate hydrogen using the electrolysis reaction of water. Furthermore, these issues are not limited to SOFCs and SOECs, but are also common to other types of electrochemical reaction cell stacks.

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

[0007] The technology disclosed in this specification can be realized, for example, in the following forms.

[0008] (1) The present specification discloses a joining member comprising: a first metal member containing a film-forming element that forms a passivation film; and a second metal member that is 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, the concentration of the film-forming element being 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 that includes a unit cell that includes a fuel electrode, an electrolyte layer, and a cathode. A composite member, wherein the joint between the first metal member and the second metal member is composed of a first fusion zone penetrating the first metal member and a second fusion zone extending from the first fusion zone into the interior of the second metal member, and in a cross section including the first fusion zone and the second fusion zone, when the width of a first region of the first fusion zone adjacent to the second fusion zone is defined as a first joining width W1 and the width of a second region of the second fusion zone adjacent to the first fusion zone is defined as a second joining width W2, the following formula (1) is satisfied.

[0009] W1>W2 (1)

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

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

[0012] With this configuration, the concentration of the film-forming element contained in the joint can be reliably increased.

[0013] (3) The joining member according to (1) or (2) above may satisfy the following formula (2) when the depth of the second fusion zone in the cross section is a joining depth D:

[0014] D×3 <W1···(2)

[0015] With this configuration, it is possible to suppress the adverse effects on the electrochemical cell stack that would be caused by the second metal member being thicker than necessary.

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

[0017] When the thickness of the first metal member, which contains a relatively large amount of the film-forming element, is smaller than the thickness of the second metal member, the film-forming element does not sufficiently diffuse into the joint, which tends to cause the joint to corrode early. The above-mentioned configuration can be suitably applied to a joint member having such a configuration.

[0018] (5) The electrochemical reaction cell stack disclosed in this specification includes the joining member according to any one of (1) to (4) above.

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

[0020] (6) The present specification discloses a method for manufacturing a joining member, which includes a first metal member containing a film-forming element that forms a passivation film, and a second metal member that is 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, the concentration of the film-forming element being lower than the concentration of the film-forming element contained in the first metal member, and which is used in an electrochemical reaction cell stack having a unit cell including a fuel electrode, an electrolyte layer, and an air electrode. A method for manufacturing a joined member, comprising: a coating formation process for forming a passivation film containing the coating element on the surface of one of the first metal member and the second metal member; a lamination process for stacking the other of the first metal member and the second metal member on the surface of the one member on which the passivation film has been formed; and a welding process for welding the first metal member and the second metal member by irradiating a high-energy ray onto an irradiation surface of the other member opposite to the surface on which the one member is arranged.

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

[0022] 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]

[0023] [Figure 1] FIG. 1 is a perspective view showing the external configuration of a fuel cell stack according to a first embodiment; [Figure 2] FIG. 2 is a cross-sectional view showing the fuel cell stack of the first embodiment taken along line II-II in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view showing the fuel cell stack of the first embodiment taken along line III-III in FIG. 1. [Figure 4]2 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, taken along the same line as line II-II in FIG. 1; [Figure 5] FIG. 3 is a cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment, taken along the same line as line III-III in FIG. 1; [Figure 6] FIG. 10 is a partially enlarged cross-sectional view showing a step of forming a joint by irradiating a laser onto a portion where an IC separator and an interconnector are superimposed in an embodiment. [Figure 7] 1 is a chart illustrating a method for determining the first bonding width W1 and the second bonding width W2 in an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] A. Implementation: A-1. Configuration of fuel cell stack 10: A first embodiment will be described with reference to Figures 1 to 7. A fuel cell stack 10 (an example of an electrochemical reaction cell stack) of this embodiment is used in a solid oxide fuel cell having an electrolyte layer 112 containing a solid oxide.

[0025] (Overall configuration of fuel cell stack 10) 1 to 3, the fuel cell stack 10 includes a power generation block 100 (an example of a reaction block), 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 this order, stacked in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0026] As shown in Fig. 1, the fuel cell stack 10 has bolt holes BH near each of the four corners, penetrating from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. A nut N is screwed onto both ends of each bolt B. These bolts B and nuts N fasten the members from the first end plate 210 to the second end plate 270 together. As shown in Figs. 2 and 3, the first plate 232 is supported by the terminal separator 230, and the four gas passage members 280 are connected to the second end plate 270.

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

[0028] (Overall configuration of 100U electrochemical reaction units) 4 and 5, the electrochemical reaction unit 100U includes a single cell 110, a single cell separator 120, an air electrode frame 130, an anode frame 140, an anode current collecting member 144, two interconnectors 190 (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 anode frame 140, and the other IC separator 180 are stacked in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are supported by the two IC separators 180, and the anode current collecting member 144 is disposed between the single cell 110 and the interconnectors 190.

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

[0030] (single cell 110) The unit cell 110 includes an electrolyte layer 112, a cathode 114, and an anode 116. As shown in Figures 4 and 5, the cathode 114, the electrolyte layer 112, and the anode 116 are stacked in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the cathode 114. The unit cell 110 of this embodiment is an anode-supported unit cell in which the anode 116 supports the other layers (electrolyte layer 112, cathode 114, and reaction prevention layer 118) that make up the unit cell 110.

[0031] 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).

[0032] (Single cell separator 120) As shown in Figures 4 and 5, the single cell separator 120 is a rectangular frame-like member having a substantially rectangular through-hole 121 near the center, and is made of, for example, metal. The plate thickness of the single cell separator 120 is relatively thin, for example, not less than 0.05 mm and not more than 0.2 mm. The peripheral portion of the through-hole 121 in the single cell separator 120 is joined to the peripheral portion of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is disposed: the upper surface in Figures 4 and 5) with a sealant 124. The sealant 124 is made of, for example, a brazing material (Ag brazing).

[0033] (Air electrode frame 130) 4 and 5, the cathode frame 130 is a rectangular frame-like member having a substantially rectangular through-hole 131 near the center, and is made of, for example, insulating ceramics (mica, etc.). The thickness of the cathode frame 130 is preferably 0.5 to 5 mm.

[0034] (fuel electrode frame 140) As shown in FIG. 5, the fuel electrode frame 140 is a rectangular frame-like member having a substantially rectangular through-hole 141 near the center, and is made of, for example, metal.

[0035] (IC separator 180) 4 and 5, IC separator 180 is a rectangular frame-shaped member having a through-hole 181 near the center. IC separator 180 is made of ferritic stainless steel containing aluminum, and as shown in Fig. 6, has base material 182 and oxide coating 183 (an example of a passivation coating) formed on the surface of base material 182 and containing alumina as its main component.

[0036] (Interconnector 190 and anode current collecting member 144) 4 and 5, the interconnector 190 includes a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collector 192 are electrically conductive and formed of ferritic stainless steel that does not contain aluminum. The coating layer 193 is electrically conductive and is disposed so as to cover one surface of the flat plate portion 191 and the surface of the air electrode current collector 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 is disposed so that the flat plate portion 191 overlaps 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 anode current collecting member 144 is a member that connects the interconnector 190 and the anode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 4 and 5, the anode current collecting member 144 has an interconnector facing portion 146, an electrode facing portion 145 that is parallel to the interconnector facing portion 146, and a connecting portion 147 that connects the electrode facing portion 145 and the interconnector facing portion 146, and has an overall U-shape. The electrode facing portion 145 is in contact with the anode 116, and the interconnector facing portion 146 is in contact with a flat portion 191 of the interconnector 190.

[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 collecting part 192 is joined to the air electrode 114 of the unit cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, and is thereby electrically connected to the air electrode 114. The flat plate part 191 is electrically connected to the anode 116 of the unit cell 110 provided in the other of the two adjacent reaction units 100U via an anode current collecting member 144. This ensures electrical continuity between the two adjacent reaction units 100U.

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

[0041] A spacer 149 made of, for example, mica is disposed between the electrode facing portion 145 and the interconnector facing portion 146. This allows the anode current collecting member 144 to follow deformation of the reaction unit 100U due to temperature cycles and fluctuations in reactant gas pressure, and good electrical connection between the anode 116 and the interconnector 190 (or second terminal plate 250) via the anode current collecting member 144 is maintained.

[0042] (Air chamber 313 and fuel chamber 323) 4 and 5, the space partitioned by the single cell separator 120, single cell 110, air electrode frame 130, IC separator 180, and interconnector 190 faces the air electrode 114 and serves as an air chamber 313 through which oxidant gas OG flows. The air electrode frame 130 partitions the entire periphery of the air chamber 313 from the external space and seals the gap between the single cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 to the external space.

[0043] 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.

[0044] The single cell separator 120 separates the air chamber 313 and the fuel chamber 323, thereby preventing gas leakage (cross leakage) from the air electrode 114 side to the fuel electrode 116 side or from the fuel electrode 116 side to the air electrode 114 side around the single cell 110. In addition, the IC separator 180 and the interconnector 190 prevent gas leakage between adjacent reaction units 100U.

[0045] (First end plate 210) The first end plate 210 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel. As shown in FIGS. 1 to 3 , the first end plate 210 includes a rectangular, frame-like flat portion 211 having a through-hole 212 near the center, and an outer convex portion 213 and an inner convex portion 214 that protrude from the flat portion 211 in the direction opposite the insulating portion 220 (upward in FIG. 2 ). The flat portion 211 has holes that form the bolt holes BH described above. The outer convex portion 213 protrudes from the outer periphery of the flat portion 211. The outer convex portion 213 is formed around the entire outer periphery of the flat portion 211. The inner convex portion 214 protrudes from the inner periphery of the flat portion 211. The inner convex portion 214 is formed around the entire inner periphery of the flat portion 211.

[0046] (insulating part 220) Insulating section 220 is a rectangular frame-shaped member with a through-hole near the center, and is made of, for example, an insulating material. As shown in Figure 2, 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.

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

[0048] (First Plate 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined by welding, for example, to the periphery of the through-hole 231 in the terminal separator 230. The terminal separator 230 and the first plate 232 separate the power generating block 100 from the external space of the fuel cell stack 10.

[0049] The first plate 232 is connected to an interconnector 190 provided in the reaction unit 100U arranged at the other end (the upper end in Figure 2) of the multiple reaction units 100U that make up the power generation block 100 via a connecting member having the same structure as the anode current collecting member 144, thereby electrically connecting this reaction unit 100U and the first plate 232.

[0050] (First terminal plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through-hole 241 near the center, and is made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. The first terminal plate 240 is electrically connected to the reaction unit 100U arranged at the other end (the upper end in FIG. 2) of the multiple reaction units 100U that make up the power generation block 100 via a first plate 232 and a terminal separator 230. One end (the right end in FIG. 2) of the first terminal plate 240 protrudes laterally from the power generation block 100, and this protruding portion functions as a positive output terminal for the fuel cell stack 10.

[0051] (2nd terminal plate 250) The second terminal plate 250 is a rectangular plate-shaped member made of a conductive material such as ferritic stainless steel that forms an alumina oxide coating on its surface. As described above, the second terminal plate 250 is connected to the anode 116 provided in the reaction unit 100U arranged at one end (the lower end in FIG. 2 ) of the multiple reaction units 100U via the anode current collecting member 144, thereby electrically connecting this reaction unit 100U to the second terminal plate 250. One end (the right end in FIG. 2 ) of the second terminal plate 250 protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0052] (Second plate 260) Second plate 260 is a rectangular, flat member made of, for example, an insulating material. The peripheral edge of second plate 260 is sandwiched between second terminal plate 250 and second end plate 270, thereby ensuring insulation between second terminal plate 250 and second end plate 270.

[0053] (Second end plate 270) The second end plate 270 is a member formed by pressing (bending) a single plate-like member, and is formed of a conductive material such as stainless steel. The second end plate 270 has a rectangular, frame-like flat portion 271 having a through-hole 272 near the center, and an outer convex portion 273 and an inner convex portion 274 that protrude from the flat portion 271 in the direction opposite to the second terminal plate 250 (downward in FIG. 2). The flat portion 271 has holes that form the bolt holes BH described above. The outer convex portion 273 protrudes from the outer periphery of the flat portion 271. The outer convex portion 273 is formed around the entire outer periphery of the flat portion 271. The inner convex portion 274 protrudes from the inner periphery of the flat portion 271. The inner convex portion 274 is formed around the entire inner periphery of the flat portion 271.

[0054] (Manifolds 311, 312, 321, 322) 1, 2, and 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are an oxidant gas supply manifold 311, an oxidant gas discharge manifold 312, a fuel gas supply manifold 321, and a fuel gas discharge manifold 322, respectively.

[0055] 2, the oxidant gas supply manifold 311 is a gas flow path that supplies the oxidant gas OG introduced from outside the fuel cell stack 10 to the air chamber 313 of each reaction unit 100U. The oxidant gas discharge manifold 312 is a gas flow path that discharges the oxidant off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the outside of the fuel cell stack 10. 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.

[0056] 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 the fuel chamber 323 of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges fuel off-gas FOG discharged from the fuel 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 arranged on opposite sides of the fuel chamber 323.

[0057] (Gas passage member 280) As shown in FIGS. 2 and 3, each of the four gas passage members 280 includes a main body portion 281 and a flange portion 282. The main body portion 281 is cylindrical and open at both ends. The flange portion 282 is provided so as to protrude outward from one end (the lower end in FIG. 2) of the main body portion 281. The flange portion 282 has a plurality of bolt holes 284. A bolt (not shown) for connecting the fuel cell stack 10 to an external device is inserted into each bolt hole 284. One end (the upper end in FIGS. 2 and 3) of the main body portion 281 provided in each of the four gas passage members 280 is joined to the second end plate 270 by, for example, welding, and the internal space of the main body portion 281 is connected to the manifolds 311, 312, 321, and 322, respectively. A gas pipe for supplying or discharging gas is connected to each of the main body portions 281.

[0058] (Joint portion 400 and joint member 500) In this embodiment, the bonding member 500 is an IC separator 180 and an interconnector 190 joined by welding. As shown in FIG. 6, in the interconnector 190, a bonding portion 194 bonded to the IC separator 180 includes a flat portion 191 and a portion of the coating layer 193 that is disposed on the surface of the flat portion 191. A thickness T2 of the bonding portion 194 is greater than a 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 FIG. 6) that contacts the bonding portion 194, and a second surface 180F2 (the upper surface of the upper oxide film 183 in FIG. 6) that is disposed parallel to the first surface 180F1 on the opposite side to the first surface 180F1. The thickness T1 of the IC separator 180 is represented by the distance between the first surface 180F1 and the second surface 180F2. The bonding region 194 has a third surface 194F1 (the upper surface in FIG. 6) that contacts the IC separator 180, and a fourth surface 194F2 (the lower surface of the coating layer 193 in FIG. 6) that is disposed parallel to the third surface 194F1 on the opposite side to the third surface 194F1. The thickness T2 of the bonding region 194 is expressed as 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 bonding region 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 a part of the IC separator 180 and a part of the interconnector 190 together, melting them together and then cooling and solidifying them. The joint 400 is located outside the through hole 181 and surrounds the entire circumference of the through hole 181. As shown in FIG. 6 , the joint 400 includes a first molten portion 410 and a second molten portion 420.

[0060] The first fusion zone 410 is a portion of the bonding portion 400 that penetrates the IC separator 180. An oxide film 430 (an example of a passivation film) mainly composed of alumina is formed on the surface of the first fusion zone 410 that is exposed from the second surface 180F2. The oxide film 430 suppresses corrosion of the bonding portion 400.

[0061] The second fusion zone 420 is a portion of the joint 400 that is continuous with the first fusion zone 410 and extends into the joining region 194. The second fusion zone 420 does not penetrate the interconnector 190. In other words, the second fusion zone 420 is not exposed from the fourth surface 194F2 of the joining region 194.

[0062] In elemental mapping analysis using an EPMA (Electron Probe Micro Analyzer), the joint 400 is identified as a region where the concentration of the film-forming element is higher than that of the base material. When the joint 400 contains two or more metal elements capable of forming a film, the metal element with the highest concentration on the outer surface of the oxide film 430 is defined 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 corrosion prevention. 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 an EPMA. As described above, the IC separator 180 of this embodiment is made of ferritic stainless steel containing aluminum and contains Cr (chromium) and Al (aluminum) as metal elements capable of forming a film. Therefore, the joint 400 also contains Cr and Al as metal elements capable of forming a film. The oxide film 430 is mainly composed of alumina as a whole, with the Al content increasing closer to the outer surface and the Cr content increasing further away from the outer surface. Therefore, Al, which is the metal element with the highest concentration at the outer surface of the oxide film 430, is the film-forming element, and the joint 400 is identified in element mapping analysis as a region with a higher Al concentration than the surrounding area.

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

[0064] W1>W2···(1)

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

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

[0067] Furthermore, when the depth of the second fusion zone 420 is defined as the joining depth D, the following formula (2) is satisfied.

[0068] D×3 <W1···(2)

[0069] The bonding depth D is determined as follows: Multiple measurement lines are set that are perpendicular to the reference line RL and overlap the second fusion zone 420. Line analysis is performed on each measurement line using EPMA, and the concentration of the film-forming element is defined as C3 and the minimum concentration of the film-forming element is defined as Cdmin. The length of the section where C1 > 0.05Cdmax is defined as the depth Dar2 of the second region on that measurement line. The maximum value of the multiple second region depths Dar2 obtained for the multiple measurement lines is defined as the value of the bonding depth D. Note that if the second metal component contains a film-forming element, the width of the section where C3 > 1.05Cdmin is defined as the depth Dar2 of the second region on that measurement line.

[0070] (Method of manufacturing the joining member 500) An example of a method for manufacturing the joining member 500 by welding the IC separator 180 and the interconnector 190 together will now be described.

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

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

[0073] Next, a laser (an example of a high-energy beam) is irradiated onto the second surface 180F2 (an example of an irradiated surface) of the IC separator 180 using the laser head LH of the welding device, thereby welding the IC separator 180 and the interconnector 190 together (welding step: see FIG. 6). The portions of the IC separator 180 and the interconnector 190 irradiated with the laser melt, and then cool and solidify, forming a joint 400.

[0074] In the welding process, heat generated by laser irradiation is transmitted from the second surface 180F2, which is the irradiated surface, to the interior, thereby partially melting the IC separator 180 and the interconnector 190. 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. Furthermore, 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, it is possible to melt the IC separator 180 over a wider area than the interconnector 190, and it is possible to make the first joint width W1 larger than the second joint width W2.

[0075] Additionally, an oxide film 183 is present on the surface of the IC separator 180. Generally, in metal members, the thermal conductivity of the passivation 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. This allows the IC separator 180 to be melted over a wider area than the interconnector 190, and the first bonding width W1 can be made larger than the second bonding width W2.

[0076] The joint 400, in which the first joint width W1 is larger than the second joint width W2, is formed by melting the IC separator 180, which contains 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 than in 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 fuel cell stack 10: 2, the oxidizing gas OG is supplied to the air chamber 313 through the gas passage member 280 and the oxidizing gas supply manifold 311. Also, as shown in FIG. 3, the fuel gas FG is supplied to the fuel chamber 323 through the gas passage member 280 and the fuel gas supply manifold 321.

[0078] When an oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and a fuel gas FG is supplied to the fuel chamber 323, power is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and the fuel gas FG. This power generation reaction is exothermic. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures electrical continuity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, a second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end in FIG. 2 ) of the multiple reaction units 100U, and a first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end in FIG. 2 ). As a result, electrical energy generated in each reaction unit 100U is extracted from the terminal plates 240, 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (e.g., 700°C to 1000°C), after startup, the fuel cell stack 10 may be heated by a heater (not shown) until the high temperature can be maintained using the heat generated by power generation.

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

[0080] During operation of the fuel cell stack 10, the interior becomes hot, raising concerns about corrosion of the joints 400. In this embodiment, the joints 400 contain Al as a film-forming element, and therefore an oxide film 430 is formed on the exposed surfaces of the joints 400, and this oxide film 430 suppresses corrosion of the joints 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 element contained in the joints 400 comes into contact with air, and a new oxide film 430 is formed. This process is repeated until the film-forming element contained in the joints 400 is depleted, and the oxide film 430 no longer forms, causing corrosion of the joints 400. As described above, the bonded portion 400 of this embodiment has a first bond width W1 larger than the second bond width W2, and therefore has a higher concentration of the film-forming element (Al) than a bonded portion in which the first bond width W1 is equal to or smaller than the second bond width W2. This relatively lengthens the time until the film-forming element is depleted, thereby suppressing corrosion of the bonded portion 400 for a long period of time.

[0081] Furthermore, if the ratio W1 / W2 of the first bond width W1 to the second bond width W2 is 1.2 or more, the concentration of the film-forming element contained in the bond portion 400 is reliably increased, and corrosion of the bond portion 400 is suppressed for a long period of time.

[0082] Such a 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 bonded portion 194 not containing the film-forming element, i.e., when the concentration of the film-forming element contained in the bonded portion 400 tends to be relatively small.

[0083] Furthermore, when the depth of the second fusion zone 420 is defined as the joining depth D, the following formula (2) is satisfied.

[0084] D×3 <W1···(2)

[0085] According to this configuration, by relatively reducing the size of the second fusion zone 420 that does not contain the film-forming element, the concentration of the film-forming element contained in the joint 400 is increased compared to when the second fusion zone 420 is relatively large. Also, the adverse effects on the fuel cell stack 10 caused by an unnecessarily large thickness of the joint region 194 are suppressed. The adverse effects include, for example, an increase in the amount of gas consumed to heat the fuel cell stack 10 to a temperature sufficient to cause an electrochemical reaction during startup, which results in the user having to pay a higher gas fee.

[0086] A-3. Advantages of this embodiment: As described above, the fuel cell stack 10 of this embodiment includes a unit cell 110 and a joining member 500. The unit cell 110 includes an anode 116, an electrolyte layer 112, and an cathode 114. The joining member 500 includes an IC separator 180 and an interconnector 190. The IC separator 180 contains a film-forming element that forms an oxide film 430. The interconnector 190 is a member that is disposed over the IC separator 180 and joined to the IC separator 180 by welding, and does not contain a film-forming element. A joining portion 400 between the IC separator 180 and the interconnector 190 is composed of a first fusion zone 410 that penetrates the IC separator 180 and a second fusion zone 420 that extends from the first fusion zone 410 into the interconnector 190. In a cross section of a joining member 500 including a first fusion zone 410 and a second fusion zone 420, when the width of a first region AR1 of the first fusion zone 410 adjacent to the second fusion zone 420 is defined as a first joining width W1, and the width of a second region AR2 of the second fusion zone 420 adjacent to the first fusion zone 410 is defined as a second joining width W2, the following formula (1) is satisfied.

[0087] W1>W2 (1)

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

[0089] Furthermore, the ratio of the first bonding width W1 to the second bonding width W2 may be equal to or greater than 1.2. With this configuration, the concentration of the film-forming element contained in the bonding portion 400 can be reliably increased.

[0090] Furthermore, in the above cross section, when the depth of the second fusion zone 420 is defined as the joining depth D, the following formula (2) is satisfied.

[0091] D×3 <W1···(2)

[0092] With this configuration, it is possible to suppress the adverse effects on the fuel cell stack 10 that would be caused by the interconnector 190 being thicker than necessary.

[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 the coating-forming element, is smaller than the thickness T2 of the interconnector 190, the coating-forming element does not sufficiently diffuse to the bonding portion 400, which is likely to cause a problem of early corrosion of the bonding portion 400. The above configuration can be suitably applied to a bonding member 500 having such a configuration.

[0094] In addition, the manufacturing method of the joining member 500 of this embodiment includes a film formation process of forming an oxide film 183 containing a film-forming element on the surface of the IC separator 180, a lamination process of overlapping 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 process of welding the IC separator 180 and the interconnector 190 by irradiating a laser to the second surface 180F2 of the interconnector 190 opposite the first surface 180F1 on which the IC separator 180 is arranged.

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

[0096] B. Variations (1) In the above embodiment, the film-forming element is aluminum. However, the film-forming element may be any element that forms a passive film, such as chromium. (2) In the above embodiment, the second metal member is a member that does 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 is the IC separator 180 and the second metal member is the interconnector 190. However, the combination of the first metal member and the second metal member is not limited to the above embodiment. For example, the first metal member may be the terminal separator 230 and the second metal member may be the first plate 232. The thickness of the terminal 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 including a metal-supported unit cell supported by a metal support, the first metal member may be a unit cell separator and the second metal member may be the metal support. In particular, the configuration disclosed in this specification can be suitably applied to components in an electrochemical reaction cell stack that are placed in a high-temperature atmosphere, an oxygen-rich atmosphere, or a water vapor-rich atmosphere. (4) When the thickness of the first metal member varies depending on the location, the "thickness of the first metal member" refers to the thickness of the portion of the first metal member that is joined to the second metal member, i.e., the portion where the joint formed by welding is located. The same applies to the thickness of the second metal member. (5) In the above embodiment, the oxide film 183 is formed on the IC separator 180 in the film forming step, but a passivation film may be formed on the surface of the second metal member in the film forming step. (6) In the above embodiment, laser welding is exemplified as a welding method. However, the welding method applicable to the technology disclosed in this specification may be any method other than laser welding, such as arc welding or electron beam welding, in which some kind of high-energy radiation is irradiated onto the irradiated surfaces of the target components to melt and join the target components. (7) In the above embodiment, the electrochemical reaction cell stack is 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 a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), or a molten carbonate fuel cell (MCFC), or an electrolysis cell stack having an electrolysis cell unit, which is a constituent unit of a solid oxide electrolysis cell (SOEC), as a single cell. [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: Anode 118: Reaction prevention layer 120: Separator for single cell 121: Through hole 124: Sealing material 130: Air electrode frame 131: Through hole 140: Anode frame 141: Through hole 144: Anode current collecting member 145: Electrode opposing portion 146: Interconnector opposing portion 147: Connection portion 149: Spacer 180: IC separator (first metal member) 180F1: First surface 180F2: Second surface (irradiated surface) 181: Through hole 182: Base material 183: Oxide film (passivation film) 190: Interconnector (second metal member) 191: Flat plate portion 192: Air electrode current collecting portion 193: Coating layer 194: Bonding portion 194F1: Third surface 194F2: Fourth surface 196: Conductive bonding material 210: First end plate 211: Flat portion 212: Through hole 213: Outer convex portion 214: Inner convex portion 220: Insulating portion 230: Terminal separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Flat portion 272: Through hole 273: Outer convex portion 274: Inner convex portion 280: Gas passage member 281: Main body portion 282: Flange portion 284: Bolt hole 311: Oxidant 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 portion 410: First fusion zone 420: Second fusion zone 430: Oxide film (passivation film) 500: Joint material 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 point 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 disposed over the first metal member and joined to the first metal member by welding, a second metal member that does not contain the film-forming element or that contains the film-forming element, but 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 joining member used in an electrochemical reaction cell stack including 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 fusion zone penetrating the first metal member; a second fusion zone extending from the first fusion zone into the second metal member; It is composed of In a cross section including the first fusion zone and the second fusion zone, A width of a first region of the first fusion zone adjacent to the second fusion zone is defined as a first joining width W1, When the width of a second region of the second fusion zone adjacent to the first fusion zone is defined as a second joining width W2, Satisfies the following formula (1): Joining material. W1>W2...(1)

2. a ratio of the first bonding width W1 to the second bonding 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 fusion zone is defined as a joining depth D, Satisfies the following formula (2): The joining member according to claim 1 or 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 2.

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

6. a first metal member containing a film-forming element that forms a passivation film; a second metal member disposed over the first metal member and joined to the first metal member by welding, a second metal member that does not contain the film-forming element or that contains the film-forming element, but 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 method for manufacturing a joining member used in an electrochemical reaction cell stack including a single cell including an anode, an electrolyte layer, and an cathode, the method comprising: a coating formation step of forming a passivation coating containing the coating-forming element on a surface of one of the first metal member and the second metal member; a lamination step of overlaying the other of the first metal member and the second metal member on the surface of the one member on which the passivation film is formed; a welding step of welding the first metal member and the second metal member by irradiating a high-energy ray onto an irradiation surface of the first metal member opposite to a surface on which the second metal member is disposed; Including, A method for manufacturing a joining member.

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