Glass ceramic sealant for fuel cell stacks

Abstract

To provide a glass ceramic seal material for solid oxide type fuel cells, a fuel cell stack and production methods thereof.SOLUTION: A glass ceramic seal material comprises 40-60% of SiO2, 25-28% of BaO, 10-20% of B2O3, 8-12% of Al2O3, 0-2% of ZrO2, 0-1% of Y2O3, 0-1% of CaO and 0-1% of MgO in terms of oxide by weight. A method for stack production comprises the steps of: mixing a first glass powder having less than 25 wt.% of barium oxide contents with a second glass powder having at least 45 wt.% of barium oxide contents; coating a composition containing the mixed first glass powder and second glass powder between an interconnect and a solid oxide-type fuel cell, thereby forming a fuel cell stack; and sintering the composition in the fuel cell stack at a raised temperature to form a glass ceramic seal between the interconnect and solid oxide-type fuel cell.SELECTED DRAWING: Figure 3B

Description

Technical Field

[0001] The present disclosure generally relates to glass-ceramic sealants, particularly glass-ceramic sealants for fuel cell stacks.

Background Art

[0002] In high-temperature fuel cell systems, such as solid oxide fuel cell (SOFC) systems, an oxidant stream passes through the cathode side of the fuel cell and a fuel stream passes through the anode side of the fuel cell. The oxidant stream is typically air, and the fuel stream may be a hydrocarbon fuel such as methane, natural gas, pentane, ethanol or methanol. The fuel cell operates at a typical temperature of 750 °C to 950 °C, enabling the movement of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ions combine with hydrogen in free hydrogen or hydrocarbon molecules to produce water vapor and / or combine with carbon monoxide to produce carbon dioxide. Excess electrons from the negatively charged ions are returned to the cathode side of the fuel cell via a completed electrical circuit between the anode and the cathode, and as a result, an electric current flows through the circuit.

[0003] A fuel cell stack can include manifolds for fuel and air, either internally or externally. In an internal manifold type stack, fuel and air are distributed to each cell using risers contained within the stack. In other words, the gas flows through the openings or pores of the support layer of each fuel cell, such as the electrolyte layer, and the gas flow separator of each cell. Also, in an external manifold type stack, the stack is open at the inlet and outlet sides for fuel and air, and the fuel and air are introduced and recovered independently of the hardware of the stack. For example, the inlet and outlet fuels and air flow through separate passages between the stack and the manifold housing in which the stack is disposed.

[0004] Fuel cell stacks are often constructed from a number of cells in the form of planar elements, tubes, or other geometries. Fuel and air must be supplied to an electrochemically active surface, which can be large. One component of a fuel cell stack is the so-called gas flow separator (called a gas flow separator plate in planar stacks), which separates the individual cells within the stack. The gas flow separator plate separates the fuel, such as hydrogen or hydrocarbon fuel, flowing to the fuel electrode (i.e., anode) of one cell in the stack from the oxidizer, such as air, flowing to the air electrode (i.e., cathode) of an adjacent cell in the stack. Often, the gas flow separator plate is also used as an interconnect, electrically connecting the fuel electrode of one cell to the air electrode of an adjacent cell. In this case, the gas flow separator plate functioning as an interconnect is manufactured from or contains a conductive material. [Overview of the Initiative]

[0005] According to various embodiments of the present disclosure, the glass ceramic seal contains, by weight on an oxide basis, 40-60% SiO2, 25-28% BaO, 10-20% B2O3, 8-12% Al2O3, 0-2% ZrO2, 0-1% Y2O3, 0-1% CaO, and 0-1% MgO.

[0006] According to various embodiments of the present disclosure, a method for manufacturing a fuel cell stack includes the steps of: mixing a first glass powder having an oxide-based barium oxide content of less than 25% by weight with a second glass powder having an oxide-based barium oxide content of at least 45% by weight; coating an interconnect and a solid oxide fuel cell with a composition containing the mixed first and second glass powders to form a fuel cell stack; and sintering the composition within the fuel cell stack at an elevated temperature to form a glass ceramic seal between the interconnect and the solid oxide fuel cell. [Brief explanation of the drawing]

[0007] The accompanying drawings incorporated herein and constituting part thereof illustrate exemplary embodiments of the present invention and, together with the above general description and the following detailed description, are useful in illustrating the features of the present invention. [Figure 1A] This is a perspective view of a conventional fuel cell column. [Figure 1B] Figure 1A is a perspective view of one counterflow type solid oxide fuel cell (SOFC) stack included in the column. [Figure 1C] Figure 1B is a side cross-sectional view of a portion of the stack. [Figure 2A] Figure 1B is a plan view of the air side of a conventional interconnect in the stack. [Figure 2B] This is a plan view of the fuel side of a conventional interconnect. [Figure 3A] This is a perspective view of a fuel cell stack according to various embodiments of the present disclosure. [Figure 3B] Figure 3A is a disassembled perspective view of a portion of the stack. [Figure 3C] Figure 3A is a plan view of the fuel side of the interconnect included in the stack. [Figure 3D] Figure 3A is a schematic diagram of the fuel cell included in the stack. [Figure 4A] This is a plan view showing the air side of the cross-flow type interconnect shown in Figure 3C, according to various embodiments of the present disclosure. [Figure 4B] This is a plan view showing the fuel side of the cross-flow interconnect shown in Figure 3C, according to various embodiments of the present disclosure. [Figure 5A] This is a plan view showing the air side of the interconnect in Figure 3C. [Figure 5B] This is a plan view showing a modified version of the interconnect shown in Figure 5A. [Figure 6A] Figures 4A and 4B show two interconnects according to various embodiments of the present disclosure, as well as a cross-sectional perspective view showing a fuel cell assembled within a fuel cell stack in Figure 3A. [Figure 6B]Figure 6A is a plan view showing the overlap of the fuel cell and seal on the fuel side of the interconnect. [Figure 7] This is a side cross-sectional view of a portion of a fuel cell stack according to various embodiments of the present disclosure. [Modes for carrying out the invention]

[0008] Various embodiments will be described in detail with reference to the accompanying drawings. The drawings are not necessarily to scale and are intended to illustrate various features of the invention. Wherever possible, the same reference numerals are used throughout the drawings to refer to the same or similar components. References to specific examples and embodiments are illustrative and not intended to limit the scope of the invention or the claims.

[0009] In this specification, a range may be expressed as a range from a specific value marked "approximately" to and / or another specific value marked "approximately". When such a range is expressed, an example would include a range from one specific value to and / or another specific value. Similarly, when a value is expressed as an approximation by using the preceding "approximately" or "substantially", it will be understood that the specific value forms another aspect. In some embodiments, a value of "approximately X" may include values ​​of X ± 1%. Furthermore, each endpoint of a range is understood to be significant in relation to and independently of other endpoints.

[0010] Figure 1A is a perspective view of a conventional fuel cell column 30, Figure 1B is a perspective view of a counterflow type solid oxide fuel cell (SOFC) stack 20 included in the column 30 of Figure 1A, and Figure 1C is a side cross-sectional view of a portion of the stack 20 of Figure 1B.

[0011] Referring to Figures 1A and 1B, the column 30 may include one or more stacks 20, a fuel inlet conduit 32, an anode exhaust conduit 34, and an anode feed / return assembly 36 (e.g., an anode splitter plate (ASP) 36). The column 30 may also include a side baffle 38 and a compression assembly 40. The fuel inlet conduit 32 is fluidly connected to the ASPs 36 and configured to provide fuel to each ASP 36, and the anode exhaust conduit 34 is fluidly connected to the ASPs 36 and configured to receive anode fuel exhaust from each ASP 36.

[0012] The ASP36 is positioned between the stacks 20 and configured to provide the stacks 20 with a fuel supply containing hydrocarbon fuel and to receive anode fuel exhaust from the stacks 20. For example, the ASP36 may be fluidly connected to an internal fuel riser passage 22 formed within the stacks 20, as described below.

[0013] Referring to Figure 1C, the stack 20 includes multiple fuel cells 1 separated by interconnects 10, which are sometimes called gas flow separator plates or bipolar plates. Each fuel cell 1 includes a cathode electrode 3, a solid oxide electrolyte 5, and an anode electrode 7.

[0014] Each interconnect 10 electrically connects adjacent fuel cells 1 within the stack 20. In particular, the interconnect 10 can electrically connect the anode electrode 7 of one fuel cell 1 to the cathode electrode 3 of an adjacent fuel cell 1. Figure 1C shows that the lower fuel cell 1 is positioned between two interconnects 10.

[0015] Each interconnect 10 includes ribs 12 that at least partially define fuel passages 8A and air passages 8B. The interconnect 10 can act as a gas - fuel separator that separates fuel, such as hydrocarbon fuel, flowing to the fuel electrode (i.e., anode 7) of one cell in the stack from an oxidant, such as air, flowing to the air electrode (i.e., cathode 3) of an adjacent cell in the stack. At one end of the stack 20, an air end plate or a fuel end plate (not shown) for supplying air or fuel to the end electrodes, respectively, may be provided.

[0016] FIG. 2A is a plan view of the air side of a conventional interconnect 10, and FIG. 2B is a plan view of the fuel side of the interconnect 10. Referring to FIGS. 1C and 2A, the air side includes air passages 8B. Air flows through the air passages 8B to the cathode electrode 3 of the adjacent fuel cell 1. In particular, air can flow across the interconnect 10 in a first direction A indicated by the arrow.

[0017] To prevent fuel from contacting the cathode electrode, the fuel holes 22A of the interconnect 10 may be surrounded by a ring seal 23. A strip - shaped peripheral seal 24 is disposed on the peripheral portion of the air side of the interconnect 10. The seals 23, 24 may be formed from a glass material. The peripheral portion may be in the form of a flat portion of a raised portion that does not include ribs or passages. The surface of the peripheral region may be coplanar with the tops of the ribs 12.

[0018] Referring to FIGS. 1C and 2B, the fuel side of the interconnect 10 may include fuel passages 8A and a fuel manifold 28 (e.g., a fuel plenum). Fuel flows from one of the fuel holes 22A into the adjacent manifold 28 and through the fuel passage 8A to the anode 7 of the adjacent fuel cell 1. Excess fuel may flow into the other fuel manifold 28 and then into the adjacent fuel hole 22A. In particular, fuel can flow across the interconnect 10 in a second direction B as indicated by the arrow. The second direction B may be orthogonal to the first direction A (see FIG. 2A).

[0019] A frame-shaped seal 26 is positioned in the fuel-side peripheral region of the interconnect 10. The peripheral region may be a flat portion of a raised area that does not include ribs or passages. The surface of the peripheral region may be coplanar with the top of the rib 12.

[0020] Therefore, conventional counterflow fuel cell columns, such as those shown in Figures 1A, 1B, 1C, 2A, and 2B, may include a complex fuel distribution system (fuel rails and anode splitter plate). Furthermore, the use of an internal fuel riser may require holes in the fuel cell and corresponding seals, thereby reducing the working surface area of ​​the fuel cell and potentially causing cracks in the ceramic electrolyte of the fuel cell 1.

[0021] The fuel manifold 28 may occupy a relatively large area of ​​the interconnect 10, which could reduce the contact area between the interconnect 10 and adjacent fuel cells by approximately 10%. Also, because the fuel manifold 28 is relatively deep, it corresponds to a relatively thin area of ​​the interconnect 10. Since the interconnect 10 is generally formed by a powder metallurgy compression process, the density of the fuel manifold area may approach the theoretical density limit of the interconnect material. Therefore, the length of the compression press stroke used in the compression process may be limited because the high-density fuel manifold area cannot be further compressed. As a result, the compression stroke limitation may limit the density achieved elsewhere in the interconnect 10 to a lower level. The resulting density variation may lead to local deviations, which could reduce the amount of contact between the interconnect 10 and the fuel cell 1, degrading the stack yield and / or performance.

[0022] Another important consideration in the design of fuel cell systems lies in the realm of operational efficiency. To achieve operational efficiency, maximizing fuel utilization is a crucial factor. Fuel utilization is the ratio of the amount of fuel consumed during operation to the amount of fuel supplied to the fuel cell. A key factor in maintaining the cycle life of a fuel cell may be avoiding fuel depletion in the fuel cell's area of ​​action by properly distributing fuel across the area of ​​action. If there is an uneven distribution of fuel, such that some flow range passages do not receive enough fuel to sustain the electrochemical reactions occurring in the area of ​​that passage, it can lead to fuel depletion in the fuel cell area adjacent to that passage. To distribute fuel more uniformly, conventional interconnect designs include variations in passage depth across the entire flow range. This not only introduces complexity in the manufacturing process but can also require complex measurements to accurately determine these dimensions. The distribution of fuel through fuel ports and distribution manifolds can constrain various passage geometries.

[0023] One possible solution to this complex geometry and fuel manifold is to have a wider fuel opening to ensure more uniform fuel distribution across the entire fuel flow range. Since the formation of the fuel manifold is a source of density variation, eliminating the fuel manifold should allow for more uniform density and permeability in the interconnect. Therefore, an improved interconnect is needed that provides uniform contact with the fuel cell while distributing fuel uniformly to the fuel cell without using a conventional fuel manifold.

[0024] Due to the overall constraints on increasing the size of the hotbox in fuel cell systems, there is also a need for improved interconnects designed to maximize fuel utilization and the working area of ​​the fuel cell without increasing the hotbox footprint.

[0025] Cross-flow fuel cell system Figure 3A is a perspective view of a fuel cell stack 300 according to various embodiments of the present disclosure. Figure 3B is an exploded perspective view of a portion of the stack 300 in Figure 3A. Figure 3C is a plan view of the fuel side of the interconnect 400 included in the stack 300. Figure 3D is a schematic diagram of the fuel cell included in the stack 300.

[0026] Referring to Figures 3A to 3D, the fuel cell stack 300, which may also be called a fuel cell column because it does not have an ASP, includes a plurality of fuel cells 310 separated by an interconnect 400, which may also be called a gas flow separator plate or bipolar plate. One or more stacks 300 may be thermally integrated with other components of the fuel cell power generation system (e.g., one or more anode exhaust gas oxidizers, fuel reformers, fluid conduits and manifolds, etc.) within a common enclosure or “hot box”.

[0027] Interconnect 400 is manufactured from a conductive metallic material. For example, interconnect 400 may include a chromium alloy, such as a Cr-Fe alloy. Interconnect 400 can typically be manufactured using powder metallurgy techniques, including pressing and sintering of Cr-Fe powder, which may be a mixture of Cr powder and Fe powder or Cr-Fe alloy powder, to form Cr-Fe interconnects of desired size and shape (e.g., a "net shape" or "near net shape" process). A typical chromium alloy interconnect 400 contains more than about 90% chromium by weight, for example, about 94-96% (e.g., 95%) chromium by weight. Interconnect 400 may also contain less than about 10% iron by weight, for example, about 4-6% (e.g., 5%) iron by weight, less than about 2% by weight, for example, about 0-1% of other materials, such as yttrium or yttria by weight, and residual or unavoidable impurities.

[0028] Each fuel cell 310 may include a solid oxide electrolyte 312, an anode 314, and a cathode 316. In some embodiments, the anode 314 and cathode 316 may be printed onto the electrolyte 312. In other embodiments, a conductive layer 318, such as a nickel mesh, may be placed between the anode 314 and the adjacent interconnect 400. The fuel cell 310 does not have through holes like the fuel holes of conventional fuel cells. Therefore, the fuel cell 310 avoids cracks that may occur due to the presence of such through holes.

[0029] The uppermost and lowermost interconnects 400 of the stack 300 may be different forms of air-side endplates or fuel-side endplates, each characterized for providing air or fuel to an adjacent end fuel cell 310. As used herein, “interconnect” may mean either an interconnect located between two fuel cells 310, or an endplate located at the end of the stack and directly adjacent to only one fuel cell 310. Since the stack 300 does not include an ASP and its associated endplates, the stack 300 may include only two endplates. As a result, changes in stack dimensions associated with the use of an in-column ASP can be avoided.

[0030] The stack 300 may include side baffles 302, a fuel plenum 304, and a compression assembly 306. The side baffles 302 can be formed from a ceramic material and may be positioned on opposite sides of the fuel cell stack 300, which includes the stacked fuel cells 310 and interconnect 400. The side baffles 302 may connect the fuel plenum 304 and the compression assembly 306 so that the compression assembly 306 can apply pressure to the stack 300. The side baffles 302 may be curved baffle plates such that each baffle plate covers at least a portion of each of the three sides of the fuel cell stack 300. For example, one baffle plate may completely cover the fuel inlet riser side of the stack 300 and partially cover the adjacent front and back sides of the stack, while the other baffle plate may completely cover the fuel outlet riser side of the stack and partially cover the adjacent front and back sides of the stack. The remaining uncovered portions of the front and back sides of the stack allow air to flow through the stack 300. The curved baffle plate improves control of the airflow through the stack compared to a conventional baffle plate 38 that covers only one side of the stack. The fuel plenum 304 may be located below the stack 300 and may be configured to provide a hydrogen-containing fuel supply to the stack 300 and may receive anode fuel exhaust from the stack 300. The fuel plenum 304 may be connected to a fuel inlet and outlet conduit 308 located below the fuel plenum 304.

[0031] Each interconnect 400 electrically connects adjacent fuel cells 310 within the stack 300. In particular, an interconnect 400 can electrically connect the anode electrode of one fuel cell 310 to the cathode electrode of an adjacent fuel cell 310. As shown in Figure 3C, each interconnect 400 can be configured to supply air to the cathode of an adjacent fuel cell 310 by flowing air in a first direction A. Alternatively, each interconnect 400 can be configured to supply fuel to the anode of an adjacent fuel cell 310 by flowing fuel in a second direction F. Directions A and F may be orthogonal to each other, or substantially orthogonal to each other. Therefore, the interconnects 400 can be called cross-flow interconnects.

[0032] The interconnect 400 may include fuel ports extending across the interconnect 400 and configured for fuel distribution. For example, the fuel ports may include one or more fuel inlets 402 and one or more fuel outlets 404, which may also be called anode exhaust outlets 404. The fuel inlets 402 and fuel outlets 404 can be located outside the periphery of the fuel cell 310. Thus, the fuel cell 310 can be formed without corresponding through-holes for fuel flow. The total length of the fuel inlets 402 and / or the total length of the fuel outlets 404 may be at least 75% of the corresponding length of the interconnect 400, for example, the length in direction A.

[0033] In one embodiment, as shown in Figure 3B, each interconnect 400 includes two fuel inlets 402 separated by a neck portion 412 of the interconnect 400. However, there may be more than two fuel inlets 402, for example, three to five inlets separated by two to four neck portions 412. In one embodiment, as shown in Figure 3B, each interconnect 400 includes two fuel outlets 404 separated by a neck portion 414 of the interconnect 400. However, there may be more than two fuel outlets 404, for example, three to five outlets separated by two to four neck portions 414.

[0034] The fuel inlets 402 of adjacent interconnects 400 can be aligned within the stack 300 to form one or more fuel inlet risers 403. The fuel outlets 404 of adjacent interconnects 400 can be aligned within the stack 300 to form one or more fuel outlet risers 405. The fuel inlet risers 403 can be configured to distribute the fuel received from the fuel plenum 304 to the fuel cell 310. The fuel outlet risers 405 can be configured to provide the anode exhaust received from the fuel cell 310 to the fuel plenum 304.

[0035] Unlike the flat side baffle 38 of the related technology shown in Figure 1A, the side baffle 302 can be curved to surround the edge of the interconnect 400. In particular, the side baffle 302 can be positioned to surround the fuel inlet 402 and fuel outlet 404 of the interconnect 400. Thus, the side baffle can more efficiently control the airflow through the air passages of the interconnect 400 that are exposed between the side baffles 302 and described in detail with respect to Figures 4A and 4B.

[0036] In various embodiments, the stack 300 may include at least 30, at least 40, at least 50, or at least 60 fuel cells, which can be supplied with fuel using only fuel risers 403, 405. In other words, compared to conventional fuel cell systems, the cross-flow configuration can supply fuel to a large number of fuel cells without requiring an external fuel manifold, such as external conduits 32, 34, of the ASP or stack shown in Figure 1A.

[0037] Each interconnect 400 may be made of a conductive material, such as a metal alloy (e.g., chromium-iron alloy) having a coefficient of thermal expansion similar to that of the solid oxide electrolyte of the cell (e.g., a difference of 0-10%), or may contain such a conductive material. For example, the interconnect 400 may contain a metal (e.g., 4-6% by weight of iron, optionally 1% by weight or less of yttrium and a chromium-iron alloy such as equilibrium chromium alloy), and may electrically connect the anode side, i.e., the fuel side, of a given fuel cell 310 to the cathode side, i.e., the air side, of an adjacent fuel cell 310. A conductive contact layer, such as a nickel contact layer (e.g., nickel mesh), may be provided between the anode and each interconnect 400. Another optional conductive contact layer may be provided between the cathode electrode and each interconnect 400.

[0038] The surface of the interconnect 400, which is exposed to an oxidizing environment (e.g., air) during operation, for example, the side of the interconnect 400 facing the cathode, may be coated with a protective coating layer to reduce the growth rate of the chromium oxide surface layer on the interconnect and suppress the evaporation of chromium vapor species that could degrade the fuel cell cathode. Typically, a coating layer containing a perovskite, such as lanthanum strontium manganite (LSM), can be formed using a thermal spray coating or dipping coating process. Alternatively, other metal oxide coatings, such as spinel, such as (Mn,Co)3O4 spinel (MCO), can be used instead of or in addition to LSM. 2-x Co 1+xAny spinel having a composition expressed as O4(0≦x≦1) or z(Mn3O4)+(1-z)(Co3O4), where (1 / 3≦z≦2 / 3) or (Mn,Co)3O4 can be used. In other embodiments, a mixed layer of LSM and MCO or a stack of LSM and MCO layers may be used as the coating layer.

[0039] Figures 4A and 4B are plan views showing the air side and fuel side, respectively, of a cross-flow interconnect 400 according to various embodiments of the present disclosure. Referring to Figure 4A, the air side of the interconnect 400 may include ribs 406 configured to at least partially define an air passage 408 configured to supply air to the cathode of a mounted fuel cell 310. The air side of the interconnect 400 can be divided into an airflow range 420 including the air passage 408 and riser seal surfaces 422 located on two opposite sides of the airflow range 420. One of the riser seal surfaces 422 may surround a fuel inlet 402, and the other riser seal surface 422 may surround a fuel outlet 404. The air passage 408 and ribs 406 can extend entirely across the air side of the interconnect 400, such that the air passage 408 and ribs 406 terminate at opposite peripheries of the interconnect 400. In other words, when assembled into the stack 300, the opposite ends of the air passages 408 and ribs 406 are positioned on opposite (e.g., front and back) outer surfaces of the stack, allowing the blown air to flow through the stack. Therefore, the stack may be equipped with an external air manifold.

[0040] A riser seal 424 may be positioned on the riser seal surface 422. For example, one riser seal 424 may surround the fuel inlet 402, and another riser seal 424 may surround the fuel outlet 404. The riser seal 424 can prevent fuel and / or anode exhaust from entering the airflow range 420 and coming into contact with the cathode of the fuel cell 310. The riser seal 424 can also function to prevent fuel from leaking out of the fuel cell stack 100 (see Figure 3A).

[0041] Referring to Figure 4B, the fuel side of the interconnect 400 may include a rib 416 that at least partially defines a fuel passage 418 configured to supply fuel to the anode of the mounted fuel cell 310. The fuel side of the interconnect 400 can be divided into a fuel flow range 430 including the fuel passage 418 and a surrounding sealing surface 432 surrounding the fuel flow range 430 as well as the fuel inlet 402 and fuel outlet 404. The rib 416 and the fuel passage 418 may extend in a direction perpendicular or substantially perpendicular to the direction in which the air-side passage 408 and the rib 406 extend.

[0042] A frame-shaped perimeter seal 434 may be positioned on the perimeter sealing surface 432. The perimeter seal 434 can be configured to prevent air from entering the fuel flow range 430 and coming into contact with the anode of an adjacent fuel cell 310. The perimeter seal 434 can also function to prevent fuel from leaving the fuel risers 403, 405 and leaking out of the fuel cell stack 300 (see Figures 3A and 3B).

[0043] The seals 424, 434 may include glass or ceramic sealing material, as will be described in detail below. The sealing material may have low conductivity. In some embodiments, the seals 424, 434 can be formed by printing one or more layers of sealing material onto the interconnect 400 and then sintering them. Figure 5A is a plan view showing the air side of the interconnect 400 without riser seals 424 according to various embodiments of the present disclosure, and Figure 5B is a plan view showing a modified version of the interconnect 400 of Figure 5A.

[0044] In conventional counterflow fuel cell system designs, the fuel cell electrolyte completely encloses the interconnects so that it acts as a dielectric layer between adjacent interconnects. In crossflow designs, the interconnects may extend beyond the perimeter of the fuel cell. This can lead to electrical short circuits between interconnects if the stack is tilted or if the seals become conductive over time.

[0045] Referring to Figures 5A and 5B, the interconnect 400 may optionally include a dielectric layer 440 disposed on the riser seal surface 422. For example, as shown in Figure 5A, each dielectric layer 440 may be annular and cover all or substantially all of the corresponding riser seal surface 422. For example, in the embodiment of Figure 5A, the dielectric layer 440 may be D-shaped and have substantially the same shape as the mounted riser seal 424 shown in Figure 4A. In other embodiments, as shown in Figure 5B, the dielectric layer 440 may be C-shaped and only cover a portion of the corresponding riser seal surface 422, for example, the portion adjacent to the outer periphery of the interconnect 400. The dielectric layer 440 forms an electrical insulating barrier between adjacent interconnects 400 to prevent electrical short circuits when the corresponding stacks are tilted or when the seals become conductive.

[0046] The dielectric layer 440 may include alumina, zircon (zirconium silicate), silicon carbide, crystalline glass (e.g., quartz or glass ceramic), or other high-temperature dielectric materials. In some embodiments, the dielectric layer 440 may include a corrosion barrier material or corrosion barrier layer. For example, the dielectric layer 440 may include a composite material containing corrosion-resistant glass, alumina, zircon, etc. For example, in some embodiments, the dielectric layer 440 includes a glass ceramic layer formed substantially from a glass barrier precursor layer, which contains at least 90 wt% glass (e.g., 90-100 wt% glass such as about 99-100 wt% amorphous glass and 0-1 wt% crystalline phase), deposited on the surface of the interconnect 400 of the SOFC stack 300. In one embodiment, the glass barrier precursor layer, which contains at least 90% by weight of glass, comprises, on an oxide weight basis, 45-55% by weight of silica (SiO2), 5-10% by weight of potassium oxide (K2O), 2-5% by weight of calcium oxide (CaO), 2-5% by weight of barium oxide (BaO), 0-1% by weight of boron trioxide (B2O3), 15-25% by weight of alumina (Al2O3), and 20-30% by weight of zirconia (ZrO2).

[0047] In some embodiments, the glass barrier precursor layer comprises, by weight, at least 90% glass (for example, about 90-100% glass, such as about 99-100% amorphous glass and 0-1% crystalline phase). For example, the glass barrier precursor layer may contain, on an oxide weight basis, about 30% to about 60%, for example, about 35% to about 55% silica (SiO2); about 0.5% to about 15%, for example, about 1% to about 12% boron trioxide (B2O3); about 0.5% to about 5%, for example, about 1% to about 4% alumina (Al2O3); about 2% to about 30%, for example, about 5% to about 25% calcium oxide (CaO); about 2% to about 25%, for example, about 5% to about 20% magnesium oxide (MgO); about 0% to about 35%, for example, about 20% to about 30% barium oxide (BaO); about 0% to about 20%, for example, about 10% to about 15% strontium oxide (SrO); and about 2% to about 12%, for example, about 5% to about 10% lanthanum oxide (La2O3). In some embodiments, the material of the glass barrier precursor may include at least one of BaO and / or SrO in a non-zero amount, for example, at least 0.5% by weight, or both BaO and SrO in a non-zero amount, for example, at least 0.5% by weight.

[0048] In some embodiments, part or all of the LSM / MCO coating can be removed in the region surrounding the riser seal 424 on the air side of the interconnect 400 to prevent the diffusion of Mn from the LSM / MCO material to the riser seal 424, thereby preventing the riser seal 424 from becoming conductive. In other embodiments, the riser seal 424 may be formed of a crystalline glass or glass ceramic material that does not react with the LSM / MCO coating, such as the borosilicate glass ceramic composition described above.

[0049] The dielectric layer 440 may be formed from independent layers, such as a tape-forming layer and a sintered layer, and may be placed between the interconnects 400 during the assembly of the fuel cell stack. In other embodiments, the dielectric layer 440 can be formed by dispersing a dielectric material in the form of an ink, paste, or slurry, and then screen printing, pad printing, or aerosol spraying it onto the interconnects 400. In some embodiments, the dielectric layer 440 can be formed by a thermal spraying process, such as an atmospheric plasma spraying (APS) process. For example, the dielectric layer 440 may contain alumina deposited by the APS process.

[0050] The dielectric layer 440 may be deposited directly on the interconnect 400. For example, the dielectric layer 440 may be placed directly on the riser seal surface 422 (i.e., the portion of the interconnect 400 around the fuel inlet 402 and fuel outlet 404 that is covered by the riser seal 424 but not by the LSM / MCO coating, excluding small overlapping regions (e.g., seams) where the riser seal surface 422 is in contact with the airflow range 420 and the dielectric layer 440 overlaps with the LSM / MCO coating), thereby preventing Cr evaporation from the exposed surface of the interconnect 400. Thus, the LSM / MCO coating is placed on the surface of the interconnect 400 in the airflow range 420, including the air passages 408 and ribs 406, but not on the riser seal surface 422 of the interconnect 400 surrounding the fuel inlet 402 and fuel outlet 404. The dielectric layer 440 is located on the riser seal surface of the interconnect 400 in the region surrounding the fuel inlet 402 and fuel outlet 404, which are not covered by the LSM / MCO coating, and on the edges of the LSM / MCO coating within the airflow range 420 adjacent to the riser seal surface 422. Alternatively, the dielectric layer 440 can be omitted, and the dielectric layer 440 is not deposited around the fuel riser opening.

[0051] The fuel cell stack and / or its components may be conditioned and / or sintered. "Sintering" includes a process of heating, melting and / or reflowing a glass seal precursor material or a glass ceramic seal precursor material to form a seal in the fuel cell stack, which can be carried out in air and / or an inert gas at an elevated temperature (e.g., 600-1000°C). "Conditioning" includes a process of reducing a metal oxide (e.g., nickel oxide) in the anode electrode to a metal (e.g., nickel) in a cermet electrode (e.g., nickel, and a ceramic material, e.g., stabilized zirconia or doped ceria, etc.), and / or a process of heating the stack 300 during performance characterization / testing, which can be carried out at an elevated temperature (e.g., 750-900°C) while the fuel flows through the stack. Sintering and conditioning of the fuel cell stack 300 can be carried out in the same thermal cycle (i.e., without cooling the stack to room temperature between sintering and conditioning).

[0052] Figure 6A is a cross-sectional perspective view showing two interconnects 400 in Figures 4A and 4B, and a fuel cell 310 assembled in the fuel cell stack 300 of Figure 3A, according to various embodiments of the present disclosure. Figure 6B is a plan view showing the fuel-side fuel cell 310 of the interconnect 400 in Figure 6A, and the overlap of seals 424 and 434.

[0053] Referring to Figures 4A, 4B, 6A, and 6B, when assembled into a fuel cell stack, the fuel cell 310 is positioned between interconnects 400 such that it faces the airflow range 420 and fuel flow range 430 of each interconnect 400. The riser seal 424 may contact the first opposing air-side surface of the fuel cell 310, and the periphery seal 434 may contact the second opposing fuel-side surface of the fuel cell 310. Thus, portions of the seals 424, 434 may be thicker on the outside of the periphery of the fuel cell 310 than on the inside (e.g., overlapping with the fuel cell 310). Portions of the periphery seal 434 adjacent to the fuel inlet 402 and fuel outlet 404 may overlap with the corresponding portions of the riser seal 424. Furthermore, portions of the fuel cell 310 can be positioned between the overlapping portions of the seals 424, 434, for example, at the corners of the fuel cell 310. Therefore, the total thickness of the overlapping portion of the fuel cell 310 and the seals 424 and 434 may be greater than the thickness of the overlapping portion of the seals 424 and 434.

[0054] To accommodate this change in thickness and / or to properly seal the fuel cell stack, the thickness of the portion of the interconnect 400 that is positioned outside the fuel cell 310 may be increased by a thickness equal to the sintered thickness of the fuel cell 310 (for example, the sintered thickness of electrodes 314, 316, electrolyte 312, and nickel mesh 318, as shown in Figure 3D).

[0055] Since the seals 424 and 434 overlap the corners of the fuel cell 310, a gap G may be formed between the corners under each of the riser seals 424 (for example, under the electrolyte 312). When the stack 300 is compressed, a downward force is transmitted through the interconnect 400 and the riser seals 424 to the unsupported edge of the fuel cell 310 adjacent to the gap G, and this downward force may produce a lever arm effect due to the adjacent gap G under the riser seals 424.

[0056] Conventionally, the electrodes and conductive layers of a fuel cell are placed only in the operating region of the fuel cell (e.g., the part of the fuel cell exposed to fuel and air). In other words, seals may be placed in the electrolyte portion that is not covered by electrodes and / or conductive layers.

[0057] According to various embodiments of this disclosure, a conductive layer 318 (e.g., nickel mesh) may be extended into the gap G to support the edge of the fuel cell 310. In some embodiments, the anode 314 and / or cathode 316 may be extended to cover the electrolyte beneath the riser seal 424, in combination with the extension of the conductive layer 318 into the gap G. In other embodiments, one or more electrolyte reinforcing layers 325 may be formed on one or both sides of the electrolyte 312 beneath the riser seal 424, and may be formed from a ceramic material, such as alumina and / or zirconia. The electrolyte reinforcing layers 325 may have substantially the same thickness as the anode 314 and / or cathode 316 and may further support the edge of the fuel cell 310 together with the conductive layer 318. In some embodiments, the electrolyte reinforcing layer 325 may be located on the cathode side of the fuel cell 310 and may be formed from a chromium gettering material, such as manganese cobalt spinel oxide. Thus, the electrolyte reinforcement layer 325 may be configured to remove chromium from the air supplied to the fuel cell 310.

[0058] During such high-temperature operations, if excessive pressure is applied to the riser seal 424, the riser seal 424 may be pushed out from the riser seal surface 422 beyond the edge of the fuel cell 310 into the fuel passage 418 of the fuel inlet 402, fuel outlet 404 and / or adjacent interconnect 400. In severe cases, this can increase the pressure drop in the fuel flow, cause uneven distribution of fuel from cell to cell, and even render the stack 300 unusable.

[0059] Therefore, in some embodiments, the riser seal surface 422 may be recessed relative to the top of the air-side rib 406. In other words, when the air-side of the interconnect 400 is viewed from above, the riser seal region may be lower than the top of the rib 406. For example, the riser seal surface 422 may be recessed by about 30 to 50 μm relative to a plane extending across the top of the rib 406. Thus, when a fuel cell 310, which may have a thickness in the range of about 20 to 30 μm, contacts the air-side of the interconnect 400, the rib 406 contacts the fuel cell 310, and a space or recess may be formed between the fuel cell 310 and each riser seal surface 422.

[0060] Once the fuel cell stack 300 is assembled, the recessed riser seal surface 422 provides additional space for accommodating the riser seal 424. As a result, the force applied to the riser seal 424 can be reduced, thereby allowing the riser seal 424 to remain within the riser seal surface 422 during high-temperature operations, such as sintering.

[0061] In some embodiments, one or more components of the fuel cell 310 may be made thicker, for example, by contact firing, to form a thicker contact-fired fuel cell layer. This increase in thickness can also reduce the force applied to the riser seal 424. In some embodiments, the thicker fuel cell 310 can be used with a recessed riser seal surface 422.

[0062] In various embodiments, chamfers 407 may be added to the air-side fuel inlet 402 and / or fuel outlet 404 of the interconnect 400. The chamfers 407 may function to capture any sealant that escapes from the riser seal surface 422. Additionally, chamfers 409 may be added to other edges of the interconnect 400, such as the edges of the fuel-side inlet 402 and outlet 404 of the interconnect 400, and / or the peripheral edge of the interconnect 400. The chamfers can provide advantages during the formation of the interconnect 400, such as preventing chipping during the powder metallurgy operation used to form the interconnect 400.

[0063] According to various embodiments, the seals 424,434 can be formed from a glass-ceramic material that is stable at high temperatures and act as a binder between the interconnect 400 and the fuel cell 310 within the stack 300, providing airtightness (to achieve high fuel utilization rates and to prevent little to no fuel leakage). The seals 424,434 are also preferably chemically stable over long periods at elevated stack operating temperatures and inert to the electrolyte 312, interconnect 400, and gases such as fuel and air used in the stack 300. Finally, the seals 424,434 should also be electrically insulating and should have dielectric integrity to prevent parasitic (short-circuit) currents.

[0064] It should be noted that an additional contact layer may exist between the interconnect 400 and the electrodes of the fuel cell 310. For example, an anode contact layer 315, such as a nickel mesh, may exist within the stack 300 between the anode 314 and the adjacent interconnect 400, as shown in Figure 7.

[0065] In one embodiment shown in Figure 7, stress arising from a temperature gradient within the stack 300 is compensated by seals that provide a certain amount of "flexibility." As used herein, "flexibility" means that the viscosity is sufficiently low so that under stress such as shear stress, the seals 424, 434 can plastically deform to relieve stress within the stack 300 without causing the fuel cell 310 to break, delaminate, or crack. This flexibility is more important in the case of large (i.e., large length and width) stacks where stress is caused by a large temperature gradient.

[0066] For example, in the case of an interconnect 400 and fuel cell 310 with a width and length of 100 mm or more, e.g., 100-200 mm, a typical temperature gradient of over 80°C can occur from corner to corner across a single fuel cell 310. Such a temperature gradient results in significant inherent stress in the fuel cell 310. Furthermore, if the coefficients of thermal expansion between the fuel cell 310 and the interconnect 400 are mismatched by 1-5%, e.g., 2-3%, the stress increases further. For example, the coefficient of thermal expansion (CTE) of the interconnect 400 may be 1-5%, e.g., 2-3%, higher than the CTE of the fuel cell 310. Such a mismatch in CTE can prevent or reduce buckling (i.e., in-plane compression) of the fuel cell during thermal or current cycling. However, if the CTEs of the fuel cell and interconnect are intentionally mismatched, the above stress increases by more than 100% compared to when the CTEs of the fuel cell and interconnect are equal. Furthermore, the mismatched CTE also causes the seals 424,434 to transmit vertically oriented stress from the interconnect 400 to the fuel cell 310, in addition to subjecting the seals to shear (i.e., lateral shear stress indicated by the horizontal arrow in Figure 7).

[0067] In one embodiment, the sealing material composition is manufactured to be more flexible, and it can then be deformed under shear. Such deformation will reduce the shear component of stress from the CTE mismatch between the fuel cell 310 and the interconnect 400. Thus, the sealing material of seals 424,434 has a relatively low viscosity at the SOFC operating temperature of 700-900°C while maintaining chemical stability, compatibility with existing materials, integrity in terms of dielectric properties, wettability, and self-healing properties. The relatively low viscosity allows the seal to undergo plastic deformation, reducing stress on the fuel cell 310. In one embodiment, the sealing material may have a viscosity of less than 7.5 dPa·s at 850°C, for example, 5.75-7 dPa·s (i.e., log h value).

[0068] Table I below shows the weight on an oxide basis. 40-60%, for example 45-55%, for example about 50% SiO2, 25-28%, for example 25.5-27%, for example about 26% BaO, 10-20%, for example 11-15%, for example about 13% B2O3, 8-12%, for example 9-11%, for example about 10% Al2O3, 0-2%, for example 0.1-1%, for example about 0.5% ZrO2, 0-1%, for example 0.1-0.75%, for example approximately 0.5% Y2O3, 0-1%, for example 0.1-0.75%, for example about 0.1% CaO and 0-1%, for example 0.1-0.75%, for example approximately 0.5% MgO A sealing material composition containing the following is described.

[0069] The sealing material composition may not contain other oxides, or may contain less than 0.1% by weight of other oxides, such as sodium, potassium, lanthanum, or phosphorus oxides. Alternative sealing material compositions may contain additional components, such as more than 0.1% by weight of other oxides.

[0070] In one embodiment, the sealing material includes a glass-ceramic material obtained after sintering glass powder in stack 300 to partially crystallize the glass powder and form seals 424, 434. While not wishing to be bound by any particular theory, after sintering, the glass-ceramic material is thought to include an amorphous glass matrix phase containing boron oxide and silica, and one or more crystalline phases embedded in the matrix. The crystalline phases may include a cristobalite phase (e.g., a crystalline silica phase) and a barium silicate phase. These may be the only crystalline phases, or additional crystalline phases may be present.

[0071] A flexible glass ceramic sealing material can be formed by mixing the above oxide powders in the above weight ratio, melting the mixed powder, solidifying the molten material, and then pulverizing the solidified molten material to form the sealing material powder.

[0072] Alternatively, flexible glass-ceramic sealants can be formed by either mixing a commercially available glass sealant powder having a relatively low barium content (e.g., less than 25% by weight barium oxide content on an oxide basis) with barium oxide powder, or by mixing it with another commercially available glass powder having a higher barium oxide content (e.g., at least % by weight barium oxide content on an oxide basis). For example, a commercially available Schott G018-281 glass powder having a relatively low barium content can be mixed with one or more other powders having a higher barium content to form a mixed powder composition. The mixed powder composition may be provided as a suspension or dispersion (e.g., ink) after the powders are mixed, or the powders may be mixed in a solvent to form an ink in a single step. The mixed powder composition (e.g., ink) is then coated between the interconnect 400 and the fuel cell 310 within the stack 300. The mixed powder composition is then sintered within the stack 300 as described above to form the flexible glass-ceramic seals 424, 434 shown in Figure 7.

[0073] In one embodiment, powders having a higher barium content may include barium oxide powder, commercially available Schott G018-354 glass powder containing at least 45% by weight of barium oxide on an oxide basis, or crystallized glass solder powder containing, by weight % on an oxide basis, 45% to 60% BaO, 25% to 40% SiO2, 5% to 15% B2O3, 0% to less than 2% Al2O3, 2% to 15% MgO and 3% to 15% Y2O3, as described in U.S. Patent No. 8,664,134 ("'134 Patent"), issued on March 4, 2014, which is incorporated in whole by reference herein. For example, 2.5 to 15% by weight, for example 2.5 to 10% by weight, or for example 2.5 to 7.5% by weight of Schott G018-354 glass powder or '134 patent crystallized glass solder powder can be mixed with 85 to 97.5% by weight, for example 90 to 97.5% by weight, or for example 92.5 to 97.5% by weight of Schott G018-281 glass powder to form a mixed powder composition used to form a flexible glass ceramic seal material in a stack.

[0074] In one embodiment, the barium content of the embodiment's sealant is increased compared to commercially available glass fuel cell sealants such as Schott G018-281 sealant. The barium content may be 4–8 wt%, for example, about 5–7 wt%, of the total sealant composition. Increasing the barium content improves the flexibility of the sealant. However, if the barium content is too high, the barium may react with the chromium in the Cr-Fe alloy interconnect (e.g., including a chromium-iron alloy containing 4–6 wt% iron and 94–96 wt% chromium), and / or the seal may become too fluid and lose structural integrity. While we do not wish to be bound by any particular theory, it is thought that barium and / or barium oxide act as a flux that lowers the glass transition temperature of the sealant.

[0075] While we do not wish to be bound by any particular theory, it is thought that mixing powders with lower and higher barium content, and then sintering the mixed powder in a stack, will surprisingly yield glass ceramic seals 424,434 that have the same composition but react less with chromium in the Cr-Fe alloy interconnect 400 than glass ceramic materials formed from molten glass frit. Specifically, it is thought that mixing Schott G018-281 glass powder with a relatively low barium content with Schott G018-354 glass powder or '134 patented crystallized glass solder powder to form a mixed powder composition, coating the components of the stack 300 with the mixed powder composition (e.g., ink), and then sintering the mixed powder composition in the stack 300 will surprisingly yield glass ceramic seals 424,434 of embodiments that have relatively high flexibility and relatively low reactivity with chromium in the Cr-Fe alloy interconnect 400. In contrast, when Schott G018-281 glass powder is melted together with Schott G018-354 glass powder, then solidified into a solid solution, pulverized into a powder, supplied to an ink to form a frit, coated onto a stack, and then sintered within the stack, the resulting seal is thought to have lower flexibility and higher reactivity with chromium in the Cr-Fe alloy interconnect 400 than the glass ceramic seals 424,434 of the embodiments formed by mixing the powders.

[0076] Flexible glass-ceramic sealing material can be used to form seals 424,434 within large stacks to prevent or reduce thermally induced stress cracks within fuel cells (e.g., SOFCs) 310. Increasing the flexibility of the seals solves long-term reliability problems such as stress cracks within fuel cells that occur over time. The flexible sealing material can also provide faster current ramping and / or thermal cycling of the stack 300, accelerating the deployment of the stack 300 and reducing downtime, and can also provide the ability to track current in real time (i.e., load following).

[0077] While interconnects, endplates, and electrolytes for solid oxide fuel cells have been described above in various embodiments, embodiments may include interconnects or endplates for any other type of fuel cell, such as electrolytes, interconnects, or endplates for molten carbonate, phosphoric acid, or PEM fuel cells, or any other metallic object, metal alloy object, compressed metal powder object, or ceramic object of any other shape not related to the fuel cell system.

[0078] The description of the method described herein is provided merely as an illustrative example and is not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As those skilled in the art will understand, the order of the steps of the embodiments described herein can be performed in any order. Words such as “then,” “next,” and “next” are not necessarily intended to limit the order of the steps and may be used to guide the reader throughout the description of the method. Furthermore, any reference to an element of a claim in the singular form using, for example, the articles “a,” “an,” or “the” should not be construed as limiting the element to the singular form. Moreover, any step or component of any embodiment described herein can be used in any other embodiment.

[0079] The above description of the disclosed embodiments is provided to enable those skilled in the art to manufacture or use the invention. Various variations of these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the scope of the invention. Accordingly, the invention is not intended to be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fuel cell stack, interconnects stacked on top of each other, A solid oxide fuel cell is placed between the interconnects, The solid oxide fuel cell includes a seal disposed between the electrolyte layer and the interconnect, The seal comprises a glass ceramic material, The glass ceramic material is oxide-based by weight, 40-60% SiO ２ , 25-28% BaO, 10-20% B ２ O ３ , 8-12% Al ２ O ３ , 0-2% ZrO ２ , 0-1% Y ２ O ３ , 0-1% CaO and Contains 0-1% MgO, A fuel cell stack comprising the glass ceramic material having a viscosity (log h) of less than 7.5 dPa·s at 850°C.

2. The glass ceramic material is, by weight of oxide base, 45 to 55% SiO ２ , 25.5-27% BaO, 11-15% B ２ O ３ , 9-11% Al ２ O ３ , 0.1–1% ZrO ２ , 0.1-0.75% Y ２ O ３ , 0.1-0.75% CaO and 0.1–0.75% MgO A fuel cell stack according to claim 1, comprising:

3. The glass ceramic material is, by weight, oxide-based 50% SiO ２ , 26% BaO, 13% B ２ O ３ , 10% Al ２ O ３ , 0.5% ZrO ２ , 0.5% Y ２ O ３ , 0.1% CaO and 0.5% MgO A fuel cell stack according to claim 2, comprising:

4. The fuel cell stack according to claim 1, wherein the glass ceramic material comprises at least one crystalline phase dispersed in an amorphous glass matrix phase.

5. The fuel cell stack according to claim 4, wherein the at least one crystalline phase comprises cristobalite crystals and barium silicate crystals.

6. The fuel cell stack according to claim 5, wherein the amorphous glass matrix phase comprises boron oxide and silicon oxide.

7. The fuel cell stack according to claim 1, wherein the glass ceramic material has a viscosity of 5.75 to 7 dPa·s at 850°C.

8. The fuel cell stack according to claim 1, wherein the thermal expansion coefficient of the interconnect differs by 1 to 5% from that of the electrolyte layer of the solid oxide fuel cell.

9. The interconnect comprises a chromium-iron alloy containing 4-6% by weight of iron and 94-96% by weight of chromium. The thermal expansion coefficient of the interconnect is 2-3% greater than the thermal expansion coefficient of the electrolyte layer of the solid oxide fuel cell. The fuel cell stack according to claim 8.

10. A step of mixing 85% to 97.5% by weight of a first glass powder having an oxide-based barium oxide content of less than 25% by weight with 2.5% to 15% by weight of a second glass powder having an oxide-based barium oxide content of at least 45% by weight, A step of forming a fuel cell stack by coating the interconnect and the solid oxide fuel cell with the composition containing the mixed first and second glass powders, The process involves sintering the composition within the fuel cell stack at an elevated temperature to form a seal between the interconnect and the electrolyte layer of the solid oxide fuel cell. Includes, The seal comprises a glass ceramic material having a viscosity (log h) of less than 7.5 dPa·s at 850°C. The glass ceramic material is oxide-based by weight, 40-60% SiO₂, 25-28% BaO, 10-20% B2O3, 8-12% Al₂O₃, 0-2% ZrO₂, 0-1% Y2O3, 0-1% CaO and 0-1% MgO A method for manufacturing a fuel cell stack, including [the specified component].

11. The second glass powder is composed of 45% to 60% BaO and 25% to 40% SiO by weight on an oxide basis. ２ , 5% to 15% B ２ O ３ , 0-2% less Al ２ O ３ , 2% to 15% MgO and 3% to 15% Y ２ O ３ The method according to claim 10, including the method described in claim 10.

12. The glass ceramic material comprises cristobalite crystals and barium silicate crystals dispersed in an amorphous glass matrix phase containing boron oxide and silicon oxide. The method according to claim 10.

13. The method according to claim 10, wherein the thermal expansion coefficient of the interconnect differs from that of the thermal expansion coefficient of the electrolyte layer of the solid oxide fuel cell by 1 to 5%.

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