Method and apparatus for preventing thermally induced stress cracking in large footprint solid oxide fuel cell columns

Abstract

To provide a method of manufacturing an interconnect for an electrochemical battery stack, an interconnect for an electrochemical battery stack, and an electrochemical battery stack.SOLUTION: A method of manufacturing an interconnect includes the following steps of: providing an interconnect; and flattening creep of the interconnect before the interconnect is arranged in an electrochemical battery stack.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates generally to fuel cell stacks and specifically to fuel cell interconnects. [Background technology]

[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 can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. The fuel cell operates at typical temperatures between 750°C and 950°C and allows the transfer of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ions combine with free hydrogen or hydrogen in hydrocarbon molecules to produce water vapor and / or 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 an electrical circuit completed between the anode and cathode, resulting in electrical current flowing through the circuit.

[0003] Fuel cell stacks can have internal or external fuel and air manifolds. In an internal manifold stack, fuel and air are distributed to each cell using risers contained within the stack. In other words, gas flows through openings or holes in the support layers of each fuel cell, such as the electrolyte layer, and through the gas flow separators of each cell. In an external manifold stack, the stack is open on the fuel and air inlet and outlet sides, and the fuel and air are introduced and withdrawn independently of the stack hardware. For example, the inlet and outlet fuel and air flow through separate passages between the stack and the manifold housing in which the stack is located.

[0004] Fuel cell stacks are often constructed from multiple cells in the form of planar elements, tubes, or other geometries. Fuel and air must be supplied to electrochemically active surfaces, which can be large. One of the components of a fuel cell stack is a so-called gas flow separator (called a gas flow separator plate in a planar stack) that separates the individual cells in the stack. The gas flow separator plate separates the fuel, e.g., hydrogen or hydrocarbon fuel, flowing to the anode (i.e., anode) of one cell in the stack from the oxidant, e.g., air, flowing to the cathode (i.e., cathode) of an adjacent cell in the stack. Often, the gas flow separator plate also serves as an interconnect, electrically connecting the anode of one cell to the cathode of an adjacent cell. In this case, the gas flow separator plate, which functions as an interconnect, is made of or includes an electrically conductive material. Summary of the Invention

[0005] According to one embodiment, a method of manufacturing an interconnect for an electrochemical cell stack includes providing an interconnect and creep-planarizing the interconnect before placing the interconnect in the electrochemical cell stack.

[0006] According to another embodiment, an interconnect for an electrochemical cell stack includes a fuel inlet and a fuel outlet extending through the interconnect adjacent opposing first and second peripheries of the interconnect, an air side including an air flow area including air side ribs and air passages extending in a first direction from a third periphery of the interconnect to a fourth periphery of the interconnect opposite the third periphery, and a riser sealing surface disposed at the first and second peripheries of the interconnect and surrounding the fuel inlet and fuel outlet. a fuel side opposite the first direction, the fuel side including a fuel flow area including fuel side ribs and fuel passages extending between the fuel inlet and the fuel outlet in a second direction substantially perpendicular to the first direction; and a coating including at least one of lanthanum strontium manganite (LSM) or (Mn,Co)O spinel (MCO) disposed on the air-side ribs but not on the riser seal face, the riser seal face being recessed relative to a plane extending across an upper surface of the coating at the tips of the air-side ribs. [Brief explanation of the drawings]

[0007] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and, together with the general description above and the detailed description below, serve to explain features of the disclosure. [Figure 1A] FIG. 1 is a perspective view of a conventional fuel cell column. [Figure 1B] FIG. 1B is a perspective view of one counterflow solid oxide fuel cell stack included in the column of FIG. 1A. [Figure 1C] FIG. 1C is a cross-sectional side view of a portion of the stack of FIG. 1B. [Figure 2A] FIG. 1C is a top view of the air side of a conventional interconnect of the stack of FIG. 1B. [Figure 2B] FIG. 1C is a top view of the fuel side of a conventional interconnect for the stack of FIG. 1B. [Figure 3A] 1 is a perspective view of a fuel cell stack according to various embodiments. [Figure 3B] 3B is an exploded perspective view of a portion of the stack of FIG. 3A according to various embodiments. [Figure 3C] FIG. 3B is a top view of the fuel side of an interconnect included in the stack of FIG. 3A according to various embodiments. [Figure 3D] 3B is a schematic diagram of a fuel cell included in the stack of FIG. 3A, according to various embodiments. [Figure 4A] FIG. 3D is a plan view of the air side of the cross-flow interconnect of FIG. 3C, according to various embodiments. [Figure 4B] FIG. 3D is a plan view of the fuel side of the cross-flow interconnect of FIG. 3C, according to various embodiments. [Figure 5] 1A and 1B are plan views illustrating the air side of an interconnect without a riser seal according to various embodiments. [Figure 6A] 4C is a perspective cross-sectional view of the two interconnects of FIGS. 4A and 4B and a fuel cell as incorporated into the fuel cell stack of FIG. 3A, according to various embodiments. [Figure 6B] 6B is a top view illustrating the overlap of the fuel cell and the seal on the fuel side of the interconnect of FIG. 6A according to various embodiments. [Figure 7] 1A and 1B are plan views of a portion of a SOFC stack including an SOFC (shown in perspective by dashed lines) overlying an interconnect, according to various embodiments. [Figure 8A] 8 is a vertical cross-sectional view of a portion of the interconnect of FIG. 7 according to various embodiments. [Figure 8B] FIG. 8B is a vertical cross-sectional view of a portion of the interconnect of FIG. 8A after a coating has been applied to the air-side ribs according to various embodiments. [Figure 8C] 8B is a vertical cross-sectional view of a portion of the interconnect of FIG. 7 having a different elevation cross-section than that of FIG. 8A in accordance with various embodiments. [Figure 8D] FIG. 8D is a vertical cross-sectional view of a portion of the interconnect of FIG. 8C after a coating has been applied to the air-side ribs, according to various embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0008] Various embodiments will be described in detail with reference to the accompanying drawings. The drawings, which are not necessarily to scale, are intended to illustrate various features of the present disclosure. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References to specific examples and embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure or the claims.

[0009] Ranges may be expressed herein as from "about" one particular value and / or to "about" another particular value. When such a range is expressed, examples include from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, by immediately using "about" or "substantially," it will be understood that the particular value constitutes another embodiment. In some embodiments, a value of "about X" may include + / - 1% of the value of X. Additionally, it is understood that the endpoints of each range are significant both in relation to the other endpoint, and independently of the other endpoint.

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

[0011] 1A and 1B, a 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 side baffle 38 may be coupled to the compression assembly 40 and to a stack component (not shown) disposed below via a ceramic connector 39. The fuel inlet conduit 32 is fluidly connected to the ASPs 36 and configured to provide a fuel supply to each ASP 36, and the anode exhaust conduit 34 is fluidly connected to the ASPs 36 and configured to receive an anode fuel exhaust from each ASP 36.

[0012] The ASP 36 is disposed between the stacks 20 and is configured to provide a fuel supply including a hydrocarbon fuel to the stacks 20 and to receive an anode fuel exhaust from the stacks 20. For example, the ASP 36 may be fluidly connected to an internal fuel riser passage 22 formed within the stacks 20, as described below.

[0013] 1C, stack 20 includes multiple fuel cells 1 separated by interconnects 10, 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 in the stack 20. In particular, an 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. FIG. 1C shows the lower fuel cell 1 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 interconnects 10 can operate as gas-fuel separators that separate fuel, e.g., a hydrocarbon fuel, flowing to the anode (i.e., anode 7) of one cell in the stack from oxidant, e.g., air, flowing to the cathode (i.e., cathode 3) of an adjacent cell in the stack. One end of the stack 20 may be provided with an air end plate or a fuel end plate (not shown) for supplying air or fuel, respectively, to the end electrodes.

[0016] Figure 2A is a plan view of the air side of a conventional interconnect 10, and Figure 2B is a plan view of the fuel side of the interconnect 10. With reference to Figures 1C and 2A, the air side includes air passages 8B. Air flows through the air passages 8B to the cathode electrodes 3 of adjacent fuel cells 1. In particular, air can flow across the interconnect 10 in a first direction A, as indicated by the arrows.

[0017] A ring seal 23 may surround the fuel holes 22A of the interconnect 10 to prevent fuel from contacting the cathode electrode. A band-shaped perimeter seal 24 is disposed around the perimeter of the air side of the interconnect 10. The seals 23, 24 may be formed from a glass material. The perimeter may be a raised plateau that does not include ribs or passages. The surface of the perimeter region may be flush with the tops of the ribs 12.

[0018] 1C and 2B, the fuel side of the interconnect 10 may include a fuel passage 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, through the fuel passage 8A, and to the anode 7 of the adjacent fuel cell 1. Excess fuel can 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 arrows. The second direction B may be perpendicular to the first direction A (see FIG. 2A).

[0019] A frame-like seal 26 is disposed on the fuel-side peripheral region of the interconnect 10. The peripheral region may be a raised plateau that does not include ribs or passages. The surface of the peripheral region may be flush with the tops of the ribs 12.

[0020] Thus, conventional counterflow fuel cell columns such as those shown in Figures 1A, 1B, 1C, 2A, and 2B may include complex fuel distribution systems (fuel rails and anode splitter plates). Additionally, the use of internal fuel risers may require holes in the fuel cells and corresponding seals, thereby reducing the active area of ​​the fuel cells 1 and potentially causing cracks in the ceramic electrolyte of the fuel cells 1.

[0021] The fuel manifold 28 may occupy a relatively large area of ​​the interconnect 10, which may reduce the contact area between the interconnect 10 and adjacent fuel cells by approximately 10%. Additionally, because the fuel manifold 28 is relatively deep, it represents a relatively thin region of the interconnect 10. Because the interconnect 10 is typically formed by a powder metallurgy compaction process, the density of the fuel manifold region may approach the theoretical density limit of the interconnect material. Therefore, the stroke length of the compaction press used in the compaction process is limited because the dense fuel manifold region cannot be further compacted. As a result, the compaction stroke limit may limit the density achieved in other locations of the interconnect 10 to a lower level. The resulting density variations may lead to localized variations, which may reduce the amount of contact between the interconnect 10 and the fuel cells 1 and reduce stack yield and / or performance.

[0022] Another important consideration in the design of fuel cell systems is the area of ​​operational efficiency. Maximizing fuel utilization is a key factor in achieving operational efficiency. 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 can be avoiding fuel starvation in the active area of ​​the fuel cell by properly distributing the fuel across the active area. Uneven fuel distribution, such that some flow field passages do not receive enough fuel to support the electrochemical reactions occurring in that passage's area, can result in fuel starvation in the adjacent fuel cell region. To achieve more uniform fuel distribution, conventional interconnect designs include variations in passage depth across the entire flow field. This not only introduces complexity into the manufacturing process but can also require complex metrology to accurately measure these dimensions. The distribution of fuel through fuel holes and distribution manifolds can constrain various passage geometries.

[0023] One possible solution to this complex geometry and fuel manifolds is to have wider fuel openings to ensure more uniform fuel distribution throughout the fuel flow range. Because the formation of fuel manifolds contributes to density variations, eliminating the fuel manifolds should allow for more uniform density and permeability in the interconnect. Therefore, there is a need for an improved interconnect that provides uniform contact with the fuel cell while distributing fuel uniformly to the fuel cell without the use of traditional fuel manifolds.

[0024] Due to the overall constraints on scaling the size of the hot box of a fuel cell system, there is also a need for improved interconnects designed to maximize fuel utilization and fuel cell active area without increasing the hot box footprint.

[0025] FIG. 3A is a perspective view of a fuel cell stack 300 according to various embodiments, FIG. 3B is an exploded perspective view of a portion of the stack 300 of FIG. 3A, FIG. 3C is a top view of the fuel side of an interconnect 400 included in the stack 300, and FIG. 3D is a schematic diagram of a fuel cell included in the stack 300.

[0026] 3A-3D, a fuel cell stack 300, which does not have an ASP and therefore may also be referred to as a fuel cell column, includes multiple fuel cells 310 separated by interconnects 400, which may also be referred to as gas flow separator plates or bipolar plates. 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] The interconnect 400 is formed from a conductive metallic material. For example, the interconnect 400 may include a chromium alloy, such as a Cr—Fe alloy. The interconnect 400 is typically fabricated using powder metallurgy techniques, including pressing and sintering a Cr—Fe powder, which may be a mixture of Cr and Fe powders or a Cr—Fe alloy powder, to form a Cr—Fe interconnect of a desired size and shape (e.g., a “net shape” or “near net shape” process). A typical chromium alloy interconnect 400 includes greater than about 90% chromium by weight, such as about 94-96% (e.g., 95%) chromium by weight. The interconnect 400 may also include less than about 10% iron, such as about 4-6% (e.g., 5%) iron by weight, less than about 2% by weight, such as about 0-1% by weight, of other materials, such as yttrium or yttria, and residual or unavoidable impurities. In another embodiment, the interconnect 400 may include 3-3.9 weight percent, e.g., 3-3.7 weight percent, iron, such as 3.2-3.5 weight percent iron and 96.1-97 weight percent chromium, e.g., 96.5-96.8 weight percent chromium, alloyed with residual or unavoidable impurities, which may provide an improved CTE compatible with larger area SOFCs.

[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 can be printed on the electrolyte 312. In other embodiments, a conductive layer 318, such as a nickel mesh, may be disposed between the anode 314 and the adjacent interconnect 400. The fuel cell 310 does not include through-holes, such as the fuel holes of conventional fuel cells. Thus, the fuel cell 310 avoids cracks that can occur due to the presence of such through-holes.

[0029] The top and bottom interconnects 400 of the stack 300 may be differently configured air-side or fuel-side end plates, each with features for providing air or fuel to the adjacent end fuel cells 310. As used herein, "interconnect" can refer to either an interconnect disposed between two fuel cells 310 or an end plate disposed at the end of the stack and directly adjacent to only one fuel cell 310. Because the stack 300 does not include an ASP and its associated end plate, the stack 300 may include only two end plates. As a result, the dimensional variations in the stack associated with the use of intra-column ASP can be avoided.

[0030] The stack 300 may include a side baffle 302, a fuel plenum 350, and a compression assembly 306. The side baffles 302 may be formed of a ceramic material and may be positioned on opposite sides of the fuel cell stack 300, which includes stacked fuel cells 310 and interconnects 400. The side baffles 302 may connect the fuel plenum 350 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, each covering at least a portion of 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 completely covers the fuel outlet riser side of the stack and partially covers adjacent portions of the front and back sides of the stack. The remaining uncovered portions of the top and back sides of the stack allow air to flow through the stack 300. The curved baffle plate improves control of airflow through the stack compared to a conventional baffle plate 38 that covers only one side of the stack. A fuel plenum 350 may be disposed below the stack 300 and may be configured to provide a hydrogen-containing fuel supply to the stack 300 and may receive an anode fuel exhaust from the stack 300. The fuel plenum 350 may be connected to a fuel inlet and outlet conduit 320 disposed below the fuel plenum 350.

[0031] Each interconnect 400 electrically connects adjacent fuel cells 310 in the stack 300. In particular, the 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 FIG. 3C , each interconnect 400 can be configured to allow air to flow in a first direction A to provide air to the cathode of the adjacent fuel cell 310. Each interconnect 400 can also be configured to allow fuel to flow in a second direction F to provide fuel to the anode of the adjacent fuel cell 310. The directions A and F can be perpendicular or substantially perpendicular to each other. Thus, the interconnect 400 can be referred to as a cross-flow interconnect.

[0032] The interconnect 400 may include fuel holes extending therethrough and configured for fuel distribution. For example, the fuel holes may include one or more fuel inlets 402 and one or more fuel (e.g., anode exhaust) outlets 404, which may also be referred to as anode exhaust outlets 404. The fuel inlets 402 and fuel outlets 404 may be located outside the periphery of the fuel cell 310. Thus, the fuel cell 310 may be formed without corresponding through-holes for fuel flow. The combined length of the fuel inlets 402 and / or the combined length of the fuel outlets 404 may be at least 75% of the corresponding length of the interconnect 400, e.g., the length in direction A.

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

[0034] The fuel inlets 402 of adjacent interconnects 400 may be aligned within the stack 300 to form one or more fuel inlet risers 403. The fuel outlets 404 of adjacent interconnects 400 may be aligned within the stack 300 to form one or more fuel outlet risers 405. The fuel inlet risers 403 may be configured to distribute fuel received from the fuel plenum 350 to the fuel cells 310. The fuel outlet risers 405 may be configured to provide anode exhaust received from the fuel cells 310 to the fuel plenum 350.

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

[0036] In various embodiments, stack 300 may include at least 30, at least 40, at least 50, or at least 60 fuel cells, which may be provided with fuel using only fuel risers 403, 405. In other words, compared to conventional fuel cell systems, the crossflow configuration may provide fuel to a large number of fuel cells without the need for external fuel manifolds, such as external conduits 32, 34, of the ASP or stack shown in FIG.

[0037] Each interconnect 400 may be made of or include a conductive material, such as a metal alloy (e.g., a chromium-iron alloy) having a thermal expansion coefficient similar to that of the cell's solid oxide electrolyte (e.g., a difference of 0-10%). For example, the interconnect 400 may include a metal (e.g., a chromium-iron alloy, such as a chromium-iron alloy, with 4-6 wt. % iron, optionally up to 1 wt. % yttrium, and the balance chromium alloy) and may electrically connect the anode side, or fuel side, of a given fuel cell 310 with the cathode side, or air side, of an adjacent fuel cell 310. In one embodiment, the interconnect 400 may include an alloy of 4-6 wt. % iron, optionally up to 1 wt. % yttrium, the remainder chromium, and residual or unavoidable impurities. In another embodiment, the interconnect 400 may contain 3 to 3.9 weight percent, e.g., 3 to 3.7 weight percent, iron, e.g., 3.2 to 3.5 weight percent iron, 96.1 to 97 weight percent chromium, e.g., 96.5 to 96.8 weight percent chromium, and an alloy of residual or unavoidable impurities. This alloy can provide an improved CTE compatible with larger-area SOFCs. A conductive contact layer, e.g., 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] Surfaces of the interconnect 400 that are exposed to an oxidizing environment (e.g., air) during operation, such as the cathode-facing side of the interconnect 400, may be coated with a protective coating layer to reduce the growth rate of the interconnect's chromium oxide surface layer and inhibit the evaporation of chromium vapor species that would otherwise degrade the fuel cell cathode. Typically, the coating layer, which may include a perovskite, e.g., LSM, may be formed using a thermal spray coating or dip coating process. Alternatively, other metal oxide coatings, such as spinels, e.g., (Mn,Co)3O4 spinel (MCO), may be used instead of or in addition to LSM. Mn 2-x Co 1+x Any spinel having a composition written as O4 (0≦x≦1), or z(Mn3O4)+(1−z)(Co3O4), where (1 / 3≦z≦2 / 3), or written as (Mn,Co)3O4, can be used. In other embodiments, a mixed layer of LSM and MCO or a stack of LSM and MCO layers can be used as the coating layer.

[0039] 4A and 4B are plan views illustrating the air side and fuel side, respectively, of a cross-flow interconnect 400 according to various embodiments. Referring to FIG. 4A, the air side of the interconnect 400 may include ribs 406 configured to at least partially define air passages 408 configured to provide air to the cathodes of the attached fuel cells 310. The air side of the interconnect 400 may be divided into an air flow area 420 including the air passages 408 and riser sealing surfaces 422 disposed on two opposite sides of the air flow area 420. One of the riser sealing surfaces 422 may surround the fuel inlet 402, and the other riser sealing surface 422 may surround the fuel outlet 404. The air passages 408 and ribs 406 may extend completely across the air side of the interconnect 400 such that the air passages 408 and ribs 406 terminate at opposite peripheries of the interconnect 400. In other words, when assembled into stack 300, opposite ends of air passages 408 and ribs 406 are positioned on opposite exterior (e.g., top and bottom) surfaces of the stack, allowing blown air to flow through the stack. Thus, the stack may be provided with an external air manifold.

[0040] Riser seals 424 may be disposed on the riser seal surface 422. For example, one riser seal 424 may surround the fuel inlet 402 and one riser seal 424 may surround the fuel outlet 404. The riser seals 424 may prevent fuel and / or anode exhaust from entering the air flow area 420 and contacting the cathodes of the fuel cells 310. The riser seals 424 may also function to prevent fuel from leaking out of the fuel cell stack 100 (see FIG. 3A).

[0041] 4B , the fuel side of the interconnect 400 may include ribs 416 that at least partially define fuel passages 418 configured to provide fuel to the anodes of the mounted fuel cells 310. The fuel side of the interconnect 400 may be divided into a fuel flow area 430 that includes the fuel passages 418 and a peripheral sealing surface 432 that surrounds the fuel flow area 430 and the fuel inlets 402 and fuel outlets 404. The ribs 416 and fuel passages 418 may extend in a direction that is orthogonal or substantially orthogonal to the direction in which the air-side passages 408 and ribs 406 extend.

[0042] A frame-shaped perimeter seal 434 may be disposed on the perimeter sealing surface 432. The perimeter seal 434 may be configured to prevent air from entering the fuel flow area 430 and contacting the anodes of adjacent fuel cells 310. The perimeter seal 434 may also function to prevent fuel from exiting the fuel risers 403, 405 and leaking out of the fuel cell stack 300 (see FIGS. 3A and 3B).

[0043] The seals 424, 434 may include a glass or ceramic seal material. The seal material may have low electrical conductivity. In some embodiments, the seals 424, 434 may be formed by printing one or more layers of the seal material onto the interconnect 400 and then sintering.

[0044] In some embodiments, the seals 424, 434 may be formed of a silicate glass seal material including SiO2, BaO, CaO, Al2O3, K2O, and / or B2O3. For example, the sealant may include SiO in an amount ranging from about 40% to about 60% by weight, e.g., from about 45% to about 55% by weight, BaO in an amount ranging from about 10% to about 35% by weight, e.g., from about 15% to about 30% by weight, CaO in an amount ranging from about 5% to about 20% by weight, e.g., from about 7% to about 16% by weight, AlO in an amount ranging from about 10% to about 20% by weight, e.g., from about 13% to about 15% by weight, and BO in an amount ranging from about 0.25% to about 7% by weight, e.g., from about 0.5% to about 5.5% by weight. In some embodiments, the sealant may additionally include KO in an amount ranging from about 0.5% to about 1.5% by weight, e.g., from about 0.75% to about 1.25% by weight.

[0045] In some embodiments, the seals 424, 434 may be formed of a silicate glass seal material including SiO2, B2O3, Al2O3, CaO, MgO, La2O3, BaO, and / or SrO. For example, the sealing material may include SiO in an amount ranging from about 30 wt% to about 60 wt%, e.g., from about 35 wt% to about 55 wt%, BO in an amount ranging from about 0.5 wt% to about 15 wt%, e.g., from about 1 wt% to about 12 wt%, AlO in an amount ranging from about 0.5 wt% to about 5 wt%, e.g., from about 1 wt% to about 4 wt%, CaO in an amount ranging from about 2 wt% to about 30 wt%, e.g., from about 5 wt% to about 25 wt%, MgO in an amount ranging from about 2 wt% to about 25 wt%, e.g., from about 5 wt% to about 20 wt%, and LaO in an amount ranging from about 2 wt% to about 12 wt%, e.g., from about 5 wt% to about 10 wt%. In some embodiments, the sealant may additionally include BaO in an amount ranging from about 0 wt. % to about 35 wt. %, e.g., from about 0 wt. % to about 30 wt. %, or from about 0.5 wt. % to about 30 wt. %, including about 20 wt. % to about 30 wt. %, and / or SrO in an amount ranging from about 0 wt. % to about 20 wt. %, e.g., from about 0 wt. % to about 15 wt. %, or from about 0.5 wt. % to about 15 wt. %, including about 10 wt. % to about 15 wt. %. In some embodiments, the sealant may additionally include a non-zero amount, e.g., at least 0.5 wt. % of at least one of BaO and / or SrO, e.g., a non-zero amount, e.g., at least 0.5 wt. % of both BaO and SrO.

[0046] 5 is a plan view showing the air side of an interconnect 400 without the riser seal 424 according to various embodiments. In conventional counterflow fuel cell system designs, the fuel cell electrolyte completely covers the interconnect, thereby acting as a dielectric layer between adjacent interconnects. In crossflow designs, the interconnects may extend beyond the perimeter of the fuel cells. This can result in electrical shorts between interconnects if the stack is tilted or if the seals become conductive over time.

[0047] 5, the interconnects 400 may include dielectric layers 440 disposed on the riser seal surfaces 422. For example, as shown in FIG. 5, each dielectric layer 440 may be annular and may cover the entire or substantially the entire corresponding riser seal surface 422. For example, in the embodiment of FIG. 5, the dielectric layers 440 may be D-shaped and may have substantially the same shape as the riser seal 424 disposed thereon, shown in FIG. 4A. In another embodiment (not shown), the dielectric layers 440 may cover only a portion of the corresponding riser seal surface 422. The dielectric layers 440 form an electrically insulating barrier between adjacent interconnects 400, preventing electrical shorts if the corresponding stacks are tilted or if the seals become conductive.

[0048] Dielectric layer 440 may include alumina, zircon (zirconium silicate), silicon carbide, crystallized glass (e.g., quartz or glass-ceramic), or other high-temperature dielectric material. In some embodiments, dielectric layer 440 may include a corrosion barrier material or layer. For example, dielectric layer 440 may include a composite material including corrosion-resistant glass, alumina, zircon, etc. For example, in some embodiments, dielectric layer 440 includes a glass-ceramic layer formed from a substantially glass-barrier precursor layer including at least 90 wt. % glass (e.g., 90-100 wt. % glass, e.g., about 99-100 wt. % amorphous glass and 0-1 wt. % crystalline phase) deposited on the surface of interconnect 400 in SOFC stack 300. In one embodiment, the glass barrier precursor layer, comprising at least 90 wt. % glass, includes, on an oxide weight basis, 45-55 wt. % silica (SiO2), 5-10 wt. % potassium oxide (KO), 2-5 wt. % calcium oxide (CaO), 2-5 wt. % barium oxide (BaO), 0-1 wt. % boron trioxide (BO), 15-25 wt. % alumina (AlO), and 20-30 wt. % zirconia (ZrO).

[0049] In some embodiments, the glass barrier precursor layer comprises at least 90 wt% glass (e.g., 90-100 wt% glass, e.g., about 99-100 wt% amorphous glass and 0-1 wt% crystalline phase). For example, the glass barrier precursor layer may contain, on an oxide weight basis, about 30% to about 60%, e.g., about 35% to about 55%, silica (SiO), about 0.5% to about 15%, e.g., about 1% to about 12%, boron trioxide (BO), about 0.5% to about 5%, e.g., about 1% to about 4%, alumina (AlO), about 2% to about 30%, e.g., about 5% to about 25%, calcium oxide (CaO), about 2% to about 25%, e.g., about 5% to about 20%, magnesium oxide (MgO), about 0% to about 35%, e.g., about 20% to about 30%, barium oxide (BaO), about 0% to about 20%, e.g., about 10% to about 15%, strontium oxide (SrO), and about 2% to about 12%, e.g., about 5% to about 10%, lanthanum oxide (LaO). In some embodiments, the glass barrier precursor may include a non-zero amount, e.g., at least 0.5 wt. %, of at least one of BaO and / or SrO, e.g., a non-zero amount, e.g., at least 0.5 wt. %, of both BaO and SrO.

[0050] In some embodiments, the LSM / MCO coating may be partially or entirely removed in the area around the riser seal 424 on the air side of the interconnect 400 to prevent diffusion of Mn from the LSM / MCO material into the riser seal 424, thereby preventing the riser seal 424 from becoming conductive. In another embodiment, the riser seal 424 may be formed of a crystalline glass or glass-ceramic material that is unreactive with the LSM / MCO coating, such as the borosilicate glass-ceramic compositions described above.

[0051] The dielectric layer 440 can be formed from a separate layer, such as a casting tape or a sintered layer, and can be placed between the interconnects 400 during fuel cell stack assembly. In another embodiment, the dielectric layer 440 can be formed by dispersing the dielectric material in the form of an ink, paste, or slurry and then screen printing, pad printing, or aerosol spraying onto the interconnects 400. In some embodiments, the dielectric layer 440 can be formed by a thermal spray process, such as an air plasma spray (APS) process. For example, the dielectric layer 440 can include alumina deposited by an APS process.

[0052] The dielectric layer 440 may be deposited directly on the interconnect 400. For example, the dielectric layer 440 may be disposed directly on the riser seal surface 422 (i.e., directly on the portion of the interconnect 400 around the fuel inlet 402 and the fuel outlet 404 in the area that would be covered by the riser seal 424 but not by the LSM / MCO coating, except for a small overlap area (e.g., a seam) where the dielectric layer 440 and the LSM / MCO coating overlap, where the riser seal surface 422 faces the air flow area 420 to prevent Cr evaporation from the exposed surface of the interconnect 400). Thus, the LSM / MCO coating is disposed on the surface of the interconnect 400 within the air flow area 420, including the air passages 408 and the ribs 406, but is not disposed on the riser seal surface 422 of the interconnect 400 surrounding the fuel inlet 402 and the fuel outlet 404. The dielectric layer 440 is disposed on the riser seal surface of the interconnect 400 in the areas surrounding the fuel inlet 402 and fuel outlet 404 that are not covered by the LSM / MCO coating, and on the edges of the LSM / MCO coating in the airflow area 420 adjacent the riser seal surface 422. Alternatively, the dielectric layer 440 may be omitted, with no dielectric layer 440 deposited around the fuel riser opening.

[0053] Figure 6A is a perspective cross-sectional view of two interconnects 400 of Figures 4A and 4B and a fuel cell 310 incorporated into the fuel cell stack of Figure 3A, according to various embodiments. Figure 6B is a top view showing the overlap of the fuel cell 310 and seals 424, 434 on the fuel side of the interconnect 400 of Figure 6A.

[0054] 4A, 4B, 6A, and 6B, when assembled into a fuel cell stack, the fuel cells 310 are positioned between the interconnects 400, thereby facing the air flow area 420 and the fuel flow area 430 of each interconnect 400. The riser seals 424 may contact first opposing air sides of the fuel cells 310, and the perimeter seals 434 may contact second opposing fuel sides of the fuel cells 310. As such, portions of the seals 424, 434 may be thicker outside the perimeter of the fuel cells 310 (e.g., overlapping the fuel cells 310) than inside the perimeter of the fuel cells 310. Portions of the perimeter seal 434 adjacent to the fuel inlets 402 and fuel outlets 404 may overlap corresponding portions of the riser seals 424. Furthermore, portions of the fuel cells 310 may be positioned between the overlapping portions of the seals 424, 434, for example, at corners of the fuel cells 310. Thus, the combined thickness of the fuel cell 310 and the seals 424, 434 may be greater than the thickness of the seals 424, 434.

[0055] To account for this thickness difference and / or to properly seal the fuel cell stack, the thickness of the portion of the interconnect 400 located outside the perimeter of the fuel cell 310 may be increased by an amount equal to the sintered thickness of the fuel cell 310 (e.g., the sintered thickness of the electrodes 314, 316, electrolyte 312, and nickel mesh 318 as shown in FIG. 3D).

[0056] Because the seals 424, 434 overlap the corners of the fuel cells 310, gaps G may be formed between the corners and beneath each riser seal 424 (e.g., beneath the electrolyte 312). When the stack 300 is compressed, a downward force may be transmitted through the interconnects 400 and the riser seals 424 to the unsupported edges of the fuel cells 310 adjacent the gaps G, which may create a leverage action based on the gaps G adjacent the underside of the riser seals 424.

[0057] Conventionally, the electrodes and conductive layers of a fuel cell are located only in the active areas of the fuel cell (e.g., where the fuel cell is exposed to fuel and air). In other words, the seal may be located in the portions of the electrolyte that are not covered by the electrodes and / or conductive layers.

[0058] According to various embodiments, a conductive layer 318 (e.g., nickel mesh) may extend into the gap G to support the edges of the fuel cell 310. In some embodiments, the anode 314 and / or cathode 316 may also extend into the gap G in combination with the extension of the conductive layer 318 to cover the electrolyte below the riser seal 424. In another embodiment, one or more electrolyte reinforcement layers 325 may be formed on one or both sides of the electrolyte 312 below the riser seal 424 and may be formed of a ceramic material such as alumina and / or zirconia. The electrolyte reinforcement layer 325 may have substantially the same thickness as the anode 314 and / or cathode 316 and, together with the conductive layer 318, may support the edges of the fuel cell 310. In some embodiments, the electrolyte reinforcement layer 325 may be disposed on the cathode side of the fuel cell 310 and may be formed of a chromium getter material, such as manganese cobalt oxide spinel. In this manner, the electrolyte reinforcement layer 325 may be configured to remove chromium from the air supplied to the fuel cell 310 .

[0059] The fuel cell stack 300 and / or its components may be conditioned and / or sintered. "Sintering" includes the process of heating, melting, and / or reflowing glass or glass-ceramic seal precursors for the formation of seals in the fuel cell stack, which may be performed in air / inert gas at elevated temperatures (e.g., 600-1000°C). "Conditioning" includes the process of reducing metal oxides (e.g., nickel oxide) in the anode electrode to metals (e.g., nickel) in the cermet electrode (e.g., nickel and ceramic materials such as stabilized zirconia or doped ceria) and / or the process of heating the stack 300 during performance characterization / testing, which may be performed at elevated temperatures (e.g., 750-900°C) while fuel is flowing through the stack. Sintering and conditioning of the fuel cell stack 300 may be performed during the same thermal cycle (i.e., without cooling the stack to room temperature between sintering and conditioning).

[0060] If excessive pressure is applied to the riser seal 424 during such high temperature operation, it may extrude from the riser seal face 422 and over the edge of the fuel cell 310 into the fuel inlet 402, fuel outlet 404 and / or fuel passages 418 of the adjacent interconnect 400. In severe cases, this can increase the pressure drop of the fuel flow, resulting in maldistribution of fuel from cell to cell, or even rendering the stack 300 unusable.

[0061] Thus, in some embodiments, the riser seal surfaces 422 may be recessed relative to the tops of the air-side ribs 406. In other words, when the air side of the interconnect 400 is viewed from above, the riser seal area may be lower than the tips of the ribs 406. For example, the riser seal surfaces 422 may be recessed relative to a plane extending across the tips of the ribs 406 by about 30 to about 50 microns. Thus, when a fuel cell 310, which may have a thickness in the range of about 20 to 30 microns, for example, is brought into contact with the air side of the interconnect 400, the ribs 406 may contact the fuel cell 310, and a space or recess may be formed between the fuel cell 310 and each riser seal surface 422.

[0062] When the fuel cell stack 300 is assembled, the recessed riser seal surface 422 provides additional space to accommodate the riser seal 424. As a result, the force applied to the riser seal 424 can be reduced, allowing the riser seal 424 to remain within the riser seal surface 422 during high temperature operations such as sintering. In some embodiments, one or more components of the fuel cell 310 can be manufactured thicker, such as by contact printing, resulting in a thicker contact-printed fuel cell layer. This increased thickness can also reduce the force applied to the riser seal 424. In some embodiments, a thicker fuel cell 310 can be used with a recessed riser seal surface 422.

[0063] In various embodiments, a chamfer 407 may be added to the fuel inlet 402 and / or fuel outlet 404 of the interconnect 400. The chamfer 407 acts to capture any seal material that has escaped from the riser seal face 422. A chamfer 409 may also be added to other edges of the interconnect 400, such as the edges of the inlet 402 and outlet 404 on the fuel side of the interconnect 400 and / or the peripheral edges of the interconnect 400. The chamfer may provide benefits during the formation of the interconnect 400, such as preventing chipping during the powder metallurgy operation used to form the interconnect 400.

[0064] The temperature gradient across the fuel cell 310 during steady state operation is I 2 The temperature difference is a function of operating conditions, including R heating, endothermic steam reforming (primarily at the fuel inlet 402), and convective cooling (e.g., the coolest air contacts the inlet of the air passage 408), as well as the physical characteristics of the stack 300, such as the thermal conductivity and thickness of the interconnect 400. As a result, during steady-state operation, certain portions of the fuel cell 310, such as the fuel inlet / air outlet corners adjacent to the fuel inlet 402 and the outlet of the air passage 408 (hot corners), may become relatively hot. The portions of the seals 424, 434 adjacent to these corners may become porous and / or leaky due to evaporation at these relatively high temperatures, especially if a barium-containing borosilicate glass sealant is used.

[0065] According to various embodiments, the seals 424, 434 may be formed of a high-temperature stable glass material, such as those described above. Alternatively, the thickness of the interconnect 400 may be increased to improve in-plane heat transfer. The increased thickness can reduce the temperature gradient in the interconnect 400, thereby reducing the temperature at the hot corners. The thickness of the interconnect 400 can be increased compared to conventional stacks without increasing the overall thickness of the stack 300, because the stack does not require the anode splitter plate of conventional stacks.

[0066] The inventors have observed that SOFCs often crack during initial operation of the SOFC stack, such as during initial power-on, heating, and / or preconditioning of SOFC stacks with metal alloy interconnects. While not wishing to be bound by any particular theory, the inventors believe that SOFC cracking may include stress-induced cracking resulting from large temperature gradients that may form across the SOFC. Such cracking may result in fuel / air mixing, burnout, excessive heat generation, and possibly cell failure.

[0067] While not wishing to be bound by any particular theory, the inventors believe that bowing (i.e., lack of flatness) and / or relatively high porosity in large-area, powder-pressed interconnects within a SOFC stack may cause or exacerbate stress-induced cracking in SOFCs that contact the interconnects within the stack. Specifically, bowed and / or low-density interconnects are believed to be subjected to greater and faster lateral movement relative to the SOFCs within the stack due to high temperature gradients across the SOFCs during the initial current ramp in the stack. These temperature gradients can create thermal stresses between the SOFC electrolyte and the interconnects due to differences in their coefficients of thermal expansion (CTE). This can create tension in the SOFC (i.e., the SOFC is subjected to tensile stress), which can cause the SOFC to exceed its tensile strength and crack.

[0068] Thus, in one embodiment, the interconnects are subjected to a creep-flattening process, which increases the flatness of the interconnects and reduces interconnect warpage and stress-induced cracking in the SOFCs within the SOFC stack. During creep-flattening, the interconnects are exposed to elevated temperatures (e.g., above room temperature) under an applied load (i.e., physical pressure due to a load (i.e., weight) applied to the interconnects). Creep-flattening improves the flatness of the interconnects and reduces interconnect warpage. Thus, it is believed that creep flattening of the interconnects prior to placement within the SOFCs reduces lateral movement of the interconnects relative to the SOFCs within the stack, thereby reducing stress-induced cracking of the SOFCs within the SOFC stack during initial stack energization, heating, and / or preconditioning (e.g., during reduction of the SOFC metal oxide (e.g., nickel oxide) anode to metal (e.g., nickel) during seal reflow and / or thermal annealing of the SOFCs in a reducing atmosphere).

[0069] 7 is a plan (i.e., top) view of a portion of a SOFC stack including SOFCs 310 (shown in perspective with dashed lines) overlying interconnects 400 as described above. Interconnects 400 in this embodiment may have three fuel inlets 402 and three fuel outlets 404 rather than two each as described above. Alternatively, two or more fuel inlets 402 and fuel outlets 404 may be provided. Air-side ribs 406 of interconnects 400 are shown below the SOFCs 310.

[0070] As discussed above, if the warped interconnect 400 is not properly creep-flattened before being placed in the stack, the warped interconnect 400 can create large tensile stresses that can lead to the development of cracks 702 in the SOFCs 310 during operation of the SOFC stack (e.g., during initial power-up of the stack). Cracks 702 can occur more frequently in SOFCs 310 that are placed lower in the stack and therefore bear the weight of the interconnects 400 above them in the stack.

[0071] In one embodiment, creep planarization may be performed in an oxidizing atmosphere (e.g., air, pure oxygen, water vapor, etc.) that oxidizes the interconnect. While not wishing to be bound by theory, the inventors believe that oxidation reduces the porosity of the interconnect and also reduces bowing of the interconnect by filling the pores with oxides of the metals that make up the interconnect. Furthermore, while not wishing to be bound by theory, it is believed that high-temperature oxidation during creep planarization results in metal oxide formation and associated geometric distortion of the interconnect prior to sealing the interconnect to the SOFCs in the stack. During subsequent high-temperature operation of the SOFC stack, physical distortion of the interconnects in the stack due to oxidation is reduced or eliminated, resulting in lower stresses on the SOFCs in the stack compared to SOFC stacks including interconnects that have not been pre-oxidized. Therefore, creep planarization, and optionally oxidation during creep planarization, is performed on the interconnects prior to placement in the SOFC stack.

[0072] Although described above with respect to SOFC stacks, it should be understood that creep-flattening of interconnects may also be used with other electrolyte stacks, such as solid oxide electrolysis stacks including ceramic electrolyte solid oxide electrolysis cells (SOECs) interspersed with creep-flattened metallic interconnects.

[0073] For solid oxide fuel cells and electrolysis stacks, the interconnect may comprise a chromium-iron alloy, e.g., a Cr—Fe—Y alloy produced by powder metallurgy techniques, e.g., by compacting and sintering Cr—Fe—Y powder. The alloy may contain 3-6 weight percent iron, e.g., 4.5-5.5 weight percent Fe, 0-1 weight percent or less yttrium, e.g., 200-2000 micrograms / gram Y, with the remainder comprising chromium and residual or unavoidable impurities. The impurities may be absent or may contain one or more of O, H, Al, Si, N, and / or C in a total amount less than 1 weight percent, e.g., less than 0.1 weight percent. In one embodiment, the interconnect comprises a chromium alloy containing 4-6 weight percent iron, 0-1 weight percent yttrium, and 94-96 weight percent chromium, and the interconnect is formed by powder metallurgy. In one embodiment, Y may be omitted, and the interconnect may include about 5 weight percent Fe, the remainder Cr (e.g., about 95 weight percent Cr), and optionally unavoidable impurities. In another embodiment, the alloy may include 3-3.9 weight percent iron, e.g., 3-3.7 weight percent, e.g., 3.2-3.5 weight percent iron, and 96.1-97 weight percent chromium, e.g., 96.5-96.8 weight percent chromium, with residual or unavoidable impurities. This alloy may provide an improved CTE compatible with larger area solid oxide fuel cells and electrolysis cells. Other metals and metal alloys having the properties desired for specific electrolysis cell materials may also be used.

[0074] A method for manufacturing an interconnect for an electrolysis cell stack, e.g., a fuel cell or electrolysis stack, includes forming the interconnect using any suitable method. In one embodiment, the interconnect can be formed by powder metallurgy techniques, in which a metal powder is fed into a die cavity of a powder press. The powder can include elemental iron and chromium powder or pre-alloyed chromium powder. The powder in the die cavity can include 3-6 weight percent iron, 0-1 weight percent or less yttrium, e.g., 200-2000 micrograms / gram Y, with the remainder including chromium and residual or unavoidable impurities. The powder in the die cavity can then be compressed by a die (i.e., one or more punches) of the powder press to form a green interconnect. Preferably, sufficient pressure is applied to the powder so that the finished interconnect (e.g., after the green interconnect is sintered) has a density of at least 6.5 grams per cubic centimeter, e.g., 6.55-6.65 grams per cubic centimeter.

[0075] The method of this embodiment also includes creep-flattening the interconnect before feeding it into the electrolysis cell stack and, optionally, oxidizing the metallic interconnect during creep-flattening. The creep-flattened, pre-oxidized interconnect may include a free-standing interconnect that is not incorporated into the electrolysis cell stack. The interconnect may then be fed into the electrolysis cell stack, e.g., a fuel cell or electrolysis stack, after the interconnect has been creep-flattened and optionally oxidized. The interconnect may then be positioned between two fuel cells or two electrolysis cells in the stack, and the interconnect may be configured to electrically connect the two fuel cells or electrolysis cells to each other.

[0076] At least one dimension of a metallic interconnect may change during the creep flattening and optional oxidation process. The size of the interconnect may increase along one or more dimensions during the creep flattening and optional oxidation process. For example, for plate-shaped interconnects (i.e., interconnects having a thickness at least one order of magnitude less than their width or length), the thickness of the interconnect may increase by at least 0.02%, e.g., by about 0.1% to about 0.9%, after the creep flattening and oxidation process. At least a surface portion of the interconnect and, optionally, pores extending through the thickness of the interconnect may be oxidized to form metal oxides. For Cr-Fe interconnects (i.e., Cr-Fe-Y interconnects with zero wt. % Y), oxidation may form chromium oxides and / or iron oxides on at least the surface of the interconnect and, optionally, in the interior pores of the interconnect.

[0077] Generally, the oxidation may be carried out for a sufficient time such that the interconnect does not undergo substantial further oxidation after it is provided in the stack and exposed to an oxidizing atmosphere during stack operation. In other words, the interconnect may be oxidized to at least 99% of its maximum oxidizability during the oxidation step. Thus, a pre-oxidized metallic interconnect will not undergo substantial further oxidation if subsequently exposed to an oxidizing atmosphere at a temperature of at least 800°C before or after being provided in the stack.

[0078] In some embodiments, the interconnect may be oxidized twice. The interconnect may be initially oxidized without any mechanical load applied to the interconnect (i.e., separate from creep planarization). This optional initial oxidation process may be performed in an oxidizing atmosphere at an elevated temperature. For example, for Cr-Fe-Y interconnects, the initial oxidation may be performed in air and / or oxygen at a temperature of at least 900°C for at least about 18 hours, e.g., 950°C in air for 20-200 hours, e.g., 168 hours. Higher temperatures, e.g., 951-1050°C, may also be used. Other temperatures and oxidation durations may be used for other interconnect materials. Thus, the initial oxidation of the interconnect is performed in an oxidizing atmosphere at a temperature above room temperature prior to creep planarization. In another embodiment, the initial oxidation step is omitted.

[0079] In a first embodiment, the interconnect may be subjected to the initial oxidation described above to form a metal oxide on the interconnect surface without applying a mechanical load to the interconnect. The metal oxide may then be removed from the interconnect by any suitable method, such as grit blasting. The interconnect may then be creep-flattened. During the creep-flattening process, the interconnect may be subjected to a load ranging from 100 lb to 500 lb. Further, during the creep-flattening process, the interconnect may be subjected to a temperature ranging from about 920°C to about 1000°C for 4 to 60 hours, such as temperatures above 950°C for 4 to 8 hours. The creep-flattening time versus temperature relationship is believed to be nonlinear. Thus, to achieve the same improvement in interconnect flatness as creep-flattening performed at 940°C for 48 hours, creep-flattening at 960°C for 4 hours may be performed. Preferably, creep planarization is performed in an oxidizing (eg, air, oxygen, or water vapor) environment (eg, atmosphere) to further oxidize pores in the interconnects and densify the interconnects.

[0080] After creep planarization, the air-side ribs 406 of the interconnect may be coated with at least one of lanthanum strontium manganite (LSM) or (Mn,Co)O4 spinel (MCO) on the air-side ribs 406 located within the airflow range of the interconnect 400, referred to as an LSM / MCO coating (e.g., an LSM coating, an MCO coating, or a coating of both LSM and MCO) 801 (shown in FIGS. 8B and 8D). Thus, in the first embodiment, the step of removing metal oxides from the surface of the interconnect 400 occurs after the initial oxidation and before creep planarization, while the formation of the coating 801 occurs after creep planarization.

[0081] In the second embodiment, the order of coating and creep-flattening is reversed compared to the first embodiment. As in the first embodiment, the interconnect may first be oxidized and then grit-blasted to remove metal oxides from the surface of the interconnect 400. In this second embodiment, the air-side ribs 406 may then be coated with an LSM / MCO coating 801 after grit-blasting but before creep-flattening. After coating, the interconnect may then be creep-flattened. In the second embodiment, the interconnect may be subjected to a temperature in the range of approximately 940°C to approximately 960°C in air for 4 to 60 hours under an applied load of 100 lb to 500 lb during creep-flattening. Thus, in the second embodiment, the metal oxide removal step occurs after the initial oxidation and before creep-flattening, while the coating formation step occurs after metal oxide removal and before creep-flattening.

[0082] In a third embodiment, the order of grit blasting and creep planarization is reversed compared to the first embodiment. As in the first embodiment, the interconnect may be oxidized first. In this third embodiment, the interconnect is creep planarized after the initial oxidation and before grit blasting. In the third embodiment, the interconnect may be subjected to a temperature ranging from approximately 940°C to approximately 960°C in air for 4 to 60 hours under a load of 100 lb to 500 lb during creep planarization. The interconnect may then be grit blasted to remove metal oxides from the surface of the interconnect, and then, after grit blasting, the air-side ribs 406 may be coated with the LSM / MCO coating 801. Thus, in the third embodiment, the creep planarization step occurs after the initial oxidation but before metal oxide removal, and the metal oxide removal step occurs after creep planarization but before coating formation.

[0083] In a fourth embodiment, oxidation and creep planarization are combined in a single process step. In other words, the initial oxidation step is omitted, and the interconnect is oxidized in a single creep planarization step performed in an oxidizing atmosphere. In this fourth embodiment, the interconnect is first subjected to a combined oxidation / creep planarization process. In the fourth embodiment, the interconnect may be subjected to a temperature ranging from approximately 920°C to approximately 1100°C in air for 4 to 60 hours under an applied load of 100 lb to 500 lb during the combined creep planarization / oxidation. The interconnect may then be grit blasted to remove metal oxides from the surface of the interconnect, and the air-side ribs 406 may then be coated with the LSM / MCO coating 801. Thus, in the fourth embodiment, the metal oxide removal step occurs after creep planarization and before the coating is applied.

[0084] In the first to fourth embodiments described above, the elevated temperature for creep flattening is 920°C to 1100°C, the load applied during creep flattening includes a load of 100 to 500 pounds, and creep flattening is performed for 4 to 60 hours. By performing the two-step or one-step oxidation process as described above, if the interconnect is subsequently exposed to an oxidizing atmosphere before or during stack operation (i.e., before or after insertion into the stack), the dimensions of the interconnect do not substantially change after the oxidation step. Thus, the dimensions of the interconnect may change by less than 0.02% if the interconnect is subsequently exposed to an oxidizing atmosphere at an elevated temperature, e.g., above 800°C, for at least 5 hours, e.g., 20 to 168 hours. Therefore, the interconnect does not further substantially deform in an oxidizing atmosphere at elevated temperatures during initial stack operation and does not damage adjacent cells in the stack. In contrast, if the interconnects are not pre-oxidized before insertion into the stack, they may deform within the stack in an oxidizing atmosphere at elevated temperatures during initial stack operation, which may cause damage (e.g., cracks 702) to adjacent cells in the stack.

[0085] FIG. 8A is a vertical cross-sectional view of a portion of the interconnect 400 of FIG. 7 , and FIG. 8B is a vertical cross-sectional view of the portion of the interconnect 400 of FIG. 8A after an LSM / MCO coating 801 has been applied to the air-side ribs 406 according to a fifth embodiment. The cross-section defining the views of FIGS. 8A and 8B is shown by line B-B′ in FIG. 7 . In this fifth embodiment, the air-side ribs 406 are recessed from a flat edge 804 of the interconnect 400. The flat edge 804 may include an inner portion of the riser seal surface 422 disposed adjacent to the air-side rib 406, as shown in FIG. 7 . The flat edge 804 is higher than the top of the air-side rib 406 by a first distance 802. The first distance 802 may be the distance from a horizontal plane 803 of the upper surface of the air-side rib 406 to a horizontal plane 805 of the top surface of the edge 804. The first distance 802 may be in the range of approximately 85 microns to 100 microns, so that the ribs 406 are offset below the flat edge 804.

[0086] As shown in FIG. 8B, the air-side ribs 406 may be coated with an LSM / MCO coating 801 as described above, while the flat edge 804 is not coated with the coating 801. The LSM / MCO coating 801 may have a thickness in the range of approximately 85 microns to 100 microns. Thus, in one embodiment, the ribs 406 are offset below the flat edge 804 by a height substantially equal to the thickness of the coating 801 (i.e., 0-10% of the thickness of the coating 801). After the LSM / MCO coating 801 is formed, the air-side ribs 406 and the (uncoated) flat edge 804 may have a common height 806 (i.e., the top surface of the LSM / MCO coating 801 on top of the ribs 406 and the top surface of the flat edge 804 are located in the same horizontal plane 806), as shown in FIG.

[0087] Figure 8C is a vertical cross-sectional view of a portion of the interconnect of Figure 7 having a cross-section at a different height than that shown in Figure 8A, and Figure 8D is a vertical cross-sectional view of the portion of the interconnect of Figure 8C after an LSM / MCO coating 801 has been applied to the air-side ribs 406 in accordance with a sixth embodiment. The cross-section defining the views of Figures 8C and 8D is also shown by line B-B' in Figure 7. As shown in Figure 8C, the flat edge 804 and the air-side ribs 406 have the same height 806 before the application of the LSM / MCO coating 801. In other words, the top surfaces of the uncoated ribs 406 and the flat edge 804 are disposed in the same horizontal plane 806.

[0088] As shown in FIG. 8D , the air-side ribs 406 may be coated with an LSM / MCO coating 801. The LSM / MCO coating 801 may have a thickness in the range of approximately 85 microns to 100 microns. Thus, after the formation of the LSM / MCO coating 801, the coated air-side ribs 406 may be higher than the flat edge 804 by a second distance 808 in the range of approximately 85 microns to 100 microns, as shown in FIG. 8D , for example. The second distance 808 may be the distance from the horizontal plane 807 of the top surface of the LSM / MCO coating 801 disposed on the air-side ribs 406 to the horizontal plane 805 of the top surface of the edge 804.

[0089] As discussed above, this height difference (i.e., second distance 808) allows riser seal surface 422 to be recessed relative to the tops of coated air-side ribs 406. In other words, when viewed from above on the air side of interconnect 400, riser seal surface 422 may be lower than the tops of ribs 406 coated with LSM / MCO coating 801. For example, riser seal surface 422 may be recessed by about 85 microns to about 100 microns relative to a plane extending across the tips of coated ribs 406. A greater recession of flat edge 804 may allow a thicker riser seal 424 (shown in FIG. 6A ) to be formed on riser seal surface 422. Due to its increased thickness, the thicker riser seal 424 may be more compliant and allow for increased thermal deformation without generating large tensile stresses that could otherwise lead to the formation of cracks 702 in SOFC 310.

[0090] In the sixth embodiment, the air sides of the interconnects 400 include riser seal surfaces 422 disposed on two opposing sides of the airflow area and surrounding the fuel inlets 402 and fuel outlets 404. The riser seal surfaces 422 (e.g., upper surfaces of the flat edges 804) are recessed relative to a plane 807 extending across the upper surface of the coating 801 at the tips of the air-side ribs 406. Within the electrochemical stack 300, a glass or glass-ceramic seal 424 is disposed between each electrochemical cell (e.g., SOEC or SOFC 310) and the riser seal surface 422 of each adjacent one of the plurality of interconnects 400 in the stack 300.

[0091] While various embodiments have been described above with respect to solid oxide fuel cell interconnects, end plates, and electrolytes, each embodiment may include any other fuel cell interconnect or end plate, such as a molten carbonate, phosphoric acid, or PEM fuel cell electrolyte, interconnect, or end plate, or any other form of metal or metal alloy or compressed metal powder or ceramic object not related to a fuel cell system, such as an electrolyzer interconnect.

[0092] The foregoing description has been provided merely as illustrative examples and is not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As one of ordinary skill in the art would understand, the order of steps in the foregoing embodiments may be performed in any order. Words such as "then," "next," and "next" are not necessarily intended to limit the order of steps; these words may be used to guide the reader through the method description. Furthermore, references to singular elements in the claims, using, for example, the articles "a," "an," or "the," should not be construed as limiting the element to the singular. Furthermore, any step or component of any embodiment described herein may be used in any other embodiment.

[0093] The above description of the disclosed aspects is provided to enable any person skilled in the art to make and / or use the disclosed embodiments. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present disclosure. Thus, the embodiments of the present disclosure are not intended to be limited to the aspects shown herein but are to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. 1. A method of manufacturing an interconnect for an electrochemical cell stack, said method comprising: forming the interconnect by a powder metallurgy process by compressing a metal powder to form a green interconnect, sintering the green interconnect, and having the interconnect have a density of at least 6.5 grams per cubic centimeter after sintering the green interconnect; creep-flattening the interconnect prior to placing the interconnect in the electrochemical cell stack after the step of sintering the green interconnect; Including, The method wherein the creep flattening is carried out at an elevated temperature ranging from 920° C. to 1100° C. for a period of 4 hours to 60 hours under a load ranging from 100 to 500 pounds (45.4 to 226.8 kg).

2. The method of claim 1 , wherein the creep planarization is performed in an oxidizing atmosphere, whereby the interconnect is oxidized during the creep planarization.

3. removing metal oxides from the surface of the interconnect; The air-side ribs located within the air flow range of the interconnect are coated with lanthanum strontium manganite (LSM) or (Mn,Co) ３ O ４ forming a coating comprising at least one of spinel (MCO); The method of claim 2 further comprising:

4. The method of claim 3 further comprising initially oxidizing said interconnect in said oxidizing atmosphere at a temperature above room temperature prior to said creep planarization.

5. removing the metal oxide occurs after the initial oxidation and before the creep planarization; forming the coating occurs after the creep flattening; The method of claim 4.

6. removing the metal oxide occurs after the initial oxidation and before the creep planarization; forming the coating occurs after removing the metal oxide and before creep planarizing; The method of claim 4.

7. the creep planarization occurs after the initial oxidation and before removing the metal oxide; removing the metal oxide occurs after the creep planarization and before forming the coating; The method of claim 4.

8. The method of claim 3 , wherein removing the metal oxide occurs after creep planarizing and before forming the coating.

9. the air side of the interconnect further includes riser sealing surfaces disposed on two opposing sides of the air flow area and surrounding a fuel inlet and a fuel outlet; the riser seal surface is recessed relative to a plane extending across an upper surface of the coating at the tip of the air-side rib. The method of claim 3.

10. the interconnect comprises a chromium alloy comprising 3 to 6 weight percent iron, 0 to 1 weight percent yttrium, and 94 to 97 weight percent chromium; The method of claim 1.

11. The method of claim 10, wherein the interconnect comprises a chromium alloy comprising 3 to 3.9 weight percent iron and 96.1 to 97 weight percent chromium.

12. 10. The method of claim 1, further comprising disposing the interconnect in the electrochemical stack after the creep planarization, the electrochemical stack comprising a solid oxide fuel cell stack including a solid oxide fuel cell or a solid oxide electrolysis cell stack including a solid oxide electrolysis cell.

13. The interconnect is a fuel inlet and a fuel outlet extending through the interconnect adjacent opposing first and second peripheries of the interconnect; an air side including an air flow area including air side ribs and air passages extending in a first direction from a third periphery of the interconnect to a fourth periphery of the interconnect opposite the third periphery, and riser sealing surfaces disposed at the first periphery and the second periphery of the interconnect and surrounding the fuel inlet and the fuel outlet; a fuel side opposite the air side, the fuel side including a fuel flow area including fuel side ribs and fuel passages extending between the fuel inlet and the fuel outlet in a second direction substantially perpendicular to the first direction; Lanthanum strontium manganite (LSM) or (Mn,Co) disposed on the air side rib but not on the riser seal face ３ O ４ A coating comprising at least one of spinel (MCO), the riser seal surface is recessed relative to a plane extending across an upper surface of the coating at the tip of the air-side rib; The method of claim 1 , comprising:

Images