The present disclosure is directed to fuel cell dielectric layers, and in particular to dielectric layers that include an amorphous component.
In a high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is passed through the cathode side of the fuel cell while a fuel flow is passed through the anode side of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. The fuel cell, operating at a typical temperature between 750° C. and 950° C., enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ion combines with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or with carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ion are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit.
Fuel cell stacks may be either internally or externally manifolded for fuel and air. In internally manifolded stacks, the fuel and air is distributed to each cell using risers contained within the stack. In other words, the gas flows through openings or holes in the supporting layer of each fuel cell, such as the electrolyte layer, and gas flow separator of each cell. In externally manifolded stacks, the stack is open on the fuel and air inlet and outlet sides, and the fuel and air are introduced and collected independently of the stack hardware. For example, the inlet and outlet fuel and air flow in separate channels between the stack and the manifold housing in which the stack is located.
Fuel cell stacks are frequently built from a multiplicity of cells in the form of planar elements, tubes, or other geometries. Fuel and air has to be provided to the electrochemically active surface, which can be large. One component of a fuel cell stack is the so called gas flow separator (referred to as a gas flow separator plate in a planar stack) that separates the individual cells in the stack. The gas flow separator plate separates fuel, such as hydrogen or a hydrocarbon fuel, flowing to the fuel electrode (i.e., anode) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e., cathode) of an adjacent cell in the stack. Frequently, the gas flow separator plate is also used as an interconnect which electrically connects the fuel electrode of one cell to the air electrode of the adjacent cell. In this case, the gas flow separator plate which functions as an interconnect is made of or contains an electrically conductive material.
According to various embodiments of the present disclosure, a fuel cell stack comprises: stacked solid oxide fuel cells; interconnects disposed between the fuel cells; and dielectric layers disposed on the interconnects, the dielectric layers comprising a first glass-containing component and a corrosion barrier material, wherein, the dielectric layer has a first glass-containing component to corrosion barrier material weight ratio ranging from about 5:95 to about 60:40, the first glass-containing component is at least 50% (e.g., by volume) amorphous, after sintering at a temperature ranging from about 950° C. to about 1050° C., for a time period of at least 15 minutes, and the corrosion barrier material comprises zirconium silicate (ZrSiO4)), potash feldspar (KAlSi3O8), alumina (Al2O3), lanthanum trisilicate (La2Si3O9), silicon carbide, or any combination thereof.
According to various embodiments of the present disclosure, a fuel cell stack comprises: stacked solid oxide fuel cells, each fuel cell comprising an anode, a cathode, and an electrolyte disposed between the anode and the cathode; cross flow interconnects containing fuel holes and disposed between the fuel cells; peripheral seals disposed between fuel sides of the interconnects and fuel sides of the fuel cells; riser seals surrounding the fuel holes disposed between air sides of the interconnects and air sides of the fuel cells; and electrolyte reinforcement layers disposed directly on the electrolytes and comprising at least one of yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), magnesia, zirconia, ZrSiO4, alumina, or a combination thereof.
According to various embodiments of the present disclosure, a fuel cell stack comprises: stacked solid oxide fuel cells, each fuel cell comprising an anode, a cathode, and an electrolyte disposed between the anode and the cathode; cross flow interconnects disposed between the fuel cells, each of the interconnects comprises an air side, an opposing fuel side, fuel holes that extend through opposing sides of the interconnect, wherein the air side each includes an air flow field and riser seal surfaces that surround the fuel holes; peripheral seals disposed between fuel sides of the interconnects and fuel sides of the fuel cells; riser seals disposed between air sides of the interconnects and air sides of the fuel cells; riser seals that completely cover the riser surfaces; and dielectric layers disposed between the riser seal surfaces and the riser seals, wherein the dielectric layers cover less than 50% of at least portions of the riser seal surfaces.
The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate example embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the features of the invention.
The 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 numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims. Ranges can 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 use of the antecedent “about” or “substantially” it will be understood that the particular value forms another aspect. In some embodiments, a value of “about X” may include values of +/- 1% X. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
Referring to
The ASP’s 36 are disposed between the stacks 20 and are configured to provide a hydrocarbon fuel containing fuel feed to the stacks 20 and to receive anode fuel exhaust from the stacks 20. For example, the ASP’s 36 may be fluidly connected to internal fuel riser holes 22 formed in the stacks 20, as discussed below.
Referring to
Each interconnect 10 electrically connects adjacent fuel cells 1 in the stack 20. In particular, an interconnect 10 may electrically connect the anode electrode 7 of one fuel cell 1 to the cathode electrode 3 of an adjacent fuel cell 1.
Each interconnect 10 includes ribs 12 that at least partially define fuel channels 8A and air channels 8B. The interconnect 10 may operate as a gas-fuel separator that separates a fuel, such as a hydrocarbon fuel, flowing to the fuel electrode (i.e. anode 7) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e. cathode 3) of an adjacent cell in the stack. At either end of the stack 20, there may be an air end plate or fuel end plate (not shown) for providing air or fuel, respectively, to the end electrode.
Ring seals 23 may surround fuel holes 22A of the interconnect 10, to prevent fuel from contacting the cathode electrode. Peripheral strip-shaped seals 24 are located on peripheral portions of the air side of the interconnect 10. The seals 23, 24 may be formed of a glass material. The peripheral portions may be in the form of an elevated plateau which does not include ribs or channels. The surface of the peripheral regions may be coplanar with tops of the ribs 12.
Referring to
A frame-shaped seal 26 is disposed on a peripheral region of the fuel side of the interconnect 10. The peripheral region may be an elevated plateau which does not include ribs or channels. The surface of the peripheral region may be coplanar with tops of the ribs 12.
Accordingly, a conventional counter-flow fuel cell column, as shown in
The fuel manifolds 28 may occupy a relatively large region of the interconnect 10, which may reduce the contact area between the interconnect 10 and an adjacent fuel cell by approximately 10%. The fuel manifolds 28 are also relatively deep, such that the fuel manifolds 28 represent relatively thin regions of the interconnect 10. Since the interconnect 10 is generally formed by a powder metallurgy compaction process, the density of fuel manifold regions may approach the theoretical density limit of the interconnect material. As such, the length of stroke of a compaction press used in the compaction process may be limited due to the high-density fuel manifold regions being incapable of being compacted further. As a result, the density achieved elsewhere in the interconnect 10 may be limited to a lower level by the limitation to the compaction stroke. The resultant density variation may lead to topographical variations, which may reduce the amount of contact between the interconnect 10 a fuel cell 1 and may result in lower stack yield and/or performance.
Another important consideration in fuel cell system design is in the area of operational efficiency. Maximizing fuel utilization is a key factor to achieving operational efficiency. Fuel utilization is the ratio of how much fuel is consumed during operation, relative to how much is delivered to a fuel cell. An important factor in preserving fuel cell cycle life may be avoiding fuel starvation in fuel cell active areas, by appropriately distributing fuel to the active areas. If there is a maldistribution of fuel such that some flow field channels receive insufficient fuel to support the electrochemical reaction that would occur in the region of that channel, it may result in fuel starvation in fuel cell areas adjacent that channel. In order to distribute fuel more uniformly, conventional interconnect designs include channel depth variations across the flow field. This may create complications not only in the manufacturing process, but may also require complex metrology to measure these dimensions accurately. The varying channel geometry may be constrained by the way fuel is distributed through fuel holes and distribution manifolds.
One possible solution to eliminate this complicated geometry and the fuel manifold is to have a wider fuel opening to ensure much more uniform fuel distribution across the fuel flow field. Since fuel manifold formation is a factor in density variation, elimination of fuel manifolds should enable more uniform interconnect density and permeability. Accordingly, there is a need for improved interconnects that provide for uniform contact with fuel cells, while also uniformly distributing fuel to the fuel cells without the use of conventional fuel manifolds.
Owing to the overall restrictions in expanding the size of a hotbox 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 footprint of a hotbox.
Referring to
The interconnects 400 are made from an electrically conductive metal material. For example, the interconnects 400 may comprise a chromium alloy, such as a Cr—Fe alloy. The interconnects 400 may typically be fabricated using a powder metallurgy technique that includes pressing and sintering a Cr—Fe powder, which may be a mixture of Cr and Fe powders or an Cr—Fe alloy powder, to form a Cr—Fe interconnect in a desired size and shape (e.g., a “net shape” or “near net shape” process). A typical chromium-alloy interconnect 400 comprises more than about 90% chromium by weight, such as about 94-96% (e.g., 95%) chromium by weight. An interconnect 400 may also contain less than about 10% iron by weight, such as about 4-6% (e.g., 5%) iron by weight, may contain less than about 2% by weight, such as about zero to 1% by weight, of other materials, such as yttrium or yttria, as well as residual or unavoidable impurities.
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 the cathode 316 may 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 an adjacent interconnect 400. The fuel cell 310 does not include through holes, such as the fuel holes of conventional fuel cells. Therefore, the fuel cell 310 avoids cracks that may be generated due to the presence of such through holes.
An upper most interconnect 400 and a lowermost interconnect 400 of the stack 300 may be different ones of an air end plate or fuel end plate including features for providing air or fuel, respectively, to an adjacent end fuel cell 310. As used herein, an “interconnect” may refer to either an interconnect located between two fuel cells 310 or an end plate located at an end of the stack and directly adjacent to only one fuel cell 310. Since the stack 300 does not include ASPs and the end plates associated therewith, the stack 300 may include only two end plates. As a result, stack dimensional variations associated with the use of intra-column ASPs may be avoided.
The stack 300 may include side baffles 302, a fuel plenum 304, and a compression assembly 306. The side baffles 302 may be formed of a ceramic material and may be disposed on opposing sides of the fuel cell stack 300 containing stacked fuel cells 310 and interconnects 400. The side baffles 302 may connect the fuel plenum 304 and the compression assembly 306, such that the compression assembly 306 may apply pressure to the stack 300. The side baffles 302 may be curved baffle plates, such each baffle plate covers at least portions of three sides of the fuel cell stack 300. For example, one baffle plate may fully cover the fuel inlet riser side of the stack 300 and partially covers the adjacent front and back sides of the stack, while the other baffle plate fully covers the fuel outlet riser side of the stack and partially covers the adjacent portions of the front and back sides of the stack. The remaining uncovered portions for the front and back sides of the stack allow the air to flow through the stack 300. The curved baffle plates provide an improved air flow control through the stack compared to the conventional baffle plates 38 which cover only one side of the stack. The fuel plenum 304 may be disposed below the stack 300 and may be configured to provide a hydrogen-containing fuel feed to the stack 300, and may receive an anode fuel exhaust from the stack 300. The fuel plenum 304 may be connected to fuel inlet and outlet conduits 308 which are located below the fuel plenum 304.
Each interconnect 400 electrically connects adjacent fuel cells 310 in the stack 300. In particular, an interconnect 400 may electrically connect the anode electrode of one fuel cell 310 to the cathode electrode of an adjacent fuel cell 310. As shown in
The interconnect 400 may include fuel holes that extend through the interconnect 400 and are configured for fuel distribution. For example, the fuel holes may include one or more fuel inlets 402 and one or more fuel outlets 404, which may also be referred to as anode exhaust outlets 404. The fuel inlets and outlets 402, 404 may be disposed outside of the perimeter of the fuel cells 310. While two of each of the fuel inlets and outlets 402, 404 are shown, it should be noted that there may be one fuel inlet 402 and one fuel outlet 404, or there may be three or more of each of the fuel inlets and outlets 402, 404. As such, the fuel cells 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 a corresponding length of the interconnect 400 e.g., a length taken in direction A.
In one embodiment, each interconnect 400 contains two fuel inlets 402 separated by a neck portion 412 of the interconnect 400, as shown in
The fuel inlets 402 of adjacent interconnects 400 may be aligned in the stack 300 to form one or more fuel inlet risers 403. The fuel outlets 404 of adjacent interconnects 400 may be aligned in the stack 300 to form one or more fuel outlet risers 405. The fuel inlet riser 403 may be configured to distribute fuel received from the fuel plenum 304 to the fuel cells 310. The fuel outlet riser 405 may be configured to provide anode exhaust received from the fuel cells 310 to the fuel plenum 304.
Unlike the flat related art side baffles 38 of
In various embodiments, the 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 the fuel risers 403, 405. In other words, as compared to a conventional fuel cell system, the cross-flow configuration allows for a large number of fuel cells to be provided with fuel, without the need for ASP’s or external stack fuel manifolds, such as external conduits 32, 34 shown in
Each interconnect 400 may be made of or may contain electrically conductive material, such as a metal alloy (e.g., chromium-iron alloy) which has a similar coefficient of thermal expansion to that of the solid oxide electrolyte in the cells (e.g., a difference of 0-10%). For example, the interconnects 400 may comprise a metal (e.g., a chromium-iron alloy, such as 4-6 weight percent iron, optionally 1 or less weight percent yttrium and balance chromium alloy), and may electrically connect the anode or fuel-side of one fuel cell 310 to the cathode or air-side of an adjacent fuel cell 310. An electrically conductive contact layer, such as a nickel contact layer (e.g., a nickel mesh), may be provided between anode and each interconnect 400. Another optional electrically conductive contact layer may be provided between the cathode electrodes and each interconnect 400.
A surface of an interconnect 400 that in operation is exposed to an oxidizing environment (e.g., air), such as the cathode-facing side of the interconnect 400, may be coated with a protective coating layer in order to decrease the growth rate of a chromium oxide surface layer on the interconnect and to suppress evaporation of chromium vapor species which can poison the fuel cell cathode. Typically, the coating layer, which can comprise a perovskite such as lanthanum strontium manganite (LSM), may be formed using a spray coating or dip coating process. Alternatively, other metal oxide coatings, such as a spinel, such as an (Mn, Co)3O4 spinel (MCO), can be used instead of or in addition to LSM. Any spinel having the composition Mn2-xCO1+xO4 (0 ≤ x ≤ 1) or written as z(Mn3O4) + (1-z)(Co3O4), where (⅓ ≤ z ≤ ⅔) or written as (Mn, Co)3O4 may 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.
Riser seals 424 may be disposed on the riser seal surface 422. For example, one riser seal 424 may surround the fuel inlets 402, and one riser seal 424 may surround the fuel outlets 404. The riser seals 424 may prevent fuel and/or anode exhaust from entering the air flow field 420 and contacting the cathode of the fuel cell 310. The riser seals 424 may also operate to prevent fuel from leaking out of the fuel cell stack 100 (see
Referring to
A frame-shaped perimeter seal 434 may be disposed on the perimeter seal surface 432. The perimeter seal 434 may be configured to prevent air entering the fuel flow field 430 and contacting the anode on an adjacent fuel cell 310. The perimeter seal 434 may also operate to prevent fuel from exiting the fuel risers 403, 405 and leaking out of the fuel cell stack 300 (see
The seals 424, 434 may comprise a glass or ceramic seal material, as discussed in detail below. The seal material may have a low electrical conductivity. In some embodiments, the seals 424, 434 may be formed by printing one or more layers of seal material on the interconnect 400, followed by sintering.
In conventional fuel cell stacks, the fuel cell electrolytes fully cover the interconnects, such that the fuel cell electrolytes operate as dielectric layers between adjacent interconnects. In a crossflow design, portions of the interconnects 400 may be disposed outside of the perimeter of the fuel cells, such as interconnect regions corresponding to the riser seal surface 422. Electrical shorting between interconnects may potentially occur in these regions, if the stack is tilted or if seals become conductive over time. Leakage current may also lead to seal degradation over time. As such, various embodiments provide dielectric layers that protect against electrical shorting and/or seal degradation.
Referring to
In other embodiments, as shown in
In other embodiments, as shown in
During sintering, the relatively narrow dielectric layer 440 may allow for an adjacent riser seal to overflow the dielectric layer 440, such that at least a portion of the riser seal material directly contacts the riser seal surface 422. As such, the relatively narrow dielectric layer 440 may allow for increased seal-to-interconnect adhesion, while still preventing electrical contact (i.e., short circuit) between adjacent interconnects 400 in the stack.
With regard to
Accordingly, in some embodiments dielectric layers 440 may include a relatively wide width (i.e., thick) interior portion 440I that covers the interior region 422I, and a relatively narrow width exterior portion 440E that covers the exterior region 422E. As used with regard to
Covering substantially all of the interior region 422I with the interior portion 440I of the dielectric layer 440 may prevent and/or reduce degradation of overlapping portions of the riser seals by reducing vapor phase reactions. Covering only a portion of exterior region 422E with the exterior portion 440E of the dielectric layer may provide for increased seal-to-interconnect adhesion.
Conventional dielectric layers may include ceramic components mixed with a glass component. The glass component may be a glass material that is configured to be sintered to provide cohesion and adhesive strength. For example, the glass component may include silica glass materials or glass-ceramic materials, such as a BaO—CaO—Al2O3—B2O3—SiO2 (BCAS) glass-ceramic material. However, the amount of the glass component included in such materials may be limited to about 15 wt.% or less, due to the relatively low dielectric strength of conventional glass component materials. In addition, the glass component may completely crystalize at relatively low temperatures. As a result, such conventional dielectric layers may lack sufficient adhesive and/or cohesive strength, due to the crystallization of the glass component, and may delaminate from adjacent seals during thermal cycling at fuel cell operating temperatures.
As such, various embodiments provide dielectric layer materials that have a dielectric strength sufficient to prevent interconnect-to-interconnect shorting (e.g., leakage currents), as well as provide sufficient seal adhesion to prevent delamination during thermal cycling.
According to various embodiments, the dielectric layers 440 may comprise a corrosion barrier material and an at least partially amorphous first glass-containing component. For example, the dielectric layers 440 may have a first glass-containing component to corrosion barrier material weight ratio ranging from about 5:95 to about 60:40, such as from about 10:90 to about 50:50. In some embodiments, the barrier material and the first glass-containing component may be present in the dielectric layers 440 as separate phases.
The first glass-containing component may include a glass or glass-ceramic material that completely or at least partially retains an amorphous/glassy state after sintering at temperatures of at least 940° C., such as temperatures from about 950° C. to about 1050° C. For example, the first glass-containing component may have, by volume, least 50%, such as at least 70%, at least 80%, or at least 90% of an amorphous phase after sintering at temperatures above 940° C., for a time period of at least 15 minutes. In some embodiments, the first glass-containing component may include a barium silicate glass-containing composition, such as Schott G018-281 (a glass-ceramic sealant for SOFC applications), available from Schott AG, Mainz, Germany, a calcium-magnesium-aluminosilicate (CMAS) glass or glass-ceramic material, combinations thereof, or the like.
In some embodiments, the first glass-containing component may include the CMAS glass or glass-ceramic material that comprises, on an oxide basis, by mol%: SiO2 in an amount ranging from about 85% to about 95%, such as from about 87% to about 93%, or about 89.2%; Al2O3 in an amount ranging from about 2.5% to about 6.5%, such as from about 4.0% to about 5.0%, or about 4.6%; CaO in an amount ranging from about 2.0% to about 5.0%, such as from about 3.0% to about 4.0%, or about 3.5%; and MgO in an amount ranging from about 1.2% to about 4.2%, such as from about 2.2% to about 3.2%, or about 2.7%.
The corrosion barrier material may comprise a glass ceramic material comprising a ceramic component and a second glass-containing component. For example, the ceramic component may include zircon (zirconium silicate (ZrSiO4)), potash feldspar (KAlSi3O8), alumina (Al2O3), lanthanum trisilicate (La2Si3O9), silicon carbide, and/or other high-temperature resistant dielectric materials. The second glass-containing component may include silica glass materials or glass-ceramic materials, such as a BaO—CaO—Al2O3—B2O3—SiO2 (BCAS) glass-ceramic material.
For example, the corrosion barrier material may include, based on a total weight of the corrosion barrier material: from about 25 wt.% to about 50 wt.%, such as from about 30 wt.% to about 45 wt.%, from about 35 wt.% to about 40 wt.%, or about 37.5 wt.% ZrSiO4; from about 25 wt.% to about 50 wt.%, such as from about 30 wt.% to about 45 wt.%, from about 35 wt.% to about 40 wt.%, or about 37.5 wt.% KAlSi3O8; from about 2 wt.% to about 25 wt.%, such as from about 4 wt.% to about 20 wt.%, from about 5 wt.% to about 15 wt.%, or about 10 wt.% Al2O3; and from about 0 wt.% to about 15 wt.%, such as from about 10 wt.% to about 15 wt.%, or from about 12 to about 15 wt.% of the second glass-containing component.
In some embodiments, the second glass-containing component may comprise, on an oxide weight basis: silica (SiO2) in an amount ranging from about 30% to about 60%, such as from about 35% to about 55%; boron trioxide (B2O3) in an amount ranging from about 0.5% to about 15%, such as from about 1% to about 12%; alumina (Al2O3) in an amount ranging from about 0.5% to about 5%, such as from about 1% to about 4%; calcium oxide (CaO) in an amount ranging from about 2% to about 30%, such as from about 5% to about 25%; barium oxide (BaO) in an amount ranging from about 0% to about 35%, such as from about 20% to about 30%; magnesium oxide (MgO) in an amount ranging from about 0% to about 25%, such as from about 5% to about 20%; strontium oxide (SrO) in an amount ranging from about 0% to about 20%, such as from about 10% to about 15%; and lanthanum oxide (La2O3) in an amount ranging from about 0% to about 12%, such as from about 5% to about 10%.
In some embodiments, the second glass-containing component may be omitted. For example, the first glass-containing component may be substituted for the second glass-containing component, such that the dielectric layers 440 may have a first glass-containing component to corrosion barrier material weight ratio ranging from about 15:85 to about 70:30, such as from about 20:80 to about 60:40.
In an alternative embodiment, the corrosion barrier material may comprise, on an oxide basis by mol%: SiO2 in an amount ranging from about 30% to about 45%, such as about 35% to about 40%, or about 39%; CaO in an amount ranging from about 23% to about 33%, such as from about 25% to about 30%, or about 27%; MgO in an amount ranging from about 15% to about 25%, such as from about 18% to about 20%, or about 19%; Al2O3 in an amount ranging from about 6% to about 7%, such as about 6.5%; B2O3 in an amount ranging from about 4% to about 5%, such as about 4.5%; La2O3 in an amount ranging from about 0.5% to about 5%, such as from about 1.5% to about 3.5%, or about 2%; and ZrO2 in an amount ranging from about 0.5% to about 5%, such as about 1.5% to about 3.5%, or about 2%. The corrosion barrier material may also comprise trace amounts of impurities, such as Na2O, P2O5, SrO, BaO, Li2O, and/or K2O. In some embodiments, the above corrosion barrier material may be at least 90% crystalline (e.g., may include at least 90% or at least 95% of one or more crystalline phases by volume). For example, the corrosion barrier material may comprise lanthanum trisilicate (La2Si3O9) as a primary crystal phase. A primary crystal phase is the crystal phase having the largest volume percent of all crystal phases, and may comprise at least 50 volume percent of all crystal phases.
In other embodiments, the corrosion barrier material may comprise, on an oxide basis by mol%: SiO2 in an amount ranging from about 45% to about 55%, such as about 47% to about 53%, or about 50.5%; CaO in an amount ranging from about 0.5% to about 3%, such as from about 1.5% to about 2.5%, or about 2.0%; MgO in an amount ranging from about 1% to about 4%, such as from about 1% to about 2%, or about 1.5%; Al2O3 in an amount ranging from about 2% to about 3%, such as about 2.5%; B2O3 in an amount ranging from about 10% to about 16%, such as from about 11% to about 13%, or about 12%; BaO in an amount ranging from about 15 to about 30%, such as from about 18% to about 24%, or about 21.5%; La2O3 in an amount ranging from about 5% to about 10%, such as from about 7% to about 9%, or about 8%; and ZrO2 in an amount ranging from about 0.5% to about 3%, such as about 1.5% to about 3.5%, or about 2%. The corrosion barrier material may also comprise trace amounts of impurities, such as Na2O, P2O5, SrO, BaO, Li2O, and/or K2O. In some embodiments, the above corrosion barrier material may be at least 90% crystalline (e.g., may include at least 90% or at least 95% of one or more crystalline phases). For example, the above corrosion barrier material may comprise lanthanum trisilicate (La2Si3O9) as a primary crystal phase. The crystalline corrosion barrier material may also include one or more secondary crystal phases such as zircon (ZrSiO4) and/or sanbornite (BaSi2O5).
The dielectric layer 440 may also include ceramic support particles (e.g., hard, round ceramic particles) configured to operate as a physical support to maintain separation between adjacent interconnects 400. For example, the support particles may be configured to maintain a minimum distance between adjacent interconnects 400 that is sufficient to prevent and/or reduce the generation of a leakage current between the interconnects 400, which may occur if the glass phase of an adjacent seal is excessively compressed. The support particles may comprise alumina, zircon (zirconium silicate (ZrSiO4)), stabilized zirconia (e.g., yttria-stabilized zirconia), or any combination thereof. The support particles may have an average particle size ranging from about 5 µm to about 50 µm, such as from about 10 µm to about 30 µm.
In some embodiments, some or all of a LSM/MCO coating may be removed on the air side of the interconnect 400 in the area around the riser seal 424, to prevent Mn diffusion from the LSM/MCO material into the riser seal 424, and thereby prevent the riser seal 424 from becoming conductive. In other embodiments, the riser seals 424 may be formed of crystalline glass or glass-ceramic materials that do not react with the LSM/MCO coating, such as the borosilicate glass-ceramic compositions discussed above.
The dielectric layer 440 can be formed from freestanding layers, such as a tape cast and sintered layer, and may be disposed between interconnects 400 during fuel cell stack assembly. In other embodiments, the dielectric layers 440 may be formed by dispersing a dielectric material in an ink, paste, or slurry form, and subsequently screen printed, pad printed, aerosol sprayed onto the interconnect 400. In some embodiments, the dielectric layer 440 may be formed by a thermal spraying process, such as an atmospheric plasma spray (APS) process. For example, the dielectric layer 440 may include alumina deposited by the APS process.
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 surfaces 422 (i.e., parts of the interconnect 400 around the fuel inlets and outlets 402, 404 in areas that will be covered by the riser seals 424 and that are not covered by the LSM/MCO coating, except for a small area of overlap (e.g., seam) where the dielectric layer 440 overlaps with a LSM/MCO coating where the riser seal surface 422 meets the air flow field 420, so as to prevent Cr evaporation from an exposed surface of the interconnect 400. Thus, the LSM/MCO coating is located on the interconnect 400 surface in the air flow field 420 containing air channels 408 and ribs 406, but not in the riser seal surface 422 of the interconnect 400 surrounding the fuel inlets and outlets 402, 404. The dielectric layer 440 is located on the riser seal surface of the interconnect 400 in the area surrounding the fuel inlets and outlets 402, 404 that is not covered by the LSM/MCO coating and on the edge of the LSM/MCO coating in the air flow field 420 adjacent to the riser seal surface 422. Alternatively, the dielectric layer 440 may be omitted and there is no dielectric layer 440 deposited around the fuel riser openings.
The fuel cell stack and/or components thereof may be conditioned and/or sintered. Stack sintering may include processes for heating, melting and/or reflowing a glass or glass-ceramic seal precursor materials to form seals in a fuel cell stack, which may be performed at elevated temperature (e.g., 600-1000° C.) in air and/or inert gas. “Conditioning” includes processes for reducing a metal oxide (e.g., nickel oxide) in an anode electrode to a metal (e.g., nickel) in a cermet electrode (e.g., nickel and a ceramic material, such as a stabilized zirconia or doped ceria) and/or heating the stack 300 during performance characterization/testing, and may be performed at elevated temperature (e.g., 750-900° C.) while fuel flows through the stack. The 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).
Referring to
Accordingly, stress may be applied to the corners of the fuel cells 310, during assembly and/or during sintering, which may result in damage to the fuel cells 310, such as cracked corners. Therefore, various embodiments of the present disclosure provide methods and stack configurations that are configured to protect the fuel cells 310 from damage during assembly and/or sintering processes.
In addition, since the seals 424, 434 overlap the corners of the fuel cell 310, gaps G may be formed along the perimeter of the fuel cell 310 and between the corners of the fuel cells 310, below each of the riser seals 424 (e.g., below the electrolyte 312) and above the perimeter seal 434. When the stack 300 is compressed, a down force may be transmitted through the interconnects 400 and seals 424, 430, and into the unsupported edges of the fuel cell 310 adjacent the gaps G, which may create a lever arm effect, due to the adjacent gaps G.
According to various embodiments of the present disclosure, in order to support the edges of the electrolyte 312, the conductive layer 318 (e.g., nickel mesh) may be extended into the gaps G. In some embodiments, the anode 314 and/or cathode 316 may also be extended to cover the electrolyte below the riser seals 424, in combination with extending the conductive layer 318 into the gaps G. In other embodiments, one or more electrolyte reinforcement layers 325 may be formed on one or both sides of the electrolyte 312 below the riser seals 424.
The electrolyte reinforcement layers 325 may be formed of a dielectric material, such as a ceramic material including yttria-stabilized zirconia (YSZ), (e.g., 3% yttria-stabilized zirconia (3YSZ)), scandia-stabilized zirconia (SSZ), magnesia, zirconia, and/or alumina. In one embodiment, the electrolyte reinforcement layers 325 may include from about 65 wt.% to about 85 wt.%, such as about 75 wt.%, 3YSZ and from about 35 wt.% to about 15 wt.%, such as about 25 wt.%, alumina.
In other embodiments, the electrolyte reinforcement layers 325 may include a dielectric material that includes YSZ, alumina, and a zircon additive. For example, the electrolyte reinforcement layers 325 may include from about 40 wt.% to about 60 wt.%, such as about 50 wt.%, 3YSZ, from about 15 wt.% to about 35 wt.%, such as about 25 wt.%, alumina, and from about 15 wt.% to about 35 wt.%, such as about 25 wt.%, ZrSiO4.
The electrolyte reinforcement layers 325 may also include a dielectric material that includes a sintering aid, such as a metal or metal oxide material, such as Ti, Mo, W, Mg, Hf, Rh, Co, Ni, Fe, Mn, Cu, Sn, oxides thereof, and combinations thereof. For example, the electrolyte reinforcement layers 325 may include from about 0.1 to about 80 wt % (e.g., 50-75 wt %) of stabilized zirconia, about 0.1 to about 60 wt % (e.g., 20-45 wt %) of alumina, about 0.1 to about 30 wt % (e.g., 1-5 wt %) of the sintering aid (e.g., metal or metal oxide material).
The electrolyte reinforcement layer 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 in conjunction with the conductive layer 318. 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. As such, the electrolyte reinforcement layer 325 may be configured to remove chromium from air supplied to the fuel cell 310.
In particular, the electrolyte reinforcement layers 327, 329 may be formed by printing a dielectric material on the electrolyte 312. For example, the dielectric material may be printed on the electrolyte 312 at a thickness ranging from about 5 µm to about 35 µm, such as from about 10 µm to about 30 µm.
The dielectric material may be similar to the dielectric material of the electrolyte reinforcement layer 325. For example, the dielectric material may include YSZ, (e.g., 3YSZ), SSZ, magnesia, zirconia, ZrSiO4, and/or alumina. In one embodiment, the reinforcement layers 327, 329 may include, based on the total weight of the electrolyte reinforcement layers 327, 329, from about 65 wt.% to about 85 wt.%, such as from about 70 wt.% to about 80 wt.%, or about 75 wt.%, 3YSZ, and from about 15 wt.% to about 35 wt.%, such as from about 20 wt.% to about 30 wt.%, or about 25 wt.%, alumina.
In other embodiments, the electrolyte reinforcement layers 327, 329 may include, based on the total weight of the electrolyte reinforcement layers 327, 329, from about 40 wt.% to about 60 wt.%, such as about 50 wt.%, 3YSZ, from about 15 wt.% to about 35 wt.%, such as about 25 wt.%, alumina, and from about 15 wt.% to about 35 wt.%, such as about 25 wt.%, ZrSiO4.
After printing, the electrolyte reinforcement layers 327, 329 may be sintered. In particular, since the dielectric material may be free of a glass material, the electrolyte reinforcement layers 327, 329 may be sintered at a higher temperature, such as a temperature ranging from about 1100° C. to about 1300° C., such as a temperature ranging from about 1150° C. to about 1250° C., or about 1200° C. As such, the electrolyte reinforcement layers 327, 329 may be completely or substantially completely crystalline. For example, the electrolyte reinforcement layer 327, 329 may comprise, by volume be at least 90%, such as at least 95%, or at least 99% of a crystalline phase, which may provide the reinforcement layers 327, 329 with improved dielectric and mechanical properties, as compared to compositions that include glass materials.
Referring again to
Accordingly, the seals 424, 434 may be formed of a glass or glass/ceramic seal material that provides good wettability and flowability and retains an amorphous phase to provide self-healing during thermal cycling. In some embodiments, the seal material may have a coefficient or thermal expansion (CTE) that closely matched the CTE of the interconnects 400 and fuel cells. For example, the seal material may have a CTE that is within +/- 10%, or +/- 5% of the CTE of fuel cell stack interconnects and/or fuel cells. For example, the seal material may have a CTE ranging from about 9 parts per million (ppm)/°K to about 11 ppm/°K (where 1 ppm = 0.0001%), when used in a fuel cell stack including interconnects 400 and fuel cells 310 having a CTE of about 10 ppm/°K.
The seal material may be chemically inert with respect to materials such as zirconia-base electrolyte materials, chromium-containing interconnect materials (such as Cr—Fe alloys containing 4 to 6 wt.% Fe and balance chromium and impurities), and coatings including manganese oxides, cobalt oxides, or the like, which may chemically react with many otherwise suitable seal materials. The seal material may also have a sintering temperature of less than about 1000° C., and may be stable at SOFC system operating temperatures (e.g., between 700 and 900° C.), when exposed to air and/or hydrogen. The seal material may have a high dielectric constant, such that the seal material may be configured to electrically isolate adjacent interconnects 400.
In some embodiments, the seals 424, 434 may be formed of a seal material that includes a primary component that comprises Si, Ca, Mg and optionally Al. In some embodiments, the primary component precursor material may include SiO2, CaO, MgO, and optionally Al2O3. The seal material may also include an optional secondary component. The secondary component precursor material may comprise non-zero amounts (e.g., at least 0.3 mol.%) of B2O3, BaO, SrO, La2O3, ZrO2, and/or Y2O3. In some embodiments, the seal material may include oxides of Si, Ca, Al, and Mg as the primary component and may optionally include B2O3, BaO, SrO, La2O3, ZrO2, Y2O3, or any combination thereof, as the secondary component. In some embodiments, the seal material may omit the secondary component (i.e., include 0 to less than 0.3 mol percent of the secondary component).
For example, the seal precursor material may include the primary component in an amount ranging from about 70 mol% to about 100 mol%, such as from about 80 mol% to 100 mol%, from about 90 mol% to about 100 mol%, or from about 92.5 mol% to about 100 mol%, and a balance of the secondary component. For example, the seal material may include from about 20 mol% to 0 mol%, from about 10 mol% to about 0.3 mol%, or from about 7.5 mol% to about 0.85 mol% of the secondary component.
In various embodiments, the seal material may include crystalline and amorphous phases after the precursor material has been applied to the interconnect and sintered. For example, the seal material may include a crystalline phase that comprises at least one of diopside ((CaO)1-x(MgO)x)2(SiO2)2, where 0.3≤ x ≤ 1.0, such as (CaMgSi2O6)), akermanite (Ca2MgSi2O7), monticellite (CaMgSiO4), wollastonite (CaSiO3), anorthite (CaAl2Si2O8) and/or magnesium aluminum silicate crystals. In one embodiment, the crystalline phase comprises primarily (e.g., at least 50 molar percent of the crystalline phase, such as 50 to 99 molar percent, such as 60 to 95 molar percent) diopside, with small quantities (e.g., 1 to 40, such as 5 to 20 molar percent) of anorthite, wollastonite, and magnesium aluminium silicate of the general formula MgOAl2O34SiO2.
In some embodiments, the seal material may include, by volume, from about 55% to about 85% of a crystalline phase and from about 45% to about 25% of an amorphous phase, such as from about 60% to about 80% of a crystalline phase and is from about 40% to about 20% of an amorphous phase, from about 65% to about 75% of a crystalline phase and from about 35% to about 25% of an amorphous phase, or about 70% of a crystalline phase and about 30% of an amorphous phase.
In some embodiments, the seal precursor material may include, on an oxide basis, by mol%: SiO2 in an amount ranging from about 25% to about 55%, such as from about 30% to about 50%, or from about 32% to about 50%; CaO in an amount ranging from about 20% to about 45%, such as from about 21% to about 43%, or from about 22% to about 41%; MgO in an amount ranging from about 5% to about 30%, such as from about 6% to about 27%, from about 7% to about 27%, or from about 5% to 25%; and Al2O3 in an amount ranging from about 0% to about 15%, such as from about 0.5% to about 15%, or from about 1% to about 14%.
In some embodiments, the seal precursor material may include a CMAS material that comprises, on an oxide basis, by mol%: SiO2 in an amount ranging from about 85% to about 95%, such as from about 87% to about 93%, or about 89.2%; Al2O3 in an amount ranging from about 2.5% to about 6.5%, such as from about 4.0% to about 5.0%, or about 4.6%; CaO in an amount ranging from about 2.0% to about 5.0%, such as from about 3.0% to about 4.0%, or about 3.5%; and MgO in an amount ranging from about 1.2% to about 4.2%, such as from about 2.2% to about 3.2%, or about 2.7%.
The foregoing method descriptions are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the order of steps in the foregoing embodiments may be performed in any order. Words such as “thereafter,” “then,” “next,” etc. are not necessarily intended to limit the order of the steps; these words may be used to guide the reader through the description of the methods. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the” is not to be construed as limiting the element to the singular.
Further, any step or component of any embodiment described herein can be used in any other embodiment.
The preceding description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Number | Date | Country | |
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63351104 | Jun 2022 | US | |
63278376 | Nov 2021 | US |