Solid oxide fuel cell stack with reduced leakage unit cells

Abstract

The present invention provides a solid oxide fuel cell stack and a method for sealing a planar solid oxide fuel cell. The unit cells in the stack each include a metal frame having a periphery that can provide a support surface for a membrane electrode assembly and form a fluid-tight seal with a bonded separator. The separator includes a peripheral lip that defines a cell receiving cavity so that a volume area is formed within the separator to accommodate at least a portion of the membrane electrode assembly, thereby creating a fluid-tight path for at least one of the reactants introduced into the corresponding anode layer or cathode layer of the membrane electrode assembly.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Application No. 16 / 000,171, filed on June 5, 2018, the entire disclosure of which is incorporated herein by reference. Background Art

[0003] The present disclosure relates generally to a solid oxide fuel cell (SOFC), and more particularly to a SOFC fuel cell stack in which each individual unit contains a metal frame that allows the corresponding membrane electrode assembly (MEA) to be sealingly bonded to adjacent flow separators as a way to reduce reactant leakage. Summary of the invention

[0004] The planar SOFC stack is composed of a plurality of mutually stacked unit cells, each of which includes an anode, a cathode and a solid oxide electrolyte sandwiched together as an MEA. The individual unit cells are physically separated from each other by a separator, which contains a channel for receiving reactants in the form of air or fuel in addition to providing an electrical connection between two individual unit cells. Regarding the flow of reactants, the fuel and air should not be mixed with each other before each reactant is introduced into the corresponding one of the anode or cathode of the MEA, as this may have an adverse effect on the performance of the fuel cell. In order to prevent such mixing and related leakage, the metal frame on which the MEA is mounted is bonded to an adjacent separator to avoid the use of glass sealants or other materials that are easily broken when subjected to slight vibrations or shocks and low-temperature sealant materials (such as polymer-based sealants) that cannot withstand typical SOFC operating temperatures.

[0005] According to one embodiment of the present disclosure, a SOFC stack includes a plurality of unit cells aligned along a stacking dimension or axis. Each unit cell includes: a metal frame, which is composed of a mounting surface on which an MEA is fixed to form a metal support cell (MSC); and a plurality of fluid-separated reactant channels, which allow fuel to be transported through the MEA anode layer and air to be transported through the MEA cathode layer, respectively. Each unit cell further includes a separator having a peripheral lip, the peripheral lip defining a cavity so that at least the anode layer of the MEA is contained within the volume area defined by the cavity and the peripheral lip. At least a portion of the mounting surface of the metal frame is bonded to the peripheral lip so that a fluid-tight seal is formed therebetween. Additional components such as the stacking upper and lower mounting plates can be mated to each other to apply a fixed pressure on each unit cell along the stacking dimension to form a SOFC stack.

[0006] According to another embodiment of the present disclosure, a method of sealing a planar SOFC includes: arranging a metal frame to have a mounting surface; placing an MEA so that it substantially fits within a hole defined by the mounting surface; and connecting a separator so that the mounting surface of the metal frame is bonded to a peripheral lip of the separator to form a fluid-tight seal therebetween. The separator includes a peripheral lip that defines a cavity so that at least an anode layer of the MEA is contained within a volumetric area defined by the cavity and the peripheral lip.

[0007] Additional features and advantages of the embodiments described herein will be set forth in the detailed description that follows, and will in part be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments described herein (including the detailed description that follows, the claims, and the accompanying drawings). BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following detailed description of specific embodiments of the present disclosure may be best understood when read in conjunction with the following drawings, in which like structures are indicated by like reference numerals, and in which:

[0009] Figure 1 is an exploded view of a dual-cell SOFC according to one or more embodiments of the present disclosure;

[0010] Figure 2A is like Figure 1 An upper perspective view of a gasket used in a SOFC stack;

[0011] Figure 2B is like Figure 1 An upper perspective view of an upper end separator used in a SOFC stack;

[0012] Figure 2C is like Figure 1 An upper perspective view of a middle partition used in a SOFC stack;

[0013] Figure 2D is like Figure 1 An upper perspective view of a lower end separator used in a SOFC stack;

[0014] Figure 3 is like Figure 1 An upper perspective view of a MSC used in a SOFC stack;

[0015] Figure 4A Is Figure 3 The MSCs are combined with Figure 1 An upper perspective view of an assembly made when an end baffle is used in a SOFC stack;

[0016] Figure 4B yes Figure 4AA side cross-sectional view of an MSC and a separator assembly, wherein the MSC and the separator are shown in an exploded view;

[0017] Figure 4C MSC and bulkhead assembly Figure 4A A side cross-sectional view of the station line CC; and

[0018] Figure 5 yes Figure 1 A perspective view of the uppermost portion of a SOFC stack depicting a distributed flow of reactants through an upper end plate according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0019] Embodiments of the present disclosure relate to an improved SOFC in which a bonded connection allows a fluid-tight seal to be formed between an MEA supported by a metal frame and an adjacent separator so as to substantially prevent air, such as air from the surrounding environment or from the cathode flow path of the MEA, from mixing with fuel in the area surrounding the anode layer of the MEA. In this way, air leakage can be minimized, which in turn promotes the reduction-oxidation stability of the anode layer of the MEA, which in turn reduces the likelihood of damage to the anode layer. Specifically, the bonded connection uses a metal structure that achieves a fluid-tight seal that is generally unaffected by physical and thermal shocks through one or both of similar coefficients of thermal expansion (CTE) or thermochemical compatibility to improve long-term stacking durability. In addition, such bonding can also simplify the manufacturing processes associated with forming the SOFC stack.

[0020] First reference Figure 1 , an exploded view of a SOFC stack 10 is shown in a theoretical dual-cell plate configuration. Thus, two unit cells 20 comprise substantially planar (i.e., flat) profiles that are stacked one on top of the other along a stacking dimension along the Y axis (i.e., vertical) in Cartesian space. Within this context, references to a particular stack, position, or dimension orientation will be understood to be in the Figure 1 , and small deviations therefrom due to slight misalignments relative to this spatial reference system are tolerable without any loss of generality. Furthermore, as used within this disclosure, the need for a particular component or feature, such as having an up or down directional attribute, will be understood to be based on Figure 1, such that a component exhibiting so-called "upper" properties will be understood to be further away from the Cartesian axis origin along the positive Y-axis shown than a component exhibiting so-called "lower" properties. For example, although the SOFC stack 10 is theoretically shown as being established along a vertical Y-axis; it will be appreciated that the SOFC stack 10 may be oriented in any suitable orientation, and any discussion of Cartesian or other directional properties associated with such an orientation will be similarly attributed to the corresponding surface, component, or other portion of the SOFC stack 10. Furthermore, although the stack 10 is shown as containing two unit cells 20 (as discussed in more detail below), it will be appreciated that a greater number of unit cells may be provided, and all such variations are considered to be within the scope of the present disclosure.

[0021] Each of the first and second unit cells 20 is spaced apart from each other along the stacking dimension of the Y axis. Additional interleaved components include intermediate partitions 30, end partitions 40, stack upper and lower placement plates 50, metal frames 60, MEAs 70, channel plates 80, gaskets 90, gasket rings 100, MSCs 110 (which are assemblies formed by joining metal frames 60 to corresponding MEAs 70 and reactant channels 120), all as will be discussed in more detail elsewhere in the present disclosure.

[0022] It will be appreciated that electrochemical interactions using fuel as one reactant and air as another reactant occur in the MEA 70, and these interactions in turn provide power in the form of electrical current for use by a load, such as an electric motor, an auxiliary power unit (APU), etc. It will also be appreciated that for simplicity, the MEA 70 is referred to as Figure 1 The structure is shown as a single layer, but is actually a three-layer structure having a substantially planar major surface and an edge-wise minor surface (e.g. Figure 4B and Figure 4C ) is constituted in which an electrolyte layer 74 is sandwiched between electrodes in the form of an anode layer 72 and a cathode layer 76, so that the O generated at the cathode layer 76 2-Ions flow through the electrolyte layer 74 and react with the fuel (e.g., H2 or CO) air at the anode layer 72, while the current generated by the free electron flow generated from the reduction of oxygen in the air at the cathode layer 76 and consumed during the oxidation of the fuel at the anode layer 72 can be used to power one or more external device loads. Within the present context, the terms "primary" and "secondary" - when used to describe a surface - refer to the amount of surface area, rather than the relative importance of this surface to the structure or operation of the SOFC stack 10 (in general or in particular one of its components). Therefore, those surfaces that protrude a larger surface area (e.g., the planar surface of the anode layer 72 or cathode layer 76 of the MEA 70 that forms a facing adjacent relationship with either of the separators 30, 40) are considered to be primary surfaces, such as surfaces to which other components or features can be mounted, attached or otherwise fixed, while those surfaces that protrude a smaller area (e.g., surfaces corresponding to edges formed on the MEA 70 or the metal frame 60) are considered to be secondary surfaces. Thus, terms such as "substantially planar", "edge" and the like will be understood within the present context as being interchangeable with terms describing such major and minor surfaces, respectively.

[0023] The remaining components that make up the SOFC stack 10 are used to provide mechanical, electrical, or fluid transport support for the MEAs 70. For example, direct structural coupling of each MEA 70 occurs through the metal frame 60, so that when they are joined to each other, a substantially integral structural coupling is formed in the form of an assembled MSC 110. Likewise, the transport of reactants into and out of each of the MEAs 70 can occur through aligned reactant channels 120. In one form, the reactant channels 120 are defined as a set of alignable holes formed in the corresponding intermediate spacers 30, end spacers 40, gaskets 90, and gasket rings 100, and are combined Figure 2A , Figure 2B , Figure 2C and Figure 5 10. In this form, the reactants can be caused to flow through the channels 120 along the stack dimensions so that the channels act as vertical manifolds. In another form, the reactant channels can be located outside the SOFC stack 10, for example in the form of structurally decoupled conduits, rather than being formed by an integrated assembly of various aligned and stacked components. It should be understood that these and other configurations regarding the degree of structural integration between the reactant channels 120 and the rest of the SOFC stack 10 are considered to be within the scope of the present disclosure. Figure 1In the form depicted in FIG. 1 , the alignment of these reactant channels 120 is such that each pair (e.g., formed by opposite corners being fluidly connected into a fluidly connected pair) promotes fluidly separated passages to respectively deliver fuel through the anode layer 72 of the MEA 70 and air through the cathode layer 76. By keeping them fluidly separated, the chance of accidental mixing of the different reactants can be minimized. In one form, the reactant channels 120 protrude primarily along the stack dimension so as to deliver sufficient amounts of the respective reactants (i.e., fuel for the anode layer 72 of the MEA 70 and air for the cathode layer 76 of the MEA 70). This is theoretically achieved by corresponding to Figure 1 The flow paths of "fuel input" and "fuel output" and "air input" and "air output" are depicted. Figure 2C , FIG. 4A to FIG. 4C as well as Figure 5 Discussed in more detail, the reactant channels 120 also include laterally oriented branch gates 130 that allow at least some of each reactant to be diverted from the main portion of the channels 120 to a corresponding one of the anode layer 72 or cathode layer 76 sides of each MEA 70. Within this context, the lateral direction of reactant flow is the direction of travel along the X-axis or Z-axis (or along the plane formed by the XZ axes) relative to the SOFC stack 10.

[0024] If combined Figure 2C (for the middle partition 30) and Figure 2D as well as FIG. 4A to FIG. 4C As discussed (for the end separator 40), the peripheral lips 34, 44 form upstanding walls that project upwardly from the generally planar major surfaces 36, 46 to define a slot-like volume area 38, 48 for receiving the placement of the major surface of the corresponding MSC 110. This volume area 38, 48 is formed as a generally U-shaped receiving cavity in one of the major surfaces 46 (in the end separator 40) or both major surfaces 36 (in the middle separator 30). As will be discussed elsewhere in this disclosure, the volume area 38, 48 is the volume area into which one of the reactants (i.e., fuel or air) flows in and out as part of their interaction with each other to produce electrical current in the MEA 70. In one form, the laterally oriented branch gate 130 is formed as a relatively small cutout in one or more of the upstanding peripheral lips 34, 44 of the respective baffles 30, 40, which define the volumetric regions 38, 48, so as to allow reactants to be introduced laterally from the reactant passage 120 and into the volumetric regions 38, 48. In one form, as Figure 1 As shown in , these laterally oriented branch gates 130 direct the corresponding reactants to flow in an XZ plane that is orthogonal to the flow of the reactants through the main portion of the reactant channel 120 .

[0025] Depending on the diameter of the flow path formed by the reactant channel 120, the size of the gasket ring 100 can be set to be assembled in the portion of the channel 120 defined by the hole 32,42 or 92 of the corresponding intermediate partition 30, the end partition 40 or the gasket 90, so that it can be parked on the lip, lug or related support structure that can be formed in these holes 32,42 or 92. By not having the same transverse cutout or related tail of the branch door 130 of the transverse orientation of the intermediate partition 30 or the end partition 40 in its periphery, the gasket 90 and the gasket ring 100 prevent the radial orientation of the corresponding channel 120 from flowing out, which then helps to provide the enhanced seal between the reactant channel 120 and the adjacent volume area 38,48, while retaining the reactant flow of the stacking size of the reactant channel 120. In addition, the gasket 90 can define a full-circle structure of the same size and shape (e.g., having substantially the same rectangular footprint) as the intermediate partition 30 or the end partition 40. In this way, when compressed between adjacent facing surfaces of one or more stacked intermediate diaphragms 30 and end diaphragms 40, the gasket 90 helps to further reduce any leakage of reactants and byproduct fluids and air from the surrounding environment. The gasket 90 can be constructed of a non-conductive compressible material. In one form, the sandwich-like alignment and compliant fit between the gasket 90, the gasket ring 100 and the intermediate diaphragm 30 and the end diaphragm 40 can be provided by the compressive clamping force of the bolt connection effect from the stacked upper and lower placement plates 50. The gasket ring 100 can be made of any of a variety of conventional or yet to be developed materials suitable for fuel cell assemblies, including, for example, glass, glass-ceramic, alumina felt, ceramic-ceramic, metal-ceramic, mica and high temperature Gu Lite (Thermiculite).

[0026] In addition to providing a compliant interface between adjacent components as a way to compensate for manufacturing tolerances by providing a minimum fixed distance between these components, the gasket 90 can also provide electrical insulation between these components. In fact, maintaining a minimum fixed distance between adjacent facing components helps to ensure such electrical insulation, wherein in a specific form, the minimum fixed distance can prevent the corresponding separators 30, 40 from electrically contacting each other. Of course, the compression effect generated on the SOFC stack 10 and the gasket 90 should not be greater than its compression limit to avoid excessive or undesirable plastic deformation of the material constituting the gasket 90, because such excessive deformation may cause a loss of electrical insulation, among other aspects.

[0027] The construction for the intermediate separator 30 as shown can allow it to act as a boundary between two adjacent stacked cells 20. In such a configuration, the intermediate separator 30 can act as a bipolar plate because the volume area 38 can be formed on two opposing side major surfaces 36. In addition, each opposing side and the accompanying volume area 38 cooperate with a corresponding one of the metal frame 60 of the MSC 110 and the MEA 70 to control the delivery and removal of the first reactant (e.g., fuel) on one side and the second reactant (e.g., air) on the other side to the corresponding volume area 38 in a manner understood by those skilled in the art of bipolar plates. In one form, the intermediate separator 30 and the end separators 40 are constructed of conductive materials and act as physical barriers between the cells 20, while the external circuit can also electrically connect the upper cells in the cells 20 to the lower cells in the cells 20 using appropriate series or parallel connections. A similarly configured volume region 48 of the end separator 40 may also be provided on a major surface arranged to adjacently face a corresponding one of the metal frame 60 of the MSC 110 and the inserted MEA 70 .

[0028] The channel plates 80 may be placed in a facing adjacent relationship relative to the cathode layer of the MEA 70 such that they are disposed between the MEA 70 and a corresponding one of the intermediate separators 30 or the end separators 40. The channel plates 80 are each positioned adjacent to a corresponding surface (e.g., an anode or cathode surface) of one of the MSCs 110. In one form, the channel plates 80 may each include one or more corresponding serpentine channels, as shown, to help facilitate air flow to the cathode layer (to be combined with the serpentine channels). Figure 4B and Figure 4C discussed in more detail). Figure 1 , but it should be understood that this is merely exemplary in nature and other configurations, such as parallel channel arrangements, are also considered to be within the scope of the present disclosure. In one form, the channel plate 80 can actually be formed of a porous, foamed or mesh-like structure to promote porosity, which in turn promotes the flow of air from the corresponding reactant channel 120 to the cathode layer of each MEA 70. In addition, the channel plate 80 can be used to establish electrical continuity with an external load or other circuit for delivering current from the unit cell 20.

[0029] In one form, the SOFC stack 10 may experience relatively high operating temperatures (i.e., up to about 1000° C.). It should be understood that when subjected to relatively high operating temperatures, various components of the SOFC stack 10 may experience thermal expansion, which may cause one or more of the first and second cells 20 and their corresponding support components to deform. The upper and lower mounting plates 50 may generate a fixing pressure on the cells 20 to reduce or substantially eliminate thermal expansion of the cells 20. More specifically, the upper and lower mounting plates 50 may each apply a compressive force along the stacking dimension by using bolts or other fastening or fixing devices. The amount of fixing pressure applied on each cell 20 may be based on the vertical height of the SOFC stack 10, which in turn may depend on the number of cells 20. More specifically, the fixing pressure required to reduce or substantially eliminate thermal expansion of the SOFC stack 10 may increase as the height of the SOFC stack 10 increases. In other words, increasing the number of cells 20 results in a higher fixing pressure required for the SOFC stack 10 to reduce or substantially eliminate the effects of thermal expansion. Similarly, reducing the number of unit cells 20 results in a lower fixing pressure required for the SOFC stack 10 .

[0030] Next reference Figures 2A to 2D , showing the gasket 90 ( Figure 2A )、Upper partition 40( Figure 2B ), the intermediate partition 30 with the inserted gasket 90 ( Figure 2C ) and the lower end partition 40 ( Figure 2D ) for each of the individual perspectives. Figure 2A , the body 94 of the gasket 90 can be shaped to define a central void 96 and a plurality of conduit-like holes 92 that correspond to the reactant channels 120 when aligned and stacked. In one form, the conduit-like holes 92 are disposed at each of the four corners of the rectangular body 94. Figure 2B , the upward facing major surface of the upper end partition 40 defines a generally smooth planar configuration to facilitate low-profile engagement with the adjacent stacked upper mounting plate 50. The thickness of the upper end partition 40 along the stacking dimension is visible along the edge of the peripheral lip 44. In addition, the recess N may be integrally formed as part of the upper end partition 40 to facilitate aligned stacking thereof with the upper mounting plate 50 and other components within the SOFC stack 10. In one form, latches or other alignment securing members may be placed within a plurality of alignment recesses N, which may be similarly formed on various other components such as the middle partition 30, the lower end partition 40, the gasket 90, etc. Specific reference is made to Figure 2C, the middle partition 30 shows a lateral turn in the form of a laterally oriented branch door 130 within the hole 32 and the reactant channel 120, which allows the introduction of at least some of each of the reactants and the subsequent removal of the main part of a set of coupled parts from the channel 120. The recessed trough-like nature of the volume area 38 can also be seen, which is formed as a cavity by the peripheral lip 34 and the lower surface 36. Specific reference Figure 2D The upwardly facing major surface of the lower end baffle 40 is connected to the lower end baffle 40 by the cooperation of the peripheral lip 44 and the lower surface 46. Figure 2C The middle partition 30 is generally similarly constructed to define a cavity and a corresponding volume area 48 as a means of forming a mating planar surface between the lower partition 40 and the MSC 110, as a means of forming a fluid-tight seal S F (If it will also be combined Figure 4B and Figure 4C Similarly, the laterally oriented branch gate 130 acts as a lateral diversion within a portion of the hole 42 to allow the introduction of at least some of each of the reactants and their subsequent removal from a main portion of a set of coupled portions of the channel 120.

[0031] Next reference Figure 3, shows a perspective view of an assembly of an MSC 110 formed by depositing or otherwise placing an MEA 70 onto a planar major surface 62 of a metal frame 60 defining a substantially planar profile. It should be appreciated that the relative thicknesses of the MEA 70 and the metal frame 60 are not shown to scale, as the edges corresponding to the minor surfaces 64 of the metal frame 60 are sometimes about 100 μm to 5000 μm or more narrowly, 100 μm to 300 μm, while the thicknesses of the deposited anode, cathode, and electrolyte layers are sometimes about 50 μm to 100 μm, or more narrowly about 200 μm. These dimensions are provided for contextual purposes only and should not be used to limit the scope of the present disclosure or claims. Direct structural coupling of each MEA 70 occurs through the metal frame 60; when engaged with each other, each MEA 70 and the corresponding metal frame 60 form a substantially integral structural coupling in the form of an assembled MSC 110. Although the MSC 110 is shown as a defined rectangular shape, it should be understood that other shapes (e.g., square, rounded rectangle, etc.) forming any number of closed polygons may also be used, and all variations are considered to be within the scope of the present disclosure. In one form, the metal frame 60 is made of a breathable metal foam (e.g., a metal foam having a chromium-rich iron-based alloy) in a manner similar to the foam-based or grid-based variations of the channel plate 80, thereby allowing reactant air to enter and exit the cathode layer 76. Such porous materials or metal foams can be produced by known methods, such as powder metallurgy, where sintering can be used as part of the entire powder metallurgy process to control the amount of this porosity. By using powdered metal, the metal frame 60 can avoid some durability issues that hinder ceramics. In one form, the cross-sectional area of ​​the MEA 70 is such that it is assembled on a planar major surface 62, which acts as a mounting surface for the metal frame 60, while leaving a peripheral border area 66 extending beyond the uncovered surface area footprint defined by the MEA 70. In the present context, components such as metal frame 60 and channel plate 80 that exhibit porous structure, construction or related properties are components that allow reactants (e.g., fuel) in gaseous form to flow through the thickness of these components in an amount sufficient to allow MEA 70 to perform its current generating function in the manner it is designed.

[0032] Next reference FIG. 4A to FIG. 4C , various views are shown showing the cooperation between one of the bulkheads 40 and the MSC 110. Figure 4A (For the sake of clarity, the exploded diagram shows that Figure 1 , Figure 4B and Figure 4C80 of the unit cells 20 of the metal frame 60, the MSC 110 is placed onto the separator 40 such that at least the downwardly facing surface of the metal frame 60 (or the optional channel plate (not shown at present)) is disposed within the volumetric area 48 of the adjacent facing lower end separator 40. The front perspective view shows the stacked and partially nested relationship between the lower end separator 40 and the MSC 110 and the substantially planar lugs of the upper surface defining the peripheral lip 44, on which the sealing bond between the separator 40 and the tab 68 is made, which defines at least a portion of the planar major surface 62 of the peripheral boundary area 66 of the metal frame 60. Although only the end separator 40 and the MSC 110 are shown at present, and as disclosed elsewhere, the present discussion is also applicable to bonding, joining or otherwise attaching the MSC 110 to one of the intermediate separators 30.

[0033] Specific reference Figure 4B and Figure 4C , Figure 4B The details associated with the MSC 110 and the lower bulkhead 40 are shown in exploded view prior to bonding, and Figure 4C1 shows an assembled view after the two components have been joined. The front cross-sectional view shows the various layers of the MEA 70, and the manner in which the MEA 70 can be fixed to the upper surface of the metal frame 60 to form the MSC 110. In one form, the metal frame 60 can include a tab 68 by compressing at least a portion of the peripheral boundary area 66 that forms a portion of the planar major surface 62. Specifically, the porous metal structure of the material from which the metal frame 60 is made is suitable for such compression along the stacking dimension, thereby allowing the formation of a thin, flat bonding surface B to be attached to the location of the corresponding upper surface of the peripheral lip 44 of the lower end separator 40. In this configuration, the tab 66 has a thinner profile along the stacking dimension than the central portion that forms the planar major surface 62. As previously mentioned, the MEA 70 includes a three-layer structure, in which the major surface of the anode layer 72 is placed on one major surface of the electrolyte layer 74, and the major surface of the cathode layer 76 is placed on the opposite major surface of the electrolyte layer 74. In one form, the anode layer 72, the electrolyte layer 74, and the cathode layer 76 are generally made of porous materials to promote the relatively free flow of reactants in gaseous form. For example, but not by way of limitation, the electrolyte layer 74 may be made of a zirconia-based electrolyte or a ceria-based electrolyte. In a specific embodiment, the zirconia-based electrolyte layer 74 may be selected from yttria-stabilized ZrO2 (YSZ), scandium-stabilized ZrO2 (ScSZ), calcium-stabilized ZrO2 (CSZ), and combinations thereof. Alternatively, the ceria-based electrolyte layer 74 may include rare earth-doped ceria. For example, the ceria-based electrolyte layer 74 may be selected from the group consisting of gadolinium-doped ceria (GDC), yttria-doped ceria (YDC), samarium-doped ceria (SmDC), and combinations thereof. Similarly, the cathode layer 76 may be made of any material that exhibits a low O2(g) reduction overpotential in the higher operating temperature range of the SOFC while having negligible interaction with the electrolyte layer 74. By way of example, but not limitation, the cathode layer 76 may be made of doped lanthanum-based perovskites and related materials, such as lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium manganite (LSM), yttria-stabilized ZrO2 / lanthanum strontium manganite (YSZ-LSM), and combinations thereof. In addition, the anode layer 72 may be made of a ceramic-metal mixture (i.e., a cermet) such as a mixture of metallic nickel based on a YSZ skeleton structure. The high porosity of the anode layer 72 helps facilitate the fuel (when in a gaseous state) delivered through its corresponding reactant channel 120. In one form, the anode layer 72 and the cathode layer 76 may be made by screen printing, plasma spraying, etc., while the electrolyte layer 74 may be made by plasma spraying, physical vapor deposition (PVD), sintering, sol-gel, screen printing, wet powder spraying, or other known thin film processes.Additional layers such as diffusion barriers (e.g., cerium gadolinium oxide (CGO), doped lanthanum-based perovskites, etc.) may be used in the interface regions between the various layers, such as in the electrolyte to cathode interface or the anode to metal substrate layer, where the metal substrate constituting the metal frame 60 may be in the form of a sintered powder or in the form of other structures that can be made with a porosity metric that can be used to promote reactant permeability. These diffusion barriers can be formed by known techniques such as PVD.

[0034] Regardless of the form of the partition 30, 40, the fluid-tight seal S formed at the bonding surface B between the partition and the metal frame 60 is F The horizontal fluid-tight seal S extends over at least some, if not all, of the common contact area of ​​its surface width in the plane formed by the XZ axis. In one form, such common contact area extends from the peripheral lip 44 of the diaphragm 40 to at least a portion of the overlapping outwardly extending tabs 68 of the metal frame 60. In one form, the horizontal fluid-tight seal S F Around the entire perimeter of the upper surface of the peripheral lip 44 of the lower end partition 40 and extending along at least a portion of the stacking dimension within the hole 42 and accompanying channel 120 of the corresponding intermediate partition 30, the hole and accompanying channel are not occupied by the laterally oriented branch door 130.

[0035] Volume area 48 acts as the previously discussed slot-shaped receiving cavity, and the vertical gap G formed by the reactant flow V How is the reactant (specifically, fuel as shown) flow permitted to encounter the channel plate 80 on its way to the metal frame 60 and subsequently to the downwardly facing major surface of the anode layer 72 of the MEA 70. Figure 4B and Figure 4C The channel 120 and the transversely oriented branch gate 130 that permits some of the fuel to be diverted from the main portion of the channel 120 are not shown, but it should be understood from the rest of the present disclosure that the delivery of fuel (also referred to as fuel flow F) after having been introduced through the transversely oriented branch gate 130 is in the vertical gap G of the reactant flow. V The reactant flow extends horizontally in the vertical gap G V Formed between the downward facing major surface of the channel plate 80 and the upward facing lower surface 46 of the lower end baffle 40 , the transversely oriented branch gate 130 permits some of the fuel flow F to be diverted from the main portion of the passage 120 .

[0036] Tabs 68 forming the periphery of the metal frame 60 may be bonded to the peripheral lip 44 so that when assembled together, a fluid-tight seal S is horizontally formed therebetween. F The joining may be in the form of welding, brazing, fastening, bonding, etc. Fluid-tight seal S FThe introduced fuel flow F is substantially prevented from leaking outwardly into the surrounding environment, and air is also substantially prevented from flowing inwardly from the surrounding environment into the anode layer 72 side of the MEA 70. In the form where the adjacent facing surfaces of the separator 40 are bonded to the metal frame 60 by welding, the material constituting the metal frame 60 is substantially resistant to deformation during welding. Similarly, the metal frame 60 and the bonded separator 40 can be made of the same conductive material, such as a metal or a metal alloy. In one form, the separator 40 and the bonded metal frame 60 can be constructed of dissimilar conductive materials, which all contain similar CTEs, as a way to help avoid cracks or other deformations during welding. In a more specific form, the CTE between the separator 40 and the metal frame 60 (and between the anode layer 72 of the MEA 70 and the metal frame 60) can be tailored to be substantially the same, wherein (for example) the diffusion barrier layer discussed previously can be used to prevent the interdiffusion of alloy components between adjacent layers.

[0037] although Figure 4B 1 and 1 , but it will be understood by those skilled in the art that in the case where the separator is configured as the middle separator 30, there is a substantially mirrored downward facing structure so that the middle separator 30 has bipolar plate characteristics. Similarly, in the case where the separator is configured as one or the other of the upper or lower end separators 40, such substantially mirrored opposite surface structures or related bipolar plate features are not required, and both configuration variations will be understood from the context and are within the scope of the present disclosure. Whether the separator is the middle separator 30 or one of the end separators 40, it can be seen that the MSC 110 is placed into the volume area 38, 48 formed within the corresponding separator 30, 40. The nested stacking of the MSC 110 with the adjacent separators of the separators 30, 40 is such that after being combined together (e.g., by welding as previously discussed, etc.), the thickness along the stacking dimension is not significantly greater than the thickness of the individual separators 30, 40. Thus, in a configuration where the SOFC stack 10 is comprised of a plurality of cells 20, the vertical height of the SOFC stack 10 can be reduced relative to an arrangement where such nesting does not exist, thereby allowing more cells 20 to be packed within a given amount of SOFC stack 10 height; it will be appreciated that such a reduction in the overall thickness of the cells 20 is particularly beneficial in transportation-based applications (such as the previously mentioned APU) where packaging and volume constraints are particularly severe. Regardless of the manner in which the metal frame 60 is coupled to the MEA 70 in the MSC 110, the planar major surface 62 can also provide the required rigidity to substantially prevent flexing or bending of the MEA 70.

[0038] MSC 110 is oriented relative to lower baffle 40 so that the vertical gap G along the reactant flow VThe exposure of the fuel flow F traveling along the upwardly facing lower surface 46 of the lower separator 40 in the lower chamber forms a substantially porous reactant flow continuum. This continuum means that the fuel flow F will sequentially encounter the anode layer 72, the planar major surface 62 of the metal frame 60, and the optional channel plate 80. In one form, the reactant flow vertical gap G V The thickness (i.e., along the stack dimension) is less than about one millimeter. With such a size, the vertical gap G V Allow fuel flow F to cross the main surface facing downwards of the channel plate 80 and the lower surface 46 facing upwards of the lower end separator 40 to be generally in a layered shape. Therefore, make fuel flow F contact as many surfaces facing reactants as possible. In one form, the surface facing reactants is the surface that first encounters corresponding air or fuel flow. For example, as shown in the figure, the channel plate 80 protrudes downwards from the rest of the MSC 110 so that it extends into the volume area 48 of the separator 40, becoming the first part exposed to fuel flow F. Similarly, in the configuration that the channel plate 80 may not be present on the fuel side of the unit cell 20, the anode layer 72 protrudes downwards from the rest of the MSC 110 so that it extends into the volume area 48 of the separator 40, becoming the first part of the MEA 70 that will be exposed to fuel flow F.

[0039] In addition, the minimum lateral inward distance along the X-axis as shown in the figure is between the edge of the MEA 70 and the fluid-tight seal S F In order to provide a thermal barrier level gap G for substantially preventing or reducing any thermal shock or related excessive heat transfer H , forming a fluid-tight seal S F MEA 70 may experience such thermal shock or related excessive heat transfer. In this form, MEA 70 is spaced inwardly from tabs 68 of metal frame 60 in the plane formed by the XZ axis to define a thermal barrier horizontal gap G H For example, if welding is used to create a fluid-tight seal S F , then the thermal barrier horizontal gap G H This helps ensure a low thermal conductivity gas-rich "dead zone" to reduce edgewise conduction of heat generated during welding or other bonding processes into the MEA 70. In some embodiments, the thermal barrier horizontal gap G is 1000 mm in a plane formed in the XZ axis. H The lateral inward extension may be at least about five millimeters to form a fluid-tight seal S F The length of the bond line is at least about four millimeters. Thus, in one form, despite the inclusion of a fluid-tight seal S F The width of the common placement area of ​​the bonding line relative to the thermal barrier horizontal gap G HThe ratio is about 0.8, but any lateral width ratio from about 0.5 to about 1.0 is also within the scope of the present disclosure.

[0040] Next, combine Figure 4B and Figure 4C refer to Figure 5 , showing a perspective elevation view of the uppermost unit cell 20 of a portion of a SOFC stack 10 in an assembled state, wherein for the sake of clarity, the Figure 1 Specifically, the aligned placement of the upper baffle plate 40 is stacked on top of the gasket 90, which in turn is stacked on the middle baffle plate 30. In one form, and assuming that the vertical upward movement of the fuel is delivered to each MEA 70 of the stack 10, the fuel flow F can traverse the inlet portion 120 formed at the opposite corners of the stack 10 through the respective holes 42, 92 and 32 of the corresponding upper end baffle plate 40, gasket 90 and middle baffle plate 30. I and corresponding outlet portion 120 O It will be appreciated that a comparable flow pattern is achieved by forming the other two inlet and outlet portions 120 in opposite corners for the other reactant (air). I , 120 O The fuel flow F initially traverses the channel 120 upward along the stack dimension and enters its inlet portion 120 I , and then through various transversely oriented branch doors 130 corresponding to each of the corresponding middle partition 30 and upper end partition 40. The fuel flow F can then pass horizontally through various vertical gaps G as shown in the figure V , where the vertical gap G of the reactant flow V The size and shape of the fuel flow F help promote the generally laminar flow discussed previously. Finally, the portion of the fuel flow F that has not yet diffused through the anode layer 72 and the electrolyte layer 74 to react with the air that has been delivered to the cathode layer 76 in a similar manner traverses the transversely oriented branch gate 130 at the opposite corner of the upper separator 40 and then passes through the outlet portion 120 along the stack dimension. O down.

[0041] It is obvious to those skilled in the art that various modifications and changes can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Therefore, this specification is intended to cover modifications and changes of the various embodiments described herein, provided that such modifications and changes fall within the scope of the attached claims and their equivalents.

[0042] It should be noted that one or more of the following claims utilize the term "wherein" as a transitional phrase. For purposes of defining the present invention, it should be noted that this term is introduced in the claims as an open transitional phrase that is used to introduce a recitation of a series of features of the structure of the claimed subject matter and should be interpreted in a similar manner to the more general open-ended introductory term "comprising."

Claims

1. A solid oxide fuel cell stack comprising a plurality of unit cells, a stacked upper placement plate and a stacked lower placement plate, wherein: The plurality of unit cells are aligned along a stacking dimension of the solid oxide fuel cell stack, At least one of the plurality of unit cells comprises a metal-supported cell and at least one separator; The metal-supported battery comprises a metal frame and a membrane electrode assembly; The metal frame includes a pair of planar major surfaces separated from each other by an edgewise minor surface; The membrane electrode assembly comprises a planar cathode layer, a planar anode layer and a planar electrolyte layer; The planar cathode layer is separated from the planar anode layer by a planar electrolyte layer such that the planar anode layer is located on a first surface of a pair of planar major surfaces of the metal frame; the at least one separator of the unit cell comprising a peripheral lip defining a cavity such that a second surface of the pair of planar major surfaces of the metal frame is received within a volumetric region defined by the cavity and the peripheral lip to form a plurality of reactant channels; The reactant channel includes an anode flow path and a cathode flow path; the anode flow path being formed between the planar major surface of the at least one separator and the second surface of the pair of planar major surfaces of the metal frame to define a vertical gap between the planar major surface of the at least one separator and the second surface of the pair of planar major surfaces of the metal frame; The cathode flow path is fluidly coupled to the planar cathode layer; At least a portion of the metal frame is bonded to the peripheral lip to form (a) a seal fluidly separating the anode flow path from the cathode flow path, and (b) a thermal barrier horizontal gap between the membrane electrode assembly and an upstanding wall of the at least one separator; The stacked lower seating plate cooperates with the stacked upper seating plate to apply a fixing pressure on the plurality of unit cells along a stacking axis. 2 . The solid oxide fuel cell stack of claim 1 , wherein the planar major surface of the metal frame comprises a porous structure.

3. The solid oxide fuel cell stack of claim 1, wherein the membrane electrode assembly is spaced laterally inward from an exposed outer edge of the metal frame in a plane orthogonal to the stacking axis to define the thermal barrier horizontal gap within the volumetric region. 4 . The solid oxide fuel cell stack according to claim 3 , wherein an uppermost portion of the cathode layer forms a corresponding upper surface of the membrane electrode assembly. 5 . The solid oxide fuel cell stack of claim 1 , wherein at least a portion of the metal frame bonded to the peripheral lip includes a tab to form at least a portion of a peripheral border region surrounding the metal frame. The solid oxide fuel cell stack of claim 1 , wherein the seal comprises a weld.

7. The solid oxide fuel cell stack of claim 1, wherein the reactant flow vertical gap defines a thickness along the stacking axis of no more than one millimeter.

8. The solid oxide fuel cell stack of claim 1, wherein the seal defines a transverse width ratio of at least 0.5 relative to the thermal barrier horizontal gap.

9. The solid oxide fuel cell stack of claim 8, wherein the thermal barrier horizontal gap defines a lateral width of five millimeters and the seal defines a lateral width of four millimeters.

10. The solid oxide fuel cell stack of claim 1, wherein the plurality of fluidly separated reactant channels are formed along the stacking dimension in the peripheral lip.

11. The solid oxide fuel cell stack of claim 1, wherein the metal frame has a coefficient of thermal expansion equivalent to a coefficient of thermal expansion of at least the portion of the peripheral lip bonded to the major surface of the metal frame. 12 . The solid oxide fuel cell stack of claim 1 , wherein the at least one separator plate comprises a plurality of separator plates, the plurality of separator plates comprising at least one of a middle separator plate and an end separator plate.

13. The solid oxide fuel cell stack according to any one of claims 1 to 12, further comprising at least one of the following: a channel plate disposed within the volume area; and a gasket disposed against the separator along the stacking dimension and adjacently facing a surface of the separator, wherein the gasket defines a plurality of holes therein, the plurality of holes comprising: a first aperture having a surface area defining a size and shape along the stack dimension that is substantially equivalent to a size and shape of the membrane electrode assembly; and A second plurality of apertures are aligned with the plurality of fluidly separated reactant channels along the stacking dimension. 14 . The solid oxide fuel cell stack of claim 13 , wherein the channel plate and the metal frame comprise a porous structure.

Images