Patent Description:
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 <NUM> and <NUM>, 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 are 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 have 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.

<CIT> discloses a fuel cell stack fuel flow structure comprising a fastening plate, an insulating plate, and a current collecting plate, wherein the insulating plate is disposed between the fastening plate and the current collecting plate.

The present invention provides a fuel cell stack fuel flow structure according to claim <NUM>, and a fuel cell stack according to claim <NUM>. Further embodiments of the present invention are disclosed in the dependent claims.

According to various embodiments of the present disclosure, provided is a fuel cell stack including the fuel plenum, cross-flow interconnects stacked on the fuel plenum; and solid oxide fuel cells disposed between the interconnects.

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 drawings are not necessarily to scale, and are intended to illustrate various features of the invention.

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 +/- <NUM> % X.

<FIG> is a perspective view of a conventional fuel cell column <NUM>, <FIG> is a perspective view of one counter-flow solid oxide fuel cell (SOFC) stack <NUM> included in the column <NUM> of <FIG> is a side cross-sectional view of a portion of the stack <NUM> of <FIG>.

Referring to <FIG>, the column <NUM> may include one or more stacks <NUM>, a fuel inlet conduit <NUM>, an anode exhaust conduit <NUM>, and anode feed/return assemblies <NUM> (e.g., anode splitter plates (ASP's) <NUM>). The column <NUM> may also include side baffles <NUM> and a compression assembly <NUM>. The side baffles <NUM> may be connected to the compression assembly <NUM> and an underlying stack component (not shown) by ceramic connectors <NUM>. The fuel inlet conduit <NUM> is fluidly connected to the ASP's <NUM> and is configured to provide the fuel feed to each ASP <NUM>, and anode exhaust conduit <NUM> is fluidly connected to the ASP's <NUM> and is configured to receive anode fuel exhaust from each ASP <NUM>.

The ASP's <NUM> are disposed between the stacks <NUM> and are configured to provide a hydrocarbon fuel containing fuel feed to the stacks <NUM> and to receive anode fuel exhaust from the stacks <NUM>. For example, the ASP's <NUM> may be fluidly connected to internal fuel riser channels <NUM> formed in the stacks <NUM>, as discussed below.

Referring to <FIG>, the stack <NUM> includes multiple fuel cells <NUM> that are separated by interconnects <NUM>, which may also be referred to as gas flow separator plates or bipolar plates. Each fuel cell <NUM> includes a cathode electrode <NUM>, a solid oxide electrolyte <NUM>, and an anode electrode <NUM>.

Each interconnect <NUM> electrically connects adjacent fuel cells <NUM> in the stack <NUM>. In particular, an interconnect <NUM> may electrically connect the anode electrode <NUM> of one fuel cell <NUM> to the cathode electrode <NUM> of an adjacent fuel cell <NUM>. <FIG> shows that the lower fuel cell <NUM> is located between two interconnects <NUM>.

Each interconnect <NUM> includes ribs <NUM> that at least partially define fuel channels 8A and air channels 8B. The interconnect <NUM> may operate as a gas-fuel separator that separates a fuel, such as a hydrocarbon fuel, flowing to the fuel electrode (i.e. anode <NUM>) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e. cathode <NUM>) of an adjacent cell in the stack. At either end of the stack <NUM>, there may be an air end plate or fuel end plate (not shown) for providing air or fuel, respectively, to the end electrode.

<FIG> is a top view of the air side of the conventional interconnect <NUM>, and <FIG> is a top view of a fuel side of the interconnect <NUM>. Referring to <FIG> and <FIG>, the air side includes the air channels 8B. Air flows through the air channels 8B to a cathode electrode <NUM> of an adjacent fuel cell <NUM>. In particular, the air may flow across the interconnect <NUM> in a first direction A as indicated by the arrows.

Ring seals <NUM> may surround fuel holes 22A of the interconnect <NUM>, to prevent fuel from contacting the cathode electrode. Peripheral strip-shaped seals <NUM> are located on peripheral portions of the air side of the interconnect <NUM>. The seals <NUM>, <NUM> 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 <NUM>.

Referring to <FIG> and <FIG>, the fuel side of the interconnect <NUM> may include the fuel channels 8A and fuel manifolds <NUM> (e.g., fuel plenums). Fuel flows from one of the fuel holes 22A, into the adjacent manifold <NUM>, through the fuel channels 8A, and to an anode <NUM> of an adjacent fuel cell <NUM>. Excess fuel may flow into the other fuel manifold <NUM> and then into the adjacent fuel hole 22A. In particular, the fuel may flow across the interconnect <NUM> in a second direction B, as indicated by the arrows. The second direction B may be perpendicular to the first direction A (see <FIG>).

A frame-shaped seal <NUM> is disposed on a peripheral region of the fuel side of the interconnect <NUM>. 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 <NUM>.

Accordingly, a conventional counter-flow fuel cell column, as shown in <FIG>, <FIG>, may include complex fuel distribution systems (fuel rails and anode splitter plates). In addition, the use of an internal fuel riser may require holes in fuel cells and corresponding seals, which may reduce an active area thereof and may cause cracks in the ceramic electrolytes of the fuel cells <NUM>.

The fuel manifolds <NUM> may occupy a relatively large region of the interconnect <NUM>, which may reduce the contact area between the interconnect <NUM> and an adjacent fuel cell by approximately <NUM>%. The fuel manifolds <NUM> are also relatively deep, such that the fuel manifolds <NUM> represent relatively thin regions of the interconnect <NUM>. Since the interconnect <NUM> 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 <NUM> 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 <NUM> a fuel cell <NUM> 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.

<FIG> is a perspective view of a fuel cell stack <NUM>, according to various embodiments of the present disclosure, <FIG> is an exploded perspective view of a portion of the stack <NUM> of <FIG> is a top view of the fuel side of an interconnect <NUM> included in the stack <NUM>, and <FIG> is a schematic view of a fuel cell included in the stack <NUM>.

Referring to <FIG>, the fuel cell stack <NUM>, which may also be referred to as a fuel cell column because it lacks ASP's, includes multiple fuel cells <NUM> that are separated by interconnects <NUM>, which may also be referred to as gas flow separator plates or bipolar plates. One or more stacks <NUM> may be thermally integrated with other components of a fuel cell power generating system (e.g., one or more anode tail gas oxidizers, fuel reformers, fluid conduits and manifolds, etc.) in a common enclosure or "hotbox.

The interconnects <NUM> are made from an electrically conductive metal material. For example, the interconnects <NUM> may comprise a chromium alloy, such as a Cr-Fe alloy. The interconnects <NUM> 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 <NUM> comprises more than about <NUM>% chromium by weight, such as about <NUM>-<NUM>% (e.g., <NUM>%) chromium by weight. An interconnect <NUM> may also contain less than about <NUM>% iron by weight, such as about <NUM>-<NUM>% (e.g., <NUM>%) iron by weight, may contain less than about <NUM>% by weight, such as about zero to <NUM>% by weight, of other materials, such as yttrium or yttria, as well as residual or unavoidable impurities.

Each fuel cell <NUM> may include a solid oxide electrolyte <NUM>, an anode <NUM>, and a cathode <NUM>. In some embodiments, the anode <NUM> and the cathode <NUM> may be printed on the electrolyte <NUM>. In other embodiments, a conductive layer <NUM>, such as a nickel mesh, may be disposed between the anode <NUM> and an adjacent interconnect <NUM>. The fuel cell <NUM> does not include through-holes, such as the fuel holes of conventional fuel cells. Therefore, the fuel cell <NUM> avoids cracks that may be generated due to the presence of such through-holes.

An upper most interconnect <NUM> and a lowermost interconnect <NUM> of the stack <NUM> 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 <NUM>. As used herein, an "interconnect" may refer to either an interconnect located between two fuel cells <NUM> or an end plate located at an end of the stack and directly adjacent to only one fuel cell <NUM>. Since the stack <NUM> does not include ASPs and the end plates associated therewith, the stack <NUM> 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 <NUM> may include side baffles <NUM>, a fuel plenum <NUM>, and a compression assembly <NUM>. The side baffles <NUM> may be formed of a ceramic material and may be disposed on opposing sides of the fuel cell stack <NUM> containing stacked fuel cells <NUM> and interconnects <NUM>. The side baffles <NUM> may connect the fuel plenum <NUM> and the compression assembly <NUM>, such that the compression assembly <NUM> may apply pressure to the stack <NUM>. The side baffles <NUM> may be curved baffle plates, such each baffle plate covers at least portions of three sides of the fuel cell stack <NUM>. For example, one baffle plate may fully cover the fuel inlet riser side of the stack <NUM> 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 <NUM>. The curved baffle plates provide an improved air flow control through the stack compared to the conventional baffle plates <NUM> which cover only one side of the stack. The fuel plenum <NUM> may be disposed below the stack <NUM> and may be configured to provide a hydrogen-containing fuel feed to the stack <NUM>, and may receive an anode fuel exhaust from the stack <NUM>. The fuel plenum <NUM> may be connected to fuel inlet and outlet conduits <NUM> which are located below the fuel plenum <NUM>.

Each interconnect <NUM> electrically connects adjacent fuel cells <NUM> in the stack <NUM>. In particular, an interconnect <NUM> may electrically connect the anode electrode of one fuel cell <NUM> to the cathode electrode of an adjacent fuel cell <NUM>. As shown in <FIG>, each interconnect <NUM> may be configured to channel air in a first direction A, such that the air may be provided to the cathode of an adjacent fuel cell <NUM>. Each interconnect <NUM> may also be configured to channel fuel in a second direction F, such that the fuel may be provided to the anode of an adjacent fuel cell <NUM>. Directions A and F may be perpendicular, or substantially perpendicular. As such, the interconnects <NUM> may be referred to as cross-flow interconnects.

The interconnect <NUM> may include fuel holes that extend through the interconnect <NUM> and that are configured for fuel distribution. For example, the fuel holes may include one or more fuel inlets <NUM> and one or more fuel (e.g., anode exhaust) outlets <NUM>, which may also be referred to as anode exhaust outlets <NUM>. The fuel inlets and outlets <NUM>, <NUM> may be disposed outside of the perimeter of the fuel cells <NUM>. As such, the fuel cells <NUM> may be formed without corresponding through-holes for fuel flow. The combined length of the fuel inlets <NUM> and/or the combined length of the fuel outlets <NUM> may be at least <NUM>% of a corresponding length of the interconnect <NUM> e.g., a length taken in direction A.

In one embodiment, each interconnect <NUM> contains two fuel inlets <NUM> separated by a neck portion <NUM> of the interconnect <NUM>, as shown in <FIG>. However, more than two fuel inlets <NUM> may be included, such as three to five inlets separated by two to four neck portions <NUM>. In one embodiment, each interconnect <NUM> contains two fuel outlets <NUM> separated by a neck portion <NUM> of the interconnect <NUM>, as shown in <FIG>. However, more than two fuel outlets <NUM> may be included, such as three to five outlets separated by two to four neck portions <NUM>.

The fuel inlets <NUM> of adjacent interconnects <NUM> may be aligned in the stack <NUM> to form one or more fuel inlet risers <NUM>. The fuel outlets <NUM> of adjacent interconnects <NUM> may be aligned in the stack <NUM> to form one or more fuel outlet risers <NUM>. The fuel inlet riser <NUM> may be configured to distribute fuel received from the fuel plenum <NUM> to the fuel cells <NUM>. The fuel outlet riser <NUM> may be configured to provide anode exhaust received from the fuel cells <NUM> to the fuel plenum <NUM>.

Unlike the flat related art side baffles <NUM> of <FIG>, the side baffles <NUM> may be curved around edges of the interconnects <NUM>. In particular, the side baffles <NUM> may be disposed around the fuel inlets <NUM> and outlets <NUM> of the interconnects <NUM>. Accordingly, the side baffles may more efficiently control air flow through air channels of the interconnects <NUM>, which are exposed between the side baffles <NUM> and are described in detail with regard to <FIG>.

In various embodiments, the stack <NUM> may include at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM> fuel cells, which may be provided with fuel using only the fuel risers <NUM>, <NUM>. 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 <NUM>, <NUM> shown in <FIG>.

Each interconnect <NUM> 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 <NUM>-<NUM>%). For example, the interconnects <NUM> may comprise a metal (e.g., a chromium-iron alloy, such as <NUM>-<NUM> weight percent iron, optionally <NUM> or less weight percent yttrium and balance chromium alloy), and may electrically connect the anode or fuel-side of one fuel cell <NUM> to the cathode or air-side of an adjacent fuel cell <NUM>. An electrically conductive contact layer, such as a nickel contact layer (e.g., a nickel mesh), may be provided between anode and each interconnect <NUM>. Another optional electrically conductive contact layer may be provided between the cathode electrodes and each interconnect <NUM>.

A surface of an interconnect <NUM> that in operation is exposed to an oxidizing environment (e.g., air), such as the cathode-facing side of the interconnect <NUM>, 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)<NUM>O<NUM> spinel (MCO), can be used instead of or in addition to LSM. Any spinel having the composition Mn<NUM>-xCo<NUM>+xO<NUM> (<NUM> ≤ x ≤ <NUM>) or written as z(Mn<NUM>O<NUM>) + (<NUM>-z)(Co<NUM>O<NUM>), where (<NUM>/<NUM> ≤ z ≤ <NUM>/<NUM>) or written as (Mn, Co)<NUM>O<NUM> 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.

<FIG> are plan views showing, respectively, an air side and a fuel side of the cross-flow interconnect <NUM>, according to various embodiments of the present disclosure. Referring to <FIG>, the air side of the interconnect <NUM> may include ribs <NUM> configured to at least partially define air channels <NUM> configured to provide air to the cathode of a fuel cell <NUM> disposed thereon. The air side of the interconnect <NUM> may be divided into an air flow field <NUM> including the air channels <NUM>, and riser seal surfaces <NUM> disposed on two opposing sides of the air flow field <NUM>. One of the riser seal surfaces <NUM> may surround the fuel inlets <NUM> and the other riser seal surface <NUM> may surround the fuel outlets <NUM>. The air channels <NUM> and ribs <NUM> may extend completely across the air side of the interconnect <NUM>, such that the air channels <NUM> and ribs <NUM> terminate at opposing peripheral edges of the interconnect <NUM>. In other words, when assembled into a stack <NUM>, opposing ends of the air channels <NUM> and ribs <NUM> are disposed on opposing (e.g., front and back) outer surfaces of the stack, to allow the blown air to flow through the stack. Therefore, the stack may be externally manifolded for air.

Riser seals <NUM> may be disposed on the riser seal surface <NUM>. For example, one riser seal <NUM> may surround the fuel inlets <NUM>, and one riser seal <NUM> may surround the fuel outlets <NUM>. The riser seals <NUM> may prevent fuel and/or anode exhaust from entering the air flow field <NUM> and contacting the cathode of the fuel cell <NUM>. The riser seals <NUM> may also operate to prevent fuel from leaking out of the fuel cell stack <NUM> (see <FIG>).

Referring to <FIG>, the fuel side of the interconnect <NUM> may include ribs <NUM> that at least partially define fuel channels <NUM> configured to provide fuel to the anode of a fuel cell <NUM> disposed thereon. The fuel side of the interconnect <NUM> may be divided into a fuel flow field <NUM> including the fuel channels <NUM>, and a perimeter seal surface <NUM> surrounding the fuel flow field <NUM> and the fuel inlets and outlets <NUM>, <NUM>. The ribs <NUM> and fuel channels <NUM> may extend in a direction that is perpendicular or substantially perpendicular to the direction in which the air-side channels <NUM> and ribs <NUM> extend.

A frame-shaped perimeter seal <NUM> may be disposed on the perimeter seal surface <NUM>. The perimeter seal <NUM> may be configured to prevent air entering the fuel flow field <NUM> and contacting the anode on an adjacent fuel cell <NUM>. The perimeter seal <NUM> may also operate to prevent fuel from exiting the fuel risers <NUM>, <NUM> and leaking out of the fuel cell stack <NUM> (see <FIG>).

The seals <NUM>, <NUM> may comprise a glass or ceramic seal material. The seal material may have a low electrical conductivity. In some embodiments, the seals <NUM>, <NUM> may be formed by printing one or more layers of seal material on the interconnect <NUM>, followed by sintering.

As shown in <FIG>, in a conventional fuel cell system, fuel and fuel exhaust are provided to and received from a fuel cell stack through metal anode splitter plates <NUM>. The anode splitter plates <NUM> which are fluidly connected to one another by the fuel inlet conduit <NUM> and the anode exhaust conduit <NUM>. The conduits <NUM>, <NUM> include metal tubes that are welded to the anode splitter plates <NUM> and to ceramic components that serve as dielectric breaks. As such, fluidly connecting the anode splitter plates <NUM> relies upon expensive dielectric components and a significant amount of on-site welding. Therefore, there is a need for a more cost effective method for providing fuel to, and receiving fuel exhaust from, a fuel cell stack.

<FIG> is an exploded top perspective view of a fuel flow structure <NUM>, according to various embodiments of the present disclosure, and <FIG> is an exploded bottom perspective view of the fuel flow structure <NUM> of <FIG>. Referring to <FIG> and <FIG>, the fuel flow structure <NUM> includes fuel conduits <NUM> and a fuel plenum <NUM>. The fuel plenum <NUM> may include a seal ring <NUM>, glass or glass ceramic seals <NUM>, a base plate <NUM>, a dielectric layer <NUM>, a cover plate <NUM>, a seal plate <NUM>, and a manifold plate <NUM>.

The fuel plenum <NUM> may be configured to form a fluid-tight connection with the fuel conduits <NUM>. The fuel conduits <NUM> may include an inlet conduit 320A configured to provide fuel to the fuel plenum <NUM>, and an outlet conduit 320B configured to receive fuel exhaust from the fuel plenum <NUM>. The fuel conduits <NUM> may include metal tubes <NUM>, metal bellows <NUM>, and dielectric rings <NUM>. The metal tubes <NUM> may be coupled to the bellows <NUM> and the dielectric rings <NUM> by brazing, welding, or press-fitting, for example. The bellows <NUM> may act to compensate for differences in coefficients of thermal expansion between fuel cell components by deforming to absorb stress. In alternate embodiments, the metal tubes <NUM> may themselves include, or be made entirely of bellows, rather than be coupled with the bellows <NUM> such that the metal tubes/bellows <NUM> may be directly coupled with the dielectric ring <NUM>. The dielectric rings <NUM> may operate as dielectric breaks, to prevent current from being conducted through the fuel conduits <NUM> and electrically shorting a fuel cell stack disposed on the fuel plenum <NUM>.

The base plate <NUM>, dielectric layer <NUM>, and cover plate <NUM> may respectively include inlet holes 361A, 365A, 367A and outlet holes 361B, 365B, 367B, which may be through-holes that extend through the respective plates and layer. The base plate <NUM> may include protrusions <NUM> configured to mate with ceramic connectors <NUM>, as shown in <FIG>. The base plate <NUM> and the cover plate <NUM> may be formed of a densified dielectric material. For example, the base plate <NUM> and the cover plate <NUM> may be formed of a substantially non-porous, electrically-insulating ceramic material, such as alumina, zirconia, yttria stabilized zirconia (YSZ) (e.g., <NUM> % yttria stabilized zirconia), or the like. The base plate <NUM> and the cover plate <NUM> may be rigid plates configured to provide support to the dielectric layer <NUM>.

In some embodiments, the dielectric layer <NUM> may be formed of a ceramic material having a higher dielectric constant than the ceramic materials of the base plate <NUM> and/or the cover plate <NUM>. In other words, the dielectric layer <NUM> may be able to withstand a higher maximum electric field without electrical breakdown and becoming electrically conductive (i.e., have a higher breakdown voltage) than the base plate <NUM> and the cover plate <NUM>. For example, the dielectric layer <NUM> may be formed of one or more layers of a porous ceramic yarn or fabric that is highly electrically insulating at high temperatures, such as Nextel ceramic fabrics numbers <NUM>, <NUM> or <NUM>, available from <NUM> Co.

In other embodiments, the dielectric layer <NUM> may be formed of a ceramic matrix composite (CMC) material, or any comparable material that has high dielectric strength, due to having a high surface area to volume ratio. The CMC may include, for example, a matrix of aluminum oxide (e.g., alumina), zirconium oxide or silicon carbide. Other matrix materials may be selected as well. The fibers may be made from alumina, carbon, silicon carbide, or any other suitable material. In one embodiment, both matrix and fibers may comprise alumina. Accordingly, the dielectric layer <NUM> may be configured to operate as a dielectric break to prevent electrical conduction through the fuel plenum <NUM>.

The cover plate <NUM> and the base plate <NUM> may have a higher density than the dielectric layer <NUM>. For example, the cover plate <NUM> and/or the base plate <NUM> may be formed of a fully dense ceramic material, such as <NUM> % to <NUM> % dense alumina, or the like. The cover plate <NUM> is configured to separate the seal plate <NUM> from the dielectric layer <NUM>. As such, the cover plate <NUM> may be configured to prevent the diffusion of metallic species from the seal plate <NUM> into the dielectric layer <NUM>. For example, the cover plate <NUM> may reduce and/or prevent the diffusion of chromium species (e.g., chromium oxides) from the seal plate <NUM> into the dielectric layer <NUM>, in order to prevent the chromium species from reducing the dielectric strength of the dielectric layer <NUM> and/or otherwise degrading the structural integrity of the dielectric layer <NUM>.

The seal plate <NUM> and the manifold plate <NUM> may be formed of a metal or metal alloy, such as stainless steel, that may be easily welded to the fuel conduits <NUM>. For example, the seal plate <NUM> and/or the manifold plate <NUM> may be formed of <NUM> stainless steel or the like. <NUM> stainless steel includes <NUM> to <NUM> weight % Cr, <NUM> weight % or less Mn, <NUM> weight % or less of one or more of Si, Ni, C, P and/or S, and balance Fe. In some embodiments, the seal plate <NUM> and/or the manifold plate <NUM> may be formed by brazing multiple metal sub-plates together. In embodiments formed using metal sub-plates, each of the sub-plates may be cut to form various structures, such as holes and/or channels, prior to, or after, the brazing process. In some embodiments, laser cutting or the like may be used to cut such structures.

The seal plate <NUM> and the manifold plate <NUM> may respectively include coatings <NUM>, <NUM> on one or both sides, such as at least on the sides of the plates <NUM>, <NUM> that face each other. The coatings <NUM>, <NUM> may have a thickness ranging from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, from about <NUM> to about <NUM>, or about <NUM>. Typically, the coatings <NUM>, <NUM> may comprise a metal oxide material, such as a perovskite material, for example, lanthanum strontium manganite (LSM). Alternatively, other metal oxide coatings, such as a spinel, such as an (Mn, Co)<NUM>O<NUM> spinel (MCO), can be used instead of or in addition to LSM. Any spinel having the composition Mn<NUM>-xCo<NUM>+xO<NUM> (<NUM> ≤ x ≤ <NUM>) or written as z(Mn<NUM>O<NUM>) + (<NUM>-z)(Co<NUM>O<NUM>), where (<NUM>/<NUM> ≤ z ≤ <NUM>/<NUM>) or written as (Mn, Co)<NUM>O<NUM> 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 coatings <NUM>, <NUM>. The coatings <NUM>, <NUM> may be formed using a spray coating or dip coating process and may be applied to substantially all the outer surfaces of the seal plate <NUM> and the manifold plate <NUM>.

The seal plate <NUM> may include an inlet hole 374A and an outlet hole 374B, which may be through-holes that extend between top and bottom surfaces thereof. The manifold plate <NUM> may include a bottom inlet hole 384A and a bottom outlet hole 384B formed in the bottom surface thereof, and top inlet holes 390A and top outlet holes 390B, which may be formed in the top surface thereof, on opposing sides of the manifold plate <NUM>. While three top inlet holes 390A and three top outlet holes 390B are shown, the present disclosure is not limited to any particular number of top outlet and inlet holes 390A, 390B. For example, the manifold plate <NUM> may include two, four, five or more top inlet holes 390A, and may include two, four, five or more top outlet holes 390B, depending on a number of fuel inlets and outlets included in the interconnects <NUM> of a corresponding fuel cell stack. For example, if the interconnects has three inlets and three outlets, then the manifold plate <NUM> has three inlet holes 390A and three outlet holes 390B.

The base plate <NUM>, dielectric layer <NUM>, cover plate <NUM>, seal plate <NUM>, and manifold plate <NUM> may be stacked on one another, such that the inlet holes 361A, 365A, 367A, 374A, 384A are aligned to form an inlet conduit passage 352A, and the outlet holes 361B, 365B, 367B, 374B, 384B are aligned to form an outlet conduit passage 352B. The inlet and outlet conduits 320A, 320B may be inserted into the respective inlet and outlet conduit passages 352A, 352B such that ends <NUM> of the inlet and outlet conduits 320A, 320B may extend up to and/or past the upper surface of the seal plate <NUM>.

<FIG> is a top view of the seal plate <NUM>, and <FIG> is a cross-sectional view taken along line L3 of <FIG>.

An inlet seal region 378A and an outlet seal region 378B may be respectively formed around the inlet hole 374A and an outlet hole 374B in areas where the coating <NUM> is not applied to the top surface of the seal plate <NUM>. As such, the inlet and outlet seal regions 378A, 378B may have a depth D2 equal to the thickness of the coating <NUM>, such as a depth D2 of about <NUM>.

<FIG> is a bottom view of the manifold plate <NUM>, <FIG> is a cross-sectional view taken along line L4 of <FIG> is a schematic top view of the manifold plate <NUM>, according to various embodiments of the present disclosure. Referring to <FIG>, inlet and outlet recesses 386A, 386B may be formed in the bottom surface of the manifold plate <NUM>, respectively surrounding the bottom inlet and outlet holes 384A, 384B. The inlet and outlet recesses 386A, 386B may have a depth D3 ranging from about <NUM> to about <NUM>.

Inlet and outlet seal regions 388A, 388B may be respectively formed around the inlet and outlet recesses 386A, 386B, in areas where the coating <NUM> is not applied to the bottom surface of the manifold plate <NUM>. As such, the inlet and outlet seal regions 388A, 388B may have a depth D4 equal to the thickness of the coating <NUM>, such as a depth D4 of about <NUM>.

The manifold plate <NUM> may also include internal inlet channels 392A and outlet channels 392B. The inlet channels 392A may fluidly connect the bottom inlet hole 384A to respective top inlet holes 390A. The outlet channels 392B may fluidly connect the bottom outlet hole 384B to respective top outlet holes 390B. The inlet channels 392A may be configured such that substantially equal amounts of fuel (e.g., equal fuel flow rates) are provided to each top inlet hole 390A from the common bottom inlet hole 384A. The outlet channels 392B may be configured such that substantially equal amounts of fuel exhaust are provided from each top outlet hole 390B to the common bottom outlet hole 384B.

In addition, the manifold plate <NUM> may include an electrical contact <NUM>. The manifold plate <NUM> may be electrically connected to the bottom of a fuel cell stack, and the electrical contact <NUM> may extend laterally from the manifold plate <NUM> and may be configured to provide a connection point for connecting the manifold plate <NUM> to a current collection circuit.

<FIG> is a vertical cross-sectional view taken along line L1 of <FIG>, showing the assembled fuel plenum <NUM> and inlet conduit 320A, and <FIG> is a vertical cross-sectional view or along line L2 of <FIG>, showing the assembled fuel plenum <NUM> and outlet conduit 320B.

Referring to <FIG>, <FIG>, <FIG>, and <FIG>, the base plate <NUM>, dielectric layer <NUM>, cover plate <NUM>, seal plate <NUM>, and manifold plate <NUM> are stacked on one another, thereby forming the inlet conduit passage 352A and the outlet conduit passage 352B. The inlet conduit 320A may be inserted in the inlet conduit passage 352A, facing the bottom inlet hole 384A. The outlet conduit 320B may be inserted in the outlet conduit passage 352B, facing the bottom outlet hole 384B.

A first seal ring 354A may be disposed in the inlet recess 386A on the bottom surface of the manifold plate <NUM> and around the inlet conduit 320A. A second seal ring 354B may be disposed in the outlet recess 386B on the bottom surface of the manifold plate <NUM> and around the outlet conduit 320B. The inlet and outlet conduits 320A, 320B may be welded to the seal plate <NUM>. In particular, the welding process may include welding the first and second seal rings 354A, 354B to the inlet and outlet conduits 320A, 320B, and welding the first and second seal rings 354A, 354B to the surface of the seal plate <NUM> to ensure that a fluid-tight seal is formed between the inlet and outlet conduits 320A, 320B and the seal plate <NUM>.

A first glass or glass ceramic seal 356A may be disposed in the inlet seal region 378A of the seal plate <NUM>, and a second glass or glass ceramic seal 356B may be disposed in the inlet seal region 388A of the manifold plate <NUM>. A third glass or glass ceramic seal 356C may be disposed in the outlet seal region 378B of the seal plate <NUM>, and a fourth glass or glass ceramic seal 356D may be disposed in the outlet seal region 388B of the manifold plate <NUM>. However, in other embodiments, a single glass or glass ceramic seal may be used. The seals 356A-356D may be heated to soften the seals 356A-356D, such that the seals 356A-356D form a fluid-tight connections that physically connect the seal plate <NUM> to the manifold plate <NUM>.

The inlet seal regions 378A, 388A may overlap to form an inlet seal area 358A, and the outlet seal regions 378B, 388B may overlap to form an outlet seal area 358B. The first and second seals 356A, 356B may be stacked on one another in the inlet seal area 358A, and the third and fourth seals 356C, 356D may be stacked on one another in the outlet seal area 358B. The coatings <NUM>, <NUM> may be stacked on one another. As such, the height of the inlet and outlet seal areas 358A, 358B may be equal to the combined thickness of the coatings <NUM>, <NUM>.

The inlet and outlet seal areas 358A, 358B may provide space for the glass or glass ceramic seals 356A-356D to expand laterally when heated to fuel cell system operating temperatures, thereby reducing stress applied to the glass or glass ceramic seals 356A-356D over time. In addition, since the seal plate <NUM> and the manifold plate <NUM> may be formed of the same materials, the seal plate <NUM> and the manifold plate <NUM> may have matched coefficients of thermal expansion (CTEs). Therefore, stress applied to the glass or glass ceramic seals 356A-356D over time may be further reduced.

The glass or glass ceramic seals 356A-356D may be formed of a high-temperature glass or glass ceramic material, such as a silicate or aluminosilicate glass or glass ceramic material. In some embodiments, the glass or glass ceramic seals 356A-356D may be formed of a silicate glass or glass ceramic seal material comprising SiO<NUM>, BaO, CaO, Al<NUM>O<NUM>, K<NUM>O, and/or B<NUM>O<NUM>. For example, the seal material may include, by weight: SiOz in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; BaO in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; CaO in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; Al<NUM>O<NUM> in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; and B<NUM>O<NUM> in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%. In some embodiments, the seal material may additionally include K<NUM>O in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%.

In some embodiments, the glass or glass ceramic seals 356A-356D may be formed of a silicate glass or glass ceramic seal material comprising SiO<NUM>, B<NUM>O<NUM>, Al<NUM>O<NUM>, CaO, MgO, La<NUM>O<NUM>, BaO, and/or SrO. For example, the seal material may include, by weight: SiO<NUM> in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; B<NUM>O<NUM> in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; Al<NUM>O<NUM> in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; CaO in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; MgO in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%; and La<NUM>O<NUM> in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%. In some embodiments, the seal material may additionally include BaO in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%, or from about <NUM>% to about <NUM>%, including about <NUM>% to about <NUM>%, and/or SrO in an amount ranging from about <NUM>% to about <NUM>%, such as from about <NUM>% to about <NUM>%, of from about <NUM>% to about <NUM>%, including about <NUM>% to about <NUM>%. In some embodiments, the seal material may additionally include at least one of BaO and/or SrO in a non-zero amount such as at least <NUM> wt. %, such as both of BaO and SrO in a non-zero amount, such at least <NUM> wt. However, other suitable seal materials may be used.

When assembled in a fuel cell stack, such as the fuel cell stack <NUM> of <FIG>, the top inlet holes 390A may be fluidly connected to the fuel inlets <NUM> of the interconnect <NUM> of the stack <NUM>, and the top outlet holes 390B may be fluidly connected to the fuel outlets <NUM> of the interconnects <NUM>, as shown in <FIG>. For example, a glass or glass ceramic seal <NUM> may be disposed between the top inlet holes 390A and the fuel inlets <NUM> of an adjacent interconnect <NUM>, and a glass or glass ceramic seal <NUM> may be disposed between the top outlet holes 390B and the fuel outlets <NUM> of the adjacent interconnect <NUM>, in order to provide fluid-tight connections.

While solid oxide fuel cells are described above in various embodiments, embodiments can include any other fuel cells, such as molten carbonate, phosphoric acid or PEM fuel cells.

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. 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.

Claim 1:
A fuel cell stack fuel flow structure comprising a fuel plenum which comprises:
a base plate comprising an inlet hole and an outlet hole;
a dielectric layer disposed on the base plate and comprising an inlet hole and an outlet hole;
a cover plate disposed on the dielectric layer and comprising an inlet hole and an outlet hole;
a seal plate disposed on the cover plate and comprising
an inlet hole;
an outlet hole;
an inlet seal region located on a top surface of the seal plate surrounding the inlet hole; and
an outlet seal region located on a top surface of the seal plate surrounding the outlet hole;
a first coating covering the top surface of the seal plate, such that the inlet seal region and the outlet seal region of the seal plate are exposed through the first coating;
a manifold plate disposed on the seal plate and comprising:
a bottom inlet hole and a bottom outlet hole formed in a bottom surface of the manifold plate;
top outlet holes and top inlet holes formed in opposing sides of a top surface of the manifold plate;
outlet channels fluidly connecting the top outlet holes to the bottom inlet hole; and
inlet channels fluidly connecting the top inlet holes to the bottom outlet hole;
an inlet seal region located on the bottom surface of the manifold plate, surrounding the bottom inlet hole, and aligned with the inlet seal region of the seal plate to form an inlet seal area; and
an outlet seal region located on the bottom surface of the manifold plate, surrounding the bottom outlet hole of the manifold plate, and aligned with the outlet seal region of the seal plate to form an outlet seal area;
a second coating covering the bottom surface of the manifold plate, such that the inlet seal region and the outlet seal region of the manifold plate are exposed through the second coating; and
glass or glass ceramic seals disposed in the inlet seal area and the outlet seal areas, the glass or glass ceramic seals configured to fluidly connect the seal plate and the manifold plate,
wherein the inlet and outlet seal areas provide space for the glass or glass ceramic seals to expand laterally when heated to fuel cell system operating temperatures,
wherein the inlet holes of the base plate, cover plate, seal plate and manifold plate are aligned to form an inlet conduit passage, and
wherein the outlet holes of the base plate, cover plate, seal plate and manifold plate are aligned to form an outlet conduit passage.