Patent Description:
Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. These fuel cells may operate using hydrogen and/or hydrocarbon fuels. There are classes of fuel cells, such as the solid oxide reversible fuel cells, that also allow reversed operation, such that water or other oxidized fuel can be reduced to unoxidized fuel using electrical energy as an input.

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 is typically a hydrogen-rich gas created by reforming a hydrocarbon fuel source. 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 is distributed to each cell using risers contained within the stack. In other words, the gas flows through openings or holes in the supporting layer of each fuel cell, such as the electrolyte layer, and gas separator of each cell. In externally manifolded stacks, the stack is open on the fuel and air inlet and outlet sides, and the fuel and air are introduced and collected independently of the stack hardware. For example, the inlet and outlet fuel and air flow in separate channels between the stack and the manifold housing in which the stack is located.

Fuel cell stacks are frequently built from a multiplicity of cells in the form of planar elements, tubes, or other geometries. Fuel and air has to be provided to the electrochemically active surface, which can be large. One component of a fuel cell stack is the so called gas flow separator (referred to as a gas flow separator plate in a planar stack) that separates the individual cells in the stack. The gas flow separator plate separates fuel, such as hydrogen or a hydrocarbon fuel, flowing to the fuel electrode (i.e., anode) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e., cathode) of an adjacent cell in the stack. Frequently, the gas flow separator plate is also used as an interconnect which electrically connects the fuel electrode of one cell to the air electrode of the adjacent cell. In this case, the gas flow separator plate which functions as an interconnect is made of or contains an electrically conductive material. <CIT> discloses reactant manifolds and corners of a molten carbonate fuel cell stack that are sealed with particulate lithium aluminate members which are sufficiently porous so as to resist significant electrolyte migration therethrough. <CIT> discloses a fuel cell apparatus that includes a fuel cell stack positioned within a housing, wherein the housing is contained entirely within a compression assembly, wherein the fuel cell stack can include a plurality of bipolar separator plates formed of a plurality of segments, the compression assembly including mating pairs of anode compression bars and cathode compression bars secured to one another and being positioned between a pair of segments. <CIT> discloses a gasket for use in a fuel cell system having at least one externally manifolded fuel cell stack, for sealing the manifold edge and the stack face, wherein the gasket accommodates differential movement between the stack and manifold by promoting slippage at interfaces between the gasket and the dielectric and between the gasket and the stack face.

According to the invention, a fuel cell column includes first and second fuel cell stacks, a fuel manifold disposed between the first and second fuel cell stacks and configured to provide fuel to the first and second fuel cell stacks, and first and second dielectric separators located between the fuel manifold and the respective first and second fuel cell stacks, and configured to electrically isolate the respective first and second fuel cell stacks from the fuel manifold. The first and second dielectric separators each include a top layer of a ceramic material, a bottom layer of the ceramic material, a middle layer disposed between the top and bottom layers and including a material having a lower density and a higher dielectric strength than the ceramic material, fuel holes; and glass or glass ceramic seals surrounding the fuel holes and which connect the middle layer to the top and bottom layers as defined in the claims.

According to another embodiment, not forming part of the invention, a fuel cell column comprises first and second fuel cell stacks, a fuel manifold disposed between the first and second fuel cell stacks and configured to provide fuel to the first and second fuel cell stacks, and first and second dielectric separators located between the fuel manifold and the respective first and second fuel cell stacks, and configured to electrically isolate the respective first and second fuel cell stacks from the fuel manifold, the first and second dielectric separators each comprising a peripheral frame, internal supports disposed inside of the frame and configured to support the peripheral frame, and fuel holes and internal openings at least partially defined by the peripheral frame and internal supports.

According to another embodiment, which is not part of the invention, a fuel cell column includes first and second fuel cell stacks, a fuel manifold disposed between the first and second fuel cell stacks and configured to provide fuel to the first and second fuel cell stacks, and first and second dielectric separators located between the fuel manifold and the respective first and second fuel cell stacks, and configured to electrically isolate the respective first and second fuel cell stacks from the fuel manifold. The first and second dielectric separators each include a top layer comprising a ceramic material, a bottom layer comprising the ceramic material, at least one protrusion which offsets the top layer from the bottom layer such that an air gap is located between the top layer and the bottom layer, and glass or glass ceramic seals which connect the top layer to the bottom layer.

According to another embodiment a method of forming a dielectric separator comprises forming an assembly comprising a middle layer comprising a dielectric material, a top layer comprising a green ceramic material, a bottom layer comprising the green ceramic material, the dielectric material of the middle layer having a lower density and a higher dielectric strength than the ceramic material, and a glass or glass ceramic seal material surrounding fuel holes and disposed between the middle layer and each of the top and bottom layers, sintering the assembly to densify the top and bottom layers and reflow the glass or glass ceramic seal material, and cutting the sintered assembly to form the dielectric separator as defined in the claims.

It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, "at least one of X, Y, and Z" can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ).

<FIG> illustrates a fuel cell stack assembly <NUM> according to various embodiments of the present disclosure. Referring to <FIG>, the fuel cell stack assembly <NUM> includes a fuel cell stack column <NUM>, side baffles <NUM> disposed on opposing sides of the column <NUM>, a lower block <NUM>, and a compression assembly <NUM> including an upper block <NUM>. The column includes eight fuel cell stacks <NUM>, fuel manifolds <NUM> disposed between the fuel cell stacks <NUM>, and termination plates <NUM> disposed on opposing ends of the column <NUM>. The fuel cell stacks <NUM> include a plurality of fuel cells stacked upon one another and separated by interconnects. A plurality of the fuel cell stack assemblies <NUM> may be attached to a base.

An exemplary fuel manifold <NUM> is described in the <CIT>. Any number of fuel manifolds <NUM> may be provided between adjacent end plates of adjacent fuel cells of the fuel cell stacks <NUM>, as desired.

The side baffles <NUM> connect the upper block <NUM> of the compression assembly <NUM> and the lower block <NUM>. The side baffles <NUM>, the compression assembly <NUM>, and the lower block <NUM> may be collectively referred to as a "stack housing". The stack housing is configured to apply a compressive load to the column <NUM>. The configuration of the stack housing eliminates costly feed-throughs and resulting tie rod heat sinks and uses the same part (i.e., side baffle <NUM>) for two purposes: to place the load on the stacks <NUM> and to direct the cathode feed flow stream (e.g., for a ring shaped arrangement of stacks, the cathode inlet stream, such as air or another oxidizer may be provided from a manifold outside the ring shaped arrangement through the stacks and the exit as a cathode exhaust stream to a manifold located inside the ring shaped arrangement). The side baffles <NUM> may also electrically isolate the fuel cell stacks <NUM> from metal components in the system. The load on the column <NUM> may be provided by the compression assembly <NUM>, which is held in place by the side baffles <NUM> and the lower block <NUM>. In other words, the compression assembly <NUM> may bias the stacks <NUM> of the column <NUM> towards the lower block <NUM>.

The side baffles <NUM> may be plate-shaped rather than wedge-shaped and include baffle plates <NUM> and ceramic inserts <NUM> configured to connect the baffle plates <NUM> to the lower block <NUM> and the compression assembly <NUM>. In particular, the baffle plates <NUM> include generally circular cutouts <NUM> in which the inserts <NUM> are disposed. The inserts <NUM> do not completely fill the cutouts <NUM>. The inserts <NUM> are generally bowtie-shaped, but include flat edges <NUM> rather than fully rounded edges. Thus, an empty space remains in the respective cutouts <NUM> above or below the inserts <NUM>.

Generally, the side baffles <NUM> are made from a high-temperature tolerant material, such as alumina or other suitable ceramic. In various embodiments, the side baffles <NUM> are made from a ceramic matrix composite (CMC). 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. The lower block <NUM> and the compression assembly <NUM> may also be made of the same or similar materials. The selection of particular materials for the compression housing is discussed in detail, below.

Any combination of the matrix and fibers may be used. Additionally, the fibers may be coated with an interfacial layer designed to improve the fatigue properties of the CMC. If desired, the CMC baffles may be made from a unitary piece of CMC material rather than from individual interlocking baffle plates. The CMC material may increase the baffle strength and creep resistance. If the baffles are made from alumina or an alumina fiber/alumina matrix CMC, then this material is a relatively good thermal conductor at typical SOFC operating temperatures (e.g., above <NUM>). If thermal decoupling of neighboring stacks or columns is desired, then the baffles can be made of a thermally insulating ceramic or CMC material.

Other elements of the compression housing, such as the lower block <NUM> and the compression assembly <NUM> may also be made of the same or similar materials. For example, the lower block <NUM> may comprise a ceramic material, such as alumina or CMC, which is separately attached (e.g., by the inserts, dovetails or other implements) to the side baffles <NUM> and to a system base. The use of the ceramic block material minimizes creation of heat sinks and eliminates the problem of linking the ceramic baffles to a metal base, which introduces thermal expansion interface problems. The selection of particular materials for the components of the compression housing is discussed in detail, below.

Fuel rails <NUM> (e.g. fuel inlet and outlet pipes or conduits) connect to fuel manifolds <NUM> located between the stacks <NUM> in the column <NUM>. The fuel rails <NUM> include ceramic tubes <NUM> brazed to metal tubes <NUM>. The metal tubes <NUM> may comprise compressible bellows tubes in one embodiment. The fuel cell rails <NUM> are used to deliver fuel to each pair of stacks <NUM> in a column <NUM> of fuel cell stacks via fuel cell manifolds <NUM>. In these systems, the ceramic tubes <NUM> are located between adjacent fuel manifolds <NUM> to prevent shorting between adjacent stacks <NUM> in a column <NUM> of stacks <NUM>. The ceramic tubes <NUM> are relatively expensive and difficult to braze to the metal tubes <NUM>. The ceramic tubes <NUM> are also prone to cracking due to thermal stresses generated during thermal cycling of the fuel cell system.

<FIG> is a three dimensional view of a fuel cell stack assembly <NUM> with an electrically isolated fuel manifold, according to various embodiments of the present disclosure, and <FIG> is an exploded view of the fuel cell stack assembly <NUM> illustrated in <FIG>. <FIG> illustrates a close up of a portion of the fuel cell stack assembly <NUM> with an electrically isolated fuel manifold illustrated in <FIG>. <FIG> illustrates a close up of another portion of the fuel cell stack assembly <NUM> with an electrically isolated fuel manifold <NUM> illustrated in <FIG>.

Referring to <FIG>, rather than braze ceramic and metal tubes the full length of the fuel rails <NUM> to provide electrical isolation between pairs of adjacent fuel cell stacks <NUM> separated by a fuel manifold <NUM>, a dielectric separator <NUM> is provided between the fuel manifolds <NUM> and the adjacent fuel cell stacks <NUM>. The dielectric separator <NUM> may comprise any suitable electrically insulating material, such as alumina, a ceramic matrix composite, etc. The fuel rails <NUM> may be made entirely of metal, not requiring dielectric (e.g., ceramic) tubes <NUM> which may be omitted. In one embodiment, the fuel rails <NUM> comprise only the metal bellows <NUM> and straight metal tubes <NUM>.

A jumper <NUM> may be provided to allow current to flow from a first fuel cell stack <NUM> to an adjacent second fuel cell stack <NUM> which is spaced from the first stack <NUM> by the fuel manifold <NUM> in a fuel cell stack column <NUM> without current flowing though the fuel manifold <NUM>. The jumper <NUM> may be placed in electrical contact with the first and second the fuel cell stacks <NUM> around the fuel manifold <NUM> and dielectric separator <NUM>. The jumper <NUM> can be made of any suitable conductor, e.g., metals or metal alloys such as Inconel <NUM> (or other Inconel alloys) or Cr - Fe <NUM> wt. % alloy, and may have a coefficient of thermal expansion close to that of the stacks <NUM> and the dielectric separator <NUM> to make sealing the various components easy. The jumper <NUM> may generally have a "C" shape in which the top and bottom portions electrically contact the respective adjacent first and second stacks <NUM> while the side of the jumper <NUM> which connects the top and bottom portions goes around the fuel manifold <NUM> and does not contact the fuel manifold <NUM>. In an embodiment, the inner surfaces of the jumper <NUM> facing the manifold <NUM> may be coated with a dielectric material instead of or in addition to the dielectric separator <NUM> or the coating of dielectric separator <NUM> on the surface of the fuel manifold <NUM>.

As illustrated in <FIG>, the dielectric separator <NUM> is provided with fuel holes <NUM> which allow the fuel from the fuel manifolds <NUM> to flow to the fuel cell stacks <NUM>. A seal may be formed around the fuel holes <NUM>, such as a glass seal or any suitable gasket. In an embodiment, other features such as thermocouple slots <NUM> are provided in the dielectric separator <NUM> to permit a thermocouple to pass through the slots <NUM>. In an embodiment illustrated in <FIG>, tabs <NUM> which may be used to attach module voltage wires are provided in the jumper <NUM>.

<FIG> is a partial perspective view of a dielectric separator <NUM>, according to various embodiments of the present disclosure, and <FIG> is an exploded perspective view of the separator <NUM> of <FIG>. Referring to <FIG>, the separator <NUM> may be utilized in the fuel cell stack assembly <NUM> of <FIG>.

The separator <NUM> includes a top layer <NUM>, a bottom layer <NUM>, a middle layer <NUM>, fuel holes <NUM> and seals <NUM>. The fuel holes <NUM> may include concentric through holes formed in the top, bottom, and middle layers <NUM>, <NUM>, <NUM>.

The top and bottom layers <NUM>, <NUM> may be formed of a densified dielectric material. For example, the top and bottom layers <NUM>, <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 top and bottom layers <NUM>, <NUM> may be in the form of rigid plates to provide structural rigidity to the separator <NUM>.

In addition, the top and bottom layers <NUM>, <NUM> may be substantially impervious to effluent species released from adjacent fuel cells, such as chromia. Accordingly, the top and bottom layers <NUM>, <NUM> may prevent effluent species from entering the middle layer <NUM> and reducing the dielectric strength thereof.

The middle layer <NUM> is sandwiched between the top and bottom layers <NUM>, <NUM>, and may be formed of a porous and/or high surface area material having a higher dielectric strength than the top and bottom layers <NUM>, <NUM>. In other words, the insulating material of the middle layer 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 insulating material of the top and bottom layers <NUM>, <NUM>. The present inventors found that maintaining a high dielectric strength while utilizing only dense ceramic materials may be difficult in a fuel cell system, due to the presence of alkali ions such as Na ions, which may increase the conductivity of such ceramic materials. Accordingly, the middle layer <NUM> may operate to increase the total dielectric strength of the separator <NUM>.

In some embodiments, the middle layer <NUM> may be formed 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 middle layer <NUM> may be formed of a ceramic matrix composite (CMC) layer, 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.

In various embodiments, the seals <NUM> may be ring seals and are formed of a high-temperature glass or glass ceramic material, such as a silicate or aluminosilicate glass or glass ceramic material. The seals <NUM> operate to connect the top and bottom layers <NUM>, <NUM> to the middle layer <NUM>, and may hermetically seal the fuel holes <NUM>.

The materials for the individual components of the separator <NUM> (e.g., the layers <NUM>, <NUM>, <NUM>, and optionally the seals <NUM>) may be selected such that the major constituent of each component is the same. Herein, the major constituent refers to a constituent that is present in the highest amount in a component. For example, in some embodiments, the major constituent of the components <NUM>, <NUM>, and <NUM>, and optionally <NUM> may be alumina. Having the same major constituent may facilitate bonding of the components <NUM>, <NUM>, <NUM>, <NUM>, and may allow for the sintering of the separator <NUM> independently from a fuel cell column <NUM>.

In some embodiments, the separator <NUM> may include additional layers. For example, the separator <NUM> may include two or more porous ceramic fabric or CMC layers disposed between three or more dense ceramic layers, with the layers being connected by corresponding glass or glass ceramic seals.

In some embodiments, inner surfaces of the top and bottom layers <NUM>, <NUM> may be provided with a roughened or shag-like texture configured to provide additional air and/or seal material entrapment. The density of portions of the top and bottom layers <NUM>, <NUM> surrounding the fuel hole <NUM> may be increased relative to a remainder of the top and bottom layers <NUM>, <NUM>, in order to provide for improved sealing of the fuel holes <NUM>.

In various embodiments, additional glass ring seals <NUM> may be disposed on top of the top layer <NUM> and on the bottom of the bottom layer <NUM>, surrounding the fuel holes <NUM>. The additional seals <NUM> may be used to seal the separator <NUM> to adjacent fuel cell column components, such as a fuel cell stack or fuel manifold.

<FIG> is a top view of the separator <NUM> including edge seals <NUM>, according to various embodiments of the present disclosure, where the top layer <NUM> has been omitted for clarity. Referring to <FIG>, the edge seals <NUM> may be included in addition to the fuel hole seals <NUM> and may extend along opposing edges of the separator <NUM>. Accordingly, the edge seals <NUM> may provide improved adhesion between the layers of the separator <NUM>. The edge seals <NUM> may be formed by tape casting, dispensing, or dip coating, for example.

<FIG> is a top view of a comparative dielectric separator <NUM>. Referring to <FIG>, the separator <NUM> may be formed of a densified ceramic material, such as the high density dielectric material described above with respect to the top and bottom layers <NUM>, <NUM> of the separator <NUM>. The separator <NUM> may include a peripheral frame <NUM> and internal supports <NUM> disposed inside of the frame <NUM>. The frame <NUM> and supports <NUM> may at least partially define internal openings <NUM> and fuel holes <NUM>. Accordingly the comparative separator <NUM> may have a uni-body construction, as opposed to a composite layered construction of the separator <NUM> according to the invention.

Ring seals <NUM> may be disposed on top and bottom surfaces of the separator <NUM>, surrounding the fuel holes <NUM>. The seals <NUM> may be formed of the same glass material as described above with respect to the seals <NUM>. The seals <NUM> may be configured to seal the separator <NUM> to adjacent fuel cell column components, such as a fuel cell stack and a fuel manifold. The separator <NUM> may optionally include relief cuts RC where the separator <NUM> is cut to reduce the effects of thermal expansion and contraction. For example, the relief cuts RC may reduce stress applied to the glass seals <NUM> due to thermal expansion of adjacent metal parts, and thereby reduce and/or prevent shearing of the glass seals <NUM> during thermal cycling.

<FIG> illustrate a comparative dielectric separator 400A. In this separator, the middle layer <NUM> is omitted and is replaced by an air gap <NUM>. Air has a higher dielectric breakdown strength than the ceramic materials of the top layer <NUM> and the bottom layer <NUM>. At least one of the top layer <NUM> or the bottom layer <NUM> includes at least one protrusion <NUM> on the side facing the other one of the top layer <NUM> or the bottom layer <NUM>. The at least one protrusion <NUM> offsets the top layer <NUM> from the bottom layer <NUM> such that the air gap <NUM> is located between the top layer <NUM> and the bottom layer <NUM>. Glass or glass ceramic seals <NUM> connect the top layer <NUM> to the bottom layer <NUM> as shown in <FIG>. The seals <NUM> may have any suitable shape described above.

In one embodiment, at least one protrusion <NUM> may be located on the bottom side of the top layer <NUM> facing the top side of the bottom layer <NUM>. The at least one protrusion <NUM> contacts the top side of the bottom layer <NUM> such that the air gap <NUM> is located between the top layer <NUM> and the bottom layer <NUM>.

In another embodiment, at least one protrusion <NUM> may be located on the top side of the bottom layer <NUM> facing the bottom side of the top layer <NUM>. The at least one protrusion <NUM> contacts the bottom side of the top layer <NUM> such that the air gap <NUM> is located between the top layer <NUM> and the bottom layer <NUM>.

In another embodiment, the protrusions <NUM> may be located on both the bottom side of the top layer <NUM> and on the top side of the bottom layer <NUM>. In this embodiment, at least one protrusion <NUM> on the bottom side of the top layer <NUM> may contact at least one protrusion <NUM> on the top side of the bottom layer <NUM>. Alternatively, the protrusions <NUM> on the top and bottom layers may be offset from each other such that at least one protrusion <NUM> on the bottom side of the top layer <NUM> may contact the top side of the bottom layer <NUM>, and at least one additional protrusion <NUM> on the top side of the bottom layer <NUM> may contact the bottom side of the top layer <NUM>. The protrusions <NUM> vertically offset the top and bottom layers from each other to form the air gap <NUM> located between the top layer <NUM> and the bottom layer <NUM>.

Any number of protrusions <NUM> may be located on the top layer <NUM> and/or the bottom layer <NUM>. For example, as shown in <FIG>, four protrusions <NUM> may be located on the bottom side of the top layer <NUM> and/or on the top side of the bottom layer <NUM>. However, one, two, three or more than four protrusions <NUM> may be formed. The protrusions <NUM> may be formed of the same ceramic material as the ceramic material of the top and bottom layers, such as alumina, zirconia or YSZ. The protrusions <NUM> may have any suitable horizontal cross sectional shape. For example, the protrusions <NUM> shown in <FIG> comprise filled cylinders having a circular horizontal cross sectional shape. However, other suitable horizontal cross sectional shapes may be used, such polygonal (e.g., triangular, square, rectangular, hexagonal, etc.), oval or irregular shapes. The protrusions <NUM> may be formed at the same time as the top or bottom layers using any suitable ceramic processing method.

<FIG> is a photograph showing seals of a dielectric separator seal formed by tape casting on a fabric middle layer <NUM>, and <FIG> is a photograph showing seals formed by dispensing a seal material ink on a CMC middle layer <NUM>, according to various embodiments of the present disclosure. Referring to <FIG>, <FIG>, in some embodiments the separator <NUM> may be formed by applying a seal material to at least one side of the middle layer <NUM>, or to one or both of the top and bottom layers <NUM>, <NUM>, so as to surround the fuel holes <NUM> and form the seals <NUM>. For example, the seal material may be applied to the middle layer <NUM> by tape casting, as shown in <FIG>. The top and bottom layers <NUM>, <NUM> may be ceramic plates formed by tape casting a ceramic material. Accordingly, the top and bottom layers <NUM>, <NUM> may initially be in a green (porous) state.

In the alternative, as shown in <FIG>, the middle layer <NUM> may be disposed on one of the top and bottom layers <NUM>, <NUM>, and a fluid seal material 410A, such as a seal material ink may be dispensed on the bottom layer <NUM> and/or the middle layer <NUM> around the fuel hole <NUM>. The seal material ink may include a silicate or aluminosilicate glass or glass ceramic seal material, a solvent, and/or a binder. In other embodiments, the seal material or any suitable sintering aid, may be applied between edges of the top and bottom layers <NUM>, <NUM>, for example by tape casting, dispensing, or dip coating, as shown in <FIG>.

The layers <NUM>, <NUM>, <NUM> may then be stacked together to form the separator <NUM>. The separator <NUM> may then be heated (e.g., sintered) at a temperature above the reflow temperature of the seal material. For example, the separator <NUM> may be heated at a temperature of at least about <NUM>, such as a temperature ranging from about <NUM> to about <NUM>, such that the glass seal flows into the middle layer <NUM> and/or around the fuel holes <NUM> and bonds with the surfaces of the top and bottom layers <NUM>, <NUM>. The heating may also sinter the top and bottom layers <NUM>, <NUM>, thereby densifying the top and bottom layers <NUM>, <NUM>. In some embodiments, the separator may be compressed during the sintering process.

In some embodiments, a vacuum may be applied to the separator <NUM> prior to the sintering. The vacuum may operate to drive the seal material into the middle layer <NUM> and/or into pores of the top and bottom layers <NUM>, <NUM>, such as pores adjacent to the fuel holes <NUM>. For example the seals <NUM> may be formed by vacuum casting with or without a liquid sintering aid.

In embodiments where the middle layer <NUM> is a CMC plate, the separator <NUM> may be formed by plasma spraying a ceramic powder onto opposing sides of the middle layer <NUM>, to form the top and bottom layers <NUM>, <NUM>. The seal material may be applied to the middle layer <NUM>, before or after the plasma spraying. The separator <NUM> may then be heated to densify the ceramic powder and bond the top and bottom layers <NUM>, <NUM> to the middle layer <NUM>. The heating may also include reflowing the seal material.

<FIG> is a perspective view depicting a method of manufacturing of a dielectric separator <NUM>, according to various embodiments of the present disclosure. Referring to <FIG>, a glass seal material may be applied to two or more ceramic plates <NUM>, which may be in a green state, and/or may be applied to one or more the porous dielectric layers <NUM>, such as CMC layers or ceramic fiber layers.

For example, in some embodiments, the seal material may be applied to specific locations corresponding to fuel holes and/or edge regions of subsequently formed separators, as discussed below. The ceramic plates <NUM> may be formed by, for example, tape casting a ceramic material, such as alumina, zirconia, yttria-stabilized zirconia, or the like.

The dielectric layers <NUM> may then be stacked between the ceramic plates <NUM>, to form a laminated assembly <NUM>. The assembly <NUM> may be sintered at a temperature sufficient to densify the ceramic plates <NUM> and reflow the seal material, such as a temperature ranging from about <NUM> to about <NUM>. As a result, the seal material physically connects the layers of the assembly <NUM>. In some embodiments, a vacuum may be applied to the assembly <NUM> before and/or during sintering, in order to facilitate impregnation of the seal material into the dielectric layers <NUM>.

The sintered assembly <NUM> then may be cut and/or shaped to form individual dielectric separators <NUM>. For example, the assembly <NUM> may be cut to form a peripheral shape of the separators <NUM> and to form fuel holes <NUM> therein.

While three ceramic plates <NUM> and two porous dielectric layers <NUM> are shown in <FIG>, the present disclosure is not limited thereto. For example, two ceramic plates <NUM> and one porous dielectric layer <NUM> may be used to form the assembly <NUM>, or the assembly <NUM> may include four or more ceramic plates <NUM> and three or more porous dielectric layers <NUM>.

In an alternative embodiment, the ceramic plates <NUM> may be formed by spraying a ceramic material onto opposing sides of a dielectric layer <NUM> and form an assembly. For example, the ceramic material may be plasma sprayed onto the dielectric layer <NUM>. The assembly may be sintered to densify the ceramic material and form ceramic plates <NUM>. The sintered assembly may optionally be cut to form individual separators <NUM>.

Claim 1:
A fuel cell column comprising:
first and second fuel cell stacks;
a fuel manifold disposed between the first and second fuel cell stacks and configured to provide fuel to the first and second fuel cell stacks; and
first and second dielectric separators located between the fuel manifold and the respective first and second fuel cell stacks, and configured to electrically isolate the respective first and second fuel cell stacks from the fuel manifold, the first and second dielectric separators each comprising:
a top layer comprising a ceramic material;
a bottom layer comprising the ceramic material;
a middle layer disposed between the top and bottom layers and comprising a material having a lower density and a higher dielectric strength than the ceramic material;
fuel holes; and
glass or glass ceramic seals surrounding the fuel holes and which connect the middle layer to the top and bottom layers.