# Patent

## Title
Fuel cell device and system

## Abstract

The present invention relates to a fuel cell system. A hot zone chamber has a wall thickness T and a heat source coupled thereto. An elongate fuel cell device is positioned with a first lengthwise portion within the hot zone chamber, a second lengthwise portion outside the hot zone chamber, and a third lengthwise portion of length T within the chamber wall. The third portion has a maximum dimension L in a plane transverse to the length where T≧1⁄2L.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of co-pending U.S. patent application Ser. No. 12/117,622 filed May 8, 2008 and entitled FUEL CELL DEVICE AND SYSTEM, the disclosure of which is incorporated herein by reference in its entirety as if completely set forth herein below. Pursuant to 37 C.F.R. §1.78(a)(4), the present application also claims the benefit of and priority to Provisional Application Ser. No. 60/917,262 filed on May 10, 2007 and entitled SOLID OXIDE FUEL CELL DEVICE AND SYSTEM, which is expressly incorporated herein by reference.


FIELD OF THE INVENTION
This invention relates to fuel cell devices and systems, and methods of manufacturing the devices, and more particularly, to a fuel cell device in the form of a multi-layer monolithic Fuel Cell StickTM.
BACKGROUND OF INVENTION
Ceramic tubes have found a use in the manufacture of Solid Oxide Fuel Cells (SOFCs). There are several types of fuel cells, each offering a different mechanism of converting fuel and air to produce electricity without combustion. In SOFCs, the barrier layer (the “electrolyte”) between the fuel and the air is a ceramic layer, which allows oxygen atoms to migrate through the layer to complete a chemical reaction. Because ceramic is a poor conductor of oxygen atoms at room temperature, the fuel cell is operated at 700° C. to 1000° C., and the ceramic layer is made as thin as possible.
Early tubular SOFCs were produced by the Westinghouse Corporation using long, fairly large diameter, extruded tubes of zirconia ceramic. Typical tube lengths were several feet long, with tube diameters ranging from 1⁄4 inch to 1⁄2 inch. A complete structure for a fuel cell typically contained roughly ten tubes. Over time, researchers and industry groups settled on a formula for the zirconia ceramic which contains 8 mol % Y2O3. This material is made by, among others, Tosoh of Japan as product TZ-8Y.
Another method of making SOFCs makes use of flat plates of zirconia, stacked together with other anodes and cathodes, to achieve the fuel cell structure. Compared to the tall, narrow devices envisioned by Westinghouse, these flat plate structures can be cube shaped, 6 to 8 inches on an edge, with a clamping mechanism to hold the entire stack together.
A still newer method envisions using larger quantities of small diameter tubes having very thin walls. The use of thin walled ceramic is important in SOFCs because the transfer rate of oxygen ions is limited by distance and temperature. If a thinner layer of zirconia is used, the final device can be operated at a lower temperature while maintaining the same efficiency. Literature describes the need to make ceramic tubes at 150 μm or less wall thickness.
There are several main technical problems that have stymied the successful implementation of SOFCs. One problem is the need to prevent cracking of the ceramic elements during heating. For this, the tubular SOFC approach is better than the competing “stack” type (made from large, flat ceramic plates) because the tube is essentially one-dimensional. The tube can get hot in the middle, for example, and expand but not crack. For example, a tube furnace can heat a 36′′ long alumina tube, 4′′ in diameter, and it will become red hot in the center, and cold enough to touch at the ends. Because the tube is heated evenly in the center section, that center section expands, making the tube become longer, but it does not crack. A ceramic plate heated in the center only would quickly break into pieces because the center expands while the outside remains the same size. The key property of the tube is that it is uniaxial, or one-dimensional.
A second key challenge is to make contact to the SOFC. The SOFC ideally operates at high temperature (typically 700-1000° C.), yet it also needs to be connected to the outside world for air and fuel, and also to make electrical connection. Ideally, one would like to connect at room temperature. Connecting at high temperature is problematic because organic material cannot be used, so one must use glass seals or mechanical seals. These are unreliable, in part, because of expansion problems. They can also be expensive.
Thus, previous SOFC systems have difficulty with at least the two problems cited above. The plate technology also has difficulty with the edges of the plates in terms of sealing the gas ports, and has difficulty with fast heating, as well as cracking. The tube approach resolves the cracking issue but still has other problems. An SOFC tube is useful as a gas container only. To work it must be used inside a larger air container. This is bulky. A key challenge of using tubes is that you must apply both heat and air to the outside of the tube; air to provide the O2 for the reaction, and heat to accelerate the reaction. Usually, the heat would be applied by burning fuel, so instead of applying air with 20% O2 (typical), the air is actually partially reduced (partially burned to provide the heat) and this lowers the driving potential of the cell.
An SOFC tube is also limited in its scalability. To achieve greater kV output, more tubes must be added. Each tube is a single electrolyte layer, such that increases are bulky. The solid electrolyte tube technology is further limited in terms of achievable electrolyte thinness. A thinner electrolyte is more efficient. Electrolyte thickness of 2 μm or even 1 μm would be optimal for high power, but is very difficult to achieve in solid electrolyte tubes. It is noted that a single fuel cell area produces about 0.5 to 1 volt (this is inherent due to the driving force of the chemical reaction, in the same way that a battery gives off 1.2 volts), but the current, and therefore the power, depend on several factors. Higher current will result from factors that make more oxygen ions migrate across the electrolyte in a given time. These factors are higher temperature, thinner electrolyte, and larger area.
SUMMARY OF THE INVENTION
The present invention relates to a fuel cell system having a hot zone chamber with a chamber wall of thickness T. One or more fuel cell devices each comprise an elongate rectangular or tubular substrate having a length that is the greatest dimension whereby thermal expansion is exhibited along a dominant axis that is coextensive with the length, a reaction zone along a first portion of the length positioned in the hot zone chamber for exposure to an operating reaction temperature, at least one cold zone along a second portion of the length extending outside the hot zone chamber and shielded by the chamber wall so as to remain at a temperature below the operating reaction temperature, and an electrolyte disposed between an anode and a cathode in the reaction zone. A third portion of the length of each fuel cell device equal to thickness T is positioned within the chamber wall, the third portion having a maximum dimension L in a plane transverse to the direction of the length wherein T≧1⁄2L. A heat source is coupled to the hot zone chamber for heating the reaction zone to the operating reaction temperature within the hot zone chamber.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.
FIGS. 1 and 1A depict, in side cross-sectional view and top cross-sectional view, respectively, one embodiment of a basic Fuel Cell StickTM device of the invention, having a single anode layer, cathode layer and electrolyte layer, and a hot zone between two end cold zones.
FIG. 2 depicts in perspective view a first end of one embodiment of a Fuel Cell StickTM device of the invention with a fuel supply tube connected thereto.
FIG. 3A depicts in perspective view a Fuel Cell StickTM device according to one embodiment of the invention, but having modified ends.
FIG. 3B depicts in perspective view a fuel supply tube connected to one modified end of the device of FIG. 3A.
FIG. 4A depicts in perspective view a metallurgical bonding attachment means to a plurality of Fuel Cell StickTM devices to make electrical connection to positive and negative voltage nodes according to one embodiment of the invention.
FIG. 4B depicts in schematic end view a connection between multiple Fuel Cell StickTM devices according to one embodiment of the invention, where each Fuel Cell StickTM device includes a plurality of anodes and cathodes.
FIG. 5 depicts in schematic end view a mechanical attachment means for making the electrical connection to positive and negative voltage nodes according to one embodiment of the invention.
FIGS. 6A and 6B depict in perspective views an alternative embodiment having a single cold zone at one end of a Fuel Cell StickTM device to which fuel and air supply tubes are attached, with the other end being in the hot zone.
FIGS. 7A and 7B are cross-sectional side and top views, respectively, illustrating a plurality of support pillars in the air and fuel passages according to one embodiment of the invention.
FIGS. 7C and 7D are micrographs depicting the use of spherical balls in the fuel and air passages as the support pillars according to another embodiment of the invention.
FIG. 8A depicts in cross-section one embodiment of the invention containing two fuel cells connected externally in parallel.
FIG. 8B depicts in cross-sectional view another embodiment of the invention similar to FIG. 8A, but having the two fuel cells connected internally in parallel through the use of vias.
FIGS. 9A and 9B depict in cross-sectional views a multi-fuel cell design according to an embodiment of the invention having shared anodes and cathodes, where FIG. 9A depicts three fuel cell layers connected in parallel and FIG. 9B depicts three fuel cells connected in series.
FIG. 10 depicts in schematic side view a Fuel Cell StickTM device according to one embodiment of the invention having a fuel supply tube connected to a cold end of the device and a side of the device open in the hot zone to an air passage for supply of heated air to the device in the hot zone.
FIG. 10A depicts in schematic side view a variation of the embodiment of FIG. 10, where the hot zone is positioned between opposing cold ends.
FIG. 10B depicts the Fuel Cell StickTM device of FIG. 10A in top cross-sectional view taken along line 10B-10B.
FIGS. 11-24 schematically depict various embodiments of the invention, where FIG. 11 provides a key for the components depicted in FIGS. 12-24.
FIGS. 25A and 27A depict in schematic top plan view and FIG. 27B depicts in schematic side view a Fuel Cell StickTM device according to one embodiment of the invention having a panhandle design with an elongate section at one cold end and a large surface area section at the opposing hot end.
FIGS. 25B and 26A depict in schematic top plan view and FIG. 26B depicts in schematic side view an alternative embodiment of the panhandle design having two elongate sections at opposing cold ends with a center large surface area section in a central hot zone.
FIGS. 28A-28D depict a Fuel Cell StickTM device according to one embodiment of the invention, having a spiral or rolled, tubular configuration, where FIGS. 28A-28C depict the unrolled structure in schematic top view, end view and side view, respectively, and FIG. 28D depicts the spiral or rolled, tubular configuration in schematic perspective view.
FIGS. 29A-29G depict another alternative embodiment of the invention wherein the Fuel Cell StickTM device has a tubular concentric form, and where FIG. 29A depicts the device in schematic isometric view, FIGS. 29B-29E depict cross-sectional views taken from FIG. 29A, FIG. 29F depicts an end view at the air input end, and FIG. 29G depicts an end view at the fuel input end.
FIG. 30A depicts in schematic cross-sectional side view an embodiment of a Fuel Cell StickTM device of the invention having an integrated pre-heat zone preceding an active zone in the hot zone, and FIGS. 30B and 30C depict the device of FIG. 30A in schematic cross-sectional view taken along lines 30B-30B and 30C-30C, respectively.
FIGS. 31A-31C are similar to FIGS. 30A-30C, but depict two cold zones with a central hot zone.
FIGS. 32A-32B depict in schematic cross-sectional side view and schematic cross-sectional top view taken along line 32B-32B of FIG. 32A, respectively, an embodiment similar to that depicted in FIGS. 31A-31C, but further including pre-heat chambers extending between the fuel inlet and the fuel passage and between the air inlet and the air passage, each pre-heat chamber extending from the cold zone into the pre-heat zone of the hot zone.
FIGS. 33A-33C depict another embodiment of the invention for pre-heating the air and fuel, where FIG. 33A is a schematic cross-sectional side view through the longitudinal center of the Fuel Cell StickTM device, FIG. 33B is a schematic cross-sectional top view taken along line 33B-33B of FIG. 33A, and FIG. 33C is a schematic cross-sectional bottom view taken along line 33C-33C of FIG. 33A.
FIGS. 34A and 34B depict in schematic oblique front view and schematic side view, respectively, an embodiment of the invention having multiple anodes and cathodes interconnected externally in series.
FIG. 35 depicts in schematic side view the structure of FIG. 34B doubled with the two structures connected externally by metal stripes to provide a series-parallel design.
FIGS. 36A and 36B depict in schematic side view and perspective view another embodiment of the invention including metal stripes to connect anodes and cathodes in series and/or parallel in the hot zone and long metal stripes extending from the hot zone to the cold zone for making low temperature connection in the cold zones to the positive and negative voltage nodes.
FIG. 37 depicts in schematic isometric view an embodiment similar to that of FIG. 36B, but having a single cold zone for the air and fuel supply connections and for the voltage node connection.
FIGS. 38A and 38B depict in schematic cross-sectional side view an embodiment of the invention having multiple exit gaps along the sides of the device for bake-out of organic material used to form passages within the structure.
FIG. 39 depicts in schematic cross-sectional end view another embodiment of the invention in which anode material is used as the supporting structure, referred to as an anode-supported version of a Fuel Cell StickTM device.
FIGS. 40A and 40B depict in schematic cross-sectional end view and schematic cross-sectional side view, respectively, an anode-supported version according to another embodiment of a Fuel Cell StickTM device of the invention in which an open fuel passage is eliminated in favor of a porous anode that serves the function of conveying the fuel through the device.
FIGS. 41A and 41B depict in schematic cross-sectional end view and schematic cross-sectional top view, respectively, another embodiment of an anode-supported version of a Fuel Cell StickTM device of the invention, in which multiple air passages are provided within the anode-supporting structure, and a single fuel passage is provided normal to the multiple air passages.
FIGS. 42A-42C depict in schematic cross-sectional view a method for forming an electrode layer in a passage of a Fuel Cell StickTM device of the invention, according to one embodiment.
FIG. 43 depicts in schematic cross-sectional side view another embodiment of the invention in which the electrolyte layer is provided with an uneven topography to increase the surface area available to receive an electrode layer.
FIG. 44 depicts in schematic cross-sectional side view an alternative embodiment of the invention for providing uneven topography on the electrolyte layer.
FIG. 45A depicts in schematic top view and FIG. 45B depicts in cross-sectional view through the hot zone an embodiment of a Fuel Cell StickTM device of the invention having a plurality of fuel cells on each of a left and right side of the device, with a bridging portion therebetween.
FIGS. 46A and 46B depict in schematic perspective view and schematic cross-sectional view, respectively, another embodiment of a Fuel Cell StickTM device of the invention having large exterior contact pads to provide a large or wide path of low resistance for electrons to travel to the cold end of the device.
FIG. 47 depicts in schematic cross-sectional side view a Fuel Cell StickTM device according to another embodiment of the invention having a single exhaust passage for both spent fuel and air.
FIGS. 48A-48C depict an alternative embodiment referred to as an “end-rolled Fuel Cell StickTM device” having a thick portion and a thin rolled portion, wherein FIG. 48A depicts the unrolled device in perspective view, FIG. 48B depicts the rolled device in cross-sectional side view, and FIG. 48C depicts the rolled device in perspective view.
FIG. 49A depicts in schematic cross sectional side view an embodiment for building a Fuel Cell StickTM device using a wire between two ceramic layers.
FIG. 49B depicts in schematic perspective view the device of FIG. 49A after lamination.
FIG. 49C depicts in schematic perspective view the device of FIG. 49B after the wire has been removed.
FIGS. 50A-50C depict in schematic cross sectional view another embodiment for building a Fuel Cell StickTM device using a combination of wire and gap-forming tape.
FIGS. 51 and 52A depict in schematic perspective view a Fuel Cell StickTM device passing through a furnace wall.
FIG. 52B depicts in schematic perspective view the portion of the Fuel Cell StickTM device of 52B within the bounds of the furnace wall.
FIG. 52C depicts in schematic perspective view a portion of a tubular Fuel Cell StickTM device where it would pass through a furnace wall.
FIG. 53 depicts in schematic perspective view a Fuel Cell StickTM device passing through a furnace wall made up of multiple layers.
FIG. 54 depicts in schematic perspective view a Fuel Cell StickTM device passing through a furnace wall made up of multiple layers and an air gap.
FIGS. 55A-55E depict in schematic cross sectional view the assembly of a Fuel Cell StickTM device having a floating current collector.
FIGS. 56A and 56B are micrographs depicting zirconia balls supporting a floating current collector.
FIGS. 57A and 57B depict in schematic cross sectional view the backfilling of the structure of FIG. 55D with anode or cathode particles suspended in a viscous liquid to form an anode or cathode.
FIGS. 58A, 58B, and 58C are micrographs depicting a current collector nearly causing a blockage of a passage.
FIG. 59 depicts in schematic cross sectional view current collectors on the surface of the anode and the cathode.
FIG. 60 depicts in schematic cross sectional view current collectors buried in the surface of the anode and the cathode.
FIGS. 61A-61C depict a method of burying a current collector in an anode or cathode.
FIG. 62 is schematic cross sectional view depicting a method of achieving an individual layer of electrolyte having two thicknesses.
FIG. 62A is a detailed view of FIG. 62.
FIG. 63 is a micrograph depicting a top view of a current collector in a hatch pattern.
FIGS. 64 and 65 are micrographs depicting side and angled cross-sectional views of a current collector over a porous anode or cathode.
FIG. 66A is a schematic cross-sectional view of a tube slipped over the end of a Fuel Cell StickTM device.
FIG. 66B is a schematic perspective view of the end of a Fuel Cell StickTM device of FIG. 66A.
FIG. 67A is a schematic cross-sectional view of a connector, including spring electrical contacts, positioned on the end of a Fuel Cell StickTM device.
FIG. 67B is a schematic perspective view of the connector of FIG. 67A.
FIGS. 68A and 68B are schematic perspective views depicting Fuel Cell StickTM devices having four points of exit.
FIG. 69 is a micrograph depicting a current collector trace that has been recessed into a porous anode or cathode.
FIG. 70 is micrograph image depicting a gap left after removing a carbon-wax sacrificial material.



DETAILED DESCRIPTION
In one embodiment, the invention provides a SOFC device and system in which the fuel port and the air port are made in one monolithic structure. In one embodiment, the SOFC device is an elongate structure, essentially a relatively flat or rectangular stick (and thus, referred to as a Fuel Cell StickTM device), in which the length is considerably greater than the width or thickness. The Fuel Cell StickTM devices are capable of having cold ends while the center is hot (cold ends being <300° C.; hot center being >400° C., and most likely >700° C.). Slow heat conduction of ceramic can prevent the hot center from fully heating the colder ends. In addition, the ends are quickly radiating away any heat that arrives there. The invention includes the realization that by having cold ends for connection, it is possible to make easier connection to the anode, cathode, fuel inlet and H2O CO2 outlet, and air inlet and air outlet. While tubular fuel cell constructions are also capable of having cold ends with a hot center, the prior art does not take advantage of this benefit of ceramic tubes, but instead, places the entire tube in the furnace, or the hot zone, such that high temperature connections have been required. The prior art recognizes the complexity and cost of making high temperature brazed connections for the fuel input, but has not recognized the solution presented herein. The Fuel Cell StickTM device of the invention is long and skinny so that it has the thermal property advantages discussed above that allow it to be heated in the center and still have cool ends. This makes it structurally sound with temperature, and makes it relatively easy to connect fuel, air and electrodes. The Fuel Cell StickTM device is essentially a stand-alone system, needing only heat, fuel, and air to be added in order to make electricity. The structure is designed so that these things can be readily attached.
The Fuel Cell StickTM device of the invention is a multi-layer structure and may be made using a multi-layer co-fired approach, which offers several other advantages. First, the device is monolithic, which helps to make it structurally sound. Second, the device lends itself to traditional high volume manufacturing techniques such as those used in MLCC (multi-layer co-fired ceramic) production of capacitor chips. (It is believed that multi-layer capacitor production is the largest volume use of technical ceramics, and the technology is proven for high volume manufacturing.) Third, thin electrolyte layers can be achieved within the structure at no additional cost or complexity. Electrolyte layers of 2 μm thickness are possible using the MLCC approach, whereas it is hard to imagine a SOFC tube with less than a 60 μm electrolyte wall thickness. Hence, the Fuel Cell StickTM device of the invention can be about 30 times more efficient than a SOFC tube. Finally, the multi-layer Fuel Cell StickTM devices of the invention could each have many hundreds, or thousands, of layers, which would offer the largest area and greatest density.
Consider the surface area of a SOFC tube of the prior art versus a Fuel Cell StickTM device of the invention. For example, consider a 0.25′′ diameter tube versus a 0.25′′×0.25′′ Fuel Cell StickTM device. In the tube, the circumference is 3.14×D, or 0.785′′. In the 0.25′′ Fuel Cell StickTM device, the usable width of one layer is about 0.2 inches. Therefore, it takes about 4 layers to give the same area as one tube. These figures are dramatically different than those for capacitor technology. The state of the art for Japanese multi-layer capacitors is currently 600 layers of 2 μm thicknesses. The Japanese will likely soon launch 1000 layer parts in production, and they make them now in the laboratory. These chip capacitors with 600 layers are only 0.060′′ (1500 μm). Applying this manufacturing technology to a Fuel Cell StickTM device of the invention, in a 0.25′′ device having a 2 μm electrolyte thickness and air/fuel passages with respective cathodes/anodes of 10 μm thickness, it would be feasible to produce a single device with 529 layers. That would be the equivalent of 132 tubes. Prior art strategies either add more tubes, increase diameter, and/or increase tube length to get more power, with result being very large structures for high power output. The invention, on the other hand, either adds more layers to a single Fuel Cell StickTM device to get more power and/or uses thinner layers or passages in the device, thereby enabling miniaturization for SOFC technology. Moreover, the benefit in the present invention is a squared effect, just like in capacitors. When the electrolyte layers are made half as thick, the power doubles, and then you can fit more layers in the device so power doubles again.
Another key feature of the invention is that it would be easy to link layers internally to increase the output voltage of the Fuel Cell StickTM device. Assuming 1 volt per layer, 12 volts output may be obtained by the Fuel Cell StickTM devices of the invention using via holes to link groups of 12 together. After that, further connections may link groups of 12 in parallel to achieve higher current. This can be done with existing methods used in capacitor chip technology. The critical difference is that the invention overcomes the brazing and complex wiring that other technologies must use.
The invention also provides a greater variety of electrode options compared to the prior art. Precious metals will work for both the anodes and cathodes. Silver is cheaper, but for higher temperature, a blend with Pd, Pt, or Au would be needed, with Pd possibly being the lowest priced of the three. Much research has focused on non-precious metal conductors. On the fuel side, attempts have been made to use nickel, but any exposure to oxygen will oxidize the metal at high temperature. Conductive ceramics are also known, and can be used in the invention. In short, the present invention may utilize any sort of anode/cathode/electrolyte system that can be sintered.
In an embodiment of the invention, it is possible that when a large area of 2 μm tape is unsupported, with air/gas on both sides, the layer might become fragile. It is envisioned to leave pillars across the gap. These would look something like pillars in caves where a stalactite and stalagmite meet. They could be spaced evenly and frequently, giving much better strength to the structure.
For attachment of the gas and air supply, it is envisioned that the end temperature is below 300° C., for example, below 150° C., such that high temperature flexible silicone tubes or latex rubber tubes, for example, may be used to attach to the Fuel Cell StickTM devices. These flexible tubes can simply stretch over the end of the device, and thereby form a seal. These materials are available in the standard McMaster catalog. Silicone is commonly used at 150° C. or above as an oven gasket, without losing its properties. The many silicone or latex rubber tubes of a multi-stick Fuel Cell StickTM system could be connected to a supply with barb connections.
The anode material or the cathode material, or both electrode materials, may be a metal or alloy. Suitable metals and alloys for anodes and cathodes are known to those of ordinary skill in the art. Alternatively, one or both electrode materials may be an electronically conductive green ceramic, which are also known to those of ordinary skill in the art. For example, the anode material may be a partially sintered metallic nickel coated with yttria-stabilized zirconia, and the cathode material may be a modified lanthanum manganite, which has a perovskite structure.
In another embodiment, one or both of the electrode materials may be a composite of a green ceramic and a conductive metal present in an amount sufficient to render the composite conductive. In general, a ceramic matrix becomes electronically conductive when the metal particles start to touch. The amount of metal sufficient to render the composite matrix conductive will vary depending mainly on the metal particle morphology. For example, the amount of metal will generally need to be higher for spherical powder metal than for metal flakes. In an exemplary embodiment, the composite comprises a matrix of the green ceramic with about 40-90% conductive metal particles dispersed therein. The green ceramic matrix may be the same or different than the green ceramic material used for the electrolyte layer.
In the embodiments in which one or both electrode materials include a ceramic, i.e., the electronically conductive green ceramic or the composite, the green ceramic in the electrode materials and the green ceramic material for the electrolyte may contain cross-linkable organic binders, such that during lamination, the pressure is sufficient to cross-link the organic binder within the layers as well as to link polymer molecular chains between the layers.
Reference will now be made to the drawings in which like numerals are used throughout to refer to like components. Reference numbers used in the Figures are as follows:
10 Full Cell StickTM device
11a First end
11b Second end
12 Fuel inlet
13 Fuel pre-heat chamber
14 Fuel passage
16 Fuel outlet
18 Air inlet
19 Air pre-heat chamber
20 Air passage
21 Exhaust passage
22 Air outlet
24 Anode layer
25 Exposed anode portion
26 Cathode layer
27 Exposed cathode portion
28 Electrolyte layer
29 Ceramic
30 Cold zone (or second temperature)
31 Transition zone
32 Hot zone (or heated zone or first temperature zone)
33a Pre-heat zone
33b Active zone
34 Fuel supply
36 Air supply
38 Negative voltage node
40 Positive voltage node
42 Wire
44 Contact pad
46 Solder connection
48 Spring clip
50 Supply tube
52 Tie wrap
54 Support pillars
56 First via
58 Second via
60 Barrier coating
62 Surface particles
64 Textured surface layer
66 Anode suspension
70 Openings
72(a,b) Organic material/sacrificial layer
80 Left side
82 Right side
84 Bridging portion
90 Bridge
92 Wire (physical) Structure
94 Gap-forming tape
96 Furnace wall
96′ Multiple-layer furnace wall
96′′ Multiple-layer furnace wall with air gap
98a,b,c Insulation
100 Fuel Cell StickTM device
102 Elongate section
104 Large surface area section
106 Elongate section
120 Air gap
122 Current collector
123 Gap
124 Electrode particles
126 Viscous fluid
128 Temporary substrate
130 Ceramic tape
132 Indentations
134 Connector
136 Electrical contacts
138 Gas flow pathway
140 O-ring
200 Spiral Tubular Fuel Cell StickTM device
300 Concentric Tubular Fuel Cell StickTM device
400 End-rolled Fuel Cell StickTM device
402 Thick portion
404 Thin portion
500 Fuel Cell StickTM device
The terms “zone,” “area,” and “region” may be used interchangeably throughout, and are intended to have the same meaning. Similarly, the terms “passage,” “channel,” and “path” may be used interchangeably throughout and the terms “outlet” and “exit” may be used interchangeably throughout.
FIGS. 1 and 1A depict, in side cross-sectional view and top cross-sectional view, respectively, one embodiment of a basic Fuel Cell StickTM device 10 of the invention, having a single anode layer 24, cathode layer 26 and electrolyte layer 28, wherein the device 10 is monolithic. The Fuel Cell StickTM device 10 includes a fuel inlet 12, a fuel outlet 16 and a fuel passage 14 therebetween. Device 10 further includes an air inlet 18, an air outlet 22 and an air passage 20 therebetween. The fuel passage 14 and the air passage 20 are in an opposing and parallel relation, and the flow of fuel from fuel supply 34 through the fuel passage 14 is in a direction opposite to the flow of air from air supply 36 through air passage 20. The electrolyte layer 28 is disposed between the fuel passage 14 and the air passage 20. The anode layer 24 is disposed between the fuel passage 14 and the electrolyte layer 28. Similarly, the cathode layer 26 is disposed between the air passage 20 and the electrolyte layer 28. The remainder of the Fuel Cell StickTM device 10 comprises ceramic 29, which may be of the same material as the electrolyte layer 28 or may be a different but compatible ceramic material. The electrolyte layer 28 is considered to be that portion of the ceramic lying between opposing areas of the anode 24 and cathode 26, as indicated by dashed lines. It is in the electrolyte layer 28 that oxygen ions pass from the air passage 20 to the fuel passage 14. As shown in FIG. 1, O2 from the air supply 36 travels through the air passage 20 and is ionized by the cathode layer 26 to form 2O−, which travels through the electrolyte layer 28 and through the anode 24 into the fuel passage 14 where it reacts with fuel, for example, a hydrocarbon, from the fuel supply 34 to first form CO and H2 and then to form H2O and CO2. While FIG. 1 depicts the reaction using a hydrocarbon as the fuel, the invention is not so limited. Any type of fuel commonly used in SOFCs may be used in the present invention. Fuel supply 34 may be any hydrocarbon source or hydrogen source, for example. Methane (CH4), propane (C3H8) and butane (C4H10) are examples of hydrocarbon fuels.
For the reaction to occur, heat must be applied to the Fuel Cell StickTM device 10. In accordance with the invention, the length of the Fuel Cell StickTM device 10 is long enough that the device can be divided into a hot zone 32 (or heated zone) in the center of the device 10 and cold zones 30 at each end 11a and 11b of the device 10. Between the hot zone 32 and the cold zones 30, a transition zone 31 exists. The hot zone 32 will typically operate above 400° C. In exemplary embodiments, the hot zone 32 will operate at temperatures >600° C., for example >700° C. The cold zones 30 are not exposed to a heat source, and due to the length of the Fuel Cell StickTM device 10 and the thermal property advantages of the ceramic materials, heat dissipates outside the hot zone 32, such that the cold zones 30 have a temperature <300° C. It is believed that heat transfer from the hot zone 32 down the length of the ceramic to the end of the cold zone 30 is slow, whereas the heat transfer from the ceramic material outside the hot zone 32 into the air is relatively faster. Thus, most of the heat inputted in the hot zone 32 is lost to the air (mainly in the transition zone 31) before it can reach the end of the cold zone 30. In exemplary embodiments of the invention, the cold zones 30 have a temperature <150° C. In a further exemplary embodiment, the cold zones 30 are at room temperature. The transition zones 31 have temperatures between the operating temperature of the hot zone 32 and the temperature of the cold zones 30, and it is within the transition zones 31 that the significant amount of heat dissipation occurs.
Because the dominant coefficient of thermal expansion (CTE) is along the length of the Fuel Cell StickTM device 10, and is therefore essentially one-dimensional, fast heating of the center is permitted without cracking. In exemplary embodiments, the length of the device 10 is at least 5 times greater than the width and thickness of the device. In further exemplary embodiments, the length of the device 10 is at least 10 times greater than the width and thickness of the device. In yet further exemplary embodiments, the length of the device 10 is at least 15 times greater than the width and thickness of the device. In addition, in exemplary embodiments, the width is greater than the thickness, which provides for greater area. For example, the width may be at least twice the thickness. By way of further example, a 0.2 inch thick Fuel Cell StickTM device 10 may have a width of 0.5 inch. It may be appreciated that the drawings are not shown to scale, but merely give a general idea of the relative dimensions.
In accordance with the invention, electrical connections to the anode 24 and cathode 26 are made in the cold zones 30 of the Fuel Cell StickTM device 10. In an exemplary embodiment, the anode 24 and the cathode 26 will each be exposed to an outer surface of the Fuel Cell StickTM device 10 in a cold zone 30 to allow an electrical connection to be made. A negative voltage node 38 is connected via a wire 42, for example, to the exposed anode portion 25 and a positive voltage node 40 is connected via a wire 42, for example, to the exposed cathode portion 27. Because the Fuel Cell StickTM device 10 has cold zones 30 at each end 11a, 11b of the device, low temperature rigid electrical connections can be made, which is a significant advantage over the prior art, which generally requires high temperature brazing methods to make the electrical connections.
FIG. 2 depicts in perspective view a first end 11a of Fuel Cell StickTM device 10 with a supply tube 50 attached over the end 11a and secured with a tie wrap 52. Fuel from fuel supply 34 will then be fed through the supply tube 50 and into the fuel inlet 12. As a result of first end 11a being in the cold zone 30, flexible plastic tubing or other low temperature type connection material may be used to connect the fuel supply 34 to the fuel inlet 12. The need for high temperature brazing to make the fuel connection is eliminated by the invention.
FIG. 3A depicts in perspective view a Fuel Cell StickTM device 10 similar to that depicted in FIG. 1, but having modified first and second ends 11a, 11b. Ends 11a, 11b have been machined to form cylindrical end portions to facilitate connection of the fuel supply 34 and air supply 36. FIG. 3B depicts in perspective view a supply tube 50 connected to the first end 11a for feeding fuel from fuel supply 34 to the fuel inlet 12. By way of example, supply tube 50 can be a silicone or latex rubber tube that forms a tight seal by virtue of its elasticity to the first end 11a. It may be appreciated that the flexibility and elasticity of the supply tubes 50 can provide a shock-absorbing holder for the Fuel Cell StickTM devices 10 when the use is in a mobile device subject to vibrations. In the prior art, the tubes or plates were rigidly brazed, and thus subject to crack failure if used in a dynamic environment. Therefore, the additional function of the supply tubes 50 as vibration dampers offers a unique advantage compared to the prior art.
Referring back to FIG. 3A, contact pads 44 are provided on the outer surface of the Fuel Cell StickTM device 10 so as to make contact with the exposed anode portion 25 and the exposed cathode portion 27. Material for the contact pads 44 should be electrically conductive so as to electrically connect the voltage nodes 38, 40 to their respective anode 24 and cathode 26. It may be appreciated that any suitable method may be used for forming the contact pads 44. For example, metal pads may be printed onto the outer surface of a sintered Fuel Cell StickTM device 10. The wires 42 are secured to the contact pads 44 by a solder connection 46, for example, to establish a reliable connection. Solders are a low temperature material, which can be used by virtue of being located in the cold zones 30 of the Fuel Cell StickTM device 10. For example, a common 10Sn88Pb2Ag solder can be used. The present invention eliminates the need for high temperature voltage connections, thereby expanding the possibilities to any low temperature connection material or means.
Also depicted in FIG. 3A, in perspective view, are the fuel outlet 16 and the air outlet 22. The fuel enters through the fuel inlet 12 at first end 11a, which is in one cold zone 30, and exits out the side of Fuel Cell StickTM device 10 through outlet 16 adjacent the second end 11b. Air enters through air inlet 18 located in the second end 11b, which is in the cold zone 30, and exits from the air outlet 22 in the side of the Fuel Cell StickTM device 10 adjacent the first end 11a. While the outlets 16 and 22 are depicted as being on the same side of the Fuel Cell StickTM device 10, it may be appreciated that they may be positioned at opposing sides, for example, as depicted below in FIG. 4A.
By having air outlet 22 close to fuel inlet 12 (and similarly fuel outlet 16 close to air inlet 18), and through the close proximity of the overlapping layers (anode, cathode, electrolyte), the air outlet 22 functions as a heat exchanger, usefully pre-heating the fuel that enters the device 10 through fuel inlet 12 (and similarly, fuel outlet 16 pre-heats air entering through air inlet 18). Heat exchangers improve the efficiency of the system. The transition zones 31 have overlapping areas of spent air and fresh fuel (and spent fuel and fresh air), such that heat is transferred before the fresh fuel (fresh air) reaches the hot zone 32. Thus, the Fuel Cell StickTM device 10 of the invention is a monolithic structure that includes a built-in heat exchanger.
With respect to FIG. 4A, there is depicted in perspective view the connection of a plurality of Fuel Cell StickTM devices 10, in this case two Fuel Cell StickTM devices 10, by aligning each contact pad 44 connected to the exposed anode portions 25 and soldering (at 46) a wire 42 connected to the negative voltage node 38 to each of the contact pads 44. Similarly, the contact pads 44 that are connected to the exposed cathode portions 27 are aligned and a wire 42 connecting the positive voltage node 40 is soldered (at 46) to each of those aligned contact pads 44, as shown partially in phantom. As may be appreciated, because the connection is in the cold zone 30, and is a relatively simple connection, if one Fuel Cell StickTM device 10 in a multi-Fuel Cell StickTM system or assembly needs replacing, it is only necessary to break the solder connections to that one device 10, replace the device with a new device 10, and re-solder the wires 42 to the contact pads 44 of the new Fuel Cell StickTM device 10.
FIG. 4B depicts in an end view the connection between multiple Fuel Cell StickTM devices 10, where each Fuel Cell StickTM device 10 includes a plurality of anodes 24 and cathodes 26. For example, the specific embodiment depicted in FIG. 4B includes three sets of opposing anodes 24 and cathodes 26, with each anode 24 exposed at the right side of the Fuel Cell StickTM device 10 and each cathode 26 exposed at the left side of the Fuel Cell StickTM device 10. A contact pad 44 is then placed on each side of the Fuel Cell StickTM device 10 to contact the respective exposed anode portions 25 and exposed cathode portions 27. On the right side, where the anodes 24 are exposed, the negative voltage node 38 is connected to the exposed anode portions 25 by securing wire 42 to the contact pad 44 via a solder connection 46. Similarly, positive voltage node 40 is connected electrically to the exposed cathode portions 27 on the left side of the Fuel Cell StickTM device 10 by securing wire 42 to contact pad 44 via the solder connection 46. Thus, while FIGS. 1-4A depicted a single anode 24 opposing a single cathode 26, it may be appreciated, as shown in FIG. 4B, that each Fuel Cell StickTM device 10 may include multiple anodes 24 and cathodes 26, with each being exposed to an outer surface of the Fuel Cell StickTM device 10 for electrical connection by means of a contact pad 44 applied to the outer surface for connection to the respective voltage node 38 or 40. The number of opposing anodes 24 and cathodes 26 in the structure may be tens, hundreds and even thousands.
FIG. 5 depicts in an end view a mechanical attachment for making the electrical connection between wire 42 and the contact pad 44. In this embodiment, the Fuel Cell StickTM devices 10 are oriented such that one set of electrodes is exposed at the top surface of each Fuel Cell StickTM device 10. The contact pad 44 has been applied to each top surface at one end (e.g., 11a or 11b) in the cold zone 30. Spring clips 48 may then be used to removably secure the wire 42 to the contact pads 44. Thus, metallurgical bonding may be used to make the electrical connections, such as depicted in FIGS. 3A, 4A and 4B, or mechanical connection means may be used, as depicted in FIG. 5. The flexibility in selecting an appropriate attachment means is enabled by virtue of the cold zones 30 in the Fuel Cell StickTM devices 10 of the invention. Use of spring clips 48 or other mechanical attachment means further simplifies the process of replacing a single Fuel Cell StickTM device 10 in a multi-stick assembly.
FIGS. 6A and 6B depict in perspective views an alternative embodiment having a single cold zone 30 at the first end 11a of Fuel Cell StickTM device 10, with the second end 11b being in the hot zone 32. In FIG. 6A, the Fuel Cell StickTM device 10 includes three fuel cells in parallel, whereas the Fuel Cell StickTM device 10 of FIG. 6B includes a single fuel cell. Thus, embodiments of the invention may include a single cell design or a multi-cell design. To enable the single end input of both the fuel and the air, the air inlet 18 is reoriented to be adjacent the first end 11a at the side surface of the Fuel Cell StickTM device 10. The air passage 20 (not shown) again runs parallel to the fuel passage 14, but in this embodiment, the flow of air is in the same direction as the flow of fuel through the length of the Fuel Cell StickTM device 10. At the second end 11b of the device 10, the air outlet 22 is positioned adjacent the fuel outlet 16. It may be appreciated that either the fuel outlet 16 or the air outlet 22, or both, can exit from a side surface of the Fuel Cell StickTM device 10, rather than both exiting at the end surface.
As depicted in FIG. 6B, the supply tube 50 for the air supply 36 is formed by making holes through the side of the supply tube 50 and sliding the device 10 through the side holes so that the supply tube 50 for the air supply 36 is perpendicular to the supply tube 50 for the fuel supply 34. Again, a silicone rubber tube or the like may be used in this embodiment. A bonding material may be applied around the joint between the supply tube 50 and the device 10 to form a seal. The electrical connections are also made adjacent the first end 11a in the cold zone 30. FIGS. 6A and 6B each depict the positive voltage connection being made on one side of the Fuel Cell StickTM device 10 and the negative voltage connection being made on the opposing side of the Fuel Cell StickTM device 10. However, it may be appreciated that the invention is not so limited. An advantage of the single end input Fuel Cell StickTM device 10 is that there is only one cold-to-hot transition instead of two transition zones 31, such that the Fuel Cell StickTM device 10 could be made shorter.
One benefit of the invention is the ability to make the active layers very thin, thereby enabling a Fuel Cell StickTM device 10 to incorporate multiple fuel cells within a single device. The thinner the active layers are, the greater the chance of an air passage 20 or fuel passage 14 caving in during manufacture of the Fuel Cell StickTM device 10, thereby obstructing flow through the passage 14 and/or 20. Therefore, in one embodiment of the invention, depicted in FIGS. 7A and 7B, a plurality of support pillars 54, for example ceramic support pillars, are provided in the passages 14 and 20 to prevent distortion of the electrolyte layer 28 and obstruction of the passages 14, 20. FIG. 7A is a cross-sectional side view, whereas FIG. 7B is a cross-sectional top view through the air passage 20. According to one method of the invention, using the tape casting method, a sacrificial tape layer may be used, with a plurality of holes formed in the sacrificial layer, such as by means of laser removal of the material. A ceramic material is then used to fill the holes, such as by spreading a ceramic slurry over the sacrificial tape layer to penetrate the holes. After the various layers are assembled together, the sacrificial material of the sacrificial layer is removed, such as by use of a solvent, leaving the support pillars 54 remaining.
In another embodiment for forming the support pillars 54, large particles of a pre-sintered ceramic can be added to an organic vehicle, such as plastic dissolved in a solvent, and stirred to form a random mixture. By way of example and not limitation, the large particles may be spheres, such as 0.002 in. diameter balls. The random mixture is then applied to the green structure, such as by printing in the areas where the fuel and air passages 14 and 20 are to be located. During the sintering (bake/fire) process, the organic vehicle leaves the structure (e.g. is burned out), thereby forming the passages 14, 20, and the ceramic particles remain to form the support pillars 54 that physically hold open the passages 14, 20. The resultant structure is shown in the micrographs of FIGS. 7C and 7D. The support pillars 54 are randomly positioned, with the average distance being a function of the loading of the ceramic particles in the organic vehicle.
FIG. 8A depicts in cross-section one embodiment of the invention containing two fuel cells in parallel. Each active electrolyte layer 28 has an air passage 20 and cathode layer 26a or 26b on one side and a fuel passage 14 and anode layer 24a or 24b on the opposing side. The air passage 20 of one fuel cell is separated from the fuel passage 14 of the second fuel cell by ceramic material 29. The exposed anode portions 25 are each connected via wire 42 to the negative voltage node 38 and the exposed cathode portions 27 are each connected via a wire 42 to the positive voltage node 40. A single air supply 36 can then be used to supply each of the multiple air passages 20 and a single fuel supply 34 may be used to supply each of the multiple fuel passages 14. The electrical circuit established by this arrangement of the active layers is depicted at the right side of the figure.
In the cross-sectional view of FIG. 8B, the Fuel Cell StickTM device 10 is similar to that depicted in FIG. 8A, but instead of having multiple exposed anode portions 25 and multiple exposed cathode portions 27, only anode layer 24a is exposed at 25 and only one cathode layer 26a is exposed at 27. A first via 56 connects cathode layer 26a to cathode layer 26b and a second via 58 connects anode layer 24a to anode layer 24b. By way of example, laser methods may be used during formation of the green layers to create open vias, which are then subsequently filled with electrically conductive material to form the via connections. As shown by the circuit at the right of FIG. 8B, the same electrical path is formed in the Fuel Cell StickTM device 10 of FIG. 8B as in the Fuel Cell StickTM device 10 of FIG. 8A.
FIGS. 9A and 9B also depict, in cross-sectional views, multi-fuel cell designs, but with shared anodes and cathodes. In the embodiment of FIG. 9A, the Fuel Cell StickTM device 10 includes two fuel passages 14 and two air passages 20, but rather than having two fuel cells, this structure includes three fuel cells. The first fuel cell is formed between anode layer 24a and cathode layer 26a with intermediate electrolyte layer 28. Anode layer 24a is on one side of a fuel passage 14, and on the opposing side of that fuel passage 14 is a second anode layer 24b. Second anode layer 24b opposes a second cathode layer 26b with another electrolyte layer 28 there between, thereby forming a second fuel cell. The second cathode layer 26b is on one side of an air passage 20 and a third cathode layer 26c is on the opposing side of that air passage 20. Third cathode layer 26c opposes a third anode layer 24c with an electrolyte layer 28 therebetween, thus providing the third fuel cell. The portion of the device 10 from anode layer 24a to cathode layer 26c could be repeated numerous times within the device 10 to provide the shared anodes and cathodes thereby multiplying the number of fuel cells within a single Fuel Cell StickTM device 10. Each anode layer 24a, 24b, 24c includes an exposed anode portion 25 to which electrical connections can be made at the outer surface of the Fuel Cell StickTM device 10 to connect to a negative voltage node 38 via a wire 42, for example. Similarly, each cathode layer 26a, 26b, 26c includes an exposed cathode portion 27 to the outside surface for connection to a positive voltage node 40 via a wire 42, for example. A single air supply 36 may be provided at one cold end to supply each of the air passages 20 and a single fuel supply 34 may be provided at the opposite cold end to supply each of the fuel passages 14. The electrical circuit formed by this structure is provided at the right side of FIG. 9A. This Fuel Cell StickTM device 10 contains three fuel cell layers in parallel trebling the available power. For example, if each layer produces 1 volt and 1 amp, then each fuel cell layer produces 1 watt of power output (volt×amp=watt). Therefore, this three-layer layout would then produce 1 volt and 3 amps for a total of 3 watts of power output.
In FIG. 9B, the structure of FIG. 9A is modified to provide a single electrical connection to each of the voltage nodes to create three fuel cells in series, as shown by the circuit at the right side of FIG. 9B. The positive voltage node 40 is connected to cathode layer 26a at exposed cathode portion 27. Anode layer 24a is connected to cathode layer 26b by via 58. Anode layer 24b is connected to cathode layer 26c by via 56. Anode layer 24c is then connected at exposed anode portion 25 to the negative voltage node 38. Thus, using the same 1 amp/1 volt per layer assumption, this three cell structure would produce 3 volts and 1 amp for a total of 3 watts of power output.
Another embodiment of the invention is depicted in side view in FIG. 10. In this embodiment, the Fuel Cell StickTM device 10 has a single cold zone 30 at the first end 11a with the second end 11b being in the hot zone 32. As in other embodiments, the fuel inlets 12 are at the first end 11a and connected to a fuel supply 34 by a supply tube 50. In this embodiment, the fuel passages 14 extend the length of the Fuel Cell StickTM device 10 with the fuel outlet 16 being at second end 11b. Thus, the fuel supply connection is made in the cold zone 30 and the outlet for the fuel reactants (e.g., CO2 and H2O) is in the hot zone 32. Similarly, the anodes have an exposed anode portion 25 in the cold zone 30 for connecting to the negative voltage node 38 via a wire 42.
In the embodiment of FIG. 10, the Fuel Cell StickTM device 10 is open at least at one side, and potentially at both opposing sides, to provide both air inlets 18 and air passages 20 in the hot zone 32. The use of support pillars 54 may be particularly useful in this embodiment within the air passages 20. The air outlet can be at the second end 11b, as depicted. Alternatively, although not shown, the air outlet may be at an opposing side from the air inlet side if the passages 20 extend through the width and the air supply is directed only toward the input side, or if the passages 20 do not extend through the width. Instead of providing only heat to the hot zone 32, in this embodiment, air is also provided. In other words, the sides of the device 10 in the hot zone 32 are open to heated air instead of supplying air through a forced air tube.
FIG. 10A shows in side view a variation of the embodiment depicted in FIG. 10. In FIG. 10A, the Fuel Cell StickTM device 10 includes opposing cold zones 30 with a central heated zone 32 separated from the cold zones 30 by transition zones 31. The air inlet 18 is provided in the central heated zone 32, in at least a portion thereof, to receive the heated air. However, in this embodiment, the air passage 20 is not completely open to the side of the Fuel Cell StickTM device 10 for an appreciable length as in FIG. 10. Rather, as shown more clearly in FIG. 10B, air passage 20 is open in a portion of the hot zone 32 and then is close to the sides for the remainder of the length and then exits at air outlet 22 at second end 11b of the Fuel Cell StickTM device 10. This embodiment allows heated air to be supplied in the hot zone 32 rather than a forced air supply tube, but also allows for the fuel and air to exit at one end 11b of the device 10 in a cold zone 30.
While specific embodiments have been depicted and described in detail, the scope of the invention should not be so limited. More general embodiments of the invention are described below and may be understood more fully with reference to the schematic views depicted in FIGS. 11-24. FIG. 11 provides a key for the components depicted schematically in FIGS. 12-24. Where fuel (F) or air (A) is shown by an arrow going into the Fuel Cell StickTM device (e.g., SOFC Stick) that indicates forced flow, such as through a tube connected to the input access point. Where air input is not depicted, that indicates that heated air is supplied in the hot zone by means other than a forced flow connection and the Fuel Cell StickTM device is open to the air passage at an access point within the hot zone.
One embodiment of the invention is a Fuel Cell StickTM device that includes at least one fuel passage and associated anode, at least one oxidant pathway and associated cathode, and an electrolyte therebetween, where the cell is substantially longer than it is wide or thick so as to have a CTE in one dominant axis and operating with a portion thereof in a heated zone having a temperature of greater than about 400° C. In this embodiment, the Fuel Cell StickTM device has integrated access points for both air and fuel input at one end of the device according to the dominant CTE direction, or air input at one end and fuel input at the other end according to the dominant CTE direction, and air and fuel inputs being located outside the heated zone. For example, see FIGS. 20 and 24.
In another embodiment of the invention, the fuel cell has a first temperature zone and a second temperature zone, wherein the first temperature zone is the hot zone, which operates at a temperature sufficient to carry out the fuel cell reaction, and the second temperature zone is outside the heated zone and operates at a lower temperature than the first temperature zone. The temperature of the second temperature zone is sufficiently low to allow low temperature connections to be made to the electrodes and a low temperature connection for at least the fuel supply. The fuel cell structure extends partially into the first temperature zone and partially into the second temperature zone. For example, see FIGS. 12, 13 and 17.
In one embodiment of the invention, the fuel cell includes a first temperature zone that is the heated zone and a second temperature zone operating at a temperature below 300° C. The air and fuel connections are made in the second temperature zone using rubber tubing or the like as a low temperature connection. Low temperature solder connections or spring clips are used to make the electrical connections to the anode and cathode for connecting them to the respective negative and positive voltage nodes. Further, the fuel outlet for carbon dioxide and water and the air outlet for depleted oxygen are located in the first temperature zone, i.e., the heated zone. For example, see FIG. 17.
In another embodiment, the fuel cell structure has a central first temperature zone that is the heated zone, and each end of the fuel cell is located outside the first temperature zone in a second temperature zone operating below 300° C. Fuel and air inputs are located in the second temperature zone, as are solder connections or spring clips for electrical connection to the anode and cathode. Finally, output for the carbon dioxide, water and depleted oxygen are located in the second temperature zone. For example, see FIGS. 19, 20 and 24.
In another embodiment of the invention, fuel inputs may be provided at each end according to the dominant CTE direction in a second temperature zone operating below 300° C. with a first temperature zone being the heated zone provided in the center between the opposing second temperature zones. The output for the carbon dioxide, water, and depleted oxygen may be located in the central heated zone. For example, see FIGS. 15 and 18. Alternatively, the output for the carbon dioxide, water and depleted oxygen may be located in the second temperature zone, i.e., outside of the heated zone. For example, see FIGS. 16 and 19.
In another embodiment, both the fuel and air input access points are located outside the first temperature zone, which is the heated zone, in a second temperature zone operating below 300° C. thereby allowing use of low temperature connections, such as rubber tubing for air and fuel supply. In addition, solder connections or spring clips are used in the second temperature zone for connecting the voltage nodes to anodes and cathodes. In one embodiment, the fuel and air input are both at one end according to the dominate CTE direction, with the other end of the Fuel Cell StickTM device being in the first heated temperature zone with the outputs of carbon dioxide, water and depleted oxygen being in the heated zone. For example, see FIG. 17. Thus, the Fuel Cell StickTM device has one heated end and one non-heated end.
In another embodiment, fuel and air are inputted into one end according to the dominant CTE direction outside the heated zone and exit at the opposite end also outside the heated zone, such that the heated zone is between two opposing second temperature zones. For example, see FIG. 20. In yet another alternative, fuel and air are inputted into both of opposing ends located in second temperature zones with the fuel and air outputs being in the central heated zone. For example, see FIG. 18.
In yet another alternative, fuel and air are inputted into both of opposing ends located in second temperature zones with the respective outputs being in the second temperature zone at the opposite end from the input. For example, see FIG. 19. Thus, the fuel cell has a central heated zone and opposing ends outside the heated zone, with fuel and air both inputted into the first end with the respective reaction outputs exiting adjacent the second end, and both fuel and air being inputted into the second end and the reaction outputs exiting adjacent the first end.
In yet another embodiment, fuel input may be at one end outside the heated zone and air input may be at the opposite end outside the heat zone. For example, see FIGS. 21-24. In this embodiment, the reaction outputs from both the air and fuel may be within the heated zone (see FIG. 21), or they both may be outside the heated zone adjacent the opposite end from the respective input (see FIG. 24). Alternatively, the carbon dioxide and water output may be in the hot zone while the depleted oxygen output is outside the hot zone (see FIG. 22), or conversely, the depleted oxygen output may be in the heated zone and the carbon dioxide and water output outside the heated zone (see FIG. 23). The variations with respect to fuel and air output depicted in FIGS. 22 and 23 could also be applied in the embodiments depicted in FIGS. 18-20, for example.
In another embodiment of the invention, depicted in top plan view in FIGS. 25A and 27A and in side view in FIG. 27B, an Fuel Cell StickTM device 100 is provided having what may be referred to as a panhandle design. The Fuel Cell StickTM device 100 has an elongate section 102, which may be similar in dimension to the Fuel Cell StickTM devices 10 depicted in prior embodiments, that has a CTE in one dominant axis, i.e., it is substantially longer than it is wide or thick. The Fuel Cell StickTM device 100 further has a large surface area section 104 having a width that more closely matches the length. Section 104 may have a square surface area or a rectangular surface area, but the width is not substantially less than the length, such that the CTE does not have a single dominant axis in section 104, but rather has a CTE axis in the length direction and the width direction. The large surface area section 104 is located in the hot zone 32, whereas the elongate section 102 is at least partially located in the cold zone 30 and the transition zone 31. In an exemplary embodiment, a portion of the elongate section 102 extends into the hot zone 32, but this is not essential. By way of example, the fuel and air supplies 34, 36 may be connected to the elongate section 102 in the manner depicted in FIG. 6B, as well as the electrical connections.
In FIGS. 25B and 26A, a top plan view is provided and in FIG. 26B a side view is provided of an alternative embodiment similar to that shown in FIGS. 25A, 27A and 27B but further having a second elongate section 106 opposite the elongate section 102 so as to position the large surface area section 104 between the two elongate sections 102 and 106. Elongate section 106 is also at least partially located in a cold zone 30 and a transition zone 31. In this embodiment, fuel may be inputted into elongate section 102 and air inputted into elongate section 106. By way of example, the air supply 36 and the fuel supply 34 could then be connected to the elongate sections 106 and 102, respectively, in the manner depicted in FIG. 2 or FIG. 3B. As depicted in FIG. 25B, the air output may be located in the elongate section 102 adjacent the fuel input, and the fuel output may be located in elongate section 106 adjacent the air input. Alternatively, one or both of the air and fuel outputs may be located in the large surface area section 104 in the hot zone 32, as depicted in FIGS. 26A and 26B in top and side views, respectively. It may be appreciated that in the embodiments of FIGS. 25A and 25B, the surface area of the opposing anode 24 and cathode 26 with intervening electrolyte 28 may be increased in the hot zone 32 to increase the reaction area, thereby increasing the power generated by the Fuel Cell StickTM device 100.
Another benefit of the Fuel Cell StickTM devices 10, 100 of the invention is low weight. Typical combustion engines weigh on the order of 18-30 lbs per kW of power. A Fuel Cell StickTM device 10, 100 of the invention can be made with a weight on the order of 0.5 lbs per kW of power. FIGS. 28A-28D depict an alternative embodiment of a Tubular Fuel Cell StickTM device 200 of the invention, having a spiral or rolled, tubular configuration. FIG. 28A is a schematic top view of device 200, in the unrolled position. The unrolled structure of device 200 has a first end 202 and a second end 204 of equal length L that will correspond to the length of the rolled or spiral Tubular Fuel Cell StickTM device 200. Fuel inlet 12 and air inlet 18 are shown on opposing sides adjacent first end 202. Fuel passage 14 and air passage 20 then extend along the width of the unrolled structure of device 200 to the second end 204 such that the fuel outlet 16 and air outlet 22 are at the second end 204, as further shown in the schematic end view of the unrolled structure of device 200 in FIG. 28B and the schematic side view of the unrolled structure of device 200 in FIG. 28C. The fuel passage 14 and air passage 20 are shown as extending nearly the length L of the unrolled structure of device 200 so as to maximize fuel and air flow, but the invention is not so limited. To form the spiral Tubular Fuel Cell StickTM device 200, first end 202 is then rolled toward second end 204 to form the spiral tube structure of device 200 depicted in the schematic perspective view of FIG. 28D. Air supply 36 may then be positioned at one end of the spiral Tubular Fuel Cell StickTM device 200 for input into air inlet 18, while the fuel supply 34 may be positioned at the opposite end of the spiral Tubular Fuel Cell StickTM device 200 to input fuel into the fuel inlet 12. The air and the fuel will then exit the spiral Tubular Fuel Cell StickTM device 200 along the length L of the device 200 through fuel outlet 16 and air outlet 22. The voltage nodes 38, 40 can be soldered to contact pads 44 formed on or adjacent to opposing ends of the spiral Tubular Fuel Cell StickTM device 200.
FIGS. 29A-29G depict an alternative embodiment of the invention wherein the Fuel Cell StickTM device is in a tubular concentric form. FIG. 29A depicts in schematic isometric view a concentric Tubular Fuel Cell StickTM device 300. FIGS. 29B-29E depict cross-sectional views of the concentric device 300 of FIG. 29A. FIG. 29F depicts an end view at the air input end of the device 300, and FIG. 29G depicts an end view at the fuel input end of device 300. The particular embodiment shown includes three air passages 20, one being in the center of the tubular structure and the other two being spaced from and concentric therewith. The concentric Tubular Fuel Cell StickTM device 300 also has two fuel passages 14 between and concentric with the air passages 20. As shown in FIGS. 29A-29D, the concentric Tubular Fuel Cell StickTM device 300 includes a fuel outlet 16 connecting the fuel passages 14 at one end and an air outlet 22 connecting the air passages 20 at the other end opposite their respective inlets 12, 18. Each air passage 20 is lined with cathodes 26 and each fuel passage 14 is lined with anodes 24, with electrolyte 28 separating opposing anodes and cathodes. As shown in FIGS. 29A-29B and 29F-29G, electrical connection may be made to the exposed anodes 25 and exposed cathodes 27 at opposing ends of the concentric Tubular Fuel Cell StickTM device 300. Contact pads 44 may be applied to the ends to connect the exposed anodes 25 and exposed cathodes 27, and although not shown, the contact pads 44 can be run along the outside of the device 300 to permit the electrical connection to be made at a point along the length of the device 300 rather than at the ends. Concentric Tubular Fuel Cell StickTM device 300 may include support pillars 54 positioned within the air and fuel passages 14, 20 for structural support.
In the embodiments of the invention having two cold zones 30 at opposing ends 11a, 11b, with air input and fuel output at one end and fuel input and air output at the opposing end, the spent fuel or air is in a heated state as it exits the central hot zone 32. The heated air and fuel cool as they travel through the transition zones 31 to the cold zones 30. Thin layers of electrodes and/or ceramic/electrolyte separate an air passage 20 from a parallel fuel passage 14, and vice-versa. In one passage, heated air is exiting the hot zone 32, and in an adjacent parallel passage, fuel is entering the hot zone 32, and vice-versa. The heated air, through heat exchange principles, will heat up the incoming fuel in the adjacent parallel passage, and vice-versa. Thus, there is some pre-heating of the air and fuel through heat exchange. However, due to the rapid loss of heat outside the hot zone 32, as discussed above, heat exchange may not be sufficient to pre-heat the air and fuel to the optimal reaction temperature before it enters the active region in the hot zone 32. In addition, in embodiments where the Fuel Cell StickTM device 10 includes one cold end (cold zone 30) and one hot end (hot zone 32), fuel and air are inputted into the same cold end 30 and exit through the same opposing hot end 32, such that there is no cross-flow of fuel and air for heat-exchange to occur. Only limited heat exchange to the incoming fuel and air is available from the electrode and ceramic materials of the Fuel Cell StickTM device 10.
FIGS. 30A-33C depict various embodiments of an Fuel Cell StickTM device 10 having integrated pre-heat zones 33a for heating the fuel and air before it enters an active zone 33b in which the anodes 24 and cathodes 26 are in opposing relation. These embodiments include Fuel Cell StickTM devices 10 in which there are two cold ends 30 with an intermediate hot zone 32 and fuel and air input at opposing cold ends 30, and Fuel Cell StickTM devices 10 in which there is one hot end 32 and one cold end 30 with fuel and air input both at the single cold end 30. In these embodiments, the amount of electrode material used can be limited to the active zone 33b with only a small amount leading to the cold zone 30 for the external connection to the voltage nodes 38, 40. Another benefit in these embodiments, which will be described in more detail later, is that the electrons have the shortest possible path to travel to the external voltage connection, which provides a low resistance.
FIG. 30A depicts a schematic cross-sectional side view of a first embodiment of a Fuel Cell StickTM device 10 having one cold zone 30 and one opposing hot zone 32 with an integrated pre-heat zone 33a. FIG. 30B depicts in cross-section a view through the anode 24 looking up toward the fuel passage 14, and FIG. 30C depicts in cross-section a view through the cathode 26 looking down toward the air passage 20. As shown in FIGS. 30A and 30B, the fuel from fuel supply 34 enters through fuel inlet 12 and extends along the length of the device 10 through fuel passage 14 and exits from the opposite end of the device 10 through fuel outlet 16. The cold zone 30 is at the first end 11a of Fuel Cell StickTM device 10 and the hot zone 32 is at the opposing second end 11b. Between the hot and cold zones is the transition zone 31. The hot zone 32 includes an initial pre-heat zone 33a through which the fuel first travels, and an active zone 33b that includes the anode 24 adjacent the fuel passage 14. As shown in FIG. 30B, the cross-sectional area of the anode 24 is large in the active zone 33b. The anode 24 extends to one edge of the Fuel Cell StickTM device 10 and an external contact pad 44 extends along the outside of the device 10 to the cold zone 30 for connection to the negative voltage node 38.
Similarly, as shown in FIGS. 30A and 30C, the air from air supply 36 enters through the air inlet 18 positioned in the cold zone 30 and the air extends along the length of the Fuel Cell StickTM device 10 through air passage 20 and exits from the hot zone 32 through the air outlet 22. Because the air and fuel are entering at the same end and traveling along the length of the Fuel Cell StickTM device 10 in the same direction, there is limited pre-heating of the air and fuel by heat exchange prior to the hot zone 32. The cathode 26 is positioned in the active zone 33b in opposing relation to the anode 24 and extends to the opposite side of the Fuel Cell StickTM device 10 where it is exposed and connected to an external contact pad 44 that extends from the active hot zone 33b to the cold zone 30 for connection to the positive voltage node 40. It is not necessary, however, that the exposed cathode 27 be on an opposite side of the device 10 as the exposed anode 25. The exposed anode 25 and exposed cathode 27 could be on the same side of the device 10 and the contact pads 44 could be formed as stripes down the side of the Fuel Cell StickTM device 10. By this structure, the air and fuel are first heated in the pre-heat zone 33a, where no reaction is taking place, and the majority of the anode and cathode material is limited to the active zone 33b where the heated air and fuel enters and react by virtue of the opposed anode and cathode layers 24, 26.
The embodiment depicted in FIGS. 31A-31C is similar to that depicted in FIGS. 30A-30C, but rather than having one hot end 32 and one cold end 30, the embodiment of FIGS. 31A-C includes opposing cold zones 30 with a central hot zone 32. Fuel from fuel supply 34 enters through the first end 11a of device 10 through fuel inlet 12 in the cold zone 30 and exits from the opposite second end 11b through fuel outlet 16 positioned in the opposing cold zone 30. Similarly, air from air supply 36 enters through the opposite cold zone 30 through air inlet 18 and exits at the first cold zone 30 through air outlet 22. The fuel enters the hot zone 32 and is pre-heated in pre-heat zone 33a, while the air enters at the opposite side of the hot zone 32 and is pre-heated in another pre-heat zone 33a. There is thus a cross-flow of fuel and air. The anode 24 opposes the cathode 26 in an active zone 33b of hot zone 32 and the reaction occurs in the active zone 33b involving the pre-heated fuel and air. Again, the majority of electrode material is limited to the active zone 33b. The anode 24 is exposed at one edge of the Fuel Cell StickTM device 10, and the cathode 26 is exposed at the other side of device 10. An external contact pad 44 contacts the exposed anode 25 in the hot zone 32 and extends toward the first cold end 11a for connection to negative voltage node 38. Similarly, an external contact pad 44 contacts the exposed cathode 27 in hot zone 32 and extends toward the second cold end 11b for connection to positive voltage node 40.
The pre-heat zones 33a provide the advantage of fully heating the gas to the optimal reaction temperature before it reaches the active region. If the fuel is colder than the optimum temperature, the efficiency of the SOFC system will be lower. As the air and fuel continue on their paths, they warm up. As they warm up, the efficiency of the electrolyte 28 increases in that region. When the fuel, air and electrolyte 28 reach the full temperature of the furnace, then the electrolyte 28 is working under its optimal efficiency. To save money on the anode 24 and cathode 26, which may be made out of precious metal, the metal can be eliminated in those areas that are still below the optimal temperature. The amount of the pre-heat zone 33a, in terms of length or other dimensions, depends on the amount of heat transfer from the furnace to the Fuel Cell StickTM device 10, and from the Fuel Cell StickTM device 10 to the fuel and air, as well as whether any heat exchange is occurring due to cross-flow of the fuel and air. The dimensions further depend on the rate of flow of fuel and air; if the fuel or air is moving quickly down the length of the Fuel Cell StickTM device 10, a longer pre-heat zone 33a will be advantageous, whereas if the flow rate is slow, the pre-heat zone 33a may be shorter.
FIGS. 32A and 32B depict an embodiment similar to that shown in FIGS. 31A-31C, but the Fuel Cell StickTM device 10 includes a pre-heat chamber 13 between the fuel inlet 12 and fuel passage 14 that extends into the hot zone 32 for pre-heating in the pre-heat zone 33a a large volume of fuel before it passes through the more narrow fuel passage 14 into the active zone 33b. The Fuel Cell StickTM device 10 similarly includes a pre-heat chamber 19 between the air inlet 18 and the air passage 20 that extends into the hot zone 32 for pre-heating a large volume of air in the pre-heat zone 33a before it passes through the more narrow air passage 20 to the active zone 33b. As disclosed in embodiments above, the Fuel Cell StickTM device 10 may include multiple fuel passages 14 and air passages 20, each of which would receive flow from a respective pre-heat chamber 13, 19.
With respect to a high-volume pre-heat chamber 13, 19 instead of a pre-heat channel, it may be imagined, by way of example only, that if it takes 5 seconds for a molecule of air to heat up to the optimal temperature, then if the molecules of air are traveling down the Fuel Cell StickTM device 10 at 1 inch per second, the Fuel Cell StickTM device 10 would need a pre-heat channel that is 5 inches in length before the air enters the active zone 33b. If, however, a large volume chamber is provided instead of a channel, the volume permits the molecules to spend additional time in the cavity before entering the more narrow channel to the active zone 33b, such that the air molecules are heated in the chamber and then a short length of channel may be used for feeding the heated air molecules to the active zone 33b. Such a cavity or pre-heat chamber 13, 19 could be prepared in a number of different ways, including taking a green (i.e., before sintering) assembly and drilling into the end of the assembly to form the chamber, or by incorporating a large mass of organic material within the green stack as it is formed, whereby the organic material is baked out of the Fuel Cell StickTM device during sintering.
FIGS. 33A-33C depict yet another embodiment for pre-heating the air and fuel prior to the air and fuel reaching the active zone 33b. FIG. 33A is a schematic cross-sectional side view, essentially through the longitudinal center of the Fuel Cell StickTM device 10. FIG. 33B is a cross-sectional top view taken along the line 33B-33B where the fuel passage 14 and anode 24 intersect, while FIG. 33C is a cross-sectional bottom view taken along the line 33C-33C where the air passage 20 intersects the cathode 26. The Fuel Cell StickTM device 10 has two opposing cold zones 30 and a central hot zone 32, with a transition zone 31 between each cold zone 30 and the hot zone 32. Fuel from fuel supply 34 enters the first end 11a of Fuel Cell StickTM device 10 through fuel inlet 12 and travels through the fuel passage 14, which extends toward the opposite end of the hot zone 32, where it makes a U-turn and travels back to the cold zone 30 of first end 11a, where the spent fuel exits through fuel outlet 16. Similarly, air from air supply 36 enters the second end 11b of Fuel Cell StickTM device 10 through the air inlet 18 and travels through the air passage 20, which extends toward the opposing end of the hot zone 32, where it makes a U-turn and travels back to the second end 11b, where the air exits from the cold zone 30 through air outlet 22. By means of these U-turned passages, the portion of the fuel passage 14 and air passage 20 from the initial entry into the hot zone 32 through the bend (U-turn) constitute a pre-heat zone for heating the fuel and air. After the bends, or U-turns, in the passages 14, 20, the passages are lined with a respective anode 24 or cathode 26, which are in opposing relation with an electrolyte 28 therebetween, which region constitutes the active zone 33b in hot zone 32. Thus, the fuel and air is heated in the pre-heat zone 33a prior to entry into the active zone 33b to increase the efficiency of the Fuel Cell StickTM device 10, and to minimize the usage of electrode material. The anode 24 is extended to the exterior of the device 10 in the cold zone 30 for connection to negative voltage node 38. Similarly, cathode 26 is extended to the exterior of the device 10 for electrical connection to positive voltage node 40. The fuel and air outlets 16 and 22 also may exit from the cold zones 30.
In many of the embodiments shown and described above, the anodes 24 and cathodes 26 travel within the layers of the Fuel Cell StickTM device 10, essentially in the center area of each layer, i.e., internal to the device, until they reach the end of the device. At that point, the anodes 24 and cathodes 26 are tabbed to the outside of the Fuel Cell StickTM device 10 where the exposed anode 25 and exposed cathode 27 are metallized with a contact pad 44, such as by applying a silver paste, and then a wire is soldered to the contact pad 44. For example, see FIGS. 4A-4B. It may be desirable, however, to build up the layers in the Fuel Cell StickTM device 10 into higher voltage combinations, for example as shown in FIGS. 8A-9B. If it is desired to make a Fuel Cell StickTM device 10 that produces 1 KW of power, the power is divided between the voltage and the current. One standard is to use 12 volts, such that 83 amps would be needed to create the total 1 KW of power. In FIGS. 8B and 9B, vias were used to interconnect the electrode layers to form parallel or series combinations.
Alternative embodiments for interconnecting the electrode layers are depicted in FIGS. 34A to 37. Rather than interconnecting the electrode layers in the interior of the Fuel Cell StickTM device 10, these alternative embodiments use exterior stripes (narrow contact pads), for example of silver paste, along the sides of the Fuel Cell StickTM device 10, in particular, multiple small stripes. Using the striping technique, a simple structure is formed that can provide series and/or parallel combinations to achieve any current/voltage ratios needed. Moreover, the external stripes will have loose mechanical tolerances compared to the internal vias, thereby simplifying manufacturing. Also, the external stripes will likely have a lower resistance (or equivalent series resistance) than the vias. Lower resistance in a conductor path will result in lower power loss along that path, such that the external stripes provide the ability to remove the power from the Fuel Cell StickTM device 10 with a lower loss of power.
Referring now specifically to FIGS. 34A and 34B, an external anode/cathode interconnect in series is depicted. FIG. 34A provides a schematic oblique front view of the alternating anodes 24a, 24b, 24c and cathodes 26a, 26b, 26c. Along the length of the Fuel Cell StickTM device 10, the anodes 24a, 24b, 24c and cathodes 26a, 26b, 26c include a tab out to the edge of the device 10 to provide the exposed anodes 25 and exposed cathodes 27. An external contact pad 44 (or stripe) is then provided on the outside of the Fuel Cell StickTM device 10 over the exposed anodes 25 and cathodes 27, as best shown in the schematic side view of FIG. 34B. By connecting the three pairs of opposed anodes 24a, 24b, 24c and cathodes 26a, 26b, 26c in series, the Fuel Cell StickTM device 10 provides 3 volts and 1 amp. In FIG. 35, the structure is doubled and the two structures are connected by long stripes down the sides of the device 10, thereby providing an external anode/cathode interconnect in a series parallel design that provides 3 volts and 2 amps.
FIGS. 36A and 36B provide an embodiment for a low equivalent series resistance path for providing low power loss. In this embodiment, the hot zone 32 is in the center of the Fuel Cell StickTM device 10 with the first end 11a and second end 11b being in cold zones 30. Fuel is inputted through fuel inlets 12 in first end 11a and air is inputted through air inlets 18 in second end 11b. Within the hot zone 32, which is the active area of the Fuel Cell StickTM device 10, the anodes 24 and cathodes 26 are exposed to the sides of the device 10, with the anodes 24 exposed to one side, and the cathodes 26 exposed to the opposite side. Contact pads 44 (or stripes) are applied over the exposed anodes 25 and cathodes 27. Then, the edges of the Fuel Cell StickTM device 10 are metallized along the length of the sides of the device 10 until the metallization reaches the cold zones 30, where the low temperature solder connection 46 is made to the negative voltage node 38 and the positive voltage node 40. The anodes 24 and cathodes 26 cannot be optimized only for low resistance because they have other functions. For example, the electrodes must be porous to allow the air or fuel to pass through to the electrolyte 28, and porosity increases resistance. Further, the electrodes must be thin to allow for good layer density in a multi-layer Fuel Cell StickTM device 10, and the thinner the electrode, the higher the resistance. By adding thicker contact pads 44 to the edges (sides) of the Fuel Cell StickTM device 10, it is possible to provide a low resistance path toward the solder connection 46. The thicker the contact pad 44, the lower the resistance. If an electron must travel 10 inches, for example, down the electrode within the Fuel Cell StickTM device 10, past all the voids in the electrode layer, the path of least resistance would be to travel 0.5 inch, for example, to the side edge of the device 10, and then travel the 10 inches down the external non-porous contact pad 44. Thus, the long contact pads 44 along the exterior of the Fuel Cell StickTM device 10 that extend to the cold zones 30 allow for the power to be removed from the Fuel Cell StickTM device 10 with a lower loss by providing a lower resistance conductor path. Thus, the striping technique may be used in the active area (hot zone 32) of the Fuel Cell StickTM device 10 for making series and parallel connections to increase power, and a long stripe down the side of the device 10 to the cold ends 30 allows that power to be efficiently removed from the Fuel Cell StickTM device 10.
FIG. 37 depicts, in schematic isometric view, an embodiment similar to that depicted in FIG. 36B, but having a single cold zone 30 at the first end 11a of the Fuel Cell StickTM device 10, with the hot zone 32 being at the second end 11b of device 10. Multiple vertical stripes or contact pads 44 are provided within the hot zone 32 to make the series and/or parallel connections, and the horizontal long stripes or contact pads 44 down the sides of the device 10 are provided from the hot zone 32 to the cold zone 30 for making the low temperature solder connections 46 to the positive voltage node 40 and negative voltage node 38.
One method for forming the fuel passages 14 and air passages 20 is to place an organic material as a sacrificial layer within the green, layered structure that can then bake out during a later sintering step. To build individual Fuel Cell StickTM devices 10 having high power output, such as 1 KW or 10 KW output, the Fuel Cell StickTM device 10 must be long, wide and have a high layer count. By way of example, the Fuel Cell StickTM devices may be on the order of 12 inches to 18 inches long. When baking the green structure to sinter the ceramic and remove the sacrificial organic material, the organic material used to form the fuel passage 14 must exit through openings 12 and 16 that form the fuel inlet and fuel outlet, respectively. Similarly, the organic material used to form the air passage 20 must bake out through the openings 18 and 22 that form the air inlet and air outlet, respectively. The longer and wider the devices, the more difficult it is for the organic material to exit through these openings. If the device is heated too fast during bake-out, the various layers can delaminate because the decomposition of the organic material occurs faster than the material can exit the structure.
FIGS. 38A and 38B depict, in schematic cross-sectional top view, an alternative embodiment that provides multiple exit gaps for bake-out of the organic material (sacrificial layer) 72. As shown in FIG. 38A, multiple openings 70 are provided on one side of the Fuel Cell StickTM device 10 to provide multiple bake-out paths for the organic material 72 to exit the structure. As depicted in FIG. 38B, after bake-out, the multiple openings 70 are then closed by applying a barrier coating 60 to the side of the Fuel Cell StickTM device 10. By way of example, the barrier coating 60 may be a glass coating. In another example, the barrier coating 60 may be a glass containing a ceramic filler. In yet another embodiment, the barrier coating 60 may be a contact pad 44, for example filled with paste, which would then also serve as the low resistance path for the generated power. The silver paste may also contain glass for increased adhesion. In an exemplary embodiment, the bake-out paths for the cathode 26 are vented to one side of the Fuel Cell StickTM device 10 and the bake-out paths for the anode 24 are vented to the opposing side of the device 10 to avoid shorting between opposite electrodes.
In an alternative embodiment for an Fuel Cell StickTM device 10, 100, 200, 300, rather than having an open air passage 20 and fuel passage 14 lined with a cathode 26 or anode 24, respectively, the cathode and air channel may be combined and the anode and fuel channel may be combined through use of porous electrode materials that permit flow of the air or fuel. The cathodes and anodes must be porous anyway to permit the reaction to occur, so in combination with forced air and fuel input, sufficient flow could be achieved through the Fuel Cell StickTM device to permit the power generating reaction to occur.
Another embodiment of the present invention is depicted in schematic cross-sectional end view in FIG. 39. This embodiment is essentially an anode-supported version of an Fuel Cell StickTM device 10. As with other embodiments, the Fuel Cell StickTM device 10 may have a hot end 32 and a cold end 30, or two cold ends 30 with an intermediate hot zone 32. Rather than having the device 10 supported by ceramic 29, the anode-supported version uses the anode material as the supporting structure. Within the anode structure, a fuel passage 14 and an air passage 20 are provided in opposing relation. The air passage 20 is lined with an electrolyte layer 28, and then with a cathode layer 26. Chemical vapor deposition could be used to deposit the internal layers, or by using solutions of viscous pastes.
In FIGS. 40A and 40B, a further embodiment is shown for an anode-supported version of the Fuel Cell StickTM device 10. In this embodiment, the separate open fuel passage 14 is eliminated, such that the porous anode 24 also serves as the fuel passage 14. In addition, the Fuel Cell StickTM device 10 is coated with a barrier coating 60, such as a glass coating or a ceramic coating, to prevent the fuel from exiting out the sides of the device 10. The Fuel Cell StickTM device 10 may have as many air passages 14 with associated electrolyte 28 and cathode 26 in the anode structure as desired. As depicted in FIG. 40B, the fuel from fuel supply 34 is forced into first end 11a through the porous anode 24, which serves as the fuel passage 14, and passes through the electrolyte layers 28 and the cathodes 26 to react with air from air supply 36, and the spent air and fuel can then exit out the air outlet 22.
In another embodiment depicted in a schematic cross-sectional end view in FIG. 41A and a schematic cross-sectional top view in FIG. 41B, the Fuel Cell StickTM device 10 may include a plurality of air passages 20 provided within the anode-supporting structure, and a single fuel passage 14 normal to the multiple air passages 20 for feeding fuel from the fuel supply 34 through the single fuel inlet 12 to multiple air passages 20. Again, the air passages 20 are lined first with an electrolyte layer 28 and then with a cathode 26. The fuel passes from the single fuel passage 14 through the anode structure 24, through the electrolyte 28, and through the cathode 26 to react with the air in the air passage 20, and the spent fuel and air exits from the air outlet 22. The spent fuel can also seep out the side of the Fuel Cell StickTM device 10 that does not include the barrier coating 60, which uncoated side would be located on the opposing side of the device 10 from the orientation of the single fuel passage 14.
In the embodiments pertaining to an anode-supported structure, it may be appreciated that the structure may be essentially reversed to be a cathode-supported structure. Fuel passages 14 coated with an electrolyte layer 28 and an anode layer 24 would then be provided within the cathode structure. A separate air passage 20 or multiple air passages 20 could also be provided, or the porosity of the cathode 26 could be used for the air flow.
FIGS. 42A-42C depict a method for forming the electrodes within the air passages 20 and fuel passages 14. Taking the fuel passage 14 and anode 24 as an example, rather than building up a green structure layer by layer using layers of green ceramic and metal tape layers, or printing metallizations, in the present embodiment, the Fuel Cell StickTM device 10 is first built without the electrodes. In other words, green ceramic material is used to form the electrolyte 28 and ceramic supporting portions 29 of the Fuel Cell StickTM device 10 and the organic material is used to form the passages, such as fuel passage 14. After the Fuel Cell StickTM device 10 has been sintered, the fuel passage 14 is filled with an anode paste or solution. The paste may be thick like that of a printing ink, or runny like that of a high-content water solution. The anode material can be filled into the fuel passage 14 by any desired means, such as sucking it in via a vacuum, by capillary forces, or forcing it in via air pressure.
Alternatively, as shown in FIGS. 42A-42C, the anode material is dissolved in solution, flowed into the fuel passage 14, and then precipitated. For example, through a change of pH, the anode particles can be precipitated and the solution drawn out. In another alternative, the anode particles can be simply allowed to settle, and then the liquid dried or baked out of the fuel passage 14. This settling can be accomplished by creating an ink or liquid carrier that will not keep the particles in suspension for any extended period of time, for example, due to low viscosity. A centrifuge could also be used to force the settling. The centrifuge can easily allow preferential settling of most particles onto one surface of the fuel passage 14 to thereby conserve electrode material and to ensure that only one surface of the fuel passage 14 acts as an electrolyte.
As shown in FIG. 42A, the anode particle-containing solution 66 is pulled into the fuel passage 14 until the passage 14 is completely filled, as shown in FIG. 42B. The particles then settle to the bottom of the passage 14 to form an anode layer 24, as shown in FIG. 42C. Flooding in of the solution 66 can be accelerated by gravity, vacuum, or centrifuge, as compared to normal capillary forces. Of course, while the anode 24 and fuel passage 14 were used as an example, any of these alternative embodiments may also be used with a cathode paste or solution to create a cathode layer 26 in an air passage 20.
In another alternative, a ceramic electrode material (anode or cathode) could be infused into the passage (fuel or air) in a liquid sol-gel state, and then deposited inside the passage. It is also possible to repeat the filling operation multiple times, such as in the case where the concentration of the desired electrode material in the liquid is low, or to provide a gradient of properties in the electrode (such as to provide a different amount of YSZ in the electrode close to the electrolyte versus the amount of YSZ in the electrode farther from the electrolyte), or if there is a desire to put multiple layers of dissimilar materials together (such as a cathode made of LSM near the electrolyte, and then silver over the top of the LSM for better conductivity).
Referring back to FIGS. 7C and 7D, in which ceramic spheres or balls were used to provide structural support to the air and fuel passages 20, 14, ceramic particles may also be used to increase the effective surface area for a greater reaction area, thus giving a higher output. Very fine-sized ceramic balls or particles can be used inside the fuel passage 14 and the air passage 20 prior to applying the electrode layer. As shown in FIG. 43 in schematic cross-sectional side view, surface particles 62 line the passage 14 to provide the electrolyte layer 28 with an uneven topography that increases the surface area available to receive the electrode layer. The anode 24 is then applied over the uneven topography with the anode material coating all around the surface particles 62 thereby increasing the reaction area.
In an alternative embodiment, depicted in schematic cross-sectional side view in FIG. 44, the electrolyte layer 28 may be laminated so as to provide the uneven topography or textured surface layer 64, such as by pressing the green electrolyte layer against a fine grading having a V-shaped pattern, which pattern is then imparted to the electrolyte layer 28. After the electrolyte layer 28 is sintered to solidify the ceramic and the textured surface layer 64, the anode layer 24 may then be applied, such as by using the backfill process described above in FIGS. 42A-42C, to provide an anode with a high reaction area.
Yet another embodiment of the invention is depicted in FIGS. 45A and 45B. FIG. 45A is a schematic top view depicting the air and fuel flow through air and fuel passages and the arrangement of the electrodes, and FIG. 45B is a cross-sectional view through the hot zone 32. Along the length of Fuel Cell StickTM device 10, the device is divided into a left side 80 and a right side 82 with an intermediate or bridging portion 84 therebetween. A plurality of air passages 20L extend from the first end 11a of Fuel Cell StickTM device 10 along the length through the left side 80 and exit out the left side 80 adjacent second end 11b, and a plurality of air passages 20R extend from first end 11a along the length through the right side 82 and exit the Fuel Cell StickTM device 10 on the right side 82 adjacent the second end 11b. The air passages 20L are offset from the air passages 20R, as best shown in FIG. 45B. A plurality of fuel passages 14L extend from the second end 11b of Fuel Cell StickTM device 10 along the length through the left side 80 and exit on the left side 80 adjacent first end 11a, and a plurality of fuel passages 14R extend from second end 11b along the length through the right side 82 and exit the right side 82 adjacent first end 11a. The fuel passages 14L are offset from the fuel passages 14R. In addition, with the exception of one fuel passage and one air passage, each fuel passage 14L is paired with and slightly offset from an air passage 20R and each air passage 20L is paired with and slightly offset from a fuel passage 14R. For each offset pair of fuel passages 14L and air passages 20R, a metallization extends along each fuel passage 14L from the left side 80 to the right side 82, where it then extends along the slightly offset air passage 20R. Similarly, for each offset pair of fuel passages 14R and air passages 20L, a metallization extends along each air passage 20L from the left side 80 to the right side 82, where it then extends along the slightly offset fuel passage 14R. The metallization serves as an anode 24L or 24R when the metallization extends along a fuel passage 14L or 14R, and the metallization serves as a cathode 26L or 26R when the metallization extends along an air passage 20L or 20R. In the bridging portion 84 of the Fuel Cell StickTM device 10, where the metallizations do not extend along any air or fuel passage, the metallization simply serves as a bridge 90 between an anode and a cathode. In one embodiment of the present invention, the metallization may comprise the same material along its length, such that the anode 24L or 24R, the bridge 90 and the cathode 26L or 26R each comprise the same material. For example, the metallizations may each comprise platinum metal, which functions well as either an anode or a cathode. Alternatively, the metallization may comprise different materials. For example, the cathodes 26R or 26L may comprise lanthanum strontium manganite (LSM), while the anodes 24R or 24L comprise nickel, NiO, or NiO+YSZ. The bridges 90 may comprise palladium, platinum, LSM, nickel, NiO, or NiO+YSZ. The present invention contemplates any combination or type of materials suitable for use as a cathode or an anode, or a bridging material therebetween, and the invention is not limited to the specific materials identified above.
On one side of the Fuel Cell StickTM device 10, shown here at the right side 82, a fuel passage 14R is provided with an associated anode 24R that extends to the right edge of the Fuel Cell StickTM device 10 to provide the external exposed anode 25. There is no offset air passage 20L associated with this fuel passage 14R, and the anode 24R need not extend into the left side 80. As depicted in FIG. 45A, an external contact pad 44 is applied over the exposed anode 25 and extends along the length of the Fuel Cell StickTM device 10 into the cold zone 30. Negative voltage node 38 can then be connected by wire 42 and solder connection 46 to the contact pad 44. The anode 24R could extend, as shown, to the right edge throughout the hot zone 32, or could just extend in a small tab portion to reduce the amount of electrode material used. Also, the anode 24R could extend to the right edge of the Fuel Cell StickTM device 10 along the length of the fuel passage 14R, although such embodiment would involve an unnecessary use of electrode material.
Similarly, on the other side of the Fuel Cell StickTM device 10, shown as the left side 80, a single air passage 20L is provided with an associated cathode 26L that extends to the left side of the Fuel Cell StickTM device 10 to form the exposed cathode 27. This air passage 20L is not associated with an offset fuel passage 14R, and it is not necessary that the cathode 26L extend to the right side 82. A contact pad 44 may be applied along the exterior of the left side 80 of the Fuel Cell StickTM device 10 from the exposed cathode 27 to a cold end 30, where a positive voltage node 40 may be connected via wire 42 and solder connection 46 to the contact pad 44.
In FIG. 45B, the single fuel passage 14R and associated anode 24R are shown at the top of the right side 82, while the single air passage 20L and associated cathode 26L are shown at the bottom of the left side 80 of the Fuel Cell StickTM device 10. However, the invention is not limited to that arrangement. For example, air passage 20L and associated cathode 26L could be provided also at the top of device 10 on the left side 80, in a similar offset manner to the single fuel passage 14R and its associated anode 24R, but the metallization would not run from the left side 80 through the bridging portion 84 to the right side 82. Rather, the bridge 90 would be absent such that the anode 24R is electrically separated from the cathode 26L. Additional arrangements are contemplated in which a Fuel Cell StickTM device 10 may be provided with two unique air pathway stacks and two unique fuel pathway stacks within a single Fuel Cell StickTM device 10, with the cells connected in series. The embodiment depicted in FIGS. 45A and 45B has an advantage of raising the voltage without raising the current, and while maintaining a low resistance. Further, this embodiment provides a high density within the Fuel Cell StickTM device 10.
In FIGS. 46A and 46B, an alternative embodiment is depicted in schematic perspective view and schematic cross-sectional view, respectively. Previous embodiments (e.g., FIG. 37) provided external stripes along the exterior sides or edges of the Fuel Cell StickTM device 10 from the hot zone 32 to the cold zone(s) 30 to provide a path of low resistance for the electrons to travel to the cold-end. In the embodiment of FIGS. 46A and 46B, instead of stripes down the sides or edges of the device 10, a contact pad 44 is applied along one side and one of the top and bottom surfaces for the external connection to the anode 24 and another contact pad 44 is applied along the opposing side and the other of the top and bottom surfaces for the external connection to the cathode 26. Thus, the electrons have a large or wide path along which to travel, thereby providing an even lower resistance. These large contact pads 44 that are applied on two adjacent surfaces could be used in any of the embodiments disclosed herein.
In FIG. 47, yet another embodiment is depicted, in schematic cross-sectional side view, of a Fuel Cell StickTM device 10 that takes advantage of heat exchange principles. After the heated air and fuel pass through the active zone 33b of the hot zone 32 (i.e., the portion of the hot zone 32 where the anode 24 is in opposing relation to the cathode 26 with an electrolyte 28 therebetween), the fuel passage 14 and air passage 20 are joined into a single exhaust passage 21. Any un-reacted fuel will burn when combined with the heated air, thus producing additional heat. The exhaust passage 21 travels back toward the cold zone 30 adjacent the active zone 33b, with the direction of flow of the exhaust (spent fuel and air) being opposite that of the incoming fuel and air in the adjacent fuel and air passages 14, 20. The additional heat generated in the exhaust passage 21 is transferred to the adjacent passages 14, 20 to heat the incoming fuel and air.
FIGS. 48A-48C depict an “end-rolled Fuel Cell StickTM device” 400 having a thick portion 402 having a greater thickness than a thin portion 404, as depicted in FIG. 48A. The fuel and air inlets 12, 18 are positioned adjacent first end 11a, which is at the end of thick portion 402, and while not shown, the air and fuel outlets (16, 22) may be provided at the sides of the device 400 adjacent opposing second end 11b, which is at the end of the thin portion 404. The thick portion 402 should be thick enough to provide mechanical strength. This may be achieved by providing thick ceramic 29 around the adjacent fuel and air inlets 12, 18. The thin portion 404 will include the active zone 33b (not shown) that includes an anode (not shown) in opposing relation to a cathode (not shown) with an electrolyte (not shown) therebetween (as in prior embodiments). The thin portion 404 should be thin enough to permit it to be rolled while in the green (unfired) state, as shown in FIG. 48B. After the thin portion 404 is rolled to a desired tightness, the device 400 is fired. The rolled thin portion 404 can then be heated to cause the reaction, while the thick portion 402 is a cold end, as discussed in other embodiments. The end-rolled Fuel Cell StickTM device 400 is a large surface area device that can fit in a small space by virtue of rolling the thin portion 404. Moreover, the thin cross-section of the active zone (33b) in the thin portion 404 reduces the heat transfer out along the ceramic and allows good temperature cycle performance.
In embodiments in which the anode 24 and cathode 26 are exposed at the edges (sides) of the Fuel Cell StickTM device 10 in the active (reaction) zone 32 and/or 33b, the ceramic 29 at the top of the device 10 may be recessed in the area of the active zone 32 and/or 33b. This allows access to both the cathode 26 and anode 24 from the top for making the electrical connections. Contact pads 44 (e.g., metallization stripes) may then be applied along the top surface of the Fuel Cell StickTM device 10 from the active zone 32 and/or 33b to the cold zone(s) 30 to provide connections to outside of the hot zone chamber/furnace.
In another embodiment in which the Fuel Cell StickTM device 10 includes two cold zones 30 at the opposing ends 11a, 11b and the hot zone 32 in the middle, contact pad(s) 44 (e.g., metallization stripes) for the anode(s) 24 and/or the cathode(s) 26 can go from the hot zone 32 out toward both ends 11a, 11b of the Fuel Cell StickTM device 10, for example, as shown in FIG. 36B. Two separate electrical connections can then be made to each of the anode(s) 24 and cathode(s) 26. By way of example and not limitation, one set of connections can be used to monitor voltage output from the cell, while the other set of connections can connect the load and allow the current flow. The ability to measure voltage separately, at the cell itself, has the advantage of giving a better idea of the total power output from the cell.
For the contact pads 44 (e.g., metallization stripes), any suitable conducting material known to those of ordinary skill in the art may be used. Examples include silver, LSM and NiO. Combinations of materials may also be used. In one embodiment, non-precious metal materials may be used along the surface of the Fuel Cell StickTM device 10 in the hot zone 32. LSM, for example, may be used where the atmosphere of the hot zone chamber/furnace is oxidizing. NiO, for example, may be used where the atmosphere of the hot zone chamber/furnace is reducing. In either case, however, the non-precious metal materials lose conductivity if the material extends outside the hot zone chamber/furnace such that the metallization material must be transitioned to a precious metal or corrosion resistant material just before the Fuel Cell StickTM device 10 exits the hot zone chamber/furnace. Silver paste is a convenient precious metal material. By way of further explanation, certain materials such as LSM will become non-conducting as the temperature drops from the reaction temperature to room temperature, and other materials such as nickel will become non-conducting when exposed to air at the cold end 30 of the device 10. Thus, the metallization material for the contact pads 44 in the cold end regions 30 of the Fuel Cell StickTM device 10 must be conductive in air (i.e., no protective atmosphere) and at low temperature. Precious metals such as silver work across the temperature/atmosphere transition area, such that the metallization material can be transitioned to the precious metal before the Fuel Cell StickTM device 10 exits the hot zone chamber/furnace. The use of a combination of materials allows for material selection based on the particular needs of conductance in a hot zone 32 versus a cold zone 30, and allows for reducing cost by reducing the amount of expensive precious metals used.
As depicted in FIGS. 49A-49C, wire 92 or other physical structure is placed into the device during the process of building up the green layers (FIG. 49A), the layers are then laminated with the wire 92 in place (FIG. 49B), and then the wire 92 is removed after lamination (FIG. 49C). This is useful, for example, at the entrance point of fuel or air, where the Fuel Cell StickTM device 10 may have a length of several inches before the gas flow passage 14, 20 enters the hot zone 32 (reaction region) of the Fuel Cell StickTM device 10. Instead of printing a polymer that must bake out slowly in the process to form the passage, the wire process may be used to remove the bake-out challenge from that part of the Fuel Cell StickTM device 10. By way of example and not limitation, a wire 92 with a 0.010 inch diameter may be used, which will pull out easily. The wire 92 may also be rolled flat, to form a ribbon-like physical structure that has a similar volume as the wire, but is shorter in cross section. Because the ribbon has more surface area, a release agent may be applied to the surfaces thereof to keep it from sticking to the ceramic layers during lamination. Thus, the term “wire” is intended to broadly include various physical structures that are long and then narrow, whether circular, oval, square, rectangular, etc. in cross-section.
FIGS. 50A-50C depict an example of forming entrance channels for a 1 layer Fuel Cell StickTM device 10. In this example, rather than using a gap-forming tape 94 (e.g., polymer or wax tape) to form the entire fuel and oxidizer passages 14, 20, the gap-forming tape 94 is only used in the active zone 33b, i.e., in the regions where the anodes 24 and cathodes 26 are positioned in opposing relation with electrolyte 28 therebetween. In the non-active regions where the fuel and oxidizer passages 14, 20 do not have an associated opposed anode 24 and cathode 26, wires 92 are used instead of the gap-forming tape 94. As shown, the wires 92 touch or overlap the gap-forming tape 94 so that the passages 14, 20 formed by the wire 92 and the gap-forming tape 94 are continuous from the inlets 12, 18 to the outlets 16, 22 (not shown).
As Fuel Cell StickTM devices 10 become more and more complicated, it can be more and more useful to use this wire concept, for example, the complex bake-out challenge of a multi-layer Fuel Cell StickTM device 10 (e.g., 50 layers) can be simplified. This is in part because the challenge for binder removal, especially in complicated structures, is that the binder bake-out products must travel from the location that they are generated (from the decomposition of polymer) to the outside of the Fuel Cell StickTM device 10. After a wire 92 is pulled out of the structure, however, the path along this void is free and clear. If wires 92 (or other suitable physical structure) can be put into a complicated structure, and then pulled out, the voids created thereby can allow many regions within the structure for bake-out products to quickly find a path out of the structure.
Another useful purpose for the wire concept is to help with pressure distribution within the Fuel Cell StickTM device 10. When a single tube is supplying air or fuel to the Fuel Cell StickTM device 10, then different flow rates may exist along the many passages/channels within the Fuel Cell StickTM device 10. For example, if there are 50 air passages 20 in the Fuel Cell StickTM device 10, corresponding to 50 active layers, then there may be one passage that has a slightly larger sectional area, and one passage that has a slightly smaller sectional area. This can arise from random variation in the dimensions of the gap-forming materials. One solution is to limit the sectional area of the exit from each layer. If the cross section of the exit point from each layer can be precisely made, so that those sectional areas are equal, and if the sectional area of the exit point is less than the area of the flow channel, and if the area of all those exit points is less that the sectional area of the input tube, then the flow will be equal on each layer. This corresponds with the practicalities of gas and fluid flow. The wire concept enables this solution. At the exit point of each layer, a wire 92 is inserted to make the final passage of the gas to the outside world. For 50 layers, 50 short wire pieces are inserted. When they are pulled out, each layer has a precision exit dimension (for example, a 5 mil diameter passageway).
Thus, the present invention contemplates a multilayer Fuel Cell StickTM device 10 in which the exit points of each layer are smaller in sectional area than the flow path sectional area itself. The present invention further contemplates a multilayer Fuel Cell StickTM device 10 in which the exit points of each layer are precision machined so that they have exactly the same cross sectional area at some given location. The present invention yet further contemplates a multilayer Fuel Cell StickTM device 10 where all exit areas put together are smaller than the sectional area of the input. In these embodiments, the sectional area of the exit point is defined as being at some location in the flow path that is beyond the end of the active portion of the layer, but before the end output point of the Fuel Cell StickTM device 10. In other words, this neck-down point in the flow path does not have to be exactly at the exit point from the Fuel Cell StickTM device 10, just somewhere downstream from the active area.
In previous embodiments, the hot zone 32 and hot zone chamber have been discussed. The hot zone chamber may also be referred to as a furnace. The cold zone or cold end regions 30 are positioned outside of the furnace. The transition zone 31 is a region of the Fuel Cell StickTM device 10 adjacent the region inside the furnace. As depicted in FIG. 51, the furnace wall 96 has a total thickness T. The Fuel Cell StickTM device 10 passes through this furnace wall 96. The length of the Fuel Cell StickTM device 10 in the wall 96 is the X dimension and is equal to thickness T. The width of the Fuel Cell StickTM device 10 as it passes through the wall 96 is the Y dimension. The thickness of the Fuel Cell StickTM device 10 is the Z dimension. For purposes of this embodiment, Z is less than or equal to Y.
According to an embodiment of the invention, for optimal conditions, the furnace wall thickness T should be greater than the width, Y, of the Fuel Cell StickTM device 10 as it passes through the wall 96. If T is less than Y, then the stress on the Fuel Cell StickTM device 10 as it passes through the wall 96 may be too high, and the Fuel Cell StickTM device 10 could crack.
In another embodiment, depicted in FIGS. 52A-52C, dimension L is the maximum dimension in a plane transverse to the direction of the length of the device 10 (i.e., in the Y-Z plane) of the Fuel Cell StickTM device 10, (100, 200, 300 or 400) at the portion where it passes through the furnace wall 96. For a rectangular Fuel Cell StickTM device 10 (100, 400), the maximum dimension L may be the diagonal, as shown in FIG. 52B. For a tubular Fuel Cell StickTM device 200, 300, the maximum dimension L may be the diameter. For optimal conditions, the dimensions should be such that T≧1⁄2L.
The wall thickness T may be made from one uniform material (insulation) 98. Alternatively, as depicted in FIG. 53, the wall thickness T may also be made from multiple, graded insulation layers, such as three insulation layers 98a, 98b, 98c, such that the heat transfer properties are optimized in each layer to give the best possible temperature transition results. In the case of a multiple-layer furnace wall 96′, the total thickness T of all layers put together should be greater than Y and/or greater than or equal to 1⁄2L, but the thickness of one layer of the wall 96′ could be less than Y and/or less than 1⁄2L.
In another embodiment, depicted in FIG. 54, a multiple-layer furnace wall 96′′ is provided in which multiple layers of insulation 98a, 98c may be separated by air gaps 120. In this design, there could be a high-temperature insulation layer 98c close to the hot zone 32, and a lower temperature insulation layer 98a close to the cold zone 30. An intermediate (medium) temperature zone then lies between the two insulation layers 98a and 98c, for example, corresponding to transition zone 31 or a preheat zone 33a. This embodiment can enable a longer preheat area for the air that is flowing into the Fuel Cell StickTM device 10, while not having to make the hottest area of the furnace larger. In this embodiment, the thickness of one layer of wall 96′′ could be made to be less than the Y dimension of the Fuel Cell StickTM device 10 and/or less than 1⁄2L as it passes through the wall 96′′. But the total dimension T of the wall 96′′, including layers 98a and 98c, and the air gap 120 would be larger than the Y dimension of the Fuel Cell StickTM device 10 and/or greater than or equal to 1⁄2L. This embodiment further contemplates more than two insulation layers.
Discussed above is the idea of first making the Fuel Cell StickTM device 10 without the anode and cathode, and then backfilling those elements later. The reason for doing this can be that a certain anode or cathode material will densify too much at the sintering temperature of Zr, and if it is too dense then it will not allow a good reaction. Or, to say it more generically, backfilling can be necessary if the different components of the system do not want to sinter optimally with the same temperature profile.
It is more difficult, however, to provide the current collectors on the top portions of the anode or cathode. A current collector 122, as shown in FIGS. 55A-55E discussed below, is known to those skilled in the art to be a high-density electrode positioned as a surface portion of an anode or cathode. It generally is a highly electrically conductive layer or matrix, like a fine wire, that can collect the electrons and move them where they need to go. The current collector 122 may be made of NiO, or LSM, or some other low cost material, or even precious electrodes. Following a backfill process for forming the anodes and cathodes, it is difficult to put on a precise current collector in a uniform way. But the challenge of a current collector is different than that of an anode or cathode. It is desirable for the anode and cathode to be porous, which causes the danger of over-firing; whereas the collector is desirably dense (for good conductivity), so potentially, it can be co-fired with the Zr. While the current collector 122 could be placed on the electrolyte 28 before back-filling, such that the current collectors are under the anode and cathode, touching the electrolyte 28, this arrangement blocks active area on the electrolyte 28, which is needlessly wasteful of active area.
In accordance with an embodiment of the invention, and as depicted in FIGS. 55A-55E, the current collectors 122 are positioned and co-fired so as to have them floating in space within the Fuel Cell StickTM device 10. This may be accomplished by printing the current collector 122 on top of a sacrificial first organic layer 72a (e.g., polymer), and then coating a sacrificial second organic layer 72b (e.g., polymer) over the top of the current collector 122 as shown schematically in FIG. 55A. The current collector 122 is thereby sandwiched between two sacrificial organic layers 72a, 72b, as shown in FIG. 55B. The Fuel Cell StickTM device 10 is built, including placing the sacrificial layers/current collector structure within a ceramic supporting structure 29, as shown in FIG. 55C, and then sintered, whereby the sacrificial organic layers 72a, 72b disappear to form a gap 123 and the current collector 122 is left floating in space within the gap 123, as shown in FIG. 55D. It is then easy to backfill the porous anode or cathode into the gap 123, to complete the anode or cathode formation. The use of support pillars 54, as described above, may also be used, such that the floating current collector 122 rests on the support pillars 54, as shown in FIG. 55E, to provide mechanical support or to standardize the location. To achieve this, periodic via holes or small gaps may be created in the first sacrificial layer 72a of polymer, so that the current collector material would periodically print down into a hole. After binder removal, this filled hole becomes a support pillar 54. Alternatively, zirconia balls may be added into the sacrificial polymer gap material. As the sacrificial polymer dissolves, the current collector 122 would stick to those balls, and the balls would stick to the ceramic supporting structure 29, as shown in FIGS. 56A and 56B, thus providing the support. The porous anode 24 or cathode 26 then can be backfilled into the space, as shown in FIGS. 57A and 57B, in which the electrode particles 124 are held in viscous liquid 126 for the back-fill, then the device is dried and the particles settle and are sintered to form the anode 24 or cathode 26. The anode or cathode particles can be selectively deposited onto one side, if that is useful (by gravity or by centrifuge).
With a current collector style that uses printed hatch lines, there may be some variation in the gap dimension of the air or fuel passage 14, 20 resulting in the passage becoming pinched or blocked at the current collector 122. This variation occurs due to random dimensional changes during sintering. FIGS. 58A-58C are micrographs that show an example of a current collector 122 that is nearly causing a blockage of a passage 14, 20. The goal for the passage 14, 20 is to have clear flow. It is possible to make the passages larger, but this will unnecessarily decrease the density of the Fuel Cell StickTM device 10 (thicker passages and thicker layers lower the power density of the multi-layer device). According to one embodiment of the invention, to reduce the possibility of the passages 14, 20 being blocked at the current collector 122, the current collector lines may be buried within the porous anode 24 and cathode 26. As depicted in FIGS. 59 and 60, in which FIG. 59 shows the current collectors 122 on the surfaces of the anode 24 and cathode 26 and FIG. 60 shows the current collectors 122 buried into the surfaces of the anode 24 and cathode 26, if the current collectors 122 are buried into the thickness of the porous anode and cathode 24,26 (or substantially buried into the anode/cathode) then the current collector 122 will be less likely to block the path of gas flow. FIG. 69 shows an actual current collector trace that has been recessed into the porous anode or cathode.
A method of burying the current collector 122 is shown in FIGS. 61A-61C. First, dispense or print the current collector 122 onto a temporary substrate 128. Then, cover this current collector 122 with the electrode material such as by printing a paste or backfilling with a viscous liquid 126 containing electrode particles 124 and drying. Finally, remove the temporary substrate 128. The temporary substrate 128 may be a piece of plastic with only moderate adhesion to the electrode material after drying such that the dried electrode-on-plastic can be turned over and the plastic peeled off. The same or similar result may be achieved by putting the current collector 122 and anode/cathode 24,26 onto the gap-forming tape 94 that is inserted into the stack, and during bake-out and sintering, the gap-forming tape 94 will disappear, leaving the same end result.
When printing the anode 24 or cathode 26 over the top of the current collector 122, if the current collector 122 tends to dissolve a little and spread out, materials with different solubilities may be used (in the extreme case, the current collector 122 can contain resin material that is soluble in polar solvents, and the porous electrode ink can have a resin material soluble in non-polar solvents). It is desirable to limit this spreading, because too much spreading of the current collector 122 will work to reduce the diffusion of gasses into the porous anode 24 or cathode 26. So, it is possible that some spreading of the current collector 122 will happen, but at least a portion of the current collector 122 is desirably buried in the porous material. Thus, this invention contemplates a current collector path where some portion of the current collector 122 is recessed into the porous anode 24 or cathode 26 in order to reduce the protrusion of the current collector 122 in to the fuel passage 14 or air passage 20.
In the active zone 33b of the multilayer Fuel Cell StickTM device 10, one would like to have the electrolyte 28 be as thin as possible, for example, 10 μm. But a super-thin electrolyte increases the possibility of having a leak between the air and fuel sides of the device. Thinner electrolyte can give higher power, but too thin will allow a crack or leak, and give zero output from the layer. According to one embodiment of this invention, a key to the minimum allowable thickness of the electrolyte 28 in the active zone 33b is that the anode and cathode thickness also contribute to the total thickness, and therefore to the total strength. By way of example only and not limitation, if 100 μm of thickness is desired to prevent cracking, and each anode 24 and cathode 26 measures 45 μm, then a 10 μm electrolyte thickness will work well. (45+45+10=100).
In the passive area (areas without an opposing anode and cathode) of a multilayer Fuel Cell StickTM device 10, there is a different thickness required. This passive area is responsible for distribution of air and fuel. This has been shown in many of the drawings as air and fuel distribution passages that overlap. The requirement here is also to have a certain thickness to prevent cracking, but without the anode 24 and cathode 26, the ceramic 29 here must be thicker than the ceramic electrolyte layer 28 in the active zone 33b. So in the example above, the ceramic 29 in the passive area must be 100 μm while the ceramic electrolyte layer 28 in the active zone 33b can be thinner, such as 10 μm.
According to an embodiment of the invention, a method is provided for achieving an individual layer of ceramic electrolyte 28, 29 with two thicknesses: thicker ceramic 29 in the passive gas passages area, and thinner ceramic electrolyte 28 in the active zone 33b. The method, depicted in FIGS. 62-62A, uses three pieces of ceramic tape 130 to create the ceramic 29 in the passive gas flow region, where two of the tape pieces 130a, 130c end and only the center layer 130b continues into the active zone 33b to serve as ceramic electrolyte 28 between the opposing anode 24 and cathode 26.
Numerous ideas are presented above in the context of an elongate structure that exits the furnace for low temperature connections. However, many of the ideas also may be used in multi-layer Fuel Cell devices that do not exit the furnace and/or that have a plate shape or the like. The densities of the devices achievable in the present invention may be achieved in other Fuel Cell devices and systems where connections are made to the hot Fuel Cell device in a furnace. For example, concepts disclosed herein that may be used in other fuel cell devices include polymer tape, polymer tape filled with round balls, a wire used to form exit or entrance passages, one passage serving two electrodes, a paddle-shaped device, drying the electrode suspension towards one side by using gravity or centrifuge, side gaps for termination and series design.
The current collector 122 has a purpose of allowing electrons that are produced or consumed in the electrodes (anode 24 and cathode 26) to travel in a low-resistance path on their way to the load (voltage nodes 38, 40). The optimal electrode design is not very conductive because it must allow several things to happen at once: there are pores to allow the gases to flow, there is ceramic in the electrodes to allow the oxygen ions to flow toward the electrolyte, and there are electronic conductors to let the electrons flow. The presence of the pores and the ceramic means that the electrode overall will have higher resistance than if it was only made of electronic conductor.
Once the electron is liberated, it is important to allow it to travel on a high conductivity path. Existing designs for current collectors are based on removing the electrolyte ceramic from the conductor, but still leaving the porosity. This creates a more conductive layer. This is printed over the entire anode or cathode. One disadvantage of this design in a multilayer structure is that if the anode/cathode materials have to be added after sintering, it can be difficult to create two distinct layers, as described. The advantage of co-firing a current collector is described above.
According to an embodiment of the invention, a current collector 122 may be used that comprises a high-density conductor material (i.e., little or no porosity, such that if it was printed over the entire anode 24 or cathode 26 it would inhibit the reaction), which is printed in a hatch pattern. In one embodiment, the collector is printed in a rectilinear pattern, also referred to as a hatch pattern, leaving open space between the hatch marks for the gas to penetrate. Gas permeability in the porous anode 24 and cathode 26 is such that the gas that enters the porous material between hatch lines will also flow under the hatch lines. By varying the pitch from line to line, and the line width itself, it is possible to find an optimal geometry. By way of example, a 0.006′′ line width and a 0.030′′ line pitch may be used. FIG. 63 depicts a top view of a current collector 122 with a hatch pattern. FIG. 64 depicts a side view of the current collector 122 over porous anode or cathode. FIG. 65 depicts an angled view, showing in order from top to bottom: current collector hatch, top porous electrode, electrolyte, and bottom electrode (sticking out from electrolyte because of fracture). As the active area becomes larger, it would also be possible to vary the line width in different regions. Small conductor lines could feed into larger conductor lines, and larger lines could feed into still larger conductor lines.
Flexible supply tubes 50 have been described above for connecting the fuel and air supplies 34,36 to the Fuel Cell StickTM device 10. By stretching the supply tube 50 open, it can be slipped over one of the ends 11a, 11b of the Fuel Cell StickTM device 10. An adhesive can hold it in place. An alternative, according to one embodiment of the invention, is to form the end 11a (and/or 11b) of the Fuel Cell StickTM device 10 with indentations 132 on the sides, as depicted in FIGS. 66A-66B, so that the Fuel Cell StickTM device 10 will mechanically hold the supply tube 50 in place. This is achieved most conveniently in the green state by machining the Fuel Cell StickTM device 10 with a router or end mill.
Based on this, a connector 134 may also be used that can clamp on to the end 11a (and/or 11b) of the Fuel Cell StickTM device 10, as depicted in FIGS. 67A-67B in top schematic cross-sectional and perspective view, respectively. The connector 134 may be a molded plastic with integrated electrical contacts 136 and a gas flow pathway 138, either one or two, depending on the design of the Fuel Cell StickTM device 10, and a gas-tight seal, such as in the form of an O-ring 140, and either one or two electrical contacts 136 for contacting the contact pad(s) 44. If the Fuel Cell StickTM device 10 is a two ended Fuel Cell StickTM device 10, such that one polarity is exiting the Fuel Cell StickTM device 10 at each end of the Fuel Cell StickTM device 10, then the connector 134 could still have two or more electrical contacts 136 at each end of the Fuel Cell StickTM device 10 in order to give lower resistance contacts. The electrical contacts 136 could be on the sides of the Fuel Cell StickTM device 10 or on the top and bottom of the Fuel Cell StickTM device 10, the latter of which would give lower resistance because the contacts are wider.
Although not shown, the connector 134 could have two O-rings, thereby providing two sections of sealing within the connector 134: one for air, the other for fuel. Such a connector could be used as a single connector on a single-ended Fuel Cell StickTM device 10, which provides positive and negative contacts, and air and fuel delivery.
The embodiments described above included two opposing ends 11a, 11b for the device. However, the concepts of the Fuel Cell StickTM device 10 described above could be applied to a device 500 that has more than 2 ends or exit points leaving the furnace. For example, FIGS. 68A-68B depict devices having 4 points of exit. The four locations could provide the air inlet 18, air outlet 22, fuel inlet 12, and fuel outlet 16. This could make it easier to recycle unburned fuel into the furnace heating operation. Exit points other than 2 and 4 may be used, such as 3 or 6.
The use of support balls (see FIGS. 7C-7D) may be used in Fuel Cell devices other than Fuel Cell StickTM devices 10, for example, square plate devices. The support balls allow large areas to be created in the multilayer structure, without having the different layers collapse on each other. The device could have large, open areas within a generic multilayer plate. Or, the device could have paths that were 0.5 inch wide, but many inches long, filling the area. In either case, the ball technology disclosed herein would be advantageous.
A key idea of the balls is that they are rounded, which can prevent puncture. Because there is a need to make the electrolytes, anodes and cathodes thin (for density, and for higher performance), it is possible for punctures to arise from the use of irregularly shaped materials. Sand or grit could dig into the electrolyte and cause a leak. On the other hand, the electrolyte can gently deform around the balls without causing leaks or tears. Similarly, the pillar concept of FIGS. 7A-7B can be used in a multilayer Fuel Cell structure other than the Fuel Cell StickTM device 10 form.
In FIGS. 38A-38B, we show the use of multiple bake-out ports that can later be sealed over. This is an advantageous concept for any multilayer approach to the SOFC or other fuel cell device. Again, regarding the large plate, the designer will have large areas of gas passages that are being created, and the need to remove the organic material that fills those spaces. Typically, however, there is only one fuel entrance point, and one fuel exit point. The same is true of the air side. With such large areas of organic material, but so few exit points, it is likely that one of the largest manufacturing challenges will be to avoid delaminations.
The solution to this is to create numerous bake-out points, small openings that can allow bake-out gasses or liquids (in the case that wax is used) to come out of the structure with minimum stress on the entire structure. After the multilayer structure is sintered, it is easy to come back later and fill in those small bake-out points with a solid material to prevent leaks (such as a glass-ceramic combination).
The wire 92 concept is a lot like the bake-out port concept above, and very useful for a multilayer structure. Imagine making a 4 inch square plate, with 20 or 50 active layers in the plate. You would like to create the bake-out ports for easier organic removal. But it would be even better if these convenient bake-out ports could reach into the center of the plate. By inserting the wire 92 and then pulling it out after lamination, this can be accomplished. The wire 92 could cut across several areas that otherwise might have very long distances to go between the middle of the plate and the outside world. The concept does not have to be a wire exactly, as discussed above. That is just the most convenient form, because it has a low surface area. The physical piece could be flat, for example 0.002′′ thick by 0.200′′ wide. In that case, it might need to be covered with a release agent to prevent the layers from sticking. Regardless, the idea is a physical piece that is inserted into the structure and then removed in order to facilitate organic removal.
In another embodiment, carbon tape with wax is used as a gap-forming tape 94. A challenge is to have the gap-forming material come out evenly without causing splitting or delamination in the Fuel Cell StickTM devices 10. It would be better if the material could magically disappear at the right time, leaving open channels so that the other polymer materials in the anode 24 and cathode 26 and electrolyte 28 could bake out. One approach is to use wax. The waxes that are used for investment casting (the so-called lost wax method) work well melting at around 90° C., above the lamination temperature used to laminate the multilayer structure, but below the binder burnout temperatures of 150-300° C. But wax is not ideal because if you cast it into a 2-mil thick sheet, it does not have desirable strength. It is brittle to the touch. The wax should be stronger in the thin section. The solution to this is to combine the wax with some kind of fiber to give it strength. One choice is carbon fiber. The carbon fiber can be purchased in a random fiber configuration, called mat, or in a woven fiber configuration, that resembles actual cloth. Other fibers may also be possible. By impregnating the wax into carbon fiber, optimal properties can be obtained. The carbon/wax composite can be put into the multilayer structure to form a gap. After lamination, the temperature is raised to the melting point of the wax, and the wax then turns to liquid and runs out of the Fuel Cell StickTM device 10. This leaves open-air pathways within the carbon fibers, which allows easy bake-out of the surrounding polymer materials inside the structure. The carbon fiber does not volatilize (turn to CO2) until temperatures near 750° C. Thus, it is possible to make a structure where one of the chief gap formation materials disappears before binder burn-out occurs, thereby leaving clear paths for binder removal. Then, at the mid temperatures, the polymer itself can volatilize. Finally, at the high temperatures, the carbon fibers can disappear. FIG. 70 is an image of the gap left once the wax and carbon fibers are gone after sintering using this carbon-wax combination.
While the invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.

## Claims

1. A fuel cell system comprising:
a hot zone chamber having a chamber wall with a thickness T;
one or more fuel cell devices each comprising an elongate rectangular or tubular ceramic substrate having a length that is the greatest dimension whereby the elongate rectangular or tubular ceramic substrate exhibits thermal expansion along a dominant axis that is coextensive with the length, a reaction zone along a first portion of the length positioned in the hot zone chamber for exposure to an operating reaction temperature, at least one cold zone along a second portion of the length extending outside the hot zone chamber and shielded by the chamber wall so as to remain at a temperature below the operating reaction temperature, an electrolyte disposed between an anode and a cathode in the reaction zone to form an active cell, wherein the active cell resides within and is substantially surrounded by the ceramic substrate, and a third portion of the length equal to thickness T positioned within the chamber wall, the third portion having a maximum dimension L in a plane transverse to the direction of the length wherein T≧ 1/2 L; and
a heat source coupled to the hot zone chamber and adapted to heat the reaction zone to the operating reaction temperature within the hot zone chamber.

2. The fuel cell system of claim 1 wherein the ceramic substrate is an elongate rectangular ceramic substrate and the maximum dimension L is a width Y of the third portion.

3. The fuel cell system of claim 2 wherein T>Y.

4. The fuel cell system of claim 1 wherein the ceramic substrate is an elongate tubular ceramic substrate and the maximum dimension L is a diameter of the third portion.

5. The fuel cell system of claim 1 wherein the chamber wall comprises a plurality of insulation layers each having different heat transfer properties and arranged to provide optimal temperature transfer from the reaction zone to the at least one cold zone.

6. The fuel cell system of claim 1 wherein the chamber wall comprises a plurality of insulation layers separated by intervening air gaps.

7. The fuel cell system of claim 6, wherein the plurality of insulation layers includes a first layer adjacent the reaction zone and a second layer adjacent the at least one cold zone, and wherein the intervening air gap is a pre-heat zone with the heat source adapted to heat the pre-heat zone to an intermediate temperature between the operating reaction temperature within the hot zone chamber and the temperature of the at least one cold zone.

8. The fuel cell system of claim 1, wherein the one or more fuel cell devices each comprise:
a plurality of fuel and oxidizer passages extending within the ceramic substrate lengthwise along at least a portion of each of the first and second lengths from respective fuel and oxidizer inlets to respective fuel and oxidizer outlets with the anode associated with each fuel passage and the cathode associated with each oxidizer passage in at least the reaction zone, the anodes and cathodes being positioned in opposing relation to each other with the electrolyte therebetween.

9. The fuel cell system of claim 8 further comprising a first exterior contact surface on the elongate rectangular or tubular ceramic substrate in the at least one cold zone electrically coupled to the anodes, a second exterior contact surface on the elongate rectangular or tubular ceramic substrate in the at least one cold zone electrically coupled to the cathodes, a first voltage connection to the first exterior contact surface, and a second voltage connection to the second exterior contact surface.

10. The fuel cell system of claim 8 further comprising:
a fuel supply coupled to the fuel inlets for supplying a fuel flow into the fuel passages; and
an air supply coupled to the oxidizer inlets for supplying an air flow into the oxidizer passages.