The present invention relates generally to fuel cells, and more particularly to fuel cells having embedded current collectors and methods of making the same.
Fuel cells use an electrochemical energy conversion of hydrogen and oxygen into electricity and heat. It is anticipated that fuel cells may be able to replace primary and secondary batteries as a portable power supply. In fuel cells, the fuel (containing a source of hydrogen) is oxidized with a source of oxygen to produce (primarily) water and carbon dioxide. The oxidation reaction at the anode, which liberates electrons, in combination with the reduction reaction at the cathode, which consumes electrons, results in a useful electrical voltage and current through the load.
As such, fuel cells provide a direct current (DC) voltage that may be used to power motors, lights, electrical appliances, etc. A solid oxide fuel cell (SOFC) is one type of fuel cell that may be useful in portable applications.
It is known that anode and cathode electrodes typically suffer from undesirable ohmic losses. As such, current collectors (high efficiency electron conductors) are typically placed on the top of the anode and/or cathode electrodes. However, current collectors placed on top of the anode/cathode may generally suffer from relatively poor current collector efficiency. It is also known that fuel cells suffer from undesirable catalytic/activation polarization losses. In addition to this, thin film current collectors generally agglomerate at high temperatures and become discontinuous. As a result, the current collectors lose efficiency.
The present invention solves the drawbacks enumerated above by providing a fuel cell which includes one or more fuel cell assemblies. Each of the fuel cell assemblies has an electrolyte having a length, an anode having a length and disposed on one side of the electrolyte, and a cathode having a length and disposed on the same or other side of the electrolyte. The fuel cell further includes a plurality of current collectors. Each of the current collectors is substantially embedded within, and continuously extends substantially the respective length of at least one of the electrolyte, anode and cathode.
Objects, features and advantages of embodiments of the present invention may become apparent upon reference to the following detailed description and drawings, in which:
The present invention is predicated upon the unexpected and fortuitous discovery that performance of a fuel cell may be improved by substantially embedding current collectors within anode, cathode and/or electrolyte. It is to be understood that the term “substantially embedded” as used herein connotes that the conductive member and/or current collector is surrounded by the respective anode/cathode/electrolyte except for a discrete area. The discrete area is covered by one of anode, cathode or electrolyte, depending upon the specific embodiment of the invention. It is to be further understood that the term “completely embedded” as used herein connotes that the current collector is surrounded on all sides by the respective anode/cathode.
In embodiment(s) of the present invention, current collector efficiency is advantageously increased. Without being bound to any theory, it is believed that this is due to increased surface area contact between the current collector and electrode (within the volume of the electrode). Further, in embodiments of the present invention, electrodeposition techniques may be used to fabricate high surface area structures; it is believed that this may advantageously decrease catalytic polarization losses. Yet further, embodiments of the present invention may enable device architecture stacking for balance of stack improvements; for example, layers are generally not terminated at the current collector deposition step. Still further, electrodeposition processes may advantageously be used to seal joints within the balance of stack.
In the fuel cells 10, 10′, 10″, 10′″, 10″″ described hereinbelow, current collectors 20, when initially deposited as conductive members 20′, may be used (if subsequent electrodeposition processes are used) as electrodes for the electrodeposition of active elements of the fuel cells, i.e. anode 16, cathode 18 and electrolyte 14, 14′, 14″. Then these electrodes for the electrodeposition of active elements may later advantageously serve the dual purpose of becoming current collectors for anode 16 and/or cathode 18.
Referring now to
Fuel cell 10 has one or more current collectors 20, each of the current collectors 20 substantially embedded within, and continuously extending substantially the respective length of the electrolyte 14, anode 16 and/or cathode 18. In, for example,
The electrical load L may include many devices, including but not limited to any or all of computers, portable electronic appliances (e.g. portable digital assistants (PDAs), portable power tools, etc.), and communication devices, portable or otherwise, both consumer and military. The electrical storage device S may include, as non-limitative examples, any or all of capacitors, batteries, and power conditioning devices. Some exemplary power conditioning devices include uninterruptible power supplies, DC/AC converters, DC voltage converters, voltage regulators, current limiters, etc.
It is also contemplated that the fuel cell 10, 10′, 10″, 10′″, 10″″ of the present invention may, in some instances, be suitable for use in the transportation industry, e.g. to power automobiles, and in the utilities industry, e.g. within power plants.
As defined herein, current collectors 20 are electrically conductive members 20′ which have become current collectors 20 by their having an electrode (anode 16 or cathode 18) placed in contact with them. Some examples of conductive members 20′ are shown in
As shown in
As shown in
Referring to
It is to be understood that the current collectors 20/conductive members 20′ may be formed from any suitable conductive material. Conductive materials may be divided into conductive metals, conductive oxides, conductive cermets, and conductive composites. It may be desirable, and in some embodiments of the present invention, preferable that the current collectors 20/conductive members 20′ be formed from a material which is able to withstand the conditions (temperatures) of anode 16/electrolyte 14/cathode 18 sintering (or annealing).
In an embodiment, the conductive material is at least one of gold, aluminum, platinum, copper, nickel, ruthenium, ruthenium oxide, silver, palladium, titanium, tantalum, chromium, LaxSryMnO3−δ, LaxSryCrO3−δ, conductive composites, conductive cermets, iron, carbon, alloys of any of the above, and mixtures thereof.
It is to be further understood that the conductive composites may be formed from any suitable material. In an embodiment, the conductive composites include at least one of LaxSryMnO3−δ+M, LaxSryCrO3−δ+M, and mixtures thereof, wherein M is at least one metal.
Some non-limitative materials which may in some instances be more suitable for current collectors 20 for anodes 16 include platinum, gold, palladium, stainless steel and plated stainless steel, alloys thereof, and mixtures thereof.
Some non-limitative materials which may in some instances be more suitable for current collectors 20 for cathodes 18 include platinum, gold, silver, ruthenium, alloys thereof, and mixtures thereof.
Some non-limitative materials which may in some instances be more suitable for conductive members 20′ which become sacrificial layers (i.e. are removed to provide gas flow channel(s) 26, and/or are removed to render a predetermined desired fuel cell 10 architecture) include aluminum, nickel, copper, carbon, alloys thereof, and mixtures thereof. One non-limitative example of a layer which may in certain instances be deemed sacrificial is designated as 30 in
It is to be understood that the fuel cell 10, 10′, 10″, 10′″, 10″″ may be one of solid oxide fuel cells, proton conducting ceramic fuel cells, alkaline fuel cells, Polymer Electrolyte Membrane (PEM) fuel cells, molten carbonate fuel cells, solid acid fuel cells, and Direct Methanol PEM fuel cells. In an embodiment of the present invention, fuel cell 10, 10′, 10″, 10′″, 10″″ is a solid oxide fuel cell.
The electrolyte 14 may be formed from any suitable material. In an embodiment of the present invention, electrolyte 14 is at least one of oxygen ion conducting membranes, proton conductors, carbonate (CO32−) conductors, OH− conductors, and mixtures thereof.
In an alternate embodiment, electrolyte 14 is at least one of cubic fluorite structures, doped cubic fluorites, proton-exchange polymers, proton-exchange ceramics, and mixtures thereof. In a further alternate embodiment, electrolyte 14 is at least one of yttria-stabilized zirconia, samarium doped-ceria, gadolinium doped-ceria, LaaSrbGacMgdO3−δ, and mixtures thereof.
It is to be understood that the anode 16 and cathode 18 may be formed from any suitable material, as desired and/or necessitated by a particular end use. In an embodiment, each of the anode 16 and cathode 18 is at least one of metals, ceramics and cermets.
In an embodiment of the present invention, some non-limitative examples of metals which may be suitable for the anode 16 include at least one of nickel, platinum and mixtures thereof. Some non-limitative examples of ceramics which may be suitable for the anode 16 include at least one of CexSmyO2−δ, CexGdyO2−δ, LaxSryCrzO3−δ, and mixtures thereof. Some non-limitative examples of cermets which may be suitable for the anode 16 include at least one of Ni—YSZ, Cu—YSZ, Ni—SDC, Ni-GDC, Cu—SDC, Cu-GDC, and mixtures thereof.
In an embodiment of the present invention, some non-limitative examples of metals which may be suitable for the cathode 18 include at least one of silver, platinum and mixtures thereof. Some non-limitative examples of ceramics which may be suitable for the cathode 18 include at least one of SmxSryCoO3−δ, BaxLayCoO3−δ, GdxSryCoO3−δ, and mixtures thereof.
In any of the embodiments described herein, the gas to which fuel cell 10, 10′, 10″, 10′″, 10″″ is exposed includes reactants and/or oxidants and/or mixtures thereof. In an embodiment, the reactants are fuels, and the oxidants are one of oxygen, air, and mixtures thereof.
It is to be understood that any suitable fuel/reactant may be used with the fuel cell 10, 10′, 10″, 10′″, 10″″ of the present invention. In an embodiment, the fuel/reactant is selected from at least one of methane, ethane, propane, butane, pentane, methanol, ethanol, higher straight chain or mixed hydrocarbons, for example, natural gas or gasoline (low sulfur hydrocarbons may be desirable, e.g. low sulfur gasoline, low sulfur kerosene, low sulfur diesel), and mixtures thereof. In an alternate embodiment, the fuel/reactant is selected from the group consisting of butane, propane, methane, pentane, and mixtures thereof. Suitable fuels may be chosen for their suitability for internal and/or direct reformation, suitable vapor pressure within the operating temperature range of interest, and like parameters.
In an embodiment of the present invention, the fuel cell 10 is a single chamber fuel cell.
In an alternate embodiment of the present invention, the fuel cell 10 is a dual chamber fuel cell.
Referring now to
Each of the plurality of current collectors 20 has a thickness 32. In an embodiment, thickness 32 may range between about 0.1 micron and about 100 microns. In an alternate embodiment, the current collector thickness 32 may range between about 1 micron and about 10 microns.
If the current collectors 20/conductive members 20′ are designed for use To as a sacrificial layer 30, to provide a gas flow channel(s) 26 and/or to render a predetermined desired fuel cell 10 architecture, it may be desirable that those current collectors 20/conductive members 20′ each have a width 28 ranging between about 40 microns and about 200 microns. It may further be desirable that those current collectors 20/conductive members 20′ each have a thickness 32 ranging between about 0.1 microns and about 5 microns.
Referring again to
Referring now to
Referring yet to
Referring now to
In an embodiment of the present invention, the width 44 between adjacent current collectors ranges between about 1 micron and about 1500 microns. In an alternate embodiment of the present invention, the width 44 between adjacent current collectors ranges between about 3 microns and about 500 microns. In another alternate embodiment of the present invention, the width 44 between adjacent current collectors ranges between about 5 microns and about 300 microns. In yet another alternate embodiment of the present invention, the width 44 between adjacent current collectors ranges between about 15 microns and about 100 microns.
Referring yet to
Referring now to
Referring now to
It is to be understood that the Figures selected to depict various widths, lengths and other dimensions were selected for illustrative purposes, and the recited values for the various dimensions are meant to apply to any of the embodiments disclosed herein and to any or all of the Figures discussed herein.
It is to be understood that the side walls of anode 16, cathode 18, electrolyte 14, and current collector 20/conductive member 20′ may be any suitable size, shape or configuration. In an embodiment of the present invention, the anode 16, cathode 18, electrolyte 14 and current collector 20/conductive member 20′ may optionally have outwardly angularly extending opposed side walls. In
In an alternate embodiment of the present invention, the anode 16, cathode 18, electrolyte 14 and current collector 20/conductive member 20′ may optionally have substantially vertically extending opposed side walls. In
Referring now to
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Referring again to
It is to be understood that the deposition of the anode layer 16 and cathode layer 18 may be accomplished by any suitable process. In an embodiment of the present invention, this deposition is accomplished by electrodeposition, Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), spin coating, atomic deposition, and/or the like. In a further embodiment of the present invention, this deposition is accomplished by electrolytic deposition and/or electrophoretic deposition.
Referring now to
The method of making fuel cell 10, 10′ may further optionally include the step of selectively removing at least one of the plurality of first 62, second 64 and third 66 conductive members 20′ to provide at least one gas flow channel 26. It is to be understood that this selective removal may be accomplished by any suitable method. However, in an embodiment, the selective removal step is accomplished by etching.
It is to be understood that deposition of the electrolyte layer 14, the second electrolyte layer 14′ and the third electrolyte layer 14″ may be accomplished by any suitable method. In an embodiment, this method is at least one of electrodeposition, Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), spin coating, atomic deposition, and the like. In a further embodiment, the electrolyte 14, 14′, 14″ layers are deposited by electrophoretic deposition, electrolytic deposition, cathodic electrolytic deposition, and/or combinations thereof. In a further alternate embodiment, the electrolyte 14, 14′, 14″ layers are deposited by electrophoretic deposition.
Electrodeposition processes are advantageous in that selective conductive members 20′/current collectors 20 allow deposition of patterned layers and/or three-dimensional encapsulation of the conductive members 20′/current collectors 20 by virtue of charge and potential. As such, no etching is required to control the shape or structure of the anode 16, cathode 18, and/or electrolyte 14, 14′, 14″.
Referring now to
If a protective layer 68 is desired and/or necessitated by a particular end use, it should be a relatively thin layer, e.g. on the order of greater than about 1 nm. It is to be understood that the protective layer 68 may be formed from any suitable material which is passive/inert and not a poison for catalysis. In an embodiment, protective layer 68 includes at least one of ceramics, aluminum, titanium, inert oxide layers, and mixtures thereof.
A protective layer(s) 68 may be useful for preventing undesirable agglomeration (discontinuity) of current collectors 20. The protective layer 68 may not be necessary if the material from which the current collector 20 is formed is sufficiently stable at high temperatures within its environment, e.g. substantially embedded within a ceramic anode 16 or cathode 18 material.
Referring now to
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It is to be understood that, in embodiments of the fuel cell 10, 10′, 10″, 10′″, 10″″ of the present invention, the deposition of the various layers (electrolytes 14, 14′, 14″, anodes 16, cathodes 18) may be by any suitable processes, including but not limited to electrodeposition, Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), spin coating, atomic deposition, and the like. In an embodiment, the electrolyte 14 is deposited by electrophoretic deposition, and the anode 16/cathode 18 is deposited by electrolytic deposition. If non-electro deposition processes are used, e.g. CVD, atomic deposition, PVD, spin coating, steps for masking and patterning should be added to the methods of the present invention.
It is to be understood that the conductive members 20′ may be deposited by any suitable process, including but not limited to non-electrodeposition processes (e.g. PVD) and the like. After deposition, the conductive members 20′ may be formed by microlithography, nano imprinting, and the like.
Referring again to
The anode 16/cathode 18 support surface 88 (upon which the first plurality 76 of conductive members 20′ is placed) is itself deposited on a non-embedded conductive member 84′. Non-embedded conductive member 84′ may be totally removed, for example by etching, to expose anode 16/cathode 18 support surface 88 to reactants and/or oxidants. If member 84′ is completely removed, the first plurality 76 of conductive members 20′ become current collectors 20 for anode 16/cathode 18 support surface 88.
Alternately, as shown in
Referring back to
A first electrolyte layer 14 is deposited on the exposed surfaces 21′ of the plurality 76 of conductive members 20′ and on the exposed area 78. The first electrolyte layer 14 may be planarized (as shown) by any suitable process, such as for example, chemical mechanical polishing (CMP). Alternately, the first electrolyte layer 14 may be left substantially as deposited (e.g., see
Either an anode layer 16 or a cathode layer 18 is deposited on the exposed surface 22′ of the first conductive member 62. The other of a cathode layer 28 or an anode layer 16 is deposited on the exposed surface 22′ of the second conductive member 64.
The alternate method of making fuel cell 10 of the present invention may further include the step of depositing a second electrolyte layer 14′ between adjacent anode 16 and cathode 18 layers. A second plurality 80 of conductive members 20′ may then be deposited on at least some of the anode layers 16 and the cathode layers 18, wherein each of the second plurality 80 of conductive members 20′ has an exposed surface 82, the exposed surface 82 being surface not in contact with either the anode layers 16 or the cathode layers 18. A third electrolyte layer 14″ may then be deposited over the second plurality 80 of conductive members 20′.
Referring now to
Referring now to
The dual chamber fuel cell″″ of
Referring now to
The completely embedded current collector(s) 96 of the embodiment of
It is to be understood that the deposition, patterning and/or removing processes of the embodiments shown in
In any of the embodiments of the methods of the present invention, after any or all desired layers, or any combination of desired layers are deposited, the fuel cell 10, 10′, 10″, 10′″, 10″″ is sintered/annealed at temperatures ranging between about 200° C. and about 1500° C. In an alternate embodiment, the fuel cell 10, 10′, 10″, 10′″, 10″″ is sintered/annealed at temperatures ranging between about 600° C. and about 1100° C. It is to be understood that the temperature should be high enough to sinter the anode 16, cathode 18 and electrolyte 14, 14′, 14″, not lower than the operating temperature of the fuel cell, and not higher than the current collectors 20 can withstand.
A method of using a fuel cell 10, 10′, 10″, 10′″, 10″″ may include the step of operatively connecting the fuel cell 10, 10′, 10″, 10′″, 10″″ to at least one of an electrical load L and an electrical storage device S. At least some of the plurality of current collectors 20 may be used to aid in accomplishing this connection.
Embodiments of the present invention are efficient in that they allow fabrication of relatively thin film fuel cells 10, 10′, 10″, 10′″, 10″″ for example, solid oxide fuel cells, by optional electrochemical techniques (e.g. electrophoretic and electrolytic depositions). Conductive members 20′ used in these techniques may then be advantageously used as highly efficient current collectors 20 and/or sacrificial structures 30 (
Embodiments of the present invention are advantageous in that the methods of the present invention are relatively simple processes. Further, there is high surface area (efficient) utilization of current collectors 20. Yet further, if desired, gas tight sealing may be achieved. Still further, embodiments of the present invention render the ability to increase surface area of anodes 16/cathodes 18 without utilizing a ceramic etch.
While several embodiments of the invention have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.
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