CA2179034C - Electrochemical fuel cell employing ambient air as the oxidant and coolant - Google Patents
Electrochemical fuel cell employing ambient air as the oxidant and coolantInfo
- Publication number
- CA2179034C CA2179034C CA002179034A CA2179034A CA2179034C CA 2179034 C CA2179034 C CA 2179034C CA 002179034 A CA002179034 A CA 002179034A CA 2179034 A CA2179034 A CA 2179034A CA 2179034 C CA2179034 C CA 2179034C
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- CA
- Canada
- Prior art keywords
- fuel cell
- anode
- assembly
- cathode
- thermally conductive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/0267—Collectors; Separators, e.g. bipolar separators; Interconnectors having heating or cooling means, e.g. heaters or coolant flow channels
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/0247—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the form
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
- H01M8/04014—Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
- H01M8/241—Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
- H01M8/2465—Details of groupings of fuel cells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
- H01M8/2465—Details of groupings of fuel cells
- H01M8/247—Arrangements for tightening a stack, for accommodation of a stack in a tank or for assembling different tanks
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0065—Solid electrolytes
- H01M2300/0082—Organic polymers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
- H01M8/249—Grouping of fuel cells, e.g. stacking of fuel cells comprising two or more groupings of fuel cells, e.g. modular assemblies
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
An electrochemical fuel cell assembly includes a membrane electrode assembly which comprises an anode, a cathode having a surface thereof exposed to ambient air, and an ion exchange membrane interposed between the anode and the cathode. A seal forms a gas-impermeable barrier around the anode to which a gaseous fuel stream is supplied.
The assembly further includes a thermally conductive plate having a plurality of thermally conductive members of fins extending from a major surface of the plate. The thermally conductive members contact portions of the exposed cathode surface. Adjacent thermally conductive members cooperate with the plate and the exposed cathode surface to form air conducting channels. Heat generated exothermically in the membrane electrode assembly is dissipated to the atmosphere through the thermally conductive members.
The assembly further includes a thermally conductive plate having a plurality of thermally conductive members of fins extending from a major surface of the plate. The thermally conductive members contact portions of the exposed cathode surface. Adjacent thermally conductive members cooperate with the plate and the exposed cathode surface to form air conducting channels. Heat generated exothermically in the membrane electrode assembly is dissipated to the atmosphere through the thermally conductive members.
Description
Wo 95/17772 2 1 7 ~ G 3 4 PCT/CA94100675 ELECT~O~ MTCAL FUEL CELL E~PLOYING
AMBIENT AIR AS Tl{E OXIDANT AND COOLANT
Fiold of Tho Invention This invention relates generally to electroehemieal fuel cells and, more partieularly, to a fuel eell whieh employs ambient air as both an S oxidant and a eoolant.
Baclcqround o~ The Invention A fuel cell is a device which generates eleetrical energy by converting chemical energy direetly into eleetrieal energy by oxidation of fuel supplied to the eell. Fuel eells are advantageous beeause they convert chemical energy directly to electrical energy without the necessity of undergoing any intermediate steps, for example, combustion of a hydrocarbon or earbonaeeous fuel as 15 takes plaee in a th,ermal power station.
A typical fuel cell includes an anode, a eathode and an eleetrolyte. Fuel and oxidant are supplied to the anode and cathode, respectively.
At the anode, the fuel permeates the electrode 20 material and reaets with an anode eatalyst layer to form eations ~protons) and eleetrons. The eations migrate through the eleetrolyte to the cathode. At the eathode, the oxygen-eontaining gas supply reaets with a eathode eatalyst layer to form 2s anions. The electrons produced at the anode travel from the fuel cell anode, through an external load, and baek into the eathode of the eell. The anions produeed at the eathode react with the cations and electrons to form a reaction product which is 2 ~ 1 7~Q34 pCrlCA94/00675 removed from the cell.
In electrochemical fuel cells employing hydrogen as the fuel and oxygen-containing air (or .' pure oxygen) as the oxidant, a catalyzed reaction 5 at the anode produces hydrogen cations from the fuel supply. This type of fuel cell is advantageous because the only reaction product is water. An ion exchanqe membrane facilitates the migration of hydrogen cations f rom the anode to the lO cathode. In addition to conducting hydrogen cations, the membrane isolates the hydrogen fuel stream from the oxidant stream comprising oxygen containing air. At the cathode, oxygen reacts at the catalyst layer to form anions. The anions 15 formed at the cathode react with the hydrogen ions that have crossed the membrane to form liquid water as the reaction product. The anode and cathode reactions in such fuel cells is shown in the following equations:
Anode reaction: H2 ~ 2H+ + 2e~
Cathode reaction: l/2O2 + 2H+ + 2e ~ H2O
A type of fuel cell Xnown as a solid polymer fuel cell ("SPFC") contains a membrane electrode assembly ("MEA") consisting of a solid polymer 2 ~ electrolyte or ion exchange membrane disposed between two electrodes formed of porous, electrically conductive sheet material. The electrodes are typically formed of carbon fiber paper ("CFP"), and are generally impregnated or coated with a hydrophobic polymer, such as polytetrafluoroethylene. The MEA contains a layer of catalyst at each membrane/electrode interface to 2 ~ 7~0~
Wo 95/17772 Pcr/cA9~/00675 induce the desired electrochemical reaction. A
finely divided platinum catalyst is typically employed. The MEA is in turn disposed between two electrically conductive plates, each of which has 5 at least one flow passage engraved or milled therein . These f luid f low f ield plates are typically formed of graphite. The flow passaqes direct the fuel and oxidant to the respective electrodes, namely, the anode on the fuel side and lO the cathode on the oxidant side. The electrodes are electrically coupled to provide a path for conducting electrons between the electrodes.
In a single cell arrangement, fluid flow field plates are provided on each of the anode and 15 cathode sides. The plates act as current collectors, provide support for the electrodes, provide access channels for the fuel and oxidant to the respective anode and cathode surf aces, and provide channels for the removal of water formed 20 during operation of the cell.
Two or more fuel cells can be connected together in series or in parallel to increase the overall power output of the assembly. In such arrangements, the cells are typically connected in 25 series, wherein one side of a given plate serves as an anode plate for one cell and the other side of the plate is the cathode plate for the adjacent cell. Such a series connected multiple fuel cell arrangement i5 referred to as a fuel cell stack, 30 and is usually held together by tie rods and end plates. The stack typically includes manifolds and inlets for directing the fuel (substantially pure hydrogen, methanol reformate or natural gas reformate) and the oxidant (substantially pure WO 95/17772 2 1 7 q Q 3 ~ PCT/CA94/00675 oxygen or oxygen-containing air~ to the anode and cathode flow field channels. The stack also usually inclllA~c a manifold and inlet for directing the coolant fluid, typically water, to interior 5 ~hz-nn~l c within the stack to absorb heat generated by the exothermic reaction of hydrogen and oxygen within the fuel cells. The stack also generally includes exhaust outlets and manifolds for expelling the unreacted fuel and oxidant gases, lO each carrying entrained water, as well as an outlet manifold for the coolant water exiting the stack.
Conventional fuel cell and stack designs have several inherent disadvantages. First, conventional designs typically employ liquid lS cooling systems for regulating the cells' operating temperature. Liquid cooling systems are disadvantageous because they require the inc~,L~o~ ion of additional components to direct coolant into thermal contact with fuel cells. The 20 power requirements to operate such additional ~ ~ ~ ts, such as pumps and cooling fans, represent an additional parasitic load on the system, thereby decreasing the net power derivable from the stack. Such additional components also 25 add volume, weight, complexity and cost to fuel cell designs.
Second, conventional designs employ further parasitic devices such as pumps for the delivery of pressuri2ed fuel and oxidant to the fuel cell. In 30 addition to adding volumè, weight, complexity and cost, these parasitic systems also reduce the overall power efficiency of the system.
Third, in conventional stack arrangements it is difficult to identify and replace defective fuel ~ Wo 9S/17772 2 1 7 9 Q 3 4 PCT/CA94/00675 cells without disrupting the operation of the entire fuel cell stack.
The present invention is directed to cir~ulllv~ ing one or more of the above-mentioned disadvantages. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.
8umm~ry of The Invention The above and other objects are achieved by an electrochemical fuel cell assembly comprising:
(a) a membrane electrode assembly comprising a porous electrically conductive anode, a porous electrically conductive cathode having a surface thereof exposed to ambient air, and an ion exchange membrane interposed between the anode and the cathode;
(b) sealant means for forming a gas-impermeable barrier around the anode;
(c) fuel delivery means for supplying agaseous fuel stream to the anode;
(d) electrical connection means for providing an electrical connection to the anode and to the cathode; and (e) a thermally conductive plate having a plurality of first thermally conductive members extending from a major surface of the plate, the first members contacting 30 portions of the exposed cathode surface, adjacent ones of the first members cooperating with the plate and the exposed cathode surface to form at least WO95/17772 2 1 7 q Q 3 4 PCT/CA94100675 ~
one air conducting channel.
In operation, at least a portion of the heat generated exothermically in the membrane electrode a6sembly is dissipated to the atmosphere through the f irst members .
The thermally conductive plate is preferably, but not necessarily, formed as a single planar piece from which the thermally conductive members extend. Alternatively, the plate could consist of a plurality of staggered bars interconnecting the thermally conductive members, which extend from the staggered bars and contact the exposed cathode surf ace.
The plate and the first members are preferably f ormed of A 1 llm i nllm, and the portions of the f irst members which contact the cathode surf ace have an inert metal applied thereto. The inert metal is preferably gold applied by electroplating.
The pref erred electrical connection means comprises electrical conductors disposed between the anode and the ion exchange membrane, and the electrical conductors preferably extend through the sealing means . The pref erred electrical conductors are formed from gold wire.
In the preferred assembly, the plate has a thermally conductive material extending from another ma~or surface of the plate, such that heat generated exothermically in the membrane electrode assembly is further dissipated to the atmosphere through the material. The material preferably comprises a plurality of thermally conductive members, or alternatively a thermally conductive foam. The preferred thermally conductive foam is an aluminum foam.
~ Wo 95/17772 2 1 7~ C ~ 4 PCr/CA94/00675 In the preferred assembly, the fuel delivery means comprises a fuel inlet and a fuel outlet, such that the fuel outlet directs unreacted components of the gaseous fuel stream away from the 5 anode. The assembly can further comprise a fan for directing the ambient air onto the exposed surface of the porous electrically conductive cathode.
Where the gaseous fuel stream comprises hydrogen, the assembly preferably further comprising means lO for accumulating water condensed on the first thermally conductive members.
A fuel cell stack incorporating the above fuel cell assemblies comprises:
l. a plurality of fuel cell assemblies as lS defined with components (a) - (e) above;
2. serial connection means for electrically connecting the plurality of fuel cell assemblies in an electrical series having a f irst assembly and a last assembly, wherein the anode of each assembly except the last assembly in the series is electrically connected to the cathode of the next adjacent assembly in the series;
AMBIENT AIR AS Tl{E OXIDANT AND COOLANT
Fiold of Tho Invention This invention relates generally to electroehemieal fuel cells and, more partieularly, to a fuel eell whieh employs ambient air as both an S oxidant and a eoolant.
Baclcqround o~ The Invention A fuel cell is a device which generates eleetrical energy by converting chemical energy direetly into eleetrieal energy by oxidation of fuel supplied to the eell. Fuel eells are advantageous beeause they convert chemical energy directly to electrical energy without the necessity of undergoing any intermediate steps, for example, combustion of a hydrocarbon or earbonaeeous fuel as 15 takes plaee in a th,ermal power station.
A typical fuel cell includes an anode, a eathode and an eleetrolyte. Fuel and oxidant are supplied to the anode and cathode, respectively.
At the anode, the fuel permeates the electrode 20 material and reaets with an anode eatalyst layer to form eations ~protons) and eleetrons. The eations migrate through the eleetrolyte to the cathode. At the eathode, the oxygen-eontaining gas supply reaets with a eathode eatalyst layer to form 2s anions. The electrons produced at the anode travel from the fuel cell anode, through an external load, and baek into the eathode of the eell. The anions produeed at the eathode react with the cations and electrons to form a reaction product which is 2 ~ 1 7~Q34 pCrlCA94/00675 removed from the cell.
In electrochemical fuel cells employing hydrogen as the fuel and oxygen-containing air (or .' pure oxygen) as the oxidant, a catalyzed reaction 5 at the anode produces hydrogen cations from the fuel supply. This type of fuel cell is advantageous because the only reaction product is water. An ion exchanqe membrane facilitates the migration of hydrogen cations f rom the anode to the lO cathode. In addition to conducting hydrogen cations, the membrane isolates the hydrogen fuel stream from the oxidant stream comprising oxygen containing air. At the cathode, oxygen reacts at the catalyst layer to form anions. The anions 15 formed at the cathode react with the hydrogen ions that have crossed the membrane to form liquid water as the reaction product. The anode and cathode reactions in such fuel cells is shown in the following equations:
Anode reaction: H2 ~ 2H+ + 2e~
Cathode reaction: l/2O2 + 2H+ + 2e ~ H2O
A type of fuel cell Xnown as a solid polymer fuel cell ("SPFC") contains a membrane electrode assembly ("MEA") consisting of a solid polymer 2 ~ electrolyte or ion exchange membrane disposed between two electrodes formed of porous, electrically conductive sheet material. The electrodes are typically formed of carbon fiber paper ("CFP"), and are generally impregnated or coated with a hydrophobic polymer, such as polytetrafluoroethylene. The MEA contains a layer of catalyst at each membrane/electrode interface to 2 ~ 7~0~
Wo 95/17772 Pcr/cA9~/00675 induce the desired electrochemical reaction. A
finely divided platinum catalyst is typically employed. The MEA is in turn disposed between two electrically conductive plates, each of which has 5 at least one flow passage engraved or milled therein . These f luid f low f ield plates are typically formed of graphite. The flow passaqes direct the fuel and oxidant to the respective electrodes, namely, the anode on the fuel side and lO the cathode on the oxidant side. The electrodes are electrically coupled to provide a path for conducting electrons between the electrodes.
In a single cell arrangement, fluid flow field plates are provided on each of the anode and 15 cathode sides. The plates act as current collectors, provide support for the electrodes, provide access channels for the fuel and oxidant to the respective anode and cathode surf aces, and provide channels for the removal of water formed 20 during operation of the cell.
Two or more fuel cells can be connected together in series or in parallel to increase the overall power output of the assembly. In such arrangements, the cells are typically connected in 25 series, wherein one side of a given plate serves as an anode plate for one cell and the other side of the plate is the cathode plate for the adjacent cell. Such a series connected multiple fuel cell arrangement i5 referred to as a fuel cell stack, 30 and is usually held together by tie rods and end plates. The stack typically includes manifolds and inlets for directing the fuel (substantially pure hydrogen, methanol reformate or natural gas reformate) and the oxidant (substantially pure WO 95/17772 2 1 7 q Q 3 ~ PCT/CA94/00675 oxygen or oxygen-containing air~ to the anode and cathode flow field channels. The stack also usually inclllA~c a manifold and inlet for directing the coolant fluid, typically water, to interior 5 ~hz-nn~l c within the stack to absorb heat generated by the exothermic reaction of hydrogen and oxygen within the fuel cells. The stack also generally includes exhaust outlets and manifolds for expelling the unreacted fuel and oxidant gases, lO each carrying entrained water, as well as an outlet manifold for the coolant water exiting the stack.
Conventional fuel cell and stack designs have several inherent disadvantages. First, conventional designs typically employ liquid lS cooling systems for regulating the cells' operating temperature. Liquid cooling systems are disadvantageous because they require the inc~,L~o~ ion of additional components to direct coolant into thermal contact with fuel cells. The 20 power requirements to operate such additional ~ ~ ~ ts, such as pumps and cooling fans, represent an additional parasitic load on the system, thereby decreasing the net power derivable from the stack. Such additional components also 25 add volume, weight, complexity and cost to fuel cell designs.
Second, conventional designs employ further parasitic devices such as pumps for the delivery of pressuri2ed fuel and oxidant to the fuel cell. In 30 addition to adding volumè, weight, complexity and cost, these parasitic systems also reduce the overall power efficiency of the system.
Third, in conventional stack arrangements it is difficult to identify and replace defective fuel ~ Wo 9S/17772 2 1 7 9 Q 3 4 PCT/CA94/00675 cells without disrupting the operation of the entire fuel cell stack.
The present invention is directed to cir~ulllv~ ing one or more of the above-mentioned disadvantages. Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.
8umm~ry of The Invention The above and other objects are achieved by an electrochemical fuel cell assembly comprising:
(a) a membrane electrode assembly comprising a porous electrically conductive anode, a porous electrically conductive cathode having a surface thereof exposed to ambient air, and an ion exchange membrane interposed between the anode and the cathode;
(b) sealant means for forming a gas-impermeable barrier around the anode;
(c) fuel delivery means for supplying agaseous fuel stream to the anode;
(d) electrical connection means for providing an electrical connection to the anode and to the cathode; and (e) a thermally conductive plate having a plurality of first thermally conductive members extending from a major surface of the plate, the first members contacting 30 portions of the exposed cathode surface, adjacent ones of the first members cooperating with the plate and the exposed cathode surface to form at least WO95/17772 2 1 7 q Q 3 4 PCT/CA94100675 ~
one air conducting channel.
In operation, at least a portion of the heat generated exothermically in the membrane electrode a6sembly is dissipated to the atmosphere through the f irst members .
The thermally conductive plate is preferably, but not necessarily, formed as a single planar piece from which the thermally conductive members extend. Alternatively, the plate could consist of a plurality of staggered bars interconnecting the thermally conductive members, which extend from the staggered bars and contact the exposed cathode surf ace.
The plate and the first members are preferably f ormed of A 1 llm i nllm, and the portions of the f irst members which contact the cathode surf ace have an inert metal applied thereto. The inert metal is preferably gold applied by electroplating.
The pref erred electrical connection means comprises electrical conductors disposed between the anode and the ion exchange membrane, and the electrical conductors preferably extend through the sealing means . The pref erred electrical conductors are formed from gold wire.
In the preferred assembly, the plate has a thermally conductive material extending from another ma~or surface of the plate, such that heat generated exothermically in the membrane electrode assembly is further dissipated to the atmosphere through the material. The material preferably comprises a plurality of thermally conductive members, or alternatively a thermally conductive foam. The preferred thermally conductive foam is an aluminum foam.
~ Wo 95/17772 2 1 7~ C ~ 4 PCr/CA94/00675 In the preferred assembly, the fuel delivery means comprises a fuel inlet and a fuel outlet, such that the fuel outlet directs unreacted components of the gaseous fuel stream away from the 5 anode. The assembly can further comprise a fan for directing the ambient air onto the exposed surface of the porous electrically conductive cathode.
Where the gaseous fuel stream comprises hydrogen, the assembly preferably further comprising means lO for accumulating water condensed on the first thermally conductive members.
A fuel cell stack incorporating the above fuel cell assemblies comprises:
l. a plurality of fuel cell assemblies as lS defined with components (a) - (e) above;
2. serial connection means for electrically connecting the plurality of fuel cell assemblies in an electrical series having a f irst assembly and a last assembly, wherein the anode of each assembly except the last assembly in the series is electrically connected to the cathode of the next adjacent assembly in the series;
3. a positive current lead electrically connected to the cathode of the f irst assembly in the series; and 4. a negative current lead electrically connected to the anode of the last assembly in the series.
The fuel cell stack can be formed as a multiplexed arrangement, wherein the plurality of fuel cell assemblies share a common ion exchange membrane .
The above and other objects are also achieved Wo 95/~7772 2 1 7 q O ~ 4 PCT/CA94/00675 ~
by an electrochemical fuel cell assembly comprising:
(aa) a bicell membrane electrode assembly comprising a first porous electrically conductive cathode having a surface thereof exposed to ambient air, a porous electrically conductive anode, a second porous electrically conductive cathode having a surface thereof exposed to ambient air, a first ion exchange membrane interposed between the f irst cathode and the anode, and a second ion exchange membrane interposed between the second cathode and the anode;
1~ (bb) sealing means for forming a gas-impermeable barrier around the anode;
(cc) fuel delivery means for delivering gaseous fuel to :the anode;
(dd) electrical connection means for providing an electrical connection to the anode, to the f irst cathode and to the second cathode;
(ee) a first thermally conductive plate having a plurality of first thermally conductive members extending from a major surface of the plate, the first members contacting portions of the exposed f irst cathode surface, adjacent ones of the first members cooperating with the first plate 3 0 and the exposed f irst cathode surf ace to form at least one air conducting channel;
and ~ff) a second thermally conductive plate having a plurality of second thermally ~ WO 9S/17772 2 1 7 ~ ~ 3 4 PC~CA94/00675 conductive members extending from a major surface thereof, the second members contacting portions of the exposed second cathode surface, adjacent ones of the s second members cooperating with the second plate and the exposed second cathode surface to form at least one air conducting channel.
In operation, at least a portion of the heat lO generated exothermically in the bicell membrane electrode assembly is dissipated to the ai srh~re through the f irst and second members.
The f irst and second members are pref erably formed of aluminum, the portions of the first and 15 second members which contact the cathode surf aces have an inert metal applied thereto. The inert metal is preferably gold applied by electroplating.
The electrical connection means preferably comprises f irst electrical conductors disposed 20 between the anode and the first membrane, and second electrical conductors disposed between the anode and the second membrane, such that the f irst and second electrical conductors extending through the sealing means. The f irst and second electrical 25 conductors are preferably formed from gold wire.
In the preferred bicell assembly, the f irst plate has a first thermally conductive material extending from another major surface of the first plate, and the second plate has a second thermally 30 conductive material extending from another major surface of the second plate, such that heat generated exothermically in the bicell membrane electrode assembly is further dissipated to the a' ~crh~ore through the first and second material.
.
2 l 7~
WO 95/17772 PCT/CA94/00675 ~
The first arld second material each preferably comprises a plurality of thermally conductive members, or alternatively a thermally conductive foam. The preferred thermally conductive foam is 5 an aluminum foam.
In the preferred bicell assembly, the sealing means comprises the first and second membranes, such that the edges of the f irst and second membranes are bonded together to form a gas-10 impermeable barrier around the anode.
In the preferred bicell assembly, the fueldelivery means comprises a fuel inlet and a fuel outlet, such that the fuel outlet directs unreacted components of the gaseous fuel stream away from the 15 anode. The preferred bicell assembly further comprises a fan for directing the ambient air onto the exposed surface of the porous electrically conductive cathode. Where the gaseous fuel stream comprises hydrogen, the bicell assembly preferably 20 further comprising means for accumulating water condensed on the first and second thermally conductive members.
A bicell stz~ck incorporating the above bicell assemblies comprises:
I. a plurality of fuel cell assemblies as deflned with components (aa) - (ff) above;
II. seri~l connection means for electrically connecting the plurality of bicell 3 o assemblies in an electrical series having a first assembly and a last assembly, wherein the anode of each assembly except the last assembly in the series is electrically connected to the cathodes of .
Wo 95/17772 2 ~ 7 q ~ 3 4 PCTICA94/00675 the next adjacent assembly in the series;
III. a positive current lead electrically connected to the cathodes of the f irst assembly in the series; and IV. a negative current lead electrically connected to the anode of the last assembly in the series.
The bicell stack can b,e formed as a multiplexed arrangement, wherein the plurality of bicell assemblies share a common f irst ion exchange membrane and a common second ion exchange membrane.
Brief DeqcriPtion Of The Dr~winqq FIG. 1 is an exploded perspective view of an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant.
FIG. 2A is a section view taken in the direction of arrows 2-2 in FIG. 1.
FIG. 2B is section view of an alternative t~mhorl; -nt of the electrochemical fuel cell assembly illustrated in FIGS. 1 ~nd 2A.
FIG. 3 is a perspective view of a fuel cell stack connected across an external load.
FIGS. 4A and 4B illustrate alternative embodiments of an interleaved membrane electrode assembly according to the present invention.
FIG. 5 is a side sectional view of an alternative embodiment of an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant.
FIG. 6 is a sectional view of a multiplexed arrangement of three bicell membrane electrode assemblies employing ambient air as the oxidant and coolant, which share common ion exchange membranes.
Wo 95/17772 2 1. 7 9 0 3 4 PCT/CA94/00675 FIG. 7 is an exploded perspective view of a first embodiment of a thermally conductive member or fin c~hAsc~mhly for an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant, which employs a slidable comb for adjusting the conf iguration of the air conducting ~h~nn~-l c.
FIG. 8 is a perspective view of second nt of a thermally conductive member or f in s~lh~cc~mhly for an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant, which employs a pivotable baffle (shown in phantom lineS) for adjusting the flow through the air conducting channels.
FIG. 9 is a perspective view of a pivotable baffle subassembly for use in conjunction with the f in subassembly shown in FIG . 8 .
FIG. 10 is a side view of the pivotable baffle Ellh~cs.oTnhly shown in FIG. 9.
FIG. 11 is a schematic view of third embodiment of an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant, which employs external dampers for adjusting the flow through the air conducting channels.
Det~ilea Description Of The Preferred Embodiment~
Referring first to FIG. 1 and FIG. 2~, an electrochemical fuel cell assembly lo, includes a bicelL membrane electrode assembly ("M~A") 14.
Bicell MEA 14 includes a f irst cathode 16, an anode 26, and a second cathode 38. A first ion exchange membrane 24 is interposed between first cathode 16 and anode 26. A second ion exchange membrane 34 is interposed between second cathode 38 and anode 26.
Wo 95/17772 2 ~ 7 q ~ 3 4 PCTICA94/00675 Fuel supply line 44 and fuel inlet 46 contain and direct fuel at a pressure slightly greater than ai ~ riC to anode 26.
The electrodes 16, 26, 38 are formed of porous 5 electrically conductive sheet material, preferably porous carbon fiber paper ("CFP") impregnated or coated with a hydrophobic polymer, such as polytetrafluoroethylene- The electrodes 16, 26, 38 are each treated with a layer of catalyst, such as 10 platinum or other suitable electrocatalytic material, on the surface(s) adjacent and in contact with the ion exchange membrane(s) 24, 34 to facilitate the desired chemical reaction. Suitable ion exchange membranes are commercially available 15 from DuPont under the trade name Nafion 117 and from DoW under the trade designation XUS 13204.10.
The electrodes 16, 26, 38 and the ion exchange membranes 24, 34 are arranged together in an interleaved or sandwich-like manner, as illustrated 20 in FIG. 1 and FIG. 2A, and placed in a high pressure press at a temperature suf f icient to soften the ion exchange membrane material. The combination of pressure and temperature forces the softened rnembrane material at least partialIy into 25 the CFP electrode material, bonding the individual layers to form a single unitary assembly.
Presently, the bicell I~EA 14 is formed by placing the layers of material in a press at a temperature and pressure suff icient to soften the material and 3 o create an intimate bond .
Low pressure can be employed to supply the gaseous fuel because the chemical reaction at the anode 26 consumes the fuel and draws it into the anode 2 6 . The porous structure of the CFP used to WO 951~7M2 2 1 7 9 ~ 3 4 PCT/CA94/00675 form the anode 26 facilitates the delivery of the gaseous fuel throughout the anode 26. The gaseous fuel reacts at the anode 26 to produce cations ~protons) and electrons. l~hen hydrogen is used as the f uel, the reaction at the anode produces hydrogen cations and electrons according to the following equation:
H2 ~ 2H+ + 2e-.
The reaction at the cathodes 16, 38 produces water according to the following equation:
1/2 2 + 2H I + 2e -- H2O.
The ion exchange membrane facilitates the migration of cations from the anode 26 to the cathodes 16, 38. In addition to conducting hydrogen cations, the ion exchange membranes 24, 34 isolate the gaseous fuel stream from the oxidant stream. This is particularly important when hydrogen is employed as a fuel source because of the reaction which occurs when hydrogen and oxygen are mixed and ignited or contacted with a catalyst.
A seal 50 provides a gas-impermeable barrier at the edges of the anode 2 6 to prevent leakage of the gaseous fuel from within anode 26. In FIG. 2~, the seal 50 is formed by extending the ion exchange membranes 24, 34 over the edges of the anode 26.
~uring the assembly process, the portions of the ion exchange membranes 24, 34 extending over the anode 26 can be adhered using heat and pressure to form a gas-impermeable seal around the anode 26.
Alternatively, as illustrated in FIG. 2B, the seal 50 may be formed by disposing layers of sealant 52a, 52~, such as a silicon based sealant, along the top and bottom edge portions, respectively, of anode 26 which extend between the ion exchange ~ WO 95117772 2 t 7 ~ ~ 3 ~ PCTtCA94tOo675 membranes z 4, 3 4 .
As shown in FIGS. 1, 2A and 2B, edge current collectors 56a, S6b are disposed between the anode 26 and the ion exchange membranes 24, 34. The first edge current collector 56a is disposed between the anode 2 6 and the f irst ion exchange membrane 2~, and the second edge current collector 56b is disposed between the anode 26 and the second ion exchange membrane 34. The edge current collectors 56a, 56b facilitate current flow (i.e., electron flow) from the anode 26 to an external load, as described in more detail below. As best shown in FIG. 2A, the edge current collectors 56a, 56b exit the bicell MEA 14 through the seal 50, thereby providing an electrical connection to the anode 2 6 .
Each of the edge current collectors 56a, 56b is preferably formed from a plurality of electrically conductive wires (not shown). The wires forming the edge current collectors 56a, 56b are in turn preferably formed from a highly conductive material such as gold, niobium, platinum, titanium or graphite. Although a single wire can provide suf f icient edge current collection, a plurality of wires is preferred. In FIG. 1, the conductive wires 56:~, 56b are shown exiting from both the top and bottom of the bicell MEA 14, whereas in FIGS. 2A and 23 the conductive wires only exit from the top of the bicell MEA 14.
As shown in FIGS. 1, 2A and 2B, the fuel cell assembly 10 further includes first and second thermally conductive plates 62a, 62b disposed on - opposite sides of the bicell MEA 14. The plates 62a, 62b are preferably constructed from aluminum WOg5/~7772 21 7 9 0 3 ~ PCT/C~94/00675 which is either milled or extruded to form the illustrated configuration. Aluminum is preferred because it is relatively inexpensive and lightweight and because it has ~avorable thermal 5 and electrical conductivity.
As shown in FIG. 1, each plate 62a, 62b includes a first set of thermally conductive members, shown in FIG. 1 as fins 66a, 66b, which extend toward the bicell MEA 14 and contact one of 10 cathodes (cathode 38 in FIG. 1 and FIG. 2A) and a second set of thermally conductive members, shown in FIG. 1 as fins 64a, 64b, which extend away from the bicell MEA 14 . The portion o~ each f in 66a, 66b which contacts the surface of a cathode is 15 preferably plated with gold to prevent oxidization of the aluminum and ensure good electrical contact between the cathode 38 and each f in 66a, 66b .
The f irst set of thermally conductive members 66a, 66b provide structural rigidity and support 20 for the bicell MEA 14, stabilize the MEA 14, and inhibit distortion of the MEA 14 from swelling due to oversaturation of the membrane.
Each of the second set of thermally conductive members, shown in FIG. 1 as fins 64a, 64b, could 25 also be formed as a thermally conductive foam, in lieu of the fins. Thermally conductive foam has an irregular three-dimensional conformation, with interstitial spaces permitting the passage of air and other coolant fluids through the irregular, 30 lattice-like structure of the thermally conductive material from which the foam if formed. The preferred thermally conductive foam is an aluminum f oam .
As shown in FIG. 1, a fastener mechanism WO95/17772 L ~ 7 9 ~3 4 PCT/CA94/00675 ecures the plates 62a, 62b and MEA 14 in assembled form and maintains contact between the fins 66a, 66b and the exposed surfaces of cathodes 16, 38.
The fastener r--h~nism preferably includes a first - 5 threaded fastener 72 extending through the upper portion of the plates 62a, 62b and a second threaded fastener 74 extending between the bottom portion of the plates 62a, 62b. The threaded fasteners 72, 74 connect the plates 62a, 62b and o allow the plates 62a, 62b to be clamped against the bicell MEA 14, thereby maintaining electrical and physical contact between the cathodes 16, 38 and the plates 62a, 62b.
Both sets of fins 64a, 64b and 66a, 66b are open at the top and bottom to allow air f low through the f ins . Heat produced by the exothermic chemical reaction of fuel (hydrogen) and oxidant (oxygen) within the bicell MEA 14 is dissipated to the a~ rh-~re through the fins 64a, 64b and 66a, 66b. It has been found that such heat dissipation produces a natural convection current which causes the ambient air to be drawn upwardly through the fins 64a, 64b and 66a, 66b. The set of fins 64a extend in a direction away from MEA 14, and function primarily as heat transfer surfaces for expelling waste heat to the atmosphere such that a desired operation temperature of the bicell MEA 14 is maintained. The sets of fins 66a, 66b, in addition to functioning as heat transfer surfaces, cooperate with the plates 62a, 62b and the adjacent cathodes to form a plurality of air conducting channels which draw oxygen-containing ambient air toward the exposed surface of the cathodes. For example, fins 66a cooperate with plate 62a and WO 95117772 2 1 7 ~ Q 3 4 PCT/C~94100675 cathode 16 to form an air conducting channel ~8 (see FIG. l). A similar plurality of air conducting channels draws oxygen-containing ambient air toward the exposed surface of cathode 38. The 5 vertical orientation of the air supply channels 78 allows the water produced at the cathode 16 to flow downwardly toward the bottom of the fuel cell assembly lO where it can be drained from the assembly, thereby preventing oversaturation of the lO ion exchange membrane 24.
In employing ambient air as the oxidant and coolant for the fuel cell assembly lO, the following operating conditions should be present:
(l) ambient air flow through the air conducting channels to provide a sufficient stoichiometric supply of reactant oxygen to support the reaction at the membrane electrode assembly;
(2) ambient air flow and operating temperature should be such that the water removal capacity of the ambient air f low is less than the rate of production of reactant water to prevent dehydration of the ion exchange membranes;
(3) the operating temperature of the cell should be high enough to provide reasonable fuel cell performance; and (4) the operating temperature of the fuel:
cell should be high enough to allow the cell to reject waste heat to the atmosphere by natural convection.
With these considerations in mind, the size, spacing, and number of members or fins is empirically optimized to provide temperature ~ WO 9S117772 2 1 7 ~ Q ~ 4 PCTICA94/00675 &tability and performance stability over a wide range of loads.
Turning now to FIG. 3, a plurality of the fuel cell assemblies, six of which are designated in - 5 FIG. 3 as assemblies 102, lob, loc, lOd, lOe, and lOf, can be combined to form a fuel cell stack loo.
Fuel inlets, one of which is designated in FIG. 3 as fuel inlet 146, each direct a fuel stream to one of the respective fuel cell assemblies lOa-f. The fuel inlets are connected to a main fuel supply line 104, which is in turn connected to a fuel supply source (not shown) for delivering gaseous fuel at a pressure slightly greater than atmospheric to the stack loo.
In FIG. 3, the fuel cells assemblies lOa-f are electrically connected in series so that the fuel cell stack loo produces a voltage potential equal to the sum of the voltages of the individual fuel cell assemblies lOa-f. More specifically, the edge 20 current collectors 156 are used to electrically couple the anode of one bicell MEA to the cathodes of the next adjacent bicell MEA in the stack lOo.
For example, in FIG. 3 the anode of the first fuel cell assembly lOa is electrically connected to the 25 cathodes of the second fuel cell assembly lob.
This electrical connection is preferably made by connecting the edge current collec~ors 156 from one fuel cell assembly to the plate 162 adjacent the next fuel cell assembly in the stack loo The full electrical potential of the stack loo is imposed between a positive lead 108 and a negative lead 110. The positive lead 108 is formed by connecting an electrical conductor 112 to a positively charged portion of the first cell lOa in WO 95/17M2 2 1 7 9 0 3 ~ PCT/CA94/00675 the stack lOo. Specifically, the positive lead 108 can be connected to either of the end plates, the f ins, the threaded f asteners, or the cathodes of the f irst cell lOa . The negative lead llo is 5 formed by joining the edge current collectors of the last fuel cell assembly lOf to form a single conductor 114.
As is illustrated schematically in FIG. 3, when the stack 100 is installed in an electrical circuit, a load 118 and a contactor switch 120 can be connected between the positive and negative leads 108, llo. The contactor switch 120 can be selectively opened and closed to deliver power from the stack loO to the load 118.
FIGS. 4A and 4B illustrate alternative embodiments for serially connecting individual bicell NEAs to form a stack conf iguration . In both FIGS. 4A and 4B, the electrodes of successive bicell MEAs are interleaved to form serial 20 electrical connections. Each bicell MEA 114 includes a center anode 116 interposed between two cathodes 120, 122. Two sheets of solid polymer ion exchange membranes 126, 128 are interposed between the anode 116 and the cathodes 120, 122. In FIG.
25 4~, sealant material 132 is disposed at both ends of the anode 116 to prevént leakage of the gaseous fuel supplied to the anode 116. In FIG. 4B, a single sheet of material is used to form ion exchange membranes 126, 128. The membrane material 30 is looped around one end of the anode 116 and sealant material 132 is used to seal the other end of the anode 116.
In both embodiments illustrated in FIGS. 41~
and 4B, the cathodes 120, 122 extend beyond one end Wo 95/17772 PCT/CA94~00675 2 ~ 72~Q34 of a respective anode 116 and are joined around an electrical conductor 136. The electrical conductor 136 in turn extends through the sealant 132 and into the anode 116 of the next bicell NEA 114b in 5 the stack.
FIG. 5 illustrates an alternative t~mhorlir r-t of a fuel cell assembly which employs ambient air as the oxidant and coolant. In FIG. 5, a unicell MEA 214 is employed as opposed to the bicell MEA
arrangement of FIGS. 1, 2A and 2B. MEA 214 includes an ion exchange membrane 224, which is interposed between anode 226 and cathode 216. A
seal 250, formed of sealant material disposed along the exterior surfaces of the anode 226, is also shown in FIG. 5. Seal 250 forms a gas-impermeable barrier to prevent leakage of gaseous fuel supplied to the anode 226. A fuel deliver~y me-~h~n;sm 244 delivers gaseous fuel (preferably substantially pure hydrogen) to the anode 226 of the unicell MEA
21~. The fuel delivery means 244 includes at least one fuel inlet 246 which extends partially into the anode 226. The fuel inlet 246 delivers gaseous fuel to the anode z26 at a low pressure or at slightly greater than atmospheric pressure.
In the t~mho~ nt illustrated in FIG. s, a clamping r~-h~ni~m 218 secures the plate 262, together with its fins 264, 266, against the cathode 216 of the unicell MEA 214. The clamping means 218 is illustrated in FIG. 5 as a pair of threaded fasteners 272, 274 and an end plate 220.
FIG. 6 shows a multiplexed arrangement 302 of three bicell assemblies employing ambient air as the oxidant and coolant. The multiplexed arrangement includes first cathodes 304a, 304b, ~VO 9511M72 2 1 7 ~ ~ 3 4 PCT/CA94100675 304e, anodes 306a, 306b, 306c, and second cathodes 314~, 314b, 31~e. As shown in FIG. 6, first cathode 304a, anode 306a and second cathode 31~1a are arranged in a first bicell MEA 310a, with first 5 ion exchange membrane 316 interposed between first anode 306~ and cathode 304a, and second ion exchange membrane 3Z6 interposed between anode 306a and second cathode 314a. Similarly, first cathode 30~b, anode 306b and second cathode 314b are o arranged in a second bicell MEA 310b, with first ion exchange membrane 316 interposed between f irst anode 306b and cathode 304b, and second ion exchange membrane 326 interposed between anode 306b and second cathode 314b. Finally, first cathode 1~ 304e, anode 306e and second cathode 314c are arranged in a third bicell MEA 310e, with first ion exchange membrane 316 interposed between first anode 306e and cathode 304e, and second ion exchange membrane 326 interposed between anode 306e 20 and second cathode 314e. As shown in FIG. 6, first, second and third bicell assemblies 310a, 310b, 310e share a common f irst ion exchange membrane 316 and a common second ion exchange membrane 326. FIG. 6 also shows the location of 25 one of the thermally conductive member or fin subassemblies 360. Fin sl,h~ccPmhly 360 includes a thermally conductive plate 362, a first set of thermally conductive members or fins 366, which extend toward bicell MEA 310b and contact cathode 30 304b, and a second set of thermally conductive _ members or fins 364, which extend away from bicell MEA 310b. Channels 332a and 332b are the fuel flow ~ h~nnPl ~ which interconnect the anodes in the multiplexed arrangement 302 shown in F~G. 6.
WO 95/17772 2 1 7 9 a 3 4 PCTtC~94/00675 .
Multiplexed arrangement 302 is sealed on both ends by seals 320a, 320b, preferably formed by the fusing together of first and second ion exchange membranes 316, 326.
- s FIG. 7 shows a thermally conductive member or fin cllh~ccP~hly 460 which employs a slidable comb ~,62 for adjusting the conf iguration of the air conducting rh~nnPl c The air conducting channels are formed by the spaces between the fins, one of which is designated in FIG. 7 as fin 466a. As shown in FIG. 7, slidable comb 462 includes a plurality of tines 462a, which extend into the t~h~nnPl c formed by the spaces between the fins.
FIG. 8 shows another fin subassembly 560 which employs pivotable baffles (one of which is shown in phantom lines in FIG. 8 as baffle 574a) Fin 51lh~ccPTnhl y 560 includes a thermally conductive plate 562. A plurality of thermally conductive fins 566~, 566b, 566c, 566d extend from one major surface of plate 562. In the completed fuel cell assembly incorporating fin subassembly 560, fins 566a-d contact the outwardly facing surface of the adjacent cathode ~not shown in FIG. 8) A
plurality of thermally conductive fins 564a, 564b, 564c, 56~d, 564e, 564f extend from the other major surface of plate 562. Each of fins 564a-f has a slotted opening formed therein, one of which is shown in FIG. 8 as slot 570. A pivotable baffle subassembly, one baffle of which is shown in FIG. 8 as baffle 57~a, is suspended in the slots by pivot pin 572. Rotation of baffle 574a about pivot pin 572 regulates the amount of air flow through the air conducting channels.
Arrows ~ in FIG. 8 show the direction of air WO 95/17772 2 ~ 7 9 ~ 3 J PCr/CA94/0067~ ~
flow through the channels formed between fins s66;~-d., and represent the air supply for the electrochemical reaction at the adjacent cathode (not shown). Arrow B in FIG. 8 shows the direction 5 of air flow through the channels formed between fins 564~-f, and represents the air supply for conducting heat from the adjacent fuel cell structure (not shown), thereby providing thermal management to the adjacent fuel cell structure.
FIG. 9 shows pivotable baffle stlh~qc~mhly 574 for use in conjunction with the fin sl~h~ mhly 560 in FIG. 8. Subassembly S74 includes a plurality of baffles 574a, 57~b, S74c mounted on central pivot pin 572. FIG. lo shows a side view of pivotable 15 baffle subassembly 574.
FIG. 11 shows schematically an electrochemical ~uel cell assembly employing ambient air as the oxidant and coolant, which employs external dampers - 676, 678 having pivotable baffles 674, 684, respectively, for adju5ting the flow through the air conducting channels 664, 666. In FIG. 11, anode 626, ion exchange membrane 624 and cathode 616 form the membrane electrode assembly. Fins (not shown) extend from each major surface of plate 662. The spaces formed between the extending fins form air conducting channels 664, 666. Dampers 676, 678 include baffles 674, 684, which are mounted on pivot pins 672, 682, respectively.
Rotation of baffle 674, 684 about the respective pivot pins 672, 682 regulates the amount of air flow through the air conducting channels 664, 666.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be unders~ood, of _ Wo 95/17772 2 1 7 9 0 3 ~ PCT/CA94~aO675 course, that the invention is not limited thereto since modif ications may be made ~y those skilled in the art, particularly in light of the foregoing teachings. It is therefore contemplated by the 5 appended claims to cover such modif ications as incorporate those features which come within the spir~t and scope of the in~ention.
The fuel cell stack can be formed as a multiplexed arrangement, wherein the plurality of fuel cell assemblies share a common ion exchange membrane .
The above and other objects are also achieved Wo 95/~7772 2 1 7 q O ~ 4 PCT/CA94/00675 ~
by an electrochemical fuel cell assembly comprising:
(aa) a bicell membrane electrode assembly comprising a first porous electrically conductive cathode having a surface thereof exposed to ambient air, a porous electrically conductive anode, a second porous electrically conductive cathode having a surface thereof exposed to ambient air, a first ion exchange membrane interposed between the f irst cathode and the anode, and a second ion exchange membrane interposed between the second cathode and the anode;
1~ (bb) sealing means for forming a gas-impermeable barrier around the anode;
(cc) fuel delivery means for delivering gaseous fuel to :the anode;
(dd) electrical connection means for providing an electrical connection to the anode, to the f irst cathode and to the second cathode;
(ee) a first thermally conductive plate having a plurality of first thermally conductive members extending from a major surface of the plate, the first members contacting portions of the exposed f irst cathode surface, adjacent ones of the first members cooperating with the first plate 3 0 and the exposed f irst cathode surf ace to form at least one air conducting channel;
and ~ff) a second thermally conductive plate having a plurality of second thermally ~ WO 9S/17772 2 1 7 ~ ~ 3 4 PC~CA94/00675 conductive members extending from a major surface thereof, the second members contacting portions of the exposed second cathode surface, adjacent ones of the s second members cooperating with the second plate and the exposed second cathode surface to form at least one air conducting channel.
In operation, at least a portion of the heat lO generated exothermically in the bicell membrane electrode assembly is dissipated to the ai srh~re through the f irst and second members.
The f irst and second members are pref erably formed of aluminum, the portions of the first and 15 second members which contact the cathode surf aces have an inert metal applied thereto. The inert metal is preferably gold applied by electroplating.
The electrical connection means preferably comprises f irst electrical conductors disposed 20 between the anode and the first membrane, and second electrical conductors disposed between the anode and the second membrane, such that the f irst and second electrical conductors extending through the sealing means. The f irst and second electrical 25 conductors are preferably formed from gold wire.
In the preferred bicell assembly, the f irst plate has a first thermally conductive material extending from another major surface of the first plate, and the second plate has a second thermally 30 conductive material extending from another major surface of the second plate, such that heat generated exothermically in the bicell membrane electrode assembly is further dissipated to the a' ~crh~ore through the first and second material.
.
2 l 7~
WO 95/17772 PCT/CA94/00675 ~
The first arld second material each preferably comprises a plurality of thermally conductive members, or alternatively a thermally conductive foam. The preferred thermally conductive foam is 5 an aluminum foam.
In the preferred bicell assembly, the sealing means comprises the first and second membranes, such that the edges of the f irst and second membranes are bonded together to form a gas-10 impermeable barrier around the anode.
In the preferred bicell assembly, the fueldelivery means comprises a fuel inlet and a fuel outlet, such that the fuel outlet directs unreacted components of the gaseous fuel stream away from the 15 anode. The preferred bicell assembly further comprises a fan for directing the ambient air onto the exposed surface of the porous electrically conductive cathode. Where the gaseous fuel stream comprises hydrogen, the bicell assembly preferably 20 further comprising means for accumulating water condensed on the first and second thermally conductive members.
A bicell stz~ck incorporating the above bicell assemblies comprises:
I. a plurality of fuel cell assemblies as deflned with components (aa) - (ff) above;
II. seri~l connection means for electrically connecting the plurality of bicell 3 o assemblies in an electrical series having a first assembly and a last assembly, wherein the anode of each assembly except the last assembly in the series is electrically connected to the cathodes of .
Wo 95/17772 2 ~ 7 q ~ 3 4 PCTICA94/00675 the next adjacent assembly in the series;
III. a positive current lead electrically connected to the cathodes of the f irst assembly in the series; and IV. a negative current lead electrically connected to the anode of the last assembly in the series.
The bicell stack can b,e formed as a multiplexed arrangement, wherein the plurality of bicell assemblies share a common f irst ion exchange membrane and a common second ion exchange membrane.
Brief DeqcriPtion Of The Dr~winqq FIG. 1 is an exploded perspective view of an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant.
FIG. 2A is a section view taken in the direction of arrows 2-2 in FIG. 1.
FIG. 2B is section view of an alternative t~mhorl; -nt of the electrochemical fuel cell assembly illustrated in FIGS. 1 ~nd 2A.
FIG. 3 is a perspective view of a fuel cell stack connected across an external load.
FIGS. 4A and 4B illustrate alternative embodiments of an interleaved membrane electrode assembly according to the present invention.
FIG. 5 is a side sectional view of an alternative embodiment of an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant.
FIG. 6 is a sectional view of a multiplexed arrangement of three bicell membrane electrode assemblies employing ambient air as the oxidant and coolant, which share common ion exchange membranes.
Wo 95/17772 2 1. 7 9 0 3 4 PCT/CA94/00675 FIG. 7 is an exploded perspective view of a first embodiment of a thermally conductive member or fin c~hAsc~mhly for an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant, which employs a slidable comb for adjusting the conf iguration of the air conducting ~h~nn~-l c.
FIG. 8 is a perspective view of second nt of a thermally conductive member or f in s~lh~cc~mhly for an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant, which employs a pivotable baffle (shown in phantom lineS) for adjusting the flow through the air conducting channels.
FIG. 9 is a perspective view of a pivotable baffle subassembly for use in conjunction with the f in subassembly shown in FIG . 8 .
FIG. 10 is a side view of the pivotable baffle Ellh~cs.oTnhly shown in FIG. 9.
FIG. 11 is a schematic view of third embodiment of an electrochemical fuel cell assembly employing ambient air as the oxidant and coolant, which employs external dampers for adjusting the flow through the air conducting channels.
Det~ilea Description Of The Preferred Embodiment~
Referring first to FIG. 1 and FIG. 2~, an electrochemical fuel cell assembly lo, includes a bicelL membrane electrode assembly ("M~A") 14.
Bicell MEA 14 includes a f irst cathode 16, an anode 26, and a second cathode 38. A first ion exchange membrane 24 is interposed between first cathode 16 and anode 26. A second ion exchange membrane 34 is interposed between second cathode 38 and anode 26.
Wo 95/17772 2 ~ 7 q ~ 3 4 PCTICA94/00675 Fuel supply line 44 and fuel inlet 46 contain and direct fuel at a pressure slightly greater than ai ~ riC to anode 26.
The electrodes 16, 26, 38 are formed of porous 5 electrically conductive sheet material, preferably porous carbon fiber paper ("CFP") impregnated or coated with a hydrophobic polymer, such as polytetrafluoroethylene- The electrodes 16, 26, 38 are each treated with a layer of catalyst, such as 10 platinum or other suitable electrocatalytic material, on the surface(s) adjacent and in contact with the ion exchange membrane(s) 24, 34 to facilitate the desired chemical reaction. Suitable ion exchange membranes are commercially available 15 from DuPont under the trade name Nafion 117 and from DoW under the trade designation XUS 13204.10.
The electrodes 16, 26, 38 and the ion exchange membranes 24, 34 are arranged together in an interleaved or sandwich-like manner, as illustrated 20 in FIG. 1 and FIG. 2A, and placed in a high pressure press at a temperature suf f icient to soften the ion exchange membrane material. The combination of pressure and temperature forces the softened rnembrane material at least partialIy into 25 the CFP electrode material, bonding the individual layers to form a single unitary assembly.
Presently, the bicell I~EA 14 is formed by placing the layers of material in a press at a temperature and pressure suff icient to soften the material and 3 o create an intimate bond .
Low pressure can be employed to supply the gaseous fuel because the chemical reaction at the anode 26 consumes the fuel and draws it into the anode 2 6 . The porous structure of the CFP used to WO 951~7M2 2 1 7 9 ~ 3 4 PCT/CA94/00675 form the anode 26 facilitates the delivery of the gaseous fuel throughout the anode 26. The gaseous fuel reacts at the anode 26 to produce cations ~protons) and electrons. l~hen hydrogen is used as the f uel, the reaction at the anode produces hydrogen cations and electrons according to the following equation:
H2 ~ 2H+ + 2e-.
The reaction at the cathodes 16, 38 produces water according to the following equation:
1/2 2 + 2H I + 2e -- H2O.
The ion exchange membrane facilitates the migration of cations from the anode 26 to the cathodes 16, 38. In addition to conducting hydrogen cations, the ion exchange membranes 24, 34 isolate the gaseous fuel stream from the oxidant stream. This is particularly important when hydrogen is employed as a fuel source because of the reaction which occurs when hydrogen and oxygen are mixed and ignited or contacted with a catalyst.
A seal 50 provides a gas-impermeable barrier at the edges of the anode 2 6 to prevent leakage of the gaseous fuel from within anode 26. In FIG. 2~, the seal 50 is formed by extending the ion exchange membranes 24, 34 over the edges of the anode 26.
~uring the assembly process, the portions of the ion exchange membranes 24, 34 extending over the anode 26 can be adhered using heat and pressure to form a gas-impermeable seal around the anode 26.
Alternatively, as illustrated in FIG. 2B, the seal 50 may be formed by disposing layers of sealant 52a, 52~, such as a silicon based sealant, along the top and bottom edge portions, respectively, of anode 26 which extend between the ion exchange ~ WO 95117772 2 t 7 ~ ~ 3 ~ PCTtCA94tOo675 membranes z 4, 3 4 .
As shown in FIGS. 1, 2A and 2B, edge current collectors 56a, S6b are disposed between the anode 26 and the ion exchange membranes 24, 34. The first edge current collector 56a is disposed between the anode 2 6 and the f irst ion exchange membrane 2~, and the second edge current collector 56b is disposed between the anode 26 and the second ion exchange membrane 34. The edge current collectors 56a, 56b facilitate current flow (i.e., electron flow) from the anode 26 to an external load, as described in more detail below. As best shown in FIG. 2A, the edge current collectors 56a, 56b exit the bicell MEA 14 through the seal 50, thereby providing an electrical connection to the anode 2 6 .
Each of the edge current collectors 56a, 56b is preferably formed from a plurality of electrically conductive wires (not shown). The wires forming the edge current collectors 56a, 56b are in turn preferably formed from a highly conductive material such as gold, niobium, platinum, titanium or graphite. Although a single wire can provide suf f icient edge current collection, a plurality of wires is preferred. In FIG. 1, the conductive wires 56:~, 56b are shown exiting from both the top and bottom of the bicell MEA 14, whereas in FIGS. 2A and 23 the conductive wires only exit from the top of the bicell MEA 14.
As shown in FIGS. 1, 2A and 2B, the fuel cell assembly 10 further includes first and second thermally conductive plates 62a, 62b disposed on - opposite sides of the bicell MEA 14. The plates 62a, 62b are preferably constructed from aluminum WOg5/~7772 21 7 9 0 3 ~ PCT/C~94/00675 which is either milled or extruded to form the illustrated configuration. Aluminum is preferred because it is relatively inexpensive and lightweight and because it has ~avorable thermal 5 and electrical conductivity.
As shown in FIG. 1, each plate 62a, 62b includes a first set of thermally conductive members, shown in FIG. 1 as fins 66a, 66b, which extend toward the bicell MEA 14 and contact one of 10 cathodes (cathode 38 in FIG. 1 and FIG. 2A) and a second set of thermally conductive members, shown in FIG. 1 as fins 64a, 64b, which extend away from the bicell MEA 14 . The portion o~ each f in 66a, 66b which contacts the surface of a cathode is 15 preferably plated with gold to prevent oxidization of the aluminum and ensure good electrical contact between the cathode 38 and each f in 66a, 66b .
The f irst set of thermally conductive members 66a, 66b provide structural rigidity and support 20 for the bicell MEA 14, stabilize the MEA 14, and inhibit distortion of the MEA 14 from swelling due to oversaturation of the membrane.
Each of the second set of thermally conductive members, shown in FIG. 1 as fins 64a, 64b, could 25 also be formed as a thermally conductive foam, in lieu of the fins. Thermally conductive foam has an irregular three-dimensional conformation, with interstitial spaces permitting the passage of air and other coolant fluids through the irregular, 30 lattice-like structure of the thermally conductive material from which the foam if formed. The preferred thermally conductive foam is an aluminum f oam .
As shown in FIG. 1, a fastener mechanism WO95/17772 L ~ 7 9 ~3 4 PCT/CA94/00675 ecures the plates 62a, 62b and MEA 14 in assembled form and maintains contact between the fins 66a, 66b and the exposed surfaces of cathodes 16, 38.
The fastener r--h~nism preferably includes a first - 5 threaded fastener 72 extending through the upper portion of the plates 62a, 62b and a second threaded fastener 74 extending between the bottom portion of the plates 62a, 62b. The threaded fasteners 72, 74 connect the plates 62a, 62b and o allow the plates 62a, 62b to be clamped against the bicell MEA 14, thereby maintaining electrical and physical contact between the cathodes 16, 38 and the plates 62a, 62b.
Both sets of fins 64a, 64b and 66a, 66b are open at the top and bottom to allow air f low through the f ins . Heat produced by the exothermic chemical reaction of fuel (hydrogen) and oxidant (oxygen) within the bicell MEA 14 is dissipated to the a~ rh-~re through the fins 64a, 64b and 66a, 66b. It has been found that such heat dissipation produces a natural convection current which causes the ambient air to be drawn upwardly through the fins 64a, 64b and 66a, 66b. The set of fins 64a extend in a direction away from MEA 14, and function primarily as heat transfer surfaces for expelling waste heat to the atmosphere such that a desired operation temperature of the bicell MEA 14 is maintained. The sets of fins 66a, 66b, in addition to functioning as heat transfer surfaces, cooperate with the plates 62a, 62b and the adjacent cathodes to form a plurality of air conducting channels which draw oxygen-containing ambient air toward the exposed surface of the cathodes. For example, fins 66a cooperate with plate 62a and WO 95117772 2 1 7 ~ Q 3 4 PCT/C~94100675 cathode 16 to form an air conducting channel ~8 (see FIG. l). A similar plurality of air conducting channels draws oxygen-containing ambient air toward the exposed surface of cathode 38. The 5 vertical orientation of the air supply channels 78 allows the water produced at the cathode 16 to flow downwardly toward the bottom of the fuel cell assembly lO where it can be drained from the assembly, thereby preventing oversaturation of the lO ion exchange membrane 24.
In employing ambient air as the oxidant and coolant for the fuel cell assembly lO, the following operating conditions should be present:
(l) ambient air flow through the air conducting channels to provide a sufficient stoichiometric supply of reactant oxygen to support the reaction at the membrane electrode assembly;
(2) ambient air flow and operating temperature should be such that the water removal capacity of the ambient air f low is less than the rate of production of reactant water to prevent dehydration of the ion exchange membranes;
(3) the operating temperature of the cell should be high enough to provide reasonable fuel cell performance; and (4) the operating temperature of the fuel:
cell should be high enough to allow the cell to reject waste heat to the atmosphere by natural convection.
With these considerations in mind, the size, spacing, and number of members or fins is empirically optimized to provide temperature ~ WO 9S117772 2 1 7 ~ Q ~ 4 PCTICA94/00675 &tability and performance stability over a wide range of loads.
Turning now to FIG. 3, a plurality of the fuel cell assemblies, six of which are designated in - 5 FIG. 3 as assemblies 102, lob, loc, lOd, lOe, and lOf, can be combined to form a fuel cell stack loo.
Fuel inlets, one of which is designated in FIG. 3 as fuel inlet 146, each direct a fuel stream to one of the respective fuel cell assemblies lOa-f. The fuel inlets are connected to a main fuel supply line 104, which is in turn connected to a fuel supply source (not shown) for delivering gaseous fuel at a pressure slightly greater than atmospheric to the stack loo.
In FIG. 3, the fuel cells assemblies lOa-f are electrically connected in series so that the fuel cell stack loo produces a voltage potential equal to the sum of the voltages of the individual fuel cell assemblies lOa-f. More specifically, the edge 20 current collectors 156 are used to electrically couple the anode of one bicell MEA to the cathodes of the next adjacent bicell MEA in the stack lOo.
For example, in FIG. 3 the anode of the first fuel cell assembly lOa is electrically connected to the 25 cathodes of the second fuel cell assembly lob.
This electrical connection is preferably made by connecting the edge current collec~ors 156 from one fuel cell assembly to the plate 162 adjacent the next fuel cell assembly in the stack loo The full electrical potential of the stack loo is imposed between a positive lead 108 and a negative lead 110. The positive lead 108 is formed by connecting an electrical conductor 112 to a positively charged portion of the first cell lOa in WO 95/17M2 2 1 7 9 0 3 ~ PCT/CA94/00675 the stack lOo. Specifically, the positive lead 108 can be connected to either of the end plates, the f ins, the threaded f asteners, or the cathodes of the f irst cell lOa . The negative lead llo is 5 formed by joining the edge current collectors of the last fuel cell assembly lOf to form a single conductor 114.
As is illustrated schematically in FIG. 3, when the stack 100 is installed in an electrical circuit, a load 118 and a contactor switch 120 can be connected between the positive and negative leads 108, llo. The contactor switch 120 can be selectively opened and closed to deliver power from the stack loO to the load 118.
FIGS. 4A and 4B illustrate alternative embodiments for serially connecting individual bicell NEAs to form a stack conf iguration . In both FIGS. 4A and 4B, the electrodes of successive bicell MEAs are interleaved to form serial 20 electrical connections. Each bicell MEA 114 includes a center anode 116 interposed between two cathodes 120, 122. Two sheets of solid polymer ion exchange membranes 126, 128 are interposed between the anode 116 and the cathodes 120, 122. In FIG.
25 4~, sealant material 132 is disposed at both ends of the anode 116 to prevént leakage of the gaseous fuel supplied to the anode 116. In FIG. 4B, a single sheet of material is used to form ion exchange membranes 126, 128. The membrane material 30 is looped around one end of the anode 116 and sealant material 132 is used to seal the other end of the anode 116.
In both embodiments illustrated in FIGS. 41~
and 4B, the cathodes 120, 122 extend beyond one end Wo 95/17772 PCT/CA94~00675 2 ~ 72~Q34 of a respective anode 116 and are joined around an electrical conductor 136. The electrical conductor 136 in turn extends through the sealant 132 and into the anode 116 of the next bicell NEA 114b in 5 the stack.
FIG. 5 illustrates an alternative t~mhorlir r-t of a fuel cell assembly which employs ambient air as the oxidant and coolant. In FIG. 5, a unicell MEA 214 is employed as opposed to the bicell MEA
arrangement of FIGS. 1, 2A and 2B. MEA 214 includes an ion exchange membrane 224, which is interposed between anode 226 and cathode 216. A
seal 250, formed of sealant material disposed along the exterior surfaces of the anode 226, is also shown in FIG. 5. Seal 250 forms a gas-impermeable barrier to prevent leakage of gaseous fuel supplied to the anode 226. A fuel deliver~y me-~h~n;sm 244 delivers gaseous fuel (preferably substantially pure hydrogen) to the anode 226 of the unicell MEA
21~. The fuel delivery means 244 includes at least one fuel inlet 246 which extends partially into the anode 226. The fuel inlet 246 delivers gaseous fuel to the anode z26 at a low pressure or at slightly greater than atmospheric pressure.
In the t~mho~ nt illustrated in FIG. s, a clamping r~-h~ni~m 218 secures the plate 262, together with its fins 264, 266, against the cathode 216 of the unicell MEA 214. The clamping means 218 is illustrated in FIG. 5 as a pair of threaded fasteners 272, 274 and an end plate 220.
FIG. 6 shows a multiplexed arrangement 302 of three bicell assemblies employing ambient air as the oxidant and coolant. The multiplexed arrangement includes first cathodes 304a, 304b, ~VO 9511M72 2 1 7 ~ ~ 3 4 PCT/CA94100675 304e, anodes 306a, 306b, 306c, and second cathodes 314~, 314b, 31~e. As shown in FIG. 6, first cathode 304a, anode 306a and second cathode 31~1a are arranged in a first bicell MEA 310a, with first 5 ion exchange membrane 316 interposed between first anode 306~ and cathode 304a, and second ion exchange membrane 3Z6 interposed between anode 306a and second cathode 314a. Similarly, first cathode 30~b, anode 306b and second cathode 314b are o arranged in a second bicell MEA 310b, with first ion exchange membrane 316 interposed between f irst anode 306b and cathode 304b, and second ion exchange membrane 326 interposed between anode 306b and second cathode 314b. Finally, first cathode 1~ 304e, anode 306e and second cathode 314c are arranged in a third bicell MEA 310e, with first ion exchange membrane 316 interposed between first anode 306e and cathode 304e, and second ion exchange membrane 326 interposed between anode 306e 20 and second cathode 314e. As shown in FIG. 6, first, second and third bicell assemblies 310a, 310b, 310e share a common f irst ion exchange membrane 316 and a common second ion exchange membrane 326. FIG. 6 also shows the location of 25 one of the thermally conductive member or fin subassemblies 360. Fin sl,h~ccPmhly 360 includes a thermally conductive plate 362, a first set of thermally conductive members or fins 366, which extend toward bicell MEA 310b and contact cathode 30 304b, and a second set of thermally conductive _ members or fins 364, which extend away from bicell MEA 310b. Channels 332a and 332b are the fuel flow ~ h~nnPl ~ which interconnect the anodes in the multiplexed arrangement 302 shown in F~G. 6.
WO 95/17772 2 1 7 9 a 3 4 PCTtC~94/00675 .
Multiplexed arrangement 302 is sealed on both ends by seals 320a, 320b, preferably formed by the fusing together of first and second ion exchange membranes 316, 326.
- s FIG. 7 shows a thermally conductive member or fin cllh~ccP~hly 460 which employs a slidable comb ~,62 for adjusting the conf iguration of the air conducting rh~nnPl c The air conducting channels are formed by the spaces between the fins, one of which is designated in FIG. 7 as fin 466a. As shown in FIG. 7, slidable comb 462 includes a plurality of tines 462a, which extend into the t~h~nnPl c formed by the spaces between the fins.
FIG. 8 shows another fin subassembly 560 which employs pivotable baffles (one of which is shown in phantom lines in FIG. 8 as baffle 574a) Fin 51lh~ccPTnhl y 560 includes a thermally conductive plate 562. A plurality of thermally conductive fins 566~, 566b, 566c, 566d extend from one major surface of plate 562. In the completed fuel cell assembly incorporating fin subassembly 560, fins 566a-d contact the outwardly facing surface of the adjacent cathode ~not shown in FIG. 8) A
plurality of thermally conductive fins 564a, 564b, 564c, 56~d, 564e, 564f extend from the other major surface of plate 562. Each of fins 564a-f has a slotted opening formed therein, one of which is shown in FIG. 8 as slot 570. A pivotable baffle subassembly, one baffle of which is shown in FIG. 8 as baffle 57~a, is suspended in the slots by pivot pin 572. Rotation of baffle 574a about pivot pin 572 regulates the amount of air flow through the air conducting channels.
Arrows ~ in FIG. 8 show the direction of air WO 95/17772 2 ~ 7 9 ~ 3 J PCr/CA94/0067~ ~
flow through the channels formed between fins s66;~-d., and represent the air supply for the electrochemical reaction at the adjacent cathode (not shown). Arrow B in FIG. 8 shows the direction 5 of air flow through the channels formed between fins 564~-f, and represents the air supply for conducting heat from the adjacent fuel cell structure (not shown), thereby providing thermal management to the adjacent fuel cell structure.
FIG. 9 shows pivotable baffle stlh~qc~mhly 574 for use in conjunction with the fin sl~h~ mhly 560 in FIG. 8. Subassembly S74 includes a plurality of baffles 574a, 57~b, S74c mounted on central pivot pin 572. FIG. lo shows a side view of pivotable 15 baffle subassembly 574.
FIG. 11 shows schematically an electrochemical ~uel cell assembly employing ambient air as the oxidant and coolant, which employs external dampers - 676, 678 having pivotable baffles 674, 684, respectively, for adju5ting the flow through the air conducting channels 664, 666. In FIG. 11, anode 626, ion exchange membrane 624 and cathode 616 form the membrane electrode assembly. Fins (not shown) extend from each major surface of plate 662. The spaces formed between the extending fins form air conducting channels 664, 666. Dampers 676, 678 include baffles 674, 684, which are mounted on pivot pins 672, 682, respectively.
Rotation of baffle 674, 684 about the respective pivot pins 672, 682 regulates the amount of air flow through the air conducting channels 664, 666.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be unders~ood, of _ Wo 95/17772 2 1 7 9 0 3 ~ PCT/CA94~aO675 course, that the invention is not limited thereto since modif ications may be made ~y those skilled in the art, particularly in light of the foregoing teachings. It is therefore contemplated by the 5 appended claims to cover such modif ications as incorporate those features which come within the spir~t and scope of the in~ention.
Claims (30)
1. An electrochemical fuel cell assembly comprising:
a membrane electrode assembly comprising a porous electrically conductive anode, a porous electrically conductive cathode having a surface thereof exposed to ambient air, and an ion exchange membrane interposed between said anode and said cathode;
sealant means for forming a gas-impermeable barrier around said anode:
fuel delivery means for supplying a gaseous fuel stream to said anode;
electrical connection means for providing an electrical connection to said anode and to said cathode;
a thermally conductive plate having a major surface contacting the atmosphere, said plate having a plurality of first thermally conductive members extending from a major surface thereof, said first members contacting portions of said exposed cathode surface, adjacent ones of said first members cooperating with said plate and said exposed cathode surface to form at least one air conducting channel.
a membrane electrode assembly comprising a porous electrically conductive anode, a porous electrically conductive cathode having a surface thereof exposed to ambient air, and an ion exchange membrane interposed between said anode and said cathode;
sealant means for forming a gas-impermeable barrier around said anode:
fuel delivery means for supplying a gaseous fuel stream to said anode;
electrical connection means for providing an electrical connection to said anode and to said cathode;
a thermally conductive plate having a major surface contacting the atmosphere, said plate having a plurality of first thermally conductive members extending from a major surface thereof, said first members contacting portions of said exposed cathode surface, adjacent ones of said first members cooperating with said plate and said exposed cathode surface to form at least one air conducting channel.
2. The electrochemical fuel cell of claim 1, wherein said plate is formed as a single planar piece.
3. The eloctrochemical fuel cell of claim 1, wherein said plate and said first members are formed of aluminum, the portions of said first members contacting said cathode surface having an inert metal applied thereto.
4. The electrochemical fuel cell of claim 3, wherein said inert metal is gold.
5. The electrochemical fuel cell assembly of claim 1, wherein said electrical connection means comprises electrical conductors disposed between said anode and said ion exchange membrane, said electrical conductors extending through said sealing means.
6. The electrochemical fuel cell of claim 5, wherein said electrical conductors are formed from gold wire.
7. The electrochemical fuel cell assembly of claim 1, wherein said plate has a thermally conductive material extending from another major surface thereof, whereby heat generated exothermically in said membrane electrode assembly is further dissipated to the atmosphere through said material.
8. The electrochemical fuel cell assembly of claim 7, wherein said material comprises a plurality of thermally conductive members.
9. The electrochemical fuel cell assembly of claim 7, wherein said material comprises a thermally conductive foam.
10. The electrochemical fuel cell assembly of claim 9, wherein said thermally conductive foam is an aluminum foam.
11. The electrochemical fuel cell assembly of claim 1, wherein said fuel delivery means comprises a fuel inlet and a fuel outlet, said fuel outlet directing unreacted components of said gaseous fuel stream away from said anode.
12, The electrochemical fuel cell assembly of claim 1, further comprising a fan for directing said ambient air onto the exposed surface of said porous electrically conductive cathode.
13. The electrochemical fuel cell assembly of claim 1, said assembly further comprising means for accumulating water condensed on said first members.
14. A fuel cell stack comprising:
a plurality of fuel cell assemblies as defined in claim 1:
serial connection means for electrically connecting said plurality of fuel cell assemblies in an electrical series having a first assembly and a last assembly, wherein the anode of each assembly except the last assembly in said series is electrically connected to the cathode of the next adjacent assembly in said series;
a positive current lead electrically connected to the cathode of said first assembly in said series and a negative current lead electrically connected to the anode of the last assembly in said series.
a plurality of fuel cell assemblies as defined in claim 1:
serial connection means for electrically connecting said plurality of fuel cell assemblies in an electrical series having a first assembly and a last assembly, wherein the anode of each assembly except the last assembly in said series is electrically connected to the cathode of the next adjacent assembly in said series;
a positive current lead electrically connected to the cathode of said first assembly in said series and a negative current lead electrically connected to the anode of the last assembly in said series.
15. The fuel cell stack of claim 14, wherein said plurality of fuel cell assemblies share a common ion exchange membrane.
16. An electrochemical fuel cell assembly comprising:
a bicell membrane electrode assembly comprising a first porous electrically conductive cathode having a surface thereof exposed to ambient air, a porous electrically conductive anode, a second porous electrically conductive cathode having a surface thereof exposed to ambient air, a first ion exchange membrane interposed between said first cathode and said anode, and a second ion exchange membrane interposed between said second cathode and said anode;
sealing means for forming a gas-impermeable barrier around said anode fuel delivery means for delivering gaseous fuel to said anode;
electrical connection means for providing an electrical connection to said anode, to said cathode, and to said second cathode:
a first thermally conductive plate having a plurality of first thermally conductive members extending from a major surface thereof, said first members contacting portions of said exposed first cathode surface, adjacent ones of said first members cooperating with said first plate and said exposed first cathode surface to form at least one air conducting channel;
a second thermally conductive plate having a plurality of second thermally conductive members extending from a major surface thereof, said second members contacting portions of said exposed second cathode surface, adjacent ones of said second members cooperating with said second plate and said exposed second cathode surface to form at least one air conducting channel.
a bicell membrane electrode assembly comprising a first porous electrically conductive cathode having a surface thereof exposed to ambient air, a porous electrically conductive anode, a second porous electrically conductive cathode having a surface thereof exposed to ambient air, a first ion exchange membrane interposed between said first cathode and said anode, and a second ion exchange membrane interposed between said second cathode and said anode;
sealing means for forming a gas-impermeable barrier around said anode fuel delivery means for delivering gaseous fuel to said anode;
electrical connection means for providing an electrical connection to said anode, to said cathode, and to said second cathode:
a first thermally conductive plate having a plurality of first thermally conductive members extending from a major surface thereof, said first members contacting portions of said exposed first cathode surface, adjacent ones of said first members cooperating with said first plate and said exposed first cathode surface to form at least one air conducting channel;
a second thermally conductive plate having a plurality of second thermally conductive members extending from a major surface thereof, said second members contacting portions of said exposed second cathode surface, adjacent ones of said second members cooperating with said second plate and said exposed second cathode surface to form at least one air conducting channel.
17. The electrochemical fuel cell of claim 16, wherein said plate and said first and second members are formed of aluminum, the portions of said first and second members contacting said cathode surface having an inert metal applied thereto.
18. The electrochemical fuel cell of claim 17, wherein said inert metal is gold.
19. The electrochemical fuel cell assembly of claim 16, wherein said electrical connection means comprises first electrical conductors disposed between said anode and said first membrane, and second electrical conductors disposed between said anode and said second membrane, said first and second electrical conductors extending through said sealing means.
20. The electrochemical fuel cell of claim 19, wherein said first and second electrical conductors are formed from gold wire.
21. The electrochemical fuel cell assembly of claim 16, wherein said first plate has a first thermally conductive material extending from another major surface thereof and wherein said second plate has a second thermally conductive material extending from another major surface thereof, whereby heat generated exothermically in said membrane electrode assembly is further dissipated to the atmosphere through said first and second material.
22. The electrochemical fuel cell assembly of claim 21, wherein said first and second material each comprises a plurality of thermally conductive members.
23. The electrochemical fuel cell assembly of claim 21, wherein said material comprises a thermally conductive foam.
24. The electrochemical fuel cell assembly of claim 23, wherein said thermally conductive foam is an aluminum foam.
25. The fuel cell assembly as in claim 16, wherein said sealing means comprises said first and second membranes, the edges of the first and second membranes bonded together to form a gas-impermeable barrier around said anode.
26. The electrochemical fuel cell assembly of claim 16, wherein said fuel delivery means comprises a fuel inlet and a fuel outlet, said fuel outlet directing unreacted components of said gaseous fuel stream away from said anode.
27. The electrochemical fuel cell assembly of claim 16, further comprising a fan for directing said ambient air onto the exposed surface of said porous electrically conductive cathode.
28. The electrochemical fuel cell assembly of claim 16, said assembly further comprising means for accumulating water condensed on said first members.
29. A fuel cell stack comprising:
a plurality of fuel cell assemblies as defined in claim 16;
serial connection means for electrically connecting said plurality of fuel cell assemblies in an electrical series having a first assembly and a last assembly, wherein the anode of each assembly except the last assembly in said series is electrically connected to the cathodes of the next adjacent assembly in said series;
a positive current lead electrically connected to the cathodes of said first assembly in said series; and a negative current lead electrically connected to the anode of the last assembly in said series.
a plurality of fuel cell assemblies as defined in claim 16;
serial connection means for electrically connecting said plurality of fuel cell assemblies in an electrical series having a first assembly and a last assembly, wherein the anode of each assembly except the last assembly in said series is electrically connected to the cathodes of the next adjacent assembly in said series;
a positive current lead electrically connected to the cathodes of said first assembly in said series; and a negative current lead electrically connected to the anode of the last assembly in said series.
30. The fuel cell stack of claim 29, wherein said plurality of fuel cell assemblies share a common first ion exchange membrane and a common second ion exchange membrane.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/171,732 US5470671A (en) | 1993-12-22 | 1993-12-22 | Electrochemical fuel cell employing ambient air as the oxidant and coolant |
| US08/171,732 | 1993-12-22 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2179034A1 CA2179034A1 (en) | 1995-06-29 |
| CA2179034C true CA2179034C (en) | 1999-01-05 |
Family
ID=22624922
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002179034A Expired - Fee Related CA2179034C (en) | 1993-12-22 | 1994-12-07 | Electrochemical fuel cell employing ambient air as the oxidant and coolant |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5470671A (en) |
| EP (1) | EP0736226B1 (en) |
| JP (1) | JP2777287B2 (en) |
| AU (1) | AU680577B2 (en) |
| CA (1) | CA2179034C (en) |
| DE (1) | DE69417442T2 (en) |
| WO (1) | WO1995017772A1 (en) |
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-
1993
- 1993-12-22 US US08/171,732 patent/US5470671A/en not_active Expired - Fee Related
-
1994
- 1994-12-07 AU AU11888/95A patent/AU680577B2/en not_active Ceased
- 1994-12-07 WO PCT/CA1994/000675 patent/WO1995017772A1/en active IP Right Grant
- 1994-12-07 CA CA002179034A patent/CA2179034C/en not_active Expired - Fee Related
- 1994-12-07 DE DE69417442T patent/DE69417442T2/en not_active Expired - Fee Related
- 1994-12-07 JP JP7517061A patent/JP2777287B2/en not_active Expired - Fee Related
- 1994-12-07 EP EP95902722A patent/EP0736226B1/en not_active Expired - Lifetime
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| Publication number | Publication date |
|---|---|
| JP2777287B2 (en) | 1998-07-16 |
| DE69417442T2 (en) | 1999-08-19 |
| EP0736226B1 (en) | 1999-03-24 |
| WO1995017772A1 (en) | 1995-06-29 |
| EP0736226A1 (en) | 1996-10-09 |
| AU680577B2 (en) | 1997-07-31 |
| US5470671A (en) | 1995-11-28 |
| AU1188895A (en) | 1995-07-10 |
| CA2179034A1 (en) | 1995-06-29 |
| DE69417442D1 (en) | 1999-04-29 |
| JPH09503619A (en) | 1997-04-08 |
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