Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
  • B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
  • B01D63/08—Flat membrane modules
• • 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
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0223—Composites
  • H01M8/0228—Composites in the form of layered or coated products
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2317/00—Membrane module arrangements within a plant or an apparatus
  • B01D2317/02—Elements in series
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2317/00—Membrane module arrangements within a plant or an apparatus
  • B01D2317/04—Elements in parallel
• • 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
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0206—Metals or alloys
• • 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
  • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
  • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous 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
• • 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

Definitions

• the present invention relates in general to the field of proton exchange membrane (“PEM”) fuel cell stack assemblies, and more particularly, to an improved polarized gas separator for use in the bipolar construction of fuel cell stack assemblies.
• a fuel cell is an electrochemical device that converts fuel and oxidant into electricity and a reaction by-product through an electrolytic reaction that strips hydrogen molecules of their electrons and protons. Ultimately, the stripped electrons are collected into some form of usable electric current, by resistance or by some other suitable means. The protons react with oxygen to form water as a reaction by-product.
• Natural gas is the primary fuel used as the source of hydrogen for a fuel cell. If natural gas is used, however, it must be reformed prior to entering the fuel cell. Pure hydrogen may also be used, if stored correctly.
• the products of the electrochemical exchange in the fuel cell are DC electricity, liquid water, and heat.
• the overall PEM fuel cell reaction produces electrical energy equal to the sum of the separate half-cell reactions occurring in the fuel cell, less its internal and parasitic losses. Parasitic losses are those losses of energy that are attributable to any energy required to facilitate the ternary reactions in the fuel cell.
• Fuel cells have been used in a few applications, engineering solutions to successfully adapt fuel cell technology for use in electric utility systems have been elusive. The challenge is for the generation of power in the range of 1 to 100 kW that is affordable, reliable, and requires little maintenance. Fuel cells would be desirable in this application because they convert fuel directly to electricity at much higher efficiencies than internal combustion engines, thereby extracting more power from the same amount of fuel. This need has not been satisfied, however, because of the prohibitive expense associated with such fuel cell systems. For example, the initial selling price of the 200 kW PEM fuel cell was about $3500/kW to about $4500/kW. For a fuel cell to be useful in utility applications, the life of the fuel cell stack must be a minimum of five years and operations must be reliable and maintenance-free.
• Fuel cells are usually classified according to the type of electrolyte used in the cell. There are four primary classes of fuel cells: (1) proton exchange membrane (“PEM”) fuel cells, (2) phosphoric acid fuel cells, and (3) molten carbonate fuel cells. Another more recently developed type of fuel cell is a solid oxide fuel cell. PEM fuel cells, such as those in the present invention, are low-temperature, low-pressure systems, and are, therefore, well-suited for residential and light commercial applications. PEM fuel cells are also advantageous in these applications because there is no corrosive liquid in the fuel cell and, consequently, there are minimal corrosion problems.
• PEM proton exchange membrane
• a single PEM fuel cell consists of three major components - an anode gas dispersion field ("anode”); a membrane electrode assembly (“MEA”); and a cathode gas and liquid dispersion field (“cathode”).
• the anode typically comprises an anode gas dispersion layer 106 and an anode gas flow field 104;
• the cathode typically comprises a cathode gas and liquid dispersion layer 110 and a cathode gas and liquid flow field 112.
• the anode and the cathode are electrically coupled to provide a path for conducting electrons between the electrodes through an external load.
• MEA 108 facilitates the flow of electrons and protons produced in the anode, and substantially isolates the fuel stream on the anode side of the membrane from the oxidant stream on the cathode side of the membrane.
• the ultimate purpose of these base components, namely, the anode, the cathode, and MEA 108, is to maintain proper ternary phase distribution in the fuel cell.
• Ternary phase distribution as used herein refers to the three simultaneous reactants in the fuel cell, namely, hydrogen gas, water vapor, and air.
• PEM fuel cells have not been able to efficiently maintain proper ternary phase distribution.
• Catalytic active layers 100 and 102 are located between the anode, the cathode, and the electrolyte.
• the catalytic active layers 100 and 102 induce the desired electrochemical reactions in the fuel cell. Specifically, catalytic active layer 100, the anode catalytic active layer, rejects the electrons produced in the anode in the form of electric current. The oxidant from the air that moves through the cathode is reduced at the catalytic active layer 102, referred to as the cathode catalytic active layer, so that it can oxidate the protons flowing from anode catalytic active layer 100 to form water as the reaction by-product. The protons produced by the anode are transported by the anode catalytic active layer 100 to the cathode through the electrolyte polymeric membrane.
• the anode gas flow field and cathode gas and liquid flow field are typically comprised of pressed, polished carbon sheets machined with serpentine grooves or channels to provide a means of access for the fuel and oxidant streams to the anode and cathode catalytic active layers.
• the costs of manufacturing these plates and the associated materials costs are very expensive and have placed constraints on the use of fuel cells in residential and light commercial applications.
• the use of these planar serpentine arrangements to facilitate the flow of the fuel and oxidant through the anode and cathode has presented additional operational drawbacks in that they unduly limit mass transport through the electrodes, and therefore, limit the maximum power achievable by the fuel cell.
• the anode disburses the anode gas onto the surface of the catalytic active layer, which is comprised of a platinum catalyst electrolyte
• the cathode disburses the cathode gas onto the surface of the cathode catalytic active layer of the electrolyte.
• the anode gas and the cathode gas are not uniformly disbursed onto these layers.
• Nonuniform distribution of the anode and cathode gas at the membrane surfaces results in an imbalance in the water content of the electrolyte. This results in a significant decrease in efficiency in the fuel cell.
• the second most problematic drawback associated with serpentine arrangements in the electrodes relates to the ternary reactions that take place in the fuel cell itself. Serpentine arrangements provide no pressure differential within the electrodes. This prohibits the necessary ternary reactions from taking place simultaneously. This is particularly problematic in the cathode as both a liquid and a gas are transported simultaneously through the electrode's serpentine pattern.
• Figure 2 is an illustration of a conventional frame for the communication of the reactants to a fuel cell.
• This pressure differential causes the reactants, especially the fuel, to be fed into the flow fields unevenly, which results in distortions in the flow fields, ultimately causing hot spots. This also results in nonuniform disbursement of the reactants onto the catalytic active layers.
• this conventional method of supplying the necessary fuel and oxidant to a fuel cell results in a very inefficient process.
• PEM Proton Exchange Membrane
• bipolar separator plates are used between adjacent individual cells. More specifically, in these bipolar plates, one side of the plate serves as the anode side and services the anode side of one fuel cell assembly; and the other side of the plate serves as the cathode side and services the cathode side of another fuel cell assembly. This is often described as bipolar construction.
• a barrier to free water and gas flow between the two sides of the bipolar plate exists to keep the hydrogen gas flow and the oxygen gas flow separate from one another.
• a bipolar plate also collects electrons liberated at one electrode, conducts the electrons through the barrier plate, and delivers the electrons to the face of the other electrode on the opposing side of the barrier.
• a first gas flow field an internal barrier or separator plate
• a second gas flow field specifically a gas and liquid flow field (both referred to in the following generically as flow fields).
• the flow fields are made from sheets constructed from metals, such as titanium, nickel, and stainless steel, or nonmetallic conductors, such as graphitic carbon. These sheets typically have a series of channels or grooves machined into their surfaces that allow for the passage of gases and liquids such as those described above. These channels or grooves are usually arranged in a serpentine-like pattern, and thus, are subject to the difficulties and problems described above.
• the internal barriers or separator plates of conventional assemblies are often fabricated from graphite or metal, such as stainless steel, titanium, or nickel as well.
• the internal barrier or separator plate and the gas flow fields are mechanically bonded together.
• the bonding mechanism has historically been sintering. Whenever the gas flow fields are bonded to the internal barrier or separator plate by mechanical means, the electrical resistance in the bipolar plate increases, which leads to efficiency losses in the fuel cell stack assembly. Typically, the resistance in such bipolar plates is at best 3.4 ohms. This is undesirable, as excessive resistance diminishes the power potential of the fuel cell stack.
• the mechanical bonding may also be problematic if not completely accurate because air gaps may be created between the flow fields and the internal barrier.
• Another problem with conventional bipolar plates is that the mechanical bonding process can introduce contaminants, which are primarily oxidants, into these metallurgical bonds between the flow fields and the internal barrier, which thereby contaminate the system and cause efficiency losses. This is also undesirable.
• bipolar flow field assembly that is suitable for use in bipolar construction of a fuel cell stack assembly, that introduces minimal resistance to the system, that separates the reactant gases completely, that effectively manages heat and produced water on both sides of the bipolar assembly itself, and that can be mass produced efficiently and economically.
• the present invention provides a polarized gas separator comprising a flow field that may function as a bipolar flow field mechanism useful in the bipolar construction of a fuel stack assembly that is not only easy to manufacture in a mass production operation, but also reduces resistance, increases cell power potential, effectively manages heat and water within the separator itself, and facilitates a more effective distribution of the reactants to their respective catalytic active layers. It is greatly improved over conventional bipolar plate assemblies commonly used in bipolar construction, as it is a single component system having improved electrical connectivity and conductivity.
• the present invention comprises a polarized gas separator comprising a porous conductive substrate and a barrier layer, the barrier layer having a first side and a second side, and laterally extending through the porous conductive substrate so that a first portion of the porous conductive substrate extends from the first side of the barrier layer and a second portion of the porous conductive substrate extends from the second side of the barrier layer.
• the present invention provides a single component laterally bisected to effectively create a three-component system without disturbing the electrical properties of the single component.
• the polarized gas separator of the present invention is greatly improved over conventional bipolar plate assemblies as it is a single-component system rather than a composition of three components.
• the present invention provides one layer of material in a configuration that allows it to function as both an anode flow field and a cathode flow field, but the component itself is unbroken. Because the polarized gas separator of the present invention is a single component, it avoids the resistance problems encountered in manufacturing conventional assemblies. In fact, it is now possible to achieve 1.5 x 10 "4 ohms of resistance or less within the separator. This is a great improvement over conventional bipolar plate assemblies, which have an internal resistance of at least 3.4 ohms. This single component system also increases connectivity and conductivity within the separator itself. Furthermore, the separator of the present invention is able to effectively seal the reactant gases from each other.
• polarized gas separator of the present invention may be used in conjunction with the distribution frame and fuel cell stack assemblies described in U.S. Application No. 09/669,344, filed September 26, 2000.
• Suitable materials for the porous conductive substrate include, but are not limited to: metal wool; wire mesh; three-dimensional open-cell foamed structures; carbon filaments; other conductive metal substrates; and aerated nickel wool.
• Suitable construction materials for the materials include: hastelloys, inconel, nickel, conductive plastics, metal composites, metal and plastic composites, plastic composites, tin oxides, stainless steel, and their derivatives.
• any material that has sufficient porosity and surface texture is suitable in the present invention.
• a typical construction material for the barrier layer is a thermal-setting epoxy. The flexibility of the design of this polarized gas separator enhances the desirability of the present invention, especially as the push for affordable fuel cell operations for residential use increases.
• Figure 1 is a schematic of a typical PEM fuel cell assembly.
• Figure 2 is an illustration of a conventional frame for housing and supplying reactants to a fuel cell assembly.
• Figure 3 is an edge-on view of an embodiment of the polarized gas separator of the present invention wherein the porous conductive substrate is corrugated.
• Figure 4 is a top view of an embodiment of the polarized gas separator of the present invention wherein the porous conductive substrate is corrugated.
• Figure 5 is an exploded view of an embodiment of a fuel cell assembly of the present invention.
• Figure 6 is an edge-on view of an embodiment of the polarized gas separator of the present invention wherein the porous conductive substrate is continuously-folded.
• Figure 7 is a top view of an embodiment of the polarized gas separator of the present invention wherein the porous conductive substrate is continuously- folded.
• Figure 8 is an edge-on view of an embodiment of the polarized gas separator of the present invention wherein the porous conductive substrate is discontinuously-folded.
• Figure 9 is a top view of an embodiment of the present invention wherein the porous conductive substrate is discontinuously-folded.
• Shown generally at 300 in Figure 3 is an edge-on view of one embodiment of the polarized gas separator of the present invention. Shown in Figure 3 are the primary components of the polarized gas separator, porous conductive substrate 302, and barrier layer 304.
• Porous conductive substrate 302 is essentially a flow field that, in this particular embodiment, has rounded corrugations created by peaks and troughs in the flow field.
• a corrugated porous conductive substrate is one configuration of the porous conductive substrate that enables the polarized gas separator to be suitable for bipolar construction of a fuel cell stack assembly.
• the rounded corrugations have a pitch and a run that are defined by the peaks and the troughs of the corrugations.
• FIG. 4 illustrates these microchannels at 402. If used in conjunction with the distribution frame described in U.S. Application No. 09/669,344, filed September 26, 2000 and shown generally at 500 in Figure 5, these microchannels run parallel to the air inlet 502 and the air and water outlet and perpendicular to fuel inlets 504. Because the microchannels run parallel to the air and water outlet, the microchannels can effectively remove the water from the anode side flow field and the cathode side flow field out air and water outlet 506.
• This corrugated configuration for the porous conductive substrate provides for effective management of the liquid-phase water in the anode side, previously unaddressed by conventional bipolar plate assemblies. It also provides for effective water management in the cathode side flow field.
• barrier layer 304 laterally spans porous conductive substrate 302 and effectively bisects it so that a portion of porous conductive substrate 302 extends from the top side of barrier layer 304 and a second portion of porous conductive substrate 302 extends from the bottom side of barrier layer 304.
• the bisected portions of the porous conductive substrate extending from the barrier layer may or may not be equal in size. Preferably, however, the bisected portions should be approximately equal in size, or one side may be approximately half the size of the other side if the smaller side is used as the anode side.
• the barrier layer material effectively and completely fills the porous holes of porous conductive substrate 302 to prevent the passage of the gas reactants through the barrier layer but does not destroy the integrity of porous conductive substrate 302. Continuous electrical conductivity is maintained through porous conductive substrate 302 on both sides of barrier layer 304 despite the presence of barrier layer 304 because the electrical conductivity of the porous conductive substrate is not interrupted by barrier layer 304.
• the holes in the porous conductive substrate at the intersections between the porous conductive substrate and the barrier layer are full of the barrier material, and therefore, the reactant gases cannot pass through the barrier; but the electrical connections between the anode side and the cathode side of the porous conductive substrate are continuous because there is no interruption in the flow field despite the presence of barrier layer 304. Gases cannot penetrate barrier layer 304, and therefore, the reactant gases are effectively sealed from one another; however, because of the porosity and surface texture of porous conductive substrate 302, the reactant gases can move relatively freely within the two flow fields themselves that are formed by barrier layer 304, and are able to diffuse to the respective catalytic active layers of the membrane electrode assembly ("MEA") effectively.
• MEA membrane electrode assembly
• barrier layer 304 may act as an insulator, and depending on the particular construction material used for barrier layer 304, the barrier layer may in fact enhance the electrical continuity of the porous conductive substrate because it has no electrical properties of its own that detract from the electrical continuity within the flow field.
• the structure of the polarized gas separator of the present invention requires no mechanical bonding mechanism, and therefore, electrical continuity is enhanced because resistance is not introduced via a bonding mechanism. Further, there are no air gaps in the connections between the flow fields and the barrier, as is often the case in conventional bipolar assemblies that would ordinarily create added resistance. A substantial reduction in disruptive electrical resistance is achieved as a result of this design.
• Barrier layer 304 can be comprised of any thermal setting nonconductive thermoplastic that has sufficient insulating properties.
• barrier layer 304 is a thermal setting epoxy or an epoxy derivative. Epoxy is preferred because of its good insulating properties and because of its suitable lack of electrical properties.
• the materials used as or to form barrier layer 304 should have no porosity and, preferably, should be completely dense. Most preferably, barrier layer 304 should be a monolithic layer.
• barrier layer 304 may be formed by a hardened formerly fluid composition such as a thermosetting thermoplastic; it is also contemplated that barrier layer 304 may be formed by a material that is able to completely seal the two portions of the flow field when used in its original form as long as it is able to bisect the porous conductive substrate, seal the reactant gases from each other effectively, and fill the holes in the porous conductive substrate at the intersections between the substrate and the barrier layer without disturbing the electrical properties of the porous conductive substrate.
• the preferable thickness of barrier layer 304 is about V ⁇ of the height or pitch of porous conductive substrate 302.
• this thickness may vary, one must be conscious of the potential for voids in the barrier layer if it is made too thin. Also, thicker barriers may lead to a loss in area in the flow field—a loss in area in a flow field could possibly lead to problems in distributing the reactants to their designated catalytic active layers.
• Porous conductive substrate 302 can be made from a variety of different materials that may be, in turn, comprised of a variety of construction materials that may take on a variety of different configurations as illustrated in Figures 3, 6, and 8.
• the materials that can be used as the porous conductive substrate include, but are not limited to: metal wool; wire mesh; three-dimensional open-cell foamed structures suitable for gas diffusion; and aerated nickel wool.
• the two main criteria that are useful in choosing which particular material is suitable for porous conductive substrate 302 are: (1) sufficient porosity, and (2) adequate surface textures.
• the pitch of the corrugations be equal to about five to six times the thickness of the material that forms the substrate, and the run of the corrugations be equal to about two to three times the thickness of the material.
• the number of peaks and troughs is dictated by the total length of the flow field based on these parameters. Of course, these specifications may be varied if suitable for the intended use.
• the advantage obtained from utilizing a three-dimensional open-cell foamed flow field in the present invention is that mass transfer within the resultant flow fields is enhanced. This is because the mass transfer rate is supplemented by the foamed flow field itself and its wicking ability, which allows the molecules to electromosatically move through the flow field.
• Another advantage associated with the foamed flow fields over conventional serpentine arrangements is that they facilitate the deposit of the reactants uniformly along the surfaces of the catalytic active layers.
• Suitable construction materials for the above materials possess good electrical conductivity properties are conducive to flow distribution and include, but are not limited to: hastelloys, inconel, nickel, copper, conductive plastics, metal composites, plastic composites, tin oxides, gold, epitaxial substrates, stainless steel, and their derivatives. Iridium may also be used if it has sufficient electrical properties. Stainless steel 416, however, does not appear to be suitable at this time because of the potential for staining; staining is undesirable. If, for example, a plating technique or some other technique were developed that combated the potential for stainless steel 416 to stain, then it would be a suitable construction material. Other construction materials may be suitable as well. Another specific example of a suitable material of construction is a plastic material having sufficient porosity wherein carbon fibers have been imbedded so that it also has sufficient electrical properties.
• porous conductive substrate Suitable configurations for the porous conductive substrate include but are not limited to: corrugated (as shown in Figure 3), continuously-folded (as shown in Figure 6), and discontinuously-folded (as shown in Figure 8). Although these three seem especially suitable configurations for the porous conductive substrate of the polarized gas separator, other configurations that may or may not be variations of these, are also contemplated within the present invention.
• Figure 6 depicts an edge-on view of an alternative embodiment of the polarized gas separator having a corrugated porous conductive substrate of the present invention wherein the porous conductive substrate is a continuously-folded porous conductive substrate.
• the continuously-folded porous conductive substrate embodiment of the present invention may be an improvement over the corrugated embodiment having rounded peaks in some instances as a result of the substantially flat top surfaces and bottom surfaces of the resultant corrugations or folds that provide a larger contact area with the contiguous layers of the fuel cell assembly.
• the continuously-folded embodiment is another version of a corrugated flow field wherein the peaks created by the peaks and troughs are square rather than rounded.
• the peaks and troughs in the continuously-folded substrate have a pitch and a run that are defined by the substantially flat top surfaces, the substantially flat bottom surfaces, and the substantially vertical portions of the corrugations in the continuously-folded substrate.
• the vertical portion of the folds should be substantially perpendicular and connected to the top and bottom surfaces.
• the pitch is equal to about five to six times the thickness of the material used to form the porous conductive substrate.
• the run which is the length of the horizontal top or bottom surface of an individual fold, is equal to about two to three times the thickness of the material used to form porous conductive metal substrate 12.
• FIG. 8 depicts another alternative embodiment of the polarized gas separator of the present invention wherein a discontinuously-folded porous conductive substrate is used.
• the discontinuously-folded configuration is made up of independent pods 802 formed from a chosen material that is porous and conductive. The same materials and construction materials discussed above for the corrugated embodiment may also be used in this embodiment. Additionally, each pod can be constructed from the same or a different material, and the same or a different construction material.
• the pods are concentrically folded and arranged along a horizontal axis defined by barrier layer 804. The pods have a pitch and a run that are defined by the length of the horizontal top and bottom surfaces of each pod and the height of that pod.
• the pitch is equal to about five to six times the thickness of the material used to form the individual pod, and the run is equal to about two to three times the thickness of the material used to form the pod.
• the spacing between the independent pods can vary from no spacing between the pods to as much as desired. Preferably, however, the spacing between the pods ranges from 2 to 6 times the thickness of one of the construction materials used to form one of the pods. This spacing can be guided by the desired width of the resultant microchannels created in the flow field as shown in Figure 9 at 901. Of course, these specifications may be varied to optimize the system for an intended use. For example, one pod can be formed from a wire mesh made from nickel while another pod is formed from a stainless steel wool.
• the number of pods needed is dictated by the length of the flow field and the above criteria. If the pods are concentrically folded, they should include an outside layer and at least one internal layer formed from concentrically folding the porous conductive substrate. More folds may be appropriate in a given application, however.
• the empty space created between the layers by the concentric folds is preferably twice the thickness of the substrate used for the pod.
• Microchannels are created in the flow fields between the individual pods that facilitate the removal of heat and water from the fuel cell assembly as shown in Figure 9 at 901.
• the discontinuously-folded embodiment may also be particularly advantageous as a result of the increased surface area on the horizontal top and bottom surfaces that contact the next contiguous layer in the fuel cell; however, it may be more expensive to manufacture than the other embodiments.
• One method of manufacturing the polarized gas separator of the present invention involves shrinking a thermal setting epoxy around the porous metal substrate so that a first portion of the porous conductive substrate extends upward from the top surface of the epoxy barrier layer and a second portion of the porous conductive substrate extends from the bottom surface of the epoxy barrier layer.
• the method involves providing a porous conductive substrate, providing a mold, placing the porous conductive substrate in the mold, adding a thermal setting epoxy to the mold containing the porous conductive substrate, adding a hardener to the thermal setting epoxy in the mold to cause the epoxy to harden and shrink to form the barrier that bisects the porous conductive substrate to form a polarized gas separator, and then removing the resultant polarized gas separator from the mold.
• Enhancements to this method are contemplated within the present invention.
• the polarized gas separators of the present invention may be used in conjunction with conventional distribution frames like those illustrated in Figure 2, they are preferably and effectively used in conjunction with the fuel cell stack assemblies and distribution frames described in U.S. Application No.
• the polarized gas separator of the present invention may provide an enhancement to the fuel cell stack assemblies described in U.S. Application No. 09/669,344, filed September 26, 2000.
• the polarized gas separator of the present invention can be used at 508 and 510 in conjunction with the distribution frame to help facilitate transportation of the fuel and the oxidant to the fuel cell necessary for the electrochemical exchange.
• Figure 5 depicts the components of a fuel cell assembly of one embodiment of the present invention, namely, distribution frame 500, primary polarized gas separator 508, MEA 512, and secondary polarized gas separator 510.
• Primary polarized gas separator 508 consists of primary anode flow field formed from the lateral spansion of the barrier layer and the secondary cathode flow field also formed from the spansion of the barrier layer.
• MEA 512 is composed of an electrolyte and two catalytic active layers, one for the anode and one for the cathode. Any known MEAs are suitable in the present invention.
• the procession of contiguous layers in the fuel cell assembly is: primary anode gas flow field (from polarized gas separator 508), barrier layer (from polarized gas separator 508), primary cathode flow field (from polarized gas separator 508), MEA 512, secondary anode flow field (from polarized gas separator 510), barrier layer (from polarized gas separator 510), and secondary cathode flow field (from polarized gas separator 510).
• Fuel inlets 504 and air inlet 502 on the distribution frame provide the reactants to the respective flow fields. Specifically, fuel inlet 502 provides fuel to the secondary anode flow field (as part of polarized gas separator 510).
• Fuel supply channels stretch from the interior sides or surfaces of the fuel inlets to supply the fuel to the flow fields. Air is fed to the cathode flow fields through air supply channels that are integral to the air inlet of the distribution frame. Two or more of these individual fuel cell assemblies can be combined to form a node. Two or more nodes can be combined to form a fuel cell stack assembly. Typically, these individual fuel cells will be interposed between end plates, which are preferably circular members, to form stacks or nodes. Stacks can be placed in series to increase voltage to a desired level, or such stacks can be arranged in parallel to increase amperes. In one embodiment of the present invention, one end plate is used for every six fuel cell assemblies to provide desirable and enhanced torsional properties to the stack assembly.
• a coalescer on the anode side and/or a coalescer on the cathode side may be used between the respective anode and cathode catalytic active layers of the MEA and the respective anode and cathode flow fields of the polarized gas separators.
• An anode side coalescer aids in the removal of the liquid-phase water, a by-product of humidification, in the anode flow field from the face of the anode catalytic active layer of the MEA and its ultimate removal from the fuel cell. Removing this water increases the diffusion rate within the anode flow field of the reactant to the catalytic active layer.
• a cathode side coalescer aids in the management of the free water in the cathode flow field formed as a by-product of the electrochemical exchange.
• the water vapor or fine mist coalesces and is quickly converted to larger droplets that are removed from the flow fields by the coalescer and microchannel combination (the microchannels being formed by the configuration of the porous conductive substrate as described above and depicted in Figures 4, 7, and 9).
• Suitable materials for either coalescer include but are not limited to fibrous materials, that can be either woven or nonwoven. Suitable woven materials include cotton muslin or linen. Glass or KEVLARTM may also be used in a woven form.
• Nonwoven materials are also suitable if they have sufficient coalescing properties. Their coalescing properties may be enhanced by treating the surface of the nonwoven with a known stamping or punching technique.
• the construction materials for a woven or a nonwoven anode side coalescer should be hydrophilic; the construction materials for a woven or a nonwoven cathode side coalescer should be more hydrophobic than those used for an anode side coalescer.

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