Patent Publication Number: US-6989216-B2

Title: Fuel cell with overmolded electrode assemblies

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is a continuation-in-part of, and is entitled to the benefit of the earlier filing date and priority of, co-pending U.S. Pat. No. 6,828,057, which is assigned to the same assignee as the current application, entitled “Fuel Cell With Framed Electrodes”, filed Apr. 29, 2002, the disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to fuel cells. More particularly, the present invention relates to alkaline fuel cells wherein the frames are overmolded around the electrodes to provide stability and superior gas and electrolyte flow characteristics within the fuel cell. 
     BACKGROUND OF THE INVENTION 
     Fuel cells use gaseous hydrogen streams, gaseous oxygen streams, and electrolyte streams to produce an electric current. The oxygen stream may be pure oxygen, air, or another oxygen containing mixture. Air, however, is the most abundant and attainable source of oxygen. With air containing only 21% oxygen, a greater air flow rate is needed when air is used as a source of oxygen, as compared to a pure oxygen stream. As a result of the high flow rate of the oxygen stream, the pressure inside the fuel cell increases. The pressure increases inside fuel cells may cause design problems for other streams entering and exiting the fuel cell because the pressure of the streams will need to be adjusted according to the pressure within the fuel cell. As such, a fuel cell allowing for a high flow rate while maintaining a low pressure within the fuel cell is very desirable. The fuel cell as disclosed in the present invention allows for high flow rates while maintaining low pressure by utilizing multiple flow channels throughout the fuel cell. Such flow channels are formed in electrode containing frames which allow for high flow rates and provide mechanical stability to the fuel cell. 
     The present invention discloses a fuel cell having framed electrodes wherein the frames are overmolded around the electrodes. Such a process allows for excellent reproducibility of the electrode containing layers of the fuel cell resulting in increased efficiency in production techniques. Such processing eliminates the use of epoxies in fuel cells for adhering the layers together which can be time consuming and labor intensive. 
     Many fuel cells utilize plastics to form the many layers within the fuel cell. The use of plastics allows for production of the fuel cell layers using injection molding techniques which can reduce production time and costs. Plastics, however, may become damaged over time due to a phenomenon called creep. Creep results from constant stress on the plastic over long periods of time. This time dependent strain is irreversible and can cause deformation or rupture of the plastic. Each kind of plastic has a limit to the amount of strain it can handle. Such deformation or rupturing may be accelerated when exposed to higher temperatures present in fuel cells. The frames as used in the present invention are formed from a plastic material exhibiting improved creep strength thereby resulting in a longer lifetime of the fuel cell. The material also exhibits other characteristics beneficial in fuel cells such as reduction in part shrinkage, improved dimensional stability, improved thermal conductivity, and improved electrical isolation properties. 
     The fuel cells of the present invention utilize parallel flow of an electrolyte solution with respect to the electrodes. The frames distribute electrolyte solution and either air or hydrogen across the respective electrodes. The frames containing the electrodes are sealed together and flow channels in the frames distributes air, hydrogen, and electrolyte solution across the electrodes while maintaining low pressure throughout the fuel cell. The present invention provides a compacted fuel cell design while allowing for a high air flow while maintaining a low pressure throughout the fuel cell. 
     As the world&#39;s population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces the harmful gas. Experts say atmospheric levels of carbon dioxide may be double that of the pre-industrial era by the end of the next century, but they also say the levels would be much higher except for a trend toward lower-carbon fuels that has been going on for more than 100 years. Furthermore, fossil fuels cause pollution and are a causative factor in the strategic military struggles between nations. Furthermore, fluctuating energy costs are a source of economic instability worldwide. 
     In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. It had been predicted that this evolution will produce a carbon-free energy system by the end of the 21 st  century. The present invention is another product which is essential to shortening that period to a matter of years. In the near term, hydrogen will be used in fuel cells for cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But, with the problems of storage and infrastructure solved (see U.S. Pat. No. 6,305,442, issued Oct. 23, 2001 for Ovshinsky, et al., which is herein incorporated by reference and U.S. Pat. No. 6,193,929, issued Feb. 27, 2001 for Ovshinsky et al., which is herein incorporated by reference), hydrogen will also provide a general carbon-free fuel to cover all fuel needs. 
     A dramatic shift has now occurred, in which the problems of global warming and climate change are now acknowledged and efforts are being made to solve them. Therefore, it is very encouraging that some of the world&#39;s biggest petroleum companies now state that they want to help solve these problems. A number of American utilities vow to find ways to reduce the harm done to the atmosphere by their power plants. DuPont, the world&#39;s biggest chemicals firm, even declared that it would voluntarily reduce its emissions of greenhouse gases to 35% of their level in 1990 within a decade. The automotive industry, which is a substantial contributor to emissions of greenhouse gases and other pollutants (despite its vehicular specific reductions in emissions), has now realized that change is necessary as evidenced by their electric and hybrid vehicles. 
     Hydrogen is the “ultimate fuel.” In fact, it is considered to be “THE” fuel for the future. Hydrogen is the most plentiful element in the universe (over 95%). Hydrogen can provide an inexhaustible, clean source of energy for our planet which can be produced by various processes. Utilizing the inventions of subject assignee, the hydrogen can be stored and transported in solid state form in trucks, trains, boats, barges, etc. (see the &#39;810 and &#39;497 applications). 
     A fuel cell is an energy-conversion device that directly converts the energy of a supplied gas into an electric energy. Researchers have been actively studying fuel cells to utilize the fuel cell&#39;s potential high energy-generation efficiency. The base unit of the fuel cell is a cell having an oxygen electrode, a hydrogen electrode, and an appropriate electrolyte. Fuel cells have many potential applications such as supplying power for transportation vehicles, replacing steam turbines and power supply applications of all sorts. Despite their seeming simplicity, many problems have prevented the widespread usage of fuel cells. 
     Presently most of the fuel cell R &amp; D focus is on P.E.M. (Proton Exchange Membrane) fuel cells. The P.E.M. fuel cell suffers from relatively low conversion efficiency and has many other disadvantages. For instance, the electrolyte for the system is acidic. Thus, noble metal catalysts are the only useful active materials for the electrodes of the system. Unfortunately, not only are the noble metals costly, they are also susceptible to poisoning by many gases, and specifically carbon monoxide (CO). Also, because of the acidic nature of the P.E.M fuel cell, the remainder of the materials of construction of the fuel cell need to be compatible with such an environment, which again adds to the cost thereof. The proton exchange membrane itself is quite expensive, and because of its low conductivity, inherently limits the power performance and operational temperature range of the P.E.M. fuel cell (the PEM is nearly non-functional at low temperatures, unlike the fuel cell of the instant invention). Also, the membrane is sensitive to high temperatures, and begins to soften at 120° C. The membrane&#39;s conductivity depends on water and dries out at higher temperatures, thus causing cell failure. Therefore, there are many disadvantages to the P.E.M. fuel cell which make it somewhat undesirable for commercial/consumer use. 
     The conventional alkaline fuel cell has some advantages over P.E.M. fuel cells in that they have higher operating efficiencies, they use less expensive materials of construction, and they have no need for expensive membranes. The alkaline fuel cell also has relatively higher ionic conductivity in the electrolyte, therefore it has a much higher power capability. Unfortunately, conventional alkaline fuel cells still suffer from certain disadvantages. For instance, conventional alkaline fuel cells still use expensive noble metals catalysts in both electrodes, which, as in the P.E.M. fuel cell, are susceptible to gaseous contaminant poisoning. While the conventional alkaline fuel cell is less sensitive to temperature than the PEM fuel cell, the active materials of conventional alkaline fuel cell electrodes become very inefficient at low temperatures. 
     Fuel cells, like batteries, operate by utilizing electrochemical reactions. Unlike a battery, in which chemical energy is stored within the cell, fuel cells generally are supplied with reactants from outside the cell. Barring failure of the electrodes, as long as the fuel, preferably hydrogen, and oxidant, typically air or oxygen, are supplied and the reaction products are removed, the cell continues to operate. 
     Fuel cells offer a number of important advantages over internal combustion engine or generator systems. These include relatively high efficiency, environmentally clean operation especially when utilizing hydrogen as a fuel, high reliability, few moving parts, and quiet operation. Fuel cells potentially are more efficient than other conventional power sources based upon the Carnot cycle. 
     The major components of a typical fuel cell are the hydrogen electrode for hydrogen oxidation and the oxygen electrode for oxygen reduction, both being positioned in a cell containing an electrolyte (such as an alkaline electrolytic solution). Typically, the reactants, such as hydrogen and oxygen, are respectively fed through a porous hydrogen electrode and oxygen electrode and brought into surface contact with the electrolytic solution. The particular materials utilized for the hydrogen electrode and oxygen electrode are important since they must act as efficient catalysts for the reactions taking place. 
     In an alkaline fuel cell, the reaction at the hydrogen electrode occurs between the hydrogen fuel and hydroxyl ions (OH − ) present in the electrolyte, which react to form water and release electrons:
 
H 2 +2OH − →2H 2 O+2e − .
 
At the oxygen electrode, the oxygen, water, and electrons react in the presence of the oxygen electrode catalyst to reduce the oxygen and form hydroxyl ions (OH − ):
 
O 2 +2H 2 O+4e − →4OH − .
 
The flow of electrons is utilized to provide electrical energy for a load externally connected to the hydrogen and oxygen electrodes.
 
     The catalyst in the hydrogen electrode of the alkaline fuel cell has to not only split molecular hydrogen to atomic hydrogen, but also oxidize the atomic hydrogen to release electrons. The overall reaction can be seen as (where M is the catalyst):
 
M+H 2 →2MH→M+2H + +2e − .
 
Thus the hydrogen electrode catalyst must efficiently dissociate molecular hydrogen into atomic hydrogen. Using conventional hydrogen electrode material, the dissociated hydrogen atoms are transitional and the hydrogen atoms can easily recombine to form molecular hydrogen if they are not used very quickly in the oxidation reaction. With the hydrogen storage electrode materials of the inventive instant startup fuel cells, the atomic hydrogen is immediately captured and stored in hydride form, and then used as needed to provide power.
 
     In addition to being catalytically efficient on both interfaces, the catalytic material must be resistant to corrosion in the alkaline electrolyte environment. Without such corrosion resistance, the electrodes would quickly lose efficiency and the cell will die. 
     One prior art fuel cell hydrogen electrode catalyst is platinum. Platinum, despite its good catalytic properties, is not very suitable for wide scale commercial use as a catalyst for fuel cell hydrogen electrodes, because of its very high cost. Also, noble metal catalysts like platinum cannot withstand contamination by impurities normally contained in the hydrogen fuel stream. These impurities can include carbon monoxide which may be present in hydrogen fuel. 
     The above contaminants can cause what is commonly referred to as a “poisoning” effect. Poisoning occurs where the catalytically active sites of the material become inactivated by poisonous species invariably contained in the fuel cell. Once the catalytically active sites are inactivated, they are no longer available for acting as catalysts for efficient hydrogen oxidation reaction at the hydrogen electrode. The catalytic sites of the hydrogen electrode therefore are reduced since the overall number of available catalytically active sites is significantly lowered by poisoning. In addition, the decrease in catalytic activity results in increased over-voltage at the hydrogen electrode and hence the cell is much less efficient adding significantly to the operating costs. Over-voltage is the difference between the actual working electrode potential and it&#39;s equilibrium value, the physical meaning of over-voltage is the voltage required to overcome the resistance to the passage of current at the surface of the hydrogen electrode (charge transfer resistance). The over-voltage represents an undesirable energy loss which adds to the operating costs of the fuel cell. 
     In related work, U.S. Pat. No. 4,623,597 (“the &#39;597 patent”) and others in it&#39;s lineage, the disclosure of which is hereby incorporated by reference, one of the present inventors, Stanford R. Ovshinsky, described disordered multi-component hydrogen storage materials for use as negative electrodes in electrochemical cells for the first time. In this patent, Ovshinsky describes how disordered materials can be tailor made (i.e., atomically engineered) to greatly increase hydrogen storage and reversibility characteristics. Such disordered materials are amorphous, microcrystalline, intermediate range order, and/or polycrystalline (lacking long range compositional order) wherein the polycrystalline material includes topological, compositional, translational, and positional modification and disorder. The framework of active materials of these disordered materials consist of a host matrix of one or more elements and modifiers incorporated into this host matrix. The modifiers enhance the disorder of the resulting materials and thus create a greater number and spectrum of catalytically active sites and hydrogen storage sites. 
     The disordered electrode materials of the &#39;597 patent were formed from lightweight, low cost elements by any number of techniques, which assured formation of primarily non-equilibrium metastable phases resulting in the high energy and power densities and low cost. The resulting low cost, high energy density disordered material allowed the batteries to be utilized most advantageously as secondary batteries, but also as primary batteries. 
     Tailoring of the local structural and chemical order of the materials of the &#39;597 patent was of great importance to achieve the desired characteristics. The improved characteristics of the hydrogen electrodes of the &#39;597 patent were accomplished by manipulating the local chemical order and hence the local structural order by the incorporation of selected modifier elements into a host matrix to create a desired disordered material. Disorder permits degrees of freedom, both of type and of number, within a material, which are unavailable in conventional materials. These degrees of freedom dramatically change a materials physical, structural, chemical and electronic environment. The disordered material of the &#39;597 patent have desired electronic configurations which result in a large number of active sites. The nature and number of storage sites were designed independently from the catalytically active sites. 
     Multiorbital modifiers, for example transition elements, provided a greatly increased number of storage sites due to various bonding configurations available, thus resulting in an increase in energy density. The technique of modification especially provides non-equilibrium materials having varying degrees of disorder provided unique bonding configurations, orbital overlap and hence a spectrum of bonding sites. Due to the different degrees of orbital overlap and the disordered structure, an insignificant amount of structural rearrangement occurs during charge/discharge cycles or rest periods there between resulting in long cycle and shelf life. 
     The improved battery of the &#39;597 patent included electrode materials having tailor-made local chemical environments which were designed to yield high electrochemical charging and discharging efficiency and high electrical charge output. The manipulation of the local chemical environment of the materials was made possible by utilization of a host matrix which could, in accordance with the &#39;597 patent, be chemically modified with other elements to create a greatly increased density of electro-catalytically active sites and hydrogen storage sites. 
     The disordered materials of the &#39;597 patent were designed to have unusual electronic configurations, which resulted from the varying 3-dimensional interactions of constituent atoms and their various orbitals. The disorder came from compositional, positional and translational relationships of atoms. Selected elements were utilized to further modify the disorder by their interaction with these orbitals so as to create the desired local chemical environments. 
     The internal topology that was generated by these configurations also allowed for selective diffusion of atoms and ions. The invention that was described in the &#39;597 patent made these materials ideal for the specified use since one could independently control the type and number of catalytically active and storage sites. All of the aforementioned properties made not only an important quantitative difference, but qualitatively changed the materials so that unique new materials ensued. 
     Disorder can be of an atomic nature in the form of compositional or configurational disorder provided throughout the bulk of the material or in numerous regions of the material. The disorder also can be introduced by creating microscopic phases within the material which mimic the compositional or configurational disorder at the atomic level by virtue of the relationship of one phase to another. For example, disordered materials can be created by introducing microscopic regions of a different kind or kinds of crystalline phases, or by introducing regions of an amorphous phase or phases, or by introducing regions of an amorphous phase or phases in addition to regions of a crystalline phase or phases. The interfaces between these various phases can provide surfaces which are rich in local chemical environments which provide numerous desirable sites for electrochemical hydrogen storage. 
     These same principles can be applied within a single structural phase. For example, compositional disorder is introduced into the material which can radically alter the material in a planned manner to achieve improved and unique results, using the Ovshinsky principles of disorder on an atomic or microscopic scale. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an improved fuel cell. The fuel cell of the present invention allows for a high air flow rate, when air is used as the source of oxygen, while maintaining low pressure throughout the fuel cell. The cell design also provides mechanical support within the fuel cell. The fuel cell contains at least one hydrogen electrode in contact with a hydrogen stream, at least one oxygen electrode in contact with an oxygen stream, and at least one electrolyte chamber in contact with the hydrogen electrode and the oxygen electrode. The hydrogen stream may be composed of gaseous hydrogen and the oxygen stream may be composed of pure oxygen or air from the environment. An electrolyte solution, such as potassium hydroxide, flows through the electrolyte chamber and contacts the hydrogen electrode and the oxygen electrode. The fuel cell also contains multiple rubber compression plates used to distribute oxygen and hydrogen to the electrodes and help maintain mechanical support throughout the fuel cell while accommodating expansion and contraction of the hydrogen electrodes. 
     Frames are overmolded around the hydrogen and the oxygen electrodes to form electrode assemblies. The frames are comprised of a polymer material allowing for production via injection molding. Preferably the polymer material is mixture comprising polyphenylene ether, high impact polystyrene, and glass fiber. An electrolyte chamber is placed between the hydrogen electrode and the oxygen electrode and the frames are adhered together forming an electrode chamber. The frames provide flow channels allowing the electrolyte solution to flow between the hydrogen, and oxygen electrode. The frames are configured to uniformly distribute the electrolyte solution between the electrodes. 
     Compression are placed outside the frames within the fuel cell. The compression plates are configured to uniformly distribute hydrogen or oxygen to the electrodes. The compression plates have a series of flow channels which evenly distribute the hydrogen and oxygen across the respective electrodes. The compression plates are also adapted to absorb expansion of the hydrogen electrode while providing mechanical support within the fuel cell. The compression plate may be comprised of rubber or another elastomeric compound capable of absorbing the expansion of the hydrogen electrodes. 
     The electrolyte chambers may be composed of a porous support structure disposed between a pair of membranes. The membranes prevent excess electrolyte solution from contacting the hydrogen electrodes and the oxygen electrode. The membranes also prevent the oxygen stream and the hydrogen stream from penetrating into the electrolyte. The porous support structure may be an expanded polymer sheet. The polymer may be of polyolefin or another rigid polymer. The electrolyte chambers contact an electrolyte interface of the hydrogen electrodes and the oxygen electrodes. The electrolyte chamber is adapted to provide mechanical support within the fuel cell and provide a pathway for uninterrupted flow of the electrolyte solution throughout the fuel cell. The electrolyte chambers allow the electrolyte solution to contact the hydrogen electrodes and the oxygen electrodes. 
     The hydrogen electrode may be composed of an anode active material having hydrogen storage capacity, the bulk of which is located between the hydrogen interface and the electrolyte interface. The hydrogen interface is adapted to dissociate and adsorb gaseous hydrogen while the electrolyte interface is adapted to react said stored hydrogen with an electrolyte solution. The bulk of said anode active material is adapted to store said adsorbed hydrogen. 
     The hydrogen electrode may comprise an anode active material layer, a porous polytetrafluoroethylene (PTFE) layer, and a current collector grid. The anode active material layer may be composed of a mixture of AB 5  type of alloy, AB 2  type of alloy, Raney nickel, graphite, and PTFE powder. The anode active material layer is disposed between the current collector grid and the polytetrafluoroethylene layer. The anode active material layer may be dispersed throughout the current collector grid. Examples of current collector grids include, but are not limited to, mesh, grid, matte, expanded metal, foil, foam and plate. 
     The oxygen electrode has an oxygen interface, an electrolyte interface, and a bulk of a cathode active material. The bulk of the cathode active material is disposed between the oxygen interface and the electrolyte interface. The oxygen interface is adapted to dissociate gaseous oxygen. The bulk of the cathode active material is adapted to adsorb and provide the dissociated oxygen for further electrochemical reaction. The electrolyte interface is adapted to react the absorbed oxygen with an electrolyte solution. The oxygen electrode is composed of a gas diffusion layer, a catalyst layer, a polytetrafluoroethylene layer, and a current collector grid. The catalyst layer is disposed between the gas diffusion layer and the current collector grid. The gas diffusion layer is disposed between the catalyst layer and the polytetrafluoroethylene layer. The polytetrafluoroethylene layer is in intimate contact with the oxygen stream. The current collector grid is in intimate contact with said electrolyte stream. The current collector grid may be a mesh, grid, matte, expanded metal, foil, foam and plate. The gas diffusion layer may be composed of a mixture of polytetrafluoroethylene and carbon black. The catalyst layer may be composed of a mixture of a mixture of polytetrafluoroethylene and carbon black, additional carbon black, graphite, silver oxide, or other catalysts. The silver oxide may contain modifiers such as a lithium aluminum alloy, gallium, molybdenum, or nickel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , shows the fuel cell of the present invention. 
         FIG. 2 , shows a side view of the fuel cell of the present invention. 
         FIG. 3 , shows a magnified cross sectional view of the fuel cell of the present invention as shown in  FIG. 2 . 
         FIG. 4 , shows an exploded view of the fuel cell of the present invention. 
         FIG. 5 , shows a detailed view of the hydrogen electrode in accordance with the present invention. 
         FIG. 6 , shows a detailed view of the oxygen electrode in accordance with the present invention. 
         FIG. 7 , shows a detailed view of the inner side of a hydrogen electrode assembly in accordance with the present invention. 
         FIG. 8 , shows a detailed view of the outer side of a hydrogen electrode assembly in accordance with the present invention. 
         FIG. 9 , shows a detailed view of the inner side of an oxygen electrode assembly in accordance with the present invention. 
         FIG. 10 , shows a detailed view of the outer side of an oxygen electrode assembly in accordance with the present invention. 
         FIG. 11 , shows a detailed view of a compression plate in accordance with the present invention. 
         FIG. 12 , shows a detailed cross sectional view of a electrolyte chamber in accordance with the present invention. 
         FIG. 13 , shows a cross sectional view of the preferred embodiment of the hydrogen electrode in accordance with the present invention. 
         FIG. 14 , shows a cross sectional view of the preferred embodiment of the oxygen electrode in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the past, fuel cells have been designed to use air as a source of oxygen. When air is used as an oxygen source, the air flow rate must be approximately 5 times the required flow rate of pure oxygen, due to air containing 21% oxygen. The high air flow rate can substantially raise the pressure within the fuel cell thereby creating design problems. The present invention allows for a high air flow rate while maintaining a low pressure throughout the fuel cell. This invention applies parallel flow of a hydrogen stream, an oxygen stream, and an electrolyte stream throughout a fuel cell with respect to the electrodes. The components of the fuel cell are pressed tightly together to provide mechanical support throughout the fuel cell while allowing for electrode expansion. While the fuel cell may be pressed tightly together, the fuel cell allows uninterrupted flow of hydrogen, oxygen, and an electrolyte solution across the electrodes. Gases and liquids flow through the cell via flow channels and porous structures. The design of the fuel cell allows for high speed gas flow throughout the fuel cell while maintaining a low pressure throughout the cell. The fuel cell also allows for expansion of the electrodes by using layers designed to absorb the expansion of the electrodes in the Z direction as the electrodes absorb hydrogen. 
     The fuel cell  10  of the present invention is shown in  FIG. 1 . The layers of the fuel cell have multiple holes which serve as passages through which the oxygen, hydrogen, and electrolyte streams flow to reach flow channels designed to distribute the streams across the appropriate surfaces of the respective electrodes. When the layers are stacked and pressed together, the holes of each layer line up to allow uninterrupted flow throughout the cell. The fuel cell has a hydrogen inlet  11 , an oxygen inlet  12 , two electrolyte inlets  13 , a hydrogen outlet  14 , a oxygen outlet  15 , and two electrolyte outlets  16 . 
     The hydrogen flows into the fuel cell through the hydrogen inlet  11  to the hydrogen electrode. The hydrogen is distributed across the hydrogen interface of the hydrogen electrode and is absorbed by the hydrogen electrode with any excess hydrogen flowing out of the fuel cell through the hydrogen outlet  14 . Any excess hydrogen may be used to help remove heat generated by the absorption of hydrogen from the fuel cell. Any excess hydrogen may also be combusted to provide heat needed to desorb hydrogen from hydrogen storage vessels employing hydrogen storage alloys. The fuel cell may also be designed to utilize all of the hydrogen being input into the fuel cell thereby removing the need for a hydrogen outlet. 
     Oxygen or an oxygen containing mixture, such as air, flows into the fuel cell through the oxygen inlet  12  to the oxygen electrode. The oxygen stream is distributed across the oxygen interface of the oxygen electrode and oxygen is reduced by the oxygen electrode. The remaining oxygen stream containing unconsumed oxygen and nitrogen then flows out of the fuel cell through the oxygen outlet  15 . An oxygen outlet  15  may not be needed when a pure oxygen stream is used as the oxygen source, where the system is configured to consume all oxygen input into the fuel cell. When air is used as the oxygen source, the air flows across the oxygen electrode and the oxygen is absorbed from the air. The remaining nitrogen and carbon dioxide left from the air stream flow out of the fuel cell through the oxygen outlet. The remaining air stream may also help remove heat from the fuel cell. 
     The electrolyte solution flows into the fuel cell through the electrolyte inlets to the electrolyte chamber. The electrolyte solution is distributed through the electrolyte chamber and contacts the electrolyte interface of the hydrogen and oxygen electrodes. The electrolyte solution preferably flows across the shorter side of the electrodes to enhance reactivity at the electrolyte interface of the electrodes. After the electrolyte solution flows past the electrodes, the electrolyte solution flows out of the fuel cell through the electrolyte outlets  16 . The exiting electrolyte solution may also help remove heat from the fuel cell resulting from absorption of hydrogen. 
     A side view of the fuel cell is shown in  FIG. 2 . A cross-sectional view of the fuel cell of  FIG. 2  is shown in  FIG. 3  and an exploded view of the fuel cell of  FIG. 2  is shown in  FIG. 4 . The fuel cell has a stack formation with multiple layers. The fuel cell contains at least one hydrogen electrode  20  and at least one oxygen electrode  40 . A hydrogen electrode frame is overmolded around the hydrogen electrode  20  to form a hydrogen electrode assembly  30  and an oxygen electrode frame is overmolded around the oxygen electrode  40  to form an oxygen electrode assembly  50 . An electrolyte chamber  60  is placed between the hydrogen electrode assembly  30  and the oxygen electrode assembly  50 . The hydrogen electrode assembly  30  and the oxygen electrode assembly  50  are adhered together to form an electrode chamber containing the hydrogen electrode  20 , the oxygen electrode  40 , and the electrolyte chamber  60 . Rubber compression plates  70  are placed outside the hydrogen electrode assembly  30  and the oxygen electrode assembly  50  and electrode end plates  80  are placed outside the rubber compression plates  70  to complete the stack. The electrode end plates  80  are bolted together and provide mechanical support and compression to the fuel cell. 
     The fuel cell is easily expandable by addition of hydrogen electrode assemblies, oxygen electrode assemblies, electrode chambers, and rubber compression plates as dictated by design requirements. The layers may be positioned as earlier described with respect to one another for operation of the fuel cell. 
     A more detailed view of an hydrogen electrode in accordance with the present invention is shown in  FIG. 5 . The hydrogen electrode is substantially rectangular in shape. An aspect ratio of 1 to 1 for the hydrogen electrode is preferred to better accommodate electrode expansion, current distribution, and current collection, however, other aspect ratios may be used in accordance with the present invention. The hydrogen electrode is flat with a current collector  21  running along one of the longer sides of the hydrogen electrode  20 . The current collector  21  is electrically connected to the hydrogen electrode  20 . 
     A more detailed view of an oxygen electrode in accordance with the present invention is shown in  FIG. 6 . The oxygen electrode is substantially rectangular in shape. An aspect ratio of 1 to 1 for the oxygen electrode is preferred to optimize current distribution and current collection, however, other aspect ratios may be used in accordance with the present invention. The oxygen electrode is flat with a current collector  41  running along one of the longer sides of the oxygen electrode. The current collector  41  is electrically connected to the oxygen electrode  40 . 
     Each hydrogen electrode assembly  30  has an inner side  31  and an outer side  32  and each oxygen electrode assembly  50  has an inner side  51  and an outer side  52 . A detailed view of the inner side  31  of the hydrogen electrode assembly  30  is depicted in  FIG. 7  and a detailed view of the outer side  32  of the hydrogen electrode assembly  30  is depicted in  FIG. 8 . A detailed view of the inner side  51  of the oxygen electrode assembly  50  is depicted in  FIG. 9  and a detailed view of the outer side  52  of the oxygen electrode assembly  50  is depicted in  FIG. 10 . 
     The electrode frames with all of the necessary flow channels are overmolded around the respective electrodes using an injection molding process. Other molding processes such as Reaction Injection Molding may be used as well. These processes reduce the time necessary to produce the fuel cell stacks and allow for excellent reproducibility. 
     The electrode frames are composed of a polymeric mixture and glass fiber. The polymeric mixture is composed of polyphenylene ether (PPE) and high impact polystyrene (HIPS) in the ratios of 75:25 PPE/HIPS to 35:65 PPE/HIPS by weight. The glass fiber may be present in the range of 0.0 to 40 percent by weight. A preferable composition of the frames is 80 weight percent of a 50:50 PPE/HIPS mixture and 20 weight percent glass fiber. The glass fiber is a necessity for improving creep strength, reducing part shrinkage, improving dimensional stability, improving thermal conductivity, and improving electrical isolation properties. The glass fibers used in the mixture may be short glass fibers ranging from 37.5×10 −5  to 100×10 −5  inches in diameter. 
     An electrolyte chamber  60  is placed between the hydrogen electrode assembly  30  and the oxygen electrode assembly  50  and the assemblies are adhered together to form an electrode chamber. The hydrogen electrode assembly  30  and the oxygen electrode assembly  50  are substantially similar in design, however, the hydrogen electrode assembly  30  has a tongue  33  along its inner side  31  which fits into a groove  53  along the inner side  51  of the oxygen electrode assembly  50 . This tongue and groove design allows for proper assembly of the fuel cell prior to adhering the hydrogen electrode assembly and the oxygen electrode assembly together. Similar designs may also be used to ensure proper orientation of the electrode assemblies with respect to each other. The hydrogen electrode assembly and the oxygen electrode assembly are preferably adhered together using vibration welding or ultrasonic welding. This allows the assemblies to be quickly assembled with excellent part dimensions and tolerances. Another benefit is that the joint between the oxygen electrode assembly and the hydrogen electrode assembly is chemically inert and chemically sound just like the parent material since the plastic is melting onto itself during the welding process. 
     The inner side  31  of the hydrogen electrode assembly  30  and the inner side  51  of the oxygen electrode assembly  50  have flow distributing structures  34  located within electrolyte flow channels  35  which evenly distribute the electrolyte solution across through the electrolyte chamber thereby eliminating the need for manifolds while maintaining low pressure throughout the fuel cell. The flow distributing structures  34  may also provide mechanical support to the fuel cell. The flow distributing structures  34  are located where the electrolyte solution enters the electrolyte chamber. The flow distributing structures  34  preferably have a triangular shape, however other shapes may be used in accordance with the present invention. The oxygen electrode assembly and the hydrogen electrode assembly together form the flow distributors  34 . One half of the flow distributors protrude from each assembly and when the assemblies are adhered together, the halves line up and form the flow distributors. The flow distributors thereby extend from the hydrogen electrode assembly  30  to the oxygen electrode assembly  50  and force the electrolyte solution to flow around the flow distributors, thereby evenly distributing the electrolyte solution between the hydrogen and oxygen electrode. 
     The outer side  32  of the hydrogen electrode assembly  30  has a depression  36  into which a rubber compression plate  70  is placed and the outer side  52  of the oxygen electrode assembly  50  has a depression  56  into which a second compression plate  70  is placed. The thickness of the compression plate  70  may be greater than the depth of the depressions  36 / 56  in the outer sides  32 / 52  of the hydrogen and oxygen electrode assemblies  30 / 50  to provide mechanical support and proper sealing within the fuel cell  10 . When placed in the depression on the outer side of the assemblies, cutouts in the compression plates  70  form flow channels  71  providing pathways for the hydrogen or oxygen to flow across the gas interfaces of the respective electrodes. 
     Compression plates  70  are inserted into the fuel cell to absorb volumetric expansion of the electrodes, distribute hydrogen and oxygen across the gas interfaces of the respective electrodes, and help maintain mechanical support of the fuel cell stack. A detailed view of a rubber compression plate in accordance with the present invention is shown in  FIG. 11 . The compression plates are placed in contact with the outer sides of the hydrogen electrode assembly and the oxygen electrode assembly. The compression plates  70  have cutout sections  71  which form the flow channels in the fuel cell. The flow channels evenly distribute hydrogen or air across the gas interface of the respective electrodes. The compression plates are located between the electrode end plates and the electrode assemblies. The compression plates are also designed to absorb expansion of the electrodes in the Z direction as the electrodes expand and contract as hydrogen and oxygen are absorbed and reacted by the respective electrodes. The compression plates may be constructed from any rubber type material, however the rubber material must not be reactive with the alkaline electrolyte solution and must be able to withstand the operating temperatures of the fuel cell, especially under the applied force. 
     Electrolyte chambers may be used to maintain mechanical support within the fuel cell while creating an electrolyte chamber which allows the electrolyte solution to flow throughout the fuel cell. A more detailed view of an electrolyte chamber in accordance with the present invention is shown in  FIG. 12 . The electrolyte chambers  60  may be composed of an expanded polyolefin sheet having a thin membrane on each side. The membrane helps prevent excess electrolyte from contacting the electrode and also prevents hydrogen or oxygen from penetrating into the electrolyte solution. The electrolyte chamber  60  may be placed between the hydrogen electrode electrolyte interface and the oxygen electrode electrolyte interface in the fuel cell. The electrolyte chamber may be in direct contact with the electrodes. While the electrolyte chamber is preferably constructed from an expanded polyolefin sheet, any porous material that allows unrestricted flow throughout its structure while maintaining mechanical support of the fuel cell may be substituted. The porous material must also be one that does not react with the alkaline electrolyte solution and must be able to withstand the operating temperatures of the fuel cell. Inside the electrolyte chamber, the electrolyte solution contacts the hydrogen electrode electrolyte interface and the oxygen electrode electrolyte interface. The electrolyte solution enters the fuel cell and flows through the electrolyte chamber. After passing through the electrolyte chamber, the electrolyte solution flows out of the fuel cell. 
     The hydrogen electrode may be generally composed of an anode active material having hydrogen storage capacity. The anode active material is designed to have a high density of active catalytic sites, resistance to poisoning, and long operating life to provide efficient low cost fuel cell operation. 
     The hydrogen electrode also needs a barrier means to isolate the electrolyte interface of the hydrogen electrode from the gaseous (hydrogen) interface of the hydrogen electrode. A beneficial means of accomplishing this is by inclusion of a hydrophobic component comprising a halogenated organic compound, particularly polytetrafluoroethylene (PTFE) within the electrode. 
     An anode active material of the instant invention may be a composite of a hydrogen storage material and an additional catalytic material. The preferable anode active material is one which can reversibly absorb and release hydrogen irrespective of the hydrogen storage capacity and has the properties of a fast hydrogenation reaction rate, a good stability in the electrolyte and a long shelf-life. It should be noted that, by hydrogen storage capacity, it is meant that the material stores hydrogen in a stable form, in some nonzero amount higher than trace amounts. Preferred materials will store about 1.0 weight % hydrogen or more. Preferably, the alloys include, for example, rare-earth/Misch metal alloys, zirconium and/or titanium alloys or mixtures thereof. The hydrogen electrode material may even be layered such that the material on the hydrogen interface is formed from a material which has been specifically designed to be highly catalytic to the dissociation of molecular hydrogen into atomic hydrogen, while the material on electrolyte interface is designed to be highly catalytic to the electrochemical oxidation of hydrogen. 
     Certain hydrogen storage materials are exceptionally useful as alkaline fuel cell hydrogen electrode materials. The useful hydrogen storage alloys have excellent catalytic activity for the formation of hydrogen atoms from molecular hydrogen and also have superior catalytic activity toward the electrochemical oxidation of hydrogen atoms. In addition to having exceptional catalytic capabilities, the materials also have outstanding corrosion resistance toward the alkaline electrolyte of the fuel cell. In use, the alloy materials act as 1) a molecular hydrogen decomposition catalyst throughout the bulk of the hydrogen electrode; and 2) as an internal hydrogen storage buffer to insure that a ready supply of hydrogen atoms is always available at the electrolyte interface. 
     The hydrogen electrode  20  in the preferred embodiment of the present invention has a layered structure and is shown in  FIG. 13 . The layered structure promotes hydrogen dissociation and absorption within the hydrogen electrode  20 . Each hydrogen electrode is composed of an active material layer  22 , a current collector grid  23 , and a porous polytetrafluoroethylene layer  24 . The active material layer  22  is disposed between the current collector grid  23  and the polytetrafluoroethylene layer  24 . The active material layer  22  may be dispersed throughout the current collector grid  23 . Examples of current collector grids include, but are not limited to, mesh, grid, matte, expanded metal, foil, foam and plate. The preferable current collector grid is a conductive mesh having 40 wires per inch horizontally and 20 wires per inch vertically. The wires comprising the mesh may have a diameter between 0.005 inches and 0.01 inches, preferably between 0.005 inches and 0.008 inches. This design provides optimal current distribution due to the reduction of the ohmic resistance. Where more than 20 wires per inch are vertically positioned, problems may be encountered when affixing the active material to the substrate. The current collector grid may be composed of a conductive material such as nickel. Other conductive materials may be substituted as required by design constraints. The polytetrafluoroethylene layer  24  may be approximately 0.0007 inches thick. The current collector grid  23  is located on the electrolyte interface  27  of the hydrogen electrode  20  and the polytetrafluoroethylene layer  24  is located on the hydrogen interface  26  of the hydrogen electrode  20 . 
     The active material layer  22  may be composed of Misch metal nickel alloy, Raney nickel, graphite, and polytetrafluoroethylene powder. The composition of the active material layer  23  may be by weight 35 to 40% Mischmetal nickel alloy, 45 to 50% Raney nickel, 4% graphite, and 6 to 16% polytetrafluoroethylene. A preferred composition of the active material layer is by weight 39% Mischmetal nickel alloy, 49% Raney nickel, 4% graphite, and 15% polytetrafluoroethylene A preferred Misch metal nickel alloy has the following composition by weight percent: 
     50.07% Ni, 10.62% Co, 4.6% Mn, 1.8% Al, 20.92% La, 8.63% Ce, 0.87% Pr, and 2.49% Nd. The graphite may be one with isotropic shape having high electrical and thermal conductivity. A typical example of such graphite is called TIMREX KS-75 (Trademark of Timcal Group). Raney nickel and polytetrafluoroethylene are well known in the art and do not need any further discussion. 
     The oxygen electrode may contain an active material component which is catalytic to the dissociation of molecular oxygen and adsorption of atomic oxygen, catalytic to the formation of hydroxyl ions (OH − ) from water and oxygen ions, corrosion resistant to the electrolyte, and resistant to poisoning. Materials useful as active materials in the oxygen electrode are redox couples, particularly metal/oxides couples selected from the group of metals consisting of copper, silver, zinc, manganese, nickel, cobalt, and cadmium. These types of oxygen electrodes are discussed in detail in the commonly U.S. Pat. No. 6,620,539, issued Sep. 16, 2003 the disclosure of which is hereby incorporated by reference. 
     The oxygen electrodes of the instant invention may also include a catalytic material which promotes and speeds the dissociation of molecular oxygen into atomic oxygen (which reacts with the redox couple). A particularly useful catalyst is carbon. This carbon should be very porous and may be electrically conductive. 
     The oxygen electrode also needs a barrier means to isolate the electrolyte interface of the oxygen electrode from the gaseous interface of the oxygen electrode. A beneficial means of accomplishing this is by inclusion of a hydrophobic component comprising a halogenated organic compound, particularly polytetrafluoroethylene (PTFE) within the electrode. 
     The oxygen electrodes, may also include a current collector grid or current collecting system extending within said active material. The current collector may comprise an electrically conductive mesh, grid, foam or expanded metal. The most preferable current collector grid is a conductive mesh having 40 wires per inch horizontally and 20 wires per inch vertically. The wires comprising the mesh may have a diameter between 0.005 inches and 0.01 inches, preferably between 0.005 inches and 0.008 inches. This design provides optimal current distribution due to the reduction of the ohmic resistance. Where more than 20 wires per inch are vertically positioned, problems may be encountered when affixing the active material to the substrate, although by modifying the electrode fabrication conditions, it is possible to use such a grid. 
     The oxygen electrodes in the preferred embodiment of the present invention have a layered structure and are shown in  FIG. 14 . The layered structure promotes oxygen dissociation and absorption within the oxygen electrode  40 . Each oxygen electrode  40  is composed of a gas diffusion layer  42 , a active material layer  43 , a current collector grid  44 , and a polytetrafluoroethylene layer  45 . The gas diffusion layer  42  may be composed of carbon particles coated with polytetrafluoroethylene. The carbon particles may be carbon black known as Vulcan XC-72 carbon (Trademark of Cabot Corp.), which is well known in the art. The gas diffusion layer  42  may contain approximately 40 percent by weight polytetrafluoroethylene with the remainder consisting of carbon particles. The active material layer may be composed of the gas diffusion layer material and additional carbon particles, graphite and silver oxide. The active material layer  43  may contain approximately 70 to 80 weight percent of a mixture by weight of 20 percent polytetrafluoroethylene and 80 percent carbon black, and 20 to 30 weight percent silver oxide. The carbon added to the active material layer  43  is carbon black known as Black Pearl 2000 (Trademark of Cabot Corp.). The graphite is preferably TIMREX SFG 44 graphite (Trademark of Timcal Group). The silver oxide may also contain a lithium-aluminum alloy, gallium, or other modifiers for improved performance. 
     Reactive elements such as lithium may be added to the redox couple in the form of a non-reactive alloy such as a LiAl alloy. Other elements which may be alloyed with the lithium include boron and silicon. Specifically the LiAl alloy is a 50:50 At. % alloy. Ga may also be added to the silver oxide. Specific examples of silver oxides containing an Li—Al alloy or Ga are shown in Table 1. Such materials are disclosed in commonly owned U.S. Pat. No. 6,620,539, issued Sep. 16, 2003, the disclosure of which is hereby incorporated by reference. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Analysis (ICP for 1–6; 
               
               
                   
                 Sample Description 
                 EDS rest) 
               
               
                   
                   
               
             
            
               
                   
                 5% LiAl, 95% Ag from 
                 Li: 0.006%, Al: 0.07%, 
               
               
                   
                 nitrates 
                 Ag: 99.924% 
               
               
                   
                 1% LiAl, 99% Ag from 
                 Li: 0.001, Ag 99.999% 
               
               
                   
                 alloy 
               
               
                   
                 10% LiAl, 90% Ag from 
                 Li: 0.82%, Al: 5.16%, 
               
               
                   
                 alloy 
                 Ag: 94.02 
               
               
                   
                 5% LiAl, 95% Ag from 
                 Li: 0.034%, Al: 0.29%, 
               
               
                   
                 alloy 
                 Ag: 99.676% 
               
               
                   
                 LiAl, Ag 
                 Ag: 100% 
               
               
                   
                 1% Ga, 99% Ag 
                 Ag: 100% 
               
               
                   
                 5% Ga, 95% Ag 
                 Ga: 0.7%, Ag: 99.3% 
               
               
                   
                   
               
            
           
         
       
     
     The current collector grid  44  is placed on top of the active material layer  43  which is placed on top of the gas diffusion layer  42 . The active material layer  43  may be dispersed throughout the current collector grid  44 . Examples of current collector grids include, but are not limited to, mesh, grid, matte, expanded metal, foil, foam and plate. The current collector grid may be composed of a conductive material such as nickel. Other conductive materials may be substituted as required by design constraints. The other side of the gas diffusion layer  42  is coated with a film of polytetrafluoroethylene  45 . The nickel wire mesh is located at the electrolyte interface  47  and the polytetrafluoroethylene layer is located at the oxygen interface  46 . 
     The foregoing is provided for purposes of explaining and disclosing preferred embodiments of the present invention. Modifications and adaptations to the described embodiments, particularly involving changes to the shape of the fuel cell, the type of hydrogen storage alloy, the cathode active material, the shape and design of the electrodes within the fuel cell, and the shape and design of the electrode flow channels, will be apparent to those skilled in the art. These changes and others may be made without departing from the scope or spirit of the invention in the following claims.