HK1024566A - Surface replica fuel cell for micro fuel cell electrical power pack - Google Patents

Description

Surface replica fuel cell for micro fuel cell power pack

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Fuel cells convert chemical energy into electrical energy by reacting with a gas or liquid in the presence of an electrolyte, electrodes, and a catalyst. Previous patent 4,673,624 and replica (replica) fuel cell patent application 08/531,378 describe methods of forming fuel cells that use expensive catalysts with high efficiency and are easy to mass produce. Recent advances in electrocatalysts have produced catalysts that use alcohol fuels directly and efficiently. Small compact fuel cell system designs are now economically feasible.

Us patents 5,364,711 and 5,342,023 describe small fuel cells for driving "OA (office automation) equipment, audio equipment, and radio equipment". These patents describe the advantages of using small fuel cells and a summary of the technology for making fuel cells. Basically, both patents use a wick to direct the liquid fuel and electrolyte to the fuel cell and remove excess water from the fuel. There are four basic problems with adsorbing incoming fuel and water in low power fuel cells. The first problem is in the delivery of methanol fuel to the fuel cell because in a single membrane type fuel cell, the solution of sulfuric acid and methanol risks shorting the non-bipolar elements. A second problem is that in low power per unit area operation, and in low humidity environments, there is often a water retention and reuse problem in the fuel cell, rather than water removal.

While water removal adsorption systems may be beneficial in stabilizing the water content around the fuel cell electrodes, excess water is removed only when there is excess water. In low power applications, maintaining water in the electrolyte and maintaining water balance becomes a problem rather than removing it. Furthermore, the mechanism for moving the condensed water from the porous gas electrode to the wick is not described. The adsorption system alone cannot pump water away unless there is physical contact with liquid water or some other mechanism that transports water vapor from the fuel cell microstructure to the adsorption surface. Conventional gas diffusion electrodes have the electrode coated with a hydrophobic material.

Patent application 08/531,378 describes vapor phase transport to a hydrophilic outer surface of a gas manifold (manifold). Also in patent application 08/531,378, a surface tension gradient is used to guide the migration of the condensed water to the desired location. A third problem is that the assemblies described in us 5,364,711 and us 5,432,023 represent a system of separate parts that are mechanically put together. The complex assembly is not suitable for mass production. A fourth problem is that the methanol fuel that traverses the proton conducting electrolyte cannot be addressed properly to achieve reasonable fuel efficiency for low power operation with a homogeneous electrolyte and porous electrodes.

In us patent 4,931,168, a gas permeable electrode is in contact with methanol fuel. The purpose of this is to prevent carbon dioxide bubbles from accumulating on the fuel cell electrode. A gas permeable resin and catalytic particle electrode allows reactants and ions to enter and exit the electrode. The gas permeable membrane does not provide a means to block the passage of methanol fuel.

It is desirable to use fuel cells for small appliances. The H-Power Corporation and the AnalyticPower Corporation have collaborated to produce a 25 watt fuel cell to drive a video recorder. It is desirable that the pressurized metal hydride hydrogen cylinder or decomposition hydride be used as a fuel source.

The disadvantage is that these fuel cells are bipolar stacked cells and the fuel supply is inconvenient. Bipolar fuel cell stacks are expensive to assemble and require electrically conductive porous gas cell separators. The stacked cells require additional labor. There are typically at least four hermetic seals for each cell and two gas volumes stacked in series. For small appliances such as cell phones, a 6 volt output is required, while each individual fuel cell may average 0.5 volts. This represents 48 gas seals between dissimilar materials. Electrical contact of the cell via mechanical contact in a humid environment leads to significant corrosion and wear problems. The component cost is increased by the large amount of expensive materials required to form the battery.

With the advent of new binary catalysts for direct methanol electrocatalysis at room temperature, such as Pt (platinum)/Ru (ruthenium), new parameters were opened for fuel cells. It is possible to utilize a direct feed fuel cell that is socially receptive to fuels at high energy densities. There is no thermal or complexity scaling factor that limits the size or power size of the fuel cell if it can operate at room temperature and pressure. The next step in the development is to reduce the catalyst cost and simplify the fuel cell assembly to reduce cost.

The present invention uses the fuel cell described in patent 4,673,624 and in co-pending surface replica fuel cell application 08/531,378 to form a small power source with or without an electrical storage device such as a rechargeable battery for the purpose of providing power to a portable electronic device. An output power regulating device may be incorporated with the fuel cell to allow the cell to provide a desired electrical output. The electronic control regulates the dc voltage output, using electronic switching to provide a constant voltage when the voltage across the fuel cell is reduced for larger currents, or providing an arbitrary ac waveform power current and periodically electrically starting the fuel cell catalyst. The assembly is contained within a container that protects it and assembles it into a product. The fuel and electrical connections to the fuel cell can be reduced to two connections. In subsequent assembly, the electrical connections are separated to make the electrode pattern simpler and avoid any high voltage transition (tension) regions in the cell. The gas connection is a press fit (rivet, ratchet, or nut and bolt connection). This makes the fuel cell easy to assemble in mass production.

The new fuel cell with non-bipolar stacking eliminates the above fuel cell problem and reduces the total number of seals to two or three. The number of mechanical contacts is two or three and can be kept away from the humid environment. For the small appliance market, it is critical that the new fuel cell design allow for rapid assembly and repeatable performance of the cell.

Another feature of the new invention is that because the surface replica fuel cells are a flexible film package, they can be wrapped in a protective container. The fuel cell can be folded to package the cell in a compact volume while still maintaining the airflow path. The fuel cell may be packaged in a standard cell physical form to fit into a variety of appliances designed for the cell.

For high power applications, the cells may be stacked along a common power and gas supply tube. As in smaller cells, the electrical and fuel connections are common.

For higher power applications where it is convenient to operate the fuel cell at elevated temperatures and actively flow oxidant air, the new invention uses a water and heat convection exchanger to maintain the temperature and high humidity of the fuel cell while exchanging gases from the cooler fuel or oxidant gas sources. Heat and water are exchanged through the membrane in the heat exchanger. The membrane may be a porous membrane impregnated with a solid polymer electrolyte, or a similar water permeable membrane. By impregnating a mechanically strong porous membrane, the strength and utilization of the permeable material is improved over simply using a uniform membrane of permeable material, as compared to typical low mechanical strength permeable materials. There are new variations in the microstructure of fuel cells, fuel cell electrodes can be made in layers, and a special inner electrode layer can be used to isolate the electrolyte and to prevent diffusion of the electrolyte through the reactants or products. A non-porous hydrogen-only permeable metal film can be formed by plugging the pores of a plastic substrate with a thin film deposited metal. Such membranes may be incorporated into fuel cells as electrodes, or may be used alone in an electrolyte.

A simplified assembly can be formed by masking the electrode patterns as they are deposited, and ion milling can be used to clear gaps between fuel cells. The fuel cell array may be assembled by folding a fuel cell array, wherein cell interconnect lines, cell breakers, and fuel and oxidant electrodes are fabricated on one side of the membrane.

Fuel cells operate with concentrated methanol and air by using non-porous membrane electrodes with unique characteristics. The non-porous membrane electrode, which was tested for its diffusion properties, has very unique properties of isolating itself from oxygen and inert gases when hydrated with hydrogen. The thin Pd film has very small voids therein due to the sputtered film deposition structure. It is assumed that when hydration occurs, the palladium expands and fills the small voids. This sealing characteristic was also observed when the palladium/platinum/palladium membrane was hydrated for 21 hours with argon on the opposite side of the membrane. The hydrogen diffusion also dropped to 17% of the initial diffusion rate. After exposure to air and oxygen, the original high diffusion rate is restored. The theory is that hydrocarbons from the piping in the system, as well as void closure poison the palladium catalytic application.

The characteristics of semi-permeable membrane electrodes have decisive differences with other fuel cells.

Small fuel cell systems use porous plastic films as fuel cell substrates. The low cost non-porous electrode or intermediate electrolyte foil is permeable only to hydrogen as an ion. The new electrode directly improves the efficiency of the alcohol fuel cell. It interrupts the toxic alcohol diffusion through the electrolyte. The composite electrode is formed by a vacuum deposition method and a paste. This results in a printed circuit architecture for a small fuel cell system integrated with a rechargeable battery and power electronics to power appliances that are currently powered by batteries. By directly utilizing alcohol fuel, the new fuel cell has higher energy per unit mass and higher energy per unit volume. They are more convenient for energy users, less harmful to the environment, and less expensive than conventional batteries.

The subject of the present application is to add the advances that have occurred in replica batteries since the last application and to describe various novel uses of replica fuel cells. A key new advance is the further development of low cost non-porous electrodes that are permeable only to hydrogen as an ion. This in turn increases the efficiency and utility of the direct alcohol fuel cell because it interrupts the toxic alcohol diffusion through the electrolyte. A fuel cell that powers small alcohol is practical.

The most obvious use of small fuel cells is the use that is currently powered by batteries, particularly rechargeable batteries. By directly utilizing alcohol fuel, fuel cells have higher energy per unit mass, higher energy per unit volume, greater convenience to energy users, less environmental hazards, and lower prices than conventional batteries.

These and further and other objects and features of the present invention are apparent in the disclosure, which includes the above and ongoing written specification, as well as the claims and drawings.

Fig. 1A and 1B are front and side cross-sectional views of a fuel cell configured to power a cellular telephone with a rechargeable battery. Fig. 1A is an internal cellular telephone view. Fig. 1B is a centerline sectional view.

Fig. 2 is an enlarged cross-sectional view of a needle-fuel (needle-fuel) connection within the cell shown in fig. 1B.

Fig. 3A is an external gas manifold view of the fuel cell shown in fig. 1A and electrical connections of the fuel cell. The outer gas manifold layer is shown in an enlarged cross-sectional view in FIG. 3B.

Fig. 4A shows an air electrode layer deposition pattern for the fuel cell of fig. 1A and 1B.

Fig. 4B is an enlarged cross-sectional view of the deposition electrode.

Fig. 5A shows an electrolyte matrix layer under the air electrode of fig. 4A.

Fig. 5B is an enlarged sectional view through the connection.

Fig. 5C is an enlarged, facing view of a substrate with a core particle track film (core particle track membrane) etched.

FIG. 6A shows a fuel electrode layer deposition pattern (pattern) opposite the air electrode of FIG. 4A. An enlarged cross-sectional view of the electrode deposition is shown in fig. 6B.

Figure 7A shows a fuel manifold in the center of the fuel cell stack of figures 1A and 1B.

Fig. 7B is an enlarged sectional view of fig. 1A.

Fig. 8 is an exploded view of a fuel cell assembly for use in the power supply of the cellular telephone shown in fig. 1A and 1B.

Fig. 9 is an enlarged cross-sectional view of a fuel cell electrode of the present invention using a powder supported catalyst, methanol fuel, a non-porous electrode, and a surface replica.

Figure 10 shows an electrode deposition pattern for a folded fuel cell assembly. The exaggerated thickness of the deposited layer is shown in fig. 10B.

Figure 11 is an exploded view of a folded fuel cell assembly with an inner electrolyte membrane.

Figure 12 is an exploded view of the gas manifolds stacked around the folded fuel cell assembly.

Fig. 13 is an exploded view of a folded fuel cell equipped with liquid fuel ampoules in a D-cell battery physical configuration.

Fig. 14A, 14B, and 14C are external vertical and horizontal cross-sectional views of a D-cell configuration.

Figure 15 shows a new fuel cell invention with water and heat exchange convection exchangers.

Two exemplary embodiments of the invention are shown in the drawings. Fig. 1 to 8 show one configuration of a power supply cellular phone. Fig. 9 shows the difference between the microstructure of the fuel cell and the replica fuel cell electrode. Fig. 10 to 14 show a fuel cell power pack formed by a folding method and arranged in a standard D-cell configuration. Figure 15 illustrates how the air input to the fuel cell uses a water and heat exchanger to allow the fuel cell to operate at higher humidity and temperature conditions.

Fig. 1A and 1B show a surface replica fuel cell 12 configured as a plastic housing 3 with a rechargeable battery 11 to power a cellular telephone. The fuel cell is held in place by rivets 1 and a fuel pin 6 with a rubber seal 9. Electrical contact is made through the electrical contact 10 on the fuel electrode and the contact rivet 1 on the oxygen electrode. In the fuel cell stack, the fuel cell 12 surrounds the rechargeable battery 11. Fuel 5 is contained in a fuel tank bottle 4. Fuel 5 is delivered to the fuel cell 12 via a fuel needle 6. The operation of re-supplying fuel is to open the housing 3 and to snap into the fuel bottle 4 after piercing the rubber membrane 8 held by the cap 7. The fuel bottle 4 is held in place by a retaining spring 2. The retention spring also carries a snap-in flange 159 to lock onto the cellular telephone. The retention spring 2 and the positive electrode 14 in this embodiment are a cut and formed sheet metal piece. The negative electrode 13 also has a monolithic structure. For this particular embodiment, positive electrode 14 and negative electrode 13 are configured to interface with Motorola (Motorola) MicroTAC^The cellular phone and charging yoke are paired. The power source may be charged and supplied with fuel.

Fig. 2 shows an enlarged cross-sectional view of the fuel needle connection. In this figure, a fuel bottle 4 containing fuel 5 is shown pierced on a fuel needle 6. In operation, fuel 5 is drawn into the fuel needle 6 through the capillary 15 in the needle. Capillary 15 is fitted or sized as a fuel wick for carrying fuel to the fuel cell in a controlled manner. Once the fuel reaches the base of the fuel needle 6, fuel flow ports 27 on the side of the needle allow fuel to be drawn into and evaporated into the fuel manifold 22 and delivered to the fuel electrode 21. Transport through the fuel manifold 22 may be by evaporation and condensation, or by liquid intake through the center of the fuel manifold 22. The electrolytes 20 of both fuel cells 12 are shown. Which is a system of two fuel cells 12 stacked back-to-back. To ensure the sealing of the fuel bottle 4 to the fuel cell 12, there are three gaskets: the first is a rubber membrane 8 that seals the cap 7 with the fuel bottle 4 and with the fuel needle 6. The second is an upper annular gasket 24 retained with rivet flap 16. The gasket seals the fuel needle 6 and the fuel cell 12 and also acts as a soft mechanical clamp for the paper-like fuel cell 12. The third gasket is a low gasket 25 that forms the other side of the soft mechanical clamp and seals against the fuel cell 12 and fuel electrode contact 26. Electrical contact is made to the fuel cell by way of the fuel contact electrode 26 and the contact pad 28. The air manifold 18 and air electrode 19 are cleaned around the puncture point of the electrical contacts. The negative plate-like metal contact electrode 13 is shown to take current out of the figure.

Fig. 3A and 3B show external views of what the appearance of the fuel cell 12 is when laid flat. The positive air electrical rivet connection 14 is shown as clamping the end of the fuel cell 12 outside the fuel cell region 30, and an edge seal 32. The basic principle is to keep the air electrode contact area 29 away from the electrolyte 20. The fuel rivet 31 forms its fuel and electrical connections in the center of the fuel cell 12. The current from the fuel cell is delivered to the external solid electrical contacts via the sheet metal contacts 13, 14. One of the engineering challenges with these contacts is making connections from systems of large amounts of metal to thin mechanical and electrical fuel cell structures without tearing or fatiguing the structure of the fuel cell 12. The edge seal 32 is a heat weld or adhesive seal. In the view of fig. 3A, the air manifold 30 covers the fuel cell. The microscopic cross-sectional view of the manifold in FIG. 3B schematically shows an expanded Teflon (polytetrafluoroethylene) structure 34, using Nafion^35 wet the outer surface of the Teflon fibres 34. In Nafion^35 is covered on the outer surface by a water vapor impermeable and oxygen permeable membrane 157. The coating 157 has a coating of Nafion^35 open up when expanded at high humidity and close at low humidity, and holes 158. This provides a mechanism for regulating the humidity around the fuel cell. This tissue also keeps the condensed water from collecting on the surface of the electrode while allowing the water to condense on the outer surface of the air manifold. The condensed water is drawn through the outer surface of the air manifold or evaporated into the outside air 36. The outer zone 35 provides a source of humidity conditioning for the fuel cell.

In fig. 4A, the contact rivets 14, 31 and the air manifold 30 have been removed and only the air electrode pattern is shown. The air electrode pattern 38 is deposited through a mask on top of the porous plastic substrate 43. As shown in FIG. 4B, the first layer that is laid down is the electrolyte 20, which is 5% Nafion in an alcohol solvent^Solution deposition (Solution Technology Inc., p.o. box 171, Mendenhall, Pennsylvania 19357). It is then dried, ion milled to roughen the surface, and covered with a sprayed layer of catalyst film 46, such as platinum, in a vacuum chamber. A bulk conductor film 47 such as gold is sputtered. A hydrophobic film 44, such as plasma polymerized Teflon, is deposited on the outer surface of the electrode. With the present system, the electrolyte 20 is kept free of condensed water by the hydrophobic layer 44, and the air 49 electrolyte interface 48 is kept within the fuel cell electrode pores 45. The diffusion path of the air 49 is kept short by using the secondary pore diameter 45. The fuel electrical connection 10 shown in fig. 1B is provided by keeping the masked oxygen electrodes 47, 46, 44 away from the fuel connection 40. The positive electrical connection 14 is provided by shielding the electrolyte 20 and the hydrophobic membrane 44, leaving a gold contact area 37. The electrolyte 20 may be removed by ion milling. During deposition of the catalyst film 46 and the bulk conductor film 47, the spacers 42 between the fuel cells may be masked. In the isolation regions 42 between the fuel cells, the ions mill away the electrolyte and deposit a hydrophobic film 44. The fuel cell system is provided with two sets of fuel cells 39 and 41 remote from the fuel connection area 40.

In fig. 5A, the underlying electrolyte matrix layer is shown. The starting material was a porous film, etched nuclear particle track plastic film Nuclepore as shown in FIGS. 5B and 5C^59. The penetration contact regions 51, 52, 57 are obtained by thermally spraying a bulk conductor through a porous film 59. The strike-through deposition is produced by using a series of bulk conductor depositions followed by ion milling to deposit through the holes 58 in the film prior to depositing the electrolyte 20. This is done for both sides of the film to complete the penetration contact areas 51, 52, 57. Electrolyte 58 was used as 5% Nafion in alcohol solvent by dipping and drying^Is deposited. Fuel cell gap removal in the electrolyte 20, 58 by ion milling50. The surface of the penetrating contacts 51, 52 in the electrolyte 20, 58 can also be removed by ion milling. For the fuel cell electrode 38 shown in fig. 4A, the fuel cell regions 53, 54 are left covered with electrolyte.

In fig. 6A and 6B, fuel electrode deposition is shown. The fuel electrode region 60 is shielded by the cell isolation gap 42. The electrical contacts 55 are bulk metal (bulk metal) through contacts. Microscopic details of the electrode are shown in cross-section. To form the fuel electrode, the same sequential deposition of the opposite side of the apertured plastic film substrate 59 is used. Nafion^Electrolyte 58 is deposited onto porous substrate 59. A fuel electrode pattern 60 is deposited through a mask on top of the porous substrate 59. The first layer that is deposited is the electrolyte 20, 58 as 5% Nafion in an alcohol solvent^Solution deposition (Solution Technology Inc., p.o. box 171, Mendenhall, Pennsylvania 19357). The layer is then dried, ion milled to roughen the surface, and covered with a sprayed layer of catalyst film 63 such as platinum in a vacuum chamber. A bulk conductor film 62 such as gold is sputtered. A hydrophobic film 61 such as plasma polymerized Teflon is deposited on the outer surface of the electrode. With the present system, the electrolyte 58 is kept free of condensed water by the hydrophobic layer 61 and the fuel gas 150 electrolyte interface 64 is kept within the fuel cell electrode pores 45. The electrolyte matrix shown previously in fig. 5 is covered with a fuel electrode deposition layer to make a through connection 51.

In fig. 7A and 7B, a fuel manifold is shown. This is the central layer of fuel cells 12 and the manifold 22 presses against both sets of fuel cells 12. The second group of fuel cells is a replica group. In microscopic cross-section, the manifold material is a hydrophobic material, such as expanded Teflon fibers 34. The central region 65 of the manifold is provided by means of a coating such as Nafion (r)^Becomes hydrophilic. The outer surface 66 of the manifold is hydrophobic. A hole 67 is provided for the fuel inlet.

Fig. 8 shows an exploded view of the battery assembly. The air electrode contact rivet 1 is shown with rivet flaps 16 that hold together and make electrical contact with the air electrodes 19. The fuel needle 6 penetrates the center of the fuel electrode 21 and the fuel manifold 22 to make electrical contact via the contact pad 28. The clamping pressure and sealing is achieved by a lower gasket ring 24, and an upper gasket ring 25. The penetrating contact 51 is shown at the trailing edge of the air electrode pattern 19 and then up to the edge of the leading edge of the fuel electrode 21. This pattern of connections enables the desired series cell connection current path to be "stitched" through the single membrane 59. The air manifold 23 is shown sandwiching a first group of fuel cells 68, a fuel manifold 22 and a second group of fuel cells 69. At the outer edge 32, which is sealed to the edge of the air manifold 23, a stack of sealing films is heat or adhesive. The fuel cell assembly 12 is disposed in the power supply system shown in fig. 1.

Figure 9 shows an enlarged view of a hybrid design of a surface replica fuel cell with a powdered catalyst and a semi-permeable electrode. A first noteworthy feature of this structure is the semi-permeable electrode made of three layers. The first film is a hydrogen permeable metal film 79 deposited using a wide angle sputtering source to form plugs 80 within pores 82 in a porous material 81 or coated directly onto a solid electrolyte 83. One example is in Nuclecore with 15 nm diameter pores^20 nm thick palladium membrane on filter membrane. A second layer of structural metal film 78, such as platinum, is deposited onto the hydrogen permeable metal film 79 to mitigate hydration-induced cracking that occurs in many highly permeable metals, such as palladium. A third hydrogen permeable metal film 77, such as palladium, is deposited on the structural metal film 78. The third layer metal, such as a mixture of Pt/Ru/Pd, needs to be able to accept hydrogen ions and be catalytically active for alcohol fuels.

The dynamic characteristics of the layered structure are that the two outer metal films 77 and 79 have high hydrogen permeability, have high hydrogen ion concentration, and have a high hydrogen ion surface receiving rate. They serve as reservoirs for mobile ionized hydrogen on either side of the structural metal film 78. The structural metal film 78 itself has a low hydrogen ion receiving surface rate and has a low equilibrium concentration of hydrogen ions, but the surface coatings 77 and 79 act as efficient conduits for hydrogen ions, and it does not crack due to hydration. Another method of forming a semi-permeable electrode is deposition with a metal alloy that exhibits high permeability to hydrogen ions, low permeability to other ions, does not rupture due to hydrogen hydration, and has a surface that is catalytically active with hydrogen and alcohol.

On the surface of the electrodes 77, 78, 79, which are permeable only to hydrogen ions, powdered catalyst particles 76, such as Pt/Ru coated activated carbon (20 wt% Pt, 10 wt% Ru on VULCAN X-72 carbon, from Electrochem Inc., 400 w. cummings Park, Woburn, MA 01801), as Nafion with 5% electrolyte dissolved in alcohol^Is deposited from a Solution of (Solution Technology Inc., p.o. box 171, Mendenhall, Pennsylvania 19357). The deposited paste 76 is dried, ion milled, and sprayed with a 30 nm Pt/Ru film 74 to enhance the electrical connection 75 of the catalyst particles 76 to the outer permeable membrane 77. The 30 nm Pt/Ru film 75 has pores 73 for the penetration of the alcohol fuel 71 due to the covering of the particles 76 and the expansion of the electrolyte 72 when hydrated.

The alcohol fuel 71, represented as a 1: 1 mixture of methanol and water 96, diffuses into the fuel electrolyte 72 and then catalytically cracks on the catalyst surfaces 76 and 77 with a net production of hydrogen ions 151. The hydrogen ions 151 move from the catalyst particles 76 into the outer permeable membrane 77, either by diffusion through the particles 76 or into the fuel electrolyte 72 and into the permeable membrane 77. The hydrogen ions formed on the outer permeable membrane 77 by the cracking of methanol and water 96 diffuse into the permeable membrane 77. Electrons 152 removed from the fuel 96 during the formation of hydrogen ions move through the electrodes 76, 77, 78 to an external electrical load and reach the oxygen electrodes 86, 87, 88, 89.

To deliver fuel to the fuel electrodes 75, 76, 78 and 79, a porous hydrophobic fuel manifold 70 is used to allow only fuel vapor to reach the electrode surface 74. The fuel manifold 70 is made of a material such as expanded Teflon or Microporous^Polypropylene (3M company) or the like.

Hydrogen ions 151, after they are absorbed into the outer permeable metal 77, diffuse through the structural metal 78And onto the electrolyte interface of the plugged holes 80 and the electrolyte 83. The electrolyte may be solution deposited Nafion^And it may be chemically different from the fuel electrolyte 72 in that it is separated by electrodes 77, 78, 79 that are permeable only to hydrogen. At the interface of the plugged holes 80 and the electrolyte 83, it is where hydrogen ions enter the electrolyte 83. The hydrogen ions are then passed through a nuclear reactor such as Nuclecore^Electrolyte filled pores 82, 84 of a porous substrate plastic layer such as a filter media run. The pores 84 in the inner porous membrane 84 are selected to optimize porosity to optimize conductivity, diffusion rate, and system cost. When the hydrogen ions 151 reach the oxygen electrodes 86, 87, 88, 89, 154, 155, they combine with the oxygen ions 153 near the catalytic surfaces of the oxygen electrodes 86, 88, 89, 154.

Oxygen ions 153 are generated by the catalytic action of the catalysts 86, 88, 89, 155 on oxygen 91 dissolved in the electrolyte 83. The final product of the combination of hydrogen ions 151 and oxygen ions 153 is water 94. Product water 94 dissolves in the electrolyte 83 and then diffuses out as product water vapor 94. A porous hydrophobic coating is deposited on the surfaces of the catalyst particles 89 and the electrolyte 83 to prevent liquid water from condensing on the outer surfaces of the oxygen electrodes 89, 83.

The oxygen electrodes 153, 154 are formed by sputtering a layer of a metal conductor film 154, such as gold, onto the porous substrate 81, and then depositing a catalyst film 155, such as platinum, onto the metal conductor 154. The electrodes 154, 155 and the porous substrate 81 are coated with a solution such as Nafion^Such as an electrolyte 83.

The oxygen electrodes 86, 87, 88 are formed by sputtering a layer of catalyst film 86, such as Pt, onto Nafion^Coated porous substrate plastic 81. A second bulk conductor metal film 87, such as gold, is then sputtered. An outer catalyst surface film 88 is sprayed on the bulk conductor film 87. The stack of the fuel electrode membrane 81, 77, 78, 79 and the oxygen electrode 81, 83, 86, 87, 88 with the inner porous membrane 84 is made with 5% Nafion^The solution was assembled and dried. Powdered catalyst particles 89 were added as 5% Nafion^A solution of an ink paste. By means of PTFE monomersThe hydrophobic coating 90 is deposited by plasma polymerization. This film is added to prevent the liquid product water from condensing on the surface of the air electrode 89. An ion milling step may be added to increase the electrolyte 83 surface-air contact 91.

The outer electrode surfaces 89, 93 are made permeable to air by masking and scratching the surface pits 93 of the inclined deposit of PTFE, or by simply depositing a porous film deposition layer. Pressing against the fuel electrode 90 is a layer of hydrophobic porous gas manifold membrane 92, such as expanded PTFE. Two membranes that regulate the water content of the fuel cell are built on the fuel cell. The first layer is a membrane 90 disposed on the surface of the oxygen electrodes 89, 83 that is preferably permeable to oxygen and less permeable to water. The membrane is formed, for example, by plasma polymerization of a polychlorofluoroethylene (polychlorofluoroethylene) membrane 157, formed in a reactor such as a Nuclecore^On the surface of a porous substrate 161 such as a filter. The output of the fuel cell is delivered by electrons 152 through an electrical load 160.

Figure 10 shows a deposition pattern on a porous plastic substrate to form a folded assembly fuel cell. In this embodiment, a coating such as Nuclepore is applied by using the material layer described in FIG. 9^A single piece of porous plastic film 97, such as a filter membrane, forms the fuel electrode 107 and the air electrode 103.

There are four layers forming a common deposition for fuel cells. The first layer is a bulk electrode metal deposition, such as gold, deposited through a mask in all of the fuel electrode area 107, the periphery of the electrode 106, the air electrode area 103, the positive crimp contact 104, and the negative crimp contact 101. The hem contact areas 104, 101 are slit 98 to form finger contacts with a body metal end cap. These bulk electrically conductive electrodes may be tapered in thickness to optimize conductivity and cost: being thinnest at the edge of the fuel cell membrane 97 parallel to the electrode folds 105 and thickest around the electrode 106. The fuel tab 100 may also be coated with a bulk metal conductor to improve impermeability to fuel. The fuel tabs 100, cell breakers 102, and crimp contacts may be impermeable regions of the membrane produced by thermal annealing after irradiation but before etching the Nuclepore material substrate 97.

The second coating of the fuel cell electrode 107 is sputtered, evaporated or sprayed through a mask onto the electrode area as described earlier.

The third set of electrodes, the air electrode 103, is sputtered, evaporated or sprayed through a mask onto the electrode areas. The fourth layer is, for example, a solution deposited Nafion^Such as an electrolyte and typically impregnates through the interior porous region of the etched nuclear particle track membrane 97. The electrolyte is deposited on fuel cell electrodes 107, and 103. Fig. 9 shows details of the electrolyte deposition. The electrolyte is either not deposited on the crimp contacts 103, 101, the fuel tabs 100 and the cell electrical separator 102, or is removed therefrom by ion milling. The edge seal area of fuel cell 99 is shown as surrounding the edges of fuel tab 100 and fuel cell electrode 107 when the cell is folded over centerline 105.

Figure 11 shows the insertion of the inner membrane and the folding assembly. Inner porous membrane 109, e.g. Nafion^An impregnated Nuclepore filter is interposed between a fuel electrode 107 and an air electrode 103 having a fold line 105. Electrolyte solution 108, e.g. 5% Nafion^The solution is added between the fuel electrode 107 and the air electrode 103. With Nafion^The assembly of (a) is dried and cured at a temperature between 80 and 110 degrees celsius. The surrounding housing of electrode 106 is shown around electrode fold 105. The hem contacts 110, 104, 101 represent slits 98 in the film. The illustrated edge seal surrounds the fuel electrode 107 and the cell interrupter 102. Fuel inlet tab 100 is shown.

Fig. 12 shows an exploded view of a folded fuel cell 112 assembled with an air manifold 113 and a fuel manifold 111. The air manifold 113 is a hydrophobic air permeable sheet material, such as expanded PTFE, that is pressed against the fuel membrane 112. The fuel manifold has an inner porous hydrophobic surface, such as expanded PTFE, and an inner region 65 as shown in fig. 7 that draws fuel. The outer surface of the fuel manifold is a membrane impermeable to fuel and water and permeable to carbon dioxide, such as polyvinyl chloride-fluoride (Kel-F)^3M company). The outer surface of the fuel manifold is permeable to carbon dioxideThe carbon dioxide product of the cracking of methanol and other hydrocarbons provides an outlet. To provide sufficiently high carbon dioxide permeability and low cost, the outer surface of the fuel manifold may be Nuclecore^The film vacuum deposits a laminate of chlorofluoroethylene and a coating of a protective gas permeable lacquer such as nitrocellulose. The fuel manifold 111 is pressed against the fuel cell membrane 112 and the system is heat sealed or bonded with polyester epoxy (polyester epoxy) along the edge sealing surface 114.

Figure 13 shows an assembly of fuel cells folded into a cylindrical geometry to match the physical profile of a standard D-shaped battery. The fuel cell assembly 117 is wrapped with the air manifold surface 113 facing outward. Fuel tab 100 is bent over to be pierced by the fuel needle and end cap 115. A fuel gasket 116 is placed over the fuel tab 100 and a fuel gasket 118 is placed under the fuel tab 100. The negative hem tab 101 bends and brings a cantilever beam spring into contact against the inner surface of the negative end cap 115. The positive hem tab 104 bends and brings a cantilever beam spring into contact against the inner surface of the negative end cap 122. A fuel filled fuel tank 119, such as a methanol and water filled and sealed polyethylene cylinder, slides up and within the fuel cell assembly 117. When the wall of the fuel tank 119 is pierced by the fuel needle end cap 115, fuel connection to the fuel cell is made. The end caps 115, 122 are held together by being attached to the dielectric tube 121, such as by bonding or heat staking the dielectric tube to the end caps by and tightening the caps and tube. A gap 130 remains in the fuel cell assembly 117 and the dielectric tube 121 is made transparent to allow visual inspection of the fuel level. The dielectric tube 121 has a vent hole 120 formed therein to allow air to enter and generated gas and vapor to exit. The number and size of the vent holes are strategically used to moderate the oxygen diffusion uptake and water diffusion removal rate.

Fig. 14A, 14B and 14C show a fuel cell assembled in a standard D-shaped physical form. The three views represented are: an external side view in fig. 14A, a side sectional view through a center line in fig. 14B, and a top horizontal sectional view in fig. 14C. The external view shows the major dimensions of a standard D-cell 162 that is 5.8 cm long and 3.3 cm in diameter. In longitudinal cross-section, the positive end cap 122 electrically contacts the fuel cell 126 via the crimp contact 104. The fuel tank wall 124 is designed with an end alignment flange 123 to provide a centering and positive pressure point on the fuel tank 124. The alignment flange 123 may also be a heat seal point after filling the fuel tank. At the other end of the fuel tank 124, which is obliquely inserted over the fuel needle 127, a centering alignment is provided. The negative end cap 115 is electrically connected to the fuel cell 126 via the negative crimp contact 101. The fuel needle 127 is shown penetrating the fuel tank wall 124, immersed in the fuel 125, and sealed by the fuel gaskets 118 and 116. The fuel path mechanism through the needle and to the fuel tab 100 is the same as that shown in fig. 2, except that no contact pads 28 and rivet flaps 16 are used, since the negative electrical connection in this case is made via the crimp contacts 104 rather than the fuel connection. In a horizontal cross-sectional view, a fuel window gap 130 is shown to allow for convenient visual inspection of the fuel level. For the fuel inspection scheme to be effective, the fuel tank wall 124 and the dielectric tube 121 need to be transparent in the window gap 130. Leaving an airflow gap 128 between the fuel tank and the inner surface of the fuel cell 126 to allow carbon dioxide to be removed by diffusion. A gas flow gap 129 is left between the dielectric tube 121 and the fuel cell outer surface 126 to allow oxygen diffusion and water removal from the fuel cell 126 through the gas vent 120.

Figure 15 shows a schematic of how the fuel cell is coupled to a water and heat convective heat exchanger. In this case, the power level of the fuel cell is high enough to merit active air flow, or the advantage of operating the fuel cell at ambient conditions above, such as 80 degrees celsius, is required. A solution using a convective heat exchanger with a heat transfer membrane 139 is shown. The heat transfer membrane 139 conducts heat and moisture between the incoming flow 131 and the outgoing flow 144. The water permeable membrane 139 may be a composite structure, such as Nafion^Impregnated Nuclepore filter material due to Nafion^Is water permeable and derives its structural strength from a porous Nuclepore substrate. In operation, inlet air 131 is blown into the intake line 140 via the fan 156. As the air is heated by the outlet air 144, it absorbs heat through the heat exchanger 143The moisture diffused in the film 139 is exchanged. Heat and moisture are exchanged between the incoming air 140 and the outgoing air 142 by means of relatively parallel air flows 141. The inlet air 131 reaches the heated and humidified air electrode 138. Fuel cell 136, air electrode 138, electrolyte 137, fuel electrode 134, fuel 135, and heat exchange system are thermally isolated by 132.

The above description contains specific examples which should not be construed as limiting the scope of the invention but as exemplifications of preferred embodiments. Select Nafion^Electrolytes and Nuclepore filters because of their well-known properties. Many other variations are possible.

Microstructure of

Various new concepts added to the above patent applications are to solve the problem of using hydrocarbon fuels, or simply using an impurity-containing fuel with impurities that can diffuse through the fuel cell. If these hydrocarbons, such as methanol or ethanol, diffuse to the oxygen electrode, the performance of the oxygen electrode is degraded and simply leakage of unused fuel from the fuel cell is lost. Conventional fuel cell technologies to prevent these losses are to use thicker electrolytes, run the fuel cell at sufficiently high power densities, attempt to use all of the fuel before it reaches the oxygen electrode, and reduce the fuel concentration. All three of these techniques have the problem of simply increasing the resistance to the rate of diffusion of alcohol or impurities at the expense of certain other performance parameters. The only solution is to electrochemically catalyze the hydrocarbons on the electrode and then pass the hydrogen ions through an electrode that is permeable to hydrogen but not to hydrocarbons. The hydrogen ions then re-emerge at the electrode and enter the second electrolyte and travel to the oxygen electrode. This arrangement is formed with two outer electrodes and a third inner isolating diffusion electrode or diffusion electrode may be the lower layer of the fuel or oxidant electrode. A particular case of interest for hydrocarbon electrodes is a Pt/Ru alloy dispersed on a Pd/Ta/Pd or Pd/Pt/Pd hydrogen permeable electrode. The inner support metal, identified as Ta or Pt, can be a variety of hydrogen permeable materials, such as transition metal elements that are permeable to free hydrogen. Such as an atomic percent alloy of 77% Pd/Ag to 23% Pd/Ag (suitable for use in hydroxide electrolytes). The choice of material also depends on the compatibility with the electrolyte. The Pt/Ru side of the electrode was immersed in an alcohol and sulfuric acid electrolyte. The oxygen electrode is a Pt/Ru electrode or other suitable oxygen electrocatalytic metal. The oxygen electrode uses a solid polymer electrolyte. The electrolyte is preferably

Three characteristics come from the pore geometry and electrolyte of the porous substrate. The first is a simple optimization of the electrolyte conduction versus diffusion rate for the performance range desired by the fuel cell. To optimize the fuel cell, the desired current density is estimated, and then the ohmic loss to reactant diffusion rate ratio is optimized. One example of an optimization is a fuel cell in which the reactants are delivered to the electrodes by diffusion. The current density limit is set to below about 50 milliamps per square centimeter for the purpose of removing heat by ambient air cooling for an internal air gap of 2.9 millimeters, and keeping the fuel cell temperature from rising above 80 degrees celsius. The cell density is about 1/50(US,5,234,777) of state of the art solid polymer fuel cells. Thus, the electrolyte-filled pores of the support membrane serve to interrupt diffusion and ion-conductive flow to maintain the fuel cell at optimal ion conductivity and reactant diffusion resistance values. As far as the mechanism of electrolyte inclusion and porosity reduction is concerned, it results in an overall utilization of electrolyte that is inversely proportional to the square of the porous substrate thickness, since the structure is thinned to maintain optimum performance. This reduces the amount of e.g. Nafion^The use of such a precious electrolyte, in turn, reduces the cost of the fuel cell.

The second feature comes from the speculative molecular alignment of the solid polymer electrolyte, such as Nafion, organized by etching large surface areas of nuclear particle track films or dielectric substances with similar structures^. An increase in conductivity of up to 20 times that of a homogeneous electrolyte is desired. If the diffusion permeability for a molecular species is constant, this can also result in a net 20 times increase in ions over the diffusion rate.

A third effect is that if the mean free path between the molecular diffusing species (e.g., hydrogen) is similar to or larger than the size of the side channels in the porous structure, the diffusion rate is reduced compared to the simple gradient cross-sectional mode. The diffusion characteristic falls into the field of molecular flow diffusion in vacuum systems, where wall vortices, such as in ductwork, may affect the conduction of the pipe. The result is also embodied in providing aligned conduction paths for ions and side dead-end holes for various molecular forms. A particular example is a stack of two or more membranes with pores smaller than the mean free path of the various molecular forms, wherein the gaps between the membranes act as side channels. Or simply have side channels to the major ion paths in the system in the proportion of their molecular species mean free path between molecules. The diffusion resistance mechanism can also be used in other mixed ionic and non-ionic diffusion systems, such as photovoltaic, thermoelectric, and thermionic systems.

Folding design

A very simple solution to forming all the electrodes of a fuel cell on a flexible single substrate sheet is a folded structure. In this configuration, cell interconnect routing, cell electrical isolation, and fuel and oxidant electrodes are fabricated on one side of the membrane. The fuel cell is then assembled by folding the membrane. This configuration also allows the fuel cell to be formed from a commercially available uniform porous substrate, such as a Nuclepore filter, into which any number of internal electrolyte layers can be inserted. Additional degrees of freedom in the construction of the fuel cell help to optimize the fuel cell by limiting the porosity. Control of the electrolyte micro-geometry is beneficial to the performance of the fuel cell. The use of an inner membrane preferably blocks different molecular species on ion transport by geometric or chemical properties.

Electrode layer

Fuel cell electrodes have two main functions: the first is to electrocatalyze the fuel or oxidant and the second is to electrically conduct the electrons from the fuel cell to an electrical load. These two functions and properties are often not achieved in a single secondary material: large surface area catalyst structures have low electrical conductivity due to the tortuous electrical path through the structure, while high conductivity structures have smooth surfaces with very little surface area. One approach to the advantage of both materials is to connect a smooth electrode layer with a large surface area catalyst, e.g. gold sputtered film electrodes coated with a catalyst supported by activated carbon powder.

Simple shielding

A simple method of forming a fuel cell electrode array on a porous dielectric substrate is by sputtering, vacuum evaporation or spraying a metal and electrolyte solution through a mask pattern. Guided deposition such as ink jet printing or molecular beam deposition may be used. Guided ablation methods such as ion milling and laser ablation are used to define the electrodes. The previous patent application US08/531,378 describes a more sophisticated method of producing self-shielding substrates. For commercially available homogeneous porous plastic substrates, such as Nuclepore filters, it is simple and practical to pattern the electrodes through a mask. A variety of other printing and lithographic techniques can also be used to place the fuel cells and circuits on the porous plastic substrate. Ink jet printing can be used to spray on electrode patterns and fuel cell electrodes formulated as pastes of catalytic, and conductive particles and or electrolytes. The use of electrostatic printing is also possible, wherein imaging materials, catalysts, conductors, electrolytes, or insulating particles are also electrostatically adsorbed onto the surface of the fuel cell substrate. A combination of vacuum vapor deposition electrode patterns to then be thickened by plating or attracting charged particles is used to build on the pattern from the previous deposition. Photolithographic processes and/or electrochemical processes are also used to define or form the electrode pattern.

Collimated electrolyte

A unique feature of using an electrolyte locked into a collimated dielectric material is that it has no lateral conductivity. The diffusion of the reactants is mainly limited to the direction of the collimated holes. These two properties present an advantage to fuel systems with adjacent fuel cell stacks on a single membrane. The bypass path is cut off if electrolyte is removed from the surface substrate in the electrically isolated region between adjacent fuel cells. Another variation is that the cell separation region may simply be a non-porous region of the substrate plastic prior to the addition of the electrodes and electrolyte. A simple way to do this with etched nuclear particle track films is to either not irradiate the areas or to thermally anneal them after irradiation but before etching. Another feature of collimation is that when there is a pinhole defect leak in a nonporous electrode, the lateral spread of the fuel leak is limited to passing directly through the electrolyte to the fuel cell electrode due to collimation. This limits the extent to which the oxidant electrode is poisoned.

Heat and water exchange

One particular problem with water-electrolyte fuel cells is that the water content of the electrolyte changes if they are operated in the temperature and reactant humidity ranges. This may lead to sub-optimal performance of the electrolyte, which either dries out or soaks up the electrodes. To solve this problem, a convective heat and water exchanger is used. The construction of heat and water convection exchangers is such that thin water permeable membranes are used as heat exchange elements. These membranes need to be very thin for high rates of heat and water transfer. For structural integrity, the membrane is made of a composite material using a high strength matrix. The matrix is impregnated with a moisture exchange material, such as Nafion^Or nitrocellulose.

For non-active flow fuel cell systems, a layer of moisture retaining membrane is used to operate above this point or at a temperature where the electrolyte would dehydrate if exposed directly to air. The membrane is formed by coating the oxygen electrode with a membrane or an air manifold so as to be permeable to oxygen and less permeable to water. The membrane is non-porous or has intermittent pores. The intermittent holes provide a mechanism for releasing excess liquid water.

Tapered electrode

The amount of metal in the electrically conductive electrode in these thin film fuel cell inventions is optimized if the electrode thickness is increased from a minimum thickness, for electrical conduction, to the point where the electrode leaves the fuel cell, and connection is made to the next adjacent cell.

Vapor fuel delivery

In a small fuel cell without moving parts, there are two main means of delivering methanol fuel. The first is the use of fuel pumping to the fuel cell electrodes. Liquid pumping, however, requires that the fuel be in liquid contact with the fuel cell electrodes. This can lead to the problems described earlier. If the fuel vaporizes before reaching the fuel cell electrodes, the physical contact problem is eliminated. A combination of drawing liquid fuel out of the fuel bottle, drawing the fuel into a layer adjacent the fuel cell, and then using vapor transport through a hydrophobic matrix to reach the fuel electrode surface is used. For these low power density fuel cells, where the air electrode environment is cooled and oxygen is supplied only by diffusion, the fuel vapor diffusion rate is fast enough to span distances of 0.1 mm to 20 mm.

Non-porous electrode

In the present invention a very thin flexible metal foil is supported by a plastic substrate. The practical use of these foil membranes is to meet the need in direct-fed alcohol fuel cells to block methanol diffusion through the electrolyte while efficiently conducting ionic current. Metal foils solve this problem if the foil is made thin enough to meet the necessary throughput rate and economy. To form thin foil electrodes, a large range of metal elements exhibiting hydrogen chemisorption is deposited onto a porous substrate or directly onto a solid state electrolyte. The plugging of the holes is achieved by hydrogen permeable metallization at a wide angle that is thicker than the substrate aperture. Furthermore, the metal foil may be built up in layers to provide various properties. Note that in the literature, below 200 degrees celsius, the diffusion rate of gas through metal foils is largely dominated by the chemisorption rate on the foil surface (Vielstich, 1965). For pure hydrogen fuel cells, catalyst surface layers such as platinum on both sides of the foil increase the rate of passage of hydrogen through the electrode. In the case of direct methanol and hydrocarbon fuel cells, the hydrocarbon fuel side of the membrane must include a catalyst that may or may not be affected by the hydrocarbon molecules and their products to avoid poisoning. Whereas on the side of the foil membrane facing away from the hydrocarbon fuel, the surface catalyst may be optimized for hydrogen. Other considerations in foil construction are that a variety of transition elements with appropriate permeability, such as Pd, which has very high hydrogen permeability, have the disadvantage of swelling and subsequent cracking when they are hydrated. This property is quite common in metal hydrohydration. Thus, to prevent stress and cracking problems, the thin foil is dissolved into an alloy, such as by means of the (77: 23) palladium alloy currently used in hydrogen purifiers. Another option is to layer to form a foil membrane. In one layer structure, the inner layer has a low equilibrium concentration of hydrogen, does not crack, and is a structural barrier. While the outer layer provides a rapid surface exchange reaction rate and surface area. Another characteristic of the delamination is that the first layer deposited has a high permeability rate for hydrogen ions, while if the second structural layer has a low permeability, the first layer provides a lateral diffusion path to the substrate pores, which effectively allows the entire structural film to function as a diffusion membrane.

As an example, a Nuclecore filter with 15 nm diameter pores was subjected to amperometric testing. These films have been sprayed with a first 3.7 nm Pd film, a second 15 nm Pt film and a third 7.5 nm Pd film. At these thicknesses and geometries, the film has a hydrogen diffusion rate equivalent to 10-20ma per square centimeter at 23 degrees Celsius at room temperature. This is within the desired current density range for small ambient cooling and diffusion reactant fed fuel cells. These films are also less expensive than previous 12 micron thick films because they use so little material at 1/800 a thick. The assembly constitutes a methanol fuel cell that electrocatalytically cracks methanol with electrolyte on the fuel side of the membrane and then filters out hydrogen ions or hydrogen gas, and forms a fuel cell on the other side of the membrane in the other electrolyte. The electrocatalytic process for methanol cracking requires the addition of water. Thus, it is necessary to have two electrolytes, one on the fuel side and the other on the oxygen side of the non-porous metal foil. This prevents methanol and water from passing to the oxyfuel cell electrode.

Different electrolytes

A non-porous metal foil barrier separating the electrolytes in a fuel cell allows the possibility that two different electrolytes may be placed on either side of the non-porous metal foil barrier. One arrangement is to use Nafion as the methanol fuel electrode^And sulfuric acid on the fuel side with a hydrogen-only nonporous electrode, while KOH (potassium hydroxide) electrolyte is on the oxygen side of the nonporous electrode. Oxygen mobility is more favorable in KOH electrolyte, while acid electrolyte is used for the fuel side because carbonates are formed if KOH electrolyte is used on the fuel side.

Stoichiometric fuel delivery

Non-porous electrodes or barriers in the cell also prevent ionic drag of water and methanol fuel. For hydrocarbon fuels in which the hydrocarbon is reforming hydrogen and carbon dioxide, the source of oxygen for the process is typically water. In conventional fuel cells, water must either be recycled in the electrolyte or recaptured from the waste products. If water is prevented from being pulled by the ions of the fuel cell, simply adding a stoichiometric mixture of fuel and water is sufficient to maintain the fuel in reforming equilibrium. For example, for fuel cells that are using methanol fuel electrocatalytically, it is desirable to have a stoichiometric fuel mixture with one water molecule per molecule for methanol to allow the catalytic oxidation of methanol and the formation of carbon dioxide and hydrogen. Thus to eliminate the need to recapture water from fuel cell waste, a 1: 1 molar mixture of methanol and water fuel mixture is appropriate. Without water recapture and recycle, direct methanol fuel cells become significantly simpler. The oxygen electrode need only maintain sufficient product water to avoid dehydration and reduce its performance. The fuel electrode uses water and fuel at equal rates. Thus, when the fuel cell runs out of water, it also runs out of fuel.

Body electrical connection

One of the characteristics of these fuel cells is that the apparently best bulk current carrier is gold. A good figure of merit for bulk metal conductors is to have a high coefficient of conductivity per unit mass divided by density and cost (cm)²/Ohm^*And $). The cost, high conductivity and inertness of gold gives it a figure of merit of about four times that of platinum when seeking the lowest cost bulk electrical conductor that can withstand the corrosive environment typical of fuel cells. Various other conductor arrangements in the Pt metal group are: ru 2600, Pd 1900, Au 1500, Ir 900, andthen Pt 390 (cm)²/Ohm^*And $). Ruthenium has the highest quality factor of the platinum group elements, but its low ductility and possible surface oxidation make it less versatile than gold. Palladium in combination with other materials to avoid cracking due to hydration is also being investigated as an effective bulk metal conductor. Palladium is also conveniently used as the hydrogen permeable electrode and the bulk conductor. The high conductivity of gold allows the fuel cell coating to be extremely thin, resulting in very little loss of active surface area of the electrode. The gold film acts as a hydrogen diffusion barrier due to its low permeability to hydrogen. This property is used to improve low discharge rate cell efficiency, where fuel diffusion leakage is the primary energy loss mechanism. If the fuel cell electrodes are kept small in size, the amount of gold necessary to form the cell is close to the turning point where the gold film becomes a good conductor on the surface in order to keep the average electrical path from cell to cell short. The inflection occurs around 5 nm thick in gold. The other refractory metals are, in order of merit factor, Mo 654,000, V463,000, W328,000, Ti 100,000, Ta 65,000, and C16,000 (cm)²/Ohm^*And $). The manifest continues with pure elements. Have considered such as Mo₂Si₃And WC alloys. Many of these refractory materials have a high quality factor but are difficult to deposit, can corrode in the fuel cell environment, require much thicker films, or have poor contact due to surface oxidation.

Fuel cell/battery and/or electronic device

The electrical system of the power pack is arranged to connect the battery in parallel with the fuel cell or electrically by current and voltage control means. The battery and fuel cell are connected to a source of voltage and current to recharge the battery and reduce fuel consumption of the fuel cell, or simply with a flexible power supply. For one form of fuel cell having product storage capability, electrolysis in the fuel cell is used to store energy. The external application of the charging voltage also helps to clean the fuel cell catalytic surfaces. The end product is a power device that generates its energy from fuel or charges it or both. The charging power source may be from a dc power source or a pulsed source. Photovoltaic cells are also used as energy sources. Another concept is to match the fuel cell to an arbitrary waveform generator and produce an arbitrary ac output desired by the user. Another hybrid power scheme is to actuate the flywheel with a low continuous output of the fuel cell and then pull power to meet the demand. This works well for devices such as automobiles that require high power fluctuations for acceleration and climbing, but the average power requirement is only a small fraction of the fluctuation requirement.

Use of a power supply

There are a very large number of practical applications for the fuel cell power pack of the present invention. The unique structure shown and described above has been targeted to provide power for cellular telephones and portable radio transmitters and receivers. These uses achieve a significant improvement over rechargeable batteries because the specific energy per unit mass of hydrocarbon fuels is higher, such as methanol, by a factor in the range of 10 to 100 compared to nickel cadmium batteries. Virtually all portable powered appliances that operate in human habitable conditions can be logically integrated with the new fuel cell stack. The limitation is that the fuel cell sacrifices maximum power output and requires a source of oxygen or other oxidant. To preserve the fuel cells until they are needed, the fuel cells are simply sealed in a gas-tight container to deoxygenate the fuel cells. The new fuel cell invention has been described in the context of a hydrogen-oxygen fuel cell, but variations of other fuel and oxidant sources, such as a hydrogen-hydrogen fuel cell, are possible. The non-porous electrode significantly helps to prevent chlorine diffusion.

While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.

Claims (53)

1. A fuel cell apparatus comprising: a central membrane having an oxygen side and a fuel side; electrodes positioned on the fuel side and on the oxygen side of the membrane, each electrode further comprising a first fuel catalyst membrane layer deposited on the central membrane, a metal membrane layer deposited on the catalyst membrane layer, and a hydrophobic membrane layer positioned on the metal membrane layer; an electrolyte disposed in a void between the catalyst membrane layer and the central membrane; a hydrogen permeable non-porous metal membrane interposed between the electrodes, the central membrane carrying a first water circulation; a layer of fuel circulation and conditioning membrane positioned over the fuel side electrode; a fuel channel flow manifold positioned above the first water circulation and conditioning membrane and sealed to the fuel side electrode; a fuel inlet connected to the fuel manifold for delivering fuel to an area between the fuel manifold and the first water circulation and conditioning membrane; a second water circulation and conditioning membrane positioned under the oxygen side electrode; an oxidant gas manifold positioned below the second water circulation and conditioning membrane and sealed to the oxygen side electrode; and an oxidant gas inlet connected to the oxidant gas manifold for delivering oxidant gas to a region between the oxidant oxidation manifold and the second water circulating and conditioning membrane; a first electrical contact connected to the hydrogen electrode; and a second electrical contact connected to the oxygen electrode; and a sealing edge extending around and attached to the outer edge of the cell.

2. The apparatus of claim 1, wherein the central film is a layer of porous dielectric film.

3. The apparatus of claim 1, further comprising a fuel bottle coupled to the fuel cell.

4. The apparatus of claim 1, further comprising a housing for housing the battery.

5. The apparatus of claim 1, further comprising an energy source coupled to the electrode for delivering electrical energy.

6. The apparatus of claim 5, wherein the energy source is voltage regulating electronics.

7. The apparatus of claim 5, wherein the energy source is a battery.

8. The apparatus of claim 1, wherein the central membrane is reinforced with fibers.

9. The device of claim 1, wherein the central membrane comprises at least two membranes.

10. The apparatus of claim 3, wherein the fuel bottle includes a needle cannula for effecting a fuel connection to the fuel cell.

11. The apparatus of claim 3, further comprising an evaporation manifold to draw fuel from the fuel bottle to the evaporation manifold.

12. The apparatus of claim 4, further comprising electrodes on one side of the membrane, and the folding of the membrane is used to form the fuel side and the oxygen side, and to position the electrodes opposite each other to form the fuel cell.

13. The apparatus of claim 12, further comprising an electrolyte and a membrane inserted in the membrane stack.

14. The apparatus of claim 12, further comprising an electrolyte inserted in the membrane stack.

15. The apparatus of claim 12, further comprising a membrane inserted in the membrane stack.

16. The apparatus of claim 2, further comprising a microscopic geometry on the porous dielectric substrate membrane to enhance electrolyte performance.

17. The apparatus of claim 1, further comprising an auxiliary member inserted in the electrolyte for selectively blocking different molecular species of ion transport according to their geometry or chemical properties.

18. The apparatus of claim 1, wherein the fuel is a hydrogen-bearing compound.

19. The apparatus of claim 1 wherein the fuel is a hydrogen-bearing compound used stoichiometrically by the fuel cell electrode.

20. The apparatus of claim 18, wherein the fuel is reformed before reaching the fuel electrode.

21. The apparatus of claim 1, wherein a hydrogen permeable non-porous metal membrane interposed between the fuel and oxygen electrodes is electrically connected to the fuel electrode.

22. The apparatus of claim 1, wherein a hydrogen permeable non-porous metal membrane interposed between the fuel and oxygen electrodes is electrically connected to the oxidant electrode.

23. The device of claim 1, further comprising an electrode having a plurality of electrodes and electrolyte layers on a porous substrate.

24. The device of claim 1, further comprising deposited layers on the membrane surface for electrical isolation of the battery.

25. The apparatus of claim 24, wherein depositing a layer comprises ink jet printing a deposited layer.

26. The apparatus of claim 24, wherein the deposited layer comprises a layer of spray paint.

27. The apparatus of claim 24, wherein the deposited layer comprises vapor deposited by a method selected from the group consisting of chemical vapor deposition, photolithographic process, vacuum deposition, or electrochemical deposition.

28. The apparatus of claim 1, further comprising voltage regulation electronics electrically connected to the fuel cell for pulsed scavenging of the electrodes, for maintaining performance of the fuel cell, and for varying the voltage with the same or opposite polarity of the fuel cell.

29. The apparatus of claim 1, further comprising a fuel cell having a profile that fits into the cell and an electrical profile to match the existing use of the cell.

30. The apparatus of claim 1 wherein the fuel cell is a thin bag with fuel on the inside and air on the outside.

31. The apparatus of claim 30 further comprising a support membrane on the bag for allowing the exhaust gas to diffuse out and hold the fuel gas.

32. The apparatus of claim 1, wherein the fuel cell comprises at least two back-to-back fuel cell assemblies.

33. The apparatus of claim 2 wherein the fuel bottle is a replaceable sealed fuel ampoule.

34. The apparatus of claim 2, further comprising electronics connected to the fuel cell for regulating the voltage and current output of the fuel cell to produce desired voltage and current characteristics, including alternating current, arbitrary wave function, and steady state voltage.

35. The device of claim 1, further comprising at least two different electrolytes separated by a non-porous metal membrane.

36. The apparatus of claim 1, wherein the non-porous metal film comprises at least one film of a material deposited on the porous substrate to plug pores of the substrate.

37. The apparatus of claim 1, wherein at least one film comprises at least one transition element from the periodic table of elements.

38. The apparatus of claim 1, further comprising at least two electrodes forming the fuel electrode, each comprising a base electrode and a surface replica electrode, the electrodes being formed by sputtering, vacuum evaporation, powder ink spraying, xerography, low pressure gas vapor deposition, chemical vapor deposition, electroplating, photolithography, or a co-deposition material deposition technique.

39. The apparatus of claim 1, wherein the fuel cell is adapted to drive an electronic article.

40. The apparatus of claim 39, wherein the electronic merchandise is selected from the group consisting of a cellular telephone, a portable radio, a portable computer, a pager, a portable audio device, a hearing aid, a medical device, or a portable electronic device.

41. The apparatus of claim 36 wherein the porous substrate material has a porosity aligned perpendicular to the plane of the material to draw the ink and solvent longitudinally into the material rather than laterally.

42. The apparatus of claim 41, wherein the material carrying the ink is a powder in a solvent.

43. A device as in claim 41, wherein the material comprises a substance that becomes an electrode film after delivery to the substrate.

44. The apparatus of claim 1, wherein the electrolyte is aligned so as to prevent lateral conduction through the electrolyte and to prevent electrical shorting.

45. The apparatus of claim 1, wherein the fuel cell comprises a side-by-side series stack of non-bipolar fuel cells on a single membrane having different potentials.

46. The apparatus of claim 45 wherein the electrolyte is aligned so as to limit leakage of non-porous membrane pinhole defects from laterally affecting fuel cell electrode performance.

47. The apparatus of claim 1 further comprising a water and heat convection heat exchanger for humidifying and heating air entering the fuel cell.

48. The apparatus of claim 1, wherein the electrode has a tapered thickness to optimize the bulk conductor metal.

49. The apparatus of claim 1 further comprising a wick for drawing liquid fuel out of the fuel tank, evaporating fuel from the wick, and condensing fuel on the fuel cell.

50. The apparatus of claim 1 wherein the fuel comprises a stoichiometric mixture of hydrocarbons and water for direct hydrocarbon electrocatalyst oxidation and for releasing hydrogen to the fuel cell.

51. The apparatus of claim 31, wherein the fuel comprises a 1: 1 molar mixture of methanol and water, and wherein the spent carbon dioxide product is vented as a gas through a membrane permeable to carbon dioxide and impermeable to methanol and water.

52. The apparatus of claim 1 further comprising a selectively permeable membrane proximate to the fuel cell electrode for sequestering selected molecular species while allowing passage of other species.

53. The apparatus of claim 1, further comprising a selectively permeable membrane formed as part of the gas manifold to exclude selected molecular species while allowing other species to pass therethrough.