Abstract:
A power generator including one or more fuel cells, a fuel chamber enclosing a hydrogen generating fuel, and one or more slideable cylindrical valves in contact with the fuel chamber. The one or more valves include an inner cylindrical component with first perforations, and a slideable cylindrical component with second perforations and having a plurality of separated flexible sections. The valves are useful in controlling the flow of hydrogen into the anode portion of the fuel cell.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application 61/223,324 filed Jul. 6, 2009, entitled “FUEL CELL VALVE CONFIGURATION” the contents of which application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of Invention 
     This invention relates to a slideable cylindrical valve for controlling the hydrogen flow in fuel cell. 
     2. Background 
     Fuel cells, such as PEM fuel cells, use a simple chemical reaction to combine hydrogen and oxygen into water, producing electric current in the process. Hydrogen may be produced by a chemical reaction between a fuel, such as lithium aluminum hydride, and water vapor or by absorption/desorption-adsorption/desorption of hydrogen from a metal hydride. At an anode, hydrogen molecules are ionized by a platinum catalyst, and give up electrons. The proton exchange membrane (PEM) allows protons but not electrons to flow through the membrane. As a result, hydrogen ions flow through the PEM to a cathode, while electrons flow through an external circuit. As the electrons travel through the external circuit, they can perform useful work by powering an electrical device such as an electric motor, light bulb or electronic circuitry. At the cathode, the electrons and hydrogen ions combine with oxygen to form water. The byproducts of the reaction are water and heat. 
     Valves currently suitable for controlling hydrogen flow in passively regulated micro fuel cells require high tolerances to provide adequate sealing, yet need to be capable of allowing transport of sufficient hydrogen to respond to the demand of the electrical load. High tolerance valves meeting these requirements are difficult to manufacture, expensive, and often require high actuation force. 
     SUMMARY 
     An electrical power generator includes one or more fuel cells, a fuel chamber enclosing a hydrogen generating fuel, and one or more valves in contact with the fuel chamber. The one or more valves at least partially surrounds the fuel chamber and includes concentric inner and outer components; a fixed component with first perforations, and a slideable component with second perforations and having a plurality of separated flexible sections. In one embodiment, the concentric components are cylindrical and the inner cylindrical component is fixed and the outer cylindrical component is slideable. 
     A fuel cell system valve includes concentric inner and outer components; a fixed component with first perforations, and a slideable component with second perforations and having a plurality of flexible sections positioned on the slideable cylindrical component. In one embodiment, the concentric components are cylindrical and the inner cylindrical component is fixed and the outer cylindrical component is slideable. The valve at least partially surrounds a hydrogen generating fuel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross section representation  100  of a fuel cell based power generator having a slide valve according to an exemplary embodiment. 
         FIG. 2  is an expanded view  200  of valve plates forming a low friction contact to enable relative movement or sliding, according to some embodiments. 
         FIG. 3  illustrates a perspective view  300  of a slideable cylindrical valve, according to some embodiments. 
         FIG. 4  illustrates a schematic view  400  of a perforation pattern for the slideable component  400  of the cylindrical valve, according to some embodiments. 
         FIG. 5  illustrates a schematic view  500  of a perforation pattern for the slideable component  500  of the cylindrical valve, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims. 
     The electrical power generator described herein generates hydrogen gas internally either through the reaction of water vapor with a chemical hydride fuel or by release of hydrogen from a metal hydride. The hydrogen gas is reacted with atmospheric oxygen from the air at a fuel cell to generate electrical energy. The reaction of hydrogen and oxygen also produces water molecules as a byproduct at the fuel cell. This generated water may be passively diffused from the fuel cell as water vapor to a fuel chamber or cavity that contains the chemical hydride fuel substance, where it reacts with the fuel substance to generate hydrogen gas. The electrical energy generated may be used to power large or small devices that are connected to the power generator, depending on the size of the power generator. The power generator of the embodiments of the invention is particularly useful for powering miniature devices such as wireless sensors, cellular phones or other hand held electronic devices that are electrically connected to the anode and cathode of the one or more fuel cells of the power generator. 
       FIG. 1  is a cross section representation of a fuel cell based power generator  100  according to an example embodiment. Generator  100  includes a cathode output electrode  110  and an anode output electrode  115 . In one embodiment, the generator may be shaped similar to a commercially available “dry cell” battery such as an “AA”, “AAA”, “C”, or” D″ cell, such that it can be substituted for such a battery. A fuel chamber  120  may contain a hydrogen containing fuel that provides hydrogen to a fuel cell stack  125 , which is shown in expanded form in  FIG. 2 , wherein the numbering is consistent with  FIG. 1 . 
     Fuel cell stack  125  may include a proton exchange membrane (PEM), catalyst layer, gas diffusion layer, and a micro porous layer. An anode electrode  135  is coupled to the fuel cell stack  125  between the fuel cell stack  125  and the fuel chamber  120 . It is also coupled to the anode output electrode  115 . A cathode electrode  140  is coupled to the other side of the fuel cell stack, and is coupled to the cathode output electrode  110 . It may also be exposed to ambient conditions. 
     In the embodiments exemplified herein, the electrical power generator and fuel cell system valve are shown having concentric inner and outer cylindrical components; an inner fixed cylindrical component and an outer slideable cylindrical component. It is to be understood that in alternative embodiments, the inner cylindrical component may be slideable and the outer cylindrical component may be fixed. 
     Between the fuel cell  125  and the hydrogen chamber  120  is a slide valve  143 . Slide valve  143  is made up of two cylindrical sleeves that are concentric and adjacent to each other. Slide valve  143  includes a fixed plate  145  and a slideable plate  150  that are coupled in a sliding relationship in one embodiment. A hydrogen and water vapor permeable particulate filter (not shown) may also be used between the fuel cell and the fuel or fuel chamber  120 . In one embodiment, the fixed plate  145  is supported in fixed position proximate or adjacent to the fuel chamber  120 , and the slideable plate  150  is coupled to a flexible diaphragm  155 , that flexes in response to changes in pressure between the hydrogen pressure in the fuel chamber and ambient pressure. A hole  160  provides the diaphragm access to atmospheric pressure. The diaphragm  155  acts as a pressure responsive actuator that controls the slide valve. Each of the fixed plate  145  and slideable plate  150  has openings (such as perforations) that prevent flow when in a closed position and allow flow when the openings (such as perforations) at least partially line up. 
     The slide valve  143  responds to a pressure differential between ambient and the inside of the power generator. In one embodiment the power generator is cylindrical in shape and the valve plates  145  and  150  are concentric cylinders having mating perforations. Fixed plate  145  and movable plate  150  correspond to an inner cylinder and an outer cylinder respectively. When a pressure differential exists across the membrane  155  such as when hydrogen pressure is greater than ambient pressure, the membrane  155  deflects and moves the outer cylinder  150  axially relative to the inner cylinder. The movement of the outer cylinder relative to the inner cylinder causes the perforations to become misaligned, which closes the valve. 
     The plates in one embodiment are as thin as possible to maintain high conductance, while maintaining sufficient structural rigidity to move without collapse. Thicker sections on the perimeter of the outer plate running parallel to the direction of movement of the valve may be used to improve structural rigidity while maintaining high conductance. Likewise for the inner plate, where thicker sections may be on the inner diameter. 
     Other shaped plates may also be used, and may generally conform to the shape of the fuel container and fuel cell. The valve plates may alternatively form a low friction contact fit in one embodiment as illustrated in  FIGS. 1 and 2  to enable relative movement or sliding. A lubricant  170  may be used to reduce stiction between the plates. As illustrated, the lubricant is at least on the outside of the fixed plate  145  and the inside of the slideable plate  150  where the plates contact each other. The outer dimensions, such as diameter of the fixed plate  145  is very close to the dimensions of the inner dimensions of the slideable plate  150  to form the friction fit. 
     Material combinations should have low coefficient of friction facilitate easy sliding. The materials for both the inner and outer plates can be made of the same material, for example stainless steel or brass. Alternatively they can be of different materials, for example stainless steel or brass for the outer valve, and Teflon filled acetal for the inner valve. The inner diameter of the outer plate could be slightly smaller than the outer diameter of the inner plate, creating a sealing force as the outer plate expands to accommodate the inner plate. 
     In another embodiment, the outer plate could have a cut in the side, with an inside diameter slightly smaller than the outer diameter of the inner plate, such that the outer plate is expanded slightly when placed over the inner plate, and maintains a sealing force against the inner plate. 
     The lubricant may also operate as a sealant. In one embodiment, the lubricant may be graphite or silicone or other lubricant compatible with materials used and the electrochemical reactions occurring. Oil or other hydrocarbon lubricants may also be used. 
       FIG. 3  illustrates a perspective view  300  of a slideable cylindrical valve, according to some embodiments. The slideable cylindrical valve may include two concentric annular components. The central or inner component may be a fixed valve and include perforations in a regular or irregular pattern. The outer annular slideable component may be a movable or rideable valve and may be positioned over the fixed valve. Both the fixed valve and slideable valve may include perforations  306  that line up. Grooves  304  may divide sections of the slits  302  and perforations  306 . The surface of the fixed member of valve  300  may be highly polished and may be covered in lubricant which reduces friction between the fixed valve and slideable valve and provides a gas seal between the fixed and slideable valves. When substantially sealed, the transmission of hydrogen through the valve is approximately 1% or less than the fully open transmittance. 
       FIG. 4  illustrates a schematic view  400  of a perforation pattern for the slideable component  408  of the cylindrical valve, according to some embodiments. The schematic view is shown as planar for convenience; in reality the slideable component is cylindrical. The fixed component of the cylindrical valve may be manufactured primarily of metal, such as stainless steel or brass. The slideable component  408  may also be manufactured primarily of metal such as stainless steel or brass and includes a perforation pattern  406  that substantially mimics that of the fixed component of the valve. Along the longitudinal axis of the slideable component and between the perforations may be slits  402  that separate the slideable component of the valve into flexible sections or “fingers”. The term “longitudinal axis” refers to the height of the cylindrical valve as opposed to the circumference of the cylindrical valve. Displacement of the valve takes place along the longitudinal axis. These sections may be supported at the top and bottom, for example. In one embodiment, the slits are filled with a flexible material (e.g., silicone rubber), which is substantially co-planar with the slideable valve and allow the individual sections to flex and conform to the surface of the fixed valve. The slits may have retaining features  404  that serve as hinges or sutures between the sections, keeping the silicone rubber or other flexible material in place, and keeping the sections in alignment. This provides a substantially sealed closed valve position. When substantially sealed, the transmission of hydrogen and water vapor through the valve is approximately 1% or less than the fully open transmittance. 
       FIG. 5  illustrates a schematic view  500  of a perforation pattern for the slideable component  508  of the cylindrical valve, according to some embodiments. The schematic view is shown as planar for convenience; in reality the slideable component is cylindrical. The fixed component of the cylindrical valve may be manufactured of a metal, such as stainless steel or brass. The slideable component  508  may also be manufactured primarily of metal such as stainless steel or brass and includes a perforation pattern  506  that substantially mimics that of the fixed component of the valve. Along the longitudinal axis of the slideable component and between the perforations may be slits  502  that separate the slideable component of the valve into flexible sections or “fingers”. These sections may be supported at the top and bottom, for example. 
     Grooves  504  are provided that may contain a flexible material (e.g., a rubber band) wrapped around the circumference of the slideable valve that provide compressive force which holds the moveable valve against the fixed valve, providing a gas seal. When substantially sealed, the transmission of hydrogen through the valve is approximately 1% or less than the fully open transmittance. 
     The features shown in  FIG. 4  and  FIG. 5  may be used alone or in combination. 
     In operation, slideable plate  150  may be moved by a diaphragm  155  which is pressure sensitive. If the pressure of matter in the portion of the cell assembly in the volume proximate to slideable plate  150  increases, then diaphragm  155  may bulge out from the chamber volume proximate to slideable plate  150 . Attached at about the center of diaphragm  155  may be a linkage  152  that is attached to slideable plate  150 . When diaphragm  155  bulges out at the center (upward in the  FIG. 1 .) because of pressure, then the linkage  152  may likewise pull slideable plate  150  upward closing the valve and reducing the flow of matter such as water vapor and/or hydrogen gas through the plates in response to the increased pressure. If the pressure increases even more, then diaphragm  155  may expand further outward thereby causing slideable plate  150  to have its non-perforated areas overlap the perforations in fixed plate  145  and effectively stop the flow of matter (e.g., water vapor or hydrogen gas) through plates  145  and  150 . As the pressure decreases in the chamber proximate to slideable plate  150 , then diaphragm  155  may begin returning to a less bulged state and via the linkage push slideable plate  150  so that a part of the openings in both plates  145  and  150  are uncovered or unclosed. Further reduction of the pressure in chamber may result in diaphragm  155  returning to its initial open position thereby moving slideable plate  150  so that the openings  141  and  142  of plates  145  and  150  are aligned such that none of openings  141  and  142  in the plates are effectively obscured by either plate. Again, as the chamber pressure increases, valve  143  begins to close, and as the chamber pressure decreases, the valve  143  begins to open. Thus, the amount of flow through the valve  143  may be determined by the chamber pressure. This approach may provide a regulation of the flow or volume of the gas (e.g., hydrogen) or water vapor from fuel chamber  120  through the valve or of water vapor from the anode side of the fuel cell through the valve and into the fuel chamber. The slideable valve plate  150  may move about one millimeter from fully open to fully closed. Accordingly, hydrogen gas may automatically be produced at a rate at which it is consumed. 
     The valve mechanism described in  FIGS. 1-5  may be designed into a cylindrical fuel cell device as shown in  FIG. 3 . The mechanism may also be designed into a fuel cell generator assembly having some other shape. 
     The power generator is self regulating based on the pressure and electrical demand. As electrical demand increases, hydrogen is consumed to produce the electricity needed by an electrical load. As the hydrogen is consumed, the pressure in the chamber adjacent to the fuel cells drops, valve  143  opens, and the pressure within the fuel chamber  120  also drops, resulting in the release of more hydrogen. As the electrical demand of the load decreases, less hydrogen is consumed, resulting in an increase in pressure, and preventing the further release of hydrogen from fuel  120 . The hydrogen release rate can be very fast, limited only by the rate at which heat can be transferred to the fuel. In this manner, the power generator may provide bursts of power, without great deviation in pressure. The operating temperature may affect the equilibrium pressure within the cell, as the pressure varies with temperature. 
     The power generator  100  may be maintained at an operating temperature of from about −40° C. to about 85° C., from about −20° C. to about 50° C., from about 0° C. to about 50° C. and from about 20° C. to about 50° C. while in use, for example. 
     Fuel chamber  120  may contain a chemical hydride, a metal hydride or a mixture thereof. 
     The chemical hydride is any water-reactive hydrogen-producing material that reacts with water vapor to produce hydrogen. Exemplary chemical hydrides comprise LiAlH 4 , NaAlH 4 , KAlH 4 , MgAlH 4 , CaH 2 , LiBH 4 , NaBH 4 , LiH, and MgH 2 , alkali metals, alkaline earth metals, and alkali metal salicides. Specific chemical hydrides comprise LiAlH 4 , NaAlH 4 , NaBH 4 , LiBH 4 , LiH, or any combination thereof. In one embodiment, the chemical hydride is in the form of pellets. 
     The chemical hydride pellets may be manufactured with a controlled porosity. The size of the chemical hydride particles that comprise the chemical hydride pellets should be in a range from 1-10 μm diameter to minimize resistance to the flow of water vapor through the chemical hydride, and thus adversely affect the rate of hydrogen generation. The distribution of the chemical hydride particle size can be chosen to optimize for rate of reaction or for hydrogen generation capacity. For example a monodisperse distribution of small chemical hydride particles would allow slow flow of water vapor through the chemical hydride, have a high hydrogen generation capacity but a low rate of hydrogen generation. A monodisperse large particle size distribution would allow faster flow of water vapor through the chemical hydride, have a high rate of hydrogen generation, but have a low hydrogen generation capacity. A bimodal distribution in which smaller particles of chemical hydride fit within the interstices of the larger chemical hydride particles could provide a balance between the rate of hydrogen generation and hydrogen generation capacity. Other particle size distributions are also possible. 
     Additionally, by varying which chemical hydride is used, the rate of reaction with water vapor can be adjusted, and therefore the rate of hydrogen generation. This can also be accomplished by using mixtures of two or more chemical hydrides. By varying which chemical hydride is used, and at the same time using a mixture of chemical hydrides, and particle size distribution, the rate of reaction of the chemical hydride with water vapor can further be controlled. 
     The chemical hydride is described herein as a pellet. As used herein this term is used in a broad sense to describe any shape or configuration of the chemical hydride particles that occupy in the space allotted to the chemical hydride in the fuel source. Thus, the shape of the chemical hydride pellet is not critical. It may be a, layer, disk, tablet, sphere, or have no specific shape. The shape of the chemical hydride particles may be determined by the shape of the fuel source and the need to make the most efficient use of the space allotted to the chemical hydride. If appropriate, differently shaped chemical hydride pellets can be used within one fuel source. 
     The chemical hydride pellet stack may be a part of a removable and disposable or recyclable cartridge for an electrochemical cell such as a fuel cell. In such a cartridge, the metal hydride fuel would be retained in the electrochemical cell, while the stack of chemical hydride pellets and spacers would be removable. Alternatively, the chemical hydride pellets and a portion of the enclosure may be removable from the remainder of the enclosure containing the porous metal hydride. Thus, a fresh chemical hydride pellet stack could replace an exhausted chemical hydride pellet stack allowing the portion of the electrochemical cell containing the porous metal hydride to be reused. For example, the chemical hydride pellet stack can be of a size to fit into an electrical power generator the size of a standard “AA”, “AAA”, “C”, or “D” cell (or any other battery size) that can be removed and replaced. The exhausted chemical hydride pellet stack could also be recycled by addition of new chemical hydride pellets. 
     Two or more compressed porous chemical hydride pellets may be contacted with, or at least partially surrounded or wrapped, or coated with a flexible, porous water-vapor permeable layer (such as TEFLON, GORE TEX, or NAFION) that prevents fuel particles from expanding into gas diffusion channels adjacent the pellets or other fuel source pellets. The gas diffusion channels may be constructed of porous metal hydride pellets for example. Air gaps may be located between individual chemical hydride pellets, and between the chemical hydride pellets and slide valve  143 . A liquid water impermeable, hydrogen and water-vapor permeable membrane or a particulate membrane (such as TEFLON, GORE TEX, or NAFION) may also be positioned between chemical hydride pellets and slide valve  143 . 
     When a chemical hydride is used as fuel, the water formed as a byproduct of an oxygen-hydrogen reaction at the fuel cell  125  may passively diffuse back through the slide valve into the fuel chamber  120 . On the anode side  135  of the fuel cell  125 , a relatively low humidity region may exist due to a moisture absorbing nature of the fuel substance in fuel chamber  120 . Thus, the water retention at the cathode  140  may generate a moisture concentration gradient and a gas pressure differential which causes water molecules to diffuse back through the fuel cell  125  through the slide valve and into fuel chamber  120  in the form of water vapor. This water vapor may react with the chemical hydride fuel in fuel chamber  120  and generate hydrogen gas. The generated hydrogen gas may then pass back through the slide valve and to the fuel cell anode  135  where it can react with oxygen to once again generate electricity and water molecules. This cycle may continue until all of the fuel in chamber  120  is consumed. 
     In another embodiment, a metal hydride may be chosen as a fuel substance for the fuel storage substance. Metal hydrides function as a sort of hydrogen sponge that can quickly adsorb or desorb hydrogen at an almost constant pressure. Potential metal hydrides include ab5, ab2, ab, complex alloys, intermetallic compounds or solid solution alloys. Specific materials include but are not limited to LaNi5, LaNi4.6Mn0.4, MnNi3.5Cu0.7Al0.8, MnNi4.2Cu0.2Mn0.3Al0.3, TiFe0.8Ni0.2, CaNi5, (V0.9Ti0.1) 0.95Fe0.05, (V0.9Ti0.1) 0.95Fe0.05, and LaNi4.7Al0.3 or any combination thereof. 
     In one embodiment, an AB5 type materials such as LaNi5, or alloys containing other metals such as aluminum may be used as the reversible metal hydride. The other alloys such as aluminum may be used to tailor the pressure-temperature characteristics of the fuel so that the equilibrium hydrogen pressure at room temperature, approximately 20° C. is in the range of 0.1 PSI up to about 100 PSI or higher. In one embodiment, the pressure ranges up to about 10 PSI to avoid high rates of hydrogen leakage to ambient. Some applications may use even higher pressure with stronger containers. A higher fraction of aluminum results in a lower pressure equilibrium. In one embodiment the metal hydride is such that its equilibrium pressure is in the range of approximately 0.01 to 10 atmospheres over an approximately −20 to 60° C. temperature range. 
     In one embodiment, the metal hydride fuel storage material is in the form of solid pellets and is approximately 20% porous. The porosity may be varied to control volume expansion and hydrogen generation rate. Multiple pellet segments may be stacked vertically to provide a cylindrical pellet with larger height. The height of the individual segments may also be varied to increase the pellet surface area, which may also increase the hydrogen generation rate. 
     In one embodiment, fuel chamber  120  includes multiple metal hydride fuel pellets stacked in a vertical relationship. A hydrogen permeable membrane may optionally be disposed about the fuel pellet segments, which may be cylindrical in shape. The membrane may extend over the ends of the stack of fuel pellets in some embodiments. An air gap may be provided between the membrane and fuel pellet if desired. 
     The metal hydride is described herein as a pellet. As noted above, the term metal hydride pellet used herein this term is used in a broad sense to describe any shape or configuration of the metal hydride that occupies the space allotted to the metal hydride in the fuel source. Thus, the shape in which the porous metal hydride exists is not critical. It may be present as a porous film, web, layer, disk, tablet, sphere, or have no specific shape. The shape of the porous metal hydride pellet may be determined by the shape of the fuel source and the need to make the most efficient use of the space allotted to the metal hydride. If appropriate, differently shaped metal hydride pellets can be used within one fuel source. 
     In some embodiments, the fuel source comprises a combination of a chemical hydride and a metal hydride. A power generator with a fuel consisting of chemical hydride and metal hydride can accommodate pulses of power by using some of the hydrogen stored in the metal hydride, and can thus be designed for the average power of the range, resulting in lower cost, and reduced self-discharge. Additionally, sensitivity to ambient temperature and humidity may be reduced, because the power generator can draw on the hydrogen stored in the metal hydride. 
     In one embodiment, two or more chemical hydride pellets may be separated by a metal hydride pellet. The metal hydride may act as both a gas diffusion channel, and as a reversible hydrogen storage element for rapid delivery of hydrogen. The metal hydride may be positioned such that two stacks of chemical hydride pellets are formed. The two or more chemical hydride pellets may be contacted with, or at least partially surrounded or wrapped with a flexible, porous water-vapor permeable layer (such as TEFLON, GORE TEX, or NAFION). Each chemical hydride pellet may be separated by a spacer. Air gaps are between individual chemical hydride pellets, and between the chemical hydride pellets and perforated enclosure. A liquid water impermeable, hydrogen and water-vapor permeable membrane or a particulate membrane (such as TEFLON, GORE TEX, or NAFION) may also be positioned between the pellets and enclosure. A particulate filter may be positioned between the stacks of chemical hydride pellets and slide valve  143 . 
     The walls of fuel chamber  120  may be the same as those of the inner valve or may be a separate structure that is located inside the valve. The enclosure may contain perforations to permit water ingress through the enclosure walls into the outer surface of the pellet, from where water can then diffuse inward. The enclosure may be shaped as a cylinder. 
     The fuel chamber  120  of the power generator may be sealed and fuel may added through an opening having a removable cover adjacent to or part of the fuel chamber  120  which seals fuel chamber  120  when the cover is in place. 
     While the present invention has been particularly shown and described with reference to many embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above and all equivalents thereto.