Abstract:
A device has an annulus having a first end and a second end. A valve plate is coupled to the first end of the annulus by a fastener, wherein the valve plate is adapted to contact a valve seat on a hydrogen producing fuel cover. A diaphragm is coupled to the second end of the annulus by a fastener, wherein the annulus extends through a container for holding the hydrogen producing fuel and wherein the diaphragm moves the valve plate relative to the valve seat responsive to a different in pressure across the diaphragm.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to the following two applications filed on the same date herewith: Fuel Cell Based Power Generator (Applicant Reference Number: H0019541) and Method of Manufacturing Fuel Cell Based Power Generator (Applicant Reference Number: H0020226). 
       BACKGROUND 
       [0002]    Proton exchange membrane (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. At an anode, hydrogen molecules are ionized by a platinum catalyst, and give up electrons. The PEM allows protons to flow through, but not electrons. 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. 
         [0003]    In some prior PEM fuel cell based power generator, a pneumatic valve is used to control a hydrogen generating chemical reaction that feeds hydrogen oxygen PEM fuel cells. The valve comprises a substantial portion of the power generator volume and weight, and thus reduces the energy density and specific energy of the power generator. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a block diagram of a power generator according to an example embodiment. 
           [0005]      FIG. 2  is an enlarged block diagram of a portion of the power generator of  FIG. 1 . 
           [0006]      FIG. 3A  is a top view of a segment of a fuel cell membrane pattern according to an example embodiment. 
           [0007]      FIG. 3B  is a top view of a ring shaped adhesive pattern according to an example embodiment. 
           [0008]      FIG. 3C  is a top view of a cathode metallization pattern according to an example embodiment. 
           [0009]      FIG. 3D  is a top view of a finished cathode electrode that includes multiple sections for contacting multiple fuel cell membrane segments according to an example embodiment. 
           [0010]      FIG. 3E  is a top view of an anode metallization pattern used to form an anode electrode according to an example embodiment. 
           [0011]      FIG. 3F  is a top view of an anode electrode formed from the pattern of  FIG. 3E . 
           [0012]      FIG. 4  is a cross sectional block schematic diagram illustrating electrical connections between segments of fuel cell stacks according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    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. 
         [0014]    Various embodiments of a PEM fuel cell based power generator of various shapes are described. In one embodiment, the power generator is formed with the shape of a CR2032 battery, which is commonly used in watches, sensors and other electronic equipment. Such reduced height form factor may be achieved by one or more of several innovative features described herein. 
         [0015]      FIG. 1  is a cross section block diagram of a power generator  100  according to an example embodiment.  FIG. 2 , is a blown up cross section block diagram view of one side of the power generator  100 , with numbering consistent with  FIG. 1 . Power generator  100  has a container  110  adapted to hold a hydrogen generating fuel. The container may be cylindrical or rectangular in shape. Many other shapes, such as other polygons may be used as desired. A valve assembly having a valve plate  112  has a border that fits within a border of the container  110 . A fuel cell  114 , having multiple segmented fuel cells connected in series as described in further detail below, is laterally disposed outside and around the valve assembly. The fuel cell  114  has a lateral width that fits within the border of the container  110 . A cover indicated generally at  115  is adapted to mate with the container  110  and enclose the valve plate  112  and fuel cell  114 . Many of the components of power generator  100  may be formed of stainless steel 316, or nickel plated steel. Other materials may also be used in further embodiments that provide suitable conductive, corrosion resistant and structural properties. 
         [0016]    In one embodiment, the fuel cell is ring shaped, with multiple fuel cells electrically coupled with one another. In one embodiment, the fuel cell comprises five arc shaped fuel cells, referred to as fuel cell segments, serially coupled to form a full circular fuel cell. Other shaped fuel cells may be used with different power generator shapes in further embodiments, such as a straight or angled segments for polygon shaped power generators. Each fuel cell segment in one embodiment produces approximately 0.6 V under load, for a total of 3V. The fuel cell has multiple layers extending radially from outside the valve plate  112 . Fuel cell  114  in one embodiment is a proton exchange membrane (PEM) type of fuel cell. 
         [0017]    In one embodiment, a portion of the cover  115  is electrically coupled to the fuel cell  114  to form an anode cap  118  via an anode tab  120 , and the container  110  is electrically coupled to the fuel cell  114  to form a cathode via a cathode tab  122 , which may be adhesive backed in one embodiment. Cover  115  in one embodiment comprises anode cap  118  coupled to a fuel cap  124 . The anode cap  118  and fuel cap are electrically insulated from each other by an insert  126 . In one embodiment, the insert  126  may be formed of PET. Other electrically insulative materials may also be used in further embodiments. 
         [0018]    In one embodiment, the power generator  100  container  110  and cover  115  when assembled define a low height cylindrical exterior of the power generator and have dimensions compatible with a CR2032 battery form factor having an outer diameter of approximately 20 mm and height of approximately 3.2 mm. The anode cap diameter is approximately 16.5 mm in this embodiment. The power generator  100  may be formed with many other dimensions. Power generator  100  is well suited to lower height designs due to the ability to form both the valve plate and fuel cell in a similar planar region above the fuel container  110  defined by the cover  115 . The term, “diameter” refers to the distance between opposing borders, and may be used for cylinders or power generators of other shapes. 
         [0019]    In one embodiment, the fuel cap  124  has a valve seat  128  positioned laterally inside the fuel cell  114  and formed to mate with the valve plate  112  to regulate flow of water vapor generated by the fuel cell  114  to fuel  130  contained within the container  110 . PTFE or other suitable material may be used at the interface between the valve seat  128  and valve plate  112  to prevent stiction and to provide a better seal. 
         [0020]    In one embodiment, the valve assembly includes a valve stem assembly  132  coupled to the valve plate  112  at a first end, extending through an opening in the fuel container  110  defined by a side wall  134 . The valve stem assembly  132  is coupled to a diaphragm  136  at a second end. The diaphragm  136  is retentively coupled to the fuel container by a diaphragm support  138  fastened to the container within a recess of the container indicated at  140 . The use of such a recess provides a fairly flat bottom of the container, which in some embodiments may be consistent with a CR2032 form factor battery. In one embodiment, the diaphragm support  138  is electrically coupled to the container  110  and also serves as part of the cathode. The diaphragm support  138  has an opening  142  proximate the diaphragm  136  such that a difference in pressure across the diaphragm  136  controls the position of valve plate  112 . In one embodiment, a bottom end of the valve stem assembly  132  is recessed within the recess  140  such that motion of the diaphragm will not result in movement of the bottom of the valve stem assembly beyond the bottom of the container  110 . 
         [0021]    The use of a recess  140  for the diaphragm  136 , combined with the use of a diaphragm  136  having a smaller border than the fuel container  110 , allows for more fuel to be contained within container  110  than in fuel cells having larger diaphragms. The border of the diaphragm need not be the same as the valve plate  112 , but should provide sufficient deflection of the valve plate  112  for expected operating conditions of the power generator  100 . 
         [0022]    The fuel  130  may be formed in a pellet with multiple levels corresponding to the area of the container without the recess, and the area with the recess. In one embodiment, the fuel  130  is a pressed pellet utilizing LiAlH4 as the fuel. In further embodiments, one or more pellets may be used having a metal hydride, or combination of areas of metal hydride and chemical hydride to supply higher rates of hydrogen during pulse power demand. Many different types of metal and chemical hydrides to provide hydrogen in response to water vapor may be used in further embodiments. One or more diffusion channels  131  may be provided in the fuel pellet in ensure penetration of water vapor and utilization of a higher percentage of the fuel over the life of the power generator. The channels also allow the fuel pellet to expand without adversely deforming container  110 , and may be selected to be just wide enough for such expansion to optimize the volume of fuel that may be provided within a desired form factor. In one embodiment, channel  131  is an annular channel. Further channels or holes may be provided in various patterns through one or more fuel pellets to optimize water vapor penetration. 
         [0023]    In one embodiment, fuel cap  124  contains openings allowing water vapor and hydrogen to pass through. The openings are located within a radius of the valve seat  128 . A membrane  143 , such as a Gore-Tex® membrane may be disposed over the openings to serve as a particulate filter and a hydrogen and water vapor permeable, liquid water impermeable barrier to prevent water in liquid form from reaching the fuel. The fuel cap  124  has an opening  144  for the valve stem assembly  132 . 
         [0024]    In one embodiment, the valve stem assembly  134  includes an annulus  146  disposed between the valve plate  112  and the diaphragm  136 . The annulus  146  may be cylindrical with internal threads on each end to mate with fasteners, such as screws  148 ,  150  for coupling the valve plate  112  and diaphragm  136  respectively to the annulus  146 . In one embodiment, the head of the screw  150  may be reduced in height such that it is approximately 1/16 th  of an inch to provide more clearance for movement of the diaphragm without the screw  150  head moving outside the bottom of diaphragm support  138 . In one embodiment, the screws have approximately 160 threads per inch. The screw  150  creates a gas seal about the diaphragm  136  and annulus  146  in one embodiment. 
         [0025]    The use of the annulus  146  and fasteners  148 ,  150  provides flexibility in manufacturing, as either end may be assembled first. Opening  142  also provides access to fastener  150 , allowing the flexibility of fastening the diaphragm  136  to the valve stem assembly  132  when desired. Other types of fasteners, such as snap fit fasteners may also be used with suitable modifications to the annulus  146  to mate with such snap fit fasteners  148 ,  150 . 
         [0026]    In one embodiment, fuel cell  114  is formed as a fuel cell stack having multiple layers, including a cathode layer that is disposed proximate, yet insulated from the anode cap  118 . Anode cap  118  has openings therein to allow oxygen to contact the cathode layer, which as illustrated at  122 , has an electrically conducting tab extending down to contact the fuel cap  124 . 
         [0027]    In one embodiment, the fuel cell  114  contains the following layers extending downward toward the fuel container in this embodiment. A 1 mil EPTFE membrane, a 1 mil adhesive, 4 mil adhesive and gas diffusion layer, Gore MEA (membrane electrode assembly), 4 mil adhesive and gas diffusion layer and 2 mil Kapton® layer. This is followed by an optional porous compliant material indicated at  152  to help keep the fuel cell in place. An open gap  153  may be filled with epoxy or other material if desired. 
         [0028]    In one embodiment, the EPTFE membrane may be used to prevent shorting problems between the gas diffusion layer and anode cap  118 . The membrane may be a dielectric gas permeable membrane that prevents shorts between anode cap  118  and the fuel cell stack. The next adhesive layer is a double sided adhesive, such as a Kapton® membrane with adhesive on both sides to hold adjacent layers of the fuel cell stack together and provide a gas seal. The next Kapton layer serves as the cathode electrode. The layer has a gold surface with laser cut through holes patterned on it. Further detail is provided in the following figures. The adhesive and gas diffusion layer is like a frame of adhesive with inside regions cut out to expose the fuel cell membrane to gas. The fuel cell membrane may be a Gore MEA (membrane electrode assembly) that serves as the active fuel cell membrane for the power generator  100 . The following adhesive and gas diffusion layer and 2 mil Kapton® layer are also patterned with gold, forming the anode electrode. 
         [0029]    As shown in  FIGS. 1 and 2 , the anode electrode cap  118  contains two annular ring posts  154 ,  156  defining an annular opening for the fuel cell  114 . An outside annular post  158  forms an opening for mating with the insulative insert  126 , and also defines the outer diameter of the anode. The fuel cap  124  contains an annular portion  160  that mates with a top outside portion of the fuel container  110  which may contain a chamfered edge  161  to provide for self alignment. The mating provides a gas seal by use of epoxy, laser weld or other connection method. Similarly, sidewall  134  of container  110  may also have a chamfer to mate in a self aligning manner with an internal annular edge  161  of the fuel cap  124 . 
         [0030]      FIGS. 3A ,  3 B,  3 C,  3 D,  3 E and  3 F are top views of various components that may be assembled to form the fuel cell  114  stack.  FIG. 3A  illustrates a membrane pattern  310  that may be duplicated such that five of them in one embodiment are disposed in a ring pattern in the stack. A ring shaped adhesive pattern is shown at  315  in  FIG. 3B . Adhesive free areas  317  are shown and are generally of the same shape as membrane patters  310 . A conductive layer  318  is disposed between the adhesive free areas, and may be formed of a conductor, such as gold. Conductive layer  318  allows sections of the fuel cell to be electrically serially connected. Adhesive  319  is disposed on both sides of the adhesive pattern in the remaining portions of pattern  315 . 
         [0031]      FIG. 3C  illustrates a cathode metallization pattern  325 . Segmented metal areas  327  corresponding to the membrane pattern  310  are formed, along with metal free areas  328 . A tab  330 , corresponding to tab  122  in  FIGS. 1 and 2 , is also formed with metal coating to provide the cathode tab for connection to an external cathode for the power generator  100 .  FIG. 3D  illustrates a finished cathode electrode  333  that includes five sections for contacting 5 fuel cell membranes. The sections have holes  335  cut through the segmented metal areas  327  to allow gas diffusion to an from the fuel cell membrane. 
         [0032]      FIGS. 3E and 3F  show an anode metallization pattern  340  used to form anode electrode  345  respectively. Metallized segments  342  are formed with holes  346 . Non metal areas  348  are also indicated. An anode electrode tab  350 , corresponding to tab  120  in  FIGS. 1 and 2 , is also formed and used to provide a connection to an external anode for the power generator  100 . 
         [0033]      FIG. 4  is a cross sectional block schematic diagram illustrating electrical connections between segments of fuel cell stacks indicated generally at  400 . Five segments of fuel cell stacks are illustrated, each having a cathode electrode  410 , first adhesive and gas diffusion layer  415 , membrane electrode assembly  420 , second adhesive and gas diffusion layer  425  and anode electrode  430 . Conductive tabs  435 , such as gold tabs, are provided between the segments, and provide a series electrical connection between stacks, connecting an anode of one stack to a cathode of the next stack. An anode electrode output tab  440 , corresponding to tab  120  in  FIGS. 1 and 2 , is coupled to the anode electrode  430  of one stack, and a cathode electrode output tab  445 , corresponding to tab  122  in  FIGS. 1 and 2 , is coupled to the cathode electrode  410  of a stack at the other end of the series connected serial string of stacks. 
         [0034]    In one embodiment, a method of manufacturing power generator  100  may be performed by separately building top (cover  115 ) and bottom (container  110 ) halves and creating an electrical coupling between them utilizing the anode and cathode tabs  120 ,  122 . The fuel cell  114  may be assembled as part of the anode. Part of the valve assembly  132  is placed within the fuel cap  124  that has an integrated valve seat  128 . The anode  118  and fuel cap  124  are then assembled with the “U” shaped electrical insulator  126  between them to electrically isolate anode and cathode. The fuel pellet  130  is then inserted into the cathode/fuel container  110 , and the diaphragm support  138  and diaphragm  136  are assembled into the fuel container recess  140  to maintain the CR2032 battery form factor or other desired form factor. After the fuel container bottom half  110  and top half  115  containing the fuel cell  114  and valve assembly  132  are assembled together, a final screw  150  or snap fit is used to secure the diaphragm  136  to the rest of the valve assembly  132  though the hole  142  in the bottom of the anode. Some of the assembly steps described herein may be performed in a different order than that presented. For instance, the fuel pellet may be inserted in the container  110  well before, during or after assembly of the top half of the fuel cell. In further embodiments, the anode  118  may be the last element coupled to the fuel cell, with screw  148  being attached just prior to coupling of the anode  118 . 
       CONCLUSION 
       [0035]    A hydrogen fuel cell based power generator has a self regulating valve assembly in a low height profile. A valve plate has a smaller border than the border of the power generator, with a fuel cell laterally disposed in a somewhat coplanar ring or other shape around the valve plate. A valve assembly diaphragm also has a smaller border, making room for a larger, multi-level shaped fuel pellets that partially surround the diaphragm. Both of these arrangements combine to provide sufficient valve movement within the form factor height limits, and also allow more fuel to be on board for a power generator with high energy content. 
         [0036]    An annulus (threaded cylinder) may be used to which the valve plate and diaphragm are attached on opposite ends by fasteners, such as screws or snap fit members to clamp them in place. The annulus/fasteners provide a valve pin or stem function. The structure allows for manufacturability given the small form factor. 
         [0037]    A method of manufacturing may be performed by separately building top and bottom halves and creating an electrical coupling between them. The fuel cell is assembled as part of the cathode, and part of the valve is positioned proximate a fuel cap that has an integrated valve seat. The cathode and fuel cap are then assembled with a “U” shaped electrical insulator between them to electrically isolate anode and cathode. The fuel pellet is then inserted into the anode/fuel container, and a diaphragm support and diaphragm are assembled into the fuel container to maintain the CR form factor. After the fuel container bottom half and top half containing the fuel cell and valve parts are assembled together, a final fastener such as a screw or snap fit may be used to secure the diaphragm to the rest of the valve assembly though a hole in the bottom of the anode. 
         [0038]    The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.