Abstract:
A power generator has a hydrogen source, such as a hydrogen producing fuel and a fuel cell having a proton exchange membrane separating the hydrogen producing fuel from ambient. A valve is disposed between the fuel cell and ambient such that water is controllably prevented from entering or leaving the fuel cell by actuation of the valve. In one embodiment, multiple fuel cells are arranged in a circle around the fuel, and the valve is a rotatable ring shaped gate valve having multiple openings corresponding to the fuel cells.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/757,823, filed Jan. 10, 2006, under 35 U.S.C. §119(e). The specification of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     In some fuel cell based power generators, hydrogen is extracted from a fuel in the presence of water and then is introduced into a fuel cell to produce electricity. Power generators based on hydrogen generators and proton exchange membrane (PEM) fuel cells typically offer a narrow range of power outputs over which the power generator operates efficiently. Changing the power output of a power generator usually requires a redesign of the power generator, which is undesirable. 
     SUMMARY 
     A power generator has a hydrogen source, such as a hydrogen producing fuel and a multiple layer fuel cell configuration. The multiple layers or stack of fuel cells provides a power generator that is easily modified to produce a wide range of power outputs without redesign. 
     In one embodiment, each fuel cell in a layer has a proton exchange membrane separating the hydrogen producing fuel from ambient. The layers are arranged in such a manner that ambient, which is a source of oxygen is provided on a cathode side of the membrane, and hydrogen produced from the hydrogen producing fuel is available on the anode side of the proton exchange membrane. Fuel cells may be electrically coupled in series and/or parallel to provide a desired voltage/current. The power generator is designed such that an additional layer or layers may be easily added in series or parallel to increase power output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a cylindrical power generator having multiple layers of fuel cells according to an example embodiment. 
         FIG. 2  is a block schematic diagram of fuel cells in a layer according to an example embodiment. 
         FIGS. 3A and 3B  are electrical schematic diagrams illustrating various electrical connections between fuel cells in a layer according to an example embodiment. 
         FIGS. 4A and 4B  are electrical schematic diagrams illustrating various electrical connections between layers according to an example embodiment. 
         FIG. 5  is a block schematic diagram of fuel cells in a layer according to a further example embodiment. 
         FIG. 6  is a cross section view of a fuel cell stack of layers illustrating electrical connection and the use of water vapor permeable hydrogen impermeable membranes according to an example embodiment. 
     
    
    
     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 is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims. 
     An electrical power generator is provided which generates hydrogen gas internally through the reaction of water vapor with a moisture absorbing, solid fuel substance. The hydrogen gas is reacted with oxygen at a fuel cell, such as a fuel cell containing a proton exchange membrane, 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 that contains the solid 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 may be useful for powering miniature devices such as wireless sensors, cellular phones or other handheld electronic devices that are electrically connected to the anode and cathode of the one or more fuel cells of the power generator. Multiple layers of fuel cells may be supported by a structure that provides access of the fuel cells to oxygen, such as from ambient and hydrogen for generation of power. 
     A single power generator design may accommodate a wide variety of power levels simply by stacking a desired number of fuel cell layers. The fuel cells in each layer may be connected in series, and the layers connected in parallel (to give more current). If, for example, one layer of fuel cells may provide a 10 mW power generator. If 20 mW were required, two layers may be used, and so on. The electrical and gas connections may be made through a central column in the stack of fuel cells. The fuel cells and layers may be electrically coupled in series and/or parallel as desired to provide higher or lower voltages and currents. Layers may be added to increase power output, or removed to decrease power output. 
       FIG. 1  is a cross sectional view of a multiple layer stacked power generator  100 . Power generator  100  contains a hydrogen producing fuel  105  in a container  110 . A support structure  115  is coupled to the container and contains a plurality of plates  120 ,  125 ,  130 ,  135 ,  140  and  145  in a stacked relationship in one embodiment. The plates are coupled together via an inside column  150  and via an outside ring structure  155 . This coupling provides an accordion like cross section, and allows ambient  157  to flow to cathode sides of multiple fuel cells in multiple layers indicated at  160 ,  162  and  164 . The inside column  150  allows hydrogen generated from fuel  105  to flow to anode sides of the multiple fuel cells in multiple layers as indicated at  166 ,  168  and  170 . Electrodes  180  are also shown coupling the multiple layers together to provide desired power levels. The electrodes may also be disposed within the inside column  150  in one embodiment, or located elsewhere in further embodiments. 
     Each of the assembled component parts of the power generator  100  may further be enclosed in a suitable hollow structure such as a tube formed from a suitable material, such as polyethylene terephthalate (not shown), which enclosure may also be capped on the top and/or bottom surfaces with a suitable cap (not shown), which cap may be removable and may be formed of a similar or different material as the enclosure. 
     In one embodiment, as shown, three levels of fuel cells are provided. For example, if each layer provided 10 mW of power, the power generator provides 30 mW of power. Layers may provide different power levels depending on design and size. Additional layers of plates with corresponding fuel cells may be added to increase the power output, or fewer layers may be used to decrease the power output. The power generator is easily configured to meet the requirements of different devices it may be used to power without having to re-design the power generator. In further embodiments, multiple layers of fuel cells may be provided, but only a desired number of layers need be electrically connected. This would allow the same power generator to be configured to provide different power output levels. 
     Support structure  115  is electrically isolated from the fuel cells in one embodiment. It may be constructed of PET, or steel, or other materials that provide sufficient support. 
     In one embodiment, the outside ring structure  155  may have holes or openings corresponding to passages or channels between plates or support structure  115  to allow passage of ambient air to the cathodes. It may also be completely open as indicated, or simply have pillars or other supporting structures to provide mechanical stability as desired. The inside column  150  may be similarly constructed to allow access of the anodes to hydrogen. 
     Plates  125 ,  135  and  145  provide support structures for supporting the fuel cells. As indicated above, each fuel cell has a cathode and an electrode. The plates also ensure that each side of the fuel cell is exposed to the proper medium, such as ambient for cathode sides and hydrogen for anode sides of the fuel cells. Plates  120 ,  130  and  135 , which alternate with the support plates, serve as a barrier to ambient for the anodes, and also provide a path or channel from ambient to the cathodes. 
     In one embodiment, a pressure regulated valve  182  is disposed between the hydrogen producing fuel and the fuel cells. The valve consists of a pressure responsive flexible diaphragm  184  disposed on a first side of the hydrogen producing fuel, and a piston or stem  186  connecting a plate valve  188  for seating on a plate  120  of the support structure. Plate  120  may have an annular seat ring  190  for making a sealing contact with the plate valve  188 . 
     In the embodiment shown, the diaphragm is opposite the fuel cells from the fuel. In further embodiments, the diaphragm may be positioned on the same side, or in various different places on the power generator as desired. The diaphragm operates in a manner similar to the above described embodiments. The fuel  805  may also be constructed in a manner similar to the above described embodiments. 
     In a further embodiment, a rotating ring gate valve may be placed between plates, such as plates  125  and  137  to selectively close off fuel cells supported in plate  125  from ambient. Other layers in the fuel cell may continue to operate normally. In a further embodiment, a ring gate valve may be placed to close off ambient from all fuel cells as desired. An additional plate above plate  145  may be used to support such a ring gate with respect to the fuel cells supported in plate  145 . 
     Each of the parts of the power generator  100  may be fabricated of a suitable polymeric material, a metal or other material as determined by the requirements of the intended use of the generator. One example material non-exclusively includes polyethylene terephthalate. Dimensions of the component parts of the power generator  100  may be very small in scale, but may also vary with respect to the use of the power generator  100 . Outer dimensions of such a waterless, micro-power generator may range from about 1 mm to about 100 mm in length, from about 1 mm to about 100 mm in width, and from about 1 to about 100 mm in depth, or in a further embodiment, from about 1 mm to about 25 mm in length, or long if more cells are stacked. In further embodiments, the power generator may range from about 1 mm to about 25 mm in width, and from about 1 to about 25 mm in depth. These dimensions are meant merely to be examples, and as limitations, as further embodiments may be much larger or smaller. 
       FIG. 2  is a block schematic diagram of fuel cells in one layer according to an example embodiment. Each layer may have a different fuel cell layout as desired, or the same layout. In one embodiment, the shape of the fuel cells is designed to optimize the utilization of surface are of the layer. As shown in  FIG. 2 , four fuel cells,  210 ,  220 ,  230  and  240  are pie shaped, and are supported by portions of support structure  115 . The inside column  150  is shown at the center of the layer. Electrical connections to various layers may be made through the inside column  150  in one embodiment. In further embodiments, more or fewer fuel cells of various shapes and sizes may be utilized. Other shapes include but are not limited to rectangles, squares, circles, triangles, etc. The pie shape shown may provide a higher power density by maximizing the surface area available within a fixed diameter power generator container. 
       FIGS. 3A and 3B  are electrical schematic diagrams illustrating various electrical connections between fuel cells in a layer according to an example embodiment.  FIG. 3A  illustrates a series connection between six fuel cells in a layer. The cells are coupled anode to cathode within the layer, with the anode and cathode of one set of adjacent fuel cells providing contacts  310 ,  315  for coupling with fuel cells in further layers and to an external load.  FIG. 3B  illustrates a parallel connection between six fuel cells in a layer. Each of the cathodes may be connected to each other with a contact  320 , and each of the anodes may be connected to each other with a contact  325 . Contacts  320  and  325  serve as connection points to other layers, and to an external load. 
       FIGS. 4A and 4B  are electrical schematic diagrams illustrating various electrical connections between layers according to an example embodiment.  FIG. 4A  illustrates a parallel connection between three layers. Conductor  410  is coupled to an anode in each of layers  125 ,  135  and  145 , while conductor  415  is coupled to a cathode in each of layers  125 ,  135  and  145 .  FIG. 4B  illustrates a series connection between three layers in a power generator. An anode of layer  125  is coupled to a cathode of layer  135  via a connector  420 . An anode of layer  135  is coupled to a cathode of layer  145  via a connector  425 . Anode  435  of layer  135  and cathode  440  of layer  125  may be connected to a load. In further embodiments, connectors  420  and  425  may connect different electrodes of the layers as desired. Either method of connecting the layers may be mixed with different methods of connecting the cells in a layer, providing a broad range of voltage and current options. Further layers may also be added for increased power. Fewer layers may also be used, or layers may be left unconnected to reduce power. 
     In further embodiments, the size of the layers and power generator in general may be modified to obtain a broad range of powers. Further layers may be added to increase power levels if desired. Selected fuel cells may be coupled to uncoupled in further embodiments if desired. 
     In one embodiment, the power provided by a single fuel cell is proportional to the area of the fuel cell proton exchange membrane. The voltage produced by the fuel cell is approximately 0.95 volts, and may drop when a load draws current from the fuel cell. A typical operating range for a fuel cell is between 0.6 and 0.65 volts. Connecting several cells in parallel may tend to result in a higher operating voltage for a given current draw. Similarly, to increase the voltage of a set of cells, they may be connected in series. To maintain a higher voltage under load, a set of cells, such as all cells in a layer may be coupled in series, while the different layers may be connected in parallel. These are just a few examples of configurations that may be achieved by modifying electrical connections without changing the fundamental design of the power generator. By electrically coupling fuel cells within a layer in series and/or parallel and electrically coupling layers in series and/or parallel, desired electrical characteristics such as voltage and/or current may be obtained. 
       FIG. 5  is a block schematic diagram of fuel cells in a layer  500  according to a further example embodiment. In this embodiment, five fuel cells,  510 ,  515 ,  520 ,  525  and  530  are coupled in series. A cathode of each fuel cell is coupled to an anode of an adjacent fuel cell, with the cathode  535  of fuel cell  525  electrically coupled to an access contact point  540  in a central column  545 . An anode  550  of fuel cell  530  is coupled to an access contact point  555  in central column  545 . The access points of various layers in a stacked layer power generator may be easily coupled via the central column  545 , which also provides hydrogen to the fuel cells. 
       FIG. 6  is a cross section view of a fuel cell stack  600  illustrating electrical connections  610 ,  615  to various layers of fuel cells through a column  540 , and the use of water vapor permeable hydrogen impermeable membranes  620 ,  625  and  630  according to an example embodiment. The water vapor permeable hydrogen impermeable membranes  620 ,  625  and  630  may be Nafion® membranes in one embodiment. They may be set opposite the fuel cells  640 ,  645  and  650  in one embodiment, and may be used to reclaim water produced by the fuel cells. In this configuration, the fuel cells may operate at significantly higher current density because they don&#39;t need to serve a dual purpose of generating electricity and reclaiming the water. Column  540  may be a central column, and may serve as a conduit for electrical conductors that may be used to electrically couple various layers of fuel cells in a desired manner, such as in series or in parallel. 
     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.