Abstract:
A fuel cell systems and methods involving decomposing an inorganic oxygen containing salt that decomposes into oxygen and a non-volatile salt and/or mixing fuel cell reaction byproducts with an absorbent material that endothermically reacts with the fuel cell reaction byproducts.

Description:
BACKGROUND OF THE INVENTIONS  
       [0001]     1. Field of the Inventions  
         [0002]     The present inventions are related to fuel cell systems.  
         [0003]     2. Description of the Related Art  
         [0004]     Fuel cells, which convert reactants (i.e. fuel and oxidant) into electricity and reaction products, are advantageous because they are not hampered by lengthy recharging cycles, as are rechargeable batteries, and are relatively small and lightweight. Nevertheless, the present inventors have determined that conventional fuel cells are susceptible to improvement. For example, ambient air is not available in many instances and oxidant (typically oxygen) must be stored in compressed form within the fuel cell system or host device. The present inventors have determined that because oxygen in the gas phase has relatively low density, large volumes of oxygen must be stored when the fuel cell is using relatively high energy density fuels such as hydrocarbons. The present inventors have also determined that the use of fuel cells which operate at a relatively high temperature (e.g. 200° C. and above) and/or produce relatively humid exhaust can present a variety of challenges. Extensive insulation is required to protect users and other devices from the heat, while the high levels of humidity can result in significant condensation as the exhaust cools. These issues are magnified in closed systems, including some military applications, where the exhaust from the fuel cell cannot be vented and heat cannot be detectable.  
       SUMMARY OF THE INVENTIONS  
       [0005]     An apparatus in accordance with one of the present inventions includes a fuel cell and an oxygen supply operably connected to the fuel cell. The oxygen supply may, for example, include an inorganic oxygen containing salt that decomposes into oxygen and a non-volatile salt.  
         [0006]     A method in accordance with one of the present inventions includes the steps of decomposing an inorganic oxygen containing salt into oxygen and a non-volatile salt and supplying the oxygen to a fuel cell.  
         [0007]     An apparatus in accordance with one of the present inventions includes a fuel cell and means, operably connected to the fuel cell, for decomposing an inorganic oxygen containing salt into oxygen and a non-volatile salt.  
         [0008]     An apparatus in accordance with one of the present inventions includes a power consuming device and a fuel cell system. The fuel cell system may include a fuel cell, a fuel supply, and an oxygen supply with an inorganic oxygen containing salt that decomposes into oxygen and a non-volatile salt.  
         [0009]     An apparatus in accordance with one of the present inventions includes a fuel cell and a waste products storage device. The waste products storage device may include an absorbent material that endothermically reacts with byproducts from the fuel cell.  
         [0010]     A method in accordance with one of the present inventions includes the steps of transferring fuel cell reaction byproducts to a waste products storage device and mixing the fuel cell reaction byproducts with an absorbent material that endothermically reacts with the byproducts.  
         [0011]     An apparatus in accordance with one of the present inventions includes a fuel cell and means for receiving byproducts from the fuel cell, using the byproducts in an endothermic reaction, and storing all products of the endothermic reaction.  
         [0012]     An apparatus in accordance with one of the present inventions includes a power consuming device and a fuel cell system. The fuel cell system may include a fuel cell and a waste products storage device, operably connected to the fuel cell, including an absorbent material that endothermically reacts with byproducts from the fuel cell. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Detailed description of embodiments of the inventions will be made with reference to the accompanying drawings.  
         [0014]      FIG. 1  is a diagrammatic view of a fuel cell system in accordance with an embodiment of a present invention.  
         [0015]      FIG. 2  is a section view of a fuel cell that may be employed in the system illustrated in  FIG. 1 .  
         [0016]      FIG. 3  is a section view of an oxidant supply in accordance with an embodiment of a present invention.  
         [0017]      FIG. 4  is a section view taken along line  4 - 4  in  FIG. 3 .  
         [0018]      FIG. 5  is a diagrammatic view of a power consuming apparatus in accordance with an embodiment of a present invention.  
         [0019]      FIG. 6  is a diagrammatic view of a fuel cell system in accordance with an embodiment of a present invention.  
         [0020]      FIG. 7  is a diagrammatic view of a fuel cell system in accordance with an embodiment of a present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0021]     The following is a detailed description of the best presently known modes of carrying out the inventions. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the inventions. It is noted that detailed discussions of fuel cell structures that are not pertinent to the present inventions have been omitted for the sake of simplicity. The present inventions are also applicable to a wide range of fuel cell technologies and fuel cell systems, including those presently being developed or yet to be developed. For example, although various exemplary fuel cell systems are described below with reference to solid oxide fuel cells (“SOFCs”), other types of fuel cells, such as molten carbonate fuel cells, are equally applicable to the present inventions. Also, although the exemplary fuel cells described below are multi-chamber fuel cells, the present inventions are also applicable to single chamber fuel cells.  
         [0022]     As illustrated for example in  FIGS. 1 and 2 , a fuel cell system  100  in accordance with one embodiment of a present invention includes one or more fuel cells  102  packaged in housing  104 . The exemplary fuel cell  102 , which is an SOFC, includes an anode  106  and a cathode  108  separated by an electrolyte  110 . Current collectors (not shown) are respectively associated with the anode  106  and cathode  108 . The anode  106  and cathode  108 , on opposing faces of the electrolyte  110 , are each composed of a thin catalyst layer and, optionally, a gas diffusion layer. A fuel supply  112  supplies fuel, e.g. hydrocarbon fuels such as methane (CH 4 ), ethane (C 2 H 6 ), propane (C 3 H 8 ) etc., to the anode  106  by way of a manifold (not shown) in the housing  104  and an oxidant supply  114  supplies oxidant, such as oxygen (O 2 ), to the cathode  108  by way of a manifold (not shown) in the housing. The fuel is electrochemically oxidized at the anode catalytic surface, reacting with O 2−  ions that were produced by the reaction of O 2  with the cathode catalytic surface and diffused across the O 2−  conducting electrolyte  110 . The reaction at the anode produces byproducts, i.e. water vapor (H 2 O) and carbon dioxide (CO 2 ) in the exemplary embodiment. In those instances where a plurality of fuel cells are arranged in a stack, the current collectors of the individual fuel cells may be connected to one another in series or parallel depending on the load.  
         [0023]     The exemplary fuel cell system  100  is also provided with a waste products storage device  116 , which may be used to store byproducts from the fuel cell  102 , and a heat exchanger  118 , which may be used to heat the reactants before they reach the fuel cell  102 . In some instances, unused reactants may also be stored. A controller  120  may be provided to monitor and control the operations of the exemplary fuel cell system  100 . Alternatively, the operation of the fuel cell system may be controlled by the host (i.e. power consuming) device. The system components described above are located within a housing  122 , which is preferably insulated, and a pair of electrical contacts  124   a  and  124   b  are associated with the exterior of the housing.  
         [0024]     The exemplary fuel cell system  100  is a “closed” system and, to that end, the fuel supply  112 , oxidant supply  114  and housing  122  are not configured to permit removal and replacement of the fuel and oxidant supplies. All of the reactants that will be consumed by the “closed” system are initially present in the system. The storage device  116  will also remain in the housing  122  and, to that end, all of the byproducts generated by the fuel cell reaction (as well as any unused reactants that pass through the fuel cell) will remain within the housing. Alternative fuel cell system configurations in accordance with the present inventions, which may be “open” to various degrees, are discussed below with reference to  FIGS. 6 and 7 .  
         [0025]     Referring more specifically to the manner in which reactants are stored in the exemplary fuel cell system  100 , and as noted above, the fuel and oxidant supplies  112  and  114  are located within the housing  122 . The respective configurations of the fuel and oxidant supplies  112  and  114  will depend on the manner in which the fuel and oxidant is stored. In the exemplary system  100  illustrated in  FIGS. 1 and 2 , the fuel supply  112  is a pressurized fuel storage device, such as that illustrated in U.S. patent Pub. No. 2003/0136453 A1. The pressure forces the fuel through an anode inlet line  126 . A valve  128  may be provided so that the supply of fuel can be stopped when the fuel cell system is not operating and the quantity of fuel can be precisely metered, based on the load, when the system is operating. Anode-side byproducts and unused reactant (if any) are transferred to the waste products storage device  116  through an outlet line  130 .  
         [0026]     Turning to  FIGS. 3 and 4 , the exemplary oxidant supply  116  includes a housing  132  in which an oxygen producing material  134  is stored. The oxygen producing material in the exemplary implementation is an inorganic oxygen containing salt that will decompose into O 2  and a non-volatile salt when heated. One example of an inorganic oxygen containing salt is a metal chlorate, and preferably an alkali metal chlorate, such as potassium chlorate (KClO 3 ), sodium chlorate (NaClO 3 ) or lithium chlorate (LiClO 3 ). Other examples include metal perchlorates, such as potassium perchlorate (KClO 4 ) and sodium perchlorate (NaClO 4 ), and metal permanganates, such as potassium permanganate (KMnO 4 ). The inorganic oxygen containing salt may be stored in solid form such as, for example, a thick film on a porous medium that is capable of being heated and cooled in the manner described below.  
         [0027]     As noted above, one example of an inorganic oxygen containing salt is a metal chlorate. Metal chlorates will decompose when heated to about 400° C. into a metal chloride and O 2 , e.g. 2KClO 3 →2KCl+3O 2 . Metal chlorates also have relatively high oxygen content, e.g. 1 g of KClO 3  has 0.39 g of O 2 . A solid metal chloride will remain within the housing  132  after the decomposition, and O 2  will be forced out of the oxidant supply  114 , and through a cathode inlet line  136 , due to the pressure buildup within the housing. A filter membrane  137  ( FIG. 3 ) that only allows the O 2  to pass may be positioned within the housing  132  adjacent to the inlet line  136 . Cathode-side byproducts and unused reactant (if any) are transferred to the waste products storage device  116  through an outlet line  138  ( FIG. 1 ).  
         [0028]     There are a number of advantages associated with supplying O 2  in this manner. By way of example, but not limitation, supplying O 2  in this manner allows fuel cells to perform better in situations where ambient air is not available, such as underwater and high altitude applications and those instances where the fuel cell is carried in an airtight container or used in an inert atmosphere. Supplying O 2  in this manner also provides substantial volumetric savings, e.g. 1 cm 3  of KClO 3  produces 639 cm 3  of O 2  at 25° C. and 1 atmosphere.  
         [0029]     The heat for the decomposition of the metal chlorate or other inorganic oxygen containing salt may be provided in a variety of ways, both at startup and after fuel cell operation has begun. In the exemplary implementation illustrated in  FIGS. 3 and 4 , heat is provided at startup by a parasitic heater  140 , i.e. a heater which consumes energy stored in the fuel cell system  100 . The exemplary parasitic heater  140 , which may also be used to regulate the amount of heat that is supplied to the oxygen producing material  134  in the manner described below, is a resistive heater that includes a plurality of resistors  142  in a housing  144 . The heater  140  is powered by a battery  146  that is recharged by the fuel cell  102  during fuel cell operations. The battery  146  may also be used to power the controller  120 . The resistors  142  are carried on the exterior of the housing  132  and, accordingly, the housing  132  should be formed from material that is relatively high in thermal conductivity.  
         [0030]     The parasitic heater  140  may, alternatively, be a fuel burning heater that burns fuel from the fuel supply  112 . Other types of heaters that may be used to provide heat for the decomposition reaction include, for example, microcatalytic combustors, ignition heaters and heat pipes.  
         [0031]     Once the fuel cell reaction has started, heat for the decomposition of the inorganic oxygen containing salt is provided by a heater  148  ( FIG. 4 ) that uses the byproducts from the fuel cell anode and cathode chambers. The exemplary heater  148  is a catalytic combustor which includes a housing  150  that encloses an interior region  152  in which catalytic material (not shown) is located. Referring to  FIG. 1 , the heater  148  receives some of the byproducts and unused reactants (if any) from the anode-side outlet line  130 , which are burned to produce heat, by way of an inlet line  154 . The heater  148  also receives some of the byproducts and unused reactants (if any) from the cathode-side outlet line  138  by way of an inlet line  155 . The output from the heater  148  is transferred to the waste products storage device  116  through an outlet line  156 .  
         [0032]     The heater  148  may, alternatively, be a heat exchanger that draws heat from the fuel cell exhaust. The exhaust may be from the anode, the cathode or both. Other exemplary heaters include microcatalytic combustors, ignition heaters and heat pipes.  
         [0033]     Regardless of the type of heater employed, the heater  148  may be configured in some embodiments of the inventions such that the amount of heat supplied to the oxygen producing material  134  (e.g. the inorganic oxygen containing salt) will be slightly less heat than the amount of heat required to cause substantial decomposition into non-volatile salt and O 2 . The additional heat will be supplied by the parasitic heater  140  as required based on the load on the fuel cell  102 . In other words, the amount of O 2  generated by the oxygen supply  114  may be controlled by controlling the amount of heat supplied to the oxygen supply by the parasitic heater  140 .  
         [0034]     Turning to the manner in which the exemplary system  100  stores fuel cell reaction byproducts and suppresses heat, the heat from the fuel cell reaction may be used to drive endothermic reactions of the byproducts and materials that are stored in the waste products storage device  116 . More specifically, in the exemplary system where the byproducts are H 2 O and CO 2 , the waste products storage device  116  includes a reaction chamber  158  in which an absorbent material  160  is stored. As used herein, the phrase “absorbent material” means a material that efficiently absorbs H 2 O and CO 2  in endothermic fashion. Suitable materials include metals which have a strong tendency to oxidize (e.g. calcium (Ca), strontium (Sr), magnesium (Mg) and aluminum (Al)) and metal oxides (e.g. calcium oxide (CaO), strontium oxide (SrO), magnesium oxide (MgO) and aluminum oxide (Al 2 O 3 )). Exemplary endothermic reactions include H 2 O+CaO→Ca(OH) 2 ; CO 2 +CaO→CaCO 3 ; H 2 O+Ca→CaO+H 2 ; H 2 O+CO 2 2H + +HCO 3   −  (aq.). The products of these reactions remain within the reaction chamber  158  in solid or liquid form.  
         [0035]     The waste products storage device  116  should also be thermally connected to the heat exchanger  118  so that excess heat from the fuel cell  102  can be used to drive the endothermic reaction in the waste products storage device. This may be accomplished by positioning the heat exchanger  118  and waste product storage device  116  in physical contact with one another, or by thermally connecting them to one another with a heat pipe or other heat conduction pathway. Infrared radiation from the heat exchanger  118  may also be used to heat the contents of the waste products storage device  116 .  
         [0036]     There are a variety of advantages associated with storing the byproducts in this manner. By way of example, but not limitation, fuel cell systems with the present waste products storage device do not produce the exhaust associated with conventional fuel cell systems. As such, they are especially useful in closed systems, including some military applications, where the exhaust from the fuel cell cannot be vented. They are also useful in electronic applications, where the condensation exhaust with high levels of humidity can produce significant condensation. The waste products storage arrangement also consumes much of the heat from the fuel cell reaction and, as a result, the extensive insulation associated with conventional fuel cells in not required.  
         [0037]     The waste products storage device  116  may also be used to return H 2  and any unused fuel to the anode inlet line  126 , thereby increasing the overall efficiency of the system. The H 2  and unused fuel pass through a tube  162  to the valve  128 . In the exemplary implementation, a selective membrane  163  (such as a palladium-based membrane) is positioned within the waste product storage device  116  at the inlet to the tube  162 . The selective membrane  163  allows only the H 2  and unused fuel to enter the tube  162 .  
         [0038]     There are also many instances where it is desirable to heat the reactants before they reach the fuel cell  102  and, to that end, the exemplary system  100  includes the aforementioned heat exchanger  118  ( FIG. 1 ). Reactant pre-heating prevents the reactants, which may be at a temperature that is less than the operating temperature of the fuel cell  102 , from cooling the fuel cell. Suitable heat exchangers include microchannel heat exchangers, cross flow microchannel heat exchangers, “Swiss roll” heat exchangers, and metal foam heat exchangers. The heat exchanger  118  receives heated byproducts from the anode and cathode by way of the inlet lines  154  and  155 . After traveling through the heat exchanger  118 , the byproducts are transported to the waste products storage device  116  by way of the outlet line  156 .  
         [0039]     Although the materials, dimensions, and configuration of the fuel cells in the exemplary fuel cell systems will depend upon the type of fuel cell (e.g. SOFC, molten carbonate fuel cell, etc.) and intended application, and although the present inventions are not limited to any particular materials, dimensions, configuration or type, exemplary fuel cells are described below. The exemplary fuels cells are relatively small (e.g. about 10 μm×10 μm to about 10 cm×10 cm) SOFCs. The exemplary fuel cells are also preferably “thin” (i.e. between about 0.3 to 2000 μm thick). The anodes are preferably a porous, ceramic and metal composite (also referred to as “cermet”) film that is about 0.1 to 500 μm thick. Suitable ceramics include samaria-doped ceria (“SDC”), gadolinia-doped ceria (“GDC”) and yttria stabilized zirconia (“YSZ”) and suitable metals include nickel and copper. The cathodes are preferably a porous ceramic film that is about 0.1 to 500 μm thick. Suitable ceramic materials include samarium strontium cobalt oxide (“SSCO”), lanthanum strontium manganate, and bismuth copper substituted vanadate. The electrolytes are preferably a non-porous ceramic film, such as SDC, GDC or YSZ, that is about 0.1 to 1000 μm thick, depending on the material.  
         [0040]     The exemplary fuel cell system  100  may be incorporated into a wide variety of power consuming apparatus. Examples of power consuming apparatus include, but are not limited to, information processing devices such as notebook personal computers (“PCs”), handheld PCs, laptop PCs, and personal digital assistants (“PDAs”), communication devices such as mobile telephones, wireless e-mail appliances and electronic books, video games and other toys, and audio and video devices such as compact disk players and video cameras. Other electronic devices include portable test systems, portable projectors, and portable televisions such as portable flat panel televisions. The exemplary fuel cell assembly  100  may also be used in military, high altitude and undersea applications such as, for example, communication devices, thermal imaging devices, night vision device surveillance devices, chemical detection devices, search and rescue apparatus, and undersea mines.  
         [0041]     Referring to  FIG. 5 , an exemplary apparatus  200  includes a fuel cell system  100  and a power consuming device  202  that is powered by the fuel cell system  100 . The exemplary power consuming device refers to any or all devices within the particular apparatus than consume electrical power. The fuel cell system  100  may be removably inserted into the exemplary apparatus  200  and, to that end, the exemplary apparatus includes a pair of electrical contacts  204   a  and  204   b  that will mate with the fuel cell system electrical contacts  124   a  and  124   b.    
         [0042]     Another exemplary fuel cell system, which is generally represented by reference numeral  100   a  in  FIG. 6 , is configured for use in those instances where ambient air is available as an oxidant source. The exemplary fuel cell system  100   a  is substantially similar to the fuel cell system  100  illustrated in  FIG. 1  and similar elements are represented by similar reference numerals. The fuel cell system  100   a  suppresses heat and does not emit byproducts, for example, through the use of endothermic reactions of the byproducts and materials that are stored in the waste products storage device  116 . Here, however, the oxidant supply  114   a  is simply a vent or a vent and fan arrangement that draws ambient air and the heaters  140  and  148  are not required. The exemplary fuel cell system  100   a  is especially useful in those instances where ambient air with a suitable amount of O 2  is available, and the suppression of heat and/or humid exhaust is important. Consumer electronic devices are examples of devices that may be powered by the exemplary fuel cell system  100   a.    
         [0043]     Another exemplary fuel cell system, which is generally represented by reference numeral  100   b  in  FIG. 7 , is configured for use in those instances where ambient air is not available as an oxidant source, but the emission heat and/or humid exhaust is acceptable, such as various high altitude and underwater applications. The exemplary fuel cell system  100   b  is substantially similar to the fuel cell system  100  illustrated in  FIG. 1  and similar elements are represented by similar reference numerals. The fuel cell system  100   b  includes, for example, an oxidant supply  114  which produces O 2  by decomposing an oxygen producing material  134 , such as an inorganic oxygen containing salt. Here, however, the waste products storage device  116  is replaced by a vent  164  that simply vents the byproducts out of the housing  122 . In those instances where the fuel cell system  100   b  is located within a host device, the host device will typically have a corresponding vent to transfer exhaust from the vent  164  out of the host device. A fuel recirculation system  166 , which returns H 2  and unused fuel to the anode inlet line  126 , thereby increasing the overall efficiency of the system, may also be provided.  
         [0044]     It should be noted here that the exemplary fuel cell systems described above with reference to  FIGS. 1-7  may also be configured such that the fuel supply  112 , oxidant supply  114  and/or waste products storage device  116  may be removed and replaced. Such an arrangement allows the fuel cell systems to be quickly and easily recharged. For example, the fuel supply  112 , oxidant supply  114  and/or waste products storage device  116  may be in the form of cartridges that have connectors which are configured to mate with corresponding connectors within the housing  122 . With respect to the oxidant supply  114 , the heaters  140  and  148  may be a permanent part of the fuel cell system, or part of the replaceable cartridge (with corresponding electrical and fluidic connectors added thereto).  
         [0045]     Although the present inventions have been described in terms of the preferred embodiments above, numerous modifications and/or additions to the above-described preferred embodiments would be readily apparent to one skilled in the art. It is intended that the scope of the present inventions extend to all such modifications and/or additions.