1. Field of the Inventions
The present inventions are related to fuel cell systems.
2. Description of the Related Art
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.
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.
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.
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.
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.
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.
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.
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.
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.
Detailed description of embodiments of the inventions will be made with reference to the accompanying drawings.
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.
As illustrated for example in
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 124a and 124b are associated with the exterior of the housing.
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
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
Turning to
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 O2, e.g. 2KClO3→2KCl+3O2. Metal chlorates also have relatively high oxygen content, e.g. 1 g of KClO3 has 0.39 g of O2. A solid metal chloride will remain within the housing 132 after the decomposition, and O2 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 (
There are a number of advantages associated with supplying O2 in this manner. By way of example, but not limitation, supplying O2 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 O2 in this manner also provides substantial volumetric savings, e.g. 1 cm3 of KClO3 produces 639 cm3 of O2 at 25° C. and 1 atmosphere.
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
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.
Once the fuel cell reaction has started, heat for the decomposition of the inorganic oxygen containing salt is provided by a heater 148 (
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.
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 O2. 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 O2 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.
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 H2O and CO2, 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 H2O and CO2 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 (Al2O3)). Exemplary endothermic reactions include H2O+CaO→Ca(OH)2; CO2+CaO→CaCO3; H2O+Ca→CaO+H2; H2O+CO22H++HCO3− (aq.). The products of these reactions remain within the reaction chamber 158 in solid or liquid form.
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.
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.
The waste products storage device 116 may also be used to return H2 and any unused fuel to the anode inlet line 126, thereby increasing the overall efficiency of the system. The H2 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 H2 and unused fuel to enter the tube 162.
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 (
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.
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.
Referring to
Another exemplary fuel cell system, which is generally represented by reference numeral 100a in
Another exemplary fuel cell system, which is generally represented by reference numeral 100b in
It should be noted here that the exemplary fuel cell systems described above with reference to
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.