Simplified direct oxidation fuel cell system

Abstract

A simplified direct oxidation fuel cell system is disclosed. The fuel cell is constructed in such a manner that fuel is added to the cell anode as it is consumed and water is evaporated off at cell cathode so that there is no need for recirculation of unreacted fuel at the cell anode or water at the cell cathode. In addition, carbon dioxide generated from the anodic reaction is passively vented out of the system by using a CO2 gas permeable membrane material integrated as part of the anode chamber construction. It is thus possible that, the CO2 separation from the anode fluid occurs without the recirculation of the anode fluid outside the anode chamber. In one embodiment, the simplified direct oxidation fuel cell includes a gas permeable, liquid impermeable membrane placed in close proximity to the anode to perform the carbon dioxide separation. In accordance with a further aspect of the invention, a fuel container and delivery assembly is provided, which includes separate conduits from separate containers for methanol and water and a leakproof interface. This allows for mixing of water into the methanol solution, to allow for improved ability to adjust the concentration of methanol and water in the system. The fuel container and delivery assembly operates using simple mechanical flow and simplified geometry. This design minimizes loss of methanol and water via carryover and crossover by limiting introduction of those fluids. The passive system in which fuel is added as it is consumed and CO2 separated, both without pumping, ultimately will increase net power provided to the load due to low parasitic losses.

What is claimed is:  
     
         1 . A direct oxidation fuel cell system, comprising: 
 (A) a fuel source;    (B) a direct oxidation fuel cell, having: 
 (i) a membrane electrode assembly, including; 
 (a) a protonically conductive, electronically non-conductive membrane electrolyte, having an anode face and an opposing cathode face; and  
 (b) a catalyst coating disposed on each of said anode face and said cathode face, whereby electricity-generating reactions occur upon introduction of an associated fuel solution from said fuel source including anodic dissociation of said fuel solution into carbon dioxide, protons and electrons, and a cathodic combination of protons, electrons and oxygen from an associated source of oxygen, producing water; and  
 
 (ii) an anodic diffusion layer disposed in intimate contact with said anode face of said membrane electrode assembly and having a plurality of openings therein to allow said associated fuel solution to pass through to said anode face, as fuel is consumed at said anode;  
 (iii) a cathodic diffusion layer disposed in intimate contact with said cathode face of said membrane electrode assembly and having a plurality of openings therein to allow oxygen to pass through to said cathode face of said membrane electrode assembly;  
   (C) a gas permeable layer comprised substantially of a gas permeable material, said gas permeable layer being disposed generally parallel to said anodic diffusion layer, such that said fuel solution can pass between said anodic diffusion layer and said gas permeable layer, and carbon dioxide that is released as fuel is consumed at said anode face, passes through said gas permeable layer and is vented from said fuel cell, whereby carbon dioxide is removed from said fuel cell without active transport mechanisms; and    (D) gas permeable layer load coupled across said fuel cell, said load providing a path for said electrons whereby electricity is provided as said electricity-generating reactions proceed.    
     
     
         2 . The direct oxidation fuel cell system as defined in  claim 1  further comprising a pressurized fuel delivery assembly coupled between said fuel source and said anodic diffusion layer in such a manner that as fuel is consumed at said anode face, and carbon dioxide is separated by said gas permeable layer, fuel is drawn into said fuel cell and said fuel cell is refilled by volume replacement from said fuel delivery assembly.  
     
     
         3 . The direct oxidation fuel cell system as defined in  claim 1  further comprising means for evaporating off water produced at said cathode face of said protonically conductive membrane.  
     
     
         4 . The direct oxidation fuel cell system as defined in  claim 1  wherein said gas permeable layer is comprised substantially of expanded PTFE.  
     
     
         5 . The direct oxidation fuel cell system as defined in  claim 1  wherein said gas permeable layer further includes a flow field channel formed therein to assist in the transport of liquids to said anode face of said protonically conductive membrane, while gases are drawn through said gas permeable layer.  
     
     
         6 . The direct oxidation fuel cell system as defined in  claim 4  wherein said flow field channel is sealed with a material that is liquid impermeable, gas permeable, to resist passing of fuel through said gas permeable layer, by allowing gas to pass through to said membrane.  
     
     
         7 . The direct oxidation fuel cell system as defined in  claim 1  further comprising a housing encapsulating said direct oxidation fuel cell, said housing having an inlet port for the introduction of fuel into said fuel cell.  
     
     
         8 . The direct oxidation fuel cell system as defined in  claim 6  further comprising a second port being defined in said housing into which fuel can be introduced, or removed, from the fuel cell.  
     
     
         9 . The direct oxidation fuel cell system as defined in  claim 1  wherein said protonically conductive membrane is comprised substantially of Nafion.  
     
     
         10 . The direct oxidation fuel cell system as defined in  claim 1  wherein said fuel from said fuel source is a methanol solution.  
     
     
         11 . The direct oxidation fuel cell system as defined in  claim 1  wherein said anodic diffusion layer is sandwiched between said gas permeable layer and said protonically-conductive membrane.  
     
     
         12 . The direct oxidation fuel cell system as defined in  claim 1  wherein said gas separation membrane is in intimate contact with said anodic diffusion layer.  
     
     
         13 . The direct oxidation fuel cell system as defined in  claim 7  wherein said gas permeable layer is disposed on a portion of said housing, encompassing said anode chamber.  
     
     
         14 . The direct oxidation fuel cell system as defined in  claim 11  wherein said gas permeable layer is disposed on at least one surface of said housing.  
     
     
         15 . The direct oxidation fuel cell system as defined in  claim 11  wherein said gas permeable layer comprises at least one porthole in said housing.  
     
     
         16 . A direct oxidation fuel cell, comprising: 
 (A) a membrane electrode assembly, including: 
 (i) a protonically conductive, electronically non-conductive membrane electrolyte, having an anode face and an opposing cathode face; and  
 (ii) a catalyst coating disposed on each of said anode face and said cathode face, whereby electricity-generating reactions occur upon introduction of fuel solution from an associated fuel source, including anodic dissociation of said fuel solution into carbon dioxide, protons and electrons, and cathodic combination of protons, electrons and oxygen from an associated source of oxygen, producing water;  
   (B) an anodic diffusion layer disposed in intimate contact with said anode face of said membrane electrode assembly, and having a plurality of openings therein to allow said associated fuel mixture to pass through to said anode face as fuel is consumed at said anode;    (C) a cathodic diffusion layer disposed in intimate contact with said cathode face of said membrane electrode assembly and having a plurality of openings therein to allow oxygen to pass through to said cathode face of said membrane electrode assembly; and    (D) a gas permeable, fluid impermeable membrane disposed generally parallel to said anodic diffusion layer, such that said fuel solution can pass between said anodic diffusion layer and said gas permeable membrane to separate carbon dioxide that is released at said anode face and to vent carbon dioxide from said fuel cell, whereby carbon dioxide is removed from said fuel cell without active transport mechanisms.    
     
     
         17 . The direct oxidation fuel cell as defined in  claim 16  wherein said gas permeable membrane is comprised substantially of expanded PTFE.  
     
     
         18 . The direct oxidation fuel cell as defined in  claim 17  wherein said gas permeable membrane includes a flow field channel to assist in the transport of liquids across said anode face of said protonically conductive membrane, while gases are drawn through said gas permeable membrane.  
     
     
         19 . The direct oxidation fuel cell as defined in  claim 18  wherein said flow field channel is sealed with a material that is liquid impermeable to resist passing of fuel through said gas permeable layer.  
     
     
         20 . A fuel container and delivery assembly for use with an associated direct oxidation fuel cell system, the fuel container and delivery assembly, comprising: 
 (A) an exterior housing having an opening at one end thereof;    (B) a first inner container disposed within said exterior housing, for holding a fuel solution, and a fuel conduit extending through said opening in said exterior housing, and coupling said first inner container to said associated fuel cell system;    (C) a second inner container disposed within said exterior housing, for holding water to be mixed with said fuel solution and a water conduit extending through said opening in said exterior housing, and coupling said second inner container to said associated fuel cell system;    (D) an interface for sealing the coupling of said fuel conduit and said water conduit with said associated fuel cell system;    (E) mixing assembly connecting said fuel conduit with said water conduit to mix fuel and water to adjust an amount of water mixed into fuel to result in a fuel mixture of a predetermined concentration; and    (F) delivery conduit for transporting said resulting fuel mixture to said associated direct oxidation fuel cell system.    
     
     
         21 . The fuel container and delivery assembly as defined in  claim 20  wherein said fuel conduit is constructed to intersect into said water conduit to thereby mix said fuel solution with water.  
     
     
         22 . The fuel container and delivery assembly as defined in  claim 21  further comprising a valve located along said fuel conduit to control the addition of fuel solution to be mixed with said water.  
     
     
         23 . The fuel container and delivery assembly as defined in  claim 20  wherein said water conduit is constructed to intersect into said fuel conduit to thereby mix water into said fuel solution.  
     
     
         24 . The fuel container and delivery assembly as defined in  claim 23  further comprising a valve located along said water conduit to control the addition of water to be mixed into said fuel solution.  
     
     
         25 . The fuel container and delivery assembly as defined in  claim 20  further comprising a mixing chamber into which said fuel conduit and said water conduit lead to thereby mix said fuel solution and said water.  
     
     
         26 . The fuel container and delivery assembly as defined in  claim 25  further comprising a valve located along at least one of said fuel conduit and said water conduit to control the flow of liquids into said mixing chamber.  
     
     
         27 . The fuel container and delivery assembly as defined in  claim 26  further comprising a valve located along said delivery conduit to control the flow of the resulting fuel mixture to said associated direct oxidation fuel cell system.  
     
     
         28 . The fuel container and delivery assembly as defined in  claim 27 , wherein said fuel conduit and said water conduit include openings along walls thereof, and said walls of said fuel conduit and said water conduit are disposed contiguous to said anode diffusion layer, which in turn is in intimate contact with said anode face of said fuel cell, whereby fuel and water are dispersed through said walls of said conduits to said anode diffusion layer.  
     
     
         29 . The fuel container and delivery assembly as defined in  claim 28  wherein said fuel conduit and said water conduit include means for controlling the amount of each substance that travels through its respective conduit to thereby control the fuel concentration of liquids presented to said anode face of said fuel cell.  
     
     
         30 . The fuel container and delivery assembly as defined in  claim 20  wherein said associated fuel cell includes a gas permeable layer disposed generally parallel to said anodic diffusion layer, said gas permeable layer removing carbon dioxide from said fuel cell.  
     
     
         31 . The fuel container and delivery assembly as defined in  claim 30  wherein said gas permeable layer is comprised substantially of expanded PTFE.  
     
     
         32 . The fuel container and delivery assembly as defined in  claim 30  wherein said fuel cell includes means for evaporating off water produced at said cathode face of said membrane electrode assembly.  
     
     
         33 . The fuel container and delivery assembly as defined in  claim 20  wherein said exterior housing includes a pressure-applying element which applies pressure to at least one of said fuel container and said water container to place liquids in said fuel conduit and said water conduit under pressure.  
     
     
         34 . The fuel container and delivery assembly as defined in  claim 20  further comprising a pump to transport liquid fuel from said fuel container into said fuel conduit.  
     
     
         35 . The fuel container and delivery assembly as defined in  claim 20  further comprising a pump to transport water from said water container into said water conduit.  
     
     
         36 . A method of removing carbon dioxide from a direct oxidation fuel cell, said fuel cell having a protonically conductive membrane, said protonically conductive membrane having an anode, and an anode diffusion layer, and a cathode, the method including the steps of: 
 separating carbon dioxide from said anode by providing a gas permeable layer, comprised substantially of a gas permeable, liquid impermeable material contiguous to an anodic diffusion layer, which is in turn, in intimate contact with said protonically conductive membrane allowing removal of carbon dioxide generated at said anode, and while allowing fuel solution to penetrate to said anode.    
     
     
         37 . A gas management component for use in a direct oxidation fuel cell having a catalyzed membrane electrolyte with an anode aspect and a cathode aspect, comprising: 
 an element substantially comprised of a gas-permeable, liquid-impermeable material, which element is disposed in close proximity to the anode aspect of the catalyzed membrane electrolyte assembly.    
     
     
         38 . The gas management component as defined in  claim 37  wherein said material is gas-selective in such a manner that it is permeable to anodic effluent gas, but is substantially less permeable to oxygen.  
     
     
         39 . The gas management component as defined in  claim 37  wherein said gas management component is made part of a flow field element, providing said flow field element with gas releasing properties while effectively delivering fuel to active area of the membrane electrolyte.  
     
     
         40 . The gas management component as defined in  claim 39  wherein fuel is delivered to said active area of the membrane electrolyte through an associated anodic diffusion layer.  
     
     
         41 . The gas management component as defined in  claim 39  wherein said flow fields encourage removal of anodically-generated gasses such that they are released from the direct oxidation fuel cell prior to excessive collection of gaseous anodic product within the said anode chamber in said fuel cell.  
     
     
         42 . The gas management component as defined in  claim 37  wherein said gas management component is disposed within said fuel cell in such a manner that anodically-generated gasses are released prior to coalescing and impeding the flow of fuel from an associated fuel source into said anode chamber.  
     
     
         43 . A membrane electrode assembly of a direct oxidation fuel cell, comprising: 
 (A) a protonically-conductive, electronically non-conductive catalyzed membrane electrolyte;    (B) a catalyst disposed on said membrane electrolyte;    (C) an anode diffusion layer disposed contiguous to an anode aspect of the membrane electrolyte;    (D) a cathode diffusion layer disposed contiguous to a cathode aspect of the membrane electrolyte; and    (E) a gas-permeable, liquid-impermeable layer coupled to, or in close proximity with said anode diffusion layer.    
     
     
         44 . The membrane electrode assembly as defined in  claim 43  wherein said gas-permeable, liquid-impermeable layer is mechanically attached or bonded to said anode diffusion layer.  
     
     
         45 . A method of managing anodic effluent in a direct oxidation fuel cell, said fuel cell having a catalyzed membrane electrolyte with an anode aspect and a cathode aspect, the method including the step of: 
 removing gaseous anodic effluent from a liquid by providing a gas management component comprised substantially of a gas-permeable, liquid-impermeable layer disposed in close proximity to the anode aspect of the direct oxidation fuel cell.    
     
     
         46 . The method, as defined in  claim 45 , including providing said gas-permeable, liquid-impermeable layer in contact with the anode aspect of the membrane electrolyte assembly.  
     
     
         47 . A method of separating anodically-generated gasses in a direct oxidation fuel cell, said fuel cell having a catalyzed membrane electrolyte with an anode aspect and a cathode aspect, and an anode chamber being defined between said anode aspect and an exterior of said fuel cell, the method including the steps of: 
 separating said anodically-generated gasses from a fluid volume of fuel contained within said anode chamber of said fuel cell, without recirculating said volume of fuel.