Modified diffusion layer for use in a fuel cell system
원문보기
IPC분류정보
국가/구분
United States(US) Patent
등록
국제특허분류(IPC7판)
H01M-004/96
H01M-008/10
H01M-004/88
출원번호
US-0078728
(2002-02-19)
발명자
/ 주소
Beckmann, Gerhard
Ren, Xiaoming
Mutolo, Paul F.
Kovacs, Frank W.
Gottesfeld, Shimshon
출원인 / 주소
MTI MicroFuel Cells Inc.
대리인 / 주소
Cesari and McKenna, LLP
인용정보
피인용 횟수 :
19인용 특허 :
19
초록▼
A fuel cell diffusion layer providing a preferential path by which liquid reactants or byproducts may be supplied to or removed from a direct oxidation fuel cell is described. The modified diffusion layer will be typically on the cathode side of the fuel cell and its use is to eliminate or minimize
A fuel cell diffusion layer providing a preferential path by which liquid reactants or byproducts may be supplied to or removed from a direct oxidation fuel cell is described. The modified diffusion layer will be typically on the cathode side of the fuel cell and its use is to eliminate or minimize flooding of the cathode diffusion layer area, which is a performance limiting condition in direct methanol fuel cells. In accordance with one embodiment of the invention, the diffusion layer includes a substrate that is coated with a microporous layer. A pattern may be embossed into the diffusion layer, to create preferential flow paths by which water will travel and thereby be removed from the cathode catalyst area. This avoids cathode flooding and avoids build up of potentially destructive pressure by possible cathodic water accumulation. This also provides a means for collecting cathode water for redirection In accordance with another aspect of the invention, the preferential path is established by applying a thicker microporous layer to the carbon cloth or carbon paper and drying it in such a fashion so that when it dries, the surface of the microporous layer cracks to provide the pathways.
대표청구항▼
1. A diffusion layer for a direct oxidation fuel cell, the fuel cell having a protonically conductive membrane, comprising:a substrate comprised substantially of carbon, said substrate facilitating the transport of reactants towards a catalyst in intimate contact with said protonically conductive me
1. A diffusion layer for a direct oxidation fuel cell, the fuel cell having a protonically conductive membrane, comprising:a substrate comprised substantially of carbon, said substrate facilitating the transport of reactants towards a catalyst in intimate contact with said protonically conductive membrane and being coated with an electrically conductive layer that forms a microporous layer on said substrate, said microporous layer having indented channels formed therein, providing preferential flow paths to cause fluids to travel in predetermined directions in the fuel cell and to improve a distribution of the reactant to the catalytic layer. 2. The diffusion layer as defined in claim 1 wherein a catalyst has been applied to at least one side of the membrane of the fuel cell.3. The diffusion layer as defined in claim 2 wherein said catalyst is applied to both sides of the membrane.4. The diffusion layer as defined in claim 1 wherein said fluid is substantially water, and said indented channels are formed such that fluid is directed away from the membrane.5. The diffusion layer as defined in claim 1 wherein said substrate is comprised substantially of carbon cloth.6. The diffusion layer as defined in claim 1 wherein said substrate is comprised of at least one sheet of carbon paper.7. The diffusion layer as defined in claim 6 wherein said substrate is comprised of a plurality of sheets of carbon paper.8. The diffusion layer as defined in claim 1 wherein said electrically conductive layer is substantially hydrophobic.9. The diffusion layer as defined in claim 8 wherein said electrically conductive layer includes polytetrafluoroethylene and high surface area carbon particles.10. The diffusion layer as defined in claim 1 wherein said substrate is placed in intimate contact with said protonically conductive membrane.11. The diffusion layer as defined in claim 1 wherein said indented channels are formed in a spiral pattern.12. The diffusion layer as defined in claim 1 wherein said indented channels are formed in a lattice pattern.13. The diffusion layer as defined in claim 1 wherein said indented channels are formed in such a geometric pattern as to draw fluids away from an active electrode area of the membrane.14. A membrane electrode assembly comprising:a protonically conductive, electronically non-conductive membrane; at least one diffusion layer comprising a carbon substrate being coated thereon with an electrically conductive layer that forms a miroporous layer which includes indented channels formed therein, providing preferential flow paths to cause fluids to travel in predetermined directions in the assembly thereby providing a path through which reactants and byproducts may be preferentially transported to direct said reactants and byproducts in predetermined directions in said assembly and to improve a distribution of the reactant to the catalytic layer; and a catalyst disposed on said membrane and catalyst forming an active area of said assembly. 15. The membrane electrode assembly as defined in claim 14 wherein said catalyst is applied to at least one surface of the membrane.16. The membrane electrode assembly as defined in claim 15 wherein said catalyst is applied to both surfaces of the membrane.17. The membrane electrode assembly as defined in claim 14 including a plurality of diffusion layers and wherein at least one said diffusion layer is substantially hydrophobic.18. The membrane electrode assembly as defined in claim 14 further comprising a membrane to which a catalyst has been applied is disposed between two diffusion layers, at least one of which diffusion layer provides said preferential flow path to direct fluids away from said active area of said assembly.19. The membrane electrode assembly as defined in claim 14 wherein said membrane is comprised substantially of polyperfluorosulfonic acid.20. The membrane electrode assembly as defined in claim 14 wherein said membrane is comprised substantially of a cation exchange membrane based on perflouorocarbon polymers with side chain termini of perfluorosulfonic acid groups.21. The membrane electrode assembly as defined in claim 14 wherein the catalyst applied to at least one surface of the membrane contains platinum.22. The membrane electrode assembly as defined in claim 21 wherein the catalyst applied to at least one surface of the membrane also contains ruthenium.23. 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 at least one 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 conversion 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 which allows said associated fuel mixture to pass through to said anode face as fuel is consumed at said anode, and which also allows anodically-generated CO2 to be transported away from the anode face of the membrane; (C) a cathodic diffusion layer disposed in intimate contact with said cathode face of said membrane electrode assembly and which allows oxygen to pass through to said cathode face of said membrane electrode assembly, which cathode diffusion layer is comprised of a carbon-containing substrate and a microporous layer having channels formed therein to provide preferential flow paths such that reactants and byproducts in said fuel cell travel in predetermined directions along said channels and to improve a distribution of the reactant to the catalytic layer; and (D) means for collecting electric current generated in said electricity-generating reactions to provide said electric current to a load. 24. The direct oxidation fuel cell as defined in claim 23 wherein said substrate of said cathode diffusion layer is comprised substantially of carbon cloth.25. The direct oxidation fuel cell as defined in claim 23 wherein said substrate of said cathode diffusion layer is comprised substantially of carbon paper.26. A direct oxidation fuel cell system comprising:(A) a direct oxidation fuel cell including: (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 at least one 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 conversion 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; (ii) an anodic diffusion layer disposed in intimate contact with said anode face of said membrane electrode assembly which allows said associated fuel mixture to pass through to said anode face as fuel is consumed at said anode, and also allows anodically-generated CO2 to be transported from the anode face of the membrane; (iii) a cathodic diffusion layer disposed in intimate contact with said cathode face of said membrane electrode assembly which allows oxygen to pass through to said cathode face of said membrane electrode assembly, and which cathodic diffusion layer is comprised of a carbon-containing substrate and a microporous layer having channels formed therein to provide preferential flow paths such that reactants and byproducts in said fuel cell travel in predetermined directions along said channels and to improve a distribution of the reactant to the catalytic layer; and (iv) means for collecting electric current generated in said electricity-generating reactions to provide said electric current to a load; (B) a fuel source; (C) fuel container and delivery assembly coupled between said fuel source and said direct oxidation fuel cell; (D) means for removing reactants from the fuel cell; (E) means for removing byproducts from the membrane electrode assembly; and (F) an electrical coupling means for connecting the fuel cell with an external device to which is it providing power. 27. The direct oxidation fuel cell system as defined in claim 26 further comprising a coupling between an anode chamber and a cathode chamber of said fuel cell, by which water collected from the cathode face of the membrane is recirculated to the anode chamber of the fuel cell.28. The direct oxidation fuel cell system as defined in claim 27 further comprising means for mixing water recirculated from said cathode face of said membrane with a fuel substance and means for introducing a fuel and water mixture to the anode face of the membrane electrode assembly.29. The diffusion layer as defined in claim 1 wherein said microporous layer is substantially comprised of a material that has been allowed to form cracks extending substantially to the edges of the diffusion layer thereby providing a pathway for fluid to be transported away from the active electrode area.30. The diffusion layer as defined in claim 1 wherein said substrate and microporous layer are substantially comprised of materials selectively chosen such that a fuel substance can pass through said substrate, while carbon dioxide is directed through said preferential flow paths to be released or directed to another portion of said fuel cell.
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