Fuel cell membrane electrode assemblies with improved power outputs and poison resistance

Abstract

An electrode-membrane combination for use in a fuel cell and providing improved power outputs and resistance to poisoning. Multiple embodiments are described which generally involve use of a vapor deposited zone or layer of one or more catalytically active metals. Vapor deposition can be carried out by, for example, sputtering or physical vapor deposition.

What is claimed is:  
     
         1 . An electrode-membrane combination comprising: 
 at least one reactant diffusive, electronically conductive electrode, wherein the electrode is substantially free of first catalytically active metal; and    at least one ionically conductive membrane contacting the electrode to form an electrode-membrane interfacial region,    wherein the interfacial region comprises at least one zone consisting essentially of at least two second catalytically active metals, different from each other, and having a zone thickness of about 3 angstroms to about 5,000 angstroms.    
     
     
         2 . A combination according to    claim 1   , wherein the electrode is free of first catalytically active metal.  
     
     
         3 . A combination according to    claim 1   , wherein the electrode comprises at least one tonically conductive polymer.  
     
     
         4 . A combination according to    claim 1   , wherein the electrode is free of first catalytically active metal and comprises ionically conductive polymer.  
     
     
         5 . A combination according to    claim 1   , wherein the zone thickness is about 50 angstroms to about 1500 angstroms.  
     
     
         6 . A combination according to    claim 4   , wherein the zone thickness is about 50 angstroms to about 1500 angstroms.  
     
     
         7 . A combination according to    claim 1   , wherein the zone thickness is about 150 angstroms to about 500 angstroms.  
     
     
         8 . A combination according to    claim 4   , wherein the zone thickness is about 150 angstroms to about 500 angstroms.  
     
     
         9 . A combination according to    claim 1   , wherein the electrode comprises conductive carbon and at least one hydrophobic binder polymer for the carbon.  
     
     
         10 . A combination according to    claim 1   , wherein at least two of the second catalytically active metals are noble metals.  
     
     
         11 . A combination according to    claim 1   , wherein at least two of the second catalytically active metals are alloyed with each other.  
     
     
         12 . A combination according to    claim 1   , wherein the combination further comprises at least one catalyzed gas diffusion medium.  
     
     
         13 . A combination according to    claim 1   , wherein the zone consists essentially of at least three second catalytically active metals.  
     
     
         14 . A combination according to    claim 1   , wherein the zone consists essentially of at least four second catalytically active metals.  
     
     
         15 . A combination according to    claim 1   , wherein the electrode comprises at least one ionically conductive polymer, and the ionically conductive membrane comprises an ionically conductive polymer which is substantially the same as the ionically conductive polymer of the electrode.  
     
     
         16 . A combination according to    claim 1   , wherein the electrode further comprises at least one solvent.  
     
     
         17 . A combination according to    claim 1   , wherein the membrane has a thickness of about 3 microns to about 75 microns.  
     
     
         18 . A combination according to    claim 1   , wherein the membrane has a thickness less than about 30 microns and a Gurley number greater than 10,000 seconds, and the membrane comprises a microporous polymer impregnated with at least one ionically conductive polymer.  
     
     
         19 . A combination according to    claim 18   , wherein the microporous polymer is expanded polytetrafluoroethylene and the ionically conductive polymer is a perfluoroionomer.  
     
     
         20 . A combination according to    claim 19   , wherein the electrode is free of first catalytically active metal and comprises ionically conductive polymer, and wherein the zone thickness is about 50 angstroms to about 1,500 angstroms.  
     
     
         21 . An electrode-membrane combination comprising: 
 at least one reactant diffusive, electronically conductive electrode, wherein the electrode is substantially free of first catalytically active metal; and    at least one ionically conductive membrane contacting the electrode to form an electrode-membrane interfacial region,    wherein the interfacial region consists essentially of at least one zone comprising at least two second catalytically active metals, different from each other, and having a zone loading of about 0.001 mg metal/cm 2  to about 0.7 mg metal/cm 2 .    
     
     
         22 . The combination according to    claim 21   , wherein the zone is a vapor deposited zone and the zone loading is 0.01 mg/cm 2  to 0.4 mg/cm 2 .  
     
     
         23 . The combination according to    claim 21   , wherein the zone is vapor deposited by physical vapor deposition.  
     
     
         24 . The combination according to    claim 21   , wherein the zone is vapor deposited by electron beam physical vapor deposition.  
     
     
         25 . A combination according to    claim 21   , wherein the zone is vapor deposited with ion beam assisted deposition.  
     
     
         26 . A combination according to    claim 21   , wherein the zone consists essentially of sequentially deposited zones of catalytic metal.  
     
     
         27 . The combination according to    claim 21   , wherein the zone is vapor deposited by sputtering.  
     
     
         28 . The combination according to    claim 21   , wherein the zone is vapor deposited by magnetron sputtering with use of multiple independent sputtering targets.  
     
     
         29 . The combination according to    claim 21   , wherein the zone is deposited by chemical vapor deposition, physical vapor deposition, thermal deposition, cathodic arc deposition, ion sputtering, ion beam assisted deposition, or jet vapor deposition.  
     
     
         30 . The combination according to    claim 21   , wherein the membrane has a thickness less than 30 microns and a Gurley number greater than 10,000 seconds.  
     
     
         31 . The combination according to    claim 21   , wherein the membrane comprises at least one microporous polymeric film impregnated with at least one ion exchange resin.  
     
     
         32 . The combination according to    claim 21   , wherein the electrode further comprises at least one ionically conductive polymer.  
     
     
         33 . The combination according to    claim 31   , wherein the electrode further comprises at least one ionically conductive polymer.  
     
     
         34 . The combination according to    claim 32   , wherein the ionically conductive polymer of the electrode impregnates the electrode at the membrane-electrode interface.  
     
     
         35 . The combination according to    claim 33   , wherein the ionically conductive polymer of the electrode impregnates the electrode at the membrane-electrode interface.  
     
     
         36 . The combination according to    claim 21   , wherein at least two of the second catalytically active metals are alloyed with each other, and the zone loading is less than 0.3 mg/cm 2 .  
     
     
         37 . The combination according to    claim 31   , wherein at least two of the second catalytically active metals are alloyed with each other.  
     
     
         38 . The combination according to    claim 35   , wherein at least two of the second catalytically active metals are alloyed with each other.  
     
     
         39 . The combination according to    claim 38   , wherein the zone is a vapor deposited zone.  
     
     
         40 . The combination according to    claim 38   , wherein the zone is deposited by chemical vapor deposition, physical vapor deposition, thermal deposition, cathodic arc deposition, ion sputtering, ion beam assisted deposition, or jet vapor deposition.  
     
     
         41 . An electrode membrane combination in which noble metal in the combination is substantially concentrated at an electrode membrane interface for fuel cell catalysis, the combination consisting essentially of (i) at least one electronically conductive electrode which allows for fuel cell reactant transport and which is surface enriched with at least one ionically conductive polymer, and (ii) at least one ionically conductive membrane which contacts the electrode at the electrode surface which is enriched with ionically conductive polymer, thereby forming an electrode membrane interfacial region, wherein a vapor deposited layer comprising at least two vapor deposited noble metals is disposed at the interfacial region.  
     
     
         42 . The combination according to    claim 41   , wherein the layer is deposited by chemical vapor deposition, physical vapor deposition, thermal deposition, cathodic arc deposition, ion sputtering, ion beam assisted deposition, or jet vapor deposition.  
     
     
         43 . The combination according to    claim 41   , wherein the layer comprises an alloy of metals.  
     
     
         44 . The combination according to    claim 41   , wherein the layer comprises multiple layers of noble metal.  
     
     
         45 . The combination according to    claim 41   , wherein the layer is deposited by multiple target sputtering.  
     
     
         46 . The combination according to    claim 41   , wherein the layer has a layer loading of about 0.001 mg metal/cm 2  to about 0.7 mg metal/cm 2 .  
     
     
         47 . The combination according to    claim 41   , wherein the layer has a layer thickness of about 3 angstroms to about 5,000 angstroms.  
     
     
         48 . The combination according to    claim 41   , wherein the layer has a layer thickness of about 50 angstroms to about 1,500 angstroms.  
     
     
         49 . The combination according to    claim 41   , wherein the layer has a layer thickness of about 50 angstroms to about 500 angstroms.  
     
     
         50 . The combination according to    claim 41   , wherein the electrode is substantially free of noble metal except for the noble metal of the layer at the interface.  
     
     
         51 . The combination according to    claim 41   , wherein the membrane has a thickness less than about 30 microns, has a Gurley number greater than about 10,000 seconds, and comprises expanded polytetrafluoroethylene impregnated with ionomer.  
     
     
         52 . The combination according to    claim 41   , wherein the layer comprises at least three vapor deposited noble metals.  
     
     
         53 . The combination according to    claim 41   , wherein all noble metal in the combination is at the electrode membrane interface.  
     
     
         54 . The combination according to    claim 41   , wherein the metals of the layer are at least partially alloyed in situ as the metals are vapor deposited from separate sputtering targets.  
     
     
         55 . The combination according to    claim 41   , wherein the layer is vapor deposited onto the electrode before an impregnation of the ionically conductive polymer into the electrode to provide enrichment and before formation of the interfacial region between the membrane and the electrode.  
     
     
         56 . A membrane electrode assembly for use in a solid polymer electrolyte fuel cell which has enhanced resistance to poisoning comprising two electrodes sandwiching a layer of solid polymer electrolyte to form two membrane electrode interfacial regions, 
 wherein the solid polymer electrolyte layer is air impermeable and has a thickness less than about 75 microns,    wherein the electrode is catalyzed with a vapor deposited zone consisting essentially of a composition of at least two noble metals which is formulated to enhance poison resistance during fuel cell operation.    
     
     
         57 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.65 or less when subjected to hydrogen feed with 5 ppm CO and 0.85 or less when subjected to hydrogen feed with 50 ppm CO.  
     
     
         58 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.50 or less when subjected to hydrogen feed with 5 ppm CO and 0.85 or less when subjected to hydrogen feed with 50 ppm CO.  
     
     
         59 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.25 or less when subjected to hydrogen feed with 5 ppm CO and 0.60 or less when subjected to hydrogen feed with 50 ppm CO.  
     
     
         60 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.65 or less when subjected to hydrogen feed with 5 ppm CO.  
     
     
         61 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.25 or less when subjected to hydrogen feed with 5 ppm CO.  
     
     
         62 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.85 or less when subjected to hydrogen feed with 50 ppm CO.  
     
     
         63 . The assembly according to    claim 56   , wherein the assembly provides a poison resistance lambda parameter at 0.6 V of 0.60 or less when subjected to hydrogen feed with 50 ppm CO.  
     
     
         64 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 350 mA/cm 2  when subjected to hydrogen feed with 5 ppm CO and at least 150 mA/cm 2  when subjected to hydrogen feed with 50 ppm CO.  
     
     
         65 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 450 mA/cm 2  when subjected to hydrogen feed with 5 ppm CO and at least 200 mA/cm 2  when subjected to hydrogen feed with 50 ppm CO.  
     
     
         66 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 500 mA/cm 2  when subjected to hydrogen feed with 5 ppm CO and at least 175 MA/cm 2  when subjected to hydrogen feed with 50 ppm CO.  
     
     
         67 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 350 mA/cm 2  when subjected to hydrogen feed with 5 ppm CO.  
     
     
         68 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 450 mA/cm 2  when subjected to hydrogen feed with 5 ppm CO.  
     
     
         69 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 150 mA/cm 2  when subjected to hydrogen feed with 50 ppm CO.  
     
     
         70 . The assembly according to    claim 56   , wherein the assembly provides a current density at 0.6 V of at least 175 mA/cm 2  when subjected to hydrogen feed with 50 ppm CO.  
     
     
         71 . A fuel cell comprising a plurality of membrane electrode assemblies according to    claim 56   .  
     
     
         72 . A transportation vehicle comprising a fuel cell according to    claim 71   .  
     
     
         73 . A membrane electrode assembly prepared by the combination of steps comprising: 
 providing assembly elements including (i) at least one reactant diffusive, electronically conductive electrode which comprises at least one ionically conductive polymer but which is substantially free of a first catalytically active metal, and (ii) at least one ionically conductive membrane;    depositing onto at least one of the assembly elements a zone consisting essentially of at least two second catalytically active metals having a zone thickness of about 3 angstroms to about 5,000 angstroms, wherein the zone deposition is (i) a direct deposition onto the assembly element, or (ii) an indirect deposition onto the assembly element wherein the deposited zone is first deposited onto a substrate and then transferred from the substrate onto the assembly element, and    optionally, assembling the membrane electrode assembly from the assembly elements.    
     
     
         74 . A membrane electrode assembly according to    claim 73   , further comprising the assembly step.  
     
     
         75 . A membrane electrode assembly according to    claim 73   , wherein the assembly element is the membrane.  
     
     
         76 . A membrane electrode assembly according to    claim 73   , wherein the assembly element is the electrode.  
     
     
         77 . A membrane electrode assembly according to    claim 73   , wherein the deposition is chemical vapor deposition, physical vapor deposition, thermal deposition, cathodic arc deposition, ion sputtering, ion beam assisted deposition, or jet vapor deposition.  
     
     
         78 . A membrane electrode assembly according to    claim 73   , the assembly further comprising at least one catalyzed gas diffusion medium.  
     
     
         79 . A combination according to    claim 21   , wherein the zone consists essentially of simultaneously deposited catalytic metal.