Membrane electrode assemblies

Abstract

Membrane electrode assemblies are described that include an ion conductive membrane a catalyst adjacent to the major surfaces of the ion conductive membrane and a porous particle filled polymer membrane adjacent to the ion conductive membrane. The catalyst can be disposed on the major surfaces of the ion conductive membrane. Preferably, the catalyst is disposed in nanostructures. The polymer film serving as the electrode backing layer preferably is processed by heating the particle loaded porous film to a temperature within about 20 degrees of the melting point of the polymer to decrease the Gurley value and the electrical resistivity. The MEAs can be produced in a continuous roll process. The MEAs can be used to produce fuel cells, electrolyzers and electrochemical reactors.

What is claimed is:  
     
         1 . An electrochemical MEA comprising: 
 an ion conductive membrane, said membrane having a first and second major surface;    catalyst adjacent to said first and second major surfaces; and    a porous, electrically conductive polymer film adjacent to said ion conductive membrane, said film comprising a polymer matrix and about 45 to about 98 percent by weight electrically conductive particles embedded within said polymer matrix.    
     
     
         2 . The electrochemical MEA of  claim 1 , wherein the Gurley value of said polymer film is less than about 50 s/50 cc.  
     
     
         3 . The electrochemical MEA of  claim 1 , wherein said polymer matrix comprises a polymer selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, poly(tetrafluoroethylene-co-perfluoro-(propyl vinyl ether)) and mixtures thereof.  
     
     
         4 . The electrochemical MEA of  claim 1 , wherein said electrically conductive particles comprise carbon.  
     
     
         5 . The electrochemical MEA of  claim 1 , wherein said porous polymer film has an electrical resistivity of less than about 20 ohm-cm.  
     
     
         6 . The electrochemical MEA of  claim 1 , wherein said catalytic material is disposed at an interface between said ion conductive membrane and said porous, electrically conductive polymer film.  
     
     
         7 . The electrochemical MEA of  claim 1 , wherein said catalytic material is disposed upon at least one of said surfaces of said ion conductive membrane.  
     
     
         8 . The electrochemical MEA of  claim 1 , wherein said catalyst is disposed in nanostructured elements.  
     
     
         9 . An electrochemical MEA comprising: 
 an ion conductive membrane, said membrane having a first and second major surface;    catalyst adjacent to said first and second major surfaces; and    a porous, electrically conductive polymer film adjacent to said ion conductive membrane, said film comprising electrically conductive particles and a porous matrix of fibrillated PTFE fibrils.    
     
     
         10 . The electrochemical MEA of  claim 9 , wherein said catalytic material is disposed at an interface between said ion conductive membrane and said porous, electrically conductive polymer film.  
     
     
         11 . The electrochemical MEA of  claim 9 , wherein said catalytic material is disposed upon at least one major surface of said ion conductive membrane.  
     
     
         12 . The electrochemical MEA of  claim 9 , wherein said conductive particles comprise carbon.  
     
     
         13 . The electrochemical MEA of  claim 9 , wherein said porous polymer film has a Gurley value of less than 50 s/50 cc.  
     
     
         14 . The electrochemical MEA of  claim 9 , wherein said porous polymer film has an electrical resistivity of less than 20 ohm-cm.  
     
     
         15 . A method of producing an electrically conductive polymer film comprising the step of heating a porous, polymer film comprising a polymer matrix and about 45 to about 98 percent by weight electrically conductive particles to a temperature within 20° C. of the melting point of said polymer matrix for sufficient time to decrease the Gurley value of said film by at least about 25 percent and decrease the electrical resistivity of said film by at least about 25 percent while substantially maintaining the physical integrity and mechanical properties of said film upon cooling.  
     
     
         16 . The method of  claim 15 , wherein said polymer matrix comprises a polymer selected from the group consisting of polyethylene, polypropylene, polyvinylidene fluoride, poly(tetrafluoroethylene-co-perfluoro-(propyl vinyl ether)) and mixtures thereof.  
     
     
         17 . The method of  claim 15 , wherein said conductive particles comprise carbon.  
     
     
         18 . The method of  claim 15 , wherein said conductive particles comprise one or more conductive metals.  
     
     
         19 . The method of  claim 15 , wherein said porous film comprises between about 80 and about 98 percent by weight conductive particles.  
     
     
         20 . The method of  claim 15 , wherein said temperature is about 5 to about 20 degree centigrade above said melting temperature.  
     
     
         21 . The method of  claim 15 , wherein said Gurley value of said film following heating is less than 50 s/50 cc .  
     
     
         22 . The method of  claim 15 , further comprising the step of differential cooling for quenching the film to create an asymmetric film.  
     
     
         23 . A method of forming an electrode backing layer for an electrochemical is MEA comprising the steps of: 
 (a) forming a polymeric film comprising a crystallizable polyolefin polymer matrix, conductive particles and a diluent for said polymer,    (b) applying surface texture to said polymeric film; and    (c) removing said oil before or after applying said surface texture.    
     
     
         24 . A method of forming an electrochemical MEA comprising the step of placing an electrode backing layer on both sides of a polymeric ion conductive membrane, said electrode backing layers each comprising a gas permeable, electrically conductive porous film prepared according to the method of  claim 1 , wherein a catalyst layer is disposed between each of said ion conductive membrane and said electrode backing layers.  
     
     
         25 . A method of forming an electrochemical MEA comprising the step of placing an electrode backing layer on both sides of a polymeric ion conductive membrane, said electrode backing layers each comprising a gas permeable, electrically conductive porous fibrillated PTFE film and conductive particles embedded in said film, wherein a catalyst layer is disposed between each of said ion conductive membrane and said electrode backing layers.  
     
     
         26 . A method of producing a plurality of 5-layer MEAs, comprising the step of applying catalyst layers and electrode backing layers at suitable locations along a web of ion conduction membrane such that a plurality of 5-layer MEAs can be cut from said web of ion conduction membrane.  
     
     
         27 . A film comprising greater than about 45 percent by weight conducting particles, said film having a surface exhibiting under contact with water a receding and advancing contact angles greater than 90°, wherein said advancing contact angle is no more than 50° greater than said receding contact angle.  
     
     
         28 . The film of  claim 27 , wherein said advancing contact angle is no more than 30° greater than said receding contact angle.  
     
     
         29 . The film of  claim 27 , wherein said advancing contact angle is no more than 20° greater than said receding contact angle.  
     
     
         30 . A method of producing a film comprising a polymer and greater than about 45 percent by weight conducting particles, said method comprising the steps of heating to a temperature from about the melting point to about 20 degrees C. above the melting point and then stretching the film from about 25 percent to about 150 percent of their original length.  
     
     
         31 . A polymer web comprising a plurality of MEA elements.  
     
     
         32 . The polymer web of  claim 31 , wherein said MEA elements are disposed along a continuous web of ion conducting polymeric material.  
     
     
         33 . The polymer web of  claim 32 , further comprising suitably located seal material.  
     
     
         34 . The polymer web of  claim 31 , further comprising nanostructured catalyst layers.