Highly conductive composites for fuel cell flow field plates and bipolar plates

Abstract

This invention provides a fuel cell flow field plate or bipolar plate having flow channels on faces of the plate, comprising an electrically conductive polymer composite. The composite is composed of (A) at least 50% by weight of a conductive filler, comprising at least 5% by weight reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes; (B) polymer matrix material at 1 to 49.9% by weight; and (C) a polymer binder at 0.1 to 10% by weight; wherein the sum of the conductive filler weight %, polymer matrix weight % and polymer binder weight % equals 100% and the bulk electrical conductivity of the flow field or bipolar plate is at least 100 S/cm. The invention also provides a continuous process for cost-effective mass production of the conductive composite-based flow field or bipolar plate.

1 . A fuel cell flow field plate or bipolar plate having flow channels on at least a face of the plate, comprising an electrically conductive polymer composite having: 
 (A) at least 50% by weight of a conductive filler, comprising at least 5% by weight reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes;    (B) thermoplastic matrix material at 1 to 49.9% by weight; and    (C) thermoset resin binder at 0.1 to 10% by weight;    wherein the sum of said conductive filler weight %, thermoplastic matrix weight % and thermoset resin binder weight % equals 100% and the bulk electrical conductivity of said flow field or bipolar plate is at least 100 S/cm.    
   
   
       2 . The flow field or bipolar plate as defined in  claim 1 , wherein said plate has a major surface having a skin layer less than 100 μm in thickness and said skin layer has a polymer volume fraction less than 20% and a conductive filler greater than 80%.  
   
   
       3 . The flow field or bipolar plate as defined in  claim 1 , wherein the bulk conductivity is at least 200 S/cm.  
   
   
       4 . The flow field or bipolar plate as defined in  claim 1  wherein said thermoset resin binder is selected from the group consisting of unsaturated polyester resins, vinyl esters, epoxies, phenolic resins, polyimide resins, bismaleimide resins, polyurethane resins, and combinations thereof.  
   
   
       5 . The flow field or bipolar plate as defined in  claim 1  wherein said conductive filler comprises a conductive material selected from the group consisting of graphite powder, carbon/graphite fibers, metal fibers, carbon nano-tubes, graphitic nano-fibers, nano-scaled graphene plates, carbon blacks, metal particles, and combinations thereof.  
   
   
       6 . The flow field or bipolar plate as defined in  claim 1 , wherein said reinforcement fibers, carbon nano-tubes, graphitic nano-fibers, and/or expanded graphite platelets form an overlapping, contiguous-strand backbone structure.  
   
   
       7 . The flow field or bipolar plate as defined in  claim 1  wherein said reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes are bonded together by said thermoset resin binder.  
   
   
       8 . The flow field or bipolar plate as defined in  claim 1  wherein said reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes are bonded together by said thermoset resin binder and said thermoplastic matrix material.  
   
   
       9 . The flow field or bipolar plate as defined in  claim 1  wherein said reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes form a mat.  
   
   
       10 . A fuel cell flow field plate or bipolar plate having flow channels on at least a face of the plate, comprising an electrically conductive polymer composite having: 
 (A) at least 50% by weight of a conductive filler, comprising at least 5% by weight reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes;    (B) a polymer matrix material at 1 to 49.9% by weight; and    (C) a polymer binder at 0.1 to 10% by weight;    wherein the sum of said conductive filler weight %, polymer matrix material weight % and polymer binder weight % equals 100% and the bulk electrical conductivity of said flow field plate or bipolar plate is at least 100 S/cm.    
   
   
       11 . The flow field or bipolar plate as defined in  claim 10  wherein said polymer matrix material comprises a material selected from a thermoset resin, an interpenetrating network, a semi-interpenetrating network, an elastomer, or a combination thereof.  
   
   
       12 . The flow field or bipolar plate as defined in  claim 10  wherein said polymer binder comprises a water soluble polymer.  
   
   
       13 . The flow field or bipolar plate as defined in  claim 10 , wherein the bulk conductivity is at least 200 S/cm.  
   
   
       14 . The flow field or bipolar plate as defined in  claim 10  wherein said polymer matrix material is selected from the group consisting of unsaturated polyester resins, vinyl esters, epoxies, phenolic resins, polyimide resins, bismaleimide resins, polyurethane resins, and combinations thereof.  
   
   
       15 . The flow field or bipolar plate as defined in  claim 10  wherein said conductive filler comprises a conductive material selected from the group consisting of graphite powder, carbon/graphite fibers, metal fibers, carbon nano-tubes, graphitic nano-fibers, nano-scaled graphene plates, carbon blacks, metal particles, and combinations thereof.  
   
   
       16 . The flow field or bipolar plate as defined in  claim 10 , wherein said conductive filler comprises nano-scaled graphene plates.  
   
   
       17 . The flow field or bipolar plate as defined in  claim 10 , wherein said reinforcement fibers, carbon nano-tubes, graphitic nano-fibers, and/or expanded graphite platelets form an overlapping, contiguous-strand backbone structure.  
   
   
       18 . The flow field or bipolar plate as defined in  claim 10  wherein said reinforcement fibers, expanded graphite platelets, graphitic nano-fibers, and/or carbon nano-tubes form a mat.  
   
   
       19 . The flow field or bipolar plate as defined in  claim 10 , wherein said plate has a major surface having a skin layer less than 100 μm in thickness and said skin layer has a polymer volume fraction less than 20% and a conductive filler volume fraction greater than 80%.  
   
   
       20 . A process for producing a fuel cell flow field plate or bipolar plate as defined in  claim 1 , said process comprising: 
 (A) continuously or intermittently feeding and moving a sheet of porous substrate toward a desired direction, said substrate having through-thickness pores;    (B) mixing and feeding said conductive filler, said thermoset binder, said thermoplastic matrix material and a carrier fluid onto said porous substrate and directing said carrier fluid to substantially flow through said pores, leaving behind a layer of a solid mixture of said filler, binder and matrix material on said substrate;    (C) moving said substrate so as to allow said solid mixture layer to go through a compaction stage; and    (D) heating and consolidating said solid mixture layer and generating flow channels on a surface of said solid mixture layer to form said flow field or bipolar plate.    
   
   
       21 . The process as defined in  claim 20 , wherein said carrier fluid comprises water and said step of mixing and feeding comprises slurry molding.  
   
   
       22 . The process as defined in  claim 20 , wherein said carrier fluid comprises compressed air.  
   
   
       23 . The process as defined in  claim 20 , wherein said step of heating and consolidating comprises a step of embossing or matched-die molding said mixture layer.  
   
   
       24 . The process as defined in  claim 23 , further comprising a step of coating an embossing tool surface or mold surface with a layer of fine graphite, expanded graphite and/or nano-scaled graphene plate powder prior to embossing or molding.  
   
   
       25 . The process as defined in  claim 20 , further comprising a step of curing said thermoset resin binder before, during, and/or after said compaction stage.  
   
   
       26 . A process for producing a fuel cell flow field plate or bipolar plate as defined in  claim 10 , said process comprising: 
 (A) continuously or intermittently feeding and moving a sheet of porous substrate toward a desired direction, said substrate having through-thickness pores;    (B) mixing and feeding said conductive filler, said polymer binder, said polymer matrix material and a carrier fluid onto said porous substrate and directing said carrier fluid to substantially flow through said pores, leaving behind a layer of a solid mixture of said filler, binder and matrix material on said substrate;    (C) moving said substrate so as to allow said solid mixture layer to go through a compaction stage; and    (D) heating and consolidating said solid mixture and generating flow channels on at least a surface of said solid mixture layer to form said flow field or bipolar plate.    
   
   
       27 . The process as defined in  claim 26 , wherein said carrier fluid comprises water and said step of mixing and feeding comprises slurry molding.  
   
   
       28 . The process as defined in  claim 26 , wherein said carrier fluid comprises compressed air.  
   
   
       29 . The process as defined in  claim 26 , wherein said step of heating and consolidating comprises a step of embossing or matched-die molding said mixture layer.  
   
   
       30 . The process as defined in  claim 29 , further comprising a step of coating an embossing tool surface or a mold surface with a layer of fine graphite, expanded graphite and/or nano-scaled graphene plate powder prior to embossing or molding.