Highly conductive composites for fuel cell flow field plates and bipolar plates
View Patent ↗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 continuous, in-line roll-to-roll process for producing a fuel cell flow field plate or bipolar plate, said process comprising:
(A) continuously feeding and unwinding a sheet of porous substrate from a roller toward a desired direction, said substrate having through-thickness pores;
(B) mixing and feeding a conductive filler, a thermoset binder, a 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, wherein said binder is in an amount of at least 0.1% but less than 5% by weight of the total weights of the conductive filler, thermoset binder, and thermoplastic matrix combined;
(C) moving said substrate so as to allow said solid mixture layer to go through a compaction stage;
(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; and
(E) rewinding the porous substrate onto a roller.
2. The process as defined in claim 1 , wherein said carrier fluid comprises water and said step of mixing and feeding comprises slurry molding.
3. The process as defined in claim 1 , wherein said carrier fluid comprises compressed air.
4. The process as defined in claim 1 , wherein said step of heating and consolidating comprises a step of embossing or matched-die molding said mixture layer.
5. The process as defined in claim 4 , 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.
6. The process as defined in claim 1 , further comprising a step of curing said thermoset resin binder before, during, and/or after said compaction stage.
7. A continuous roll-to-roll process for producing a fuel cell flow field plate or bipolar plate, said process comprising:
(A) continuously feeding and unwinding a sheet of porous substrate from a roller toward a desired direction, said substrate having through-thickness pores;
(B) mixing and feeding a conductive filler, a polymer binder, a 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, wherein said binder is in an amount of at least 0.1% but less than 5% by weight of the total weights of the conductive filler, thennoset polymer binder, and thermoplastic polymer matrix combined and said conductive filler is selected from the group consisting of graphite powder, carbon/graphite fibers, expanded graphite platelets, carbon blacks, metal particles, and combinations thereof;
(C) moving said substrate so as to allow said solid mixture layer to go through a compaction stage;
(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; and
(E) rewinding the porous substrate onto a roller.
8. The process as defined in claim 7 , wherein said carrier fluid comprises water and said step of mixing and feeding comprises slurry molding.
9. The process as defined in claim 7 , wherein said carrier fluid comprises compressed air.
10. The process as defined in claim 7 , wherein said step of heating and consolidating comprises a step of embossing or matched-die molding said mixture layer.
11. The process as defined in claim 10 , further comprising a step of coating an embossing tool surface or a old surface with a layer of fine graphite, expanded graphite and/or nano-scaled graphene plate powder prior to embossing or molding.
12. The process as defined in claim 1 , wherein said binder occupies an amount of from 0.1% to 3% by weight of the total weights of the conductive filler, thermoset binder, and thermoplastic matrix combined.
13. The process as defined in claim 7 , wherein said binder occupies an amount of from 0.1% to 3% by weight of the total weights of the conductive filler, thermoset binder, and thermoplastic matrix combined.