Exfoliated graphite composite compositions for fuel cell flow field plates
This invention provides an electrically conductive, less anisotropic, and structurally sound composite composition for fuel cell flow field plate or bipolar plate applications. The composition comprises: (a) expanded or exfoliated graphite; (b) particles of non-expandable graphite or carbon, wherein the particles are between 3% and 60% by weight based on the total weight of the particles and the expanded graphite; and (c) a binder or matrix material to bond the expanded graphite and the particles of non-expanded graphite or carbon for forming a highly conductive composite, wherein the binder or matrix material is between 3% and 60% by weight based on the total composite composition weight. The composite plate exhibits a thickness-direction conductivity typically greater than 35 S/cm, more typically greater than 50 S/cm, most typically greater than 100 S/cm, and a thickness-direction specific areal conductivity greater than 200 S/cm 2 , more typically greater than 500 S/cm 2 .
1 . An electrically conductive composite composition for fuel cell flow field plate or bipolar plate applications, said composition comprising:
(a) expanded or exfoliated graphite;
(b) particles of non-expandable graphite or carbon, wherein said non-expandable graphite or carbon particles are in the amount of between 3% and 60% by weight based on the total weight of said particles and said expanded graphite; and
(c) a binder or matrix material to bond said expanded graphite and said particles of non-expanded graphite or carbon for forming a highly conductive composite, wherein said binder or matrix material is between 3% and 60% by weight based on the total composite composition weight.
2 . The composite composition as defined in claim 1 wherein said composition, after molding to form a flow field plate or bipolar plate, has a thickness-direction electrical conductivity no less than 50 S/cm.
3 . The composite composition as defined in claim 1 wherein said composition, after molding to form a flow field plate or bipolar plate, has a thickness-direction electrical conductivity no less than 100 S/cm.
4 . The composite composition as defined in claim 1 wherein said composition, after molding to form a flow field plate or bipolar plate, has a thickness-direction electrical conductivity no less than 200 S/cm.
5 . The composite composition as defined in claim 1 , further comprising a reinforcement or filler selected from the group consisting of graphite or carbon fiber, graphite or carbon nano-fiber, nano-tube, glass fiber, ceramic fiber, polymer fiber, metal fiber, metal particle, polymer particle, organic particle, inorganic particle, or a combination thereof, wherein said reinforcement or filler is between 0.5% and 30% by weight based on the total weight of expanded graphite, particles of non-expanded graphite or carbon, and reinforcement or filler.
6 . The composite composition as defined in claim 1 , wherein said binder or matrix material comprises a polymer, ceramic, glass, metal, carbon, polymeric carbon, asphalt, tar, coal tar pitch, petroleum pitch, mesophase pitch, or a combination thereof.
7 . The composite composition as defined in claim 1 , wherein said binder or matrix material comprises a polymer selected from the group consisting of polyethylene, polypropylene, nylon, polyesters, polytetrafluoroethylene, polyvinylidene fluoride, fluoro polymers, polyacrylonitrile, acrylic resins, epoxides, polyimide, bismale imide, phenol formaldehydes, vinyl ester, isocyanate resins, and combinations thereof.
8 . The composite composition as defined in claim 1 , wherein said binder or matrix material comprises an inorganic vitreous glass-forming material which contains at least one of the compounds selected from the group consisting of boric oxide, silica, phosphorous pentaoxide, germanium oxides, vanadium pentoxides, and beryllium fluoride.
9 . The composite composition as defined in claim 1 , wherein said binder or matrix material comprises a glass-forming composition containing at least two oxides selected from the group consisting of silica, aluminum oxide, sodium oxide, potassium oxide, magnesium oxide, cuprous oxide, barium oxide, lead oxide, and boric oxide.
10 . The composite composition as defined in claim 1 wherein said composition, after molding to form a plate, has a flexural strength no less than 50 MPa.
11 . The composite composition as defined in claim 2 wherein said composition, after molding to form a plate, has a flexural strength no less than 50 Mpa.
12 . The composite composition as defined in claim 5 wherein said composition, after molding to form a plate, has a flexural strength no less than 50 MPa.
13 . The composite composition as defined in claim 1 wherein said binder is selected from the group consisting of unsaturated polyester resin, vinyl ester resin, epoxy resin, phenolic resin, polyimide resin, bismaleimide resin, polyurethane resin, thermoplastic resin, and combinations thereof.
14 . The composite composition as defined in claim 3 wherein said composition, after molding to form a plate having a plate thickness direction and a surface plane perpendicular to said plate thickness direction, has an electrical conductivity parallel to surface plane no less than 1,000 S/cm, a thickness-direction conductivity no less than 35 S/cm, or a specific areal electrical conductivity no less than 200 S/cm 2 .
15 . The composite composition as defined in claim 1 , wherein said composition is molded into a flow filed plate having two primary exterior surfaces having flow field channels on at least one of the two exterior surfaces.
16 . The composite composition as defined in claim 1 , wherein said composite composition is shaped into a plate having a thickness of 1 mm or thinner.
17 . The composite composition as defined in claim 1 , wherein said composite composition is shaped into a plate having a thickness of 0.5 mm or thinner.
18 . The composite composition as defined in claim 1 , wherein said exfoliated graphite comprises exfoliated natural graphite, synthetical graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nano-fiber, graphite oxide, graphite fluoride, chemically modified graphite, or a combination thereof.