Gas diffusion backing for fuel cells
AssigneeE. I. Du Pont de Nemours and Company
InventorsKelly Barton, Shoibal Banerjee
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Abstract
A gas diffusion backing for fuel cells wherein a porous carbonaceous paper or fabric, impregnated with a first fluorinated polymer, bears a microporous coating of a second fluorinated polymer admixed with carbon particles. Also, a process for making the composite wherein the fluorinated polymers are coalesced by heating above their glass transition temperature or melting point is described. A membrane electrode assembly prepared using these gas diffusion backing and a fuel are also provided.
Claims47
A gas diffusion backing adapted for use in fuel cells consisting essentially of a porous first layer and a microporous second layer in electrically conductive contact therewith, said first layer consisting essentially of a porous carbonaceous paper or fabric comprising carbon fibers, wherein the carbon fibers comprise at least 50% by volume of the layer, said fibers being at least partially coated by a first fluorinated polymer disposed thereupon, and said second layer consisting essentially of a second fluorinated polymer having carbon particles intermixed therewith, the first and second fluorinated polymers (i) being the same or different, (ii) each being a melt processable polymer selected from the group consisting of:
- (a) amorphous polymers having a glass transition temperature (Tg) of less than about 250° C.;
- (b) crystalline or semi-crystalline polymers having a melting point of less than about 315° C.;
- and
- (c) mixtures thereof.
A process for forming a gas diffusion backing comprising:
- (W) contacting a porous carbonaceous paper or fabric comprising carbon fibers with a first fluorinated polymer to impregnate said first fluorinated polymer into the paper or fabric and at least partially coat said fibers, thereby forming a porous first layer containing at least 50% by volume of carbon fibers;
- (X) applying a second layer to the first layer from a composition comprising a second fluorinated polymer, carbon particles, a first component, and a second component, wherein the second component has a boiling point greater than that of the first component, and wherein the first and second fluorinated polymers are (i) the same or different, (ii) each comprises a melt processable polymer selected from the group consisting of:
- (a) amorphous polymers having a glass transition temperature (Tg) of less than about 250° C.;
- (b) crystalline or semi-crystalline polymers having a melting point of less than about 315° C.;
- and
- (c) mixtures thereof;
- (Y) drying the first and second layers after each of steps (W) and (X), or after completion of step (X) to remove the low boiling solvent;
- and
- (Z) heating the first and second layers individually, or after they have been brought into contact, to form the gas diffusion backing having a microporous second layer in electrical contact with the first layer.
A membrane electrode assembly comprising:
- (a) a solid polymer electrolyte membrane having a first and second surface;
- (b) at least one electrode present on either the first or second surface of the solid polymer electrolyte membrane;
- and
- (c) at least one gas diffusion backing adjacent to at least one electrode, wherein the gas diffusion backing consists essentially of a porous first layer and a microporous second layer in electrically conductive contact therewith, said first layer consisting essentially of a porous carbonaceous paper or fabric comprising carbon fibers, wherein the carbon fibers comprise at least 50% by volume of the layer, said fibers being at least partially coated by a first fluorinated polymer disposed thereupon, and said second layer consisting essentially of a second fluorinated polymer having carbon particles intermixed therewith, the first and second fluorinated polymers (i) being the same or different, (ii) each being a melt processable polymer selected from the group consisting of
- (a) amorphous polymers having a glass transition temperature (Tg) of less than about 250° C.;
- (b) crystalline or semi-crystalline polymers having a melting point of less than about 315° C.;
- and
- (c) mixtures thereof.
A fuel cell comprising a membrane electrode assembly, wherein the membrane electrode assembly comprises:
- (a) a solid polymer electrolyte membrane having first and second surfaces;
- (b) at least one electrode present on either the first or second surface of the solid polymer electrolyte membrane;
- and
- (c) a gas diffusion backing adjacent to at least one electrode, wherein the gas diffusion backing consists essentially of a porous first layer and a microporous second layer in electrically conductive contact therewith, said first layer consisting essentially of a porous carbonaceous paper or fabric comprising carbon fibers, wherein the carbon fibers comprise at least about 50% by volume of the layer, said fibers being at least partially coated by a first fluorinated polymer disposed thereupon, and said second layer consisting essentially of a second fluorinated polymer having carbon particles intermixed therewith, the first and second fluorinated polymers (i) being the same or different, (ii) each being a melt processable polymer selected from the group consisting of
- (a) amorphous polymers having a glass transition temperature (Tg) of less than about 250° C.;
- (b) crystalline or semi-crystalline polymers having a melting point of less than about 315° C.;
- and
- (c) mixtures thereof.
Dependencies are inferred from the claim text.