Method of producing conducting polymer-transition metal electro-catalyst composition and electrodes for fuel cells

• US 20090020734A1
• Filed: 07/19/2007
• Published: 01/22/2009
• Est. Priority Date: 07/19/2007
• Status: Active Grant

• Current Assignee: Nanotek Instruments Group, LLC
• Original Assignee: Aruna Zhamu, Bor Z. Jang
• Inventors: Zhamu, Aruna, Jang, Bor Z.
• Granted Patent: US 7,785,498 B2
• Time in Patent Office: Days
• US Class Current: 252/519.340
• CPC Class Codes: C08G 2261/1452 containing sulfonyl or sulfonate-groups
• CPC Class Codes: C08G 2261/3221 containing one or more nitrogen atoms as the only heteroatom, e.g. pyrrole, pyridine or triazole
• CPC Class Codes: C08G 2261/3223 containing one or more sulfur atoms as the only heteroatom, e.g. thiophene
• CPC Class Codes: C08G 2261/51 Charge transport
• CPC Class Codes: C08G 2261/794 with polymeric dopants
• CPC Class Codes: C08L 65/00 Compositions of macromolecular compounds obtained by reactions forming a carbon-to-carbon link in the main chain C08L7/00 - C08L57/00, C08L61/00 take precedence; Compositions of derivatives of such polymers
• CPC Class Codes: C08L 71/00 Compositions of polyethers obtained by reactions forming an ether link in the main chain of polyacetals C08L59/00; of epoxy resins C08L63/00; of polythioether-ethers C08L81/02; of polyether-sulfones C08L81/06; Compositions of derivatives of such polymers
• CPC Class Codes: H01B 1/122 Ionic conductors
• CPC Class Codes: H01B 1/128 comprising six-membered aromatic rings in the main chain, e.g. polyanilines, polyphenylenes
• CPC Class Codes: H01M 4/8807 Gas diffusion layers
• CPC Class Codes: H01M 4/881 Electrolytic membranes
• CPC Class Codes: H01M 4/8828 Coating with slurry or ink
• CPC Class Codes: H01M 4/8846 Impregnation
• CPC Class Codes: H01M 4/9008 Organic or organo-metallic compounds
• CPC Class Codes: H01M 8/1011 Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC]
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A method of producing an electro-catalyst composition for use as an electrode, gas diffusion layer-supported electrode, catalyst-coated solid electrolyte layer, and membrane-electrode assembly in a proton exchange membrane (PEM) type fuel cell. The method comprises: (a) preparing a proton- and electron-conducting polymer having an electronic conductivity no less than 10⁻³ S/cm and a proton conductivity no less than 10⁻⁴ S/cm; (b) mixing and reacting this conducting polymer with a plurality of transition metal coordination complexes to produce the desired electro-catalyst composition having at least one heteroatom per backbone monomer unit thereof and a plurality of neutral transition metal atoms covalently bonded to at least a portion of the heteroatoms. The step of reacting preferably comprises (b1) complexing the conducting polymer with the plurality of transition metal coordination complexes to form a polymer-transition metal complex and (b2) reducing the polymer-transition metal complex to place the transition metal in a neutral oxidation state. A hydrogen-oxygen PEM fuel cell or a direct methanol fuel cell (DMFC) featuring such an electro-catalyst composition in a thin-film electrode exhibits a superior current-voltage response.

Claims

1. A method of preparing a fuel cell electro-catalyst composition, said method comprising:

(a) preparing a proton- and electron-conducting polymer having an electronic conductivity no less than 10<sup>−

3</sup> S/cm and a proton conductivity no less than 10<sup>−

4</sup> S/cm;

(b) mixing and reacting said conducting polymer with a plurality of transition metal coordination complexes to produce said electro-catalyst composition having at least one heteroatom per backbone monomer unit thereof and a plurality of neutral transition metal atoms covalently bonded to at least a portion of said heteroatoms.

2. The method of claim 1, wherein said step of reacting comprises (b1) complexing said conducting polymer with said plurality of transition metal coordination complexes to form a polymer-transition metal complex and (b2) reducing said polymer-transition metal complex to place said transition metal in a neutral oxidation state.

3. The method of claim 1, wherein said step of reacting produces a plurality of catalytically active particles of a transition metal, which are nucleated around said covalently bonded transition metal atoms.

4. The method of claim 1, further comprising a step of dispersing a plurality of catalytically active particles of a transition metal in said polymer.

5. The method of claim 3, wherein said catalytically active particles of a transition metal have an average dimension smaller than 2 nanometers.

6. The method of claim 1, wherein said polymer is selected from the group consisting of sulfonated polyaniline, sulfonated polypyrrole, sulfonated polythiophene, sulfonated polyfuran, sulfonated bi-cyclic polymers, derivatives thereof, and combinations thereof.

7. The method of claim 2, wherein said polymer is selected from the group consisting of sulfonated polyaniline, sulfonated polypyrrole, sulfonated polythiophene, sulfonated polyfuran, sulfonated bi-cyclic polymers, derivatives thereof, and combinations thereof.

8. The method of claim 1, wherein said transition metal atoms include atoms selected from the group consisting of platinum, iridium, osmium, rhenium, ruthenium, rhodium, palladium, iron, cobalt, nickel, chromium, manganese, copper, vanadium, and combinations thereof.

9. The method of claim 2, wherein said transition metal atoms include atoms selected from the group consisting of platinum, iridium, osmium, rhenium, ruthenium, rhodium, palladium, iron, cobalt, nickel, chromium, manganese, copper, vanadium, and combinations thereof.

10. The method of claim 3, wherein said transition metal atoms include non-platinum atoms selected from the group consisting of iron, cobalt, nickel, chromium, manganese, copper, and vanadium and said catalytically active particles of a transition metal have an average dimension smaller than 1.5 nm.

11. The method of claim 3, wherein said transition metal atoms include non-platinum atoms selected from the group consisting of iron, cobalt, nickel, chromium, manganese, copper, and vanadium and said catalytically active particles of a transition metal have an average dimension smaller than 1 nm.

12. The method of claim 1, wherein said polymer comprises a mixture of an electron-conducting polymer and a proton-conducting polymer;

said proton-conducting polymer is selected from the group consisting of poly(perfluoro sulfonic acid), sulfonated polytetrafluoroethylene, sulfonated perfluoroalkoxy derivatives of polytetra-fluoroethylene, sulfonated polysulfone, sulfonated poly(ether ketone), sulfonated poly(ether ether ketone), sulfonated polystyrene, sulfonated polyimide, sulfonated styrene-butadiene copolymers, sulfonated poly chloro-trifluoroethylene, sulfonated perfluoroethylene-propylene copolymer, sulfonated ethylene-chlorotrifluoroethylene copolymer, sulfonated polyvinylidenefluoride, sulfonated copolymers of polyvinylidenefluoride with hexafluoropropene and tetrafluoroethylene, sulfonated copolymers of ethylene and tetrafluoroethylene, polybenzimidazole, and chemical derivatives, copolymers, and blends thereof.

13. The method of claim 2, wherein said sub-step (b2) of reducing comprises steps of mixing said complex with an aqueous solution of a reductant selected from the group consisting of sodium borohydride, formaldehyde, and hydrazine.

14. The method of claim 1, further comprising (c) dissolving or dispersing said electro-catalyst composition in a solvent to form a solution or suspension;

(d) impregnating an electrically conductive sheet with said solution or suspension; and

(e) drying said impregnated sheet to produce a fuel cell electrode.

15. The method of claim 3, further comprising (c) dissolving or dispersing said electro-catalyst composition in a solvent to form a solution or suspension;

(d) impregnating an electrically conductive sheet with said solution or suspension; and

(e) drying said impregnated sheet to produce a fuel cell electrode.

16. The method of claim 14, wherein said electrically conductive sheet comprises a carbon paper, carbon fabric, carbon or graphite mat, carbon or graphite foam, carbon nanotube or carbon nano-fiber-containing sheet, exfoliated graphite flake-containing sheet, or a combination thereof.

17. The method of claim 15, wherein said electrically conductive sheet comprises a carbon paper, carbon fabric, carbon or graphite mat, carbon or graphite foam, carbon nanotube or carbon nano-fiber-containing sheet, exfoliated graphite flake-containing sheet, or a combination thereof.

18. The method of claim 14, wherein said electrically conductive sheet comprises a gas diffusion sheet.

19. The method of claim 1, further comprising (c) dissolving or dispersing said electro-catalyst composition in a solvent to form a solution or suspension;

(f) dispensing, printing, or coating said solution or suspension onto at least one surface of a proton conducting membrane; and

(g) drying said solution or suspension on said membrane surface to produce a catalyst-coated membrane.

20. The method of claim 3, further comprising (c) dissolving or dispersing said electro-catalyst composition in a solvent to form a solution or suspension;

(f) dispensing, printing, or coating said solution or suspension onto at least one surface of a proton conducting membrane; and

(g) drying said solution or suspension on said membrane surface to produce a catalyst-coated membrane.