Method of producing an electrode substrate made of carbon fibers

Abstract

A porous electrode substrate has a form of a tape material and contains a structure made of carbon fibers and a carbon matrix. A specific surface area, porosity, and pore distribution are determined by the carbon matrix. The carbon matrix contains carbon particles including activated carbon with a high specific surface area and a carbonized or graphitized residue of a carbonizable or graphitizable binder.

Claims

1. A method for producing a porous electrode substrate as a line material, which comprises the steps of: carbonizing a precursor fiber structure resulting a structure of carbon fibers; and performing at least one of impregnating, drying or hardening the structure of carbon fibers with a dispersion containing carbon particles including activated carbon and a carbonizable binder resulting in an impregnated structure of carbon fibers into a carbonized matrix, wherein the carbon matrix comprises carbon particles including activated carbon with a specific surface area of more than 1000 m.sup.2/g and a carbonized or graphitized residue of a carbonizable or graphitizable binder, and that at least a part of interstices in the structure of carbon fibers and the carbon matrix is filled with the activated carbon, as well as with the carbonized or graphitized residue of a carbonizable or graphitizable binder, further wherein specific surface area, porosity and pore distribution are determined by the carbon matrix; carbonizing in a continuous furnace at 800-3,000 C. in an inert gas atmosphere; the impregnated structure of carbon fibers resulting in a carbonized structure.

2. The method according to claim 1, wherein the precursor fiber structure has fibers selected from the group consisting of polyacryl nitrile fibers, oxidized polyacryl nitrile fibers (PANOX), Novoloid (phenol resin fibers), cellulose fibers, cellulose acetate fibers, lignine fibers, polyaramide fibers, polyimide fibers, polyoxodiazole fibers, polyvinyl alcohol fibers, polyamide fibers, and pitch fibers.

3. The method according to claim 1, wherein the carbon fibers are short cut fibers, staple fibers or continuous filaments.

4. The method according to claim 1, which further comprises setting a carbon fiber proportion in the precursor fiber structure to be 10 to 90%.

5. The method according to claim 1, wherein the dispersion contains at least one dispersion agent selected from the group consisting of lignine sulfonates, naphtaline sulfonate condensates, polyalkylphenyl ether, polyethylene oxide polypropylene oxide copolymers, polyacrylate and polyvinyl alcohols, polyvinyl pyrrolidone, polyethylenimine, polyaminobenzol sulfonic acid, polybenzyl viologenes and polydiallyldimethyl ammonium chloride.

6. The method according to claim 1, wherein the carbonized substrate is additionally impregnated with at least one impregnating agent.

7. The method according to claim 1, which further comprises doping the structure of carbon fibers with at least one doping agent.

8. The method according to claim 6, wherein the impregnating agent contains a water-repellent polymer, and a proportion of the impregnating agent in the porous electrode substrate is between 2 and 40% by weight.

9. The method according to claim 7, wherein the dispersion additionally contains the at least one doping agent, the at least one doping agent containing at least one of H.sub.2 inhibitors, metals, metal salts, or metal oxides.

10. The method according to claim 2, wherein the carbonized structure is thermally or wet-chemically oxidized after the carbonizing step.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The following examples explain the invention.

Example 1

(2) A line of carbon fiber raw paper (square measures 20 g/m.sup.2), produced in wet fluid processing with short cut carbon fibers (3-12 mm), is impregnated by a foulard in an aqueous dispersion consisting of 50 kg water, 0.75 kg polyvinyl pyrrolidone, 6.75 kg acetylene soot, 0.75 kg activated carbon (BET>1,000 m.sup.2/g), 0.75 kg 2-aminopropanole, 0.1 kg ammonium hydrogen carbonate, and 18.75 kg resorcinol formaldehyde resin dispersion and dried and/or hardened in a continuous furnace. Carbonization subsequently takes place under inert gas atmosphere in a continuous furnace at 1,400 C.

Example 2

(3) A roll of carbon fiber fleece (40 g/m.sup.2), produced by carbonizing a water-jet hardened fleece on the basis of polyacryl nitrile or oxidized polyacryl nitrile staple fibers (20 to 80 mm), is impregnated on a foulard in an aqueous dispersion consisting of 56 kg water, 0.95 kg polyvinyl alcohol, 7.5 kg acetylene soot (BET surface 60 m.sup.2/g), and 20.65 kg melamine formaldehyde resin (40%) and dried and/or hardened in a continuous furnace. Carbonization subsequently takes place under inert gas atmosphere in a continuous furnace at 1,400 C.

(4) The following table shows the material parameters for examples 1 and 2, with a reference sample for comparison. A 2-point measurement at a load of 100 N/cm.sup.2 was conducted to measure the resistance.

(5) TABLE-US-00001 Resistance Element Thickness Porosity (mOhm/ analysis BET (m) (%) cm.sup.2) C N O (m.sup.2/g) Reference 370 87.8 4.2 98.5 0.3 0.1 0.8 GDL 10AA Example 210 91.2 6.2 97.8 0.9 0.6 70 1 Example 380 88.7 9.8 97.5 1.4 0.1 34 2

(6) In order to assess electrochemical activity, cyclic voltammetry measurements of untreated electrode materials were conducted in 1 mM Fe(CN).sub.6.sup.3/4 in 0.1 M potassium chloride solution.

(7) An ideally reversible redox pair results in a separation of 60 mV between the oxidation (E.sub.p.sup.ox) and reduction peak (E.sub.p.sup.red) (A. J. Bard, L. M. Faulkner (eds.), Electrochemical Methods: Fundamentals and Applications, Wiley, 2001). The considerably smaller peak separations for the materials in examples 1 and 2, compared to the reference material, confirm the significantly improved electrochemical kinetics of the materials from embodiment examples 1 and 2.

(8) TABLE-US-00002 E.sub.p.sup.ox-E.sub.p.sup.red Reference GDL 10AA 322 mV Example 1 70 mV Example 2 100 mV