KR20010071286A - Membrane-electrode unit for a fuel cell - Google Patents

Abstract

The present invention relates to a membrane electrode unit for a fuel cell comprising an anode optionally coated with a catalyst, a cathode optionally coated with a catalyst, and a quantum conductor between the anode and the cathode. The quantum conductor is formed of a fine fiber fleece material impregnated to an saturation point with an electrolyte, the fleece material being chemically inert to the electrolyte under temperature and redox conditions up to + 200 ° C., and the weight of the fleece material is 20 to 200 g / m 2, the thickness of the fleece material is at most 1 mm and the pore volume is 65 to 92%.

Description

Membrane electrode unit for fuel cell {MEMBRANE-ELECTRODE UNIT FOR A FUEL CELL}

Such units are known. The unit separates the ionic and electrical pathways in the reaction of a reactant gas or flow component comprising hydrogen and oxygen to directly convert chemical energy into electrical energy in a fuel cell.

Several types of fuel cells and their actions are described in K.-D. Kreuer and J. Maier, "Spektrum der Wissenschaft" (1995, July), 92-96.

The electrode should be a very good electron conductor (electrical resistance about 0.1Ωcm ⁻¹ ). The reaction of the electrode with the surface of the electrolyte must be facilitated by a catalyst. The electrolyte should have a high ionic conductivity with as low a electron conductivity as possible. The electrolyte must also not pass the starting gas. All materials should be chemically inert with respect to each other and to the reaction partner. That is, undesired compounding should not occur with each other under strong oxidizing conditions at the cathode and strong reducing conditions at the anode.

In order to connect multiple individual cells into a cell stack, the solid components contained in the individual cells must provide sufficient mechanical resistance. In addition, material cost, process cost, battery component life and environmental friendliness are important.

When the operating temperature was 80 to 90 ° C., a quantum conductive polymer membrane was inserted into the fuel cell. The membrane incorporates the solid's ability to stabilize the liquid's ability and morphology to give molecules and both free mobility. This need is almost ideally met by perfluorinated lonomer membranes based on polytetrafluoroethylene with sulfonated perfluorovinylether side chains. The material consists of hydrophobic and hydrophilic regions which are not mixed by the formation of a morphologically stable film in the gel state in the presence of water. The hydrophobic backbone of the polymer is resistant to oxidation and reduction and provides a morphologically stable backbone to the membrane even in the expanded state. Hydrophilic, liquid-like sulfonic acid-containing side chains expanded in water allow for very good quantum conductivity. A pore size of several nanometers corresponds to the size of a small number of water molecules. The presence of water provides high mobility of both in the channel and in the pores.

The cation exchanger, as is already known in the cited publications, is disadvantageous due to the high cost due to the complicated production process. Its disposal or recycling also causes ecological problems.

In operation of a fuel cell, in particular, combustion oxygen is supplied to the cell by air flow, but if the water molecules move from the anode to the cathode due to the nature of the quantum flow, the membrane tends to dry.

The upper limit of the thermal stability of a known membrane or its sulfonic acid group is 90-100 degreeC. Morphological composition begins to break at higher temperatures.

Thus, at higher operating temperatures, perfluorinated lonomer membranes, known as proprietary membranes, are closed, such membranes are inadequate when:

a) using hydrogen from methanol reformed at temperatures above 130 ° C. as fuel (this method is U.Benz, “Spektrum der Wissenschaft” (July 1995) 97-104);

b) when used at a temperature of at least 130 ° C., typically 150-200 ° C., for the direct oxidation of methanol at the anode.

The present invention relates to a membrane electrode unit for a fuel cell comprising an anode optionally coated with a catalyst, a cathode optionally coated with a catalyst, and a quantum conductor between the anode and the cathode.

It is an object of the present invention to provide the following properties in addition to the above-mentioned preferred properties of the perfluorinated RONomer membrane:

1. Reduced manufacturing costs compared to polymer membranes according to the prior art

2. Reduction of harmful substances at disposal

3. Heat resistance up to 200 ° C. for reduced catalytic poison effect, possibility of using hydrogen from reformed methanol as fuel, internal reforming of methanol or direct oxidation of methanol

To provide a fuel cell membrane electrode unit having a.

This object is achieved according to the invention by the features of claim 1. Preferred embodiments are presented in the dependent claims.

According to the invention the quantum conductor is formed of a fine fiber fleece material impregnated to the saturation point with an electrolyte; The place material is chemically inert to the electrolyte under temperatures up to + 200 ° C. and redox conditions. The weight of the place material is 20 to 200 g / m 2. The thickness of the fleece material is at most 1 mm and the pore volume is from 65 to 92%.

The average pore radius of the fine fiber place material is 20 nm to 10 μm.

In the unit according to the invention, the skeleton of the fine fiber pleated material ensures the mechanical resistance of the membrane, so that the electrolyte does not have to solve the above problem. Due to this, the cost of producing the membrane can be reduced by up to 90%, for example, compared to a proprietary membrane consisting of perfluorinated rheomers of corresponding dimensions.

The fine fiber fleece material may be filled with a perfluorinated rheomer. The perfluorinated ronomer may be polytetrafluoroethylene with sulfonated perfluorovinylether side chains. As an alternative, the fine fiber fleece material is impregnated with 1 to 5 moles of aqueous sulfuric acid solution or concentrated phosphoric acid. It is also possible to use hydrated zirconium phosphate and ammonium dihydrogen phosphate.

In the following examples it should be shown that the present invention is identical to the pure polymer membranes made of perfluorinated rheomers with respect to the output of the fuel cell (ion conductivity), without the need to use expensive materials up to now.

In the examples described below, the base materials are common:

Fleece material: Polysulfone fibers with rectangular cross section (6-13 μm wide, 1.7-2.4 μm high).

Mechanical Properties of Polysulfone Material: Melting Range 343-399 ° C.

Tensile Strength: 70 MPa

Elongation at break: 50 to 100%

Modulus of elasticity: 2.4 GPa

Bending temperature under 1.8 MPa load: 174 ° C

Preparation of fibers: spinning of polysulfone solution dissolved in methylene chloride in electrostatic field. For example, a device according to German Patent Publication No. 26 20 399 can be used. The fibers gather on a fabric support that moves linearly and continuously.

Fleece Material Properties:

Weight: 150 g / ㎡

Thickness (compressed): 0.05 mm

Thickness (impregnated with electrolyte): 0.18 mm

Average pore radius, uncompressed: 8 μm

Average pore radius in the compressed state: 4 μm

Porous Volume: 83%

The heat resistance of the membranes according to the invention is determined by the fleece material unless otherwise objected, thus reaching about 174 ° C. for polysulfone which is a pure fibrous material. Due to the mechanical bonding of the fibers in the flake material, the mechanical stability is increased to 250 ° C. Thus, high temperature operation of the fuel cell becomes possible, which significantly reduces the toxicity of the anode catalyst.

Example 1

The fine fiber fleece material is coated with a liquid Nafion in a 16 mm diameter glass frit, ie perfluorinated rhomer from DuPont. By providing some low pressure, the liquid phase is sucked into the porous structure of the place material. To remove the solvent, the impregnated membrane is treated at 60 ° C. in a drying chamber. It is then also possible to store in distilled water for subsequent processing.

Examples 2-4

The fine fiber place material is impregnated with three different moles of aqueous sulfuric acid solution as in Example 1, but the sulfuric acid is heated to about 70 ° C. to lower the viscosity. If no other results are obtained, the flake material can be boiled for several minutes in an acid heated to 70 ° C.

The membrane thus obtained can preferably be stored in the corresponding impregnation medium.

In membranes prepared in this way the following intrinsic conductivity was detected by the method according to DIN 53 779 of March 1979:

Example Measurement temperature (℃) Specific Conductivity (S / cm) One 23 0.016 21 MH ₂ SO ₄ 18 0.031 33 MH ₂ SO ₄ 18 0.041 45 MH ₂ SO ₄ 18 0.080 5 (comparative example) 25 0.070

Example 5 in the table is a comparative example measured on a 125 μm thick, self-supporting polymer membrane according to the prior art, consisting of perfluorinated rhomer (Nafion-117, DuPont).

The value for the intrinsic conductivity (S / cm) is much lower than that of pure Nafion, the structure is simpler, and the membrane according to the invention with higher mechanical resistance allows operation of the fuel cell at a power corresponding to the prior art. It is displayed. When used at temperatures above 100 ° C., concentrated phosphoric acid can be used as the ion conductor.

For example, compared to the expanded Nafion membrane with a thickness of 125 μm, the electrolyte-impregnated flake material used in Examples 1 to 4 has twice the thickness.

The output of the fuel cell, expressed as the product of voltage and current intensity, can be obtained by higher acid concentrations, ie higher intrinsic conductivity (S / cm), and a reduction in diffusion prevention by the use of thin place material.

1 shows the current / voltage curves at room temperature, corresponding to Examples 1, 2, and 3. FIG. The membrane according to the invention appears to yield a curve comparable to the prior art (Example 5). The above effect of high cell output by high acid concentration or thin place material is shown by the shift of the curve in the positive direction of the ordinate in this figure.

Due to the high heat resistance of the flake material, concentrated phosphoric acid may be used as the electrolyte when used at temperatures above 100 ° C.

Claims (7)

A membrane electrode unit for a fuel cell comprising an anode optionally coated with a catalyst, a cathode optionally coated with a catalyst, and a quantum conductor between the anode and the cathode, The quantum conductor is formed of a fine fiber fleece material impregnated to an saturation point with an electrolyte, the fleece material being chemically inert to the electrolyte under temperature and redox conditions up to + 200 ° C., and the weight of the fleece material is 20-200 g / m 2, membrane material unit having a thickness of up to 1 mm and a porous volume of 65 to 92%. The method of claim 1, The film type electrode unit, wherein the fine fiber fleece material has an average pore radius of 20 nm to 10 μm. The method according to claim 1 or 2, And the fine fiber pleated material is filled with a perfluorinated rheomer. The method of claim 3, wherein The membrane electrode unit according to claim 1, wherein the perfluorinated ronomer is polytetrafluoroethylene having sulfonated perfluorovinylether side chains. The method according to claim 1 or 2, The membrane type electrode unit, wherein the fine fiber flake material is impregnated with 1 to 5 moles of sulfuric acid solution. The method according to claim 1 or 2, The membrane type electrode unit, wherein the fine fiber flake material is impregnated with concentrated phosphoric acid. The method according to claim 1 or 2, Membrane electrode unit, characterized in that the fine fiber flake material is impregnated with hydrated zirconium phosphate or ammonium dihydrogen phosphate.