KR20050093491A - Polyelectrolyte complex membrane for fuel cell and method for preparation the same - Google Patents

Abstract

The present invention relates to a polymer electrolyte complex membrane for a fuel cell and a method for manufacturing the same, and more particularly, an anionic polysaccharide-based polymer alone or an anionic polymer interpenetrating into the anionic polysaccharide-based polymer. The anionic polymer matrix of and the anionic matrix are immersed in an aqueous cationic metal solution, and the anion present on the surface of the matrix and the metal of the cation are crosslinked by a complex bonding reaction, thereby improving the strength of the network structure and high proton transfer function. A polymer electrolyte complex membrane for a fuel cell exhibiting hydrogen ion conductivity and low methanol permeability, and a method of manufacturing the same.

Description

Polyelectrolyte complex membrane for fuel cell and method for preparation the same

The present invention relates to a polymer electrolyte complex membrane for a fuel cell and a method for manufacturing the same, and more particularly, an anionic polysaccharide-based polymer alone or an anionic polymer interpenetrating into the anionic polysaccharide-based polymer. The anionic polymer matrix of and the anionic matrix are immersed in an aqueous cationic metal solution, and the anion present on the surface of the matrix and the metal of the cation are crosslinked by a complex bonding reaction, thereby improving the strength of the network structure and high proton transfer function. A polymer electrolyte complex membrane for a fuel cell exhibiting hydrogen ion conductivity and low methanol permeability, and a method of manufacturing the same.

In general, polymer electrolyte membrane fuel cells have high current density, are not concerned about corrosion and electrolyte loss, and can be operated at lower temperatures than other fuel cells, and thus are being developed as a power source for military or spacecraft. The research has been actively conducted to apply it as a power source or a mobile power source for automobiles by using high power density, simple device, and modularity.

A polymer electrolyte membrane fuel cell generally consists of a porous cathode coated with platinum, which is a noble metal catalyst, and an anode, and a separator tube forming a gas passage at the same time around the polymer electrolyte membrane. Hydrogen as fuel enters the anode and oxygen or air as an oxidant flows into the cathode, and electrical energy is generated by electrochemical oxidation of the fuel gas and electrochemical reduction of the oxidant. In this case, each electrochemical reaction occurring at the electrode generates hydrogen ions and electrons by the following Reaction Equation 1 at the anode, and hydrogen and hydrogen ions and electrons are reacted by the following Reaction Equation 2 at the cathode to generate water. The overall fuel cell reaction can be represented by the following equation.

A fuel electrode _{(anode): H 2 → 2H} + + 2e -

An air electrode _{(cathode): 1 / 2O 2} + 2H + + 2e - → H 2 O

Battery reaction: H ₂ + 1 / 2O ₂ → H ₂ O

That is, the reduction reaction of oxygen and the oxidation reaction of hydrogen occur in the air electrode and the fuel electrode, respectively, and as a result, electricity and water are generated. In the case of the polymer electrolyte membrane fuel cell, the voltage generated in the battery is about 1.2 V in the open circuit state, and when the load is applied from the outside, the voltage of the battery increases according to the load.

When a polymer electrolyte membrane is used in a fuel cell, the membrane must have hydrogen ion conductivity in order to transfer the hydrogen ions produced from the anode to the cathode, and the gasket prevents gas from leaking with the function of an electrical insulator that prevents the anode from contacting the cathode. Play a role. Therefore, the polymer electrolyte membrane requires high hydrogen ion conductivity, gas impermeability, and suitable mechanical strength.

A polymer electrolyte membrane that is widely used in a polymer electrolyte fuel cell is a Nafion ™ -based membrane which is a polymer containing a perfluorinated sulfonic acid group manufactured by DuPont, USA. The membrane has an ion conductivity of 0.068 S / cm, excellent mechanical strength and chemical resistance when saturated water content is present, and has stable performance as an electrolyte membrane for use in fuel cells for automobiles.

Commercial membranes of a similar type include Asahi Chemicals' Aciplex-S membrane, Dow Chemical's Dow membrane, and Asahi Glass's Flemion. Flemion membranes are also being developed and research is underway at the Ballard Power System of Canada for polymers that are perfluorinated in alpha and beta form.

However, the membranes are used in a limited form because of their high cost and the high efficiency of the polymer electrolyte membrane due to methanol crossover in electrical energy systems such as direct methanol fuel cells [M. Hogarth and X. Glipa, Fuel Cell Today, and reference therein (2001); S. Faure, N. Cornet, G. Gebel, R. Mercier, M. Pineri, and B. Sillion, in Proceedings of the Second International Symposium on New Materials for Fuel Cell and Modern Battery Systems, O. Savadogo and PR Roberge, eds., Montreal, Canada, July 6-10, 818 (1997).

For this reason, many studies are being conducted on non-fluorine-based polymer electrolyte membranes, and representative examples thereof include sulfonated polystyrenes, polysulfones, polyetheretherketones, and polyimide-based compounds [M. Rikukawa and K. Sanui, Progress in Polymer Science, 25, 1463 (2000).

However, since their ion conductivity is proportional to the degree of sulfonation, when sulfonated above a critical concentration, the molecular weight decrease cannot be avoided, and there is a disadvantage that it cannot be used for a long time due to the reduction of mechanical properties during hydration. Selective sulfonation methods have also been researched and developed (US Pat. Nos. 5,585,74, 5679482, 6110616), but do not completely solve the problems of high temperature stability and long-term use.

Therefore, there is an urgent need for a new method that can reduce the cost and improve the high temperature stability and chemical resistance of the existing polymer electrolyte membrane.

Accordingly, the present inventors have made efforts to improve the problems such as the crossover phenomenon of methanol, thermal and chemical stability, economical efficiency and fluorine-based use of the conventional polymer electrolyte membrane as described above, and anionic polysaccharide-based polymers or specific anionic The net structure is improved by the crosslinking reaction of the cationic metal which forms a complex bond with the anion present on the surface of the matrix by immersing the anionic polymer matrix of the net structure formed by the mixture with the polymer in the form of mutual penetration. In addition to forming a complex membrane of the present invention, it was found that it has excellent proton transfer functions because it contains a large number of functional groups in the form of strong acids and weak acids.

Accordingly, an object of the present invention is to provide a polymer electrolyte complex membrane for a non-fluorine fuel cell having a strong mesh structure by mutual penetration and complexing, and having a proton transfer functional group in a molecule.

The present invention is characterized by a polymer electrolyte complex membrane for a fuel cell comprising an anionic polysaccharide-based polymer matrix and a complex layer formed by crosslinking a cationic metal forming a complex bond with an anion present on the surface of the matrix.

Hereinafter, the present invention will be described in more detail.

The present invention is an anionic polymer matrix of the net structure formed by mixing the polymer mixture showing anionic properties in the form of mutual penetration and the complex of the net structure is improved crosslinked by the complex bonding of the anion and cationic metal present on the surface of the matrix The present invention relates to a polymer complex membrane for a fuel cell containing excellent proton transfer functional groups in the membrane and the molecule.

Conventionally, a patent for the polymer complex membrane using anionic polymer and cationic polymer [Korean Patent Registration No. 0376379] has already been disclosed, but the present invention is a method of forming a complex film and the structure of the complex membrane itself. Is a different thing.

The above-mentioned conventional patent is an organic-organic complex membrane in which an anionic polymer is applied to a porous support surface to form an anionic matrix, and the coated surface is re-coated and laminated with a cationic polymer. It is an organic-inorganic complex membrane formed by an organic-inorganic bond in which anionic matrix of a net structure is formed by interpenetrating reaction between polymers, and the matrix is immersed in a low molecular weight aqueous solution of cationic metal to perform a complex crosslinking reaction. That is, unlike coating the polymer material with the support, the metal ions in the aqueous solution form a complex reaction by immersion, and thus may contain a large number of strong and weak acid functional groups, thereby improving the function of the proton transfer group. The membrane also has a net structure. The complex membrane formed according to the present invention exhibits high hydrogen ion conductivity and very low methanol permeability, and thus can be used as a polymer electrolyte membrane for direct methanol fuel cells.

In the present invention, when the anionic polymer matrix is formed, the anionic polymer may be mixed with the anionic polysaccharide-based polymer alone or the anionic polysaccharide-based polymer.

Anionic polysaccharide-based polymers used in the present invention are agaroses, carrageenans, alginates, celluloses, dextrans, glycosaminoglycans, teicophosphates, xylans, XM-6 polysaccharai One kind or two or more kinds selected from the group consisting of Drew and their derivatives can be used. At this time, it is more preferable to use two or more kinds of mixtures rather than using one kind of anionic polysaccharide-based polymer alone.

In addition, the derivatives thereof include carboxylic acid groups, sulfonic acid groups and phosphoric acid groups. For example, agarose sulfate, alginic acid, kappa-carrageenan, iota-carrageenan, lambta-carrageenan, kappa-purselanan, Chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, heparan sulfate, keratan sulfate, hyaluronate, heparin, succiniglycans. Teicophosphate, cellulose sulfate, sodium carboxymethyl cellulose, xylan sulfate, cellulose chianthate, starch phosphate ethers and sulfates, metal chelate phosphorylated chitin and chitosan, and the like.

The anionic polymer used in admixture with the anionic polysaccharide-based polymer may be salts or poly (acrylic acid), poly (methacrylic acid), poly (acrylic acid), vinyl sulfonate, acrylate, methacrylate and styrene sulfonate-based salts, One or two or more selected from acid-type polymers such as poly (ethylenesulfonic acid), poly (vinylphenylsulfonic acid), poly (vinylsulfonic acid), poly (styrenesulfonic acid) and the like can be used.

It is preferable to use 0.05 to 90% by weight of the anionic polymer, and if it is out of the above range, it is more preferable to maintain the above range because the anionic polymer matrix of the present invention cannot be obtained.

Each of the heterogeneous polymers was dissolved in water and stirred at room temperature for 24 hours to prepare an aqueous solution. The prepared aqueous solution is mixed at a constant ratio to prepare a mixed solution, and then dried at room temperature to 50 ° C. for 6 to 12 hours to form a solid anion polymer matrix. The matrix has a net structure in which the polymers penetrate each other.

The formed anionic polymer matrix is immersed in an aqueous metal solution in which 0.05 to 35% by weight of cationic metal is dissolved, and the complex reaction proceeds for 30 seconds to 24 hours. At this time, the matrix of the net structure will form a stronger crosslinking by the complex reaction.

The cationic metal used for the complexing may be a divalent ion selected from barium, cadmium, chromium, copper, iron, lead, magnesium, manganese, mercury, strontium, nickel, zinc and tin or a trivalent ion selected from aluminum, chromium and iron. Etc. can be used.

After the complex reaction, it is immersed in pure water and deionized water, washed, and dried to prepare a polymer electrolyte complex membrane. At this time, the pure water washing is more than three times, the ion removal water washing is preferably performed at least one time.

As described above, the polymer electrolyte complex membrane according to the present invention is mechanically stable with a strong net structure, is a non-fluorine-based proton-transfer functional group in a molecule, and has an excellent effect on thermal and chemical stability and economics. In particular, the electrolyte complex membrane of the present invention exhibits high hydrogen ion conductivity and very low methanol permeability, which is effective for use as a polymer electrolyte membrane for direct methanol fuel cells.

The present invention as described above will be described in more detail based on the following examples, but the present invention is not limited thereto.

Examples 1-4

Sodium alginate and sodium polystyrene sulfonate were added to pure water at a ratio of 2% by weight, respectively, and stirred at room temperature for at least 24 hours to prepare a uniform aqueous solution of polymer electrolyte. The sodium alginate and sodium polystyrene sulfonate aqueous solution prepared above were prepared by mixing sodium alginate / polystyrene sulfonate in a mixed ratio of 95: 5, 90: 10, 80: 20, 50: 50, and then drying at room temperature for 24 hours. A solid matrix was prepared.

The prepared matrix was subjected to a complex reaction for 1 hour in a 5% by weight aqueous solution of divalent calcium, and then immersed and washed three times or more in pure water, sufficiently washed with deionized water, and then dried. 2, Example 3, and the polymer electrolyte complex membrane of Example 4 were prepared.

Examples 5-8

Sodium alginate and lambda type carrageenan were added to pure water at a ratio of 2% by weight for each, followed by stirring at room temperature for 24 hours or more to prepare a uniform aqueous solution of polyelectrolyte.

The sodium alginate and lambda type carrageenan aqueous solution prepared above was prepared by mixing sodium alginate / lambda type carrageenan solution in a mixing ratio of 95: 5, 90: 10, 80: 20, 50: 50, and then drying at room temperature for 24 hours. A solid matrix was prepared.

Example 5, after complexing the matrix prepared above in a 5% by weight aqueous solution of divalent calcium for 1 hour, immersion-washed in pure water, washed with ionic deionized water sufficiently and dried. The polymer electrolyte complex membranes of Example 6, Example 7, and Example 8 were prepared.

Comparative Example 1

Nafion 115, which is widely used as a polymer electrolyte membrane for a fuel cell, is set as Comparative Example 1.

Experimental Example 1

In order to measure the hydrogen ion conductivity of the polymer electrolyte complex membranes of Examples 1 to 8 and Comparative Example 1, each of the prepared membranes were sufficiently washed with deionized water and dried to obtain a polymer electrolyte membrane by a quadrupole method of AC impedance measurement. Hydrogen ion conductivity was measured and shown in Table 1.

division Ionic Conductivity (S / cm) Example 1 1.5 × 10 ^-1 Example 2 1.4 × 10 ^-1 Example 3 1.32 × 10 ^-1 Example 4 1.28 × 10 ^-1 Example 5 1.27 × 10 ^-1 Example 6 1.15 × 10 ^-1 Example 7 0.97 × 10 ^-1 Example 8 0.91 × 10 ^-1 Comparative Example 1 7.8 × 10 ^-2

Experimental Example 2

In order to know the permeation degree of methanol with the ion exchange membrane for direct methanol fuel cells of the polymer electrolyte complex membranes of Examples 1 to 8 and Comparative Examples, the polymer electrolyte membranes prepared in Examples 1 to 8 were cut to a size of 4 cm in diameter, followed by two chambers. Mounted in two chamber diffusion cells, filled with distilled water on one side, aqueous methanol solution on the other side, and magnetically stirred so that there is no concentration gradient. The permeation concentration was analyzed by GC) and the results are shown in Table 2.

In addition, in order to observe the methanol crossover phenomenon with temperature, a methanol permeation experiment was performed for Example 1 at a temperature range of 40 to 100 ° C. in a thermostat, and the results are shown in Table 3.

division Methanol Permeate (wt%) Example 1 3.1 × 10 ^-8 Example 2 1.6 × 10 ^-8 Example 3 9.5 × 10 ^-8 Example 4 6.7 × 10 ^-8 Example 5 4.5 × 10 ^-7 Example 6 3.8 × 10 ^-7 Example 7 3.9 × 10 ^-8 Example 8 7.0 × 10 ^-8 Comparative Example 1 2.9 × 10 ^-6

division Temperature (℃) Methanol Permeate (wt%) Example 1 40 5.8 × 10 ^-8 60 No detection 80 No detection 100 No detection

As described in Table 1, Table 2 and Table 3, the polymer electrolyte complex membranes of Examples 1 to 8 according to the present invention have a higher hydrogen ion of 10 ^-2 S / cm or more than Nafion 115, which is a commercial membrane of Comparative Example 1 It was confirmed that the conductivity and low methanol permeability of 10 ⁻⁷ or less were shown.

In addition, methanol permeability was not detected as the temperature improved, and it was confirmed that the effect was improved at a high temperature.

As described above, the polymer electrolyte complex membrane according to the present invention exhibits high hydrogen ion conductivity and very low methanol permeability, and thus exhibits better performance than a commercial membrane Nafion membrane, which is used as a polymer electrolyte membrane for direct methanol fuel cells. This is possible.

1 is a block diagram of an electric energy device generated from a fuel cell using a polymer electrolyte complex membrane prepared in an embodiment according to the present invention.

[Description of Code for Major Parts of Apparatus Diagram of FIG. 1]

(1) polymer electrolyte complex membranes (2) anodes of fuel cells

(3) cathode of fuel cell (4) external circuit

(5) Methanol / water or hydrogen (6) Hydrogen ions formed by fuel oxidation of the anode

(7) oxygen (8) water formed by the reduction of oxygen at the cathode

Claims (8)

A polymer electrolyte complex membrane for a fuel cell, characterized in that the anionic polysaccharide-based polymer matrix and a complex layer formed by crosslinking a cationic metal forming a complex bond with an anion present on the surface of the matrix. The method of claim 1, wherein the anionic polysaccharide-based polymer is agarose, carrageenan, alginate, cellulose, dextran, glycosaminoglycans, teicophosphate, xylan, XM-6 Polymer electrolyte complex membrane for a fuel cell, characterized in that one or two or more selected from polysaccharides and derivatives thereof. According to claim 1, In addition to the anionic polysaccharide-based polymer, an anionic polymer in the form of salt or acid of vinylsulfonate, acrylate, methacrylate and styrene sulfonate Or a polymer electrolyte complex membrane for a fuel cell, characterized in that two or more kinds are included. The polymer electrolyte complex membrane for a fuel cell of claim 1, wherein the anionic polymer matrix has a net structure. The method of claim 1, wherein the cationic metal is a divalent ion selected from barium, cadmium, chromium, copper, iron, lead, magnesium, manganese, mercury, strontium, nickel, zinc and tin or a trivalent selected from aluminum, chromium and iron. Polymer electrolyte complex membrane for a fuel cell, characterized in that the ion. A polymer electrolyte for fuel cell, wherein the anionic polysaccharide-based polymer matrix is immersed in an aqueous solution of 0.05 to 35% by weight of a cationic metal to form a complex layer by a complex crosslinking reaction between an anion and a cationic metal present on the surface of the matrix. Method for producing a complex membrane. According to claim 6, In addition to the anionic polysaccharide-based polymer, an anionic polymer in the form of a salt or acid of vinyl sulfonate, acrylate, methacrylate and styrene sulfonate is one kind. Or a polymer electrolyte complex membrane for a fuel cell, characterized in that two or more kinds are included. A polymer electrolyte complex membrane fuel cell provided with a polymer electrolyte complex membrane prepared according to any one of claims 1 to 5.