KR100622995B1 - Preparation of multilayered proton conducting membrane for direct methanol fuel cell - Google Patents

Abstract

The present invention relates to a method for producing a hydrogen ion exchange membrane of a multilayer thin film for a direct methanol fuel cell by coating a thin film on both sides of a blend of a hydrogen fluoride-based polymer and a perfluoronate-based polymer in an ionomer whose main chain is a perfluoronate-based resin. will be.

According to the above configuration, it is possible to manufacture an excellent polymer electrolyte which suppresses methanol crossover and has excellent interfacial adhesion between electrodes as compared with a conventional polymer film for direct methanol fuel cells, which ensures long-term stability of the cell.

Description

Preparation of multilayered proton conducting membrane for direct methanol fuel cell             

1 is a block diagram of a polymer electrolyte for a direct methanol fuel cell according to the present invention [1: ionomer of the main chain is a perfluoroate-based polymer, 2: a polymer in which the main chain is a hydrogen fluoride-based polymer and a main chain is a perfluoronate-based polymer] to be.

Figure 2 is a graph of the measurement results of methanol permeability obtained for the polymer electrolyte composition for direct methanol fuel cell according to the present invention.

3 is a graph showing initial cell performance of the polymer electrolyte membrane for a direct methanol fuel cell and commercial Nafion 117 according to the present invention.

Figure 4 is a graph showing the cell performance (cell performance) after 7 days after the initial performance test of the polymer electrolyte membrane for direct methanol fuel cell and the commercial Nafion 117 according to the present invention.

5 is an electron scanning micrograph showing the contact between the polymer electrolyte membrane for direct methanol fuel cell according to the present invention and the electrode of commercial Nafion 117.

The present invention relates to a method for producing a hydrogen ion exchange membrane of a multilayer thin film for a direct methanol fuel cell by coating a thin film on both sides of a blend of a hydrogen fluoride-based polymer and a perfluoronate-based polymer in an ionomer whose main chain is a perfluoronate-based resin. will be. More specifically, the present invention relates to a composition and a method for preparing a polymer electrolyte for direct methanol fuel cell having excellent hydrogen ion conductivity and mechanical properties and adhesiveness while suppressing methanol permeability.

Fuel cell is a kind of direct current generator that directly converts chemical energy of fuel into electrical energy through electrode reaction. Unlike other generator tubes, fuel cell is not restricted by carnot cycle, so it has high energy efficiency and exhaust gas. little. In addition, while primary and secondary cells store and supply limited energy, fuel cells have the advantage of being able to generate power as long as fuel is continuously supplied.

Fuel cells can be melted according to the operating temperature and the type of electrolyte.Proton Exchange Membrane Fuel Cell (PEMFC), Alkali Fuel Cell (AFC), Phosphoric Acid Fuel Cell (PAFC) Molten Carbonate Fuel Cell (MCFC), Solid Oxide Fuel Cell (SOFC), etc.

Among them, a polymer electrolyte fuel cell is a fuel cell using a polymer membrane having hydrogen ion conductivity as an electrolytic material. When a fuel is used instead of hydrogen, a polymer electrolyte fuel cell is called a direct methanol fuel cell (DMFC). It is also classified differently. The polymer electrolyte fuel cell or direct methanol fuel cell using the polymer membrane as an electrolyte has a lower operating temperature, a shorter startup time, and a faster response to load changes than other fuel cells. In particular, since the polymer membrane is used as the electrolyte, corrosion and pH control of the electrolyte are not necessary and are less sensitive to changes in the pressure of the reactor. In addition, the design is simple and easy to manufacture, and the volume and weight are smaller and lighter than the phosphate fuel cells with the same operation principle.

In addition to these characteristics, it is possible to produce a wide range of output, the fuel cell using the polymer membrane as an electrolyte can be applied to a wide variety of fields such as power source of pollution-free vehicles, residential power generation, spacecraft power, mobile power, military power. In particular, the direct methanol fuel cell is expected to be able to replace the existing secondary battery with a small mobile power source such as a mobile phone, a notebook computer, a camcorder due to the characteristics of operating at room temperature and pressure.

However, the biggest limitation of direct methanol fuel cell development is the methanol crossover phenomenon, where methanol moves through the polymer electrolyte membrane to the anode at the fueled cathode and degrades cell performance. This reduces the potential difference between the anode and the cathode, loses fuel and reduces the current density by interrupting the reduction reaction at the anode. Therefore, for practical application of direct methanol fuel cell, it is essential to develop a membrane that can minimize methanol crossover.

In order to minimize the methanol crossover of a direct methanol fuel cell, the prior arts have been solved by blending a second polymer having no ion groups in an ionomer, which is a perfluoronate, or mixing inorganic salts. However, these methods resulted in reduced methanol crossover, but reduced ionic conductivity or reduced long-term stability.

Prior art related to the present invention, US Patent No. 5,981,097 (Multiple layer membranes for fuel cells employing direct methanol fuel cell) focused on inhibiting the methanol permeation of the multilayer membrane, and also Hobson et al., (LJ Hobson et al., Targeting improved DMFC performance, Journal of power source, 2002, 104, pp79) coated both sides of Nafion with poly-benzimidazole in order to suppress Nafion's methanol crossover. coating). However, the present invention differs in the technical configuration as a membrane for DMFC, in order to suppress methanol permeation and increase interfacial adhesion (stability) of the membrane / electrode, thereby reducing interfacial resistance (improvement of cell performance).

An object of the present invention is to provide a method and composition for manufacturing a polymer electrolyte for direct methanol fuel cell which can be made thinner than the conventional, and can improve the long-term stability of the cell by increasing the methanol permeability and adhesion while maintaining the hydrogen ion conductivity. Is in.

In order to overcome methanol crossover, which is a serious problem in direct methanol fuel cells, the inventors have applied a thin film on both sides of a blend of a hydrogen fluoride-based polymer and a perfluoronate-based polymer in an ionomer whose main chain is a perfluoronate-based resin. The electrolyte membrane was prepared while maintaining the hydrogen ion conductivity while reducing the methanol crossover, thereby preparing an electrolyte membrane having excellent adhesion.

In the present invention, a multilayer film is prepared by thinly coating a blend of a main chain of a hydrogen fluoride series polymer and a main chain of a perfluoronate polymer on both sides of an ionomer made of a perfluoronate resin.

Examples of ionomers whose main chains are perfluoronates include, for example, Nafion (Dupont), Flemion (Asahi Glass), Aciplex (Aciplex, Asahi Chemical), etc. The above is used as a mixed ionomer. The ionomers are added from 0.1 to 99.9 weight percent, more preferably from 60 to 95 weight percent, in the brand. However, in some cases, the blend amount may be used in the range of 5 to 30% by weight based on the Nafion ionomer when coating Nafion. When Nafion blends PVdF polymer and Nafion ionomer, the ratio of PVdF polymer and Nafion ionomer can be controlled in various ways.

For example, when blending the hydrogen fluoride polymer and the Nafion ionomer, the ratio may be adjusted to 80:20 to 95: 5.

In case of using Nafion as an example of ionomer whose main chain is perfluoronate, Nafion membrane which is already commercialized is selected from Nafion 112 (thickness 50um), Nafion 1135 (thickness 75um) and Nafion 115 (thickness 125um) in addition to Nafion 117. Any one selected can be used.

When the main chain is a perfluoronate-based ionomer when the main chain is composed of a hydrogen fluoride-based polymer and a main chain is a perfluoronate-based polymer, the ion conductivity may be considerably lowered if it is added less than 0.1% by weight. If exceeded, the ion conductivity is improved, but there is a fear that the methanol crossover is significantly increased.

Hydrogen fluoride polymers do not require special limitations as long as they have excellent mechanical properties, thermal stability, chemical resistance, processability, and methanol barrier properties. Representative polymers that meet these requirements include polyvinylidene fluoride (PVDF) and copolymers of vinylidene fluoride-hexafluoropropylene (PVDF-Co-HFP). In particular, polyvinylidene fluoride is inexpensive and is widely applied as an electrochemical material, and preferably may be selected from the range of molecular weight of 50,000g / mol ~ 1,000,000g / mol.

The vinylidene fluoride-hexafluoropropylene preferably has a content of hexafluoropropylene in the copolymer of 0.1 to 50% by weight, preferably in a range of 100,000 g / mol to 500,000 g / mol in molecular weight. Can be selected.

At least one organic solvent selected from dimethylformamide (DMF), dimethylsulfoxide, and 1-methyl-2-pyrrolidone (NMP) may be used as a solvent for dissolving the hydrogen fluoride-based polymer. Can be used.

In the polymer electrolyte for direct methanol fuel cell of the present invention, first, after dissolving a hydrogen fluoride polymer in a suitable organic solvent, a polymer having a main chain of perfluoroate is mixed and stirred for a predetermined time, and the ionomer having a main chain of perfluoronate is the solution. Or coating the polymer solution to a certain thickness using a doctor blade or the like on a glass plate and stacking a polymer having a perfluoronate-based backbone thereon. .

In order to facilitate a clearer understanding of the present invention, the contents of the present invention will be described in detail through preferred embodiments of the above-described manufacturing steps. However, these examples are only presented to understand the content of the present invention, and the scope of the present invention should not be construed as being limited to these embodiments.

<Example 1>

A copolymer of vinylidene fluoride-hexafluoropropylene having a melting temperature of 135 ° C. and a hexafluoropropylene content of 15% by weight (PVDF-co-HFP, trade name: Kynar Flex 2751, Atopina) ) 80% by weight was dissolved in dimethylformamide (DMF). The Nafion solution (20 wt%, EW1,000, DuPont) was quantified so that the weight ratio of Nafion was 20 wt% purely and mixed with the Kynar Flex 2751 solution (C8020).

At 80 ℃ of H ₂ O ₂ 2 hours, 1M H ₂ SO 2 hours at _4, then the commercially available Nafion 117 membrane to perform a pre-treatment for 2 hours in a H ₂ 0 hamchin the above solution was then dried (see Fig. 1).

The hydrogen ion conductivity calculated based on the measured resistance of the membrane using the frequency response analyzer (FRA) for these formed membranes is shown in [Table 1].

In addition, the result of measuring the methanol permeability of the prepared polymer electrolyte membrane is shown in FIG. The experimental results showed that the methanol crossover was suppressed while maintaining the hydrogen ion conductivity similar to that of commercial Nafion membranes.

In addition, the adhesion of the membrane / electrode resulted in the adhesion of Nafion as a result of the coating layer and is shown in FIG. 5.

Table 1. Resistance and hydrogen ion conductivity of polymer electrolyte membrane

Notation conductivity (S / cm) conductance (S / cm ² ) C8020 1.36 X 10 ^-2 1.03 C8515 1.12 X 10 ^-2 0.85 C9010 8.49 X 10 ^-3 0.64 C9505 3.18 X 10 ^-3 0.24 Nafion 117 1.85 X 10 ^-2 One

<Example 2>

A polymer electrolyte membrane was manufactured in the same manner as in Example 1, except that a commercial Nafion polymer membrane (Nafion 112) having a different thickness was used instead of the commercial Nafion 117 membrane. The initial cell performance of the membrane-direct methanol fuel cell and the cell performance after a predetermined time are shown in [Fig. 3] and [Fig. 4].

<Example 3>

It was prepared in the same manner as in Example 1 except for using a different ionomer whose main chain was a perfluoronate instead of a commercial Nafion membrane.

<Example 4>

It was prepared in the same manner as in Example 1, except that a hydrogen fluoride polymer having a hexafluoropropylene content of 15% was not used and the hexafluoropropylene content was 12%, 8%, and 0%. .

Example 5

It was prepared in the same manner as in Example 1 except that a Nafion solution having an EW of 1000 was not used.

According to the present invention, it is possible to prepare an excellent polymer electrolyte having improved adhesion and excellent long-term performance while reducing methanol crossover as compared to a conventional polymer membrane for direct methanol fuel cells.

Claims (9)

Dissolving a polymer (B) having a main chain of hydrogen fluoride in an organic solvent, and then mixing and stirring the polymer (C) having a main chain of perfluoronate, and preparing a blend; and a main chain of perfluoro in the mixed solution. A method of manufacturing a hydrogen ion exchange membrane of a multilayer thin film for a direct methanol fuel cell, comprising the step of forming a multilayer membrane by coating both sides with a blend of an ionomer made of a nate resin (A). 2. The multilayer thin film of a direct methanol fuel cell according to claim 1, wherein the mixed solution of the polymer (B) and the polymer (C) is impregnated with an ionomer or cast to a predetermined thickness by a doctor blade on a glass plate to stack the polymer. Of hydrogen ion exchange membrane The method of claim 1, wherein the solvent of the polymer (B) is dimethylformamide (DMF), acetone (Acetone), dimethyl sulfoxide (dimethylsulfoxide), 1-methyl-2pyrrolidone (1-methyl-2-pyrrolidone, NMP Method for producing a hydrogen ion exchange membrane of a multilayer thin film for direct methanol fuel cell, characterized in that at least one organic solvent selected from The method of claim 1, wherein the ionomer resin (A) is pretreated for 2 hours at 80 ° C in H ₂ O ₂ , 2 hours at 1M H ₂ SO ₄ , and 2 hours at H ₂ 0, followed by polymers (A) and (B Method for producing a hydrogen ion exchange membrane of a multi-layered thin film for direct methanol fuel cell, characterized in that laminated on a mixed solution of The ionomer resin (A) and the polymer (C), wherein the main chain is perfluoronate-based, include one or two or more mixed ionomers selected from Nafion, Flemion or Asiplex. Method for producing hydrogen ion exchange membrane of multilayer thin film for direct methanol fuel cell The method for producing a hydrogen ion exchange membrane of a multilayer thin film of a direct methanol fuel cell according to claim 1, wherein the content of the polymer (C) in the main chain perfluoronate blend is 0.1 to 99.9 wt%. The hydrogen ion exchange membrane of a multilayer thin film for a direct methanol fuel cell according to claim 1, wherein the main chain hydrogen fluoride polymer (B) in the blend is a copolymer of polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene. Manufacturing Method The method of manufacturing a hydrogen ion exchange membrane of a multilayer thin film for direct methanol fuel cell according to claim 1, wherein the content of the hydrogen fluoride polymer in the brand is 0.1 to 99.9 wt%. 9. The hydrogen of the multilayer thin film for direct methanol fuel cell according to claim 8, wherein the content of hexafluoropropylene in the copolymer of vinylidene fluoride-hexafluoropropylene, which is one of the hydrogen fluoride polymers, is 0.1 to 50% by weight. Manufacturing method of ion exchange membrane

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