KR100484499B1 - Composition of Polymer Electrolytes for Direct Methanol Fuel Cell - Google Patents

Abstract

The present invention relates to a polymer electrolyte composition for a direct methanol fuel cell comprising a hydrogen fluoride-based polymer and an ionomer having a main chain of perfluoronate, wherein the main chain is a hydrocarbon-based ionomer such as a sulfonated styrene polymer ionomer, an acrylic acid polymer ionomer, and Disclosed is a polymer electrolyte composition for a direct methanol fuel cell comprising two or more mixed ionomers of these polymer ionomers.

According to the above configuration, it is possible to produce a polymer electrolyte which has a small thickness and excellent mechanical properties and hydrogen ion conducting properties while minimizing methanol crossover compared to a conventional polymer film for direct methanol fuel cells.

Description

Polymer electrolyte composition for direct methanol fuel cell {Composition of Polymer Electrolytes for Direct Methanol Fuel Cell}

The present invention is a polymer electrolyte composition for a direct methanol fuel cell comprising a hydrogen fluoride-based polymer and an ionomer having a main chain of perfluoronate, and more particularly, to a polymer electrolyte composition for a direct methanol fuel cell having improved mechanical properties and hydrogen ion conductivity. It is about.

Fuel cell is a DC generator that directly converts chemical energy of fuel into electrical energy by 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.

The fuel cell 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). Among them, a polymer electrolyte fuel cell is a fuel cell using a polymer membrane having hydrogen ion conductivity as an electrolyte. 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 separately from. 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 its volume and weight are smaller and lighter than phosphate fuel cells with the same principle of operation. 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 a crossover phenomenon where methanol is transferred from the fueled cathode to the anode and degraded. 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. Thus, the success of direct methanol fuel cells lies in the development of membranes with minimal methanol crossover.

The present inventors have studied ways to overcome the drawbacks of the prior art described above. In the case of blending an ionomer having a main chain of hydrocarbon type in a blend containing a hydrogen fluoride series polymer and an ionomer having a main chain of perfluoronate as a main component, the methanol cross The present invention has been completed by discovering that the mechanical properties and hydrogen ion conduction properties are improved while minimizing over, and having a small thickness.

Accordingly, an object of the present invention is to provide a polymer electrolyte composition for a direct methanol fuel cell, which can be made thinner and has improved mechanical properties and hydrogen ion conductivity compared with the related art.

The present invention is a polymer electrolyte composition for a direct methanol fuel cell comprising a hydrogen fluoride-based polymer and an ionomer whose main chain is perfluoronate-based,

It includes a polymer electrolyte composition for direct methanol fuel cell, characterized in that the main chain comprises a hydrocarbon-based ionomer.

Hydrogen fluoride polymers do not require special limitations so long as they are excellent in 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. Preferably, the polyvinylidene fluoride may be selected from the range of 50,000 g / mol to 1,000,000 g / mol. Vinylidene fluoride-hexafluoropropylene preferably has a content of hexafluoropropylene in the copolymer in the range of 0.1 to 50% by weight, preferably in the range of 100,000 g / mol to 500,000 g / mol in molecular weight. Can be selected.

The content of the hydrogen fluoride polymer in the blend {(hydrogen fluoride polymer) + (the ionomer whose main chain is a perfluoronate), hereinafter same} is preferably 0.1 to 99.9% by weight, more preferably 60 to 90% by weight. % to be. If it is added less than 0.1% by weight, there is a fear that methanol crossover is high, and when it exceeds 99.9% by weight methanol crossover is low but there is a fear that the ion conductivity is lowered.

Examples of ionomers whose main chains are perfluoronates include Nafion (Dupont), Flemion (Dupont), and Aciplex (Dupont) as trade names. It is provided with the above mixed ionomer. The ionomers are preferably added in the blend at 0.1 to 99.9% by weight, more preferably at 10 to 40% by weight. If the content is less than 0.1% by weight, the ion conductivity may be lowered. If the content is more than 99.9% by weight, the ion conductivity may be improved, but methanol crossover may be increased.

Examples of ionomers whose main chain is hydrocarbon-based include sulfonated styrene polymer ionomers, acrylic acid polymer ionomers and two or more mixed ionomers of these polymer ionomers, the molecular weight of which is not particularly limited but is preferably 5,000 g / mol to 500,000 g / mol.

Examples of the sulfonated styrenic polymer ionomer include poly (sodium-4-styrenesulfonate), polystyrene (sulfonic acid-co-malic acid) or sulfonated polystyrene-block-poly (ethylene-lan-butylene)- Block-polystyrene. Further examples of the acrylic acid polymer ionomer include polymethyl methacrylate ionomers. The sulfonated styrene-based polymer ionomer and acrylic acid-based polymer ionomer may be added to the blend alone or in combination of two or more kinds of components.

The ionomer whose main chain is hydrocarbon-based does not require any particular limitation, but is added in an amount of 0.01 to 50 phr, more preferably 0.1 to 5 phr, based on the weight of the blend. If the amount is less than 0.01 phr, the mechanical strength of the blend membrane may be weak and the ion conductivity may be lowered. If it exceeds 50 phr, the mechanical strength of the blend membrane may be weakened.

Method for producing a polymer electrolyte composition for direct methanol fuel cell of the present invention,

First, the hydrogen fluoride-based polymer is dissolved in a suitable organic solvent, followed by mixing the main chain perfluoronate ionomer and the main chain hydrocarbon ionomer and stirring the mixture for a predetermined time. Casting to a constant thickness and drying.

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>

Hydrogen fluoride-based polymer was dissolved in a certain amount of acetone PVDF-co-HFP (trade name: Kynar Flex 2751, Atopina) having a melting temperature of 135 ℃ and a hexafluoropropylene content of 15% by weight. Nafion solution (20% by weight, EW1,000, DuPont) was quantified so that the weight ratio of Nafion was 20% by weight, and mixed with the Kynar Flex 2751 solution. The solution was mixed for about 5 minutes and then casted to a thickness of 50 micrometers on a glass plate using a doctor blade. After drying at room temperature for about 2 hours, the blend membrane was removed from the glass plate using distilled water.

The process of the polymer electrolyte for 2 hours at H ₂ O ₂ of 80 ℃ using film made of, 1M H ₂ SO 2 hours at _4, after performing a pre-treatment for 2 hours in H ₂ 0 (Frequency Response Analyzer) with this destination FRA The resistance of the membrane was measured by reading the real impedance at imaginary impedance 0, and the hydrogen ion conductivity was calculated.

In addition, the tensile strength and elongation of the polymer electrolyte membrane were measured at a speed of 200 mm / min using a UTM (Universal Testing Machine).

Each experimental result is summarized in Table 1.

<Example 2>

1.2 g of Kynar Flex 2751 (80% by weight blend) were dissolved in 10 mL of acetone (solution 1). Sodium salt of polystyrene (sulfonic acid-co-malic acid) (Mw: 20,000, sulfonic acid in the form of SO ₃ ^- NA ^{+ in the} molecular structure.Manufacturer: Aldrich) 0.0015 g (0.1 phr) of Nafion solution (20wt% , EW1,000, DuPont) and dissolved in 5 minutes (solution 2). After completely dissolved solution 1 and solution 2 were mixed, the mold was performed to a thickness of 50 micrometers using a doctor blade on a glass plate. Hydrogen ion conductivity and mechanical properties were measured in the same manner as in Example 1.

<Example 3>

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.0045 g (0.3 phr) of sodium salt (Mw: 20,000) of polystyrene (sulfonic acid-co-malic acid) was added.

<Example 4>

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.0075 g (0.5 phr) of sodium salt (Mw: 20,000) of polystyrene (sulfonic acid-co-malic acid) was added.

Example 5

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.015 g (1 phr) of sodium salt (Mw: 20,000) of polystyrene (sulfonic acid-co-malic acid) was added.

<Example 6>

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.0015 g (0.1 phr) of poly (sodium-4-styrenesulfonate) (Mw: 70,000) was added.

<Example 7>

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.0045 g (0.3 phr) of poly (sodium-4-styrenesulfonate) (Mw: 70,000) was added.

<Example 8>

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.0075 g (0.5 phr) of poly (sodium-4-styrenesulfonate) (Mw: 70,000) was added.

Example 9

A polymer electrolyte membrane was prepared in the same manner as in Example 2, except that 0.015 g (1 phr) of poly (sodium-4-styrenesulfonate) (Mw: 70,000) was added.

<Test Example 1>

The ionic conductivity, conductance, yield strength, elongation and methanol crossover of the polymer membrane for the direct methanol fuel cell prepared by Examples 1 to 9 are measured as shown in Table 1 below.

TABLE 1

Item Ionic Conductivity (S / cm) * 10 ^-3 Conductance (S / cm ² ) * 10 ^-1 Yield Tensile Strength (kgf / cm ² ) % Elongation Methanol Crossover (cm ² / s) * 10 ^-6 Nafion 117 8.84 4.21 No yield point 75.8 2.5 Example 1 1.52 3.04 164.3 71.6 0.15 Example 2 1.84 3.68 197.5 232.9 0.15 Example 3 2.07 4.14 207.6 183.2 0.17 Example 4 2.11 4.22 209.4 141.9 0.17 Example 5 2.45 4.90 212.1 103.5 0.18 Example 6 1.69 3.38 198.7 212.1 0.15 Example 7 1.73 3.46 206.1 176.7 0.15 Example 8 1.85 3.70 211.1 129.0 0.16 Example 9 2.16 4.32 216.4 101.3 0.17

As shown in Table 1, as the sodium salt of poly (sodium-4-styrenesulfonate) or polystyrene (sulfonic acid-co-malic acid) is added, it can be seen that the ionic conductivity and conductance increase and the yield tensile strength also increases. However, the elongation tended to decrease with increasing sodium salt content of poly (sodium-4-styrenesulfonate) or polystyrene (sulfonic acid-co-malic acid), and the ionic conductivity and conductance showed almost the same value, but the yield point tensile strength And elongation was found to be somewhat different.

The polymer membranes according to the above examples were all manufactured in a thickness of about 30 micrometers to 150 micrometers, and were thinner than conventional commercial membranes (trade name: Nafion 117) while having low methanol permeability, excellent mechanical strength, and content of Nafion. When it is adjusted to about 20% by weight it can be seen that the price of the hydrogen ion conductive polymer membrane can be lowered to about one fifth the level of the existing Nafion membrane is economical.

In addition, the conductance value corresponding to the inverse of the resistance per unit area, which is directly related to the performance in MEA manufacturing, is superior to the existing Nafion 117, which is expected to have excellent results in fuel cell performance in MEA manufacturing.

According to the present invention, it is possible to produce a polymer electrolyte which has a small thickness and excellent mechanical properties and hydrogen ion conducting properties while minimizing methanol crossover compared to a conventional polymer membrane for direct methanol fuel cells.

Claims (10)

A polymer electrolyte composition for a direct methanol fuel cell comprising a hydrogen fluoride polymer and an ionomer whose main chain is a perfluoronate, Polymer electrolyte composition for direct methanol fuel cell, characterized in that the main chain comprises a hydrocarbon-based ionomer The ionomer of claim 1, wherein the main chain is hydrocarbon-based Polymer electrolyte composition for direct methanol fuel cell, characterized in that it is selected from sulfonated styrene polymer ionomer, acrylic acid polymer ionomer and two or more mixed ionomers of these polymer ionomers. The ionomer according to claim 1 or 2, wherein the main chain is hydrocarbon-based. Polymer electrolyte composition for direct methanol fuel cell, characterized in that selected from polymers having a molecular weight of 5,000 g / mol to 500,000 g / mol The method of claim 1, wherein the sulfonated styrenic polymer Polymer electrolyte for direct methanol fuel cells characterized as poly (sodium-4-styrenesulfonate), polystyrene (sulfonic acid-co-malic acid) or sulfonated polystyrene-block-poly (ethylene-lan-butylene) -block-polystyrene Composition The method of claim 1, The ionomer having a hydrocarbon-based main chain is added in an amount of 0.01-50 phr based on the weight of the blend. The method of claim 1, wherein the hydrogen fluoride series polymer Polymer electrolyte composition for direct methanol fuel cell, characterized in that the copolymer of polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene The method of claim 1, Polymer electrolyte composition for direct methanol fuel cell, characterized in that the content of the hydrogen fluoride polymer in the blend is 0.1 to 99.9 wt% The method of claim 6, Polymer electrolyte composition for direct methanol fuel cell, characterized in that the content of hexafluoropropylene in the copolymer of vinylidene fluoride-hexafluoropropylene is 0.1 to 50% by weight. The ionomer according to claim 1, wherein the ionomer whose main chain is perfluoroate-based Polymer electrolyte composition for direct methanol fuel cell, characterized in that it comprises one or two or more mixed ionomers selected from Nafion, Flemion, and Asiplex The method of claim 1, The polymer electrolyte composition for direct methanol fuel cell, characterized in that the content of the ionomer whose main chain is perfluoronate in the blend is 0.1 to 99.9% by weight.