KR101353078B1 - Nano composite membranes of proton conducting polymer electrolytes by using polyhedral oligomeric silsesquioxane having phosphonic acid group - Google Patents

Abstract

The present invention relates to a proton-conducting polymer nanocomposite membrane using silsesquioxane having a phosphate group, and more particularly, to a proton-containing proton conductive polymer having a silsesquioxane having a cage structure and a fluorine-based proton conductive polymer The present invention relates to a proton conductive polymer nanocomposite membrane having excellent conductivity and remarkably improved mechanical properties.

Description

Nano composite membranes of proton conducting polymer electrolytes by using polyhedral oligomeric silsesquioxane having phosphonic acid group

The present invention relates to a proton-conducting polymer nanocomposite membrane using silsesquioxane having a phosphate group, and more particularly, to a proton-containing proton conductive polymer having a silsesquioxane having a cage structure and a fluorine-based proton conductive polymer The present invention relates to a proton conductive polymer nanocomposite membrane having excellent conductivity and remarkably improved mechanical properties.

A fuel cell, which has recently been in the spotlight, is a power generation system that directly converts energy generated by reacting fuel and an oxidant into electric energy, and increases efficiency due to environmental problems, exhaustion of energy sources, and fuel cell vehicles. In order to make it possible to develop a polymer film that can be used at high temperature has been made in various ways.

The fuel cell is mainly a molten carbonate electrolyte fuel cell operating at high temperature (500 to 700 ° C.), a phosphate electrolyte fuel cell operating at around 200 ° C., an alkaline electrolyte fuel cell and a polymer electrolyte type operating at room temperature to about 100 ° C. It is divided into a fuel cell.

Among these, the polymer electrolyte fuel cell is also a clean energy source, but has high power density and energy conversion efficiency, can operate at room temperature, and can be miniaturized and sealed, so that it can be used in pollution-free cars, household power generation systems, mobile communication equipment, medical devices, military equipment, space It is widely used in the field of business equipment and the research is being concentrated more.

Among these polymer electrolyte fuel cells, Proton Exchange Membrane Fuel Cell (PEMFC), which uses hydrogen gas as a fuel, is a power generation system for producing direct current electricity from an electrochemical reaction between hydrogen and oxygen. The cathode has a structure in which a proton conductive polymer film having a thickness of 50 to 200 µm is interposed between the cathodes. Therefore, when hydrogen is supplied as a reactive gas, an oxidation reaction occurs at the anode to convert hydrogen molecules into hydrogen ions and electrons. At this time, the converted hydrogen ions are transferred to the cathode through the proton conductive polymer membrane, and the oxygen molecules receive electrons at the cathode. A reduction reaction occurs in which oxygen ions are converted, at which time the generated oxygen ions react with the delivered hydrogen ions from the anode and are converted into water molecules.

In this process, the proton-conducting polymer membrane for the fuel cell is electrically insulated, but acts as a medium for transferring hydrogen ions from the cathode to the anode during cell operation, and simultaneously serves to separate fuel gas or liquid from oxidant gas. The chemical stability must be excellent and the requirements must be met such as thermal stability at operating temperature, manufacturability as a thin film to reduce resistance, and low expansion effect when containing liquid.

Since the polymer electrolyte membrane for the conventional polymer electrolyte fuel cell is manufactured based on a sulfone group capable of conducting protons only when there is water, it cannot be used in the absence of water (high temperature and no humidification).

In addition, the conventional polymer electrolyte membrane is manufactured in the form of a composite membrane in which inorganic particles are mixed to improve conductivity, and the composite membrane is composited using inorganic particles of micro size or several tens to hundreds of nano size. Particles interfere with the movement of protons in ion channels, leading to a problem of poor proton conductivity.

In addition, due to the size and agglomeration of the inorganic particles also has a problem that the mechanical strength during the composite film manufacturing falls.

A representative material widely used as an electrolyte membrane used in a conventional representative polymer electrolyte fuel cell is Nafion developed by DuPont. However, Nafion has a fatal problem of having good proton conductivity (0.1 S / cm) but low strength and low humidity, for example, inherent performance is not exhibited at high temperatures of 100 ° C. or higher. The reason is known to arise due to the ion conduction mechanism of the sulfone groups contained in Nafion.

Nafion / ZrSPP composite membrane for high temperature operation of PEMFCs Electrochimica Acta, 50, 645 (2004) proposes an electrolyte membrane with excellent proton conductivity under high temperature and humidification conditions by combining with Zr-based inorganic particles with sulfone groups at the ends of Nafion and Zr phosphate. It is.

In Korean Patent Publication No. 2005-0024812, the size ranges from several nanometers to several hundred nanometers, and the sulfonic acid group is introduced to have a conductivity similar to that of the conductive polymer, and the sulfonic acid group does not fall even at high temperature, and maintains high conductivity. Hydrogen ion conductive inorganic nanoparticles have been proposed, but here they are composed of silicon oxide (SiO 2), aluminum oxide (SiO 2), zirconium oxide (ZrO 2), zeolites, mesoporous materials and their complexes and are several tens of nanometers in size to several hundred nanometers. There is a problem that the ionic conductivity decreases rapidly because nanoparticles reaching a meter are used.

Meanwhile, Korean Laid-Open Patent Publication No. 2012-010420 by the present inventors describes a polymer electrolyte including a proton conductive polymer having improved chemical durability and mechanical strength as a PhosPani polymer electrolyte membrane including a chemically bound phosphate group. In the present invention, there is no focus on improving durability and mechanical strength. Instead, the phosphate group is directly attached to the matrix to exhibit excellent ionic conductivity at high temperature.

In Korean Patent No. 1085358, a silane compound having a hydrocarbon-based polymer having a cation exchange group and an amino group substituted with phosphoric acid is combined with 3-aminopropyltriethoxysilane to have excellent electrochemical properties, mechanical properties and thermal stability, and room temperature. And proton conductive polymer membranes having excellent proton conductivity at high temperature have been proposed.

In addition, Korean Patent No. 0969011 includes a pore structure of 3-aminopropyltriethylsilane and tetraethyl orthosilicate in the sock end, and a polymer and side chain composed of an inorganic polymer whose main chain is polydimethylsiloxane in which phosphoric acid is chemically bonded. A polymer blend electrolyte membrane composed of a proton conducting polymer having a cation exchange group at is proposed.

However, although the mechanical properties of the conventional polymer electrolyte membrane were improved to some extent, there was still much room for improvement in mechanical strength and performance. It is thought that there is room for improvement of physical properties such as strength due to the influence of the polymer having a phosphate group even when introducing an insulator.

As a result of steadily researching for a long time to prepare a polymer electrolyte membrane having the problems and the improved properties in the prior art as described above, the present inventors have introduced a polyhedral oligomeric silsesquioxane; When the electrolyte composite membrane is manufactured using POSS), the present invention has been found to be excellent in conductivity and greatly improved in strength when applied to a fuel cell.

Accordingly, an object of the present invention is to provide a proton conductive polymer nanocomposite membrane comprising silsesquioxane having a chemically bonded phosphoric acid group.

Another object of the present invention is to provide a proton conductive polymer nanocomposite membrane having excellent proton conductivity and remarkably improved mechanical properties.

In order to solve this problem, the present invention provides a proton conductive polymer nanocomposite membrane in which silsesquioxane in which a phosphate group is introduced into a fluorine-based proton conductive polymer substrate is mixed.

The proton-conducting polymer nanocomposite membrane according to the present invention as described above has an effect of having excellent proton conductivity even under high temperature and no humidification conditions, and has an effect of exhibiting excellent mechanical strength compared to a fluorine-based polymer membrane for PEMFC.

In addition, it can be used as an electrolyte membrane for fuel cells under low temperature (<90 ^° C) and humidification conditions as well as high temperature and no humidification conditions.

In addition, since the strength is maintained even by reducing the thickness in half compared to the conventional film, it is possible to manufacture at low cost.

Therefore, the proton conductive polymer nanocomposite membrane according to the present invention is very useful as an electrolyte membrane for fuel cells.

1 is a graph illustrating a comparison of proton conductivity measurement results for the polymer nanocomposite membrane and the electrolyte membrane prepared in Example 1 and Comparative Example of the present invention.
FIG. 2 is a graph illustrating a comparison of proton conductivity measurement results in a humidified condition (120 ° C.) for a polymer nanocomposite membrane and an electrolyte membrane prepared in Example 2 and Comparative Example of the present invention.
Figure 3 is a graph showing the comparison of the measurement results of the mechanical strength for the polymer nanocomposite membrane and the electrolyte membrane prepared in Example and Comparative Example 3 of the present invention.

Hereinafter, the present invention will be described in detail as an embodiment.

The present invention relates to a proton-conducting polymer nanocomposite membrane useful for a fuel cell, comprising a conventional fluorine-based proton-conducting polymer for electrolyte membranes as a base material and a proton-conducting polymer nanocomposite membrane mixed with silsesquioxane having a phosphate group introduced therein. It is about.

As the fluorine-based proton conductive polymer substrate used in the present invention, for example, a fluorine-based polymer having a functional group selected from a sulfone group, a phosphate group, or a carboxyl group can be used. Typically, Nafion, Hyflon, and Fle. Flemion, Dow, Aquivion, Gore or ACplex can be used.

In addition, in this invention, the silsesquioxane which introduce | transduced 1-16 phosphate groups represented by following formula (1) as a silsesquioxane which introduce | transduced a phosphate group is used, for example.

[Formula 1]

In Formula 1, R is a halogen group, amine group, hydroxy group, phenyl group, alkyl group, phenol group, ester group, nitrile group, ether group, ester group, aldehyde group, formyl group, carbonyl group or ketone group Or at least one of R is -PO ₃ H ₂ , -R ¹ -PO ₃ H ₂ , and a substituent represented by the following Chemical Formula 2, Chemical Formula 3 or Chemical Formula 4, wherein R ¹ is O, NH, NH- CH ₂ or (CH ₂ ) n where n is an integer from 1 to 6.

(2)

(3)

[Chemical Formula 4]

That is, the substituent R may be substituted with up to eight substituents of the formula (2) or (4) having two phosphate groups, so that the phosphoric acid group substituted with silsesquioxane may be substituted with 1 to 16.

In the present invention, the fluorine-based proton conductive polymer substrate and the silsesquioxane in which the phosphate group is introduced may be mixed in a weight ratio of 2 to 35: 1, more preferably in a weight ratio of 2 to 10: 1. If the amount of silsesquioxane used is too small, the effect of improving the high temperature conductivity and mechanical strength cannot be expected. If the amount of the silsesquioxane is used too much, the silsesquioxane may be agglomerated with each other to deteriorate the performance and may not form a film.

In the present invention, the physical properties are greatly improved by using silsesquioxane having a phosphoric acid group introduced into the polymer electrolyte membrane.

In the present invention, it is characterized by using silsesquioxane (POSS) as the phosphate group introduction nucleus. POSS is basically a silica cage structure, and has excellent thermal and physical properties due to its stable structure. The basic structure is hydrophobic silica structure, and the terminal has 8 functional groups, so that more than one functional group can be attached. In the case of particles used in conventional fuel cells, one or two phosphate groups are connected and used, while POSS can easily attach eight or more functional groups, thereby increasing its own ion conduction ability.

In addition, the POSS has a fundamental structure of 1.5 nm in actual nanoscale size, which is significantly smaller than other inorganic materials. When the composite membrane is manufactured by introducing into the fuel cell, it is possible to solve the problem of lowering ion conductivity, which is the biggest problem of the composite membrane, by preventing the movement of ions in the ion channel as little as possible.

In addition, the swelling phenomenon can be lowered due to the hydrophobic structure due to the silica structure, and when the hydrophilic functional group is connected to the terminal, the ionic conductivity can be improved due to the clear phase separation. In addition, due to the nature of silica, water retention is high, so it has a moisturizing ability at high temperatures. POSS also has the advantage of reducing degradation due to its high resistance to oxygen atoms, which is less affected by radicals.

As such, the silsesquioxanes are particles of several nm size, which are very small compared to tens to hundreds of nm of the existing inorganic particles. Therefore, when applied to the proton conductive polymer composite membrane, it is possible to implement excellent proton conductivity without disturbing the proton movement. In addition, by forming a molecular composite of the silsesquioxane molecule (molecular composite), the strength is strong, thereby significantly improving the mechanical properties of the proton conductive polymer membrane.

In addition, in the present invention, by introducing and using a phosphate group in silsesquioxane, the physical properties of the electrolyte membrane can be improved. The phosphoric acid is an ideal proton conductor, and the melting point (Tm) is 42 ° C., and pure phosphoric acid is an expanded molecule. It has the property of a high viscous liquid with hepatic hydrogen bonding, and in contrast to water, its conductivity is not affected by the degree of hydration. In the case of pure phosphoric acid, the proton conductivity of the additive is easily shifted by the diffusion of the structure and exhibits a property showing very high self-dissociation.

According to the present invention, a silsesquioxane having a phosphoric acid group introduced therein can be easily obtained by selecting one of the silsesquioxanes having a substituent which is easy to introduce a phosphate group, and dissolving the phosphoric acid salt to reflux therein. For example, halogen, amine, hydroxy, phenyl, alkyl, phenol, ester, nitrile or formaldehyde Silsesquioxanes having a terminal group selected from among them can be preferably used. The silsesquioxane in which the phosphate group is introduced may be preferably used having a structure represented by Chemical Formula 1.

The present invention

Dissolving the fluorine-based proton conductive polymer substrate in a solvent;

Dissolving silsesquioxane into which the phosphoric acid group is introduced in the same solvent as the solvent;

Mixing the prepared fluorine-based proton conductive polymer-based solution with a silsesquioxane solution;

Sonicating the mixed solution to disperse silsesquioxane in the fluorine-based polymer;

Casting in a vacuum oven and removing residue;

It includes a method for producing a proton conductive polymer nanocomposite membrane comprising a.

The present invention also includes a membrane-electrode assembly including the proton-conducting polymer nanocomposite membrane as described above.

The present invention also includes a fuel cell including the proton conductive polymer nanocomposite membrane as described above.

In another aspect, the present invention includes an electrode binder comprising a proton conductive polymer nanocomposite membrane as described above.

Proton-conducting polymer nanocomposite membrane according to the present invention does not interfere with proton conduction because silsesquioxane is very small in size of several nanosized membrane compared to the conventional composite membrane when silsesquioxane having a phosphate group is introduced. Compared to the membrane, the proton conductivity is higher, and the mechanical strength is also increased. In addition, since the functional groups of silsesquioxane can be basically applied to eight, it has the advantage that there are many functional groups that can be applied compared to the existing materials. In particular, in the case of phosphate-substituted silsesquioxane, the proton conductivity at a high temperature is remarkably increased because the phosphate group can bind 2 to 16 phosphate groups to 1 to 8 functional groups. Therefore, it exhibits excellent proton conductivity at high temperature and no humidification conditions, and shows excellent mechanical strength compared to the conventional fluorine-based polymer film for PEMFC, so that the same or similar effect can be expected even with a thickness of 1/2 or less of the existing film thickness. It also has improved features that can be used in low temperature (<90 ^° C), humid conditions as well as high temperature and no humidification conditions.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to Examples.

Preparation Example: Preparation of Silsesquioxane (PA-POSS) with Phosphoric Acid Group

Dissolve 1 g of OctaKis (dibromoethyl) POSS and 16 g of trimethyl phosphite in 200 ml of tetrahydrofuran (THF) and reflux at 120 ^o C for 6 hours.

After the reaction, unreacted trimethyl phosphite and solvent THF are removed by vacuum drying. After vacuum drying, 200 ml of hydrochloric acid 2M aqueous solution was added, followed by stirring at 70 ^° C for 12 hours. Then remove all material except PA-POSS through the filter, and wash several times with methanol to remove the residue. Finally it was dried in a vacuum oven at 100 ^° C to prepare a PA-POSS with a phosphate group.

Example 1 Preparation of Nafion / PA-POSS Molecular Composite Membrane

Nafion solution manufactured by Dupont is dried under vacuum to remove the solvent, and dissolved in dimethylacetamide (DMAc) in a 1:19 weight ratio.

0.05 g of PA-POSS prepared in the above preparation is dissolved in 0.95 g of DMAc. 9 g of Nafion / DMAc solution thus obtained (0.45 g of Nafion) and 1 g of PA-POSS / DMAc (0.05 g of PA-POSS) were mixed, followed by stirring at room temperature for 12 hours. At this time, PA-POSS is well dispersed in Nafion through intermediate ultrasonication.

The dispersed solution is cast on a Teflon substrate in a 120 ^° C. vacuum oven for 24 hours. The Nafion / PA-POSS composite membrane prepared by casting was boiled in deionized water for 1 hour to remove the residue, thereby preparing a Nafion / PA-POSS molecular composite membrane.

Example 2 Preparation of Nafion / PA-POSS Molecular Composite Membrane

The same procedure as in Example 1 except that Nafion / DMAc solution 8 g (Nafion content 0.40 g) and PA-POSS / DMAc 2 g (PA-POSS content 0.10 g) were mixed in the same manner. / PA-POSS molecular composite membrane was prepared.

Comparative Example: Preparation of Nafion Electrolyte Membrane

Using only Nafion as a substrate, a cast electrolyte membrane having the same specifications as in Example 1 was prepared.

Experimental Example 1 Proton Conductivity Experiment

Proton conductivity was measured by constant current four-terminal method to check the difference of alternating potential occurring in the center of the specimen while applying a constant alternating current to both ends of the specimen in a room of 0.5 x 2 cm size controlled temperature and humidity. .

Proton conductivity according to temperature was measured for the composite membrane and the electrolyte membrane prepared in Examples and Comparative Examples. Here, since the temperature of the humidifier is fixed at 95 ° C, a humidification state of about <40 RH% is shown at 120 ° C. The measurement results are shown in FIG.

In FIG. 1, in the case of Examples 1 and 2, the proton conductivity was slightly decreased even at a temperature of 100 to 120 ° C., but in the comparative example, it was confirmed that the proton conductivity was significantly lowered, and the conductivity was substantially 0 at 120 ° C. That is, although the comparative example has a better proton conductivity at the condition of 100 ° C. or lower, when the water evaporates at 100 ° C. or higher, the proton conductivity decreases rapidly in the comparative example, whereas the example shows the proton conductivity and excellent performance.

Experimental Example 2 Proton Conductivity Experiment Under No Humidification Conditions

The composite membrane and the electrolyte membrane prepared in Examples and Comparative Examples were measured by the constant current four-terminal method. The specimen of size 0.5 x 2 cm is applied to both ends of the specimen in a room where temperature and humidity are controlled, and the humidifier is not operated by checking the difference of alternating potential occurring at the center of the specimen. Proton conductivity was measured under no humid conditions. The measurement results are shown in FIG.

In FIG. 2, in the case of Examples 1 and 2, the proton conductivity was high even at 120 ° C. and the non-humidified condition, but the conductivity was 0 in the comparative example. That is, the comparative example shows a low proton conductivity of 10-7 S / cm while the example showed a high proton conductivity of 0.021, 0.029 S / cm. This can be seen as the effect of the phosphate group in POSS.

Experimental Example 3 Mechanical Strength Measurement Experiment

The composite membrane and the electrolyte membrane prepared in Examples and Comparative Examples were measured by the Instron 4201 / ASTM D882 method, and the specimen was prepared at 0.5 cm x 5 cm to measure the extent of stretching and mechanical strength at a rate of 5 mm / min. It was. The measurement results are shown in FIG. 3.

3, it was confirmed that Examples 1 and 2 exhibited much better mechanical strength than Comparative Examples.

Experimental Example 4 Comparative Experiment of PA-POSS Physical Properties

In order to confirm the effect of PA-POSS, a composite membrane of Zr ₃ P (Zr phosphophenyl phosphate) and Nafion (10 wt%) having a phosphate group attached to the terminal of the currently available Nafion and Zr-based inorganic particles, The properties of the composite membranes (10 wt%) of POSS and Nafion were compared. The results are shown in Table 1 below.

In Table 1, the change in ion conductivity at 80 degrees is less than that of Zr ₃ P, and it was confirmed that the effect is much better at 120 degrees. In particular, the mechanical strength of the Zr ₃ P film was almost unchanged, whereas the PA-POSS film was increased 1.5 times.

This is because the particle size of Zr ₃ P is 200 ~ 400 nm, while PA-POSS is several nano size, it can be confirmed that the small particles of POSS helped strengthen mechanical strength and ionic conductivity.

The Nafion / PA-POSS molecular composite membrane according to the present invention was confirmed to have excellent proton conductivity under the same conditions as the Nafion electrolyte membrane, and in particular, even in a non-humidified condition, the conductivity was confirmed to be excellent. It became. In addition, the mechanical strength was also confirmed that the composite membrane of the present invention is excellent.

Claims (9)

A proton conductive polymer nanocomposite membrane in which a silsesquioxane in which 1 to 16 phosphoric acid groups represented by the following Chemical Formula 1 is introduced is mixed on a fluorine-based proton conductive polymer substrate.
[Chemical Formula 1]

Wherein R is a halogen group, amine group, hydroxy group, phenyl group, alkyl group, phenol group, ester group, nitrile group, ether group, ester group, aldehyde group, formyl group, carbonyl group or ketone group Or at least one of R is -PO ₃ H ₂ , -R ¹ -PO ₃ H ₂ , and a substituent represented by the following Chemical Formula 2, Chemical Formula 3 or Chemical Formula 4, wherein R ¹ is O, NH, NH- CH ₂ or (CH ₂ ) n where n is an integer from 1 to 6.
(2)

(3)

[Chemical Formula 4]

.
The polymer nanocomposite membrane of claim 1, wherein the fluorine-based proton conductive polymer substrate is a fluorine-based polymer having a functional group selected from a sulfone group, a phosphoric acid group, or a carboxyl group in an end group.
The method of claim 1, wherein the fluorine-based polymer substrate is Nafion, Hyflon, Flemion, Dow, Aquivion, Gore or ACiplex. Polymer nanocomposite membrane, characterized in that.
delete The polymer nanocomposite membrane of claim 1, wherein the silsesquioxane in which the fluorine-based polymer substrate and the phosphate group are introduced is mixed at a weight ratio of 2 to 35: 1.
Dissolving the fluorine-based proton conductive polymer substrate in a solvent;
Dissolving silsesquioxane having 1 to 16 phosphoric acid groups represented by Formula 1 in the same solvent as the solvent;
Mixing the prepared fluorine-based proton conductive polymer-based solution with a silsesquioxane solution;
Sonicating the mixed solution to disperse silsesquioxane in the fluorine-based polymer; And
Casting in a vacuum oven and removing residue;
Method for producing a proton conductive polymer nanocomposite membrane comprising a.
[Chemical Formula 1]

Wherein R is as defined in claim 1 above.
A membrane-electrode assembly comprising a proton conductive polymer nanocomposite membrane according to any one of claims 1 to 3 and 5.
A fuel cell comprising a proton conductive polymer nanocomposite membrane according to any one of claims 1 to 3 and 5.
An electrode binder comprising a proton conductive polymer nanocomposite membrane according to any one of claims 1 to 3 and 5.

Images