JP3978493B2 - Solid polymer electrolyte and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid polymer electrolyte made of a non-fluorine polymer having high ionic conductivity. The present invention also relates to a method for producing the solid polymer electrolyte and a polymer electrolyte fuel cell using the solid polymer electrolyte.
[0002]
[Prior art and problems to be solved by the invention]
Solid polymer electrolyte membrane fuel cells (PEFCs) have attracted a great deal of attention as small and lightweight power sources. In particular, research on solid polymer electrolyte membranes is central to the development of PEFC, and many studies use perfluoroalkyl sulfonic acid polymers with sulfonic acid groups attached to the side chains of the perfluoro skeleton. .
[0003]
However, the conductivity of perfluoroalkyl sulfonic acid type polymers is not fully satisfactory in practical use. For example, when a perfluoroalkyl sulfonic acid type polymer is used as an electrolyte membrane of a solid polymer fuel cell, there is a drawback that the perfluoroalkyl sulfonic acid type polymer conceals the active sites of the electrode catalyst. In addition, the perfluoroalkyl sulfonic acid type polymer is a fluorocarbon material having a complicated structure, and thus has a drawback that the manufacturing process becomes complicated. Therefore, the use of perfluoroalkylsulfonic acid type polymer increases the cost of the solid polymer electrolyte membrane. Thus, various solid polymer electrolyte membranes have been proposed that can achieve high electrical conductivity with a chemical structure that does not have a fluoropolymer. For example, a mixture of Nafion and silica, a solid acid, a fullerene derivative, and the like have been proposed. Furthermore, polymer blend technology is used (see Non-Patent Documents 1 and 2). However, the ionic conductivity of the blended polymer is not higher than that of Nafion.
[0004]
[Non-Patent Document 1]
RW Kopitzke, CA Linkous, HR Anderson and GL Nelson, J. Electrochem. Soc. 147, p.1677 (2000).
[Non-Patent Document 2]
L. Hong and N. Chen, J. Polym. Sci. Part B 38, p. 1530 (2000).
[0005]
Accordingly, an object of the present invention is to provide a solid polymer electrolyte that is easy to manufacture and has high ionic conductivity at low cost.
[0006]
[Means for Solving the Problems]
The present invention, Ri Do polyion complex formed from a polymer having a polymer and a basic group having an acidic group,
The polymer having an acidic group is polystyrene sulfonic acid,
Polymer having a basic group is obtained by achieving the above object by providing a solid polymer electrolyte, characterized in Oh Rukoto polyethylenimine.
[0007]
The present invention is also a method for producing the polyion complex,
The acidic group in the polymer having an acidic group and / or a part of the basic group in the polymer having a basic group is ion-exchanged, and then both are mixed to form an aqueous solution thereof. Coating and drying the coating film to form a precursor film of the polyion complex, obtaining the polyion complex by treating the precursor film with acid or alkali ,
The polymer having an acidic group is polystyrene sulfonic acid,
The present invention provides a method for producing a solid polymer electrolyte, wherein the polymer having a basic group is polyethyleneimine .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on preferred embodiments thereof. The solid polymer electrolyte of the present invention comprises a polyion complex of a polymer having an acidic group (hereinafter referred to as an acidic polymer) and a polymer having a basic group (hereinafter referred to as a basic polymer). In the polyion complex, the acidic group in the acidic polymer and the basic group in the basic polymer are bonded by ionic bonds. In general, a membrane obtained by casting an aqueous solution of a polymer having an acidic group is water-soluble and thus does not function as a proton conducting membrane. However, the inventors have found that a water-insoluble proton conducting membrane can be obtained by forming a polyion complex from a polymer having an acidic group. Of course, this polyion complex membrane can be produced as a cation exchange membrane or an anion exchange membrane. Since a normal polyion complex is insoluble in an aqueous solvent, a ternary solvent (for example, hydrochloric acid-water-dioxane) is used for its preparation. However, since a strong acid is used in the ternary solvent, a simple film formation cannot be performed. As a result of various studies, the present inventors have found that a polyion complex can be easily prepared from an aqueous solution system, and have completed the present invention.
[0010]
As the acidic polymer used in the present invention, a polymer having a proton acid group is used. The proton acid group, using a sulfonic acid group in terms of ease and high ionic conductivity forming a port Li ion complex.
[0011]
The acidic polymer having a protonic acid group described above is preferably a polymer containing no fluorine, that is, a non-fluorine polymer, from the viewpoint of obtaining a target solid polymer electrolyte at low cost . Japanese to Ru with polystyrene sulfonic acid in terms of ease and high ionic conductivity forming a polyion complex.
[0012]
On the other hand, as the basic polymer used in the present invention, those having a basic group capable of ionic bonding with the protonic acid group contained in the acidic polymer are used. Used is -NH- group in nitrogen-containing group in view of ease and high ionic conductivity forming a port Li ion complex.
[0013]
Even a polymer having the above-described basic group, like the acidic polymer Ru with non-fluorinated polymer. As a basic high content child Ru with polyethylene imine in terms of ease and high ionic conductivity forming a polyion complex especially.
[0014]
In a polyion complex consisting of an acidic polymer and a basic polymer, the acidic group and the basic group are ion-bonded at an appropriate ratio, which prevents the polyion complex film from forming and preventing the formation of precipitates. It is preferable from the point. Specifically, the ratio of the molar equivalent of the acidic group to the molar equivalent of the basic group is 1.2 to 10, It is preferable that it is 5-3. The ratio of molar equivalents of the basic group to the molar equivalents of acid groups are 1.2 to 10, 1. It is preferable that it is 5-3. When the ratio of the molar equivalent of the basic group to the molar equivalent of the basic group (and the ratio of the molar equivalent of the basic group to the molar equivalent of the acidic group) is 1 or very close to it, a stable polyion complex is formed, but the proton Conductivity is extremely lowered.
[0015]
The acidic polymer and the basic polymer have a molecular weight (weight average molecular weight) of 1,000 to 1,000,000, particularly 5,000 to 500,000. This is preferable from the viewpoint of ensuring the water solubility of each polymer before complex formation.
[0016]
For the solid polymer electrolyte of the present invention comprising a polyion complex, an appropriate thickness is selected according to the specific application. For example, when the solid polymer electrolyte of the present invention is used as an electrolyte membrane of a solid polymer fuel cell, the thickness is preferably about 5 to 300 μm.
[0017]
In the present invention, the polyion complex is preferably prepared by the following method. First, in the case of an acidic polymer in which the acidic group is in the form of a salt, since the acidic polymer is generally water-soluble, an ion exchange resin or the like is added to the aqueous solution of the acidic polymer to A part of the acidic groups is ion-exchanged to adjust the number of free acidic groups. At this time, if all the acidic groups are returned to a free form, care must be taken because the acidic polymer becomes water-insoluble when a basic polymer is added. On the contrary, in the case of an acidic polymer in which the acidic group is in a free form, the acidic polymer is generally insoluble in water. Therefore, the acidic polymer is dispersed in water and added with an ion exchange resin or the like. A part of the acidic groups in the polymer is ion-exchanged (for example, partially neutralized with a metal cation) to make the acidic polymer water-soluble and adjust the number of free acidic groups. An aqueous solution of a basic polymer is added to this aqueous solution and mixed. In this case, in addition to or instead of adjusting the number of free acidic groups in the acidic polymer, ion exchange of a part of the basic groups in the polymer is performed in an aqueous solution of the basic polymer. The number of free basic groups may be adjusted by partially neutralizing with a low molecular anion such as a halide ion, sulfonic acid group or carboxyl group. Thereby, the film-forming property and proton conductivity of the polyion complex can be made appropriate. Whether the acidic group or the basic group is ion-exchanged, the ratio of the molar equivalent of the acidic group in the acidic polymer to the basic molar equivalent in the basic polymer is in the range described above. It is preferable to adjust the addition amount of the acidic polymer and the basic polymer.
[0018]
An aqueous solution (coating solution) in which both polymers are dissolved is applied onto a substrate to form a coating film. Since this coating solution is almost neutral, there is an advantage that a polyion complex can be easily produced as compared with a conventional polyion complex coating solution using a ternary solvent containing a strong acid. Water in the coating film is removed and dried to form a polyion complex precursor film. The thickness of the coating film is adjusted to an appropriate range depending on the specific use of the finally obtained polyion complex membrane.
[0019]
After the obtained polyion complex precursor film is peeled from the substrate, the precursor film is treated with acid or alkali. As a result, the ion exchange of the counter ion in the acidic group or the basic group existing in the precursor film is performed, and the proton conductivity of the target polyion complex film is increased. For example, when treating with an acid, the precursor film is immersed in an aqueous solution of hydrochloric acid, sulfuric acid, nitric acid or the like for a predetermined time, and metal ions contained in the acidic group are ion-exchanged with protons. On the other hand, when treating with an alkali, the precursor film is immersed in an aqueous solution of sodium hydroxide, potassium hydroxide or the like for a predetermined time to ion-exchange the anion contained in the basic group. In any case, the processing time is from several minutes to several hours depending on the type of the precursor film. By this operation, the desired polyion complex membrane is obtained.
[0020]
The solid polymer electrolyte of the present invention is preferably used as a material for an ion exchange membrane, an electrolyte membrane of a polymer electrolyte fuel cell, or a modified electrode because of its high ion conductivity. In particular, when used as an electrolyte membrane of a polymer electrolyte fuel cell, if it is disposed at a site in contact with the noble metal electrode catalyst, there is an advantage that a decrease in catalyst activity is prevented. On the other hand, as described above, the electrolyte membrane made of a perfluoroalkyl sulfonic acid type polymer has a problem that the catalytic activity is lowered. From such a viewpoint, when the polyion complex membrane of the present invention is mixed with the electrode catalyst particles, there is an advantage that the catalyst can be effectively utilized. In this case, the weight ratio of the catalyst particles to the polyion complex is suitably from 1: 0.1 to 1:10. Perfluoroalkylsulfonic acid type polymers are expensive. On the other hand, the solid polymer electrolyte of the present invention has an advantage that it is economical because an expensive material is not used.
[0021]
When the solid polymer electrolyte of the present invention is used as an electrolyte membrane of a polymer electrolyte fuel cell, a membrane electrode assembly (MEA) is formed by forming an anode and a cathode containing a catalyst such as platinum on each surface of a polyion complex membrane. It is preferable that
[0022]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.
[0023]
[Example 1]
As the acidic polymer, polystyrene polystyrene sulfonate (hereinafter referred to as PSSNa) having a weight average molecular weight of 70,000 was used. Polyethyleneimine (hereinafter referred to as PEI) having a weight average molecular weight of 50,000 to 100,000 was used as the basic polymer. Each polymer was dissolved in water to form a 10% by weight aqueous solution.
[0024]
A 10-fold amount of cation exchange resin (Amberlite (registered trademark) manufactured by Rohm and Haas) with respect to the weight of dissolved PSSNa is added to the aqueous PSSNa solution, and the solution is heated with a hot stirrer for 30 minutes. Stir. The liquid temperature was kept at about 40 ° C. As a result, sodium sulfonate in PSSNa was ion-exchanged to obtain a polystyrene sulfonic acid (hereinafter referred to as PSS) aqueous solution partially having a sulfonic acid group.
[0025]
A molar ratio of a styrene sulfonic acid monomer (hereinafter referred to as SS) to an ethyleneimine monomer (hereinafter referred to as EI) of a PSS aqueous solution obtained by filtering the ion exchange resin and a separately prepared PEI aqueous solution is 1.5, The mixture was mixed to 2, 2.5 and 3. The mixed aqueous solution was cast on a polyethylene terephthalate film and dried at about 40 ° C. under normal pressure to obtain a polyion complex precursor film.
[0026]
The obtained polyion complex precursor membrane was immersed in 1N hydrochloric acid for 3 hours, and sodium ions in the sulfonic acid group were completely ion-exchanged with protons to obtain a target polyion complex membrane. Thereafter, the membrane was washed with pure water and stored in pure water. The polyion complex film thus obtained was sandwiched between ^two gold electrodes (electrode area 0.01 cm ² ), and the conductivity in the film thickness direction was measured by impedance measurement. The result is shown in FIG.
[0027]
As is clear from the results shown in FIG. 1, it can be seen that the conductivity tends to increase as the SS / EI ratio increases. In particular, when this ratio exceeds 2, it can be seen that the conductivity is equivalent to that of a commercially available perfluoroalkylsulfonic acid polymer film.
[0028]
[Example 2]
In Example 1, a PSS aqueous solution and a PEI aqueous solution were mixed so as to have an SS / EI ratio of 2, and cast to form a polyion complex precursor film having a film thickness of 25 μm, 50 μm, and 90 μm. The polyion complex precursor film was immersed in 1N hydrochloric acid for 5 hours, and sodium ions in the sulfonic acid group were ion-exchanged with protons to obtain a target polyion complex film. The conductivity in the film thickness direction of the obtained polyion complex film was measured. The result is shown in FIG. The film thickness was measured using a stylus type step thickness meter.
[0029]
As is apparent from the results shown in FIG. 2, it can be seen that the proton conductivity exhibits a constant value in the range of the film thickness of 25 to 90 μm. From this result, it is understood that the polyion complex has a uniform film composition in this range of film thickness. When the conductivity changes due to the difference in film thickness, it means that the composition is different between the inside and the surface of the film due to the hydrochloric acid treatment, resulting in a non-uniform film.
[0030]
Example 3
A polyion complex membrane was obtained in the same manner as in Example 2 except that acid treatment was performed using 1N sulfuric acid and nitric acid instead of hydrochloric acid in Example 2. The film thickness was 50 μm. The conductivity in the film thickness direction of the obtained polyion complex film was measured. The result is shown in FIG. FIG. 3 also shows the result of acid treatment with 1N hydrochloric acid under the same conditions.
[0031]
As is clear from the results shown in FIG. 3, it can be seen that the polyion complex film obtained by acid treatment with hydrochloric acid or sulfuric acid exhibits high conductivity.
[0032]
Example 4
A polyion complex membrane was obtained in the same manner as in Example 2 except that the acid treatment time with hydrochloric acid was changed in Example 2. The film thickness was 50 μm. The conductivity in the film thickness direction of the obtained polyion complex film was measured. The result is shown in FIG.
[0033]
As is apparent from the results shown in FIG. 4, it is understood that almost no difference is observed in the conductivity when the acid treatment time is in the range of 1 to 6 hours. This means that ion exchange is sufficiently performed to the inside of the membrane within the range of the treatment time.
[0034]
【The invention's effect】
According to the present invention, a solid polymer electrolyte that is easy to manufacture and has high ionic conductivity is provided at low cost. In particular, when the solid polymer electrolyte of the present invention is used as an electrolyte membrane of a polymer electrolyte fuel cell, the activity of the electrode catalyst is prevented from being lowered, so that the amount of expensive noble metal catalyst used can be reduced. In addition, the manufacturing cost of the electrolyte decreases.
In addition, since the solid polymer electrolyte of the present invention can be formed from a neutral coating solution, it can be produced more easily than a conventional polyion complex coating solution using a ternary solvent containing a strong acid. it can.
The solid polymer electrolyte of the present invention is extremely useful as a substitute for a perfluoroalkylsulfonic acid type polymer.
[Brief description of the drawings]
1 is a graph showing the relationship between the styrene sulfonic acid monomer / ethyleneimine monomer ratio and conductivity in Example 1. FIG.
2 is a graph showing the relationship between the film thickness of a polyion complex film and conductivity in Example 2. FIG.
3 is a graph showing the relationship between the type of acid used for acid treatment and conductivity in Example 3. FIG.
4 is a graph showing the relationship between acid treatment time and conductivity in Example 4. FIG.

Claims (4)

Ri Do polyion complex formed from a polymer having a polymer and a basic group having an acidic group,
The polymer having an acidic group is polystyrene sulfonic acid,
The polymer having a basic group is polyethyleneimine,
Or the ratio of molar equivalents of acid groups to the molar equivalent of basic groups is 1.2 to 10, or a molar equivalent ratio of basic groups to molar equivalents of acid groups of 1.2 to 10 der Rukoto A characteristic solid polymer electrolyte. The solid polymer electrolyte according to claim 1 , wherein the weight average molecular weight of the acidic polymer and the basic polymer is 1,000 to 1,000,000 . The solid polymer electrolyte according to any one of claims 1 to 3, which is a membrane having a thickness of 5 to 300 µm and is used as an electrolyte membrane of a solid polymer fuel cell . A method for producing a solid polymer electrolyte according to claim 1,
The acidic group in the polymer having an acidic group and / or a part of the basic group in the polymer having a basic group is ion-exchanged, and then both are mixed to form an aqueous solution thereof. Coating and drying the coating film to form a precursor film of the polyion complex, obtaining the polyion complex by treating the precursor film with acid or alkali,
The polymer having an acidic group is polystyrene sulfonic acid,
A method for producing a solid polymer electrolyte, wherein the polymer having a basic group is polyethyleneimine .

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