JP2013197025A - Method for manufacturing solid polymer electrolyte membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing solid polymer electrolyte membrane which is capable of improving waterproofness and proton conductivity.SOLUTION: In a process for manufacturing solid polymer electrolyte membrane, a polyvinyl alcohol and a sulfonated polymer are dissolved in a solvent containing water to provide a precursor solution, which is heated to provide a solid polymer electrolyte membrane. The temperature of the precursor solution is favorably 80°C or more and 200°C or less.

Description

  The technology of the present disclosure relates to a method for producing a solid polymer electrolyte membrane used as an electrolyte of a solid polymer fuel cell.

  In recent years, solid polymer fuel cells have been researched and developed as a power source that can reduce the release of gas containing environmentally hazardous substances. In a polymer electrolyte fuel cell, a chemical reaction that generates electric power proceeds by protons being conducted through a solid polymer electrolyte membrane serving as an electrolyte. Until now, as such solid polymer electrolyte membranes, fluorine-based electrolyte membranes such as Nafion (registered trademark) manufactured by DuPont have been mainly used. However, since the synthesis route of the fluorine-based electrolyte membrane is complicated, the manufacturing cost is inevitably increased. Therefore, as a solid polymer electrolyte membrane that can be manufactured at a relatively low cost, for example, as described in Patent Literature 1 and Non-Patent Literature 1, an electrolyte membrane using polyvinyl alcohol and a sulfonated polymer has been proposed.

  When producing an electrolyte membrane using polyvinyl alcohol and a sulfonated polymer, a crosslinked structure of polyvinyl alcohol is usually formed by adding a crosslinking agent in order to increase the water resistance and mechanical strength of the electrolyte membrane. ing. For example, in Patent Document 1, terephthalaldehyde or glutaraldehyde having two aldehyde groups capable of reacting with the hydroxy group of polyvinyl alcohol is used as a cross-linking agent, and a cross-linking structure of polyvinyl alcohols by reaction of these functional groups. Is formed. In Non-Patent Document 1, sulfonated succinic acid is used as a crosslinking agent, and a crosslinked structure between polyvinyl alcohols is formed by esterification of two carboxy groups of sulfonated succinic acid and the hydroxy group of polyvinyl alcohol. ing.

  Thus, conventionally, the crosslinked structure of polyvinyl alcohol in the solid polymer electrolyte membrane is formed via a crosslinking agent having two or more functional groups capable of reacting with the hydroxyl group of polyvinyl alcohol.

JP 2006-156055 A

C. W. Lin, Y .; F. Huang, A .; M.M. Kannan, Journal of Power Sources, Volume 164, Issue 2, 2007, p449-456.

  By the way, in the above-mentioned polymer electrolyte fuel cell, water is generated by a reaction between a fuel such as hydrogen and oxygen, so that the polymer electrolyte membrane constituting the fuel is required to have high water resistance. In response to such a request, according to the above-mentioned crosslinked structure, the hydrophilic hydroxy group is converted into a crosslinked chain, so that the solubility of water between the polyvinyl alcohols is lowered. Therefore, the sulfonated polymer retained in the cross-linked structure of the matrix-formed polyvinyl alcohol is suppressed from being eluted into water, and as a result, the water resistance as the solid polymer electrolyte membrane can be improved.

  On the other hand, in order to obtain the water resistance required for the solid polymer electrolyte membrane by adding a crosslinking agent, it is necessary to add a large amount of polyvinyl alcohol and a large amount of crosslinking agent to the sulfonated polymer. However, since sulfonated polymers have high proton conductivity, polyvinyl alcohol and crosslinking agents have low proton conductivity. Therefore, the higher the proportion of polyvinyl alcohol and crosslinking agent, the higher the proton conductivity of the solid polymer electrolyte membrane. Will be lower. On the other hand, if high proton conductivity is to be obtained, the proportion of polyvinyl alcohol and crosslinking agent must be reduced, and the water resistance of the solid polymer electrolyte membrane is inevitably lowered. As a result, the water resistance and proton conductivity in the solid polymer electrolyte membrane are so-called trade-off relationships where one increases and the other decreases, so it is extremely difficult to increase both of them. It has become.

  The technology of the present disclosure has been made in view of such circumstances, and provides a method for producing a solid polymer electrolyte membrane that can improve both water resistance and proton conductivity in the solid polymer electrolyte membrane The purpose is to do.

  One aspect of the method for producing a solid polymer electrolyte membrane in the present disclosure is to insolubilize through a step of preparing a precursor solution in which polyvinyl alcohol and a sulfonated polymer are dissolved in a solvent containing water, and heating the precursor solution. The gist of the present invention is to produce a solid polymer electrolyte membrane.

  According to said aspect, the dehydration reaction and crosslinking reaction of polyvinyl alcohol which used the sulfonated polymer as an acid catalyst advance by heat processing. As a result, since a crosslinked structure is directly formed between polyvinyl alcohols, a solid polymer electrolyte membrane with improved water resistance can be obtained. Moreover, since this can form a crosslinked structure in polyvinyl alcohol without using a crosslinking agent, proton conductivity other than the sulfonated polymer in the solid polymer electrolyte membrane is lower than in the case of using a crosslinking agent. It becomes possible to reduce the ratio of the compound. As a result, since the ion exchange capacity of the solid polymer electrolyte membrane is increased as compared with the case of using a crosslinking agent, a solid polymer electrolyte membrane with improved proton conductivity can be obtained. In addition, by eliminating the need for a cross-linking agent, the composition of the solid polymer electrolyte membrane is simplified, and the manufacturing process is simplified by eliminating the need for a step of adding the cross-linking agent, thereby reducing manufacturing costs. It is also possible.

One aspect of the method for producing a solid polymer electrolyte membrane in the present disclosure is that the heating temperature of the precursor solution during the heating is 80 ° C. or higher and 200 ° C. or lower.
According to said aspect, it becomes possible to advance simultaneously the removal of a solvent, and heat processing with respect to the solution used as the precursor of a solid polymer electrolyte membrane. Therefore, since the manufacturing process can be simplified, the cost for manufacturing the solid polymer electrolyte membrane can be reduced.

  One aspect of the method for producing a solid polymer electrolyte membrane in the present disclosure is selected from the group consisting of polystyrene sulfonic acid, polyvinyl sulfonic acid, and poly (2-acrylamido-2-methylpropane sulfonic acid) as the sulfonated polymer. The gist is to use at least one.

  According to the above aspect, polystyrene sulfonic acid, polyvinyl sulfonic acid, and poly (2-acrylamido-2-methylpropane sulfonic acid) are sulfonated polymers having a high ion exchange capacity. Proton conductivity can be further increased. In addition, since these compounds can be obtained as industrial chemicals or reagents at a relatively low cost, it is possible to reduce the cost for the production of the solid polymer electrolyte membrane.

  According to the method for producing a solid polymer electrolyte membrane of the present disclosure, it is possible to produce a solid polymer electrolyte membrane with improved both water resistance and proton conductivity.

In one embodiment of the method for producing a solid polymer electrolyte membrane of the present disclosure, an X-ray diffraction spectrum showing the crystallinity of polyvinyl alcohol, wherein (a) is a polyvinyl alcohol membrane to which a sulfonated polymer is not added. It is a figure which shows the X-ray-diffraction spectrum after heat processing, (b) is a figure which shows the X-ray-diffraction spectrum after heat processing in the solid polymer electrolyte membrane which consists of a sulfonated polymer and polyvinyl alcohol. The perspective view which decomposes | disassembles and shows the perspective structure of the membrane electrode assembly using the solid polymer electrolyte membrane manufactured by the manufacturing method of the embodiment, and a polymer electrolyte fuel cell.

Hereinafter, an embodiment embodying the method for producing a solid polymer electrolyte membrane of the present disclosure will be described with reference to FIGS. 1 and 2.
[Material of solid polymer electrolyte membrane]
First, the material used for the manufacturing method of the solid polymer electrolyte membrane of this embodiment is demonstrated. The material for forming the solid polymer electrolyte membrane includes polyvinyl alcohol and a sulfonated polymer.

  The degree of saponification of polyvinyl alcohol is preferably high. Specifically, the saponification degree is 70 mol% or more, and more desirably 85 mol% or more. Since industrial polyvinyl alcohol is usually obtained by hydrolysis of polyvinyl acetate, it easily dissolves in water when the degree of saponification is higher than 70% and forms a complex with a water-soluble sulfonated polymer in an aqueous system. Suitable for Therefore, the above saponification degree is preferable.

  The molecular weight of polyvinyl alcohol is preferably 1000 or more, and more preferably 10,000 or more and 1,000,000 or less. If the molecular weight is 1000 or more, the viscosity at the time of film formation of the solid polymer electrolyte membrane is increased to such an extent that the film thickness of the solid polymer electrolyte membrane is sufficiently obtained. Moreover, if the molecular weight is 1000 or more, the same mechanical strength as a solid polymer electrolyte membrane having a structure crosslinked with a crosslinking agent can be obtained. On the other hand, if the molecular weight is 1000000 or less, the viscosity of the solid polymer electrolyte membrane can be suppressed to such an extent that sufficient uniformity can be obtained in the thickness of the solid polymer electrolyte membrane.

  As the sulfonated polymer, aliphatic sulfonated polymers such as sulfonated polystyrene, sulfonated polyvinyl, and poly (2-acrylamido-2-methylpropanesulfonic acid) can be used. Since these materials are used as functional materials in the field of electronic equipment, they can be easily obtained and are inexpensive. In addition, these materials have high ion exchange capacity and high proton conductivity, and are suitable for use as a sulfonated polymer. In addition, as the sulfonated polymer, aromatic sulfonated polymers such as sulfonated polyarylene, sulfonated polyphenylene, and sulfonated polyether ketone obtained by a known synthesis method, sulfonated polypyridine, and the like may be used.

[Method for producing solid polymer electrolyte membrane]
Next, the manufacturing method of the solid polymer electrolyte membrane of this embodiment is demonstrated.
First, a precursor solution which is a solution in which polyvinyl alcohol and a sulfonated polymer are dissolved and mixed in a solvent to become a precursor of the solid polymer electrolyte membrane is prepared. As this solvent, water is used.

  In the precursor solution, the ratio of the sulfonated polymer to the polyvinyl alcohol is preferably 20% by mass or more and 150% by mass or less, and more preferably 30% by mass or more and 100% by mass or less. When this ratio is 20% by mass or more, sulfo groups contributing to proton conduction are sufficiently ensured in the solid polymer electrolyte membrane, and sufficient proton conductivity is obtained in the solid polymer electrolyte membrane. On the other hand, if this ratio is 150% by mass or more, the sulfonated polymer is increased with respect to the polyvinyl alcohol as the polymer matrix, and therefore there is a possibility that a solid polymer electrolyte membrane having sufficiently high mechanical strength cannot be obtained. is there.

Next, the precursor solution is applied to a predetermined substrate, and then the solvent is removed from the applied precursor solution and heated to produce a solid polymer electrolyte membrane.
In the removal of the solvent, a part of the solvent is removed to such an extent that the polyvinyl alcohols come into contact with each other, and the remaining part of the solvent does not solidify the polyvinyl alcohol and the sulfonated polymer. Such removal of the solvent may be performed under atmospheric pressure or under reduced pressure. Further, the removal of the solvent may be performed by heating under the pressure of an inert gas as long as it is lower than the temperature of the subsequent heating.

  In the heating of the precursor solution, the precursor solution is heated to such an extent that the crosslinking reaction between the polyvinyl alcohols proceeds, thereby obtaining a solid polymer electrolyte membrane. The solid polymer electrolyte membrane thus obtained becomes black. According to the solid polymer electrolyte membrane obtained through the removal of the solvent and heating, the sulfonated polymer is dispersed and incorporated in the polyvinyl alcohol matrixed by crosslinking.

  The temperature of the precursor solution in such heating is preferably 80 ° C. or higher and 200 ° C. or lower, and more preferably 90 ° C. or higher and 180 ° C. or lower. When the heating temperature is 80 ° C. or higher, the insolubilization reaction of polyvinyl alcohol proceeds easily, and when the heating temperature is 200 ° C. or lower, the polymer chain scission reaction in the polyvinyl alcohol or the sulfonated polymer hardly occurs.

  The removal of the solvent and the heating may be performed simultaneously by applying heat to the precursor solution. After the solvent of the precursor solution is removed, the precursor solution may be heated as separate steps. If the temperature in the removal of the solvent is within the range of the above heating temperature, the removal of the solvent and the insolubilization reaction of polyvinyl alcohol can proceed simultaneously.

As a method of applying the precursor solution to the substrate, for example, a known application method such as coating by casting, coating by a die coater, coating by an applicator, or the like can be used.
According to such a method, a solid polymer electrolyte membrane having high proton conductivity with an ion exchange capacity of 0.9 meq / g or more and 5.6 meq / g or less can be obtained. The ion exchange capacity of 5.6 meq / g or less means that excessive sulfo groups are not introduced into the solid polymer electrolyte membrane, and the solid polymer electrolyte membrane is less likely to swell due to water. This suggests that when used as an electrolyte in a polymer electrolyte fuel cell, gas leaks that cause performance degradation are unlikely to occur. In addition, an ion exchange capacity of 0.9 meq / g or more is advantageous for obtaining a solid polymer electrolyte membrane having high proton conductivity.

  That is, conventionally, in order to insolubilize polyvinyl alcohol in water and increase the water resistance of the solid polymer electrolyte membrane, it has been necessary to form a crosslinked structure in polyvinyl alcohol using a crosslinking agent. On the other hand, the inventors of the present application can advance the insolubilization of polyvinyl alcohol to water by crosslinking polyvinyl alcohol by heat treatment without the need for a crosslinking agent in the presence of a sulfonated polymer. It was found that

  As a result, it is possible to increase the water resistance of the solid polymer electrolyte membrane by forming a crosslinked structure in polyvinyl alcohol without using a crosslinking agent. Therefore, in the solid polymer electrolyte membrane, it becomes possible to reduce the ratio of the compound having low proton conductivity other than the sulfonated polymer to the sulfonated polymer, and as a result, the proton conductivity as the solid polymer electrolyte membrane is also improved. It becomes possible.

[Heat treatment]
Next, insolubilization of polyvinyl alcohol by heat treatment in the above production method will be described.

  Usually, when polyvinyl alcohol is heated to a high temperature of about 180 ° C. without solvent, the crystallization of polyvinyl alcohol itself proceeds and becomes insoluble in water. On the other hand, the inventors of the present application have found that when polyvinyl alcohol is heated in the presence of a sulfonated polymer, it becomes insoluble at a relatively low temperature of about 80 ° C. even if the above-described crystallization does not proceed.

  FIG. 1A shows an X-ray diffraction spectrum of a film obtained by heating polyvinyl alcohol in the absence of a sulfonated polymer to 90 ° C. and 180 ° C. without solvent. On the other hand, FIG. 1B uses an aqueous solution containing polyvinyl alcohol and polystyrene sulfonic acid as a sulfonated polymer in a weight ratio of 1: 1 as a precursor solution, and the temperature of the heat treatment is set to 90 ° C. and 180 ° C. The X-ray-diffraction spectrum of the solid polymer electrolyte membrane in the case is shown. The X-ray diffraction spectrum was obtained using an X-ray diffractometer (JDX-3530) manufactured by JEOL Ltd., using CuKα rays as X-rays, an acceleration voltage of 40 kV, and a beam current of 30 mA.

  As shown in FIG. 1 (a), when the solvent-free polyvinyl alcohol to which the sulfonated polymer was not added was heated, it was observed that the crystallization of the polyvinyl alcohol proceeds. At this time, it was recognized that the peak value of the diffraction intensity indicating the degree of progress of crystallization was higher when heated at 180 ° C. than when heated at 90 ° C. This is because when heated at 90 ° C., it cannot be insolubilized in water because of insufficient crystallization, whereas when heated at 180 ° C., it can be insolubilized in water. This suggests that the crystallization has progressed sufficiently.

  In contrast, as shown in FIG. 1 (b), it was confirmed that when polyvinyl alcohol was heated in the presence of the sulfonated polymer, crystallization of polyvinyl alcohol did not proceed. At this time, there was no significant difference in the spectrum indicating the degree of progress of crystallization between the case where the heat treatment was performed at 90 ° C. and the case where the heat treatment was performed at 180 ° C. This suggests that insolubilization of polyvinyl alcohol in the presence of a sulfonated polymer is not due to the progress of crystallization. That is, the above-mentioned X-ray diffraction spectrum suggests that insolubilization of polyvinyl alcohol in the presence of a sulfonated polymer is based on a dehydration reaction and a crosslinking reaction of polyvinyl alcohol.

Hereinafter, the reaction that can proceed in the above heat treatment will be described.
As described above, from the analysis of the X-ray diffraction spectrum, the insolubilization of polyvinyl alcohol in the presence of the sulfonated polymer does not result from the progress of crystallization. In general, as the pi-conjugated system between carbons constituting the film spreads due to the generation of C═C bonds, the absorption of visible light in the thin film increases and the film is colored. In Examples 1, 2, and 3 to be described later, a black film is obtained. Further, in this heat treatment process, a process of coloring brown may be performed.

  For this reason, when polyvinyl alcohol is heated in the presence of a sulfonated polymer, first, as shown in the following reaction formula (1), a part of the polyvinyl alcohol chain is dehydrated and carbonized by the acid catalysis of the sulfonated polymer. A double bond is formed between them. Thereby, it is thought that the unit which the conjugated system spread in the polyvinyl alcohol molecule is also generated.

次いで、下記反応式（２）あるいは反応式（３）に示されるように、上記反応式（１）にて形成された炭素間の二重結合と他のポリビニルアルコール分子中のヒドロキシ基とが反応してポリビニルアルコール同士が架橋される。

Next, as shown in the following reaction formula (2) or reaction formula (3), the double bond between carbons formed in the above reaction formula (1) reacts with the hydroxy group in another polyvinyl alcohol molecule. Thus, the polyvinyl alcohols are cross-linked.

また、下記反応式（４）に示されるように、スルホン化ポリマーの酸触媒作用によって、ポリビニルアルコール同士の脱水縮合反応が進行して、ポリビニルアルコール同士がエーテル結合を介して架橋される。

Further, as shown in the following reaction formula (4), the dehydration condensation reaction between the polyvinyl alcohols proceeds by the acid catalytic action of the sulfonated polymer, and the polyvinyl alcohols are cross-linked via an ether bond.

このように、スルホン化ポリマー共存下でポリビニルアルコールを加熱すると、スルホン化ポリマーが酸触媒として作用して、ポリビニルアルコールの脱水反応及び架橋反応が進行すると考えられる。そして、この脱水反応及び架橋反応によってポリビニルアルコールが水に不溶化すると考えられる。なお、この不溶化に関しては、スルホン化ポリマーのスルホ基とポリビニルアルコールのヒドロキシ基との間で、イオン交換容量に実質的に影響を及ぼさない程度にスルホン酸エステル化反応が生じることによって不溶化が促進される効果もあると考えられる。

Thus, when polyvinyl alcohol is heated in the presence of a sulfonated polymer, it is considered that the sulfonated polymer acts as an acid catalyst and the dehydration reaction and crosslinking reaction of the polyvinyl alcohol proceed. And it is thought that polyvinyl alcohol becomes insoluble in water by this dehydration reaction and crosslinking reaction. With respect to this insolubilization, insolubilization is promoted by a sulfonic acid esterification reaction occurring between the sulfo group of the sulfonated polymer and the hydroxy group of the polyvinyl alcohol to the extent that the ion exchange capacity is not substantially affected. There is also an effect.

[Configuration of membrane electrode assembly and polymer electrolyte fuel cell]
Next, a membrane electrode assembly and a solid polymer fuel cell including a solid polymer electrolyte membrane produced by the production method of the present embodiment will be described with reference to FIG.

  As shown in FIG. 2, the polymer electrolyte fuel cell 10 is configured as a laminate centered on the polymer electrolyte membrane 1. The solid polymer electrolyte membrane 1 is provided with a pair of electrode catalyst layers 2a and 2b facing each other with the solid polymer electrolyte membrane 1 interposed therebetween. The electrode catalyst layers 2a and 2b are made of, for example, carbon particles carrying platinum and Nafion (registered trademark: manufactured by DuPont). The electrode catalyst layers 2a and 2b are directly applied to the solid polymer electrolyte membrane 1 or are laid on the solid polymer electrolyte membrane 1 using a hot press method.

  Each of the electrode catalyst layers 2a and 2b is covered with a solid polymer electrolyte membrane 1 and a pair of gas diffusion layers 3a and 3b facing each other with the electrode catalyst layers 2a and 2b interposed therebetween. Among these, the electrode catalyst layer 2a and the gas diffusion layer 3a on one side of the solid polymer electrolyte membrane 1 serve as an air electrode (cathode) 4, and the electrode catalyst layer 2b and the gas diffusion layer 3b on the other side serve as a fuel electrode (anode). ) 5. A membrane electrode assembly 6 is composed of the solid polymer electrolyte membrane 1, the electrode catalyst layers 2a and 2b, and the gas diffusion layers 3a and 3b.

  Furthermore, the membrane electrode assembly 6 is sandwiched between a pair of separators 7a and 7b facing each other. In each of the separators 7 a and 7 b, gas flow paths 8 a and 8 b are recessed in the side surfaces facing the membrane electrode assembly 6, and a cooling water flow path is provided on the side surface opposite to the membrane electrode assembly 6. 9a and 9b are recessed. The membrane electrode assembly 6 and the separators 7a and 7b constitute a polymer electrolyte fuel cell 10.

  In the polymer electrolyte fuel cell 10 configured as described above, for example, oxygen gas is caused to flow through the gas flow path 8 a of the separator 7 a facing the air electrode 4, and the gas flow path 8 b of the separator 7 b facing the fuel electrode 5. For example, hydrogen gas is flowed. Further, cooling water flows through each of the cooling water flow paths 9a and 9b of the separators 7a and 7b. Then, by supplying gas from the gas flow paths 8a and 8b to the air electrode 4 and the fuel electrode 5, an electrode reaction accompanied by proton conduction in the solid polymer electrolyte membrane 1 proceeds, whereby the air electrode 4 An electromotive force is generated between the fuel electrode 5 and the fuel electrode 5.

  As described above, the solid polymer electrolyte membrane according to the production method of the present embodiment has improved water resistance and proton conductivity, so that the sulfonated polymer contributing to proton conduction is prevented from being eluted into water. It is possible to maintain high proton conductivity. Therefore, by using such a solid polymer electrolyte membrane, a highly reliable membrane electrode assembly can be obtained, and a solid polymer fuel cell with high power generation efficiency and stability can be obtained.

  As the fuel cell, a single polymer electrolyte fuel cell 10 may be used alone, or a plurality of polymer electrolyte fuel cells 10 may be stacked and connected in series to be used as one fuel cell. May be.

  The manufacturing method of the above-mentioned solid polymer electrolyte membrane will be described below with reference to specific examples and comparative examples. In the following examples and comparative examples, proton conductivity was measured by a four-terminal method using an impedance analyzer (SI-1260) manufactured by Solartron.

[Example 1 and Comparative Examples 1, 2, 3]
10 g of 5% aqueous solution of polyvinyl alcohol (manufactured by Kuraray: PVA-124, saponification degree: 98 mol% to 99 mol%, polymerization degree: 2400), polystyrene sulfonic acid (manufactured by Akzo Nobel: Versa-TL 72, average molecular weight: 75,000) 18% aqueous solution was mixed with 2.8 g and stirred at 60 ° C. for 3 hours to prepare a precursor solution of a solid polymer electrolyte membrane. At this time, the weight ratio of polyvinyl alcohol and polystyrene sulfonic acid in the precursor solution was about 1: 1. Subsequently, as a solvent removal treatment, the precursor solution was applied to a base material made of polyethylene terephthalate, and then dried at 60 ° C. under atmospheric pressure until tack-free. As the heat treatment, first, the heat treatment is performed for 2 hours under a reduced pressure of 90 ° C. that is the first temperature, and then the heat treatment is performed for 2 hours under the reduced pressure of 130 ° C. that is the second temperature. A black solid polymer electrolyte membrane of Example 1 was obtained. Note that tack-free is a state in which the precursor film component is not transferred to the stacked base material even if the surface of the other base material is overlapped on the surface of the precursor film from which the solvent has been removed. In this embodiment, specifically, even when the finger is pressed against the film, the film component does not adhere to the finger.

  Further, the 5% aqueous solution of succinic acid was added to the precursor solution of Example 1 so that the amount of succinic acid was 0.12 by weight with respect to polyvinyl alcohol, and the other steps were the same as in Example 1. Thus, a solid polymer electrolyte membrane of Comparative Example 1 was obtained.

A membrane of Comparative Example 2 was obtained in the same manner as in Example 1 except that an aqueous solution of polyvinyl alcohol to which polystyrene sulfonic acid was not added was used.
Also, different weights of succinic acid were added to the precursor solution of Example 1 such that the weight ratios of succinic acid to polyvinyl alcohol were 0.06, 0.12, 0.18, 0.24, and 0.3, respectively. A 5% aqueous solution was added and mixed, and the other steps were performed in the same manner as in Example 1 to obtain a film of Comparative Example 3. The succinic acid having a weight ratio of 0.12 is the same as Comparative Example 1.

  And about each of Example 1, the comparative example 1, and the comparative example 2, the proton conductivity in the environment of temperature 80 degreeC and relative humidity 95% was measured. For each of Example 1 and Comparative Example 3, the weight loss rate before and after the solid polymer electrolyte membrane was immersed in hot water at 80 ° C. for 3 hours was measured. Table 1 shows the measurement results of the weight loss rate. As described above, the sample having a succinic acid weight ratio of 0.12 is the same as the sample of Comparative Example 1. A sample having a succinic acid weight ratio of 0 corresponds to the sample of Example 1.

［プロトン伝導性］
実施例１のプロトン伝導度は０．２５Ｓ／ｃｍであり、実施例１のイオン交換容量は２．７ミリ当量／ｇであった。

[Proton conductivity]
The proton conductivity of Example 1 was 0.25 S / cm, and the ion exchange capacity of Example 1 was 2.7 meq / g.

On the other hand, the proton conductivity of Comparative Example 1 was 0.21 S / cm, and the ion exchange capacity of Comparative Example 1 was 2.5 meq / g. Moreover, the proton conductivity of Comparative Example 2 was 10 ⁻⁴ S / cm.

  Since the proton conductivity of Example 1 was higher than that of Comparative Example 1, it was confirmed that the solid polymer electrolyte membrane to which no cross-linking agent was added showed higher proton conductivity. Moreover, since the proton conductivity of the comparative example 2 was a very low value, it was also recognized that the high proton conductivity of Example 1 originates in polystyrene sulfonic acid.

  Here, the weight reduction due to the insolubilization reaction of the solid polymer electrolyte membrane composed of polyvinyl alcohol and polystyrene sulfonic acid was confirmed. First, three types of films obtained by mixing a polyvinyl alcohol film, a polystyrene sulfonic acid film, and a polyvinyl alcohol and an aqueous polystyrene sulfonic acid solution were dried at 60 ° C. for 2 hours under reduced pressure, and then further dried at 90 ° C. under reduced pressure. Thus, the weight loss by this series of treatments was compared. As a result, the weight loss rates of the three types of membranes were 3.7% for the polyvinyl alcohol film, 2.6% for the polystyrene sulfonic acid film, and 4.8% for the film made of polyvinyl alcohol and polystyrene sulfonic acid. Here, the film made of polyvinyl alcohol and polystyrene sulfonic acid was completely blackened. As described above, the difference in weight reduction between the composite film (a film made of polyvinyl alcohol and polystyrene sulfonic acid) and the single material film (polyvinyl alcohol film, polystyrene sulfonic acid film) constituting the composite film is about 2%. Therefore, it was recognized that the weight loss due to the insolubilization reaction of the solid polymer electrolyte membrane composed of polyvinyl alcohol and polystyrene sulfonic acid is such that it does not substantially affect the calculated value of the ion exchange capacity.

[water resistant]
As shown in Table 1, the weight reduction rate of Example 1 in which succinic acid was not added was 0%, whereas when succinic acid was added, the weight reduction rate increased with the increase in the addition ratio. It can be seen that it has increased. This increase in the weight reduction rate is considered to be due to elution of unreacted crosslinking agent and the like.

  Thus, it can be seen that Example 1 in which succinic acid is not added has a lower weight reduction rate and water resistance of the solid polymer electrolyte membrane is higher than that in the case where succinic acid is added. This improvement in water resistance is considered to be an effect due to the fact that a dehydration reaction and a crosslinking reaction involving the hydroxy group of polyvinyl alcohol occur in the presence of a strongly acidic sulfonated polymer, and the polyvinyl alcohol is directly crosslinked.

  Moreover, about the some sample which changed the temperature of the heat processing of Example 1 between 80 degreeC and 200 degreeC, it immersed in water and compared water resistance, but in any case, sufficient water resistance is shown. It was. Note that the film of Comparative Example 2 made of only polyvinyl alcohol was clearly swollen due to water absorption when immersed in water due to insufficient crystallization at 130 ° C.

Thus, it was confirmed that both the proton conductivity and the water resistance were improved in the solid polymer electrolyte membrane of Example 1 to which no crosslinking agent was added.
[Example 2 and Comparative Example 4]
In place of the polystyrene sulfonic acid of Example 1, an aqueous solution of polyvinyl sulfonic acid (manufactured by Asahi Kasei Finechem: average molecular weight 118000) was used, and the weight ratio of polyvinyl sulfonic acid to polyvinyl alcohol was set to 0.8: 1. In the same manner as in Example 1, the black solid polymer electrolyte membrane of Example 2 substantially insoluble in water was obtained.

  Further, succinic acid having a weight ratio of 0.12 to polyvinyl alcohol was added to and mixed with the precursor solution of Example 2, and the other steps were performed in the same manner as in Example 2 to obtain the solid polymer electrolyte of Comparative Example 4. A membrane was obtained.

And about each of Example 2 and Comparative Example 4, the proton conductivity in the environment of temperature 80 degreeC and relative humidity 95% was measured.
The proton conductivity of Example 2 was 0.22 S / cm, and the ion exchange capacity of Example 2 was 4.1 meq / g.

On the other hand, the proton conductivity of Comparative Example 4 was 0.13 S / cm, and the ion exchange capacity of Comparative Example 4 was 3.9 meq / g.
Thus, since the proton conductivity of Example 2 is higher than the proton conductivity of Comparative Example 4, the solid polymer electrolyte membrane to which no cross-linking agent is added also shows a higher proton conductivity. Admitted.

  Even when two types of polyvinyl sulfonic acids (manufactured by Asahi Kasei Finechem) having an average molecular weight of 57000 and 13000 are used, a solid polymer having higher proton conductivity when no succinic acid is added, as described above. An electrolyte membrane was obtained.

  Regarding the calculation of the ion exchange capacity, as in the case of Example 1, the difference in weight reduction between the composite membrane and the single substance film constituting the composite membrane by heat drying was compared. As in the case of. Therefore, it was shown that the weight loss based on the dehydration and insolubilization reaction of the solid polymer electrolyte membrane composed of polyvinyl alcohol and polyvinyl sulfonic acid is such that it does not substantially affect the calculated value of the ion exchange capacity. .

[Example 3 and Comparative Example 5]
Instead of the polystyrenesulfonic acid of Example 1, a commercially available aqueous solution of poly (2-acrylamido-2-methylpropanesulfonic acid) (average molecular weight 2000000) was used, and poly (2-acrylamido-2-methylpropanesulfonic acid) and A solid polymer electrolyte membrane of Example 3 in black and insoluble in water at room temperature was obtained in the same manner as in Example 1 except that polyvinyl alcohol was used at a weight ratio of 1: 1.

  In addition, to the precursor solution of Example 3, 0.12 by weight of succinic acid with respect to polyvinyl alcohol was added and mixed, and the other steps were performed in the same manner as in Example 3 to perform the solid polymer electrolyte of Comparative Example 5. A membrane was obtained.

And about each of Example 3 and Comparative Example 5, the proton conductivity in the environment of temperature 80 degreeC and relative humidity 95% was measured.
The proton conductivity of Example 3 was 0.15 S / cm, and the ion exchange capacity of Example 3 was 2.4 meq / g.

In contrast, the proton conductivity of Comparative Example 5 was 0.11 S / cm, and the ion exchange capacity of Comparative Example 5 was 2.3 meq / g.
Thus, since the proton conductivity of Example 3 is higher than the proton conductivity of Comparative Example 5, the solid polymer electrolyte membrane to which no cross-linking agent is added also exhibits higher proton conductivity. Admitted.

  Regarding the calculation of the ion exchange capacity, as in the case of Example 1, the difference in weight reduction between the composite membrane and the single substance film constituting the composite membrane by heat drying was compared. As in the case of. Therefore, the weight reduction based on the dehydration and insolubilization reaction of the solid polymer electrolyte membrane composed of polyvinyl alcohol and poly (2-acrylamido-2-methylpropanesulfonic acid) does not substantially affect the calculated value of the ion exchange capacity. It was shown to be about.

As described above, according to the method for producing a solid polymer electrolyte membrane of the present embodiment, the effects listed below can be obtained.
(1) Since polyvinyl alcohol is directly cross-linked by heat treatment, a solid polymer electrolyte membrane with improved water resistance can be obtained.

  (2) A compound having low proton conductivity other than the sulfonated polymer in the solid polymer electrolyte membrane as compared with the case of using a crosslinking agent because a crosslinked structure can be formed in polyvinyl alcohol without using a crosslinking agent. The solid polymer electrolyte membrane with improved proton conductivity can be obtained.

  (3) By eliminating the need for a cross-linking agent, the composition of the solid polymer electrolyte membrane is simplified, and the manufacturing process is simplified by eliminating the need for a step of adding the cross-linking agent, thus reducing the manufacturing cost. It is also possible to do.

  (4) The solid polymer electrolyte membrane with improved both water resistance and proton conductivity can maintain high proton conductivity because the sulfonated polymer contributing to proton conduction can be prevented from eluting into water. Is possible. Therefore, as a solid polymer electrolyte membrane with excellent stability and low cost, it can be used as a power source for automobiles such as electric vehicles and fuel cell vehicles, mobile devices such as notebook computers, mobile phones and personal digital assistants, and household power generators. When used in a polymer electrolyte fuel cell, it is highly useful.

(5) Since the film which is the precursor solution from which the solvent has been removed is in a tack-free state, it is also easy to transport such a film to the subsequent heat treatment.
(6) Polystyrene sulfonic acid, polyvinyl sulfonic acid, and poly (2-acrylamido-2-methylpropane sulfonic acid) are sulfonated polymers having a high ion exchange capacity. Therefore, by using these compounds as sulfonated polymers, solids can be obtained. It becomes possible to further increase the proton conductivity of the polymer electrolyte membrane.

In addition, the said embodiment can also be implemented with the following forms, for example.
-In addition to polyvinyl alcohol and a sulfonated polymer, a water-soluble polymer as a plasticizer may be added to the precursor solution of the solid polymer electrolyte membrane. According to this, it becomes possible to improve the mechanical strength of the solid polymer electrolyte membrane. As the water-soluble polymer, for example, polyvinylpyrrolidone, polyethylene oxide, poly N-vinylacetamide and the like can be used.

  -In a solid polymer electrolyte membrane, a polymer short fiber, a nonwoven fabric, etc. may be contained in the film | membrane which consists of precursor solutions. According to this, it becomes possible to improve the mechanical strength of the solid polymer electrolyte membrane and the dimensional stability during moisture absorption. As the composite material, a material substantially insoluble in water may be used. For example, polyethylene terephthalate, polyarylate, vinylon, aramid, or the like can be used.

In the above embodiment, one kind of substance is used as the sulfonated polymer, but two or more kinds of substances may be mixed and used.
As long as the insolubilization reaction of polyvinyl alcohol can be promoted, a polymer containing another acid may be combined to produce a solid polymer electrolyte membrane.

  The heat treatment for the precursor solution of the solid polymer electrolyte membrane may be performed at a single temperature, or may be performed by changing the temperature in two or more stages.

  DESCRIPTION OF SYMBOLS 1 ... Solid polymer electrolyte membrane, 2a, 2b ... Electrode catalyst layer, 3a, 3b ... Gas diffusion layer, 4 ... Air electrode, 5 ... Fuel electrode, 6 ... Membrane electrode assembly, 7a, 7b ... Separator, 8a, 8b ... gas flow path, 9a, 9b ... cooling water flow path, 10 ... solid polymer fuel cell.

Claims (3)

Preparing a precursor solution in which polyvinyl alcohol and a sulfonated polymer are dissolved in a solvent containing water;
A method for producing an insolubilized solid polymer electrolyte membrane by heating the precursor solution. The method for producing a solid polymer electrolyte membrane according to claim 1, wherein the heating temperature of the precursor solution during the heating is 80 ° C. or higher and 200 ° C. or lower. The sulfonated polymer is at least one selected from the group consisting of polystyrene sulfonic acid, polyvinyl sulfonic acid, and poly (2-acrylamido-2-methylpropane sulfonic acid). A method for producing the solid polymer electrolyte membrane described.

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