JP6156982B2 - Method for producing solid polymer electrolyte, solid polymer electrolyte, ionic conductor, and membrane electrode assembly - Google Patents

Description

  The technology of the present disclosure relates to a solid polymer electrolyte used as a battery electrolyte, an ion conductor, a membrane electrode assembly including the solid polymer electrolyte, and a method for producing the solid polymer electrolyte.

  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. Yes. For example, Patent Document 1 uses terephthalaldehyde, glutaraldehyde, or the like having two aldehyde groups that can react with the hydroxy group of polyvinyl alcohol as a cross-linking agent. It is disclosed that a crosslinked structure is formed. In Non-Patent Document 1, sulfonated succinic acid is used as a crosslinking agent, and a crosslinked structure between polyvinyl alcohol molecules is formed by esterification reaction between two carboxy groups of sulfonated succinic acid and a hydroxy group of polyvinyl alcohol. It is stated that it will be.

  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 in the molecule. Non-Patent Document 2 describes that polyvinyl alcohol is crystallized by heat treatment and its solubility in water is lowered.

JP 2006-156055 A

C. W. Lin, Y .; F. Huanga, A .; M.M. Kannan, Journal of Power Sources, Volume 164, Issue 2, 2007, p449-456. Koichi Nagano, Saburo Yamane, Kentaro Toyoshima, Poval, Kobunshi Shuppankai, Kyoto, 1970, p98, p149

  However, the addition of a crosslinking agent increases the water resistance of the electrolyte membrane, while causing a decrease in proton conductivity. On the other hand, the inventors of the present application can crosslink polyvinyl alcohol molecules by heat treatment to promote insolubilization of polyvinyl alcohol in water without the need for a crosslinking agent in the presence of a sulfonated polymer. I found it possible. Thereby, the water resistance of the electrolyte membrane can be improved while suppressing a decrease in proton conductivity.

  On the other hand, the cross-linked structure between the polyvinyl alcohol molecules is formed by partially dehydrating and condensing polyvinyl alcohol to form a rigid conjugated double bond, so that the flexibility of the obtained electrolyte membrane tends to be low There is. Therefore, there is still room for improvement in the mechanical strength of the electrolyte membrane.

  An object of the technology of the present disclosure is to provide a method for producing a solid polymer electrolyte, a solid polymer electrolyte, an ionic conductor, and a membrane electrode assembly capable of improving mechanical strength.

  A method for producing a solid polymer electrolyte in the technology of the present disclosure was prepared using a dissolution step of dissolving polyvinyl alcohol, a polymer having a proton-dissociable group, and a polyvalent thiol in a solvent to form a solution, and the solution. Heating a solid polymer electrolyte precursor to obtain a solid polymer electrolyte.

  According to the above method, a double bond is formed by dehydration reaction of polyvinyl alcohol using a polymer having a proton dissociable group as an acid catalyst by heat treatment, and a polyvalent thiol is added to the double bond. Another thiol in the polyvalent thiol molecule is added to another polyvinyl alcohol chain in which a double bond is formed by a dehydration reaction to form a cross-linked bond. As a result, it is possible to improve the mechanical strength of the obtained solid polymer electrolyte.

In the above method, the polyvalent thiol, 1,4-bis (3-mercaptobutyryloxy) butane, 1,3,5-tris (3-Melka flop preparative butyryloxy-ethyl) 1,3,5 - triazine-2,4,6 (IH, 3H, 5H) - trione, pentaerythritol tetrakis (3-mercapto preparative butyrate), be at least one selected from 2,3-dimercapto-propanesulfonic acid salt preferable.

According to said method, since the polyvalent thiol which can be obtained easily is used, manufacture of a solid polymer electrolyte can be performed easily.
In the above method, the weight ratio of the polyvinyl alcohol and the polyvalent thiol contained in the solution is preferably 2 or more and 15 or less when the polyvinyl alcohol is 100.

  According to said method, the reaction of the double bond in polyhydric alcohol produced by dehydration condensation and a polyvalent thiol advances effectively, and the solid polymer electrolyte with high mechanical strength is obtained. Moreover, it can suppress that the polyvalent thiol which does not give to a crosslinking reaction remains in a solid polymer electrolyte excessively, and mechanical strength and proton conductivity fall.

  In the above method, the polymer having a proton dissociable group is preferably polystyrene sulfonic acid, polyvinyl sulfonic acid, or poly (2-acrylamido-2-methyl-1-propanesulfonic acid).

  According to the above method, since the sulfonated polymer having a high ion exchange capacity is used as a polymer having a proton dissociable group, the proton conductivity of the solid polymer electrolyte can be increased. In addition, since these sulfonated polymers are easily available, it is possible to easily produce a solid polymer electrolyte.

In said method, it is preferable that the heating temperature of the said precursor in the said heating process is 80 degreeC or more and 200 degrees C or less.
According to the above method, the dehydration reaction of polyvinyl alcohol is likely to proceed, and the polymer chain scission reaction in the polymer having polyvinyl alcohol or proton dissociable group is unlikely to occur. Can proceed.

The ionic conductor in the technique of the present disclosure is an ionic conductor including polyvinyl alcohol and a polymer having a —SO ₃ M group (M is an alkali metal), and the polyvinyl alcohol is represented by the following general formula (1). Having a crosslinked skeleton .
According to the ionic conductor, the ionic conductor has an ionic conductivity of M ⁺ ions. For this reason, since an alkali metal ion functions as a conductive medium, the use of the ion conductor as an electrolyte can be expanded to a range where the alkali metal ion is used.

  The solid polymer electrolyte in the technique of the present disclosure is a solid polymer electrolyte containing polyvinyl alcohol and a polymer having a proton dissociable group, and the polyvinyl alcohol has a crosslinked skeleton represented by the following general formula (1). .

但し、一般式（１）にてＲは有機基を示す。

However, in General formula (1), R shows an organic group.

According to the solid polymer electrolyte, since the polymer having a proton dissociable group is dispersed in the crosslinked polyvinyl alcohol in the solid polymer electrolyte, the mechanical strength of the solid polymer electrolyte is improved. It becomes possible.
The membrane electrode assembly in the technique of the present disclosure includes the solid polymer electrolyte as a membrane between a pair of electrode catalyst layers.
According to the membrane electrode assembly, since the membrane electrode assembly is provided with the solid polymer electrolyte having high mechanical strength, the reliability of the membrane electrode assembly can be improved.

  According to the technique of the present disclosure, the mechanical strength of the solid polymer electrolyte can be improved.

It is a figure which shows the relationship between a heating temperature and an ultraviolet-visible absorption spectrum at the time of heat-processing the precursor for formation of the film | membrane which consists of polyvinyl alcohol and polystyrene sulfonic acid. It is a perspective view which decomposes | disassembles and shows the perspective structure of the membrane electrode assembly and the polymer electrolyte fuel cell which used the solid polymer electrolyte in the technique of this indication.

  Hereinafter, an embodiment embodying a method for producing a solid polymer electrolyte, a solid polymer electrolyte, an ionic conductor, and a membrane electrode assembly according to the present disclosure will be described with reference to FIGS. 1 and 2. In this embodiment, a solid polymer electrolyte membrane, which is a membrane-like solid polymer electrolyte, is manufactured as the electrolyte of the solid polymer fuel cell.

[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, a sulfonated polymer, and a polyvalent thiol.

  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, when the degree of saponification is lower than 70%, formation of double bonds (—CH═CH— groups) and crosslinking with polyvinyl alcohol The progress of the reaction is limited, and it becomes easy to dissolve in water. Therefore, in order for polyvinyl alcohol to function as a polymer matrix that forms a three-dimensional network structure and holds other molecules, the above-described 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 mechanical strength of the solid polymer electrolyte membrane can be increased. 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.

The polyvalent thiol has two or more thiol groups per molecule and is compatible with a solvent that dissolves polyvinyl alcohol and a sulfonated polymer, and is a double bond (—CH═CH— group) formed in polyvinyl alcohol. Anything can be used as long as it is added to. Among them is a polyvalent thiols that are actually sold, 1,4-bis (3-mercaptobutyryloxy) butane, 1,3,5-tris (3-Melka flop preparative butyryloxy-ethyl) -1,3 , 5-triazine-2,4,6 (1H, 3H, 5H) -trione, pentaerythritol tetrakis (3-mercaptobutyrate), 2,3-dimercaptopropanesulfonate are available Is preferably used because of its ease.

  As the sulfonated polymer, 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 for forming a precursor of a solid polymer electrolyte membrane, is prepared by dissolving and mixing polyvinyl alcohol, a sulfonated polymer, and a polyvalent thiol in a solvent as a dissolution step. As this solvent, an organic solvent or 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, sulfonic acid groups (—SO ₃ H) contributing to proton conduction are sufficiently secured in the solid polymer electrolyte membrane, and sufficient proton conductivity is obtained in the solid polymer electrolyte membrane. Is obtained. On the other hand, if this ratio is 150% by mass or less, since the polyvinyl alcohol serving as the polymer matrix is not much relative to the sulfonated polymer, the mechanical strength of the solid polymer electrolyte membrane can be increased.

  In the precursor solution, the weight ratio of the polyvalent thiol to the polyvinyl alcohol 100 is preferably 2 or more and 15 or less, and more preferably 5 or more and 10 or less. If this ratio is 2 or more, the reaction between the double bond (—CH═CH— group) formed in the polyvinyl alcohol by dehydration condensation and the polyvalent thiol proceeds effectively, and the polymers are crosslinked with each other. A solid polymer electrolyte membrane with high mechanical strength can be obtained. On the other hand, if this ratio is 15 or more, polyvalent thiols that are not subjected to the cross-linking reaction remain excessively in the solid polymer electrolyte membrane, resulting in a decrease in mechanical strength and proton conductivity.

  As in the past, in order to crosslink polyvinyl alcohol using polyhydric aldehydes, it is necessary to impregnate a polymer electrolyte membrane precursor composed of poly (vinyl alcohol) and a sulfonated polymer into a solution containing polyhydric aldehyde. Yes, the manufacturing process was complicated. On the other hand, in this embodiment, since the precursor solution is prepared by dissolving and mixing polyvinyl alcohol, the sulfonated polymer, and the polyvalent thiol, the manufacturing process of the solid polymer electrolyte membrane is simplified.

  Next, the precursor solution is applied to a predetermined substrate to form a precursor of the solid polymer electrolyte membrane, and then the solvent is removed from the precursor and the solid polymer is heated. An electrolyte membrane is produced.

  By removing the solvent, a part of the solvent is removed to such an extent that the polyvinyl alcohols come into contact with each other, and a precursor in a state where the polyvinyl alcohol and the sulfonated polymer are not solidified by the remainder of the solvent is obtained. Such removal of the solvent may be performed under atmospheric pressure or under reduced pressure.

  In the heating of the precursor, a double bond (—CH═CH— group) is formed in polyvinyl alcohol by dehydration condensation of polyvinyl alcohol, the film becomes black, and the formed double bond (—CH═CH— The addition reaction of polyvalent thiol to a part of the group proceeds. 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. By forming a crosslinked structure, it is possible to obtain a solid polymer electrolyte membrane having improved mechanical strength and stable retention of the sulfonated polymer, excellent water resistance and high proton conductivity.

  The temperature of the precursor 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, or the precursor may be heated as a separate step after the solvent of the precursor is removed. If the temperature for removing the solvent is within the range of the above heating temperature, the removal of the solvent, the dehydration condensation reaction of polyvinyl alcohol, and the addition crosslinking reaction of polyvalent thiol can also 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 1 meq / g or more and 6 meq / g or less can be obtained. The ion exchange capacity of 6 meq / g or less means that excessive sulfonic acid groups (—SO ₃ H) are not introduced into the solid polymer electrolyte membrane and the solid polymer electrolyte membrane is swollen by water. This suggests that gas leaks that cause performance degradation are less likely to occur when used as an electrolyte in a polymer electrolyte fuel cell.

  That is, conventionally, the solid polymer electrolyte membrane tends to be brittle because polyvinyl alcohol is insolubilized by dehydration condensation that proceeds in the presence of a strong acid to increase the water resistance of the solid polymer electrolyte membrane. As a result of diligent research to solve this problem, the present inventors added a polyvalent thiol that crosslinks to a double bond (—CH═CH— group) formed on a polyvinyl alcohol chain by dehydration condensation. It has been found that the polyvinyl alcohol chains are cross-linked to such an extent that the mechanical strength of the solid polymer electrolyte membrane can be improved.

  In addition, as compared with the conventional case where a polyhydric aldehyde is reacted with a hydroxy group of polyvinyl alcohol to form a crosslinked structure, even when the addition ratio of polyvalent thiol is small, the solid polymer electrolyte membrane by crosslinking is The effect of improving mechanical strength is remarkable. As a result, it is possible to reduce the ratio of the compound having low proton conductivity other than the sulfonated polymer to the sulfonated polymer in the solid polymer electrolyte membrane with a very small amount. As a result, the proton conductivity as the solid polymer electrolyte membrane is achieved. Is not substantially reduced.

[Heat treatment]
Next, the insolubilization of polyvinyl alcohol by heat treatment and the improvement of the mechanical strength of the solid polymer electrolyte membrane by crosslinking in the above production method will be described.

  When heated to a high temperature of about 180 ° C. without solvent, it is known that the crystallization of polyvinyl alcohol itself proceeds and becomes insoluble in water (see Non-Patent Document 2). On the other hand, the inventors of the present application show that when polyvinyl alcohol is heated in the presence of an acid such as a polymer sulfonic acid, a double bond is formed by dehydration condensation even at a relatively low temperature of about 80 ° C. And found insolubilized. The reaction is represented by the following reaction formula (2).

一般に、膜を構成する炭素間の共役系が広がるほど、膜における可視光の吸収が高まって膜が黒色をおびる。図１はポリビニルアルコールとポリスチレンスルホン酸の１：１（重量比）からなる溶液から石英基板上に約１μｍの塗布膜を形成して、加熱処理を行い、その熱処理温度と吸光度の関係を示す図である。本紫外可視吸収スペクトルは島津製作所製ＵＶ−２５５０分光光度計を用いて得られたものである。

Generally, as the conjugated system between carbons constituting the film spreads, the absorption of visible light in the film increases and the film becomes more black. FIG. 1 is a diagram showing the relationship between heat treatment temperature and absorbance after forming a coating film of about 1 μm on a quartz substrate from a solution consisting of 1: 1 (weight ratio) of polyvinyl alcohol and polystyrene sulfonic acid on a quartz substrate. It is. This ultraviolet-visible absorption spectrum was obtained using a Shimadzu UV-2550 spectrophotometer.

  As shown in FIG. 1, the absorption of the ultraviolet-visible region in the coating film is increased by heating the coating film made of polyvinyl alcohol and polystyrene sulfonic acid. Therefore, it is clear that the formation of a conjugated double bond chain by dehydration condensation of polyvinyl alcohol proceeds as the heat treatment temperature increases. In addition, when polystyrene sulfonic acid is used in a composite with polyvinyl alcohol obtained by using polyvinyl sulfonic acid or poly (2-acrylamide-2-methylpropane sulfonic acid) (PAMPS) instead of polystyrene sulfonic acid. As with, it was found that the film was blackish when heated. This indicates that polyvinyl alcohol generates a —CH═CH— group by causing a dehydration reaction to proceed by heating in the presence of polysulfonic acid.

  Therefore, when a solid polymer electrolyte precursor in which polyvinyl alcohol, a sulfonated polymer and a polyvalent thiol coexist is heated, a part of the polyvinyl alcohol chain is first dehydrated by the acid catalysis of the sulfonated polymer. A double bond (—CH═CH— group) is formed. In addition, a part of the double bond forms a pi-conjugated system, and the spread of the double bond is larger as the heating temperature is higher as apparent from FIG. In the case where the polyvalent thiol is not added, in the polyvinyl alcohol in which —CH═CH—double bond is formed, the double bond (—CH═CH— group) and the —OH group of polyvinyl alcohol Due to the reaction, a partial crosslinking reaction proceeds and the solubility in water decreases. On the other hand, since the polymer becomes rigid due to the formation of a conjugated double bond, the resulting film tends to become brittle.

  Multivalent thiols have the property of being easily added to double bonds. Therefore, by adding as described above, polyvalent thiol is added to the formed double bond, and other thiol groups in the polyvalent thiol molecule are generated in other polyvinyl alcohol. In addition to the heavy bond, the polyvinyl alcohol chain is crosslinked. As a result, the mechanical strength of the solid polymer electrolyte membrane is improved.

  An example of the reaction formula of the crosslinking reaction is represented by the following reaction formula (3). In addition, in the conjugated double bond of the polyvinyl alcohol chain, it is considered that the addition reaction to the 1,4-butadiene skeleton also proceeds.

上記前駆体の加熱により得られた複合体中にはポリスチレンスルホン酸等の−ＳＯ_３Ｈを有する高分子が含まれるので、この複合体はプロトン伝導性を有する。また、この複合体中の−ＳＯ_３Ｈ基はアルカリ金属の化合物（ＬｉＯＨ，ＬｉＨ，ＮａＨ等）により−ＳＯ_３Ｍ基（Ｍはアルカリ金属）に容易に変換される。このように変換された複合体はＭ^＋イオンのイオン伝導性を有するイオン伝導体である。このため、例えばＭをリチウムにすることにより、上記イオン伝導体をリチウムイオン二次電池の固体電解質として使用することが可能である。こうした場合には、膜状でない形状に固体高分子電解質を製造してもよい。
［膜電極接合体及び固体高分子形燃料電池の構成］
次に、本実施形態の製造方法によって製造される固体高分子電解質膜を備える膜電極接合体及び固体高分子形燃料電池について、図２を参照して説明する。

Since the composite obtained by heating the precursor contains a polymer having —SO ₃ H such as polystyrene sulfonic acid, the composite has proton conductivity. Further, the -SO ₃ H group of the compound of the alkali metal in the complex (LiOH, LiH, NaH, etc.) -SO ₃ M group with (M is alkali metal) is readily converted to. The complex thus converted is an ionic conductor having an ionic conductivity of M ⁺ ions. For this reason, it is possible to use the said ion conductor as a solid electrolyte of a lithium ion secondary battery, for example by making M into lithium. In such a case, you may manufacture a solid polymer electrolyte in the shape which is not a film | membrane form.
[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 solid polymer fuel cell is configured as a laminate having a solid polymer electrolyte membrane 1 as a center. 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.

  The electrode catalyst layers 2a and 2b are 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), and a cathode electrode 4a for current collection is laminated on the air electrode. The other electrode catalyst layer 2b and the gas diffusion layer 3b serve as a fuel electrode (anode), and an anode electrode 4b for current collection is laminated on the fuel electrode. A membrane / electrode assembly 5 is composed of the solid polymer electrolyte membrane 1, the electrode catalyst layers 2a and 2b, and the gas diffusion layers 3a and 3b.

  Further, the membrane electrode assembly 5, the cathode electrode 4a and the anode electrode 4b are sandwiched by a pair of separators 6a and 6b facing each other. In each of the separators 6 a and 6 b, gas flow paths 7 a and 7 b are recessed in the side surfaces facing the membrane electrode assembly 5, and the cooling water flow paths are provided on the side surface opposite to the membrane electrode assembly 5. 8a and 8b are recessed.

  In the polymer electrolyte fuel cell configured as described above, for example, oxygen gas is caused to flow through the gas flow path 7a of the separator 6a facing the cathode electrode 4a, and for example, to the gas flow path 7b of the separator 6b facing the anode electrode 4b. Hydrogen gas is flowed. In addition, cooling water flows through each of the cooling water flow paths 8a and 8b of the separators 6a and 6b. Then, by supplying gas from the gas flow paths 7a and 7b to the air electrode and the fuel electrode, an electrode reaction accompanied by proton conduction in the solid polymer electrolyte membrane 1 proceeds, so that the cathode electrode 4a and An electromotive force is generated between the anode electrode 4b.

  As described above, since the solid polymer electrolyte membrane according to the production method of the present embodiment has high mechanical strength, water resistance and proton conductivity, the sulfonated polymer contributing to proton conduction elutes in water. Therefore, high proton conductivity and excellent physical properties of the membrane can be maintained. 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 a fuel cell, a single polymer electrolyte fuel cell may be used alone, or a plurality of polymer electrolyte fuel cells may be stacked and connected in series to be used as one fuel cell. Good.
[Example]
The manufacturing method of the above-mentioned solid polymer electrolyte membrane will be described below with reference to specific examples and comparative examples. In addition, this invention is not limited to a following example. In the following Examples and Comparative Examples, proton conductivity was measured by a 4-terminal method using an impedance analyzer (SI-1260) manufactured by Solartron.
Example 1
<Solid comprising a composite in which a sulfonated polymer is dispersed in a cross-linked matrix comprising highly saponified polyvinyl alcohol and pentaerythritol tetrakis (3-mercaptobutyrate) (Karenz MT (registered trademark) PE1: manufactured by Showa Denko KK) Preparation of polymer electrolyte membrane-1>
A commercially available polystyrene sulfonic acid aqueous solution (manufactured by Azo Nobel, Versa-TL (registered trademark) 72 average molecular weight 75000, concentration 18%: hereinafter abbreviated as PSS) was dried under reduced pressure at 110 ° C. to obtain PSS powder. 0.5 g of PSS powder was dissolved in 10 g of dimethyl sulfoxide (DMSO).

  Subsequently, 0.5 g of polyvinyl alcohol (No. 124, saponification rate 98 to 99%, polymerization degree 2400: hereinafter abbreviated as PVA-124) manufactured by Kuraray Co., Ltd. was added to this DMSO solution. Further, 0.25 g of a 10% dimethyl sulfoxide solution of Karenz MT (registered trademark) PE1 was added and stirred at 60 ° C.

  The DMSO solution thus obtained was poured into a container of polyethylene terephthalate (hereinafter abbreviated as PET), dried under reduced pressure at 90 ° C. to remove almost DMSO, then peeled off from the PET container, and dried at 130 ° C. under reduced pressure for 2 hours. To obtain a film. This includes PVA-124, PSS and Karenz MT® PE1 in a ratio (weight ratio) of 100: 100: 5.

The obtained film exhibited a proton conductivity of 0.32 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.
When this film was cut into 38 mm × 6 mm and subjected to a tensile test (pulling speed 5 mm / min) with Shimadzu AG-2000B, the breaking stress was 25.5 MPa (average value of two pieces).
(Example 2)
<Preparation of Solid Polymer Electrolyte Membrane Consisting of Suspended Polymer Dispersed in Crosslinked Matrix of High Saponified Polyvinyl Alcohol and Pentaerythritol Tetrakis (3-mercaptobutyrate) (Karenz MT (registered trademark) PE1) ―Part 2 ＞
Example 1 except that the addition ratio of Karenz MT (registered trademark) PE1 was increased so that PVA-124, PSS and Karenz MT (registered trademark) PE1 were included in a ratio (weight ratio) of 100: 100: 10. In the same manner, a film was obtained.

This film exhibited a proton conductivity of 0.37 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.
When this film was subjected to a tensile test in the same manner as in Example 1, the breaking stress was 25.5 MPa (average value of two pieces).
(Comparative Example 1)
A film was produced in the same manner as in Example 1 except that Karenz MT (registered trademark) PE1 was not added. When this film was subjected to a tensile test under the same conditions as in Example 1, the breaking stress was 12.5 MPa (average value of two pieces). This film exhibited a proton conductivity of 0.25 Scm ⁻¹ at 80 ° C. and 95% environment.

From a comparison between Example 1 and Example 2 and Comparative Example 1, it is clear that the tensile strength of the film is improved by adding Karenz MT (registered trademark) PE1. In Comparative Example 1, PVA is dehydrated and condensed to form a conjugated double bond with a partially rigid molecular structure, as can be inferred from the fact that PVA is colored in black by heating in the presence of PSS of a strong acid. Therefore, it is estimated that the obtained film becomes brittle. In Examples 1 and 2, Karenz MT (registered trademark) PE1 was added to add Karenz MT (registered trademark) PE1 to the double bond portion, and the PVA molecular chains were cross-linked to form a mechanical film. The mechanical strength is improved.
(Example 3)
<Preparation of Solid Polymer Electrolyte Membrane Composed of Composite Dispersed with Sulfonated Polymer in Crosslinked Matrix Made of Highly Saponified Polyvinyl Alcohol and Sodium 2,3-Dimercaptopropanesulfonate-Part 1>
PVA-124 in the same manner as in Example 1 except that sodium 2,3-dimercaptopropanesulfonate (hereinafter abbreviated as DMPS) was used instead of Karenz MT (registered trademark) PE1, and the solvent was replaced with water. A film containing PSS and DMPS at a weight ratio of 100: 100: 5 was prepared.

The resulting film exhibited a proton conductivity of 0.15 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.
When this film was subjected to a tensile test under the same conditions as in Example 1, the breaking stress was 45 MPa (average value of two pieces). The film was immersed in 2N dilute hydrochloric acid and dried, and the proton conductivity was measured in an environment of 80 ° C. and 95%. As a result, it was 0.18 Scm ⁻¹ . This _{by -SO} 3 Na in DMPS is acid-treated, is converted to a -SO ₃ H, proton is also effective for participating in proton conductivity.
Example 4
<Preparation of Solid Polymer Electrolyte Membrane Composed of Composite Dispersed with Sulfonated Polymer in Crosslinked Matrix Made of Highly Saponified Polyvinyl Alcohol and Sodium 2,3-Dimercaptopropanesulfonate-Part 2>
A film was produced in the same manner as in Example 3 except that PVA-124, PSS and DMPS were contained at a weight ratio of 100: 100: 10.

The resulting film exhibited a proton conductivity of 0.22 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.
When this film was subjected to a tensile test under the same conditions as in Example 1, the breaking stress was 45 MPa (average value of two pieces).
(Comparative Example 2)
A film was produced in the same manner as in Example 3 except that DMPS was not added. The resulting film exhibited a proton conductivity of 0.15 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.

When this film was subjected to a tensile test under the same conditions as in Example 1, the breaking stress was 13.5 MPa (average value of two pieces).
From the comparison between Example 3 and Example 4 and Comparative Example 2, it is clear that the strength of the film is improved by adding DMPS. As in the case of Comparative Example 2 where the solvent is water as in the case of DMSO, the polyvinyl alcohol is heated in the presence of polystyrene sulfonic acid so that it is colored black, as can be inferred from the dehydration condensation. Since a rigid conjugated double bond is formed, the obtained film becomes brittle. In Examples 3 and 4, DMPS is added to the double bond portion by adding DMPS, and PVA chains are cross-linked in the same manner as in Karenz MT (registered trademark) PE1, so that the mechanical properties of the film are increased. Strength is improved.
(Example 5)
<Solid polymer comprising a composite in which a sulfonated polymer is dispersed in a crosslinked matrix comprising highly saponified polyvinyl alcohol and 1,4-bis (3-mercaptobutyryloxy) butane (Karenz MT (registered trademark) BD1) Production of electrolyte membrane>
PVA-124, PSS, and Karenz MT (registered trademark) BD1 were used in the same manner as in Example 1 except that Karenz MT (registered trademark) BD1 was used instead of Karenz MT (registered trademark) PE1 of Example 1. A film containing 100: 100: 5 was prepared. The obtained film exhibited a proton conductivity of 0.14 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.

Although this film was not subjected to a tensile strength test, it was observed that the strength was clearly improved in durability to the bending operation as compared with the case where Karenz MT (registered trademark) BD1 was not added. In the case of Karenz MT (registered trademark) BD1, Karenz MT (registered trademark) BD1 is added to the double bond formed in the PVA-124 main chain, and further between the PVA main chain having another double bond. It is suggested that the crosslinking reaction is in progress.
(Example 6)
<High saponified polyvinyl alcohol and 1,3,5-tris (3-Melka flop preparative butyryloxy-ethyl) -1,3,5-triazine -2,4,6 (1H, 3H, 5H) - trione (Karenz Production of Solid Polymer Electrolyte Membrane Composed of Composite Dispersed with Sulfonated Polymer in Crosslinked Matrix Made of MT (Registered Trademark) NR1—Part 1>
PVA-124, PSS, and Karenz MT (registered trademark) NR1 were used in the same weight ratio as in Example 1, except that Karenz MT (registered trademark) NR1 was used instead of Karenz MT (registered trademark) PE1 of Example 1. A film containing 1: 1: 0.05 was prepared. The resulting film exhibited a proton conductivity of 0.28 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 2.5 meq / g.

Although this film was not subjected to a tensile test, it was observed that the strength was clearly improved in durability to the bending operation as compared to the case where Karenz MT (registered trademark) NR1 was not added. In the case of Karenz MT (registered trademark) NR1, Karenz MT (registered trademark) NR1 is added to the double bond generated in the PVA-124 main chain, and further between the PVA main chain having another double bond. It is suggested that the crosslinking reaction is in progress.
(Example 7)
<High saponified polyvinyl alcohol and 1,3,5-tris (3-Melka flop preparative butyl oxy) -1,3,5-triazine -2,4,6 (1H, 3H, 5H) - trione (Karenz MT Production of Solid Polymer Electrolyte Membrane Containing Composite Dispersed with Sulfonated Polymer in Crosslinked Matrix Made of (Registered Trademark) NR1-2
Instead of PSS in Example 6, a powder obtained in the same manner as in Example 1 from an aqueous polyvinyl sulfonic acid solution (Asahi Kasei Finechem: average molecular weight 118000, concentration 10%: hereinafter PVS) is 0.8 weight relative to PVA-124. A film was produced in the same manner as in Example 6 except that a part thereof was added. This film contains PVA-124, PVS and Karenz MT® NR1 in a weight ratio of 100: 80: 5. The obtained film exhibited a proton conductivity of 0.14 Scm ⁻¹ at 80 ° C. and 95% environment. At this time, the ion exchange capacity (acid value) was 4.1 meq / g.

  Although this film was not subjected to a tensile test, it was observed that the strength was clearly improved in durability to the bending operation as compared to the case where Karenz MT (registered trademark) NR1 was not added. In PVS, as in the case of PSS, a double bond is generated in the PVA-124 main chain, and it is suggested that the reaction of adding Karenz MT (registered trademark) NR1 to the double bond proceeds.

  The inventors of the present invention also use the PVA main component when the reagent poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (hereinafter abbreviated as PAMPS) (average molecular weight 2000000) from Aldrich Sigma is used as the sulfonated polymer. A similar film blackening phenomenon, which is thought to be due to the formation of conjugated double bonds accompanying the dehydration condensation of chains, is observed.

Therefore, as in the case of PSS and PVS, in the film obtained by heating from PVA-124 and PAMPS, it is obvious that the addition of polyvalent thiol causes a crosslinking reaction and the mechanical strength of the film is improved. It can be said. Furthermore, even when other highly sulfonated polymers and PVA that induce dehydration condensation of PVA are used, the mechanical strength of the film can be improved by adding a polyvalent thiol.
[Modification]
The above embodiment can be implemented with the following modifications.

  -In addition to polyvinyl alcohol, a sulfonated polymer, and a polyvalent thiol, a water-soluble polymer as a plasticizer may be added to the precursor solution of the solid polymer electrolyte membrane. According to this, it is possible to further 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.

  -Polyvalent thiols other than the polyvalent thiols shown in the above embodiments and examples can be used in the same manner as long as they are compatible with polyvinyl alcohol and a sulfonated polymer and undergo an addition reaction with a double bond. Examples of such polyvalent thiols include 2,3-dimercapto-1-propanol, meso-2,2-dimercaptosuccinic acid, bis (2-mercaptoethyl) ether, and the like.

  -The polymer electrolyte membrane may contain polymer short fibers or non-woven fabrics. 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 advanced, a polymer containing an acid other than sulfonic acid may be combined to produce a solid polymer electrolyte membrane. In short, any polymer having a proton dissociable group can be used as a material for forming a solid polymer electrolyte membrane together with polyvinyl alcohol and polyvalent thiol.

  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, 4a ... Cathode electrode, 4b ... Anode electrode, 5 ... Membrane electrode assembly, 6a, 6b ... Separator, 7a, 7b ... gas flow path, 8a, 9b ... cooling water flow path.

Claims (8)

A dissolution step of dissolving polyvinyl alcohol, a polymer having a proton-dissociable group and a polyvalent thiol in a solvent to form a solution;
A heating step of obtaining a solid polymer electrolyte by heating a precursor of the solid polymer electrolyte prepared using the solution;
A method for producing a solid polymer electrolyte comprising: The polyvalent thiol, 1,4-bis (3-mercaptobutyryloxy) butane, 1,3,5-tris (3-Melka flop preparative butyryloxy-ethyl) -1,3,5-triazine -2, 4,6 (1H, 3H, 5H) - trione, pentaerythritol tetrakis (3-mercapto preparative butyrate), 2,3-solid of claim 1 at least one selected from di-mercapto propanesulfonic acid salt A method for producing a polymer electrolyte. The solid polymer according to claim 1 or 2, wherein a weight ratio of the polyvinyl alcohol and the polyvalent thiol contained in the solution is 2 or more and 15 or less when the polyvinyl alcohol is 100. Manufacturing method of electrolyte. The polymer having the proton dissociable group is any one of polystyrene sulfonic acid, polyvinyl sulfonic acid, and poly (2-acrylamido-2-methyl-1-propanesulfonic acid). A method for producing a solid polymer electrolyte according to 1. The method for producing a solid polymer electrolyte according to any one of claims 1 to 4, wherein a heating temperature of the precursor in the heating step is 80 ° C or higher and 200 ° C or lower. A solid polymer electrolyte comprising polyvinyl alcohol and a polymer having a proton dissociable group,
A solid polymer electrolyte in which polyvinyl alcohol has a crosslinked skeleton represented by the following general formula (1).

However, in General formula (1), R shows an organic group. A membrane electrode assembly comprising the solid polymer electrolyte according to claim 6 as a membrane between a pair of electrode catalyst layers. Polyvinyl alcohol and -SO 3 _M group (M is an alkali metal) an ion conductor comprising a polymer having,
An ionic conductor in which polyvinyl alcohol has a crosslinked skeleton represented by the following general formula (1).

However, in General formula (1), R shows an organic group.

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