JP2011213763A - Grafted polyimide electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grafted polyimide electrolyte exhibiting excellent proton conductivity and gas barrier properties, an electrolyte membrane for a fuel cell and a catalytic layer for a fuel cell, each comprising the electrolyte, a membrane-electrode assembly comprising the electrolyte membrane and/or the catalytic layer, and a fuel cell comprising the membrane-electrode assembly.SOLUTION: The grafted polyimide electrolyte comprises a main chain bearing an imide group of a six-membered ring structure and a side chain bearing a sulfonic group. The electrolyte membrane for a fuel cell and the catalytic layer for a fuel cell each comprise the grafted polyimide electrolyte. The membrane-electrode assembly comprises the electrolyte membrane for a fuel cell and/or the catalytic layer for a fuel cell. The fuel cell comprises any one of the electrolyte membrane for a fuel cell, the catalytic layer for a fuel cell and the membrane-electrode assembly.

Description

  The present invention relates to a polyimide resin, particularly a polyimide electrolyte used in a fuel cell such as a solid polymer fuel cell, a polymer electrolyte membrane and a catalyst layer constituted thereby, a membrane-electrode assembly including these, and a fuel It relates to batteries.

  Fuel cells are clean energy that uses hydrogen and oxygen as fuel and the only exhaust gas is water, and the fuel cell itself is quiet and has high conversion efficiency to power. Higher overall utilization efficiency of fuels is expected by using cogeneration that uses heat and combined power generation that generates power by moving the turbine with high-temperature exhaust heat.

  Among them, the polymer electrolyte fuel cell can be activated even at room temperature, can be controlled as an electrolyte membrane, can be easily controlled, and can obtain a high current density. It is attracting attention as a next-generation energy source that is expected to be used in a wide range of applications such as small-sized distributed power sources such as power sources for power supplies and portable power sources.

  Conventionally, as an electrolyte membrane of a polymer electrolyte fuel cell, a so-called fluorine-based electrolyte membrane such as Nafion (registered trademark) is known. However, it is expensive and has a low proton conductivity at high temperatures, There are problems in terms of gas barrier properties of hydrogen and oxygen as fuel. An electrolyte membrane having a low gas barrier property causes fuel crossover, which causes a decrease in power generation efficiency and promotes deterioration of the electrolyte membrane and the catalyst. Therefore, research has been conducted on hydrocarbon electrolyte membranes having sulfonic acid groups as alternative materials for the fluorine electrolyte membranes. In particular, sulfonated polyimide has produced electrolyte membranes with various structures due to its high thermal stability, mechanical strength, and chemical resistance. However, it is desired to further improve proton conductivity and membrane stability. Yes.

  In addition, the polymer electrolyte fuel cell has various advantages such as reduction in catalyst poisoning and improvement in proton conductivity depending on operating conditions at a high temperature exceeding 100 ° C. However, the fluorinated polymer electrolyte currently used mainly as an electrolyte membrane for a polymer electrolyte fuel cell has a low glass transition point and breaks the channel structure of the sulfonic acid group that controls proton transport at high temperatures. The proton conductivity decreases due to the above, and operation at 100 ° C. or higher is difficult. Therefore, early development of alternative materials that can replace the fluorine-based electrolyte membrane is desired, and among them, polysulfone (PS), polyethersulfone (PES), polyarylene ethersulfone (PAES), polyimide (PI), polyether Imide (PEI), Polybenzimidazole (PBI), Poly (organo) phosphazene (POP), Polyetherketone (PEK), Polyphenylene sulfide (PPS), Polytetrafluoroethylene (PTFE), Polyamideimide (PAI), Poly Hydrocarbon polymer electrolytes sulfonated with arylate (PAR), polyarylene ether ether ketone (PEEK), etc. are inexpensive, have high mechanical strength at high temperatures, and ease of introduction of sulfonic acid groups. Research has been actively conducted since.

  However, since the hydrocarbon-based polymer electrolyte membrane does not form a channel structure as found in a fluorine-based electrolyte membrane, the amount of sulfonic acid groups must be increased in order to improve proton conductivity. However, if the ion exchange capacity value is increased, the membrane will swell, and the membrane and catalyst carrier will be significantly degraded by radicals generated due to the decrease in mechanical strength, hydrolysis and reaction of the cross leak gas on the electrode catalyst. There are problems such as hydrolytic stability and oxidation stability.

  To solve this problem, sulfonated block copolyimides with controlled hydrophilic and hydrophobic parts of the polymer have been proposed, and reported to exhibit higher proton conductivity than random copolyimides with the same ion exchange capacity. ing. This is due to the fact that polymer units are regularly controlled at the nano or micro level to form phase separation and facilitate proton transport (see Patent Document 1 and Non-Patent Document 1). However, further improvement in proton conductivity and membrane stability is required for practical use.

JP 2005-272666 A

T.A. Nakano, S .; NAGAOKA, H .; KAWAKAMI, Preparation of novel sulfonated block forimidities for proton conductivity membranes, Polym. Adv. Technol. 2005, vol. 16, p753-757

  As described above, by controlling the phase separation structure of the polymer unit, proton conductivity and membrane stability can be improved without increasing the ion exchange capacity. In addition to the block polymer shown above, the phase separation structure control includes a graft polymer and a blend polymer obtained by mixing two or more kinds of polymers. A phase separation structure of a block polymer or a graft polymer is usually called a microphase separation structure, and has been actively studied as an electrolyte membrane material because of the characteristics shown.

  The present invention focuses on a graft structure that can be expected to change the phase separation structure more drastically than the block structure by binding a large number of side chain polymers to the main chain polymer. The purpose is to synthesize sulfonated graft copolyimides composed of side chain polymers and to produce electrolyte membranes thereof to improve proton conductivity and gas barrier properties. Another object of the present invention is to provide an electrolyte membrane and a catalyst layer constituted by the electrolyte, a membrane-electrode assembly including them, and a fuel cell using them.

  The first of the present invention is a graft-type polyimide electrolyte comprising a main chain containing an imide group having a 6-membered ring structure and a side chain containing a sulfonic acid group.

  In a preferred embodiment, the graft-type polyimide electrolyte has a structure in which a side chain including the sulfonic acid group includes an imide group having a 6-membered ring structure.

  In a preferred embodiment, the graft type polyimide electrolyte includes a main chain including an imide group having a 6-membered ring structure including a structure represented by the following general formula (1).

（式中、Ｘ：芳香族化合物基、 Ｙ：スルホン酸基が導入された側鎖を含む、芳香族化合物基、 ｍ，ｎ：繰り返し単位の比率を示す整数。）

(In the formula, X: aromatic compound group, Y: aromatic compound group containing a side chain into which a sulfonic acid group is introduced, m, n: an integer indicating the ratio of repeating units.)

  In a preferred embodiment, the graft type polyimide electrolyte includes a side chain including the sulfonic acid group including a structure represented by the following general formula (2).

（式中、Ｚ：スルホン酸基が導入された芳香族化合物基、 ｌ：繰り返し単位の数を示す整数。）

(In the formula, Z: an aromatic compound group having a sulfonic acid group introduced therein, l: an integer indicating the number of repeating units.)

  A preferred embodiment is the above graft-type polyimide electrolyte in which the sulfonic acid group is substantially contained only in the side chain.

In a preferred embodiment, the ratio of the weight average molecular weight of the graft side chain to the weight average molecular weight of the main chain [Mw (graft side chain) / Mw (main chain)] is
0.01 <[Mw (graft side chain) / Mw (main chain)] <4
The graft-type polyimide electrolyte satisfying the above.

  A second aspect of the present invention is an electrolyte membrane for a fuel cell containing the graft type polyimide electrolyte.

  A third aspect of the present invention is a fuel cell catalyst layer containing the graft-type polyimide electrolyte.

  A fourth aspect of the present invention is a membrane-electrode assembly including the fuel cell electrolyte membrane and / or the fuel cell catalyst layer.

  Furthermore, a fifth aspect of the present invention is a fuel cell including the fuel cell electrolyte membrane and / or the fuel cell catalyst layer and / or the membrane-electrode assembly.

  According to the present invention, it is possible to provide a polyimide resin that is particularly excellent in proton conductivity at high temperatures and excellent in gas barrier properties, particularly a polyimide electrolyte used in a fuel cell such as a polymer electrolyte fuel cell. In addition, according to the present invention, a polymer electrolyte membrane, a catalyst layer, a membrane-electrode assembly, and a fuel cell constituted by a polyimide electrolyte having excellent proton conductivity at high temperatures and excellent gas barrier properties as described above are provided. Can be provided.

It is a figure which shows typically the structure of the principal part cross section of the polymer electrolyte fuel cell concerning this Embodiment.

  An embodiment of the present invention will be described as follows. The present invention is not limited to the embodiments described below.

<1. Polymer electrolyte>
The polymer electrolyte according to the present invention is a graft-type polyimide electrolyte composed of a main chain containing an imide group having a 6-membered ring structure and a side chain containing a sulfonic acid group. The imide group having a 6-membered ring structure contained in the main chain has a structure exemplified by the following formula (3), and the portion forming the imide group is constituted cyclically by 6 atoms.

  The imide group having such a structure has high chemical stability, and the polyimide electrolyte formed by including the imide group having this structure has high stability and durability. Among such main chain structures, the structure represented by the following general formula (1) is preferable from the viewpoint of ease of synthesis, durability, handling, and the like.

（式中、Ｘ：芳香族化合物基、 Ｙ：スルホン酸基が導入された側鎖を含む、芳香族化合物基、 ｍ，ｎ：繰り返し単位の比率を示す整数。）
このような構造としては、具体的には下記式群（４）が例示される。

(In the formula, X: aromatic compound group, Y: aromatic compound group containing a side chain into which a sulfonic acid group is introduced, m, n: an integer indicating the ratio of repeating units.)
Specific examples of such a structure include the following formula group (4).

（式中、Ｘ：スルホン酸基が導入された側鎖を含む、芳香族化合物基、 ｍ，ｎ：繰り返し単位の比率を示す整数。）

(In the formula, X: an aromatic compound group including a side chain having a sulfonic acid group introduced therein, m, n: an integer indicating the ratio of repeating units.)

  The weight average molecular weight of the main chain in the present invention is preferably 10,000 g / mol or more and 1,000,000 g / mol or less. If the weight average molecular weight of the main chain is smaller than this, the strength of the film is difficult to be obtained, and if the weight average molecular weight of the main chain is larger than this, the film may not be formed due to insufficient solubility. Further, the weight average molecular weight of the main chain is more preferably 30,000 g / mol or more and 500,000 g / mol or less. Within this range, the strength and productivity of the film are balanced, and an excellent film can be produced.

  A conventionally known method can be applied to the synthesis of the main chain polymer in the present invention. That is, for example, the method described in Patent Document 1 (Japanese Patent Laid-Open No. 2005-272666) and Non-Patent Document 1 (Polym. Adv. Technol. 2005; 16: 753-757) can be applied.

  Further, the electrolyte of the present invention has a side chain containing a sulfonic acid group (hereinafter sometimes referred to as “graft side chain”). Here, the structure of the graft side chain is not limited except for including a sulfonic acid group, but from the viewpoint of high durability and ease of synthesis, a structure including an imide group, among which the same as the main chain structure described above. For the reason, those having an imide group having a 6-membered ring structure are preferable. Among such structures, the structure represented by the following general formula (2) is preferable because it can be easily synthesized.

（式中、Ｚ：スルホン酸基が導入された芳香族化合物基、 ｌ：繰り返し単位の数を示す整数。）

(In the formula, Z: an aromatic compound group having a sulfonic acid group introduced therein, l: an integer indicating the number of repeating units.)

  Specific examples of such a structure include the following formula group (5).

（式中、ｌ：繰り返し単位の数を示す整数。）

(In the formula, l: an integer indicating the number of repeating units.)

  The weight average molecular weight of the graft side chain in the present invention is preferably 10,000 (g / mol) to 1,000,000 (g / mol). When the weight average molecular weight of the graft side chain is smaller than this, the ion exchange capacity as a membrane becomes small, and sufficient proton conductivity may not be exhibited. If the weight average molecular weight of the graft side chain is larger than this, solubility may be insufficient, and the reaction with the main chain may not proceed well. Further, the weight average molecular weight of the graft side chain is more preferably 30,000 (g / mol) to 500,000 (g / mol). Within this range, the ion exchange capacity and productivity of the membrane are balanced, and an excellent membrane can be produced.

  Further, when the ratio of the weight average molecular weight (Mw) of the graft side chain to the weight average molecular weight (Mw) of the main chain, that is, Mw (graft side chain) / Mw (main chain) is larger than 0.01 and smaller than 4 Is preferred. In the case of 0.01 or less, there is a case where the phase separation structure does not change and the proton conductivity which is the object of the present invention is not improved, and in the case of 4 or more, the strength as a membrane may be lowered. is there.

  Moreover, it is preferable that the sulfonic acid group is substantially contained only in the side chain in order to facilitate the change of the phase separation structure and to improve the proton conductivity which is the object of the present invention.

  Conventionally known methods can be applied to the synthesis of the side chain polymer in the present invention, and the literature on the synthesis of the main chain can be referred to.

  The reaction between the polymer having a main chain structure and the polymer having a side chain structure is not particularly limited. However, in the case of the structure of the above formula (1), for example, Patent Document 1 (Japanese Patent Laid-Open No. 2005-272666). The reaction shown in the said nonpatent literature 1 (European Polymer Journal 43 (2007) 5047-5054, Journal of Membrane Science 311 (2008) 349-359) etc. can be applied.

  Further, the ion exchange capacity of the electrolyte can be appropriately set depending on the molar ratio of the main chain to the side chain. For example, it can be adjusted by the number of side chain branch points in the main chain and the molecular weight of the side chain. The ion exchange capacity greatly affects the properties of the electrolyte such as proton conductivity, water content, and gas barrier properties. Therefore, it may be set as appropriate according to the intended use. Specifically, a preferable ion exchange capacity is 0.5 to 4.0 [meq. / G], more preferably 1.5 to 3.5 [meq. / G]. If the ion exchange capacity is smaller than these lower limits, there is a possibility that preferable proton conductivity will not be expressed. It may not be possible. A form in which a part of the sulfonic acid group is substituted with a cation other than hydrogen is also included in the category of the electrolyte of the present invention.

<2. Electrolyte membrane>
The polymer electrolyte membrane for fuel cells according to the present invention is an electrolyte membrane comprising the polymer electrolyte according to the present invention made of graft type polyimide. A conventionally well-known method is applicable to the manufacturing method of an electrolyte membrane. Among them, a casting method in which the polymer electrolyte as a material is dissolved / dispersed in an appropriate solvent, sufficiently stirred, and then the solvent is distilled off is desirable. The casting method is a method of obtaining a film by applying an electrolyte solution on a flat plate such as a glass plate using a bar coater, a blade coater or the like, and evaporating and distilling off the solvent. Industrially, it is also common to apply a solution continuously from a coating die onto a belt and vaporize the solvent to obtain a long product. At this time, the concentration and viscosity of the solution, the vaporization conditions of the solvent, and the like are appropriately adjusted. Furthermore, after obtaining the electrolyte membrane, a treatment such as biaxial stretching may be performed to control the molecular orientation or the like, or a heat treatment may be performed to control the crystallinity and the residual stress. Furthermore, it is also within the scope of the present invention to add various fillers in order to increase the mechanical strength of the film or to combine them with a reinforcing agent such as a glass nonwoven fabric by pressing. Moreover, you may perform an appropriate chemical process at the time of film forming. For example, crosslinking for increasing the strength of the membrane, addition of a protic compound for increasing conductivity, and the like. In any case, a polymer electrolyte membrane manufactured using a polymer electrolyte according to the present invention in combination with a conventionally known technique is within the scope of the present invention. Further, in the electrolyte membrane of the present invention, various commonly used additives, for example, a compatibilizer for improving compatibility, an antioxidant for preventing resin deterioration, and charging for improving handling in a film forming process. An inhibitor, a lubricant, or the like can be appropriately used as long as it does not affect the processing and performance of the electrolyte membrane.

  The thickness of the polymer electrolyte membrane for a fuel cell according to the present invention can be selected arbitrarily depending on the application. For example, in consideration of reducing the resistance of the polymer electrolyte membrane, the polymer film is preferably as thin as possible. On the other hand, considering the gas barrier properties and handling properties of the polymer electrolyte membrane, the tear resistance during bonding with the electrode, and the like, it may be undesirable if the thickness of the polymer electrolyte membrane is too thin. Considering these, the thickness of the polymer electrolyte membrane is preferably 1.2 μm or more and 350 μm or less, and more preferably 5 μm or more and 200 μm or less. When the thickness of the polymer electrolyte membrane is within this range, the production becomes easy, and wrinkles are hardly generated during processing and drying. In addition, handling is improved such that damage is unlikely to occur.

  The ion exchange capacity of the polymer electrolyte membrane for fuel cells according to the present invention may be adjusted by the ion exchange capacity of the polymer electrolyte as described above. When the polymer electrolyte membrane includes, for example, a material other than the electrolyte, the ion exchange capacity as the membrane is thereby lowered. Therefore, for example, the ion exchange capacity of the electrolyte can be set to be high. In addition, the preferable ion exchange capacity as a membrane is 0.5 to 4.0 [meq. / G], more preferably 1.5 to 3.5 [meq. / G]. If the ion exchange capacity is smaller than these lower limits, preferable proton conductivity may not be exhibited. If the ion exchange capacity is larger than these upper limits, the mechanical strength may be lowered and sufficient strength may not be obtained.

<3. Catalyst layer>
The catalyst layer for a fuel cell according to the present invention is a catalyst layer comprising the polymer electrolyte according to the present invention. The catalyst layer for a fuel cell is generally composed of an additive such as a catalyst, a conductive catalyst carrier, a polymer electrolyte called ionomer, and other water repellents. As the fuel cell catalyst layer of the present invention, conventionally known materials and production methods can be used. This will be described in detail later in the description of the fuel cell according to the present invention.

<4. Membrane-electrode assembly>
The fuel cell membrane-electrode assembly according to the present invention (hereinafter sometimes referred to as MEA: Menbrane Electrode Assembly) is an MEA comprising the polymer electrolyte according to the present invention. The MEA is composed of an electrolyte membrane and a catalyst layer disposed on at least one side of the electrolyte membrane, and a conductive porous body called a diffusion layer disposed outside the electrolyte. There is. The MEA of the present invention includes the electrolyte of the present invention as an electrolyte membrane in MEA and / or an ionomer in a catalyst. For the MEA of the present invention, conventionally known materials and production methods can be used. This will be described in detail later in the description of the fuel cell according to the present invention.

<5. Fuel Cell According to the Present Invention>
The fuel cell according to the present invention is a fuel cell comprising the polymer electrolyte according to the present invention. At this time, it may be included as an electrolyte membrane, an ionomer of the catalyst layer, or both.

  Since the fuel cell comprising the polymer electrolyte according to the present invention includes the polymer electrolyte of the present invention having excellent performance such as proton conductivity at a high temperature as described above, it has high power generation characteristics.

  Next, an embodiment of a solid polymer fuel cell using the polymer electrolyte of the present invention will be described with reference to the drawings. In this embodiment, a solid polymer fuel cell will be described as an example. However, the present invention also applies to a direct liquid fuel cell and a direct methanol fuel cell in the same manner as the solid polymer fuel cell. It can be implemented.

  FIG. 1 is a diagram schematically showing a cross-sectional structure of a main part of a polymer electrolyte fuel cell using a polymer electrolyte according to the present embodiment. As shown in the figure, a polymer electrolyte fuel cell 10 according to this embodiment includes a polymer electrolyte membrane 1, catalyst layers 2 and 2, diffusion layers 3 and 3, and separators 4 and 4.

  The polymer electrolyte membrane 1 is located substantially at the center of the cell of the solid polymer fuel cell 10. The catalyst layer 2 is provided in contact with the polymer electrolyte membrane 1. The diffusion layer 3 is provided adjacent to the catalyst layer 2, and a separator 4 is disposed on the outer side thereof. In the separator 4, a gas (hydrogen gas or the like) or a liquid (methanol aqueous solution or the like) as a fuel, and a flow path 5 for feeding an oxidant are formed.

  In general, a polymer electrolyte membrane 1 joined with a catalyst layer 2 or a polymer electrolyte membrane 1 joined with a catalyst layer 2 and a diffusion layer 3 is referred to as MEA, which is a solid polymer fuel cell (directly It is used as a basic member of liquid fuel cells and direct methanol fuel cells.

  Methods for producing MEA are conventionally studied polymer electrolyte membranes made of perfluorocarbon sulfonic acid and other hydrocarbon polymer electrolyte membranes (for example, sulfonated polyetheretherketone, sulfonated polyethersulfone, sulfone). A known method performed with a sulfonated polysulfone, a sulfonated polyimide, a sulfonated polyphenylene sulfide, or the like is applicable.

  An example of a specific method for producing MEA is shown below, but the present invention is not limited to this.

  The catalyst layer 2 is formed by dispersing a metal-supported catalyst in a polymer electrolyte solution or dispersion to prepare a dispersion for forming the catalyst layer. The dispersion solution is applied onto a release film such as polytetrafluoroethylene by spraying, and the solvent in the dispersion solution is dried and removed to form a predetermined catalyst layer 2 on the release film. The catalyst layer 2 formed on the release film is disposed on both surfaces of the polymer electrolyte membrane 1, and hot-pressed under predetermined heating and pressurizing conditions to join the polymer electrolyte membrane 1 and the catalyst layer 2 and release them. The MEA in which the catalyst layers 2 are formed on both surfaces of the polymer electrolyte membrane 1 can be produced by peeling the mold film.

  Also, a catalyst-carrying gas diffusion electrode in which the dispersion solution is coated on the diffusion layer 3 using a coater or the like, the solvent in the dispersion solution is dried and removed, and the catalyst layer 2 is formed on the diffusion layer 3 Are arranged on both sides of the polymer electrolyte membrane 1, and the catalyst layer 2 side of the catalyst-carrying gas diffusion electrode is placed on both sides of the polymer electrolyte membrane 1 by hot pressing under predetermined heating and pressurizing conditions. An MEA in which the catalyst layer 2 and the diffusion layer 3 are formed can be manufactured. In addition, you may use a commercially available gas diffusion electrode (made by USA E-TEK company etc.) for the said catalyst carrying | support gas diffusion electrode.

  Examples of the polymer electrolyte solution include an alcohol solution of a perfluorocarbon sulfonic acid polymer compound (such as Nafion (registered trademark) solution manufactured by Aldrich) or a sulfonated aromatic polymer compound (eg, sulfonated polyether ether ketone). , Sulfonated polyethersulfone, sulfonated polysulfone, sulfonated polyimide, sulfonated polyphenylene sulfide, and the like) can be used.

  The metal-supported catalyst has a carrier and a metal catalyst supported on the carrier, and as the carrier, conductive particles having a high specific surface area can be used. For example, activated carbon, carbon black, Examples thereof include carbon materials such as ketjen black, vulcan, carbon nanohorn, fullerene, and carbon nanotube. As the metal catalyst, any catalyst that promotes the oxidation reaction of fuel and the reduction reaction of oxygen can be used, and the fuel electrode and the oxidant electrode may be the same or different. For example, noble metals such as platinum and ruthenium or alloys thereof can be exemplified, and a promoter for promoting their catalytic activity or suppressing poisoning by reaction by-products may be added.

  The dispersion solution for forming the catalyst layer may be appropriately diluted with water or an organic solvent in order to adjust the viscosity so that it can be easily applied by spraying or coated by a coater. Moreover, you may mix fluorine-type compounds, such as tetrafluoroethylene, in order to provide water repellency to the catalyst layer 2 as needed.

  As the diffusion layer 3, a porous conductive material such as carbon cloth or carbon paper can be used. In order to promote the diffusibility of the fuel and the oxidant and the discharge of reaction by-products and unreacted substances, it is preferable to use those which are coated with tetrafluoroethylene or the like to impart water repellency. Further, an adhesive layer made of a polymer electrolyte as described above may be provided between the polymer electrolyte membrane 1 and the catalyst layer 2 as necessary.

  The conditions for hot pressing the polymer electrolyte membrane 1 and the catalyst layer 2 under heating and pressurizing conditions need to be appropriately set according to the type of polymer electrolyte contained in the polymer electrolyte membrane 1 and the catalyst layer 2 to be used. is there. The above-mentioned condition is that the polymer electrolyte contained in the polymer electrolyte membrane 1 or the catalyst layer 2 is generally below the thermal degradation or thermal decomposition temperature of the polymer electrolyte contained in the polymer electrolyte membrane 1 or the catalyst layer 2. It is preferable that the temperature is higher than the glass transition point and softening point.

  As the pressurizing condition, it is preferable that the pressure is in the range of about 0.1 MPa or more and 20 MPa or less because the polymer electrolyte membrane 1 and the catalyst layer 2 are in sufficient contact with each other and there is no deterioration in characteristics due to significant deformation of the material used. In particular, when the MEA is formed only from the polymer electrolyte membrane 1 and the catalyst layer 2, the diffusion layer 3 may be disposed outside the catalyst layer 2 and used only by contacting without being joined.

  The MEA obtained by the method as described above is inserted between a pair of separators 4 and 4 in which a gas or liquid serving as a fuel and a flow path 5 for feeding an oxidant are formed. The solid polymer fuel cell 10 according to the embodiment is obtained.

  As the separator 4, a conductive material such as carbon graphite or stainless steel can be used. In particular, when a metal material such as stainless steel is used, it is preferable to perform a corrosion resistance treatment.

  For the polymer electrolyte fuel cell 10 described above, as a gas or liquid serving as a fuel, a gas containing hydrogen as a main component, a gas or liquid containing methanol as a main component, and a gas containing oxygen as an oxidant ( Oxygen or air) is supplied to the catalyst layer 2 from the separate flow paths 5 via the diffusion layer 3, whereby the polymer electrolyte fuel cell generates electric power. At this time, for example, when a hydrogen-containing liquid is used as the fuel, a direct liquid fuel cell is obtained, and when methanol is used, a direct methanol fuel cell is obtained. That is, it can be said that the above-described embodiment exemplified for the polymer electrolyte fuel cell 10 can be applied to a direct liquid fuel cell and a direct methanol fuel cell as they are.

  In addition, the polymer electrolyte fuel cell 10 according to the present embodiment can be used alone or in a stacked manner to form a stack, or a fuel cell system incorporating them.

  In addition to the examples described above, the polymer electrolyte membrane according to the present invention is disclosed in JP 2000-90944, JP 2001-313046, JP 2001-313047, JP 2001-93551, JP 2001-93558, JP 2001-93561, JP 2001-102069, JP 2001-102070, JP 2001-283888, JP 2000-268835, JP 2000. It can be used as an electrolyte membrane of a polymer electrolyte fuel cell or a direct methanol fuel cell, which are known in Japanese Patent Application Publication No. 268836, Japanese Patent Application Laid-Open No. 2001-283893, and the like. Based on these known documents, those skilled in the art can easily construct a solid polymer fuel cell or a direct methanol fuel cell using the polymer electrolyte of the present invention.

  Hereinafter, the present invention will be described in more detail with reference to examples. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail. Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. Embodiments obtained by appropriately combining the respective technical means disclosed herein are also the present invention. Is included in the technical scope.

(Synthesis Example 1)
<Preparation of polymer electrolyte precursor (main chain portion)>
Into the flask, 2.15 g (0.0042 mol) of 4,4 ′-[hexafluoroisopropylidenebis (p-phenyleneoxy)] dianiline (hereinafter, APPF) and 3,5-diaminobenzoic acid (hereinafter, DABA) were added. 0.61 g (0.0041 mol) was weighed, m-cresol was added, and the mixture was stirred at 80 ° C. for 4 hours. Thereafter, 2.2 g (0.0082 mol) of (1,4,5,8) -naphthalenetetracarboxylic dianhydride (hereinafter referred to as NTDA) was added and stirred at 120 ° C. for 24 hours. 1.4 mL (2.4 times mol) of triethylamine and 0.56 g (1.12 times mol) of benzoic acid were added as a catalyst and stirred at 180 ° C. for 24 hours. The polymer solution was cooled to room temperature, reprecipitated with ethyl acetate, transferred to a petri dish and vacuum dried at 150 ° C. for 15 hours, and the main chain polymer NTDA-APPF-r-DABA (50: 50) was obtained.

（式中、ｍ，ｎ：繰り返し単位の比率を示し、ここでは５０：５０。）

(In the formula, m, n are the ratios of repeating units, and here are 50:50.)

(Synthesis Example 2)
<Preparation of polymer electrolyte precursor (side chain portion: short chain length)>
In a three-necked flask equipped with a Dimroth and a nitrogen inflower, 5.5 g (0.0159 mol) of 2,2-benzidinedisulfonic acid (hereinafter referred to as BDSA) was weighed, and 50 mL (28-fold mol) of m-cresol and triethylamine 5. 4 mL (2.4 times mol) was added and dissolved at 80 ° C. Subsequently, 4.4 g (0.0164 mol) of NTDA was added and stirred at 120 ° C. for 4 hours, and 2.2 g (1.12 times mol) of benzoic acid was further added and stirred at 120 ° C. for several hours. This obtained the side chain part (short chain length) shown by the following (Formula 7).

（式中、ｌ：繰り返し単位の数を示し、ここでは約１１０。）

(In the formula, l represents the number of repeating units, and here is about 110.)

(Synthesis Example 3)
<Preparation of polymer electrolyte precursor (side chain portion: long chain length)>
BDSA (5.5 g, 0.0159 mol) was weighed into a three-necked flask equipped with a Dimroth and a nitrogen inflow device, and m-cresol (50 mL, 28 times mol) and triethylamine (5.4 mL, 2.4 times mol) were added. It was dissolved at ° C. Subsequently, 4.4 g (0.0164 mol) of NTDA was added and stirred at 120 ° C. for 24 hours, and 2.2 g (1.12 times mol) of benzoic acid was further added and stirred at 120 ° C. for several hours. As a result, side chain portions having the same structure as Synthesis Example 2 but different molecular weights (long chain length, “l” indicating the number of repeating units in Formula 7 was about 200) were obtained.

Example 1
<Preparation of grafted sulfonated polyimide>
The main chain polymer NTDA-APPF-r-DABA (50:50) prepared in (Synthesis Example 1) is added to the NTDA-BDSA solution (10-fold mol with respect to the main chain polymer) prepared in (Synthesis Example 2). , And reacted at 120 ° C. for 24 hours. Triphenylphosphine (2.4 times mol of DABA) and pyridine (5 times mol of DABA) were added and reacted at 180 ° C. for 24 hours to obtain the desired sulfonated graft copolyimide NTDA-APPF-r-DABA- g-NTDA-BDSA (short chain length) was synthesized (Example 1, Formula 8 below). The synthesized polymer solution was cooled to room temperature, then reprecipitated with methanol to remove unreacted side chains, transferred to a petri dish, and vacuum dried at 150 ° C. for 15 hours.

（式中、ｍ，ｎ：繰り返し単位の比率を示し、ここでは５０：５０、 ｌ：繰り返し単位の数を示し、ここでは約１１０。）

(In the formula, m, n represents the ratio of repeating units, here 50:50, l: the number of repeating units, here, approximately 110.)

(Example 2)
<Preparation of grafted sulfonated polyimide>
The main chain polymer NTDA-APPF-r-DABA (50:50) prepared in (Synthesis Example 1) is added to the NTDA-BDSA solution (10-fold mol with respect to the main chain polymer) prepared in (Synthesis Example 3). , And reacted at 120 ° C. for 24 hours. Triphenylphosphine (2.4 times mol of DABA) and pyridine (5 times mol of DABA) were added and reacted at 180 ° C. for 24 hours to obtain the desired sulfonated graft copolyimide NTDA-APPF-r-DABA- g-NTDA-BDSA (long chain length) was synthesized (Example 2). Compared to Example 1, the structure is the same and the molecular weight of the side chain is different (in Formula 8, “l” indicating the number of repeating units is about 200). The synthesized polymer solution was cooled to room temperature, then reprecipitated with methanol to remove unreacted side chains, transferred to a petri dish, and vacuum dried at 150 ° C. for 15 hours.

(Examples 3 and 4)
<Production of graft type sulfonated polyimide membrane>
The graft type sulfonated polyimide shown in each of Examples 1 and 2 was dissolved in dimethyl sulfoxide (hereinafter, DMSO) overnight at a concentration of 0.4 g / 10 ml (0.04 g / ml), and the polymer solution was dissolved in a petri dish. It was placed in a vacuum oven smoothed by pouring into (outer diameter 90 mm, inner diameter 86 mm, depth 20 mm). After heating to 110 ° C. with normal pressure, the solvent was evaporated by reducing the pressure to 0.1 MPa at a rate of about 0.01 MPa / h. From the time when the pressure was reduced to 0.1 MPa, heat treatment was further performed at 110 ° C. for 12 hours. The polyimide solid electrolyte membrane was produced by taking out after cooling to room temperature.
The produced film was immersed in ethanol for 4 hours to swell the film and remove impurities and residual solvent. Thereafter, the ethanol was discarded, and the ethanol was removed by immersion in ion-exchanged water for 4 hours. Next, the ion-exchanged water is discarded, and the sulfonic acid group is protonated by immersing it in a 0.1N hydrochloric acid aqueous solution for 4 hours. Finally, the excess hydrochloric acid is removed by immersing in ion-exchanged water for 4 hours. The target electrolyte membrane was produced. The electrolyte membranes corresponding to Examples 1 and 2 are referred to as Examples 3 and 4, respectively.

(Comparative Example 1)
<Production of linear sulfonated polyimide membrane>
In a three-necked flask equipped with a Dimroth and a nitrogen inlet, 1.8 g (0.0053 mol) of 2,2-benzidinedisulfonic acid (BDSA) and 4,4 ′-[hexafluoroisopropylidenebis (p-phenyleneoxy)] 1.17 g (0.0022 mol) of dianiline (APPF) was weighed out, 2.5 mL of triethylamine and 20 mL of m-cresol were added, and dissolved at 80 ° C. for 4 hours. NTDA 2.0g (0.0075mol) was added, and it stirred and heated at 120 degreeC for 24 hours. After adding 2.5 mL of triethylamine and 1.03 g (0.084 mol) of benzoic acid, the mixture was further stirred and heated at 180 ° C. for 24 hours, allowed to cool, and then reprecipitated with ethyl acetate. The obtained granular polymer was vacuum-dried at 150 ° C. for 15 hours to obtain an NTDA-BDSA-r-APPF 70:30 polymer.
0.4 g of the NTDA-BDSA-r-APPF 70:30 polymer was added to 10 mL of dimethyl sulfoxide, and the mixture was stirred and dissolved overnight to prepare a sulfonated random copolyimide salt solution. Next, the sulfonated random copolyimide salt solution was cast on a glass petri dish, and the solvent was evaporated at 110 ° C. under reduced pressure to prepare a cast film.
The produced film was immersed in ethanol for 4 hours to swell the film and remove impurities and residual solvent. Thereafter, the ethanol was discarded, and the ethanol was removed by immersion in ion-exchanged water for 4 hours. Next, the ion-exchanged water is discarded, and the sulfonic acid group is protonated by immersing it in a 0.1N hydrochloric acid aqueous solution for 4 hours. Finally, the excess hydrochloric acid is removed by immersing in ion-exchanged water for 4 hours. The target electrolyte membrane was produced.

(Comparative Example 2)
Commercially available Nafion 117 (film thickness 150 μm) was used.

<Measurement method of molecular weight by GPC (gel permeation chromatography)>
Using dimethylformamide (hereinafter DMF) to which a small amount of LiBr (10 mM) was added, the molecular weight of the synthesized side chain polymer was measured in terms of polystyrene. The sample solution was prepared by dissolving the polymer in DMF with lithium bromide at a concentration of 1 mg / ml.
As a result of the measurement, the weight average molecular weight (Mw) of the main chain polymer (Synthesis Example 1) was 7.1 × 10 ⁴ g / mol. The weight average molecular weights (Mw) of the side chain polymers (Synthesis Example 2) and (Synthesis Example 3) used in Examples 1 and 2 were 7.0 × 10 ⁴ g / mol and 1.3 × 10 ⁵ g / mol, respectively. mol.

<Measurement method of ion exchange capacity>
The ion exchange capacity (IEC) was calculated by a titration method. First, a sample film was dried at 80 ° C. for 12 hours using a vacuum oven. Thereafter, the membrane sample was weighed into a sample bottle of about 10 mg, immersed in a sufficient amount of 0.1N sodium chloride solution, and allowed to stand overnight or more to replace protons of sulfonic acid groups in the membrane with Na ions. After dropping a few drops of a phenolphthalein aqueous solution into the substituted sodium chloride solution, the solution was titrated with 0.01N sodium hydroxide until the solution changed to reddish purple. IEC [meq. / G] was calculated by the following equation.

IEC (meq./g)=Titration (μL) × Normality (N) / Membrane weight (mg)

  The IEC (meq./g) value of the produced electrolyte membrane was 2.38 and 2.40 in Examples 1 and 2, respectively. The graft ratios calculated from the IEC values were 2.2% and 1.5%, respectively. Moreover, IEC (meq./g) of Comparative Examples 1 and 2 was 2.2 and 0.91.

Here, the graft ratio is a ratio calculated with 100% as the side chain introduced into all side chain introduction sites in the main chain. For example, in Examples 3 and 4, it is 100% when all the carboxylic acid groups of DABA used in Synthesis Example 1 react with the amino groups at the side chain partial ends prepared in Synthesis Examples 2 and 3 to form amide bonds. Specifically, it is calculated by the following formula.

Graft ratio (%) = {(main chain molecular weight × IEC) / [2000− (side chain molecular weight × IEC)]} × 100

<Measurement method of proton conductivity>
Proton conductivity measurement is performed using a constant temperature and humidity chamber (manufactured by ESPEC, SH-221), keeping the temperature and humidity constant (about 3 hours), and using an impedance analyzer (manufactured by Hioki Electric Co., Ltd., 3532-50). Then, the resistance of the electrolyte was measured. Specifically, the frequency response from 50 kHz to 5 MHz was measured with an impedance analyzer, and the proton conductivity was calculated from the following equation.

Proton conductivity (S / cm) = D / (W × T × R)

Here, D is a distance between electrodes (cm), W is a film width (cm), T is a film thickness (cm), and R is a measured resistance value (Ω). In this measurement, D = 1 cm and W = 1 cm, and the film thickness was a value measured using a micrometer for each sample. The temperature and humidity were 90 ° C. and 98% RH, respectively.

<Measurement method of gas permeability coefficient>
Gas permeation measurement was performed using a permeation measuring device (Rika Seiki, Inc., K-315-H). Using oxygen gas, the measurement conditions are a low-pressure side capacity of 57.41 (cc), a membrane area of 7.065 (cm ² ), 1 atm, and a measurement temperature of 35 ° C. The calculation method of gas permeability coefficient is
P = DS
When,
D = L ^2/6 × θ
Was used. Here, P is a gas permeation coefficient [× 10 ⁻¹⁰ (cm ³ (STP) · cm / cm ² · sec · cmHg)], and D is a diffusion coefficient (× 10 ⁻⁸ (cm ² / sec)). , S is a solubility coefficient [× 10 ⁻² (cm ³ (STP) / cm ³ · sec · cmHg)], L is a film thickness [cm], and θ is a delay time [sec].

  Examples 3 and 4 and Comparative Examples 1 and 2 were evaluated by the above method. The results are shown in Table 1. From Table 1, the example using the graft type polyimide electrolyte of the present invention shows higher proton conductivity and lower gas permeability coefficient, that is, higher than the comparative example using the linear sulfonated polyimide or the fluorine-based electrolyte membrane. It was found that gas barrier properties were exhibited.

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte membrane 2 Catalyst layer 3 Diffusion layer 4 Separator 5 Flow path 10 Polymer electrolyte fuel cell

Claims (10)

  A graft type polyimide electrolyte comprising a main chain containing an imide group having a 6-membered ring structure and a side chain containing a sulfonic acid group.   The graft polyimide electrolyte according to claim 1, wherein the side chain containing the sulfonic acid group has a structure containing an imide group having a 6-membered ring structure. The graft type polyimide electrolyte according to claim 1 or 2, wherein the main chain containing an imide group having a 6-membered ring structure includes a structure represented by the following general formula (1).

(In the formula, X: aromatic compound group, Y: aromatic compound group containing a side chain into which a sulfonic acid group is introduced, m, n: an integer indicating the ratio of repeating units.) The graft type polyimide electrolyte according to any one of claims 1 to 3, wherein the side chain including the sulfonic acid group includes a structure represented by the following general formula (2).

(In the formula, Z: an aromatic compound group having a sulfonic acid group introduced therein, l: an integer indicating the number of repeating units.)   The graft type polyimide electrolyte according to any one of claims 1 to 4, wherein the sulfonic acid group is substantially contained only in a side chain. The ratio of the weight average molecular weight of the graft side chain and the weight average molecular weight of the main chain [Mw (graft side chain) / Mw (main chain)]
0.01 <[Mw (graft side chain) / Mw (main chain)] <4
The graft-type polyimide electrolyte according to any one of claims 1 to 5, wherein:   A fuel cell electrolyte membrane comprising the graft polyimide electrolyte according to any one of claims 1 to 6.   A catalyst layer for a fuel cell, comprising the graft-type polyimide electrolyte according to any one of claims 1 to 6.   A membrane-electrode assembly comprising the fuel cell electrolyte membrane according to claim 7 and / or the fuel cell catalyst layer according to claim 8.   A fuel comprising the fuel membrane electrolyte membrane according to claim 7, and / or the fuel cell catalyst layer according to claim 8, and / or the membrane-electrode assembly according to claim 9. battery.

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