JP2009259808A - Solid polymer electrolyte membrane, manufacturing method of solid polymer electrolyte membrane, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte membrane suitable for power generation by a high-concentration alcohol fuel, and to provide a method of manufacturing the same. <P>SOLUTION: The solid polymer electrolyte membrane has at least a porous polymer membrane and a proton conductive constituent containing proton conducting groups. The solid polymer electrolyte membrane has, as the proton conductive constituent, a first proton conductive constituent and a second proton conductive constituent low in the degree of acid dissociation relative to the first proton conductive constituent, and is characterized in that the second proton conductive constituent is present to close pores of the porous polymer membrane in the membrane surface direction of the porous polymer membrane; and the number of proton conducting groups of the first proton conductive constituent present in the solid polymer electrolyte membrane is more than the number of the proton conducting groups of the second proton conductive constituent present in the solid polymer electrolyte membrane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid polymer electrolyte membrane, a method for producing a solid polymer electrolyte membrane, and a solid polymer fuel cell.

  Perfluorosulfonic acid membranes are widely used as electrolyte membranes for polymer electrolyte fuel cells. A perfluorosulfonic acid membrane is excellent in proton conductivity, but when a liquid alcohol fuel such as a methanol aqueous solution is used, there is a problem that the membrane swells and the power generation efficiency is low because the fuel easily permeates.

  In order to solve these problems, an electrolyte membrane in which a proton conductive polymer is filled in the pores of an insulating porous membrane has been studied. This electrolyte membrane has the advantage that the dimensional change due to water content can be suppressed by using an insulating porous membrane as a base material, and alcohol permeability can be suppressed even in a water-containing state.

  As an example of such a solid polymer electrolyte membrane, Patent Document 1 describes an electrolyte membrane obtained by filling a polyimide porous film with 2-acrylamido-2-methylpropanesulfonic acid and a crosslinking agent and polymerizing them. .

  As another solid polymer electrolyte membrane, Patent Document 2 describes an electrolyte membrane obtained by filling a crosslinked polyethylene membrane with 2-methacrylamide-2-methylpropanesulfonic acid and a crosslinking agent and polymerizing them.

JP 2003-263998 A JP 2004-253336 A

  However, although the solid polymer electrolyte membranes described in Patent Document 1 and Patent Document 2 are suitable for suppressing permeation of a low-concentration methanol aqueous solution, it was difficult to say that the permeation of a high-concentration methanol solution could be sufficiently suppressed. The energy storage density of the methanol aqueous solution fuel used in the direct methanol fuel cell becomes high when the methanol concentration is high. Since water is also required for the reaction of the fuel electrode, when water is supplied from the fuel, about 64% by weight where methanol and water are equimolar is the ideal concentration of the aqueous methanol fuel.

  Therefore, an object of the present invention is to provide a solid polymer electrolyte membrane adapted for power generation using a high-concentration alcohol fuel, a production method thereof, and a solid polymer fuel cell.

The first invention of the present application is a solid polymer electrolyte membrane having at least a porous polymer membrane and a proton conducting component containing a proton conducting group,
As the proton conduction component, it has a first proton conduction component and a second proton conduction component having a lower acid dissociation degree than the first proton conduction component,
The second proton conducting component is present so as to close the pores of the porous polymer membrane in the membrane surface direction of the porous polymer membrane,
The number of proton conductive groups of the first proton conductive component present in the solid polymer electrolyte membrane is the number of proton conductive groups of the second proton conductive component present in the solid polymer electrolyte membrane. It is a solid polymer electrolyte membrane characterized by having more.

  The second invention of the present application includes a first fixing step of fixing the first proton conductive component in the pores of the porous polymer membrane, and a second proton conductive component in the vicinity of the surface of the porous polymer membrane. It has a 2nd fixing process to fix, It is a manufacturing method of the solid polymer electrolyte membrane characterized by the above-mentioned.

  Furthermore, the third invention of the present application is a polymer electrolyte fuel cell having at least the solid polymer electrolyte membrane according to the first invention and a pair of electrodes sandwiching the solid polymer electrolyte membrane.

  According to the present invention, it is possible to provide a solid polymer electrolyte membrane suitable for power generation using a high-concentration alcohol fuel, a manufacturing method thereof, and a solid polymer fuel cell.

It is a cross-sectional schematic diagram which shows an example of a structure of the polymer electrolyte fuel cell using the polymer electrolyte membrane of this invention.

  Hereinafter, modes for carrying out the present invention will be described.

[Solid polymer electrolyte membrane]
The solid polymer electrolyte membrane according to the present invention comprises a porous polymer membrane and a proton conducting component containing a proton conducting group. Further, the proton conducting component includes a first proton conducting component and a second proton conducting component having a degree of acid dissociation smaller than that of the first proton conducting component, and is present in the solid polymer electrolyte membrane. The number of proton conductive groups of the first proton conductive component is greater than the number of proton conductive groups of the second proton conductive component present in the solid polymer electrolyte membrane.

  In the present invention, “degree of acid dissociation” indicates the relative magnitude of the degree of dissociation of hydrogen ions in the proton dissociation equilibrium reaction of acid. In the case of the present invention, the number of dissociated protons per proton conductive group in a static state is used to compare the magnitude relation of the degree of acid dissociation for each proton conductive component. More specifically, the number of dissociated protons per proton conductive group can be obtained by dividing “the number of dissociated protons in the system” by “the number of proton conductive groups in the system”. The number of proton conductive groups can be determined by conversion from the structural formula of the raw material compound or by measuring the ion exchange capacity. The number of dissociated protons in the system can be determined by preparing an aqueous solution with a constant concentration and measuring the dissociated proton concentration with a commercially available pH meter or the like.

  The proton conducting component having a high degree of acid dissociation plays a role of improving the proton transport ability of the solid polymer electrolyte membrane because the dissociated proton has high mobility. Therefore, the larger the number of proton conductive groups of the proton conductive component having a large acid dissociation degree in the solid polymer electrolyte membrane, the smaller the proton conductive resistance of the membrane, and the more suitable as an electrolyte membrane of a direct methanol fuel cell. Become.

  Since the proton conducting component having a low acid dissociation degree has a small polarity, it has an effect of suppressing methanol permeation. On the other hand, proton conductivity decreases. However, since the amount of protons can be controlled by the number of charged proton conductive groups, the number of proton conductive groups in the proton conductive component having a high degree of acid dissociation is the number of proton conductive groups in the proton conductive component having a low degree of acid dissociation. As long as the amount is larger, the influence on the proton conductivity lowering of the entire electrolyte membrane is small.

  It is preferable that the proton conducting component (that is, the first proton conducting component) having a high degree of acid dissociation is present in the pores of the porous polymer membrane. In other words, the first proton conducting component is preferably filled in the pores of the porous polymer membrane. Here, “the proton conducting component is present (filled) in the pores of the porous polymer membrane” does not require that all of the pores are filled with the proton conducting component. It suffices if the proton conductive component is present in an amount of at least%.

  The proton conducting component having a low acid dissociation degree that suppresses methanol permeation (ie, the second proton conducting component) has a certain effect regardless of the position of the electrolyte membrane. Can be exerted in all permeation paths as long as it is present in the direction of the membrane surface of the porous polymer membrane. Here, “existing pores of the porous polymer membrane in the direction of the membrane surface of the porous polymer membrane” means a path from one of the membrane surfaces of the solid polymer electrolyte membrane to the other membrane surface. Of these, in the porous polymer membrane, when an arbitrary path of protons passing only through the internal pores is considered, the second proton conductive component is present so that the proton always passes through the second proton conductive component. Represents the state. That is, in the above path, either from the membrane surface of the solid polymer electrolyte membrane to the membrane surface of the porous polymer membrane closer to the membrane surface, or in the pores in the porous polymer membrane. It is sufficient that two proton conducting components are present. “Membrane surface” represents one of a pair of surfaces having the largest area among the opposing surfaces of the solid polymer electrolyte membrane or the porous polymer membrane.

  Among such shapes, a shape in which the second proton conducting component is present in the vicinity of at least one surface of the electrolyte membrane outside the porous polymer membrane is preferable in terms of easy realization.

  Here, “near the surface” represents the membrane surface of the solid polymer electrolyte membrane, the outside of the membrane surface, and the inside of the hole having a depth from the membrane surface to 20% of the film thickness.

  More preferably, the second proton conductive component is present in the vicinity of both surfaces of the porous polymer membrane.

  For example, it is better to provide a plurality of films made of the second proton conducting component and to reduce the film thickness per sheet. This is because, in consideration of hopping movement when protons pass through the solid polymer electrolyte membrane, when the entire film thickness is the same, it is more than when a single membrane composed of the second proton conducting component is provided. This is because the proton conduction resistance of the entire electrolyte membrane is reduced. This reason is valid even when it is not film-like. Therefore, the presence of the second proton conducting component in the vicinity of the surfaces of both surfaces of the porous polymer membrane makes the methanol barrier property better than when the same amount of the second proton conducting component is present only on one side. Proton conductivity can be improved without loss. Further, from the viewpoint of easy manufacture, the polymer film having such a shape is preferable.

  In the present invention, the porous polymer film represents a polymer film having a large number of fine pores. These holes are not independent, but are preferably connected in a non-linear manner so that gas and liquid can pass from one side of the membrane to the other side.

  The material for the porous polymer film in the present invention is not particularly limited, but a polymer material that is insoluble in alcohols and water and does not swell is preferable in consideration of the use of an aqueous alcohol solution. Specifically, polyimide resin (eg, Upilex (registered trademark) manufactured by Ube Industries), polytetrafluoroethylene resin (eg, porous PTFE membrane manufactured by Nitto Denko Corporation), polyacrylonitrile resin, polyamide system Various resin materials such as resin, polyamideimide resin, and polyolefin resin can be used. Here, the “polyimide resin” is a resin made of polyimide or a polyimide derivative, and the same applies to other materials. Of these materials, polyimide resins are particularly excellent in terms of insolubility in methanol and water, physical strength, and chemical stability.

  The film thickness and porosity of the porous polymer membrane are selected from the material thereof, the strength of the target solid polymer electrolyte membrane, the characteristics of the target polymer electrolyte fuel cell, and the like. Here, the thickness of the porous polymer membrane is preferably 15 μm or more from the viewpoint of maintaining sufficient strength when assembling the membrane electrode assembly or when used as a polymer electrolyte fuel cell. On the other hand, from the viewpoint of improving the power generation efficiency by shortening the proton movement distance, the thickness of the porous polymer film is preferably 150 μm or less.

  Further, from the viewpoint of improving the power generation efficiency by increasing the portion where the proton conductive component can exist, it is desirable that the average porosity of the porous polymer film is 30% or more in terms of volume. On the other hand, from the viewpoint of ensuring the strength of the solid polymer membrane, the average porosity of the porous polymer membrane is preferably 90% or less in terms of volume. The average porosity in terms of volume is the ratio of the volume (strictly speaking, the volume) occupied by the pores in the porous polymer film. The average porosity (unit:%) is calculated by calculating the apparent specific gravity of the porous polymer membrane from the weight and volume of the porous polymer membrane, and then [1- (Porous Polymer Membrane). (Apparent specific gravity / specific gravity of the polymer material itself)] × 100.

  The first proton conducting component is preferably composed of a polymer compound having a proton conducting group. The role of the proton conductive group is to transport protons from the fuel electrode side to the air electrode side of the solid polymer electrolyte membrane. In addition, by using a polymer compound as the base of the first proton conducting component, the first proton conducting component is physically or chemically fixed to the porous polymer membrane with a strength that does not flow out during the power generation reaction. It becomes easy to make.

  Examples of proton conductive groups include sulfonic acid groups, sulfinic acid groups, carboxylic acid groups, phosphonic acid groups, phosphoric acid groups, phosphinic acid groups, and boronic acid groups.

  In order to make the acid dissociation degree of the first proton conducting component larger than the acid dissociation degree of the second proton conducting component, the proton conducting group contained in the first proton conducting component must be a sulfonic acid group. preferable. Since the sulfonic acid group has a high degree of acid dissociation, the effect of improving proton transport efficiency is high.

  Further, the content of the proton conductive group in the first and second proton conductive components is not particularly limited, but per proton conductive group from the viewpoint of keeping the proton conductivity of the solid polymer electrolyte membrane high. The proton conductive component preferably has a molecular weight of 1000 or less.

  The second proton conductive component is preferably made of a polymer compound having a proton conductive group from the viewpoint of easy physical or chemical immobilization on the porous polymer membrane.

  Examples of proton conductive groups include sulfonic acid groups, sulfinic acid groups, carboxylic acid groups, phosphonic acid groups, phosphoric acid groups, phosphinic acid groups, and boronic acid groups.

  In order to relatively reduce the acid dissociation degree of the second proton conductive component, the proton conductive group contained in the second proton conductive component is preferably a phosphate group or a phosphonic acid group. The phosphoric acid group or phosphonic acid group is proton-conductive, does not hinder proton conduction of the solid electrolyte membrane, and has a function of suppressing methanol permeation because the acid dissociation degree is small.

The solid polymer electrolyte membrane of the present invention preferably has a proton conductivity of 0.10 S / cm or more and a methanol permeability coefficient of 1.0 × 10 ⁻⁷ or less.

[Method for producing solid polymer electrolyte membrane]
The method for producing a solid polymer electrolyte membrane according to the present invention includes a first fixing step of fixing a first proton conducting component in the pores of the porous polymer membrane, and the first polymerizing component in the vicinity of the surface of the porous polymer membrane. A second immobilization step of immobilizing a second proton conductive component having a lower degree of acid dissociation than one proton conductive component and a smaller number of proton conductive groups than the number of proton conductive groups of the first proton conductive component And at least.

  In the first fixing step, the pores of the porous polymer membrane are filled with the first proton conducting component precursor, and the first proton conducting component precursor is converted into the first proton conducting component to convert the porous polymer membrane to the porous polymer membrane. A step of fixing to a membrane is preferable. The first proton conductive component precursor may be a compound having a proton conductive group (for example, a sulfonic acid group-containing compound) as long as it can be converted into the first proton conductive component. It may be a mixture containing a compound having a functional group and other additives.

  The method for filling the first proton conductive component precursor in the pores of the porous polymer membrane is not particularly limited. For example, the porous polymer membrane may be simply immersed in the first proton conducting component precursor. In order to further increase the contact efficiency, ultrasonic vibration may be applied as necessary, or a vacuum filtration or pressure filtration technique may be used in combination.

  As a method for converting the first proton conducting component precursor to the first proton conducting component and fixing it to the porous polymer membrane, a heat polymerization reaction using a polymerization initiator, polymerization by electron beam irradiation or ultraviolet irradiation, etc. Reaction is possible. In addition, methods such as cross-linking with a coupling agent (cross-linking agent) and sol-gel reaction are also conceivable.

  As a method for polymerizing the first proton conductive component precursor filled in the pores in the first fixing step, it is particularly preferable to use electron beam irradiation. This is because the first proton-conducting component in the vicinity of the surface can be effectively removed during the removing step described later. The first proton conducting component after polymerization is preferably a solid or gel proton conducting component.

  In the electron beam irradiation, from the viewpoint of increasing the amount of chemical bond formation between the compounds, the electron beam irradiation amount is preferably set to 100 Gy or more, and more preferably set to 5 kGy or more. On the other hand, from the viewpoint of suppressing denaturation of the porous polymer membrane and the proton conducting component, the electron beam irradiation amount is preferably set to 10 MGy or less, and more preferably set to 200 kGy or less.

  Although the acceleration voltage of the electron beam varies depending on the thickness of the electrolyte membrane, for example, an acceleration voltage of about 50 kV to 2 MV is preferable for a film of about 15 μm to 150 μm. A plurality of electron beams having different acceleration voltages may be irradiated simultaneously. Further, the acceleration voltage may be changed during the electron beam irradiation. Moreover, you may heat-process during the irradiation of an active energy ray or immediately after irradiation as needed.

  The type of the first proton conductive component precursor used in the first fixing step is not particularly limited, but it is preferable to use a sulfonic acid group-containing compound for proton conductivity of the solid polymer electrolyte membrane. Among them, it is preferable to use a compound having a large proportion of sulfonic acid groups in the compound. For example, the molecular weight per functional group is preferably 500 or less.

  The first proton conducting component precursor is more preferably a compound having a functional group having activity in an electron beam because the chemical bond in the first fixing step is further strengthened. Examples of the functional group having activity on the electron beam include unsaturated bonds such as double bonds and triple bonds. Among them, particularly active functional groups are methacrylic acid groups, acrylic acid groups, vinyl groups, and styrene groups.

  Examples of the compound having a sulfonic acid group and a functional group having activity in an electron beam as the first proton conductive component precursor include vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, sulfobutyl methacrylate, sulfopropyl Examples include methacrylates, 2-acrylamido-2-methylpropane sulfonic acid, sulfobenzene methacrylates, and sulfobenzyl methacrylates.

  Moreover, you may use the compound which introduce | transduced the fluorine into the said compound. A plurality of these compounds may be used in combination.

  The first proton conductive component precursor may contain a compound having no sulfonic acid group. For example, by adding a compound having a heterocyclic structure, an effect of strengthening the fixation of the proton conducting component formed in the first fixing step to the porous polymer membrane can be expected. Note that the compound having a heterocyclic structure may have a functional group having activity in an electron beam. Further, as a compound having no sulfonic acid group, an appropriate amount of a crosslinking agent may be added in order to strengthen the chemical bond between the polymers or between the polymer and the porous polymer membrane. As such a crosslinking agent, what has activity with respect to an electron beam is preferable. For example, acrylamide, methylene bisacrylamide, acrylonitrile, N-vinyl pyrrolidone, glycerin dimethacrylate and the like can be mentioned as suitable crosslinking agents. For the purpose of adjusting the viscosity, a small amount of a suitable solvent may be added to the functional compound. It is preferable to provide a removal step for removing the first proton conducting component in the vicinity of the surface of the porous polymer membrane between the first fixing step and the second fixing step. This is because the hole in the vicinity of the surface of the polymer membrane is exposed by the removing step to improve the fixability of the second proton conducting component. At this time, it is not necessary to remove all the first proton conductive components in the vicinity of the surface of the porous polymer membrane, and it may be removed to such an extent that the second proton conductive components are sufficiently fixed. The removal method is not particularly limited, but it can be effectively removed by immersing in a solvent that is soluble in the first proton conducting component before electron beam irradiation and carrying out a rubbing treatment therein.

  In the second fixing step, the second proton conducting component is brought into contact with the surface of the porous polymer membrane, and the second proton conducting component precursor is converted into the second proton conducting component to form a porous polymer membrane. It is the process of fixing. The second proton conductive component precursor is a mixture containing a compound having a proton conductive group (for example, a phosphate group or phosphonic acid group-containing compound) and other additives.

  The method for bringing the second proton conductive component into contact with the vicinity of the surface of the porous polymer membrane is not particularly limited. For example, the porous polymer membrane may be simply immersed in the second proton conducting component. In order to further increase the contact efficiency, ultrasonic vibration may be applied as necessary.

  As a method for polymerizing the second proton conducting component precursor attached to the surface of the porous polymer membrane in the second fixing step, the same method as in the first fixing step can be used. The second proton conducting component after polymerization is preferably present in the vicinity of at least one surface of the porous polymer membrane as a membrane-like proton conducting component.

  The electron beam irradiation dose and acceleration voltage conditions in the second fixing step are the same as those in the first fixing step, and are not particularly limited. In order to protect the proton conduction component formed in the first fixing step, the electron beam irradiation amount and the acceleration voltage in the second fixing step may be relatively reduced.

  In addition, if an unnecessary mixture remains on the surface of the film after electron beam irradiation, it may be removed by washing with water or the like.

  The type of the second proton conducting component precursor used in the second fixing step is not particularly limited, but a phosphate group or phosphonic acid group-containing compound is used for proton conductivity of the solid polymer electrolyte membrane and methanol permeation suppression. It is preferable. In particular, it is preferable to use a compound having a large proportion of phosphoric acid groups or phosphonic acid groups in the compound. For example, the molecular weight per functional group is preferably 500 or less.

  The second proton-conducting component precursor is more preferably a compound having a functional group having activity in an electron beam because the chemical bond in the second fixing step is further strengthened. Examples of the functional group having activity in electron beam irradiation include unsaturated bonds such as double bonds and triple bonds. Among them, particularly active functional groups are methacrylic acid groups, acrylic acid groups, vinyl groups, and styrene groups. Among them, the functional groups that are easy to obtain a film-like polymer are a methacryl group and an acrylic group.

  As a compound having a phosphate group and a functional group active on an electron beam as the second proton conducting component precursor, a (meth) acrylic acid ester derivative having a phosphate group in the side chain is preferably used. it can. The phosphate group-containing compound may contain a compound having no phosphate group as an additive. Examples of compounds that can be added are the same as in the case of the sulfonic acid group-containing compound.

  When the polymer electrolyte membrane according to the present invention is used, a polymer electrolyte fuel cell suitable for high-concentration alcohol fuel can be formed. Such a polymer electrolyte fuel cell has at least the polymer electrolyte membrane of the present invention and a pair of electrodes that sandwich the membrane. This fuel cell can generate power even when hydrogen gas fuel is used.

  For forming a polymer electrolyte fuel cell, generally known techniques can be applied to the cell configuration, manufacturing method, materials of various members, and the like. For example, a catalyst layer is provided on both sides of a solid polymer electrolyte membrane, and a fuel diffusion layer and an oxidant diffusion layer (generally, an air diffusion layer or an oxygen diffusion layer) are provided outside thereof. Thereby, a fuel electrode can be arranged on one surface of the solid polymer electrolyte membrane, and an oxygen electrode or an oxidizer electrode can be arranged on the other surface to form a membrane electrode assembly. A fuel cell can be obtained by providing the membrane electrode assembly with a fuel supply path, a fuel tank, and an air (or oxygen) supply path. Note that an air supply pump or an oxygen tank for supplying air may be provided.

  A specific example of such a fuel cell is a fuel cell having the structure shown in FIG. FIG. 1 shows an example of the minimum configuration of a fuel cell to which the solid polymer electrolyte membrane of the present invention is applied, and the actual shape is arbitrary. A plurality of membrane electrode assemblies may be combined in series or in parallel.

  In the figure, 1 is a membrane electrode assembly, 101 is a solid polymer electrolyte membrane of the present invention, 102 is a catalyst layer, 103 is a diffusion layer, 2 is a fuel electrode (anode), and 3 is an oxidant electrode (cathode). In this example, a joined body composed of the solid polymer electrolyte membrane 101, the pair of catalyst layers 102, and the pair of diffusion layers 103 is referred to as a membrane electrode assembly. In this example, the catalyst layer 102 and the diffusion layer 103 are part of the anode 2 or the cathode 3. In this example, the portions of the anode 2 and the cathode 3 other than the catalyst layer 102 and the diffusion layer 103 serve as both the outer wall of the fuel or oxidant supply path and part of the circuit for taking out current. Although not shown, a sealing material is provided on at least a part of the periphery of the solid polymer electrolyte membrane 101, the catalyst layer 102, and the diffusion layer 103 so that the contact between these members (at least a part thereof) and the outside air is achieved. Can be prevented.

  When the second proton conducting component is present in the vicinity of only one surface of the porous polymer membrane, the battery may be configured with the surface having a relatively low acid dissociation degree as the fuel electrode side. preferable. For example, the fuel electrode is preferably disposed so as to be in contact with the second proton conductive component having a lower acid dissociation degree than the first proton conductive component. The methanol concentration in the case of using a methanol aqueous solution as the fuel is suitably from 3% to 60% by weight. In particular, the effect of the present invention, that is, suppression of methanol permeation, appears in a high concentration region.

  When the solid polymer electrolyte membrane according to the present invention is applied to a fuel cell, the second proton conducting component does not necessarily exist so as to block the pores of the porous polymer membrane over the entire surface in the direction of the membrane surface of the porous polymer membrane. You may not have to. For example, when the size of an electrode (generally a catalyst layer) sandwiching the polymer electrolyte membrane is smaller than that of the solid polymer electrolyte membrane, it exists so as to close the pores of the porous polymer membrane existing between the electrodes in the membrane surface direction. If so, the effects of the present invention can be achieved.

  This is because when a path from one electrode to the other electrode is considered (any path of protons that pass only through the internal pores in the porous polymer membrane), the proton always passes through the second proton conducting component. In this way, the second proton conductive component is present. Specifically, in the fuel cell having the structure shown in FIG. 1, a membrane composed of a second proton conductive component is formed in the vicinity of the surface in contact with the catalyst layer 102 on one or both sides of the solid polymer electrolyte membrane 101. The structure provided can be mentioned.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is construed based on the description of the scope of claims, and is not limited by the following examples.

(Example of production of solid polymer electrolyte membrane)
(Example 1)
A vinyl sulfonic acid polymer was selected as the first proton conducting component, and methacryloyloxyethyl phosphate as the second proton conducting component. Vinylsulfonic acid was made into an aqueous solution in advance, and the acid dissociation degree was measured with a pH meter (D-50 manufactured by Horiba, Ltd.). As a result, the number of dissociated protons per proton conductive group of vinyl sulfonic acid was 0.56. When measured in the same manner, the number of dissociated protons per proton conductive group of methacryloyloxyethyl phosphate was 0.24.

  In a plastic container, 28.0 g of vinyl sulfonic acid, 9.2 g of acryloylmorpholine, and 1.2 g of methylenebisacrylamide were mixed to prepare a mixed solution containing sulfonic acid groups. A polyimide film having a thickness of 27 μm, an average pore diameter of 0.1 μm, and an average porosity of 40% before filling was immersed in this solution as a porous polymer film, and the solution was filled into the pores of the polyimide film. The polyimide film taken out from the container was transferred onto a smooth PTFE film, and an electron beam with an acceleration voltage of 200 kV and a dose of 50 kGy was irradiated using an electron beam irradiation apparatus (EC250 / 15 / 180L manufactured by Iwasaki Electric Co., Ltd.). The liquid mixed solution filled in the pores of the polyimide film by electron beam irradiation was fixed.

  The polyimide film after electron beam irradiation was transferred to a methanol / water mixed solution (equal volume mixing) heated to 60 ° C., and both surfaces thereof were scrubbed with a sponge to remove the filler near the surface. The washed membrane was once naturally dried.

  When the washed film was observed with a scanning electron microscope, a large number of holes having an average diameter of 0.1 μm were observed from the surface to a depth of about 1 μm.

  Next, 28.0 g of methacryloyloxyethyl phosphate (trade name P-1M, manufactured by Kyoeisha Chemical Co., Ltd.), 9.2 g of acryloylmorpholine, and 0.7 g of methylenebisacrylamide were mixed in another plastic container, A mixed solution was prepared. A membrane which was washed and naturally dried was immersed in this solution. This film was taken out from the container, transferred onto a PTFE film, and irradiated with an electron beam having an acceleration voltage of 150 kV and a dose of 30 kGy. The liquid mixture adhering to the vicinity of the surface of the polyimide film by electron beam irradiation was fixed in the form of a film to obtain a solid polymer electrolyte membrane (hereinafter referred to as PEM-1) of this example. The film thickness of PEM-1 was 29 μm.

  The ratio of the number of proton conductive groups of the first proton conductive component present in the solid polymer electrolyte membrane to the number of proton conductive groups of the second proton conductive component is determined by the respective proton conductive groups in the membrane. Comparison was made by obtaining the abundance ratio of.

First, it was assumed that the specific gravity of the first proton conducting component precursor and the second proton conducting component precursor were the same, and that there was no volume change due to chemical bonding after electron beam irradiation. Then, the number of proton conductive groups in the membrane can be multiplied by "the number of proton conductive groups in the proton conductive component precursor in a unit volume" multiplied by "the volume in which the proton conductive component exists in the solid polymer electrolyte membrane". Can be obtained. When the ratio of the number of proton conductive groups of the first proton conductive component in the membrane to the number of proton conductive groups of the second proton conductive component is taken, the following equation is obtained.
(Number of functional groups per unit volume of the proton conducting component in the first proton conducting component precursor × approximate thickness of the first proton conducting component)
/ (Number of functional groups per unit volume of proton conduction component in second proton conduction component precursor × approximate thickness of second proton conduction component)
= The ratio of the number of proton conductive groups of the first proton conductive component to the number of proton conductive groups of the second proton conductive component in the solid polymer electrolyte membrane. The proton conducting component, which is the sum of the thickness of the proton conducting component present outside and the thickness of the proton conducting component present in the pores of the porous polymer membrane multiplied by the average porosity. Approximate value of film thickness. The approximate film thickness of Example 1 was determined as follows.

  Subtracting “the thickness of the pores of the membrane observed after cleaning” 1 μm × 2 from “the thickness of the porous polymer membrane” 27 μm, and multiplying by “40% of the average porosity of the membrane before filling” The approximate film thickness of the first proton conducting component was used. “PEM-1 film thickness” 29 μm minus “porous polymer film thickness” 27 μm, and “film pore depth observed after cleaning” 1 μm × 2 “film before filling” The average film thickness multiplied by 40% was added to obtain the approximate thickness of the second proton conducting component.

  When the calculation was performed using the obtained approximate film thickness value, “the number of proton conductive groups of the first proton conductive component and the proton conductive group of the second proton conductive component in the solid polymer electrolyte membrane” The ratio to the number was 7.36.

  From this, it was found that more proton conductive groups of the first proton conductive component exist in the solid polymer electrolyte membrane.

(Example 2)
A solid polymer electrolyte membrane was produced in the same manner as in Example 1 except that dimethacloyloxyethyl phosphate was used as the second proton conducting component and the following points.

  First, when the acid dissociation degree of dimethacloyloxyethyl phosphate was measured in the same manner as in Example 1, the number of dissociated protons per proton conductive group was 0.18.

  In the same manner as in Example 1, a porous polyimide film having a sulfonic acid group-containing component fixed by electron beam irradiation was produced. The polyimide film after electron beam irradiation was immersed in room temperature ion-exchanged water, and both surfaces thereof were scrubbed with a sponge to remove the filler near the surface. The washed membrane was once naturally dried.

  When the film which had been washed and dried naturally was observed with a scanning electron microscope, many pores having an average diameter of 0.1 μm were observed from the surface to a depth of about 0.5 μm.

  Next, 28.0 g of dimethacryloyloxyethyl phosphate (trade name P-2M, manufactured by Kyoeisha Chemical Co., Ltd.) and 9.2 g of acryloylmorpholine were mixed in another plastic container to prepare a mixed solution containing a phosphate group. The washed membrane was immersed again in this solution. This film was taken out from the container, transferred onto a PTFE film, and irradiated with an electron beam having an acceleration voltage of 150 kV and a dose of 30 kGy. The liquid mixture adhering to the vicinity of the surface of the polyimide film by the electron beam irradiation was fixed in the form of a film to obtain a solid polymer electrolyte membrane (hereinafter referred to as PEM-2) of this example.

  The film thickness of PEM-2 was 30 μm.

  Using the same method as in Example 1, the number of proton conductive groups of the first and second proton conductive components present in the solid polymer electrolyte membrane was compared. The ratio between the number of proton conductive groups of the first proton conductive component and the number of proton conductive groups of the second proton conductive component in the solid polymer electrolyte membrane was 7.42. From this, it was found that more proton conductive groups of the first proton conductive component exist in the solid polymer electrolyte membrane.

(Example 3)
A solid polymer electrolyte membrane was produced in the same manner as in Example 1 except that the second proton conducting component was provided only on one side of the porous polymer membrane and the following treatment was performed accordingly.

  In the same manner as in Example 1, a porous polyimide film having a sulfonic acid group-containing component fixed by electron beam irradiation was produced. The polyimide film after the electron beam irradiation was immersed in a methanol / water mixed solution heated to 60 ° C., and only one surface of the polyimide film was scrubbed with a sponge to remove the filler near the surface. The washed membrane was once naturally dried.

  When the washed film was observed with a scanning electron microscope, a large number of holes having an average diameter of 0.1 μm were observed from the scrubbed surface to a depth of about 1 μm.

Next, 28.0 g of dimethacryloyloxyethyl phosphate and 4.6 g of acryloylmorpholine were mixed in another container to prepare a mixed solution containing phosphate groups. The washed membrane was fixed on a PTFE film, and the phosphate group-containing solution was applied only to the scrubbed surface by the doctor blade method. By irradiating this polyimide film with an electron beam with an acceleration voltage of 150 kV and a dose of 30 kGy, the liquid mixture adhering to the vicinity of the surface is fixed in the form of a film, and the solid polymer electrolyte membrane (hereinafter referred to as PEM-3) of this example. )
The film thickness of PEM-3 was 30 μm.

  Using the same method as in Example 1, the number of proton conductive groups of the first and second proton conductive components present in the solid polymer electrolyte membrane was compared. The ratio of the number of proton conductive groups of the first proton conductive component and the number of proton conductive groups of the second proton conductive component in the solid polymer electrolyte membrane was 5.42. From this, it was found that more proton conductive groups of the first proton conductive component exist in the solid polymer electrolyte membrane.

(Comparative Example 1)
For comparison with Examples 1 and 3, a porous filled polyimide membrane having only the first proton conducting component, which is an intermediate state of the solid polymer electrolyte membrane in Example 1, was prepared.

  That is, in the same manner as in Example 1, the same porous polyimide film as used in Example 1 was immersed in a sulfonic acid group-containing mixed solution composed of vinyl sulfonic acid, acryloylmorpholine, and methylenebisacrylamide. The polyimide film taken out from the container was irradiated with electron beam irradiation in the same manner as in Example 1 to obtain a comparative solid polymer electrolyte membrane (hereinafter referred to as REF-1).

(Comparative Example 2)
Acrylamide methylpropyl sulfonic acid, methylene-bis-acrylamide and 2,2′-azobis (2-amidinopropane) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) in a weight ratio of 50: 30: 1 A solution was prepared by dissolving at a ratio. The same porous polyimide film as used in Example 1 was immersed in this solution, and then the porous polyimide film was taken out and sandwiched between glass plates. As it was, it was left to stand in a dryer at 50 ° C. for 12 hours to carry out heat polymerization. This was repeated three times to fill the inside of the porous polymer membrane with the polymer. Finally, the excess polymer adhering to the surface of the membrane with a weak force was removed with pure water to smooth the membrane. Thus, a comparative solid polymer electrolyte membrane (hereinafter referred to as REF-2) was obtained.

(Comparative Example 3)
A solid polymer electrolyte membrane was produced in the same manner as in Example 1 except that instead of the second proton conducting component, a polyvinyl alcohol membrane having no proton conductivity was provided and the following treatment was performed accordingly. .

  In the same manner as in Example 1, a porous polyimide film having a sulfonic acid group-containing component fixed by electron beam irradiation was produced. Further, the membrane surface was washed and dried in the same manner as in Example 1.

  Next, a 1% by weight aqueous solution of polyvinyl alcohol (manufactured by Kishida Chemical Co., Ltd., polymerization degree 2000, saponification degree 78-82 mol%) was prepared in another plastic container. The washed membrane was immersed in this solution. The membrane was taken out from the container, transferred onto a PTFE film, and naturally dried at room temperature. Thus, a comparative solid polymer electrolyte membrane (hereinafter referred to as REF-3) was obtained.

(Measurement of proton conductivity)
The solid polymer electrolyte membranes obtained in each Example and each Comparative Example were cut into a width of 2 mm and a length of 3 cm, and platinum electrodes provided at an interval of 1 cm were adhered to both surfaces. This electrode was connected to an impedance analyzer (manufactured by Solartron, SI-1260), and impedance measurement was performed from a frequency of 10 MHz to 1 Hz in an environment of a temperature of 50 ° C. and a relative humidity of 90%. The conductivity was calculated from the diameter of the semicircle appearing in the Cole-Cole plot. Table 1 shows the results.

(Measurement of methanol permeability)
The solid polymer electrolyte membrane obtained in each example and each comparative example was sandwiched between glass cells, and a permeation test was performed at 25 ° C. One cell containing the electrolyte membrane was filled with a 50 wt% aqueous methanol solution, and the other cell was filled with the same volume of ion-exchanged water. The methanol permeation coefficient was calculated from the permeation rate obtained by measuring the amount of methanol penetrating into the ion-exchanged water side with a methanol concentration meter (manufactured by Kyoto Electronics Industry Co., Ltd., MCM-600) over time. The lower the permeability coefficient, the more difficult it is for methanol to permeate through the electrolyte membrane.

(Production example and output measurement of membrane electrode assembly and polymer electrolyte fuel cell)
A membrane electrode assembly and a polymer electrolyte fuel cell having a configuration as schematically shown in FIG. 1 were prepared, and the polymer electrolyte membrane for comparison with the present invention was evaluated.

  1 g of platinum-ruthenium catalyst (“TEC90110” manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and 5 g of 5 wt% Nafion solution (manufactured by Aldrich) are mixed well as a precursor paste of the catalyst-supporting conductive material constituting the anode side catalyst layer. A paste was prepared. As a precursor paste of the catalyst-supporting conductive material constituting the cathode-side catalyst layer, 1 g of platinum catalyst (“AY-1020” manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and 5 g of 5 wt% Nafion solution (manufactured by Aldrich) are sufficiently used. A mixed paste was prepared.

Each of these pastes was applied to carbon paper (“TGP-H-060” manufactured by Toray Industries, Inc., 200 μm thick) so as to be ² mg / cm ^{2 in} terms of metal catalyst, and then dried to form a diffusion layer with an anode side catalyst layer and A diffusion layer with a cathode catalyst layer was formed.

The solid polymer electrolyte membranes obtained in each example and each comparative example were sandwiched between a diffusion layer with an anode side catalyst layer and a diffusion layer with a cathode side catalyst layer, respectively, and subjected to hot press treatment at 100 ° C. and 2 kN to form membrane electrodes A joined body was obtained.
The membrane electrode assembly was attached to a fuel cell (Demiconductor Chemistry, DFC-012, single cell, catalyst layer area 10 cm ² ) to obtain solid polymer fuel cells for this example and for comparison.
The obtained polymer electrolyte fuel cell is supplied with 50 wt% methanol as the fuel on the anode side, and is supplied with normal pressure air on the cathode side, and generates electricity while keeping the whole cell at 50 ° C. It was. For the output measurement, a fuel cell test system (manufactured by Scribner, 890B) was used to read the maximum output value when the current value was changed. Table 1 shows the maximum output value for each battery cell.

  The solid polymer electrolyte membrane of each example showed high proton conductivity and a small methanol permeability coefficient despite using a high concentration methanol fuel. As a result, the fuel cell using the solid polymer electrolyte membrane of each example showed a large output value. On the other hand, although REF-1 and REF-2 of the comparative examples are excellent in proton conductivity, the output of the fuel cell using them was low because of the large amount of methanol permeation compared to the examples. . REF-3 has a very low proton conductivity because it has a layer that does not exhibit proton conductivity, although the permeation of methanol is suppressed. Therefore, the output of the fuel cell using REF-3 was extremely low.

DESCRIPTION OF SYMBOLS 1 Membrane electrode assembly 2 Anode 3 Cathode 101 Solid polymer electrolyte membrane 102 Catalyst layer 103 Diffusion layer

Claims (10)

A solid polymer electrolyte membrane having at least a porous polymer membrane and a proton conducting component containing a proton conducting group,
As the proton conduction component, it has a first proton conduction component and a second proton conduction component having a lower acid dissociation degree than the first proton conduction component,
The second proton conducting component is present so as to close the pores of the porous polymer membrane in the membrane surface direction of the porous polymer membrane,
The number of proton conductive groups of the first proton conductive component present in the solid polymer electrolyte membrane is the number of proton conductive groups of the second proton conductive component present in the solid polymer electrolyte membrane. A solid polymer electrolyte membrane characterized in that it is more than the above.   The solid polymer electrolyte membrane according to claim 1, wherein the first proton conducting component is present in pores of the porous polymer membrane.   The solid polymer electrolyte membrane according to claim 1 or 2, wherein the second proton conducting component is present in the vicinity of the surface of at least one membrane surface of the porous polymer membrane.   The solid polymer electrolyte membrane according to claim 3, wherein the second proton conducting component is present in the vicinity of the surfaces of both surfaces of the porous polymer membrane.   5. The solid polymer electrolyte membrane according to claim 1, wherein the second proton conductive component is a polymer compound having at least one of a phosphoric acid group and a phosphonic acid group.   6. The solid polymer electrolyte membrane according to claim 1, wherein the first proton conducting component is a polymer compound having a sulfonic acid group.   A first fixing step of fixing the first proton conducting component in the pores of the porous polymer membrane, and the acid dissociation degree is smaller than that of the first proton conducting component in the vicinity of the surface of the porous polymer membrane; And a second immobilization step of immobilizing a second proton conductive component having a smaller number of proton conductive groups than the number of proton conductive groups of the first proton conductive component. Manufacturing method of electrolyte membrane.   A removal step of removing the first proton conducting component in the vicinity of the surface of the porous polymer membrane to expose the pores on the surface of the porous polymer membrane between the first fixing step and the second fixing step The method for producing a solid polymer electrolyte membrane according to claim 7, comprising:   In at least one of the first fixing step and the second fixing step, the porous polymer membrane and the first proton conducting component precursor or the second proton conducting component precursor are chemically bonded by electron beam irradiation. The method for producing a solid polymer electrolyte membrane according to claim 7 or 8, wherein the solid polymer electrolyte membrane is fixed.   7. A solid polymer fuel cell comprising at least the solid polymer electrolyte membrane according to claim 1 and a pair of electrodes sandwiching the solid polymer electrolyte membrane.