JP2007109634A - Membrane for proton conductive fuel cell capable of operating under nonaqueous and high temperature condition and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane for a proton conductive fuel cell having high proton conductivity in a nonaqueous or low humidity and high temperature condition and being capable of applying to a fuel cell. <P>SOLUTION: A polymer electrolyte membrane for the fuel cell comprises processes for: (1) preparing a precursor (varnish) for a polymer electrolyte membrane by adding and mixing a varnish-like precursor for a polymer electrolyte obtained by mixing 20-200 pts.wt. benzimidazole (B) or 20-200 pts.wt. 1,2,4-triazole (C) to 100 pts.wt. perfluorocarbon sulfonic acid polymer (A) by using a solvent; (2) extending and spreading the varnish in a film state on a substrate; (3) heating to temperature vaporizing solvent and moisture; and (4) peeling off the polymer electrolyte membrane for the fuel cell formed on the substrate from the substrate, if necessary. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a membrane for a proton conductive fuel cell that exhibits excellent proton (hydrogen ion) conductivity under anhydrous and high temperature, and a method for producing the same.

  In recent years, attention has been focused on fuel cells that obtain electric power by reacting clean energy, particularly hydrocarbon raw materials containing hydrogen gas or hydrogen as a fuel, and oxygen gas as an oxidant. The polymer electrolyte fuel cell (PEFC) using such a hydrogen source and oxygen gas is the next generation of powerful energy production because of its clean and environmentally friendly energy production system and high efficiency of energy production. It is attracting attention as a system device, and there is a need to develop a system that uses stable and efficient materials, or a combination of efficient materials as the materials used, such as cells constituting fuel cells and proton conductive polymer membranes. .

  Here, the fuel cell is defined as an electrochemical device that generates electricity and water by causing a chemical reaction between the fuel and the oxidant. A typical fuel supplied to the fuel cell is hydrogen and a typical oxidant supplied to the fuel cell is oxygen (or ambient air). Other fuels or oxidants can be used depending on the operating conditions and type of the fuel cell.

  The characteristics of the fuel cell include that the reaction process is extremely efficient, and in particular, in a fuel cell directly supplied with hydrogen, it is completely pollution-free. Since fuel cells can be easily assembled into stacks of various sizes, a variety of forms have been developed, from small forms to those that can generate power on a relatively wide and large scale. Therefore, it can be used not only for various industrial fields but also for home use, and is expected to develop greatly in the future.

  In addition, the output system of the fuel cell generates an electromotive force by causing a chemical reaction between fuel and oxygen at each electrode interface sharing one electrolyte. For example, in a proton exchange membrane fuel cell, the cell structure includes a proton exchange membrane that not only functions as an electrolyte but also functions as a barrier that prevents mixing of hydrogen and oxygen. One of the commercially available proton exchange membranes is made of a perfluorosulfonic acid polymer material sold by DuPont under the name Nafion (trade name) as will be described later. Not. That is, proton exchange membranes can be purchased from other commercial sources. It should be understood that the proton exchange membrane is positioned between and in contact with the two electrodes that form the anode and cathode of the fuel cell.

  In the case of a PEM type fuel cell, hydrogen gas is introduced into a first electrode (anode), where the hydrogen gas undergoes an electrochemical reaction in the presence of a catalyst to generate electrons and protons. The electrons flow from the first electrode to the second electrode (cathode) through an electrical circuit that couples each of these electrodes. Furthermore, protons flow through the solid polymer electrolyte (proton exchange membrane) to the second electrode (cathode). At the same time, an oxidant such as oxygen gas (or air) is introduced into the second electrode, where the oxidant reacts electrochemically in the presence of the catalyst, and the electrons and protons that have flowed through the electronic circuit. Combined with (which has passed through the proton exchange membrane) to form water. By this reaction, electricity is output.

  As a polymer membrane for a fuel cell that has been conventionally designed, a Nafion (registered trademark of DuPont), which is a kind of perfluorosulfonic acid polymer, is used as described above. PEFCs designed to work with: have been used. However, a fuel cell that can operate at a high temperature and has a higher tolerance for CO poison is required, and a fuel cell that can operate at a high temperature (100 to 200 ° C.) is strongly desired. In other words, PEFCs that can be operated at higher temperatures are expected to improve the tolerance of platinum electrodes for CO, enabling highly efficient and simple thermal management and cogeneration.

  In a fuel cell, the proton conductive membrane serves to carry protons generated at the anode to the cathode side. Proton conducting membranes are therefore key and important in polymer electrolyte fuel cells. To date, several ion exchange membranes such as perfluorinated ionomers and their composites, polymer / low molecular composites, inorganic-organic composites, and the like are known.

However, these electrolyte membranes are unstable at high temperatures, that is, when used at a high temperature of 100 ° C. or higher for a long time, moisture evaporates from the membrane, the water content decreases, the ionic conductivity decreases, and the voltage decreases. As a result, the battery performance deteriorates and the irreversible reaction causes a collapse of the molecular structure, which decreases proton conductivity and makes it unusable. Furthermore, in such a fuel cell, H ₂ may pass through H ₂ without dissociating at the anode (fuel electrode), which may cause problems such as a decrease in electromotive voltage and a decrease in power generation amount. It was.

  Therefore, recently, it is considered that the above problem can be solved if an electrolyte membrane having excellent proton conductivity under anhydrous (or low humidity) and high temperature conditions is obtained. The focus has been on acid-base composite electrolytes for application to mobile PEFCs (Non-Patent Document 1, et al.).

  On the other hand, as disclosed in Patent Document 1, an organic amine material having a tertiary nitrogen atom capable of “quaternization” capable of realizing anhydrous proton conduction is made of a nanoparticulate oxide such as silica and a stable oxide. Proton conductive films that are anhydrous and operate even at high temperatures (190 ° C.) have been obtained by bonding with a binder (such as Teflon).

M.M. Yamada and I.I. Honma: Electrochim. Acta 48 (2003) 2411-2415 JP-T-2005-516345

  Also in the present invention, in response to the above-mentioned demand, excellent proton conductivity is exhibited under conditions of anhydrous (or low humidity) and high temperature (temperature of 10 to 180 ° C. or higher), and hydrogen source fuels such as methanol and methane are directly used. It is an object of the present invention to provide a novel membrane for a proton conductive fuel cell that can also be used for a supplied direct fuel type fuel cell, and a method for producing the membrane.

Therefore, as a result of intensive studies by the present inventors, varnish-like polymer obtained by blending a specific ratio of benzimidazole (hereinafter also abbreviated as Bz) or 1,2,4-triazole to perfluorocarbon sulfonic acid polymer. A membrane that can meet the above requirements by spreading, stretching and heating the composite in layers on a substrate, that is, a membrane for a proton conductive fuel cell that exhibits excellent proton (hydrogen ion) conductivity under anhydrous and high temperature conditions The present invention has been made based on this finding. That is, the configuration is as described in the following items (1) to (6).
(1) 20 parts by weight to 200 parts by weight of benzimidazole (B) or 20 parts by weight to 100 parts by weight of 1,2,4-triazole (C) with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A). A polymer electrolyte membrane for a fuel cell obtained by spreading and stretching a blended precursor for a varnish-like polymer electrolyte membrane on a substrate in a layered form and heating it.
(2) The polymer electrolyte membrane for fuel cells according to (1), wherein the film thickness is 200 μm or less.
(3) The polymer electrolyte membrane for fuel cells according to (1) or (2) above, wherein the membrane itself has a film thickness of 20 μm to 200 μm and the membrane itself is self-supporting.
(4) The polymer electrolyte membrane for fuel cells according to any one of (1) to (3), wherein the specific conductivity is 0.001 (S / cm) or more at a temperature of 80 to 200 degrees.
(5) A method for producing a polymer electrolyte membrane for a fuel cell, comprising the following steps.
1. Using a solvent, 20 to 200 parts by weight of benzimidazole (B) or 20 to 100 parts by weight of 1,2,4-triazole (C) with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing to prepare a precursor for a varnish-like polymer electrolyte membrane;
2. Developing and stretching the varnish into a film on a substrate;
3. A step of heating to a temperature at which the solvent and moisture are volatilized.
(6) A method for producing a polymer electrolyte membrane for a fuel cell, comprising the following steps.
1. Using a solvent, 20 to 200 parts by weight of benzimidazole (B) or 20 to 100 parts by weight of 1,2,4-triazole (C) with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing to prepare a precursor for a varnish-like polymer electrolyte membrane;
2. Developing and stretching the varnish into a film on a substrate;
3. A step of heating to a temperature at which the solvent and moisture are volatilized.
4). The process of peeling the polymer electrolyte membrane for fuel cells formed on the board | substrate from a board | substrate.

The present invention relates to 20 to 200 parts by weight of benzimidazole (B) or 20 to 100 parts by weight of 1,2,4-triazole (C) with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A). The present invention relates to a polymer electrolyte membrane for a fuel cell obtained by spreading and stretching a precursor for a varnish-like polymer electrolyte membrane blended with a layer on a substrate and heating the precursor.
As a result, a novel polymer electrolyte membrane for fuel cells is provided that has proton conductivity without degradation in performance at anhydrous and high temperatures.

The present invention also relates to a method for producing a polymer electrolyte membrane for a fuel cell comprising the following steps.
(1) Using a solvent, benzoimidazole (B) 20 parts by weight to 200 parts by weight or 1,2,4-triazole (C) 20 parts by weight with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing 100 parts by weight to prepare a polymer electrolyte membrane precursor (varnish);
(2) A step of spreading and stretching the varnish into a film on a substrate;
(3) A step of heating to a temperature at which the solvent and moisture are volatilized.
By this process, a substrate with a polymer electrolyte membrane for a fuel cell in which a polymer electrolyte membrane is formed on one surface of the substrate can be easily obtained.

Furthermore, the present invention also relates to a method for producing a polymer electrolyte membrane for a fuel cell comprising the following steps.
(1) Using a solvent, benzoimidazole (B) 20 parts by weight to 200 parts by weight or 1,2,4-triazole (C) 20 parts by weight with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing 100 parts by weight to prepare a polymer electrolyte membrane precursor (varnish);
(2) A step of spreading and stretching the varnish into a film on a substrate;
(3) A step of heating to a temperature at which the solvent and moisture are volatilized.
(4) The process of peeling the polymer electrolyte membrane for fuel cells formed on the board | substrate from a board | substrate.
By this process, a self-supporting polymer electrolyte membrane for fuel cells can be easily obtained.

The polymer electrolyte membrane for fuel cells obtained by the present invention exhibits good proton conductivity of 10 ⁻³ S / cm to 10 ⁻² S / cm even at a high temperature of 100 to 200 ° C. Therefore, it can be applied to a fuel cell that can operate under anhydrous (or low humidity) and high temperature conditions.
In addition, the production method of the present invention makes it possible to easily and inexpensively produce a substrate with a polymer electrolyte membrane for fuel cells or a polymer electrolyte membrane for fuel cells (having self-supporting properties).

  Hereinafter, the present invention will be described in detail with reference to examples and drawings. However, these examples are disclosed for specifically explaining the present invention, and the present invention is not limited to these examples.

As described above, the polymer electrolyte membrane for a fuel cell of the present invention has 20 to 200 parts by weight of benzimidazole (base component; B) with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (acid component; A). Or a varnish-like precursor for a polymer electrolyte membrane (mixed solution) containing 20 parts by weight to 100 parts by weight of 1,2,4-triazole (C) is developed (stretched) in layers on a substrate, This is a polymer electrolyte membrane for a fuel cell obtained by heating (removing the solvent and moisture).
Here, the “perfluorocarbon sulfonic acid polymer” refers to a polymer that includes a C—F bond and does not include a C—H bond in a polymer chain and has a sulfonic acid group (—SO ₃ H). For example, Nafion (registered trademark of DuPont). FIG. 1 shows the chemical structural formula of Nafion, the chemical structural formula of benzimizole (b), and FIG. 6 shows the chemical structural formula of 1,2,4-triazole.
In addition, the “substrate” may be a glass plate, a polyfluorinated ethylene (Teflon) plate, a metal plate or the like on the premise that the obtained polymer electrolyte membrane for fuel cells is peeled off, and is not premised on peeling. A current collector plate (current collector plate having a gas flow path), palladium (hydrogen storage, hydrogenation catalyst) or the like serving as an electrode may be used. In such a case, the thickness of the polymer electrolyte membrane for a fuel cell can be reduced to 50 μm or less.

As described above, the polymer electrolyte membrane for a fuel cell can be produced through the following steps.
(1) Using a solvent, benzoimidazole (B) 20 parts by weight to 200 parts by weight or 1,2,4-triazole (C) 20 parts by weight with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing 100 parts by weight to prepare a polymer electrolyte membrane precursor (varnish);
(2) A step of spreading and stretching the varnish into a film on a substrate;
(3) A step of heating to a temperature at which the solvent and moisture are volatilized.
In addition, you may add the process of peeling the polymer electrolyte membrane for fuel cells from a board | substrate after the said process (3). By doing so, it is possible to obtain a substrate with a polymer electrolyte membrane for a fuel cell in which a polymer electrolyte membrane is formed on one side of the substrate, or a membrane-only polymer electrolyte membrane for a fuel cell having a self-supporting property. You can also get
As the solvent for preparing the mixed solution of the acid component and the base component, a perfluorocarbon sulfonic acid polymer or a solvent capable of dissolving benzimidazole or 1,2,4-triazole can be used. In the case of Nafion (a kind of perfluorocarbon sulfonic acid polymer), in addition to the solvent contained in the Nafion liquid (commercial product) (removal is not necessary), a solvent such as isopropanol can be used to dilute it. Ethanol, methanol, isopropanol, etc. can be used as a solvent for benzimidazole or 1,2,4-triazole.

The blending amount of benzimidazole (base component; B) with respect to the perfluorocarbon sulfonic acid polymer (acid component; A) is 20 to 200 parts by weight (solid weight basis) with respect to 100 parts by weight of the acid component (nonvolatile content basis). ), Preferably 50 to 200 parts by weight, more preferably 100 to 200 parts by weight. When the base component is less than 20 parts by weight, sufficient specific conductivity (specific proton conductivity; specific ionic conductivity; specific resistance; (S / cm), etc.) is sufficient on the high temperature (160 to 200 ° C.) side. However, when the amount exceeds 200 parts by weight, it is difficult to form a homogeneous film.
The blending amount of 1,2,4-triazole (base component; C) with respect to the perfluorocarbon sulfonic acid polymer (acid component; A) is 20 parts by weight to 100 parts by weight with respect to 100 parts by weight of the acid component (non-volatile basis). Parts (solid weight basis), preferably 100 parts by weight. When the basic component is less than 100 parts by weight, the specific conductivity is not sufficiently improved on the high temperature (80 to 160 ° C.) side, and when it exceeds 100 parts by weight, a hard film is formed.

  The thickness of the polymer electrolyte membrane for fuel cells is preferably 200 μm or less. The lower limit of the film thickness may be very thin as long as it is not damaged, and may be on the order of nm. If it exceeds 200 μm, the resistance of the electrolyte membrane increases, which tends to be undesirable. In addition, the thickness of the polymer electrolyte membrane for fuel cells on the premise of peeling from the substrate is preferably 20 μm to 200 μm in order to provide self-supporting properties, and the polymer for fuel cells not premised on peeling from the substrate. The thickness of the electrolyte membrane can be reduced to 50 μm or less because self-supporting properties are not required. The lower limit may be extremely thin as long as it is not damaged, and may be on the order of nm.

  In addition, in order that the polymer electrolyte membrane for a fuel cell of the present invention can be operated on a high temperature (about 100 to 200 ° C.) side for a fuel cell, the specific conductivity (S / cm) is 100 to 100 ° C. It is preferably 0.001 (S / cm) or more at 200 degrees, more preferably 0.01 (S / cm) or more, and even higher the better.

Example 1;
(1) Preparation of polymer electrolyte membrane for fuel cell One Nafion solution (5% solution) as a raw material was manufactured by Electrochem Co. , Ltd., Ltd. The one purchased from is used. Another raw material benzimidazole (C ₇ H ₆ N ₂ ; MW = 118.14) is Alfa Co. , Ltd., Ltd. The one purchased from (solid) was used.
A precursor for a polymer electrolyte membrane (varnish) containing Nafion and benzimidazole in a weight ratio of 5: 1 is 3 g of Nafion liquid (5% solution) (containing 0.15 g of Nafion) and 15 ml of isopropanol (for dilution). A solution of 0.03 g of benzimidazole (dissolved in 3 ml of isopropanol) was added to a mixed solution (hereinafter referred to as Nafion diluted solution), and both were mixed to prepare. A precursor for a polymer electrolyte membrane (varnish) containing Nafion and benzimidazole in a weight ratio of 5: 5 was dissolved in 3 g of Nafion diluted solution (containing 0.15 g of Nafion) in 0.15 g of benzimidazole (3 ml of isopropanol). ) Solution was added and both were prepared. A precursor for a polymer electrolyte membrane (varnish) containing Nafion and benzimidazole at a weight ratio of 5:10 was dissolved in 3 g of Nafion diluted solution (containing 0.15 g of Nafion) in 0.3 g of benzimidazole (3 ml of isopropanol). ) Solution was added and both were prepared. As a comparison (control), the above Nafion diluted solution (no benzimidazole added) was used.
A predetermined amount of the obtained precursor (varnish) for polymer electrolyte membrane was poured into a petri dish and heat-treated at 60 ° C. for 1 day in a dry state to form a membrane (a homogeneous membrane was obtained). Further, heat treatment was carried out at 100 ° C. for 1 day to completely remove the residual solvent and water molecules, thereby obtaining a polymer electrolyte membrane for fuel cells of the present invention (also referred to as a composite membrane; white opaque or white translucent). Although the thickness of the obtained film was dependent on the volume poured into the Petri dish, it was in the range of 53-154 μm. In the present specification, “%” means weight (wt)% unless otherwise specified.

(2) Evaluation of the obtained composite film The molecular structure of the composite film and the comparative product was examined by IR analysis with a diamond attenuated total reflection prism having a resolution of 4 cm ⁻¹ . FIG. 2 shows the result. Recast (recast) Nafion film: For (Bz in (b) 0% comparative product), the absorption of water ^{[ν O-H (3458cm -1} ), δ O-H (1630cm -1)], and _{H 3} O ⁺ (1720 cm ⁻¹ ) is seen. This RSO ₃ coexisting decomposed with liberation of water ^- bound to suggest that RSO 3 _H occurs with the progress of dehydration in the membrane.
On the other hand, the Nafion-Bz composite film has (in each case) absorption peaks of Nafion and Bz. N—H (3100 cm ⁻¹ ), C—N (1620 cm ⁻¹ ), C—C (1454 cm ⁻¹ ) and N—H (748 cm ⁻¹ ) bonds of Bz in the Nafion-Bz composite film. The Nafion-Bz composite membrane does not show water absorption like O—H or H ₃ O ⁺ . However, SO ₃ deprotonated ^- peak remains (after the generation Nafion -Bz composite also). Therefore, the protons migrate from the acid residue to the Bz base site, causing benzimidazole protonation and the formation of sulfonated anions, which cause the Coulomb attractive force to form ion channels in these molecules. It is thought to let you.

  The thermal stability of the composite membrane and the comparative membrane was determined by thermogravimetric analysis TG / DTA6200 (SII Co., Ltd.). The sample was heated from room temperature to 500 ° C. in a nitrogen atmosphere at a rate of 5 ° C./min. FIG. 3 shows the TG results of the composite film and the comparative film, and FIG. 4 shows the DTA results of the composite film and the comparative film. The weight loss below 100 ° C. in the recast Nafion membrane (i) is related to the desorption of water bound to the sulfonic acid groups and the desorption of water in the air absorbed by the composite membrane. In addition, the weight loss of the recast Nafion membrane (i) decreased sharply between 320 ° C. and 390 ° C., which was based on the decomposition of the sulfonic acid groups prior to the complete decomposition of the polymer. is there. On the other hand, the thermal behavior of the composite membrane ((ii) to (iv)) is very similar to the recast Nafion membrane (i). In the composite membrane (ii) of Nafion 5 wt% -1 wt% Bz, The recast Nafion membrane (i) is slightly shifted to the right. Further, in the composite film (iv) of Nafion 5 wt% -10 wt% Bz, a large weight loss is observed between 200 ° C. and 300 ° C., which is the melting of Bz in the film (160-170 ° C. from the endothermic peak). Based on

The proton conductivity of the composite membrane and the comparative membrane was measured by a two-terminal impedance spectrometer (SI 1260 Impedance Analyzer, Solatron). The resulting film two ring gold plate blocking electrodes: sandwiched between (area about 0.2 cm ^2). For measuring impedance, the frequency range was 1 Hz to 1 MHz, and the peak-to-peak voltage was 100 mV. Proton conductivity was measured by raising the temperature to 200 ° C. in a dry (non-wet) nitrogen stream. FIG. 4 is a graph plotting the temperature vs. specific conductivity of the composite film and the comparative film (Bz: 0%) (Arrhenius plot not shown). Proton conductivity generally follows Arrhenius law, which indicates that proton conductivity is governed by a thermal activation process. Comparison films sufficiently humidified conditions: specific conductivity of (Bz 0%) is, 0.1 S / cm but is well known to be about (<90 ℃), in anhydrous conditions 10 ^{- It is} about ⁶ S / cm and has little temperature dependence. On the other hand, the specific conductivity of the Nafion-Bz composite film increases as the temperature is increased, and 3.6 × 10 ⁻³ S / cm (temperature: 180 ° C.) in the composite film (iii) of Nafion 5 wt% -5 wt% Bz. The composite film (iv) of Nafion 5 wt% -10 wt% Bz showed 1.4 × 10 ⁻² S / cm (temperature: 160 ° C.). The activation energies of each of the Nafion 5 wt% -1 wt% Bz and Nafion 5 wt% -5 wt% Bz composite films are 1.4 eV, and the Nafion 5 wt% -10 wt% Bz composite films are 2.4 eV, respectively. It was higher than the two. This may be because the protonated protons are based on differences in proton conduction pathways that maintain a special position of the Nafion sulfone group and the Bz base site.

Example 2;
(1) Preparation of polymer electrolyte membrane for fuel cell One Nafion solution (5% solution) as a raw material was manufactured by Electrochem Co. , Ltd., Ltd. The one purchased from is used. Another raw material 1,2,4-triazole (C ₂ H ₃ N ₃ ; MW = 69.07) is available from Aldrich Co. , Ltd., Ltd. The one purchased from (solid) was used.
A precursor for a polymer electrolyte membrane (varnish) containing Nafion and 1,2,4-triazole at a weight ratio of 5: 1 was added to 3 g of Nafion liquid (5% solution) (containing 0.15 g of Nafion). A solution was prepared by adding 0.03 g of 1,2,4-triazole (dissolved in 0.4 ml of isopropanol) and mixing both. A precursor for a polymer electrolyte membrane (varnish) containing Nafion and 1,2,4-triazole in a weight ratio of 5: 2 was added to 3 g of Nafion diluted solution (containing 0.15 g of Nafion), 1,2,4-triazole. A solution of 0.06 g (dissolved in 0.4 ml of isopropanol and 0.2 ml of methanol) was added, and both were mixed to prepare. A precursor for a polymer electrolyte membrane (varnish) containing Nafion and 1,2,4-triazole at a weight ratio of 5: 5 was added to 3 g of Nafion diluted solution (containing 0.15 g of Nafion), 1,2,4-triazole. A 0.15 g solution (dissolved in 0.4 ml of isopropanol and 0.2 ml of methanol) was added, and both were mixed to prepare.
A predetermined amount of the obtained precursor for the polymer electrolyte membrane (varnish) is poured into a Teflon dish and heat-treated at 60 ° C. for 1 day in a dry state to form a membrane (a homogeneous membrane was obtained). A polymer electrolyte membrane for a fuel cell of the invention (also referred to as a composite membrane; transparent, white opaque, or white translucent) was obtained. The thickness of the obtained film was in the range of 70 to 110 μm, although it depended on the volume poured into the Teflon dish.
(2) Evaluation of the obtained composite film

The proton conductivity of the composite membrane and the comparative membrane was measured in the same manner as described in Example 1. FIG. 7 is a graph plotting the temperature vs. specific conductivity of the composite film (Arrhenius plot not shown). The specific conductivity of Nafion-1,2,4-triazole composite membrane increases with increasing temperature, and 2.3 × 10 ⁻² S for Nafion 5 wt% -5 wt% 1,2,4-triazole composite membrane (iii). / Cm (temperature: 160 ° C.). The activation energy of each of Nafion 5 wt% -1 wt% 1,2,4-triazole and Nafion 5 wt% -2 wt% 1,2,4-triazole composite film is 0.9 eV, and Nafion 5 wt% -5 wt%. % 1,2,4-triazole composite film was 0.3 eV. This may be because the special position of the base site relative to the sulfone group of Nafion is based on an increase in carrier concentration and mobility by increasing the number of protons of 1,2,4-triazole. Proton conductivity generally follows Arrhenius law, which indicates that proton conductivity is governed by a thermal activation process. It is well known that the specific conductivity of the Nafion film under sufficiently humidified conditions is about 0.1 S / cm (<90 ° C., 0.02 eV). The protons of the Nafion membrane under humidified conditions move with water at a very low energy within the membrane cluster structure (proton conduction channel) and show high conductivity. On the other hand, the proton under the non-humidified condition cannot have a conduction path for carrying the proton as in the humidified condition, and the conductivity becomes very low. However, by introducing an organic monomer such as Bz or 1,2,4-triazole into the acid nanocluster structure to create a proton conduction path, it is possible to realize a conductor with high proton conductivity even without humidification. (See FIG. 8).

Industrial applicability

  Fuel cells will be increasingly required in the future, and are expected to develop greatly. Along with this, the use conditions are required to withstand higher temperatures and longer use in the future in order to eliminate platinum CO poison. Conventional proton conductive fuel cell membranes are practically up to about 80 ° C., and cannot meet the above requirements. A polymer membrane for anhydrous / high-temperature fuel cells that can operate at high temperatures has also been proposed, but it has only just begun and has not been sufficiently reliable. According to the present invention, a durable proton conductive fuel cell membrane that can operate for a long time in an anhydrous / high temperature environment can be obtained inexpensively and easily from a known material, and its significance is extremely large. . In the future, it will be used in various fuel cell designs and is expected to contribute to providing high-power fuel cells at low cost.

(A) Molecular structure of Nafion, (b) Molecular structure of benzimidazole (Bz). (A) pure Bz, (b) recast Nafion membrane (Bz: 0%), (c) Nafion 5 wt% -1 wt% Bz composite membrane, (d) Nafion 5 wt% -5 wt% Bz composite membrane, (E) IR spectrum of each of Nafion 5 wt% -10 wt% Bz composite film. (I) Recast Nafion membrane (Bz: 0%), (ii) Nafion 5 wt% -1 wt% Bz composite membrane, (iii) Nafion 5 wt% -5 wt% Bz composite membrane, (iv) Nafion 5 wt% TG for each of the 10 wt% Bz composite films. (I) Recast Nafion membrane (Bz: 0%), (ii) Nafion 5 wt% -1 wt% Bz composite membrane, (iii) Nafion 5 wt% -5 wt% Bz composite membrane, (iv) Nafion 5 wt% DTA of each of the 10 wt% Bz composite films. (I) Recast Nafion membrane (Bz: 0%), (ii) Nafion 5 wt% -1 wt% Bz composite membrane, (iii) Nafion 5 wt% -5 wt% Bz composite membrane, (iv) Nafion 5 wt% A graph plotting the temperature vs. conductivity of a composite film of −10 wt% Bz. Molecular structure of 1,2,4-triazole. (I) Nafion 5 wt% -1 wt% 1,2,4-triazole composite film, (ii) Nafion 5 wt% -2 wt% 1,2,4-triazole composite film, (iii) Nafion 5 wt% -5 wt% 1 The graph which plotted the temperature vs. conductivity of a 2,4-triazole composite film. Non-humidified proton conductor model with proton conduction path introduced into nanocluster structure, using Nafion polymer as nanocluster and Bz or 1,2,4-triazole as non-humidified proton conduction path.

Claims (6)

  Varnish in which 20 parts by weight to 200 parts by weight of benzimidazole (B) or 20 parts by weight to 100 parts by weight of 1,2,4-triazole (C) is blended with 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A). A polymer electrolyte membrane for a fuel cell obtained by spreading and stretching a precursor for a polymer electrolyte membrane in layers on a substrate and heating the precursor.   The polymer electrolyte membrane for fuel cells according to claim 1, wherein the thickness is 200 μm or less.   The polymer electrolyte membrane for a fuel cell according to claim 1 or 2, wherein the membrane has a thickness of 20 µm to 200 µm and the membrane itself has a self-supporting property.   The polymer electrolyte membrane for fuel cells according to any one of claims 1 to 3, wherein the specific conductivity is 0.001 (S / cm) or more at a temperature of 80 to 200 degrees. A method for producing a polymer electrolyte membrane for a fuel cell, comprising the following steps.
(1) Using a solvent, benzoimidazole (B) 20 parts by weight to 200 parts by weight or 1,2,4-triazole (C) 20 parts by weight with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing 100 parts by weight to prepare a varnish-like polymer electrolyte membrane precursor;
(2) A step of spreading and stretching the varnish into a film on a substrate;
(3) A step of heating to a temperature at which the solvent and moisture are volatilized. A method for producing a polymer electrolyte membrane for a fuel cell, comprising the following steps.
(1) Using a solvent, benzoimidazole (B) 20 parts by weight to 200 parts by weight or 1,2,4-triazole (C) 20 parts by weight with respect to 100 parts by weight of the perfluorocarbon sulfonic acid polymer (A) Adding and mixing a varnish-shaped polymer electrolyte precursor containing 100 parts by weight to prepare a varnish-shaped polymer electrolyte membrane precursor;
(2) A step of spreading and stretching the varnish into a film on a substrate;
(3) A step of heating to a temperature at which the solvent and moisture are volatilized.
(4) Peeling the polymer electrolyte membrane for fuel cells formed on the substrate from the substrate