JP2007200794A - Acid-base composite electrolyte, its manufacturing method, and membrane electrode assembly and fuel cell containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte which has both of high proton conductivity and water resistance under a low-humidity atmosphere. <P>SOLUTION: In an acid-base composite electrolyte film 1 which comprises an acid polymer 2 having an acid functional group 3 and a basic polymer 4 having a basic functional group 5, the acid polymer 2 and basic polymer 4 are combined at a molecular level, and the acid density is 3.0×10<SP>-3</SP>mol/g or more, while the basic density is 1.0×10<SP>-3</SP>mol/g or more. Either one of the acid polymer 2 or basic polymer 4 has a number average molecular weight of 10,000 or more, while the other has that of 200 or more and 3,000 or less. This invention includes a membrane electrode assembly and a fuel cell using such an electrolyte film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an acid-base composite electrolyte used for fuel cells and other electrochemical cells, a method for producing the same, a membrane electrode assembly including an acid-base composite electrolyte, and a fuel cell.

  A fuel cell that uses a polymer electrolyte as an electrolyte is a polymer electrolyte membrane comprising an anode electrode that supplies fuel, a cathode electrode that supplies an oxygen-containing gas such as air, and a polymer electrolyte sandwiched between these electrodes ( Hereinafter referred to as an electrolyte membrane). Currently, perfluorosulfonic acid electrolyte membranes represented by Nafion (registered trademark) manufactured by Du Pont are widely used as electrolyte membranes. A perfluorosulfonic acid electrolyte membrane requires water in its proton conduction mechanism. Therefore, it is necessary to perform moisture management so that the moisture content of the electrolyte membrane does not decrease during fuel cell power generation.

  On the other hand, as a method for improving the output of the fuel cell, a method of operating the fuel cell at a high temperature of 100 ° C. or higher has been studied. When operated at a high temperature, it is expected that the voltage is improved due to reduction of catalyst poisoning and reduction of electrode reaction resistance. However, perfluorosulfonic acid-based electrolyte membranes currently used are difficult to use because the conductivity is remarkably lowered in the temperature range of 100 ° C. or higher and the heat resistance of the electrolyte membrane is also problematic. .

As an electrolyte membrane that can be used in a temperature range of 100 ° C. to 200 ° C., there is polybenzimidazole (hereinafter also referred to as PBI). By doping PBI with a strong acid such as phosphoric acid, proton conduction has been confirmed even in a high temperature region of 100 ° C to 160 ° C. The phosphoric acid-doped PBI membrane exhibits a high proton conductivity of 10 ⁻² S / cm or higher even in a low humidity atmosphere, so that moisture management is unnecessary, and the fuel cell can be operated with a simple system (for example, Patent Document 1 and Patent Document 2).

  However, when the fuel cell is operated, water is generated at the cathode. However, when the generated water comes into contact with the phosphoric acid-doped PBI membrane, the doped phosphoric acid is eluted into the water and the conductivity is lowered (water resistance). There is a problem related to sex. As a countermeasure to alleviate this problem, a method of combining a PBI polymer with an acid polymer has been proposed (for example, see Patent Document 3).

In addition, as an example of a polymer electrolyte excellent in ion conductivity and durability, a method of combining an acid and a base polymer has been proposed (see, for example, Patent Document 4).
Japanese National Patent Publication No. 11-503262 JP 2000-38472 A JP 2004-55284 A JP 2003-22824 A

  However, although the electrolyte obtained by the method described in Patent Document 3 is confirmed to have improved water resistance, both the acid and base are polymers, so the mobility of the molecular chain is low and the proton conductivity is low. The problem is considered. Furthermore, in order to suppress the elution of the doped acid into water, increasing the molecular weight of the doped acid can be considered as a countermeasure. However, increasing the molecular weight decreases the mobility of the molecule and reduces the conductivity. There is a problem that will be reduced.

  Moreover, in the manufacturing method described in Patent Document 2, since the product is in the form of powder, in order to use it as an electrolyte membrane, a process such as pressurization to form a pellet is required, which complicates the manufacturing process. There is.

  In addition, in the method described in Patent Document 4, an acid and a base polymer are combined, but good proton conductivity in a low humidity atmosphere cannot be obtained simply by mixing an acid and a base polymer.

  The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a polymer electrolyte having both high proton conductivity in a low-humidity atmosphere and durability against water.

In order to solve the conventional problems, the polymer electrolyte of the present invention is an acid-base composite electrolyte comprising an acidic polymer having an acidic functional group and a basic polymer having a basic functional group,
An acidic polymer and a basic polymer are combined at the molecular level,
The density of the acidic functional group is 3.0 × 10 ⁻³ mol / g or more, the density of the basic functional group is 1.0 × 10 ⁻³ mol / g or more,
One of the acidic polymer and the basic polymer has a number average molecular weight of 10,000 or more, and the other has a number average molecular weight of 200 or more and 3000 or less. The acid-base composite electrolyte having this configuration has proton conductivity even at a high temperature of 100 ° C. or higher, and can suppress elution of the doped acid or base into water even when contacted with water.

The method for producing an acid-base composite electrolyte of the present invention includes a first step of containing a monomer of an acidic compound in an electrolyte composed of a basic polymer,
And a second step of polymerizing the acidic monomer in the electrolyte obtained in the first step. The first step may be a step of containing a basic monomer in an electrolyte composed of an acidic polymer, and the second step may be a step of polymerizing a basic monomer in the electrolyte. By these production methods, an acid-base composite electrolyte can be obtained directly after the polymerization reaction without any special processing.

  The membrane electrode assembly of the present invention is a membrane electrode assembly in which an electrolyte membrane and two electrodes (an anode electrode and a cathode electrode) sandwiching the electrolyte membrane are joined, and at least one of the electrolyte membrane and the electrode This is characterized by containing the acid-base composite electrolyte of the present invention. Since the membrane electrode assembly of this configuration contains the electrolyte of the present invention, it has proton conductivity even at a high temperature of 100 ° C. or higher, and even when it comes into contact with water, the doped acid or base into water Elution can be suppressed.

  The fuel cell of the present invention is a fuel cell including an electrolyte membrane, an anode electrode and a cathode electrode sandwiching the electrolyte membrane, and the electrolyte membrane includes the acid-base composite electrolyte of the present invention. . Since the fuel cell having this configuration includes the electrolyte of the present invention, it is possible to generate power even at a high temperature of 100 ° C. or higher.

  The acid-base composite electrolyte of the present invention has high proton conductivity in a low humidity atmosphere. Moreover, it has the durability with respect to water also in the area | region where liquid water of 100 degrees C or less exists. The fuel cell using this electrolyte does not require a humidifier, and the entire system can be miniaturized, and power can be generated in a high temperature region of 100 ° C. or higher where no liquid water is present. For this reason, the use of this electrolyte achieves downsizing and high output of the entire system.

  The electrolyte according to the present invention is applicable not only to fuel cells, but also to various devices using ion conductors such as primary batteries, secondary batteries, capacitors, sensors, electrochromic devices, electrolysis cells, etc. Can bring about improvements.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic view of an acid-base composite electrolyte formed in a film shape in the present embodiment, and FIGS. 2 and 3 are schematic views of the inside of the acid-base composite electrolyte membrane in the present embodiment. 2 and 3 are schematic views of the acid-base composite electrolyte in the inside 1a of the acid-base composite electrolyte membrane 1. FIG.

  In FIG. 2, an acidic polymer 2 having an acidic functional group 3 and a basic polymer 4 having a basic functional group 5 are complexed at a molecular level. The number average molecular weight of the acidic polymer 2 is 10,000 or more, and the number average molecular weight of the basic polymer 4 is 200 or more and 3000 or less.

  The number average molecular weight can be measured by, for example, gel permeation chromatography or rotational viscosity method.

  Another form of this embodiment is shown in FIG. 3 is the same as FIG. 2 in that the acidic polymer 2 having the acidic functional group 3 and the basic polymer 4 having the basic functional group 5 are complexed at the molecular level. The number average molecular weight of the polymer 4 is 10,000 or more, and the number average molecular weight of the acidic polymer 2 is 200 or more and 3000 or less. The acidic polymer 2 and the basic polymer 4 are “complexed at the molecular level” means that an acid-base bond is formed between the acidic functional group 3 and the basic functional group 5, and the acidic polymer. 2 or the polymer chains forming the basic polymer 4 are combined without phase separation.

The acid-base composite electrolyte of the present embodiment may be in any form shown in FIG. 2 or FIG. That is, the acidic polymer 2 having the acidic functional group 3 and the basic polymer 4 having the basic functional group 5 are complexed at the molecular level, and the acidic polymer 2 and the basic polymer 4 are The number average molecular weight of either one is 10,000 or more, and
The other number average molecular weight is 200 or more and 10,000 or less. If the number average molecular weight of any one of the acidic polymer 2 and the basic polymer 4 is 10,000 or more, the film shape and mechanical strength of the acid-base composite electrolyte membrane 1 can be maintained. On the other hand, when the other number average molecular weight is smaller than 200, durability against water becomes poor. When the other number average molecular weight is increased, the mobility of the molecular chain is lowered, and proton conductivity in a low humidified atmosphere cannot be ensured. In the present invention, it has been confirmed that when the number average molecular weight of the polymer molecular weight is 3000 or less, the proton conductivity does not significantly decrease and shows a high value.

In the acid-base composite electrolyte of the present embodiment, it is necessary that the density of the acidic functional group 3 is 3 × 10 ⁻³ mol / g or more and the density of the basic functional group 5 is 1 × 10 ⁻³ mol / g or more. It is. By defining the density of the acidic functional group 3 and the basic functional group 5, a channel through which protons are conducted in a low humidified atmosphere is secured, and the number of free protons that can exist in the low humidified atmosphere is secured. It becomes possible.

The acidic polymer 2 includes a phosphonyl group (—HPO), a phosphinyl group (—H ₂ PO), a sulfonyl group (—SO ₂ —), a sulfinyl group (—SO—), a carboxyl group (—COOH), a phosphonic acid group ( -PO _{(OH) 2),} phosphinic acid group (-HPO (OH)), sulfonic acid _(-SO 3 H), sulfinic acid group _(-SO 2 H), mercapto group (-SH), hydroxyl (-OH ), And at least one acidic functional group 3 among functional groups consisting of a group such as a phosphate group (—PO ₄ ). Particularly preferred are organic molecules having a highly acidic carboxyl group, phosphonic acid group, sulfonic acid group and the like. This is because the higher the acidity, the higher the degree of proton dissociation, and the number of free protons that can be dissociated even in a low humidified atmosphere increases, and the proton conductivity tends to be excellent.

  The basic polymer 4 is a group of heterocyclic nitrogen-containing groups such as primary amines, secondary amines, tertiary amines, quaternary ammonium groups, amino groups, amide groups, imide groups and imidazole groups. Among them, it is preferable to have at least one functional group as the basic functional group 5. Among them, a polymer having a quaternary ammonium group, an amino group, a heterocyclic nitrogen-containing group and the like is preferable. The reason for this is that nitrogen-containing ring compounds have a strong basicity and a high proton acceptability, and are excellent in thermal and chemical stability.

  The acid-base composite electrolyte of the present embodiment may contain a non-polymerizable acidic compound having no reactivity in addition to the acidic polymer 2. Although there is no restriction | limiting in particular as an acidic compound, Acidic compounds with high dissociation constants, such as strong acid, such as phosphoric acid and a sulfuric acid, monosubstituted sulfuric acids, such as methanesulfonic acid and ethanesulfonic acid, and monosubstituted phosphoric acids, such as phenylphosphoric acid, are preferable. By adding a non-polymeric acidic compound, proton conductivity can be improved and the molecular weight of the polymer can be adjusted.

  The acid-base composite electrolyte of the present embodiment described above has proton conductivity even in a low humidified atmosphere assumed in a high temperature region of 100 ° C. or higher, and a region where liquid water of 100 ° C. or lower exists. Even underneath, it has high water resistance.

(Embodiment 2)
Next, a method for producing the acid-base composite electrolyte of the present invention will be described. The production method of the present embodiment includes a first step in which an acidic compound monomer is contained in an electrolyte composed of a basic polymer, and a basic electrolyte containing the acidic monomer is produced. And a second step of polymerizing the acidic monomer in the basic electrolyte obtained in (1). The first step is a step of preparing an acidic electrolyte containing a basic monomer by containing a basic monomer in an electrolyte composed of an acidic polymer, and the second step is a base in the acidic electrolyte. It may be a step of polymerizing a reactive monomer. By these production methods, an acid-base composite electrolyte can be obtained directly after the polymerization reaction without any special processing.

  In the first step, an acidic or basic electrolyte containing a basic or acidic monomer is obtained by immersing a film-like acidic or basic polymer in a solution comprising a basic or acidic monomer.

  The first step is a mixing step of mixing an acidic monomer with a basic polymer solution, a casting step of casting the mixed solution obtained in the mixing step on a substrate, and a step of removing the solvent of the cast film obtained in the casting step The process which consists of these may be sufficient. Alternatively, the first step includes a mixing step of mixing a basic monomer into an acidic polymer solution, a casting step of casting the mixed solution obtained in the mixing step onto a substrate, and a solvent for the cast film obtained in the casting step. It may be a process consisting of a process of removing. As the substrate, a flat plate such as a glass plate or a PTFE (Teflon (registered trademark)) plate can be used. In this method, a basic or acidic monomer can be easily contained at a desired doping rate, and a high doping rate can also be achieved.

  Here, the boiling point of the solvent that dissolves the acidic or basic polymer is preferably lower than the boiling point of the basic or acidic monomer. This is because, in the step of casting and drying a mixed solution of an acidic or basic polymer and a basic or acidic monomer, it is easy to remove only the solvent by, for example, distillation, and the electrolyte of the present invention can be produced by a simple production method. This is because

  There is no particular limitation in the second step, but as a method for polymerizing a basic or acidic monomer in the state contained in the film, for example, radical polymerization method using an initiator, anionic polymerization method, cationic polymerization method, photopolymerization A UV polymerization method using an initiator or an electron beam polymerization method in which polymerization is initiated by electron beam irradiation is used. Among these, it is preferable to use a method in which a polymerization reaction is performed by energy irradiation typified by a UV polymerization method or an electron beam polymerization method. This is because the reaction, purification, etc. are simple and the acid-base composite electrolyte of the present invention can be easily obtained.

(Embodiment 3)
Next, a membrane electrode assembly including the acid-base composite electrolyte in the present invention and a fuel cell using the acid-base composite electrolyte in the present invention will be described.

  FIG. 4 is a schematic diagram of a membrane electrode assembly 12 including an acid-base composite electrolyte according to Embodiment 3 of the present invention. In FIG. 4, the membrane electrode assembly 12 includes the electrolyte membrane 10 including any one of the acid-base composite electrolytes according to Embodiment 1 of the present invention described above, the anode electrode, and the cathode electrode 11, and the electrolyte membrane 10 is connected to the anode electrode. It has a structure sandwiched between the cathode electrode 11. In FIG. 4, since the anode electrode is disposed so as to face the cathode electrode, it is not shown in this drawing. The anode electrode and the cathode electrode 11 are not particularly limited, and general known electrodes may be used. Further, at least one of the anode electrode and the cathode electrode may contain the acid-base composite electrolyte in the present invention.

  There are no particular restrictions on the method for producing the membrane electrode assembly 12, but the anode electrode, the cathode electrode 11, and the electrolyte membrane 10 may be pressure-bonded by pressing or the like, and a catalyst, a conductive agent, and an electrolyte are formed on both surfaces of the electrolyte membrane 10. You may form the anode electrode and the cathode electrode 11 by apply | coating.

  Since the membrane electrode assembly 12 of the present invention enables high proton conduction even in a low humidified atmosphere of 100 ° C. or higher, the membrane electrode assembly 12 capable of high output can be obtained.

  FIG. 5 is a schematic diagram of a fuel cell according to Embodiment 3 of the present invention.

  The fuel cell shown in FIG. 5 has a membrane electrode assembly 12 including the electrolyte membrane 10 of the present invention, a cathode electrode 11 and an anode electrode, and each electrode portion of the membrane electrode assembly 12 is an anode gas diffusion layer. 25 and the cathode gas diffusion layer 26. In the fuel cell shown in FIG. 5, an anode separator 21 and a cathode separator 22 are disposed outside the gas diffusion layer. A fuel supply manifold 23 is formed in the anode separator 21, and an oxidant supply manifold 24 is formed in the cathode separator. When an electrode catalyst is supported on the gas diffusion layer, it is not always necessary to provide electrode layers on both surfaces of the electrolyte membrane.

  In such a fuel cell, since the above-described electrolyte membrane of the present invention is used, a high-power fuel cell capable of operating at a high temperature of 100 ° C. or higher can be obtained.

  The material used for portions other than the electrolyte membrane and the structure thereof are not particularly limited. What is necessary is just to be the same as a general polymer electrolyte fuel cell. For example, the anode electrode and the cathode electrode may contain Pt as a catalyst and a carbon material powder as a conductive agent. The electrolyte membrane and each electrode may be crimped by, for example, a press. The same applies to the fuel to be used. For example, it may be a fuel containing at least one gas or liquid selected from hydrogen and hydrocarbons. More specifically, for example, alcohols such as methanol, ethanol and ethylene glycol, ethers such as dimethyl ether, or an aqueous solution thereof may be used. When the fuel is liquid, for example, the fuel may be supplied from a cartridge or the like to the fuel cell.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to the Example shown below.

Example 1
In Example 1, an electrolyte membrane was prepared using polybenzimidazole (number average molecular weight: about 100,000) as the film polymer and vinyl phosphoric acid (manufactured by Aldrich) as the acid monomer. Since the polybenzimidazole used here has a number average molecular weight of 10,000 or more, it can be easily formed into a film.

  First, a 20% by weight polybenzimidazole (PBI) / dimethylacetamide solution (DMAc) was cast on a glass plate, dried at 60 ° C. for 15 minutes, then dried at 120 ° C. for 15 minutes, and naturally cooled before glass. It peeled from the board and vacuum-dried at 90 degreeC for 12 hours. Since the dried PBI film contains LiCl salt, the salt was removed by treatment in boiling water for 2 hours. A PBI film is manufactured by this process. The PBI film thus produced was cut to a size of 3 cm × 3 cm and used for the following experiment.

Subsequently, the PBI film was impregnated with an acid monomer. After immersing the PBI membrane in an aqueous vinyl phosphate solution adjusted to 5M for 3 days, it was vacuum-dried at 60 ° C. for 12 hours (first step). When the dope rate of vinyl phosphoric acid was calculated | required from the weight change before and behind immersion, it was 4.8. Here, the doping rate indicates the number of vinyl phosphates (PBI / unit) compounded per monomer unit of PBI. This sample has an acidic functional group density of 1.0 × 10 ⁻² mol / g and a basic group density of 2.4 × 10 ⁻³ mol / g, which enables high proton conduction in a low humidified atmosphere. .

  Subsequently, polymerization of vinyl phosphoric acid was performed. A PBI membrane doped with vinyl phosphoric acid was impregnated in 10 ml of toluene, and 0.1 g of azobisisobutyronitrile (AIBN, manufactured by Kanto Chemical Co., Ltd.) dissolved in toluene under reflux was added in a nitrogen atmosphere while stirring with a stirrer. The reaction was carried out at 2 ° C. for 2 hours (second step).

  After the reaction, the membrane was washed with toluene, unreacted initiator was removed, and then vacuum-dried at 80 ° C. for 12 hours. As a result, electrolyte membranes 1a and 1b, which were PBI-polyvinyl phosphate composite electrolytes, were obtained. In addition, as shown in Table 1 described later, it is considered that the characteristics of the electrolyte membranes 1a and 1b are different due to the manufacturing process and the like.

(Example 2)
In Example 2, as in Example 1, PBI was used as the polymer and vinyl phosphoric acid was used as the monomer. However, instead of impregnating the membrane with the acid solution in the first step, the cast was performed after mixing the acid and base in the solution state. Then, a method of forming a film was used. A PBI film prepared by the same method as in Example 1 was dissolved in trifluoroacetic acid to obtain a 10 wt% solution, and then the doping rate was 5.0 (acid group density: 1.2 × 10 ⁻² mol / g, base The density of the functional group was 2.3 × 10 ⁻³ mol / g), and vinyl phosphoric acid was added thereto.

  By this method, a vinyl phosphate-doped PBI film was obtained. After film formation, the film was cut into 3 cm × 3 cm, and doped vinyl phosphate was polymerized using the same method as in Example 1. As a result, electrolyte membranes 2a and 2b were obtained. As shown in Table 1 described later, it is considered that the characteristics of the electrolyte membranes 2a and 2b are different due to the manufacturing process and the like.

(Example 3)
In Example 3, as in Examples 1 and 2, PBI was used as the polymer, vinyl phosphoric acid was used as the monomer, a direct mixing method was used in the first step, and a UV curing polymerization method was used as the polymerization reaction. Vinyl phosphoric acid was added so that the dope rate was 5.0. In order to carry out UV polymerization, 1 wt% of 1-hydroxy-cyclohexyl-phenyl-ketone as a UV polymerization initiator is added to vinyl phosphoric acid in the production process 1, and after forming a film by the same method as in Example 2, irradiation with ultraviolet rays is performed. Then, the doped vinyl phosphoric acid was polymerized to obtain electrolyte membranes 3a and 3b. As shown in Table 1 described later, it is considered that the characteristics of the electrolyte membranes 3a and 3b are different due to the manufacturing process and the like.

Example 4
In Example 4, PBI was used as a support, vinyl phosphoric acid was used as a reactive organic acid, and phosphoric acid was used as a non-reactive acid. In the first step, the PBI solution, vinyl phosphoric acid and phosphoric acid were mixed by a direct mixing method, and then cast on a glass plate to form a film. The doping rate of vinyl phosphoric acid is 4.5, the doping rate of phosphoric acid is 0.5 (acidic group density: 1.5 × 10 ⁻² mol / g, basic group density: 2.3 × 10 ⁻³ mol / g) The acid was added so that After film formation, vinyl phosphoric acid doped in the same manner as in Example 1 was polymerized to obtain an electrolyte membrane 4.

(Comparative Example 1)
As a comparative example, a phosphoric acid-impregnated polybenzimidazole electrolyte membrane was used. After forming a PBI film in the same manner as in Example 1, an electrolyte film A having a doping rate of 5.2 was obtained by impregnating the PBI film in a phosphoric acid aqueous solution adjusted to 11M.

(Characteristic evaluation)
The proton conductivity was measured for each electrolyte membrane obtained in Examples 1 to 4. In the measurement, the electrolyte membrane was sandwiched between gold electrodes, and the proton conductivity was measured by an alternating current impedance measurement method in an atmosphere of hydrogen atmosphere at 140 ° C. and a relative humidity of 20%.

  Water resistance evaluation of the obtained electrolyte membrane was performed. As a simple water resistance test, the electrolyte membrane obtained in each example was immersed in 30 ml of pure water at room temperature for 10 minutes and then vacuum-dried at 100 ° C. for 1 day. The amount of acid elution was determined.

In addition, as a water resistance test, the conductivity was measured by alternating current impedance measurement in a hydrogen atmosphere and a relative humidity of 20% for a film that was vacuum-dried after a sample was immersed in 30 ml of pure water to maintain the conductivity. The rate was determined. The conductivity retention is (conductivity retention) = (conductivity after water immersion) / (conductivity before water immersion)
It was used as a scale for comparing water resistance. The results are shown in Table 1.

  The polymer molecular weight of the obtained sample was determined. The molecular weight of the acidic polymer was determined by immersing the sample in boiling water for 12 hours and performing gel permeation chromatography (GPC) on the eluted acid to determine the number average molecular weight. The number average molecular weight was determined by pullulan conversion by preparing a calibration curve using eight kinds of pullulan (manufactured by Showa Denko) having different molecular weights as standard substances.

  The GPC measurement conditions are shown below.

Apparatus: Lc-10AdVP (manufactured by Shimadzu Corporation)
Column: OH-Pak SB802, OH-Pak SB806HM
Column temperature: 40 ° C., sample flow rate: 1 cc / min
Solvent: Water (0.5 Mol / L LiCl added)
Standard material: Pullulan (Showa Denko)

  As shown in Table 1, the electrolyte membrane according to the present invention has a proton conductivity higher than that of the electrolyte membrane A in a low humidity atmosphere at a high temperature of 140 ° C. and a relative humidity of 20%, and has a practically usable level. confirmed. A decrease in proton conductivity is predicted as the molecular weight of the acidic electrolyte responsible for proton conduction increases. However, in the electrolyte membrane of the present invention, no significant decrease was observed in the region of molecular weight of 3000 or less.

  In the water resistance test, the water resistance of the sample subjected to polymerization treatment was improved from the results of measuring the weight change of the sample before and after immersion in water, and the acid doped inside the membrane was eluted out of the membrane when immersed in water at room temperature. No longer. In the state of low molecular weight, the acid doped in the film is complexed with the basic polymer PBI at the molecular level, and the acid molecules in the film are polymerized in a state where acid-base bonds are formed. This is probably because the molecular diffusivity was lowered because the molecular size was increased in the space.

  Moreover, the electrical conductivity retention determined from the electrical conductivity change showed a very large value compared with the electrolyte membrane A, and the improvement of water resistance was confirmed.

  In the production method of the present invention, only a sample having an acidic polymer having a molecular weight of 3000 or less was obtained as the electrolyte membrane. However, in the molecular weight range of the present invention, no significant decrease in conductivity was confirmed, which was effective for practical use. It was confirmed that a high conductivity could be achieved.

  FIG. 6 shows the relationship between the molecular weight of the polymer and the conductivity retention. Thereby, it can also be confirmed that when the polymer molecular weight is increased, the water resistance is improved, and when the molecular weight is 200 or more, the water resistance is dramatically improved. Since the polymerization reaction proceeds in a state where the acidic electrolyte and the basic electrolyte are combined at the molecular level, even if the degree of polymerization is very low, the diffusion capacity of the acidic polymer in the basic polymer As a result, it was remarkably lowered and it was not eluted out of the membrane.

  From the above, it was confirmed that the number average molecular weight of the polymer is in the range of 200 or more and 3000 or less, which is necessary for ensuring conductivity and improving water resistance in a low humidified atmosphere.

(Example 5)
In Example 6, a membrane electrode assembly using the electrolyte membrane prepared in Examples 1 to 4 was produced, and a fuel cell power generation test using this was performed. The thickness of each electrolyte membrane is about 50 μm. Let the fuel cells produced using the electrolyte membranes 1-5 be the samples 1-5, respectively.

Samples 1 to 5 were prepared by the following procedure. First, a membrane electrode assembly was prepared by arranging an anode electrode and a cathode electrode so as to sandwich the electrolyte membrane between both surfaces of the electrolyte membrane. Next, a fuel cell was fabricated by disposing a carbon separator in which flow paths through which fuel and air flow were formed so as to further sandwich the membrane electrode assembly. The anode electrode used was a catalyst electrode carrying PtRu catalyst (manufactured by Electrochem, 1 mg / cm ^{2 of} Pt supported), and the cathode electrode was a catalyst electrode carrying Pt (manufactured by Electrochem, 1 mg / kg of Pt supported). cm ² ) was used. Before joining with the electrolyte membrane, a catalyst-supported electrode was impregnated with 5M phosphoric acid aqueous solution, and water was removed by vacuum drying to obtain a membrane electrode assembly.

(Comparative Example 2)
For comparison, a fuel cell was fabricated in the same manner as in Example 7 using the phosphoric acid-impregnated polybenzimidazole electrolyte membrane used in Comparative Example 1 as the electrolyte membrane. The fuel cell thus produced was designated as Sample A.

The power generation conditions were as follows: hydrogen gas (supply amount 30 ml / min, relative humidity 80%) and air (supply amount 200 ml / min, relative humidity 80%) were supplied to the fuel, and the fuel cell power generation temperature was 140 ° C. As evaluation items, an open circuit voltage (OCV) of each sample and a battery voltage at a current density of 0.1 A / cm ² were measured as a voltage during power generation. The results are shown in Table 2.

  As shown in Table 2, it was possible to generate power in all samples 1-4. In addition, the fuel cells of Samples 1 to 4 showed a battery voltage comparable to that of the sample A using the phosphoric acid-impregnated PBI membrane, and high battery characteristics were obtained. This is because the electrolyte membranes of Examples 1 to 5 have effective ionic conductivity under the power generation conditions.

  In addition, the electrolyte in the present invention exhibits the same characteristics as a phosphoric acid-impregnated polybenzimidazole film as power generation conditions, and further has improved water resistance as compared with a phosphoric acid-impregnated polybenzimidazole film. Was confirmed to be a very good electrolyte.

  According to the present invention, it is possible to provide an electrolyte that can operate in a high-temperature or low-humidity atmosphere of 100 ° C. or higher with a simple system without using a system such as a humidifier.

  In addition, a membrane electrode assembly and a fuel cell using such an electrolyte can be provided.

  In addition to the fuel cell, the electrolyte of the present invention can be used in various electrochemical devices such as a primary battery, a secondary battery, an electrochemical capacitor, various gas sensors, and an electrochromic element.

Schematic of the acid-base composite electrolyte membrane in Embodiment 1 of the present invention Schematic of the acid-base composite electrolyte in Embodiment 1 of the present invention Schematic of the acid-base composite electrolyte in Embodiment 1 of the present invention Schematic diagram of membrane electrode assembly according to Embodiment 2 of the present invention Schematic of the fuel cell in Embodiment 2 of the present invention The graph which shows the polymer molecular weight-electrical conductivity retention in the Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Acid-base composite electrolyte membrane 2 Acid polymer 3 Acid functional group 4 Basic polymer 5 Basic functional group 10 Electrolyte membrane 11 Cathode electrode 12 Membrane electrode complex 20 Fuel cell 21 Anode separator 22 Cathode separator 23 Fuel supply manifold 24 Oxidation Agent supply manifold 25 Anode gas diffusion layer 26 Cathode gas diffusion layer

Claims (10)

An acid-base composite electrolyte comprising an acidic polymer having an acidic functional group and a basic polymer having a basic functional group,
The acidic polymer and the basic polymer are complexed at a molecular level,
The acidic functional group density is 3.0 × 10 ⁻³ mol / g or more, the basic functional group density is 1.0 × 10 ⁻³ mol / g or more,
The number average molecular weight of either one of the acidic polymer and the basic polymer is 10,000 or more, and
The other number average molecular weight is 200 or more and 3000 or less,
An acid-base composite electrolyte. The acidic polymer has, as a functional group, a phosphonyl group, a phosphinyl group, a sulfonyl group, a sulfinyl group, a carboxyl group, a phosphonic acid group, a phosphinic acid group, a sulfonic acid group, a sulfinic acid group, a mercapto group, a hydroxyl group, and a phosphoric acid group. Having at least one functional group in the group consisting of:
The acid-base composite electrolyte according to claim 1. The basic polymer has at least one functional group selected from the group consisting of primary amines, secondary amines, tertiary amines, quaternary ammonium groups, amino groups, amide groups, imide groups and imidazole groups. Having a functional group,
The acid-base composite electrolyte according to claim 1. Containing a non-polymeric acidic compound,
The acid-base composite electrolyte according to any one of claims 1 to 3, wherein: A method for producing an acid-base composite electrolyte, comprising:
A first step of containing a monomer of an acidic or basic compound in the electrolyte composed of the basic or acidic polymer;
A second step of polymerizing an acidic monomer or a basic monomer in the electrolyte obtained in the first step,
The method for producing an acid-base composite electrolyte according to any one of claims 1 to 4. The second step is a step of causing a polymerization reaction by irradiating the electrolyte with energy;
The method for producing an acid-base composite electrolyte according to claim 5. The first step is a mixing step of mixing a basic or acidic monomer with an acidic or basic polymer solution; and
A casting step of casting the mixed solution obtained in the mixing step on a substrate;
Removing the solvent of the cast film obtained in the casting step,
The method for producing an acid-base composite electrolyte according to claim 5. The boiling point of the solvent of the polymer solution is lower than the boiling point of the monomer;
The method for producing an acid-base composite electrolyte according to claim 7. A membrane electrode assembly in which an electrolyte membrane, and an anode electrode and a cathode electrode sandwiching the electrolyte membrane are joined,
At least one selected from the group consisting of the electrolyte membrane, the anode electrode, and the cathode electrode includes the acid-base composite electrolyte according to any one of claims 1 to 4,
A membrane electrode composite characterized by the above. A fuel cell comprising an electrolyte membrane, and an anode electrode and a cathode electrode sandwiching the electrolyte membrane,
The electrolyte membrane includes the acid-base composite electrolyte according to any one of claims 1 to 4,
A fuel cell.