JP2007238806A - Proton conductive material, proton conductive electrolyte for fuel battery and fuel battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive material comprising a new polymer, to provide a proton conductive electrolyte, and to provide a fuel battery using the same. <P>SOLUTION: This proton conductive material is characterized by comprising a poly(phosphophenylene oxide) having at least phosphonic group-containing side chains on a main chain comprising polyphenylene oxide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a proton conductive material composed of a novel polymer compound, a proton conductive electrolyte, and a fuel cell equipped with this proton conductive electrolyte, and in particular, has high proton conductivity, good film formability and heat resistance. The present invention also relates to a proton conductive electrolyte comprising a novel polymer compound that has chemical stability and can be produced with a small number of reaction stages under mild conditions.

Fluoropolyethylenesulfonic acid is widely used industrially for salt electrolysis, seawater desalination, water treatment, proton conducting membranes, and the like. Representative examples thereof include Nafion (registered trademark), Flemion, Aciplex, and Dow film, and all are synthesized and polymerized in multiple stages.
However, these have problems such as containing fluorine and being expensive.

  Polystyrene sulfonic acid or the like is used as an ion exchange resin or ion exchange membrane used for water treatment or the like, but it is not necessarily environmentally compatible, for example, polystyrene is sulfonated under the severe conditions of fuming sulfuric acid.

In the following Patent Document 1, poly (sulfonatoalkoxyphenylene oxide) is excellent in proton conductivity and film formability, and can be synthesized under mild conditions compared to various sulfonic acid group-containing polymers. It has been shown to be effective as a proton conducting electrolyte membrane.
JP-A-2005-171087

  However, since the sulfonic acid group of poly (sulfonatoalkoxyphenylene oxide) described in Patent Document 1 starts decomposing at around 200 ° C., the sulfonic acid group decomposes during the long-term test of the fuel cell, so There is a problem that proton conductivity is lowered because conductivity is not exhibited.

  The present invention has been made in view of the above circumstances, and can be substituted for a polymer compound containing a sulfonic acid group that is widely used in the industrial field, and has excellent thermal and chemical stability compared to a sulfonic acid compound. Proton-conducting materials, proton-conducting electrolytes, and fuel cells using the same, comprising novel polymer compounds obtained by producing polymer compounds containing acid groups under mild reaction conditions and mild conditions The purpose is to do.

In order to achieve the above object, the present invention employs the following configuration.
The proton conductive material of the present invention is characterized by being made of poly (phosphophenylene oxide) in which a main chain made of polyphenylene oxide is provided with at least a side chain containing a phosphonic acid group.
In the proton conductive material of the present invention, the poly (phosphophenylene oxide) is preferably a random copolymer represented by the structural formula represented by the following formula (1).
However, in Formula (1), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group, and n is in the range of 100 to 100,000. A, b, c are numerical values indicating the ratio of the three structures in parentheses in the formula (1), and a: (b + c) = 3: 5-6: 2 .

Furthermore, in the proton conductive material of the present invention, the poly (phosphophenylene oxide) is preferably synthesized by oxidative polymerization of phosphophenols represented by the following formula (2).
However, in Formula (2), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group.

Furthermore, in the proton conductive material of the present invention, the phosphophenol is a compound synthesized in one step by reacting catechols represented by the following formula (3) with diphosphorus pentoxide. preferable.
However, in Formula (3), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group.

In the proton conductive material of the present invention, the catechol represented by the above formula (3) is preferably catechol.
Furthermore, in the proton conductive material of the present invention, the catechol represented by the above formula (3) is preferably 3-methylcatechol.

  Next, a proton conductive electrolyte for a fuel cell according to the present invention includes at least the proton conductive material described above.

Next, the fuel cell according to the present invention includes a pair of electrodes and an electrolyte membrane disposed between the electrodes, and the electrolyte membrane is the proton conductive electrolyte described above.
In the fuel cell of the present invention, it is preferable that the proton conductive electrolyte described above is contained in a part of the electrode.

According to the proton conductive material of the present invention, the phosphonic acid group is provided in the side chain, so that the proton conductivity is excellent, and it is used as salt electrolysis, seawater desalination, water treatment, proton conductive membrane, and the like. It can be used as a substitute for fluorinated polyethylene sulfonic acid.
In addition, since the proton conductive electrolyte of the present invention is excellent in heat resistance, the above poly (phosphophenylene oxide) is used as an electrolyte membrane, so that the operating temperature is 100 ° C. or higher and 200 ° C. or lower, and the relative humidity is 50%. Even in the following cases, it is possible to provide a polymer electrolyte fuel cell with high current density, high output and long life.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
“Proton Conducting Material (Proton Conducting Electrolyte)”
The inventors of the present invention (1) react catechols with diphosphorus pentoxide in an extremely easy and high yield to produce phosphophenol. (2) Although it has an electron-withdrawing phosphate group, by using water as a polymerization solvent, it undergoes oxidative polymerization in a very high yield under mild conditions in the atmosphere to produce poly (phosphophenylene oxide) . As a result of obtaining the above findings (1) and (2), it was found that the poly (phosphophenylene oxide) of the present invention was produced, and that it exhibited high ion exchange capacity and proton conductivity. .

That is, the proton conductive material of the present invention is generally composed of poly (phosphophenylene oxide) in which a main chain composed of polyphenylene oxide is provided with at least a side chain containing a phosphonic acid group.
Poly (phosphophenylene oxide) is a random copolymer represented by the structural formula represented by the above formula (1). However, in Formula (1), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group, and n is in the range of 100 to 100,000. A, b, c are numerical values indicating the ratio of the three structures in parentheses in the formula (1), and a: (b + c) = 3: 5-6: 2 .

  As shown in the above formula (1), the poly (phosphophenylene oxide) includes a group composed of at least three aromatic rings, and each group is constituted by random copolymerization. Each group is composed of the same starting materials as will be described later, and is in a relation of structural isomers to each other.

The abundance ratio in each group of poly (phosphophenylene oxide) is represented by a ratio of a, b, and c. The ratios of a, b and c are all molar ratios and can be represented by the formula a: (b + c), and the numerical range of this formula is preferably a: (b + c) = 3: 5 to 6: 2. More preferably, the range is 4: 4 to 5: 3, and most preferably is 5: 3. The ratio of b and c is arbitrary, but is in the range of b: c = 1: 1 to 1:10, more preferably in the range of b: c = 1: 1.5 to 1: 5, most preferably Is b: c = 1: 2.
These a, b, and c are determined by the reaction yield of the intermediate in the production process of poly (phosphophenylene oxide), and do not greatly affect the proton conductivity. Therefore, even if the ratio of a, b, and c varies, the proton conductivity does not change greatly.

  N indicating the average degree of polymerization of poly (phosphophenylene oxide) is preferably in the range of 100 to 100,000. When n is 100 or more, the phosphonic acid group becomes a sufficient amount, and there is no possibility of lowering the proton conductivity. If n is 100,000 or less, the average molecular weight of the entire poly (phosphophenylene oxide) is not excessive, the solubility in the solvent is not lowered, the moldability by the so-called casting method is improved, and the proton conductivity It becomes easy to make a material into a desired shape.

  The proton conductive material of the present embodiment may be made of only poly (phosphophenylene oxide), or may be a mixture of a reinforcing agent such as polytetrafluoroethylene in order to improve the film strength. Furthermore, a basic polymer or the like may be mixed and used as an ion complex electrolyte.

"Production Method of Proton Conducting Material (Proton Conducting Electrolyte)"
A synthesis scheme of the proton conductive material is shown in the following formula (4). As shown in formula (4), in this synthesis scheme, catechols (i) are reacted with diphosphorus pentoxide (ii) to produce phosphophenol (iii), and this phosphophenol (iii) is used as a monomer. In addition, by using water as a polymerization solvent, oxidative polymerization is performed under mild conditions such as in the air to produce poly (phosphophenylene oxide) (iv).

  The formula (4) will be described in detail. First, catechols represented by the following formula (5) are prepared. R in Formula (5) is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group.

When catechols and diphosphorus pentoxide are reacted to synthesize phosphophenols, the following formula (6) and catechols and diphosphorus pentoxide are stirred for several hours at the melting temperature of the catechols. The phosphophenols represented by formula (7) are synthesized easily and with high yield.
The synthesized phosphophenols have two kinds of positional isomers as shown in the formulas (6) and (7). The ratio of the isomer represented by formula (6) and the isomer represented by formula (7) is a value corresponding to the above-mentioned a: (b + c), and is preferably in the range of 3: 5 to 6: 2. Is in the range of 4: 4 to 5: 3, most preferably 5: 3.

  Unreacted diphosphorus pentoxide after the synthesis of phosphophenols can be completely removed by solvent extraction with ether and water. Unreacted catechols can be completely removed by a recrystallization method using dichloromethane and ether. In addition, catechol disubstitutes are rarely generated due to steric hindrance, but are suppressed by making the molar amount of diphosphorus pentoxide used in the reaction less than the stoichiometric amount relative to catechols Can do.

Next, in order to synthesize poly (phosphophenylene oxide) by oxidative polymerization of the produced phosphophenols, an oxidizing agent is added to an alkaline aqueous solution of phosphophenols, and it is violently at atmospheric pressure and at room temperature for 12 hours to 24 hours or more. What is necessary is just to stir.
The base constituting the alkaline solution is preferably a strong base such as sodium hydroxide or potassium hydroxide, and the amount of the base in the polymerization solution is preferably equimolar with the phosphophenol monomer.
As the oxidizing agent, silver oxide, lead oxide, manganese oxide, copper amine complex, iron amine complex, manganese amine complex, potassium hexacyanoferrate (III), etc. are used. When metal oxide such as silver oxide is used, After the oxidative polymerization, the oxidant can be easily removed by filtration or centrifugation.

In the phosphophenol isomer represented by the formula (6), the p-position of the phenol group has the highest reaction activity. On the other hand, in the phosphophenol isomer represented by the formula (7), the phosphonic acid The m-position of the group (OPO ₃ H ₂ ) has the highest reaction activity, and then the reaction activity at the p-position of the phenol group becomes high. For this reason, the polymer (poly (phosphophenylene oxide)) synthesized by the monomer composed of these isomers is in a form in which three groups are randomly polymerized as shown in the above formula (1).

Through the above steps, the proton conductive material made of poly (phosphophenylene oxide) of the present embodiment is synthesized.
The proton conductive material may be composed only of the obtained poly (phosphophenylene oxide), or may be a mixture of a reinforcing agent such as polytetrafluoroethylene in order to improve the film strength. Furthermore, a basic polymer or the like may be mixed and used as an ion complex electrolyte.

"Fuel cell"
Next, an example of the fuel cell of the present embodiment will be described with reference to the drawings.
In FIG. 1, the schematic diagram of the single cell which comprises the fuel cell of this embodiment is shown. A single cell 1 shown in FIG. 1 includes an oxygen electrode 2, a fuel electrode 3, and the proton conductive electrolyte 4 sandwiched between the oxygen electrode 2 and the fuel electrode 3 (hereinafter referred to as an electrolyte membrane 4 in some cases). And an oxidant distribution plate 5 having an oxidant flow path 5 a disposed outside the oxygen electrode 2, and a fuel distribution plate 6 having a fuel flow path 6 a disposed outside the fuel electrode 3. The operation temperature is 100 ° C. to 200 ° C. and the humidity is not humidified or the relative humidity is 50% or less.

  The fuel electrode 3 and the oxygen electrode 2 are each generally composed of porous catalyst layers 2a and 3a and porous carbon sheets (carbon porous bodies) 2b and 3b that hold the catalyst layers 2a and 3a. The catalyst layers 2a and 3a contain an electrode catalyst (catalyst), a hydrophobic binder for solidifying and molding the electrode catalyst, and a conductive material.

  The catalyst is not particularly limited as long as it is a metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen. For example, lead, iron, manganese, cobalt, chromium, gallium, vanadium, tungsten, ruthenium, iridium, palladium, platinum, There may be mentioned rhodium or an alloy thereof. An electrode catalyst can be constituted by supporting such a metal or alloy on activated carbon.

  For example, a fluororesin can be used as the hydrophobic binder. Among the fluororesins, those having a melting point of 400 ° C. or less are preferable. Examples of such fluororesins include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polyvinylidene fluoride, tetrafluoroethylene / hexafluoroethylene copolymer. A resin excellent in hydrophobicity and heat resistance such as a polymer and perfluoroethylene can be used. By adding the hydrophobic binder, it is possible to prevent the catalyst layers 2a and 3a from being wetted excessively by the water generated in response to the power generation reaction, and the fuel gas and oxygen in the fuel electrode 3 and the oxygen electrode 2 can be prevented. Can be prevented.

  Further, the conductive material may be any material as long as it is an electrically conductive material, and examples thereof include various metals and carbon materials. Examples thereof include carbon black such as acetylene black, activated carbon and graphite, and these are used alone or in combination.

  The catalyst layers 2a and 3a may contain the proton conductive electrolyte according to the present invention instead of the hydrophobic binder or together with the hydrophobic binder. By adding the proton conductive electrolyte according to the present invention, the proton conductivity in the fuel electrode 3 and the oxygen electrode 2 can be improved, and the internal resistance of the fuel electrode 3 and the oxygen electrode 2 can be reduced.

  The oxidant distribution plate 5 and the fuel distribution plate 6 are made of a conductive metal or the like, and function as a current collector by being joined to the oxygen electrode 2 and the fuel electrode 3 respectively. Oxygen and fuel gas are supplied to the pole 3. That is, the fuel electrode mainly containing hydrogen is supplied to the fuel electrode 3 through the fuel flow path 6 a of the fuel flow distribution plate 6, and the oxidant flow path 5 a of the oxidant flow distribution plate 5 is supplied to the oxygen electrode 2. Through this, oxygen as an oxidizing agent is supplied. The hydrogen supplied as fuel may be supplied by hydrogen generated by reforming hydrocarbon or alcohol, and oxygen supplied as oxidant is supplied in a state of being contained in air. Also good.

  In this single cell 1, hydrogen is oxidized on the fuel electrode 3 side to generate protons, which are conducted through the electrolyte membrane 4 to reach the oxygen electrode 2, and protons and oxygen are electrochemically connected to the oxygen electrode 2. It reacts to produce water and generates electrical energy.

  According to the above fuel cell, it is possible to obtain a fuel cell that stably exhibits good power generation performance for a long period of time within an operating temperature range of 70 ° C. or higher and 100 ° C. or lower, and is suitable for automobiles, home power generation, or portable devices Can be used.

"Example 1"
(Synthesis of methylphosphophenol)
To a 100 ml three-necked eggplant flask, 5.61 g (40 mmol) of 3-methylcatechol was added and heated to a melting point (95 ° C.) or higher to be melted. Next, while stirring with a forced stirrer, 3.83 g (27 mmol) of diphosphorus pentoxide was gradually added, followed by stirring at 95 ° C. for 3 hours and at 160 ° C. for 1 hour. After completion of the reaction, the solution is gradually cooled to room temperature, solidified, and subjected to solvent extraction using water and ether to separate unreacted diphosphorus pentoxide in the aqueous layer and extract the reaction product in the ether layer. It was.

  After drying the ether solution with sodium sulfate, the ether was distilled off and recrystallized with dichloromethane / ether to recover a white solid. The recovered white solid was 3.92 g (yield 48%) of a mixture of 2-methyl-6-phosphophenol and 2-phospho-3-methylphenol, which is its positional isomer.

When the obtained white solid was identified, it was found to be 2.20 (s, CH ₃ ), 6.70 (t, Ph), 6.93 (d by ¹ H-NMR (acetone-d6, 500 MHz, ppm). , Ph), 7.03 (d, Ph) to show the spectrum of 2-methyl-6-phosphotransferase _{phenol, 2.26 (s, CH 3)} , 6.71 (d, Ph), 6.76 (d , Ph), 6.92 (t, Ph) show the spectrum of 2-phospho-3-methylphenol which is a regioisomer.
^From the integrated value of the spectrum of 2-methyl-6-phosphophenol and the regioisomer 2-phospho-3-methylphenol in ¹ H-NMR, the mixing ratio of both monomers was 5: 3.

Further, in IR measurement, absorption attributed to phosphate groups ^{(977,1031,1083,1209,1276cm -1 (vP = O)} , 1619cm -1 (δPOH)) were detected, respectively.
Further, ESI-MS showed a spectrum at 203.5 (m / e, M ⁻ ).

(Synthesis of poly (phosphophenylene oxide))
Next, 0.300 g (7.5 mmol) of sodium hydroxide and 0.305 g (1.5 mmol) of methylphosphophenol containing the positional isomer obtained by the above method were dissolved in 15 ml of water, and silver oxide 1. After adding 74 g (7.5 mmol), the mixture was stirred at room temperature for 24 hours. After completion of the reaction, silver oxide is removed, 15 ml of 10% hydrochloric acid is added to the solution, and the mixture is stirred and dialyzed with water (fraction molecular weight: Mw = 1000). As a result, 0.22 g (yield 70%) of a light brown solid was obtained.

The obtained light brown solid is soluble in water, hydrochloric acid, aqueous sodium hydroxide solution, methanol, ethanol, acetonitrile, chloroform, hexane, benzene, toluene, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl. It was insoluble in sulfoxide. The obtained light brown solid had a spectrum of 1.58-2.27 (m, CH ₃ ), 6.00-7.35 (m, Ph) by ¹ H-NMR (D 2 O, 500 MHz, ppm). showed that.
In the IR measurement, absorption attributed to phosphate groups ^{(989,1105,1199,1270cm -1 (vP = O)} , 1629cm -1 (δPOH)) showed the respective absorption peaks of.
The molecular weight was Mw = 1.2 × 10 ⁵ (GPC measurement, water eluent, polystyrene sulfonic acid standard).
Further, when thermogravimetric analysis was performed, the 10% thermal decomposition temperature (Td _10% ) was 355 ° C.

  When the poly (phosphophenylene oxide) obtained as described above was dissolved in water, cast on a Teflon (registered trademark) plate and dried by heating at 70 ° C., a light brown transparent film having a thickness of 78 μm was obtained. was gotten. For this purpose, the proton conductive electrolyte membrane of Example 1 was produced.

(Proton conductivity)
The proton conductive electrolyte membrane of Example 1 was sandwiched between disc-shaped platinum electrodes having a diameter of 13 mm, and proton conductivity was determined by complex impedance measurement. The temperature dependence of proton conductivity is shown in FIG. The proton conductivity at 170 ° C. was 2.4 × 10 ⁻³ Scm ⁻¹ .

(Fuel cell evaluation)
Next, carbon powder carrying 50% by mass of platinum was added to the aqueous solution of the proton conductive electrolyte membrane of Example 1 and sufficiently stirred to obtain a suspension. At this time, it adjusted so that the weight ratio of platinum carrying | support carbon powder and proton conductive electrolyte might be set to 2: 1 by weight ratio of solid content. This suspension was applied onto a carbon porous body (porosity 75%) and dried to obtain a porous electrode for a fuel cell.
Then, the proton conductive electrolyte membrane of Example 1 was sandwiched between the pair of porous electrodes to form a single cell. When hydrogen was supplied to the fuel and air was supplied to the oxidant, and a power generation test was performed at 150 ° C., a voltage of 0.435 V was obtained at an open circuit voltage of 0.965 V and a current density of 100 mA / cm ² .

"Example 2"
A proton conducting electrolyte membrane of Example 2 is produced in the same manner as in Example 1 except that the starting material is catechol (R in formula (3) is replaced by a hydrogen atom) instead of 3-methylcatechol. did.

"Example 3"
The proton conductive electrolyte of Example 3 was the same as Example 1 except that 3-phenylcatechol was replaced by 3-phenylcatechol (R in Formula (3) was substituted with a phenyl group). A membrane was produced.

Example 4
The proton-conducting electrolyte of Example 4 was the same as Example 1 except that 3-methoxycatechol (in which R in Formula (3) was replaced with a methoxy group) was used instead of 3-methylcatechol. A membrane was produced.

“Comparative Example 1”
In 100 ml of an aqueous solution in which 80 mg (2 mmol) of sodium hydroxide is dissolved, 0.58 g (2 mmol) of methylsulfonatopropoxyphenol sodium salt is dissolved, and then 0.93 g (4 mmol) of silver oxide is added as an oxidizing agent, and at room temperature. Stir vigorously. Immediately after the addition of silver oxide, the solution turned brown. After stirring for 12 hours, silver oxide was filtered off from the reaction solution. Then, water was removed under reduced pressure to obtain a pale yellow powder.

  Next, the obtained powder was washed with ethanol to remove sodium hydroxide. The powder after washing was dissolved in 0.5 ml of water, and further 500 ml of ethanol was poured. The precipitate was collected by filtration and washed with ethanol to obtain 0.41 g of white powder (yield 77). %).

When the obtained white powder was identified, strong absorption derived from a sulfonic acid group (1196 cm ⁻¹ , 1060 cm ⁻¹ (vSO ₂ )) in IR spectrum and absorption derived from phenylene ether (1273 cm ⁻¹ , (vC—O—). C)), and further by 6.0-6.56 ppm (m, 2H), 3.58 ppm (t, 2H), 2.86 ppm (t, 2H), 1.86 ppm (m) by ¹ H-NMR. , 2H) and 1.80 ppm (s, 3H), the white powder was identified as poly (methylsulfonatopropoxyphenylene oxide) sodium salt. The molecular weight was 3,200 (GPC measurement, polystyrene standard, eluent: chloroform).

Next, 0.27 g of the obtained white powder (poly (methylsulfonatopropoxyphenylene oxide) sodium salt) was dissolved in 10 ml of pure water, 0.5 ml of 35% hydrochloric acid was added, and the mixture was stirred for 10 minutes to be protonated. .
Further, an aqueous polymer solution was cast on a Teflon (registered trademark) plate and dried under reduced pressure to obtain a flexible and tough poly (methylsulfonatopropoxyphenylene oxide) film having a thickness of 60 μm.
In this way, the proton conductive electrolyte membrane of Comparative Example 1 was produced.

For each of the proton conductive electrolyte membranes of Examples 1 to 4 and Comparative Example 1, the thermal decomposition onset temperature, the 10% weight reduction temperature (Td10), the proton conductivity, and the open circuit voltage when incorporated in a fuel cell were measured.
The results are shown in Table 1. Table 1 shows the structural formula of each polymer.

As shown in Table 1, between Examples 1 to 4 and Comparative Example 1, there is no significant difference in proton conductivity and open circuit voltage, while for Comparative Example 1, the thermal decomposition onset temperature and It can be seen that the 10% weight reduction temperature (Td _10% ) is significantly lower than in the other examples.

  From the above, it can be seen that the proton conductive electrolytes of Examples 1 to 4 are superior in heat resistance as compared with Comparative Example 1 and are suitable as an electrolyte membrane for a fuel cell.

FIG. 1 is a schematic cross-sectional view showing the structure of a single cell of a fuel cell according to an embodiment of the present invention. FIG. 2 is a graph showing the temperature dependence of the proton conductivity of the proton conducting electrolyte membrane of Example 1. The vertical axis is the common logarithm of proton conductivity σ (s / cm), and the horizontal axis is the temperature. It is a number obtained by multiplying the reciprocal of (T) by 1000.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Single cell (fuel cell), 2 ... Oxygen electrode (electrode), 3 ... Fuel electrode (electrode), 4 ... Electrolyte membrane (proton conductive electrolyte)

Claims (9)

  A proton conductive material comprising a poly (phosphophenylene oxide) having at least a side chain containing a phosphonic acid group in a main chain made of polyphenylene oxide. The proton conductive material according to claim 1, wherein the poly (phosphophenylene oxide) is a random copolymer represented by a structural formula represented by the following formula (1).
However, in Formula (1), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group, and n is in the range of 100 to 100,000. A, b, c are numerical values indicating the ratio of the three structures in parentheses in the formula (1), and a: (b + c) = 3: 5-6: 2 .

The proton conductivity according to claim 1 or 2, wherein the poly (phosphophenylene oxide) is synthesized by oxidative polymerization of a phosphophenol represented by the following formula (2). material.
However, in Formula (2), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group.

4. The proton conductive material according to claim 3, wherein the phosphophenol is a compound synthesized in one step by reacting catechols represented by the following formula (3) with diphosphorus pentoxide. .
However, in Formula (3), R is any one of a hydrogen atom, an alkyl group, an ester group, a phenyl group, a carboxylic acid group, a sulfonic acid group, a sulfamic acid group, and a phosphoric acid group.

  The proton conductive material according to claim 4, wherein the catechol represented by the formula (3) is catechol.   The proton conductive material according to claim 4, wherein the catechol represented by the formula (3) is 3-methylcatechol.   A proton conductive electrolyte for a fuel cell, comprising at least the proton conductive material according to any one of claims 1 to 6.   8. A fuel cell comprising a pair of electrodes and an electrolyte membrane disposed between the electrodes, wherein the electrolyte membrane is the proton conducting electrolyte according to claim 7. The fuel cell according to claim 8, wherein the proton conductive electrolyte according to claim 7 is contained in a part of the electrode.

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