JP2007115426A - Fuel cell, proton-conductive electrolyte membrane therefor, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton-conductive electrolyte membrane having improved acid-resistant solubility that can show improved power generation performance under high-temperature and low-moisture operation conditions of no humidification or a relative humidity of 50% or smaller in a temperature range of 100-300°C, and can maintain improved power generation performance stably for a long time by delaying the dissolution of the electrolyte membrane to acid as compared with a conventional one. <P>SOLUTION: The proton-conductive electrolyte membrane for a fuel cell is composed by dipping inorganic phosphates and organophosphonic acids in polybenzimidazoles. In this case, for repetition structure units for composing the polybenzimidazoles, the total amount of inorganic phosphates and organophosphonic acids ranges from 20 mol% or larger to 2,000 mol% or smaller, and the molar ratio (inorganic phosphates:organophosphonic acids) of the inorganic phosphates to the organophosphonic acids ranges from 5:95 to 90:10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a proton conductive electrolyte membrane for a fuel cell, a method for producing the same, and a fuel cell. In particular, the present invention has excellent resistance to dissolution in an acid, and is not humidified at an operating temperature of 100 ° C. to 300 ° C. Alternatively, the present invention relates to a polymer electrolyte membrane that stably exhibits good power generation performance for a long period of time even when the relative humidity is 50% or less, a manufacturing method thereof, and a fuel cell using the same.

An ion conductor in which ions move by applying a voltage is known. This ion conductor is widely used as an electrochemical device such as a battery or an electrochemical sensor.
For example, in a fuel cell, from the viewpoint of power generation efficiency and system efficiency, proton conduction that exhibits good proton conductivity at an operating temperature of about 100 ° C. to 300 ° C. under non-humidified or low humidified operating conditions with a relative humidity of 50% or less. The body is desired.

  In the development of a conventional polymer electrolyte fuel cell, it has been studied in view of the above requirements, but in a polymer electrolyte fuel cell using a perfluorocarbon sulfonic acid membrane as an electrolyte membrane, an operating temperature of 100 ° C. or more and 300 ° C. or less. Below, there was a drawback that sufficient power generation performance could not be obtained at a relative humidity of 50% or less.

Conventionally, a material containing a proton conductivity-imparting agent (for example, Patent Document 1), a silica dispersion film (for example, Patent Document 2), or an inorganic-organic composite film (for example, Patent Document 3). ), A phosphoric acid-doped graft membrane (for example, Patent Literature 4), or an ionic liquid composite membrane (for example, Patent Literature 5 and Patent Literature 6).
Further, Patent Document 7 discloses a technique using a polymer electrolyte membrane made of polybenzimidazole doped with a strong acid such as phosphoric acid.
JP 2001-35509 A JP-A-6-1111827 JP 2000-90946 A JP 2001-213987 A JP 2001-167629 A JP 2003-123791 A US Pat. No. 5,525,436

However, the techniques disclosed in Patent Documents 1 to 6 can exhibit sufficient power generation performance under an operating temperature of 100 ° C. or higher and 300 ° C. or lower, in a non-humidified environment or a relative humidity of 50% or lower. There is a problem that you can not.
In addition, in a phosphoric acid fuel cell, a solid oxide fuel cell, and a molten salt fuel cell, the operating temperature greatly exceeds 300 ° C., so that the requirements are not sufficiently satisfied from the viewpoint of cost.
Furthermore, the technique disclosed in Patent Document 7 discloses an electrolyte membrane in which a polybenzimidazole membrane is doped with orthophosphoric acid. Polybenzimidazole can swell to orthophosphoric acid at a high level at room temperature due to its molecular structure, and can exhibit high ionic conductivity, but originally polybenzimidazole is disclosed in U.S. Pat. No. 3,337,783, U.S. Pat. Since it is a polymer produced by polycondensation using polyphosphoric acid as a polymerization field, as described in Japanese Patent No. 3509108, US Pat. No. 3,555,389, etc., it is particularly easily dissolved in orthophosphoric acid, This tendency becomes more prominent as the temperature increases.

  Polymer electrolyte membranes used in polymer electrolyte fuel cells are required to have high proton conductivity and excellent long-term stability, but polymer electrolyte membranes doped with orthophosphoric acid on polybenzimidazole membranes are protonated for the above reasons. Although it shows excellent results in conductivity and initial fuel cell characteristics, it has sufficient performance from the viewpoint of long-term stability of the fuel cell because it gradually dissolves in the doped acid during high temperature operation. Not.

  The present invention has been made to solve the above-mentioned problems, and can exhibit good power generation performance under high temperature and low humidity operating conditions in the range of 100 ° C. to 300 ° C. without humidification or with a relative humidity of 50% or less. PROBLEM TO BE SOLVED: To provide a proton conductive electrolyte membrane having a good acid solubility resistance capable of stably maintaining a good power generation performance for a long period of time by delaying the dissolution of the membrane in an acid as compared with the conventional one, a method for producing the same, and a fuel cell With the goal.

  In order to solve the above problems, focusing on the imidazole skeleton part contained in polybenzimidazoles and the phenylene skeleton part that is more organic than the imidazole skeleton part, inorganic phosphates and organic phosphates can be converted into specific moles. It has been found that an electrolyte membrane having high proton conductivity can be obtained without dissolving polybenzimidazole by doping polybenzimidazole with acid mixed in a ratio.

  That is, the proton conductive electrolyte membrane for a fuel cell of the present invention is obtained by impregnating polybenzimidazoles with inorganic phosphoric acids and organic phosphonic acids, and with respect to the repeating structural units constituting the polybenzimidazoles. The total amount of inorganic phosphoric acids and organic phosphonic acids is in the range of 20 mol% to 2000 mol%, and the molar ratio of the inorganic phosphoric acids to the organic phosphonic acids (inorganic phosphoric acids: organic phosphonic acids) is 5:95. To 90:10.

  In the method for producing a proton conductive electrolyte membrane for a fuel cell according to the present invention, the inorganic phosphoric acid and the organic phosphonic acid are mixed in a molar ratio (inorganic phosphoric acid: organic phosphonic acid) in the range of 5:95 to 90:10. And a step of impregnating polybenzimidazoles with the mixed solution.

  Further, the fuel cell of the present invention includes an oxygen electrode, a fuel electrode, an electrolyte membrane sandwiched between the oxygen electrode and the fuel electrode, and an oxidant distribution plate provided with an oxidant channel on the oxygen electrode side. A fuel cell in which a fuel flow plate provided with a fuel flow path is disposed on the fuel electrode side as a unit cell, and the electrolyte membrane is a proton conductive electrolyte membrane for a fuel cell as described above It is characterized by being.

According to the proton conductive electrolyte membrane for a fuel cell of the present invention, polybenzimidazoles are impregnated with inorganic phosphoric acids and organic phosphonic acids at a specific molar ratio and at a specific impregnation rate, so that high proton conductivity is obtained. At the same time, dissolution of polybenzimidazoles by an acid can be prevented, and proton conductivity can be stably maintained over a long period of time even at high temperatures.
Further, according to the method for producing a proton conductive electrolyte membrane of the present invention, it is sufficient to impregnate polybenzimidazoles with a mixed solution in which inorganic phosphoric acids and organic phosphonic acids are mixed at a specific molar ratio. It is possible to easily produce a proton-conducting electrolyte membrane that is excellent in solubility.
In addition, according to the fuel cell of the present invention, since it has an electrolyte membrane that is highly soluble in acid and excellent in proton conductivity, it is not humidified in the range of 100 ° C. to 300 ° C. or a high relative humidity of 50% or less. Stable power generation performance can be maintained over a long period of time even under low humidity operating conditions.

Hereinafter, embodiments of the present invention will be described in detail.
A proton conductive electrolyte membrane (hereinafter referred to as an electrolyte membrane) for a fuel cell according to this embodiment is constituted by impregnating polybenzimidazoles with inorganic phosphoric acids and organic phosphonic acids.
Hereinafter, each component contained in the electrolyte membrane of the present embodiment will be described.

The polybenzimidazoles are the backbone of the electrolyte membrane of this embodiment, and the shape of the electrolyte membrane is kept constant by the polybenzimidazoles. In the present invention, an electrolyte membrane is obtained by impregnating a film-like polybenzimidazole with an inorganic phosphoric acid and an organic phosphonic acid.
Polybenzimidazoles are excellent in heat resistance, and can be retained in a large amount when impregnated with inorganic phosphoric acids or organic phosphonic acids, and are suitable as a constituent of an electrolyte membrane for a fuel cell. is there.
Examples of polybenzimidazoles according to the present embodiment include polymers represented by the following chemical formulas (a) to (c) or derivatives thereof. In particular, methylated polybenzimidazoles having a methyl group introduced are preferable as the derivative.

  In the chemical formulas (a) to (c), n indicating the number of repeating structural units is 10 to 100,000. If n is 10 or more, the mechanical strength of polybenzimidazoles can be improved and an electrolyte membrane excellent in strength can be formed. If n is 100,000 or less, the solubility of polybenzimidazoles in organic solvents can be achieved. This improves the moldability of polybenzimidazoles and increases the degree of freedom of the shape of the electrolyte membrane.

  Polybenzimidazoles can be produced by known techniques. For example, the production methods described in US Pat. No. 3,313,783, US Pat. No. 3,509,108, US Pat. No. 3,555,389 are preferable.

Next, the inorganic phosphoric acid impregnated in the polybenzimidazoles is preferably, for example, metaphosphoric acid, orthophosphoric acid, paraphosphoric acid, triphosphoric acid, tetraphosphoric acid, and more preferably orthophosphoric acid.
In addition, the organic phosphoric acid impregnated in the polybenzimidazoles is preferably an alkylphosphonic acid such as methylphosphonic acid, ethylphosphonic acid, or propylphosphonic acid, or vinylphosphonic acid or phenylphosphonic acid, and more preferably vinylphosphonic acid. .

  The impregnation rate (doping amount) of these inorganic phosphoric acids and organic phosphoric acids with respect to polybenzimidazoles is the sum of inorganic phosphoric acids and organic phosphoric acids, and is 20 mol% or more and 2000 mol with respect to the repeating structural units of polybenzimidazoles. % Or less is preferable, and a range of 50 mol% or more and 1500 mol% or less is more preferable.

Impregnation rate, the weight before and after the film impregnating the acid W _i and W _d, molecular weight M _u of the repeating structural unit of _{polybenzimidazole,} a molar ratio of inorganic phosphorus acids and organic phosphonic acids a: 100-a When the molecular weights of inorganic phosphoric acids and organic phosphonic acids are M _ip and M _op , respectively, it can be obtained by the following mathematical formula.

  When the impregnation rate is 20 mol% or more, the proton conductivity of the electrolyte membrane is sufficiently high, and good power generation characteristics can be exhibited when this electrolyte membrane is incorporated in a fuel cell. Further, when the impregnation rate is 2000 mol% or less, the impregnation rate with respect to the polybenzimidazoles is not excessive, the polybenzimidazoles are not dissolved, and the proton conductivity can be stably maintained over a long period of time. .

  The molar ratio of the inorganic phosphoric acid and the organic phosphonic acid is preferably in the range of inorganic phosphoric acid: organic phosphonic acid = 5: 95 to 90:10, and more preferably in the range of 10:90 to 85:15. When the molar ratio of the inorganic phosphoric acid and the organic phosphonic acid is within this range, dissolution of the electrolyte membrane at a high temperature can be prevented without impairing the electrochemical characteristics of the electrolyte membrane.

When polybenzimidazoles are impregnated with either inorganic phosphoric acid or organic phosphonic acid alone, polybenzimidazoles are easily dissolved.
Polybenzimidazoles have a phenylene skeleton (carbon six-membered ring) and imidazole skeleton (carbon and nitrogen five-membered ring) in the molecule. The imidazole moiety has a hydrogen atom bonded to a nitrogen atom, and the molecular chains of polybenzimidazoles strongly interact with each other by intermolecular hydrogen bonds generated between the nitrogen and hydrogen atoms. In addition, this imidazole skeleton part is relatively hydrophilic compared to the phenylene skeleton part. On the other hand, the phenylene skeleton part has organic (hydrophobic) properties compared to the imidazole skeleton part.

  When such polybenzimidazoles are impregnated with inorganic phosphoric acid typified by orthophosphoric acid, the inorganic phosphoric acid easily interacts with an imidazole skeleton portion having a lower organic property than the phenylene skeleton portion. When orthophosphoric acid acts on the imidazole, the imidazole moiety is solvated by inorganic phosphoric acids. Thereby, it is considered that the interaction between the molecular chains of the polybenzimidazoles is cut, and as a result, the polybenzimidazoles are dissolved. Electrolyte membranes impregnated only with inorganic phosphoric acids in polybenzimidazoles have been considered promising as electrolyte membranes for fuel cells because of their excellent proton conductivity. It is easy to dissolve at the above high temperatures.

  In addition, when polybenzimidazoles are impregnated with organic phosphonic acids, the organic phosphonic acids easily interact with the phenylene skeleton portion, and when orthophosphoric acid acts on the phenylene portion, the phenylene portion is solvated by the organic phosphonic acids. The Thereby, it is considered that the interaction between the molecular chains of the polybenzimidazoles is cut, and as a result, the polybenzimidazoles are dissolved.

  On the other hand, in the electrolyte membrane of this embodiment, polybenzimidazoles are impregnated with both inorganic phosphoric acids or organic phosphonic acids, thereby preventing the dissolution of polybenzimidazoles. This is because, by mixing inorganic phosphoric acid and organic phosphoric acid at a specific molar ratio, organic phosphonic acid inhibits the coordination of inorganic phosphoric acid to the imidazole skeleton, while inorganic phosphoric acid is phenylene of organic phosphonic acid. Inhibits coordination to the skeleton, resulting in moderate inhibition of solvation of inorganic and organic phosphates with respect to polybenzimidazoles, thereby reducing the solubility of polybenzimidazoles in acids. This is probably because of this.

  Therefore, in the electrolyte membrane of the present embodiment, since inorganic phosphoric acids and organic phosphonic acids are impregnated in polybenzimidazoles, high proton conductivity can be expressed and at the same time, dissolution of polybenzimidazoles by acids is prevented. The proton conductivity can be stably maintained over a long period of time even at high temperatures.

The method for producing an electrolyte membrane of the present embodiment is obtained by mixing polybenzimidazoles and inorganic phosphoric acids and organic phosphonic acids in a molar ratio (inorganic phosphoric acids: organic phosphonic acids) in the range of 5:95 to 90:10. It can be easily produced by dipping in a mixed solution and impregnating (doping) polybenzimidazoles with inorganic phosphoric acids and organic phosphonic acids.
More specifically, for example, a polybenzimidazole film formed into a film shape is obtained by applying a solution in which polybenzimidazoles are dissolved to a glass plate and heating. Next, this membrane is immersed in a mixed solution in which inorganic phosphoric acids and organic phosphonic acids are mixed in the above molar ratio, and polybenzimidazoles are impregnated (doped) with inorganic phosphoric acids and organic phosphonic acids. The impregnation rate can be controlled, for example, by adjusting the impregnation temperature and the impregnation time.

  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 is disposed outside the oxygen electrode 2, the fuel electrode 3, the electrolyte membrane 4 of the present embodiment sandwiched between the oxygen electrode 2 and the fuel electrode 3, and the oxygen electrode 2. It is composed of an oxidant flow plate 5 having an oxidant flow channel 5a, and a fuel flow plate 6 having a fuel flow channel 6a disposed outside the fuel electrode 3, and has an operating temperature of 100 ° C to 300 ° C and humidity is not humidified. Or it operates under the condition of relative humidity of 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 components constituting the electrolyte membrane of this embodiment instead of the hydrophobic binder or together with the hydrophobic binder. By adding the components constituting the electrolyte membrane of the present embodiment, 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 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.

  The operating temperature of the fuel cell is about 100 ° C. to 300 ° C. Under such conditions, the solubility of the polybenzimidazoles constituting the electrolyte membrane increases, and therefore the electrolyte membrane of this embodiment includes polyphosphoric imidazoles and inorganic phosphoric acids. Since it is impregnated with organic phosphonic acids, it can exhibit high proton conductivity and at the same time prevent acid dissolution of polybenzimidazoles and stabilize proton conductivity over a long period of time even at high temperatures. Can be maintained.

  With the above configuration, a fuel cell that stably exhibits good power generation performance for a long period of time even when the operating temperature is 100 ° C. or more and 300 ° C. or less, no humidification, or relative humidity 50% or less can be obtained. It can be suitably used for home power generation or portable equipment.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Examples 1-8 and Comparative Examples 1-5)
First, a polybenzimidazole membrane was produced by the following steps.
Poly-2,2 ′-(m-phenylene) -5,5′- with reference to production methods described in U.S. Pat. No. 3,313,783, U.S. Pat. No. 3,509,108, U.S. Pat. No. 3,555,389. Bibenzimidazole (PBI) was prepared. Next, 1 g of this PBI was dissolved in 10 g of dimethylacetamide (DMAC) on an oil bath, the solution was cast on a glass plate on a hot plate, and DMAC was distilled off until a film was obtained. Furthermore, it vacuum-dried at 120 degreeC for 12 hours, DMAC was distilled off completely, and the 20-micrometer-thick PBI film | membrane was manufactured.

Next, orthophosphoric acid having a purity of 85% (manufactured by Tokyo Chemical Industry Co., Ltd.) as inorganic phosphoric acids and vinylphosphonic acid having a purity of 85% (manufactured by Tokyo Chemical Industry Co., Ltd.) as organic phosphonic acids are prepared, and orthophosphoric acid and vinylphosphonic acid are prepared. Were mixed at a predetermined molar ratio to prepare a mixed solution. Then, the previously prepared PBI membrane was immersed in this mixed solution at room temperature for 2 hours to impregnate (dope) the PBI membrane with orthophosphoric acid and vinylphosphonic acid.
Thus, the electrolyte membrane of Examples 1-8 and Comparative Examples 1-5 was manufactured. Table 1 shows the mixing ratio (molar ratio) of orthophosphoric acid and vinylphosphonic acid in each electrolyte membrane.
Moreover, the total amount (impregnation rate) of orthophosphoric acid and vinylphosphonic acid with respect to the repeating structural unit of PBI in each Example and each Comparative Example was calculated according to the above formula (1), and Table 1 shows the results.

  The obtained electrolyte membrane was measured for mass retention and proton conductivity at 150 ° C. by the following procedure. The results are shown in Table 1 and FIG.

(Mass retention)
An undoped PBI film is prepared, and the PBI film is immersed in a mixed solution of orthophosphoric acid and vinylphosphonic acid having a mixing ratio (molar ratio) shown in Table 1 and is heated in an oven at 150 ° C. Held for hours. Thereafter, the PBI membrane was pulled up, washed with water and dried, and the mass retention rate was measured from the mass difference before and after immersion. This mass retention rate indicates the solubility of the PBI film in the mixed solution, and the higher the mass retention rate, the lower the solubility in the mixed solution. This mass retention rate is a result of performing the phosphoric acid in an extremely large amount with respect to the electrolyte membranes of Examples and Comparative Examples, and corresponds to an accelerated test for evaluating acid solubility of Examples and Comparative Examples. It will be a thing.

(Proton conductivity)
The electrolyte membranes of Examples 1 to 8 and Comparative Examples 1 to 5 were sandwiched between platinum electrodes (diameter 13 mm), and proton conductivity was determined from the resistance values obtained by complex impedance measurement at 150 ° C.

As shown in Table 1, when the molar ratio of vinylphosphonic acid is in the range of 10 to 95%, the mass retention is excellent at 80% or higher, and at the same time excellent at 0.01 S / cm or higher. It was found to show proton conductivity.
On the other hand, when the molar ratio of vinylphosphonic acid is in the range of less than 0 to less than 10% and more than 95%, there is no significant difference in proton conductivity compared to the examples, but in the mass retention measurement as an accelerated test, the PBI membrane Was partially or completely dissolved, and the acid dissolution resistance was found to be inferior.

  Next, a commercially available fuel cell electrode (manufactured by Electrochem) was used as a pair of porous electrodes, and the electrolyte membranes of Example 6 and Comparative Example 1 were sandwiched to form a single cell (fuel cell).

Hydrogen was supplied to the fuel and air was supplied to the oxidant, and a power generation test was conducted at 150 ° C. FIG. 3 shows the power generation efficiency at the initial stage of power generation.
In addition, power generation was performed under the condition of obtaining a constant current corresponding to a current density of 300 mA / cm ² , the battery was operated for a long time, and the change over time in the closed circuit voltage was measured. Moreover, the time-dependent change of the circuit voltage (OCV) was measured simultaneously. The results are shown in FIG.

  As shown in FIG. 3, there was no difference in the initial power generation efficiency between Example 6 and Comparative Example 1. However, as shown in FIG. 4, in the power generation test over a long period of time, even when Example 6 reaches about 500 hours, the circuit voltage and the closed circuit voltage are hardly deteriorated, whereas in Comparative Example 1, it is 300 hours. From around this time, the closed circuit voltage and the open circuit voltage gradually decreased. This is presumably because the PBI component contained in the electrolyte membrane was gradually dissolved.

  As described above, the electrolyte membranes of Examples 1 to 8 are not inferior in electrical characteristics and superior in acid solubility resistance to the electrolyte membranes of Comparative Examples 1 to 5. Recognize.

Example 9
Methylphosphonic acid (manufactured by Aldrich) was prepared as an organic phosphonic acid, and a mixed liquid in which the molar ratio of orthophosphoric acid and methylphosphonic acid was orthophosphoric acid: methylphosphonic acid = 80: 20 was prepared, and the PBI membrane was immersed in the mixed liquid An electrolyte membrane of Example 9 was produced in the same manner as in Examples 1 to 8 and Comparative Examples 1 to 5 except for those described above. The impregnation rate of this Example 9 was 1050 mol%.
When the mass retention rate and proton conductivity at 150 ° C. of the electrolyte membrane of Example 9 were measured in the same manner as described above, the weight retention rate was 90.3% and the proton conductivity was 0.016 S / cm. The performance equivalent to 1-9 was shown.

(Examples 10-11 and Comparative Examples 6-7)
A mixed solution of orthophosphoric acid and vinylphosphonic acid was prepared. The molar ratio of vinylphosphonic acid in this mixed solution is 80 mol%, which is the same as in Example 6. In this mixed solution, a PBI membrane was prepared at room temperature for 10 minutes in Example 10, 30 minutes at 80 ° C. in Example 11, 5 minutes at room temperature in Comparative Example 6, 90 minutes at 80 ° C. in Comparative Example 7, The electrolyte membranes of Examples 10 to 11 and Comparative Examples 6 to 7 were manufactured in the same manner as Example 6 except that each was immersed. Table 2 shows the impregnation rate of the obtained electrolyte membrane. Table 2 also shows the mass retention rate of each electrolyte membrane and the proton conductivity at 150 ° C.

As shown in Table 2, when the impregnation rate is in the range of 20 to 2000 mol% (Examples 10 and 11), the mass retention is excellent at 80% or more, and at the same time, 0.01 S / It was found that excellent proton conductivity of cm or more was exhibited.
On the other hand, when the impregnation rate was less than 20 mol% (Comparative Example 6), although the acid solubility was excellent, the proton conductivity was greatly reduced. Moreover, when the impregnation rate exceeded 2000 mol% (Comparative Example 7), it was found that the PBI film was partially or completely dissolved in mass retention measurement as an accelerated test, and the acid solubility resistance was poor. In the proton conductivity measurement, when the electrolyte membrane was sandwiched between platinum electrodes, excess acid oozed out of the membrane and could not be measured stably.

  The proton conductive electrolyte membrane of the present invention is a novel polymer electrolyte membrane that not only exhibits excellent proton conductivity as a polymer electrolyte membrane that can be operated under high-temperature and non-humidified conditions, but also exhibits sufficient practical characteristics in terms of durability. It is. Taking advantage of this characteristic, the proton conductive electrolyte membrane of the present invention can be used in a wide range of applications such as various battery electrolyte membranes, sensors, capacitors, and electrolytic membranes, and can contribute to the development and growth of the industrial world.

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 relationship between the molar ratio of vinylphosphonic acid in the electrolyte membrane, the mass retention rate, and the proton conductivity. FIG. 3 is a graph showing the relationship between the initial closed circuit voltage and the generated current density of the fuel cells provided with the electrolyte membranes of Example 6 and Comparative Example 1. FIG. 4 is a graph showing the relationship between the closed circuit voltage and the closed circuit voltage in the power generation condition of the fuel cell having the electrolyte membrane of Example 6 and Comparative Example 1 at a current density of 0.3 mA / cm ² and the power generation time.

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 membrane)

Claims (3)

Polybenzimidazoles are impregnated with inorganic phosphoric acids and organic phosphonic acids,
The total amount of the inorganic phosphoric acid and the organic phosphonic acid is in the range of 20 mol% or more and 2000 mol% or less with respect to the repeating structural unit constituting the polybenzimidazole, the inorganic phosphoric acid and the organic phosphonic acid, A proton conductive electrolyte membrane for a fuel cell, wherein the molar ratio (inorganic phosphoric acid: organic phosphonic acid) is in the range of 5:95 to 90:10.   A step of impregnating polybenzimidazoles with a mixed solution in which inorganic phosphoric acids and organic phosphonic acids are mixed in a molar ratio (inorganic phosphoric acids: organic phosphonic acids) in the range of 5:95 to 90:10. A method for producing a proton conductive electrolyte membrane for a fuel cell. An oxidant distribution plate comprising an oxygen electrode, a fuel electrode, an electrolyte membrane sandwiched between the oxygen electrode and the fuel electrode, and provided with an oxidant channel is disposed on the oxygen electrode side to provide a fuel channel. A fuel cell having a unit cell of a fuel flow plate arranged on the fuel electrode side, wherein the electrolyte membrane is a proton conductive electrolyte membrane for a fuel cell according to claim 1. Fuel cell.

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