KR100668316B1 - Gel electrolyte and fuel cell employing the same - Google Patents

Abstract

The present invention provides a gel electrolyte comprising a mixture of an acid and a polymer compound swelling with respect to the acid, wherein the polymer compound is a partially methylated polybenzimidazole having at least a part of a substituent R having a polybenzimidazole structure as a methyl group. A gel electrolyte and a fuel cell employing the same are provided. The gel electrolyte can exhibit long-term stable good proton conductivity at an operating temperature of about 100 to 300 ° C., under an operating condition of no humidification or a relative humidity of 50% or less.

Description

Gel electrolyte and fuel cell employing the same {Gel electrolyte and fuel cell employing the same}

1 is a graph showing the relationship between the swelling ratio of the gel electrolyte of Examples 1-3 and Comparative Example 1 and the immersion time of phosphoric acid,

2 is a graph showing the relationship between the voltage and the current density of the fuel cells of Example 4 and Comparative Example 2. FIG.

The present invention relates to a gel electrolyte and a fuel cell employing the same. More specifically, the present invention relates to a gel electrolyte and a gel electrolyte showing good proton conductivity even under an operating temperature of 100 to 300 ° C. even at 50% or less of humidity. Relates to a fuel cell.

In the fuel cell, from the viewpoint of power generation efficiency, system efficiency, and long-term durability of the constituent members, good proton conductivity can be achieved under operating conditions of no humidity or low humidity of 50% or less relative humidity at an operating temperature of about 100 to 300 ° C. There is a demand for a nut electrolyte membrane that exhibits long-term stability. Considering the above requirements in the development of a conventional solid polymer electrolyte fuel cell, sufficient proton conductivity and output can be obtained in a perfluorocarbon sulfonic acid membrane at an operating temperature of 100 to 300 ° C. and a relative humidity of 50% or less. There was an uncountable flaw.

Japanese Patent Laid-Open No. 11-503262 discloses a solid electrolyte membrane made of polybenzimidazole doped with a strong acid such as phosphoric acid. According to such a solid electrolyte membrane, it has excellent oxidation resistance and heat resistance, and can operate | operate even at high temperature up to 200 degreeC.

However, even in the solid electrolyte membrane described in the above patent publication, there is a problem that sufficient proton conductivity cannot be obtained under an environment with low relative humidity.

The technical problem of the present invention is to solve the above-described problems, a gel capable of exhibiting a long-term stable good proton conductivity at operating conditions of about 100 to 300 ℃, no humidity or 50% or less relative humidity An electrolyte and a fuel cell using the same are provided.

In order to achieve the above technical problem, the present invention adopts the following configuration.

The gel electrolyte of the present invention is a gel electrolyte formed by mixing an acid and a high molecular compound swelling with respect to the acid, wherein the high molecular compound has at least a part of a substituent R having a polybenzimidazole structure represented by the following formula (1) as a methyl group. Methylated polybenzimidazole.

Examples of the acid include phosphoric acid. This phosphoric acid also includes both orthophosphoric acid and condensed phosphoric acid.

[Formula 1]

In Formula 1, R is CH ₃ or H, and n is 10-100000.

According to the above structure, partially methylated polybenzimidazole is used as the polymer compound, and the higher the degree of methylation, the more acid is taken in and swollen (gelled), so that the proton conductivity of the gel electrolyte is higher than that in the case where it is not methylated. Can improve.

The gel electrolyte of the present invention is also the gel electrolyte described above, wherein the partially methylated polybenzimidazole is polymethylated benzimidazole having a methylation rate of less than 80 mol%.

According to the said structure, since the methylation rate is less than 80 mol%, partially methylated polybenzimidazole does not melt | dissolve by an acid.

In addition, the gel electrolyte of the present invention is the gel electrolyte described above, wherein the partially methylated polybenzimidazole is composed of a mixture of polyN methylbenzimidazole having a methylation rate of 100 mol% and a polybenzimidazole having 0 mol% of methylation, , The content rate of the polyN methylbenzimidazole is less than 80 mol%.

According to the above constitution, a mixture of polymethylbenzimidazole and polybenzimidazole having a methylation rate of 0 mol% is used as the partially methylated polybenzimidazole. The methylation rate can be easily changed, and the optimization of the gel electrolyte characteristics can be easily performed.

In addition, the gel electrolyte of the present invention is a gel electrolyte as described above, wherein the partially methylated polybenzimidazole is a mixture of polymethylated benzimidazole having a methylation rate of X mol% and a polybenzimidazole having a methylation rate of 0 mol%. When the weight of the polymethylated benzimidazole is A and the weight of the polybenzimidazole is B, f (mol%) = A / B is less than 80 mol%. It features.

However, said X is 80 mol% or more and less than 100 mol%.

According to the above structure, as the partially methylated polybenzimidazole, a mixture of polymethylated benzimidazole having a methylation rate of X% and polybenzimidazole having a methylation rate of 0 mol% is used, and partially methylated poly by changing the blending of the mixture. The methylation rate of benzimidazole can be easily changed, and the optimization of the characteristic of a gel electrolyte can be made easy.

Next, the fuel cell of the present invention is composed of a pair of electrodes and an electrolyte membrane disposed between each electrode, and part or all of the electrolyte membrane consists of the gel electrolyte according to any one of the above, and also a part of the electrode. It is characterized in that the gel electrolyte is contained.

According to the above configuration, since the gel electrolyte having excellent proton conductivity is provided as the electrolyte membrane and the gel electrolyte is also provided in part of the electrode, the internal impedance of the fuel cell can be reduced and the current density can be increased. In particular, by containing a gel electrolyte in a part of the electrode, protons are easily conducted to the inside of the electrode, and the internal resistance of the electrode itself can be reduced.

In addition, the fuel cell of the present invention preferably has an operating temperature in the range of 100 to 300 ° C.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail.

The fuel cell according to the present invention is composed of a hydrogen electrode (electrode), an oxygen electrode (electrode), and a gel electrolyte disposed between the hydrogen electrode and the oxygen electrode, and operates at a temperature of 100 to 300 ° C. The gel electrolyte according to the present invention has proton conductivity, and conducts protons (hydrogen ions) generated at the hydrogen electrode side to the oxygen electrode side. Protons conducted by the gel electrolyte electrochemically react with oxygen ions in the oxygen electrode to generate water and generate electrical energy.

In the fuel cell according to the present invention, the gel electrolyte is also contained in the hydrogen electrode and the oxygen electrode. That is, the hydrogen electrode and the oxygen electrode contain an electrode material such as activated carbon and a binder for solidifying the electrode material, and part or all of the binder is composed of the gel electrolyte according to the present invention. This configuration makes protons easier to conduct between the inside of the electrode and the outside of the electrode, and the internal resistance of the electrode is reduced.

Next, the gel electrolyte which concerns on this invention is comprised by mixing phosphoric acid and the high molecular compound swelling about phosphoric acid. As phosphoric acid, ortho phosphoric acid and condensed phosphoric acid can be illustrated. Moreover, as a high molecular compound, the partially methylated polybenzimidazole which made at least one part of the substituent R of the polybenzimidazole structure shown by the said Formula (1) as a methyl group can be illustrated. In addition, in Formula 1, R is CH ₃ or H, and n is 10-100000. If n is less than 10, mechanical strength is usually poor, and if n is more than 100,000, solubility in a solvent or the like is remarkably lowered.

Partially methylated polybenzimidazole accepts and gelatinizes phosphoric acid. Particularly, the higher the degree of methylation, the greater the amount of phosphoric acid to receive and swell. As described above, the gel electrolyte according to the present invention may contain a large amount of phosphoric acid, thereby increasing proton conductivity.

As the partially methylated polybenzimidazole according to the present invention, any one of the following (1) to (3) can be used.

(1) Polymethylated benzimidazole in which the methylation rate is adjusted to 5 mol% or more and less than 80 mol%, Preferably it is 20 mol% or more and less than 80 mol%.

(2) It consists of a mixture of polyN methylbenzimidazole of 100 mol% of methylation rates, and polybenzimidazole of 0 mol% of methylation rates, and the content rate of polyN methylbenzimidazole is 5 mol% or more and 80 mol Less than%, Preferably it is 20 mol% or more and less than 80 mol%.

(3) A mixture of polymethylated benzimidazole having a methylation rate of X mol% and polybenzimidazole having a methylation rate of 0 mol%, wherein the weight of polymethylated benzimidazole is A, and the polybenzimidazole When the weight of is B, f obtained by f (mol%) = AX / (A + B) is not less than 5 mol% and less than 80 mol%, preferably not less than 20 mol% and less than 80 mol%. However, said X is 80 mol% or more and less than 100 mol%.

According to the structure of said (1)-(3), all the methylation rates of partially methylated polybenzimidazole can be 5 mol% or more and less than 80 mol%, Preferably it is 20 mol% or more and less than 80 mol%. That is, in (1), the methylation rate can be adjusted by adjusting the reaction degree for methylation. In (2), the methylation rate can be substantially adjusted by adjusting the content ratio of polyN methylbenzimidazole. In (3), the methylation rate can be substantially adjusted by adjusting the value of f.

If the methylation rate of the partially methylated polybenzimidazole is less than 5 mol%, it is not preferable because the phosphoric acid cannot be sufficiently received and the proton conductivity becomes insufficient (decreases), and the methylation rate is 80 mol% or more. It is not preferable because the phosphoric acid is so accepted that the partially methylated polybenzimidazole is dissolved.

In addition, in this specification, one part of substituent R of the polybenzimidazole structure shown by the said General formula (1) is made into methyl, and the other part made into hydrogen is called "polymethylated benzimidazole." In addition, what made all the substituent R of the polybenzimidazole structure shown by the said Formula (1) into a methyl group is called "polyN methylbenzimidazole." In addition, what made hydrogen of all the substituents R of the polybenzimidazole structure shown by the said Formula (1) is called "polybenzimidazole."

As described above, according to the gel electrolyte according to the present invention, the proton conductivity can be increased, and the current density of the fuel cell can be increased by using this gel electrolyte as a fuel cell, and a high output fuel cell can be constituted. have.

Hereinafter, the present invention will be described with reference to the following examples, but the present invention is not limited only to the following examples.

EXAMPLE

Next, the gel electrolyte of Example 1-4 and Comparative Example 1-2 and the fuel cell using each gel electrolyte were produced, and the various characteristics were evaluated.

Example 1.

Partial Methylation of Polybenzimidazole

A dimethylacetamide solution prepared by adjusting polybenzimidazole to 10% by weight was prepared, and this was taken by weighing 30.08 g in a Schlenk tube. Under argon gas flow, an excess amount (0.24 g) of lithium hydride was added little by little at room temperature, and then refluxed at 80 ° C. After the temperature was once lowered to room temperature, the reaction solution was cooled to 0 ° C. using an ice bath, 1.56 g of methyl iodide was weighed out, and the reaction solution was slowly added dropwise to the reaction solution. After dropping, the reaction solution was gradually returned to room temperature while stirring, and refluxed again at 60 ° C. After lowering the obtained reaction solution to room temperature, it developed by tetrahydrofuran and obtained the powdery solid. Furthermore, the solid was washed with water until pH reached 7, and then dried in vacuo to obtain the desired partially methylated polybenzimidazole. The methylation rate was about 20 mol%, as confirmed by the integral ratio of NMR.

Preparation of Gel Electrolyte

The synthesized partially methylated polybenzimidazole is once again dissolved in a dimethylacetamide solution at a concentration of 10% by weight, the solution is coated on a glass plate using a doctor blade, and once the surface becomes opaque, It dried at 50 degreeC, and further dried at 150 degreeC. Thereafter, the glass was immersed in each glass plate to remove the swollen film. Then, vacuum drying was performed on 60 degreeC and 0.1 torr conditions, and the polymer membrane was obtained. The film thickness was about 30 micrometers.

Subsequently, the obtained polymer membrane was directly immersed in 85% phosphoric acid at room temperature. After 2 hours, the membrane was pulled up and the surface phosphoric acid was wiped off with a Kimberly wipe. Thus, the gel electrolyte of Example 1 was prepared.

Example 2-3

The gel electrolyte of Example 2 was prepared in the same manner as in Example 1 except that the methylation rate was changed to 40 mol% by changing the injection ratio of methyl iodide. In the same manner, the gel electrolyte of Example 3 having a methylation rate of 60 mol% was prepared.

Example 4

A dimethylacetoamide solution containing 10% by weight of fully methylated polyN methylbenzimidazole and a dimethylacetoamide solution containing 10% by weight of polybenzimidazole not methylated at a weight ratio of 1 Mixed to 1 :. The polymer film was obtained by apply | coating on a Hiya glass plate like Example 1 using this mixed solution, and drying and immersing in a water tank. The polymer electrolyte was immersed in phosphoric acid as in Example 1 to prepare a gel electrolyte of Example 4 having a substantial methylation rate of 50 mol%.

Moreover, after apply | coating thinly the 10 times dilution solution of the above-mentioned polymer film to the carbon paper which apply | coated the platinum bearing carbon of EIectrochem company make, it vacuum-dried to make an electrode. Two coin electrodes were prepared, and the fuel cell of Example 4 was manufactured by sandwiching the gel electrolyte of Example 4 between electrodes.

Comparative Example 1

A polymer membrane of partially methylated polybenzimidazole was obtained in the same manner as in Example 1 except that the methylation rate was changed to 80 mol% by changing the injection ratio of methyl iodide. This was used as a sample of Comparative Example 1.

Comparative Example 2

The gel electrolyte and fuel cell of the comparative example 4 which consist of polybenzimidazole of 0% of methylation rates were manufactured.

evaluation

Swelling Rate and Proton Conductivity of Gel Electrolyte

For the gel electrolytes of Examples 1-3 and Comparative Example 1, the swelling ratio was calculated from the weight (M1) of the polymer membrane before being immersed in phosphoric acid and the weight (M2) of the gel electrolyte after phosphoric acid immersion. Swelling ratio (weight%) was calculated | required as swelling ratio (weight%) = M2 / M1 * 100. The relationship between the immersion time in phosphoric acid and a swelling ratio is shown in FIG.

In addition, the proton conductivity of the gel electrolyte of Example 1-4 and Comparative Example 1 is shown in Table 1. Proton conductivity is to measure the proton conductivity in a condition close to unhumidity, and to penetrate the gel electrolyte into a circle having a diameter of 13 mm, insert a platinum blocking electrode therein, and leave it at 70 ° C. for 1 hour, and then change the resistance between the electrodes to AC. Measured by the impedance method.

As shown in FIG. 1, the swelling ratio reached an equilibrium at about 30 minutes. The equilibrium swelling ratio measured at the passage of 70 minutes was 450% in Example 1, 530% in Example 2, and 660% in Example 3. It can be seen that as the methylation rate is higher, the swelling rate of the gel electrolyte is increased. On the other hand, in the comparative example 1 whose methylation rate is 80 mol%, after 70 minutes passed after immersion in phosphoric acid, the gel electrolyte itself melt | dissolved.

Next, as shown in Table 1, it can be seen that for Example 1-4, the higher the methylation rate, the higher the proton conductivity. On the other hand, in Comparative Example 1, since it was not obtained as a self-supporting film as described above, the ion conductivity could not be measured.

Similarly, the swelling ratio and proton conductivity of the gel electrolyte of Example 4 were measured, and the equilibrium swelling ratio after about 70 minutes was about 600%, and the proton conductivity at 70 ° C. was 4.00 mS · cm ⁻¹ .

In addition, when the swelling ratio and proton conductivity were measured also about the comparative example 2, the equilibrium swelling ratio was about 400% and the proton conductivity in 70 degreeC was 1.90 mS * cm <^-1> .

TABLE 1

Methylation Rate (mol%) Proton Conductivity (mScm ^-1 ) Example 1 20 2.78 Example 2 40 2.50 Example 4 50 4.00 Example 3 60 5.72 Comparative Example 1 80 Not measurable Comparative Example 2 0 1.90

Fuel cell performance

In the fuel cells of Example 4 and Comparative Example 2, the laminate of the electrode and the gel electrolyte was separated by a carbon separator, and a power generation test was performed using hydrogen as an anode gas and oxygen as a cathode gas. Battery temperature was 130 degreeC, the supply amount of hydrogen and oxygen was 100 ml / min, and humidification of the supply gas was not performed in particular. In addition, the electrode area of Example 4 was 7.84 cm ² , and the electrode area of Comparative Example 2 was 10.24 cm ² . 2 shows the relationship between the voltage of the fuel cell and the current density.

As shown in FIG. 2, in Example 4, power generation was possible until the current density was 1.6A / cm ² , whereas in Comparative Example 2, power generation was possible up to 0.8A / cm ² . Since the fuel cell of Example 4 has a high proton conductivity of the gel electrolyte, it is considered that the internal resistance of the fuel cell is suppressed low, whereby a high output is obtained.

As described above, according to the gel electrolyte of the present invention, the proton conductivity can be increased, and the current density of the fuel cell can be increased by using this gel electrolyte as a fuel cell, and a high output fuel cell can be constituted.

Claims (7)

A gel electrolyte formed by mixing an acid and a high molecular compound swelling with respect to the acid, The polymer electrolyte is a partially methylated polybenzimidazole having at least a part of the substituent R of the polybenzimidazole structure represented by the following formula (1) as a methyl group. [Formula 1]

In Formula 1, R is CH ₃ or H, and n is 10-100000. The gel electrolyte according to claim 1, wherein the partially methylated polybenzimidazole is polymethylated benzimidazole having a methylation rate of less than 80 mol%. The polymethylmethylbenzide according to claim 1, wherein the partially methylated polybenzimidazole is a mixture of polyNmethylbenzimidazole having a methylation rate of 100 mol% and a polybenzimidazole having a methylation rate of 0 mol%. A gel electrolyte, characterized in that the content of imidazole is less than 80 mol%. The polymethylated benzimidazole according to claim 1, wherein the partially methylated polybenzimidazole is a mixture of polymethylated benzimidazole having a methylation rate of X mol% and a polybenzimidazole having a methylation rate of 0 mol%, When the weight of the doazole is A and the weight of the polybenzimidazole is B, f (mol%) = AX / (A + B), provided that X is 80 mol% or more and less than 100 mol%. The gel electrolyte obtained f is less than 80 mol%. A pair of electrodes and an electrolyte membrane disposed between the electrodes, A part or all of the said electrolyte membrane consists of the gel electrolyte in any one of Claims 1-4, The fuel cell characterized by the above-mentioned. The fuel cell according to claim 5, wherein the gel electrolyte is contained in a part of the electrode. A fuel cell according to claim 5, wherein the operating temperature is in the range of 100 to 300 ° C.

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