KR100707159B1 - Gel electrolyte, electrode for fuel cell, and fuel cell - Google Patents

Abstract

Provided is a gel electrolyte that exhibits high proton conductivity even under conditions of no humidification and high temperature, and has excellent mechanical strength. The gel electrolyte includes an acid and a matrix polymer that swells with respect to the acid, wherein the matrix polymer is a polyparavanic acid or polyparavanic acid derivative.

Gel Electrolyte, Proton Conductivity, Polybaraban Acid

Description

Gel electrolyte, electrode for fuel cell, and fuel cell {Gel electrolyte, electrode for fuel cell, and fuel cell}

1 is a graph showing the relationship between the cell voltage and the current density of the fuel cell of Example 3. FIG.

The present invention relates to a gel electrolyte, a fuel cell electrode and a fuel cell, and more particularly, to a gel electrolyte, a fuel cell electrode and a fuel cell excellent in heat resistance and proton conductivity.

In the fuel cell, from the viewpoint of power generation efficiency, system efficiency, and long-term durability of the components, it is possible to stably maintain long-term stable proton conductivity under operating conditions of 100 ° C to 300 ° C and low humidity of 50% or less relative humidity. An electrolyte membrane is required. In the development of a conventional solid polymer electrolyte fuel cell, it has been examined in view of the above requirements, but in a perfluorosulfonic acid membrane, sufficient proton conductivity and output power are provided at an operating temperature of 100 ° C. to 300 ° C. and a relative humidity of 50% or less. There was a defect that could not be obtained.

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 this type of solid electrolyte membrane, it has excellent oxidation resistance and heat resistance, and can be operated even at a high temperature of 200 ° C.

However, even in a solid electrolyte membrane made of polybenzimidazole doped with phosphoric acid, phosphoric acid of 4-5 times the weight of polybenzimidazole must be contained in order to obtain sufficient proton conductivity for fuel cell operation. Such a film having a high phosphoric acid content has a low mechanical strength and may cause gas crossover when assembled into a fuel cell. On the other hand, if the doping rate of phosphoric acid is lowered to increase the mechanical strength of the film, there is a problem that the proton conductivity is lowered.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a gel electrolyte that exhibits high proton conductivity even under conditions of no humidification and high temperature, and excellent mechanical strength, an electrode for fuel cells and a fuel cell using the gel electrolyte. .

In order to achieve the above object, the present invention provides a gel electrolyte comprising an acid and a matrix polymer swelling with respect to the acid, wherein the matrix polymer is a polyparabanic acid or a polyparabanic acid derivative.

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

Polyparabanic acid is suitable as an electrolyte membrane of a fuel cell because of its high insulation and excellent heat resistance. In addition, polyparabanic acid can contain a large amount of phosphoric acid due to its molecular structure, and can be formed as an integral film without separating from phosphoric acid, thereby increasing proton conductivity.

The gel electrolyte of the present invention is characterized by further containing a water-insoluble heterocyclic nitrogen compound as the gel electrolyte described above.

According to the said structure, by adding a heterocyclic nitrogen compound, the content of phosphoric acid in a gel electrolyte can be improved and proton conductivity can be further improved. In addition, since the heterocyclic nitrogen compound is insoluble in water, even when water is produced as a reaction product of the fuel cell, the heterocyclic nitrogen compound does not have to leak out of the gel electrolyte together with the water, so that the proton conductivity can be maintained for a long time. have.

In the gel electrolyte of the present invention, the heterocyclic nitrogen compound is preferably at least one of imidazole, benzimidazole, pyrazole, pyridine, pyrimidine, pyrazine, pyrrole, purine, phthalocyanine and porphyrin. .

The gel electrolyte of the present invention is the gel electrolyte described above, wherein the content of the heterocyclic nitrogen compound relative to the sum of the matrix polymer and the heterocyclic nitrogen compound is less than 50% by mass. According to this configuration, the mechanical strength of the gel electrolyte can be increased.

Next, the fuel cell electrode of the present invention is characterized by comprising an electrode material and the gel electrolyte according to any one of the above.

According to the above structure, since a gel electrolyte having excellent proton conductivity is provided as part of the electrode, protons are easily conducted to the inside of the electrode, thereby reducing the internal resistance of the electrode itself.

In addition, the fuel cell of the present invention includes a pair of electrodes and an electrolyte membrane disposed between the electrodes, wherein part or all of the electrolyte membrane is one of the gel electrolytes described above, and the gel electrolyte is part of the electrode. It is characterized by containing.

According to the above structure, since the gel electrolyte having excellent proton conductivity is provided, 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.

As described above, the gel electrolyte of the present invention can provide a gel electrolyte that exhibits high proton conductivity even under conditions of no humidification and high temperature, and excellent mechanical strength, an electrode for fuel cells and a fuel cell using the gel electrolyte. .

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 ° C to 300 ° C. The gel electrolyte according to the present invention has proton conductivity and conducts protons (hydrogen ions) generated from the hydrogen electrode side to the oxygen electrode. Protons conducted by the gel electrolyte electrochemically react with oxygen ions at 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 a gel electrolyte according to the present invention. By this configuration, the proton is easily conducted between the inside of the electrode and the outside of the electrode, thereby reducing the internal resistance of the electrode.

Next, the first example of the gel electrolyte according to the present invention is a mixture of phosphoric acid and a matrix polymer that swells with phosphoric acid.

Moreover, the 2nd example of the gel electrolyte which concerns on this invention mixes phosphoric acid, the matrix polymer which swells about phosphoric acid, and a heterocyclic nitrogen compound.

Examples of the phosphoric acid include orthophosphoric acid and condensed phosphoric acid. As the matrix polymer, polyparavanic acid or polyparavanic acid derivatives can be exemplified.

Polyparabanic acid has a structure represented by the formula (1). In formula (1), n ₁ representing a repeating unit is in the range of ₁₀ to 10000, and X is a molecular unit depending on the monomer of the synthetic raw material. For example, when synthesized using diisocyanate as a raw material, An isocyanate group contributes and X becomes a molecule except an isocyanate group. Y is O or NH. This polyparabanic acid is suitable as an electrolyte membrane of a fuel cell because of its high insulation and excellent heat resistance. In addition, polyparabanic acid can contain a large amount of phosphoric acid due to its molecular structure, and can increase the proton conductivity because it can form an integral film without separating from phosphoric acid.

Moreover, polyparabanic acid itself shows weak basicity by the presence of nitrogen contained in the molecule of polyparavanic acid. Polyparabanic acid is low in basicity and relatively close to neutrality in comparison with conventional polybenzimidazole. Because of this, the interaction with phosphoric acid is weaker than that of polybenzimidazole, and phosphoric acid is not constrained in the matrix polymer, so that it can move relatively freely. This can exhibit high conductivity even with a small amount of phosphoric acid. In addition, since the content of phosphoric acid can be lowered, the mechanical strength of the gel electrolyte can be improved.

As the polyparavanic acid derivative, one obtained by introducing cyanide gas in a solvent such as dimethylformamide and polymerizing the diisocyanate compound can be used.

Here, the diisocyanate compounds used for the synthesis of the polyparavanic acid derivatives include diphenylmethane diisocyanate (MDI), 2,4-tolylene diisocyanate (TDI), 4,4'-diphenyl ether diisocyanate (ODI), Xylylene diisocyanate (XDI), naphthylene 1,5-diisocyanate (NDI), tetramethylene xylylene diisocyanate (TMXDI) can be illustrated, but is not limited to these, dicyanoformamides and the diisocyanate. It can also synthesize | combine from a nate and cyanoformamidyl isocyanate.

As an example of the polyparavanic acid derivative obtained by superposing | polymerizing, what is represented by following formula (2) and formula (3) can be illustrated, for example. Formula 1 is synthesized from diphenylmethane diisocyanate (MDI), formula 2 is synthesized from 2,4-tolylene diisocyanate (TDI), and formula 3 is 4,4'-diphenylether diisocyanate (ODI) Formula 4 is synthesized from xylylene diisocyanate (XDI), formula 5 is synthesized from naphthylene 1,5-diisocyanate (NDI), and formula 6 is tetramethylene xylylene diisocyanate (TMXDI). Synthesized from Also n ₂ represents the repeating units of Formulas 1 to 6 is in the range of 10-10000.

All of the polyparavanic acid derivatives have a structure of paravanic acid in the molecule, and may contain a large amount of phosphoric acid, and thus, proton conductivity can be enhanced because an integral film can be formed without being separated from phosphoric acid. Moreover, since it has aromatic substituents, such as a benzene substituent, in a molecule | numerator, heat resistance can be improved rather than polyparavanic acid.

Moreover, the interaction of a polyparavanic acid derivative and phosphoric acid can be adjusted by increasing the freedom of molecular design by selection of a diisocyanate compound.

Next, by adding a heterocyclic nitrogen compound to the matrix polymer, it is possible to increase the content (swelling ratio) of phosphoric acid in the matrix polymer, thereby further increasing the proton conductivity. In other words, since polyparavanic acid and its derivatives have a low swelling degree to phosphoric acid, the swelling degree of polyparavanic acid can be increased by dissolving or dispersing the heterocyclic nitrogen compound in polyparavanic acid or its derivatives. As a result, a gel electrolyte can be obtained that exhibits high ionic conductivity even at high humidity without humidification and can be used in an electrolyte for fuel cells.

If the amount of the heterocyclic nitrogen compound added to the matrix polymer is too high, the mechanical strength of the gel electrolyte is lowered. Therefore, in this invention, the content rate of the said heterocyclic nitrogen compound with respect to the sum total of a matrix polymer and a heterocyclic nitrogen compound is made into less than 50 mass%.

Moreover, it is preferable that a heterocyclic nitrogen compound is water-insoluble. Thus, even when water is produced as a reaction product of the fuel cell, there is no fear that the heterocyclic nitrogen-containing compound will flow out of the gel electrolyte together with the water, so that the proton conductivity can be maintained for a long time.

As the heterocyclic nitrogen compound, at least one of imidazole, benzimidazole, pyrazole, pyridine, pyrimidine, pyrazine, pyrrole, purine, phthalocyanine, and porphyrin is preferably added. Particularly, benzimidazole is insoluble in water. It is preferable at the point.

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

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

<Production of Polyparabanic Acid Derivatives>

As diisocyanate compound, diphenylmethane diisocyanate (MDI), 2,4-tolylene diisocyanate (TDI), 4,4'- diphenyl ether diisocyanate (ODI), xylylene diisocyanate (XDI), naphthylene 1, A solution containing 10% by mass of 5-diisocyanate (NDI) and tetramethylene xylene diisocyanate (TMXDI), respectively, was prepared using a mixed solvent of nitrobenzene and toluene (nitrobenzene: toluene = 10: 1). In an ice bath, a nitrobenzene solution containing 10% by mass of hydrogen cyanide is mixed with an excess of diisocyanate solution prepared first, and a saturated N-methyl-2-pyrrolidinone solution of sodium cyanide is added dropwise, Precipitation occurred. The reaction was carried out for about 1 hour while returning to room temperature. The polymer of the produced precursor was filtered and washed with water, washed with methanol, and dried at 40 ° C. for 8 hours. The precursor polymer was dispersed in concentrated hydrochloric acid and stirred at 60 ° C. for 2 hours to perform hydrolysis. In this manner, polyparavanic acid derivatives of each kind were prepared. The polyparabanic acid derivatives synthesized from the above MDI, TDI, ODI, XDI, NDI, and TMXDI were PPAMDI, PPATDI, PPAODI, PPAXDI, PPANDI, and PPATMXDI, respectively.

Preparation of Gel Electrolyte of Example 1

Next, the obtained PPAMDI was dissolved in N-methylpyrrolidone, respectively, to make a 10% by weight solution. This solution was coated on a glass plate using a doctor blade, pre-dried at 60 ° C., and then dried at 150 ° C. for 15 minutes to form a coating film of PPAMDI. Next, the PPAMDI film was immersed in water while holding a glass plate to remove the swollen PPAMDI film. Thereafter, vacuum drying was performed at 60 ° C. and 0.1torr. The film thickness at this time was about 30 micrometers.

The PPAMDI membrane was then directly immersed in 85% phosphoric acid at room temperature. After 2 hours, the PPAMDI film was taken out and the phosphoric acid on the surface of the film was wiped off with a wiping cross. Thus, the gel electrolyte of Example 1 was manufactured.

Preparation of Gel Electrolyte of Examples 2 to 18 and Comparative Example 1

In the same manner as in Example 1, PPAMDI, PPATDI, PPAODI, PPAXDI, PPANDI, and PPATMXDI were each dissolved in N-methylpyrrolidone to prepare a 10% by weight solution. Benzimidazole, imidazole, purine, and pyrazole were added to this solution so that it might be 10-50 mass% with respect to a polyparavanic acid derivative, respectively.

And in the same manner as in Example 1, these solutions were coated on a glass plate using a doctor blade, preliminarily dried at 60 ° C, and dried at 150 ° C for 15 minutes to form a coating film made of various polyparavanic acid derivatives. Next, the obtained coating film was immersed in water, respectively, with a glass plate, and the swollen film was peeled off. Thereafter, vacuum drying was performed at 60 ° C under 0.1 torr. The film thickness at this time was about 30 micrometers, respectively.

And the membrane consisting of the various polyparavanic acid derivatives was directly immersed in 85% phosphoric acid at room temperature. After 2 hours the membrane was taken out and the phosphoric acid on the membrane surface was wiped off with a wiping cross. In this manner, gel electrolytes of Examples 2 to 18 and Comparative Example 1 were prepared.

<Production of Gel Electrolyte of Comparative Example 2>

In the same manner as in Example 1, polybenzimidazole was dissolved in N-methylpyrrolidone to prepare a solution, followed by swelling by coating film, predrying, main drying, and immersion in water in order, and then having a poly thickness of 30 μm. A benzimidazole membrane was obtained.

The polybenzimidazole membrane was directly immersed in 85% phosphoric acid at room temperature, and after 2 hours, the polybenzimidazole membrane was removed and wiped with a wiping cross. Thus, the gel electrolyte of Comparative Example 2 was prepared.

[evaluation]

Swelling Rate and Proton Conductivity of Gel Electrolyte

Phosphoric acid swelling ratio and proton conductivity were measured for the gel electrolytes of Examples 1 to 18 and Comparative Examples 1 and 2.

The swelling rate of the phosphoric acid was calculated from the mass (M1) of the polyparabanic acid derivative film before being immersed in phosphoric acid and the mass (M2) of the gel electrolyte after phosphate immersion. Swelling rate (%) was calculated | required as swelling rate (%) = M2 / M1 * 100. The results are shown in Table 1.

In order to measure proton conductivity under conditions of close humidification, the proton conductivity was made by drilling a gel electrolyte in a circular shape having a diameter of 13 mm, sandwiching it between the platinum blocking electrodes, and leaving the electrode at 70 ° C for 1 hour. The resistance of the liver was measured by the AC impedance method. The results are shown in Table 1.

Table 1 also shows the complexes of the types of the matrix polymers (polyparabanic acid derivatives), the types of the heterocyclic nitrogen compounds, and the sum of the matrix polymers and the heterocyclic nitrogen compounds of Examples 1 to 18 and Comparative Examples 1 and 2. The content rate of a summon-containing nitrogen compound is also shown.

Polyparavanic acid derivatives Heterocyclic Nitrogen Compounds Content rate (%) Swelling Rate (%) Conductivity (mScm ^-1 ) Example 1 PPAMDI none - 124 0.11 Example 2 PPAMDI Benzimidazole 10 135 0.20 Example 3 PPAMDI Benzimidazole 20 153 2.35 Example 4 PPAMDI Benzimidazole 30 167 5.12 Example 5 PPAMDI Benzimidazole 40 186 7.60 Comparative Example 1 PPAMDI Benzimidazole 50 Inability to measure Inability to measure Example 6 PPAMDI Imidazole 20 129 0.14 Example 7 PPAMDI Purine 10 130 0.13 Example 8 PPAMDI Pyrazole 10 132 0.18 Example 9 PPATDI Benzimidazole 10 136 0.99 Example 10 PPATDI Imidazole 10 130 0.34 Example 11 PPAODI Benzimidazole 10 140 1.5 Example 12 PPAODI Imidazole 10 132 0.78 Example 13 PPAXDI Benzimidazole 10 137 0.88 Example 14 PPAXDI Imidazole 10 130 0.22 Example 15 PPANDI Benzimidazole 10 137 1.20 Example 16 PPANDI Imidazole 10 126 0.43 Example 17 PPATMXDI Benzimidazole 10 132 0.89 Example 18 PPATMXDI Imidazole 10 128 0.23 Comparative Example 2 Polybenz imidazole none - 120 0.01 or less

As shown in Table 1, in Examples 1 to 5 and Comparative Example 1, in which the addition rate of benzimidazole as a heterocyclic nitrogen compound was adjusted in the range of 0 to 50%, swelling of phosphoric acid with increasing addition rate of benzimidazole It can be seen that the rate increases and also the proton conductivity increases. Example 1, in which no benzimidazole was added, had a slightly low proton conductivity, but had sufficient conductivity as an electrolyte of a fuel cell. On the other hand, in Comparative Example 1 in which benzimidazole was added 50%, the mechanical strength of the electrolyte was lowered, making it difficult to form a uniform film.

It can also be seen that other Examples 6 to 18 exhibit relatively high proton conductivity.

In addition, it can be seen that the gel electrolyte of Comparative Example 2 was significantly reduced in conductivity despite the fact that the swelling ratio of phosphoric acid was about the same as in other examples. This is considered to be due to the strong interaction between phosphoric acid and polybenzimidazole because polybenzimidazole, which is a matrix polymer, is relatively strong base, which hinders the conduction of hydrogen ions.

As described above, it can be seen that the gel electrolyte according to the present invention exhibits high proton conductivity even though the phosphoric acid content is relatively low. In addition, since the content of phosphoric acid is low, it is considered that the mechanical strength of the film is relatively improved.

<Performance of Fuel Cell>

In the fuel cell of Example 3, a laminate composed of an electrode containing activated carbon as an electrode material and a gel electrolyte was inserted into a carbon separator, and a power generation test was carried out using hydrogen for the anode gas and oxygen for the cathode gas. The battery temperature was set at 130 ° C., the supply amounts of hydrogen and oxygen were 100 ml / min, and the supply gas was not humidified in particular. Moreover, the electrode area of Example 3 was 7.84 cm <2>. 1 shows the relationship between the voltage and the current density of the fuel cell.

As shown in FIG. 1, in Example 3, power generation was possible until the current density became 0.25 A / cm 2. Since the fuel cell of Example 3 has a high proton conductivity of the gel electrolyte, it is considered that the internal resistance of the fuel cell is suppressed to be low, thereby obtaining a high output.

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

Claims (6)

A gel electrolyte comprising an acid and a matrix polymer that swells with respect to the acid, wherein the matrix polymer is a polyparabanic acid or a polyparabanic acid derivative. The gel electrolyte according to claim 1, wherein the polyparavanic acid or polyparavanic acid derivative which is the matrix polymer further contains a water-insoluble heterocyclic nitrogen compound. The gel electrolyte according to claim 2, wherein the heterocyclic nitrogen compound is at least one of imidazole, benzimidazole, pyrazole, pyridine, pyrimidine, pyrazine, pyrrole, purine, phthalocyanine, and porphyrin. The gel electrolyte according to claim 2, wherein the content of said heterocyclic nitrogen compound is less than 50 mass% with respect to the sum of said matrix polymer and said heterocyclic nitrogen compound. An electrode material and a fuel cell electrode comprising the gel electrolyte according to any one of claims 1 to 4. A pair of electrodes and an electrolyte membrane disposed between each electrode, wherein part or all of the electrolyte membrane is composed of the gel electrolyte according to any one of claims 1 to 4, and a part of the electrode A fuel cell comprising the gel electrolyte.

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