JP5021864B2 - Membrane / electrode assembly for solid polymer electrolyte fuel cell and solid polymer electrolyte membrane - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a polymer electrolyte fuel cell (hereinafter, referred to as. "PEFC") and the solid polymer electrolyte membrane used in, relates to a membrane-conductive Gokuse' polymer comprising the same.
[0002]
[Prior art]
As shown in FIG. 3, the PEFC is composed of a joined body of a film-like polymer electrolyte membrane 31 that is an electrolyte and gas diffusion electrodes 36 and 37, and both are joined by hot pressing. And in the negative electrode catalyst layer 33, Formula (1):
H ₂ → 2H ⁺ + 2e ⁻ (1)
In the positive electrode catalyst layer 35, the reaction represented by formula (2):
1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
The reaction represented by When the above reaction occurs, protons generated in the negative electrode move to the positive electrode through the polymer electrolyte membrane 31.
Such a PEFC is required to have a high output current density, but the polymer electrolyte membrane to be used is required to have high proton conductivity, that is, low internal resistance.
[0003]
For the polymer electrolyte of PEFC, a polymer electrolyte membrane made of perfluorosulfonic acid ionomer typically represented by Nafion 112 manufactured by DuPont USA is used, and a membrane having a thickness of about 30 to 50 μm has been put into practical use. ing.
Examples of the polymer electrolyte membrane made of perfluorosulfonic acid ionomer having proton conductivity higher than that of Nafion include Flemion SH membrane manufactured by Asahi Glass Co., Ltd. and Aciplex-S manufactured by Asahi Kasei Co., Ltd. It contains more sulfone groups than Nafion 112 membrane. In PEFC, in order to produce a high output current density, a polymer electrolyte membrane having higher proton conductivity and containing more sulfone groups has been developed.
[0004]
[Problems to be solved by the invention]
However, polymer electrolytes such as perfluorosulfonic acid ionomers with high proton conductivity contain many hydrophilic groups such as sulfonic acid groups in the molecular chain, so that they easily dissolve in water, and the ionomer gradually increases during the operation of the fuel cell. However, it tended to flow out to a gas diffusion layer such as carbon paper. Therefore, at the interface between the solid polymer electrolyte membrane and the electrode, a three-phase formed by a pore serving as a reaction gas supply path, a polymer electrolyte having proton conductivity due to water content, and an electrode material of an electron conductor There was a problem that the reaction area at the interface gradually narrowed and the output decreased.
Further, when the current collector having a gas flow path disposed outside the assembly of the solid polymer electrolyte membrane and the electrode is made of metal, the current collector is gradually corroded by the dissolved acidic ionomer, and the fuel There is also a problem that the reliability of the battery is remarkably lowered.
[0005]
Therefore, in order to solve the conventional problems as described above, the present invention uses a solid polymer electrolyte having high proton conductivity, and has excellent durability and high performance. It is an object of the present invention to provide a solid polymer electrolyte fuel cell constituted by using the joined body.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention comprises a solid polymer electrolyte membrane and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane, each having a catalyst layer and a gas diffusion layer, At least one of the catalyst layers comprises a mixture of a noble metal catalyst and a carbon powder, a first polymer electrolyte, and a polyfunctional basic compound, wherein the first polymer electrolyte comprises a plurality of A sulfonic acid group, a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded, and a main chain portion of the polyfunctional basic compound is fluorine-substituted. A membrane / electrode assembly for a solid polymer electrolyte fuel cell is provided.
In this joined body, it is effective that the polyfunctional basic compound is a polyfunctional amine.
In addition, it is effective that the catalyst layer contains 0.1 to 10 wt% of a polyfunctional basic compound with respect to the first polymer electrolyte.
Another aspect of the present invention includes a solid polymer electrolyte membrane and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane, each having a catalyst layer and a gas diffusion layer. At least one of the catalyst layers includes a catalyst body including a noble metal catalyst and carbon powder, a first polymer electrolyte, and a mixture of a polyfunctional basic compound, and the first polymer electrolyte includes a plurality of sulfonic acids. Provided is a membrane / electrode assembly for a solid polymer electrolyte fuel cell in which a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded.
[0008]
Furthermore, the present invention comprises a solid polymer electrolyte membrane and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane, each having a catalyst layer and a gas diffusion layer, the solid polymer electrolyte membrane comprises: A second polyelectrolyte and a polyfunctional basic compound, wherein the second polyelectrolyte has a plurality of sulfonic acid groups, a part of the plurality of sulfonic acid groups and the polyfunctionality Provided is a membrane / electrode assembly for a solid polymer electrolyte fuel cell in which a basic compound is ionically bonded and the main chain portion of the polyfunctional basic compound is substituted with fluorine.
Also in this case, it is effective that the polyfunctional basic compound is a polyfunctional amine.
In addition, it is effective that the solid polymer electrolyte membrane contains 1 to 10 wt% polyfunctional basic compound of the second polymer electrolyte.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Conjugate for a polymer electrolyte fuel cell comprising a solid polymer electrolyte membrane and the gas diffusion electrode according to the present invention has the greatest feature that include a polyfunctional basic compound.
This polyfunctional basic compound can be included in the solid polymer electrolyte membrane and / or catalyst layer constituting the joined body, and is bonded to a part of the sulfonic acid group of the ionomer that is the polymer electrolyte to form a three-dimensional structure. The ionomer is made difficult to flow out to the gas diffusion layer by the drain water .
Thereby, the gas diffusion layer maintains the gas permeability, and the catalyst layer and the polymer electrolyte membrane exhibit the function of making it difficult to impair the proton conductivity.
[0010]
Embodiment 1
A membrane / electrode assembly for a solid polymer electrolyte fuel cell comprising a solid polymer electrolyte membrane according to the present invention and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane will be described.
When the catalyst layer contains a polyfunctional basic compound, the membrane / electrode assembly for a solid polymer electrolyte fuel cell of the present invention is a pair of a polymer electrolyte membrane and a solid polymer electrolyte membrane disposed on both sides of the membrane. And at least one of the electrodes is composed of a catalyst body made of a noble metal catalyst and carbon powder, a catalyst layer made of a mixture containing a polyelectrolyte and a polyfunctional basic compound, carbon paper, carbon cloth, etc. And a gas diffusion layer.
As shown in FIG. 1, the polyfunctional basic compound 11 is bonded to a part of the sulfonic acid group of the ionomer 12 to form a three-dimensional network, and has an effect of suppressing the outflow of the ionomer.
[0011]
The polyfunctional basic compound may be any compound having at least two functional groups capable of reacting with a sulfone group in one molecule, such as ethylenediamine, 1,2-propylenediamine, tetramethylenediamine, hexamethylenediamine. , Bifunctional amines such as heptamethylenediamine, octamethylenediamine, nonamethylenediamine, trifunctional amines such as diethylenetriamine, benzenediamine, 1,2,3-triaminobenzene, 1,2,3,4-tetraaminobenzene, etc. An aromatic polyfunctional amine, a compound having an amidino group such as 1,5-diazabicyclo [4.3.0] non-5-ene, 1,8-diazabicyclo [5.4.0] undec-7-ene, N-containing polysaccharides such as streptomycin, vitamins such as vitamin B2 and vitamin B12 Azanaphthalenes such as xampterin, leucopterin, methotrexate, alkaloids such as quinine, strikine, brucine, polypeptides such as glycylalanine, alanylglycine, aspartame, glutathione, pyridazine, pyrimidine, triazines, tetrazines, cinnoline Quinazoline, phthalazine, quinoxaline, pteridine, lysergic acid diethylamide, adenine, benzimidazole, purine, hydrazide, nicotine, tetrahydrofolic acid, hexamethylenetetramine, 4,4′-diaminobiphenyl and the like.
Among these, a polyfunctional amine is preferable from the viewpoint that a chemical reaction between an acid and a base occurs under relatively mild conditions.
[0012]
Moreover, it is preferable that hydrogen of the skeleton part of the polyfunctional basic compound is fluorine-substituted. This is because by being substituted with fluorine, decomposition due to a hydrogen atom extraction reaction or the like can be prevented, and high reliability can be realized.
Examples of the fluorine-substituted polyfunctional amine include tetrafluoro-p-phenylenediamine, 4,4′-diaminooctafluorobiphenyl, 2,4,6-tris (perfluoroheptyl) -1,3,5-triazine and the like. .
[0013]
Moreover, it is preferable that the polyfunctional basic compound in the said catalyst layer is 0.1-10 wt% with respect to a polymer electrolyte. This is because if the substitution rate is about several percent of the total number of acid groups such as sulfonic acid, the influence on proton conductivity is small.
Next, the case of the reference embodiment containing carbon powder having a basic surface functional groups to the catalyst layer, membrane-electrode assembly of the solid polymer electrolyte membrane fuel battery, the solid polymer electrolyte membrane a polymer electrolyte membrane A catalyst body made of a noble metal catalyst and a carbon powder having a basic surface functional group, a catalyst layer made of a polymer electrolyte, and a gas diffusion layer. It consists of.
As shown in FIG. 2, the basic surface functional group 21 of the carbon powder 23 in the catalyst layer is bonded to a part of the sulfonic acid group of the ionomer 24, thereby suppressing the outflow of the ionomer. The basic surface functional group 21 on the carbon powder 23 is substituted with, for example, a carboxyl group on the surface of the carbon powder before mixing with the ionomer. The basic surface functional group is preferably an amine from the viewpoint that a chemical reaction between an acid and a base occurs under relatively mild conditions.
The number of basic surface functional groups on the carbon powder may be one. In the case where the basic substance is a single molecule, there is no crosslinking effect unless it has two or more functional groups, so the basic substance flows out together with the ionomer. On the other hand, when the basic substance substrate is carbon powder, since the carbon powder is fixed in the catalyst layer, even one basic functional group does not flow out together with the ionomer. Moreover, in view of the above-mentioned action, there is no need for a basic functional group to be present on the surface of all carbon powder. Further, it is not necessary that all ionomers and surface functional groups are bonded. This is because the outflow can be sufficiently suppressed if it is combined with some ionomers by the anchoring effect.
[0014]
Embodiment 2
When the polyelectrolyte membrane includes a polyfunctional basic compound, the membrane / electrode assembly for a solid polymer electrolyte fuel cell according to the present invention comprises a solid polymer electrolyte membrane and electrodes disposed on both sides of the membrane. The solid polymer electrolyte membrane contains a polyfunctional basic compound.
Here, as described above, the polymer electrolyte has a plurality of sulfonic acid groups, and a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded, The polyfunctional basic compound is preferably a polyfunctional amine, and the weight of the polyfunctional basic compound with respect to the solid polymer electrolyte is preferably 1 to 10 wt%. This is because if the substitution rate of acid groups such as sulfonic acid is low, the influence on proton conductivity is small.
[0015]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited only to these.
Example 1
First, 6.0 g of carbon fine powder carrying 25% by weight of a platinum catalyst is put into 50.0 g of n-butyl acetate (CH ₃ COOCH ₂ (CH ₂ ) ₂ CH ₃ ), and a stirrer is used while applying ultrasonic waves. And stirred and dispersed for 10 minutes. Next, 40.0 g of a 9 wt% ethanol solution of a polymer electrolyte (Flemion manufactured by Asahi Glass Co., Ltd.) is gradually added to the above dispersion with stirring, and a fine carbon powder carrying a catalyst with a colloid of the polymer electrolyte. Adsorbed on the surface. One hour after the addition of all the polyelectrolyte solution was completed, when the stirring was stopped, the supernatant liquid changed to transparent. 0.10 g of hexamethylene diamine was mixed with this catalyst mixed solution and ultrasonically dispersed for 1 hour to obtain a catalyst paste.
Next, about 30 μm of the catalyst paste was applied onto a carbon paper substrate manufactured by Toray Industries, Inc., which was dipped in a fluororesin dispersion (Daikin Industries, Ltd. ND-1) and then fired at 300 ° C.
Furthermore, the electrode was hot pressed for 10 minutes at a temperature of 120 to 140 ° C. and a pressure of 50 to 70 kg / cm ^{2 on} both sides of a solid polymer electrolyte membrane having a thickness of 50 μm (Flemion SH50 manufactured by Asahi Glass Co., Ltd.) A membrane / electrode assembly was prepared.
This membrane / electrode assembly is sandwiched between separators and assembled into a single cell. The battery temperature is 75 ° C., the hydrogen dew point is 70 ° C., the air dew point is 65 ° C., the hydrogen utilization rate is 70%, the oxygen utilization rate is 40%, and the current density is 0.7 A / cm. ^The operation was performed for 250 hours under the condition ² , but the decrease in voltage from the initial 0.65V was 0.03V.
[0016]
<< Comparative Example 1 >>
In 50.0 g of n-butyl acetate (CH ₃ COOCH ₂ (CH ₂ ) ₂ CH ₃ ), 6.0 g of carbon fine powder carrying 25% by weight of a platinum catalyst was put, and a stirrer was used while applying ultrasonic waves. Stir and disperse for 10 minutes. Next, 40.0 g of a 9 wt% ethanol solution of a polymer electrolyte (Flemion manufactured by Asahi Glass Co., Ltd.) is gradually added to the above dispersion with stirring, and a fine carbon powder carrying a catalyst with a colloid of the polymer electrolyte. Adsorbed on the surface. After adding all the polymer electrolyte solutions, the mixture was further stirred for 1 hour to obtain a catalyst paste.
Next, about 30 μm of the catalyst paste was applied onto a carbon paper substrate manufactured by Toray Industries, Inc., which was dipped in a fluororesin dispersion (Daikin Industries, Ltd. ND-1) and then fired at 300 ° C.
Furthermore, the electrode was hot pressed for 10 minutes at a temperature of 120 to 140 ° C. and a pressure of 50 to 70 kg / cm ^{2 on} both sides of a solid polymer electrolyte membrane having a thickness of 50 μm (Flemion SH50 manufactured by Asahi Glass Co., Ltd.) A membrane / electrode assembly was prepared.
When this battery was operated for 250 hours under the same conditions as in Example 1, a decrease of 0.12 V from the initial voltage of 0.67 V was observed.
[0017]
<< Reference Example 1 >>
First, 7.0 g of carbon fine powder carrying 25% by weight of a platinum catalyst, 20 ml of ethanol, and 1.0 g of hexamethylenediamine were placed in a three-necked flask and boiled at reflux for 10 minutes. Next, the dispersion is filtered, thoroughly washed with ethanol and water on the filter paper, and then dried to obtain a platinum catalyst-carrying carbon fine powder in which a part of the surface carboxyl groups are amide-bonded with hexamethylenediamine. It was.
Add 50.0 g of n-butyl acetate (CH ₃ COOCH ₂ (CH ₂ ) ₂ CH ₃ ) to 6.0 g of the platinum catalyst-supported carbon fine powder, and stir and disperse for 10 minutes using a stirrer while applying ultrasonic waves. It was. Next, 40.0 g of a 9 wt% ethanol solution of a polymer electrolyte (Flemion manufactured by Asahi Glass Co., Ltd.) is gradually added to the above dispersion with stirring, and a fine carbon powder carrying a catalyst with a colloid of the polymer electrolyte. Adsorbed on the surface. Stirring was further continued for 1 hour after the addition of all the polymer electrolyte solution to obtain a catalyst paste.
Next, the catalyst paste was immersed in a fluororesin dispersion (Daikin Industries, Ltd. ND-1) in the same manner as in Example 1 and then fired at 300 ° C. on a carbon paper substrate manufactured by Toray Industries, Inc. Painted.
Furthermore, the electrode was hot pressed for 10 minutes at a temperature of 120 to 140 ° C. and a pressure of 50 to 70 kg / cm ^{2 on} both sides of a solid polymer electrolyte membrane having a thickness of 50 μm (Flemion SH50 manufactured by Asahi Glass Co., Ltd.) A membrane / electrode assembly was prepared.
When this membrane-electrode assembly was sandwiched between separators, a unit cell was assembled, and operated for 250 hours under the same conditions as in Example 1, the voltage drop from the initial 0.66 V was 0.04 V.
[0018]
<< Reference Example 2 >>
Polymer electrolyte (Flemion manufactured by Asahi Glass Co., Ltd.) 7% ethanol solution 40ml It was dried at 130 ° C. for 2 hours to obtain a solid polymer electrolyte cast membrane having a thickness of 50 μm. A membrane / electrode assembly was produced by sandwiching this between carbon paper with a catalyst layer produced in the same manner as in Comparative Example 1, and a single cell was obtained.
When this membrane / electrode assembly was sandwiched between separators, a single cell was assembled and operated for 250 hours under the same conditions as in Example 1, the voltage drop from the initial 0.63 V was 0.05 V.
In this example and comparative example, a catalyst paste was applied onto a carbon paper substrate to produce a gas diffusion electrode. However, the present invention is characterized by the composition of the catalyst layer and / or the solid polymer electrolyte membrane. Other preparation methods, for example, a catalyst paste in which platinum-supported carbon fine powder and polymer electrolyte are dispersed in ethanol is applied once to a film of polypropylene, Teflon (registered trademark), and then thermally transferred to a solid polymer electrolyte membrane. -Needless to say, the same effect can be obtained by a method of producing an electrode assembly or a method of directly applying a catalyst paste to a solid polymer electrolyte membrane.
[0019]
【Effect of the invention】
As described above, according to the present invention, a solid polymer electrolyte membrane having a high proton conductivity, a solid polymer electrolyte membrane and electrode having excellent durability and high performance are obtained. Thus, a polymer electrolyte fuel cell constructed by using it can be obtained.
[Brief description of the drawings]
Schematic diagram illustrating the interaction of ionomer and bifunctional amines of the solid polymer electrolyte fuel catalyst layer of the membrane electrode assembly cell according to Example 1 of the present invention in Figure 2 Reference Example 1 Schematic diagram showing the interaction between the ionomer in the catalyst layer of the solid polymer electrolyte fuel cell membrane-electrode assembly and basic functional groups on the fine carbon powder. [Fig. 3] Membrane-electrode junction according to Comparative Example 1 Body cross section

Claims (9)

A solid polymer electrolyte membrane, and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane, each having a catalyst layer and a gas diffusion layer,
At least one of the catalyst layers of the electrode includes a mixture of a catalyst body including a noble metal catalyst and carbon powder, a first polymer electrolyte, and a polyfunctional basic compound,
The first polymer electrolyte has a plurality of sulfonic acid groups, and a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded,
A membrane / electrode assembly for a solid polymer electrolyte fuel cell, wherein a main chain portion of the polyfunctional basic compound is substituted with fluorine. A solid polymer electrolyte membrane, and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane, each having a catalyst layer and a gas diffusion layer,
The solid polymer electrolyte membrane includes a second polymer electrolyte and a polyfunctional basic compound,
The second polymer electrolyte has a plurality of sulfonic acid groups, and a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded,
A membrane / electrode assembly for a solid polymer electrolyte fuel cell, wherein a main chain portion of the polyfunctional basic compound is substituted with fluorine.   The membrane / electrode assembly for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the polyfunctional basic compound is a polyfunctional amine.   2. The membrane / electrode for a solid polymer electrolyte fuel cell according to claim 1, wherein the catalyst layer contains 0.1 to 10 wt% of the polyfunctional basic compound with respect to the first polymer electrolyte. Joined body.   The membrane / electrode for a solid polymer electrolyte fuel cell according to claim 2, wherein the solid polymer electrolyte membrane contains 1 to 10 wt% of a polyfunctional basic compound with respect to the second polymer electrolyte. Joined body. Containing a polyelectrolyte and a polyfunctional basic compound,
The polyelectrolyte has a plurality of sulfonic acid groups, a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded,
The main chain part of the said polyfunctional basic compound is a solid polymer electrolyte membrane by which fluorine substitution is carried out. The solid polymer electrolyte membrane according to claim 6 , wherein the polyfunctional basic compound is a polyfunctional amine. The solid polymer electrolyte membrane according to claim 6 , wherein the solid polymer electrolyte membrane contains 1 to 10 wt% of a polyfunctional basic compound with respect to the polymer electrolyte. A solid polymer electrolyte membrane, and a pair of electrodes disposed on both sides of the solid polymer electrolyte membrane, each having a catalyst layer and a gas diffusion layer,
At least one of the catalyst layers of the electrode includes a mixture of a catalyst body including a noble metal catalyst and carbon powder, a first polymer electrolyte, and a polyfunctional basic compound,
The first polymer electrolyte has a plurality of sulfonic acid groups,
A membrane / electrode assembly for a solid polymer electrolyte fuel cell, wherein a part of the plurality of sulfonic acid groups and the polyfunctional basic compound are ionically bonded.

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