JP2008166050A - Polymer electrolyte membrane/catalyst assembly and its manufacturing method, as well as fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte membrane/catalyst assembly with durability improved without giving rise to deterioration of protonic conductivity. <P>SOLUTION: The polymer electrolyte membrane/catalyst assembly comprises a polymer electrolyte membrane containing polymers expressed in formula (1) and formula (2), and an electrode catalyst layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a novel polymer electrolyte membrane, a polymer electrolyte membrane / catalyst assembly (hereinafter sometimes simply referred to as “membrane / catalyst assembly”), a method for producing the same, and the polymer electrolyte membrane / electrode assembly. The present invention relates to a fuel cell using

  In recent years, new power generation technologies with excellent energy efficiency and environmental friendliness have attracted attention. Above all, polymer electrolyte fuel cells using polymer electrolyte membranes have high energy density, and because they have features such as being easy to start and stop because of lower operating temperatures than other types of fuel cells. Developments as power supply devices for electric vehicles and distributed power generation are advancing.

  As the polymer solid electrolyte membrane, a proton conductive ion exchange membrane is usually used. In addition to proton conductivity, the polymer solid electrolyte membrane must have characteristics such as fuel permeation deterrence and mechanical strength that prevent permeation of hydrogen and the like of the fuel. As such a polymer solid electrolyte membrane, for example, a membrane containing a perfluorocarbon sulfonic acid polymer into which a sulfonic acid group is introduced as represented by Nafion (trade name) manufactured by DuPont, USA is known.

  Perfluorocarbon sulfonic acid ion exchange membranes have well-balanced characteristics as electrolyte membranes for fuel cells, but hydrocarbon ion exchange membranes are actively developed to obtain better membranes in terms of cost and performance. Has been done. Fluorine ion exchange membranes such as perfluorocarbon sulfonic acid ion exchange membranes, when used in fuel cells, may generate harmful hydrofluoric acid in the exhaust gas depending on the operating conditions, or may cause environmental impact during disposal. There is also a problem such as large.

  On the other hand, a polymer electrolyte membrane made of a hydrocarbon polymer that does not contain halogen such as fluorine has been actively studied. Among hydrocarbon polymer electrolyte membranes, those made of aromatic polymers have excellent proton conductivity and other properties, so their application to fuel cells is being studied. However, durability is a problem due to brittleness during drying. There was a case. Therefore, in order to improve brittleness at the time of drying, it has been proposed to blend a sulfonated aromatic polymer and a basic polymer (see, for example, Patent Documents 1 and 2).

  However, by blending a basic polymer with a sulfonated aromatic polymer, there is a tendency that proton conductivity tends to be lowered, and the tendency is particularly remarkable under low humidity.

Japanese Patent No. 3688201 Japanese Patent No. 3729735

  The present invention has been made against the background of the problems of the prior art. The polymer electrolyte membrane, the polymer electrolyte membrane / catalyst assembly improved in durability without causing a decrease in proton conductivity, the production method thereof, and the An object of the present invention is to provide a fuel cell using a membrane / catalyst assembly.

  As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention provides the following.

(1) The polymer (A) having a structure represented by the following chemical formula (1) and the polymer (B) having a structure represented by the following chemical formula (2) have a weight fraction of the polymer (B) of 5 A polymer electrolyte membrane for a fuel cell comprising a mixture mixed so as to be ˜15% by weight.

（上記式中、ｎ１、ｎ２、ｍ１、ｍ２、ｍ３は下記数式（１）〜（３）を満たす１以上の整数を表す。）

(In the above formula, n1, n2, m1, m2, and m3 represent an integer of 1 or more that satisfies the following mathematical formulas (1) to (3).)

（上記式中、ｎ３は1以上の整数を、ｍ４、ｍ５は下記数式（４）を満たす１以上の整数を、それぞれ表す。）

(In the above formula, n3 represents an integer of 1 or more, and m4 and m5 each represents an integer of 1 or more that satisfies the following formula (4).)

(2) The polymer electrolyte membrane for fuel cells according to (1) and an electrode catalyst layer directly bonded to at least one surface of the polymer electrolyte membrane, and the surface roughness of the membrane / catalyst interface is 1 μm or less A polymer electrolyte membrane / catalyst assembly characterized in that:

(3) A catalyst slurry containing an electrode catalyst, a polymer electrolyte, and a solvent is applied to at least one surface of the polymer electrolyte membrane for fuel cells according to (1), and the surface roughness of the membrane / catalyst interface is 1 μm or less. A method for producing a polymer electrolyte membrane / catalyst assembly for a fuel cell using hydrogen as a fuel, wherein the electrode catalyst layer is formed by direct coating so that

(4) A fuel cell using hydrogen as a fuel, wherein the polymer electrolyte membrane / catalyst assembly according to (2) is used.

  The polymer electrolyte membrane / catalyst assembly according to the present invention has improved durability without lowering proton conductivity as compared with the conventional one, and when used in a fuel cell, it has durability and low humidity. It has the effect of being excellent in output characteristics.

  Hereinafter, the present invention will be described in detail.

  The polymer electrolyte membrane of the present invention comprises a polymer (A) having a structure represented by the following chemical formula (1) and a polymer (B) having a structure represented by the following chemical formula (2). It is a polymer electrolyte membrane for fuel cells which consists of a mixture mixed so that the weight fraction may become 5 to 15 weight%.

（上記式中、ｎ１、ｎ２、ｍ１、ｍ２、ｍ３は下記数式（１）〜（４）を満たす１以上の整数を表す。）

(In the above formula, n1, n2, m1, m2, and m3 represent an integer of 1 or more that satisfies the following mathematical formulas (1) to (4).)

（上記式中、ｎ３は1以上の整数を、ｍ４、ｍ５は下記数式（４）を満たす１以上の整数を、それぞれ表す。）

(In the above formula, n3 represents an integer of 1 or more, and m4 and m5 each represents an integer of 1 or more that satisfies the following formula (4).)

  In the polymer A represented by the chemical formula (1), n1 / (n1 + n2) is preferably in the range of 0.45 to 0.60, and more preferably between 0.45 and 0.50. When n1 / (n1 + n2) is smaller than 0.40, sufficient output cannot be obtained when used in a fuel cell using hydrogen as fuel. When n1 / (n1 + n2) is larger than 0.70, the swelling property of the film becomes too large, which causes problems such as a decrease in durability.

  Further, m3 / (m1 + m2 + m3) is preferably between 0.01 and 0.03. When m3 / (m1 + m2 + m3) is less than 0.005, the durability of the membrane / electrode bondability may be lowered. When m3 / (m1 + m2 + m3) is larger than 0.05, it may be difficult to obtain a polymer having a high degree of polymerization.

  Furthermore, m2 / (m1 + m2) is preferably in the range of 0.05 to 0.15. When m2 / (m1 + m2) is smaller than 0.01, proton conductivity may be lowered under low humidification. When m2 / (m1 + m2) is larger than 0.20, the swellability of the film increases and the durability may decrease.

  N1 + n2 + m1 + m2 + m3 in the polymer (A) may be an integer of 5 or more, but is preferably between 10 and 10,000. If it is less than 10, it may be difficult to obtain a film, which is not preferable. If it is greater than 10,000, problems such as excessive increase in the viscosity of the solution tend to occur, which is not preferable. Further, (n1 + n2) / (m1 + m2 + m3) is preferably in the range of 0.9 to 1.1, more preferably in the range of 0.95 to 1.05, and in the range of 0.99 to 1.01. More preferably.

  The degree of polymerization of the polymer (A) can be determined by, for example, gel permeation chromatography, light scattering method, osmotic pressure method, terminal group amount measurement method, etc. As a method for simply evaluating the degree of polymerization, dilute solution Logarithmic viscosities can also be used. For example, the polymer powder is dissolved in N-2-methylpyrrolidone at a concentration of 0.5 g / dL, and the viscosity is measured using an Ubbelohde viscometer in a constant temperature bath at 30 ° C., and ln [ta / tb] / c The logarithmic viscosity (ta is the sample solution dropping time, tb is the solvent dropping time, and c is the polymer concentration) is preferably between 0.1 and 3.0, More preferably, it is between 2.0.

  For the polymer (B) represented by the chemical formula (2), m5 / (m4 + m5) is preferably between 0.65 and 0.75. If m5 / (m4 + m5) is smaller than 0.60, the durability may be lowered, and if it is larger than 0.80, the solubility may be lowered.

  N3 + m4 + m5 in the polymer (B) may be an integer of 2 or more, but is preferably between 10 and 10,000. If it is less than 10, it may be difficult to obtain a film, which is not preferable. If it is greater than 10,000, problems such as excessive increase in the viscosity of the solution tend to occur, which is not preferable. Further, (n3) / (m4 + m5) is preferably in the range of 0.9 to 1.1, more preferably in the range of 0.95 to 1.05, and in the range of 0.99 to 1.01. More preferably.

  The degree of polymerization of the polymer (B) can be determined by, for example, gel permeation chromatography, light scattering method, osmotic pressure method, terminal group amount measurement method, etc. As a method for simply evaluating the degree of polymerization, dilute solution Logarithmic viscosities can also be used. For example, the polymer powder is dissolved in methanesulfonic acid at a concentration of 0.5 g / dL, the viscosity is measured using an Ostwald viscometer in a constant temperature bath at 30 ° C., and it is obtained by ln [ta / tb] / c. The logarithmic viscosity (ta is the number of seconds that the sample solution falls, tb is the number of seconds that the solvent is dropped, and c is the polymer concentration) is preferably in the range of 0.25 to 10, preferably in the range of 0.40 to 8. Is more preferable. When the logarithmic viscosity is less than 0.25, it may be difficult to obtain a molded product due to a decrease in viscosity, which is not preferable. On the other hand, when the logarithmic viscosity exceeds 10, it may be difficult to form a viscosity increase, which is not preferable.

  The mixing ratio of the polymer (A) and the polymer (B) is such that the content of the polymer (B) is 5 to 15% by weight. When the content of the polymer (B) is less than 5% by weight, the durability may be lowered, and when it is more than 15% by weight, the proton conductivity may be lowered. The mixing ratio of the polymer (A) and the polymer (B) can be measured by any known method such as NMR method, IR method, GPC method, and elemental analysis method.

  The polymer (A) can be synthesized by any known method. For example, the polymer (A) can be easily polymerized by using an aromatic nucleophilic substitution reaction. Examples of the monomer include 4,4′-biphenol, bis (4-hydroxyphenyl) sulfide, 10- (2,5-dihydroxyphenyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10. -Oxides, 2,6-dichlorobenzonitrile, sodium 4,4'-dichlorodiphenylsulfone-3,3'-disulfonate can be used. The polymer (A) can be used by heating these monomers in the presence of a basic substance.

  The polymerization can be carried out in the temperature range of 0 to 350 ° C., but is preferably 50 to 250 ° C. When the temperature is lower than 0 ° C., the reaction does not proceed sufficiently, and when the temperature is higher than 350 ° C., the polymer tends to be decomposed. The reaction can be carried out in the absence of a solvent, but is preferably carried out in a solvent. Examples of the solvent that can be used include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, and the like. And any solvent that can be used as a stable solvent in the aromatic nucleophilic substitution reaction. These organic solvents may be used alone or as a mixture of two or more.

  In the above polymerization reaction, 4,4′-biphenol, bis (4-hydroxyphenyl) sulfide, 10- (2,5-dihydroxyphenyl) -9,10-dihydro-9- is used without using a basic compound. Oxa-10-phosphaphenanthrene-10-oxide reacted with an isocyanate compound such as phenyl isocyanate to carbamoylate, 2,6-dichlorobenzonitrile, 4,4′-dichlorodiphenylsulfone-3,3 ′ It is also possible to react directly with sodium disulfonate.

  Examples of the basic compound include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and the like, but 4,4′-biphenol, bis (4-hydroxyphenyl) sulfide, 10 As long as it can convert-(2,5-dihydroxyphenyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide into an active phenoxide structure, it is not limited to these. it can. Basic compounds are 4,4′-biphenol, bis (4-hydroxyphenyl) sulfide, 10- (2,5-dihydroxyphenyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-. Polymerization can be satisfactorily performed when an amount of 100 mol% or more based on the total amount of oxides is used, and preferably 4,4′-biphenol, bis (4-hydroxyphenyl) sulfide, 10- (2,5-dihydroxyphenyl). ) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in a range of 105 to 125 mol%. An excessive amount of the basic compound is not preferable because it causes side reactions such as decomposition.

  In the aromatic nucleophilic substitution reaction, water may be generated as a by-product. In this case, regardless of the polymerization solvent, water can be removed from the system as an azeotrope by coexisting toluene or the like in the reaction system. As a method for removing water out of the system, a water absorbing material such as molecular sieve can also be used. When the aromatic nucleophilic substitution reaction is carried out in a solvent, it is preferable to charge the monomer so that the resulting polymer concentration is 5 to 50% by weight. When the amount is less than 5% by weight, the degree of polymerization tends to be difficult to increase. On the other hand, when the amount is more than 50% by weight, the viscosity of the reaction system becomes too high, and the post-treatment of the reaction product tends to be difficult. After completion of the polymerization reaction, the solvent is removed from the reaction solution by evaporation, and the residue is washed as necessary to obtain the desired polymer. In addition, the polymer can be obtained by precipitating the polymer as a solid by adding the reaction solution in a solvent having low polymer solubility, and collecting the precipitate by filtration. In addition, a polymer solution can be obtained by removing by-product salts by filtration.

  The reaction temperature can be any temperature, but it is preferably in the range of 150 to 250 ° C. Although reaction time can be made into arbitrary time, it is preferable that it is the range of 3 to 60 hours. The reaction is preferably carried out with stirring. Moreover, it is preferable to carry out in inert gas atmosphere, such as nitrogen, or airflow.

  In the polymer (A), the arrangement order of the structural units in the structure represented by the chemical formula (1) may be any of alternating, block, and random, and is not particularly limited. If it is a block copolymer, it will show the tendency for proton conductivity and water absorption to become high.

  The polymer (B) can be polymerized by any known method. For example, the polymer (B) can be easily obtained by polymerizing by a polycondensation reaction. As the monomer, for example, 3,3 ′, 4,4′-tetraaminodiphenyl sulfone, 2-sulfoterephthalic acid monosodium salt, and 3,5-dicarboxybenzenephosphonic acid can be used.

  These monomers are described, for example, in J. Org. F. Wolfe, Encyclopedia of Polymer Science and Engineering, 2nd Ed. , Vol. 11, p. 601 (1988), and can be synthesized by dehydration and cyclopolymerization using polyphosphoric acid as a solvent. In addition, polymerization by a similar mechanism using a mixed solvent system of methanesulfonic acid / phosphorus pentoxide instead of polyphosphoric acid can be applied. In order to synthesize a polybenzimidazole compound having high thermal stability, polymerization using polyphosphoric acid that is commonly used is preferred.

  In addition, a precursor polymer having a polyamide structure or the like is synthesized by reaction in a suitable organic solvent or in the form of a mixed raw material monomer melt, and then the desired polybenzimidazole structure is obtained by a cyclization reaction by appropriate heat treatment or the like. The method of converting to can also be used.

  The reaction temperature can be any temperature, but it is preferably in the range of 150 to 250 ° C. The reaction time can be any time, but is preferably in the range of 2 to 30 hours. The reaction is preferably carried out with stirring. Moreover, it is preferable to carry out in inert gas atmosphere, such as nitrogen, or airflow.

  In the polymer (B), the arrangement order of the structural units in the structure represented by the chemical formula (2) may be any of alternating, block, and random, and is not particularly limited. If it is a block copolymer, it will show the tendency for proton conductivity and water absorption to become high.

  The polymer electrolyte membrane comprising the polymer (A) and the polymer (B) can be obtained by any known method. As an example, a solution containing polymer (A) and polymer (B) can be prepared, and the solution can be cast and dried to obtain a film.

  In order to prepare a solution containing the polymer (A) and the polymer (B), the respective polymers may be separately dissolved in a solvent and then mixed, or the respective polymers may be dissolved in the same solvent. Although dissolution can be performed at any temperature, it is preferably performed in the range of 30 to 150 ° C. Solvents include aprotic such as N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, hexamethylphosphonamide, N-morpholine oxide, etc. Examples include organic polar solvents, polar solvents such as alcohol solvents such as methanol and ethanol, ketone solvents such as acetone, ether solvents such as diethyl ether, mixtures of these organic solvents, and mixtures with water. However, it is not limited to these.

  In addition, as described in Patent Document 1 or 2, a mixture is prepared using a salt of a sulfonic acid group of a polymer, and then an electrolyte membrane is formed by performing a treatment for returning the sulfonic acid group to an acid type by acid treatment. It can also be obtained.

  The concentration of the polymer solution is preferably in the range of 0.1 to 50% by weight. From the viewpoint of moldability, it is more preferably in the range of 5 to 40% by weight, and still more preferably in the range of 10 to 30% by weight.

  The electrolyte membrane made of the mixture of the polymer (A) and the polymer (B) can have any thickness, but if it is less than 10 μm, it becomes difficult to satisfy the predetermined characteristics, so that it is preferably 10 μm or more, and 20 μm More preferably. Moreover, since manufacture will become difficult when it exceeds 300 micrometers, it is preferable that it is 300 micrometers or less.

  The polymer electrolyte membrane / electrode assembly of the present invention is a membrane / catalyst having an electrode catalyst layer (preferably a catalyst layer comprising a platinum-supported carbon powder, an ionomer and a solvent) on at least one side of the polymer electrolyte membrane of the present invention. It is a joined body. The membrane / catalyst assembly of the present invention can be produced by directly joining a catalyst layer having a membrane / catalyst interface surface roughness of 1 μm or less to the ion exchange membrane of the present invention.

  More specifically, the membrane / catalyst assembly can be prepared by any method, and is not limited to a specific method, but as an example, a catalyst slurry containing an electrode catalyst, a polymer electrolyte, and a solvent. Can be produced by a method of applying to one or both sides of the polymer electrolyte membrane. By using this method, an electrode catalyst layer containing an electrode catalyst and a polymer electrolyte can be disposed on one side or both sides of the polymer electrolyte membrane.

  The electrode catalyst can be used without particular limitation as long as it promotes the electrode reaction, but preferably a conductive carrier carrying a catalyst component can be used.

  The catalyst component only needs to have a catalytic action in the oxygen reduction reaction in the cathode catalyst layer, and may have any catalytic action in the hydrogen oxidation reaction in the anode catalyst layer. Specifically, selected from platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof, and the like can do. Among these, those containing at least platinum are preferable in order to improve catalytic activity, poisoning resistance to carbon monoxide, heat resistance, and the like. The composition of the alloy varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art. However, platinum is preferably 30 to 90 atomic%, and other metals to be alloyed are preferably 10 to 70 atomic%. The composition of the alloy when the alloy is used as the cathode catalyst varies depending on the type of metal to be alloyed and can be appropriately selected by those skilled in the art, but platinum is 30 to 90 atomic%, and other metals to be alloyed are 10 to 70. It is preferable to use atomic%.

  The shape and size of the catalyst component may be the same shape and size as known catalyst components, and is not particularly limited. The catalyst component is preferably granular. The smaller the average particle size of the catalyst component used in the electrode catalyst layer, the higher the catalytic activity because the effective electrode area where the electrochemical reaction proceeds increases, which is preferable. However, if it is too small, the catalytic activity may decrease instead. The average particle diameter of the catalyst particles contained in the electrode catalyst layer is preferably in the range of 1.5 to 15 nm, more preferably in the range of 2 to 10 nm, and further preferably in the range of 2 to 5 nm.

The conductive carrier in the electrode catalyst may be any material as long as it has a specific surface area for supporting the catalyst component in a desired dispersed state and has sufficient electron conductivity as a current collector. The specific surface area of the conductive carrier is preferably 20 to 1000 m ² / g, more preferably 80 to 800 m ² / g. The specific surface area is less than 20 m 2 / ^g, the dispersibility of the catalyst component and later to polymer electrolyte in the conductive carrier is not preferred not sufficient power generation performance can be obtained by reduction, the 1000 m 2 / ^g If it exceeds, the effective utilization rate of the catalyst component and the polymer electrolyte may decrease, which is not preferable.

  The conductive carrier is preferably composed mainly of carbon. Specific examples include carbon black, activated carbon, coke, natural graphite, mesophase pitch graphite, and flake shaped artificial graphite. Among these, mesophase pitch graphite and / or flake artificial graphite is preferably used as the conductive carrier. Mesophase pitch-based graphite and flake-shaped artificial graphite have a structure in which flake-like crystals are oriented outward, and thus have excellent water absorption and have the effect of improving the water retention of the catalyst.

  Further, the size of the conductive carrier is not particularly limited, but the average particle size is 5 from the viewpoint of easy loading, catalyst utilization, and control of the electrode catalyst layer to an appropriate thickness. It is preferably ˜200 nm, more preferably about 10 to 100 nm.

  Although content of the electrode catalyst in the said catalyst slurry is not specifically limited, It is preferable to set it as 45-65 mass% with respect to a catalyst slurry, and it is more preferable to set it as 50-60 mass%. By setting the content within the above range, an electrode catalyst layer having high power generation performance can be produced.

  The polymer electrolyte used for the catalyst slurry is not particularly limited and may be a known one, but preferably has at least proton conductivity. Thereby, an electrode catalyst layer having high power generation performance is obtained.

  In certain embodiments, ionomers are preferred as the polymer electrolyte. Although it does not specifically limit as an ionomer, The polyether sulfone (PES) which introduce | transduced the sulfonic acid group into the perfluorosulfonic acid polymer represented by Nafion, and the non-fluorine-type aromatic ring containing polymer, polyether ketone (PEK), Examples thereof include polymers having proton conductivity such as polyether ether ketone (PEEK) and polyether ketone ketone (PEKK).

  The content of the polymer electrolyte in the catalyst slurry is not particularly limited, but is usually 20 to 75% by mass and preferably 30 to 60% by mass with respect to the catalyst slurry. It is more preferable to set it as the mass%. When the content of the polymer electrolyte is less than 20% by mass, the content of the polymer electrolyte contained in the electrode catalyst layer is not sufficient, and sufficient bondability between the electrolyte membrane and the electrode catalyst layer may not be obtained. If the amount exceeds 75% by mass, the content of the electrode catalyst in the obtained electrode catalyst layer may be reduced, and the power generation performance of the electrode catalyst layer may be reduced.

  Although it does not specifically limit as a solvent used for the said catalyst slurry, Alcohol solvents, such as methanol, ethanol, 1-propanol (NPA), 2-propanol, ethylene glycol, propylene glycol, N-methyl-2- An organic solvent such as pyrrolidone (NMP), a mixture of the organic solvent and water, water and the like can be mentioned.

  The catalyst slurry may be applied to the electrolyte membrane by a known method, for example, curtain coating method, extrusion coating method, roll coating method, spin coating method, dip coating method, bar coating method, spray coating method, slide coating method. A printing coating method or the like can be used.

The gas diffusion layer used in the present invention is not particularly limited, and known materials can be used in the same manner. For example, conductive materials such as carbon fabrics such as carbon paper and carbon cloth, paper-like paper bodies, felts, and nonwoven fabrics. And at least a sheet-like conductive porous substrate having porosity. Thereby, high gas diffusibility is obtained.
The thickness of the conductive porous substrate may be appropriately determined in consideration of the characteristics of the gas diffusion layer to be obtained, but may be about 30 to 500 μm. If the thickness is less than 30 μm, sufficient mechanical strength or the like may not be obtained. If the thickness exceeds 500 μm, the distance through which gas or water permeates becomes undesirably long, and is not desirable on both sides of the electrolyte membrane / catalyst assembly. A gas diffusion layer is disposed.

  The fuel cell of the present invention can be produced using the polymer electrolyte membrane / catalyst assembly of the present invention and a pair of gas diffusion layers. (It can be obtained by joining the catalyst layer and the gas diffusion layer in layers on the membrane). The fuel cell of the present invention is suitable for a polymer electrolyte fuel cell using hydrogen as a fuel, and particularly suitable for an automobile fuel cell.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these Examples. Various measurements were performed as follows.

  Logarithmic viscosity (Polymer A): Polymer powder was dissolved in N-methyl-2-pyrrolidone at a concentration of 0.5 g / dL, and the viscosity was measured using a Ubbelohde viscometer in a thermostatic bath at 30 ° C. Evaluation was performed using ln [ta / tb] / c (ta is the falling seconds of the sample solution, tb is the falling seconds of the solvent alone, and c is the polymer concentration).

  Logarithmic Viscosity (Polymer B): Polymer powder was dissolved in methanesulfonic acid at a concentration of 0.5 g / dL, and the viscosity was measured using an Ostwald viscometer in a constant temperature bath at 30 ° C., and the logarithmic viscosity ln [ta / tb] / c (ta is the drop time of the sample solution, tb is the drop time of the solvent only, and c is the polymer concentration).

Proton conductivity: A platinum wire (diameter: 0.2 mm) is pressed against the surface of the electrolyte membrane sample on a probe for self-made measurement (made of tetrafluoroethylene resin) and held in a constant temperature and humidity chamber at 80 ° C. and 95% relative humidity. The impedance between the platinum wires was measured by SOLARTRON 1250 FREQUENCY RESPONSE ANALYSER. The measurement was performed while changing the distance between the electrodes, and the conductivity obtained by canceling the contact resistance between the film and the platinum wire was calculated from the gradient obtained by plotting the distance measured between the electrodes and the resistance measurement value estimated from the CC plot.
Conductivity [S / cm] = 1 / film width [cm] × film thickness [cm] × resistance interelectrode gradient [Ω / cm]

Ion exchange capacity: Weighed the electrolyte membrane which was dried at 100 ° C. for 1 hour and allowed to stand overnight at room temperature in a nitrogen atmosphere, stirred with an aqueous sodium hydroxide solution, and then obtained an ion exchange capacity by back titration with an aqueous hydrochloric acid solution. .

Durability evaluation:
Hydrogen was supplied as fuel to the anode side of the fuel cell, oxygen was supplied as the oxidant to the cathode side, and an endurance test in a continuous open circuit holding test was performed to evaluate changes in the open circuit voltage.

Synthesis Example 1 Synthesis of Polymer (A) 3,3′-sodium disulfonate-4,4′-dichlorodiphenylsulfone (abbreviation: S-DCDPS) 54.492 g (110.93 mmol), 2,6-dichlorobenzo Nitrile (abbreviation: DCBN) 20.670 g (120.17 mol), 4,4′-biphenol (abbreviation: BP) 37.868 g (203.36 mmol), bis (4-hydroxyphenyl) sulfide (abbreviation: BPS) 044 g (23.11 mmol), 10- (2,5-dihydroxyphenyl) -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (abbreviation: DHPPP) 1.499 g (4.62 mol) , 35.134 g (254.20 mmol) of potassium carbonate, dried molecular sieve 3 -A 50 g was weighed into a 100 ml four-necked flask and flushed with nitrogen. Add 300 ml of N-methyl-2-pyrrolidone (abbreviation: NMP) and stir at 150 ° C. for 30 minutes, then raise the reaction temperature to 195-200 ° C. Continued (about 13 hours). After standing to cool, the precipitated molecular sieve was removed and the mixture was precipitated in water as a strand. The resulting polymer was washed in boiling water for 1 hour. Thereafter, the polymer was immersed in 1 L of 1 M sulfuric acid twice for 1 hour, washed with pure water until the washing water became neutral, and dried. Polymer A has the structure of the chemical formula (1), n1: n2 = 44: 56, m1: m2: m3 = 88: 10: 2, n1 + n2 = m1 + m2 + m3, and n1 / (n1 + n2) = 0.44. m3 / (m1 + m2 + m3) = 0.02 and m2 / (m1 + m2) = 0.10. The logarithmic viscosity of the obtained polymer (A) was 1.65 dL / g.

Synthesis Example 2 Synthesis of Polymer (B) 3.660 g (13.15 mmol) of 3,3 ′, 4,4-tetraaminodiphenylsulfone (abbreviation: TAS), monosodium 2,5-dicarboxybenzenesulfonate ( Abbreviation: STA, purity 99%) 1.058 g (3.946 mmol), 5-dicarboxyphenylphosphonic acid (abbreviation: DCP, purity 98%) 2.266 g (9.20 mmol), polyphosphoric acid (phosphorus pentoxide content 75) %) 50.00 g and phosphorus pentoxide 40.00 g are weighed in a polymerization vessel. Flow nitrogen and raise the temperature to 100 ° C while stirring gently on an oil bath. After maintaining at 100 ° C. for 1 hour, the temperature was raised to 150 ° C. for 1 hour, and the temperature was raised to 200 ° C. and polymerized for 6 hours. After completion of the polymerization, the mixture was allowed to cool, water was added, the polymer was taken out, and washing with water was repeated until the pH test paper was neutral using a household mixer. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. The polymer B has the structure of the chemical formula (2), m4: m5 = 30: 70, n3 = m4 + m5, and m5 / (m4 + m5) = 0.70. The logarithmic viscosity of the obtained polymer (B) was 1.20 dL / g.

Example 1 Production of Electrolyte Membrane 27.0 g of polymer (A) and 63.0 g of NMP were placed in a 200 mL branch flask and dissolved by stirring at 100 ° C. for 5 hours in a nitrogen atmosphere. 3.0 g of polymer (B) and 27.0 g of NMP were placed in a 50 mL branch flask and dissolved by stirring at 120 ° C. for 5 hours under a nitrogen atmosphere. The total amount of the polymer (B) solution was added to the polymer (A) solution, and the mixture was further stirred and mixed at 100 ° C. for 5 hours under a nitrogen atmosphere to obtain a brown transparent uniform solution. The resulting solution was cast on a glass plate with a thickness of 300 μm and heated at 80 ° C. for 1 hour, 120 ° C. for 1 hour, and 150 ° C. for 1 hour. After cooling to room temperature, the glass plate was immersed in pure water to peel off the film, and the film was immersed in pure water for 12 hours. The obtained membrane was freed from moisture adhering to the surface, sandwiched between filter papers, left under load for 24 hours, and dried to obtain a polymer electrolyte membrane having a thickness of about 30 μm. The obtained polymer electrolyte membrane had a proton conductivity of 0.17 S / cm and an ion exchange capacity of 2.27 meq / g.

<Example 2> Production of membrane / catalyst assembly Production of membrane / catalyst assembly 1 part by weight of an electrode catalyst comprising 50% by weight of platinum having an average particle diameter of 3 nm as a catalyst component on carbon as a catalyst carrier, 4 parts by weight of water, 8 parts by weight of a 5% by weight Nafion solution, isopropanol A catalyst slurry was prepared by mixing 1.5 parts by mass. Using the pulse slurry made by Nordson on both sides of the electrolyte slurry (polymer electrolyte membrane comprising the above-mentioned polymer (A) and polymer (B), thickness 30 μm, area 7 cm × 7 cm) in an environment of 25 ° C. The catalyst slurry was directly applied to prepare a membrane / catalyst assembly in which electrode catalyst layers (thickness 25 μm, area 5 cm × 5 cm) were arranged on both surfaces of the electrolyte membrane. The cross section of the produced membrane / catalyst assembly was observed with a scanning electron microscope, and it was confirmed that the surface roughness of the membrane / catalyst assembly was 1 μm or less.

2. Preparation of Gas Diffusion Layer A base material was prepared by punching carbon paper (carbon paper TGP-H-060 manufactured by Toray Industries, Inc., thickness 190 μm) into 50 mm square. After immersing this base material in a PTFE fluorine-based aqueous dispersion solution (polyflon D-1E manufactured by Daikin Industries, Ltd., containing PTFE 60 wt%) to a predetermined concentration with pure water for 5 minutes, PTFE was dispersed in the substrate by drying at 60 ° C. for 30 minutes. At this time, the PTFE content was 25 wt%. As a result, a water repellent treated substrate was obtained.
Subsequently, 5.4 g of carbon black (VULCAN (registered trademark) XC-72R manufactured by CABOT), 1.0 g of the same PTFE fluorine-based aqueous dispersion solution used above, and 29.6 g of water were used in a homogenizer. The slurry was prepared by mixing and dispersing for 3 hours. This slurry was uniformly applied to one surface of the water-repellent treated substrate prepared previously by a bar coater and heat-treated in an oven at 60 ° C. for 1 hour to obtain a gas diffusion layer.

3. Fabrication of Fuel Cell In an environment of room temperature (25 ° C.) and relative humidity of 80%, the membrane electrode assembly is sandwiched by the gas diffusion layer so that the carbon particle layer is in contact with the electrode catalyst layer, and the electrode catalyst layer is disposed. A sealing material made of silicone rubber was placed on the outer periphery of the exposed electrolyte membrane, and both sides were sandwiched by a separator. This was further sandwiched between two stainless steel end plates via a current collector plate and an insulating plate, and the end plates were fastened with a fastening rod at a pressure of 1 MPa to obtain a fuel cell.
The separator is made of carbon, and the outer dimensions are 2 mm in thickness, 130 mm in height, and 260 mm in width. On the surface facing the cathode or anode, the separator plate has a central portion of 20 cm × 9 cm. An oxidant gas channel or a fuel channel having a pitch of 2.9 mm and a width of about 2 mm was formed. Further, the cooling water channel has a pitch of 2.9 mm and a width of about 2 mm. The separator was provided with manifold holes for oxidant gas, fuel gas, and cooling water.

4). Evaluation The power generation performance of the fuel cell produced above was evaluated according to the following procedure.
Hydrogen was supplied as a fuel to the anode side of the fuel cell, and oxygen was supplied as an oxidant to the cathode side. For both gases, the cell outlet pressure is atmospheric pressure, hydrogen is 44.6 ° C., R.V. H. 30% and 0.261 L / min, air is 44.6 ° C., R.V. H. 30% and 1.041 L / min, the cell temperature was set to 90 ° C., the hydrogen utilization rate was 30%, and the oxygen utilization rate was 30%. Under these conditions, a continuous open circuit holding test was performed to evaluate changes in holding time and open circuit voltage.

<Comparative Example 1>
A sulfonic acid group-containing polymer represented by the following chemical formula (3) (with a logarithmic viscosity of 1.31 dL / g measured by the same method as the polymer (A)) was used in the same manner as in Example 1 except that the polymer (A) was used. A polymer electrolyte membrane was prepared. The obtained polymer electrolyte membrane had a proton conductivity of 0.16 S / cm and an ion exchange capacity of 2.06 meq / g. From the obtained polymer electrolyte membrane, a membrane / catalyst assembly was produced and evaluated in the same manner as in Example 2.

（化学式（３）において、ｎ４、ｎ５、ｍ６は、ｎ４＝ｎ５、及びｍ６＝ｎ４＋ｎ５を満たす、正の整数を表す。）

(In chemical formula (3), n4, n5, and m6 represent positive integers that satisfy n4 = n5 and m6 = n4 + n5.)

<Comparative example 2>
30 g of the polymer of Comparative Example 1 having a known structure and 90 g of NMP were placed in a 200 mL branch flask and dissolved by stirring at 100 ° C. for 5 hours in a nitrogen atmosphere. The resulting solution was cast on a glass plate with a thickness of 300 μm and heated at 80 ° C. for 1 hour, 120 ° C. for 1 hour, and 150 ° C. for 1 hour. After cooling to room temperature, the glass plate was immersed in pure water to peel off the film, and the film was immersed in pure water for 12 hours. The obtained membrane was freed from moisture adhering to the surface, sandwiched between filter papers, left under load for 24 hours, and dried to obtain a polymer electrolyte membrane having a thickness of about 30 μm. The obtained polymer electrolyte membrane had a proton conductivity of 0.27 S / cm and an ion exchange capacity of 1.97 meq / g. The membrane / catalyst assembly was produced in the same manner as in Example 2.

（化学式（３）において、ｎ４、ｎ５、ｍ６は、ｎ４＝ｎ５、及びｍ６＝ｎ４＋ｎ５を満たす、正の整数を表す。）

(In chemical formula (3), n4, n5, and m6 represent positive integers that satisfy n4 = n5 and m6 = n4 + n5.)

  Table 1 shows the evaluation results of the fuel cells using the polymer electrolyte membranes and the membrane / catalyst assemblies in Examples and Comparative Examples. In addition, when the open circuit voltage was 0 V and the test could not be continued, “X” was marked, and when the test could be continued, “◯” was marked.

  The polymer electrolyte membrane of the present invention exhibits excellent characteristics and can greatly improve the output and durability under low humidification by being used in a fuel cell as a membrane / electrode assembly. It is.

It is an enlarged view which shows the cross section of the membrane / catalyst assembly interface produced by the Example and the comparative example.

Explanation of symbols

1 catalyst layer 2 electrolyte layer

Claims (3)

The polymer (A) having a structure represented by the following chemical formula (1) and the polymer (B) having a structure represented by the following chemical formula (2) have a weight fraction of the polymer (B) of 5 to 15 weights. % Of a polymer electrolyte membrane for a fuel cell containing a mixture mixed so as to be an electrode and an electrode catalyst layer directly bonded to at least one surface of the polymer electrolyte membrane, and the surface roughness of the membrane / catalyst interface is A polymer electrolyte membrane / catalyst assembly for a fuel cell, characterized by being 1 μm or less.

(In the above formula, n1, n2, m1, m2, and m3 represent an integer of 1 or more that satisfies the following mathematical formulas (1) to (3).)

(In the above formula, n3 represents an integer of 1 or more, and m4 and m5 each represents an integer of 1 or more that satisfies the following formula (4).)

  The polymer (A) having the structure represented by the chemical formula (1) and the polymer (B) represented by the chemical formula (2) have a weight fraction of the polymer (B) of 5 to 15% by weight. A catalyst slurry containing an electrode catalyst, a polymer electrolyte, and a solvent with respect to at least one surface of the polymer electrolyte membrane for a fuel cell containing the mixture thus mixed has a surface roughness of the membrane / catalyst interface of 1 μm or less. A method for producing a polymer electrolyte membrane / catalyst assembly for a fuel cell using hydrogen as a fuel, characterized in that the electrode catalyst layer is formed by direct coating.   A fuel cell using hydrogen as a fuel, wherein the polymer electrolyte membrane / catalyst assembly for a fuel cell according to claim 1 is used.

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