JP4530635B2 - Electrocatalyst layer for fuel cells - Google Patents

Description

  The present invention relates to an electrode catalyst layer for a polymer electrolyte fuel cell.

A fuel cell is one that converts the chemical energy of a fuel directly into electrical energy by electrochemically oxidizing hydrogen, methanol, etc. within the cell, and is attracting attention as a clean electrical energy supply source. ing. In particular, solid polymer fuel cells are expected to be used as alternative power sources for automobiles, household cogeneration systems, and portable generators because they operate at a lower temperature than others.
Such a polymer electrolyte fuel cell is provided with at least a membrane electrode assembly (hereinafter referred to as MEA) in which electrode catalyst layers are bonded to both surfaces of a proton exchange membrane. As the electrode catalyst layer, a thin sheet of a catalyst composition comprising composite particles in which electrode catalyst particles are supported on carbon particles and a perfluorocarbon sulfonic acid polymer as shown in Non-Patent Document 1 is suitably used. (Hereinafter referred to as a conventional electrode catalyst layer). Note that a structure in which the MEA is sandwiched between a pair of gas diffusion layers may be used as necessary. In this case, the laminate of the electrode catalyst layer and the gas diffusion layer is referred to as a gas diffusion electrode.

The fuel cell having the above MEA supplies fuel (for example, hydrogen) to the gas diffusion electrode on the anode side and oxidant (for example, oxygen or air) to the gas diffusion electrode on the cathode side, and connects both electrodes with an external circuit. It works by. Specifically, when hydrogen is used as a fuel, hydrogen is oxidized on the anode catalyst to generate protons, which pass through the perfluorocarbon sulfonic acid polymer in the anode electrode catalyst layer and then pass through the proton exchange membrane. It moves and reaches the cathode catalyst through the perfluorocarbon sulfonic acid polymer in the cathode electrode catalyst layer. On the other hand, electrons generated simultaneously with protons due to oxidation of hydrogen reach the cathode side gas diffusion electrode through an external circuit, and react with protons and oxygen in the oxidizing agent on the cathode catalyst to generate water. Electric energy can be taken out. In general, a polymer electrolyte fuel cell can obtain high power generation efficiency and output by operating under an appropriate humidifying condition around 80 ° C.
By the way, when the polymer electrolyte fuel cell is used for automobiles, it is assumed that the vehicle is driven in summer, and is under high-temperature and low-humidification conditions (operating temperature of 100 to 120 ° C, low humidity of 50 to 80 ° C (humidity of 12 to It is desired that the fuel cell can be operated at 30RH%))). However, when the fuel cell operation is performed under the high temperature and low humidity conditions using the conventional electrode catalyst layer as described above, the perfluorocarbon sulfonic acid polymer is likely to be deteriorated by thermal oxidative decomposition, and fluorine ion elution occurs. End up. That is, the durability was insufficient.

As a method for improving the electrode catalyst layer, a method in which fine particle and / or fibrous silica is contained in the anode electrode catalyst layer (see, for example, Patent Document 1), and a fine particle of a crosslinked polyacrylate as a water-absorbing material is used as an electrode catalyst. Disclosed are a method for containing in a layer (for example, see Patent Document 2), a method for providing a metalloxane polymer in an electrode catalyst layer (for example, see Patent Documents 3 and 4), and an electrode catalyst layer containing a polyfunctional basic compound. (For example, refer to Patent Document 5). Although this technique has improved the durability slightly, it has not been sufficient.
Journal of Applied electrochemistry, 22, p. 1-7 (1992) JP-A-6-1111827 JP 7-326361 A JP 2001-11219 A JP 2001-325963 A JP 2002-26041 A

  An object of the present invention is to provide an electrode catalyst layer which is excellent in heat-resistant oxidation and has little thermal oxidative decomposition even under high temperature and low humidification conditions.

As a result of diligent research to solve the above problems, the present inventors have found that an electrode catalyst layer for a fuel cell composed of a perfluorocarbon polymer having an ion exchange group, polybenzimidazole, and an electrode catalyst has been subjected to thermal oxidation. It has been found that it has good resistance. And, by providing a membrane electrode assembly manufactured using the electrode catalyst layer of the present invention, a fuel cell that exhibits high durability even when operated under high temperature and low humidification conditions and has little fluorine ion emission The present invention has been found out and can be achieved. That is, the present invention is as follows.
(1) 30.00% by mass to 80.00% by mass of composite particles in which electrocatalyst particles are supported on conductive particles, 19.99% by mass to 60.00% by mass of a perfluorocarbon polymer having an ion exchange group, and polybenzimidazole. An electrode catalyst layer for a fuel cell, characterized by containing 0.01% by mass or more and 10.00% by mass or less .
( 2 ) A membrane electrode assembly comprising the electrode catalyst layer according to ( 1) .
( 3 ) A polymer electrolyte fuel cell comprising the electrode catalyst layer according to ( 1) .
Hereinafter, the electrode catalyst layer for a fuel cell of the present invention will be described in detail.

  By providing the membrane electrode assembly produced using the electrode catalyst layer of the present invention, it is possible to provide a fuel cell that exhibits high durability even when operated under high-temperature and low-humidification conditions and has little fluorine ion elution Have

（式中、Ｘ¹ 、Ｘ² およびＸ³ は、それぞれ独立に、ハロゲン元素または炭素数１以上３以下のパーフルオロアルキル基、０≦ａ＜１、０＜ｇ≦１、ａ＋ｇ＝１、ｂは０以上8 以下の整数、ｃは０または１、ｄ、ｅおよびｆはそれぞれ独立に０以上6 以下の整数（但し、ｄ＋ｅ＋ｆは０に等しくない）、Ｒ¹ およびR²は、それぞれ独立にハロゲン元素、炭素数１以上１０以下のパーフルオロアルキル基またはフルオロクロロアルキル基、Ｘ⁴ は、ＣＯＯＺ、ＳＯ₃ Ｚ、ＰＯ₃ Ｚ₂ 、ＰＯ₃ ＨＺ（Ｚは水素原子、金属原子（Ｎａ、Ｋ、Ｃａ等）、アミン類（ＮＨ₄ 、ＮＨ₃ Ｒ、ＮＨ₂ Ｒ₂ 、ＮＨＲ₃ 、ＮＲ₄ （Ｒはアルキル基及び／又はアレーン基）） The electrode catalyst layer for a fuel cell of the present invention is characterized by comprising a perfluorocarbon polymer having an ion exchange group, polybenzimidazole, and an electrode catalyst.
A typical example of the perfluorocarbon polymer is a polymer represented by the chemical formula (1).

Wherein X ¹ , X ² and X ³ are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms, 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, b Is an integer of 0 to 8, c is 0 or 1, d, e and f are each independently an integer of 0 to 6 (where d + e + f is not equal to 0), R ¹ and R ² are each independently Halogen element, perfluoroalkyl group or fluorochloroalkyl group having 1 to 10 carbon atoms, X ⁴ is COOZ, SO ₃ Z, PO ₃ Z ₂ , PO ₃ HZ (Z is a hydrogen atom, metal atom (Na, K , Ca, etc.), amines (NH ₄ , NH ₃ R, NH ₂ R ₂ , NHR ₃ , NR ₄ (R is an alkyl group and / or an arene group))

（式中、０≦ａ＜１、０＜ｇ≦１、ａ＋ｇ＝１） Among these, a perfluorocarbon sulfonic acid polymer of X ⁴ = SO ₃ H is preferable, and a short side chain type perfluorocarbon sulfonic acid polymer represented by the chemical formula (2) is particularly preferable.

(Where 0 ≦ a <1, 0 <g ≦ 1, a + g = 1)

The perfluorocarbon polymer may be a copolymer containing a third component such as perfluoroolefin such as hexafluoropropylene or chlorotrifluoroethylene, or perfluoroalkyl vinyl ether.
The equivalent mass EW (dry mass in grams per equivalent of ion-exchange group) of such a perfluorocarbon polymer is not particularly limited, but is preferably 250 or more and 2000 or less, and more preferably 250 or more and 1200 or less. Preferably, it is 400 or more and 800 or less. By using the perfluorocarbon polymer having a lower EW, that is, a large proton exchange capacity, it exhibits excellent proton conductivity even under high-temperature and low-humidity conditions, and when used in a fuel cell, a high output during operation can be obtained. it can.
Examples of the polybenzimidazole include a compound represented by the chemical formula (3), a polybenzobisimidazole represented by the chemical formula (4), and a poly 2,5-benzimidazole represented by the chemical formula (5). .

（式中、ｘは、１０以上１．０×１０⁷ 以下の整数である）

(Wherein x is an integer of 10 or more and 1.0 × 10 ⁷ or less)

（式中、ｌは、１０以上１．０×１０⁷ 以下の整数、ＲとＲ₁ は、化学式（３）と同じである）

（式中、ｍは、１０以上１．０×１０⁷ 以下の整数である）

(In the formula, l is an integer of 10 or more and 1.0 × 10 ⁷ or less, and R and R ₁ are the same as those in chemical formula (3)).

(In the formula, m is an integer of 10 or more and 1.0 × 10 ⁷ or less)

The mass ratio of polybenzimidazole to the perfluorocarbon polymer is preferably 0.0001 or more and 1 or less, more preferably 0.001 or more and 0.1 or less, and 0.01 or more and 0.05 or less. Most preferably.
The mixed state of the perfluorocarbon polymer and polybenzimidazole is not particularly limited, but preferably forms a polymer alloy. The category of polymer alloys includes (I) incompatible mechanical kneaded materials, (II) partially compatible mixtures, and (III) completely compatible homogeneous mixtures. In the electrode catalyst layer of the present invention, a form in which the perfluorocarbon polymer and polybenzimidazole are completely or partially compatible is more preferable.
The electrode catalyst layer of the present invention further has an electrode catalyst. The electrode catalyst is a catalyst that oxidizes fuel (for example, hydrogen) at the anode and easily generates protons, and at the cathode, reacts protons and electrons with an oxidizing agent (for example, oxygen or air) to generate water. Although there is no restriction | limiting in the kind of electrode catalyst, Platinum is used preferably. In order to enhance the resistance of platinum to impurities such as CO, an electrode catalyst obtained by adding or alloying ruthenium or the like to platinum may be preferably used.

The supported amount of the electrode catalyst with respect to the electrode area is preferably 0.001 mg / cm ^{2 to} 10 mg / cm ² , more preferably 0.01 mg / cm ^{2 to} 5 mg / cm ² in the state where the electrode catalyst layer is formed. Most preferably, it is 0.1 mg / cm ² or more and 1 mg / cm ² or less.
Usually, the electrode catalyst is used in the form of composite particles in which electrode catalyst particles are supported on conductive particles. Any conductive particles may be used as long as they have conductivity. For example, carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and various metals are used. The particle diameter of these conductive particles is preferably 10 angstroms or more and 10 μm or less, more preferably 50 angstroms or more and 1 μm or less, and most preferably 100 angstroms or more and 5000 angstroms or less.
The particle diameter of the electrocatalyst particles is not limited, but is preferably 10 angstroms or more and 1000 angstroms or less, more preferably 10 angstroms or more and 500 angstroms or less, and most preferably 15 angstroms or more and 100 angstroms or less.

As the composite particles, the electrocatalyst particles are preferably 1% by mass to 99% by mass, more preferably 10% by mass to 90% by mass, and most preferably 30% by mass to 70% by mass with respect to the conductive particles. It is preferable that it is supported on. Specifically, commercially available Degussa Co., Ltd. F101RA / W, Tanaka Kikinzoku Kogyo Co., Ltd. TEC10E40E etc. are mentioned as a suitable example.
The electrode catalyst layer of the present invention preferably has a structure in which composite particles are bound by the perfluorocarbon polymer and polybenzimidazole.
The content of the composite particles, the perfluorocarbon polymer, and the polybenzimidazole in the electrode catalyst layer of the present invention is 30.00% by mass or more and 80.00% by mass or less, and 19.99% by mass or more and 60.00% by mass, respectively. Hereafter, 0.01 mass% or more and 10.00 mass% or less (total 100 mass%) are preferable, and 40.00 mass% or more and 75.00 mass% or less and 24.95 mass% or more and 55.00 mass%, respectively. Hereafter, 0.05 mass% or more and 5.00 mass% or less (total 100 mass%) are more preferable, and also 50.00 mass% or more and 70.00 mass% or less, 29.90 mass% or more and 49.00 mass%, respectively. % Or less, 0.10% by mass or more and 1.00% by mass or less (total of 100% by mass) is most preferable.

The thickness of the electrode catalyst layer of the present invention is preferably 0.01 μm or more and 200 μm or less, more preferably 0.1 μm or more and 100 μm or less, and most preferably 1 μm or more and 50 μm or less.
The porosity of the electrode catalyst layer of the present invention is not particularly limited, but is preferably 10% by volume to 90% by volume, more preferably 20% by volume to 80% by volume, and most preferably 30% by volume to 60% by volume. It is.
In order to improve water repellency, the electrode catalyst layer of the present invention may further contain polytetrafluoroethylene (hereinafter referred to as PTFE). In this case, the shape of PTFE is not particularly limited, but may be any shape as long as it has a regular shape, and is preferably in the form of particles or fibers, and these may be used alone or in combination. I do not care.

The content when PTFE is contained in the electrode catalyst layer of the present invention is preferably 0.001% by mass or more and 20% by mass or less, more preferably 0.01% by mass or more and 10% by mass with respect to the total mass of the electrode catalyst layer. It is not more than mass%, most preferably not less than 0.1 mass% and not more than 5 mass%.
Moreover, the electrode catalyst layer of this invention may contain a metal oxide further for hydrophilicity improvement. In this case, the metal oxide is not particularly limited, but Al ₂ O ₃ , B ₂ O ₃ , MgO, SiO ₂ , SnO ₂ , TiO ₂ , V ₂ O ₅ , WO ₃ , Y ₂ O ₃ , ZrO ₂ , Zr ₂ O _3, and ZrSiO ₄ , a metal oxide having at least one member selected from the group consisting of ZrSiO ₄ is preferable. Of these, Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ are preferable, and SiO ₂ is particularly preferable.

As a content rate in case the electrode catalyst layer of this invention contains a metal oxide, Preferably it is 0.001 mass% or more and 20 mass% or less with respect to the total mass of an electrode catalyst layer, More preferably, it is 0.01 mass%. It is 10 mass% or less, Most preferably, it is 0.1 mass% or more and 5 mass% or less.
The metal oxide may be in the form of particles or fibers, but it is particularly desirable that the metal oxide be amorphous. The term “amorphous” as used herein means that no particulate or fibrous metal oxide is observed even when observed with an optical microscope or an electron microscope. In particular, even when the electrode catalyst layer is magnified up to several hundred thousand times using a scanning electron microscope (SEM), no particulate or fibrous metal oxide is observed. In addition, even when the electrode catalyst layer is observed by magnifying it to several hundred thousand to several million times using a transmission electron microscope (TEM), it is possible to clearly observe a particulate or fibrous metal oxide. Can not. Thus, within the scope of the current microscopic technique, it means that the particle shape or fiber shape of the metal oxide cannot be confirmed.

Next, the manufacturing method of the electrode catalyst layer of this invention is demonstrated.
(Method for producing electrode catalyst layer)
The electrode catalyst layer of the present invention is obtained by, for example, treating an electrode catalyst composition in which an electrode catalyst is dispersed in a polymer solution containing a perfluorocarbon polymer having an ion exchange group and polybenzimidazole on a proton exchange membrane or a PTFE sheet. After coating on another substrate, it can be dried and solidified. In the present invention, the electrode catalyst composition can be applied by various commonly known methods such as a spray method.
The electrocatalyst composition is used after further adding a solvent as necessary. Solvents that can be used include single solvents such as water, alcohols (ethanol, 2-propanol, ethylene glycol, glycerin, etc.), nitrogen compounds (dimethylformamide, dimethylacetamide, etc.), sulfur compounds (dimethyl sulfoxide, etc.), and chlorofluorocarbons. A composite solvent may be mentioned. The addition amount of such a solvent is preferably 0.1% by mass or more and 90% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and most preferably 5% by mass with respect to the total mass of the electrode catalyst composition. % Or more and 20% by mass or less is desirable.

On the other hand, a polymer solution containing the perfluorocarbon polymer and polybenzimidazole is applied to or immersed in a gas diffusion electrode such as ELAT (registered trademark) manufactured by DE NORA NORTH AMERICA, in which a gas diffusion layer and an electrode catalyst layer are laminated. -After apply | coating, the electrode catalyst layer of this invention can be obtained also by drying and solidifying.
Furthermore, the electrode catalyst layer may be produced and then immersed in an inorganic acid such as hydrochloric acid to convert the ion-exchange group of the perfluorocarbon polymer into a proton group. The acid treatment temperature is preferably 5 ° C. or higher and 90 ° C. or lower, more preferably 10 ° C. or higher and 70 ° C. or lower, and most preferably 20 ° C. or higher and 50 ° C. or lower.

（式中、Ｘ¹ 、Ｘ² およびＸ³ は、それぞれ独立に、ハロゲン元素または炭素数１以上３以下のパーフルオロアルキル基、０≦ａ＜１、０＜ｇ≦１、ａ＋ｇ＝１、ｂは０以上８以下の整数、ｃは０または１、ｄ、ｅおよびｆはそれぞれ独立に０以上６以下の整数（但し、ｄ＋ｅ＋ｆは、０に等しくない）、Ｒ¹ およびR²はそれぞれ独立にハロゲン元素、炭素数１以上１０以下のパーフルオロアルキル基またはフルオロクロロアルキル基、Ｘ⁵ はＣＯＯＲ³ ，ＣＯＲ⁴ 、ＳＯ₂ Ｒ⁴ 、ＰＯ₂ ＨＲ⁴ 、またはＰＯ₂ Ｒ⁴ （Ｒ³ は炭素数１〜３の炭化水素系アルキル基、Ｒ⁴ はハロゲン元素）） Next, a method for producing a polymer solution containing the perfluorocarbon polymer having an ion exchange group and polybenzimidazole will be described in detail.
<(1) Method for producing perfluorocarbon polymer having ion exchange group>
The above-mentioned perfluorocarbon polymer having an ion exchange group can be produced by polymerizing a precursor polymer represented by the following chemical formula (6), followed by hydrolysis.

Wherein X ¹ , X ² and X ³ are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms, 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, b Is an integer from 0 to 8, c is 0 or 1, d, e and f are each independently an integer from 0 to 6 (where d + e + f is not equal to 0), R ¹ and R ² are each independently Halogen element, perfluoroalkyl group or fluorochloroalkyl group having 1 to 10 carbon atoms, X ⁵ is COOR ³ , COR ⁴ , SO ₂ R ⁴ , PO ₂ HR ⁴ , or PO ₂ R ⁴ (R ³ is carbon number 1 to 3 hydrocarbon alkyl groups, R ⁴ is a halogen element))

1) Method for Producing Precursor Polymer A precursor polymer is produced by copolymerizing a fluorinated olefin and a vinyl fluoride compound. Specific fluorinated _{olefin, CF 2 = CF 2, CF} 2 = CFCl, CF 2 = CCl 2 , and examples of the specific fluorinated vinyl _{compounds, CF 2 = CFO (CF 2} ) Z -SO 2 _{F, CF 2 = CFOCF 2 CF} (CF 3) O (CF 2) Z -SO 2 F, CF 2 = CF (CF 2) Z -SO 2 F, CF 2 = CF (OCF 2 CF (CF 3)) _{Z - (CF 2) Z-} 1 -SO 2 F, CF 2 = CFO (CF 2) Z -CO 2 R, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) Z -CO 2 R, CF _{2 = CF (CF 2) Z} -CO 2 R, CF 2 = CF (OCF 2 CF (CF 3)) Z - (CF 2) 2 -CO 2 R (Z is an integer of 1 to 8, R represents the number of carbon atoms 1 to 3 hydrocarbon alkyl groups).

The polymerization method of the precursor polymer includes a solution polymerization method in which a vinyl fluoride compound is dissolved in a solvent such as chlorofluorocarbon, and then reacted with a tetrafluoroethylene gas to polymerize, or a bulk polymer that is polymerized without using a solvent such as chlorofluorocarbon. Examples thereof include an emulsion polymerization method in which a vinyl fluoride compound is mixed with water in a surfactant and emulsified in water and then reacted with a tetrafluoroethylene gas for polymerization.
The melt index MI (g / 10 minutes) measured at 270 ° C., load 21.2 N, orifice inner diameter 2.09 mm based on JIS K-7210 of the precursor polymer is not limited, but is 0.001 or more and 1000 or less. More preferably, it is 0.01 or more and 100 or less, and most preferably 0.1 or more and 10 or less.

2) Method of hydrolysis of precursor polymer Next, the precursor polymer is immersed in a basic reaction liquid to perform a hydrolysis treatment.
The reaction liquid is not limited, but an aqueous solution of an alkali metal or alkaline earth metal hydroxide such as potassium hydroxide or sodium hydroxide is preferred. The content of the alkali metal or alkaline earth metal hydroxide in the reaction liquid is not limited, but is preferably 10% by mass or more and 30% by mass or less. The reaction liquid preferably contains a swellable organic compound such as dimethyl sulfoxide or methyl alcohol. The content of the swellable organic compound in the reaction liquid is preferably 1% by mass or more and 30% by mass or less. After the hydrolysis treatment, the perfluorocarbon polymer is produced by dipping in an aqueous solution of a suitable salt or an inorganic acid such as hydrochloric acid.

<(2) Method for Producing Polymer Solution Containing Polybenzimidazole>
By mixing the polymer solution B in which the perfluorocarbon polymer is dissolved in dimethylacetamide and the polymer solution C in which polybenzimidazole is dissolved in dimethylacetamide, a polymer solution in which the perfluorocarbon polymer and polybenzimidazole are uniformly mixed is obtained. Can be manufactured. As another method, the polymer solution B and the polymer solution C are mixed, and the polymer solution A in which the perfluorocarbon polymer is dissolved in water and / or alcohol is added and mixed. The polymer solution thus obtained may be concentrated as necessary.

An example of the production method of the polymer solutions A to C is as follows.
1) Polymer solution A
A polymer solution A in which the perfluorocarbon polymer is dissolved in a solvent containing water and / or alcohol can be obtained by a method such as heat treatment at 40 to 200 ° C. in an autoclave. As the solvent, a mixed solvent of water and alcohol is preferable, and in particular, a mixed solvent of water / ethanol = 3/1 to 1/3 (volume ratio), water / isopropanol = 3/1 to 1/3 (volume ratio), and the like. Is more preferable. The content of the perfluorocarbon polymer in the polymer solution A is preferably 1% by mass or more and 10% by mass or less.
2) Polymer solution B
The polymer solution B can also be obtained by dissolving the perfluorocarbon polymer in dimethylacetamide by heat treatment in an autoclave as described above. Alternatively, dimethylacetamide may be added to the polymer solution A, and water and / or an alcohol solvent may be volatilized with an evaporator or the like to obtain the polymer solution B. The content of the perfluorocarbon polymer in the polymer solution B is preferably 1% by mass or more and 10% by mass or less.

3) Polymer solution C
The polymer solution C can be obtained by a method in which polybenzimidazole and dimethylacetamide are put in an autoclave and heat-treated at 40 to 300 ° C. The content of polybenzimidazole in the polymer solution C is preferably 1% by mass or more and 10% by mass or less.
Polybenzimidazole can be polymerized by methods described in known literature (see, for example, Experimental Chemistry Lecture 28 Polymer Synthesis 4th Edition, edited by The Chemical Society of Japan, Maruzen Co., Ltd.). The weight average molecular weight of polybenzimidazole is not limited, but is preferably 10,000 to 1,000,000, more preferably 20,000 to 100,000, and most preferably 50,000 to 100,000.

In addition, the intrinsic viscosity iv (dL / g) of a polymer solution in which polybenzimidazole is dissolved (hereinafter referred to as PBI polymer solution) is preferably 0.1 dL / g or more and 10.0 dL / g or less, more preferably 0.8. It is 3 dL / g or more and 5.0 dL / g or less, Most preferably, it is 0.5 dL / g or more and 1.0 dL / g or less.
The intrinsic viscosity iv is determined from the viscosity ηp (mPa · s) of the PBI polymer solution, the viscosity ηs (mPa · s) of dimethylacetamide, and the concentration Cp (g / dL) of the PBI polymer solution using the following formula: Can do. The viscosity referred to here is, for example, a value measured at 25 ° C. using a conical plate type rotary viscometer (E-type viscometer).
iv = ln (ηp / ηs) / Cp

(Membrane electrode assembly)
The effect of the electrode catalyst layer of the present invention can be demonstrated by evaluating it as a polymer electrolyte fuel cell. The evaluation method will be described below.
The electrode catalyst layer of the present invention is used as an MEA (membrane electrode assembly) in which the electrode catalyst layer is bonded via a proton exchange membrane, and is used as both or at least one of the electrode catalyst layers used as an anode and a cathode. There is an effect. In addition, when the electrode catalyst layer of this invention is used for any one electrode, it is more preferable to use for the cathode side. Moreover, you may make it the structure which joined so that a pair of gas diffusion layer might oppose through MEA as needed.

The type of proton exchange membrane used in the MEA of the present invention is not limited, but a proton exchange membrane composed of a perfluorocarbon sulfonic acid polymer or a proton exchange membrane composed of a perfluorocarbon sulfonic acid polymer and polybenzimidazole is preferable. In this case, the content of the perfluorocarbon polymer with respect to the total weight of the proton exchange membrane is preferably 80.00% by mass or more and 99.99% by mass or less, more preferably 90.00% by mass or more and 99.90% by mass or less. Preferably, it is 95.00% by mass or more and 99.00% by mass or less. The content of polybenzimidazole with respect to the total weight of the proton exchange membrane is preferably 0.01% by mass or more and 20.00% by mass or less, more preferably 0.10% by mass or more and 10.00% by mass or less. 0.000% by mass or more and 5.00% by mass or less is most preferable. The EW of the proton exchange membrane is not limited, but is preferably 250 or more and 2000 or less, more preferably 300 or more and 1200 or less, and most preferably 400 or more and 800 or less. Moreover, although there is no restriction | limiting in a film thickness, 1 micrometer or more and 500 micrometers or less are preferable, More preferably, they are 2 micrometers or more and 100 micrometers or less, Most preferably, they are 10 micrometers or more and 50 micrometers or less.
MEA forms an electrode catalyst layer directly on a proton exchange membrane, or is applied and molded on a substrate other than a proton exchange membrane such as a PTFE sheet, and then dried and solidified to obtain an electrode catalyst layer and a proton exchange membrane. Can be obtained by using a method in which the film is heated and pressed at 100 ° C. to 200 ° C. for transfer and bonding. In addition, when joining a gas diffusion layer and MEA, it can obtain similarly by heat-pressing.

(Fuel cell)
The MEA obtained as described above has a pair of gas diffusion layers facing each other as necessary, and is combined with components used for a general polymer electrolyte fuel cell such as a bipolar plate and a backing plate. In general, it is used as a polymer electrolyte fuel cell.
Of these, the bipolar plate is a graphite or resin composite material with a groove for flowing gas such as fuel or oxidant on its surface, a metal plate, etc., and transmits electrons to an external load circuit. In addition, it has a function as a flow path for supplying fuel and oxidant to the vicinity of the electrode catalyst. A fuel cell is manufactured by inserting and stacking a plurality of MEAs between such bipolar plates. The fuel cell is finally operated by supplying hydrogen to one electrode and oxygen or air to the other electrode.
The electrode catalyst layer of the present invention can also be used for chloralkali, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor and the like.

The present invention will be described based on examples.
[Example 1]
The electrode catalyst layer for a fuel cell of the present invention was evaluated as follows.
(Fuel cell evaluation)
Various electrode catalyst layers are formed in the gas diffusion electrode, and the following fuel cell evaluation is performed. First, an anode side gas diffusion electrode and a cathode side gas diffusion electrode are faced to each other, a proton exchange membrane is sandwiched between them, and hot pressing is performed at 160 ° C. and a pressure of 4.9 MPa to produce an MEA.
This MEA is incorporated into an evaluation cell and set in an evaluation apparatus. Battery operation is performed at normal pressure and cell temperature of 120 ° C. using hydrogen gas as fuel and air gas as oxidant. A water bubbling method was used for gas humidification, and both hydrogen gas and air gas were humidified at 80 ° C. and supplied to the cell, and the voltage was maintained at 0.9V. After the fuel cell operation was continued for 20 hours, the evaluation cell was cooled and the operation was terminated.

(Fluorine ion concentration measurement)
The fluorine ion concentration in the wastewater discharged in the fuel cell evaluation as described above is measured using a fluorine composite electrode (Model 9609BNionplus ^™ ) manufactured by ThermoOrion and an ion meter (Model 920Aplus ^™ ). First, a calibration curve is prepared by measuring the fluorine ion concentrations of standard solutions having fluorine ion concentrations of 0.1 ppm, 1 ppm, and 10 ppm, respectively. Next, 4 ml of battery drainage is sampled, 0.4 ml of an ionic strength adjusting agent is added thereto and mixed, and then the fluorine composite electrode is immersed and waited until it is stabilized, and the fluorine ion concentration is measured.

[Example 1]
As a precursor polymer of perfluorocarbon sulfonic acid polymer, a perfluorocarbon polymer of tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F (EW = 710, MI (JIS K-7210, 270 ° C., load) 2.16 kgf, orifice inner diameter 2.09 mm, g / 10 min) = 3.0) was produced. This precursor polymer was subjected to a hydrolysis treatment by bringing it into contact with an aqueous solution in which potassium hydroxide (15% by mass) and dimethyl sulfoxide (30% by mass) were dissolved at 60 ° C. for 4 hours. Then, it was immersed in 60 degreeC water for 4 hours. Next, it was immersed in a 2N hydrochloric acid aqueous solution at 60 ° C. for 3 hours, then washed with ion-exchanged water and dried to obtain a perfluorocarbon sulfonic acid polymer (EW = 710).

This perfluorocarbon sulfonic acid polymer was placed in an autoclave together with a water / ethanol mixed solvent (water: ethanol = 50.0: 50.0 (mass ratio)), sealed, heated to 180 ° C. and held for 5 hours. Thereafter, the autoclave was naturally cooled to obtain a polymer solution A having a composition of perfluorocarbon sulfonic acid polymer: water: ethanol = 5.0: 47.5: 47.5 (mass ratio).
Further, dimethylacetamide was added to the polymer solution A, and then water and ethanol were removed by an evaporator, whereby a polymer solution having a composition of perfluorocarbonsulfonic acid polymer: dimethylacetamide = 1.5: 98.5 (mass ratio). B was also obtained.

On the other hand, polybenzimidazole (Sigma Aldrich Japan Co., Ltd.) represented by the chemical formula (7) and having a weight average molecular weight of 27000 was sealed together with dimethylacetamide in an autoclave, heated to 200 ° C. and heated to 5 ° C. Held for hours. Thereafter, the autoclave was naturally cooled to obtain a polymer solution having a composition of polybenzimidazole: dimethylacetamide = 10.0: 90.0 (mass ratio). The intrinsic viscosity iv of this polymer solution was 0.8 dL / g. Further, this polymer solution was diluted 10 times with dimethylacetamide to prepare a polymer solution C having a composition of polybenzimidazole: dimethylacetamide = 1.0: 99.0 (mass ratio).

Next, with stirring, 0.65 g of the polymer solution A was gradually added to 4.00 g of the polymer solution B and mixed to obtain a uniform polymer solution. Next, 11.71 g of the polymer solution C was gradually added and mixed while stirring to obtain a uniform polymer solution.
15.00 g of this polymer solution was placed in an eggplant flask, set in an evaporator, and concentrated twice in an oil bath at 90 ° C. The concentration of the perfluorocarbon sulfonic acid polymer in the polymer solution after concentration was 7.95% by mass, and the concentration of polybenzimidazole was 0.08% by mass.
This polymer solution was applied to a gas diffusion electrode ELAT (registered trademark) (Pt loading 0.4 mg / cm ² ) manufactured by DE NORA NORTH AMERICA, USA, dried and fixed at 160 ° C. in an air atmosphere, and further 2N After being immersed in an aqueous hydrochloric acid solution for 3 hours, washed with water and dried to form the electrode catalyst layer of the present invention in the gas diffusion electrode. The amount of polymer supported on this electrode catalyst layer was 0.8 mg / cm ² .

As the proton exchange membrane, the same precursor polymer of perfluorocarbon sulfonic acid polymer as described above is polymerized, this precursor polymer is melt extruded at 270 ° C. to form a 50 μm thick film, and the same hydrolysis treatment as above is performed. The perfluorocarbon sulfonic acid membrane (EW = 710) obtained above was used.
Thus, MEA was produced using the gas diffusion electrode on which the electrode catalyst layer of the present invention was formed on both sides of the anode and cathode, and the above fuel cell evaluation was performed. The concentrations of fluorine ions in the battery drainage on the cathode side and on the anode side were as low as 5 ppm and 4 ppm, respectively, and the electrode catalyst layer of the present invention showed excellent durability even at high temperatures.

[Comparative Example 1]
The polymer solution A prepared in Example 1 was applied to a gas diffusion electrode ELAT (registered trademark) (Pt loading: 0.4 mg / cm ² ) manufactured by DE NORA NORTH AMERICA, USA, and then dried at 160 ° C. in an air atmosphere. -Immobilized and further immersed in 2N hydrochloric acid aqueous solution for 3 hours, washed with water and dried. The amount of polymer supported on this electrode catalyst layer was 0.8 mg / cm ² .
Using such a gas diffusion electrode on both sides of the anode and cathode, an MEA was produced using the same proton exchange membrane as that used in Example 1, and the above fuel cell evaluation was performed. The fluorine ion concentrations of the battery drainage on the cathode side and the anode side were 126 ppm and 32 ppm, respectively, which were significantly higher than those in Example 1, and the durability at high temperatures was insufficient.

  The electrode catalyst layer of the present invention is excellent in heat-resistant oxidation and suitable for a fuel cell that operates under high temperature and low humidification conditions.

Claims (3)

30.00% by mass to 80.00% by mass of composite particles in which electrocatalyst particles are supported on conductive particles, 19.99% by mass to 60.00% by mass of perfluorocarbon polymer having an ion exchange group, 0.01% by mass of polybenzimidazole An electrode catalyst layer for a fuel cell, which is contained in an amount of 10.00% by mass or less . A membrane electrode assembly comprising the electrode catalyst layer according to claim 1 . A polymer electrolyte fuel cell comprising the electrode catalyst layer according to claim 1 .