JP2010225585A - Electrode catalyst layer for fuel cell, membrane electrode assembly, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell having excellent output characteristics even under a high-temperature and low humidifying condition of an operation temperature of 80-120°C and humidity of 60% RH or less, and to provide an electrode catalyst layer and a membrane electrode assembly for fuel cell which enable the solid polymer fuel cell to be achieved. <P>SOLUTION: The electrode catalyst layer for fuel cell contains a proton conductive fluorine-based polymer electrolyte having: a repeating unit as expressed by following general formula (1) and a repeating unit represented by following general formula (2); an equivalent weight of 250-680; and composite particles each carrying catalyst particles on a conductive particle. The general formula (1) is represented -(CF<SB>2</SB>CF<SB>2</SB>), and the general formula (2) is represented -(CF<SB>2</SB>-CF(-O-(CF<SB>2</SB>CFXO)<SB>m</SB>-(CF<SB>2</SB>)<SB>n</SB>-SO<SB>3</SB>Z)), herein, in the general formula (2), X is a fluorine atom, a chlorine atom or a perfluoroalkyl group, m is an integer of 0-5, n is an integer of 0-6, and m and n are not 0 simultaneously. Z is an alkali metal atom, an alkali earth metal atom, a transition metal atom or a hydrogen atom. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel cell electrode catalyst layer, a membrane electrode assembly, and a polymer electrolyte fuel cell.

A fuel cell is one that converts the chemical energy of the fuel directly into electrical energy by electrochemically oxidizing fuel such as hydrogen or methanol in the battery, and is used as a clean electrical energy supply source. Attention has been paid.
In particular, the polymer electrolyte fuel cell is expected to be used for an in-vehicle power source or a home cogeneration system because it operates at a lower temperature than other fuel cells.

  A polymer electrolyte fuel cell includes a membrane electrode assembly (hereinafter referred to as “MEA”) in which an electrode catalyst layer, that is, an anode catalyst layer including an anode catalyst and a cathode catalyst layer including a cathode catalyst, are bonded to both surfaces of a polymer electrolyte membrane. At least). Moreover, what joined a pair of gas diffusion layers so that it might oppose further on the outer side of an electrode catalyst layer may be called MEA. The “polymer electrolyte membrane” here is a membrane material having a strongly acidic group such as a sulfonic acid group or a carboxylic acid group in the polymer chain and a property of selectively transmitting protons. As such a polymer electrolyte membrane, a fluorine-based polymer electrolyte membrane represented by Nafion (registered trademark, manufactured by DuPont, USA) having high chemical stability is suitably used.

  In addition, as the electrode catalyst layer, for example, as described in Non-Patent Document 1, composite particles in which electrode catalyst particles are supported on carbon particles and a fluorine-based polymer electrolyte as a proton conductive polymer (binder polymer) A catalyst sheet made of a thin sheet is preferably used. In addition, in order to supply gas uniformly to the whole electrode catalyst layer, the MEA may be sandwiched between a pair of gas diffusion layers as necessary. In this case, a laminate in which the electrode catalyst layer and the gas diffusion layer are stacked is referred to as a gas diffusion electrode.

  The fuel cell operates by supplying a fuel (for example, hydrogen) to the anode catalyst layer and an oxidant (for example, oxygen or air) to the cathode catalyst layer, and connecting both electrodes with an external circuit. Specifically, when hydrogen is used as a fuel, hydrogen is oxidized on the anode catalyst to generate protons, and after the protons pass through the fluorine-based polymer electrolyte in the anode catalyst layer, And reaches the cathode catalyst via the fluorine-based polymer electrolyte in the cathode catalyst layer. On the other hand, electrons generated simultaneously with protons due to oxidation of hydrogen reach the cathode catalyst layer via an external circuit. Then, on the cathode catalyst, the protons and oxygen in the oxidant react to generate water, and electric energy generated at this time is taken out.

  Conventional polymer electrolyte fuel cells exhibit high power generation efficiency and output when operated under appropriate humidification conditions around 80 ° C. However, if the humidification is insufficient, the polymer electrolyte in the polymer electrolyte membrane and the electrode catalyst layer is dried, the proton conductivity is remarkably lowered, the internal resistance of the battery is increased, and the output is lowered. When a polymer electrolyte fuel cell is used for in-vehicle use, it is desired that the fuel cell can be operated even under conditions of high temperature and low humidity, for example, operating temperature around 100 ° C. and humidification at 60 ° C. (equivalent to a humidity of 20% RH). Yes. Also, when used as a stationary application, humidification conditions lower than the current operating conditions, for example, operating temperature 80 ° C., 80 ° C. humidification (conditions corresponding to humidity 100% RH), for example, operating temperature 80 ° C., 65 ° C. humidification ( A fuel cell capable of obtaining high output characteristics even under conditions corresponding to a humidity of 53% RH is desired.

  Here, membrane electrode bonding using a conventional fluoropolymer electrolyte membrane having an equivalent weight (hereinafter also referred to as “EW”) of about 1100 as the polymer electrolyte membrane, for example, Nafion (registered trademark, manufactured by DuPont). A fuel cell provided with a body cannot obtain sufficient proton conductivity under high temperature and low humidity conditions. As a result, such a fuel cell does not have sufficient battery performance.

As a technique for solving the above problems, a technique for improving battery performance by increasing the number of sulfonic acid groups having water absorption in a polymer electrolyte and reducing EW is known (see, for example, Patent Document 1). .
Patent Document 2 discloses a fluorinated polymer electrolyte having an EW of 555 to 715 and including a repeating unit having two specific functional groups in the side chain. The power generation cell using this fluorine-based polymer electrolyte realizes a relatively high output voltage under low humidification conditions of a cell temperature of 80 ° C., a hydrogen fuel gas humidification temperature of 50 ° C., and an air gas humidification temperature of 70%. ing.

JP-T 62-500759 JP 2008-186784 A

However, fuel cells are required to have better output characteristics under high temperature and low humidification conditions.
The present invention has been made in view of the above circumstances, and a polymer electrolyte fuel cell having good output characteristics even under high temperature and low humidification conditions of an operating temperature of 80 to 120 ° C. and a humidity of 60% RH or less, Another object of the present invention is to provide a fuel cell electrode catalyst layer and a membrane electrode assembly capable of realizing the fuel cell.

  As a result of intensive studies to achieve the above object, the present inventors have used a proton conductive fluorine-based polymer electrolyte having a specific repeating unit and a specific EW as an electrode catalyst layer together with catalyst particles. It has been found that even under high temperature and low humidification conditions of operating temperature of 80 to 120 ° C. and humidity of 60% RH or less, better output characteristics can be realized than high temperature and high humidification conditions of 80 to 120 ° C. and 100% RH. The present invention has been completed.

That is, the present invention is as follows.
[1]
A proton-conducting fluoropolymer electrolyte having a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2) and having an equivalent weight of 250 to 680; An electrode catalyst layer for a fuel cell, comprising: composite particles having catalyst particles supported on the particles.
-(CF ₂ CF ₂ )-(1)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) m - (CF 2) n -SO 3 Z)) - (2)
(In general formula (2), X represents a fluorine atom, a chlorine atom or a perfluoroalkyl group, m represents an integer of 0 to 5, and n represents an integer of 0 to 6. However, m and n are simultaneously (Z does not represent 0. Z represents an alkali metal atom, an alkaline earth metal atom, a transition metal atom, or a hydrogen atom.)
[2]
The electrode catalyst layer for a fuel cell according to the above [1], wherein m is 0, n is 2, and Z is a hydrogen atom.
[3]
The fluorine-based polymer electrolyte is obtained from a repeating unit represented by the following general formula (3) and a precursor having a repeating unit represented by the following general formula (4).
The melt flow rate of the precursor is 10.0 g / 10 min or less,
The mass retention of the post-treatment electrolyte obtained by allowing the fluoropolymer electrolyte to stand in hot water at 90 ° C. for 5 hours is 97% by mass or more based on the mass of the fluoropolymer electrolyte, The electrode catalyst layer for fuel cells according to [1] or [2].
− (CF ₂ CF ₂ ) − (3)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) m - (CF 2) n -SO 2 F)) - (4)
(In general formula (4), X, m, and n are as defined in general formula (2).)
[4]
The electrode catalyst layer for a fuel cell according to any one of [1] to [3], wherein a mass ratio of the fluorine-based polymer electrolyte to the catalyst particles is 0.1 to 10.
[5]
A proton-conducting fluoropolymer electrolyte having a repeating unit represented by the general formula (1) and a repeating unit represented by the general formula (2) and having an equivalent weight of 250 to 680; The amount of lower alcohol solvent (lower alcohol / SO ₃ H) (mol ratio) per mole of the sulfonic acid unit of the fluorine-based polymer electrolyte is 100, which includes composite particles supporting catalyst particles on the particles and lower alcohol. This is the fuel cell electrode catalyst composition.
[6]
The electrode catalyst composition for a fuel cell according to the above [5], wherein m is 0, n is 2, and Z is a hydrogen atom.
[7]
The fluorine-based polymer electrolyte is obtained from a repeating unit represented by the general formula (3) and a precursor having a repeating unit represented by the general formula (4).
The melt flow rate of the precursor is 10.0 g / 10 min or less,
The mass retention of the post-treatment electrolyte obtained by allowing the fluoropolymer electrolyte to stand in hot water at 90 ° C. for 5 hours is 97% by mass or more based on the mass of the fluoropolymer electrolyte, The electrode catalyst composition for fuel cells according to [5] or [6].
[8]
The electrode catalyst composition for a fuel cell according to any one of [5] to [7], wherein a mass ratio of the fluorine-based polymer electrolyte to the catalyst particles is 0.1 to 10.
[9]
A fuel cell electrode catalyst layer formed from the fuel cell electrode catalyst composition according to any one of [5] to [8] above.
[10]
A membrane electrode assembly comprising the fuel cell electrode catalyst layer according to any one of [1] to [4] and [9].
[11]
A polymer electrolyte fuel cell comprising the membrane electrode assembly according to the above [10].
[12]
A polymer electrolyte fuel cell comprising a membrane electrode assembly in which a fuel electrode is disposed on one side of a proton conductive polymer electrolyte membrane and an air electrode is disposed on the other side,
The fuel electrode and the air electrode are gas diffusion electrodes containing a catalyst and a proton conductive fluorine-based polymer electrolyte,
A polymer electrolyte fuel cell that satisfies the following formula (7) when the operating temperature is T ° C.
Unit current density when fuel gas and / or air gas humidification temperature is (T-15) ° C. (A / cm ² ) ≧ unit current when fuel gas and / or air gas humidification temperature is T ° C. Density (A / cm ² ) (7)
[13]
The solid polymer fuel cell according to the above [12], wherein the operating voltage is maintained at a constant voltage of 0.7 V for 20 hours, and then satisfies the formula (7).
[14]
The polymer electrolyte fuel cell according to [12] or [13], wherein the proton conductive polymer electrolyte membrane includes a proton conductive fluorine-based polymer electrolyte.
[15]
The polymer electrolyte fuel cell according to any one of [12] to [14], wherein the membrane electrode assembly is the membrane electrode assembly according to [10].

  INDUSTRIAL APPLICABILITY According to the present invention, a polymer electrolyte fuel cell having good output characteristics and a fuel cell capable of realizing the fuel cell even under high temperature and low humidification conditions of an operating temperature of 80 to 120 ° C. and a humidity of 60% RH or less An electrode catalyst layer can be provided.

Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail.
The electrode catalyst layer for a fuel cell of the present embodiment (hereinafter also simply referred to as “electrode catalyst layer”) includes a repeating unit represented by the following formula (1) and a repeating unit represented by the following general formula (2). And a fluorine-based polymer electrolyte having an equivalent weight (hereinafter referred to as “EW”) of 250 to 680.
-(CF ₂ CF ₂ )-(1)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) m - (CF 2) n -SO 3 Z)) - (2)

  Here, in formula (2), X represents a fluorine atom, a chlorine atom or a perfluoroalkyl group, m represents an integer of 0 to 5, and n represents an integer of 0 to 6. However, m and n are not 0 at the same time. Z represents an alkali metal atom, an alkaline earth metal atom, a transition metal atom, or a hydrogen atom.

  In the fluorine-based polymer electrolyte according to this embodiment, Z is preferably a hydrogen atom, m is preferably 0 to 1, and n is more preferably 0 to 4.

  Among the fluorine-based polymer electrolytes according to this embodiment, a polymer in which X is a fluorine atom, n is 2, m is 0, and Z is a hydrogen atom is an object of the present invention. Is preferable from the viewpoint of achieving more efficiently.

  The EW of the fluorine-based polymer electrolyte, that is, the dry weight per equivalent of proton exchange groups is 250 to 680, preferably 300 to 600, more preferably 350 to 520, and still more preferably 400 to 500. By setting the EW in the above range in a fluorine-based polymer electrolyte having a specific structural formula and coexisting composite particles described later, it becomes possible to achieve a high output during operation of the fuel cell.

  The mass retention rate of the electrolyte obtained by allowing the fluorine-based polymer electrolyte according to the present embodiment to stand in hot water at 90 ° C. for 5 hours (hereinafter referred to as “post-treatment electrolyte”) is the mass of the fluorine-based polymer electrolyte. Is preferably 97% by mass or more, and more preferably 99.7% by mass or more. In other words, the mass reduction of the treated electrolyte relative to the fluoropolymer electrolyte is preferably 3% by mass or less, and more preferably 0.3% by mass or less. Such a fluorine-based polymer electrolyte can be more excellent in heat-resistant water solubility. Here, the mass of the fluorine-based polymer electrolyte and the post-treatment electrolyte is a mass after standing for 24 hours in an environment of 23 ° C. and 50% RH.

  Further, the electrode catalyst layer according to the present embodiment contains composite particles in which catalyst particles are supported on conductive particles. Thereby, the function as an electrode catalyst layer can be exhibited more effectively. The electrode catalyst layer has a basic skeleton having a structure in which a plurality of the composite particles are bound by a fluorine-based polymer electrolyte.

  The material constituting the conductive particles is not particularly limited as long as it has conductivity, and examples thereof include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and various metals. These are used singly or in combination of two or more.

  The average particle diameter of the conductive particles is preferably 10 angstroms to 10 μm, more preferably 50 angstroms to 1 μm, and further preferably 100 angstroms to 5000 angstroms. When the conductive particles have such an average particle diameter that is finely divided, an effect of increasing the surface area and efficiently dispersing and supporting the catalyst particles can be obtained. The average particle diameter of the conductive particles can be measured visually with a transmission electron microscope.

  The catalyst particles easily generate protons by oxidizing a fuel such as hydrogen in the anode electrode layer, and react with protons and electrons and an oxidizing agent such as oxygen and air in the cathode electrode layer. It has the function to generate.

  The material constituting the catalyst particles is not particularly limited as long as it contributes to the above reaction, but platinum is particularly preferable because the catalytic activity for the above reaction tends to be high. Moreover, in order to reinforce the resistance of platinum to impurities such as CO, those obtained by adding noble metals such as ruthenium to platinum or alloys thereof are also preferable. A noble metal is used individually by 1 type or in combination of 2 or more types.

  The average particle diameter of the catalyst particles is preferably from 10 angstroms to 1000 angstroms, more preferably from 10 angstroms to 500 angstroms, and further preferably from 15 angstroms to 100 angstroms. When the catalyst particles have an average particle diameter in the above range, the surface area can be increased and the contact area with the binder polymer can be increased. The average particle diameter of the catalyst particles can be measured visually with a transmission electron microscope.

  In the composite particles according to this embodiment, the catalyst particles are preferably supported by 1 to 99% by weight, more preferably 10 to 90% by weight, and still more preferably 20 to 80% by weight with respect to 100% by weight of the composite particles. Preferably it is. By adjusting the supported amount of catalyst particles within the above range, the desired catalytic activity tends to be easily obtained.

  The composite particles according to this embodiment may be produced by a conventional method in which catalyst particles are supported on solid particles, or commercially available products may be obtained. Examples of commercially available composite particles include Tanaka Kikinzoku Kogyo Co., Ltd., trade name “TEC10E40E”, Degussa Co., Ltd., trade name “F101RA / W”.

The content of the composite particle in the electrode catalyst layer, the area of the one main surface of the electrode catalyst layer is preferably 0.001 to 10 mg / cm ^2, more preferably 0.01 to 5 mg / cm ² More preferably, it is 0.1-1 mg / cm < ² >. Since the power generation amount depends on the total area of the catalyst particles, that is, the mass, it is easy to obtain high power generation characteristics by setting the composite particle content to 0.001 mg / cm ² or more. Moreover, since the voltage loss due to the proton conduction resistance of the electrolyte can be suppressed by setting the content of the composite particles to 10 mg / cm ² or less, higher power generation characteristics tend to be obtained.

  The mass ratio of the fluorine-based polymer electrolyte to the catalyst particles is preferably 0.1 or more, more preferably 0.5 or more, from the viewpoint of improving proton conductivity. The mass ratio is preferably 10 or less, more preferably 2 or less, from the viewpoint of improving the electron conductivity and the fuel gas diffusibility.

  The thickness of the electrode catalyst layer of the present embodiment is preferably 0.1 to 50 μm, more preferably 0.5 to 30 μm, and still more preferably 1 to 20 μm. When the thickness is 0.1 μm or more, it becomes easy to form an electrode catalyst layer having a catalyst carrying amount capable of exhibiting sufficient power generation performance. In addition, when the thickness is 50 μm or less, it is possible to suppress a decrease in gas diffusibility in the electrode catalyst layer and to reduce electric resistance.

  The electrode catalyst layer of the present embodiment has a porosity of preferably 1% by volume or more, more preferably 10% by volume or more, and still more preferably 20% by volume or more, from the viewpoint of improving ion conductivity. . Further, from the viewpoint of improving the diffusibility of water generated by fuel gas and power generation, the porosity is preferably 99% by volume or less, more preferably 90% by volume or less, and further preferably 80% by volume or less. preferable. The porosity of the electrode catalyst layer can be measured by a mercury intrusion method.

Next, the manufacturing method of the electrode catalyst layer for fuel cells which concerns on this embodiment is demonstrated.
It does not specifically limit as a manufacturing method of the electrode catalyst layer for fuel cells, A conventionally well-known manufacturing method may be sufficient. For example, each of the following (first step) to (fifth step),
(First Step) A step of obtaining a precursor of a fluorine-based polymer electrolyte;
(Second step) A step of subjecting the precursor to a chemical treatment to obtain a fluoropolymer electrolyte;
(Third step) a step of dissolving or suspending the fluorine-based polymer electrolyte in a solvent to obtain a fluorine-based polymer electrolyte solution;
(Fourth Step) A step of obtaining a mixed liquid obtained by mixing the fluorine-based polymer electrolyte solution, the composite particles and the solvent,
(Fifth step) forming an electrode catalyst layer on the polymer electrolyte membrane using the mixed solution;
including. Hereinafter, each step will be described.

[First step]
In the first step, a fluoropolymer electrolyte precursor is obtained.
The precursor is not particularly limited as long as it can generate the fluorine-based polymer electrolyte according to the present embodiment. The precursor preferably has a group that can be converted into a group represented by the following general formula (5) by chemical treatment.
-SO ₃ Z (5)
Here, in Formula (5), Z is synonymous with the thing in the said General formula (2).

Specifically, an ethylenic fluoromonomer and a fluorinated vinyl ether compound (hereinafter simply referred to as “vinyl fluoride compound”) having a group that can be converted into the group represented by the general formula (5) by chemical treatment. It is preferable to obtain the precursor by copolymerizing.
The vinyl fluoride compound is preferably a vinyl fluoride compound represented by the following general formula (6).
_{CF 2 = CF (-O- (CF} 2 CFXO) m - (CF 2) n -SO 2 F (6)
Here, in formula (6), X represents a fluorine atom, a chlorine atom or a perfluoroalkyl group, m represents an integer of 0 to 5, and n represents an integer of 0 to 6. However, m and n are not 0 at the same time.

In the general formula (6), X is preferably a fluorine atom.
Accordingly, the precursor preferably has a repeating unit represented by the following general formula (3) and a repeating unit represented by the following general formula (4).
− (CF ₂ CF ₂ ) − (3)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) m - (CF 2) n -SO 2 F)) - (4)
(In general formula (4), X, m, and n are as defined in general formula (2).)
From the viewpoint of reducing EW, m is preferably 0 or 1, and more preferably 0. Moreover, since the effect produced by the present invention tends to become more prominent, n is preferably 2 or 4, and n is more preferably 2. In addition, the said vinyl fluoride compound is used individually by 1 type or in combination of 2 or more types.

  Examples of the ethylenic fluoromonomer include those represented by the above formula (1). If desired, a third monomer may be polymerized in addition to the ethylenic fluoromonomer and the vinyl fluoride compound.

  In the case of obtaining the precursor by polymerization in the first step, examples of the polymerization method include solution polymerization; bulk polymerization; emulsion polymerization; emulsion polymerization represented by miniemulsion polymerization and microemulsion polymerization; and suspension polymerization. It is done.

  In solution polymerization, polymerization is performed in a state where at least one of the monomers is dissolved in a polymerization solvent. Examples of the solution polymerization include a method in which a polymerization solvent such as a fluorine-containing hydrocarbon is used, and a vinyl fluoride compound filled and dissolved in the polymerization solvent is polymerized with an ethylenic fluoromonomer gas. Examples of the fluorine-containing hydrocarbon include compounds generally referred to as “fluorocarbons” represented by trichlorotrifluoroethane, 1, 1, 1, 2, 3, 4, 4, 5, 5, 5-decafluoropentane. Are preferably used.

  In bulk polymerization, polymerization is performed using the monomer itself as a polymerization solvent without using a polymerization solvent. As bulk polymerization, for example, a vinyl fluoride compound is polymerized using the vinyl fluoride compound itself as a polymerization solvent.

In emulsion polymerization, an aqueous solution of a surfactant is used as a polymerization solvent, and polymerization is performed in a state where at least one of the monomers is dissolved in the polymerization solvent. Examples of the emulsion polymerization include a method of polymerizing a vinyl fluoride compound filled and dissolved in an aqueous solution of a surfactant and an ethylenic fluoromonomer gas. Although it does not specifically limit as surfactant, A thing with small chain transfer property is used preferably, for example, the emulsifier represented by RfZ3 is used. Here, Rf represents an alkyl group having 4 to 20 carbon atoms, part or all of hydrogen atoms are replaced by fluorine, may contain an etheric oxygen atom, and can be copolymerized with an ethylenic fluoromonomer. It may have an unsaturated bond. Z3 represents a dissociative polar group, and Z3 is preferably —COO-M ⁺ or —SO ₃ —M ⁺ . Here, M ⁺ represents a monovalent cation such as an alkali metal ion, ammonium ion, or hydrogen ion.

Examples of the emulsifier represented by RfZ3 include Y (CF ₂ ) _n COO-M ⁺ (n represents an integer of 4 to 20, Y represents a fluorine atom or a hydrogen atom), CF ₃ —OCF ₂ CF _{2. ^{-OCF 2 CF 2 COO-M +}} , CF 3 - (OCF (CF 3) CF 2) ( where n represents an integer of 1~3) _n COO-M ⁺ can be mentioned.

  In emulsion polymerization, polymerization is performed in a state where at least one of the monomers is emulsified in an aqueous solution containing a surfactant and an auxiliary emulsifier such as alcohol. Examples of emulsion polymerization include a method in which an aqueous solution containing a surfactant and an auxiliary emulsifier such as alcohol is used, and a vinyl fluoride compound and an ethylenic fluoromonomer gas in a state of being filled and emulsified in the aqueous solution are polymerized. It is done.

  In suspension polymerization, polymerization is performed in a state where at least one of the monomers is suspended in an aqueous solution of a suspension stabilizer. Examples of suspension polymerization include a method in which an aqueous solution of a suspension stabilizer is used, and a vinyl fluoride compound and an ethylenic fluoromonomer gas that are filled and suspended in the aqueous solution are polymerized.

  Among these, from the viewpoint of more efficiently obtaining a fluorine-based polymer electrolyte having an EW of 250 to 680, either emulsion polymerization or emulsion polymerization is preferable. As emulsion polymerization, any of miniemulsion polymerization and microemulsion polymerization is preferable. Is preferred.

  When an ethylenic fluoromonomer and a vinyl fluoride compound are used as the monomer, in order to control the EW of the fluorine-based polymer electrolyte to 250 to 680, for example, the proportion of the vinyl fluoride compound in the monomer is increased. preferable.

  In the first step, it is preferable to obtain a precursor of a fluorine-based polymer electrolyte by a polymerization method of either emulsion polymerization or emulsion polymerization at a polymerization temperature of 0 to 40 ° C. As a result, an electrode catalyst layer that exhibits higher conductivity even at low humidity can be finally obtained. Although the reason is not clarified in detail, the present inventors consider as follows. That is, when the polymerization reaction is performed at a polymerization temperature in the above range, the distance between the ion clusters of the precursor at 25 ° C. and 50% RH is within a specific range, that is, 0.1 nm to 3.0 nm, preferably 0.5 nm or more. As a result of being able to be controlled to 2.8 nm or less, more preferably 1.0 nm to 2.6 nm, and even more preferably 2.0 nm to 2.5 nm, an electrode catalyst layer that exhibits higher conductivity even at low humidity It is considered possible to obtain The polymerization temperature is more preferably 5 ° C. or higher, and more preferably 35 ° C. or lower.

  The precursor of the fluorine-based polymer electrolyte has a melt flow rate (hereinafter referred to as “MFR”) of 10 g / 10 min or less from the viewpoint of maintaining the high output characteristics of the obtained fuel cell for a long time. And preferably 4.0 g / 10 min or less. Further, from the viewpoint of efficiently dissolving the fluoropolymer electrolyte, the MFR is preferably 0.1 g / 10 min or more, and more preferably 0.3 g / 10 min or more.

  In order to set the MFR of the precursor to 0.1 to 10 g / min, emulsion polymerization, microemulsion polymerization or miniemulsion polymerization of a vinyl fluoride compound and an ethylenic fluoromonomer at a temperature of 0 ° C. or more and 40 ° C. or less. Is preferred. When the temperature is 40 ° C. or lower, the rate of the disproportionation reaction in which polymerization is terminated by radical rearrangement of the polymer terminal radicals can be reduced, and a polymer having a high molecular weight can be easily obtained. The temperature is more preferably 35 ° C. or lower, and further preferably 30 ° C. or lower. On the other hand, when the temperature is 0 ° C. or higher, the polymerization rate is increased and the productivity is improved. The temperature is more preferably 5 ° C. or higher, and further preferably 10 ° C. or higher.

[Second step]
In the second step, the precursor is chemically treated to obtain a fluorinated polymer electrolyte. Examples of the chemical treatment include hydrolysis treatment and acid treatment. As a hydrolysis process, the process which immerses the said precursor in a basic solution is mentioned, for example.

  The basic solution is not particularly limited, but an aqueous solution of an alkali metal or alkaline earth metal hydroxide such as sodium hydroxide or potassium hydroxide is preferred. The content of the alkali metal or alkaline earth metal hydroxide in the aqueous solution is not particularly limited, but is preferably 10 to 30% by mass. The basic solution preferably contains a swellable organic compound typified by methyl alcohol, ethyl alcohol, acetone, dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), and N, N-dimethylformamide (DMF). As a result, the effect of shortening the processing time, that is, improving the productivity is exhibited. Moreover, it is preferable that content of the swellable organic compound in a basic solution is 1-30 mass%.

The treatment temperature in the hydrolysis treatment varies depending on the type of solvent, the solvent composition, etc., but the treatment time can be shortened as the treatment temperature is increased. When using a basic solution, it is preferable that processing temperature is 20-160 degreeC. When the treatment temperature exceeds 160 ° C., the precursor tends to be dissolved in the basic solution and difficult to handle. In addition, from the viewpoint of imparting high conductivity to the fluorine-based polymer electrolyte, it is preferable that all functional groups that can be converted into —SO ₃ H by hydrolysis are hydrolyzed in the second step. From this viewpoint and a viewpoint of ensuring high productivity, the treatment time of the hydrolysis treatment is preferably 0.5 to 48 hours.

[Third step]
In the third step, the fluoropolymer electrolyte is dissolved or suspended in a solvent to obtain a fluoropolymer electrolyte solution. The fluorine-based polymer electrolyte solution also includes a fluorine-based polymer electrolyte suspension obtained by suspending the fluorine-based polymer electrolyte in a solvent. More specifically, as a state of the fluorine-based polymer electrolyte solution, more specifically, an emulsion in which liquid particles are dispersed as colloidal particles or coarser particles in a liquid to form a milky state, and solid particles in a liquid are colloidal particles. Or a suspension dispersed as particles that can be seen under a microscope, a colloidal liquid in which macromolecules are dispersed, or a micellar liquid that is a lyophilic colloidal dispersion system formed by associating many small molecules with intermolecular forces Are also included. The fluorine-based polymer electrolyte solution may be in one of these states or in a combination of two or more.

  As the solvent, a solvent having good affinity with the fluorine-based polymer electrolyte is preferable, and specifically, a protic organic solvent represented by water, ethanol, methanol, n-propanol, isopropyl alcohol, butanol, and glycerin; Examples include aprotic solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, and N-methylpyrrolidone. These are used singly or in combination of two or more. When one type of solvent is used, water is particularly preferable as the solvent. Moreover, when using in combination of 2 or more types of solvent, the liquid mixture of water and a protic organic solvent is especially preferable.

  The method for dissolving or suspending the fluoropolymer electrolyte in a solvent is not particularly limited. For example, first, a fluoropolymer electrolyte is added to a solvent (for example, a mixed solvent of water and a protic organic solvent) to obtain a composition. Next, the obtained composition is housed in an autoclave having a glass inner cylinder as necessary, and after replacing the air inside the autoclave with an inert gas such as nitrogen, the internal temperature is 50 ° C to 250 ° C. Heat and stir under conditions 0.25-12 hours. Thereby, a fluorine-type polymer electrolyte solution is obtained. The total solid content concentration in the fluorine-based polymer electrolyte solution is preferably 0.5 to 50% by mass, more preferably 1 to 50% by mass, further preferably 3 to 40% by mass, and 5 to 30% by mass. % Is particularly preferred. When the total solid content concentration is 0.5% by mass or more, the yield of the electrode catalyst layer tends to be improved. When the total solid content concentration is 50% by mass or less, handling difficulty associated with increase in viscosity and undissolved matter. It tends to be possible to suppress the occurrence of.

  When using a mixed solution of water and a protic organic solvent as the solvent, the mixing ratio depends on the dissolution method, dissolution conditions, type of fluoropolymer electrolyte, total solid content concentration, dissolution temperature, stirring speed, etc. It is selected appropriately. However, when the amount of the protic organic solvent is increased, the solution viscosity is increased, and when the amount of water is increased, it is difficult to dissolve. Therefore, the mass ratio of the protic organic solvent to water is preferably 0.1 to 10, and 0.1 It is more preferable that it is ~ 5.

  The fluorine-based polymer electrolyte solution may be concentrated before being subjected to the fourth step. The concentration method is not particularly limited. Examples of the concentration method include a method of heating the fluorine-based polymer electrolyte solution to volatilize the solvent and a method of concentrating under reduced pressure. The total solid content concentration in the fluorinated polymer electrolyte solution obtained by concentration is preferably 0.5 to 50% by mass, more preferably 1 to 50% by mass, and further preferably 3 to 40% by mass. 5 to 30% by mass is particularly preferable. If the total solid content concentration is 0.5% by mass or more, the yield of the electrode catalyst layer tends to be improved. If the total solid content concentration is 50% by mass or less, it is difficult to handle due to increase in viscosity and undissolved matter. It tends to be able to suppress the occurrence.

  By further filtering the unconcentrated or concentrated fluoropolymer electrolyte solution obtained as described above, it is possible to obtain an undissolved polymer, gelled polymer, large dispersion polymer, or fluoropolymer electrolyte solution. Dust mixed in during the process can be removed. It does not specifically limit as a filter medium used for filtration, For example, a polypropylene, polyester, polytetrafluoroethylene, and a cellulose are mentioned. The pore diameter of the filter medium is not particularly limited, and may be in the range of 0.5 to 100 μm, for example.

[Fourth step]
In the fourth step, a mixed solution obtained by mixing the fluorine-based polymer electrolyte solution, the composite particles, and the solvent, that is, an electrode catalyst composition for a fuel cell (hereinafter also referred to as “electrode catalyst composition”) is obtained. They are mixed by a conventional method, and in order to improve the dispersibility of the fluorine-based polymer electrolyte solution and the composite particles in the solvent, they may be dispersed using various apparatuses. Examples of the apparatus include a homogenizer, a ball mill, ultrasonic treatment, and pressure dispersion treatment.

Examples of the solvent for the electrode catalyst composition include water, lower alcohols such as ethanol, 1-propanol, and 2-propanol, ethylene glycol, propylene glycol, glycerin, and dimethyl sulfoxide, and preferably water, ethanol, and 1-propanol. These are used singly or in combination of two or more. The electrode catalyst composition preferably has a lower alcohol solvent amount (lower alcohol / SO ₃ H) (molar ratio) per mole of sulfonic acid unit of the fluoropolymer electrolyte of 100 or more, more preferably 170 or more. When the ratio is 100 or more, gelation of the composition tends to be suppressed. This gelling suppression effect is remarkable in an electrode catalyst composition containing a fluorine-based polymer electrolyte having an equivalent weight of 250 to 680. On the other hand, in an electrode catalyst composition containing a fluorine-based polymer electrolyte having an equivalent weight of 700 or more, gelation does not proceed significantly even when the ratio is less than 100, and an ink with high fluidity can be obtained.

[Fifth step]
In the fifth step, an electrode catalyst layer is formed on the polymer electrolyte membrane using the mixed solution. The electrode catalyst layer of this embodiment is obtained by applying an electrode catalyst composition, which is a mixed solution containing the above-mentioned fluorine-based polymer electrolyte solution and composite particles, onto a polymer electrolyte membrane, preferably a fluorine-based polymer electrolyte membrane. Further, it is formed by further drying and heat treatment.
Alternatively, the electrode catalyst composition is coated on a substrate, for example, a polytetrafluoroethylene (PTFE) sheet, and further subjected to drying and heat treatment to obtain an electrode catalyst layer. The electrode catalyst layer of this embodiment is formed by laminating and joining the membrane. In this case, the electrode catalyst layer and the polymer electrolyte membrane can be bonded by heating and pressing at 100 to 200 ° C. in the stacking direction.

  As a method for applying the electrode catalyst composition, for example, various generally known application methods such as a spray method and a screen printing method can be used.

  From the viewpoint of improving the hot water solubility of the electrode catalyst layer of the present embodiment obtained as described above, it is preferable to heat-treat the electrode catalyst layer after obtaining the electrode catalyst layer in the fifth step. . The heating temperature of the electrode catalyst layer in this heat treatment is preferably 130 to 200 ° C, more preferably 150 to 180 ° C. The heating temperature is preferably 130 ° C. or higher from the viewpoint of suppressing dissolution of the electrode catalyst layer in hot water and battery performance, and 200 ° C. or lower from the viewpoint of suppressing thermal oxidative decomposition of the polymer electrolyte.

  The heating time of the electrode catalyst layer in this heat treatment is preferably 5 to 120 minutes, more preferably 10 to 90 minutes. The heating time is preferably 5 minutes or longer from the viewpoint of suppressing dissolution of the electrode catalyst layer in hot water and battery performance, and 120 minutes or shorter from the viewpoint of suppressing thermal oxidative decomposition of the polymer electrolyte.

  The membrane electrode assembly of this embodiment may have the same configuration as the conventional membrane electrode assembly except that the electrode catalyst layer of the present embodiment is provided as an anode catalyst layer and / or a cathode electrode layer. . For example, the membrane electrode assembly of the present embodiment includes a polymer electrolyte membrane, and an anode catalyst layer and a cathode catalyst layer bonded to both surfaces of the polymer electrolyte membrane, and at least of the anode catalyst layer and the cathode electrode layer. One is the electrode catalyst layer of this embodiment. The membrane electrode assembly of the present embodiment includes the electrode catalyst layer of the present embodiment exhibiting high heat-resistant water solubility, so that the fuel cell including the membrane electrode assembly is high even under high temperature and low humidification conditions. There is an effect that output characteristics can be imparted. In addition, when using the electrode catalyst layer of this embodiment as any one of the electrode catalyst layers, it is preferable from a viewpoint of a voltage characteristic to use the electrode catalyst layer of this embodiment as a cathode catalyst layer.

  Although it does not specifically limit as a kind of polymer electrolyte membrane with which the membrane electrode assembly of this embodiment is equipped, The polymer electrolyte which has the same molecular structure as the polymer electrolyte which comprises the electrode catalyst layer with which the membrane electrode assembly is equipped is contained A polymer electrolyte membrane containing a fluorine-based polymer electrolyte having the same molecular structure as that of the fluorine-based polymer electrolyte constituting the electrode catalyst layer of the present embodiment is more preferable.

In addition, such a polymer electrolyte membrane contains 0.1 to 10% by mass of a polymer having a polyazole and / or a thioether group, or instead of / in addition, a known active radical scavenger H ₂ O ₂ decomposition catalyst It is preferable from the viewpoint of chemical stability to contain a substance having an action. Moreover, the film | membrane reinforced with the well-known reinforcing material may be sufficient. Even if the electrolyte membrane contains a known hydrocarbon electrolyte, if necessary, the bonding according to the present embodiment can be improved by providing an adhesive layer or the like that does not affect ionic conduction. It can be used as a molecular electrolyte membrane.

  Furthermore, although there is no restriction | limiting in particular as EW of such a polymer electrolyte membrane, It is preferable that it is 250-1100, and it is more preferable that it is 250-680. As a film thickness, it is preferable in it being 1-500 micrometers, it is more preferable in it being 2-100 micrometers, and it is still more preferable in it being 5-50 micrometers.

The membrane electrode assembly of the present embodiment may further include a pair of gas diffusion layers outside each electrode catalyst layer as necessary.
The MEA of this embodiment is obtained by joining an electrode catalyst layer on a polymer electrolyte membrane. When the MEA includes a gas diffusion layer, the gas diffusion layer may be bonded by heating and pressing the electrode catalyst layer in the same manner as the electrode catalyst layer and the polymer electrolyte membrane are bonded.

  The polymer electrolyte fuel cell according to the present embodiment may include components used for general polymer electrolyte fuel cells such as a bipolar plate and a backing plate, except that the membrane electrode assembly according to the present embodiment is provided. it can.

  Of these, the bipolar plate is graphite or a composite material of graphite and resin, a metal plate, or the like in which grooves for allowing a gas such as fuel or oxidant to flow are formed on the surface thereof. In addition to the function of transmitting electrons to an external load circuit, the bipolar plate has a function as a flow path for supplying fuel and an oxidant to the vicinity of the electrode catalyst.

  For example, the polymer electrolyte fuel cell of the present embodiment is manufactured by stacking a plurality of composites each including a pair of bipolar plates and an MEA inserted between the bipolar plates.

  The polymer electrolyte fuel cell is operated by supplying hydrogen to one electrode and oxygen or air to the other electrode.

  The polymer electrolyte fuel cell according to the present embodiment has good output characteristics even under high temperature and low humidification conditions of an operating temperature of 80 to 120 ° C. and a humidity of 60% RH or less.

Furthermore, the polymer electrolyte fuel cell according to this embodiment is
A polymer electrolyte fuel cell comprising a membrane electrode assembly in which a fuel electrode is disposed on one side of a proton conductive polymer electrolyte membrane and an air electrode is disposed on the other side,
The fuel electrode and the air electrode are gas diffusion electrodes containing a catalyst and a proton conductive fluorine-based polymer electrolyte,
The polymer electrolyte fuel cell satisfies the following formula (7) when the operating temperature is T ° C.
Unit current density when fuel gas and / or air gas humidification temperature is (T-15) ° C. (A / cm ² ) ≧ unit current when fuel gas and / or air gas humidification temperature is T ° C. Density (A / cm ² ) (7)

  Here, the fuel electrode refers to the gas diffusion electrode having the anode catalyst layer and the gas diffusion layer described above, and the air electrode refers to the gas diffusion electrode having the cathode catalyst layer and the gas diffusion layer described above.

  The polymer electrolyte fuel cell preferably satisfies the above formula (7) after holding the operating voltage at a constant voltage of 0.7 V for 20 hours.

  Moreover, it is preferable that the proton conductive polymer electrolyte membrane used for the polymer electrolyte fuel cell contains a proton conductive fluorine-based polymer electrolyte.

  Furthermore, the membrane electrode assembly used in the polymer electrolyte fuel cell herein may be a membrane electrode assembly including the above-described fuel cell electrode catalyst layer of the present embodiment.

  The electrode catalyst layer of the present embodiment is an electrode provided for chloralkali, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor, etc. in addition to the use as an electrode catalyst layer of a fuel cell. It can also be used as a catalyst layer.

As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said form, It can implement in various deformation | transformation within the range of the summary. For example, in the first step of the method for producing the electrode catalyst layer, by adding a crosslinking agent to the precursor, a small amount of crosslinking may be performed between molecules in a later step to reduce the eluted components. In this case, for example, after the film formation, it may be formed crosslinked structure among -SO ₃ H between small amounts of molecules. Further, by a crosslinking reaction to proceed with moderate heating after film formation, between molecules of the fluoropolymer electrolyte may form a crosslinked structure in any position other than -SO ₃ H. In this case, the reaction may be allowed to proceed together with a crosslinking reaction at an arbitrary position between the polymers contained in the electrode catalyst layer other than the fluorine-based polymer electrolyte.

In addition, in order to improve the durability of the fluorine-based polymer electrolyte, the unstable terminal group possessed by the precursor of the fluorine-based polymer electrolyte obtained in the first step is stabilized before the second step. May be processed. Examples of the unstable terminal group of the precursor include a carboxylic acid group (—COOH), a carboxylate group (—COOM; M is a metal atom forming a salt), a carboxylic acid ester group (—COOR; R is 1 Valent organic group), carbonate group (—OCOOR; R is a monovalent organic group), alkyl group, and methylol group (—CH ₂ OH). The unstable terminal group varies depending on the polymerization method in the first step, the type of initiator, chain transfer agent, polymerization terminator, and the like used in the polymerization method. For example, when emulsion polymerization is selected as the polymerization method and no chain transfer agent is used, most of the unstable end groups are carboxylic acid groups.
The method for stabilizing the unstable terminal group of the precursor is not particularly limited. For example, the precursor is treated with a fluorinating agent to convert the unstable terminal group to —CF _3. Examples of the stabilization method include a method in which the precursor is heated and decarboxylated to convert the unstable end group to —CF ₂ H to be stabilized.

  Prior to the third step, the fluorine-based polymer electrolyte obtained in the second step is sufficiently washed with warm water as necessary, and then the fluorine-based polymer electrolyte is further subjected to acid treatment. It is also preferable to obtain a protonated fluorine-based polymer electrolyte. Examples of the acid used for the acid treatment include mineral acids (inorganic acids) such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid.

  The various parameters described above are measured according to the measurement methods described in the examples described later unless otherwise specified.

  Hereinafter, although this embodiment is concretely demonstrated based on an Example, this embodiment is not restrict | limited to the following Example.

(Measurement of EW)
While the counter ion of the sulfonic acid group is in a proton state, a fluorine-based polymer electrolyte membrane having an area of one main surface of approximately ² to 20 cm ² is immersed in 30 mL of a saturated NaCl aqueous solution at 25 ° C. while stirring. Left for 30 minutes. Subsequently, the proton in the saturated NaCl aqueous solution was neutralized and titrated using 0.01N aqueous sodium hydroxide solution using phenolphthalein as an indicator. The electrolyte membrane obtained after neutralization titration in which the counter ion of the sulfonic acid group was in the form of sodium ion was rinsed with pure water, further vacuum-dried, and weighed. The amount of sodium hydroxide required for neutralization is M (mmol), and the weight of the electrolyte membrane in which the counter ion of the sulfonic acid group is sodium ion is W (mg). The weight EW (g / eq) was determined.
EW = (W / M) −22 (A)

(Measurement of melt flow rate (MFR))
The MFR of the precursor of the fluorine-based polymer electrolyte was measured using MELT INDEXER TYPE C-5059D (trade name, manufactured by Toyo Seiki Co., Ltd.) under the conditions of 270 ° C. and a load of 2.16 kg in accordance with ASTM standard D1238. As a unit of MFR, the mass of the extruded precursor was expressed in grams per 10 minutes.

(Conductivity measurement)
The conductivity of the fluorine-based polymer electrolyte membrane was measured using a polymer membrane moisture test apparatus MSB-AD-V-FC (trade name) manufactured by Nippon Bell Co., Ltd.

(90 ° C hot water dissolution test)
The fluorine-based polymer electrolyte membrane was left in a constant temperature and humidity chamber at 23 ° C. and 50% RH for 24 hours, and then weighed to obtain a pre-treatment mass. Next, the electrolyte membrane was immersed in hot water at 90 ° C. and subjected to heat treatment for 5 hours. Next, after the hot water was cooled in the state where the electrolyte membrane was immersed, the electrolyte membrane was taken out from the water, left in a constant temperature and humidity chamber at 23 ° C. and 50% RH for 24 hours, and weighed to obtain a post-treatment mass. . This post-treatment mass corresponds to the mass of the post-treatment electrolyte. The mass reduction rate of the electrolyte membrane was calculated from the following formula (B). The lower the numerical value of the mass reduction rate, the higher the hot water solubility.
Mass reduction rate (%) = (mass before treatment−mass after treatment) / mass before treatment × 100 (B)

(Fuel cell evaluation)
In order to investigate the battery characteristics (hereinafter referred to as “initial characteristics”) of the electrode catalyst layer (fluorine polymer electrolyte membrane) and membrane electrode assembly produced as described below, the following fuel cell evaluation was performed.
First, the anode-side gas diffusion layer and the cathode-side gas diffusion layer were opposed to each other, and the MEA produced as described below was sandwiched between them and incorporated in an evaluation cell. A carbon cloth (manufactured by DE NORA NORTH AMERICA, ELAT (registered trademark) B-1) was used as the gas diffusion layer on the anode side and the cathode side. After this evaluation cell was installed in an evaluation apparatus (manufactured by Chino Co., Ltd.) and heated to 80 ° C., hydrogen gas was supplied to the anode side at 300 cc / min, and air gas was supplied to the cathode side at 800 cc / min. Both the side and cathode side were pressurized to normal pressure or 0.15 MPa (absolute pressure). These gases were previously humidified, and both hydrogen gas and air gas were humidified at a desired temperature by the water bubbling method and supplied to the evaluation cell. Then, under the conditions of the cell temperature of 80 ° C. and the desired humidification, the evaluation cell was held at a voltage of 0.7 V for 20 hours, and then the current was measured.

[Example 1]
A fluorine-based polymer electrolyte having a repeating unit derived from CF ₂ ═CF ₂ and CF ₂ ═CF—O— (CF ₂ ) ₂ —SO ₃ H and having an EW of 560 was prepared as follows.
2970 g of reverse osmosis membrane water, 60 g of C ₇ F ₁₅ COONH ₄ , and 510 g of CF ₂ = CFOCF ₂ CF ₂ SO ₂ F were added to a 6-liter pressure vessel made of SUS-316 equipped with a stirring blade and a temperature control jacket. Prepared. Next, the system was replaced with nitrogen and then evacuated, and then tetrafluoroethylene (TFE) was introduced until the internal pressure reached 0.2 MPaG. Next, while stirring the mixed solution in the pressure vessel at 400 rpm, the temperature is adjusted so that the internal temperature becomes 38 ° C., and CF ₄ as an explosion prevention material is introduced to 0.1 MPaG, and then the internal pressure is 0.58 MPaG. TFE was further introduced so that Subsequently, 6 g of (NH ₄ ) ₂ S ₂ O ₈ dissolved in 20 g of water was introduced into the system to initiate polymerization. Thereafter, TFE was added as needed to maintain the internal pressure of the pressure vessel at 0.57 MPaG.

  110 minutes after the start of the polymerization, when a total of 164 g of additional TFE was introduced, the TFE was released to terminate the polymerization. 3500 g of water was added to 3500 g of the obtained polymerization solution, and nitric acid was further added to coagulate the polymer. After the coagulated polymer was filtered, the redispersion of the polymer by adding water and the filtration were repeated three times. Then, the polymer was dried at 90 ° C. for 12 hours and then at 120 ° C. for 12 hours using a hot air dryer to obtain 380 g of polymer.

280 g of the polymer was quickly charged into a 1 L Hastelloy vibration reactor (Okawara Seisakusho) and heated to 100 ° C. while being evacuated and vibrated at a frequency of 50 rpm. Nitrogen was then introduced into the reactor until the gauge pressure was 0.05 MPaG. Subsequently, a gaseous halogenating agent obtained by diluting fluorine gas with nitrogen gas to 20% by mass was introduced into the reactor until the gauge pressure reached 0.00 MPaG, and held for 30 minutes.
Next, the gaseous halogenating agent in the reactor was evacuated and evacuated, and then the gaseous halogenating agent obtained by diluting the fluorine gas to 20 mass% with nitrogen gas was adjusted to a pressure of 0.00 MPaG. It introduced into the reactor until it became, and hold | maintained for 3 hours.
Thereafter, the reactor was cooled to room temperature, the gaseous halogenating agent in the reactor was evacuated, evacuated and purged with nitrogen three times, then the reactor was opened and 280 g of precursor was obtained.
The obtained precursor had an MFR of 2.9 g / 10 min.

The precursor of the fluoropolymer electrolyte thus obtained was brought into contact with an aqueous solution in which potassium hydroxide (18% by mass) and methyl alcohol (45% by mass) were dissolved at 80 ° C. for 20 hours. Decomposition was performed. The obtained hydrolyzed product was washed with ion-exchanged water. Next, the treatment of immersing the hydrolyzed product in a 2N hydrochloric acid aqueous solution at 60 ° C. for 1 hour was repeated 5 times by exchanging the hydrochloric acid aqueous solution every time, and then the hydrolyzed product was washed with ion-exchanged water, dried, and fluorinated. A polymer electrolyte was obtained.
This fluoropolymer electrolyte was introduced into a glass inner cylinder of a 5 L autoclave together with an ethanol aqueous solution (water: ethanol = 50.0: 50.0 (mass ratio)) as a mixed solution, and sealed with a stirring blade. While stirring, the temperature in the inner cylinder was raised to 164 ° C. and held for 7 hours. Thereafter, the inside of the inner cylinder was naturally cooled to obtain a fluorine-based polymer electrolyte solution AS1 having a uniform composition distribution with a solid content concentration of 5.5% by mass.

  Fluoropolymer electrolyte solution AS2 having a solid content concentration of 13% by mass obtained by concentrating this electrolyte solution AS1 under reduced pressure at 80 ° C. (fluorine polymer electrolyte / ethanol / water = 13/5/82 (mass ratio)) Was poured onto a glass plate and applied (cast). Next, the glass plate cast with the electrolyte solution AS2 is placed in an oven and preliminarily dried at 60 ° C. for 30 minutes, then dried at 80 ° C. for 30 minutes to remove the solvent, and further subjected to heat treatment at 160 ° C. for 1 hour, A fluorine-based polymer electrolyte membrane having a thickness of about 33 μm was obtained.

  The EW of this fluoropolymer electrolyte membrane was 560. Further, when the conductivity of the electrolyte membrane at 110 ° C. and 40% RH was measured, a high conductivity of 0.10 S / cm was obtained. When this electrolyte membrane was subjected to a 90 ° C. hot water dissolution test, the mass reduction rate was 0.1% by mass.

An electrode catalyst layer was produced using the electrolyte solution AS2 as follows.
Pt-supported carbon (commercial name “TEC10E40E”, supported by Pt 36.0% by mass, manufactured by Tanaka Kikinzoku Co., Ltd.), which is a composite particle in which platinum (Pt) particles as catalyst particles are supported on carbon particles as conductive particles To 0.70 g, 2.22 g of the electrolyte solution AS2 and 8.08 g of ethanol were added, and then they were sufficiently mixed with a homogenizer to obtain an electrode catalyst composition. This electrocatalyst composition had an ethanol / SO ₃ H (mol ratio) of 350 and was a highly fluid ink without gelation. On the other hand, the electrocatalyst composition having an ethanol / SO ₃ H (mol ratio) of 90 is an ink with very low fluidity due to gelation, and it is difficult to produce a homogeneous electrode catalyst layer. . This electrode catalyst composition was applied on a PTFE sheet by a screen printing method. After the application, it was dried in air at room temperature for 1 hour, and then at 160 ° C. for 1 hour. Thus, an electrode catalyst layer having a thickness of about 10 μm was obtained on the PTFE sheet. Of these electrode catalyst layers, those having a Pt loading of 0.15 mg / cm ² are used as anode catalyst layers (thickness: 5 μm), and those having a Pt loading of 0.30 mg / cm ² are cathode catalyst layers (thickness: 10 μm).

  The anode catalyst layer and the cathode catalyst layer are opposed to each other, and a polymer electrolyte membrane (trade name “Aciplex SF7202”, manufactured by Asahi Kasei Chemicals Corporation) is sandwiched between them. Then, the anode catalyst layer and the cathode catalyst layer were transferred and joined to the polymer electrolyte membrane by hot pressing to prepare an MEA.

Using this MEA, fuel cell evaluation was performed as described above. As a result, the current density after holding for 20 hours at a voltage of 0.7 V under conditions of saturated water vapor pressure (corresponding to a humidity of 53% RH) at a cell temperature of 80 ° C. and 65 ° C. is 0.42 A / cm ² , which is high. Current density is shown. Thereafter, the current density after holding at a voltage of 0.7 V for 20 hours under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure of 50 ° C. (corresponding to a humidity of 26% RH) is 0.39 A / cm ² , which is lower. High current density was maintained even under humidity conditions. On the other hand, the current density after holding for 20 hours at a voltage of 0.7 V under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure of 80 ° C. (equivalent to a humidity of 100% RH) is 0.23 A / cm ² , which is higher. The current density decreased under humidity conditions.

[Example 2]
2980 g of reverse osmosis membrane water, 60 g of C ₇ F ₁₅ COONH ₄ , and 943 g of CF ₂ = CFOCF ₂ CF ₂ SO ₂ F are added to a 6-liter pressure vessel made of SUS-316 equipped with a stirring blade and a temperature control jacket. Prepared. Next, the system was replaced with nitrogen and then evacuated, and then TFE was introduced until the internal pressure reached 0.2 MPaG. Next, while stirring the mixed solution in the pressure vessel at 400 rpm, the temperature is adjusted so that the internal temperature becomes 38 ° C., and CF ₄ as an explosion prevention material is introduced to 0.1 MPaG, and then the internal pressure is 0.50 MPaG. TFE was further introduced so that Subsequently, 6 g of (NH ₄ ) ₂ S ₂ O ₈ dissolved in 20 g of water was introduced into the system to initiate polymerization. Thereafter, TFE was added as needed to maintain the internal pressure of the pressure vessel at 0.51 MPaG.

408 minutes after the start of polymerization, when a total of 381 g of additional TFE was introduced, the TFE was released and the polymerization was stopped. 4400 g of water was added to 4260 g of the obtained polymerization solution, and nitric acid was further added to coagulate the polymer. After the coagulated polymer was filtered, the redispersion of the polymer by adding water and the filtration were repeated three times. Then, the polymer was dried at 90 ° C. for 12 hours and then at 120 ° C. for 12 hours using a hot air dryer to obtain 893 g of a precursor.
The obtained precursor had an MFR of 16 g / 10 min.

  From the precursor, a fluoropolymer electrolyte was obtained in the same manner as in Example 1. A fluorinated polymer electrolyte solution AS4 and a fluorinated polymer electrolyte membrane were prepared in the same manner as in Example 1 except that the fluorinated polymer electrolyte was used. The EW of the electrolyte membrane was measured and found to be 520. Further, when the conductivity of the electrolyte membrane was measured, a high conductivity of 0.12 S / cm was obtained at 110 ° C. and 40% RH. When the 90 degreeC hot water dissolution test was done about this electrolyte membrane, the mass decreasing rate was 5.2 mass%.

Further, an MEA was produced in the same manner as in Example 1 except that the electrolyte solution AS4 was used instead of the electrolyte solution AS2.
Using this MEA, fuel cell evaluation was performed as described above. As a result, the current density after holding for 20 hours at a voltage of 0.7 V under conditions of saturated water vapor pressure (corresponding to a humidity of 53% RH) at a cell temperature of 80 ° C. and 65 ° C. was 0.30 A / cm ² . . Thereafter, the current density after holding at a voltage of 0.7 V for 20 hours under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure (corresponding to a humidity of 26% RH) at 50 ° C. was 0.19 A / cm ² . It is considered that the polymer electrolyte precursor showed a high MFR, and the results were inferior to those of Example 1 under lower humidification conditions. On the other hand, the current density after holding at a voltage of 0.7 V for 20 hours under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure (corresponding to a humidity of 100% RH) at 80 ° C. was 0.05 A / cm ² .

[Example 3]
The electrolyte solution AS2 described in Example 1 was poured onto a glass plate and applied (cast). Next, the glass plate casted with the electrolyte solution AS2 is put in an oven and preliminarily dried at 60 ° C. for 30 minutes, then dried at 80 ° C. for 30 minutes to remove the solvent, and further subjected to heat treatment at 120 ° C. for 1 hour, A fluorine-based polymer electrolyte membrane having a thickness of about 32 μm was obtained.
The EW of this fluoropolymer electrolyte membrane was 560. When the 90 degreeC hot water dissolution test was done about this electrolyte membrane, the mass decreasing rate was 8.7 mass%.
In the production of the electrode catalyst layer and the MEA, the electrode catalyst layer and the MEA were all formed in the same manner as in Example 1 except that the electrode composition was applied and then dried in air at room temperature for 1 hour and subsequently at 120 ° C. for 1 hour. Produced. Using this MEA, fuel cell evaluation was performed as described above. As a result, the current density after holding for 20 hours at a voltage of 0.7 V under conditions of saturated water vapor pressure (corresponding to a humidity of 53% RH) at a cell temperature of 80 ° C. and 65 ° C. was 0.26 A / cm ² . . Thereafter, the current density after holding at a voltage of 0.7 V for 20 hours under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure (corresponding to a humidity of 26% RH) at 50 ° C. was 0.14 A / cm ² . It is considered that due to the heat treatment conditions of the polymer electrolyte membrane, the results were inferior to those of Example 1 under lower humidification conditions. On the other hand, the current density after holding for 20 hours at a voltage of 0.7 V under conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure (corresponding to a humidity of 100% RH) at 80 ° C. was 0.03 A / cm ² .

[Example 4]
The electrolyte solution AS2 described in Example 1 was poured onto a glass plate and applied (cast). Next, the glass plate cast with the electrolyte solution AS2 is placed in an oven and preliminarily dried at 60 ° C. for 30 minutes, then dried at 80 ° C. for 30 minutes to remove the solvent, and further subjected to heat treatment at 160 ° C. for 1 minute, A fluorine-based polymer electrolyte membrane having a thickness of about 32 μm was obtained.
The EW of this fluoropolymer electrolyte membrane was 560. When the 90 degreeC hot water dissolution test was done about this electrolyte membrane, the mass decreasing rate was 10.2 mass%.
In the production of the electrode catalyst layer and the MEA, the electrode catalyst layer and the MEA were all applied in the same manner as in Example 1 except that the electrode composition was applied and then dried in air at room temperature for 1 hour and then at 160 ° C. for 1 minute. Produced. Using this MEA, fuel cell evaluation was performed as described above. As a result, the current density after holding for 20 hours at a voltage of 0.7 V under the conditions of a saturated water vapor pressure (corresponding to a humidity of 53% RH) at a cell temperature of 80 ° C. and 65 ° C. was 0.22 A / cm ² . . Thereafter, the current density after holding for 20 hours at a voltage of 0.7 V under conditions of saturated water vapor pressure (corresponding to a humidity of 26% RH) at a cell temperature of 80 ° C. and 50 ° C. was 0.10 A / cm ² . It is considered that the result is inferior to that of Example 1 under lower humidification conditions due to the heat treatment conditions of the polymer electrolyte membrane. On the other hand, the current density after holding for 20 hours at a voltage of 0.7 V under conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure (corresponding to a humidity of 100% RH) at 80 ° C. was 0.03 A / cm ² .

[Comparative Example 1]
In a pressure-resistant container made of SUS-316 having an internal volume of 189 liters equipped with a stirring blade and a temperature control jacket, 90.5 kg of reverse osmosis membrane water, 0.945 g of C ₇ F ₁₅ COONH ₄ , and CF ₂ = CFOCF ₂ CF ₂ SO ₂ F 5.68 kg was charged. Next, the system was replaced with nitrogen and then evacuated, and then TFE was introduced until the internal pressure reached 0.2 MPaG. Next, while stirring the liquid mixture in the pressure vessel at 189 rpm, the temperature is adjusted so that the internal temperature becomes 47 ° C., and CF ₄ as an explosion prevention material is introduced to 0.1 MPaG, and then the internal pressure is 0.70 MPaG. TFE was further introduced so that Subsequently, 47 g of (NH ₄ ) ₂ S ₂ O ₈ dissolved in 3 L of water was introduced into the system, and polymerization was started. Thereafter, TFE was added as needed to maintain the internal pressure of the pressure vessel at 0.7 MPaG. At that time, every time 1 kg of TFE was supplied, 0.7 kg of CF ₂ = CFOCF ₂ CF ₂ SO ₂ F was supplied to continue the polymerization.

  360 minutes after the start of polymerization, when a total of 24 kg of additional TFE was introduced, the TFE was released and the polymerization was stopped. 200 kg of water was added to 140 kg of the obtained polymerization solution, and nitric acid was further added to coagulate the polymer. The coagulated polymer was centrifuged, washed with circulating ion-exchanged water, and then dried with a hot air dryer at 90 ° C. for 24 hours and then at 150 ° C. for 24 hours to obtain 34 kg of polymer.

28 kg of the above polymer was quickly charged into a 50 L Hastelloy vibration reactor (Okawara Seisakusho) and heated to 100 ° C. while being evacuated and vibrated at a frequency of 50 rpm. Nitrogen was then introduced into the reactor until the gauge pressure was 0.05 MPaG. Subsequently, a gaseous halogenating agent obtained by diluting fluorine gas with nitrogen gas to 20% by mass was introduced into the reactor until the gauge pressure reached 0.00 MPaG, and held for 30 minutes.
Next, the gaseous halogenating agent in the reactor was evacuated and evacuated, and then the gaseous halogenating agent obtained by diluting the fluorine gas to 20 mass% with nitrogen gas was adjusted to a pressure of 0.00 MPaG. It was introduced into the reactor until it was, and held for 3 hours.
Thereafter, the reactor was cooled to room temperature, the gaseous halogenating agent in the reactor was evacuated, evacuated and purged with nitrogen three times, and then the reactor was opened to obtain 28 kg of precursor.
The obtained precursor had an MFR of 3.0 g / 10 min.

  From the precursor, a fluoropolymer electrolyte was obtained in the same manner as in Example 1. A fluorinated polymer electrolyte solution AS3 and a fluorinated polymer electrolyte membrane were prepared in the same manner as in Example 1 except that the fluorinated polymer electrolyte was used. The EW of the electrolyte membrane was measured and found to be 720. Further, when the conductivity of the electrolyte membrane was measured, a high conductivity of 0.04 S / cm was not obtained at 110 ° C. and 40% RH. When this electrolyte membrane was subjected to a 90 ° C. hot water dissolution test, the mass reduction rate was 0.1% by mass.

Further, an MEA was produced in the same manner as in Example 1 except that the electrolyte solution AS3 was used instead of the electrolyte solution AS2.
Using this MEA, fuel cell evaluation was performed as described above. As a result, the current density after holding for 20 hours at a voltage of 0.7 V under the conditions of a saturated water vapor pressure (corresponding to a humidity of 53% RH) at a cell temperature of 80 ° C. and 65 ° C. was 0.30 A / cm ² . Compared with the MEA of Example 1, the current density was low. Thereafter, the current density after holding at a voltage of 0.7 V for 20 hours under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure (corresponding to a humidity of 26% RH) is 0.12 A / cm ² , which is lower. Only lower current densities were obtained under humidity conditions. On the other hand, the current density after holding for 20 hours at a voltage of 0.7 V under the conditions of a cell temperature of 80 ° C. and a saturated water vapor pressure of 80 ° C. (corresponding to a humidity of 100% RH) is 0.37 A / cm ² , The current density increased at high humidity conditions.

From these results, the following contents can be read.
(1) The electrode catalyst layer and MEA of this embodiment can realize a fuel cell having high battery performance under low humidification conditions.
(2) Setting the MFR of the precursor appropriately is preferable from the viewpoint of maintaining good output performance under high temperature and low humidification conditions.
(3) Appropriate heat treatment of the polymer electrolyte membrane is preferable from the viewpoint of maintaining good output performance under high temperature and low humidification conditions.

  The electrode catalyst layer and membrane electrode assembly of the present invention provide a high-performance solid polymer fuel cell even under high temperature and low humidification conditions such as a battery operating temperature of 80 to 120 ° C. and a humidity of 60% RH or less. it can. The electrode catalyst layer of the present invention can also be used in various fuel cells including direct methanol fuel cells, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrators, humidity sensors, gas sensors, etc. is there.

Claims (15)

A proton-conducting fluoropolymer electrolyte having a repeating unit represented by the following general formula (1) and a repeating unit represented by the following general formula (2) and having an equivalent weight of 250 to 680; An electrode catalyst layer for a fuel cell, comprising: composite particles having catalyst particles supported on the particles.
-(CF ₂ CF ₂ )-(1)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) m - (CF 2) n -SO 3 Z)) - (2)
(In general formula (2), X represents a fluorine atom, a chlorine atom or a perfluoroalkyl group, m represents an integer of 0 to 5, and n represents an integer of 0 to 6. However, m and n are simultaneously (Z does not represent 0. Z represents an alkali metal atom, an alkaline earth metal atom, a transition metal atom, or a hydrogen atom.)   The electrode catalyst layer for a fuel cell according to claim 1, wherein the m is 0, the n is 2, and the Z is a hydrogen atom. The fluorine-based polymer electrolyte is obtained from a repeating unit represented by the following general formula (3) and a precursor having a repeating unit represented by the following general formula (4).
The melt flow rate of the precursor is 10.0 g / 10 min or less,
The mass retention of the post-treatment electrolyte obtained by allowing the fluoropolymer electrolyte to stand in hot water at 90 ° C. for 5 hours is 97% by mass or more based on the mass of the fluoropolymer electrolyte. Item 3. The fuel cell electrode catalyst layer according to Item 1 or 2.
− (CF ₂ CF ₂ ) − (3)
_{- (CF 2 -CF (-O- (} CF 2 CFXO) m - (CF 2) n -SO 2 F)) - (4)
(In general formula (4), X, m, and n are as defined in general formula (2).)   The electrode catalyst layer for a fuel cell according to any one of claims 1 to 3, wherein a mass ratio of the fluorine-based polymer electrolyte to the catalyst particles is 0.1 to 10. A proton-conducting fluoropolymer electrolyte having a repeating unit represented by the general formula (1) and a repeating unit represented by the general formula (2) and having an equivalent weight of 250 to 680; The amount of lower alcohol solvent (lower alcohol / SO ₃ H) (mol ratio) per mole of the sulfonic acid unit of the fluorine-based polymer electrolyte is 100, which includes composite particles supporting catalyst particles on the particles and lower alcohol. This is the fuel cell electrode catalyst composition.   The electrode catalyst composition for a fuel cell according to claim 5, wherein the m is 0, the n is 2, and the Z is a hydrogen atom. The fluorine-based polymer electrolyte is obtained from a repeating unit represented by the general formula (3) and a precursor having a repeating unit represented by the general formula (4).
The melt flow rate of the precursor is 10.0 g / 10 min or less,
The mass retention of the post-treatment electrolyte obtained by allowing the fluoropolymer electrolyte to stand in hot water at 90 ° C. for 5 hours is 97% by mass or more based on the mass of the fluoropolymer electrolyte. Item 7. The fuel cell electrode catalyst composition according to Item 5 or 6.   The electrode catalyst composition for a fuel cell according to any one of claims 5 to 7, wherein a mass ratio of the fluorine-based polymer electrolyte to the catalyst particles is 0.1 to 10.   The electrode catalyst layer for fuel cells formed from the electrode catalyst composition for fuel cells of any one of Claims 5-8.   A membrane electrode assembly comprising the fuel cell electrode catalyst layer according to any one of claims 1 to 4.   A polymer electrolyte fuel cell comprising the membrane electrode assembly according to claim 10. A polymer electrolyte fuel cell comprising a membrane electrode assembly in which a fuel electrode is disposed on one side of a proton conductive polymer electrolyte membrane and an air electrode is disposed on the other side,
The fuel electrode and the air electrode are gas diffusion electrodes containing a catalyst and a proton conductive fluorine-based polymer electrolyte,
A polymer electrolyte fuel cell that satisfies the following formula (7) when the operating temperature is T ° C.
Unit current density when fuel gas and / or air gas humidification temperature is (T-15) ° C. (A / cm ² ) ≧ unit current when fuel gas and / or air gas humidification temperature is T ° C. Density (A / cm ² ) (7)   The polymer electrolyte fuel cell according to claim 12, wherein the operation voltage is maintained at a constant voltage of 0.7 V for 20 hours, and then the formula (7) is satisfied.   The solid polymer fuel cell according to claim 12 or 13, wherein the proton conductive polymer electrolyte membrane comprises a proton conductive fluorine-based polymer electrolyte.   The polymer electrolyte fuel cell according to any one of claims 12 to 14, wherein the membrane electrode assembly is the membrane electrode assembly according to claim 10.