WO2018012435A1 - Gas diffusion member and membrane electrode assembly for solid polymer fuel cell - Google Patents

Abstract

Provided are: a gas diffusion member capable of imparting sufficient electrical conductivity to an electrode and improving gas diffusivity and drainage performance in the electrode; and a membrane electrode assembly exhibiting excellent power generation performance even under high humidity conditions. A gas diffusion member 10 includes: a sheet-like porous substrate 12 made of a thermoplastic resin material; and a conductive material 14 at least partly impregnated into the porous substrate 12, the conductive material 14 containing carbon fibers and an ion exchange resin. The membrane electrode assembly for a solid polymer fuel cell is provided with: an anode having a catalyst layer and a gas diffusion layer; a cathode having a catalyst layer and a gas diffusion layer; and a polymer electrolyte membrane disposed between the catalyst layer of the anode and the catalyst layer of the cathode. The gas diffusion layer of any one or both of the anode and the cathode has the gas diffusion member 10.

Description

Gas diffusion member and membrane electrode assembly for polymer electrolyte fuel cell

The present invention relates to a gas diffusion member and a membrane electrode assembly for a polymer electrolyte fuel cell including the gas diffusion member.

The polymer electrolyte fuel cell has a structure in which, for example, a cell is formed by sandwiching a membrane electrode assembly between two separators, and a plurality of cells are stacked. The membrane electrode assembly includes an anode and a cathode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte membrane disposed between the anode and the cathode.

In order to improve the electric conductivity, gas diffusibility, drainage, etc. of the electrode, particularly the cathode, and to improve the power generation performance of the membrane electrode assembly, as the gas diffusion layer, the carbon material and the surface of the porous carbon substrate One provided with a porous carbon layer containing a polymer may be used (Patent Document 1, etc.).

International Publication No. 2007/052650

It is said that the conductivity, gas diffusibility, and drainage of the electrode can be improved by having the carbon layer in the gas diffusion layer.
However, even in an electrode having a porous carbon layer containing a carbon material and a polymer, in a highly humidified state (for example, 50 ° C., 100% RH), gas diffusibility and drainage in the electrode become insufficient, The power generation performance of the membrane electrode assembly may deteriorate.

The present invention provides a gas diffusion member capable of imparting sufficient conductivity to an electrode of a membrane electrode assembly and improving gas diffusibility and drainage in the electrode; and a membrane electrode excellent in power generation performance even in a highly humidified state Provide a joined body.

<1> a sheet-like porous base material made of a thermoplastic resin material, and a conductive material at least partially impregnated in the porous base material, wherein the conductive material is a carbon fiber and an ion exchange resin. The gas diffusion member characterized by including.
<2> The gas diffusion member according to <1>, wherein the carbon fiber is a vapor growth carbon fiber.
<3> The gas diffusion member according to <1> or <2>, wherein an average fiber diameter of the carbon fibers is 1 to 1000 nm, and an average fiber length of the carbon fibers is 1 to 100 μm.
<4> The gas diffusion member according to any one of <1> to <3>, wherein the amount of the carbon fiber is 0.1 to 10 mg per 1 cm ² of the gas diffusion member.
<5> The gas diffusion member according to any one of <1> to <4>, wherein the ion exchange capacity of the ion exchange resin is 0.5 to 2.0 meq / g dry resin.
<6> The gas diffusion according to any one of <1> to <5>, wherein the mass ratio of the content of the ion exchange resin to the content of the carbon fiber is 0.05 to 1.5. Element.
<7> The gas diffusion member according to any one of <1> to <6>, wherein the ion exchange resin is a polymer having a unit represented by the formula u1 described later.
<8> The gas diffusion member according to any one of <1> to <6>, wherein the ion exchange resin is a polymer having a unit represented by the formula u2 described later.
<9> The gas diffusion member according to any one of <1> to <8>, wherein the conductive material further includes a fluororesin other than the ion exchange resin.
<10> The gas diffusion member according to any one of <1> to <9>, wherein the porous substrate is a nonwoven fabric.
<11> The gas diffusion member according to any one of <1> to <10>, wherein the thermoplastic resin material comprises an olefin resin or a fluororesin.
<12> The gas diffusion member according to <10>, wherein the nonwoven fabric has a basis weight of 1 to 10 g / m ² .
<13> The gas diffusion member according to any one of <1> to <12>, wherein the thermoplastic resin material includes an olefin resin or a fluororesin.
<14> The gas diffusion member according to any one of <1> to <13>, wherein the thickness of the gas diffusion member is 10 to 300 μm.
<15> An anode having a catalyst layer and a gas diffusion layer, a cathode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte membrane disposed between the catalyst layer of the anode and the catalyst layer of the cathode A membrane electrode assembly for a polymer electrolyte fuel cell, wherein the gas diffusion layer of any one or both of the anode and the cathode has the gas diffusion member of any one of <1> to <14>.

The gas diffusion member of the present invention can impart sufficient conductivity to the electrode of the membrane electrode assembly, and can improve the gas diffusibility and drainage of the electrode.
The membrane / electrode assembly for a polymer electrolyte fuel cell of the present invention is excellent in power generation performance even in a highly humidified state.

It is a schematic cross section of an example of the gas diffusion member of the present invention. It is a schematic cross section of the other example of the gas diffusion member of this invention. It is the schematic which shows an example of the manufacturing method of the gas diffusion member of this invention. It is the schematic which shows the other example of the manufacturing method of the gas diffusion member of this invention. It is a schematic cross section which shows an example of the membrane electrode assembly for polymer electrolyte fuel cells of this invention. It is a schematic cross section which shows the other example of the membrane electrode assembly for polymer electrolyte fuel cells of this invention. It is a schematic cross section which shows the other example of the membrane electrode assembly for polymer electrolyte fuel cells of this invention.

The meanings of terms in the present specification are as follows.
The “unit” in the polymer refers to a polymer unit derived from the monomer formed by polymerizing the monomer, and a polymer unit in which a part of the polymer unit is converted into another structure by treating the polymer. means.
The “ion exchange group” means a group in which a part of the cation contained in the group can exchange with another cation, and examples thereof include a sulfonic acid group, a sulfonimide group, and a sulfonemethide group.
"Sulfonic acid group" _are ^-SO 3 - ^{H +} or _-SO ³ - ^{M +} (However, ^{M +} is a monovalent metal ion or one or more hydrogen atoms may be substituted with a hydrocarbon group It is an ammonium ion.
The numerical range represented by “to” indicates a numerical range in which the numerical values before and after “to” are the lower limit value and the upper limit value.
In this specification, the unit represented by the formula u1 is referred to as “unit u1”. Units represented by other formulas are also described in the same manner. The monomer represented by the formula m1 is referred to as “monomer m1”. The same applies to monomers represented by other formulas.

The gas diffusion member of the present invention is a sheet-like member obtained by impregnating a sheet-like porous substrate with a conductive material. The sheet-like gas diffusion member may be a sheet cut into a predetermined size, or may be a long web-like member (continuous body).

The thickness of the gas diffusion member is preferably 10 to 300 μm, more preferably 30 to 200 μm, and even more preferably 50 to 150 μm. When the thickness is not less than the lower limit of the above range, a gas diffusion member having excellent mechanical properties can be obtained. If the thickness is not more than the upper limit of the above range, a gas diffusion member having excellent conductivity, gas diffusibility and drainage can be obtained.

The density of the gas diffusion member is preferably 0.1 to 0.6 g / cm ³ , more preferably 0.2 to 0.5 g / cm ³ . When the density is not less than the lower limit of the above range, a gas diffusion member having excellent mechanical properties can be obtained. If this density is below the upper limit of the said range, the gas diffusion member excellent in gas diffusibility and drainage will be obtained.

FIG. 1 is a schematic cross-sectional view showing an example of a gas diffusion member of the present invention.
The gas diffusion member 10 includes a porous substrate 12 and a conductive material 14 that is partially impregnated into the porous substrate 12 and the remaining part covers the first surface of the porous substrate 12.
The conductive material 14 includes an impregnation portion 14 a impregnated in the porous substrate 12 and a base portion 14 b that covers the first surface of the porous substrate 12.

FIG. 2 is a schematic cross-sectional view showing another example of the gas diffusion member of the present invention. The gas diffusion member 10 includes a porous substrate 12 and a conductive material 14 that is entirely impregnated in the porous substrate 12.
The porous base material is a sheet-like base material made of a thermoplastic resin material. The sheet-like porous substrate may be a sheet cut into a predetermined size, or may be a long web-like (continuous body).
Examples of the porous substrate include a nonwoven fabric, a woven fabric, and a porous body (sponge etc.). As the porous substrate, a nonwoven fabric is preferable because a gas diffusion member having excellent gas diffusibility and drainage can be obtained.

Basis weight of the nonwoven fabric is preferably 1 ~ 10g / ^{m 2,} and more preferably 3 ~ 7g / ^{m 2.} When the basis weight is not less than the lower limit of the above range, a gas diffusion member having excellent mechanical properties can be obtained. When the basis weight is not more than the upper limit of the above range, the pore volume of the porous substrate becomes sufficiently large, so that a gas diffusion member excellent in conductivity, gas diffusibility and drainage can be obtained.

The thermoplastic resin material includes a thermoplastic resin. The thermoplastic resin material may contain other components (such as various fillers and various additives) as necessary.
As the thermoplastic resin, an olefin resin or a fluororesin is preferable because a gas diffusion member having excellent drainage properties is obtained, and an olefin resin is more preferable because it is inexpensive and easily processed into a porous substrate.
Examples of the olefin resin include ethylene resins (polyethylene, ethylene-α-olefin copolymers, etc.) and propylene resins (polypropylene, propylene-α-olefin copolymers, etc.). As the olefin resin, polypropylene is preferable from the viewpoint of processability and chemical stability.

As the fluororesin, a fluororesin that can be melt-molded is preferable because it can be easily processed into a porous substrate. Examples of the melt-moldable fluororesin include, for example, a tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer (hereinafter also referred to as PFA) and a tetrafluoroethylene-hexafluoropropylene copolymer (hereinafter also referred to as FEP). , Ethylene-tetrafluoroethylene copolymer (hereinafter also referred to as ETFE), polyvinylidene fluoride (hereinafter also referred to as PVDF), polychlorotrifluoroethylene (hereinafter also referred to as PCTFE), ethylene-chlorotrifluoroethylene And a copolymer (hereinafter also referred to as ECTFE).

The conductive material is preferably impregnated in the entire porous substrate from the viewpoint that a gas diffusion member having excellent conductivity, gas diffusibility and drainage can be obtained.
For example, as shown in FIG. 1, a part of the conductive material is impregnated into the porous substrate, and the remaining part covers either one or both of the first surface and the second surface of the porous substrate. As shown in FIG. 2, the entire amount may be impregnated in the porous substrate.

The conductive material includes carbon fiber and ion exchange resin. The conductive material preferably further contains a fluororesin other than the ion exchange resin from the viewpoint that a gas diffusion member having excellent drainage properties can be obtained. The conductive material may contain other components (such as various fillers and various additives) as necessary.

Examples of the carbon fiber include vapor grown carbon fiber, carbon nanotube (single wall, double wall, multi-wall, cup laminated type, etc.), PAN-based carbon fiber, and pitch-based carbon fiber. Examples of the form of carbon fiber include chopped fiber and milled fiber.
As the carbon fiber, a vapor-grown carbon fiber is preferable, and since good dispersibility can be obtained, a carbon fiber containing a linear vapor-grown carbon fiber is preferable.
Commercially available carbon fibers can be used. Examples of commercially available carbon fibers include VGCF-H (product name of Showa Denko KK) and HCNTs series (product name of Shenzhen SUSN Sinotech New Materials Co., Ltd.).

The average fiber diameter of the carbon fibers is preferably 1 to 1000 nm, more preferably 20 to 500 nm, and further preferably 50 to 250 nm. If the average fiber diameter is not less than the lower limit of the above range, the conductive material itself is sufficiently formed with pores, so that a gas diffusion member excellent in gas diffusibility and drainage can be obtained. When the average fiber diameter is not more than the upper limit of the above range, the impregnation property of the conductive material into the porous substrate is excellent. Moreover, when preparing the electroconductive material paste mentioned later, carbon fiber can be favorably disperse | distributed to a dispersion medium.

The average fiber length of carbon fibers is preferably 1 to 100 μm, more preferably 5 to 40 μm. When the average fiber length is equal to or greater than the lower limit of the above range, the conductive material itself is sufficiently formed with pores, so that a gas diffusion member excellent in gas diffusibility and drainage can be obtained. When the average fiber length is not more than the upper limit of the above range, the impregnation property of the conductive material into the porous substrate is excellent. Moreover, when preparing the electroconductive material paste mentioned later, carbon fiber can be favorably disperse | distributed to a liquid medium.

The carbon fiber content in the gas diffusion member is preferably 0.1 to 10 mg, more preferably 0.5 to 6 mg, and further preferably 1 to 4 mg per 1 cm ^{2 of the} gas diffusion member. If the content is not less than the lower limit of the above range, the conductive material itself is sufficiently formed with pores, so that a gas diffusion member having excellent gas diffusibility and drainage can be obtained. If this content is below the upper limit of the said range, it is excellent in the impregnation property of the electroconductive material to a porous base material. Moreover, when preparing the electroconductive material mentioned later, carbon fiber can be favorably disperse | distributed to a dispersion medium.

The ion exchange resin is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, and more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an etheric oxygen atom). Examples of the perfluorocarbon polymer include a polymer H described later, a polymer Q described later, and a polymer having a unit derived from a perfluoromonomer having an ion exchange group and a 5-membered ring described in International Publication No. 2011/013577. Known polymers may be mentioned, and polymer H or polymer Q is preferable from the viewpoint of availability and manufacturing, and polymer H is more preferable from the viewpoint of ease of manufacturing.

The polymer H is a polymer having the unit u1.

However, Q ¹ is a single bond or a perfluoroalkylene group which may have an etheric oxygen atom, R ^f1 is a perfluoroalkyl group which may have an etheric oxygen atom, X ¹ is an oxygen atom, a nitrogen atom or a carbon atom, a is 0 when X ¹ is an oxygen atom, ¹ when X ¹ is a nitrogen atom, and 2 when X ¹ is a carbon atom , Y ¹ is a fluorine atom or a monovalent perfluoro organic group, and s is 0 or 1. A single bond means that the carbon atom of CFY ¹ and the sulfur atom of SO ₂ are directly bonded. An organic group means a group containing one or more carbon atoms.

When the perfluoroalkylene group of Q ¹ has an etheric oxygen atom, the oxygen atom may be one or may be two or more. Further, the oxygen atom may exist between the carbon atoms of the perfluoroalkylene group, or may exist between the CFY ¹ group of the perfluoroalkylene group and the adjacent carbon atom. The perfluoroalkylene group may be linear or branched.
The perfluoroalkylene group preferably has 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms.

The perfluoroalkyl group for R ^f1 may be linear or branched, and is preferably linear. The perfluoroalkyl group preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. As the perfluoroalkyl group, a perfluoromethyl group, a perfluoroethyl group and the like are preferable.

_{^{- (SO 2 X 1 (SO}} 2 R f1) a) - H + group is an ion-exchange group, preferably a sulfonic acid group _(-SO ³ - ^{H +} group), a sulfonimide group _(-SO 2 N (SO ₂ R ^f1 ) ⁻ H ⁺ group) or a sulfonemethide group (—SO ₂ C (SO ₂ R ^f1 ) ₂ ) ⁻ H ⁺ group).
Y ¹ is preferably a fluorine atom or a C 1-6 perfluoroalkyl group, particularly preferably a fluorine atom or a trifluoromethyl group.

The unit u1 is preferably the unit u1-1. From the viewpoint of easy production of the polymer H and easy industrial implementation, the unit u1-11, the unit u1-12, the unit u1-13 or the unit u1-14 Is more preferable.

In the formula (u1-1), Z is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1 and m + p> 0.

The polymer H may further have units derived from other monomers (hereinafter referred to as “other units 1”) other than the monomer that provides the unit u1. What is necessary is just to adjust the ratio of the other unit 1 suitably so that the ion exchange capacity of the polymer H may become the below-mentioned preferable range.
The other unit 1 is preferably a unit derived from a perfluoromonomer from the viewpoint of mechanical properties and chemical durability, and more preferably a unit derived from tetrafluoroethylene (hereinafter also referred to as TFE).

Polymer H is produced by polymerizing monomer m1 and, if necessary, another monomer other than monomer m1 to obtain a precursor polymer, and then converting —SO ₂ F groups in the precursor polymer into sulfonic acid groups. it can. The conversion of —SO ₂ F group to sulfonic acid group is performed by hydrolysis and acidification treatment.
CF ₂ ═CF— (CF ₂ ) _s OCF ₂ —CFY ¹ —Q ¹ —SO ₂ F Formula m1.

Polymer Q is a polymer having unit u2. As the polymer Q, those belonging to the polymer H are excluded.

However, Q ²¹ is an etheric good perfluoroalkylene group which may have an oxygen atom, Q ²² is a single bond, or which may have an etheric oxygen atom perfluoroalkylene group, R ^f2 is a perfluoroalkyl group which may have an etheric oxygen atom, X ² is an oxygen atom, a nitrogen atom or a carbon atom, and b is 0 when X ² is an oxygen atom. , X ² is 1 when X ² is a nitrogen atom, ² when X ² is a carbon atom, Y ² is a fluorine atom or a monovalent perfluoro organic group, and t is 0 or 1. The single bond means that the carbon atom of CY ² and the sulfur atom of SO ₂ are directly bonded. An organic group means a group containing one or more carbon atoms.

When the perfluoroalkylene group of Q ²¹ and Q ²² has an etheric oxygen atom, the oxygen atom may be one or two or more. Further, the oxygen atom may exist between the carbon atoms of the perfluoroalkylene group, or may exist between the CY ² group of the perfluoroalkylene group and the adjacent carbon atom.
The perfluoroalkylene group may be linear or branched, and is preferably linear.
The perfluoroalkylene group preferably has 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms. If the number of carbon atoms is 6 or less, the boiling point of the raw fluorine-containing monomer is lowered, and distillation purification becomes easy.

Q ²² is preferably a C 1-6 perfluoroalkylene group which may have an etheric oxygen atom. When Q ²² is a perfluoroalkylene group having 1 to 6 carbon atoms which may have an etheric oxygen atom, the polymer electrolyte fuel cell was operated over a longer period than when Q ²² is a single bond. In particular, the stability of the power generation performance is excellent.
At least one of Q ²¹ and Q ²² is preferably a C 1-6 perfluoroalkylene group having an etheric oxygen atom. Since the fluorine-containing monomer having a C 1-6 perfluoroalkylene group having an etheric oxygen atom can be synthesized without undergoing a fluorination reaction with a fluorine gas, the yield is good and the production is easy.

The perfluoroalkyl group for R ^f2 may be linear or branched, and is preferably linear. The perfluoroalkyl group preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. As the perfluoroalkyl group, a perfluoromethyl group, a perfluoroethyl group and the like are preferable.
When the unit u2 has two or more R ^{f2 s} , the R ^f2s may be the same group or different groups.

The — (SO ₂ X ² (SO ₂ R ^f2 ) _b ) ^— H ⁺ group is an ion exchange group.
^{_{- (SO 2 X 2 (SO}} 2 R f2) b) - as the ^{H +} group, a sulfonic acid group _(-SO ³ - ^{H +} group), a sulfonimide group ^{_{(-SO 2 N (SO 2 R}} f2) - H ⁺ Group) or a sulfonemethide group (—SO ₂ C (SO ₂ R ^f2 ) ₂ ) ^— H ⁺ group).
Y ² is preferably a fluorine atom or a linear perfluoroalkyl group having 1 to 6 carbon atoms which may have an etheric oxygen atom.

The unit u2 is preferably the unit u2-1, more preferably the unit u2-11, the unit u2-12 or the unit u2-13 from the viewpoint of easy production of the polymer Q and easy industrial implementation.

R ^F21 is a linear perfluoroalkylene group having 1 to 6 carbon atoms which may have a single bond or an etheric oxygen atom, and R ^F22 is a linear chain having 1 to 6 carbon atoms. Perfluoroalkylene group.

The polymer Q may further have units other than the unit u2 (hereinafter referred to as other units 2). What is necessary is just to adjust the ratio of the other unit 2 suitably so that the ion exchange capacity of the polymer Q may become the below-mentioned preferable range. The other unit 1 and the other unit 2 may include units derived from the same type of monomer.
The other unit 2 is preferably a unit derived from a perfluoromonomer, more preferably a unit derived from TFE, from the viewpoint of mechanical properties and chemical durability.
The polymer Q can be produced by, for example, a method described in International Publication No. 2007/013533.

The ion exchange capacity of the ion exchange resin in the conductive material is preferably 0.5 to 2.0 meq / g dry resin from the viewpoint of obtaining a gas diffusion member having excellent conductivity and gas permeability. A 1.5 meq / g dry resin is particularly preferred.
The ratio (F / C) of the ion exchange resin content F to the carbon fiber content C (F / C) in the conductive material is preferably 0.05 to 1.5, more preferably 0.05 to 1.2, and 1 to 0.7 is more preferable. If F / C is not less than the lower limit of the above range, the carbon fiber will not increase too much and the conductive material will not easily become brittle. If F / C is less than or equal to the upper limit of the above range, the amount of ion exchange resin does not increase too much, and pores are sufficiently formed in the conductive material itself. Therefore, a gas diffusion member having excellent gas permeability and drainage properties is obtained. can get.

Examples of the fluororesin other than the ion exchange resin contained in the conductive material include polytetrafluoroethylene (hereinafter also referred to as PTFE), PVDF, polyvinyl fluoride (PVF), PCTFE, PFA, FEP, ETFE, and ECTFE. Can be mentioned. PTFE is preferable because a gas diffusion member having excellent drainage can be obtained.

The ratio (P / C) of the fluororesin content P to the carbon fiber content C in the conductive material is preferably 0.05 to 0.5, more preferably 0.1 to 0.4. If P / C is not less than the lower limit of the above range, the carbon fiber will not increase too much and the conductive material will not easily become brittle. If P / C is less than or equal to the upper limit of the above range, the fluororesin will not increase too much and the conductive material will not easily become brittle. Moreover, the gas diffusion member excellent in electroconductivity is obtained.

(Method for producing gas diffusion member)
A gas diffusion member is manufactured by the following method, for example.
As shown in FIG. 3, a conductive material paste is applied to the surface of the first carrier film 100 and dried to form the base portion 14b.
Next, the porous substrate 12 is placed on the base portion 14b. Next, a conductive material paste is applied to the surface of the porous substrate 12, impregnated on the entire porous substrate 12, and dried to form an impregnation portion 14 a, thereby forming the conductive material on the porous substrate 12. A gas diffusion member 10 in which a part of 14 is impregnated is obtained. Next, a method of peeling the first carrier film 100 from the gas diffusion member 10.

As shown in FIG. 4, the porous substrate 12 is placed on the first carrier film 100.
Next, a conductive material paste is applied to the surface of the porous substrate 12, impregnated on the top of the porous substrate 12, and dried to form the first semi-impregnated portion 14c.
Next, the second carrier film 102 is adhered to the first semi-impregnated portion 14c, and the first carrier film 100 is peeled off.
Next, the conductive material paste is applied to the surface of the porous substrate 12, impregnated in the non-impregnated portion of the porous substrate 12, and dried to form the second semi-impregnated portion 14d. The gas diffusion member 10 in which the material 12 is impregnated with the entire amount of the conductive material 14 is obtained.
Next, a method of peeling the second carrier film 102 from the gas diffusion member 10.

The conductive material paste includes carbon fiber, ion exchange resin, and liquid medium. The conductive material paste may contain a fluororesin other than the ion exchange resin and other components as necessary.

The liquid medium preferably contains an organic solvent and water.
As the organic solvent, alcohols are preferable. Examples of alcohols include non-fluorine alcohols (methanol, ethanol, 1-propanol, 2-propanol, etc.), fluorine alcohols (2,2,2-trifluoroethanol, 2,2,3,3, etc.). 3-pentafluoro-1-propanol, 2,2,3,3-tetrafluoro-1-propanol, 4,4,5,5,5-pentafluoro-1-pentanol, 1,1,1,3 3,3-hexafluoro-2-propanol, 3,3,3-trifluoro-1-propanol, 3,3,4,4,5,5,6,6,6-nonafluoro-1-hexanol, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8-tridecafluoro-1-octanol).

The mass ratio of the organic solvent to water (organic solvent: water) is preferably 55:45 to 30:70, and more preferably 50:50 to 40:60. If the organic solvent is less than or equal to the upper limit of the range (water is greater than or equal to the lower limit of the range), the conductive material is less likely to crack. If the organic solvent is not less than the lower limit of the above range (water is not more than the upper limit of the above range), the dispersion stability of the conductive material paste is good.

The solid content concentration of the conductive material paste is preferably 5 to 40% by mass, more preferably 8 to 30% by mass, and particularly preferably 10 to 25% by mass. When the solid content concentration is within the above range, the viscosity is suitable for coating and impregnation.

Examples of carrier films include ETFE films and olefin resin films. As a method for applying the conductive material paste, a known coating method such as a die coating method may be used. The drying temperature is preferably 40 to 130 ° C, more preferably 45 to 80 ° C. As a drying method, a known drying method may be used.

The gas diffusion member of the present invention described above has conductivity because the porous base material is impregnated with the conductive material containing carbon fiber and ion exchange resin. Therefore, sufficient conductivity can be imparted to the electrode by using the gas diffusion member in the gas diffusion layer of the electrode of the membrane electrode assembly.
Further, since the gas diffusion member of the present invention described above is based on a porous base material, a carbon layer containing a conventional carbon material and polymer even after impregnation with a conductive material. As compared with the above, the pore volume can be increased. Therefore, the gas diffusion member of the present invention is excellent in gas diffusibility and drainage as compared with a conventional carbon layer. Therefore, by using the gas diffusion member for the gas diffusion layer of the electrode of the membrane electrode assembly, the gas diffusibility and drainage of the electrode can be improved.

A membrane electrode assembly for a polymer electrolyte fuel cell of the present invention (hereinafter referred to as a membrane electrode assembly) includes an anode having a catalyst layer and a gas diffusion layer, a cathode having a catalyst layer and a gas diffusion layer, and an anode A polymer electrolyte membrane disposed between the catalyst layer and the cathode catalyst layer, and either or both of the anode and cathode gas diffusion layers have the gas diffusion member of the present invention.

In the membrane / electrode assembly, it is preferable that at least the gas diffusion layer of the cathode has the gas diffusion member of the present invention for the following reasons.
The reaction in the polymer electrolyte fuel cell is represented by the following formulas (R1) and (R2).
Anode: H ₂ → 2H ⁺ + 2e ⁻ (R1),
Cathode: 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (R2).
In the polymer electrolyte fuel cell, it is said that the reaction at the cathode represented by the formula (R2) is rate-limiting, and in order to promote the reaction, it is necessary to increase the proton concentration and the oxygen concentration in the reaction field. Therefore, the cathode is required to have sufficient conductivity and gas diffusibility. In order to maintain the conductivity of the cathode, a highly humidified oxidant gas (air) humidified by a humidifier or the like is supplied to the cathode. Further, since water vapor is generated by reaction at the cathode, pore clogging (flooding) due to condensation of water vapor is likely to occur. Therefore, the cathode is also required to have sufficient drainage.
Therefore, it is preferable that at least the gas diffusion layer of the cathode has the gas diffusion member of the present invention that improves conductivity, gas diffusion property, drainage property and the like.

FIG. 5 is a schematic cross-sectional view showing an example of the membrane electrode assembly of the present invention.
The membrane electrode assembly 1 includes an anode 20 having a catalyst layer 22 and a gas diffusion layer 24; a cathode 30 having a catalyst layer 32 and a gas diffusion layer 34; and a catalyst layer 22 of the anode 20 and a catalyst layer 32 of the cathode 30. And a polymer electrolyte membrane 40 disposed therebetween.
The gas diffusion layer 24 of the anode 20 includes a porous carbon base material 26 and a porous carbon layer 28 provided between the catalyst layer 22 and the carbon base material 26. The gas diffusion layer 34 of the cathode 30 includes a porous carbon base material 36 and the gas diffusion member 10 of the present invention provided between the catalyst layer 32 and the carbon base material 36.

FIG. 6 is a schematic cross-sectional view showing another example of the membrane electrode assembly of the present invention. The gas diffusion layer 34 of the cathode 30 is the same as the description of FIG. 5 except that the gas diffusion layer 34 of the present invention is composed of the gas diffusion member 10 of the present invention.
FIG. 7 is a schematic cross-sectional view showing another example of the membrane electrode assembly of the present invention. The gas diffusion layer 24 of the anode 20 is made of the gas diffusion member 10 of the present invention, and the gas diffusion layer 34 of the cathode 30 is the same as the description of FIG. 5 except that it is made of the gas diffusion member 10 of the present invention.

In the membrane / electrode assembly, the catalyst layer is a layer containing a catalyst and an ion exchange resin. The anode catalyst layer and the cathode catalyst layer may be the same component, composition, thickness, or the like, or may be different layers.
The catalyst may be any catalyst that promotes the oxidation-reduction reaction in the polymer electrolyte fuel cell, and a catalyst containing platinum is preferable, and a supported catalyst in which platinum or a platinum alloy is supported on a carbon support is particularly preferable.
Examples of the carbon carrier include activated carbon and carbon black. From the viewpoint of high chemical durability, those graphitized by heat treatment or the like are preferable.
The specific surface area of the carbon support is preferably 200 m ² / g or more. The specific surface area of the carbon support is measured by nitrogen adsorption on the carbon surface with a BET specific surface area apparatus.

Platinum alloys include platinum group metals other than platinum (ruthenium, rhodium, palladium, osmium, iridium), gold, silver, chromium, iron, titanium, manganese, cobalt, nickel, molybdenum, tungsten, aluminum, silicon, zinc, An alloy of platinum and one or more metals selected from the group consisting of tin and platinum is preferable. The platinum alloy may contain a metal alloyed with platinum and an intermetallic compound of platinum. The supported amount of platinum or platinum alloy is preferably 10 to 70% by mass of the supported catalyst.

The amount of platinum contained in the catalyst layer is preferably 0.01 to 0.5 mg / cm ² from the viewpoint of the optimum thickness of the catalyst layer for efficiently carrying out the electrode reaction, and the balance between the cost and performance of the raw material is preferable. From the viewpoint, 0.05 to 0.35 mg / cm ² is more preferable.

The ion exchange resin is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an etheric oxygen atom), and the above-mentioned polymer H or Polymer Q is more preferred, and polymer H is particularly preferred.
The ion exchange capacity of the fluorine-containing ion exchange resin is preferably 0.5 to 2.0 meq / g dry resin, particularly preferably 0.8 to 1.5 meq / g dry resin.

The gas diffusion layer of the anode and the gas diffusion layer of the cathode may be the same or different from each other in components, composition, thickness and the like.
The gas diffusion layer may be composed of only the gas diffusion member of the present invention; it may have the gas diffusion member of the present invention and a carbon substrate; and it has a carbon substrate and a carbon layer. It may be composed of only a carbon substrate.

For the reasons described above, it is preferable that at least the cathode gas diffusion layer has the gas diffusion member of the present invention.
When the gas diffusion layer has the gas diffusion member of the present invention, it is preferable that the gas diffusion member is adjacent to the catalyst layer from the viewpoint of sufficiently improving the conductivity, gas diffusion property and drainage property of the electrode.

When the gas diffusion layer does not have the gas diffusion member of the present invention, the gas diffusion layer preferably has a carbon base material and a carbon layer from the viewpoint of improving the conductivity, gas diffusibility and drainage in the anode. .
Examples of the carbon substrate include carbon paper, carbon cloth, carbon felt and the like.
The carbon layer is a layer containing a carbon material and a polymer. Examples of the carbon material include carbon particles, carbon fibers, and the like, and carbon fibers are preferable because the effect of improving the power generation performance is sufficiently exhibited. Examples of the carbon particles include carbon black.

Examples of the carbon fiber include vapor grown carbon fiber, carbon nanotube (single wall, double wall, multi-wall, cup laminated type, etc.), PAN-based carbon fiber, and pitch-based carbon fiber. Examples of the form of carbon fiber include chopped fiber and milled fiber.

The average fiber diameter of the carbon fibers is preferably 20 to 500 nm, more preferably 50 to 250 nm. If the average fiber diameter of the carbon fiber is not less than the lower limit of the above range, the carbon layer has good gas diffusibility and drainage. When the average fiber diameter of the carbon fibers is not more than the upper limit of the above range, the carbon fibers can be favorably dispersed in the dispersion medium when preparing the carbon layer forming paste described later.

Examples of the polymer include fluorine resins other than fluorine-containing ion exchange resins and fluorine-containing ion exchange resins, and fluorine-containing ion exchange resins are preferable from the viewpoint of the durability of the carbon layer and the dispersion stability of the carbon fibers. An example of the fluororesin is PTFE.

As the fluorine-containing ion exchange resin, a perfluorocarbon polymer having an ion exchange group is preferable, the above-described polymer H or polymer Q is more preferable, and polymer H is particularly preferable.
The ion exchange capacity of the fluorine-containing ion exchange resin is preferably 0.5 to 2.0 meq / g dry resin, and 0.8 to 1.5 meq / g dry resin from the viewpoint of conductivity and gas permeability. Is particularly preferred.

The polymer electrolyte membrane is a membrane containing an ion exchange resin.
The ion exchange resin is preferably a fluorine-containing ion exchange resin from the viewpoint of durability, more preferably a perfluorocarbon polymer having an ion exchange group (which may contain an etheric oxygen atom), and the above-mentioned polymer H or Polymer Q is more preferred, and polymer H is particularly preferred.
The ion exchange capacity of the fluorine-containing ion exchange resin is preferably 0.5 to 2.0 meq / g dry resin, particularly preferably 0.8 to 1.5 meq / g dry resin.

The polymer electrolyte membrane may be reinforced with a reinforcing material. Examples of the reinforcing material include porous bodies, fibers, woven fabrics, and nonwoven fabrics. The polymer electrolyte membrane may contain cerium ions or manganese ions.

The thickness of the polymer electrolyte membrane is preferably 10 to 30 μm, more preferably 15 to 25 μm. When the thickness is equal to or less than the upper limit of the above range, a decrease in power generation performance of the polymer electrolyte fuel cell under low humidification conditions can be suppressed. Moreover, gas leakage and an electrical short circuit can be suppressed by making this thickness more than the lower limit of the said range.
The thickness of the polymer electrolyte membrane is measured by observing the cross section of the polymer electrolyte membrane with a scanning electron microscope or the like.

The membrane electrode assembly 1 in FIG. 5 may have two frame-shaped subgaskets (not shown) arranged so as to sandwich the polymer electrolyte membrane 40 at the peripheral edge of the membrane electrode assembly 1.
In the membrane electrode assembly 1 of FIG. 5, for example, a catalyst layer 22 is formed on the first surface of the polymer electrolyte membrane 40, and a catalyst layer 32 is formed on the second surface to obtain a membrane catalyst layer assembly. Then, the carbon base material 26 with the carbon layer 28, the membrane catalyst layer assembly, the gas diffusion member 10, and the carbon base material 36 are stacked in this order, and are manufactured by a method of heat treating them.

In the membrane electrode assembly 1 of FIG. 6, for example, the catalyst layer 22 is formed on the first surface of the polymer electrolyte membrane 40 and the catalyst layer 32 is formed on the second surface to obtain a membrane catalyst layer assembly. Then, the carbon base material 26 with the carbon layer 28, the membrane catalyst layer assembly, and the gas diffusion member 10 are stacked in this order and manufactured by a method of heat treating them.

In the membrane electrode assembly 1 of FIG. 7, for example, the catalyst layer 22 is formed on the first surface of the polymer electrolyte membrane 40, and the catalyst layer 32 is formed on the second surface to obtain a membrane catalyst layer assembly. Then, the gas diffusion member 10, the membrane catalyst layer assembly, and the gas diffusion member 10 are stacked in this order and are manufactured by a method of heat treating them.

The polymer electrolyte membrane 40 can be formed, for example, by a method in which a liquid composition containing an ion exchange resin and a liquid medium is applied to the surface of a carrier film and dried.
The liquid medium preferably contains an organic solvent and water. Examples of the alcohols include non-fluorinated alcohols and fluorinated alcohols.

Examples of the method for forming the catalyst layer include the following methods.
A method in which a catalyst layer forming paste is applied to the surface of a carrier film, dried to form a catalyst layer, and then the catalyst layer is transferred to the surface of the polymer electrolyte membrane 40.
A method in which the catalyst layer forming paste is applied to the surface of the polymer electrolyte membrane 40 and dried.
The paste for forming a catalyst layer includes an ion exchange resin, a catalyst, and a liquid medium. The catalyst layer forming paste can be prepared, for example, by mixing a liquid composition containing an ion exchange resin and a liquid medium and a dispersion containing the catalyst and the liquid medium.

The carbon layer can be formed, for example, by a method of applying a carbon layer forming paste to the surface of the carbon substrate and drying it. The carbon layer forming paste includes a carbon material, a polymer, and a liquid medium.

In the membrane electrode assembly of the present invention described above, the gas diffusion layer of either one or both of the anode and the cathode can impart sufficient conductivity to the electrode of the membrane electrode assembly, and gas diffusion in the electrode can be performed. Since the gas diffusion member of the present invention that can improve the performance and drainage is provided, the power generation performance is excellent even in a highly humidified state.

The membrane electrode assembly of the present invention includes an anode having a catalyst layer and a gas diffusion layer, a cathode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte disposed between the anode catalyst layer and the cathode catalyst layer. It is only necessary that the gas diffusion layer of any one or both of the anode and the cathode has the gas diffusion member of the present invention, and is not limited to the membrane electrode assembly of the illustrated example.
For example, the gas diffusion layer of the anode may have the gas diffusion member of the present invention, and the gas diffusion layer of the cathode may not have the gas diffusion member of the present invention.
The gas diffusion layer may have a carbon layer between the carbon base material and the gas diffusion member of the present invention. Moreover, the manufacturing method of a membrane electrode assembly is not limited to the method mentioned above, You may manufacture a membrane electrode assembly by another method.

The membrane electrode assembly of the present invention is used for a polymer electrolyte fuel cell. A polymer electrolyte fuel cell is manufactured, for example, by forming a cell by sandwiching a membrane electrode assembly between two separators and stacking a plurality of cells. Examples of the separator include a conductive carbon plate in which a groove serving as a passage for an oxidant gas (air, oxygen, etc.) containing fuel gas or oxygen is formed.
Examples of the polymer electrolyte fuel cell include a hydrogen / oxygen fuel cell and a direct methanol fuel cell (DMFC). The methanol or methanol aqueous solution used for the DMFC fuel may be a liquid feed or a gas feed.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. Examples 1 to 3 are examples, and examples 4 to 6 are comparative examples.

(Cell voltage)
The temperature of the membrane electrode assembly in the power generation cell is maintained at 50 ° C., hydrogen (dew point: 50 ° C., utilization rate: 70%) at the anode, and air (dew point: 50 ° C., utilization rate: 50%) at the cathode , Each was pressurized to 50 kPa (absolute pressure) and supplied. Both hydrogen and air were supplied at a relative humidity of 100% RH, and the cell voltage was measured when the current density was 1.0 A / cm ² .

(Internal resistance)
The internal resistance was calculated by applying an alternating current to the cell and dividing the amplitude of the voltage generated between the terminals by the amplitude of the alternating current.

The materials used in the following examples are as follows.
Platinum catalyst 1: manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E (a catalyst in which platinum is supported on a carbon support so that 50% by mass of the total mass of the catalyst is included).
Platinum catalyst 2: manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10EA20E (a catalyst in which platinum is supported on a carbon carrier so that 20% by mass of the total mass of the catalyst is contained).
Vapor growth carbon fiber: VGCF-H (average fiber diameter: 150 nm, average fiber length: 10 to 20 μm) manufactured by Showa Denko KK
Non-woven fabric: manufactured by Japan Vilene (polypropylene, basis weight: 5 g / m ² ).
PTFE dispersion: Fluon (registered trademark of Asahi Glass Co., Ltd.) AD911E (solid content concentration: 60% by mass).

Carbon base material a: manufactured by NOK, X0086 T10X13 (without carbon layer).
Carbon substrate b: manufactured by NOK, X0086 IX92 CX320 (carbon substrate with carbon layer). The carbon layer includes carbon black and PTFE.
Carbon substrate c: X0086 IX52 CX320 (carbon substrate with carbon layer) manufactured by NOK. The carbon layer includes carbon black and PTFE.

(Carbon substrate d)
A carbon layer forming paste containing vapor grown carbon fiber, polymer H-1, ethanol and water (ethanol / water = 50/50 (mass ratio)) was prepared. In the carbon layer forming paste, the mass ratio of the ion exchange resin content to the carbon fiber content was 0.3, and the solid content concentration was 20 mass%.
A carbon layer forming paste is applied to the surface of the carbon substrate a using a die coater and dried at 80 ° C. for 10 minutes to obtain a carbon substrate d with a carbon layer having a carbon layer of 0.3 mg / cm ^2. It was.

(Polymer H)
Polymer H-1 (ion exchange capacity: 1.1 meq / g dry resin) composed of units derived from TFE and units u1-11 was prepared.

(Liquid composition)
Polymer H-1 was dispersed in a mixed solvent of ethanol and water (ethanol / water = 60/40 (mass ratio)), and cerium carbonate hydrate (Ce ₂ (CO ₃ ) ₃ · 8H ₂ O) was further added. In addition, a liquid composition having a solid content concentration of 25% by mass was prepared.

(Electrolyte membrane (1))
The liquid composition was applied to the surface of the ETFE film using a die coater, dried at 80 ° C. for 15 minutes, further heat-treated at 160 ° C. for 30 minutes, and electrolyte membrane (1) (thickness: 17 μm, cerium content: 15 A polymer electrolyte membrane with an ETFE film having a mol%) was obtained. Here, “cerium content” means the ratio (mol%) of the number of cation exchange groups substituted with cerium ions to the number of cation exchange groups contained in the polymer electrolyte membrane.

(Catalyst layer 1)
A catalyst layer forming paste 1 containing platinum catalyst 1, polymer H-1, ethanol and water (ethanol / water = 50/50 (mass ratio)) was prepared. The catalyst layer forming paste 1 had a mass ratio of the ion exchange resin content to the carbon carrier content of 0.95 and a solid content concentration of 9 mass%.
The catalyst layer forming paste 1 is applied to the surface of the ETFE film using a die coater, dried at 80 ° C. for 10 minutes, and provided with a catalyst layer (1) having a platinum amount of 0.5 mg / cm ^2. A catalyst layer was obtained.

(Example 1)
A conductive material paste 1 containing vapor-grown carbon fiber, polymer H-1, ethanol and water (ethanol / water = 40/60 (mass ratio)) was prepared. In the conductive material paste 1, the mass ratio of the ion exchange resin content to the carbon fiber content was 0.3, and the solid content concentration was 20% by mass.
The conductive material paste 1 was applied to the surface of the ETFE film using a die coater so that the carbon fiber content was 0.4 mg / cm ^2, and dried at 80 ° C. for 10 minutes to form a base part. .

Then, the nonwoven fabric was mounted on the base part. Next, the conductive material paste 1 is applied to the surface of the nonwoven fabric so that the carbon fiber content is 1.6 mg / cm ² , impregnated throughout the nonwoven fabric, dried at 80 ° C. for 10 minutes, and further 130 Heat treatment was performed at 0 ° C. for 30 minutes. A gas diffusion member 1 was obtained in which a part of the conductive material was impregnated into the nonwoven fabric, and the remaining part of the conductive material covered one side of the nonwoven fabric.
Next, the ETFE film was peeled from the gas diffusion member 1. Table 1 shows the thickness, density, and carbon fiber content (contained) of the gas diffusion member 1. Similarly, in Examples 2 and 3, the thickness, density, and amount of carbon fiber of the gas diffusion member are shown in Table 1.

Next, the polymer electrolyte membrane with an ETFE film provided with the electrolyte membrane (1) and the catalyst layer with an ETFE film provided with the catalyst layer 1 are overlapped so that the electrolyte membrane (1) and the catalyst layer (1) are in contact with each other. The laminate 1 was obtained by heat treatment at 120 ° C. and 3 MPa for 6 minutes.
In the laminate 1, an electrolyte membrane (1) obtained by peeling an ETFE film from a polymer electrolyte membrane with an ETFE film provided with the electrolyte membrane (1), and an ETFE provided with another catalyst layer (1) The catalyst layer (1) of the catalyst layer with a film was stacked so as to be in contact with each other, and heat-treated at 120 ° C. and 3 MPa for 6 minutes. Next, heat treatment was performed at 120 ° C. and 0.5 MPa for 24 minutes. The ETFE film was peeled from the catalyst layer with the ETFE film provided with the catalyst layer (1) disposed on both surfaces of the electrolyte membrane (1) to obtain a membrane-catalyst layer assembly.

The carbon base material b, the frame-shaped subgasket, the membrane catalyst layer assembly, the gas diffusion member 1, the frame-shaped subgasket, and the carbon base material a in this order, the carbon layer in the carbon base material b and the catalyst in the membrane catalyst layer assembly. In the other catalyst layer (1) and gas diffusion member (1) in the membrane-catalyst layer assembly, the conductive material paste is applied to the first surface of the nonwoven fabric so that the layer (1) is in contact with the first surface of the nonwoven fabric. There was laminated so as to be in contact and the coated formed surface so that 1.6 mg / cm ^2, these 160 ° C., and heat-treated for 2 minutes at 3 MPa, electrode area of 25 cm ² membrane electrode assembly (1 ) The membrane electrode assembly (1) was incorporated in a power generation cell so that the electrode having the gas diffusion member (1) was a cathode.
Table 1 shows the cell voltage and the internal resistance. Table 1 shows the cell voltage and the internal resistance in the following examples.

(Example 2)
A conductive material paste 2 containing vapor-grown carbon fiber, polymer H-1, PTFE, ethanol and water (ethanol / water = 50/50 (mass ratio)) was prepared using a PTFE dispersion. In the conductive material paste 2, the mass ratio of the ion exchange resin content to the carbon fiber content is 0.3, and the fluororesin content to the carbon fiber content is 0.3. The solid content concentration was 20% by mass.

A nonwoven fabric was placed on the first ETFE film.
Next, the conductive material paste 2 is applied to the surface of the nonwoven fabric so that the amount of carbon fibers is 1.2 mg / cm ² , impregnated on the top of the nonwoven fabric, dried at 80 ° C. for 10 minutes, A semi-impregnated part was formed.
Subsequently, the 2nd ETFE film was stuck to the 1st semi-impregnation part, and the 1st ETFE film was peeled from the nonwoven fabric.

Next, the conductive material paste 2 was applied to the surface of the nonwoven fabric obtained by peeling off the first ETFE film so that the amount of carbon fiber was 1.2 mg / cm ^2, and was applied to the non-impregnated portion of the nonwoven fabric. It was impregnated, dried at 80 ° C. for 10 minutes, and further heat treated at 130 ° C. for 30 minutes. A gas diffusion member (2) in which the nonwoven fabric was impregnated with the entire amount of the conductive material was obtained.
Next, the second ETFE film was peeled from the gas diffusion member (2).

A membrane electrode assembly (2) having an electrode area of 25 cm ² is obtained in the same manner as in Example 1 except that the gas diffusion member (2) of Example 2 is used instead of the gas diffusion member (1) of Example 1. It was. The membrane electrode assembly (2) was incorporated into a power generation cell so that the electrode having the gas diffusion member (2) was a cathode.

(Example 3)
The same conductive material paste 1 as in Example 1 was prepared.
After changing the amount of carbon fiber of the conductive material paste 1 applied to the surface of the nonwoven fabric placed on the first ETFE film to 0.6 mg / cm ² to form the first semi-impregnated portion, Example 2 except that the amount of carbon fiber of the conductive material paste 1 applied to the surface of the nonwoven fabric on the side where the first ETFE was peeled was changed to 2.4 mg / cm ^2. Similarly, a gas diffusion member (3) in which the nonwoven fabric was impregnated with the entire amount of the conductive material was obtained.

A membrane electrode assembly (3) having an electrode area of 25 cm ² was obtained in the same manner as in Example 1 except that the gas diffusion member (3) of Example 3 was used instead of the gas diffusion member (1) of Example 1. It was. The membrane electrode assembly (3) was incorporated in a power generation cell so that the electrode having the gas diffusion member (3) was a cathode. In addition, the membrane electrode assembly (3) has a conductive material on the surface of the catalyst layer (1) in the membrane catalyst layer assembly (1) and the nonwoven fabric on the side where the first ETFE in the gas diffusion member (3) is peeled off. The paste 1 was laminated so that the surface formed by applying the carbon fiber of the paste 1 to 2.4 mg / cm ² was in contact.

(Example 4)
A membrane catalyst layer assembly was obtained in the same manner as in Example 1.
The carbon base material b, the frame-shaped subgasket, the membrane catalyst layer assembly, the frame-shaped subgasket, and the carbon base material d in this order, the catalyst of the carbon layer and the carbon catalyst layer assembly in the carbon base material d. The layers (1) were stacked so as to be in contact with each other, and these were heat-treated at 160 ° C. and 3 MPa for 2 minutes to obtain a membrane / electrode assembly (4) having an electrode area of 25 cm ² . The membrane electrode assembly (4) was incorporated into a power generation cell so that the electrode having the carbon base material d would be a cathode.

(Example 5)
A membrane catalyst layer assembly was obtained in the same manner as in Example 1.
The carbon base material b, the carbon layer in the carbon base material c, and the catalyst layer (1) are in the order of the carbon base material b, the frame-shaped subgasket, the membrane catalyst layer assembly, the frame-shaped subgasket, and the carbon base material c. They were stacked so as to be in contact with each other, and heat-treated under conditions of 160 ° C. and 3 MPa for 2 minutes to obtain a membrane / electrode assembly (5) having an electrode area of 25 cm ² . The membrane electrode assembly (5) was incorporated into a power generation cell so that the electrode having the carbon base material b would be a cathode.

(Example 6)
A catalyst layer forming paste 2 containing platinum catalyst 2, polymer H-1, ethanol and water (ethanol / water = 50/50 (mass ratio)) was prepared. In the catalyst layer forming paste 2, the mass ratio of the content of the ion exchange resin to the content of the carbon support was 0.8, and the solid content concentration was 8% by mass.
The catalyst layer forming paste 2 is applied to the surface of the ETFE film using a die coater, dried at 80 ° C. for 10 minutes, and provided with a catalyst layer (2) having a platinum amount of 0.05 mg / cm ^2. A catalyst layer was obtained.

The liquid composition is applied to the surface of the catalyst layer (2) of the catalyst layer with the ETFE film provided with the catalyst layer (2) using a die coater, dried at 80 ° C. for 10 minutes, and further heat-treated at 160 ° C. for 30 minutes. , An ETFE film, a catalyst layer (2), and an electrolyte membrane (1) (thickness: 17 μm, cerium content: 15 mol%) were obtained in this order to obtain a laminate 2.

For formation of a catalyst layer containing platinum catalyst 1, polymer H-1, ethanol, water and 1,1,2,2,3,3,4-heptafluorocyclopentane (Zeon Corporation (registered trademark) H) Paste 3 was prepared. In the catalyst layer forming paste 3, the mass ratio of ethanol / water / Zeorolla (registered trademark) H was 46/50/4. The catalyst layer forming paste 3 had a mass ratio of the ion exchange resin content to the carbon support content of 0.95 and a solid content concentration of 10 mass%.
The catalyst layer forming paste 3 is applied to the surface of the carbon layer of the carbon base material d using a die coater, dried at 80 ° C. for 10 minutes, and a platinum layer having a platinum amount of 0.5 mg / cm ² (3) Thus, an electrode 1 was obtained.

The laminate 2 and the electrode 1 were laminated so that the electrolyte membrane (1) of the laminate 2 and the catalyst layer (3) of the electrode 1 were in contact with each other, and heat-treated at 160 ° C. and 3 MPa for 2 minutes. Next, heat treatment was performed at 160 ° C. for 30 minutes in a nitrogen gas atmosphere.

Next, the ETFE film is peeled off, and the carbon layer in the carbon base material b and the catalyst layer (2) obtained by peeling off the ETFE film are stacked so that they are in contact with each other. A membrane electrode assembly (6) having an area of 25 cm ² was obtained. The membrane electrode assembly (6) was incorporated into the power generation cell so that the electrode 1 side of the membrane electrode assembly 6 was the cathode.

Since the membrane electrode assemblies of Examples 1 to 3 had the gas diffusion member of the present invention in the gas diffusion layer, the cell voltage was relatively high even in a highly humidified state (50 ° C., 100% RH). It can be seen that the internal resistance of the membrane electrode assemblies of Examples 1 to 3 is relatively low, and the electrodes of the membrane electrode assemblies have sufficient conductivity. Further, since the cell voltage of the membrane electrode assemblies of Examples 1 to 3 is high, it can be seen that the gas diffusibility and drainage of the electrode are excellent.
In Examples 4 to 6, since the gas diffusion member of the present invention was not included in the gas diffusion layer, the cell voltage was relatively low in a highly humidified state (50 ° C., 100% RH).

The gas diffusion member of the present invention is useful as a gas diffusion layer in a membrane electrode assembly for a polymer electrolyte fuel cell.

1: membrane electrode assembly, 10: gas diffusion member, 12: porous base material, 14: conductive material, 14a: impregnation part, 14b: base part, 14c: first semi-impregnation part, 14d: second Semi-impregnated part, 20: anode, 22: catalyst layer, 24: gas diffusion layer, 26: carbon substrate, 28: carbon layer, 30: cathode, 32: catalyst layer, 34: gas diffusion layer, 36: carbon substrate 40: polymer electrolyte membrane, 100: first carrier film, 102: second carrier film.

The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2016-140605 filed on July 15, 2016 are cited here as disclosure of the specification of the present invention. Incorporate.

Claims (15)

1. A sheet-like porous base material made of a thermoplastic resin material, and a conductive material at least partially impregnated in the porous base material, wherein the conductive material contains carbon fiber and an ion exchange resin. A gas diffusion member characterized by the above.
2. The gas diffusion member according to claim 1, wherein the carbon fiber is a vapor-grown carbon fiber.
3. 3. The gas diffusion member according to claim 1, wherein the average fiber diameter of the carbon fibers is 1 to 1000 nm, and the average fiber length of the carbon fibers is 1 to 100 μm.
4. The gas diffusion member according to any one of claims 1 to 3, wherein a content of the carbon fiber is 0.1 to 10 mg per 1 cm ² of the gas diffusion member.
5. The gas diffusion member according to any one of claims 1 to 4, wherein the ion exchange capacity of the ion exchange resin is 0.5 to 2.0 meq / g dry resin.
6. The gas diffusion member according to any one of claims 1 to 5, wherein a mass ratio of the content of the ion exchange resin to the content of the carbon fiber is 0.05 to 1.5.
7. The gas diffusion member according to any one of claims 1 to 6, wherein the ion exchange resin is a polymer having a unit represented by the following formula u1.
   

   

   However, Q ¹ is a single bond or a perfluoroalkylene group which may have an etheric oxygen atom, R ^f1 is a perfluoroalkyl group which may have an etheric oxygen atom, X ¹ is an oxygen atom, a nitrogen atom or a carbon atom, a is 0 when X ¹ is an oxygen atom, ¹ when X ¹ is a nitrogen atom, and 2 when X ¹ is a carbon atom , Y ¹ is a fluorine atom or a monovalent perfluoro organic group, and s is 0 or 1.
8. The gas diffusion member according to any one of claims 1 to 6, wherein the ion exchange resin is a polymer having a unit represented by the following formula (u2).
   

   

   However, Q ²¹ is an etheric good perfluoroalkylene group which may have an oxygen atom, Q ²² is a single bond, or which may have an etheric oxygen atom perfluoroalkylene group, R ^f2 is a perfluoroalkyl group which may have an etheric oxygen atom, X ² is an oxygen atom, a nitrogen atom or a carbon atom, and b is 0 when X ² is an oxygen atom. , X ² is 1 when X ² is a nitrogen atom, ² when X ² is a carbon atom, Y ² is a fluorine atom or a monovalent perfluoro organic group, and t is 0 or 1. The single bond means that the carbon atom of CY ² and the sulfur atom of SO ₂ are directly bonded. An organic group means a group containing one or more carbon atoms.
9. The gas diffusion member according to any one of claims 1 to 8, wherein the conductive material further includes a fluororesin other than the ion exchange resin.
10. The gas diffusion member according to any one of claims 1 to 9, wherein the porous substrate is a nonwoven fabric.
11. The gas diffusion member according to any one of claims 1 to 10, wherein the porous substrate is made of an olefin resin or a fluororesin.
12. The gas diffusion member according to claim 10, wherein the basis weight of the nonwoven fabric is 1 to 10 g / m ² .
13. The gas diffusion member according to any one of claims 1 to 12, wherein the thermoplastic resin material contains an olefin resin or a fluororesin.
14. The gas diffusion member according to any one of claims 1 to 13, wherein the gas diffusion member has a thickness of 10 to 300 µm.
15. An anode having a catalyst layer and a gas diffusion layer, a cathode having a catalyst layer and a gas diffusion layer, and a polymer electrolyte membrane disposed between the catalyst layer of the anode and the catalyst layer of the cathode,
    A membrane electrode assembly for a polymer electrolyte fuel cell, wherein the gas diffusion layer of either one or both of the anode and the cathode has the gas diffusion member according to any one of claims 1 to 14.

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