JP2009021235A - Membrane-electrode-gas diffusion layer assembly and fuel cell having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode-gas diffusion layer assembly in which a hydrocarbon-based high polymer electrolyte is used for an electrolyte membrane and a catalyst layer, and a fuel cell capable of obtaining sufficient power generation performance in spite of a low humidity state can be formed. <P>SOLUTION: The membrane-electrode-gas diffusion layer assembly comprises: an electrolyte membrane formed by the hydrocarbon-based high polymer electrolyte; the catalyst layer arranged at least one side of the electrolyte membrane and including a catalyst material and the hydrocarbon-based high polymer electrolyte; and a gas diffusion layer arranged on the other side of the catalyst layer against the electrolyte membrane. A porous layer having a porous structure exists between the catalyst layer and the gas diffusion layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane-electrode-gas diffusion layer assembly and a fuel cell including the same.

  Fuel cells, in particular polymer electrolyte fuel cells using a solid polymer electrolyte as an electrolyte, are expected to be applied to automobiles and the like as an energy source with a low environmental load because the only substance discharged is water. . In general, a polymer electrolyte fuel cell is a membrane-electrode-gas diffusion layer assembly in which a catalyst layer functioning as an electrode and a gas diffusion layer are sequentially arranged on both sides of an electrolyte membrane made of a polymer electrolyte having ion conductivity. (Hereinafter abbreviated as “MEGA”).

  Conventionally, a polymer electrolyte membrane made of a fluorine-based polymer electrolyte (for example, Nafion (registered trademark, manufactured by DuPont)) is often used. In general, the catalyst layer provided adjacent to the polymer electrolyte membrane also contains a polymer electrolyte in order to impart proton conductivity. As the polymer electrolyte to be contained in the catalyst layer, the above-described fluorine-based polymer electrolyte has been mainstream.

On the other hand, in recent years, it has been attempted to apply a cheaper hydrocarbon polymer electrolyte instead of the fluorine polymer electrolyte. An electrolyte membrane made of a hydrocarbon-based polymer electrolyte is characterized by being cheaper than a fluorine-based membrane and excellent in heat resistance. Conventionally, when a fluorine polymer electrolyte is included in the catalyst layer, the fluorine polymer electrolyte in the catalyst layer is decomposed by long-time driving of the fuel cell, which may generate fluorine ions. However, in order to avoid such a problem, it has been studied to apply a hydrocarbon-based polymer electrolyte to the catalyst layer (see, for example, Patent Document 1).
Japanese Patent No. 3689322

  By the way, the fuel cell as described above is generally operated with humidification in order to obtain sufficient ion conductivity by the polymer electrolyte. However, in recent years, for the purpose of simplifying the power generation system, it is desired that the fuel cell can sufficiently operate even in a low humidified state. When the fuel cell is operated in a low humidified state, the ionic conductivity of the polymer electrolyte is usually decreased. However, in the case of the above-described hydrocarbon polymer electrolyte, such a decrease in ionic conductivity is particularly remarkable. There was a trend. Therefore, a fuel cell including MEGA using a hydrocarbon-based polymer electrolyte as an electrolyte membrane or a catalyst layer cannot exhibit sufficient power generation performance in a low humidified state, and is a fuel applied to a simplified power generation system. It was not very suitable as a battery.

  Therefore, the present invention has been made in view of such circumstances, and sufficient power generation performance can be obtained even when a hydrocarbon polymer electrolyte is used for the electrolyte membrane and the catalyst layer and the humidity is reduced. An object of the present invention is to provide a membrane-electrode-gas diffusion layer assembly capable of forming a fuel cell.

  In order to achieve the above object, a membrane-electrode-gas diffusion layer assembly (MEGA) of the present invention is disposed on an electrolyte membrane composed of a hydrocarbon-based polymer electrolyte and at least one side of the electrolyte membrane. A catalyst layer containing a substance and a hydrocarbon-based polymer electrolyte, a gas diffusion layer disposed on the opposite side of the catalyst layer with respect to the electrolyte membrane, and disposed between the catalyst layer and the gas diffusion layer to form a porous structure. It has the porous layer which has.

  According to the MEGA of the present invention having the above-described configuration, a fuel cell having high power generation performance can be obtained even in a low humidified state despite having an electrolyte membrane containing a hydrocarbon polymer and a catalyst layer. . Although the reason for this is not clear, the porous layer is arranged between the catalyst layer and the gas diffusion layer, so that the water absorption amount to the electrolyte membrane and the catalyst layer can be sufficiently secured. This is probably because both the electrolyte membrane and the catalyst layer in MEGA have excellent proton conductivity even in a low humidified state.

  In the MEGA of the present invention, the average pore diameter of the pores of the porous layer is preferably 10 nm to 10 μm. It is considered that the porous layer having such an average pore diameter can further advantageously supply water to the electrolyte membrane and the catalyst layer. Therefore, by having such a porous layer, proton conductivity in a low humidified state can be obtained better. From the viewpoint of obtaining such an effect even better, the average pore diameter of the pores of the porous layer is more preferably 20 nm to 300 nm.

  Further, it is preferable that at least the hydrocarbon-based polymer electrolyte constituting the electrolyte membrane is made of a block copolymer. A hydrocarbon-based polymer electrolyte made of a block copolymer can exhibit good proton conductivity by itself and is effective as an electrolyte material for MEGA used in a low humidified state.

  Furthermore, the catalyst layer includes at least one solvent selected from water and a hydrophilic solvent, a catalyst material, and a hydrocarbon polymer electrolyte, and at least a part of the hydrocarbon polymer electrolyte is a solvent. A layer formed from a catalyst ink contained in a dispersed state is preferable. Such a catalyst layer has a structure in which a catalyst material and a hydrocarbon-based polymer electrolyte are uniformly dispersed in the layer, and the catalyst material is less deteriorated by the polymer electrolyte during the production process, and the fuel cell electrode As a result, high conductivity and proton conductivity can be exhibited.

  The present invention also provides a fuel cell comprising the MEGA of the present invention. Since such a fuel cell includes the MEGA of the present invention, it can exhibit excellent power generation characteristics even in a low humidified state even though the electrolyte membrane and the catalyst layer contain a hydrocarbon polymer electrolyte. Therefore, the fuel cell of the present invention is low in production cost, has excellent heat resistance, and can operate well even in a low humidified state.

  According to the present invention, a membrane-electrode-gas diffusion layer junction capable of forming a fuel cell in which a hydrocarbon polymer electrolyte is used for the electrolyte membrane and the catalyst layer and sufficient power generation performance can be obtained even in a low humidified state. The body can be provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as necessary.

[Fuel cell]
FIG. 1 is a diagram schematically showing a cross-sectional configuration of a fuel cell according to a preferred embodiment. As illustrated, the fuel cell 10 includes catalyst layers 14a and 14b, porous layers 15a and 15b, gas diffusion layers 16a and 16b, and a separator 18a on both sides of an electrolyte membrane 12 made of a polymer electrolyte. , 18b are formed in order. In the fuel cell 10, a membrane-electrode assembly (hereinafter abbreviated as “MEA”) 20 is composed of an electrolyte membrane 12 and a pair of catalyst layers 14 a and 14 b sandwiching the electrolyte membrane 12.

(Electrolyte membrane)
The electrolyte membrane 12 is a membrane in which a hydrocarbon polymer electrolyte is formed. The hydrocarbon-based polymer electrolyte has a structure including a main chain mainly composed of hydrocarbons and an ion exchange group substituted on the main chain or a side chain bonded to the main chain. This hydrocarbon polymer electrolyte corresponds to, for example, a structure in which the content ratio of halogen atoms such as fluorine atoms in the structure is 15% by weight or less.

The ion exchange group possessed by the hydrocarbon-based polymer electrolyte is not particularly limited, such as an acidic group or a basic group, but is preferably an acidic group from the viewpoint of obtaining good proton conductivity. Examples of acidic groups include sulfonic acid groups (—SO ₃ H), carboxyl groups (—COOH), phosphonic acid groups (—PO ₃ H ₂ ), phosphoric acid groups (—OPO ₃ H ₂ ), sulfonylamide groups (—SO ₃ ). ₂ NHSO _2- ), phenolic hydroxyl group and the like. Of these, a sulfonic acid group or a phosphonic acid group is preferable, and a sulfonic acid group is particularly preferable.

  Examples of the hydrocarbon-based polymer electrolyte having the above-described configuration include those having the following structure. That is, first, (A) a polymer electrolyte in which a sulfonic acid group and / or a phosphonic acid group are introduced into a hydrocarbon polymer whose main chain is composed of an aliphatic hydrocarbon, and (B) the main chain has an aromatic ring. Examples thereof include a polymer electrolyte in which a sulfonic acid group and / or a phosphonic acid group is introduced into the polymer.

  Further, (C) a polymer electrolyte in which a sulfonic acid group and / or a phosphonic acid group is introduced into a polymer having a main chain containing an inorganic unit structure such as a siloxane group or a phosphazene group, or (D) (A) to ( Examples thereof include a polymer electrolyte in which a sulfonic acid group and / or a phosphonic acid group is introduced into a copolymer obtained by combining two or more repeating units constituting the main chain of the polymer electrolyte of C). Further, (E) a polymer electrolyte in which an acidic compound such as sulfuric acid or phosphoric acid is introduced into a hydrocarbon polymer containing a nitrogen atom in the main chain or side chain by ionic bonding can be exemplified.

  More specifically, examples of the polymer electrolyte (A) include polyvinyl sulfonic acid, polystyrene sulfonic acid, poly (α-methylstyrene) sulfonic acid, and the like. The polymer electrolyte (B) may contain a hetero atom such as an oxygen atom in the main chain. Examples of such a polymer electrolyte include polyether ether ketone, polysulfone, polyether sulfone, poly (arylene ether), polyimide, poly ((4-phenoxybenzoyl) -1,4-phenylene), polyphenylene sulfide, poly Examples thereof include those in which a sulfonic acid group is introduced into each of homopolymers such as phenylquinoxalen. Specifically, sulfoarylated polybenzimidazole, sulfoalkylated polybenzimidazole, phosphoalkylated polybenzimidazole (for example, see JP-A-9-110882), phosphonated poly (phenylene ether) (for example, J. Org. Appl.Polym.Sci., 18, 1969 (1974)).

  Examples of the polymer electrolyte (C) include those obtained by introducing a sulfonic acid group into polyphosphazene, polysiloxane having a phosphonic acid group, and the like. These can be found in Polymer Prep. , 41, no. It can be easily produced according to 1,70 (2000).

  The polymer electrolyte of the above (D) is one in which a sulfonic acid group and / or phosphonic acid group is introduced into a random copolymer, one in which a sulfonic acid group and / or phosphonic acid group is introduced into an alternating copolymer, Any of sulfonic acid groups and / or phosphonic acid groups introduced into the block copolymer may be used. For example, the sulfonic acid group introduced into the random copolymer includes a sulfonated polyethersulfone polymer as described in JP-A-11-116679. Moreover, as what introduce | transduced the sulfonic acid group and / or the phosphonic acid group into the block copolymer, what has the block containing a sulfonic acid group as described in Unexamined-Japanese-Patent No. 2001-250567 is mentioned.

  Examples of the polymer electrolyte (E) include polybenzimidazole containing phosphoric acid as described in JP-T-11-503262.

  These polymer electrolytes may have halogen atoms such as fluorine in the main chain or side chain. However, since they are hydrocarbon polymer electrolytes, the content of halogen atoms as described above is generally increased. Satisfies.

  From the viewpoint of heat resistance and ease of recycling, the hydrocarbon polymer electrolyte is preferably an aromatic polymer electrolyte. An aromatic polymer electrolyte is a polymer compound having an aromatic ring in the main chain and a structure containing an acidic group in the molecule. As this aromatic polymer electrolyte, those soluble in a solvent are suitable. These can easily form a polymer electrolyte membrane having a desired film thickness by a known solution casting method. The acidic group of the aromatic polyelectrolyte may be directly substituted on the aromatic ring constituting the main chain, and is bonded to the aromatic ring constituting the main chain via a predetermined linking group. You may have them in combination.

  Here, the “polymer having an aromatic ring in the main chain” means, for example, polyarylene linked divalent aromatic groups to form a main chain, or a divalent aromatic A group is linked via another divalent group to form a main chain. In the latter case, the divalent group for bonding the aromatic group includes an oxy group (—O—), a thioxy group (—S—), a carbonyl group, a sulfinyl group, a sulfonyl group, an amide group (—NH—CO—). Or -CO-NH-), ester group (-O-CO- or -CO-O-), carbonate group (-O-CO-O-), alkylene group having about 1 to 4 carbon atoms, carbon number 1 And a fluorine-substituted alkylene group having about ˜4, an alkenylene group having about 2 to 4 carbon atoms, and an alkynylene group having about 2 to 4 carbon atoms. Especially, as a bivalent group which connects an aromatic group, an oxy group (-O-) and a sulfonyl group are preferable.

  Divalent aromatic groups contained in the main chain include hydrocarbon aromatic groups such as phenylene group, naphthalene group, atracenylene group, fluorenediyl group, pyridinediyl group, frangyl group, thiophenediyl group, imidazolyl group. And aromatic heterocyclic groups such as indolediyl group and quinoxalinediyl group. Further, the divalent aromatic group may have a substituent other than the above acidic group. Examples of the substituent include an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a nitro group, and a halogen atom. It is done. The aromatic ring and the divalent group connecting them may have a halogen atom as a substituent. In that case, the content of the halogen atom needs to be 15% by weight or less.

  Among the hydrocarbon polymer electrolytes constituting the electrolyte membrane 12, among the above, the polymer electrolytes (B) and (D) described above are from the viewpoint of obtaining high power generation performance and excellent durability. Preferably, the polymer electrolyte of (D), which is made of a block copolymer, is more preferable.

  A hydrocarbon-based polymer electrolyte comprising such a block copolymer is more suitable as a polymer electrolyte membrane, having a phase separated structure having both a domain having an acidic group and a domain having substantially no ion exchange group. It is easy to obtain a microphase-separated structure. In this microphase-separated structure, the former domain contributes to proton conductivity, while the latter domain contributes to mechanical strength. The microphase-separated structure referred to here is, for example, a fine structure in which the density of blocks having acidic groups is higher than the density of blocks having substantially no ion exchange groups when observed with a transmission electron microscope (TEM). A phase (microdomain) and a fine phase (microdomain) in which the density of blocks having substantially no ion exchange groups is higher than the density of blocks having acidic groups are mixed, and domains of each microdomain structure A structure having a width (constant period) of several nm to several hundred nm. As the hydrocarbon polymer electrolyte, those capable of forming a film having a microdomain structure having a domain width of 5 nm to 100 nm are preferable. In particular, in the case of an electrolyte membrane made of an aromatic polymer electrolyte, one that can form a membrane having such a microdomain structure is preferable.

  The block copolymer forms a microphase-separated structure well because microscopic phase separation on the order of molecular chain size is likely to occur due to chemical bonds between different polymer blocks. can do. The block copolymer here includes a linear polymer composed of a plurality of blocks and a graft copolymer having some blocks as branched chains. As a block copolymer, the block copolymer which has the form of the linear polymer mentioned above is suitable.

  Here, in the block copolymer, the “block having an acidic group” is a block in which 0.5 or more acidic groups are contained on an average per repeating unit constituting the block. And more preferably an average of 1.0 or more blocks per repeating unit. On the other hand, the “block having substantially no ion-exchange group” means a block having an average of less than 0.5 ion-exchange groups per one repeating unit constituting the block, and one repeating unit. It is more preferable that the average is 0.1 or less per unit, and it is further preferable that the average is 0.05 or less.

  Examples of block copolymers suitable for the electrolyte membrane 12 include, for example, an aromatic polyether structure described in JP-A-2005-126684 and JP-A-2005-139432, and an ion-exchange group. Examples thereof include a block copolymer composed of a block and a block having substantially no ion exchange group. In particular, a block copolymer having a polyarylene block having an acidic group (see International Publication No. 2006/95919 pamphlet by the present applicant) can form an electrolyte membrane that achieves ion conductivity and water resistance at a high level. preferable.

  The molecular weight of the hydrocarbon-based polymer electrolyte constituting the electrolyte membrane 12 is preferably set in an optimum range according to the structure, but for example, a number average in terms of polystyrene by GPC (gel permeation chromatography) method. The molecular weight is preferably 1,000 to 1,000,000. The lower limit of the number average molecular weight is more preferably 5000 or more, and still more preferably 10,000 or more. On the other hand, the upper limit is more preferably 500,000 or less, still more preferably 300,000 or less.

  Furthermore, the electrolyte membrane 12 may contain other components in addition to the above-described hydrocarbon polymer electrolyte in a range that does not significantly reduce proton conductivity according to desired characteristics. Examples of such other components include additives such as plasticizers, stabilizers, mold release agents, and water retention agents that are added to ordinary polymers.

In particular, the electrolyte membrane 12 preferably contains a stabilizer capable of imparting radical resistance. During the operation of the fuel cell 10, the peroxide generated in the catalyst layers 14 a and 14 b changes into radical species while diffusing into the electrolyte membrane 12, and this is a hydrocarbon polymer constituting the electrolyte membrane 12. It may degrade the electrolyte. Such an inconvenience can be avoided by including a stabilizer capable of suppressing such deterioration in the electrolyte membrane 12. As a suitable stabilizer, for example, aromatic phosphonic acids represented by the following general formula (2) as disclosed in Japanese Patent Application Laid-Open No. 2003-282096 by the present applicant are suitable.

In the formula (1a), Z represents SO ₂ or CO, x and y represent the polymerization ratio of the structural units in parentheses, and x + y = 1, each in the range of 0.01 to 0.99. Ar ¹¹ represents a C 4-18 divalent aromatic group which may contain a hetero element, and this aromatic group may have a substituent. R ¹¹ and R ¹² each independently represent a hydrogen atom or an alkyl group. z represents the average substitution number of substituents in parentheses to the aromatic group represented by Ar ^11, which is 8 or less positive integer.

［式中、Ｘ^１１はハロゲン原子を示し、Ａｒ^１２は、ヘテロ原子を含んでいてもよい炭素数４〜１８の２価の芳香族基を示す。ｙ^２はＡｒ^１２を含む高分子部分の繰り返し単位当たりのＸ^１１の置換数を示し、８以下の正の数である。］ The mode of copolymerization of the aromatic phosphonic acids represented by the general formula (1a) is not particularly limited and may be any of random copolymerization, alternating copolymerization, and block copolymerization, but from the viewpoint of ease of production Is preferably random copolymerization or alternating copolymerization. The group represented by P (O) (OR ¹¹ ) (OR ¹² ) in formula (1a) is preferably a phosphonic acid group in which R ¹¹ and R ¹² are both hydrogen atoms. Moreover, the ratio of x in Formula (1a) is preferably 0.60 to 0.90, and more preferably 0.70 to 0.90. In addition, the aromatic phosphonic acids may further contain a structural unit represented by the following general formula (1b) in addition to the structural unit represented by the general formula (1a).

[Wherein, X ¹¹ represents a halogen atom, and Ar ¹² represents a C 4-18 divalent aromatic group that may contain a hetero atom. y ² represents the number of substitutions of X ¹¹ per repeating unit of the polymer portion containing Ar ¹² and is a positive number of 8 or less. ]

  The electrolyte membrane 12 does not necessarily have a single-layer structure as described above. For the purpose of improving the mechanical strength, the hydrocarbon polymer electrolyte and a predetermined support are combined. A composite membrane can also be used. Examples of the support include substrates such as a fibril shape and a porous membrane shape.

(Catalyst layer)
The catalyst layers 14a and 14b adjacent to the electrolyte membrane 12 are layers that substantially function as electrode layers in the fuel cell. One of these is the anode electrode layer, and the other is the cathode electrode layer. The catalyst layers 14a and 14b contain a catalyst substance that substantially functions as a catalyst and a polymer electrolyte, preferably a hydrocarbon polymer electrolyte. More specifically, the catalyst substance is a hydrocarbon polymer electrolyte. It has the structure bound by.

  As a catalyst substance, the component used as a catalyst in the catalyst layer of a fuel cell can be applied. For example, platinum, platinum-ruthenium alloy, platinum-cobalt alloy, complex-based electrocatalyst (for example, edited by Fuel Cell Material Research Society of Polymer Society, “Fuel Cell and Polymer”, pages 103-112, Kyoritsu Shuppan, 2005 11 And the like described in “Monthly issue”). Further, as the catalyst material, a catalyst carrier in which a catalyst material such as the above material is supported on the surface of a predetermined conductive material is also preferable in order to facilitate the transport of electrons in the catalyst layer. Examples of the conductive material in the catalyst carrier include conductive carbon materials such as carbon black and carbon nanotubes, and ceramic materials such as titanium oxide.

  The hydrocarbon polymer electrolyte contained in the catalyst layers 14a and 14b facilitates the exchange of ions between the electrolyte membrane 12 and the catalyst material, and also functions as a binder for fixing the catalyst materials together. As the hydrocarbon polymer electrolyte of the catalyst layers 14a and 14b, the same hydrocarbon polymer electrolyte as the electrolyte membrane 12 described above can be applied. The hydrocarbon polymer electrolyte in the electrolyte membrane 12 and the hydrocarbon polymer electrolyte in the catalyst layers 14a and 14b may be the same or different. Further, the catalyst layer 14a and the catalyst layer 14b may contain different hydrocarbon polymer electrolytes.

  The content of the hydrocarbon-based polymer electrolyte in the catalyst layers 14a and 14b is preferably selected as appropriate within the range in which the above-described functions are satisfactorily exhibited. For example, when the catalyst material forms the above-described support, the content of the hydrocarbon-based polymer electrolyte is preferably 0.05 to 1.4 in terms of mass ratio to the support, and 0.10 to 1 .2 and more preferably 0.15 to 1.0.

  The catalyst layers 14a and 14b may contain other components in addition to the catalyst material and the hydrocarbon-based polymer electrolyte for the purpose of enhancing the function of the layers. Examples of other components include water repellents such as PTFE from the viewpoint of enhancing water repellency, and pore formers such as calcium carbonate from the viewpoint of enhancing gas diffusibility, thereby enhancing the durability of MEA 20. From the viewpoint, stabilizers such as metal oxides can be mentioned.

(Porous layer)
The porous layers 15a and 15b are layers that are disposed between the catalyst layers 14a and 14b and the gas diffusion layers 16a and 16b and have a porous structure in which a large number of minute holes are formed. The average pore diameter of the pores of the porous layers 15a and 15b is preferably 10 nm to 10 μm, more preferably 15 nm to 1 μm, and further preferably 20 nm to 300 nm. Here, the average pore diameter is a value obtained by measuring pore distribution using a mercury intrusion method.

  The porosity of the porous layers 15a and 15b is preferably 10% to 90%. The porosity is a ratio of the total volume of pores in a predetermined unit volume of the porous layers 15a and 15b, and can be obtained from the cumulative pore volume obtained by the mercury intrusion method described above.

  When the average pore diameter of the porous layers 15a and 15b is less than 10 nm or the porosity is less than 10%, the diffusibility of the reaction gas in the layers deteriorates, and it is difficult to generate sufficient power generation in the fuel cell 10. There is a risk of becoming. On the other hand, if the average pore diameter exceeds 10 μm or the porosity exceeds 90%, water is not sufficiently supplied to the electrolyte membrane 12 and the catalyst layers 14a and 14b in a low humidified state, and the power generation characteristics of the fuel cell 10 are deteriorated. There is a case.

  The porous layers 15a and 15b are preferably formed of a conductive material in order to sufficiently maintain the conductivity between the catalyst layers 14a and 14b and the gas diffusion layers 16a and 16b. In addition, the porous layers 15a and 15b have water repellency so that the porous layers 15a and 15b themselves do not hold too much water from the viewpoint of enhancing the water supply effect to the electrolyte membrane 12 and the catalyst layers 14a and 14b. It is preferable. Specifically, the contact angle with water on the surface when the layer is formed is preferably 90 degrees or more, more preferably 100 degrees or more, still more preferably 110 degrees or more, and 120 degrees or more. Particularly preferred. This contact angle is measured by a liquid-appropriate method under conditions of 23 ° C. and 50% relative humidity after the porous layers 15a and 15b are formed on the gas diffusion layers 16a and 16b and the like in the manufacturing process described later. You can ask for it.

  From the viewpoint of obtaining good conductivity and water repellency as described above, the porous layers 15a and 15b are made of a conductive material (hereinafter referred to as “conductive material”) and a water repellent material (hereinafter referred to as “water repellent material”). ) In combination. Examples of the conductive material include carbon particles such as Vulcan (US Cabot Corporation, registered trademark), ketjen black, and acetylene black, carbon fibers, and inorganic materials such as titanium oxide. Of these, carbon particles and carbon fibers are preferred because of good processability. Examples of the water repellent material include fluorine resins such as polytetrafluoroethylene and silicone water repellent materials. The porous layers 15a and 15b may contain materials other than the conductive material and the water repellent material as long as the effects of the present invention are not hindered.

  The thickness of the porous layers 15a and 15b is preferably 1 to 200 μm, and more preferably 10 to 180 μm. By having such a thickness, the effect of supplying water to the electrolyte membrane 12 and the catalyst layers 14a and 14b tends to be obtained particularly well.

(Gas diffusion layer)
The gas diffusion layers 16a and 16b are provided so as to sandwich the MEA 20, and promote the diffusion of the source gas into the catalyst layers 14a and 14b and the like. The gas diffusion layers 16a and 16b are preferably made of a porous material having electron conductivity. The gas diffusion layers 16a and 16b are more preferably self-supporting because the porous layers 15a and 15b are often formed thereon. For example, a porous carbon non-woven fabric or carbon paper is preferable because the raw material gas can be efficiently transported to the catalyst layers 14a and 14b. In the fuel cell 10, a membrane-electrode-gas diffusion layer assembly (MEGA) is configured by the electrolyte membrane 12, the catalyst layers 14a and 14b, the porous layers 15a and 15b, and the gas diffusion layers 16a and 16b.

(Separator)
Separator 18a, 18b is formed with the material which has electronic conductivity, As this material, carbon, resin mold carbon, titanium, stainless steel etc. are mentioned, for example. Although not shown, the separators 18a and 18b are preferably provided with a groove serving as a flow path for fuel gas or the like on the catalyst layers 14a and 14b side.

  Although the preferred configuration of the fuel cell 1 has been described above, the fuel cell 10 may be, for example, a configuration in which the above-described configuration is sealed with a gas seal body or the like (not shown). Furthermore, a plurality of the fuel cells 10 having the above structure can be connected in series to be put to practical use as a fuel cell stack. The fuel cell having these configurations can operate as a solid polymer fuel cell when the fuel is hydrogen, and as a direct methanol fuel cell when the fuel is an aqueous methanol solution.

[Fuel Cell Manufacturing Method]
Next, a preferred example of a method for manufacturing the fuel cell 10 having the above-described configuration will be described.

  As a manufacturing method of the fuel cell 10, there is a method of preparing the electrolyte membrane 12 and sequentially forming each layer on the surface thereof. That is, first, catalyst layers 14 a and 14 b are formed on both surfaces of the electrolyte layer 12. Thereby, MEA 20 in which the catalyst layers 14a and 14b are formed on both sides of the electrolyte membrane 12 is obtained.

  The catalyst layers 14a and 14b can be formed by preparing catalyst ink, applying it directly to the electrolyte membrane 12, and then drying it. Examples of the method for applying the catalyst ink include known coating methods such as die coater, screen printing, spray method, and ink jet.

  The catalyst ink includes at least one solvent selected from water and a hydrophilic solvent, a catalyst substance, and a hydrocarbon polymer electrolyte, and at least a part of the hydrocarbon polymer electrolyte is the above solvent. Those contained in a dispersed state are preferred.

  For such a catalyst ink, for example, a step of preparing a solution in which a hydrocarbon polymer electrolyte is dissolved in an organic solvent (solution preparation step), and the organic solvent used in the solution is selected from water and a hydrophilic solvent. An emulsion in which at least a part of a hydrocarbon polymer electrolyte is dispersed in a solvent selected from water and a hydrophilic solvent by substituting a solvent that is hardly soluble or insoluble in a hydrocarbon polymer electrolyte ( A step of obtaining a dispersion) (solvent replacement step), a step of adding a catalyst substance to this emulsion (catalyst addition step), and a step of removing the organic solvent used in the preparation step as necessary (solvent removal step). It can manufacture suitably by performing.

  In the catalyst ink production method, an emulsion containing a hydrocarbon polymer electrolyte is obtained by dispersing the hydrocarbon polymer electrolyte in a solvent that does not dissolve the polymer electrolyte (a solvent selected from water and a hydrophilic solvent). You can also. Here, examples of the hydrophilic solvent include alcohol solvents such as methanol and ethanol. Among these, water or a mixed solvent of water and an alcohol solvent is preferable as the solvent used in the catalyst ink from the viewpoint of reducing the burden on the environment.

  In addition, in the above catalyst addition step, for example, an emulsion containing a hydrocarbon-based polymer electrolyte is added to a dispersion in which a catalyst substance is dispersed in a solvent, and then this is added to an ultrasonic dispersion device, a homogenizer, a ball mill, a planetary planet. It can be performed by mixing with a ball mill, a sand mill or the like.

  Furthermore, the catalyst ink obtained after the catalyst addition step may be further diluted with a solvent selected from water and a hydrophilic solvent, if necessary, and is used in the solution preparation step by concentrating with an evaporator. The organic solvent may be removed, and membrane treatment using a dialysis membrane may be performed. According to the catalyst ink preparation method described above, it is possible to prepare a catalyst ink with good dispersibility of the hydrocarbon-based polymer electrolyte.

  After the formation of the catalyst layers 14a and 14b, the porous layers 15a and 15b are subsequently formed outside the catalyst layers 14a and 14b. The porous layers 15a and 15b are, for example, a dispersion liquid (hereinafter referred to as “a porous material”) in which a constituent material (conductive material or water repellent material) of the porous layer described above is dissolved or dispersed in a solvent such as water or a hydrophilic solvent. It is formed by preparing a porous layer ink) and applying it to the surfaces of the catalyst layers 14a and 14b, followed by drying to remove the solvent. As the solvent used in the ink for the porous layer, alcohol, particularly lower alcohol is preferable. As a method for applying the ink for the porous layer, a known application method such as a die coater, screen printing, a spray method, and an ink jet can be applied as in the case of the catalyst ink described above.

  When forming the porous layers 15a and 15b, it is preferable to appropriately change the type of the solvent used in the ink for the porous layer, the evaporation rate of the solvent, the concentration of the constituent material of the porous layer in the dispersion, and the like. . By adjusting these conditions, it is possible to form the porous layers 15a and 15b having the preferable average pore diameter and porosity as described above.

  In the manufacture of the fuel cell 10, the gas diffusion layers 16a and 16b are then formed by disposing a carbon non-woven fabric, carbon paper or the like outside the porous layers 15a and 15b. Thereby, MEGA in which the catalyst layers 14a and 14b, the porous layers 15a and 15b, and the gas diffusion layers 16a and 16b are sequentially arranged on both sides of the electrolyte membrane 12 is obtained.

  Thereafter, the separators 18a and 18b are disposed so as to be sandwiched from both sides of the MEGA. And the fuel cell 10 which has the structure mentioned above can be obtained by pressing the whole laminated body obtained in this way in the laminating direction and bringing the layers into close contact with each other.

  In the production of the fuel cell 10, the catalyst layers 14a and 14b and the porous layers 15a and 15b have a predetermined support in addition to the method of directly applying the catalyst ink or the porous layer ink as described above. It can also be formed by separately forming a film in which these layers are formed on a substrate and transferring each layer using this film.

  For example, the catalyst layers 14 a and 14 b are prepared by applying a catalyst ink on a predetermined support substrate and then drying it to prepare a film on which the catalyst layer is formed, and transferring the catalyst layer in this film to the electrolyte membrane 12. It can be formed by peeling the support substrate. Here, as a support base material, what can peel easily after transfer of a catalyst layer is preferable, for example, a poly (tetrafluoroethylene) film, a polyimide film, etc. are mentioned. The transfer of the catalyst layer can be performed by pressing the film after the film is stacked so that the catalyst layer is in contact with the electrolyte membrane 12.

  Similarly, the porous layers 15a and 15b can be formed by using a film in which a porous layer is formed on a predetermined support substrate and transferring the porous layer in the film to the catalyst layers 14a and 14b. In this case, the porous layer in the film can be formed by applying the porous layer ink as described above on the supporting substrate and then drying it.

  Furthermore, as a film, you may use what formed both the porous layer and the catalyst layer on the support base material. If such a film is used, both the catalyst layers 14 a and 14 b and the porous layers 15 a and 15 b can be transferred to the electrolyte membrane 12 at a time.

  In this case, carbon non-woven fabric or carbon paper for forming the gas diffusion layers 16a and 16b may be used instead of the support base material. If such a film is used, the catalyst layer, the porous layer, and the gas diffusion layer can be collectively formed on the electrolyte membrane 12, and the above-described MEGA can be easily obtained.

  The catalyst layers 14a and 14b, the porous layers 15a and 15b, and the gas diffusion layers 16a and 16b can be formed by appropriately combining the above methods. That is, for example, after the catalyst layers 14a and 14b are formed by directly applying the catalyst ink to the electrolyte membrane 12, the porous layers 15a and 15b may be formed by a method using the above-described film. Further, after the catalyst layers 14a and 14b are formed by directly applying the catalyst ink to the electrolyte membrane 12, a film in which a porous layer is formed on the gas diffusion layer is used, and the porous layers 15a and 15b and the gas diffusion layer 16a are used. 16b may be formed together. These are preferably selected as appropriate according to the material of each layer and desired properties.

  The preferred embodiments of the MEGA and the fuel cell of the present invention have been described above. However, the present invention is not necessarily limited to these embodiments, and may be changed as appropriate without departing from the spirit of the present invention. That is, the fuel cell of the present invention is not limited to the above-described fuel cell 10 having each layer, and may include other layers, or may have some layers as long as the essential configuration is provided. It does not have to be. For example, in the fuel cell 10, the porous layers 15 a and 15 b are formed on both sides of the electrolyte membrane 12, but may be formed only on either one side. If the porous layer is formed on at least one side, the effect of improving ion conductivity in a low humidified state can be sufficiently obtained. In this case, it is more preferable to install the porous layer on the cathode side than on the anode side because the effects of the present invention tend to be obtained well.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

  First, a method for measuring the molecular weight (weight average molecular weight, number average molecular weight) of the polymers produced in the following Examples and Comparative Examples and a method for measuring the ion exchange capacity (IEC) of the polymer electrolyte will be described.

(Measurement of molecular weight)
The weight average molecular weight of the polymer to be measured was calculated by performing gel permeation chromatography (GPC) measurement under the following conditions and converting the result into polystyrene. The GPC conditions were as shown below.
・ Column: TOS gel GMHHHR-M1 made by TOSOH ・ Column temperature: 40 ° C.
Mobile phase solvent: N, N-dimethylformamide (LiBr added to 10 mmol / dm ³ )
・ Solvent flow rate: 0.5 mL / min

(Ion exchange capacity)
First, the polymer electrolyte to be measured was dissolved in dimethyl sulfoxide (DMSO) to a concentration of about 10 to 30% by weight to prepare a polymer electrolyte solution. This polymer electrolyte solution was spread on a glass plate and then dried at 80 ° C. under normal pressure to obtain a polymer electrolyte membrane. Next, the obtained membrane was immersed in 2N hydrochloric acid for 2 hours and then washed with ion-exchanged water to convert the ion exchange group of the polymer electrolyte membrane into a proton type.

  Then, the dry weight of the polymer electrolyte membrane converted into the proton type was obtained by drying at 105 ° C. using a halogen moisture meter. This polymer electrolyte membrane was immersed in 5 mL of a 0.1 mol / L sodium hydroxide aqueous solution, and further 50 mL of ion exchange water was added and left for 2 hours. Thereafter, 0.1 mol / L hydrochloric acid was gradually added to the solution in which the polymer electrolyte membrane was immersed, and titration was performed to obtain the neutralization point. The IEC of the polymer electrolyte membrane was calculated from the absolute dry weight of the polymer electrolyte membrane and the amount of hydrochloric acid required for the neutralization, and this was used as the ion exchange capacity of the polymer electrolyte.

[Production of polymer electrolyte membrane]
(Synthesis of polymer electrolyte 1)
In accordance with the method described in the pamphlet of International Publication No. 2006/095919, a polymer electrolyte represented by the following chemical formula (2) was obtained (Note that the description of “block” in the chemical formula (2) is based on the repeating unit in parentheses. It is a block copolymer having a block. The obtained polymer electrolyte 1 had a weight average molecular weight of 2.3 × 10 ⁵ , a number average molecular weight of 1.1 × 10 ⁵ , and an ion exchange capacity (IEC) of 2.2 meq / g.

(Synthesis of stabilizer polymer)
(A) Synthesis of Polymer a First, a 2 L separable flask equipped with a vacuum azeotropic distillation apparatus was purged with nitrogen, and this was replaced with 63.40 g of 4,4′-dichlorodiphenylsulfone, 70. 4,4′-dihydroxybiphenyl. 81 g and 955 g of N-methyl 2-pyrrolidone (NMP) were added to obtain a uniform solution. Thereafter, 92.80 g of potassium carbonate was added, and dehydrated under reduced pressure at 135 ° C. to 150 ° C. for 4.5 hours while NMP was distilled off. Thereafter, 200.10 g of dichlorodiphenylsulfone was added, and the reaction was performed at 180 ° C. for 21 hours.

  After completion of the reaction, the reaction solution was added dropwise to methanol, and the precipitated solid was filtered and collected. The recovered solid was further washed with methanol and washed with water, and then dried with hot methanol, whereby 275.55 g of polymer a was obtained. The polymer a has a structure represented by the following chemical formula (3).

This polymer a had a polystyrene-equivalent weight average molecular weight of 18000 as measured by GPC, and the ratio of q and p determined from the integrated value of NMR measurement was q: p = 7: 3. In addition, the notation of “random” in the following formula (3) indicates that the constituent units forming the polymer a are copolymerized randomly.

(B) Synthesis of polymer b A 2 L separable flask was purged with nitrogen, and 80.00 g of the polymer a and 1014.12 g of nitrobenzene were added to obtain a uniform solution. Thereafter, 50.25 g of N-bromosuccinimide was added and cooled to 15 ° C. Subsequently, 106.42 g of 95% concentrated sulfuric acid was added dropwise over 40 minutes and reacted at 15 ° C. for 6 hours. After 6 hours, 450.63 g of a 10 wt% aqueous sodium hydroxide solution and 18.36 g of sodium thiosulfate were added while cooling to 15 ° C. Thereafter, this solution was added dropwise to methanol, and the precipitated solid was filtered and collected. The recovered solid was washed with methanol and washed with water, then again washed with methanol and dried to obtain 86.38 g of polymer b. The results of analyzing the bromine content and molecular weight of the obtained polymer b were as follows.
Bromine content 19.5% by mass
Number average molecular weight 7.7 × 10 ³
Weight average molecular weight 1.1 × 10 ⁴

(C) Synthesis of polymer c A 2 L separable flask equipped with a vacuum azeotropic distillation apparatus was purged with nitrogen, and 80.07 g of polymer b and 116.99 g of dimethylformamide were added to obtain a uniform solution. Thereafter, dehydration under reduced pressure was performed for 5 hours while distilling off dimethylformamide. After 5 hours, the mixture was cooled to 50 ° C., 41.87 g of nickel chloride was added, the temperature was raised to 130 ° C., and 69.67 g of triethyl phosphite was added dropwise, and the reaction was carried out at 140 ° C. to 145 ° C. for 2 hours. It was. After 2 hours, an additional 17.30 g of triethyl phosphite was added, and the reaction was carried out at 145 ° C. to 150 ° C. for 3 hours. After 3 hours, the mixture was cooled to room temperature, a mixed solution of 1161 g of water and 929 g of ethanol was added dropwise, and the precipitated solid was filtered and collected. Water was added to the collected solid and sufficiently pulverized, and this was washed with a 5 wt% aqueous hydrochloric acid solution and washed with water to obtain 86.83 g of polymer c.

(D) Synthesis of polymer d (stabilizer polymer) A 5 L separable flask was replaced with nitrogen, 75.00 g of polymer c, 1200 g of 35 wt% hydrochloric acid, and 550 g of water were added, and the reaction was performed at 105 ° C. to 110 ° C. for 15 hours. Stir. After 15 hours, the reaction solution cooled to room temperature was added dropwise to 1500 g of water. Thereafter, the solid in the system was filtered and collected, and the obtained solid was washed with water and hot water. After drying, 72.51 g of polymer d represented by the following formula (4), which is the intended stabilizer, was obtained. The phosphorus content determined from the elemental analysis of the obtained polymer d was 5.1%, and x in the following formula (4) calculated from the elemental analysis value was calculated based on the number of phosphonic acid groups per one biphenylyleneoxy group. The value of (number) was 1.6. This polymer d was used as a stabilizer in forming the polymer electrolyte membrane. The results of analyzing the bromine content and molecular weight of the obtained polymer d were as follows.
Bromine content 0.1% by mass
Number average molecular weight 1.4 × 10 ⁴
Weight average molecular weight 2.2 × 10 ⁴

(Manufacture of polymer electrolyte membrane)
The mixture of polymer electrolyte 1 obtained by the above production method and polymer d as an additive (polymer electrolyte: additive = 90: 10, weight ratio) is adjusted to a concentration of about 10% by weight in DMSO. To obtain a polymer electrolyte solution. Next, this polymer electrolyte solution was dropped on a glass plate. Then, the polymer electrolyte solution was uniformly spread on the glass plate using a wire coater. At this time, the coating thickness was controlled by using a wire coater having a clearance of 0.5 mm. After application, the polymer electrolyte solution was dried at 80 ° C. under normal pressure. The membrane thus obtained was immersed in 1 mol / L hydrochloric acid, then washed with ion-exchanged water, and further dried at room temperature to obtain a polymer electrolyte membrane having a thickness of 30 μm.

[Preparation of catalyst ink 1]
(Preparation of polymer electrolyte emulsion A)
(A) Synthesis of polymer compound having sulfonic acid group 9.32 parts by weight of dipotassium 4,4′-difluorodiphenylsulfone-3,3′-disulfonate in an argon atmosphere in a flask equipped with an azeotropic distillation apparatus Then, 4.20 parts by weight of potassium 2,5-dihydroxybenzenesulfonate, 59.6 parts by weight of DMSO and 9.00 parts by weight of toluene were added, and argon gas was bubbled for 1 hour while stirring them at room temperature.

  Thereafter, 2.67 parts by weight of potassium carbonate was added to the resulting mixture, and azeotropic dehydration was performed by heating and stirring at 140 ° C. Thereafter, heating was continued while distilling off toluene to obtain a DMSO solution of a polymer compound having a sulfonic acid group. The total heating time was 14 hours. The resulting solution was allowed to cool at room temperature.

(B) Synthesis of polymer compound having substantially no ion exchange group In a flask equipped with an azeotropic distillation apparatus, 8.32 parts by weight of 4,4′-difluorodiphenylsulfone, 2,6- Dihydroxynaphthalene (5.36 parts by weight), DMSO (30.2 parts by weight), NMP (30.2 parts by weight), and toluene (9.81 parts by weight) were added, and argon gas was bubbled for 1 hour while stirring at room temperature.

  Thereafter, 5.09 parts by weight of potassium carbonate was added to the obtained mixture, followed by azeotropic dehydration by heating and stirring at 140 ° C. Thereafter, heating was continued while toluene was distilled off. The total heating time was 5 hours. The resulting solution was allowed to cool at room temperature to obtain a NMP / DMSO mixed solution of a polymer compound substantially free of ion exchange groups.

(C) Synthesis of block copolymer While stirring the NMP / DMSO mixed solution of the polymer compound substantially having no ion-exchange group obtained above, the polymer compound having the sulfonic acid group was added to this. The total amount of DMSO solution, 80.4 parts by weight of NMP and 45.3 parts by weight of DMSO were added and reacted at 150 ° C. for 40 hours to obtain a block copolymer.

The obtained reaction solution was dropped into a large amount of 2N hydrochloric acid and immersed for 1 hour. Thereafter, the generated precipitate was separated by filtration, and then again immersed in 2N hydrochloric acid for 1 hour. The obtained precipitate was filtered and washed with water, and then immersed in a large amount of hot water at 95 ° C. for 1 hour. And the block copolymer represented by following formula (5) was obtained by drying this solution at 80 degreeC for 12 hours. The obtained block copolymer is referred to as polymer electrolyte 2. The ion exchange capacity of this block copolymer (polymer electrolyte 2) was 1.9 meq / g, the weight average molecular weight was 4.2 × 10 ⁵ , and the number average molecular weight was 6.0 × 10 ⁴ .

(D) Preparation of polyelectrolyte emulsion The polyelectrolyte 2 represented by the formula (5) obtained as described above is 1.0% by weight in 1-methyl-2-pyrrolidone (NMP). To 100 g of a polymer electrolyte solution. Next, 100 g of this solution was added dropwise to 900 g of distilled water at a dropping rate of 3 to 5 g / min using a burette, thereby diluting the solution. The diluted polymer electrolyte solution was treated with running water for 72 hours using a cellulose tube for dialysis membrane dialysis (UC36-32-100, manufactured by Sanko Junyaku Co., Ltd .: molecular weight cut off 14,000) to replace the solvent. Went. The solvent-substituted solution was concentrated using an evaporator to a concentration of 2.2% by weight, thereby producing a polymer electrolyte emulsion A.

(Preparation of catalyst ink 1)
To 3.35 g of the polymer electrolyte emulsion A, 0.50 g of platinum-carrying carbon carrying 70 wt% platinum was added, and 21.83 g of ethanol and 3.23 g of water were further added. The obtained mixture was subjected to ultrasonic treatment for 1 hour and then stirred with a stirrer for 6 hours to obtain catalyst ink 1.

[Preparation of catalyst ink 2]
(Preparation of polymer electrolyte emulsion B)
A 200 mL flask equipped with a Dean-Stark tube has 4.00 g (16.06 mmol) of sodium 2,5-dichlorobenzenesulfonate, 7.24 g (46.38 mmol) of 2,2′-bipyridyl, and chloro groups at both ends. Polyethersulfone (manufactured by Sumitomo Chemical Co., Ltd., trade name “SUMICA EXCEL PES 5200P”) 1.51 g, 1- (4-bromobenzyloxy) -2,5-dichlorobenzene 553 mg (1.61 mmol), dimethyl sulfoxide 100 mL and toluene After adding 35 mL and performing azeotropic dehydration under reduced pressure at 100 ° C. for 9 hours under an argon atmosphere, toluene was distilled out of the system and the mixture was allowed to cool to 70 ° C. Next, 11.70 g (42.16 mmol) of Ni (cod) ₂ was added all at once at 70 ° C. Immediately after the addition of Ni (cod) _{2, the} temperature rose to 85 ° C., but the bath temperature was kept as it was and stirred. After addition of Ni (cod) ₂ , the polymerization solution gelled in about 5 minutes, but stirring was continued for 30 minutes.

  Thereafter, the obtained gel-like polymerization solution was poured into methanol, and the resulting crosslinked aromatic polymer was repeatedly washed with methanol / filtered three times, and washed / filtered with a 6 mol / L aqueous hydrochloric acid solution three times to deionize. The washing / filtration operation was repeated until the filtrate was neutral with water. Thereafter, it was dried at 80 ° C. to obtain 3.86 g of a solid crosslinked aromatic polymer. This is designated as polymer electrolyte 3. Next, 1.40 g of the above-mentioned solid crosslinked aromatic polymer was pulverized with a sample mill for 5 minutes, mixed with 149 g of deionized water, and homogenizer (trade name “Ultrasonic Homogenizer US, manufactured by Nippon Seiki Seisakusho”). -150T "), the step of pulverizing for 20 minutes was performed three times until no precipitate was observed visually, and 0.9% by mass of polymer electrolyte emulsion B was obtained.

(Preparation of catalyst ink 2)
To 2.67 g of the obtained polymer electrolyte emulsion B, 0.50 g of platinum-carrying carbon carrying 70 wt% platinum was added, and further 28.19 g of ethanol and 4.17 g of water were added. The obtained mixture was subjected to ultrasonic treatment for 1 hour and then stirred for 6 hours with a stirrer to obtain catalyst ink 2.

[Preparation of catalyst ink 3]
(Preparation of polymer electrolyte emulsion C)
Under an argon atmosphere, in a flask equipped with an azeotropic distillation apparatus, DMSO (dimethyl sulfoxide) 600 ml, toluene 200 mL, sodium 2,5-dichlorobenzenesulfonate 26.5 g (106.3 mmol), terminal sulfone type polyethersulfone (Sumitomo Chemical Co., Ltd., trade name: Sumika Excel PES5200P, number average molecular weight = 5.4 × 10 ⁴ , weight average molecular weight = 1.2 × 10 ⁵ ) 10.0 g, and 2,2′-bipyridyl 43.8 g (280.2 mmol) was added and stirred. Then, the temperature of the oil bath was raised to 150 ° C., and water in the system was azeotropically dehydrated while distilling off toluene, then cooled to 60 ° C., and bis (1,5-cyclooctadiene) nickel ( 0) 73.4 g (266.9 mmol) was added, and the temperature of the oil bath was raised to 80 ° C., followed by stirring at the same temperature for 5 hours to obtain a reaction solution.

After allowing to cool, the reaction solution was poured into a large amount of 6 mol / L hydrochloric acid to precipitate a polymer, and the polymer was separated by filtration. Thereafter, washing and filtering of the polymer filtered off with 6 mol / L hydrochloric acid were repeated several times, and then the polymer was washed with water until the filtrate became neutral, and further stirred with hot water at 90 ° C. or higher for 2 hours. It was washed with water and filtered off. Next, 16.3 g of a polyarylene block copolymer (polymer electrolyte 4) was obtained by drying under reduced pressure. The number average molecular weight of the polymer electrolyte 4 was 100,000, and the weight average molecular weight was 260000.
In addition, these number average molecular weights and weight average molecular weights are measured by gel permeation chromatography (GPC) and determined using a standard polystyrene calibration curve.

  1.0 g of polymer electrolyte 4 was dissolved in 99 g of N-methylpyrrolidone (NMP) to prepare 100 g of a solution. Next, while stirring 900 g of water, this solution was gradually added dropwise to obtain a mixture of polymer electrolyte 4, NMP and water. This mixture was sealed in an osmotic membrane (manufactured by Sanko Junyaku Co., Ltd., trade name: UC36-32-100: molecular weight cut-off 14,000) and washed with running water for 72 hours. Thereafter, this mixture was taken out from the osmotic membrane and concentrated to 50 g using an evaporator under conditions of a temperature of 60 ° C. and a pressure of 50 mTorr to obtain a polymer electrolyte emulsion C. The concentration at this time was 0.70% by weight.

(Preparation of catalyst ink 3)
To 7.11 g of the polymer electrolyte emulsion C, 0.50 g of platinum-carrying carbon black carrying 70.0% by mass of platinum was added, and 21.83 g of ethanol and 3.23 g of water were further added. The obtained mixture was subjected to ultrasonic treatment for 1 hour and then stirred with a stirrer for 6 hours to obtain catalyst ink 3.

[Preparation of catalyst ink 4]
To 10.43 g of the polymer electrolyte emulsion C obtained above, 0.50 g of platinum-supported carbon black carrying 70.0% by mass of platinum was added, and 21.83 g of ethanol and 3.23 g of water were further added. . The obtained mixture was subjected to ultrasonic treatment for 1 hour, and then stirred for 6 hours with a stirrer to obtain catalyst ink 4.

[Production of porous layer forming film 1]
First, 5 g of Lubron LDW-40E (manufactured by Daikin Industries), which is a dispersion of polytetrafluoroethylene (polytetrafluoroethylene 40%, solvent: water), 0.5 g of Vulcan XC-72R that is carbon black, and Then, 102.5 g of ethanol was added, and the resulting mixture was subjected to ultrasonic treatment for 1 hour, and then stirred for 6 hours with a stirrer. This obtained ink 1 for porous layers.

  Subsequently, the porous layer ink 1 is applied to a 5.2 cm square region near the center of one side of a carbon paper (made by Toray, thickness 200 μm) for forming a gas diffusion layer. It apply | coated so that it might become 40 mg. At this time, the distance from the ejection opening of the porous layer ink 1 to the carbon paper was 6 cm, and the temperature of the stage on which the carbon paper was arranged was set to 75 ° C. The applied layer of the porous layer ink 1 was dried at 80 ° C. to remove the solvent, thereby obtaining a porous layer forming film 1 having a porous layer formed on carbon paper.

The pore distribution in the obtained film for forming a porous layer was measured by a mercury intrusion method. Moreover, the pore distribution of the carbon paper in which the porous layer was not formed was also measured. And from the difference of these values, the most frequent pore radius (average pore diameter) in the porous layer was determined. As a result, it was found that the average pore size of the porous layer was 35 nm. The conditions for the mercury intrusion method were as shown below.
・ Pretreatment: Drying at 80 ° C. for 4 hours ・ Measurement: Measurement of pore distribution with pore radius in the range of 0.0018-100 μm

[Production of porous layer forming film 2]
First, 12.5 g of Lubron LDW-40E (manufactured by Daikin Industries), which is a dispersion of polytetrafluoroethylene (polytetrafluoroethylene 40%, solvent: water), VGCF (manufactured by Showa Denko, registered) (Trademark) and 82.5 g of ethylene glycol were added, and the resulting mixture was subjected to ultrasonic homogenizer treatment for 5 minutes to obtain ink 2 for porous layer.

  Subsequently, this porous layer ink 2 was applied onto carbon paper to a wet thickness of 300 μm using a bar coater and dried in an oven at 80 ° C. Then, the heat processing for 30 minutes were performed at 380 degreeC, and the film 2 for porous layer formation in which the porous layer was formed on the carbon paper was obtained. The average pore diameter of the porous layer of the obtained porous layer forming film 2 was determined in the same manner as described above, and was 324 nm.

[Production of porous layer forming film 3]
First, 10 g of Lubron LDW-40E (manufactured by Daikin Industries), which is a dispersion of polytetrafluoroethylene (polytetrafluoroethylene 40%, solvent: water), VGCF (manufactured by Showa Denko KK, registered trademark) as carbon fiber. ) And 128 g of ethylene glycol were added, and the resulting mixture was subjected to ultrasonic homogenizer treatment for 5 minutes to obtain porous layer ink 3.

  Subsequently, the porous layer ink 3 was applied onto carbon paper using a bar coater so as to have a wet thickness of 300 μm, and dried in an oven at 80 ° C. Then, the heat processing for 30 minutes were performed at 380 degreeC, and the film 3 for porous layer formation in which the porous layer was formed on the carbon paper was obtained. The average pore diameter of the porous layer of the obtained porous layer forming film 3 was determined in the same manner as described above, and was 255 nm.

[Production of porous layer forming film 4]
First, 2 g of Lubron LDW-40E (produced by Daikin Industries), which is a dispersion of polytetrafluoroethylene (polytetrafluoroethylene 40%, solvent: water), and VGCF (registered trademark, manufactured by Showa Denko KK) which is carbon fiber. ) And 56 g of ethylene glycol were added, and the resulting mixture was subjected to an ultrasonic homogenizer treatment for 5 minutes to obtain a porous layer ink 4.

  Subsequently, this porous layer ink 4 was applied onto carbon paper to a wet thickness of 300 μm using a bar coater and dried in an oven at 80 ° C. Then, the heat processing for 30 minutes were performed at 380 degreeC, and the film 4 for porous layer formation in which the porous layer was formed on the carbon paper was obtained. It was 394 nm as a result of calculating | requiring the average hole diameter of the porous layer of the obtained film 4 for porous layer formation similarly to the above.

[Example 1: Production of fuel cell]
(Production of membrane-electrode assembly (MEA))
First, the catalyst ink 1 was applied by spraying to a 5.2 cm square region at the central portion of one side of the polymer electrolyte membrane obtained by the above-described production method. At this time, the distance from the discharge port to the polymer electrolyte membrane was 6 cm, and the temperature of the stage on which the polymer electrolyte membrane was disposed was set to 75 ° C. After repeatedly applying this catalyst ink 1, the resulting coating was allowed to stand on the stage for 15 minutes, thereby removing the solvent and forming an anode catalyst layer. This anode catalyst layer contained 0.16 mg / cm ² of platinum, calculated from its composition and coating weight. Subsequently, a cathode catalyst layer was formed on the other surface of the polymer electrolyte membrane by the same method using the catalyst ink 2. This cathode catalyst layer contained 0.60 mg / cm ² of platinum. Thus, an MEA was obtained in which the anode catalyst layer was disposed on one side of the polymer electrolyte membrane and the cathode catalyst layer was disposed on the other side.

(Assembly of fuel cell)
A fuel cell was manufactured using a commercially available JARI standard cell. That is, carbon paper as a gas diffusion layer was disposed on the anode catalyst layer side with respect to the above MEA. The porous layer forming film 1 was disposed on the cathode catalyst layer side so that the porous layer was in contact with the cathode catalyst layer. Thereby, a membrane-electrode-gas diffusion layer assembly (MEGA) was produced.

Next, a gasket having a thickness of 230 μm covering the periphery, a carbon separator having a gas channel groove cut, a current collector, and an end plate are sequentially arranged on both outer sides of the MEGA, and these are tightened with bolts. Thus, a fuel cell having an effective membrane area of 25 cm ² was assembled.

[Example 2: Production of fuel cell]
(Production of MEA)
An MEA was produced in the same manner as in Example 1, except that the catalyst ink 3 was used instead of the catalyst ink 1 and the catalyst ink 4 was used instead of the catalyst ink 2.

(Assembly of fuel cell)
A fuel cell was assembled in the same manner as in Example 1 except that this MEA was used and that the porous layer forming film 3 was used instead of the porous layer forming film 1. Further, by joining the MEA and the porous layer forming film 3 under the above-mentioned conditions, the mercury intrusion method is performed, and the obtained cumulative pore volume is divided by the reciprocal of the bulk density of the porous layer. The porosity was determined to be 16%. Furthermore, it was 150 micrometers when the thickness of the porous layer was measured with the thickness gauge.

[Example 3: Production of fuel cell]
(Production of MEA)
An MEA was produced in the same manner as in Example 2.

(Assembly of fuel cell)
A fuel cell was assembled in the same manner as in Example 1 except that this MEA was used and that the porous layer forming film 2 was used instead of the porous layer forming film 1. In addition, by joining the MEA and the porous layer forming film 2 with the mercury intrusion method under the above-mentioned conditions, the cumulative pore volume obtained is divided by the reciprocal of the bulk density of the porous layer. When the porosity was determined, it was 15%. Furthermore, it was 140 micrometers when the thickness of the porous layer was measured with the thickness gauge.

[Example 4: Production of fuel cell]
(Production of MEA)
An MEA was produced in the same manner as in Example 2.

(Assembly of fuel cell)
A fuel cell was assembled in the same manner as in Example 1 except that this MEA was used and that the porous layer forming film 4 was used instead of the porous layer forming film 1. Further, by joining the MEA and the porous layer forming film 4 under the above-mentioned conditions, the mercury intrusion method is performed, and the obtained cumulative pore volume is divided by the reciprocal of the bulk density of the porous layer. When the porosity was determined, it was 8%. Furthermore, it was 110 micrometers when the thickness of the porous layer was measured with the thickness gauge.

[Comparative Example 1: Production of fuel cell]
(Production of MEA)
An MEA was produced in the same manner as in Example 1.

(Assembly of fuel cell)
A fuel cell was assembled in the same manner as in Example 1 except that only the carbon paper was disposed on the cathode catalyst layer side instead of the porous layer forming film.

[Characteristic evaluation of fuel cells]
While maintaining the temperature of 80 ° C. for the fuel cells obtained in Examples 1 to 4 and Comparative Example 1, humidified hydrogen was supplied to the anode side and humidified air was supplied to the cathode side. At this time, the supply of each gas was adjusted so that the back pressure at the gas outlet of the fuel cell was 0.1 MPaG. Each gas was humidified by passing the gas through a bubbler. At this time, the water temperature of the hydrogen bubbler was 45 ° C., and the water temperature of the air bubbler was 55 ° C.

Then, the fuel cell was operated under the condition that the hydrogen gas flow rate was 529 mL / min and the air gas flow rate was 1665 mL / min, and the value of the current density when the voltage was 0.3 V was measured. Table 1 shows the results obtained using the fuel cells of each Example or Comparative Example.

  As shown in Table 1, according to the fuel cells of Examples 1 to 4 in which the porous layer was provided, a higher current density was obtained under the same humidification conditions as compared with Comparative Example 1 in which the porous layer was not provided. It was confirmed that

It is a figure which shows typically the cross-sectional structure of the fuel cell which concerns on suitable embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 12 ... Polymer electrolyte membrane, 14a, 14b ... Catalyst layer, 15a, 15b ... Porous layer, 16a, 16b ... Gas diffusion layer, 18a, 18b ... Separator, 20 ... MEA.

Claims (6)

An electrolyte membrane composed of a hydrocarbon polymer electrolyte;
A catalyst layer disposed on at least one side of the electrolyte membrane and including a catalyst substance and a hydrocarbon polymer electrolyte;
A gas diffusion layer disposed on the opposite side of the catalyst layer with respect to the electrolyte membrane;
A porous layer disposed between the catalyst layer and the gas diffusion layer and having a porous structure;
A membrane-electrode-gas diffusion layer assembly comprising:   2. The membrane-electrode-gas diffusion layer assembly according to claim 1, wherein the pores of the porous layer have an average pore diameter of 10 nm to 10 μm.   The membrane-electrode-gas diffusion layer assembly according to claim 1 or 2, wherein the pores of the porous layer have an average pore diameter of 20 nm to 300 nm.   The membrane-electrode-gas diffusion layer assembly according to any one of claims 1 to 3, wherein the hydrocarbon-based polymer electrolyte constituting the electrolyte membrane is made of a block copolymer.   The catalyst layer includes at least one solvent selected from water and a hydrophilic solvent, the catalyst substance, and the hydrocarbon polymer electrolyte, and at least a part of the hydrocarbon polymer electrolyte is the catalyst layer. The membrane-electrode-gas diffusion layer assembly according to any one of claims 1 to 4, wherein the membrane-electrode-gas diffusion layer assembly is a layer formed from a catalyst ink contained in a state dispersed in a solvent.   A fuel cell comprising the membrane-electrode-gas diffusion layer assembly according to any one of claims 1 to 5.

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