JP2009158372A - Binder composition for fuel cell, membrane electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a binder composition for a fuel cell which retains superior proton conductivity and binding property even under a non-humidified or low-humidified high-temperature operational condition, a manufacturing method for the binder composition, and a membrane electrode assembly and a fuel cell using the binder composition. <P>SOLUTION: The binder composition for the fuel cell at least has a structure: (-CF<SB>2</SB>-CF(M)CH<SB>2</SB>-CF<SB>2</SB>-), where M denotes any one of CF<SB>3</SB>, CF<SB>2</SB>H, and CFH<SB>2</SB>. The binder composition contains a fluorinated polymer to which a basic compound is added, and a hydrogen ion conductor. The basic compound is a nitrogen-containing heterocyclic compound in which at least two hydrogen atoms are replaced, and the fluorinated polymer is bridged by the basic compound. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a binder composition for a fuel cell, a membrane electrode assembly, and a fuel cell, and more particularly to a binder composition for a fuel cell, a membrane electrode assembly, and a fuel cell having excellent proton conductivity and binding properties. .

  Fluorine electrolyte membranes represented by perfluorosulfonic acid membranes such as Nafion (manufactured by DuPont) are disadvantageous in that the manufacturing process is complicated and very expensive, despite high chemical stability. is there. In the case of a purple sulfonic acid membrane, a hydrophobic main chain and a hydrophilic side chain are phase-separated to form a so-called ion cluster structure. As a proton transport form, it is understood that many water molecules are taken into this cluster structure, and the dissociation of the sulfonic acid group is promoted, and at the same time, the high mobility of the water molecules is utilized to express high proton conductivity. ing. However, under high-temperature conditions of 100 ° C. or higher (temperature environment higher than the boiling point of water), proton conductivity is reduced due to a decrease in water molecules, and the membrane itself cannot maintain its shape from the viewpoint of mechanical strength. The operation operating temperature is limited to 70 ° C. to 80 ° C., and there is a problem that moisture management becomes complicated.

  In addition, the polymer fuel cell is composed of unit cells in which the electrode catalyst layers of the fuel electrode and the air electrode are attached to both sides of the electrolyte membrane as a center. A fuel cell system for generating kW of electric power is configured. The performance of the unit cell, that is, the membrane electrode assembly (MEA) greatly affects the power generation characteristics of the fuel cell.

  Therefore, in order to develop high proton conductivity, there is conventionally an example in which the perfluorosulfonic acid electrolyte typified by Nafion is used as a binder for the electrode catalyst layer.

  However, in the case of a perfluorosulfonic acid electrolyte such as Nafion, proton conductivity is low at a high temperature of 100 ° C. or higher and a low humidity range of 50% or less, and it is easy to cause creep. There is a drawback that it cannot be applied when the operating temperature of the fuel cell is 100 ° C. or higher.

  Accordingly, the present invention has been made in view of such problems, and is a fuel cell binder having excellent proton conductivity and binding properties even under non-humidification or low humidification under high temperature operating conditions. An object is to provide a composition, a membrane electrode assembly, and a fuel cell.

As a result of intensive studies to solve the above problems, the present inventors have found that at least a (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure soluble in an organic solvent (where M is CF ₃ When a predetermined basic compound is mixed in an organic solvent with a fluorine-based polymer having any of CF ₂ H and CFH ₂ ), the fluorine-based polymer can be reacted with the basic compound, and this It has been found that a polymer in which a fluorine-based polymer is crosslinked with a basic compound can be synthesized by heat-treating the reaction product. A polymer having such a crosslinked structure has excellent heat resistance and acid resistance even under conditions of high temperature and no humidification (or low humidification), and such a polymer is impregnated with a hydrogen conductor such as an acid. By doing so, an electrolyte material for fuel cells having high proton conductivity can be obtained. The inventors have found that by using this electrolyte material as a binder in an electrode catalyst layer of a fuel cell, a binder composition having excellent proton conductivity, water repellency and binding properties can be obtained. It was.

  The present inventors have completed the present invention based on the above findings.

That is, according to an aspect of the present invention, at least a (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure (where M is any of CF ₃ , CF ₂ H, and CFH ₂ ). And a fluorine-based polymer to which a basic compound is added, and a hydrogen ion conductor, and the basic compound is a nitrogen-containing heterocyclic compound substituted with at least two hydrogen atoms, The binder composition for fuel cells in which the fluorine-based polymer is crosslinked with the basic compound is provided.

  Here, the basic compound is preferably a nitrogen-containing heterocyclic compound having at least two or more amino groups, and diaminoimidazole and a derivative thereof, diaminotriazine and a derivative thereof, diaminotriazole and a derivative thereof, diaminopyridine and a derivative thereof. More preferably, it is at least one selected from the group consisting of a derivative and diaminobenzimidazole and its derivatives.

  Examples of such basic compounds include compounds represented by any one of the following structural formulas (1) to (3).

  In addition, examples of the fluorine-based polymer include at least one of vinylidene fluoride-hexafluoropropylene copolymer and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer. .

  Examples of the hydrogen ion conductor include at least one acid selected from the group consisting of orthophosphoric acid, condensed phosphoric acid, alkyl phosphoric acid, and phosphonic acid.

  According to another aspect of the present invention, there is provided a fuel cell electrolyte, and electrode catalyst layers disposed on both sides in the thickness direction of the fuel cell electrolyte, wherein the electrode catalyst layer is a catalyst on a catalyst carrier. There is provided a membrane electrode assembly comprising a catalyst material on which a substance is supported and a binder for binding the catalyst material, wherein the binder includes the binder composition for a fuel cell as described above.

  According to still another aspect of the present invention, a membrane electrode assembly comprising a fuel cell electrolyte and electrode catalyst layers disposed on both sides in the thickness direction of the fuel cell electrolyte, and the membrane electrode assembly The electrode catalyst layer has a catalyst material having a catalyst material supported on a catalyst carrier and a binder for binding the catalyst material, and the binder is the above-mentioned A fuel cell comprising such a fuel cell binder composition is provided.

  According to the present invention, a polymer having a structure in which a fluorine-based polymer is crosslinked with a basic compound is impregnated with a hydrogen ion conductor, so that it is excellent even under non-humidified or low-humidified conditions at high temperature. It is possible to provide a fuel cell binder composition, a membrane electrode assembly, and a fuel cell that have excellent heat resistance, acid resistance, and proton conductivity, as well as excellent water repellency and binding properties.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[Structure of binder composition for fuel cell]
First, the structure of the binder composition for fuel cells according to the present invention will be described. The binder composition for fuel cells according to the present invention includes a fluorine-based polymer to which a basic compound is added and a hydrogen ion conductor. This fluoropolymer has at least a (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure and a plurality of (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structures. Has a structure crosslinked with a basic compound. However, M is any of CF ₃ , CF ₂ H, and CFH ₂ .

Here, the fluorine-based polymer having a (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure is excellent in chemical stability such as heat resistance and acid resistance, and has long-term stability and binding properties. And water repellency. In addition, the basic compound has an affinity with an acid such as phosphoric acid, that is, it exhibits a proton conductivity at a high temperature by being combined with phosphoric acid. In the present invention, a basic compound is added to a fluorine-based polymer having such a characteristic (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure, and a plurality of (—CF ₂ — By cross-linking the CF (M) CH ₂ —CF ₂ — structures, phosphoric acid, etc., while maintaining the characteristics of the fluoropolymer (chemical stability, long-term stability, binding properties, water repellency, etc.) It is possible to introduce a basic compound having a high affinity with the acid (a part of the basic compound is introduced as a cross-linked chain).

  Further, when such a polymer is used as a binder for the electrode catalyst layer, proton conductivity in the vicinity of the catalyst is better than a binder using a conventional fluororesin. In addition, since the doping rate of phosphoric acid is lower than that of binders using conventional hydrocarbon resins (for example, polybenzimidazole (PBI), etc.), volume swellability due to phosphoric acid is low, and dimensional changes as binders Since it is small, the diffusibility of the fuel gas or oxidant gas to the catalyst is also good. That is, the binder composition for a fuel cell according to the present invention has both excellent water repellency and proton conductivity since a basic hydrocarbon having affinity for phosphoric acid is bonded to a fluorine-based skeleton. In addition, a more effective three-phase interface of the electrode catalyst layer can be constructed.

  The fuel cell using the fuel cell binder composition using such a polymer as a binder for the electrode catalyst layer exhibits excellent durability and fuel cell characteristics even under high temperature and no humidification (or low humidification). Show.

  As described above, the fuel cell binder composition according to the present invention has excellent heat resistance, acid resistance, and high humidity even under non-humidified conditions or a relative humidity of 50% or less under a high operating temperature condition of 100 ° C. or higher. Exhibits proton conductivity and excellent water repellency and binding properties. In addition, the fuel cell according to the present invention using this binder composition for a membrane electrode assembly is extremely good even when it is not humidified or has a relative humidity of 50% or less under a high operating temperature condition of 100 ° C. or higher. Indicates power generation performance.

(Fluoropolymer)
As described above, the fluoropolymer contained in the fuel cell binder composition according to the present invention has at least a structure of (—CF ₂ —CF (M) CH ₂ —CF ₂ —) (where M is CF ₃ , CF ₂ H, or CFH ₂ ). Examples of such a fluorine-based polymer include a copolymer structure of vinylidene fluoride and hexafluoropropylene represented by the following structural formula (4) (M = CF ₃ , where x and y are polymerized) A degree). In addition, as a molecular weight of the fluorine-type polymer used by this invention, the thing of an average molecular weight of about several hundred thousand can be used.

From the viewpoint of producing a binder composition, it can be dissolved in an organic solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), or ethyl acetate as a fluoropolymer. Those that do are preferred. Examples of the fluorine-based polymer dissolved in such an organic solvent include vinylidene fluoride-hexafluoropropylene copolymer (hereinafter sometimes referred to as “VdF-HFP”) and vinylidene fluoride-hexafluoropropylene— And tetrafluoroethylene terpolymer (hereinafter sometimes referred to as “VdF-HFP-TFE”). These copolymers may be used alone or in combination of two or more. In any of these copolymers, M in (—CF ₂ —CF (M) CH ₂ —CF ₂ —) is a CF ₃ group having strong electron withdrawing properties. The presence of this CF ₃ group, the carbon atom to which a CF ₃ group is attached, occurs deviation in the electron cloud between the carbon atom bonded two hydrogen atoms as well as adjacent to the carbon atom, a CF ₃ group is bonded The carbon atom to be bonded is δ−, and the carbon atom to which the hydrogen atom is bonded is δ +.

(Basic compound)
The basic compound contained in the binder composition for a fuel cell according to the present invention is a nitrogen-containing heterocyclic compound in which at least two hydrogen atoms are substituted with a predetermined substituent X. In particular, the predetermined substituent X is preferably an amino group. In the present invention, the basic compound is such a nitrogen-containing heterocyclic compound, and the predetermined substituent X (when X is an amino group, the nitrogen of the (—NH—) group) is a carbon atom in the fluoropolymer. To join. At this time, since the basic compound according to the present invention has at least two or more such substituents X, the two substituents X are each bonded to the carbon atom in the fluoropolymer, so that the basic compound is basic. A polymer having a structure in which a compound is obtained by crosslinking a plurality of fluoropolymers can be synthesized. Further, in this case, a hydrogen ion conductor (for example, an acid such as phosphoric acid) is doped in the site of the nitrogen atom in the ring in the nitrogen-containing heterocyclic compound.

  Examples of the basic compound include at least one of diaminoimidazole and derivatives thereof, diaminotriazine and derivatives thereof, diaminotriazole and derivatives thereof, diaminopyridine and derivatives thereof, and diaminobenzimidazole and derivatives thereof. More specifically, for example, a compound represented by any one of the following structural formulas (1) to (3) can be given.

(Hydrogen ion conductor)
Examples of the hydrogen ion conductor contained in the fuel cell binder composition according to the present invention include at least one acid selected from the group consisting of orthophosphoric acid, condensed phosphoric acid, alkyl phosphoric acid, and phosphonic acid. Can be mentioned. The content (doping amount) of the hydrogen ion conductor such as an acid in the binder composition is preferably 10% by mass or more and 300% by mass or less, and more preferably 50% by mass or more and 200% by mass or less. When the content of the hydrogen ion conductor is less than this range, the proton conductivity is lowered, which is not preferable. On the other hand, when the content of the hydrogen ion conductor exceeds this range, the dimensional change as a binder is increased, and the diffusibility of the fuel gas and the oxidant gas in the catalyst layer is hindered.

(Structure of binder composition for fuel cell)
As described above, the binder composition for a fuel cell according to the present invention includes a polymer having a structure in which a basic compound is added to a fluorine-based polymer and the basic compound crosslinks a plurality of fluorine-based polymers. Furthermore, the polymer is doped with a hydrogen ion conductor such as an acid. Specific examples of the binder composition according to the present invention include cross-linked polymer binders represented by the following structural formulas (5) to (7).

  The polymer binder represented by the structural formula (5) is a fluorine-based polymer having a VdF-HFP structure represented by the structural formula (4), and is represented by the structural formula (1) as a basic substance. In this example, 6,4′-diamino-2-phenylbenzimidazole (hereinafter referred to as “DAPBz”) is used. The polymer binder represented by the structural formula (6) is a fluoropolymer having a VdF-HFP structure represented by the structural formula (4), and the basic substance is represented by the structural formula (2). This is an example using 2,4-diamino-6-phenyl-1,3,5-triazine (benzoguanamine) (hereinafter referred to as “DAPTZI”). The polymer binder represented by the structural formula (7) uses a fluorine-based polymer having a VdF-HFP structure represented by the structural formula (4), and a basic substance represented by the structural formula (3). This is an example using 3,5-diamino-1,2,4-triazole (guanazole) (hereinafter referred to as “DATz”) shown.

  In any case, the fluoropolymer having a VdF-HFP bond undergoes dehydrofluorination in the presence of a basic compound (such as an amine), and at that time, a C═C bond is formed. Nitrogen-containing heterocyclic compounds (imidazole-based, triazine-based, triazole-based, pyridine-based, and benzimidazole-based) nitrogen atoms are bonded to form a bond, so that the nitrogen-containing heterocyclic compound crosslinks the fluoropolymer. It is thought that there is. Thereby, it is considered that the nitrogen atom in the ring contained in the nitrogen-containing heterocyclic compound is left as it is, and a hydrogen ion conductor such as an acid is doped at the position of the nitrogen atom in the ring.

  In addition, it is considered that the formation of a cross-linked bond with a carbon atom to which a hydrogen atom of a fluorine-based polymer is bonded is performed by two substituents (for example, an amino group) included in the same basic compound molecule. That is, the basic compound that crosslinks the fluoropolymer is a monomer of a basic compound such as a nitrogen-containing heterocyclic compound, and it is considered that these polymers do not form a crosslink. For this reason, the binder composition according to the present invention has a structure in which a main chain polymer composed of a fluorine-based polymer is cross-linked with a monomer composed of a basic compound. It is considered that the thermal stability is excellent without decreasing.

  In the binder composition of the present invention, since the basic compound crosslinks the main chains of the fluorine-based polymer, the chemical stability of the electrolyte is improved. Even in the impregnated state, the binder composition does not dissolve and is excellent in acid resistance even when placed in an environment of 100 ° C. to 200 ° C. which is the operating temperature of the fuel cell. The degree of crosslinking in the polymer electrolyte of the present invention can be controlled by adjusting the amount of basic compound added.

[Method for producing binder composition for fuel cell]
Next, a method for producing a fuel cell binder composition according to the present invention having the structure as described above will be described.

  In the present invention, the production of the binder composition for a fuel cell and the production of the electrode catalyst layer are carried out at the same time, and the production method mainly comprises a step of pasting the catalyst material (first step) and A step of applying the paste to the electrode substrate (diffusion layer) to form a catalyst layer (second step), and a step of drying and heat-treating the catalyst layer (third step).

In the first step, first, fluorine having at least a (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure (where M is any of CF ₃ , CF ₂ H, and CFH ₂ ). A mixed solution in which a base polymer and a basic compound are dissolved in an organic solvent is prepared.

  The fluorine-based polymer and the basic compound may be dissolved in the same type of organic solvent, or may be mixed in different types of organic solvents after being dissolved in different types of organic solvents. When different types of organic solvents are used, compatible solvents are preferable. Examples of the organic solvent for the fluorine-based polymer include ester solvents such as N-methylpyrrolidone (NMP), N, N-dimethylformamide (DMF), and ethyl acetate, and ketone solvents such as acetone and ethyl methyl ketone. Is preferred. In particular, when the fluorine-based polymer is VdF-HFP, NMP, DMF or the like is preferable, and when the fluorine-based polymer is VdF-HFP-TFE, ethyl acetate, acetone, ethyl methyl ketone, or the like is preferable. Moreover, as an organic solvent for a basic compound, NMP, dimethylacetamide (DMAc), DMF, etc. are preferable, and water may be used. Among the organic solvents, NMP, DMF, DMAc, and ethyl acetate have compatibility, and therefore, a basic compound may be selected from compounds that are soluble in these. Further, since ethyl acetate is compatible with water, water may be used as a solvent for the basic compound.

  The mixing ratio of the fluorine-based polymer and the basic compound is preferably in the range of (fluorine polymer / basic compound) from 9/1 to 1/1 by mass ratio, and from 8/1 to 2 More preferably, the range is up to / 1. When the amount of the basic compound is less than the above range, the impregnation rate (doping amount) of the hydrogen ion conductor (for example, acid such as phosphoric acid) is not preferable. On the other hand, if the amount of the basic compound is more than the above range, the chemical stability of the resulting polymer electrolyte is lowered, which is not preferable.

  Here, in order to bind the catalyst material using a binder when forming the electrode catalyst layer, the binder polymer needs to be soluble in the solvent. This is because, for example, when the binder polymer has a cross-linked structure, it becomes insoluble in a solvent and is not suitable as a binder. Moreover, the present inventors presume as follows about the binder polymer (for example, VdF-HFP / DAPBz) of the solution state before the heat processing (180 degreeC) mentioned later. That is, the present inventors have found that the binder polymer in a solution state undergoes a cross-linking reaction by heat treatment at a predetermined temperature, but before this heat treatment, it exists stably in a state dissolved in a solvent (for example, a base). The functional compound is grafted to the fluoropolymer).

  Next, the catalyst material is made into a paste by mixing and stirring the catalyst material and the hydrogen ion conductor (phosphoric acid or the like) using the mixed solution prepared as described above.

  In the second step, the obtained paste is applied to one surface of the electrode substrate (diffusion layer) to form an electrode catalyst layer.

  In the third step, the obtained electrode catalyst layer is heat-treated at a temperature of 150 ° C. or higher and 200 ° C. or lower to crosslink the fluoropolymer with a basic compound and simultaneously impregnate the polymer with a hydrogen ion conductor. . At this time, the solvent in the electrode catalyst layer is also removed.

  Thus, in the manufacturing method described above, the hydrogen ion conductor is mixed and stirred together with the catalyst material in advance to form the electrode catalyst layer, and then the fluorine ion polymer is crosslinked with the basic compound and at the same time the hydrogen ion conductor. However, the method for producing the binder composition of the present invention (the method for forming the electrode catalyst layer) is not limited to the method described above. That is, after the catalyst material is coated with a binder composition (mixed solution) in a solution state, the coated binder composition is cross-linked by heat treatment and then the obtained binder-coated catalyst material is mixed with another binder. The electrode catalyst layer may be formed by mixing and stirring the hydrogen ion conductor together (for example, PVdF or the like) and forming a paste. In this case, after the electrode catalyst layer is formed, drying for removing the solvent in the electrode catalyst layer is performed.

[Membrane electrode assembly and fuel cell]
In a fuel cell according to an embodiment of the present invention, a plurality of single cells are held between a pair of holders. A single cell consists of a membrane electrode assembly and bipolar plates (separators) arranged on both sides in the thickness direction of the membrane electrode assembly. It operates under conditions. The bipolar plate is made of conductive metal, carbon, or the like, and functions as a current collector by being joined to the membrane electrode assembly, and is oxygenated against the electrode catalyst layer of the membrane electrode assembly. And fuel.

  Here, the membrane electrode assembly 100 according to the present embodiment will be described with reference to FIG. In addition, FIG. 1 is explanatory drawing which shows the structure of the membrane electrode assembly 100 which concerns on this embodiment.

  As shown in FIG. 1, the membrane electrode assembly 100 is laminated on, for example, an electrolyte membrane 130, electrode catalyst layers 140 and 150 disposed on both sides in the thickness direction of the electrolyte membrane 130, and electrode catalyst layers 140 and 150, respectively. Gas diffusion layers 110 and 120. The electrode catalyst layers 140 and 150 and the gas diffusion layers 110 and 120 constitute a pair of electrodes.

  The electrode catalyst layers 140 and 150 are obtained by solidifying the binder composition for a fuel cell as described above and used as the binder 170 of the catalyst material. The fluorine-based polymer is crosslinked with a basic compound and phosphoric acid or the like is used. The hydrogen ion conductor is doped.

  The electrode catalyst layers 140 and 150 function as a fuel electrode and an oxygen electrode, and are porous bodies including a catalyst material mainly composed of carbon black and the like, and a binder 170 for solid-molding the catalyst material. . The catalyst material is in a state in which the catalyst substance 161 is supported on a catalyst carrier 163 such as carbon black. The catalyst substance 161 is not particularly limited as long as it is a metal that promotes a hydrogen oxidation reaction and an oxygen reduction reaction. For example, lead, iron, manganese, cobalt, chromium, gallium, vanadium, tungsten, ruthenium, iridium, palladium , Platinum, rhodium or an alloy thereof. A catalyst material can be produced by supporting such a metal or alloy on a catalyst carrier 163 such as carbon black. As the binder 170, for example, a fluororesin excellent in heat resistance can be used in addition to the fuel cell binder composition described above. When a fluororesin is used as the binder, a fluororesin having a melting point of 400 ° C. or lower is preferable. As such a fluororesin, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinylether copolymer, polyvinylidene fluoride, tetra Resins excellent in hydrophobicity and heat resistance such as fluoroethylene-hexafluoroethylene copolymer and perfluoroethylene can be used. By adding the hydrophobic binder, it is possible to prevent the electrode catalyst layers 140 and 150 from being excessively wetted by the water generated during the power generation reaction, and to inhibit the diffusion of the fuel gas and oxygen inside the fuel electrode and the oxygen electrode. Can be prevented.

  Further, a conductive agent may be added to the catalyst layers 140 and 150. As the conductive agent, any conductive material may be used, and various metals and carbon materials may be used. Examples thereof include carbon black such as acetylene black, activated carbon and graphite, and these can be used alone or in combination.

  The gas diffusion layers 110 and 120 are made of, for example, a carbon sheet or the like, and diffuse oxygen and fuel supplied via the bipolar plate over the entire surface of the electrode catalyst layers 140 and 150.

  The fuel cell including the membrane electrode assembly 100 operates at a temperature of 100 ° C. to 200 ° C., for example, hydrogen is supplied to the one electrode catalyst layer 140 side as a fuel via a bipolar plate, and the other electrode catalyst layer. For example, oxygen is supplied to the 150 side as an oxidant via a bipolar plate. Then, hydrogen is oxidized in the electrode catalyst layer 140 to generate protons, and the protons are conducted through the electrolyte membrane 130 to reach the electrode catalyst layer 150. In the electrode catalyst layer 150, protons and oxygen react electrochemically. It generates water and generates electrical energy. The hydrogen supplied as fuel may be hydrogen generated by reforming hydrocarbons or alcohols, and oxygen supplied as an oxidant may be supplied in a state of being contained in air.

  As described above, according to the binder composition for a fuel cell according to the present invention, a part of the basic compound strongly crosslinks the fluoropolymer, so that the stability of the binder composition itself is improved. Thus, the binder is chemically stable even when it is placed in a high temperature atmosphere of about 100 ° C. to 200 ° C. in a state impregnated with a hydrogen ion conductor such as phosphoric acid. In addition, the fuel cell binder composition according to the present invention has such a crosslinked structure, so that the chemical durability of the conventional fluorine-based polymer is maintained and the basic compound and acid are combined ( Affinity) can exhibit excellent heat resistance, acid resistance, and proton conductivity even under high temperature and no humidification (high operating temperature of 100 ° C. or higher, no humidification, or relative humidity of 50% or less).

  Further, when such a polymer is used as a binder for the electrode catalyst layer, proton conductivity in the vicinity of the catalyst is better than a binder using a conventional fluororesin. In addition, since the doping rate of phosphoric acid is lower than that of binders using conventional hydrocarbon resins (for example, polybenzimidazole (PBI), etc.), volume swellability due to phosphoric acid is low, and dimensional changes as binders Since it is small, the diffusibility of the fuel gas or oxidant gas to the catalyst is also good. That is, the binder composition for a fuel cell according to the present invention has both excellent water repellency and proton conductivity since a basic hydrocarbon having affinity for phosphoric acid is bonded to a fluorine-based skeleton. In addition, a more effective three-phase interface of the electrode catalyst layer can be constructed.

  In addition, a fuel cell using such a fuel cell binder composition according to the present invention for a membrane electrode assembly can exhibit excellent fuel cell characteristics even under high temperature and no humidification. Moreover, according to the manufacturing method of the binder composition for fuel cells which concerns on this invention, the binder composition excellent in chemical stability can be manufactured cheaply.

  Next, the present invention will be described more specifically using examples and comparative examples, but the present invention is not limited to the following examples.

  In this example, an electrode was manufactured using the fuel cell binder composition to which the present invention was applied, a fuel cell was manufactured using the electrode, and the power generation characteristics of the fuel cell were evaluated. Hereinafter, the binder composition, the electrode, the method for producing the fuel cell, and the evaluation results of the characteristics of the fuel cell in each example will be described in detail.

[Production Example of Binder Composition for Fuel Cell]
First, in this example, in order to use 6,4′-diamino-2-phenylbenzimidazole (DAPBz) as a basic compound, DAPBz was synthesized as follows. First, 4-nitro-1,2-phenylenediamine and 4-nitrobenzoyl chloride are added with triethylamine, reacted in dimethylacetamide (hereinafter referred to as DMAc) and a toluene solvent, and 2-amino-4,5- Dinitrobenzanilide (A) was produced. Next, the obtained compound (A) was stirred and mixed in polyphosphoric acid at 190 ° C., and the solution was stirred in distilled water for 24 hours, and then the precipitate was filtered and washed with water. Subsequently, the recovered material after filtration was recrystallized with DMAc to obtain 6,4-dinitro-2-phenylbenzimidazole (B). Further, Compound (B) and SnCl ₂ were slurried with ethanol, HCl was added thereto, and the mixture was slowly mixed and stirred while refluxing. The solution is poured into distilled water, basified with 10% NaOH, and the filtrate filtered and washed with water is recrystallized with a DMF / H ₂ O (v / v = 1: 3) solution as described above. 4-Diamino-2-phenylbenzimidazole (DAPBz) was obtained.

  DAPBz, which is a basic compound having two amino groups thus obtained, is dissolved in N, N-dimethylformamide (hereinafter referred to as “DMF”) at 60 ° C. to obtain a 20% by mass solution. did. On the other hand, vinylidene fluoride and a hexafluoropropylene copolymer (hereinafter referred to as “VdF-HFP”) as a fluorine-based polymer were dissolved in DMF to obtain a 20 mass% solution. In this example, “KYNAR2821 (weight average molecular weight of about 232500)” manufactured by ARKEMA was used as VdF-HFP.

  Next, a 20 mass% solution in which VdF-HFP is dissolved in DMF and a 20 mass% solution in which DAPBz is dissolved in DMF are mixed at a mass ratio of VdF-HFP / DAPBz = 4/1. The reaction was stirred and refluxed at a temperature below the boiling point of (120 ° C.). The reaction time was 120 hours.

[Evaluation of proton conductivity]
FIG. 2 shows the results of measuring proton conductivity after impregnating phosphoric acid into the binder composition obtained as described above. FIG. 2 also shows proton conductivity results of polybenzimidazole (PBI) -based binder compositions (having a phosphate doping rate of 92% and 313%) that have been used for comparison. It was. As shown in FIG. 2, in the temperature range of 60 ° C. to 150 ° C., the binder composition of this example exhibits a proton conductivity that is remarkably superior to that of a PBI binder composition doped with 92% phosphoric acid. The proton conductivity was equivalent to that of a PBI binder composition doped with 313% acid. The proton conductivity at 150 ° C. is 4.6 × 10 ⁻³ (S / cm) for the binder composition of this example, and 9.9 × 10 ⁻ for the PBI binder composition doped with 92% phosphoric acid. ⁴ (S / cm), and the PBI binder composition doped with 313% phosphoric acid was 4.7 × 10 ⁻³ (S / cm). Thus, the binder composition of this example exhibits high proton conductivity (phosphoric acid) despite the lower phosphate adsorption amount (phosphate doping rate) than the conventional PBI binder composition. It was found that the dependence of proton conductivity on the phosphoric acid doping rate was lower than that of the PBI binder composition. This is considered to be due to the high degree of freedom and mobility of phosphate ions in the binder composition obtained by doping phosphoric acid into VdF-HFP / DAPBz in this example. In the binder composition of this example, the main chain polymer composed of a fluorine-based polymer has a structure crosslinked with a monomer composed of a basic compound having an affinity for phosphoric acid. A large space for proton conduction can be secured between the chain polymers, and it is less susceptible to inhibition of proton conduction due to the movement of the polymer main chain even at high temperatures of 100 ° C. or higher. Is presumed to occur.

[Production Example of Fuel Cell Electrode]
Example 1
The VdF-HFP / DAPBz reaction solution obtained as described above was dissolved in DMF so as to have a solid amount of 6 parts by mass with respect to 100 parts by mass of the catalyst, added to the catalyst, kneaded, A DMF solvent was added to adjust the viscosity of the paste. Further, an 85% phosphoric acid solution was added to this paste to obtain an electrode paste. Next, this electrode paste was applied on carbon paper (SGL Carbon Co., Ltd .: GDL34BC) having a fine carbon layer. After application, DMF was removed by drying at 180 ° C. for about 1 hour. As the catalyst, a platinum-cobalt catalyst (platinum content 46 mass%) in which a platinum-cobalt alloy was supported on carbon (Ketjen Black) was used.

In the obtained electrode, the mass ratio of the catalyst, VdF-HFP / DAPBz, and phosphoric acid was catalyst: (VdF-HFP / DAPBz): H ₃ PO ₄ = 1: 0.06: 0.72.

  As an electrolyte, an ABPBI film in which phosphoric acid was doped by 350% by mass with respect to a basic group of Poly (2,5-benzimidazolol) (ABPBI) (see the following structural formula (8)) was prepared. And the fuel cell of Example 1 was manufactured by laminating | stacking the electrode manufactured as mentioned above on electrolyte, and also arrange | positioning an oxidizing agent distribution plate and a fuel distribution plate on the outer side of each electrode.

(Example 2)
Next, the electrode of Example 2 was manufactured as follows. First, 50 ml of a DMF solution prepared by dissolving the VdF-HFP / DAPBz reaction solution (20% by mass) prepared as described above at a concentration of 10 parts by mass with respect to 100 parts by mass of the catalyst is prepared. 3 g of catalyst was added to and mixed for 12 hours. Thereafter, the mixture was recovered by filtration and dried at 180 ° C. for 2 hours under a nitrogen gas atmosphere, to obtain a coated catalyst in which the VdF-HFP / DAPBz polymer was adsorbed on the catalyst support. The mass ratio of the catalyst to VdF-HFP / DAPBz was catalyst: VdF-HFP / DAPBz = 1: 0.06. As the catalyst, a platinum-cobalt catalyst (platinum content 46 mass%) in which a platinum-cobalt alloy was supported on carbon (Ketjen Black) was used.

  Next, with respect to 1 g of the above coated catalyst, polyvinylidene fluoride (hereinafter referred to as PVdF) is dissolved in DMF so as to have a solid content of 3% by mass, added to the above coated catalyst, kneaded, and appropriately A DMF solvent was added so as to obtain a paste with a high viscosity. Further, an 85% phosphoric acid solution was added to this paste to obtain an electrode paste. Next, this electrode paste was applied on carbon paper (SGL Carbon Co., Ltd .: GDL34BC) having a fine carbon layer. After application, DMF was removed by drying at 150 ° C. for about 1 hour. In this way, the electrode of Example 2 was manufactured.

In this example, “KF polymer W # 1100” manufactured by Kureha Chemical Co., Ltd. having a structure of — (CF ₂ —CH ₂ ) _n — was used as PVdF.

  And the fuel cell of Example 2 was manufactured like Example 1 using the obtained electrode.

(Comparative Example 1)
Polyvinylidene fluoride (hereinafter referred to as PVdF) is dissolved in DMF so as to have a solid amount of 6 parts by mass with respect to 100 parts by mass of the catalyst, added to the catalyst, kneaded, and paste into an appropriate viscosity paste. DMF solvent was added to adjust. Further, an 85% phosphoric acid solution was added to this paste to obtain an electrode paste. This electrode paste was applied on carbon paper (SGL Carbon: GDL34BC) having a fine carbon layer. After application, DMF was removed by drying at 150 ° C. for about 1 hour. As the catalyst, a platinum-cobalt catalyst (platinum content 46 mass%) in which a platinum-cobalt alloy was supported on carbon (Ketjen Black) was used.

In the obtained electrode, the mass ratio of the catalyst, PVdF, and phosphoric acid was catalyst: PVdF: H ₃ PO ₄ = 1: 0.06: 0.65.

In this comparative example, “KF polymer W # 1100” manufactured by Kureha Chemical Co., Ltd. having a structure of — (CF ₂ —CH ₂ ) _n — was used as PVdF.

  And the fuel cell of the comparative example 1 was manufactured like Example 1 using the obtained electrode.

(Comparative Example 2)
Polybenzimidazole (hereinafter referred to as PBI, see the following structural formula (9)) was dissolved in DMAc so that the solid mass was 6 parts by mass with respect to 100 parts by mass of the catalyst, and after charging into the catalyst, It knead | mixed and added and adjusted the DMAc solvent so that it might become a paste of suitable viscosity. Further, an 85% phosphoric acid solution was added to this paste to obtain an electrode paste. The obtained electrode paste was apply | coated on the carbon paper (SGL carbon company_made: GDL34BC) which has a fine carbon layer. After coating, the DMAc was removed by drying at 150 ° C. for about 1 hour. As the catalyst, a platinum-cobalt catalyst (platinum content 46 mass%) in which a platinum-cobalt alloy was supported on carbon (Ketjen Black) was used.

In the obtained electrode, the mass ratio of the catalyst, PBI, and phosphoric acid was catalyst: PBI: H ₃ PO ₄ = 1: 0.06: 1.00.

  And the fuel cell of the comparative example 2 was manufactured like Example 1 using the obtained electrode.

[Evaluation of power generation characteristics]
For the fuel cells of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 manufactured as described above, air is supplied to the cathode electrode at a flow rate of 50% utilization rate, and hydrogen is utilized for the anode electrode. Power was supplied at 80%, operating temperature was 150 ° C., and no humidification was performed, and the power generation characteristics were evaluated. Power generation was performed under conditions where the output current density was 0.3 A / cm ² . Table 1 shows the output voltage of each fuel cell.

  As shown in Table 1, it was found that the batteries of Example 1 and Example 2 using the VdF-HFP / DAPBz binder showed higher output voltage than the batteries of Comparative Example 1 and Comparative Example 2. It was. This is considered to be because the fluorine-based PVdF binder alone has water repellency but is inferior in proton conductivity to the vicinity of the catalyst as compared with the case of using the VdF-HFP / DAPBz binder. In addition, hydrocarbon-based PBI binder alone has proton conductivity, but has high swellability with respect to phosphoric acid, a large dimensional change as a binder, and inhibits diffusibility of fuel gas and oxidant gas. It is thought that it is because it ends. On the other hand, in the VdF-HFP / DAPBz binder, a basic hydrocarbon having an affinity for phosphoric acid is bonded to the fluorine-based skeleton, so that both VdF-HFP / HFP / HFP / This is considered to be due to the construction of an effective three-phase interface by the catalyst layer of the DAPBz binder.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

It is explanatory drawing which shows the structure of the membrane electrode assembly which concerns on one Embodiment of this invention. It is a graph which shows the measurement result of the proton conductivity of the binder composition after impregnating the phosphoric acid in a present Example.

Claims (8)

Having at least a (—CF ₂ —CF (M) CH ₂ —CF ₂ —) structure (where M is any of CF ₃ , CF ₂ H, CFH ₂ ), and a basic compound is added A fluorine-based polymer and a hydrogen ion conductor,
The basic compound is a nitrogen-containing heterocyclic compound in which at least two hydrogen atoms are substituted,
The binder composition for a fuel cell, wherein the fluoropolymer is crosslinked with the basic compound.   2. The fuel cell binder composition according to claim 1, wherein the basic compound is a nitrogen-containing heterocyclic compound having at least two amino groups.   The basic compound is at least one selected from the group consisting of diaminoimidazole and derivatives thereof, diaminotriazine and derivatives thereof, diaminotriazole and derivatives thereof, diaminopyridine and derivatives thereof, and diaminobenzimidazole and derivatives thereof. The binder composition for fuel cells according to claim 2, wherein: The binder composition for a fuel cell according to claim 3, wherein the basic compound is a compound represented by any one of the following structural formulas (1) to (3).

  The fluorine-based polymer is at least one of vinylidene fluoride-hexafluoropropylene copolymer and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer. The binder composition for fuel cells according to any one of claims 1 to 4.   The hydrogen ion conductor is at least one acid selected from the group consisting of orthophosphoric acid, condensed phosphoric acid, alkylphosphoric acid, and phosphonic acid, according to any one of claims 1 to 5, The binder composition for fuel cells as described. A fuel cell electrolyte, and electrode catalyst layers disposed on both sides in the thickness direction of the fuel cell electrolyte,
The electrode catalyst layer has a catalyst material in which a catalyst substance is supported on a catalyst carrier, and a binder that binds the catalyst material,
The said binder contains the binder composition for fuel cells in any one of Claims 1-6, The membrane electrode assembly characterized by the above-mentioned. A membrane electrode assembly comprising a fuel cell electrolyte, and electrode catalyst layers disposed on both sides in the thickness direction of the fuel cell electrolyte;
Separators bonded to both surfaces of the membrane electrode assembly;
With
The electrode catalyst layer has a catalyst material in which a catalyst substance is supported on a catalyst carrier, and a binder that binds the catalyst material,
The said binder contains the binder composition for fuel cells in any one of Claims 1-6, The fuel cell characterized by the above-mentioned.

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