JP2013178908A - Catalyst ink and method for manufacturing fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve power generation performance of a fuel cell by improving a catalyst ink for forming a catalyst electrode layer.SOLUTION: A method for manufacturing a catalyst ink for forming a catalyst electrode layer including a polymer electrolyte having proton conductivity and a catalyst particle having a catalyst comprises steps of: preparing a polymer electrolyte precursor which turns into a polymer electrolyte having proton conductivity via hydrolysis treatment, a high oxygen permeable resin which is a fluorine resin having higher oxygen permeability than the polymer electrolyte, and a fluorine-based solvent which can dissolve the high oxygen permeable resin; and mixing the polymer electrolyte precursor, the high oxygen permeable resin, and the fluorine-based solvent and dispersing the polymer electrolyte precursor into a resin solution in which the high oxygen permeable resin is dissolved in the fluorine-based solvent.

Description

  The present invention relates to a catalyst ink and a method for producing a fuel cell.

  The polymer electrolyte fuel cell includes a polymer electrolyte membrane having proton conductivity, and an anode and a cathode which are catalyst electrode layers formed on the electrolyte membrane. The catalyst electrode layer generally includes catalyst particles including a catalyst metal and a polymer electrolyte having proton conductivity. Conventionally, various studies have been made to improve the performance of such fuel cells.

  As one of the measures for improving the performance of the fuel cell, there has been proposed a structure in which a polymer compound having high oxygen solubility is contained in the cathode catalyst electrode layer (see, for example, Patent Document 1). In this way, by incorporating a polymer compound having high oxygen solubility in the cathode, the oxygen concentration in the vicinity of the catalyst metal is increased, the water generation reaction at the cathode is promoted (the exchange current density is increased), and the activation overvoltage is reduced. Battery performance can be improved by lowering.

JP 2011-1113739 A JP 2011-241344 A JP 2011-181344 A

  Here, the catalyst electrode layer is generally formed by preparing a catalyst ink in which catalyst particles and a polymer electrolyte are dispersed in a solvent, and applying the catalyst ink on a substrate. Therefore, as a method of incorporating a polymer compound having high oxygen solubility in the catalyst electrode layer, for example, a method of mixing a polymer compound having high oxygen solubility in the catalyst ink can be considered. However, it is difficult to uniformly disperse a plurality of polymers having different properties such as a polymer compound having high oxygen solubility and a polymer electrolyte in a solvent. If a catalyst electrode layer is formed using a catalyst ink that is not in a sufficiently dispersed state, there is a possibility that the catalyst electrode layer does not have a polymer electrolyte in a sufficiently dispersed state around the catalyst metal. If the polymer electrolyte does not exist in a sufficiently dispersed state around the catalyst metal, the efficiency of proton transfer from the electrolyte membrane to the catalyst metal becomes insufficient, and the power generation efficiency of the fuel cell may be reduced.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to improve the power generation performance of a fuel cell by improving a catalyst ink for forming a catalyst electrode layer.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A method for producing a catalyst ink for forming a catalyst electrode layer comprising a polymer electrolyte having proton conductivity and catalyst particles comprising a catalyst,
A polymer electrolyte precursor that becomes a polymer electrolyte having proton conductivity by hydrolysis treatment, a high oxygen permeable resin that is a fluororesin having a higher oxygen permeability than the polymer electrolyte, and the high oxygen permeable resin. A preparation step of preparing a soluble fluorine-based solvent;
The polymer electrolyte precursor, the high oxygen permeable resin, and the fluorine solvent are mixed, and the polymer is added to a resin solution in which the high oxygen permeable resin is dissolved in the fluorine solvent. A dispersion step of dispersing the electrolyte precursor;
A method for producing a catalyst ink comprising:

  According to the method for producing the catalyst ink described in Application Example 1, in order to disperse the electrolyte precursor in the resin solution in which the high oxygen permeable resin is dissolved in the fluorinated solvent, the high oxygen permeable resin, the electrolyte precursor, Can be obtained by uniformly mixing the catalyst ink. Therefore, if a catalyst electrode layer is produced using the catalyst ink, a catalyst electrode layer can be obtained by increasing the oxygen concentration in the vicinity of the catalyst and reducing the activation overvoltage by adding a high oxygen permeable resin. At the same time, it is possible to disperse the polymer electrolyte sufficiently uniformly with respect to the catalyst. Furthermore, since the resin used as the high oxygen permeable resin is a fluororesin excellent in chemical resistance and heat resistance, the durability of the catalyst electrode layer produced from the catalyst ink is impaired by the addition of the high oxygen permeable resin. Can be suppressed.

[Application Example 2]
The method for producing a catalyst ink according to Application Example 1, wherein the high oxygen permeable tree is a fluororesin having a ring structure in a skeleton.
According to the method for producing a catalyst ink described in Application Example 2, by using the catalyst ink produced by such a production method, a catalyst electrode excellent in the effect of increasing the oxygen concentration in the vicinity of the catalyst and reducing the activation overvoltage. Layers can be made.

[Application Example 3]
It is a manufacturing method of the catalyst ink of the application example 2, Comprising: The said dispersion | distribution process WHEREIN: The said polymer electrolyte precursor is such that the weight ratio of the said high oxygen permeability resin with respect to the said polymer electrolyte precursor will be 1-50 wt%. A method for producing a catalyst ink, which is a step of mixing a body and the high oxygen permeable resin.
According to the method for producing a catalyst ink described in Application Example 3, by using the catalyst ink produced by such a production method, a catalyst particularly excellent in the effect of increasing the oxygen concentration in the vicinity of the catalyst and reducing the activation overvoltage An electrode layer can be produced.

[Application Example 4]
A method for producing a fuel cell, comprising: an electrolyte membrane exhibiting proton conductivity; and a catalyst electrode layer provided on the electrolyte membrane,
A first step of producing the catalyst ink by the catalyst ink production method according to any one of Application Examples 1 to 3,
A second step of forming a layer of the catalyst ink on a first substrate for forming the catalyst electrode layer;
A third step of subjecting the layer made of the catalyst ink formed on the first substrate to a hydrolysis treatment to form the catalyst electrode layer comprising the polymer electrolyte and the catalyst particles;
A method for manufacturing a fuel cell comprising:

  According to the method of manufacturing a fuel cell described in Application Example 4, the catalyst electrode in which the oxygen concentration in the vicinity of the catalyst is increased to lower the activation overvoltage and the polymer electrolyte is sufficiently dispersed in the catalyst. A fuel cell comprising a layer can be obtained. Therefore, the power generation performance of the entire fuel cell can be improved.

[Application Example 5]
The fuel cell manufacturing method according to Application Example 4, wherein the first substrate is a precursor film that becomes the electrolyte film by hydrolysis, and the fuel cell manufacturing method further includes the first substrate. After the step, prior to the second step, a third step of applying a layer made of the catalyst ink on the second substrate for applying the catalyst ink, and on the second substrate A fourth step of drying the applied catalyst ink layer, and the second step transfers the catalyst ink layer dried in the fourth step onto the precursor film. The method of manufacturing a fuel cell, wherein the third step is a step of subjecting the precursor film and the layer made of the catalyst ink formed on the precursor film to an integral hydrolysis treatment.
According to the method for producing a fuel cell described in Application Example 5, the catalyst ink layer is dried in the fourth step, so that the polymer electrolyte precursor is disposed in the vicinity of the catalyst particles in the catalyst ink layer. The oxygen permeable resin is disposed near the surface of the catalyst ink layer. Therefore, even if the high oxygen permeable resin does not have sufficient ion conductivity, the oxygen permeability of the entire catalyst electrode layer can be increased, and the performance of the fuel cell can be improved. Moreover, since the layer made of the catalyst ink and the precursor film are integrally hydrolyzed, the manufacturing process can be prevented from becoming complicated.

[Application Example 6]
The method of manufacturing a fuel cell according to Application Example 4, wherein after the second step, the catalyst ink layer applied on the first substrate is dried before the third step. And a sixth step of transferring the catalyst electrode layer formed on the first substrate onto the electrolyte membrane after the third step. Method.
According to the method of manufacturing a fuel cell described in Application Example 6, the catalyst ink layer is dried in the fifth step, so that the polymer electrolyte precursor is disposed in the vicinity of the catalyst particles in the catalyst ink layer. The oxygen permeable resin is disposed near the surface of the catalyst ink layer. Therefore, even if the high oxygen permeable resin does not have sufficient ion conductivity, the oxygen permeability of the entire catalyst electrode layer can be increased, and the performance of the fuel cell can be improved.

[Application Example 7]
The fuel cell manufacturing method according to Application Example 4, wherein the first substrate is a precursor film that becomes the electrolyte film by hydrolysis, and the fuel cell manufacturing method further includes the second substrate. After the step, prior to the third step, the method includes a seventh step of drying the catalyst ink layer applied on the precursor film, and the third step includes the precursor film, A method for producing a fuel cell, which is a step of subjecting the layer made of the catalyst ink formed on the precursor film to an integral hydrolysis treatment.
According to the method for producing a fuel cell described in Application Example 7, the catalyst ink layer is dried in the seventh step, so that the polymer electrolyte precursor is disposed in the vicinity of the catalyst particles in the catalyst ink layer. The oxygen permeable resin is disposed near the surface of the catalyst ink layer. Therefore, even if the high oxygen permeable resin does not have sufficient ion conductivity, the oxygen permeability of the entire catalyst electrode layer can be increased, and the performance of the fuel cell can be improved. Moreover, since the layer made of the catalyst ink and the precursor film are integrally hydrolyzed, the manufacturing process can be prevented from becoming complicated.

[Application Example 8]
The fuel cell manufacturing method according to Application Example 4, wherein the first substrate is the electrolyte membrane, and the fuel cell manufacturing method further includes the third step after the second step. Prior to the step, a method of manufacturing a fuel cell comprising an eighth step of drying the catalyst ink layer applied on the electrolyte membrane.
According to the method for producing a fuel cell described in Application Example 8, the catalyst ink layer is dried in the eighth step, so that the polymer electrolyte precursor is disposed in the vicinity of the catalyst particles in the catalyst ink layer. The oxygen permeable resin is disposed near the surface of the catalyst ink layer. Therefore, even if the high oxygen permeable resin does not have sufficient ion conductivity, the oxygen permeability of the entire catalyst electrode layer can be increased, and the performance of the fuel cell can be improved.

  The present invention can be realized in various forms other than the above, for example, a form of a catalyst electrode manufactured by the method for manufacturing a catalyst ink of the present application, or a fuel cell manufactured by a method for manufacturing a fuel cell of the present application. Can be realized.

It is a cross-sectional schematic diagram showing schematic structure of a fuel cell. It is explanatory drawing which represents the structure of a cathode typically. It is explanatory drawing showing the outline of the manufacturing process of a membrane-electrode assembly. It is explanatory drawing showing the mode in the middle of manufacture of a membrane-electrode assembly. It is explanatory drawing showing the mode in the middle of manufacture of a membrane-electrode assembly. It is explanatory drawing which shows the evaluation result of electric power generation performance. It is explanatory drawing showing the outline of the manufacturing process of a membrane-electrode assembly. It is explanatory drawing showing the outline of the manufacturing process of a membrane-electrode assembly. It is explanatory drawing showing the outline of the manufacturing process of a membrane-electrode assembly. It is explanatory drawing showing the outline of the manufacturing process of a membrane-electrode assembly.

A. Fuel cell configuration:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a fuel cell manufactured using a catalyst ink manufactured by a catalyst ink manufacturing method as a first embodiment of the present invention. The fuel cell of the present embodiment is a solid polymer fuel cell that generates power upon receiving supply of hydrogen and oxygen as reaction gases. The fuel cell has a stack structure in which a plurality of single cells 10 are stacked, and FIG. 1 shows the structure of the single cells 10.

  The single cell 10 includes an MEA (Membrane Electrode Assembly) 27, gas diffusion layers 23 and 24, and gas separators 25 and 26. The MEA 27 includes an electrolyte membrane 20 and an anode 21 and a cathode 22 that are catalyst electrode layers formed on each surface of the electrolyte membrane 20. The MEA 27 is sandwiched between the gas diffusion layers 23 and 24, and the sandwich structure composed of the MEA 27 and the gas diffusion layers 23 and 24 is further sandwiched between the gas separators 25 and 26 from both sides.

The electrolyte membrane 20 is a proton conductive ion exchange membrane formed of a polymer electrolyte material, for example, a fluororesin, and exhibits good electrical conductivity in a wet state. Specifically, for example, a membrane made of a perfluorosulfonic acid polymer having a sulfo group (—SO ₃ H group) at the end of the side chain can be used.

The cathode 22 and the anode 21 include carbon particles supporting a catalytic metal that proceeds with an electrochemical reaction, and a polymer electrolyte having proton conductivity. As the catalyst metal, for example, platinum or a platinum alloy made of platinum and another metal such as ruthenium can be used. As the polymer electrolyte, for example, a perfluorosulfonic acid polymer having a sulfo group (—SO ₃ H group) at a side chain end can be used. The polymer electrolyte provided in the catalyst electrode layer may be the same kind of polymer as the polymer electrolyte constituting the electrolyte membrane 20 or may be a different kind of polymer. In the present embodiment, the cathode 22 further includes a high oxygen permeable resin. Detailed description of the cathode 22 and the high oxygen permeable resin will be described later.

  The gas diffusion layers 23 and 24 are made of a member having gas permeability and electronic conductivity, and are formed of, for example, a metal member such as foam metal or metal mesh, or a carbon member such as carbon cloth or carbon paper. can do.

  The gas separators 25 and 26 are formed of a gas-impermeable conductive member, for example, a carbon-made member such as dense carbon that has been made to be gas-impermeable by compressing carbon, or a metal member such as press-molded stainless steel. ing. In the gas separators 25 and 26, flow channel grooves 28 and 29 through which a reaction gas flows are formed on the surface facing the catalyst electrode layer. A porous body for forming an in-cell gas flow path may be disposed between the gas separators 25 and 26 and the gas diffusion layers 23 and 24. In this case, the flow path grooves 28 and 29 are provided. May be omitted.

  An inter-cell refrigerant flow path is further formed inside the fuel cell (not shown). Such a refrigerant flow path may be formed, for example, between all the stacked single cells, or may be formed every time a predetermined number of single cells are stacked.

  Further, the fuel cell is formed with a plurality of flow paths that penetrate the fuel cell in the stacking direction. Specifically, a gas manifold for supplying / discharging the reaction gas to / from each cell and a refrigerant manifold for supplying / discharging the refrigerant to / from the refrigerant flow path described above are formed. Further, in the fuel cell, a seal member (not shown) is arranged at a predetermined position between the outer periphery of the MEA 27 or the gas separators 25 and 26. Such a seal member prevents fluid leakage and prevents short circuit between the gas separators 25 and 26.

B. Cathode configuration:
FIG. 2 is an explanatory diagram schematically showing the configuration of the cathode 22. As described above, the cathode 22 serving as the catalyst electrode layer includes the carbon particles (catalyst-supporting carbon 30) supporting the catalyst metal, and the resin layer 35 made of the polymer electrolyte and the high oxygen permeable resin. Yes. As shown in FIG. 2, the resin layer 35 includes a polymer electrolyte portion 32 disposed on the vicinity side of the catalyst-carrying carbon 30 and a high oxygen permeable resin portion 34 disposed on the surface side of the resin layer 35. It has a two-layer structure. The polymer electrolyte part 32 is mainly composed of a polymer electrolyte. The high oxygen permeable resin portion 34 is mainly composed of a high oxygen permeable resin.

  The high oxygen permeable resin used in the present embodiment is a fluororesin having a higher oxygen permeability (a larger oxygen permeability coefficient) than the polymer electrolyte provided in the resin layer 35. Specific examples of such a high oxygen permeable resin include CYTOP manufactured by Asahi Glass Co., Ltd. (CYTOP is a registered trademark), Teflon AF manufactured by Du Pont (Teflon is a registered trademark), and Solvay Solexis Hyflon AD (Hyflon is a registered trademark). The structural formula of the high oxygen permeable resin is exemplified below. Formula (1) is a structural formula of CYTOP, and Formula (2) is a structural formula of Teflon AF.

  As shown in the formulas (1) and (2), the high oxygen permeable resin has a fluorine-containing aliphatic ring structure (for example, a pentagonal oxygen-containing cyclic structure) introduced into a skeleton having a perfluoro structure. ing. Such a high oxygen permeable resin is amorphous due to the loss of regularity due to the introduction of a ring structure in the skeleton. It is considered that the oxygen permeability of the high oxygen permeable resin is increased when the ring structure is introduced as described above and the resin density is lowered (the steric structure becomes rough). For example, a plurality of types of resins having different end groups are known for CYTOP. Regardless of the structure of the terminal group, any of the high oxygen permeable resins in the present invention can be used.

C. Manufacturing process of membrane electrode assembly:
FIG. 3 is an explanatory view showing a manufacturing process of the MEA 27 of the present embodiment. 4 and 5 are explanatory diagrams showing a state during the manufacture of the MEA 27. FIG. In order to manufacture the MEA 27, first, a precursor film is prepared (step S100). A precursor film | membrane is a film | membrane used as the precursor of the electrolyte membrane 20 with which a fuel cell is provided. Specifically, it is a fluororesin similar to the electrolyte membrane 20 and is a perfluorocarbon sulfonyl fluoride having a “—SO ₂ F group” instead of a sulfo group (—SO ₃ H group) which is an ion exchange group. A film made of polymer. Such a precursor film can be made into the electrolyte film 20 by performing a hydrolysis treatment and converting a sulfo group into a “—SO ₃ H group”. In the present embodiment, the precursor film corresponds to the “first substrate” in the claims.

  Also, a catalyst ink material is prepared (step S110). Specifically, an electrolyte precursor, the above-described high oxygen permeable resin, a fluorinated solvent, and the above-described catalyst-supporting carbon 30 are prepared.

The electrolyte precursor, "- SO ₂ F groups" have, by converting the "-SO ₂ F groups" sulfo groups by hydrolysis, fluorocarbon resin as a polymer electrolyte having proton conductivity ( Perfluorocarbon sulfonyl fluoride polymer). The electrolyte precursor may be the same type of polymer as that of the fluororesin constituting the precursor film, or may be a different type of polymer.

  The fluorine-based solvent is a solvent that can dissolve the high oxygen-permeable resin. As described above, the high oxygen permeable resin is an amorphous fluororesin in which a ring structure is introduced into the skeleton. Therefore, unlike a linear fluororesin such as polytetrafluoroethylene (PTFE), it can be dissolved in a specific fluorine-based solvent. In step S110, a fluorine-based solvent capable of dissolving the high oxygen permeable resin may be prepared according to the high oxygen permeable resin to be used. As the fluorine-based solvent, hydrofluoroether (HFE), for example, Novec (Novec is a registered trademark) 7100, 7300, 7600 manufactured by Sumitomo 3M Limited can be used.

  The catalyst-supporting carbon 30 can be manufactured by, for example, dispersing carbon particles made of carbon black in a platinum compound solution and performing an impregnation method, a coprecipitation method, or an ion exchange method. As the platinum compound solution, for example, a tetraammine platinum salt solution, a dinitrodiammine platinum solution, a platinum nitrate solution, or a chloroplatinic acid solution can be used.

  After step S110, an electrolyte precursor, a high oxygen permeable resin, and a fluorinated solvent are mixed, and a high oxygen permeable resin solution (hereinafter simply referred to as a resin solution) formed by dissolving the high oxygen permeable resin in the fluorinated solvent. The electrolyte precursor is dispersed (step S120). The treatment performed in step S120 may be a treatment that can sufficiently disperse the electrolyte precursor in the resin solution. For example, the stirring treatment, the ultrasonic treatment, and the heat treatment may be appropriately combined.

  After step S120, the catalyst-supporting carbon 30 is further charged and mixed in the resin solution in which the electrolyte precursor is dispersed (step S130). The mixing amount of the catalyst-supporting carbon 30 may be, for example, in a range where the weight ratio of the electrolyte precursor to the carbon weight of the catalyst-supporting carbon 30 is 0.5 to 1.2. Further, a dispersion process (for example, a process combining a stirring process and an ultrasonic process) is performed to produce a catalyst ink in which the catalyst-supporting carbon 30 is dispersed (step S140).

  Thereafter, the produced catalyst ink is applied on the substrate and dried (step S150). Here, the substrate may be any film that can be formed into a film by applying a catalyst ink. In consideration of peelability and heat resistance, the substrate can be a thin film made of, for example, polyethylene terephthalate (PET) or polytetrafluoroethylene (PTFE). The substrate used in step S150 corresponds to the “second substrate” in the claims. Further, the coating method in step S150 is not particularly limited. For example, a spray method, a screen printing method, a doctor blade method, a die coating method, or the like can be used.

FIG. 4A shows a state in which the catalyst ink is applied on the substrate 40 in step S150 to form a layer made of the catalyst ink (hereinafter referred to as catalyst ink layer 42). FIG. 4B shows a state in which the catalyst ink is dried from the state of FIG. 4A and the fluorinated solvent in the catalyst ink is volatilized. When the catalyst ink is dried to volatilize the solvent, the catalyst ink layer 42 becomes a porous layer, and a high oxygen-permeable resin that is a solid component is deposited in the catalyst ink layer 42. At that time, since the electrolyte precursor and the high oxygen permeable resin are resins having different properties, in the catalyst ink layer 42, a portion mainly containing the electrolyte precursor and a portion mainly containing the high oxygen permeable resin Is separated. At this time, the electrolyte precursor is attracted to the catalyst-supporting carbon 30 to form the electrolyte precursor portion 43, and the high oxygen permeable resin is disposed on the surface side to form the high oxygen permeable resin portion 34. The reason why such layer separation occurs is that the “—SO ₂ F group” of the electrolyte precursor is a functional group having high adsorptivity, so that the electrolyte precursor is attracted to the catalyst-supporting carbon 30 (particularly, carbon particles). This is probably because of this. In addition, it is considered that the high oxygen permeable resin is relatively separated from the catalyst-supporting carbon 30 because the adsorptivity is reduced due to the loss of linearity due to the introduction of a ring structure in the skeleton. . For example, the high oxygen-permeable resin layer and the electrolyte precursor layer may be separated from each other by applying a dispersion in which the electrolyte precursor is dispersed in a resin solution onto a suitable substrate and drying. Then, it can be easily observed by using an optical microscope. In the drying step in step S150, at least a part of the fluorinated solvent is volatilized from the catalyst ink, and in the catalyst ink layer 42, each of the electrolyte precursor and the high oxygen permeable resin is in the entire catalyst ink layer 42. The above-mentioned phenomenon that is unevenly distributed may be generated. Therefore, the temperature and time can be set arbitrarily.

  After step S150, the catalyst ink layer 42 on the substrate 40 is transferred onto the precursor film prepared in step S100 (step S160). FIG. 4 also shows how the catalyst ink layer 42 is transferred to the precursor film 44 side. The transfer of the catalyst ink layer 42 from the substrate 40 side to the precursor film 44 side may be performed by, for example, hot pressure transfer (hot press). After the transfer, the substrate 40 is peeled from the catalyst ink layer 42. FIG. 5A shows a state in which the catalyst ink layer 42 is transferred onto the precursor film 44.

After step S160, the entire structure in which the catalyst ink layer 42 is formed on the precursor film 44 is hydrolyzed (step S170). Specific contents of the hydrolysis treatment are as follows.
(1) The precursor film 44 on which the catalyst ink layer 42 is formed is immersed in an alkaline solution (NaOH solution), and the “—SO ₂ F group” of the precursor film 44 and the electrolyte precursor of the catalyst ink layer 42 is contained. It is modified to “—SO ₃ Na group”.
(2) After the precursor film 44 on which the catalyst ink layer 42 is formed is washed with water, it is immersed in an acidic solution (H ₂ SO ₄ solution or HNO ₃ solution), and the “-SO ₃ Na group modified in the previous step is used. Is further modified into a “—SO ₃ H group”.

  By this step, proton conductivity is imparted to the electrolyte precursor contained in the precursor film 44 and the catalyst ink layer 42. That is, the precursor film 44 becomes the electrolyte membrane 20 which is an ion exchange membrane. Further, the catalyst precursor layer 43 becomes the polymer electrolyte portion 32, whereby the catalyst ink layer 42 becomes the cathode 22.

Thereafter, an anode 21 is further formed on the electrolyte membrane 20 (step S180) to complete the MEA 27. The anode 21 can be formed using, for example, a catalyst ink in which a perfluorosulfonic acid polymer having “—SO ₃ H groups” that are ion exchange groups and a catalyst-supporting carbon 30 are dispersed in a solvent. Such a catalyst ink may be applied to a predetermined substrate and dried to form the anode 21 and then transferred onto the electrolyte membrane 20.

  According to the method for producing the catalyst ink of the present embodiment configured as described above, in order to disperse the electrolyte precursor in the high oxygen permeable resin solution using the specific fluorine-based solvent, the high oxygen permeable resin and A catalyst ink in which the electrolyte precursor is uniformly mixed can be obtained. Therefore, by adding a high oxygen permeable resin to the cathode 22, an effect of increasing the oxygen concentration in the vicinity of the catalyst metal and lowering the activation overvoltage can be obtained, and the polymer electrolyte can be sufficiently uniform with respect to the catalyst metal. It can be distributed. As a result, as a whole, the reactivity at the cathode 22 can be increased, and the power generation performance of the entire fuel cell can be improved.

In producing a catalyst ink, generally, a polymer electrolyte having an ion exchange group, not an electrolyte precursor, is dispersed in a solvent. When the polymer electrolyte is dispersed in the solvent as described above, the polymer electrolyte usually forms a micelle structure. That is, the polymer electrolyte is associated with particles in a solvent to form a droplet dispersion system. For this reason, even if a high oxygen-permeable resin having properties different from those of the polymer electrolyte is further added to the catalyst ink, it is difficult to sufficiently uniformly disperse the polymer electrolyte and the high oxygen-permeable resin. In the present embodiment, a fluororesin in which a ring structure is introduced into the skeleton and oxygen permeability is increased is used as the high oxygen permeable resin. Therefore, in the fluororesin, the above ring structure is introduced. Due to its characteristic structure, it can be dissolved in a specific fluorine-based solvent. Therefore, by using such a fluorinated solvent, a high oxygen permeable resin can be prepared in a solution state. Furthermore, since the solvent capable of dissolving the high oxygen permeable resin is a hydrophobic fluorine-based solvent, and an electrolyte precursor having a “—SO ₂ F group” is used instead of the polymer electrolyte, the electrolyte precursor is It becomes possible to disperse uniformly in the resin solution without forming micelles. Therefore, a catalyst ink in which the electrolyte precursor and the high oxygen permeable resin are sufficiently uniformly dispersed can be obtained, and the polymer electrolyte can be disposed in the cathode 22 in a state in which the polymer electrolyte is sufficiently dispersed. it can.

  In particular, in the cathode 22 of the present embodiment, the polymer electrolyte portion 32 is formed in the vicinity of the catalyst-supporting carbon 30, and the high oxygen-permeable resin portion 34 is formed on the surface side. Even if the permeable resin is dissolved, the power generation performance of the entire fuel cell can be improved. The reason why the power generation performance is improved by adding a high oxygen permeable resin not having proton conductivity is considered as follows. The high oxygen permeable resin is a polymer having a higher oxygen permeability (a larger oxygen permeability coefficient) than that of the polymer electrolyte. Oxygen permeability (oxygen permeability coefficient) is generally understood as the product of oxygen solubility (oxygen solubility coefficient) and oxygen diffusivity (oxygen diffusion coefficient). The high oxygen-permeable resin used in the present embodiment is considered to have at least oxygen solubility superior to that of the polymer electrolyte by introducing a ring structure into the skeleton and making the steric structure coarse. Therefore, by disposing the high oxygen permeable resin on the surface side of the cathode 22, even if the polymer electrolyte concentration of the entire cathode 22 is somewhat reduced, the oxygen solubility is increased, and as a result, the oxygen permeability of the entire cathode 22 is increased. Is larger, and it is considered that battery performance can be improved.

  Furthermore, in this embodiment, since the catalyst ink layer 42 is formed on the precursor film 44 and both are integrally hydrolyzed, an ion exchange group is introduced into each of the catalyst electrode layer and the electrolyte film. Hydrolysis of is required only once. Therefore, even if the catalyst ink provided with the electrolyte precursor is used, the manufacturing process can be prevented from becoming complicated.

  Further, since the resin used as the high oxygen permeable resin is a fluororesin excellent in chemical resistance and heat resistance, the durability of the cathode 22 used in an acidic atmosphere is impaired by the addition of the high oxygen permeable resin. Can be suppressed.

D. Evaluation of power generation performance:
FIG. 6 is an explanatory diagram showing the results of evaluating the power generation performance of the fuel cell with different amounts, types, and manufacturing methods of the high oxygen permeable resin added to the cathode. In FIG. 6, the power generation performance is evaluated for the fuel cells of Samples 1 to 12 having different cathode configurations.

The fuel cells of Samples 1 to 5 and 11 use CYTOP (the terminal functional group is —CF ₃ ) as a high oxygen permeable resin included in the cathode, and the fuel cells of Samples 6 to 9 and 12 have a cathode of Teflon AF 2400 was used as the high oxygen permeable resin provided. In the fuel cell of Sample 10, a high oxygen permeable resin is not mixed in the cathode.

  The fuel cell membrane-electrode assemblies of Samples 1 to 9 were manufactured by the manufacturing process shown in FIG. 3 under the conditions shown in FIG. Specifically, when preparing the catalyst ink material in step S110, in samples 1, 2, 3, 4, and 5, the weight ratio of CYTOP to the electrolyte precursor is 1 wt%, 10 wt%, and 30 wt%, respectively. , 50 wt%, and 75 wt% (see FIG. 6). In Samples 6, 7, 8, and 9, the weight ratio of Teflon AF 2400 to the electrolyte precursor was 10 wt%, 30 wt%, 50 wt%, and 75 wt%, respectively (see FIG. 6).

  In any of samples 1 to 9, in step S110, catalyst-supporting carbon in which 50 wt% platinum was supported on carbon particles was prepared as catalyst-supporting particles. In Step S110, Novec7300 was prepared as a fluorine-based solvent. In addition, when the electrolyte precursor layer is dispersed in the resin solution in step S120, the ratio of the solid content (electrolyte precursor + high oxygen permeable resin) to the fluorine-based solvent is adjusted to be 5 to 10 wt%. did. In the dispersion operation in step S120, the mixture was heated to 60 ° C. and stirred for 1 hour or longer, and then ultrasonic dispersion was performed for 0.5 hour or longer. In the dispersion step of step S120, the electrolyte precursor is sufficiently uniformly dispersed in the resin solution without forming micelles. The particle size of the electrolyte precursor in the resin solution is determined by a laser particle size distribution meter. It was confirmed by measuring.

In step S130, the catalyst-carrying carbon was added to the dispersion so that the weight ratio of the electrolyte precursor to the carbon weight of the catalyst-carrying carbon was 75 wt%. In step S140, the catalyst-supporting carbon was dispersed under the same conditions as in step S120. In step S150, the catalyst ink was applied on a PTFE substrate and allowed to dry at room temperature for 5 minutes. In step S170, the precursor film coated with the catalyst ink is immersed in a 9N aqueous sodium hydroxide solution (9N-NaOH) for 20 minutes, washed with water, and then washed in a 1N aqueous nitric acid solution (1N-HNO ₃ ). Soaked for 20 minutes.

FIG. 7 is an explanatory diagram showing a manufacturing process of the membrane-electrode assembly included in the fuel cells of Samples 10 to 12. In FIG. 7, first, an electrolyte membrane was prepared (step S200). The electrolyte membrane prepared in step S200 is a membrane made of a perfluorosulfonic acid polymer having a sulfo group (—SO ₃ H group) at the end of the side chain. Examples of commercially available electrolyte membranes include Nafion membranes manufactured by Du Pont (Nafion is a registered trademark), DOW membranes manufactured by Dow Chemical (DOW is a registered trademark), and Aciplex (Aciplex is a registered trademark) manufactured by Asahi Kasei. Can be used. In order to manufacture the fuel cells of Samples 10 to 12, a DOW membrane was used.

In step S210, a catalyst ink material was prepared. Here, unlike step S110, a polymer electrolyte instead of an electrolyte precursor, specifically, a perfluorosulfonic acid polymer having a sulfo group (—SO ₃ H group) at the end of the side chain was prepared. In step S210, sample 10 does not prepare a high oxygen permeable resin, but sample 11 provides CYTOP as a high oxygen permeable resin, and sample 12 prepared Teflon AF 2400. In step S210, an aqueous alcohol solution was prepared as a solvent. As catalyst-carrying particles, the same catalyst-carrying carbon as Samples 1-9 was prepared.

  In step S220, the electrolyte, the catalyst-supporting carbon, and, in the samples 11 and 12, the high oxygen permeable resin in the solvent were mixed at the same time, and the same dispersion treatment as in step S120 was performed. At this time, the catalyst-carrying carbon and the polymer electrolyte were mixed so that the weight ratio of the polymer electrolyte to the carbon weight of the catalyst-carrying carbon was 75 wt%. In Samples 11 and 12, the weight ratio of the high oxygen permeable resin to the polymer electrolyte was 30 wt% (see FIG. 6).

  The process of applying and drying the catalyst ink in step S230 was performed in the same manner as in step S150. The transfer process in step S240 was performed in the same manner as in step S160. However, in samples 10 to 12, transfer was performed on the electrolyte membrane prepared in step S200. In Samples 10 to 12, the transfer target is an electrolyte membrane, and the catalyst ink contains a polymer electrolyte, and therefore, the hydrolysis treatment is not performed.

  In any of Samples 1 to 12, the anode was prepared in the same manner as the cathode of Sample 10. That is, a catalyst ink containing a polymer electrolyte and not containing a high oxygen permeable resin was used. In this way, a membrane-electrode assembly is prepared for each sample, and further, a single cell is manufactured by assembling the gas diffusion layers 23 and 24 and the gas separators 25 and 26, and the power generation performance is evaluated using the single cell. I did it. FIG. 6 shows the results of “power generation evaluation 1” and “power generation evaluation 2” with different evaluation conditions as the evaluation results of the fuel cells of samples 1 to 12.

The evaluation conditions of “power generation evaluation 1” are as follows. Hydrogen gas was supplied to the anode as a fuel gas, and a gas having an oxygen concentration of 1% (remaining nitrogen) was supplied to the cathode as an oxidizing gas. The flow rate of each reactive gas was 0.5 L / min (ntp) for the fuel gas and 1.1 L / min (ntp) for the oxidizing gas. Further, the fuel gas and the oxidizing gas were humidified to 75% RH. The cell temperature during power generation was 80 ° C. In “power generation evaluation 1”, power was generated at a current density of 0.1 (A / cm ² ) under such conditions, and the output voltage of the single cell at that time was measured.

The evaluation conditions of “Power generation evaluation 2” are as follows. Hydrogen gas was supplied to the anode as a fuel gas, and air (oxygen concentration 21%) was supplied to the cathode as an oxidizing gas. The flow rates of the reaction gases were 0.5 L / min (ntp) for the fuel gas and 2.0 L / min (ntp) for the oxidizing gas. Further, the fuel gas and the oxidizing gas were humidified so as to be 23% RH. The cell temperature during power generation was 95 ° C. In “power generation evaluation 2”, power was generated at a current density of 1.2 (A / cm ² ) under such conditions, and the output voltage of the single cell at that time was measured.

  “Power generation evaluation 1” improves oxygen permeability in the catalyst electrode layer by lowering the partial pressure of oxygen in the oxidizing gas and generating power at a low output while making the process of supplying oxygen to the catalyst a rate-limiting step. Is evaluated by the output voltage. Here, if the amount of humidification of the supply gas is insufficient, the polymer electrolyte in the electrolyte membrane or the catalyst electrode layer is dried, which may increase the overvoltage due to a decrease in the proton transfer rate. Further, if the amount of humidification of the supply gas is excessive, liquid concentration is generated in the catalyst electrode layer, which may increase the concentration overvoltage. Therefore, the humidification amount of the supply gas is set to 75% RH as a value that can suppress the increase in overvoltage.

  “Power generation evaluation 2” evaluated the degree of improvement in performance as a fuel cell by generating power under conditions close to the conditions under which the fuel cell is actually used. In recent years, in fuel cells, it has been desired to reduce the size or reduce the humidifier in order to simplify the configuration, and it is desired to obtain sufficient power generation performance in a lower humidified state. Therefore, in “power generation evaluation 2”, the humidification amount of the supply gas is set to 23% RH in order to evaluate the performance under more severe humidification conditions.

  As shown in FIG. 6, Samples 1 to 4 and Samples 6 to 8 had higher output voltages than Sample 10 in both “Power Generation Evaluation 1” and “Power Generation Evaluation 2”. That is, even when using either CYTOP or Teflon AF 2400 as the high oxygen permeable resin, when the weight ratio of the high oxygen permeable resin to the electrolyte precursor is 1 to 50 wt%, it does not have proton conductivity. It was confirmed that the battery performance improved despite the addition of resin.

  In both “power generation evaluation 1” and “power generation evaluation 2”, samples 1 to 4 had a higher output voltage than sample 11, and samples 6 to 8 had a higher output voltage than sample 12. That is, it is confirmed that the power generation performance of the fuel cell is improved by adopting the method for producing the catalyst ink of this embodiment regardless of whether CYTOP or Teflon AF 2400 is used as the high oxygen permeable resin. It was.

  Sample 5 has a better “power generation evaluation 1” result than sample 11, and sample 9 has a better “power generation evaluation 1” result than sample 12. Therefore, even if the weight ratio of the high oxygen permeable resin to the electrolyte precursor is increased to 75%, the oxygen permeation performance at the cathode 22 can be improved by employing the method for producing the catalyst ink of the present embodiment. Depending on the conditions, it was confirmed that the power generation performance of the fuel cell was improved.

E. Second embodiment:
FIG. 8 is an explanatory diagram showing a manufacturing process of the MEA 27 in the second embodiment. In the second and subsequent embodiments, the manufacturing process for manufacturing a fuel cell having the same configuration as that of the first embodiment is slightly different. In the description of the second and subsequent embodiments, the same reference numerals as those in the first embodiment are assigned to the components of the fuel cell, and detailed description thereof is omitted. Moreover, in the manufacturing process in each embodiment, the same reference number is attached | subjected to the process which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

In the second embodiment, to manufacture the MEA 27, first, the electrolyte membrane 20 is prepared (step S300). The electrolyte membrane prepared in step S300 is a membrane made of a perfluorosulfonic acid polymer having a sulfo group (—SO ₃ H group) at the side chain end, and can be executed in the same manner as in step S200 of FIG.

  Similarly to S110 of the first embodiment, an electrolyte precursor, a high oxygen permeable resin, a fluorine-based solvent, and catalyst-supporting carbon 30 are prepared as catalyst ink materials. Then, Steps S120 to S150 are further performed to form the catalyst ink layer 42 on the substrate.

  Thereafter, the catalyst ink layer 42 formed on the substrate is hydrolyzed (step S360). The specific content of the hydrolysis treatment is the same as in step S170. Thereby, the cathode 22 provided with the polymer electrolyte into which the ion exchange group is introduced is formed on the substrate. In the present embodiment, the substrate on which the catalyst ink is applied in step S150 corresponds to the “first substrate” in the claims.

  Thereafter, the cathode 22 formed on the substrate is transferred onto the electrolyte membrane 20 prepared in step S300 (step S370). Then, the anode 21 is further formed (step S180), and the MEA 27 is completed.

  Even with such a configuration, a catalyst ink similar to that of the first embodiment can be produced, and a fuel cell similar to that of the first embodiment can be manufactured.

F. Third embodiment:
FIG. 9 is an explanatory diagram showing the manufacturing process of the MEA 27 in the third embodiment. In the third embodiment, first, steps S100 to S140 are executed. As a result, the precursor film 44 is prepared as in the first embodiment, and a catalyst ink in which the electrolyte precursor and the high oxygen permeable resin are uniformly mixed is produced. Thereafter, the catalyst ink is applied on the precursor film 44 and dried (step S450). Thereby, the catalyst ink layer 42 is formed on the precursor film 44. Thereafter, Step S <b> 170 is performed to change the precursor film 44 into the electrolyte film 20 and the catalyst ink layer 42 into the cathode 22. Then, the anode 21 is further formed (step S180), and the MEA 27 is completed. In the present embodiment, the precursor film 44 corresponds to a “first substrate” in the claims.

  Even with such a configuration, a catalyst ink similar to that of the first embodiment can be produced, and a fuel cell similar to that of the first embodiment can be manufactured. Further, according to the third embodiment, since the catalyst ink is directly applied onto the precursor film 44, the step of transferring the catalyst ink layer 42 can be omitted. In addition, since the catalyst ink layer 42 is formed on the precursor film 44 and both are integrally hydrolyzed, the complexity of the manufacturing process associated with the hydrolyzing process can be suppressed.

G. Fourth embodiment:
FIG. 10 is an explanatory diagram showing a manufacturing process of the MEA 27 in the fourth embodiment. In the fourth embodiment, first, the electrolyte membrane 20 is prepared (step 500). The electrolyte membrane 20 prepared in step S300 is a membrane made of a perfluorosulfonic acid polymer having a sulfo group (—SO ₃ H group) at the end of the side chain, and can be executed in the same manner as in step S200 of FIG.

  Also, Steps S110 to S140 are executed to produce a catalyst ink in which the electrolyte precursor and the high oxygen permeable resin are uniformly mixed, as in the first embodiment. Thereafter, the catalyst ink is applied on the electrolyte membrane 20 and dried (step S550). Thereby, the catalyst ink layer 42 is formed on the electrolyte membrane 20. Thereafter, the catalyst ink layer 42 formed on the electrolyte membrane 20 is hydrolyzed (step S570). The specific content of the hydrolysis treatment is the same as in step S170. Thereby, the cathode 22 including the polymer electrolyte into which the ion exchange group is introduced is formed on the electrolyte membrane 20. Then, the anode 21 is further formed (step S180), and the MEA 27 is completed. In the present embodiment, the electrolyte membrane 20 to which the catalyst ink is applied in step S550 corresponds to the “first substrate” in the claims.

  Even with such a configuration, a catalyst ink similar to that of the first embodiment can be produced, and a fuel cell similar to that of the first embodiment can be manufactured.

H. Variations:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

H1. Modification 1 (Modification related to the order of steps):
In the first to fourth embodiments, when preparing the catalyst ink, first, the electrolyte precursor is dispersed in the resin solution in which the high oxygen permeable resin is dissolved, and then the catalyst-supporting carbon 30 is further mixed. However, a different configuration may be used. For example, the catalyst-supporting carbon 30 may be mixed at the same time when the electrolyte precursor, the high oxygen permeable resin, and the fluorinated solvent are mixed. Alternatively, the catalyst-supporting carbon 30 may be dispersed in the resin solution prior to dispersing the electrolyte precursor in the resin solution.

  In the first to fourth embodiments, the anode 21 is formed after the cathode 22 is formed. However, a different configuration may be used. For example, prior to forming the cathode 22, the anode 21 may be formed on the electrolyte membrane 20 prepared in step S300 or step S500.

H2. Modification 2 (deformation relating to catalyst particles):
In the first to fourth embodiments, the carbon particles carrying the catalyst metal are used as the catalyst particles including the catalyst. However, different configurations may be used. For example, catalyst particles obtained by supporting a catalyst metal on a conductive catalyst carrier other than carbon particles, such as metal particles and conductive ceramic particles, may be used. Even in such a configuration, when the catalyst ink is applied onto the base material, the precursor film, or the electrolyte film, the electrolyte precursor having higher adsorptivity is attracted to the catalyst particle side as the catalyst ink is dried. As in the first to fourth embodiments, layer separation occurs in the catalyst ink layer 42.

H3. Modification 3 (deformation relating to electrolyte and electrolyte membrane):
In the first to fourth embodiments, a membrane made of perfluorosulfonic acid polymer (fluorine resin) is used as the electrolyte membrane 20, but different configurations may be used. For example, a hydrocarbon-based polymer electrolyte membrane may be used. Applying a configuration using a hydrocarbon-based electrolyte membrane to the first embodiment, for example, in the state of the precursor membrane in step S100, and imparting proton conductivity to the precursor membrane by hydrolysis treatment It is also good. Examples of the hydrocarbon electrolyte membrane include aromatic polyether ketone such as polyether ether ketone, polyimide, polyphosphazene, polybenzimidazole, polyvinyl alcohol, and the like, which are ion exchange groups by sulfonation or the like. Is introduced.

In the first to fourth embodiments, the electrolyte precursor constituting the catalyst ink is a perfluorocarbon sulfonyl fluoride polymer having a “—SO ₂ F group” at the end of the side chain. However, different electrolyte precursors are used. May be used. For example, an ion exchange group precursor other than the “—SO ₂ F group” such as a precursor having a functional group capable of introducing a carboxyl group or a phosphate group by hydrolysis treatment may be provided. Any ion exchange group may be introduced by hydrolysis to impart proton conductivity.

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Electrolyte membrane 21 ... Anode 22 ... Cathode 23, 24 ... Gas diffusion layer 25, 26 ... Gas separator 27 ... MEA
28, 29 ... Channel groove 30 ... Catalyst support carbon 32 ... Polymer electrolyte part 34 ... High oxygen permeable resin part 35 ... Resin layer 40 ... Substrate 42 ... Catalyst ink layer 43 ... Electrolyte precursor part 44 ... Precursor film

Claims (8)

A method for producing a catalyst ink for forming a catalyst electrode layer comprising a polymer electrolyte having proton conductivity and catalyst particles comprising a catalyst,
A polymer electrolyte precursor that becomes a polymer electrolyte having proton conductivity by hydrolysis treatment, a high oxygen permeable resin that is a fluororesin having a higher oxygen permeability than the polymer electrolyte, and the high oxygen permeable resin. A preparation step of preparing a soluble fluorine-based solvent;
The polymer electrolyte precursor, the high oxygen permeable resin, and the fluorine solvent are mixed, and the polymer is added to a resin solution in which the high oxygen permeable resin is dissolved in the fluorine solvent. A dispersion step of dispersing the electrolyte precursor;
A method for producing a catalyst ink comprising: A method for producing the catalyst ink according to claim 1, comprising:
The method for producing a catalyst ink, wherein the high oxygen permeable tree is a fluororesin having a ring structure in a skeleton. A method for producing a catalyst ink according to claim 2,
The dispersion step is performed by mixing the polymer electrolyte precursor and the high oxygen permeable resin so that a weight ratio of the high oxygen permeable resin to the polymer electrolyte precursor is 1 to 50 wt%. A process for producing a catalyst ink, which is a process. A method for producing a fuel cell, comprising: an electrolyte membrane exhibiting proton conductivity; and a catalyst electrode layer provided on the electrolyte membrane,
A first step of producing the catalyst ink by the method of producing a catalyst ink according to any one of claims 1 to 3,
A second step of forming a layer of the catalyst ink on a first substrate for forming the catalyst electrode layer;
A third step of subjecting the layer made of the catalyst ink formed on the first substrate to a hydrolysis treatment to form the catalyst electrode layer comprising the polymer electrolyte and the catalyst particles;
A method for manufacturing a fuel cell comprising: A method for producing a fuel cell according to claim 4,
The first substrate is a precursor film that becomes the electrolyte film by hydrolysis treatment,
The method for manufacturing the fuel cell further includes:
After the first step, prior to the second step, a third step of applying a layer of the catalyst ink on the second substrate for applying the catalyst ink;
A fourth step of drying the catalyst ink layer coated on the second substrate;
With
The second step is a step of transferring the catalyst ink layer dried in the fourth step onto the precursor film,
The third step is a method of manufacturing a fuel cell, wherein the precursor film and a layer made of the catalyst ink formed on the precursor film are integrally hydrolyzed. The method of manufacturing a fuel cell according to claim 4, further comprising:
After the second step, prior to the third step, a fifth step of drying the catalyst ink layer applied on the first substrate;
After the third step, a sixth step of transferring the catalyst electrode layer formed on the first substrate onto the electrolyte membrane;
A method for manufacturing a fuel cell comprising: A method for producing a fuel cell according to claim 4,
The first substrate is a precursor film that becomes the electrolyte film by hydrolysis treatment,
The method for manufacturing the fuel cell further includes:
After the second step, prior to the third step, a seventh step of drying the catalyst ink layer applied on the precursor film,
The third step is a method of manufacturing a fuel cell, wherein the precursor film and a layer made of the catalyst ink formed on the precursor film are integrally hydrolyzed. A method for producing a fuel cell according to claim 4,
The first substrate is the electrolyte membrane;
The method for manufacturing the fuel cell further includes:
After the second step, prior to the third step, there is provided an eighth step of drying the catalyst ink layer applied on the electrolyte membrane.

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