JP2015090811A - Paste for fuel battery catalyst layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste for a fuel battery catalyst layer, by which a catalyst layer and a gas diffusion layer can be bonded together more reliably.SOLUTION: A paste P for a fuel battery catalyst layer comprises: a catalyst for facilitating an electrochemical reaction; an electrolyte having a fluorine component; and a dispersant, of which the solubility parameter is 18 or more. The paste is shaped in a film form by applying to a surface of each fluorine-containing film 11, 12; a face 21b, 22b is formed on the side of the surface of the fluorine-containing film 11, 12. After the shaping, to each face 21b, 22b, a gas diffusion layer of a fuel battery is bonded. Thus, the film-shaped paste will be used as a catalyst layer.

Description

  The present invention relates to a paste for a fuel cell catalyst layer which is formed into a film by being applied to the surface of a substrate and used as a catalyst layer of a fuel cell.

  In a polymer electrolyte fuel cell (hereinafter referred to as “PEFC”), a catalyst layer containing a catalyst for promoting an electrochemical reaction of fuel gas is provided, and a gas diffusion layer is adjacent to the catalyst layer. Is provided. The catalyst layer and the gas diffusion layer are joined to each other, and both constitute a PEFC.

  When the operating conditions of the PEFC change due to fluctuations in required power and the use environment of the catalyst layer and the gas diffusion layer changes accordingly, dimensional changes repeatedly occur in the catalyst layer and the gas diffusion layer. At this time, since there is a difference in the dimensional change between the catalyst layer and the gas diffusion layer, there is a risk that distortion occurs at the joint between the two, and damage starting from that occurs. For this reason, securing the bonding force between the catalyst layer and the gas diffusion layer is an important issue in maintaining the power generation performance of the PEFC.

  Patent Document 1 listed below describes a PEFC in which a polytetrafluoroethylene (PTFE) resin is contained in a water repellent layer that coats one side of a gas diffusion layer. In this PEFC, the PTFE resin is melted and moved to the outer surface of the water repellent layer by heating the gas diffusion layer to a temperature equal to or higher than the melting point of the PTFE resin during production. Thus, the joining force of a catalyst layer and a gas diffusion layer is improved by joining using PTFE resin segregated on the outer surface.

JP 2012-190752 A

  However, the PEFC described in Patent Document 1 has a problem that the bonding force between the catalyst layer and the gas diffusion layer cannot be guaranteed when a sufficient amount of PTFE resin does not segregate on the outer surface. As a result, the catalyst layer and the gas diffusion layer are separated, and there is a problem that the power generation performance of the PEFC is lowered.

  This invention is made | formed in view of such a subject, The objective is to provide the paste for fuel cell catalyst layers which can join a catalyst layer and a gas diffusion layer more reliably.

  In order to solve the above-mentioned problems, the fuel cell catalyst layer paste according to the present invention is formed into a film by coating on the surface of the substrate, and the surface formed on the surface of the substrate after the forming is the fuel cell. A paste for a fuel cell catalyst layer that is used as a catalyst layer by being joined to a gas diffusion layer of the catalyst, comprising a catalyst that promotes an electrochemical reaction, an electrolyte having a fluorine component, and a dispersion medium, The solubility parameter is 18 or more.

  According to the paste for a fuel cell catalyst layer according to the present invention, it is possible to control the segregation of the electrolyte with the solubility parameter of the dispersion medium, and by setting the solubility parameter to 18 or more, the electrolyte is on the substrate surface side. It is possible to reliably segregate the surface. As a result, the segregated electrolyte functions as an adhesive, and the catalyst layer and the gas diffusion layer can be more reliably bonded. Here, the “solubility parameter” is a dimensionless number expressed as σ or SP value.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the paste for fuel cell catalyst layers which can join a catalyst layer and a gas diffusion layer more reliably.

It is a schematic diagram showing the state which apply | coated the paste for fuel cell catalyst layers on the base-material surface. It is an enlarged view showing the hydrogen electrode catalyst layer and oxygen electrode catalyst layer of the fluorine-containing film surface vicinity. It is a schematic diagram showing transfer of the hydrogen electrode catalyst layer and the oxygen electrode catalyst layer to the electrolyte membrane. It is a schematic diagram showing the state which removed the base material after transcribe | transferring a hydrogen electrode catalyst layer and an oxygen electrode catalyst layer to an electrolyte membrane. It is a schematic diagram showing a gas diffusion layer. It is a schematic diagram showing a membrane-electrode assembly. It is a table | surface showing the test result of the joining force using the sample from which the solubility parameter of the dispersion medium of the paste for fuel cell catalyst layers differed mutually.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In order to facilitate understanding, the same components are denoted by the same reference numerals as much as possible in the drawings, and redundant description is omitted.

  First, the formation of the catalyst layer and the transfer to the electrolyte membrane will be described with reference to FIGS. FIG. 1 is a schematic view showing a state in which the fuel cell catalyst layer paste P is applied to the surfaces of the fluorine-containing films 11 and 12. FIG. 2 is an enlarged view showing the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 in the vicinity of the surfaces of the fluorine-containing films 11 and 12. FIG. 3 is a schematic diagram showing transfer of the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 to the electrolyte membrane 30. FIG. 4 is a schematic view showing a state in which the fluorine-containing films 11 and 12 are removed after the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 are transferred to the electrolyte membrane 30.

  The fuel cell catalyst layer paste P (hereinafter simply referred to as “paste P”) is a liquid substance containing a catalyst, an electrolyte having a fluorine component, and a dispersion medium. As the catalyst contained in the paste P, platinum or platinum alloys such as platinum cobalt and platinum carbon are used. As the electrolyte, Nafion (registered trademark) DE2020 having a proton conductivity with tetrafluoroethylene as the main chain is used. Further, water is used as the dispersion medium. The solubility parameter of water in the paste P is set to about 24.

  Hereinafter, the manufacturing procedure of PEFC using the paste P will be described.

(Formation of hydrogen electrode catalyst layer 21 and oxygen electrode catalyst layer 22)
First, the fluorine-containing films 11 and 12 used as a base material are prepared. And as shown in FIG. 1, the paste P is apply | coated to each surface of the fluorine-containing films 11 and 12. FIG. The paste P may be applied using a spray or a die coder.

  The paste P applied to the surfaces of the fluorine-containing films 11 and 12 is dried and has one side surface 21a and 22a on the upper surface side and the other side surface 21b and 22b on the lower surface side (the surface side of the fluorine-containing films 11 and 12). A film-like hydrogen electrode catalyst layer 21 and an oxygen electrode catalyst layer 22 having At this time, as shown in FIG. 2, the electrolyte layers 21c and 22c are formed in the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22, respectively, by the electrolyte segregating on the other side surfaces 21b and 22b. Each of the electrolyte layers 21c and 22c has a thickness of several tens to several hundreds of nanometers and functions as an adhesive as will be described later.

(Transfer to the electrolyte membrane 30)
Next, a membrane electrolyte membrane 30 is prepared. The electrolyte membrane 30 is a polymer electrolyte membrane (for example, Nafion (registered trademark) NRE212) formed of a fluorine-based sulfonic acid polymer as a solid polymer material, and has good proton conductivity in a wet state. The electrolyte membrane 30 is not limited to Nafion (registered trademark), and other fluorine-based sulfonic acid membranes such as Aciplex (registered trademark) and Flemion (registered trademark) may be used. Further, as the electrolyte membrane 30, a fluorine-based phosphonic acid film, a fluorine-based carboxylic acid film, a fluorine-hydrocarbon-based graft film, a hydrocarbon-based graft film, an aromatic film, or the like may be used, or a reinforcement such as PTFE or polyimide A composite polymer film with enhanced mechanical properties including a material may be used.

  On both sides of the electrolyte membrane 30, the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 are placed on the surfaces of the fluorine-containing films 11 and 12, and as shown in FIG. Transfer is performed such that the electrolyte membrane 30 is sandwiched between the side surfaces 21a and 22a.

  After the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 are transferred to the electrolyte membrane 30, the fluorine-containing films 11 and 12 are removed as shown in FIG. The other side surfaces 21b and 22b are exposed. As described above, the electrolyte layers 21c and 22c functioning as adhesives are formed on the other side surfaces 21b and 22b. However, the use of the fluorine-containing films 11 and 12 as the base material makes it easy after transfer. It becomes possible to remove (peel).

  Next, the creation of the gas diffusion layer and the membrane-electrode assembly will be described with reference to FIGS. FIG. 5 is a schematic diagram showing the gas diffusion layer GDL, and FIG. 6 is a schematic diagram showing the membrane-electrode assembly 50.

(Create gas diffusion layer GDL)
Separately from the formation of the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 and the transfer to the electrolyte membrane 30, a plurality of gas diffusion layers GDL provided adjacent to the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 are provided. create. The gas diffusion layer GDL is a layer for diffusing the fuel gas (anode gas and cathode gas) used for the electrochemical reaction along the surface direction of the electrolyte membrane 30, and as shown in FIG. Similarly, a film-like carbon layer 41 is laminated on the surface of the substrate 40.

  As the gas diffusion layer base material 40, for example, a carbon porous body such as carbon paper or carbon cloth, or a metal porous body such as a metal mesh or a foam metal can be used. The carbon layer 41 may be laminated on the gas diffusion layer base material 40 by applying carbon using a spray or a die coder.

(Preparation of membrane-electrode assembly 50)
Next, as shown in FIG. 6, one side surface 41 a (upper surface) of the carbon layer 41 of the gas diffusion layer GDL is joined to the other side surfaces 21 b and 22 b of the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22. At this time, the electrolyte layers 21c and 22c segregated on the other side surfaces 21b and 22b function as an adhesive. As described above, by setting the water solubility parameter in the paste P to about 24, a sufficient amount of electrolyte is segregated in the electrolyte layers 21c and 22c of the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22. Therefore, the bonding with the gas diffusion layer GDL can be strengthened without requiring an additional adhesive.

  As described above, the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 sandwiching the electrolyte membrane 30 and the gas diffusion layer GDL are joined together to form a membrane-electrode assembly (hereinafter referred to as “MEA”). 50) is formed. The PEFC is configured by sandwiching the MEA 50 with a separator or the like (not shown), and an electromotive force can be obtained by causing an electrochemical reaction in the MEA 50 by the supplied fuel gas.

  Next, with reference to FIG. 7, the test which evaluated the correlation with the solubility parameter of the dispersion medium of the paste P and joining force is demonstrated. FIG. 7 is a table showing bonding force test results using samples in which the solubility parameters of the dispersion medium of the paste P are different from each other.

  Here, three types of pastes P having different solubility parameters of the dispersion medium were prepared, and the tests were performed using the three types of MEAs prepared by the above-described manufacturing method as samples. In sample 1, water was used as the dispersion medium in paste P, and its solubility parameter was set to about 24. In Sample 2, equal amounts of water and 1-propanol were used as the dispersion medium in the paste P, and the solubility parameter was set to about 18. In Sample 3, water and 1-propanol were used as the dispersion medium in the paste P, and the solubility parameter was set to about 12.

  By carrying out a peeling test (JIS K6854-1 (Adhesive-peeling adhesive strength test method-Part 1: 90 degree peeling)) using the autograph on the above three types of samples (MEA) The joining force between the electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 and the gas diffusion layer GDL was evaluated.

  Moreover, after transferring the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 to the electrolyte membrane 30, the other side surfaces 21b and 22b of the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 are observed with an optical microscope, and the deposition rate of the electrolyte Were evaluated by image processing. Specifically, an image obtained by color imaging with an optical microscope was simply binarized by setting the luminance value 128 as a threshold value and evaluated.

  As a result of the above test, as shown in FIG. 7, in Samples 1 and 2 in which the solubility parameter of the dispersion medium is relatively large (24, 18), a sufficient amount of electrolyte was observed, and the hydrogen electrode catalyst layer 21 and It has been found that a high bonding force is exhibited between the oxygen electrode catalyst layer 22 and the electrolyte membrane 30. On the other hand, the solubility parameter of the paste P is relatively small (12) In Sample 3, the amount of electrolyte deposited was insufficient, and it was found that the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22 could not be joined to the electrolyte membrane 30. It was. From this, it can be said that the solubility parameter of the dispersion medium is preferably about 18 or more.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the present invention as long as they have the characteristics of the present invention.

  For example, in the manufacturing method described above, the fluorine-containing films 11 and 12 are used for forming the hydrogen electrode catalyst layer 21 and the oxygen electrode catalyst layer 22, but instead, a water-repellent coating layer is provided on the surface of the non-fluorine-containing film. What was provided can also be used as a base material.

  In addition, the elements included in each of the specific examples described above and their arrangement, materials, conditions, shapes, sizes, and the like are not limited to those illustrated, but can be changed as appropriate. Moreover, each element with which each embodiment mentioned above is provided can be combined as long as technically possible, and the combination of these is also included in the scope of the present invention as long as it includes the features of the present invention.

11, 12: Fluorine-containing film (base material)
21: Hydrogen electrode catalyst layer 21c: Electrolyte layer (of hydrogen electrode catalyst layer) 22: Oxygen electrode catalyst layer 22c: Electrolyte layer (of oxygen electrode catalyst layer) 30: Electrolyte layer film GDL: Gas diffusion layer

Claims (1)

A paste for a fuel cell catalyst layer, which is formed into a film by coating on the surface of the substrate, and the surface formed on the substrate surface side after the molding is joined to the gas diffusion layer of the fuel cell and used as a catalyst layer There,
A catalyst that accelerates the electrochemical reaction;
An electrolyte having a fluorine component;
A dispersion medium,
A fuel cell catalyst layer paste, wherein the dispersion medium has a solubility parameter of 18 or more.

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