JP5804449B2 - Manufacturing method of membrane electrode assembly - Google Patents

Description

  The present invention relates to a method for producing a membrane electrode assembly used in a polymer fuel cell.

  A fuel cell of a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) formed by forming a catalyst layer on both surfaces of an electrolyte membrane having hydrogen ion conductivity, and a catalyst layer of each membrane electrode assembly. It has a structure having a gas diffusion layer laminated thereon. Electricity is generated by supplying a reaction gas (fuel gas, oxidant gas) to each catalyst layer via the gas diffusion layer.

  The catalyst layer is a porous layer containing carbon carrying platinum as a catalyst and an electrolyte resin (ionomer), and constitutes an electrode layer that generates a power generation reaction with the supplied reaction gas. The catalyst layer formed on one surface of the membrane electrode assembly (MEA) constitutes an anode (fuel electrode), and the catalyst layer formed on the other surface constitutes a cathode (air electrode).

  Various methods have been proposed so far for producing a membrane electrode assembly having such a catalyst layer. For example, Patent Document 1 below discloses a method of forming a catalyst layer by preparing a catalyst ink made of carbon carrying a platinum catalyst, an electrolyte resin, and a solvent, applying the catalyst ink to a PTFE sheet, and drying the catalyst ink. Have been described. The membrane electrode assembly is formed by joining the PTFE sheet on which the catalyst layer is formed to both surfaces of the electrolyte membrane by hot pressing.

  The electrolyte resin contained in the catalyst layer is a path through which hydrogen ions generated at the anode or hydrogen ions that have passed through the electrolyte membrane and reached the cathode pass. Therefore, the power generation efficiency of the fuel cell can be improved by optimizing the arrangement and shape of the electrolyte resin in the catalyst layer so that the hydrogen ion passage resistance (proton resistance) is reduced.

JP 2010-45003 A

  In the catalyst layer formed by the method described in Patent Document 1, the carbon particles form a porous aggregate, and the electrolyte resin is disposed only along the surface of the aggregate. For this reason, the path | route through which hydrogen ion passes in a catalyst layer is only a path | route along the porous aggregate surface. That is, only a path along the wall surface of the porous void (hole), for example, a path that penetrates the inside of the void is not formed. Thus, the catalyst layer in the conventional membrane electrode assembly has room for further reducing the passage resistance of hydrogen ions.

  This invention is made | formed in view of such a subject, The objective is the membrane electrode assembly which can obtain the membrane electrode assembly whose passage resistance of the hydrogen ion in a catalyst layer is smaller than the conventional one. It is to provide a manufacturing method.

  In order to solve the above problems, a method for producing a membrane electrode assembly according to the present invention is a method for producing a membrane electrode assembly used in a polymer fuel cell, comprising a catalyst-supporting carbon, a first electrolyte resin, An electrode forming step of forming a catalyst layer containing the catalyst layer on one surface of the porous substrate formed in a sheet shape, and a space in contact with the surface of the porous substrate on which the catalyst layer is not formed And a liquid containing a second electrolyte resin, which is the same resin as the first electrolyte resin, is applied to the catalyst layer and a pressure reducing step that lowers the pressure of the space below the pressure of the space in contact with the catalyst layer. And an application step.

  The manufacturing method of the membrane electrode assembly which concerns on this invention has an electrode formation process, a pressure reduction process, and an application | coating process. The electrode forming step is a step of forming a catalyst layer containing carbon particles carrying a catalyst and a first electrolyte resin on one surface of a porous substrate formed in a sheet shape. The catalyst layer is formed by the same method as the method for forming the catalyst layer (electrode layer) in the conventional membrane electrode assembly. That is, when the electrode formation step is completed, the catalyst layer is a porous layer.

  The porous substrate on which the catalyst layer is formed constitutes a part of the membrane electrode assembly. In the subsequent step (the step after the coating step), hot pressing is performed with the surface of the porous substrate on which the catalyst layer is not formed in contact with the surface of the electrolyte membrane. A membrane electrode assembly is formed. The catalyst layer formed by the electrode forming step becomes the electrode layer of the membrane electrode assembly.

  The depressurization step is a step performed after the electrode formation step, and the pressure of the space in contact with the surface of the porous substrate on which the catalyst layer is not formed is lower than the pressure of the space in contact with the catalyst layer. It is a process of making a state. Such a process includes, for example, preparing a decompression container having an opening formed in a part of the outer wall, and mounting a porous substrate to the opening with the catalyst layer facing the outside of the decompression container. , By depressurizing the inside of the vacuum vessel. Since both the porous substrate and the catalyst layer are porous, air is flowing from the catalyst layer toward the porous substrate after the decompression step.

  The application step is a step performed after the pressure reduction step, and a step of applying a liquid containing a second electrolyte resin, which is the same resin as the first electrolyte resin used in the electrode forming step, to the catalyst layer. is there. At this time, the liquid containing the second electrolyte resin permeates into the catalyst layer by the flow of air from the catalyst layer toward the porous substrate. As a result, the second electrolyte resin is dispersedly arranged in the voids (pores) of the porous catalyst layer.

  In the catalyst layer obtained through the above steps, the carbon particles carrying the catalyst form a porous aggregate, and the first electrolyte resin is disposed along the surface of the aggregate. Further, the second electrolyte resin forms a column penetrating through the porous void (hole), and the column is arranged so as to connect the surfaces of the first electrolyte resin in a network.

  As a result, during the power generation of the fuel cell, hydrogen ions that pass through the catalyst layer not only in the path along the porous aggregate surface (path along the cavity wall surface) as in the past, but also in the interior of the cavity. It is possible to pass through a route that penetrates. For this reason, the passage resistance of hydrogen ions in the catalyst layer is smaller than the conventional one.

  As described above, according to the method for producing a membrane electrode assembly according to the present invention, a membrane electrode assembly in which the passage resistance of hydrogen ions in the catalyst layer is smaller than the conventional one can be obtained.

  In the method of manufacturing a membrane / electrode assembly according to the present invention, the amount of the second electrolyte resin contained in the liquid applied in the application step may be included in the catalyst layer formed in the electrode formation step. It is also preferable that it is 50% or less of the amount of one electrolyte resin.

  When the proportion of the second electrolyte resin in the entire electrolyte resin (first electrolyte resin and second electrolyte resin) finally contained in the catalyst layer becomes too large, the passage resistance of hydrogen ions in the catalyst layer decreases conversely. May end up. This is presumably due to a decrease in the amount of the electrolyte resin attached to the carbon particles.

  In this preferred embodiment, the amount of the second electrolyte resin contained in the liquid applied in the application step is 50% or less of the amount of the first electrolyte resin contained in the catalyst layer formed in the electrode formation step. Thereby, at least 50% of the entire electrolyte resin (first electrolyte resin and second electrolyte resin) finally contained in the catalyst layer is arranged along the surface of the aggregate as the first electrolyte resin. As a result, the adhesion amount of the electrolyte resin to the carbon particles is sufficiently secured, so that the passage resistance of hydrogen ions in the catalyst layer does not decrease.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a membrane electrode assembly which can obtain the membrane electrode assembly whose passage resistance of the hydrogen ion in a catalyst layer is smaller than the conventional one can be provided.

It is sectional drawing of the fuel cell containing the membrane electrode assembly obtained by one Embodiment of this invention. It is an exploded view for demonstrating the manufacturing method of the fuel battery cell shown in FIG. It is an exploded view for demonstrating the manufacturing method of a membrane electrode assembly among the fuel cells shown in FIG. It is a figure for demonstrating the pressure reduction process among one Embodiment of this invention. It is a figure for demonstrating an application | coating process among one Embodiment of this invention. It is the figure which showed typically the catalyst layer of the membrane electrode assembly obtained by one Embodiment of this invention.

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

  FIG. 1 is a cross-sectional view of a fuel cell including a membrane electrode assembly obtained according to an embodiment of the present invention. The fuel cell 1 is a so-called flat plate type polymer electrolyte fuel cell (PEFC), and is formed in a rectangular shape in plan view. As shown in FIG. 1, the fuel cell 1 includes a membrane electrode assembly 10, a pair of gas diffusion layers 20, and a pair of separators 30.

  The membrane electrode assembly 10 has catalyst layers 12a and 12b on both surfaces of an electrolyte membrane 11 having hydrogen ion conductivity, respectively, and is so-called MEA. Both of the catalyst layers 12a and 12b are formed on both surfaces of the electrolyte membrane 11 as catalyst layers (electrode layers) in which platinum particles are supported on carbon particles and an electrolyte (ionomer) is further contained. The catalyst layer 12a is a cathode electrode layer that reacts with an oxidant gas (for example, air), and the catalyst layer 12b is an anode electrode layer that reacts with a fuel gas (for example, hydrogen). The specific configuration and manufacturing method of the membrane electrode assembly 10 will be described in detail later.

  The gas diffusion layer 20 is a layer for improving the diffusibility of the reaction gas, and is disposed so as to sandwich the membrane electrode assembly 10 from both sides. That is, the fuel cell 1 has two gas diffusion layers 20 including a cathode side gas diffusion layer 20a and an anode side gas diffusion layer 20b. A cathode side gas diffusion layer 20 a is laminated on the catalyst layer 12 a of the electrolyte membrane 11, and an anode side gas diffusion layer 20 b is laminated on the catalyst layer 12 b of the electrolyte membrane 11.

  These two gas diffusion layers 20 are both conductive porous layers formed of a material having conductivity and water repellency on one surface of a diffusion layer substrate (22a, 22b) made of carbon paper. (21a, 21b). The gas diffusion layer 20 is arranged with the surface on the conductive porous layer (21a, 21b) side facing the membrane electrode assembly 10 side. For this reason, the conductive porous layer 21a is in contact with the catalyst layer 12a, and the conductive porous layer 21b is in contact with the catalyst layer 12b. In addition to the function of increasing the diffusibility of the reaction gas, the gas diffusion layer 20 has a function of discharging generated water and humidified water from the membrane electrode assembly 10 side, and a current efficiently from the catalyst layer 12a and the catalyst layer 12b. It also has a function to take out.

  The separator 30 is a conductive layer disposed on the outermost side of the fuel cell 1 and is made of carbon. The separator 30 includes a cathode side separator 30a disposed adjacent to the cathode side gas diffusion layer 20a and an anode side separator 30b disposed adjacent to the anode side gas diffusion layer 20b. These are the same as each other. It has a shape.

  A plurality of grooves 31a having a rectangular cross section are formed in parallel with each other on the surface of the cathode side separator 30a in contact with the diffusion layer base material 22a. These grooves 31a are channels for sharing the oxidant gas from the outside with respect to the diffusion layer base material 22a. Similarly, a plurality of grooves 31b having a rectangular cross section are formed in parallel with each other on the surface of the anode separator 30b in contact with the diffusion layer base material 22b. These grooves 31b are flow paths for sharing the fuel gas from the outside with respect to the diffusion layer base material 22b.

  Although FIG. 1 shows only one fuel cell 1 (single cell), in an actual fuel cell device, a plurality of fuel cells 1 are stacked and electrically connected in series via a separator 30. (Cell stack). Although the power generation voltage of one fuel cell 1 is about 1V, a high voltage of several hundreds V can be output by connecting a plurality of fuel cells 1 in series as described above. As described above, the separator 30 has a role of electrically connecting the plurality of fuel cells 1 and a role of supplying a reaction gas to each fuel cell 1. Note that a refrigerant flow path for cooling the fuel cell 1 may be formed between the cathode side separator 30a and the anode side separator 30b adjacent to each other.

  A method of manufacturing the fuel cell 1 having the above-described configuration will be briefly described with reference to FIG. FIG. 2 is an exploded view for explaining a manufacturing method of the fuel battery cell 1. As shown in FIG. 2, first, the membrane electrode assembly 10 with the catalyst layer 12a and the catalyst layer 12b formed on the electrolyte membrane 11, the cathode side gas diffusion layer 20a, and the anode side gas diffusion layer 20b are individually provided. To be created.

  Thereafter, the conductive porous layer 21a is brought into contact with the catalyst layer 12a of the membrane electrode assembly 10, and the conductive porous layer 21b is brought into contact with the catalyst layer 12b of the membrane electrode assembly 10. To do. That is, the membrane electrode assembly 10 is sandwiched between the cathode side gas diffusion layer 20a and the anode side gas diffusion layer 20b from both sides.

  In this state, hot pressing is performed to join and integrate the cathode side gas diffusion layer 20a, the membrane electrode assembly 10, and the anode side gas diffusion layer 20b. Thereafter, this is sandwiched between the cathode side separator 30a and the anode side separator 30b. In the state of the fuel cell 1 alone, the separator 30 and the gas diffusion layer 20 are not particularly joined. These are fixed by holding the whole fuel cell 1 so as to be compressed along the stacking direction in a state where a plurality of fuel cells 1 are stacked to form a cell stack.

  Then, the manufacturing method of the membrane electrode assembly 10 is demonstrated, referring FIG. FIG. 3 is an exploded view for explaining a manufacturing method of the membrane electrode assembly 10 in the fuel battery cell 1. As illustrated in FIG. 3, the membrane electrode assembly 10 includes an electrolyte sheet 110 and a pair of catalyst sheets 40 a and 40 b disposed on both sides of the electrolyte sheet 110.

  The electrolyte sheet 110 is a dense electrolyte film formed in a sheet shape, and occupies most of the electrolyte film 11.

  The catalyst sheet 40a is obtained by forming a porous catalyst layer 12a on one surface of a porous substrate 111a which is a porous PTFE sheet. Further, the catalyst sheet 40b is obtained by forming a porous catalyst layer 12b on one surface of a porous substrate 111b which is a porous PTFE sheet. The catalyst sheet 40a and the catalyst sheet 40b have the same shape and material.

  In forming the membrane electrode assembly 10, the surface on the porous substrate 111a side of the catalyst sheet 40a is opposed to the surface on one side of the electrolyte sheet 110, and the surface on the porous substrate 111b side of the catalyst sheet 40b. Is made to face the other surface of the electrolyte sheet 110, and the catalyst sheet 40a, the electrolyte sheet 110, and the catalyst sheet 40b are overlaid. Thereafter, these are joined together by hot pressing to form a membrane electrode assembly 10. At this time, the porous substrate 111 a, the electrolyte sheet 110, and the porous substrate 111 b are integrated to form the electrolyte membrane 11.

  Next, the method for forming the catalyst sheet 40a will be described in more detail with reference to FIGS. In addition, about the method of forming the catalyst sheet 40b, since it is the same as the case of the catalyst sheet 40a, description is abbreviate | omitted.

  <Electrode formation step> First, water is added to and mixed well with carbon particles carrying a platinum catalyst. To this, an electrolyte solution (Nafion 20 wt% solution: manufactured by Aldrich) and ethanol as a solvent are added and mixed to prepare a catalyst ink.

  Subsequently, the catalyst ink is applied to one surface of the porous base material 111a which is a porous PTFE sheet. The catalyst ink is applied so that its thickness is uniform. Thereafter, the applied catalyst ink is heated and dried. Water and ethanol are removed from the catalyst ink to form a porous catalyst layer 12a.

  <Decompression step> Next, the porous substrate 111a (catalyst sheet 40a) on which the catalyst layer 12a has been formed in the electrode formation step is attached to a decompression vessel. A decompression container is a container which can exhaust and depressurize internal air with an exhaust pump. The decompression container has a rectangular opening in a part of the wall W separating the internal space and the external space. The shape of the opening is substantially the same as the outer shape of the catalyst sheet 40a in plan view. As shown in FIG. 4, the catalyst sheet 40a is attached so as to be fitted into the opening with the catalyst layer 12a facing the outside of the decompression vessel. In FIG. 4, the left side of the wall W is the inside of the decompression container, and the right side of the wall W is the outside (external space) of the decompression container.

  In this state, the air inside the decompression container is discharged, and the pressure inside the decompression container is set to a state lower than the external atmospheric pressure. In other words, the pressure in the space in contact with the surface of the porous substrate 111a where the catalyst layer 12a is not formed is set lower than the pressure in the space in contact with the catalyst layer 12a.

  At this time, since both the porous base material 111a and the catalyst layer 12a are porous, air is flowing from the catalyst layer 12a toward the porous base material 111a. Such an air flow is indicated by an arrow AF in FIG.

  <Coating Step> Next, a coating solution obtained by mixing water and ethanol with the same electrolyte solution (Nafion 20 wt% solution: manufactured by Aldrich) as used in preparing the catalyst ink in the electrode forming step. Prepare the LQ. The coating liquid LQ can be said to be a liquid containing the same electrolyte resin as the electrolyte resin (Nafion) contained in the catalyst ink.

  As shown in FIG. 5, the coating liquid LQ is sprayed from the tip of the spray nozzle NZ and sprayed onto the surface of the catalyst layer 12a. The spray nozzle NZ can be moved along the surface of the catalyst layer 12a by a drive mechanism (not shown). The spray nozzle NZ sprays the coating liquid LQ while moving along the surface of the catalyst layer 12a so that the coating liquid LQ is uniformly applied to the entire surface of the catalyst layer 12a.

  At this time, the total amount of the electrolyte resin (Nafion) contained in the coating liquid LQ applied to the surface of the catalyst layer 12a is 50% or less of the amount of the electrolyte resin contained in the catalyst layer 12a formed in the electrode formation step. In this way, the spraying speed and spraying time of the coating liquid LQ from the spray nozzle NZ are adjusted.

  Due to the flow of air from the catalyst layer 12a toward the porous substrate 111a, the coating liquid LQ applied to the surface of the catalyst layer 12a penetrates into the catalyst layer 12a. As a result, the electrolyte resin contained in the coating liquid LQ is dispersedly arranged in the voids (holes) of the porous catalyst layer 12a. Thereafter, the catalyst layer 12a is heated and dried.

  The arrangement and shape of the electrolyte resin in the catalyst layer 12a obtained through the above steps will be described with reference to FIG. FIG. 6 is a diagram schematically showing the catalyst layer 12 a of the membrane electrode assembly 10. Among these, FIG. 6 (A) shows a part of the catalyst layer 12a obtained by the conventional manufacturing process in which the decompression process and the coating process are not performed for reference, and schematically shows the vicinity of the void PO. It shows. FIG. 6B shows a part of the catalyst layer 12a obtained through the pressure reducing step and the coating step as described above, and schematically shows the vicinity of the void PO.

  As shown in FIG. 6A, in the catalyst layer 12a obtained by the conventional manufacturing process, the carbon particles CB carrying the catalyst form a porous aggregate, and a resin layer made of an electrolyte resin. PE1 is disposed only along the surface of the aggregate. That is, the electrolyte resin is disposed only along the wall surface of the porous void PO.

  On the other hand, as shown in FIG. 6 (B), in the catalyst layer 12a obtained by the manufacturing process according to the present embodiment, the carbon particles CB carrying the catalyst are porous bones as in FIG. 6 (A). A resin layer PE1 made of an electrolyte resin is disposed along the surface of the aggregate. Further, in FIG. 6B, the electrolyte resin contained in the coating material forms columns PE2 that penetrate through the porous voids (holes), and the columns PE2 cover the surfaces of the resin layer PE1. It is arranged so as to be connected in a mesh shape.

  As a result, the hydrogen ions passing through the catalyst layer 12a during power generation of the fuel cell 1 are not only the path along the porous aggregate surface (path along the wall surface of the void PO) as in the prior art, A path that penetrates the inside of the void PO can also be passed. For this reason, the passage resistance of hydrogen ions in the catalyst layer 12a is smaller than the conventional one shown in FIG.

  As described above, according to the method for manufacturing the membrane electrode assembly 10 according to the present embodiment, it is possible to obtain the membrane electrode assembly 10 in which the hydrogen ion passage resistance in the catalyst layers 12a and 12b is smaller than the conventional one. .

  In the present embodiment, the amount of the electrolyte resin contained in the coating liquid LQ applied in the application step is 50% or less of the amount of the electrolyte resin contained in the catalyst layer 12a formed in the electrode formation step. Thereby, at least 50% of the entire electrolyte resin (resin layer PE1 and pillar PE2) finally included in the catalyst layer is disposed along the surface of the aggregate as the resin layer PE1. As a result, the adhesion amount of the electrolyte resin to the carbon particles CB is sufficiently secured, so that the hydrogen ion passage resistance in the catalyst layer 12a does not decrease.

  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, 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.

DESCRIPTION OF SYMBOLS 10: Membrane electrode assembly 11: Electrolyte membrane 12a, 12b: Catalyst layer 20: Gas diffusion layer 20a: Cathode side gas diffusion layer 20b: Anode side gas diffusion layer 21a, 21b: Conductive porous layer 22a, 22b: Diffusion layer Base material 30: Separator 30a: Cathode side separator 30b: Anode side separator 31a, 31b: Groove 40a, 40b: Catalyst sheet 110: Electrolyte sheet 111a, 111b: Porous base material CB: Carbon particles LQ: Coating liquid NZ: Spray nozzle PE1: Resin layer PE2: Pillar PO: Air gap W: Wall

Claims (2)

A method for producing a membrane electrode assembly used in a polymer fuel cell,
An electrode forming step of forming a catalyst layer containing carbon particles carrying a catalyst and a first electrolyte resin on one surface of a porous substrate formed into a sheet;
A pressure reducing step in which the pressure of the space in contact with the surface of the porous substrate where the catalyst layer is not formed is lower than the pressure of the space in contact with the catalyst layer;
In the decompression step, an application step of applying a liquid containing a second electrolyte resin, which is the same resin as the first electrolyte resin, to the catalyst layer;
A process for producing a membrane electrode assembly, comprising:   The amount of the second electrolyte resin contained in the liquid applied in the application step is 50% or less of the amount of the first electrolyte resin contained in the catalyst layer formed in the electrode formation step. The method for producing a membrane electrode assembly according to claim 1.

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