JP2010073484A - Method of manufacturing membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a composite electrolyte membrane which secures gas diffusivity and water retention of a catalyst layer and improves power generation characteristics of a fuel cell. <P>SOLUTION: The method for manufacturing a membrane electrode assembly 1, including at least the electrolyte membrane 10 containing electrolyte resin, and catalyst layers 21, 22 joined to a surface of the electrolyte membrane 10, includes at least a process for making a surface layer 21a of an anode catalyst layer 21 hydrophilic by implanting helium gas ions on a surface of the anode side catalyst layer 21 joined to the electrolyte membrane 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a membrane electrode assembly for a polymer electrolyte fuel cell in which catalyst layers are bonded to both surfaces of an electrolyte membrane, and in particular, a membrane electrode junction capable of improving the power generation efficiency of the fuel cell. The present invention relates to a method for manufacturing a body.

  A polymer electrolyte fuel cell using an electrolyte membrane can be operated at a low temperature, and can be reduced in size and weight. Therefore, application to a moving body such as an automobile is being studied. In particular, fuel cell vehicles equipped with polymer electrolyte fuel cells are gaining social interest as ecological cars.

  As shown in FIG. 5, such a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) 95 as a main component, and includes a fuel (hydrogen) gas passage and an air gas passage. One fuel cell 90 called a single cell is formed by being sandwiched between separators 96 and 96. In the membrane electrode assembly 95, an anode side electrode (anode catalyst layer) 93a is laminated on one side of an electrolyte membrane 91 which is an ion exchange membrane, and a cathode side electrode (cathode catalyst layer) 93b is laminated on the other side. In the structure, diffusion layers 94a and 94b are disposed in the anode catalyst layer 93a and the cathode catalyst layer 93b, respectively.

  Such a membrane electrode assembly 95 of the fuel cell 90 is configured to ensure water retention in order to develop proton conduction performance during power generation. In particular, in order to efficiently conduct protons from the anode side to the cathode side, it is important to maintain the hydrophilicity of the catalyst layer on the anode side.

  In view of such points, in order to ensure water retention of the membrane electrode assembly, as shown in FIG. 4, the anode-side catalyst layer is first sprayed from the surface of the electrolyte membrane 91 using a spray or the like. The catalyst layer 93d and the second catalyst layer 93f are sequentially stacked, and the ratio of the electrolyte of the second catalyst layer 93f to the first catalyst layer 93d is increased, or the ratio of the water repellent is adjusted. Thus, the hydrophilicity of the second catalyst layer 93f is increased.

  As another aspect, a membrane electrode in which the catalyst-supporting carbon constituting the catalyst is plasma-treated to hydrophilize the surface of the catalyst-supporting carbon, and a catalyst layer is laminated using a solution containing the catalyst-supporting carbon and an ion exchange resin. A joined body has been proposed (see, for example, Patent Document 1).

  However, when the second catalyst layer 93f is sprayed to form a two-layered catalyst layer as shown in FIG. 4, the porous holes on the surface of the first catalyst layer 93d In some cases, a solution-like catalyst entered and clogged the porous pores. Further, when the ratio of the water repellent agent is adjusted, the composition of the solution catalyst (catalyst ink) of the first catalyst layer 93d and the second catalyst layer 93f is different. Sometimes changed.

  When such a membrane electrode assembly is incorporated in a fuel cell, the first catalyst layer formed on the electrolyte membrane 91 during the power generation of the fuel cell due to the above-described blockage of the porous holes in the catalyst layer or the like. Since the gas flow path is closed, the gas diffusibility of the reaction gas is lowered, and the power generation characteristics of the fuel cell may be lowered.

  Furthermore, as described in Patent Document 1, when the plasma treatment is performed on the catalyst-supporting carbon, the affinity with the electrolyte resin can be increased. However, such a catalyst-supporting carbon is used. However, it may be difficult to sufficiently increase the hydrophilicity of the surface layer of the catalyst layer. Therefore, even when a catalyst layer is formed from such catalyst-supporting carbon, in order to increase the hydrophilicity, a method of laminating a catalyst layer having a multilayer structure by spraying as described above is employed.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to provide a membrane electrode joint capable of ensuring gas diffusibility and water retention in the catalyst layer and improving the power generation characteristics of the fuel cell. It is in providing the manufacturing method of a body.

  As a result of intensive investigations to solve the above-mentioned problems, after forming the catalyst layer, ion diffusion is performed on the surface of the catalyst layer (surface with which the gas comes into contact), so that the gas diffusion can be performed without blocking the porous holes. The new knowledge that the water retention of the catalyst layer which ion-implanted was ensured and can be improved was acquired.

  The present invention is based on the above-mentioned new knowledge, and the method for producing a membrane / electrode assembly according to the present invention comprises at least an electrolyte membrane containing an electrolyte resin and a catalyst layer bonded to the surface of the electrolyte membrane. A method for manufacturing a membrane electrode assembly, the method comprising the step of injecting rare gas ions into the surface of the catalyst layer bonded to the electrolyte membrane, thereby It includes at least a step of hydrophilizing the layer.

  According to the present invention, by injecting rare gas ions into the surface of the catalyst layer, the surface layer of the catalyst layer that is the ion implantation site can be hydrophilized. In particular, since the catalyst layer has a porous structure and has irregularities on its surface, the surface energy is likely to increase due to ion implantation, the surface energy that is ion-implanted is likely to increase, and hydrophilization is likely to occur. It is further accelerated. Thereby, the water retention of a membrane electrode assembly can be improved.

  In addition, since there is no need to change the ratio of the electrolyte in the catalyst layer or to change the type of the electrolyte to make the catalyst layer hydrophilic, the characteristics of the interface between the electrolyte membrane and the catalyst layer can be reduced. There is no change. Further, as in the past, there is no need to make the catalyst layer multi-layered by coating, so there is no blockage of the pores in the catalyst layer serving as a base. Furthermore, since the surface layer is modified by implantation of rare gas ions in the hydrophilization step, the surface layer including the surface can be modified without leaving the implanted ions inside, and further, the catalyst It can be processed without destroying the porous structure of the layer.

  In this way, during power generation, gas diffusibility and water retention in the catalyst layer can be ensured, activation overvoltage and resistance overvoltage can be reduced, and the power generation efficiency of the fuel cell can be improved. A membrane electrode assembly that can be obtained can be obtained.

  In the method for producing a membrane / electrode assembly according to the present invention, the surface layer of the catalyst layer to be hydrophilized in the hydrophilization step is more preferably the surface layer of the catalyst layer on the anode side. According to the present invention, the hydrophilicity of the catalyst layer on the anode side where the catalyst surface tends to dry is promoted, the reverse diffusion in which moisture moves from the anode side to the cathode side, and further the power generation characteristics of the fuel cell can be improved. it can.

  Furthermore, in the method for producing a membrane electrode assembly according to the present invention, it is more preferable to use helium ions or neon ions as the rare gas ions. By using relatively light rare gas ions in this way, the surface of the catalyst layer can be further increased. In the hydrophilization step, it is more preferable to implant rare gas ions so that the surface of the catalyst layer has a water contact angle of 60 ° C. or less.

  According to the present invention, the power generation characteristics of the fuel cell can be improved by ensuring gas diffusibility and water retention in the catalyst layer.

  Below, with reference to drawings, the manufacturing method of the membrane electrode assembly concerning the present invention is explained based on one embodiment.

  FIG. 1 is a view for explaining a method for producing a membrane / electrode assembly according to this embodiment, wherein (a) is a step of forming a catalyst layer on the surface of an electrolyte membrane, and (b) It is the figure which showed the process of inject | pouring rare gas ion to the surface, (c) is a figure for demonstrating the membrane electrode assembly after injection | pouring.

  As shown in FIG. 1, an electrolyte membrane 10 including a polymer electrolyte (perfluoro proton exchange resin) having a predetermined size is prepared. The polymer electrolyte contained in the electrolyte membrane 10 has an ion exchange function. For example, a perfluoro proton exchange resin of a fluoroalkyl copolymer having a fluoroalkyl ether side chain and a perfluoroalkyl main chain is preferable. Used. For example, Nafion (trade name) manufactured by DuPont, Aciplex (trade name) manufactured by Asahi Kasei, Flemion (trade name) manufactured by Asahi Glass, Gore-Select (trade name) manufactured by Japan Gore-Tex, etc. are exemplified. Examples thereof include a polymer of trifluorostyrene sulfonic acid and a product obtained by introducing a sulfonic acid group into polyvinylidene fluoride. Further, there are styrene-divinylbenzene copolymer, polyimide resin, etc., which are hydrocarbon proton exchange resins, in which sulfonic acid groups are introduced. These should be appropriately selected according to the use and environment in which the fuel cell is used, but a perfluoro type is preferable from the viewpoint of the life of the fuel cell.

  The electrolyte membrane 10 may be composed of an electrolyte alone, or may be one obtained by impregnating a porous water-repellent polymer resin sheet with the electrolyte described above. Such a polymer resin reinforcing sheet can act as a reinforcing material for the electrolyte membrane 10, and further, condensation and retention of water in the polymer electrolyte fuel cell hinder the supply of the electrode reactant and is effective. is there. In particular, fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) are preferably used because they have high water repellency. It is done. In addition, non-fluorine films such as polyethylene terephthalate, polyethylene, polypropylene, and polyimide can also be used.

  Next, a volatile solution L such as ethanol containing an electrolyte (precursor polymer) and platinum-supported carbon (catalyst-supported conductor) is prepared. Examples of the electrolyte include polymer electrolytes that constitute the above-described electrolyte membrane, and it is preferable to select the same type of electrolyte as the electrolyte membrane 10. Thereby, the adhesiveness etc. of the catalyst layer 21 and 22 and the electrolyte membrane 10 of the anode side and cathode side which are mentioned later are securable.

  In addition, although platinum-supported carbon is given as an example of the catalyst-supporting conductor, the catalyst is not particularly limited as long as it causes a catalytic reaction, and the activation overvoltage in the catalytic reaction is small. Noble metal catalysts such as palladium, ruthenium and iridium are preferably used. Two or more elements such as alloys and mixtures of these noble metal catalysts may be contained. Furthermore, the conductor is not particularly limited as long as it is an electrically conductive substance. For example, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black, and the like is used. And the size of the specific surface area is preferable.

  Then, as shown in FIG. 1A, the prepared solution L is sprayed on both surfaces of the electrolyte membrane 10 using a spray 60 or the like, and an anode catalyst layer (anode-side catalyst layer) is formed on the surface of the electrolyte membrane 10. 21 and a cathode catalyst layer (cathode-side catalyst layer) 22, and these catalyst layers are dried to bond the catalyst layers 21 and 22 to the electrolyte membrane 10.

  Next, as shown in FIG. 1B, the surface layer of the anode catalyst layer 21 is hydrophilized by implanting rare gas ions into the surface of the anode catalyst layer 21 joined to the electrolyte membrane 10. . Specifically, the electrolyte membrane 10 on which the catalyst layers 21 and 22 are formed is placed in an ion implantation apparatus, and helium ions are electrically accelerated to high energy, so that the surface of the anode catalyst layer 21 of the electrolyte membrane 10 Helium ions are implanted into the. At this time, the helium ions are implanted until the helium ions are accelerated with a predetermined acceleration energy and the surface layer of the anode catalyst layer has an implantation amount (dose amount) at which desired hydrophilicity is obtained. Considering the power generation efficiency of the fuel cell, the hydrophilicity of the anode catalyst layer 21 is preferably such that the contact angle of water on the surface is 60 ° or less. In order to obtain such a surface layer, the acceleration energy of helium ions It can be set as appropriate according to the dose. Thereby, as shown in FIG.1 (c), as for the membrane electrode assembly 1, helium ion is inject | poured into the anode catalyst layer 21, and the surface layer 21a hydrophilized is formed.

  In this manner, the rare gas ions can make the anode catalyst layer 21 hydrophilic without destroying the porous structure of the catalyst layer of the anode catalyst layer 21. Further, by injecting rare gas ions, the ions hardly remain inside the catalyst layer 21 and the surface can be modified. In addition, since the catalyst layers 21 and 22 have a porous structure and have irregularities formed on the surfaces thereof, the surface energy is likely to increase due to ion implantation, and the surface energy that is ion-implanted is likely to increase. Is further accelerated. Here, helium ions are used as the rare gas ions, but the same effect can be obtained even with rare gas ions such as neon ions, argon ions, krypton ions, or xenon ions.

  When power is generated using a fuel cell including such a membrane electrode assembly 1, gas diffusibility and water retention in the catalyst layer can be ensured during power generation, and the power generation characteristics of the fuel cell are improved. be able to. Further, the hydrophilicity of the surface layer 21a of the anode catalyst layer 21 can improve the water retention on the anode catalyst layer 21 side without impairing gas diffusibility, so that reverse diffusion from the anode side to the cathode side can be achieved. Promoted.

<Confirmation test>
An electrolyte membrane made of an electrolyte (Nafion DE2020 (manufactured by Dupont)) is prepared, and a solution containing platinum-supported carbon and the same electrolyte as the electrolyte of the electrolyte membrane is applied to both surfaces of the electrolyte membrane to form a catalyst layer. An electrode assembly was manufactured. Then, with respect to the catalyst layer on the surface of the formed membrane electrode assembly, the electrolyte membrane in which the catalyst layer is formed is arranged in the ion implantation apparatus, and acceleration is performed using an accelerator as shown in the following table. Helium ions were implanted into the catalyst layer so that the energy was a constant value in the range of 0 to 500 eV and the dose amount was 1 × 10 ¹² ions / cm ² . And the average penetration depth of the ion with respect to these catalyst layers and the contact angle of water were measured. The results are shown in Table 1.

  As is apparent from Table 1, it can be seen that the average depth of the ions entering the catalyst layer increases as the acceleration energy of the helium ions increases. Furthermore, in order to improve the power generation characteristics as a fuel cell, the hydrophilicity of the catalyst layer is a region where the water contact angle is preferably 60 ° or less. The acceleration energy of ions is more preferably 400 keV or more.

Below, based on an Example, the manufacturing method of the membrane electrode assembly which concerns on this invention is demonstrated.
Example 1
An electrolyte membrane made of an electrolyte (Nafion DE2020 (manufactured by Dupont)) is prepared, and a solution containing platinum-supported carbon and the same electrolyte as the electrolyte of the electrolyte membrane is applied to both surfaces of the electrolyte membrane, and a catalyst is applied to the anode side and the cathode side. A layer was formed to produce a membrane electrode assembly.

Then, an electrolyte membrane in which a catalyst layer is formed is placed in the ion implantation apparatus, and an anode catalyst is used so that the acceleration energy is 500 eV and the dose amount is 1 × 10 ¹² pieces / cm ² using an accelerator. Helium ions were implanted into the layer.

<Evaluation method>
As shown in FIG. 2, the relative pressure of water vapor is changed to 0 to 1, and then the relative pressure of water vapor is changed to 1 to 0. The amount of adsorption was measured. The result is shown in FIG.

(Comparative Example 1)
In the same manner as in Example 1, a membrane electrode assembly was produced. The difference from Example 1 is that helium ions were not implanted into the surface of the catalyst layer. As in Example 1, the water vapor adsorption amount was measured while changing the relative pressure of water vapor. The result is shown in FIG.

<Result>
As shown in FIG. 2, the catalyst layer of the membrane electrode assembly of Example 1 has a higher water vapor adsorption amount than that of Comparative Example 1, and this is because helium ions are injected into the catalyst layer of Example 1. However, it is considered that the catalyst layer was made hydrophilic.

(Example 2)
In the same manner as in Example 1, helium ions were implanted into the anode catalyst layer to produce a membrane electrode assembly that was made hydrophilic. Then, a gas diffusion layer composed of carbon particles and PTFE was laminated on the surface of the catalyst layer of the membrane electrode assembly, and this laminate was sandwiched between a pair of separators to produce a fuel cell. Here, generally known materials are used for the ratio of the material of the gas diffusion layer used, the material and shape of the separator, and the like.

[Evaluation methods]
Hydrogen gas humidified to 100% RH was supplied to the cathode electrode of the fuel cell, oxygen gas humidified to 100% RH was supplied to the anode electrode, and the cell temperature was maintained at 80 ° C. to generate electricity. Further, in order to change the output current of the fuel cell, power generation is performed while changing the external load connected to the fuel cell, and the fuel cell voltage (cell) relative to the current density (1.0 A / m ² ) generated by the fuel cell Voltage) and the resistance of the fuel cell. The result is shown in FIG.

(Comparative Example 2)
As shown in FIG. 4, the anode-side catalyst layer is first sprayed from the surface of the electrolyte membrane so as to increase the ratio of the electrolyte of the second catalyst layer to the first catalyst layer using a spray or the like. The membrane electrode assembly was manufactured by sequentially laminating one catalyst layer and the second catalyst layer. The ratio of the electrolyte in the first catalyst layer is almost the same as that in the catalyst layer of Example 1. Then, as in Example 2, gas diffusion layers were laminated, and this laminate was sandwiched between a pair of separators. Then, in the same manner as in Example 1, the fuel cell voltage (cell voltage) and the fuel cell resistance (cell resistance) with respect to the current density (1.0 A / m ² ) were measured. The result is shown in FIG.

[Results and discussion]
The cell voltage in Example 2 was higher than that in Comparative Example 2. From this, it was confirmed that the fuel cell of Example 2 was able to reduce the activation overvoltage as compared with that of Comparative Example 2.

  Furthermore, the resistance of the fuel cell of Example 2 was lower than that of Comparative Example 2. From this, it was confirmed that the fuel cell of Example 2 was able to reduce the resistance overvoltage as compared with that of Comparative Example 2.

  In the case of Example 2, by injecting helium ions into the anode-side catalyst layer of the membrane electrode assembly, the anode-side catalyst layer is hydrophilized, and the water retention is improved. It is considered that the reverse diffusion in which moisture moves from the cathode side to the cathode side is promoted, thereby improving the power generation characteristics of the fuel cell. Further, in the case of Comparative Example 2, the gas diffusibility is lowered by closing the porous pores on the surface of the first catalyst layer or reducing the pore diameter when the second catalyst layer is laminated by spraying. Therefore, as a result, it is considered that the power generation characteristics of the fuel cell are lowered as compared with those of Example 2.

  As mentioned above, although embodiment of this invention has been explained in full detail using drawing, a concrete structure is not limited to this embodiment, Even if there is a design change in the range which does not deviate from the gist of the present invention. These are included in the present invention.

  In the present embodiment, the catalyst layer is formed by spraying the catalyst by spraying. However, if the catalyst layer can be joined to the electrolyte membrane, for example, the catalyst layer is disposed on a backing sheet, and the catalyst layer is used as the electrolyte. The layers may be joined by transferring them by heating and pressing using a jig or a coating die.

It is a figure for demonstrating the manufacturing method of the membrane electrode assembly which concerns on embodiment of this invention, (a) is a process of forming a catalyst layer in the surface of an electrolyte membrane, (b) On the surface of a catalyst layer It is the figure which showed the process of inject | pouring rare gas ion, (c) is a figure for demonstrating the membrane electrode assembly after implantation. The figure which showed the relationship between the relative pressure of the water vapor | steam of the membrane electrode assembly which concerns on Example 1, and Comparative Example 1, and the water vapor | steam adsorption amount. The figure which showed the result of the cell voltage and cell resistance when the fuel cell which concerns on Example 2 and Comparative Example 2 was made to generate electric power. The figure for demonstrating the conventional membrane electrode assembly. The schematic diagram explaining an example of a polymer electrolyte fuel cell (single cell).

Explanation of symbols

  1: membrane electrode assembly, 10: electrolyte membrane, 21: anode catalyst layer, 22: cathode catalyst layer, 21a: hydrophilized surface layer

Claims (3)

A method for producing a membrane electrode assembly, comprising at least an electrolyte membrane containing an electrolyte resin and a catalyst layer bonded to the surface of the electrolyte membrane,
The manufacturing method includes at least a step of hydrophilizing the surface layer of the catalyst layer by injecting rare gas ions into the surface of the catalyst layer.   The method for producing a membrane electrode assembly according to claim 1, wherein the surface layer of the catalyst layer to be hydrophilized in the hydrophilization step is a surface layer of a catalyst layer on the anode side.   The method of manufacturing a membrane electrode assembly according to claim 1 or 2, wherein the rare gas ions are helium ions or neon ions.

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