JP2009043692A - Manufacturing method and membrane electrode assembly for fuel cell, and membrane electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability of a fuel cell by controlling the contact resistance between an electrode and an electrolyte membrane. <P>SOLUTION: The manufacturing method of an membrane electrode assembly for a fuel cell includes a first process in which an electrolyte membrane 20 constituted of a polymer electrolyte is prepared; a second process in which a catalyst ink, containing a catalyst, a polymer electrolyte and a solvent, is coated on a base material and the coated catalyst ink is half-dried and the ratio of the solvent amount in the catalyst ink, after the half-drying against the solvent amount in the coated catalyst ink, is set at 20-70%; and a third process, in which the half-dried catalyst ink and the electrolyte membrane 20 are overlapped and pressure-bonded, and the jointed catalyst ink is further dried to constitute an electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane-electrode assembly for a fuel cell and a membrane-electrode assembly.

  In general, a polymer electrolyte fuel cell includes an electrode including a catalyst and an electrolyte as an electrode formed on an electrolyte membrane. As one method for forming such an electrode on an electrolyte membrane, a catalyst ink containing a catalyst and an electrolyte is applied on a predetermined transfer film, and then dried to form an electrode. A method of hot pressing the formed electrode on an electrolyte membrane is known. Thus, when hot pressing the electrode formed on the transfer film onto the electrolyte membrane, the electrolyte is softened by heating, so that the electrolyte and the electrolyte membrane in the electrode are integrated, and the electrode and the electrolyte membrane are integrated. (See, for example, Patent Document 1).

JP 2004-39474 A JP 2004-193109 A

  However, when the electrode formed on the transfer film as described above is hot-pressed on the electrolyte membrane, the electrolyte membrane may be damaged by heating during pressing, and a fuel using such an electrolyte membrane is used. The battery has a problem that the durability of the fuel cell is lowered. In order to suppress the decrease in durability, the heating temperature at the time of pressing may be decreased. However, when the heating temperature at the time of pressing is decreased, the electrode is transferred onto the electrolyte membrane to form the electrode on the electrolyte membrane. That itself can be difficult. As the battery performance improves as the adhesion between the electrode and the electrolyte membrane is ensured and the contact resistance between them is reduced, the heating temperature during pressing, which makes it difficult to transfer the electrode to the electrolyte membrane, Generally, it is difficult to adopt as a measure to suppress damage.

  The present invention has been made in order to solve the above-described conventional problems, and an object thereof is to improve the durability of a fuel cell while suppressing contact resistance between an electrode and an electrolyte membrane.

In order to achieve the above object, a method for producing a membrane-electrode assembly for a fuel cell comprising the electrolyte membrane of the present invention and an electrode,
A first step of preparing the electrolyte membrane made of a polymer electrolyte;
A catalyst ink containing a catalyst, a polymer electrolyte, and a solvent is applied onto a substrate, and the applied catalyst ink is semi-dried, and the amount of the solvent in the catalyst ink after semi-drying relative to the amount of solvent in the applied catalyst ink is A second step in which the proportion is 20-70%;
The semi-dried catalyst ink and the electrolyte membrane are superposed and pressure bonded, and a third step of further drying the bonded catalyst ink to form the electrode is provided.

  According to the method for producing a membrane-electrode assembly of the present invention configured as described above, the ratio of the amount of solvent in the catalyst ink after semi-drying to the amount of solvent in the applied catalyst ink is 20 to 70%. Thus, after the catalyst ink is semi-dried, it is transferred onto the electrolyte membrane to form an electrode. Therefore, the adhesion between the electrode and the electrolyte membrane can be secured, the contact resistance between the electrode and the electrolyte membrane can be suppressed, and by producing a fuel cell using the membrane-electrode assembly of the present invention, Battery performance can be improved. Moreover, since the adhesiveness between the catalyst ink and the electrolyte membrane is ensured when the catalyst ink is in a semi-dry state, heating when the catalyst ink is transferred onto the electrolyte membrane can be suppressed. Therefore, damage to the electrolyte membrane due to heating can be suppressed, and the durability of the fuel cell including the membrane-electrode assembly of the present invention can be improved. Furthermore, according to the method for producing a membrane-electrode assembly of the present invention, since the catalyst ink is semi-dried prior to the pressure bonding between the catalyst ink and the electrolyte membrane, the supply of the solvent from the catalyst ink side to the electrolyte membrane is suppressed. Can do. Thereby, the effect of ensuring the adhesion between the electrolyte membrane and the electrode can be further enhanced. In such a method for producing a membrane-electrode assembly of the present invention, the catalyst contained in the catalyst ink may be dispersed and supported on carbon particles.

  In the method for producing a membrane-electrode assembly of the present invention, the pressure bonding between the catalyst ink and the electrolyte membrane may be a pressure bonding without heating. Adhesiveness between the catalyst ink and the electrolyte membrane even when the electrolyte membrane and the catalyst ink are joined by pressure joining without heating by making the catalyst ink semi-dry prior to joining with the electrolyte membrane Can be secured. Therefore, the deterioration of the electrolyte membrane due to heating can be prevented.

  In the method for producing a membrane-electrode assembly according to the present invention, the third step is a step of peeling the base material from the catalyst ink after the pressure bonding, and further drying the catalyst ink. It's also good. With such a configuration, the solvent remaining in the semi-dry catalyst ink can be easily evaporated.

  The present invention can be realized in various forms other than the above, for example, a membrane-electrode assembly manufactured by the method for manufacturing a membrane-electrode assembly of the present invention, or a fuel including the membrane-electrode assembly of the present invention. It can be realized in the form of a battery or the like.

A. Fuel cell configuration:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a single cell 10 constituting a fuel cell as a preferred embodiment of the present invention. The unit cell 10 includes an electrolyte membrane 20, an anode 21 and a cathode 22 that are electrodes formed on each surface of the electrolyte membrane 20, and a gas diffusion layer 23 that sandwiches the electrolyte membrane 20 on which the electrode is formed from both sides, 24 and gas separators 25 and 26 disposed further outside the gas diffusion layers 23 and 24.

  The fuel cell of this example is a solid polymer fuel cell, and the electrolyte membrane 20 includes a solid polymer electrolyte exhibiting proton conductivity. In the present embodiment, the electrolyte membrane 20 is formed of a fluorine polymer electrolyte. The anode 21 and the cathode 22 include, for example, platinum or a platinum alloy as a catalyst. More specifically, the anode 21 and the cathode 22 include carbon particles carrying the catalyst and an electrolyte similar to the polymer electrolyte that constitutes the electrolyte membrane 20. The anode 21 and the cathode 22 together with the electrolyte membrane 20 constitute an MEA (Membrane Electrode Assembly) 30. The manufacturing process of the MEA 30 will be described in detail later.

  The gas diffusion layers 23 and 24 can be formed of a conductive member having gas permeability, such as carbon paper or carbon cloth, metal mesh, or foam metal. The gas diffusion layers 23 and 24 of the present embodiment are both formed as flat plate members. Such a gas diffusion layer 24 serves as a flow path for a gas used for an electrochemical reaction and collects current.

  The gas separators 25 and 26 are formed of a gas impermeable conductive member, for example, a member made of compressed carbon or stainless steel. Each of the gas separators 25 and 26 has a predetermined uneven shape. Due to this uneven shape, an in-cell fuel gas channel 47 through which a fuel gas containing hydrogen flows is formed between the gas separator 25 and the gas diffusion layer 23. In addition, due to the uneven shape, an in-single cell oxidizing gas channel 48 through which an oxidizing gas containing oxygen flows is formed between the gas separator 26 and the gas diffusion layer 24.

  Further, a sealing member such as a gasket is disposed on the outer peripheral portion of the single cell 10 in order to ensure gas sealing performance in the single-cell fuel gas flow channel 47 and the single-cell oxidizing gas flow channel 48 (FIG. Not shown). In addition, the fuel cell of this embodiment has a stack structure in which a plurality of single cells 10 are stacked. The outer periphery of the stack structure is parallel to the stacking direction of the single cells 10 and is fuel gas or oxidation. A plurality of gas manifolds through which gas flows are provided (not shown). The fuel gas flowing through the fuel gas supply manifold among the plurality of gas manifolds is distributed to each single cell 10 and passes through each single cell fuel gas flow channel 47 while being subjected to an electrochemical reaction. Collect in the gas exhaust manifold. Similarly, the oxidizing gas flowing through the oxidizing gas supply manifold is distributed to each single cell 10 and passes through each single cell oxidizing gas flow path 48 while being subjected to an electrochemical reaction, and then gathers in the oxidizing gas discharge manifold. To do.

B. Manufacturing process of MEA30:
FIG. 2 is a process diagram showing a method for manufacturing the MEA 30. FIG. 3 is an explanatory view schematically showing a part of the process shown in FIG. In FIG. 3, unlike FIG. 1, the MEA is shown in a direction in which the film surface is horizontal.

  In order to manufacture the MEA 30, first, a polymer electrolyte membrane to be the electrolyte membrane 20 is prepared (step S100). In this embodiment, an electrolyte membrane made of a perfluorosulfonic acid electrolyte is prepared.

  In addition to the electrolyte membrane 20, a catalyst ink for forming an electrode is prepared, and this catalyst ink is used as a predetermined substrate (for example, polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyethylene naphthalate). (PEN) or a substrate made of polyethylene (PE)) (step S110). The catalyst ink is a paste containing carbon particles carrying platinum or a platinum alloy as a catalyst and a fluorine-based polymer electrolyte similar to the electrolyte membrane 20. For example, the carbon particles carrying platinum are dispersed in a platinum compound solution (for example, tetraammine platinum salt solution, dinitrodiammine platinum solution, platinum nitrate solution, or chloroplatinic acid solution). Then, it is produced by an impregnation method, a coprecipitation method, or an ion exchange method. The catalyst-supported carbon particles thus prepared are dispersed in an appropriate water and an organic solvent, and an electrolyte solution containing the above-described electrolyte (for example, Nafion solution, manufactured by Aldrich) is further mixed. A catalyst ink is obtained. Such application of the catalyst ink onto the substrate can be performed by, for example, gravure printing, spraying method, screen printing, doctor blade method, or ink jet method. According to gravure printing, screen printing, or ink-jet method, pattern application for applying the catalyst ink to a desired electrode shape can be easily performed, and the catalyst ink that is the material for application is not wasted. The ratio of the amount of solvent in the catalyst ink used for coating may be appropriately adjusted depending on the coating method and solvent type to be employed. FIG. 3A shows a state in which the catalyst ink is applied on the substrate.

  Thereafter, the catalyst ink applied on the substrate is semi-dried. Specifically, the catalyst applied on the substrate so that the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the initial catalyst ink applied” is 20 to 70%. The ink is dried (step S120). The solvent in the catalyst ink is a combination of the above-described solvent in which the catalyst-carrying carbon particles are dispersed and the solvent in the electrolyte solution used for preparing the catalyst ink. The temperature at which the catalyst ink is dried may be a temperature at which the constituent material of the catalyst ink, such as a polymer electrolyte, does not deteriorate. Here, the amount of solvent in the catalyst ink after semi-drying can be known by performing the drying step while measuring the weight of the catalyst ink coated on the substrate. In this example, drying was performed while measuring the weight of the catalyst ink on the substrate with the drying conditions such as the temperature being constant, and “the catalyst after semi-drying” with respect to “the amount of solvent in the initial catalyst ink applied” The time required until the ratio of “amount of solvent in ink” reaches a desired value is examined in advance. A desired semi-dry state is realized by reproducing the above-mentioned constant drying conditions for the required time. FIG. 3B shows a state in which the catalyst ink applied on the substrate is semi-dried.

  Next, the catalyst ink on the base material semi-dried in step S120 is pressure transferred onto the electrolyte membrane 20 prepared in step S100 (step S130). The pressure transfer may be performed by applying a pressure at which the catalyst ink is transferred so that sufficient adhesion can be secured between the catalyst ink and the electrolyte membrane 20. For example, pressure may be applied to the entire contact surface between the electrolyte membrane 20 and the catalyst ink, or a roll press that sequentially applies pressure linearly between the electrolyte membrane 20 and the catalyst ink may be used. Further, at the time of pressure transfer in step S120, it is possible to further heat in addition to pressure. A state of the pressure transfer is shown in FIG.

  Thereafter, the substrate is peeled and removed, and the semi-dried catalyst ink transferred onto the electrolyte membrane 20 is further dried (step S140) to form electrodes from the semi-dry catalyst ink, thereby completing the MEA 30. The drying process in step S140 can be performed under the same temperature conditions as the semi-drying process in step S120. Here, if the substrate is peeled and removed prior to further drying of the semi-dry catalyst ink as described above, it is desirable that the solvent remaining in the semi-dry catalyst ink can be easily evaporated. However, it is also possible to dry the semi-dry catalyst ink prior to peeling and removal of the substrate. In this case, the solvent may be evaporated through the electrolyte membrane 20 to which the semi-dry catalyst ink is bonded. it can. FIG. 3D shows a state in which the semi-dried catalyst ink is further dried and an electrode is formed on the electrolyte membrane 20.

  Note that when forming the MEA 30, in order to form electrodes on both sides of the electrolyte membrane 20, steps S110 to S140 in FIG. 2 may be performed one by one for each of the anode side and the cathode side.

  According to the method of manufacturing the MEA 30 included in the fuel cell of the present embodiment configured as described above, the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the initial catalyst ink applied” However, after the catalyst ink is semi-dried so as to be 20 to 70%, the catalyst ink is transferred onto the electrolyte membrane 20 to form an electrode. As described above, since the catalyst ink and the electrolyte membrane 20 are joined in a semi-dry state having excellent adhesiveness, the catalyst ink and the electrolyte membrane 20 can be integrated at a good interface, and the electrode and the electrolyte membrane 20 can be integrated. The contact resistance between the electrode and the electrolyte membrane 20 can be suppressed, and the battery performance can be improved.

  Moreover, since the adhesiveness between the catalyst ink and the electrolyte membrane 20 is ensured by the catalyst ink being in a semi-dry state as described above, heating when the catalyst ink is transferred onto the electrolyte membrane 20 can be suppressed. . For example, when the catalyst ink applied on the base material is transferred onto the electrolyte membrane after being sufficiently dried, the catalyst ink is heated to a temperature at which the polymer electrolyte constituting the electrolyte membrane is softened together with pressurization. Therefore, it is necessary to ensure adhesion between the electrode and the electrolyte membrane. In contrast, in this embodiment, transfer is performed using a semi-dry catalyst ink having a high viscosity, so that it is possible to ensure adhesion between the electrode and the electrolyte membrane without heating. Even when heating is performed at the time of transfer, the heating temperature can be lowered or the heating time can be shortened as compared with the case of transferring a sufficiently dried catalyst ink. Therefore, damage to the electrolyte membrane caused by heating can be suppressed, and the durability of the fuel cell can be improved.

  Furthermore, according to this embodiment, since the catalyst ink used for joining to the electrolyte membrane 20 is in a semi-dry state having high adhesiveness, the catalyst ink that has been sufficiently dried is transferred onto the electrolyte membrane. In comparison, the pressure to be applied for bonding with the electrolyte membrane can be set lower. Therefore, damage to the electrolyte membrane 20 due to pressurization can be suppressed, and the durability of the fuel cell can be improved. Further, in the catalyst ink applied on the base material, even when the catalyst-carrying carbon particles and the like form an aggregate, the catalyst ink is dried in a semi-dry state and bonded to the electrolyte membrane 20. The solvent in the dry catalyst ink and the softened electrolyte can alleviate the impact applied from the aggregate to the electrolyte membrane 20. Therefore, the effect of suppressing damage to the electrolyte membrane accompanying the bonding operation can be further enhanced as compared with the case where the sufficiently dried catalyst ink is transferred onto the electrolyte membrane.

  Further, according to the present embodiment, the catalyst ink applied on the base material is transferred onto the electrolyte membrane 20 after the above-mentioned predetermined semi-dry state, and therefore, the solvent supply from the catalyst ink side to the electrolyte membrane 20 is performed. Can be suppressed. As a method for producing an MEA capable of ensuring the adhesion between the electrode and the electrolyte membrane, a method of directly applying the catalyst ink on the electrolyte membrane is also conceivable. In such a case, the catalyst ink is supplied to the electrolyte membrane. If the amount of the solvent to be excessive is increased, the electrolyte membrane swells, and then the electrolyte membrane contracts as the electrolyte membrane is dried, so that the adhesion between the electrolyte membrane and the electrode may be lowered. In addition, wrinkles are likely to occur in the electrolyte membrane, which may make it difficult to handle the electrolyte membrane. In this embodiment, since the catalyst ink is dried to some extent and then transferred onto the electrolyte membrane, the supply of the solvent from the catalyst ink to the electrolyte membrane can be suppressed to ensure the adhesion between the electrolyte membrane and the electrode.

  As described above, the catalyst ink contains the catalyst-supporting carbon and the polymer electrolyte as solid contents, but the constituent ratio of these solid contents can be changed. Even when the composition ratio of the solid content in the catalyst ink is varied, the viscosity of the catalyst ink at the time of transfer is set by bringing the catalyst ink into the semi-dry state described above prior to joining with the electrolyte membrane 20. As a result, the same effect can be obtained that ensures adhesion while suppressing the supply of the solvent to the electrolyte membrane 20. Further, the catalyst ink may contain solids other than the catalyst-supporting carbon and the polymer electrolyte. When the catalyst ink contains other solids, it is desirable that such solids have conductivity or proton conductivity. For example, as the other solids, ensure porosity in the electrode. It can be set as the carbon fiber which is an electroconductive material for doing.

  Further, instead of forming both electrodes by a method of transferring the semi-dried catalyst ink onto the electrolyte membrane 20, only one of the anode 21 and the cathode 22 may be formed by the above method. In this case, the other electrode may be formed by directly applying the catalyst ink on the electrolyte membrane, or after applying the catalyst ink on the base material and drying it completely, It may be transferred to the top. If at least one of the electrodes is formed by transferring a semi-dried catalyst ink, on the side where the electrode is formed in this way, while suppressing heating of the electrolyte membrane and supply of the solvent to the electrolyte membrane, the electrolyte membrane The same effect assuring the adhesion between the electrode and the electrode can be obtained.

  In the embodiment, the polymer electrolyte included in the electrolyte membrane 20 is a fluorine-based polymer electrolyte similar to the polymer electrolyte included in the electrode, but may have a different configuration. As the polymer electrolyte constituting the electrolyte membrane 20, for example, a hydrocarbon polymer electrolyte can be used in addition to the fluorine polymer electrolyte. Even when the electrolyte membrane 20 is composed of different types of polymer electrolytes, the adhesiveness of the catalyst ink at the time of transfer can be improved by putting the catalyst ink in the semi-dry state described above. The same effect as the example can be obtained.

C. Evaluation results of fuel cells of Examples:
The fuel cells of Experimental Examples 1 to 3 were manufactured according to the above-described Examples, and the performance was evaluated together with the fuel cell of the Comparative Example. The manufacturing process of each fuel cell is different only in the manufacturing process of MEA, and the MEA included in the fuel cell of each example was manufactured according to the manufacturing process of the example described above, only the cathode. The production conditions for the MEA provided in each fuel cell are as follows. In addition, as a manufacturing condition of MEAs other than Experimental Example 1, only the parts different from Experimental Example 1 are described.

Experimental Example 1 (30% of the solvent is evaporated):
In step S100, an ion exchange membrane (trade name: Nafion 112, manufactured by DuPont) made of a perfluorocarbon polymer having a sulfonic acid group was prepared as an electrolyte membrane.

  In Step S110, a Nafion solution (manufactured by DuPont) was used as the electrolyte solution for producing the catalyst ink. Further, water, ethanol and 1-propanol were used as the solvent contained in the catalyst ink. Moreover, as a catalyst with which the catalyst-carrying carbon is provided, a platinum-cobalt alloy was used, and the catalyst-carrying amount in the catalyst-carrying carbon was 50 wt%. The composition of the catalyst ink is shown in FIG. In step S110, each material having the composition shown in FIG. 4 was mixed and stirred, and then dispersed in a bead mill for 20 minutes using 100 μm beads to prepare a catalyst ink. And this catalyst ink was pattern-coated by the gravure printing on the PTFE sheet | seat which is a base material so that it might become the shape of a cathode.

  In step S120, the catalyst ink was semi-dried so that 30% of the solvent in the catalyst ink applied on the substrate was evaporated. That is, drying was performed such that the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the applied catalyst ink” was 70%. The temperature condition during drying was 50 ° C. In step S130, the catalyst ink on the base material semi-dried in step S120 was bonded to the electrolyte membrane, and roll press was performed at a linear pressure of 10 kgf / cm. In step S140, after the PTFE sheet as the base material was peeled off, it was dried at 80 ° C. so that the solvent in the catalyst ink was further evaporated, so that the residual ratio of the solvent was 8%, and a cathode was formed on the electrolyte membrane. The solvent remaining rate is the ratio of the solvent weight remaining in the dried catalyst ink to the total weight of the dried catalyst ink.

  In addition, after forming the cathode as described above, the anode is coated by the spray method using the above-described catalyst ink whose composition is shown in FIG. It was produced by performing. The coating by the spray method for forming such an anode is performed by placing the electrolyte membrane on a hot plate at 40 to 50 ° C. Therefore, the sprayed catalyst ink is immediately dried to form an electrode. Is done.

Experimental Example 2 (Evaporation of 50% of the solvent):
In Experimental Example 2, 50% of the solvent in the catalyst ink was evaporated by drying under the temperature condition of 50 ° C. in Step S120. That is, the catalyst ink was semi-dried so that the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the applied catalyst ink” was 50%. In step S130, the catalyst ink on the substrate semi-dried in step S120 was bonded to the electrolyte membrane, and roll press was performed at a linear pressure of 15 kgf / cm. Processes other than steps S120 and S130 were manufactured in the same manner as in Experimental Example 1.

Experimental Example 3 (Evaporation of 80% of the solvent):
In Experimental Example 3, 80% of the solvent in the catalyst ink was evaporated by drying under the temperature condition of 50 ° C. in Step S110. That is, the catalyst ink was semi-dried so that the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the applied catalyst ink” was 20%. In step S130, the catalyst ink on the substrate semi-dried in step S120 was bonded to the electrolyte membrane, and roll press was performed at a linear pressure of 15 kgf / cm. Processes other than steps S120 and S130 were manufactured in the same manner as in Experimental Example 1.

Comparative example (transferred with a residual solvent ratio of 8%):
In Comparative Example 1, the solvent remaining rate in the catalyst ink was set to 8% by drying under the temperature condition of 80 ° C. in Step S110. Further, instead of steps S130 and S140, the catalyst ink on the substrate dried in step S120 is bonded to the electrolyte membrane, and the catalyst ink is transferred to the electrolyte membrane under pressure at a temperature of 150 ° C. and a pressure of 4 MPa. The process was performed. The processes other than the above were manufactured by the same processes as in Experimental Example 1.

  Using each MEA produced as described above, a fuel cell was produced in a single cell state as shown in FIG. 1 and connected to a load to generate power. FIG. 5 is an explanatory diagram showing the results of examining the output characteristics (IV characteristics) in each fuel cell. Specifically, for each fuel cell, the measured value of the output voltage when the output current density is changed while keeping the temperature at 80 ° C. is shown. In such output characteristics, it can be evaluated that the higher the output voltage value is for a predetermined output current density, the better the battery performance is. That is, when the output current density is shown on the horizontal axis and the output voltage is shown on the vertical axis as shown in FIG. 5, it can be evaluated that the battery performance is superior as the graph shifts upward. At this time, for the anode and cathode of each fuel cell, hydrogen and oxygen are in large excess (specifically, the so-called stoichiometric value which is the ratio of the actual supply amount to the theoretically required amount is 2). Hydrogen gas or air was supplied so as to be), and the supplied hydrogen gas and air were humidified using a bubbler.

  As shown in FIG. 5, the fuel cells of Experimental Examples 1 to 3 all showed superior output characteristics as compared with the comparative example. That is, after the catalyst ink is semi-dried so that the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the applied catalyst ink” is 20 to 70%, it is bonded to the electrolyte membrane. In this case, as the initial performance, superior performance was obtained as compared with the case where the catalyst ink applied on the base material was more completely dried and then joined to the electrolyte membrane. Here, in particular, when bonding to the electrolyte membrane, the higher the ratio of “solvent amount in catalyst ink after semi-drying” to “solvent amount in applied catalyst ink” is, the higher the output characteristics are. The result was excellent. From the above results, in the case where the catalyst ink applied on the base material is semi-dried and joined as in the examples, the electrolyte membrane and the electrode are compared with the case where the catalyst ink is more completely dried and joined. It was confirmed that the adhesion between the electrodes increased and the contact resistance between the electrolyte membrane and the electrodes decreased. Moreover, when joining the catalyst ink apply | coated on the base material semi-drying, it was confirmed that the contact resistance between an electrolyte membrane and an electrode becomes small, so that there are many amounts of the solvent to contain.

  FIG. 6 shows the result of investigating the durability of the fuel cell by causing each fuel cell to generate power for the load under a temperature condition of 80 ° C. and repeating the connection and disconnection with the load at regular time intervals. Is shown. The durability of the fuel cell was examined based on the amount of gas cross leak through the electrolyte membrane. That is, when the electrolyte membrane gradually deteriorates, for example, slight damage is caused to the electrolyte membrane, so that the cross leak of the gas through the electrolyte membrane increases. The durability of the battery was evaluated. Specifically, every time power generation is turned on and off for a certain period of time, the fuel gas supplied to the anode is replaced with nitrogen, and the amount of nitrogen transferred to the cathode is measured to determine the amount of gas cross leak. It was. In FIG. 6, the amount of cross leak of such gas is shown on the vertical axis.

  As described above, when the gas cross-leakage amount increases with the deterioration of the electrolyte membrane, the gas utilization rate in the battery reaction decreases, and the power generation performance decreases. Specifically, the output voltage value when outputting a predetermined current gradually decreases. Therefore, a reference value of the cross leak amount is set in advance as the gas cross leak amount when such a performance deterioration starts to occur. The reference value of the gas cross leak amount is indicated by a line parallel to the horizontal axis in FIG. In FIG. 6, the elapsed time until the gas cross-leakage amount in the fuel cell of the comparative example reaches the above-mentioned reference value (accumulation when the operation of repeating power on / off is performed while examining the gas cross-leakage amount). The relative value of the elapsed time until the cross leak amount of the gas in the fuel cell of another embodiment reaches the reference value is shown on the horizontal axis as the endurance time. When measuring the endurance time, hydrogen gas or air is supplied to the anode and cathode of each fuel cell so that the stoichiometry becomes 2, and the supplied hydrogen gas and air are bubbled. Was humidified.

  As shown in FIG. 6, all of the fuel cells of Experimental Examples 1 to 3 exhibited significantly longer endurance time than the fuel cell of Comparative Example. Here, in particular, as the semi-dry state of the catalyst ink bonded to the electrolyte membrane, the higher the ratio of the “solvent amount in the catalyst ink after semi-drying” to the “solvent amount in the applied catalyst ink”, The result that durability time became long was obtained. This is considered to be due to the fact that the electrolyte membrane is less deteriorated due to heating and pressurization at the time of joining with the electrolyte membrane. That is, in the embodiment, since the catalyst ink applied on the base material is semi-dried and joined, the adhesion between the catalyst ink and the electrode is high, and it is not necessary to heat at the time of joining. Therefore, it is considered that the deterioration of the electrolyte membrane due to heating was suppressed. On the other hand, in the comparative example, the catalyst ink is more completely dried and bonded. Therefore, in order to ensure adhesion with the electrolyte membrane, heating is performed together with pressure at the time of bonding. It is considered that the rate at which the amount of gas cross leak increases with time increases due to deterioration. Furthermore, in the fuel cell of Example 1, the amount of solvent in the catalyst ink after semi-drying is larger than in the other examples, and the adhesion of the catalyst ink to the electrolyte membrane is particularly high, so the pressure applied during bonding is lower. Even so, the contact resistance between the electrode and the electrolyte membrane can be sufficiently reduced. Thus, by setting the pressure at the time of joining lower, the fuel cell of Example 1 was able to suppress deterioration of the electrolyte membrane due to pressurization at the time of joining, and exhibited particularly excellent durability. Conceivable.

  As in the examples, the catalyst ink applied on the substrate was semi-dried and joined to the electrolyte membrane, and the “in the catalyst ink after semi-drying” relative to the “amount of solvent in the applied catalyst ink” When the ratio of the “solvent amount” exceeds 70%, there was a problem that wrinkles were generated in the electrolyte membrane after joining (data not shown). This is because the solvent content of the catalyst ink after semi-drying is large, and excess solvent is supplied from the catalyst ink to the electrolyte membrane at the time of joining with the electrolyte membrane, and the electrolyte membrane swells. This is probably because the electrolyte membrane contracted due to drying. When wrinkles occur in the electrolyte membrane as described above, the adhesion at the interface between the electrolyte membrane and the electrode after bonding is lowered even though the adhesion exhibited by the catalyst ink before bonding is high, and the battery performance is reduced. A decline is caused. As described above, in order to sufficiently enhance the durability of the fuel cell while ensuring the adhesion between the electrolyte membrane and the electrode and improving the battery performance, the semi-dried state of the catalyst ink bonded to the electrolyte membrane is It was confirmed that the ratio of “the amount of solvent in the catalyst ink after semi-drying” to “the amount of solvent in the applied catalyst ink” is preferably 20 to 70%.

2 is a schematic cross-sectional view illustrating a schematic configuration of a single cell 10. FIG. 5 is a process diagram illustrating a method for manufacturing MEA 30. FIG. It is explanatory drawing which shows typically the mode of a part of process shown in FIG. It is explanatory drawing which shows the composition of a catalyst ink. It is explanatory drawing which shows the result of having investigated the output characteristic in the fuel cell of an Example and a comparative example. It is explanatory drawing which shows the result of having investigated the durability of the fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Electrolyte membrane 21 ... Anode 22 ... Cathode 23, 24 ... Gas diffusion layer 25, 26 ... Gas separator 30 ... MEA
47 ... Fuel gas flow path in single cell 48 ... Oxidation gas flow path in single cell

Claims (6)

A method for producing a membrane-electrode assembly for a fuel cell comprising an electrolyte membrane and an electrode,
A first step of preparing the electrolyte membrane made of a polymer electrolyte;
A catalyst ink containing a catalyst, a polymer electrolyte, and a solvent is applied onto a substrate, and the applied catalyst ink is semi-dried, and the amount of the solvent in the catalyst ink after semi-drying relative to the amount of solvent in the applied catalyst ink is A second step in which the proportion is 20-70%;
The semi-dried catalyst ink and the electrolyte membrane are stacked and pressure bonded, and the bonded catalyst ink is further dried to form the electrode, and a third step of manufacturing the membrane-electrode assembly. . A method for producing a membrane-electrode assembly according to claim 1,
The method for producing a membrane-electrode assembly, wherein the catalyst contained in the catalyst ink is dispersedly supported on carbon particles. A method for producing a membrane-electrode assembly according to claim 1 or 2,
The pressure bonding between the catalyst ink and the electrolyte membrane is a pressure bonding without heating. A method for producing a membrane-electrode assembly. A method for producing a membrane-electrode assembly according to any one of claims 1 to 3,
The third step is a method of manufacturing a membrane-electrode assembly, which is a step of peeling the base material from the catalyst ink after the pressure bonding and then further drying the catalyst ink.   A membrane-electrode assembly produced by the method for producing a membrane-electrode assembly according to any one of claims 1 to 4.   A fuel cell comprising the membrane-electrode assembly according to claim 5.

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