JP2021086747A - Method for manufacturing membrane-electrode assembly - Google Patents

Abstract

To keep down the possibility of an ionomer of a catalyst layer swelled by liquid water, preventing a reaction gas from getting in contact with a catalyst metal supported by a conductive carrier.SOLUTION: A method for manufacturing a membrane-electrode assembly comprises the steps of: (a)adding a sulfonic group-containing ionomer to a mixture containing carriers made to support a catalyst, and 25-75 mass% of diacetone alcohol to produce a catalyst ink; (b)coating a substrate with the catalyst ink and drying the catalyst ink, thereby producing a catalyst layer; and (c)bonding the catalyst layer and an electrolyte membrane by thermocompression, which is performed at a temperature equal to or higher than a glass transition temperature of the ionomer and equal to or lower than a boiling point of the diacetone alcohol.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for manufacturing a membrane electrode assembly of a fuel cell.

Conventionally, there is a method for manufacturing a membrane electrode structure of a fuel cell disclosed in Patent Document 1. In the technique of Patent Document 1, an ink-like composition containing an ionomer A having a glass transition temperature of a, an ionomer B having a glass transition temperature of b (a <b), and a conductive carrier carrying a catalyst metal is used. It is made. The ink-like composition is applied onto the base material sheet, and the ink-like composition is dried to prepare a catalyst layer. The catalyst layer is heat treated at a temperature T (a <T <b). The catalyst layer and the electrolyte membrane are thermocompression bonded at a temperature T'(a <T'<b).

In the technique of Patent Document 1, since the heat treatment temperature T is higher than the glass transition temperature a of the ionomer A, the crystallinity of the ionomer A can be increased and the strength of the catalyst layer structure can be increased in the heat treatment. As a result, the pore structure of the catalyst layer is prevented from being crushed in the thermocompression bonding step. Further, since the heat treatment temperature T is lower than the glass transition temperature b of the ionomer B, the water content of the ionomer B can be maintained high. As a result, the proton conductivity of the catalyst layer under low humidification can be maintained.

JP-A-2010-61865

However, the following problems are not taken into consideration in the method for manufacturing the membrane electrode structure of the fuel cell of Patent Document 1. That is, when the fuel cell is operated under a high load, the liquid water generated by the power generation causes the ionoma of the catalyst layer to swell, making it difficult for the reaction gas to come into contact with the catalyst metal supported on the conductive carrier. , So-called flooding occurs. As a result, the power generation performance of the fuel cell deteriorates.

The present disclosure can be realized in the following forms.

According to one embodiment of the present disclosure, there is provided a method for manufacturing a membrane electrode assembly of a fuel cell. The method for producing this membrane electrode conjugate is to add ionomer containing a sulfonic acid group to a mixture containing (a) a carrier carrying a catalyst and 25 to 75% by mass of diacetone alcohol to obtain a catalyst ink. The step of forming, (b) the step of applying the catalyst ink on the substrate and drying to form the catalyst layer, and (c) the step of heat-bonding the catalyst layer and the electrolyte film, wherein the catalyst layer is formed. The step includes a step in which the thermal bonding is performed at a temperature equal to or higher than the glass transition temperature of the ionomer and lower than the boiling point of the diacetone alcohol.
According to such an embodiment, a membrane electrode assembly containing an appropriate amount of diacetone alcohol in the catalyst layer can be produced. As a result, the ionoma of the catalyst layer is less likely to swell due to the generated water of power generation as compared with the embodiment in which the content of diacetone alcohol in the catalyst ink is less than 25% by weight, and as a result, the reaction gas is reacted with the catalyst supported on the particles. It is possible to obtain a membrane electrode assembly that is easy to contact with. Further, the catalyst ink on the substrate can be dried to form the catalyst layer in a short time as compared with the embodiment in which the content of diacetone alcohol in the catalyst ink is higher than 75% by weight.

It is a flowchart which shows the manufacturing method of the membrane electrode assembly of the fuel cell of this embodiment. It is explanatory drawing which shows the manufacturing apparatus which executes a part of the process of FIG. These are the current-voltage characteristics of Examples 1 and 4 when the fuel cell is operated in a highly humidified environment. It is a bar graph which shows the power generation performance of Examples 1 to 4 at the time of operation of a fuel cell in a highly humidified environment. It is a bar graph which shows the power generation performance of Example 1 and Example 4 at the time of operation of a fuel cell in a low humidification environment. It is a schematic diagram which shows the state of the catalyst carrier 100 in Example 4 which the content ratio of diacetone alcohol is 0 mass%. It is a schematic diagram which shows the state of the catalyst carrier 100 in Example 1 which the content ratio of diacetone alcohol is 46% by mass. It is a graph which shows the time change of the drying rate of a mixture of diacetone alcohol and water. It is a graph which shows the average value of the drying rate of a mixture of diacetone alcohol and water. It is a graph which shows the water content of the ionomer cast film by the ionomer solution of Example 1 to Example 4. It is a bar graph which shows the power generation performance of Examples 1 to 4 at the time of operation of a fuel cell in a highly humidified environment.

A. Embodiment:
A1. Manufacturing method of membrane electrode assembly:
The fuel cell in the present embodiment includes a membrane electrode assembly and gas diffusion layers arranged on both sides of the membrane electrode assembly. The membrane electrode assembly is supplied with a fuel gas containing hydrogen through one gas diffusion layer and an oxidation gas containing oxygen through the other gas diffusion layer to generate electricity by an electrochemical reaction. The side of the membrane electrode assembly to which the fuel gas is supplied functions as an anode. The side of the membrane electrode assembly to which the oxidation gas is supplied functions as a cathode. Hydrogen ions flow from the anode to the cathode through the electrolyte membrane 62 in the membrane electrode junction. Electrons flow from the anode to the cathode through an external circuit that connects the anode and the cathode.

The membrane electrode assembly includes an electrolyte membrane 62 and catalyst layers 25 arranged on both sides of the electrolyte membrane 62. The electrolyte membrane 62 is a proton-conducting ion exchange membrane formed of a solid polymer material, for example, a fluororesin, and exhibits good electrical conductivity in a wet state. In the present embodiment, the electrolyte membrane 62 and the catalyst layer 25 include the same ionomer.

The catalyst layer 25 is formed by a carrier 100 carrying a catalyst 120 and an ionomer 200 covering the periphery of the carrier. The catalyst 120 promotes the reaction of hydrogen at the anode and the reaction of oxygen at the cathode, respectively. The catalyst layer 25 functions as an electrode, that is, an anode and a cathode. Therefore, the configuration including the electrolyte membrane 62 and the catalyst layers 25 arranged on both sides of the electrolyte membrane 62 is called a “membrane electrode assembly”. Hereinafter, a method for manufacturing a membrane electrode assembly will be described.

FIG. 1 is a flowchart showing a method for manufacturing a membrane electrode assembly of a fuel cell according to the present embodiment. In step S100, the carrier 100 on which the catalyst was supported, the ionomer 200 containing a sulfonic acid group, and 25 to 75% by weight of diacetone alcohol (CH ₃ C (= O) CH ₂ C (OH) (CH _{3 ) 2} ). ), And a catalyst ink for the cathode is produced. Specifically, first, a carbon carrier carrying a platinum catalyst and ion-exchanged water are mixed. Diacetone alcohol is then added to the mixture and mixed. Then, an ionomer solution is added to the mixture, and dispersion treatment is performed using an ultrasonic homogenizer. As a result, a catalytic ink for the cathode is produced.

A catalyst ink for the anode is produced in the same manner. However, diacetone alcohol is not added in the production of the catalyst ink for the anode.

As the conductive carrier 110 on which the catalyst is supported, for example, a carbon material such as carbon black, carbon nanotubes, or carbon nanofibers, or a carbon compound typified by silicon carbide or the like can be used.

As the catalyst 120, for example, platinum, a platinum alloy, palladium, rhodium, gold, silver, osmium, iridium and the like can be used. Platinum alloys include, for example, platinum and among aluminum, chromium, manganese, iron, cobalt, nickel, gallium, zirconium, molybdenum, ruthenium, rhodium, palladium, vanadium, tungsten, renium, osmium, iridium, titanium and lead. Alloys with at least one type can be used.

Examples of Ionoma 200 include perfluorosulfonic acid resin materials (for example, Nafion (registered trademark)), sulfonated polyether ketones, sulfonated polyether sulfones, sulfonated polyether ether sulfones, sulfonated polysulfones, and sulfonated polysulfides. Sulfonized plastic electrolytes such as sulfonated polyphenylene, sulfoalkylated polyether ether ketones, sulfoalkylated polyether sulfone, sulfoalkylated polyether ether sulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, sulfoalkylated polyphenylene, etc. A sulfoalkylated plastic electrolyte or the like can be used.

In step S200, the catalyst layer 25 is formed on the substrate 11. Specifically, in step S220, the catalyst ink generated in step S100 is applied onto the substrate 11 using the coating device 20. Then, in step S240, the catalyst ink on the substrate 11 is dried in the dryer 30. As a result, the catalyst layer 25 is formed on the substrate 11. The residual amount of the solvent in the catalyst layer at this time is 10% or less of the amount at the time of coating by the coating apparatus 20. The solvent in the catalyst layer referred to here includes ion-exchanged water, diacetone alcohol, and ion-exchanged water and ethanol contained in the ionomer solution. The process of step S200 is performed on the catalyst layer for the cathode and the catalyst layer for the anode, respectively.

In step S300, the catalyst layer 25 generated in step S200 and the electrolyte membrane 62 are thermocompression bonded. Specifically, the catalyst layer 25 and the electrolyte membrane 62 are laminated and thermocompression bonded by a hot press machine. Thermocompression bonding is performed at a temperature equal to or higher than the glass transition temperature of ionomer contained in the electrolyte membrane 62 and the catalyst layer 25 and lower than the boiling point of diacetone alcohol. After that, the substrate 11 is peeled off. The process of step S300 is performed in order on the catalyst layer 25 for the cathode and the catalyst layer 25 for the anode. As a result, a membrane electrode assembly including the electrolyte membrane 62, the catalyst layers 25 for the cathode and the catalyst layers 25 for the anode arranged on both sides of the electrolyte membrane 62 is produced.

FIG. 2 is an explanatory diagram showing a manufacturing apparatus that executes a part of the processing of FIG. The upper half of FIG. 2 shows a step of forming a catalyst layer 25 on the substrate 11 and winding the catalyst layer 25 to prepare a catalyst transfer sheet 45 (see S200 in FIG. 1). The lower half of FIG. 2 shows a step of transferring the catalyst layer 25 on the catalyst transfer sheet 45 onto the electrolyte membrane 62 (see S300 in FIG. 1). The device that carries out the steps in the upper half of FIG. 2 is called a catalyst transfer sheet preparation device 10. The device that carries out the steps in the lower half of FIG. 2 is called a catalyst layer transfer device 50.

In the catalyst transfer sheet preparation device 10, the substrate 11 is unwound from the wound state and conveyed to the coating device 20. The coating device 20 stores the catalyst ink for forming the catalyst layer. The coating device 20 is a catalyst ink on a substrate 11 conveyed between the coating roller 21 and the coating device 20. Is applied to a predetermined thickness (see S220 in FIG. 1).

As the material of the substrate 11, it is preferable to use PTFE glass cloth (Nippon Balker "Balflon glass cloth", Yodogawa Hu-Tech "TG cloth", etc.) or PTEF coated polyimide sheet (Chukou Kasei FPI series, etc.). In addition, polyethylene film, polypropylene film, polytetrafluoroethylene film, ethylene / tetrafluoroethylene copolymer film, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer film, polyfluorinated vinylidene film, polyimide film, polyamide film, A sheet made of these materials such as a polyethylene terephthalate film may be laminated to form a base material, or a Teflon sheet (Teflon: registered trademark, DuPont) may be used as a commercially available material.

After the catalyst ink is applied to the substrate 11 by the coating device 20, the substrate 11 is conveyed to the drying device 30. The drying device 30 evaporates the solvent of the coated catalyst ink on the substrate 11 to dry the catalyst ink. The drying device 30 evaporates the dispersion solvent in the catalyst ink and dries the catalyst ink (see S240 in FIG. 1). As a result, the catalyst layer 25 is formed on the surface of the substrate 11.

The substrate 11 carried out from the drying apparatus 30 is conveyed by the transfer rollers 41 and 42, and is wound up as a catalyst transfer sheet 45 together with the catalyst layer 25. The roll wound up as the catalyst transfer sheet 45 is transferred to the catalyst layer transfer device 50.

The catalyst layer transfer device 50 is a device that transfers the catalyst layer onto the electrolyte membrane 62. In the catalyst layer transfer device 50, the electrolyte membrane sheet 60 in which the electrolyte membrane 62 is formed is prepared on the back sheet 61. Examples of the back sheet 61 include fluorine-based sheets such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), and ETFE (ethylene-tetrafluoroethylene copolymer), and PET. (Polyethylene terephthalate), PEN (polyethylene naphthalate) and other polyester-based, polystyrene and other polymer sheets are coated with ETFE (ethylene-tetrafluoroethylene copolymer), COP (cycloolefin polymer), etc. as a release layer. Alternatively, a laminated sheet can be used.

The electrolyte membrane sheet 60 is conveyed by the transfer rollers 63 and 65, and is fed to the transfer rollers 71 and 72 together with the catalyst transfer sheet 45 unwound by a feeding mechanism (not shown). The transfer rollers 71 and 72 are arranged so as to face each other. A pressing force is applied to the transfer roller 72 toward the transfer roller 71. The transfer rollers 71 and 72 pull in the catalyst transfer sheet 45 and the electrolyte membrane sheet 60 in a state where the catalyst layer 25 and the electrolyte membrane 62 are bonded to each other, and the catalyst transfer sheet is placed on the electrolyte membrane 62 of the electrolyte membrane sheet 60. The catalyst layer 25 of 45 is transferred and transported downstream.

The catalyst layer 25 on the catalyst transfer sheet 45 is transferred onto the electrolyte membrane 62 of the electrolyte membrane sheet 60 by heating and pressurizing by the transfer rollers 71 and 72 (see S300 in FIG. 1). The electrolyte membrane sheet 60 to which the catalyst layer 25 is transferred is conveyed by the transfer roller 65 and is sent to a subsequent process. The catalyst transfer sheet 45 returns to the original state of the substrate 11 as a result of the catalyst layer 25 being transferred to the electrolyte membrane sheet 60 side (see the upper left part of FIG. 2). The substrate 11 is conveyed and wound up via the conveying rollers 67, 95, 96.

A2. Evaluation of catalyst layer:
In step S100 of FIG. 1, a plurality of cathode catalyst inks having different amounts of diacetone alcohol mixed with the catalyst ink were prepared, a membrane electrode assembly and a fuel cell were formed, and various measurements were performed.

A2-1. Examples of Membrane Electrode Assembly 1-4:
The membrane electrode assembly was generated as follows (see S100 in FIG. 1).

(1) Example 1:
To 1 g of the catalyst in which 50% by mass of platinum was supported on the carbon carrier, 4 g of ion-exchanged water was added and stirred. Then, 7 g of diacetone alcohol was added to the mixture and the mixture was stirred. The ratio of the mass of diacetone alcohol to the total mass of the mixture after adding diacetone alcohol was 46% by mass. Then, an ionomer solution of a perfluorosulfonic acid resin material as an ionomer was added to the mixture, and a dispersion treatment was carried out for 30 minutes using an ultrasonic homogenizer. The glass transition temperature of the perfluorosulfonic acid resin material as an ionomer is 135 ° C. The amount of the ionomer solution was set so that the mass ratio of carbon and ionomer of the catalyst carrier was 1: 1. The catalyst ink thus produced formed a cathode catalyst layer.

13 g of ion-exchanged water was added to 1 g of the catalyst in which 25% by mass of platinum was supported on the carbon carrier, and the mixture was stirred. Then, 8 g of ethanol was added to the mixture, and the mixture was stirred. Then, an ionomer solution was added to the mixture, and dispersion treatment was performed for 30 minutes using an ultrasonic homogenizer. The glass transition temperature of ionomer is 110 ° C. The amount of the ionomer solution was set so that the mass ratio of carbon and ionomer of the catalyst carrier was 1.1: 1. The catalyst ink thus produced formed a catalyst layer for an anode.

The catalyst ink was applied onto the substrate 11 so that the platinum mass was 0.2 mg / cm ² (see S220 in FIG. 1). The catalyst ink was dried at 120 ° C. for 30 minutes (see S240 in FIG. 1). The thermocompression bonding between the catalyst layer 25 and the electrolyte membrane 62 was performed by applying a pressure of 3 MPa for 3 minutes in an environment of 160 ° C. (see S300 in FIG. 1). Then, carbon paper functioning as a gas diffusion layer was attached to both sides of the membrane electrode assembly to form a fuel cell.

(2) Examples 2-4:
In the catalyst ink for the cathode, the catalyst ink is prepared so that the ratio of the mass of diacetone alcohol to the total mass of the mixture after adding diacetone alcohol is 18% by mass, 5% by mass, and 0% by mass. A catalyst layer for the cathode was formed. Examples 2 to 4 of the membrane electrode assembly provided with the catalyst layer for the cathode were prepared. Other points of Examples 2 to 4 are the same as those of Example 1. Then, carbon paper functioning as a gas diffusion layer was attached to both sides of the membrane electrode assembly to form a fuel cell.

A2-2. Evaluation of power generation performance:
Each of the above fuel cells was installed in the power generation evaluation cell. Hydrogen gas was used as the fuel gas. Air was used as the oxidation gas. For fuel gas and oxidation gas, the flow rate was controlled with a constant utilization rate. The back pressure was 150 kPa_abs. As humidification conditions, a high humidification environment in which the bubbler temperature was set to 55 ° C. and the cell temperature was 60 ° C., and a low humidification environment in which the cell temperature was 90 ° C. were prepared. Then, the current and voltage measurements were performed in a high humidification environment and a low humidification environment.

FIG. 3 shows the current-voltage characteristics of Examples 1 and 4 when the fuel cell is operated in a highly humidified environment. In FIG. 3, diacetone alcohol is referred to as "DAA". Similarly, in other figures, diacetone alcohol is referred to as "DAA". The content ratio of diacetone alcohol in Example 1 is 46% by mass, and the content ratio of diacetone alcohol in Example 4 is 0% by mass.

The power generation performance of a fuel cell can be evaluated by the amount of power generation per unit time, that is, current × voltage. As can be seen from FIG. 3, the curve of the current-voltage characteristic of the fuel cell of Example 1 in which the content ratio of diacetone alcohol is 46% by mass shows the fuel of Example 4 in which the content ratio of diacetone alcohol is 0% by mass. It is above the curve of the current-voltage characteristics of the battery. That is, it can be seen that the fuel cell of Example 1 has higher power generation performance in a highly humidified environment than the fuel cell of Example 4.

FIG. 4 is a bar graph showing the power generation performance of Examples 1 to 4 when the fuel cell is operated in a highly humidified environment. In FIG. 4, the vertical axis represents the power generation performance when the output voltage is a certain voltage. Specifically, in FIG. 4, the vertical axis is the current density [A / cm ² ] when the output voltage is 0.6 V. In FIG. 4, each bar graph is arranged from left to right in descending order of the content ratio of diacetone alcohol in the catalyst ink.

As can be seen from FIG. 4, the higher the content ratio of diacetone alcohol in the catalyst ink, the higher the power generation performance of the fuel cell of the fuel cell in a highly humid environment.

FIG. 5 is a bar graph showing the power generation performance of Examples 1 and 4 when the fuel cell is operated in a low humidification environment. In FIG. 5, the vertical axis represents the power generation performance when the output voltage is a certain voltage. Specifically, in FIG. 5, the vertical axis is the current density [A / cm ² ] when the output voltage is 0.6 V. However, the vertical axis of FIG. 4 and the vertical axis of FIG. 5 have different scales. The vertical axis of FIG. 5 represents a narrower range than the vertical axis of FIG. In FIG. 5, each bar graph is arranged in the same order as the bar graph of FIG.

As can be seen from FIG. 5, the power generation performance of the fuel cell in a low humidification environment does not differ greatly depending on the content ratio of diacetone alcohol in the catalyst ink. That is, the fuel cell having a high content ratio of diacetone alcohol in the catalyst ink is not significantly inferior in performance to the fuel cell having a low content ratio of diacetone alcohol in the catalyst ink. From this, it can be seen that the diacetone alcohol in the catalyst ink does not deteriorate the proton conductivity in the membrane electrode assembly even in an environment with low water content.

In a highly humidified environment, it is considered that the following phenomena occur in the catalysts of each example.

FIG. 6 is a schematic view showing the state of the catalyst carrier 100 in Example 4 in which the content ratio of diacetone alcohol is 0% by mass. The catalyst carrier 100 includes a catalyst 120 and a carbon 110 on which the catalyst 120 is supported. Ionomer 200 is further attached to the catalyst carrier 100. In the fuel cell of Example 4 in which the content ratio of diacetone alcohol is 0% by mass, the ionomer adhering to the catalyst carrier 100 swells with water. As a result, hydrogen ions can contact the catalyst 120 via the ionomer 200, while oxygen in the oxidizing gas is blocked from contacting the catalyst 120 by the swollen ionomer 200. As a result, the power generation performance of the fuel cell of the fuel cell deteriorates, especially in a highly humidified environment (see FIGS. 3 and 4).

FIG. 7 is a schematic view showing the state of the catalyst carrier 100 in Example 1 in which the content ratio of diacetone alcohol is 46% by mass. The reference numerals shown in FIG. 7 represent the same components as the reference numerals shown in FIG. In the example of FIG. 7, since the water content of the ionomer adhering to the catalyst carrier 100 is low, the ionomer is not swollen as compared with the example of FIG. As a result, the oxygen in the oxidizing gas can easily come into contact with the catalyst 120 supported on the catalyst carrier 100. The water content of the ionomer at this time is considered to be 100 to 110%.

A3. Consideration:
(1) About the amount of diacetone alcohol in the catalyst ink and the swelling of ionomer:
When producing the catalyst ink in step S100 of FIG. 1, the diacetone alcohol covers the catalyst carrier 100. The sulfonic acid group of ionomer faces the familiar diacetone alcohol rather than water (see the upper right part of FIG. 7). As a result, the ionomer adheres to the catalyst carrier 100 with the sulfonic acid group facing inward and the hydrophobic skeleton portion facing outward.

Then, the catalyst ink is applied to the substrate 11 in step S220 of FIG. 1 and dried in step S240. Water has a boiling point of 100 ° C. and diacetone alcohol has a boiling point of 166 ° C. Therefore, even in the drying step of step S240, the amount of diacetone alcohol in the catalyst layer 25 is not significantly reduced as compared with water. As a result, the above-mentioned structure of the ionomer attached to the catalyst carrier 100 is maintained.

In the subsequent thermocompression bonding in step S300 of FIG. 1, the degree of entanglement of the skeleton portion of the ionomer is increased. As a result, the above-mentioned structure of the ionomer with the hydrophobic skeletal portion facing outward is more easily maintained (see FIG. 7).

Based on the above principle, it is considered that the greater the amount of diacetone alcohol in the catalyst ink, the lower the water content in a highly humidified environment, and as a result, the less likely the power generation performance is to deteriorate (see FIGS. 3 and 4). ..

(2) Volatilization of diacetone alcohol and water in the drying process:
1.45 cc of a mixture of diacetone alcohol and water was spread thinly on a jig, and the drying rate was measured for 10 minutes in an environment of 60 ° C. As an example, the content of diacetone alcohol is 1%, the content of diacetone alcohol is 25% by mass, the content of diacetone alcohol is 50% by mass, and the content of diacetone alcohol is 75% by mass. An example of% is prepared.

FIG. 8 is a graph showing the time variation of the drying rate of the mixture of diacetone alcohol and water. In FIG. 8, the horizontal axis is the elapsed time. In FIG. 8, the vertical axis is the drying rate of each example of the mixture of diacetone alcohol and water.

As can be seen from FIG. 8, it can be seen that the larger the proportion of diacetone alcohol in the mixture of diacetone alcohol and water, the smaller the amount of decrease in the drying rate with the passage of time. Therefore, the larger the proportion of diacetone alcohol, the more the volatile amount of diacetone alcohol and the catalyst layer in each step in the production of the membrane electrode assembly of the fuel cell, particularly in the step of drying the catalyst ink (see S240 in FIG. 1). It is easy to control the residual amount of.

FIG. 9 is a graph showing the average value of the drying rates of the mixture of diacetone alcohol and water. In FIG. 9, the horizontal axis is the content of diacetone alcohol in the mixture of diacetone alcohol and water. In FIG. 9, the vertical axis is the average value of the drying rate of the mixture of diacetone alcohol and water for 10 minutes from the start of drying.

As can be seen from FIG. 9, the average value of the drying rate of the mixture of diacetone alcohol and water has a maximum value PK when the content of diacetone alcohol is between 50% by mass and 75% by mass. From this, it can be seen that the higher the content of diacetone alcohol, the higher the drying rate, and the higher the content of diacetone alcohol, the lower the drying rate. That is, it can be seen that the content of diacetone alcohol in the catalyst ink can be adjusted within a certain range while keeping the lead time in the drying step of the catalyst ink short.

However, in order to increase the drying rate, it can be seen that the content of diacetone alcohol in the catalyst ink is preferably 25% by mass or more. Further, it can be seen that the content of diacetone alcohol in the catalyst ink is preferably 85% by mass or less.
It can be seen that the content of diacetone alcohol in the catalyst ink is preferably 50% by mass or more in order to further increase the drying rate. Further, it can be seen that the content of diacetone alcohol in the catalyst ink is preferably 75% by mass or less.

(3) Ratio of diacetone alcohol in catalyst ink and power generation performance:
The relationship between the ratio of diacetone alcohol in the catalyst ink, the water content of ionomer during power generation, and the power generation performance was investigated. The ionomer solution was prepared by mixing diacetone alcohol and ion-exchanged water at the ratios of Examples 1 to 4 above. Note that these ionomer solutions do not contain a carbon carrier carrying a catalyst. The ionomer solutions were added dropwise to a glass petri dish and dried in a hot air drying oven at 100 ° C. for 1 hour to prepare an ionomer cast film. The dry weights of these ionomacast membranes after vacuum drying at 80 ° C. for 30 minutes and (ii) the water content mass after being immersed in ion-exchanged water at 80 ° C. for 30 minutes were used. The water content of each ionomacast film was calculated according to the following formula.
Moisture content = (moisture content-dry mass) / dry mass

FIG. 10 is a graph showing the water content of the ionomer cast membrane by the ionomer solutions of Examples 1 to 4. In FIG. 10, the horizontal axis is the content ratio of diacetone alcohol in the ionomer solution when the ionomer cast film is prepared. In FIG. 10, the vertical axis is the water content of the ionomacast membrane. The content ratio of diacetone alcohol in Example 1 was 46% by mass, the content ratio of diacetone alcohol in Example 2 was 18% by mass, and the content ratio of diacetone alcohol in Example 3 was 5% by mass. The content ratio of diacetone alcohol in Example 4 is 0% by mass.

As can be seen from FIG. 10, the higher the diacetone alcohol content of the ionoma solution, the lower the water content of the ionomer cast membrane, and the closer the diacetone alcohol content of the ionoma solution is to 0% by mass, the more the ionomer. The water content of the cast film is high. From this, it can be considered that the higher the content ratio of diacetone alcohol in the catalyst ink, the less the swelling of ionomer in a highly humidified environment (see FIGS. 6 and 7).

FIG. 11 is a bar graph showing the power generation performance of Examples 1 to 4 when the fuel cell is operated in a highly humidified environment. In FIG. 11, the horizontal axis is the content ratio of diacetone alcohol in the catalyst ink. In FIG. 11, the vertical axis represents the power generation performance [A / cm ² ] when the output voltage is a certain voltage. FIG. 11 is created based on the same measurement result as in FIG. However, in FIG. 4, each bar graph is arranged from left to right in descending order of the content ratio of diacetone alcohol in the catalyst ink, whereas in FIG. 11, the diacetone alcohol in the catalyst ink is arranged. The content ratio increases toward the right.

From the graph of FIG. 11, it can be seen that in the region where the content ratio of diacetone alcohol in the catalyst ink is lower than 25% by mass, the power generation performance changes significantly with respect to the content ratio of diacetone alcohol. On the other hand, in the region where the content ratio of diacetone alcohol in the catalyst ink is higher than 25% by mass, high power generation performance is exhibited, and it can be seen that the power generation performance does not change significantly with respect to the content ratio of diacetone alcohol.

Further, from the graph of FIG. 10, in the region where the content ratio of diacetone alcohol in the ionoma solution is higher than 25% by mass, the water content of the ionomer cast membrane is lower than 10% by mass, and the eye is compared with the content ratio of diacetone alcohol. It can be seen that the water content of the onomacast film does not change significantly. On the other hand, it can be seen that the water content of the ionomer cast membrane changes significantly in the region where the content ratio of diacetone alcohol in the ionomer solution is lower than 25% by mass. From this, even in the region where the content ratio of diacetone alcohol in the catalyst ink containing the carbon carrier supporting the catalyst is high (see the right part of FIG. 11), the water content of the ionomacast film is low and the diacetone alcohol is low. It can be seen that the water content of the ionomacast membrane does not change significantly with respect to the content ratio of.

From the above, it can be seen that in the production of the catalyst ink, it is preferable to produce the catalyst ink so that the content ratio of diacetone alcohol in the catalyst ink is 25% by mass or more.

B. Other embodiments:
(1) In the above embodiment, the catalyst ink was applied onto the substrate 11 so that the platinum mass was 0.2 mg / cm ² (see S220 in FIG. 1). However, the coating of the catalyst ink on the substrate may be performed in other amounts such that ^{the platinum mass is 0.1 mg / cm 2} or 0.3 mg / cm ^2.

(2) In the above example, the catalyst ink was dried at 120 ° C. for 30 minutes (see S240 in FIG. 1). However, the catalytic ink may be dried at other temperatures and times. However, it is preferable that the catalyst ink is dried at a temperature lower than the glass transition temperature of the ionomer contained in the catalyst ink.

(3) In the above embodiment, the thermocompression bonding between the catalyst layer 25 and the electrolyte membrane 62 was performed by applying a pressure of 3 MPa for 3 minutes in an environment of 160 ° C. (see S300 in FIG. 1). However, thermocompression bonding between the catalyst layer and the electrolyte membrane may be performed under other temperatures, pressures, and times. However, thermocompression bonding between the catalyst layer and the electrolyte membrane is performed at a temperature equal to or higher than the glass transition temperature of ionomer of the catalyst layer and lower than the boiling point of diacetone alcohol.

(4) In the above embodiment, the carbon carrier and the ion-exchanged water are mixed in the production of the catalyst ink for the anode. However, the solvent mixed with the catalyst carrier may be water other than ion-exchanged water, alcohol, or other solvent. Further, the solvent of the ionoma solution may be various solvents such as ion-exchanged water, water other than ion-exchanged water, and alcohol.

(5) In the above embodiment, diacetone alcohol is not added in the production of the catalyst ink for the anode. However, diacetone alcohol may be added in the production of the catalytic ink for the anode. By forming the anode catalyst layer with the catalyst ink thus produced, the ionoma of the catalyst layer is less likely to swell due to the generated water generated at the cathode or the water added to the reaction gas, and as a result, it is supported on the particles. It is possible to obtain a membrane electrode assembly in which the fuel gas easily comes into contact with the catalyst.

(6) According to one embodiment of the present disclosure, a method for manufacturing a membrane electrode assembly of a fuel cell is provided. The method for producing this membrane electrode conjugate is to add ionomer containing a sulfonic acid group to a mixture containing (a) a carrier carrying a catalyst and 25 to 75% by mass of diacetone alcohol to obtain a catalyst ink. The step of forming, (b) the step of applying the catalyst ink on the substrate and drying to form the catalyst layer, and (c) the step of heat-bonding the catalyst layer and the electrolyte film, wherein the catalyst layer is formed. The step includes a step in which the thermal bonding is performed at a temperature equal to or higher than the glass transition temperature of the ionomer and lower than the boiling point of the diacetone alcohol.
According to such an embodiment, it is possible to generate a membrane electrode assembly in which ionomers in the catalyst layer are less likely to swell. As a result, the ionoma of the catalyst layer is less likely to swell due to the generated water of power generation as compared with the embodiment in which the content of diacetone alcohol in the catalyst ink is less than 25% by weight, and as a result, the reaction gas is reacted with the catalyst supported on the particles. It is possible to obtain a membrane electrode assembly that is easy to contact with. Further, the catalyst ink on the substrate can be dried to form the catalyst layer in a short time as compared with the embodiment in which the content of diacetone alcohol in the catalyst ink is higher than 75% by weight.
Further, since thermocompression bonding is performed at a temperature equal to or higher than the glass transition temperature of the electrolyte membrane, the catalyst layer and the electrolyte membrane can be effectively bonded.

The present disclosure is not limited to the above-described embodiment, and can be realized by various configurations within a range not deviating from the gist thereof. For example, the technical features of the embodiments corresponding to the technical features in each embodiment described in the column of the outline of the invention are for solving a part or all of the above-mentioned problems, or a part of the above-mentioned effects. Alternatively, they can be replaced or combined as appropriate to achieve all of them. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

10 ... Catalyst transfer sheet preparation device, 11 ... substrate, 20 ... coating device, 21 ... coating roller, 25 ... catalyst layer, 30 ... drying device, 45 ... catalyst transfer sheet, 50 ... catalyst layer transfer device, 60 ... Electrolyte film sheet, 61 ... back sheet, 62 ... electrolyte film, 63 ... transfer roller, 65 ... transfer roller, 67 ... transfer roller, 71 ... transfer roller, 72 ... transfer roller, 95 ... transfer roller, 96 ... transfer roller, 100 ... catalyst carrier, 110 ... conductive carrier, 120 ... catalyst, 200 ... ionoma, PK ... maximum value

Claims (1)

A method for manufacturing a membrane electrode assembly of a fuel cell.
(A) A step of adding an ionomer containing a sulfonic acid group to a mixture containing a carrier carrying a catalyst and 25 to 75% by mass of diacetone alcohol to generate a catalyst ink.
(B) A step of applying the catalyst ink on the substrate and drying it to form a catalyst layer.
(C) A step of thermocompression bonding the catalyst layer and the electrolyte membrane, wherein the thermocompression bonding is performed at a temperature equal to or higher than the glass transition temperature of the ionomer and lower than the boiling point of diacetone alcohol. , A method for manufacturing a membrane electrode assembly.

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