JP2021125390A - Method for manufacturing electrolyte membrane - Google Patents

Abstract

To provide a method for manufacturing an electrolyte membrane, by which an electrolyte membrane small in water content and capable of keeping the proton conductivity can be produced.SOLUTION: A method for manufacturing an electrolyte membrane comprises the steps of: preparing a solution which contains a sulfonate group-containing electrolyte membrane material, diacetone alcohol and water; and coating a base with the solution, followed by drying. The weight percentage of the diacetone alcohol to a total weight of the diacetone alcohol and water is 50 wt.% or more and 75 wt.% or less.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for producing an electrolyte membrane.

Conventionally, in the production of a polymer solid electrolyte membrane (hereinafter referred to as an electrolyte membrane) of a fuel cell, there is a method for producing an electrolyte membrane using alcohol as a solvent (Patent Document 1). In the technique of Patent Document 1, diacetone alcohol is presented as one of the alcohol options.

Japanese Unexamined Patent Publication No. 2013-168368

By the way, some electrolyte membranes exhibit proton conductivity when used in a wet state. The sulfonic acid groups in the ionomers constituting the electrolyte membrane are randomly arranged in the electrolyte membrane. Therefore, the water content of the electrolyte membrane may increase due to the ionic bonding between the randomly arranged sulfonic acid groups and water. When the water content of the electrolyte membrane increases, the water in the electrolyte membrane may come out of the electrolyte membrane and freeze when the temperature is below freezing, and the catalyst layer adjacent to the electrolyte membrane may be damaged.

The present disclosure can be realized in the following forms.

(1) According to one embodiment of the present disclosure, a method for producing an electrolyte membrane is provided. The method for producing the electrolyte membrane includes a step of preparing a solution containing the electrolyte membrane material containing a sulfonic acid group, diacetone alcohol, and water, and applying the solution onto a substrate and drying it. The step is provided, and the weight% of the diacetone alcohol is 50% by weight or more and 75% by weight or less with respect to the total weight of the diacetone alcohol and the water. In such an embodiment, when the weight% of diacetone alcohol is 50% by weight or more and 75% by weight or less, the weight% of diacetone alcohol is smaller than 50% by weight or larger than 75% by weight. In comparison, the drying time can be shortened. Further, when the weight of the diacetone alcohol is 50% by weight or more, the water content of the electrolyte membrane becomes smaller than that in the case where the weight of the diacetone alcohol is less than 50% by weight. It is considered that the reason why the water content becomes small is that the sulfonic acid groups, which are hydrophilic groups, face each other. As a result, the proportion of sulfonic acid groups that react with the water around the electrolyte membrane is reduced, so the water content of the electrolyte membrane is higher than when a solution containing diacetone alcohol of 50% by weight or more and 75% by weight or less is not used. It becomes smaller. Therefore, when the temperature is below freezing, the possibility that the water in the electrolyte membrane goes out of the electrolyte membrane and freezes is reduced. In addition, the facing of the sulfonic acid groups facilitates the movement of protons between the sulfonic acid groups. Therefore, it is considered that the proton conductivity can be maintained even if the water content of the electrolyte membrane becomes small.

Schematic diagram of the electrolyte membrane of this embodiment. The flowchart which shows the electrolyte membrane and the manufacturing method of the 3rd electrolyte membrane, the 4th electrolyte membrane and the 5th electrolyte membrane. The graph which shows the relationship between the weight% of diacetone alcohol and the drying rate. The graph which shows the relationship between the weight% of diacetone alcohol and the water content. The graph which shows the relationship between the weight% of diacetone alcohol and the proton resistance value. Schematic diagram of the fifth electrolyte membrane.

A. Embodiment A1. Method for Manufacturing Electrolyte Membrane 10 FIG. 1 is a schematic schematic diagram of the electrolyte membrane 10 of the present embodiment. The electrolyte membrane 10 functions as an ion exchange membrane that conducts protons. The electrolyte membrane 10 exhibits high proton conductivity when it is in a wet state. The electrolyte membrane 10 has a structure in which polymers containing a Teflon skeleton 110 as a main chain (Teflon is a registered trademark) and a sulfonic acid group 120 as a side chain are intricately entangled with each other. The Teflon skeleton 110 is a PTFE (polytetrafluoroethylene) skeleton. The Teflon skeleton 110 has hydrophobicity. A plurality of sulfonic acid groups are bonded to one Teflon skeleton 110. The sulfonic acid group 120 has hydrophilicity and selectively allows protons to permeate within the electrolyte membrane 10.

FIG. 2 is a flowchart showing a manufacturing method of the electrolyte membrane 10, the third electrolyte membrane 150, the fourth electrolyte membrane 160, and the fifth electrolyte membrane 200. The third electrolyte membrane 150, the fourth electrolyte membrane 160, and the fifth electrolyte membrane 200 will be described later.

In step S100, a solution containing the material of the electrolyte membrane containing the sulfonic acid group is prepared. Specifically, the alcohol of diacetone alcohol (CH ₃ C (= O) CH ₂ C (OH) (CH ₃ ) ₂ ) or ethanol (CH ₃ CH ₂ OH) is mixed with a polymer electrolyte (hereinafter referred to as ionomer). ) Is melted and water is added. A perfluorocarbon sulfonic acid resin is used as the ionomer. As the ionomer, sulfonated polyether sulfone, sulfonated polyether ether sulfone, or the like can be used.

In step S200, the solution prepared in the step S100 is applied onto the PTFE (polytetrafluoroethylene) substrate. First, a 100 μm-thick PTFE base material is prepared and fixed to an iron plate. Examples of the base material include a single layer such as a polyethylene terephthalate (PET) base material, a polyethylene naphthalate (PEN) base material, a polyethylene (PE) base material, a cycloolefin polymer (COP), or a titanium base material, or a coating. A multilayer base material may be used.

Next, using a bar coater, the solution prepared in step S100 is applied onto the PTFE substrate so as to have a thickness of 200 μm. As the coating method, various general coating methods such as spin coating and die coater can be used in addition to the bar coater.

In step S300, heating evaporates the alcohol and water in the solution prepared in step S200. First, an iron plate on which a PTFE base material is fixed is placed in an oven, and the solution prepared in step S200 is evaporated at 140 degrees for 3 minutes. The oven temperature is then raised to 160 degrees and the solution prepared in step S200 is evaporated for an additional 3 minutes. By evaporating at 140 degrees, which is lower than the boiling point of diacetone alcohol, and then at 160 degrees, it is possible to prevent water and alcohol from evaporating while foaming and the surface of the electrolyte membrane becoming uneven. can. By evaporating at a temperature of 160 degrees for 3 minutes, the diacetone alcohol in the solution prepared in step S200 can be evaporated almost completely.

Next, the PTFE base material is removed from the iron plate taken out of the oven. Finally, the dried membrane is peeled off from the PTFE substrate to prepare an electrolyte membrane having a thickness of 8 μm.

A2. Examples As the solutions, a first solution, a second solution, a third solution, a fourth solution, and a fifth solution are prepared. The first solution, the second solution, the third solution, and the fourth solution have different contents of water and diacetone alcohol. The fifth solution differs from the first to fourth solutions in that it contains ethanol rather than diacetone alcohol.

A method for preparing the first solution will be described. First, 0.3 g of ionomer having an ion exchange capacity of 1.9 (meq./g) is immersed in 1.35 g of diacetone alcohol. The first solution is prepared by adding 1.35 g of water to the diacetone alcohol in which the ionomer is immersed. In the first solution, when the total weight of 2.7 g of diacetone alcohol and water is 100% by weight, the weight% of diacetone alcohol is 50% by weight. Hereinafter, the weight% of diacetone alcohol means the weight of diacetone alcohol when the total weight of diacetone alcohol and water is 100% by weight. The weight% of diacetone alcohol referred to here is the weight% of diacetone alcohol immediately before the solution is applied to the PTFE base material.

A method for preparing the second solution will be described. 0.3 g of ionomer having an ion exchange capacity of 1.9 (meq./g) is immersed in 2.025 g of diacetone alcohol. Next, 0.675 g of water is added to the diacetone alcohol in which the ionomer is immersed to prepare a second solution. In the second solution, the weight% of diacetone alcohol is 75% by weight with respect to the total weight of 2.7 g of diacetone alcohol and water.

A method for preparing the third solution will be described. A third solution is prepared by immersing 0.3 g of ionomer with an ion exchange capacity of 1.9 (meq./g) in 2.7 g of diacetone alcohol. In the third solution, since water is not contained, the weight% of diacetone alcohol is 100% by weight.

A method for preparing the fourth solution will be described. 0.3 g of ionomer having an ion exchange capacity of 1.9 (meq./g) is immersed in 0.675 g of diacetone alcohol. Next, 2.025 g of water is added to the diacetone alcohol in which the ionomer is immersed to prepare a fourth solution. In the fourth solution, the weight% of diacetone alcohol is 25% by weight with respect to the total weight of 2.7 g of diacetone alcohol and water.

A method for preparing the fifth solution will be described. 0.3 g of ionomer having an ion exchange capacity of 1.9 (meq./g) is immersed in 1.35 g of ethanol. Next, 1.35 g of water is added to the ethanol in which the ionomer is immersed to prepare a fourth solution. Since the fourth solution does not contain diacetone alcohol, the weight% of diacetone alcohol is 0% by weight. Hereinafter, when the first solution to the fifth solution are collectively referred to, they are referred to as "each solution".

The electrolyte membrane prepared using the first solution is the first electrolyte membrane 130, the electrolyte membrane prepared using the second solution is the second electrolyte membrane 140, and the electrolyte membrane prepared using the third solution is the third. The electrolyte membrane 150 prepared using the fourth solution is referred to as the fourth electrolyte membrane 160, and the electrolyte membrane prepared using the fifth solution is referred to as the fifth electrolyte membrane 200. The first electrolyte membrane 130 and the second electrolyte membrane 140 are also referred to as “electrolyte membrane 10”. When the first electrolyte membrane 130 to the fifth electrolyte membrane 200 are collectively referred to, they are referred to as "each electrolyte membrane".

A3. Evaluation (1) Evaluation of drying rate For the first solution, the second solution, the third solution, and the fourth solution, the drying rate in the drying in step S300 was measured. The drying rate was calculated as follows. First, three samples of the first solution, the second solution, the third solution, and the fourth solution, which are coated on the PTFE base material so as to have the same area, are prepared. Next, all samples are weighed. The sample is then dried at 160 degrees for 60 seconds. After drying, the weight of each sample is measured, and the value obtained by subtracting the weight after drying from the weight before drying is calculated. The unit of weight is grams. Divide that number by the area of the applied solution for each sample and the drying time of 60 seconds. In this way, the amount of evaporation of the solution per ^{second in 1 m 2 of the applied solution of each sample is calculated.} The average amount of evaporation of the three samples was taken as the drying rate.

FIG. 3 is a graph showing the relationship between the weight% of diacetone alcohol and the drying rate. As shown in FIG. 3, when the weight% of diacetone alcohol is 50% by weight or more and 75% by weight or less, the drying speed becomes high. This is because when the weight% of diacetone alcohol is 50% by weight or more and 75% or less, the strong interaction between water and diacetone alcohol efficiently attracts it to water and evaporates, so that the drying speed becomes faster. it is conceivable that.

On the other hand, if the weight% of diacetone alcohol is less than 50% by weight or more than 75% by weight, the drying rate becomes slow. It is considered that when the weight% of diacetone alcohol is larger than 75% by weight, the interaction between diacetone alcohol and water is small, so that the amount of diacetone alcohol attracted to water is reduced. If the weight% of diacetone alcohol is less than 50% by weight, the amount of water is too large with respect to diacetone alcohol, so that the interaction between diacetone alcohol and water is weakened and the water evaporates first. It is thought that it will end up.

From the above, when the weight% of diacetone alcohol is 50% by weight or more and 75% or less, the drying time can be shortened.

(2) Evaluation of Moisture Content The water content of the first electrolyte membrane 130, the second electrolyte membrane 140, and the fifth electrolyte membrane 200 was evaluated. Specifically, the water content was calculated based on the following mathematical formula (1) from the mass after vacuum drying at 80 ° C. for 30 minutes and the mass after being immersed in hot water at 80 ° C. for 30 minutes.
Moisture content (%) = (mass of electrolyte membrane after immersion in hot water-mass of electrolyte membrane after vacuum drying) / mass of electrolyte membrane after vacuum drying ... (1)

FIG. 4 is a graph showing the relationship between the weight% of diacetone alcohol and the water content. As shown in FIG. 4, when the weight% of diacetone alcohol is 50% by weight or more, the water content is about 5%.

As described above, since the fifth electrolyte membrane 200 is not produced using diacetone alcohol, the weight% of diacetone alcohol is 0% by weight. As shown in FIG. 4, when the weight% of diacetone alcohol is 0% by weight, the water content is about 70%. Therefore, it can be seen that the water content of the electrolyte membrane 10 is lower than that of the fifth electrolyte membrane 200.

(3) Evaluation of Proton Resistance The ionic conduction resistance (hereinafter referred to as proton resistance) of the first electrolyte membrane 130, the second electrolyte membrane 140, and the fifth electrolyte membrane 200 was evaluated. It can be said that the lower the proton resistance value, the higher the ionic conductivity. First, 10 sheets of each electrolyte membrane are prepared and laminated. Next, the laminated body of each of the laminated electrolyte membranes was hot-pressed at 140 ° C. and 3 MPa, and punched into a disk shape having a diameter of 6 mm. The laminated body of each punched electrolyte membrane was set on a jig and allowed to stand in a constant temperature and high humidity bath at 80 ° C. and 98% RH for 12 hours. After that, the setting of the high temperature and high humidity tank was changed to 80 ° C. and 30% RH, and each electrolyte membrane was allowed to stand for another one and a half hours. Each electrolyte membrane was taken out from a high temperature and high humidity bath, and measurement was carried out at a frequency of 1 kHz with an LCR meter (1260 type impedance analyzer manufactured by Solartrоn) to evaluate proton resistance.

FIG. 5 is a graph showing the relationship between the weight% of diacetone alcohol and the proton resistance value. FIG. 5 shows that the proton resistance value is substantially constant regardless of the weight% value of diacetone alcohol. In general, it is known that an electrolyte membrane exhibits high ionic conductivity when used in a wet state, so that an electrolyte membrane having a low water content has low ionic conductivity. However, the electrolyte membrane 10 shows substantially the same proton resistance value as the fifth electrolyte membrane 200 even if the water content is low as described above.

A4. Discussion FIG. 6 is a schematic schematic diagram of the fifth electrolyte membrane 200. In the present embodiment, the direction in which the white arrows in FIGS. 1 and 6 are directed will be described as the inside of the electrolyte membrane 10 and the fifth electrolyte membrane 200. As shown in FIGS. 1 and 6, the sulfonic acid group 120 of the electrolyte membrane 10 faces inward as compared with the fifth electrolyte membrane 200. This is thought to occur because water evaporates before diacetone alcohol during drying.

Ionomers are dried soaked in alcohol and water. At this time, the hydrophilic sulfonic acid group 120 faces the water and alcohol side. Here, as described above, due to the ionic bond with water, diacetone alcohol is pulled by water and evaporates when the water evaporates. At this time, it is presumed that not all diacetone alcohol evaporates with water, and a small amount of diacetone alcohol having a high boiling point remains. It is believed that this small amount of diacetone alcohol causes the sulfonic acid groups to face inward and dry.

When the sulfonic acid group 120, which is a hydrophilic group, faces the inside of the electrolyte membrane 10, the following effects are obtained. First, even if water covers the electrolyte membrane 10, the outside of the electrolyte membrane 10 is covered with the Teflon skeleton 110 which is a hydrophobic group. Therefore, the proportion of the sulfonic acid group 120 that reacts with the water around the electrolyte membrane 10 is smaller than that of the fifth electrolyte membrane 200. Therefore, the water content of the electrolyte membrane 10 is smaller than that of the fifth electrolyte membrane 200. Therefore, the possibility that the water in the electrolyte membrane 10 goes out of the electrolyte membrane 10 and freezes when the temperature is below freezing is reduced.

In general, the electrolyte membrane to contain water, oxonium ions (H 3 _O ⁺⁾ next to protons supplied from the outside of the electrolyte membrane are bonded with water molecules to move between sulfonic acid groups. In the present specification, the transfer of protons and the transfer of oxonium ions are synonymous. When the hydrophilic sulfonic acid group 120 has a structure in which the hydrophilic sulfonic acid groups 120 are randomly oriented inward and outward as in the fifth electrolyte membrane 200, water molecules are easily dispersed and the generation of oxonium ions becomes unstable. Therefore, it is necessary to add a large amount of water to the electrolyte membrane. Further, if the direction in which the sulfonic acid group faces is random, the distance between the sulfonic acids becomes unstable, and the movement of the oxonium ion may be slowed down.

As described above, the electrolyte membrane 10 has a lower water content than the fifth electrolyte membrane 200. However, since the hydrophilic group sulfonic acid group 120 faces the inside of the membrane, it is considered that water can enter the inside of the membrane and efficiently generate oxonium ions. Further, since the sulfonic acid groups 120 face each other, the distance between the sulfonic acid groups 120 becomes short, so that the oxonium ion easily moves between the sulfonic acid groups 120 as compared with the fifth electrolyte membrane 200. Therefore, it is considered that the proton conductivity can be maintained even if the water content of the electrolyte membrane 10 becomes small.

B. Other Embodiment (B1) In the above embodiment, water was added after immersing the ionomer in alcohol. However, alcohol may be added after, for example, immersing the ionomer in water.

(B2) In the above embodiment, the first solution and the second solution were used to prepare the electrolyte membrane 10. However, for example, in order to prepare an electrolyte membrane, a solution using 1.62 g of diacetone alcohol and 1.08 g of water may be prepared in an amount of 60% by weight of diacetone alcohol. The weight% of diacetone alcohol is preferably 50% by weight or more and 75% by weight or less.

(B3) In the above embodiment, 0.3 g of ionomer was used. However, for example, 0.5 g of ionomer may be used.

(B4) As the structure of the electrolyte membrane, a porous film such as PTFE, polypropylene, or polyethylene can be used as the core material, and a multilayer structure such as an electrolyte layer / core material / electrolyte can be obtained.

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 of the embodiments described in the summary of disclosure column may be used to solve some or all of the above problems, or some of the above 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 ... Electrolyte membrane, 110 ... Teflon skeleton, 120 ... Sulfonic acid group, 130 ... First electrolyte membrane, 140 ... Second electrolyte membrane, 150 ... Third electrolyte membrane, 160 ... Fourth electrolyte membrane, 200 ... Fifth electrolyte membrane

Claims (1)

It is a method of manufacturing an electrolyte membrane.
A step of preparing a solution containing the material of the electrolyte membrane containing a sulfonic acid group, diacetone alcohol, and water.
The step of applying the solution on the substrate and drying it,
With
The weight% of the diacetone alcohol is 50% by weight or more and 75% by weight or less with respect to the total weight of the diacetone alcohol and the water.
A method for producing an electrolyte membrane.

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