JP5453860B2 - Electrolyte membrane for fuel cell - Google Patents

Description

  The present invention relates to a method for producing a resin-made porous membrane, and more particularly to a method for producing a porous membrane suitable as a reinforcing material for an electrolyte membrane for a polymer electrolyte fuel cell.

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

  Such a polymer electrolyte fuel cell has a membrane electrode assembly (MEA) as a main component, and is sandwiched between separators each having a fuel (hydrogen) gas flow path and an air gas flow path. Is formed as one fuel cell. Specifically, as shown in FIG. 5, the membrane electrode assembly 95 includes an anode side electrode (anode catalyst layer) 93a laminated on one side of an electrolyte membrane 91 that is an ion exchange membrane, and a cathode on the other side. The side electrode (cathode catalyst layer) 93b is laminated, and gas diffusion layers 94a and 94b are disposed in the anode catalyst layer and the cathode catalyst layer, respectively.

  The electrolyte membrane needs to have a low membrane resistance. Therefore, it is desirable that the thickness of the electrolyte membrane be as thin as possible. However, if the film thickness is too thin, there are problems such as damage to the film during film formation and short circuit between the electrodes. Further, since the electrolyte membrane is used in a wet state, there is a problem that the durability of the fuel cell is lowered due to swelling or deformation of the electrolyte membrane due to the wetness.

  In order to solve such a problem, a method for producing a porous film in which a fine through path is formed from the front surface to the back surface of a resin substrate has been proposed as a porous film that serves as a reinforcing material for such an electrolyte film. Yes. Such a porous membrane is manufactured using a phase separation structure of a polymer containing an aromatic hydrocarbon, and a membrane having a porous structure with a high through porosity can be obtained (for example, Patent Document 1). reference). As an electrolyte membrane for fuel cells, an electrolyte membrane in which pores of a porous base material (porous membrane) are filled with a polymer having proton conductivity has been proposed (see, for example, Patent Document 2).

JP 2004-359860 A International Publication No. 00/54351

  However, when a porous film is manufactured by the method described in Patent Document 1, the pore shape is flattened due to the effect of π-π stacking in material molecules (aromatic hydrocarbons) due to the characteristics of the material. Therefore, the pore diameter and porosity of the porous membrane fall within a certain range, and there is a limit to the structure of the porous membrane that can be manufactured.

  Further, when an electrolyte membrane in which a porous membrane described in Patent Document 2 is filled with an electrolyte resin is applied to a fuel cell, it is not fully deformed (stretched) in the film thickness direction. The electrolyte membrane may swell in the film thickness direction and the film thickness may increase. In particular, due to changes in humidity in the atmosphere, it is difficult to maintain sufficient bonding between the porous film and the electrolyte against the expansion and contraction of the electrolyte layer in the film thickness direction, and the electrolyte is easily peeled off. In some cases, the durability of the resin may deteriorate.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to maintain the durability of the membrane even under conditions where a wet and dry cycle and a heat / cool cycle are added without impairing proton conductivity. It is an object of the present invention to provide a method for producing a porous membrane capable of improving the temperature, and an electrolyte membrane for a fuel cell produced thereby.

  The inventors can improve the mechanical strength of the resin-made porous film in the direction in which the film extends by the conventional stretching method, but improve the mechanical strength in the film thickness direction. Thus, in order to improve the durability of the porous membrane, it was simply determined that the conventional stretching method was not possible. Therefore, as a result of intensive studies, the inventors have used the volume expansion due to freezing of water to increase the hole diameter in the holes extending in the direction intersecting the film thickness direction, thereby The present inventors have obtained new knowledge that it is possible to perform stretching in the film thickness direction of the porous film.

  The present invention is based on the inventors' new knowledge, and the porous membrane manufacturing method according to the present invention includes a plurality of pores extending in a direction intersecting the film thickness direction. Impregnating the formed porous resin membrane with a fluid, filling the pores with the fluid, expanding the fluid filled in the pores while freezing, and freezing the fluid Thawing and discharging the liquid from the holes.

  According to the present invention, first, a resin porous membrane having a plurality of pores extending in a direction intersecting the film thickness direction is prepared, and the porous membrane is impregnated with a fluid. Then, the fluid is filled in the holes. Then, the fluid is expanded by freezing the fluid, and the diameter of the holes is expanded by the expansion of the fluid. Since these holes extend in a direction intersecting with the film thickness direction, a part of the direction of increasing the diameter of the holes coincides with the film thickness direction.

  As a result, the porous film can be stretched in the film thickness direction so as to increase the film thickness of the porous film, and the mechanical strength in the film thickness direction of the porous film can be improved. That is, such a porous film has a high Young's modulus in the in-plane direction (direction in which the surface extends), and has a low Young's modulus in the film thickness direction.

  In particular, to obtain a porous film having an unprecedented pore diameter and porosity by expanding the pores to a porous film having a flat pore shape due to the influence of π-π stacking Can do. Specifically, a porous film having a porosity of 5 to 95% by volume, a pore diameter of 0.001 to 1.0 mm, and a film thickness of 1 to 100 mm can be manufactured.

  The fluid used in the method for producing a porous membrane according to the present invention is not limited as long as it can be expanded by freezing, and examples thereof include liquids and sols. More preferably, it is a mixed solution of a water-soluble organic solvent and water, or an aqueous solution (liquid) containing a surfactant.

  According to the present invention, by using the above-described aqueous solution, when this aqueous solution is impregnated with the porous membrane, the aqueous solution can easily penetrate into and fill the pores. From such a viewpoint, in another aspect, the fluid used in the method for producing a porous membrane according to the present invention is more preferably an aqueous solution containing an organic solvent.

  Moreover, in the method for producing an electrolyte membrane according to the present invention, it is more preferable to activate the surface of the porous membrane and perform a hydrophilic treatment using a plasma treatment or the like before the filling step. By performing such hydrophilic treatment, the fluid can be more preferably impregnated (permeated) into the porous membrane in the filling step.

  Furthermore, in the present invention, since the frozen fluid is thawed and discharged from the pores, the electrolyte can be filled by filling the pores of the porous membrane with the electrolyte. A catalyst layer and a diffusion layer were sequentially laminated on both sides of the electrolyte membrane thus manufactured to manufacture a membrane electrode assembly, and the manufactured membrane electrode assembly was sandwiched by separators from both sides. In the fuel cell, since the porous membrane is reinforced in the film thickness direction as a reinforcing material, dimensional change due to swelling can be suppressed even when wet, and durability can be improved.

  The porous membrane constituting the present invention may be a reinforcing material made of a polymer resin having a mechanical strength higher than that of the electrolyte, and examples of the material include a hydrocarbon resin material and a fluoride resin material. More preferred are aromatic hydrocarbon resin materials and saturated hydrocarbon resin materials (including engineering plastic materials). These materials can increase the thickness in the film thickness direction more effectively through the series of steps. Specifically, materials such as polyether ketone ketone (PEKK), polyether ether ketone (PEEK), polyether imide (PEI), polyimide (PI), PAI, etc. can be used. It is preferable to contain molecules, and the water-repellent polymer is effective because the condensation and retention of water in the polymer electrolyte fuel cell hinders supply of the electrode reactant.

  As the electrolyte (electrolyte resin) constituting the present invention, a polymer resin having a cation exchange functional group is preferably used. As such a functional group, a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group are preferably used. A perfluoro proton exchange resin of a fluoroalkyl copolymer having a fluoroalkyl ether side chain and a perfluoroalkyl main chain is preferably used. For example, Nafion (trade name) manufactured by DuPont, Aciplex (trade name) manufactured by Asahi Kasei, Flemion (trade name) manufactured by Asahi Glass, and the like are exemplified. In which a sulfonic acid group is introduced. Further, there are styrene-divinylbenzene copolymer, polyimide resin, etc., which are hydrocarbon proton exchange resins, in which sulfonic acid groups are introduced. These are appropriately selected according to the use and environment in which the fuel cell is used.

  According to the present invention, the durability of the membrane can be improved even under conditions where a dry / wet cycle and a heat / cool cycle are added without impairing proton conductivity.

(A) is the figure which showed the porous membrane before the process which concerns on this embodiment, (b) is the figure which showed the electrolyte membrane manufactured by the manufacturing method which concerns on this invention. (A) is the figure which modeled the porous membrane shown to Fig.1 (a), (b) is for demonstrating the filling process which fills the void | hole of the porous membrane shown to (a) with aqueous solution. 2C is a step of freezing and expanding the aqueous solution shown in FIG. 2B, and FIG. 2D is a step of thawing the frozen aqueous solution and discharging the aqueous solution from the pores. (E) is a figure explaining the process of filling electrolyte with the porous membrane shown to (d), and manufacturing an electrolyte membrane. It is the figure which showed the cross-sectional photograph of the porous film of Example 1, (a) is the figure which showed the cross-sectional photograph of the porous film before a process, (b) is the figure of the porous film after a process. The figure which showed the cross-sectional photograph. It is the figure which showed the cross-sectional photograph of the electrolyte membrane of Example 1 and Comparative Example 1, (a) is the figure which showed the cross-sectional photograph of the electrolyte membrane before the process of Example 1, (b) is implementation. 2 is a diagram showing a cross-sectional photograph of the electrolyte membrane after treatment of Example 1, and (c) is a diagram showing a cross-sectional photograph of the electrolyte membrane after treatment of Comparative Example 1. FIG. The schematic diagram explaining an example of the conventional membrane electrode assembly and electrolyte membrane.

  Hereinafter, a method for producing a porous membrane according to the present invention and an embodiment of an electrolyte membrane produced by this method will be described with reference to the drawings.

  Fig.1 (a) is the figure which showed the porous membrane before the process which concerns on this embodiment, (b) is the figure which showed the electrolyte membrane manufactured by the manufacturing method which concerns on this invention. FIG. 2 is a schematic view showing a method for producing a porous membrane and a method for producing an electrolyte membrane according to the present invention.

  Specifically, (a) in FIG. 2 is a schematic view of the porous membrane shown in FIG. 1 (a), and (b) shows an aqueous solution in the pores of the porous membrane shown in (a). It is a figure for demonstrating the filling process filled. 2 (c) is a process for freezing and expanding the aqueous solution shown in (b), and (d) is a process for thawing the frozen aqueous solution and discharging the aqueous solution from the pores. (E) is a figure explaining the process of filling the porous membrane shown to (d) with electrolyte, and manufacturing an electrolyte membrane. In the present embodiment, a porous membrane is manufactured through the following series of processing steps (filling step to discharging step).

  First, as shown in FIG. 1A and FIG. 2A, a porous membrane 21A (before processing) is prepared. The porous film 21A has a plurality of (before processing) holes 21a extending in a direction intersecting the film thickness direction D.

  Such a porous membrane 21A can form a plurality of pores 21a with respect to the substrate by a known method such as phase separation, foaming, or stretching. A method for producing the porous membrane A using phase separation will be briefly described below.

  In this embodiment, first, a polyimide precursor or a polymer solution of polyimide is prepared as a starting material. Next, this solution is cast on a smooth substrate such as a glass substrate or a stainless steel substrate to form a cast. A soluble solvent or non-solvent and a protective solvent layer composed of a mixed solvent of these are laminated on the casting to prepare a laminated liquid. Examples of the protective solvent layer include solvents such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylformaldehyde (DMF), N, N-dimethylacetamide, methanol, ethanol and propanol. Is preferred.

  And while maintaining the state (lamella structure) where the polymer solution and the protective solvent layer as the laminating liquid are not completely mixed and have a concentration gradient (lamella structure), the laminating liquid is coagulated in the range of 0.5 to 600 seconds. Immerse in. Thereby, a polyamic acid or a polyimide is deposited from a laminated liquid. The coagulation liquid is not particularly limited as long as it is a polyimide precursor or a non-solvent of polyimide. For example, these non-solvents such as water, methanol, isopropanol, and N-methyl-2-pyrrolidone (NMP), N, N- A mixed solvent with a soluble solvent such as dimethylformaldehyde (DMF) or N, N-dimethylacetamide is preferred.

  Thereafter, the substrate and the deposited polyamic acid or polyimide film are immersed in water, the film is peeled off from the substrate, dried, and then heat treated to obtain the porous film 21A. A plurality of pores extending in the direction intersecting the film thickness direction are formed in the porous film 21A thus obtained. Such a porous membrane has a flat pore shape (see FIG. 3A described later).

  Thus, by producing a porous film by a phase separation method using an aromatic hydrocarbon such as a polyimide resin or a saturated hydrocarbon, a plurality of flat pores are formed in the film thickness direction. Since it can be made to extend in the crossing direction, as a result, the porous film can be more effectively stretched in the film thickness direction through the steps described later.

  Next, as shown in FIG. 2B, the porous membrane 21A thus manufactured is impregnated with an aqueous solution L containing a surfactant, and the pores are filled with the aqueous solution. This aqueous solution L may contain an organic solvent instead of the surfactant. As described above, by containing the surfactant or the organic solvent, the aqueous solution (water) can be more reliably permeated into the pores 21a of the porous membrane 21A. Moreover, since the volume expansion coefficient of water (aqueous solution) is higher than that of other aqueous solutions at the time of freezing, by using such an aqueous solution L, it is possible to further increase the pore diameter (increase the film thickness).

  The filling rate of the aqueous solution filled in the porous membrane 21A is preferably 95% by volume or more with respect to the volume of the pores. Thereby, the pore diameter can be more effectively expanded at the time of freezing when water is used.

  From such a viewpoint, it is desirable that the surfactant or the organic solvent is contained in an amount of 95% by mass, and the surfactant or the organic solvent empties the aqueous solution at a higher rate than when impregnated with water alone. As long as it can be filled in the pores, there is no particular limitation such as a cationic surfactant, an anionic surfactant, and a nonionic surfactant, and examples thereof include sodium laurylbenzenesulfonate. Moreover, as an organic solvent, acetone, DMF, NMP, ethanol etc. can be mentioned, for example.

  Next, as shown in FIG. 2C, the aqueous solution L is frozen. By this freezing, the aqueous solution L expands in volume, and the diameter of these pores is expanded by the volume expansion. Since these holes 21a extend in a direction intersecting with the film thickness direction D, the direction in which the diameter of the flat holes 21a expands (mainly the direction in which expansion is easy) is the film thickness direction D. It almost matches. Through such a series of processing steps, the pores 21b whose pore diameter is enlarged (increased) are formed, whereby the porous membrane 21B having an increased film thickness can be obtained.

  Next, as shown in FIG. 2 (d), the frozen aqueous solution L is thawed, and the aqueous solution L is discharged from the air holes 21b. Specifically, the porous membrane 21B is immersed in a liquid having a temperature equal to or higher than the freezing point temperature of the frozen aqueous solution, and the liquid is circulated to wash the aqueous solution. After the washing, the liquid is discharged.

  Finally, as shown in FIG. 2 (c), the electrolyte (resin) is filled in the pores 21b of the porous membrane 21B to manufacture the electrolyte membrane. More specifically, the electrolyte precursor (monomer) or multimer (oligomer) 31 is impregnated in the pores 21b, and the electrolyte precursor (monomer) or multimer (oligomer) 31 is polymerized therein. Let Thereby, as shown in FIG.1 (b), the electrolyte membrane 10 with which the linear or gel-like electrolyte 31 was filled to the void | hole 21b and the film thickness increased to t2 can be manufactured.

  The filling ratio of the electrolyte precursor (monomer) or multimer (oligomer) 31 to the pores 21b is preferably 95% by volume or more, and such polymerization is performed by external stimulation such as heat or ultraviolet rays, or You may carry out by the internal stimulation by a catalyst etc.

  In this way, the shape of the flat pores can be expanded by freezing the aqueous solution from the inside of the pores. By repeating the discharging process from the filling process, the pores can be formed to the limit diameter. Can be spread. As a result, it is possible to realize a hole diameter and porosity that could not be manufactured by the conventional methods, and at the same time, it is possible to improve the mechanical strength in the film thickness direction.

  Furthermore, since a porous membrane toughened in the film thickness direction is used, even if there is a volume variation of the electrolyte membrane in the pores due to dry / wet / cool heat, it is difficult for the void between the electrolyte and the porous membrane or the electrolyte membrane to drop off. A highly reliable electrolyte membrane can be obtained.

Hereinafter, the present invention will be described by way of examples.
(Reference Example 1)
A polyimide porous membrane as a starting material was produced by the following method.

<Preparation of polyamic acid solution>
3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) as the tetracarboxylic acid component, 4,4′-diaminodiphenyl ether (ODA) as the diamine component, and N— Using methylpyrrolidone (NMP), the raw materials were adjusted and blended so that the total mass of the monomer components was 7% by mass, and charged into a separable flask. Polymerization was carried out with stirring at a temperature of 40 ° C. for 16 hours under nitrogen flow. The resulting polyamic acid solution had a viscosity of 750 poise, and the intrinsic viscosity of the polyamic acid was 3.15.
(Solution viscosity was measured using a rotational viscometer. The intrinsic viscosity of polyamic acid was measured under the conditions of NMP and 30 ° C.)

<Preparation of polyimide porous membrane>
A spacer having a thickness of 230 μm was attached on two parallel sides of a stainless steel 20 cm square substrate whose surface was mirror-polished. The polyamic acid solution described above was cast in the form of a band between spacers, and uniformly stretched on the substrate using a glass rod.

  After applying MNP uniformly as a protective solvent layer on the polyamic acid solution applied on the substrate, using a doctor knife having a spacing of 100 μm with respect to the polyamic acid solution surface, and let stand for 1 minute The entire substrate was put into a methanol bath. In the meantime, the polymer solution and the protective solvent layer were not completely mixed, but the concentration gradient was maintained in the thickness direction, and the polymer was dissolved. After the addition, the mixture was allowed to stand for 5 minutes to precipitate polyamic acid on the substrate. The substrate was taken out and immersed in water for 5 minutes, and then the polyamic acid film deposited on the substrate was peeled off to obtain a polyamic acid film. After this polyamic acid film was dried at room temperature, it was attached to a 10 cm square pin tenter and heat treated at 320 ° C. to obtain a polyimide porous film.

(1) Evaluation method of porous film 1) Thickness: A 4 cm square film test piece was prepared, and the thickness at 9 points was measured at equal intervals in the vertical and horizontal directions with a dot thickness meter. The average value of the measured values was taken as the thickness.

2) Porosity (weight method): The weight of a film test piece cut out to a size of 10 cm square or more was measured, and the porosity was calculated by the following formula. The density of the polyimide was 1.34 g / cm ³ .

Porosity (%) = {1- (W / ρ)} / (L1 × L2 × t)} × 100
W: Test piece weight (g)
ρ: Density of test piece material (g / cm ³ )
L1: Length of test piece (cm)
L2: Specimen length (cm)
t: Test piece thickness (cm)

3) Average pore diameter: Measurement was performed based on the valve point method (ASTM F316, JIS / K3832). Using a palm porometer manufactured by PMI, the average pore diameter was calculated from the average flow rate.

4) Surface observation: The film surface was observed with a scanning electron microscope.

(2) Evaluation results The obtained polyimide porous membrane has a thickness of 27 μm, a porosity of 44%, an average pore diameter of 0.05 μm, and a pore size of 0.1 to several μm on the membrane surface (both sides). It was confirmed that there are many.

Example 1
The polyimide porous membrane manufactured in Reference Example 1 was prepared as a polyimide porous membrane that was a starting material. Next, an aqueous solution in which 0.5% by mass of a surfactant: sodium laurylbenzenesulfonate was dissolved in 10 ml of pure water was prepared as a fluid to be filled in the porous membrane. The petri dish containing this aqueous solution was charged into the porous membrane, the inside of the petri dish was degassed, and the aqueous solution was filled into the porous membrane. The petri dish in this state was taken out, cooled at −20 ° C. in a constant temperature and humidity chamber, the aqueous solution was frozen, the aqueous solution was then thawed, and the aqueous solution was discharged from the porous membrane. Such a series of steps from filling to discharging was repeated five times.

  When the electrolyte membrane thus obtained was subjected to cross-sectional observation with FE-SEM after CP polishing, the film thickness increased to about 50 μm. The porosity by the mercury porosimeter increased to 54% by volume, and the average pore diameter increased to 0.10 μm. The result of cross-sectional observation at this time is shown in FIG. FIG. 3 (a) is a photograph showing a cross-sectional observation of the porous film before treatment, which is a starting material.

  Next, an electrolyte monomer (2-acrylamido-2-methylpropanesulfonic acid manufactured by Aldrch) 49.45% by mass and a cross-linking agent (same as N, N-methylenebisacrylamide) 0.5 were added to the porous membrane. % By weight, polymerization initiator (Wako Pure Chemical Industries, Ltd., 2,2-azobismethylpropionamidine-dihydrochloride) 0.05% by weight in each ratio, pure water + surfactant (Nacalai Tesque Urylbenzenesulfone) (Sodium 0.5% by mass dissolved) Impregnated in 30 ml of solution, degassed and sonicated to remove air in the system, then taken out and heated at 60 ° C. for 6 hours to gel ( Polymerization), and then the porous membrane was washed with pure water. This impregnation to polymerization was repeated twice to produce a composite electrolyte membrane filled with the electrolyte membrane at a filling rate of 96.4% by volume when converted to the pore volume.

(Evaluation)
For the electrolyte membrane of Example 1, (1) proton conductivity, (2) in-plane swelling rate, film thickness, and (3) hydrogen permeation amount were measured.

  (1) The proton conductivity was measured using a Hioki Electric Chemical Impedance Meter 3532-50 under the conditions of 60 ° C. and 95% RH. (2) The in-plane swell ratio was measured by immersing the electrolyte membrane at room temperature for 1 minute to perform a swelling test, and measuring these areas with a dial thickness thickness gauge. The swelling rate indicates the swelling rate in the extending direction of the electrolyte membrane, and was calculated by [area after swelling test−area before swelling test] / area before swelling test. The film thickness after the swelling test was also measured. (3) The amount of hydrogen permeation was measured using a gas permeability measuring device manufactured by GTR Tech under the conditions of 60 ° C. and 20% RH.

  Furthermore, 60 cycles each of the wet and dry cycle (60 ° C. hot water for 30 minutes, 60 ° C. vacuum drying for 1 hour) and the cold cycle (60 ° C., warm water for 30 minutes, −20 ° C. freezing for 1 hour) were performed on the electrolyte membrane of Example 1. After repeating, proton conductivity, in-plane swelling rate, film thickness, and hydrogen permeation amount were measured. The results are shown in Table 1. Moreover, the cross-sectional photograph of the electrolyte membrane after the wet and dry cycle is shown in FIG. FIG. 4A is a view showing a cross-sectional photograph of the electrolyte membrane before the cooling and heating cycle.

  In addition, (dry type) in the column with a cycle in Table 1 shows the result of the dry cycle, and (cold heat) shows the result of the cold cycle. It shows that it became the same value.

(Example 2)
The same polyimide porous membrane as in Example 1 was prepared as a starting material. Next, an organic solvent: 30 ml of acetone (purity 99%) manufactured by Nacalai Tesque and 70 ml of pure water were mixed and stirred as a fluid to be filled in the porous membrane. In a sealed bottle, the porous membrane was immersed in an aqueous solution, defoamed by ultrasonic treatment, and sufficiently impregnated. This was taken out, immediately cooled and solidified directly in liquid nitrogen, and returned to the above solution after 3 minutes. This cycle was repeated 15 times.

  The electrolyte membrane thus obtained was subjected to cross-sectional observation with FE-SEM after CP polishing in the same manner as in Example 1. As a result, the film thickness increased to about 43 μm, and the porosity by a mercury porosimeter Increased to 38% by volume, and the average pore size increased to 0.10 μm.

  Further, in the same manner as in Example 1, the electrolyte monomer, the crosslinking agent, and the polymerization initiator were immersed in a solution obtained by dissolving in pure water and a surfactant, and the polymerization operation was repeated twice from the same impregnation. A composite electrolyte membrane filled with 8% electrolyte was fabricated. With respect to this electrolyte membrane, the proton conductivity, the in-plane swelling rate, the film thickness, and the hydrogen permeation amount were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example)
An electrolyte membrane was produced in the same manner as in Example 1. The difference from Example 1 is that the electrolyte membrane was manufactured without treating the porous membrane of the starting material (without performing the refrigeration treatment for expanding the pore diameter). Then, after performing the wet and dry cycle / cooling cycle as in Example 1, the proton conductivity, in-plane swell ratio, film thickness, and hydrogen permeation amount of the electrolyte membrane were measured as in Example 1. . The results are shown in Table 1. In addition, the cross-sectional photograph of the electrolyte membrane after the wet and dry cycle is shown in FIG.

[result]
It is considered that the porous membranes of Examples 1 and 2 were filled with an aqueous solution and frozen, so that the film thickness increased and the pore diameter also increased. That is, from the cross-sectional state shown in FIGS. 3A and 3B, the displacement of the porous membrane is caused by the stress during freezing (volume expansion) of water in the film thickness direction by such a series of treatments. It is thought that it occurred.

  Further, as shown in FIG. 3 (a), the porous membrane of the starting material is manufactured by a phase separation method using a polyimide resin containing an aromatic hydrocarbon as shown in the embodiment. It is considered that the flat pores of the above formed a porous structure arranged in a direction intersecting the film thickness direction, and as a result, the porous film could be effectively stretched in the film thickness direction. .

  Further, in Examples 1 and 2, proton conductivity is not inhibited in either the wet / dry cycle or the heat / cool cycle, but in the comparative example, it is considered that the proton conductivity is impaired by these cycles.

  Further, in Examples 1 and 2, there was almost no change in film thickness in both the wet and dry cycles and the thermal cooling cycle, and the rate of change in film thickness was small compared to the comparative example. Further, as is clear from FIGS. 4B and 4C, in the comparative example, more voids are generated between the electrolyte and the porous body (FIG. 4C has more voids). It is thought that the membrane was swollen. In addition, it is considered that in Examples 1 and 2, the mechanical strength in the film thickness direction of the porous film was improved by increasing the film thickness (stretching in the film thickness direction).

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

  For example, in this embodiment, a series of steps from the filling step in FIG. 2 (b) to the discharge step in FIG. 2 (d) was performed once, and the polymerization shown in FIG. 2 (e) was performed once. A series of steps may be repeated and polymerization may be repeated.

  10: electrolyte membrane, 21A: porous membrane (before treatment), 21a: pores (before treatment), 21B: porous membrane after treatment, 21b: (after treatment) pores, L: aqueous solution, D : Thickness direction, 31: electrolyte, t1: film thickness of porous film (before treatment), t2: film thickness of porous film (after treatment)

Claims (3)

A step of impregnating a fluid with a porous film made of resin in which a plurality of pores extending in a direction intersecting the film thickness direction is formed, and filling the pores with the fluid;
Expanding the fluid filled in the pores while freezing;
Extract the frozen fluid, wherein the vacancies and the step of discharging the liquid, the porous membrane produced by the production method of including multi-porous membrane, a fuel cell electrolyte, characterized in that the filled Electrolyte membrane . 2. The fuel cell electrolyte membrane according to claim 1, wherein the fluid is an aqueous solution containing a surfactant. 2. The fuel cell electrolyte membrane according to claim 1, wherein the fluid is an aqueous solution containing an organic solvent.

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