Porous support and method for manufacturing the same, and electrolyte membrane including porous support and method for manufacturing the same

Abstract

The present invention provides at least one of a porous support capable of producing an electrolyte membrane exhibiting high proton conductivity and a method for producing the same, and an electrolyte membrane including the porous support and a method for producing the same. [Solution] A porous membrane made of fibers and a hydrophilic filler, having a porosity of 50% or more, A porous support characterized in that the hydrophilic filler is attached to 60% or more of the outer peripheral surface of the fibers.

Description

[Technical Field]

[0001] The present disclosure relates to a porous support and a method for producing the same, as well as an electrolyte membrane including the porous support and a method for producing the same. [Background technology]

[0002] Solid polymer fuel cells using electrolyte polymers have attracted attention because they have a high maximum current density and can operate at low temperatures, making them suitable for use as a mobile power source for automobiles and small-capacity power sources for portable electronic devices.

[0003] The electrolyte membrane for polymer electrolyte fuel cells exhibits proton conductivity by transferring sulfonic acid groups in the electrolyte membrane while carrying water molecules. Therefore, to increase proton conductivity, it is effective to retain more water within the electrolyte membrane.

[0004] However, the amount of water produced by a fuel cell varies depending on the power generation state, and the amount of water retained in the electrolyte membrane also varies accordingly. Therefore, studies have been conducted to improve the water retention of the electrolyte membrane by incorporating hydrophilic fillers into the membrane.

[0005] For example, Patent Document 1 discloses an electrolyte membrane that uses a porous membrane as a substrate and contains a hydrophilic filler that is 0.1 times or more and 50 μm or less than the average pore size of the pores in the porous membrane, and an ion exchange resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-217921 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the electrolyte membrane described in Patent Document 1, the hydrophilic filler is uniformly attached to a substrate made of a porous membrane to form a layer, which results in the pores of the porous membrane being blocked, making it difficult to improve the proton conductivity.

[0008] An object of the present disclosure is to provide at least one of a porous support capable of producing an electrolyte membrane exhibiting high proton conductivity and a method for producing the same, and an electrolyte membrane including the porous support and a method for producing the same. [Means for solving the problem]

[0009] In the present disclosure, a porous support having a porous membrane and a hydrophilic filler was investigated, focusing on the structure of the porous membrane and the hydrophilic filler. As a result, it was found that the above-mentioned object can be achieved by using a porous membrane made of fibers as the porous membrane and forming a porous support in which the fibers are attached with a hydrophilic filler in a specific state.

[0010] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A porous membrane made of fibers and a hydrophilic filler, having a porosity of 50% or more, and A porous support characterized in that the hydrophilic filler is attached to 60% or more of the outer peripheral surface of the fibers. [2] The porous support according to the above [1], wherein the average primary particle size of the hydrophilic filler is 50 nm or less. [3] The porous support according to [1] or [2] above, wherein the hydrophilic filler is one or more selected from the group consisting of silicon oxide, siloxane compounds, silane compounds, zeolites, aluminum oxide, titanium oxide, and tungsten oxide. [4] The porous support according to any one of the above [1] to [3], wherein the fibers are made of a hydrocarbon-based resin or a fluorine-based resin. [5] A method for producing a porous support according to any one of [1] to [4] above, A method for producing a porous support, comprising: a first impregnation step of impregnating a porous membrane with a dispersion of a hydrophilic filler; and a first drying step of removing the dispersion medium from the porous membrane. [6] An electrolyte membrane having a structure comprising a water-retaining reinforcing layer and a contact layer, the water-retaining reinforcing layer being sandwiched between the contact layers, The water-retaining reinforced layer is made of the porous support according to any one of [1] to [4] above, The porous support contains at least an electrolyte polymer in its pores, and The electrolyte membrane wherein the contact layer is made of an electrolyte polymer. [7] The electrolyte membrane according to the above [6], wherein the thickness of the contact layer is 45 μm or less. [8] The electrolyte membrane according to [6] or [7] above, which is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis. [9] A method for producing an electrolyte membrane, comprising: a second impregnation step of impregnating the porous support according to any one of [1] to [4] above with an electrolyte polymer solution; and a second drying step of drying the porous support containing the electrolyte polymer solution. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide at least one of a porous support capable of producing an electrolyte membrane exhibiting high proton conductivity and a method for manufacturing the same, and an electrolyte membrane including a porous support and a method for manufacturing the same. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram showing a state in which a hydrophilic filler is attached to the outer peripheral surface of the fibers of a porous membrane. [Figure 2] 1 is a schematic diagram showing a cross section of an electrolyte membrane according to the present disclosure. [Figure 3] 1 is a SEM image of the surface of a porous support of Comparative Example 1. [Figure 4] 1 is a SEM image of the surface of the porous support of Example 1. [Figure 5] 1 is a SEM image of the surface of a porous support of Comparative Example 2. [Figure 6] 1 is a cross-sectional SEM-EDX image of the porous support of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure will be described below with reference to an example of an embodiment. The present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of upper and lower limits of the ranges disclosed herein. In this specification, the symbol "to" includes both the upper and lower limits. <Porous support> This embodiment is a porous support comprising a porous membrane made of fibers and a hydrophilic filler, and characterized in that the porosity is 50% or more and the hydrophilic filler is attached to 60% or more of the outer peripheral surface of the fibers.

[0014] The porous membrane is preferably a stretched porous film, a nonwoven fabric, a woven fabric or a mesh sheet.

[0015] The thickness of the porous membrane can be 1 μm or more, 5 μm or more, or 10 μm or more, and can be 30 μm or less, 25 μm or less, or 20 μm or less.The thickness of the porous membrane can be 1 μm or more and 30 μm or less, 5 μm or more and 25 μm or less, or 10 μm or more and 20 μm or less.

[0016] The porous membrane is made of fibers. This allows the hydrophilic filler to adhere to the fibers, preventing the pores of the porous membrane from being blocked by the hydrophilic filler. The fibers are preferably made of a hydrocarbon resin or a fluororesin, and more preferably made of a hydrocarbon resin. The hydrocarbon resin is preferably one or more selected from the group consisting of polyolefin, polyester, polyphenylene sulfide, polyetherimide, polyimide, polyurethane, and polyethersulfone, and more preferably polyolefin. The fluororesin is preferably one or more selected from the group consisting of polytetrafluoroethylene, perfluoroalkoxyalkane, and polyvinylidene fluoride, and more preferably polytetrafluoroethylene.

[0017] The average diameter of the fibers constituting the porous membrane is, for example, 1 μm or more, 5 μm or more, or 10 μm or more, and is, for example, 50 μm or less, 30 μm or less, or 20 μm or less.The average diameter of the fibers constituting the porous membrane is, for example, 1 μm or more and 50 μm or less, 5 μm or more and 30 μm or less, or 10 μm or more and 20 μm or less.

[0018] The hydrophilic filler may be at least one of a compound having a hydroxyl group (OH group) and a metal oxide, and examples thereof include one or more selected from the group consisting of silicon oxide, siloxane compounds, silane compounds, zeolite, aluminum oxide, titanium oxide, and tungsten oxide.

[0019] The hydrophilic filler may have a size smaller than the average opening diameter of the porous membrane or the diameter of the fibers constituting the porous membrane, and may have an average primary particle size of 1 nm or more, 5 nm or more, or 10 nm or more. The average primary particle size of the hydrophilic filler is preferably 50 nm or less, and may be 30 nm or less or 25 nm or less. When the average primary particle size of the hydrophilic filler is within this range, it can penetrate into the porous membrane without blocking the openings of the porous membrane, and can improve water retention even when covering the outer surfaces of the fibers inside the porous membrane. The average primary particle size may be 1 nm or more and 50 nm or less, 5 nm or more and 30 nm or less, or 10 nm or more and 25 nm or less.

[0020] In this embodiment, the average primary particle size of the hydrophilic filler can be determined by measuring the primary particle sizes of 100 particles in an observation image using a transmission electron microscope (for example, device name: JEM-2100F, manufactured by JEOL Ltd.) and using the average value.

[0021] Accelerating voltage: 200 kV Observation magnification: 50,000x The porous support of the present embodiment has a porous membrane made of fibers and a hydrophilic filler, and may have a structure in which the hydrophilic filler is attached to the fibers constituting the porous membrane, and the fibers are partially or entirely coated with the hydrophilic filler, thereby exhibiting high proton conductivity when used as an electrolyte membrane.

[0022] The porosity of the porous support is 50% or more, and may be 55% or more, 60% or more, or 65% or more, or may be 80% or less, 75% or less, or 70% or less. Examples of the porosity of the porous support in this embodiment are 50% or more and 80% or less, 55% or more and 75% or less, or 65% or more and 70% or less. By having the porosity in the above range, when formed into an electrolyte membrane, proton conductivity at 100% RH can be maintained, and even if the electrolyte membrane is placed in an environment where it dries due to the supply of a low-humidity gas, a decrease in proton conductivity can be suppressed.

[0023] The porosity of the porous support can be calculated, for example, from the specific gravity of the material that constitutes the porous support and the weight of the apparent volume as follows.

[0024] Porosity (%) = 100 × [mass of porous support (g)] / [(volume of porous support (cm 3 ) × specific gravity of the material constituting the porous support (g / cm 3 )] The porous support of this embodiment may have an electrolyte polymer on the surface of the fibers. By having the fibers contain a hydrophilic filler and an electrolyte polymer having proton conductivity, it is possible to prevent the hydrophilic filler from falling off the fibers without reducing the proton conductivity. <Method of manufacturing porous support> The porous support of this embodiment may be produced by any method as long as it satisfies the above-mentioned requirements. A preferred production method includes a first impregnation step (hereinafter also referred to as "first impregnation step") of impregnating a porous membrane with a dispersion of a hydrophilic filler, and a step (hereinafter also referred to as "first drying step") of removing the dispersion medium from the porous membrane.

[0025] The porous membrane used in the first impregnation step is a porous membrane made of fibers.

[0026] The dispersion of the hydrophilic filler used in the first impregnation step is a dispersion containing a dispersion medium and a hydrophilic filler.

[0027] The hydrophilic filler may be at least one of a compound having a hydroxyl group (OH group) and a metal oxide, and examples thereof include one or more selected from the group consisting of silicon oxide, siloxane compounds, silane compounds, zeolite, aluminum oxide, titanium oxide, and tungsten oxide.

[0028] The concentration of the hydrophilic filler in the dispersion is, for example, 6% by mass or more, 7% by mass or more, or 8% by mass or more, and is, for example, 12% by mass or less, 11% by mass or less, or 10% by mass or less, and is, for example, 6% by mass or more and 12% by mass or less, 7% by mass or more and 11% by mass or less, or 8% by mass or more and 10% by mass or less. When the concentration of the hydrophilic filler is within this range, it can penetrate into the interior of the porous membrane without blocking the pores, and the outer peripheral surfaces of the fibers constituting the porous membrane can be covered with the hydrophilic filler.

[0029] The average pore size of the porous membrane may be 10 nm or more, 20 nm or more, or 30 nm or more, and may be 200 nm or less, 100 nm or less, or 50 nm or less. The average pore size of the porous membrane may be 10 nm or more and 200 nm or less, 20 nm or more and 200 nm or less, or 30 nm or more and 200 nm or less.

[0030] The dispersion medium may be any solvent that has affinity with the porous membrane and penetrates into the interior of the porous membrane through its fibers. For example, the dispersion medium may be at least one of water and an organic solvent. Because it has a high affinity with many porous membranes and can be dried at a low temperature below the melting point of the porous membrane, alcohol is preferred as the dispersion medium, and isopropyl alcohol is more preferred.

[0031] A preferred impregnation method for the first impregnation step is to place the porous membrane on a horizontally placed, smooth plate such as a glass plate, and drop a predetermined amount of hydrophilic filler dispersion according to the total surface area of ​​the fibers constituting the porous membrane into two or more regions where the hydrophilic filler dispersion can penetrate, and then spread the dispersion horizontally using a glass plate or a rod. This method allows the dispersion to penetrate into the interior of the porous membrane in just the right amount along the fibers of the porous membrane without impregnating the porous membrane with excess dispersion. This allows the hydrophilic filler to be efficiently attached to the outer surface of the fibers without blocking the pores of the porous membrane.

[0032] In the first drying step, heating is preferably performed at a temperature equal to or lower than the melting point of the fibers constituting the porous membrane. By heating at a temperature equal to or lower than the melting point, the dispersion medium can be evaporated and dried while suppressing deformation or deterioration of the porous support. The drying time varies depending on the amount of dispersion medium used, but may be, for example, 0.2 hours or more, 0.5 hours or more, or 1 hour or more, and may be 24 hours or less, 18 hours or less, or 12 hours or less.

[0033] Furthermore, after the first drying step, a solution containing an electrolytic polymer may be added to the porous support. By spraying a solution of the electrolytic polymer onto the porous membrane to which the hydrophilic filler has been attached, or by mixing the electrolytic polymer in the hydrophilic filler dispersion and impregnating the porous membrane with the mixture and drying, the electrolytic polymer acts as a binder, fixing the hydrophilic filler to the surface of the fibers and improving adhesion to the porous membrane.

[0034] The concentration of the electrolyte polymer solution may be set to a concentration more suitable for the opening size of the porous membrane, and may be 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more, and may be 10% by mass or less, 8% by mass or less, or 5% by mass or less, and from the viewpoint of the viscosity and impregnation property of the solution, it is preferably 0.1% by mass or more and 10% by mass or less. <Electrolyte membrane> The electrolyte membrane of the present embodiment includes a water retention reinforcing layer and a contact layer, and has a structure in which the water retention reinforcing layer is sandwiched between the contact layers, The water-retaining reinforcing layer is made of the porous support of this embodiment, and The contact layer is an electrolyte membrane made of an electrolyte polymer.

[0035] The electrolyte membrane of this embodiment has a structure in which the water retention reinforcing layer is sandwiched between contact layers. That is, the structure is such that both sides of the water retention reinforcing layer are sandwiched between contact layers, and it is preferable that the contact layer, the water retention reinforcing layer, and the contact layer are laminated in this order and integrated into one structure.

[0036] The contact layer is made of an electrolyte polymer, and the hydrophilic filler and the fibers of the porous membrane are not exposed on the surface. Therefore, the electrolyte polymer and the catalyst particles of the electrode are in close contact with each other, and the entire surface of the electrolyte membrane becomes a proton conduction path, and the proton conduction path is not narrowed by the hydrophilic filler or the fibers of the porous membrane. The contact layer is only required to be made essentially of an electrolyte polymer, and may contain inevitable impurities, etc. The electrolyte polymer of the contact layer and the electrolyte polymer of the water retention reinforcing layer may be the same or different.

[0037] The water-retaining reinforcement layer is made of a porous support containing an electrolyte polymer within its pores. Hydrophilic filler is attached to more than 60% of the outer surface of the fibers that make up the porous support, which provides high water retention and maintains high proton conductivity even under low humidity conditions.

[0038] The porous support has a porosity of 50% or more, and therefore has many pores with short proton conduction paths, which can improve proton conductivity.

[0039] The thickness of the contact layer depends on the water retention capacity of the water retention reinforcing layer, the electrolyte polymer, etc., but is preferably 45 μm or less, and may be 40 μm or less, or 35 μm or less. When the contact layer is a thin layer with a thickness of 45 μm or less, the water retention reinforcing layer can maintain the wet state of the contact layer and prevent the contact layer from drying out, thereby preventing a decrease in proton conductivity under low humidity conditions. The thickness of the contact layer can be 1 μm or more, 5 μm or more, or 10 μm or more, for example, 1 μm or more to 45 μm or less, 1 μm or more to 40 μm or less, or 1 μm or more to 35 μm or less. The thicknesses of the contact layers sandwiching the water retention reinforcing layer may be different from each other, but the thickness of at least one of the contact layers is preferably 1.5 times or less the thickness of the water retention reinforcing layer. This allows the wet state to be maintained up to the outermost surface of the contact layer.

[0040] The total thickness of the electrolyte membrane, including the contact layer and the water-retaining reinforcing layer, may be 10 μm or more, 20 μm or more, or 30 μm or more, and may be 75 μm or less, 70 μm or less, or 65 μm or less. The total thickness of the electrolyte membrane may be 10 μm or more and 75 μm or less, 20 μm or more and 70 μm or less, or 30 μm or more and 65 μm or less.

[0041] The electrolyte membrane of the present embodiment can be used as an electrolyte membrane for a polymer electrolyte fuel cell or an electrolyte membrane for water electrolysis, and can maintain a wet state. Therefore, it is particularly preferable to use the electrolyte membrane for an on-vehicle polymer electrolyte fuel cell in which a humid state and a dry state are repeatedly changed over a short period of time. <Method of manufacturing electrolyte membrane> The electrolyte membrane of this embodiment may be produced by any method as long as it satisfies the above-described requirements. A preferred production method includes a step of impregnating a porous support with an electrolyte polymer solution (hereinafter also referred to as a "second impregnation step") and a step of drying the porous support containing the electrolyte polymer solution (hereinafter also referred to as a "second drying step").

[0042] In the second impregnation step, the porous support of this embodiment is used. This eliminates the need to disperse a hydrophilic filler in the electrolyte polymer solution. Furthermore, it is not necessary to add other components that do not contribute to proton conduction, such as an activator. Therefore, the hydrophilic filler is unevenly distributed near the fibers that make up the porous support, making it easier to form proton conduction paths through the electrolyte polymer in the center of the pores.

[0043] In the second impregnation step, the method for impregnating the porous support with the electrolyte polymer solution may be, for example, one or more methods selected from the group consisting of solution casting, dispersion casting, melt pressing, and melt extrusion.

[0044] The electrolyte polymer used in the second impregnation step can be one type alone or a mixture of two or more types, and the electrolyte polymer of the contact layer and the electrolyte polymer used in the second impregnation step may be the same or different.

[0045] The solvent used for the electrolyte polymer solution is not particularly limited as long as it is a solvent capable of dissolving the electrolyte polymer, and may be an organic solvent, for example, one or more selected from the group consisting of N-methyl-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, 1,3-dimethyl-2-imidazolidinone, dimethyl ether, tetramethylurea, and alcohol.

[0046] In the second drying step, heating is preferably performed at a temperature below the melting point of the fibers constituting the porous membrane. Heating at a temperature below the melting point prevents deformation or deterioration of the porous support, and allows the solvent in the electrolyte polymer solution to volatilize and dry. The drying time varies depending on the type and amount of solvent used, but can be, for example, 0.2 hours or more, 0.5 hours or more, or 1 hour or more, and can be 24 hours or less, 18 hours or less, or 12 hours or less.

[0047] In the method for manufacturing the electrolyte membrane of this embodiment, the water retention reinforcing layer and the contact layer may be manufactured simultaneously, or the electrolyte membrane may be manufactured by forming the water retention reinforcing layer and then forming the contact layer on the water retention reinforcing layer. Since this reduces the number of steps required for manufacturing the electrolyte membrane, it is preferable to manufacture the water retention reinforcing layer and the contact layer simultaneously.

[0048] When the water-retaining reinforcing layer and the contact layer are produced simultaneously, the electrolyte membrane is produced by passing a porous support impregnated with an electrolyte polymer solution through a gap adjusted to the thickness of the electrolyte membrane, which is the sum of the thickness of the porous support and the thickness of the contact layer, adjusting the thickness of the applied electrolyte polymer solution, and drying it.

[0049] By simultaneously producing the water retention reinforcing layer and the contact layer, an electrolyte membrane can be obtained in which the water retention reinforcing layer and the contact layer are continuous, without creating an interface between them.

[0050] Furthermore, if you want to use electrolyte polymers with different molecular structures for the reinforcing layer and the contact layer, or if you want to prevent the solvent from remaining in the reinforcing layer even if the electrolyte polymers for the reinforcing layer and the contact layer are the same, the impregnation process can be carried out in two stages.

[0051] Specifically, after the pores of the porous substrate are filled with an electrolyte polymer solution and dried, the electrolyte polymer solution is further applied onto the surface of the porous substrate.

[0052] Then, the reinforcing layer is crosslinked in a crosslinking step, and the contact layer is dried to produce an electrolyte membrane.

[0053] It is also possible to prepare the reinforcing layer and the contact layer separately, and then bond the contact layers to both sides of the reinforcing layer to prepare the electrolyte membrane. [Example]

[0054] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. [Comparative Example 1] (Preparation of porous support) Colloidal silica (PL-1-IPA; primary particle size 10 to 15 nm, silica concentration 12 mass%, dispersion medium: isopropyl alcohol, manufactured by Fuso Chemical Co., Ltd.) was diluted with isopropyl alcohol to a silica concentration of 5.2 mass%, to obtain a hydrophilic filler dispersion.

[0055] A polyolefin porous membrane (nonwoven fabric with an average fiber diameter of 10 μm, porosity of 80%, and a thickness of 20 μm) cut to a size of 20 mm x 20 mm was placed on a horizontally placed glass plate and divided into 10 mm x 10 mm (100 mm 2) 2.5 μL of hydrophilic filler dispersion was dropped at intervals of 10 mm, and the dispersion was spread using a glass preparation to allow it to penetrate into the interior of the porous membrane. The membrane was then turned over, and 2.5 μL of the hydrophilic filler dispersion was dropped at the same intervals to allow it to penetrate into the porous membrane. The glass plate was then placed on a hot plate at 60°C, the pressure reduced to 100 kPa, and held for 1 hour to dry the dispersion medium, thereby obtaining a porous support. (Preparation of electrolyte membrane) The porous support was placed on a glass substrate, and an electrolyte polymer solution (Nafion polymer dispersion D2020CS; manufactured by Chemours) was cast onto the porous support, passed through the gap of a glass rod with a gap adjusted to 35 μm, dried to the touch, and peeled off from the glass substrate. The support was then turned over and placed again on the glass substrate, and the electrolyte polymer solution was cast onto the support. The solution was passed through the gap of a glass rod with a gap adjusted to 50 μm, and heated at 60 ° C for 6 hours to dry the electrolyte polymer, yielding an electrolyte membrane with a thickness of 50 μm. The thickness was measured at three points in the plane using a micrometer, and the average value was used. [Example 1] (Preparation of porous support) A porous support was obtained in the same manner as in Comparative Example 1, except that a hydrophilic filler dispersion with a silica concentration of 9.5% by mass was used. (Preparation of electrolyte membrane) An electrolyte membrane was obtained in the same manner as in Comparative Example 1, except that the porous support was used and the gap was adjusted to a membrane thickness of 65 μm. Comparative Example 2 (Preparation of porous support) A porous support was obtained in the same manner as in Comparative Example 1, except that a hydrophilic filler dispersion with a silica concentration of 12% by mass was used. (Preparation of electrolyte membrane) An electrolyte membrane was obtained in the same manner as in Comparative Example 1, except that the porous support was used and the gap was adjusted to a membrane thickness of 60 μm. Comparative Example 3 An electrolyte membrane having a thickness of 60 μm was obtained in the same manner as in Example 1, except that no porous support was used. Comparative Example 4 An electrolyte membrane having a thickness of 62 μm was obtained in the same manner as in Example 1, except that no hydrophilic filler dispersion was used. <Evaluation> (Porosity) The porosity was calculated using the following formula.

[0056] Porosity (%) = 100 × [mass of porous support (g)] / [(volume of porous support (cm 3 ) × specific gravity of the material constituting the porous support (g / cm 3 )] The measurement results are summarized in Table 1, and surface observation images of the porous supports after retaining the hydrophilic filler in Example 1, Comparative Example 1, and Comparative Example 2 are shown in FIGS. (Adhesion rate) The porous support was subjected to ion milling to prepare a cross section, and the deposition rate of the hydrophilic filler was measured by averaging the Si distribution at three points from SEM-EDX of the cross section image taken with a scanning electron microscope (Carl Zeiss: ULTRA55).

[0057] The measurement results are shown in Table 1, and the distribution of Si on the fiber surface of Example 1 is shown in FIG.

[0058] The white parts in Figure 6 are Si, and it was confirmed from this that the hydrophilic filler (silica) was distributed along the outer surface of the fiber. (proton conductivity) The electrolyte membrane was cut into a piece of 1 cm x 3 cm, and the proton conductivity of the electrolyte membrane was measured by the four-probe method.

[0059] Measurement cell: BT-115 (Scribner) Probe diameter: 0.5mm Probe material: Pt wire The membranes were tested for water retention by supplying 100% RH gas to the test fixture from the gas supply system. After the electrolyte membranes were fully hydrated, the rate of decline in proton conductivity was measured by starting the gas supply at 30% RH. Specifically, the test fixture was maintained at 80°C with 100% RH H2 gas flowing at 100 mL / min for 30 minutes to allow the electrolyte membranes to fully hydrate. The test fixture was then stopped to maintain 100% RH. The humidity in the gas supply system was allowed to stabilize at 30% RH. After confirming that the RH had reached 30%, 30% RH H2 gas was flowed through the test fixture at 100 mL / min. The proton conductivity was measured 15 and 30 minutes after the start of the gas supply, and the rate of decline was compared.

[0060] [Table 1]

[0061] In Table 1, the proton conductivity at 100% RH is a relative value with Comparative Example 4 set as 1 (reference), and the decrease in proton conductivity at 30% RH is a relative value with the proton conductivity at 100% RH of each Example and Comparative Example set as 1 (reference).

[0062] The results of the proton conductivity at 100% RH showed that the proton conductivity decreased as the porosity of the porous support decreased, and a comparison between Example 1 and Comparative Example 2 confirmed that the hydrophilic filler blocked the pores of the porous support, inhibiting proton conduction in the electrolyte.

[0063] However, in Example 1, the effect of retaining the hydrophilic filler was small, and the proton conductivity was maintained at 90% or more of that of Comparative Example 4.

[0064] Comparative Example 1 has a high porosity and therefore good proton conductivity at 100% RH. However, because the adhesion rate is less than 60%, the proton conductivity at 30% RH is almost the same as that of Comparative Example 4, and it is thought that the effect of the hydrophilic filler in a dry environment is insufficient.

[0065] In Example 1, the effect of maintaining proton conductivity at 30% RH was confirmed.

[0066] In Comparative Example 2, as can be seen in Figure 3, the hydrophilic filler is fixed so as to block the pores of the porous support, which significantly inhibits the movement of protons and water in the thickness direction of the electrolyte membrane. As a result, the proton conductivity at 100% RH is also lower than that of Comparative Example 4, and the decrease in proton conductivity at 30% RH is also significant.

[0067] From the above results, it was confirmed that in order to maintain the proton conductivity at 100% RH as much as possible while minimizing the decrease in proton conductivity even in an environment where the electrolyte membrane is dried due to the supply of low-humidity gas, it is possible to improve the situation by ensuring the porosity and adhesion rate by arranging a hydrophilic filler in the porous support, as in Example 1. [Explanation of symbols]

[0068] 1 Electrolyte membrane 2 contact layer 3 Water-retaining reinforcement layer 31 Porous support 32 Fiber 33 Hydrophilic filler

Claims

1. A porous membrane made of fibers and a hydrophilic filler, having a porosity of 50% or more, A porous support characterized in that the hydrophilic filler is attached to 60% or more of the outer peripheral surface of the fibers.

2. 2. The porous support according to claim 1, wherein the average primary particle size of the hydrophilic filler is 50 nm or less.

3. 3. The porous support according to claim 1, wherein the hydrophilic filler is at least one selected from the group consisting of silicon oxide, siloxane compounds, silane compounds, zeolites, aluminum oxide, titanium oxide, and tungsten oxide.

4. 3. The porous support according to claim 1, wherein the fibers are made of a hydrocarbon resin or a fluorine-based resin.

5. A method for producing the porous support according to claim 1 or 2, comprising: A method for producing a porous support, comprising: a first impregnation step of impregnating a porous membrane with a dispersion of a hydrophilic filler; and a first drying step of removing the dispersion medium from the porous membrane.

6. An electrolyte membrane having a structure comprising a water-retaining reinforcing layer and a contact layer, the water-retaining reinforcing layer being sandwiched between the contact layers, The water-retaining reinforcement layer is made of the porous support according to claim 1 or 2, The porous support contains at least an electrolyte polymer in its pores, and The electrolyte membrane wherein the contact layer is made of an electrolyte polymer.

7. 7. The electrolyte membrane according to claim 6, wherein the thickness of the contact layer is 45 μm or less.

8. 7. The electrolyte membrane according to claim 6, which is an electrolyte membrane for a fuel cell or an electrolyte membrane for water electrolysis.

9. 3. A method for producing an electrolyte membrane, comprising: a second impregnation step of impregnating the porous support according to claim 1 or 2 with an electrolyte polymer solution; and a second drying step of drying the porous support containing the electrolyte polymer solution.

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