JP7179311B2 - LAMINATED ELECTROLYTE MEMBRANE, METHOD FOR MANUFACTURING SAME ELECTROLYTE MEMBRANE, AND FUEL CELL - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to an electrolyte membrane having proton conductivity used as an electrolyte layer of a fuel cell.

A fuel cell is a clean power generation device that generates electricity through an electrochemical reaction between a fuel and an oxidant to produce water. A fuel cell comprises, for example, an electrolyte membrane having proton conductivity, two catalyst layers arranged to sandwich the electrolyte membrane, and two gas diffusion layers arranged to sandwich the electrolyte membrane with each catalyst layer interposed therebetween. and two separators arranged to sandwich an electrolyte membrane with each gas diffusion layer interposed therebetween. Many polymer electrolyte membranes have been proposed as electrolyte membranes having proton conductivity (Non-Patent Documents 1 to 3).

Applied Energy, 88, 981-1007 (2011) J. Hydro. Eng., 38, 4901-4934 (2013) J. ECS., 164, F387-F399 (2017)

A proton-conducting electrolyte membrane plays a role of proton transport and gas barrier. From the viewpoint of improving proton conductivity, it is effective to make the electrolyte membrane thinner. On the other hand, when the electrolyte membrane becomes thin, the mechanical strength of the electrolyte membrane decreases, and the gas barrier properties also decrease. That is, conventional polymer electrolyte membranes have limitations in thinning.

One aspect of the present disclosure is a first electrolyte membrane that includes a first proton-conducting polymer and a synthetic resin, and a second electrolyte membrane that includes a second proton-conducting polymer and is integrated with the first electrolyte membrane. and wherein the synthetic resin is a condensable resin.

Another aspect of the present disclosure is a first electrolyte membrane that includes a first proton-conducting polymer and a synthetic resin, and a second electrolyte that includes a second proton-conducting polymer and is integrated with the first electrolyte membrane. a membrane, wherein the synthetic resin is at least one selected from the group consisting of polyvinyl acetal resin, polyimide, phenol formaldehyde resin, melamine formaldehyde resin, urea resin and polyamide.

Yet another aspect of the present disclosure relates to a fuel cell comprising the laminated electrolyte membrane and a pair of catalyst layers sandwiching the laminated electrolyte membrane from both sides.

According to the present disclosure, it is possible to obtain a laminated electrolyte membrane that is thin and has excellent mechanical strength and gas barrier properties.

FIG. 2 is a conceptual diagram showing a comparison between a conventional electrolyte membrane (a) and a laminated electrolyte membrane (b) according to an embodiment of the present disclosure; 1 is a cross-sectional schematic diagram showing the structure of a single cell of a fuel cell according to an embodiment of the present disclosure; FIG.

A laminated electrolyte membrane according to an embodiment of the present disclosure includes a first electrolyte membrane containing a first proton-conducting polymer and a synthetic resin, and a second proton-conducting polymer integrated with the first electrolyte membrane. and a second electrolyte membrane. Here, the laminated electrolyte membrane satisfies at least one condition selected from conditions A to C below.

Condition A is a condition that the synthetic resin is a condensable resin. A condensable resin is a resin obtained by polycondensation of its precursor. Synthetic resin (condensable resin) precursors are condensed or ring-opened, for example, in a solution to produce a synthetic resin. Here, the precursor of the synthetic resin may be, for example, one that can be dissolved in the solution containing the first proton-conducting polymer and condensed or ring-opened in the solution to form a synthetic resin. Since such a synthetic resin is sufficiently mixed with the first proton-conducting polymer in the liquid phase to form a composite, it can reinforce the first proton-conducting polymer at the molecular level. The synthetic resin may have a crosslinked structure.

Condition B is that the synthetic resin is at least one selected from the group consisting of polyvinyl acetal resin, polyimide, phenol formaldehyde resin, melamine formaldehyde resin, urea resin and polyamide. These synthetic resins can usually satisfy condition A at the same time. Among them, polyvinyl acetal resin, phenol-formaldehyde resin, melamine-formaldehyde resin, and urea resin can form a crosslinked structure, so that the mechanical strength of the first electrolyte membrane can be easily increased. Polyvinyl acetal resins are acetalized polyvinyl alcohols, and may for example be formalized polyvinyl alcohols (so-called vinylon).

Condition C is a condition that the tensile strength of the first electrolyte membrane is greater than the tensile strength of the second electrolyte membrane. Tensile strength is measured according to JIS K7161 (2014). A method for measuring the tensile strength of the first and second electrolyte membranes is not particularly limited, but the tensile strength in the direction orthogonal to the thickness direction of the electrolyte membranes may be compared. For example, the first or second electrolyte membrane may be peeled off from the laminated electrolyte membrane, the respective tensile strengths may be measured, and the tensile strengths may be compared. Further, the tensile strength (Nt) of the entire laminated electrolyte membrane may be compared with the tensile strength (N2) of a membrane having the same thickness as the laminated electrolyte membrane and entirely composed of the second proton-conducting polymer. . Condition C is satisfied if Nt>N2. It is preferable that the tensile strength (n1) of the first electrolyte membrane and the tensile strength (n2) of the second electrolyte membrane satisfy 1.1≦n1/n2.

A proton-conducting polymer is generally a polymer having a plurality of acid groups in its molecule. Proton transfer within the proton-conducting polymer is carried out, for example, via sulfonic acid groups, phosphoric acid groups, and the like. The first proton-conducting polymer and the second proton-conducting polymer may be the same proton-conducting polymer or different proton-conducting polymers.

A proton-conducting polymer having a sulfonic acid group is described below.
A proton-conducting polymer having a sulfonic acid group has an EW (Equivalent Weight) value of at least 2000 g/mol or less. Here, the EW value represents the number of grams of polymer in a dry state per mole of sulfonic acid groups. For example, when the polymer Wg in a dry state contains n moles of sulfonic acid groups, the EW value is indicated by the W/n ratio. Therefore, the smaller the EW value, the larger the number of sulfonic acid groups and the greater the proton conductivity.

The EW value is obtained from the equivalent weight of sulfonic acid groups (ion exchange capacity). Ion exchange capacity (IEC) is the amount of NaOH solution ([A] ml) required to titrate a proton-conducting polymer sample with a given concentration of NaOH solution and neutralize it to pH 7. and the concentration of the NaOH solution ([B] g/ml) by the following formula.

Ion exchange capacity (IEC) (meq/g) = [A] x [B]/sample weight (g)

A synthetic resin is an artificially or industrially synthesized resin other than the first and second proton-conducting polymers. The synthetic resin may have some proton conductivity, but from the viewpoint of maintaining mechanical strength, the EW value of the synthetic resin should be at least 2000 g/mol.

The content of the synthetic resin in the first electrolyte membrane may be, for example, 1% by mass or more, preferably 5% by mass or more, from the viewpoint of making the mechanical strength of the first electrolyte membrane sufficiently large. On the other hand, from the viewpoint of ensuring sufficient proton conductivity in the first electrolyte membrane, the content of the synthetic resin may be, for example, 60% by mass or less.

The second electrolyte membrane usually does not contain synthetic resin, but may contain a small amount of synthetic resin. Therefore, the content of the synthetic resin satisfies the relationship of second electrolyte membrane<first electrolyte membrane. From the viewpoint of ensuring sufficient gas barrier properties and flexibility, more than 99 mass % of the second electrolyte membrane should be the second proton-conducting polymer. In this case, it can be said that the second electrolyte membrane does not substantially contain a synthetic resin. However, from the viewpoint of proton conductivity, the second electrolyte membrane preferably does not contain a synthetic resin. In the vicinity of the boundary between the first electrolyte membrane and the second electrolyte membrane, the synthetic resin diffused from the first electrolyte membrane may exist in the second electrolyte membrane.

The laminated electrolyte membrane preferably comprises a pair of second electrolyte membranes sandwiching the first electrolyte membrane from both sides. In this case, the laminated electrolyte membrane comprises at least one first electrolyte membrane and at least two second electrolyte membranes. Such a sandwich structure can further enhance gas barrier properties. Further, when the catalyst layer and the second electrolyte membrane are brought into contact with each other, it becomes easier to suppress the interfacial resistance between the laminated electrolyte membrane and the catalyst layer.

FIG. 1(a) is a conceptual diagram of a conventional electrolyte membrane 1a. A conventional electrolyte membrane 1a does not substantially contain a synthetic resin and is formed only of a proton-conducting polymer. When the conventional electrolyte membrane 1a is thinned, it cannot maintain its mechanical strength, resulting in a decrease in productivity and a decrease in gas barrier properties. By adding a fibrous reinforcing material (eg, polytetrafluoroethylene (PTFE) fiber) to the conventional electrolyte membrane 1a, it is possible to make the electrolyte membrane 1a thinner. However, it is impossible to obtain an electrolyte membrane 1a thinner than the thickness of the fiber. Also, such fibrous reinforcing materials are generally expensive. Furthermore, the conventional electrolyte membrane 1a is likely to swell due to water content or the like.

From the viewpoint of obtaining a thin electrolyte membrane that is excellent in mechanical strength and gas impermeability, an electrolyte membrane (first electrolyte membrane) that includes a synthetic resin and is sufficiently thin and an electrolyte membrane that does not substantially contain a synthetic resin and is sufficiently thin It is effective to laminate a thin electrolyte membrane (second electrolyte membrane). The synthetic resin functions as a reinforcing material for the first electrolyte membrane. Therefore, since the first electrolyte membrane is superior in mechanical strength to the second electrolyte membrane, it can be easily made thin. However, defects such as cracks and pinholes are likely to occur in the first electrolyte membrane containing a synthetic resin, and it may be difficult to ensure a high level of gas barrier property alone. On the other hand, when the second electrolyte membrane is laminated on the first electrolyte membrane, the gas barrier properties are greatly improved even when the second electrolyte membrane is very thin.

FIG. 1(b) is a conceptual diagram of a laminated electrolyte membrane 1 according to an embodiment of the present disclosure. The laminated electrolyte membrane 1 of the illustrated example includes a first electrolyte membrane 11 and a pair of second electrolyte membranes 12 sandwiching the first electrolyte membrane 11 from both sides. As a result, even if defects such as cracks and pinholes are generated in the first electrolyte membrane 11, the effects of the defects are reduced, the gas barrier property is not greatly impaired, and swelling due to water absorption is suppressed. Moreover, the productivity of the laminated electrolyte membrane 1 is also improved due to the improvement in mechanical strength due to the contribution of the first electrolyte membrane 11 . In this case, the thickness of the laminated electrolyte membrane 1 can be made very small while maintaining the mechanical strength. In addition, synthetic resins are less expensive than reinforcing materials.

At least one selected from the group consisting of fluorine-based polymers and hydrocarbon-based polymers can be used for at least one of the first proton-conducting polymer and the second proton-conducting polymer. Both fluorine-based polymers and hydrocarbon-based polymers have excellent proton conductivity.

Among proton-conducting polymers, fluorine-based polymers can be fluorohydrocarbonsulfonic acids, perfluorocarbonsulfonic acids, and the like. Perfluorocarbon sulfonic acid has, for example, a tetrafluoroethylene skeleton and a perfluoro side chain having a sulfonic acid group. Examples of such perfluorocarbon sulfonic acids include non-crosslinked copolymers of tetrafluoroethylene and perfluorovinyl monomers. The perfluorovinyl monomer may be, for example, a vinyl ether, preferably (2-sulfoethoxy)propyl vinyl ether. When the first proton-conducting polymer is a fluoropolymer, the second proton-conducting polymer is also preferably a fluoropolymer. Perfluorocarbon sulfonic acids are, for example, the following general formula (A):

is indicated by Here, x, y, m and n can be, for example, x=1.5-14, y=500-1500, m=0-3 and n=1-5, respectively.

Among proton-conducting polymers, hydrocarbon-based polymers have, for example, a skeleton in which aromatic rings such as benzene rings are linked in a straight chain. At least part of the aromatic ring is sulfonated with a sulfonic acid group, a sulfoalkyl group, or the like. Specifically, the hydrocarbon-based polymer includes, for example, a polyphenylsulfone skeleton, a polyetheretherketone skeleton, a polyimide skeleton, a polyethersulfone skeleton, a polyetherimide skeleton, a polysulfone skeleton, a polystyrene skeleton, and a polyaryleneethersulfoneketone skeleton. etc., and has a structure in which the aromatic ring contained in the skeleton is sulfonated. When the first proton-conducting polymer is a hydrocarbon-based polymer, the second proton-conducting polymer is also preferably a hydrocarbon-based polymer.

The first proton-conducting polymer and the second proton-conducting polymer may have the same skeleton. For example, when the first proton-conducting polymer has a tetrafluoroethylene skeleton, the second proton-conducting polymer preferably also has a tetrafluoroethylene skeleton. Further, the first proton-conducting polymer has, for example, a polyphenylsulfone skeleton, a polyetheretherketone skeleton, a polyimide skeleton, a polyethersulfone skeleton, a polyetherimide skeleton, a polysulfone skeleton, a polystyrene skeleton, or a polyaryleneethersulfoneketone skeleton. If so, the second proton-conducting polymer preferably also has a corresponding skeleton. By adopting the same type of skeleton in this way, the dimensional changes of the electrolyte membranes due to external forces, thermal expansion, etc. are made to the same degree, so that separation between the first electrolyte membrane and the second electrolyte membrane is less likely to occur. . Moreover, since the behavior of the laminated electrolyte membrane becomes uniform, deterioration in the durability and proton conductivity of the laminated electrolyte membrane is suppressed.

The EW value (EW2) of the second electrolyte membrane may be smaller than the EW value (EW1) of the first electrolyte membrane. At this time, the second electrolyte membrane is preferably brought into contact with the catalyst layer. For example, when the laminated electrolyte membrane has a three-layer structure comprising a pair of second electrolyte membranes sandwiching the first electrolyte membrane from both sides, the pair of second electrolyte membranes are in contact with the anode and cathode catalyst layers, respectively. When the second electrolyte membrane having a small EW value and a relatively large number of sulfonic acid groups is in contact with the catalyst layer, it is possible to secure more proton transfer paths and suppress rate-limiting of proton supply. Note that when more proton transfer paths are secured, local concentration of power generation is prevented, so deterioration of the catalyst and the electrolyte membrane is likely to be suppressed.

As the EW value decreases (the number of sulfonic acid groups increases), the hydrophilicity increases, making it difficult to form a membrane with the proton-conducting polymer, and the mechanical strength of the electrolyte membrane tends to decrease. In contrast, in the case of the laminated electrolyte membrane, the mechanical strength is ensured by the first electrolyte membrane, so the EW value of the second electrolyte membrane can be made sufficiently small. In other words, even when a second electrolyte membrane having a small EW value and low mechanical strength is used, the overall mechanical strength of the laminated electrolyte membrane can be maintained high.

The ratio of the EW value (EW2) of the second electrolyte membrane to the EW value (EW1) of the first electrolyte membrane: EW2/EW1 satisfies, for example, 0.2≦EW2/EW1<1, more preferably 0.5≦EW2 /EW1≤0.9. EW1 satisfies, for example, 400 g/mol<EW1≦2000 g/mol, and EW2 satisfies, for example, 400 g/mol≦EW1≦1500 g/mol.

The thickness of the laminated electrolyte membrane can be, for example, 15 μm or less, and can be reduced to 10 μm or less. At that time, sufficient mechanical strength can be maintained without using a reinforcing material or the like. On the other hand, in the case of conventional electrolyte membranes that do not contain synthetic resin, it is difficult to maintain mechanical strength if the thickness is reduced to 15 μm or less unless reinforcing materials are used.

The first electrolyte membrane may contain a fibrous reinforcing material from the viewpoint of further increasing the mechanical strength. obtain. Therefore, it is preferable that the first electrolyte membrane does not contain a fibrous reinforcing material.

When the laminated electrolyte membrane has a three-layer structure comprising a pair of second electrolyte membranes sandwiching the first electrolyte membrane from both sides, the thickness (T1) of the first electrolyte membrane is equal to the thickness (T2) of the second electrolyte membrane. may be greater than Here, T2 is the thickness of each of the pair of second electrolyte membranes. Therefore, the thickness (T) of the laminated electrolyte membrane having a three-layer structure is derived from the equation T=T1+2×T2. By setting T1≧T2, it is possible to efficiently increase the mechanical strength while reducing the thickness T of the entire laminated electrolyte membrane. The ratio of T1 to T2: T1/T2 satisfies, for example, 1.0≦T1/T2≦300, more preferably 1.5≦T1/T2≦100.

T1 satisfies, for example, 1 μm≦T1≦150 μm, and T2 satisfies, for example, 0.5 μm≦T2≦50 μm. For example, when it is desired to improve the proton conductivity of the laminated electrolyte membrane, the thickness T of the laminated electrolyte membrane is preferably 15 μm or less. This is because the distance traveled by protons is shortened and the proton resistance is reduced. On the other hand, when emphasizing the gas barrier property of the laminated electrolyte membrane, the thickness T of the laminated electrolyte membrane is not limited to 15 μm or less, and may exceed 15 μm.

Next, a fuel cell according to an embodiment of the present disclosure includes the laminated electrolyte membrane and a pair of catalyst layers sandwiching the laminated electrolyte membrane from both sides. The catalyst layer may contain a third proton-conducting polymer. At least one selected from the group consisting of fluorine-based polymers and hydrocarbon-based polymers can also be used as the third proton-conducting polymer.

The third proton-conducting polymer may be the same proton-conducting polymer as at least one of the first proton-conducting polymer and the second proton-conducting polymer. A proton-conducting polymer different from the proton-conducting polymer may also be used.

When the laminated electrolyte membrane has a three-layer structure comprising a pair of second electrolyte membranes sandwiching the first electrolyte membrane from both sides, the skeleton of the third proton-conducting polymer is the same as that of the second proton-conducting polymer. is preferably For example, when the second proton-conducting polymer has a tetrafluoroethylene skeleton, the third proton-conducting polymer preferably also has a tetrafluoroethylene skeleton. Since the third proton-conducting polymer contained in the catalyst layer and the second proton-conducting polymer of the second electrolyte membrane in contact with the catalyst layer have the same skeleton, the interfacial resistance between the catalyst layer and the laminated electrolyte membrane is reduced. can be reduced.

Hereinafter, a method for manufacturing a laminated electrolyte membrane having a three-layer structure including a pair of second electrolyte membranes sandwiching a first electrolyte membrane from both sides will be exemplified.

[1] Manufacture of First Electrolyte Membrane First, a mixed solution containing a first proton-conducting polymer and a synthetic resin or a precursor of a synthetic resin is prepared. The mixed solution may be prepared by any method. For example, a first solution containing a first proton-conducting polymer and a second solution containing a synthetic resin or a precursor of a synthetic resin may be prepared, and the first solution and the second solution may be mixed to prepare. good. The solvent for the mixed solution, the first solution, or the second solution is not particularly limited, but preferably contains at least water from the viewpoint of facilitating handling. The thickness of the first electrolyte membrane can be controlled by, for example, the concentration of the first proton-conducting polymer and the concentration of the synthetic resin or its precursor in the mixed solution.

Hereinafter, the method for manufacturing the first electrolyte membrane will be further described with respect to examples of typical synthetic resins. All of the following synthetic resins are condensable resins that can be produced by condensing precursors in a solution or through ring-opening.

(1) When using a polyvinyl acetal resin (here, vinylon) First, a first solution containing a first proton-conducting polymer is prepared. Perfluorocarbon sulfonic acid or Nafion (Nafion (registered trademark)), for example, can be used as the first proton-conducting polymer. A mixed solvent of alcohol and water can be used as the solvent for the first solution. As alcohol, for example propanol can be used.

Also, a second solution containing polyvinyl alcohol (PVA), which is a precursor of vinylon, is prepared. Water, for example, can be used as the solvent for the second solution.

Next, the first solution and the second solution are mixed, and the obtained mixed solution is cast on a substrate having a smooth surface and dried to form an intermediate film. The intermediate membrane is a composite of the first proton-conducting polymer and PVA. After that, by immersing the intermediate film in an acidic aqueous solution containing formaldehyde, the PVA is formalized (acetalized) to produce vinylon having a crosslinked structure. A formalization reaction is a kind of dehydration condensation reaction. As a result, a first electrolyte membrane is obtained in which vinylon, which is a synthetic resin, and the first proton-conducting polymer are combined. Since vinylon contains a crosslinked structure, it has excellent mechanical strength.

(2) When polyimide is used A second solution containing polyamic acid is prepared and mixed with the same first solution as above to prepare a mixed solution. Polyamic acid is a precursor of polyimide, which is a synthetic resin, and is generally synthesized using an aromatic diamine and an aromatic tetracarboxylic dianhydride as raw materials. After that, an intermediate film is formed from the mixed solution, and polyamic acid contained in the intermediate film is imidized by heating or using an imidizing agent. As a result, a first electrolyte membrane is obtained in which the polyimide, which is a synthetic resin, and the first proton-conducting polymer are combined. The imidization reaction is a dehydration condensation reaction of polyamic acid.

(3) When using phenol-formaldehyde resin A second solution containing a phenol compound is prepared and mixed with the same first solution as above to prepare a mixed solution. After that, an intermediate film is formed from the mixed solution, and the intermediate film is immersed in an acidic or alkaline aqueous solution containing formaldehyde, whereby the addition reaction (methylolation) and condensation reaction of formaldehyde to the phenol compound proceed. As a result, a first electrolyte membrane is obtained in which the phenol-formaldehyde resin, which is a synthetic resin, and the first proton-conducting polymer are combined. Phenolic resin has a three-dimensional crosslinked structure.

(4) When using melamine formaldehyde resin A second solution containing a melamine compound is prepared and mixed with the same first solution as above to prepare a mixed solution. After that, an intermediate film is formed from the mixed solution, and the intermediate film is immersed in an alkaline aqueous solution containing formaldehyde, whereby the addition reaction (methylolation) of formaldehyde to the melamine compound proceeds. After that, by heating the intermediate film, methylolmelamine undergoes a polycondensation reaction (methylenation) and crosslinks in a network to form a melamine-formaldehyde resin. As a result, a first electrolyte membrane is obtained in which the melamine-formaldehyde resin, which is a synthetic resin, and the first proton-conducting polymer are combined.

(5) When Urea Resin is Used A second solution containing a urea compound is prepared and mixed with the same first solution as above to prepare a mixed solution. After that, an intermediate film is formed from the mixed solution, and the intermediate film is immersed in an acidic or alkaline aqueous solution containing formaldehyde, whereby the addition reaction of formaldehyde to the urea compound (methylolation) and the polycondensation reaction (methylenation) proceed. do. As a result, a first electrolyte membrane is obtained in which the urea resin, which is a synthetic resin, and the first proton-conducting polymer are combined.

(6) When Polyamide is Used A second solution containing a polyamide precursor is prepared and mixed with the same first solution as above to prepare a mixed solution. After that, an intermediate film is formed from the mixed solution, and polyamide is produced by heating and polymerizing. As a result, a first electrolyte membrane is obtained in which the polyamide, which is a synthetic resin, and the first proton-conducting polymer are combined. Water-soluble caprolactam, water-soluble AH salt, and the like can be used as the polyamide precursor. Caprolactam is a cyclic compound and forms a polymer upon ring opening. An AH salt is an equivalent mixture of a dicarboxylic acid and a diamine. Dicarboxylic acids such as adipic acid and sebacic acid can be used. Diaminobutane, hexamethylenediamine and the like can be used as the diamine.

[2] Manufacture of Second Electrolyte Membrane Next, a second electrolyte membrane is formed on at least one surface of the first electrolyte membrane, and the first electrolyte membrane and the second electrolyte membrane are integrated. For example, a third solution containing the second proton-conducting polymer may be prepared, cast on at least one surface of the first electrolyte membrane, and dried to form a laminated electrolyte membrane. Perfluorocarbonsulfonic acid, for example, can also be used for the second proton-conducting polymer. A mixed solvent of alcohol and water can also be used as the solvent for the second solution. The thickness of the second electrolyte membrane can be controlled, for example, by the concentration of the second proton-conducting polymer in the third solution. Alternatively, the second electrolyte membrane may be formed first, and then the first electrolyte membrane may be formed so as to be laminated thereon. Moreover, after forming a laminated film of the intermediate film and the second electrolyte film, the intermediate film may be changed to a synthetic resin.

The fuel cell according to this embodiment will be exemplified below.
A fuel cell comprises the laminated electrolyte membrane and a pair of catalyst layers sandwiching the laminated electrolyte membrane from both sides. A gas diffusion layer may be disposed on each main surface of the pair of catalyst layers opposite to the laminated electrolyte membrane.

FIG. 2 is a cross-sectional schematic diagram showing the structure of a fuel cell (single cell) 10 according to an embodiment of the present disclosure. Usually, a plurality of single cells 10 are stacked to form a stack, but one single cell 10 is shown alone here.

The unit cell 10 includes a membrane electrode assembly (MEA) 5, and an anode-side separator 6A and a cathode-side separator 6B arranged so as to sandwich the membrane electrode assembly 5 therebetween. The membrane electrode assembly 5 includes a laminated electrolyte membrane 1, an anode catalyst layer 2A and an anode gas diffusion layer 3A arranged in order on one side of the laminated electrolyte membrane 1, and an anode catalyst layer 2A and an anode gas diffusion layer 3A arranged in order on one side of the laminated electrolyte membrane 1, and in order on the other side of the laminated electrolyte membrane 1. It comprises a cathode catalyst layer 2B and a cathode gas diffusion layer 3B which are arranged, and a pair of sealing members 4 which sandwich the peripheral portion of the laminated electrolyte membrane 1. As shown in FIG. A fuel gas channel 7A is formed on the surface of the anode-side separator 6A on the anode gas diffusion layer 3A side. An oxidant gas channel 7B is formed on the surface of the cathode-side separator 6B on the cathode gas diffusion layer 3B side.

Each catalyst layer includes, for example, a carbon material, catalyst particles supported on the carbon material, and a third proton-conducting polymer. Materials having conductivity, such as carbon black and carbon nanofiber, can be used as the carbon material. Noble metals such as platinum, cobalt, and ruthenium may be used for the catalyst particles.

Each gas diffusion layer includes, for example, a conductive water-repellent layer and a substrate layer that supports it. The water-repellent layer contains, for example, a conductive agent and a water-repellent agent. Examples of conductive agents include carbon black. Examples of water repellents include fluorine resins such as polytetrafluoroethylene. Carbon paper, carbon cloth, and the like are used for the base material layer. Alternatively, a gas diffusion layer without a substrate layer may be used. Such a gas diffusion layer can be obtained by molding a mixture containing a conductive agent, a fluororesin, etc. into a sheet.

As a material for each separator, for example, a carbon material, a metal material, or the like can be used. As shown in FIG. 2, one surface of each separator may have a plurality of recesses or protrusions to form gas flow paths.

Hereinafter, the present disclosure will be described in more detail based on examples. However, the present disclosure is not limited to the following examples.

[Example 1]
(1) Preparation of laminated electrolyte membrane As the first solution, 5% by mass Nafion (registered trademark) solution (DE520, 1-propanol/2-propanol/H ₂ O, EW value 1000 g/mol, manufactured by Wako Pure Chemical Industries, Ltd. )It was used.

As a second solution, a polyvinyl alcohol (PVA) aqueous solution (PVA content: 3.5% by mass) was prepared.

The first solution and the second solution were mixed in a mass ratio of 95:5 to obtain a mixed solution.

As the third solution, the same solution as the first solution was used.

First, the third solution was cast on a glass substrate to a thickness of about 2 μm and dried at room temperature for 12 hours or more to form a second electrolyte membrane. Next, a mixed solution of the first solution and the second solution was cast on the second electrolyte membrane so as to have a film thickness of about 6 μm and dried at room temperature for 12 hours or longer to form an intermediate membrane. Finally, the third solution was cast on the intermediate film so as to have a film thickness of about 2 μm and dried for 12 hours or more to form a laminated film having a three-layer structure.

Next, the laminated film was heat-treated at 60° C. for 3 hours and then at 180° C. for 3 hours. After that, using H ₂ SO ₄ , Na ₂ SO ₄ and HCHO, PVA was subjected to a formalization reaction to be vinylonized.

After that, it is activated with boiling water for 2 hours, 1 M H ₂ O ₂ aqueous solution at 80° C. for 2 hours, 1 M H ₂ SO ₄ aqueous solution at 80° C. for 2 hours, and further boiling water for 2 hours to increase the thickness. A laminated electrolyte membrane with a three-layer structure of 10 μm was completed.

(2) Preparation of catalyst layer 100 parts by mass of carbon black and 30 parts by mass of catalyst particles (Pt) supported thereon are dispersed in an appropriate amount of water, and an appropriate amount of ethanol is added to the resulting dispersion. , and 40 parts by mass of perfluorocarbon sulfonic acid (Nafion (registered trademark), EW value 1100 g/mol) were further added to prepare a catalyst dispersion for the catalyst layer.

Next, the smooth surfaces of the two PET sheets were coated with the catalyst dispersion to a uniform thickness using a screen printing method and dried to form an anode catalyst layer and a cathode catalyst layer (thickness 10 μm), respectively. did.

<Fabrication of single cell>
The obtained catalyst layers were transferred to both surfaces of the laminated electrolyte membrane to form an anode catalyst layer on one side and a cathode catalyst layer on the other side of the laminated electrolyte membrane. Next, a water-repellent layer containing carbon black and polytetrafluoroethylene as main components and a pair of gas diffusion layers comprising carbon paper were prepared and bonded to each catalyst layer to form an anode and a cathode. Next, a frame-shaped sealing member was arranged so as to surround the anode and cathode to form an MEA. Next, the MEA was sandwiched between an anode-side separator having a fuel gas channel and a cathode-side separator having an oxidant gas channel to complete a single cell A1.

<Evaluation>
Hydrogen gas humidified with water vapor having a dew point of 65° C. was supplied to the anode at a utilization rate of 75%, and oxygen gas humidified with water vapor having a dew point of 65° C. was supplied to the cathode at a utilization rate of 55%. did. The cell temperature was set at 80°C. Then, using a load control device, the current density with respect to the electrode area of the anode and cathode is changed between 0 and about 3.0 A/cm ² , and the IV characteristics, maximum output density and impedance (resistance) of the single cell A1 are measured. did.

[Example 2]
As the perfluorocarbon sulfonic acid used in the first solution, instead of Nafion, 6% by mass Aquivion (registered trademark) solution (D83-06A, 1-propanol/2-propanol/H ₂ O, EW value 830 g / mol, Solvay The procedure was the same as in Example 1, except that Then, in the same manner as in Example 1, a laminated electrolyte membrane having a three-layer structure with a thickness of about 10 μm was produced, and a single cell A2 of a fuel cell was assembled and evaluated.

[Comparative Example 1]
In the same manner as in Example 1, except that a commercially available perfluorocarbon sulfonic acid membrane (NRE212 (registered trademark), EW value 1100 g/mol, manufactured by DuPont) having a thickness of 50 μm was used as the electrolyte membrane instead of the laminated electrolyte membrane. , a single cell B1 of a fuel cell was assembled and evaluated.

Table 3 shows relative values (multiples) of the maximum output density and the resistance value of the single cells A1 and A2 when the maximum output density and the resistance value of the single cell B1 are set to 1, respectively.

According to Table 3, the resistances of the single cells A1 and A2 are significantly lower than that of the single cell B1, and it can be understood that the thickness of the electrolyte membrane has a large effect. By reducing the resistance of the electrolyte membrane in this manner, the maximum power density is also greatly improved. In addition, it can be understood that in the case of the single cell A2 in which the EW value of the first electrolyte membrane is lower, the resistance is less likely to increase even in the high current density region, and a high electromotive force can be maintained.

The laminated electrolyte membrane according to the present disclosure is suitable, for example, as a material for fuel cells used in automobiles, portable electronic devices, outdoor leisure power sources, emergency backup power sources, and the like. In particular, it is most suitable for fuel cells for high-output applications because it is easy to obtain the effect at a high current density.

1: laminated electrolyte membrane, 1a: conventional electrolyte membrane, 2A: anode catalyst layer, 2B: cathode catalyst layer, 3A: anode gas diffusion layer, 3B: cathode gas diffusion layer, 4: sealing member, 5: membrane electrode assembly (MEA), 6A: anode-side separator, 6B: cathode-side separator, 7A: fuel gas channel, 7B: oxidant gas channel, 11: first electrolyte membrane, 12: second electrolyte membrane, 10: fuel cell ( single cell)

Claims (11)

a first electrolyte membrane comprising a composite of a first proton-conducting polymer and a synthetic resin;
a second electrolyte membrane that includes a second proton-conducting polymer and is integrated with the first electrolyte membrane;
The laminated electrolyte membrane , wherein the synthetic resin is at least one selected from the group consisting of polyvinyl acetal resin, phenol-formaldehyde resin, melamine-formaldehyde resin, and urea resin . 2. The method according to claim 1 , wherein at least one of the first proton-conducting polymer and the second proton-conducting polymer is at least one selected from the group consisting of fluorine-based polymers and hydrocarbon-based polymers. laminated electrolyte membrane. 3. The laminated electrolyte membrane according to claim 1, comprising a pair of said second electrolyte membranes sandwiching said first electrolyte membrane from both sides. 4. The laminated electrolyte membrane according to claim 3 , wherein the thickness of said first electrolyte membrane is greater than the thickness of said second electrolyte membrane. The laminated electrolyte membrane according to any one of claims 1 to 4 , wherein the thickness of the laminated electrolyte membrane is 15 µm or less. The laminated electrolyte membrane according to any one of claims 1 to 5 , wherein the first electrolyte membrane does not contain a fibrous reinforcing material. 7. The laminated electrolyte membrane according to claim 1, wherein said first proton-conducting polymer and said second proton-conducting polymer have the same skeleton. The laminated electrolyte membrane according to any one of claims 1 to 7 , wherein the content of said synthetic resin in said first electrolyte membrane is 1% by mass or more and 60% by mass or less. A laminated electrolyte membrane according to any one of claims 1 to 8 ;
a pair of catalyst layers sandwiching the laminated electrolyte membrane from both sides;
fuel cell. The catalyst layer contains a third proton-conducting polymer,
10. The fuel cell according to claim 9 , wherein the skeleton of said third proton-conducting polymer is the same as the skeleton of said second proton-conducting polymer. A method for producing a laminated electrolyte membrane according to any one of claims 1 to 8,
forming the first electrolyte membrane by polymerizing the precursor in a solution containing the first proton-conducting polymer and the precursor of the synthetic resin;
A method of manufacturing a laminated electrolyte membrane, comprising forming the second electrolyte membrane on at least one surface of the first electrolyte membrane, and integrating the first electrolyte membrane and the second electrolyte membrane.

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