JP2011233347A - Proton conductive polymer electrolyte membrane and membrane-electrode assembly using it and polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a proton conductive polymer electrolyte membrane having a polyimide based polymer electrolyte membrane and exhibiting sufficient adhesion to an electrode.SOLUTION: The proton conductive polymer electrolyte membrane includes a polyimide based polymer electrolyte membrane and a fluorine based polymer electrolyte membrane laminated on one side thereof. The polyimide based polymer electrolyte membrane is mainly composed of polyimide resin formed by polycondensation of a tetracarboxylic dianhydride, a first aromatic diamine having a proton conductive group, and a second aromatic diamine not having a proton conductive group but having a condensation ring skelton consisting of three or more rings. The electrolyte membrane is suitable for a polymer electrolyte fuel cell (PEFC), especially for a direct methanol fuel cell (DMFC).

Description

  The present invention relates to a proton conductive polymer electrolyte membrane, a membrane-electrode assembly using the same, and a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as the next-generation energy source. In particular, polymer electrolyte fuel cells (PEFC) that use polymer membranes with proton conductivity as electrolytes have high energy density and are used in a wide range of fields such as household cogeneration systems, power supplies for portable devices, and power supplies for automobiles. Is expected to be used. The PEFC electrolyte membrane functions as an electrolyte that conducts protons between the fuel electrode and the oxygen electrode, as well as a partition that separates the fuel supplied to the fuel electrode and the oxidant supplied to the oxygen electrode. Function is required. If the function as one of the electrolyte and the partition is insufficient, the power generation efficiency of the fuel cell is lowered. For this reason, a polymer electrolyte membrane that is excellent in proton conductivity, electrochemical stability, and mechanical strength, and has low fuel and oxidant permeability is desired.

  At present, fluorine-based polymers such as perfluorosulfonic acid having a sulfonic acid group as a proton conductive group (for example, “Nafion (registered trademark)” manufactured by DuPont) are widely used as an electrolyte membrane of PEFC. Although the fluorine-based polymer electrolyte membrane is excellent in electrochemical stability, the fluororesin used as a raw material is not a general-purpose product and is very expensive because its synthesis process is complicated. The high cost of the electrolyte membrane is a major obstacle to the practical use of PEFC. In addition, one type of PEFC is a direct methanol fuel cell (DMFC) in which a solution containing methanol is supplied to the fuel electrode, and since it is excellent in fuel supply and portability, future practical application is attracting attention. However, since the fluorine-based polymer electrolyte membrane easily permeates methanol, it is difficult to use it in DMFC.

  As an alternative to such a fluorine-based polymer electrolyte membrane, development of a hydrocarbon-based polymer electrolyte membrane is underway. The resin used as the raw material for the hydrocarbon-based polymer electrolyte membrane is less expensive than the fluororesin, and a low-cost PEFC using this resin is expected.

  JP 2000-510511 A discloses a hydrocarbon polymer electrolyte membrane composed of tetracarboxylic dianhydride, an aromatic diamine having a proton conductive group, and an aromatic diamine having no proton conductive group. An electrolyte membrane comprising a polyimide resin formed by condensation has been disclosed. This electrolyte membrane has excellent mechanical and electrochemical stability, and can be manufactured at a lower cost than a fluoropolymer electrolyte membrane. Are listed. However, Japanese Patent Publication No. 2000-510511 does not consider the methanol permeation resistance (methanol blocking characteristics) of the electrolyte membrane, and the electrolyte membrane disclosed in the gazette does not necessarily have excellent methanol permeation resistance.

  A similar polyimide-based polymer electrolyte membrane is also disclosed in Japanese Patent Application Laid-Open No. 2003-68326, which overcomes the point that imide bonds are easily hydrolyzed and is superior in hydrolysis resistance (long-term water resistance). An attempt has been made to produce a polymer electrolyte membrane. However, the technique disclosed in Japanese Patent Application Laid-Open No. 2003-68326 does not consider the methanol permeation resistance of the electrolyte membrane, and the electrolyte membrane disclosed in the gazette does not necessarily have excellent methanol permeation resistance.

  By the way, the polymer electrolyte membrane is incorporated into PEFC as a membrane-electrode assembly bonded to an electrode. This membrane-electrode assembly is produced by disposing a polymer electrolyte membrane between an anode electrode and a cathode electrode and bonding them by a hot press method or a direct coating method. The hot press method is a method in which the polymer electrolyte membrane and the electrode are integrated by heating the polymer electrolyte membrane to near the melting point to soften the surface, pressing the electrode against the polymer electrolyte, and then cooling. In the direct coating method, for example, an ink containing a catalyst as an electrode is applied or transferred onto a polymer electrolyte membrane, and the polymer electrolyte membrane and the electrode are integrated by sandwiching the ink with carbon paper as a gas diffusion layer. Is the method.

  However, in the hot press method, since the electrolyte membrane is subjected to a sudden change in temperature and humidity, the dimensions of the electrolyte membrane may change greatly, and the electrolyte membrane may peel from the electrode. Further, in the direct coating method, contact failure may occur because the ink containing the catalyst does not become familiar with the electrolyte membrane. As described above, the electrolyte membrane having low adhesion with the electrode has a problem that, when used as a fuel cell, it causes a decrease in power generation characteristics such as an increase in internal resistance and an increase in time required for the output to stabilize. is there.

JP 2000-510511 A JP 2003-68326 A

  An object of the present invention is to provide an electrolyte membrane that is a proton conductive polymer electrolyte membrane having a polyimide-based polymer electrolyte membrane and has sufficient adhesion with an electrode.

The proton conductive polymer electrolyte membrane of the present invention comprises a polyimide polymer electrolyte membrane and a fluorine polymer electrolyte membrane laminated on at least one surface of the polyimide polymer electrolyte membrane,
The polyimide-based polymer electrolyte membrane is formed by polycondensation of tetracarboxylic dianhydride, a first aromatic diamine having a proton conductive group, and a second aromatic diamine having no proton conductive group. Mainly composed of polyimide resin.

  According to the present invention, as the aromatic diamine to be polycondensed with tetracarboxylic dianhydride, the first aromatic diamine having a proton conductive group and the second aromatic diamine having no proton conductive group are used. By providing the fluorine-based polymer electrolyte membrane on at least one surface of the polyimide-based polymer electrolyte membrane, a proton conductive polymer electrolyte membrane that can realize high adhesion with the electrode can be obtained. According to a preferred embodiment of the present invention, a proton conductive polymer electrolyte membrane having high proton conductivity and high methanol permeation resistance can be obtained.

It is a schematic diagram which shows an example of the membrane-electrode assembly of this invention. It is a schematic diagram which shows an example of the fuel cell of this invention. It is a figure which shows the relationship between the operation time of the fuel cell in Example 2 and the comparative example 2, and an electric current. It is a figure which shows the relationship between the load current density of the fuel cell in Example 2 and the comparative example 2, and an output characteristic. It is a photograph when the cross section of the membrane-electrode assembly in Example 2 is observed with a scanning electron microscope.

(Polyimide resin)
In the proton conductive polymer electrolyte membrane of the present invention, the polyimide resin (A) contained in the polyimide-based polymer electrolyte membrane as a main component is a tetracarboxylic dianhydride, a first aromatic diamine having a proton conductive group, and , A resin formed by polycondensation with a second aromatic diamine having no proton conducting group. According to a preferred embodiment of the present invention, the polyimide resin (A) is excellent in proton conductivity and methanol permeation resistance.

  The polyimide resin (A) is composed of a structural unit (B) formed by polycondensation of tetracarboxylic dianhydride and a first aromatic diamine, and a weight of tetracarboxylic dianhydride and a second aromatic diamine. It has a structural unit (C) formed by condensation. The structural unit (B) is shown in the following formula (1), and the structural unit (C) is shown in the following formula (2).

R ^{1 in the} formula (1) corresponds to a portion other than the carboxylic anhydride in the tetracarboxylic dianhydride, and R ² corresponds to a portion other than the amino group in the first aromatic diamine.

R ^{3 in} formula (2) corresponds to a moiety other than carboxylic anhydride in tetracarboxylic dianhydride, similarly to R ¹ in formula (1), and R ⁴ represents an amino group in the second aromatic diamine. Corresponds to other parts. R ⁴ preferably has a condensed ring skeleton composed of three or more rings.

  The structural unit (B) mainly contributes to the proton conductivity of the polyimide resin (A) and the polyimide polymer electrolyte membrane containing the resin as a main component. The structural unit (C) mainly contributes to the methanol permeation resistance of the polyimide resin (A) and the polyimide-based polymer electrolyte membrane containing the resin as a main component.

  The tetracarboxylic dianhydride is not particularly limited as long as it has a structure in which a polyimide resin is formed by polycondensation with an aromatic diamine. For example, para-terphenyl-3, 4, 3 ″, 4 ″- Tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,7′-biphenyl ether tetracarboxylic dianhydride, 12,5,6-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 2 , 3,5,6-pyridinetetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, 4,4′-ketodinaphthalene-1,1 ′, 8,8 ′ -Tetracarboxylic Dianhydride, 4,4′-binaphthyl-1,1 ′, 8,8′-tetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4′-sulfonyl Diphthalic dianhydride, 3,3 ′, 4,4′-tetraphenylsilanetetracarboxylic dianhydride, meta-terphenyl-3,3 ″, 4,4 ″ -tetracarboxylic dianhydride 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride, 1,3-bis (3,4-dicarboxyphenyl) -1,1,3,3-tetramethyldisiloxane dianhydride, 1- (2,3-dicarboxyphenyl) -3- (3,4-dicarboxyphenyl) -1,1,3,3-tetramethyldisiloxane dianhydride, 2,2-bis (3,4- Dicarboxyphenyl) hexafluoropropanoic acid 1,2,3,4-butanetetracarboxylic dianhydride, 1,3,3a, 4,5,9b-hexahydro-5- (tetrahydro-2,5-dioxo-3-furanyl) -naphtho 1,2-c] furan-1,3-dione.

  Considering water resistance, oxidation resistance, and electrochemical stability as a polymer electrolyte membrane, tetracarboxylic dianhydride is naphthalene-1,4,5,8-tetracarboxylic dianhydride, 4,4 At least selected from '-ketodinaphthalene-1,1', 8,8'-tetracarboxylic dianhydride and 4,4'-binaphthalene-1,1 ', 8,8'-tetracarboxylic dianhydride One is preferred.

  The polyimide resin (A) may be formed by polycondensation of the first and second aromatic diamines and two or more kinds of tetracarboxylic dianhydrides.

  The first aromatic diamine is not particularly limited as long as it has a structure in which a polyimide resin is formed by polycondensation with tetracarboxylic dianhydride and has a proton conductive group.

  The proton conductive group is, for example, a sulfonic acid group, a phosphoric acid group, or a carboxyl group, and is preferably a sulfonic acid group because it exhibits high proton conductivity. The sulfonic acid group and the phosphoric acid group include a group in a salt state such as a sodium salt or an ammonium salt (for example, a sodium sulfonate group). However, when the sulfonic acid group and the phosphoric acid group are in a salt state, it is preferable to change the group to a proton type (proton exchange) by an acid treatment or the like before finally forming the electrolyte membrane.

  The first aromatic diamine is, for example, a sulfonic acid group-containing aromatic diamine described in JP-T-2000-510511 and JP-A-2003-68326. More specific examples are aromatic diamines represented by the following formulas (3) to (10).

The aromatic diamine is a diamine in which at least one amino group is bonded to the aromatic group. An aromatic diamine typically has a structure in which two amino groups are bonded to an aromatic group. In this case, the aromatic groups to which each amino group is bonded may be the same or different. Good. The aromatic group may be monocyclic or polycyclic. In the case of polycyclic, the aromatic group may have a condensed ring. The aromatic group may be an aromatic hydrocarbon group or a heteroaromatic group, and a part of the hydrogen atoms of the aromatic ring may be an alkyl group having 1 to 6 carbon atoms, 6 may be substituted by a substituent such as a perfluoroalkyl group, a halogen group, a hydroxy group, or a phenyl group. The substituent is typically an alkyl group having 1 to 6 carbon atoms (for example, a methyl group), a perfluoroalkyl group having 1 to 6 carbon atoms (for example, a CF ₃ group), or a phenyl group.

  The second aromatic diamine is not particularly limited as long as it has a structure in which a polyimide resin is formed by polycondensation with tetracarboxylic dianhydride.

  In order to improve the methanol permeation resistance of the polyimide resin (A), the second aromatic diamine preferably has a condensed ring skeleton (D) composed of three or more rings. Although the reason why the polyimide resin (A) having better methanol permeation resistance (methanol blocking property) is obtained by the second aromatic diamine having the condensed ring skeleton (D) is not clear, the present inventors Because the planarity of polyimide molecules is extremely high, the molecules are likely to be stacked in a state parallel to the surface direction of the electrolyte membrane, and the permeation of methanol in the film thickness direction is likely to be blocked. Is presumed to be the cause.

  The second aromatic diamine preferably has a structure in which two amino groups are directly bonded to the condensed ring skeleton (D). In this case, the methanol permeation resistance of the polyimide resin (A) is further improved.

  The condensed ring skeleton (D) is, for example, a fluorene skeleton in which the carbon atom at the 9-position may be substituted with an oxygen atom, a nitrogen atom, or a sulfur atom. Hydrogen atoms bonded to carbon atoms other than the 9-position may be substituted with the substituents exemplified in the description of the aromatic group.

The fluorene skeleton is represented by the following formula (11). In the formula (11), when the 9-position atom, that is, X ¹ is a carbon atom, R ⁵ and R ⁶ are independently of each other a hydrogen atom, a hydroxy group, a carbonyl group, a phenyl group (the hydrogen atom is a methyl group, CF ₃ may be substituted with a hydroxy group), an alkyl group having 1 to 6 carbon atoms, or a perfluoroalkyl group having 1 to 6 carbon atoms. When X ¹ is an oxygen atom, R ⁵ and R ⁶ do not exist. When X ¹ is a nitrogen atom, R ⁵ is a hydrogen atom and R ⁶ does not exist. When X ¹ is a sulfur atom, R ⁵ and R ⁶ are oxygen atoms.

  When the condensed ring skeleton (D) is the fluorene skeleton, it is preferable that two amino groups are directly bonded to the fluorene skeleton as shown in the following formula (12). ) Resistance to methanol permeation is further improved. At this time, as shown in Formula (12), it is preferable that one amino group is bonded to a carbon atom at positions 1-4 and one is bonded to a carbon atom at positions 5-8. Examples of the second aromatic diamine having such a condensed ring skeleton (D) are shown in the following formulas (13) and (14).

  The aromatic diamine represented by the formula (13) is 2,7-diaminofluorene (DAF), and the aromatic diamine represented by the formula (14) is 3,7-diamino-2,8-dimethyldibenzothiophene sulfone (DDBT). ).

  An example of the condensed ring skeleton (D) different from the fluorene skeleton is a condensed ring skeleton having an orthopericondensed ring. When the condensed ring skeleton (D) has an orthopericondensed ring, its planarity is higher than that of a condensed ring skeleton composed only of an orthofused ring. For this reason, the methanol permeation resistance characteristics of the polyimide resin (A) are further improved.

  The condensed ring skeleton (D) having an ortho-perfused ring is, for example, a pyrene skeleton or a phenanthrene skeleton. Moreover, it is preferable that two amino groups are directly bonded to the condensed ring skeleton (D). In this case, the methanol permeation resistance of the polyimide resin (A) is further improved. An example of the second aromatic diamine having such a condensed ring skeleton (D) is shown in the following formula (15).

  The aromatic diamine represented by the formula (15) is 1,6-diaminopyrene (DAP).

  The condensed ring skeleton (D) may be a phenanthridine skeleton. In this case, it is preferable that two amino groups are directly bonded to the phenanthridine skeleton. Thereby, the methanol permeation resistance characteristics of the polyimide resin (A) are further improved. An example of the second aromatic diamine having such a condensed ring skeleton (D) is shown in the following formula (16).

  The aromatic diamine represented by the formula (16) is 3,8-diamino-6-phenylphenanthridine (D6PPT).

  The proportion of the structural units (B) and (C) in the total structural units of the polyimide resin (A) (contents of the structural units (B) and (C) in the polyimide resin (A)) is not particularly limited. The structural unit (B) is 50 to 95 mol%, and the structural unit (C) is 5 to 50 mol%. The polyimide-based polymer electrolyte membrane in the proton-conducting polymer electrolyte membrane of the present invention has an unprecedented balance (for example, a ratio of proton conductivity κ to methanol permeability MCO [κ / MCO] has never been It is also possible to increase it).

  The ion exchange capacity of the polyimide resin (A) is preferably 0.5 to 3.0 meq / g, and more preferably 1.0 to 2.5 meq / g. When the ion exchange capacity is excessively large, the membrane is deformed due to the high degree of swelling of the electrolyte membrane during use, and the methanol permeation resistance is lowered. On the other hand, if the ion exchange capacity is excessively small, the proton conductivity of the electrolyte membrane is lowered, and sufficient power generation characteristics as the electrolyte membrane cannot be obtained. The ion exchange capacity of the polyimide resin (A) can be adjusted by the type of the first aromatic diamine and the contents of the structural units (B) and (C).

  A known method for producing a polyimide resin can be applied to the production of the polyimide resin (A). At this time, the content rate of the structural units (B) and (C) in the obtained polyimide resin (A) can be controlled by adjusting the amounts of the first and second aromatic diamines in the polymerization system.

(Polyimide polymer electrolyte membrane)
The polyimide polymer electrolyte membrane in the present invention contains a polyimide resin (A) as a main component. Here, the main component means a component having the maximum content in the electrolyte membrane, and the content is typically 50% by weight or more, preferably 60% by weight or more, and more preferably 70% by weight or more. The polyimide polymer electrolyte membrane in the proton conductive polymer electrolyte membrane of the present invention may be composed of a polyimide resin (A).

  As for the thickness of the polyimide type polymer electrolyte membrane in this invention, 5-100 micrometers is preferable.

  The polyimide-based polymer electrolyte membrane in the present invention has high methanol permeation resistance characteristics, for example, the methanol permeability (MCO) at 60 ° C. is 0.025 mmol / (hr · cm) or less. Depending on the structure (type of the second aromatic diamine) of the structural unit (C) in the polyimide resin (A) and the content thereof, the content is 0.020 mmol / (hr · cm) or less.

  The polyimide-based polymer electrolyte membrane in the present invention has high proton conductivity, for example, a proton conductivity κ measured in Examples is 0.13 S / cm or more. Depending on the configuration of the polyimide resin (A), κ is 0.15 S / cm or more.

  The polyimide-based polymer electrolyte membrane according to the present invention has an unprecedented balance between methanol permeation resistance and proton conductivity. For example, the ratio of proton conductivity κ to methanol permeability (MCO) measured in the examples. (Κ / MCO) is 7000 (S · hr) / mol or more, and depending on the structure of the polyimide resin (A), it is 7500 (S · hr) / mol or more, 8000 (S · hr) / mol or more, 8500 (S · hr) / mol or more.

  The polyimide-based polymer electrolyte membrane in the present invention contains the polyimide resin (A) as a main component and may contain a resin or additive other than the polyimide resin (A) as long as the effects of the present invention are obtained. Resins other than the polyimide resin (A) are, for example, a polyarylene ether resin and a polyether sulfone resin. Additives are inorganic fillers, such as a crosslinking agent, antioxidant, a radical quencher, a silica gel, for example.

(Fluorine polymer electrolyte membrane)
The fluorine-based polymer electrolyte membrane in the proton-conductive polymer electrolyte membrane of the present invention is particularly defined as long as it is an electrolyte membrane made of a fluorine-based resin that is excellent in ion conductivity and electrochemical stability and suitable for use in PEFC. Not. The fluororesin is preferably composed of a fluororesin composition that is a copolymer of a non-proton conductive tetrafluoroethylene and a proton conductive fluoroethylene, typically Perfluorosulfonic acid resins represented by “Nafion (registered trademark)” manufactured by DuPont, “Flemion (registered trademark)” manufactured by Asahi Glass Co., and “Aciplex (registered trademark)” manufactured by Asahi Kasei.

  Although the thickness of a fluorine-type polymer electrolyte membrane is based also on the use of the proton conductive polymer electrolyte membrane of this invention, 1-100 micrometers is preferable. If the thickness of the fluorine-based polymer electrolyte membrane is too small, the effect of closely adhering the polyimide-based polymer electrolyte membrane and the electrode cannot be obtained. On the other hand, if the thickness is excessive, the proton conductivity is lowered, making it difficult to use in PEFC and DMFC, and the cost is increased.

(Proton conducting polymer electrolyte membrane)
The proton conductive polymer electrolyte membrane of the present invention comprises the above polyimide polymer electrolyte membrane and the fluorine polymer electrolyte membrane, and the fluorine polymer electrolyte membrane is laminated on at least one surface of the polyimide polymer electrolyte membrane. Has been. When laminating a fluorine polymer electrolyte membrane on both sides of a polyimide polymer electrolyte membrane, the two fluorine polymer electrolyte membranes may be the same or different. As a method of laminating these electrolyte membranes, a known method such as a hot press method or a direct coating method can be adopted. The structure of the proton conductive polymer electrolyte membrane of the present invention is not particularly limited as long as the effects of the present invention can be obtained.

  The thickness of the proton conductive polymer electrolyte membrane in the present invention depends on its use, but is preferably 10 to 200 μm when used for a general PEFC including DMFC, and has mechanical strength, proton conductivity and methanol resistance. Considering the balance of transmission characteristics, 20 to 100 μm is preferable. When the thickness of the proton conductive polymer electrolyte membrane becomes too small, the proton conductivity improves, but the mechanical strength and methanol permeability resistance decrease more than that, and the practicality as an electrolyte membrane decreases. . On the other hand, if the thickness is excessive, the mechanical strength and the methanol permeation resistance are improved, but the proton conductivity is lowered, making it difficult to use for PEFC and DMFC.

  The use of the electrolyte membrane of the present invention is not particularly limited, but is suitable for use as a polymer electrolyte membrane (PEM) in PEFC, particularly as a PEM in DMFC using a solution containing methanol as a fuel.

(Membrane-electrode assembly)
An example of the membrane-electrode assembly (MEA) of the present invention is shown in FIG.

  The MEA 1 shown in FIG. 1 includes an electrolyte membrane 2 and a pair of electrodes (an anode electrode 3 and a cathode electrode 4) arranged so as to sandwich the electrolyte membrane 2. The electrolyte membrane 2 and the electrodes 3 and 4 are Are joined together. Here, the electrolyte membrane 2 is the proton conductive polymer electrolyte membrane of the present invention described above, and the fluorine-based polymer electrolyte membrane 22 is laminated on both surfaces of the polyimide-based polymer electrolyte membrane 21. The configurations of the anode electrode (fuel electrode) 3 and the cathode electrode (oxygen electrode) 4 may be the same as those of a general MEA anode electrode and cathode electrode, respectively. The MEA 1 can be formed by a known method such as a hot press method or a direct coating method. In the hot pressing method, the electrolyte membrane 2 is disposed between the electrode 3 and the electrode 4, and MEA 1 is obtained by hot pressing this. In the direct coating method, for example, a membrane-electrode assembly is obtained by applying a fluorine-based polymer electrolyte solution to the surface of a polyimide-based polymer electrolyte membrane, slowly evaporating the solvent, and then applying heat by superimposing electrodes on this. Can be made. By disposing a fluorine-based polymer electrolyte membrane between the polyimide-based polymer electrolyte membrane and the electrode, it is not necessary to heat-fuse the polyimide-based polymer electrolyte membrane at a high temperature. Damage to the can be reduced.

  During power generation of the fuel cell, the amount of water generated by protons reacting with oxygen in the catalyst layer in the cathode electrode changes due to the change in current density, and the thickness of the catalyst layer also changes accordingly. The fluorine-based polymer electrolyte membrane easily follows such a change in the thickness of the catalyst layer. Therefore, when a fluorine-based polymer electrolyte membrane is laminated on only one side of a polyimide-based polymer electrolyte membrane to form a proton conductive polymer electrolyte membrane, the fluorine-based polymer electrolyte membrane side should be the cathode electrode side. It is preferable to prepare a membrane-electrode assembly (MEA) by arranging the proton conductive polymer electrolyte membrane.

  The membrane-electrode assembly (MEA) of the present invention has excellent adhesion between the electrolyte membrane and the electrode. By incorporating the MEA into the PEFC, the power generation characteristics of the PEFC, particularly the DMFC using a solution containing methanol as the fuel, can be improved.

(Polymer electrolyte fuel cell)
An example of the polymer electrolyte fuel cell of the present invention is shown in FIG.

  The fuel cell 11 shown in FIG. 2 sandwiches the electrolyte membrane 2, a pair of electrodes (anode electrode 3 and cathode electrode 4) disposed so as to sandwich the electrolyte membrane 2, and the pair of electrodes. It is provided with a pair of separators (anode separator 5 and cathode separator 6) arranged, and each member is joined in a state where pressure is applied in a direction perpendicular to the main surface of the member. The electrolyte membrane 2 and the electrodes 3 and 4 constitute the MEA 1. Here, the electrolyte membrane 2 is the proton conductive polymer electrolyte membrane of the present invention described above, and the fluorine-based polymer electrolyte membrane 22 is laminated on both surfaces of the polyimide-based polymer electrolyte membrane 21.

  The configurations of the anode electrode (fuel electrode) 3, the cathode electrode (oxygen electrode) 4, the anode separator 5 and the cathode separator 6 may be the same as those of each member in a general PEFC.

  The fuel cell of the present invention may include members other than the members shown in FIG. 2 as necessary. 2 is a so-called single cell, the fuel cell of the present invention may be a stack in which a plurality of such single cells are stacked.

  With the proton conductive polymer electrolyte membrane of the present invention, a fuel cell 11 having excellent power generation characteristics (particularly excellent in power generation characteristics when DMFC using a solution containing methanol as fuel) can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the examples shown below. First, a method for evaluating an electrolyte membrane will be described.
(Ion exchange capacity)
The prepared electrolyte membrane (area: about 12 cm ² ) was immersed in an aqueous sodium chloride solution having a concentration of 3 mol / L, and the aqueous solution was heated to 60 ° C. with a water bath and held for 12 hours or more. Next, after the aqueous solution was cooled to room temperature, the electrolyte membrane was taken out of the aqueous solution and sufficiently washed with ion-exchanged water. All the ion exchange water used for washing was added to the aqueous solution after the electrolyte membrane was taken out. Next, the amount of protons (hydrogen ions) contained in the aqueous solution after taking out the electrolyte membrane was measured using a potentiometric automatic titrator (AT-510, manufactured by Kyoto Denshi Kogyo Co., Ltd.) and a sodium hydroxide aqueous solution having a concentration of 0.05N. The ion exchange capacity [meq / g] of the produced electrolyte membrane was obtained from the proton amount obtained by titration and the weight of the electrolyte membrane measured in advance before being immersed in the sodium chloride aqueous solution.

(Proton conductivity: κ)
The membrane resistance Rm in the film thickness direction of the produced electrolyte membrane was measured in a state where the electrolyte membrane was immersed in a sulfuric acid aqueous solution having a concentration of 1M. The membrane resistance Rm is the slope of the voltage drop (potential difference generated in the thickness direction of the electrolyte membrane) measured by applying an electric current in the range of 0 to 0.3 A in the thickness direction of the electrolyte membrane. (Slope with respect to applied current). The electrolyte membrane used for the measurement was previously immersed in water at 25 ° C. for 1 hour or more and swollen before being immersed in the sulfuric acid aqueous solution. The proton conductivity κ can be obtained by the following equation (17).

κ = d1 / (Rm × A) (17)
In equation (17), κ is proton conductivity [S / cm], Rm is membrane resistance [Ω], d1 is the thickness of the electrolyte membrane before measurement [cm], and A is the measurement area [cm ² ] in the electrolyte membrane. It is.

(Methanol permeability: MCO)
A pair of glass containers having the same shape were connected to each other at the opening using the produced electrolyte membrane as a partition. Next, in one glass container, an aqueous methanol solution (temperature 60 ° C.) having a concentration of 3 mol / L from an opening different from the above in the container, and an opening different from the above in the container in the other glass container. After pouring distilled water (temperature 60 ° C.) from the part, the amount of methanol permeated to the distilled water side through the electrolyte membrane was quantified at regular intervals while the entire container was held at 60 ° C. with a water bath. . Methanol was quantified by gas chromatography (GC), and a calibration curve prepared from GC measurement on a methanol aqueous solution having a predetermined concentration was used for quantification. The determined amount of methanol was plotted against the elapsed time, and the methanol permeability MCO of the electrolyte membrane was determined from the slope t of the plot by the following equation (18).

MCO = t × d2 / S (18)
In formula (18), MCO is the methanol permeability [mmol / (hr · cm)], t is the slope of the plot [mmol / hr], and d2 is the thickness of the swollen electrolyte membrane measured immediately after evaluating the MCO. [Cm] and S are the area [cm ² ] of the partition walls in the electrolyte membrane.

(Reference Example 1)
As the first aromatic diamine, 2.43 g of 4,4′-bis (4-aminophenoxy) biphenyl-3,3′-disulfonic acid (BAPBDS) represented by the following formula (19), the second aromatic diamine As a diamine, 0.451 g of 2,7-diaminofluorene (DAF) represented by the formula (13), 15 mL of m-cresol as a polymerization solvent, and 1.32 mL of triethylamine were added to a 100 mL four-necked flask. The whole was uniformly dissolved while stirring at an internal temperature of 80 ° C. under a nitrogen stream. After dissolution, 1.85 g of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) as a tetracarboxylic dianhydride and 1.32 g of benzoic acid as a reaction catalyst in a four-necked flask In addition, while allowing the nitrogen to flow into the flask as it was and stirring the contents, the polymerization was allowed to proceed at 180 ° C. for 20 hours. After the completion of the polymerization, the obtained polymerization solution was added dropwise to acetone, and the solid matter precipitated by the addition was filtered and dried.

  Next, the obtained solid was dissolved in m-cresol to form a cast solution having a concentration of 8% by weight, and the solution was cast on a glass plate at a thickness of 800 μm. After casting, the whole was dried at 120 ° C. for 12 hours, and the obtained cast membrane was immersed in sulfuric acid having a concentration of 1 mol / L at 60 ° C. for 24 hours to exchange protons. Next, the cast membrane after proton exchange was washed with pure water, and then vacuum-dried at 150 ° C. for 12 hours to obtain a polyimide polymer electrolyte membrane.

(Reference Example 2)
The amount of BAPBDS used was 2.11 g, 0.465 g of 1,6-diaminopyrene (DAP) represented by formula (15) was used as the second aromatic diamine, the amount of m-cresol used was 25 mL, and triethylamine The amount used is 1.15 mL, the amount of NTDA used is 1.61 g, the amount of benzoic acid used is 1.15 g, the concentration of the casting solution is 6.5% by weight, and the thickness cast on the glass plate is A polyimide polymer electrolyte membrane was obtained in the same manner as in Reference Example 1 except that the thickness was 900 μm.

(Reference Example 3)
Except that 0.63 g of 3,7-diamino-2,8-dimethyldibenzothiophenesulfone (DDBT) represented by the formula (14) was used as the second aromatic diamine and the amount of m-cresol used was 25 mL. A polyimide polymer electrolyte membrane was obtained in the same manner as in Reference Example 1.

(Reference Example 4)
A polyimide polymer electrolyte in the same manner as in Reference Example 3 except that 0.656 g of 3,8-diamino-6-phenylpentylphenanthridine (D6PPT) represented by the formula (16) was used as the second aromatic diamine. A membrane was obtained.

(Reference Example 5)
A polyimide polymer electrolyte membrane was obtained in the same manner as in Reference Example 3 except that 0.249 g of 1,4-phenylenediamine (PPD) represented by the following formula (20) was used as the second aromatic diamine. The thickness of this film was about 40 μm.

(Reference Example 6)
A polyimide polymer electrolyte membrane was obtained in the same manner as in Reference Example 1 except that 0.364 g of 1,5-naphthalenediamine (15ND) represented by the following formula (21) was used as the second aromatic diamine.

(Comparative Reference Example 1)
A polyimide polymer electrolyte membrane was obtained in the same manner as in Reference Example 1 except that the amount of BAPBDS used was 3.65 g and the second aromatic diamine was not used.

(Comparative Reference Example 2)
A Nafion 115 membrane (thickness 125 μm) manufactured by DuPont, which is a commercially available perfluorosulfonic acid membrane, was used as the electrolyte membrane.

  Table 1 below shows the results of measuring the ion exchange capacity, proton conductivity and methanol permeability of the electrolyte membranes of Reference Examples 1 to 6 and Comparative Reference Examples 1 and 2. In Table 1, “Φ” is the ratio (κ / MCO) of proton conductivity κ to methanol permeability (MCO). It can be judged that the higher the value of Φ of the electrolyte membrane, the greater the degree of selective permeation of protons to methanol, and the better the performance of the membrane.

  The electrolyte membranes of Reference Examples 1 to 6 are polyimide polymer electrolyte membranes according to the present invention, and use the first aromatic diamine and the second aromatic diamine. Thus, the electrolyte membranes of Reference Examples 1 to 6 are high membranes exhibiting high proton conductivity and low methanol permeability, and having high values of Φ. In particular, the electrolyte membranes of Reference Examples 1 to 4 have an extremely high Φ because the second aromatic diamine having a condensed ring skeleton composed of three or more rings is used. On the other hand, in Comparative Reference Example 1, since the second aromatic diamine having no proton conductive group is not used, the value of Φ is low. Comparative Reference Example 2 is a conventional fluorine-based polymer electrolyte membrane, and the proton conductivity and the value of Φ are extremely low.

Example 1
On both sides of the polyimide polymer electrolyte membrane (thickness: about 40 μm) obtained in Reference Example 5, a commercially available perfluorosulfonic acid membrane Nafion membrane (NRE-212CS, thickness) as a fluoropolymer electrolyte membrane. 50 μm). The laminate composed of the three electrolyte membranes was hot-pressed at 135 ° C. and 20 MPa for 3 minutes, then taken out from the press and allowed to cool naturally to room temperature. The laminated film thus obtained was used as a proton conductive polymer electrolyte membrane. The proton conductive polymer electrolyte membrane has a thickness of 136 μm. Among these, the polyimide polymer electrolyte membrane has a thickness of 40 μm, and the thickness of each of the two fluoropolymer electrolyte membranes is Both were 48 μm.

  Using this electrolyte membrane, a membrane-electrode assembly was prepared as described below, and the output characteristics of the fuel cell were evaluated.

(Preparation of anode electrode)
Platinum-ruthenium alloy black powder (Johnson Massey UK, HiSPEC6000 Pt-Ru Black, Pt to Ru weight ratio = 2) 10 g, Nafion powder (Dupon Nafion solution DE-520 powdered by spray drying) 0.15 g, pure water 8 g, 2-propanol 6.4 g, and 1-propanol 6.4 g were pulverized and mixed at 200 rpm for 3.0 hours in a planetary ball mill pulverizer to obtain a paste. The paste containing the catalyst was obtained by removing the balls for grinding from the paste. The paste was applied on a 5 cm square conductive water-repellent layer-supporting carbon paper with a coating machine (PI-1210 automatic coating apparatus manufactured by Tester Sangyo), heated at 60 ° C. for 5 minutes and dried, then 135 An electrode plate was obtained by hot press molding at 1 ° C. for 1 minute. The solid content supported on the carbon paper was 115 mg, and the supported amount of platinum-ruthenium was 112 mg (4.5 mg / cm ² ). This electrode plate was cut into 2.3 cm square to form an anode electrode.

(Preparation of cathode electrode)
6.7 g of conductive carbon black powder catalyst (TEC10E50E manufactured by Tanaka Kikinzoku Co., Ltd.) carrying 46% by weight of platinum, 3.4 g of Nafion powder (same as above), 16 g of pure water, 12 g of 1-propanol, 2-propanol 12 g was pulverized and mixed at 200 rpm for 3.0 hours with a planetary ball mill pulverizer to obtain a paste. The paste containing the catalyst was obtained by removing the balls for grinding from the paste. In the same manner as above, this paste was applied onto a 5 cm square conductive water-repellent layer-carrying carbon paper with a coating machine, heated at 80 ° C. for 30 minutes and dried to obtain an electrode plate. The amount of the solid content supported on the carbon paper was 115 mg, and the amount of platinum supported was 32.5 mg (1.3 mg / cm ² ). This electrode plate was cut into 2.3 cm square to form a cathode electrode.

(Preparation of membrane-electrode assembly)
The proton conductive polymer electrolyte membrane was cut into 5 cm square. The anode electrode was placed so that the surface on the carbon paper side was down, the electrolyte membrane was overlaid thereon, and the cathode electrode was overlaid thereon so that the surface on the carbon paper side was up. The laminate was pressed at 135 ° C. and 3 MPa for 3 minutes, then taken out of the press and allowed to cool naturally to room temperature to obtain a membrane-electrode assembly.

(Evaluation of fuel cell output characteristics)
The membrane-electrode assembly was incorporated into a fuel cell (manufactured by Electrochem), and the cell temperature was adjusted to 70 ° C. using a fuel cell evaluation device (manufactured by Toyo Technica). Oxygen is supplied to the cathode electrode at a humidifier temperature of 70 ° C. and a flow rate of 250 mL / min at atmospheric pressure, and hydrogen is supplied to the anode electrode at a humidifier temperature of 70 ° C. (corresponding to a relative humidity of 100%) and a flow rate of 100 mL / min at atmospheric pressure. Supplied. Sweeping the cell potential from 0.9 V to 0.2 V was repeated 15 times, and the maximum output density was determined from the current-output curve at the 15th time. As a result, the maximum power density was 480 mW / cm ² .

Next, the performance of the fuel cell as a DMFC was evaluated. First, the fuel supply path on the anode electrode side of the fuel cell was replaced with a 1 M concentration aqueous methanol solution, and held at a flow rate of 1.5 mL / min for 3 hours. Then, it substituted similarly with the methanol solution of concentration 10M, and hold | maintained for 1 hour. Thereafter, the cell temperature was set to 70 ° C. using a fuel cell evaluation device (manufactured by Toyo Technica Co., Ltd.). Oxygen is supplied to the cathode electrode at a humidifier temperature of 70 ° C. and a flow rate of 250 mL / min, and an aqueous methanol solution having a concentration of 10 M is supplied to the anode electrode at a humidifier temperature of 70 ° C. (corresponding to a relative humidity of 100%) and a flow rate of 1.5 mL / min. did. The potential of the cell was swept from 0.7 V to 0.2 V three times, and the maximum output density was determined from the current-output curve at the third time. As a result, the maximum power density was 110 mW / cm ² .

(Comparative Example 1)
Using a Nafion 115 membrane (thickness: 125 μm) manufactured by DuPont of Comparative Reference Example 2 as a proton conductive polymer electrolyte membrane, a membrane-electrode assembly was produced in the same manner as in Example 1 and evaluated for a fuel cell. As a result, the maximum output density in the case where hydrogen as fuel is the maximum power density in the case of 450 mW / cm ^2, methanol and fuel was 80 mW / cm ^2.

(Example 2)
An anode electrode having a size of 2.3 cm square was produced in the same manner as in Example 1. On this electrode, the polyimide polymer electrolyte membrane obtained in Reference Example 5 was cut into a 5 cm square and placed, and a polyimide tape was attached to the surface of the polyimide polymer electrolyte membrane and surrounded by the polyimide tape. A 2.3 cm square window was formed. A fluorine-based polymer electrolyte solution (Nafion DE-520 manufactured by DuPont) was dropped little by little on this window portion, and applied to a uniform thickness throughout. The solvent contained in the coating film was air dried at room temperature for about 1 hour and evaporated to obtain a coating film having a thickness of 3 μm. A cathode electrode similar to that in Example 1 was placed on this coating film, and this laminate was hot-pressed at 135 ° C. and 3 MPa for 3 minutes to obtain a membrane-electrode assembly.

  A photograph of the cross section of this membrane-electrode assembly observed with a scanning electron microscope is shown in FIG. A polyimide-based polymer electrolyte membrane with high surface smoothness and an electrode with many irregularities on the surface are closely bonded via a Nafion membrane.

This membrane-electrode assembly was incorporated into a fuel cell (manufactured by Electrochem) and the temperature of the cell was set to 70 ° C. using a fuel cell evaluation device (manufactured by Toyo Technica Co., Ltd.). Synthetic air (nitrogen: oxygen = 80: 20) is supplied to the cathode electrode at a humidifier temperature of 70 ° C. and a flow rate of 250 mL / min under atmospheric pressure, and hydrogen is supplied at a humidifier temperature of 70 ° C. and a flow rate of 150 mL / min under atmospheric pressure. Supply to the anode electrode. This cell was held at a load current density of 0 mA / cm ² for 1 hour for the purpose of keeping the temperature and humidity inside the cell constant. Thereafter, the cell potential was fixed at 0.6 V, the operation was started, the operation time and the current value were measured, and these relations were examined. As a result, as shown in FIG. 3A, the output of the cell was stabilized at a current value of 7.0 A in 20 hours, and the internal resistance was 8 mΩ.

After the fuel cell was stabilized, the output characteristics when the load current density was changed were measured to investigate this relationship. The result is shown in FIG. The output density at a potential of 0.6 V was 168 mW / cm ² . Further, the internal resistance of the cell was 8.3 mΩ without depending on the load current density.

(Comparative Example 2)
Using the polyimide-based polymer electrolyte membrane obtained in Reference Example 5 as a proton conductive polymer electrolyte membrane, a membrane-electrode assembly was produced. Note that, when a membrane-electrode assembly was produced by the same method as in Example 1, the membrane was easily peeled off from the electrode. Therefore, the membrane-electrode assembly was produced by using a membrane fixing mold. That is, the proton conductive polymer electrolyte membrane was cut into a 5 cm square and fixed to a fixing mold having a 2.3 cm square window. This was disposed between an anode electrode and a cathode electrode similar to those in Example 1 to obtain a membrane-electrode assembly.

A fuel cell was produced in the same manner as in Example 2 except that this membrane-electrode assembly was used, and the relationship between the operation time and the current value was examined. As a result, as shown in FIG. 3B, the output of the cell stabilized at a current value of 7.0 A in 41 hours, and the internal resistance was 10 mΩ. Further, when the relationship between the load current density after the cell was stabilized and the output characteristics was examined, the result shown in FIG. 4B was obtained. The output density at a potential of 0.6 V was 168 mW / cm ² . The internal resistance of the cell was 9.6 mΩ regardless of the load current density.

As described above, the fuel cell of Example 1 uses the proton conductive polymer electrolyte membrane of the present invention. When hydrogen is used as the fuel, the maximum output is 480 mW / cm ^{2 and} when methanol is used as the fuel. The maximum output was as high as 110 mW / cm ^2, and excellent power generation characteristics were obtained.

In contrast, the fuel cell of Comparative Example 1 does not use the polyimide-based polymer electrolyte membrane of the present invention, so that the maximum output when hydrogen is used as fuel and when methanol is used as fuel is 450 mW / cm, respectively. ² and 80 mW / cm ^2, and the power generation characteristics of the cell are inferior.

  In each of the fuel cells of Example 2 and Comparative Example 2, the polyimide polymer electrolyte membrane of the present invention is used. For this reason, in both cells, the current value when the cell potential was fixed at 0.6 V and stabilized was 7.0 A, and the output characteristics when the load current was changed were substantially equal.

  The fuel cell of Example 2 uses the proton conductive polymer electrolyte membrane of the present invention in which a fluorine polymer electrolyte membrane is formed on the cathode side of the polyimide polymer electrolyte. As a result, the time required from the start of operation of the cell to its stability was as short as 20 hours, and the internal resistance was as small as 8.3 mΩ, and excellent power generation characteristics were obtained.

  On the other hand, in the fuel cell of Comparative Example 2, the polyimide polymer electrolyte is used alone as a proton conductive polymer electrolyte membrane. For this reason, the adhesion between the membrane and the electrode is low, the time required from the start of operation of the cell to the stabilization is as long as 41 hours, the internal resistance is as large as 9.6 mΩ, and the power generation characteristics of the cell are inferior.

  As described above, in the present invention, by appropriately selecting a polyimide polymer membrane and laminating an appropriate fluorine polymer electrolyte membrane on at least one surface, the proton conductivity is high and the methanol permeability resistance is improved. An excellent proton conductive polymer electrolyte membrane can be obtained. Further, in the present invention, a membrane-electrode assembly having high adhesion between the electrolyte membrane and the electrode can be obtained without damaging the electrolyte membrane, the electrode and the like due to temperature and pressure. Furthermore, in the fuel battery cell of the present invention using this, excellent power generation characteristics can be obtained regardless of whether hydrogen or methanol is used as the fuel.

  The proton conductive polymer electrolyte membrane of the present invention can be suitably used as an electrolyte membrane of a polymer electrolyte fuel cell (PEFC), particularly a direct methanol fuel cell (DMFC) for supplying a solution containing methanol to a fuel electrode. Thus, PEFC and DMFC, which have better power generation characteristics than conventional fluoropolymer electrolyte membranes, can be realized.

1 Membrane-electrode assembly (MEA)
2 Polymer electrolyte membrane (PEM)
3 Anode electrode 4 Cathode electrode 5 Anode separator 6 Cathode separator 11 Polymer electrolyte fuel cell (PEFC)
21 Polyimide polymer electrolyte membrane 22 Fluorine polymer electrolyte membrane

Claims (11)

A proton conductive polymer electrolyte membrane comprising a polyimide polymer electrolyte membrane and a fluorine polymer electrolyte membrane laminated on at least one side of the polyimide polymer electrolyte membrane,
The polyimide-based polymer electrolyte membrane is formed by polycondensation of tetracarboxylic dianhydride, a first aromatic diamine having a proton conductive group and a second aromatic diamine having no proton conductive group. Proton-conducting polymer electrolyte membrane comprising a polyimide resin as a main component.   The proton conductive polymer electrolyte membrane according to claim 1, wherein the second aromatic diamine has a condensed ring skeleton composed of three or more rings.   The proton conductive polymer electrolyte membrane according to claim 2, wherein the second aromatic diamine has a structure in which two amino groups are directly bonded to the condensed ring skeleton.   The proton-conducting polymer electrolyte membrane according to claim 2, wherein the condensed ring skeleton is a fluorene skeleton in which the carbon atom at the 9-position may be substituted with an oxygen atom, a nitrogen atom or a sulfur atom.   The proton conductive polymer electrolyte membrane according to claim 4, wherein two amino groups are directly bonded to the fluorene skeleton.   The proton conductive polymer electrolyte membrane according to claim 2, wherein the condensed ring skeleton has an ortho-pericondensed ring.   The proton conductive polymer electrolyte membrane according to claim 2, wherein the condensed ring skeleton is a phenanthridine skeleton.   The proton conductive polymer electrolyte membrane according to claim 1, wherein the proton conductive group is a sulfonic acid group. A polymer electrolyte membrane, and a pair of electrodes arranged to sandwich the electrolyte membrane,
A membrane-electrode assembly, wherein the electrolyte membrane is the proton conductive polymer electrolyte membrane according to any one of claims 1 to 8. A polymer electrolyte membrane;
A pair of electrodes arranged to sandwich the electrolyte membrane;
A pair of separators arranged to sandwich the pair of electrodes, and
A polymer electrolyte fuel cell, wherein the polymer electrolyte membrane is the proton conductive polymer electrolyte membrane according to any one of claims 1 to 8. The polymer electrolyte fuel cell according to claim 10, which is a direct methanol type.