JP2009013374A - Dispersion, preparation method thereof, proton conductive material, solid electrolyte film obtained using the proton conductive material as substrate, method for manufacturing the solid electrolyte film and polymer electrolyte fuel cell equipped with the solid electrolyte film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high dispersion of a carbon nanotube which could not be highly dispersed in an aqueous or non-aqueous solvent, to obtain a proton conductive material obtained by improving mechanical strength of polybenzimidazole (PBI) that serves as an alternative to a fluorine electrolyte, has a proton conductivity and is excellent in heat resistance etc. , and to provide a solid polymer electrolyte film particularly suitable for a polymer electrolyte fuel cell. <P>SOLUTION: The dispersion contains (A) a polybenzimidazole or a polybenzimidazole derivative, or a polybenzimidazole or a polybenzimidazole derivative into which a proton conductive group is introduced and (B) the carbon nanotube or the carbon nanotube into which the proton conductive group is introduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dispersion of carbon nanotubes, which has been conventionally difficult to achieve high dispersion, and a method for producing the same. The present invention also relates to a proton conductive material that can replace a conventional fluorine-based polymer electrolyte. Furthermore, the present invention relates to a solid electrolyte membrane based on the proton conductive material, a method for producing the solid electrolyte membrane, and a solid polymer fuel cell including the solid electrolyte membrane.

  A solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source.

  Conventionally, as an electrolyte membrane of a polymer electrolyte fuel cell, it has high proton conductivity and excellent oxidation resistance, so that it is a perfluorocarbon sulfonic acid membrane represented by Nafion (trade name, manufactured by DuPont). Has been commonly used. However, the perfluorocarbon sulfonic acid membrane is expensive because it uses a fluorine-based resin, and is one of the factors that hinder the cost reduction of the fuel cell.

  Therefore, the development of electrolyte membranes using inexpensive materials has been promoted. Among them, polybenzimidazole (PBI) is complexed with proton conductive compounds such as sulfonic acid and phosphoric acid, or sulfo group and phosphoric acid. It is attracting attention because it is possible to introduce a proton conductive group such as a group and is excellent in heat resistance and mechanical properties.

  For example, an electrolyte membrane obtained by doping a polybenzimidazole membrane with an acid that is a proton conductive compound (Patent Document 1), or an electrolyte membrane in which a side chain having a proton conductive group is introduced into polybenzimidazole (Patent Document 2) Etc. have been proposed.

  In order to improve the proton conductivity of the electrolyte membrane using polybenzimidazole, it is possible to increase the amount of acid doped into the polybenzimidazole membrane or increase the amount of proton conductive groups introduced into the polybenzimidazole. Has been done. However, there is a problem in that the mechanical strength of the electrolyte membrane decreases with an increase in the acid doping amount or the introduction amount of proton conductive groups.

  In other words, polybenzimidazole is doped with phosphoric acid, and exhibits proton conductivity even under non-humidified conditions. Therefore, application to a non-humidified fuel cell electrolyte membrane is expected. However, when (1) the acid (liquid) is doped, the acid itself acts as a plasticizer, and the electrolyte membrane softens and mechanical strength decreases. (2) The doped acid cannot be stably retained in the electrolyte membrane for a long period of time. Therefore, it was difficult to put it to practical use due to the problem of elution from the electrolyte membrane.

  On the other hand, there has been proposed a proton conductive membrane that has improved durability at high temperatures by adding an ozone-treated carbon material to a polyarylene having a sulfo group (Patent Document 3).

  In the method of Patent Document 3, since a sufficient dispersibility cannot be obtained in an organic solvent in which polyarylene to be mixed is dissolved in a hydrophilic group modified to carbon by ozone treatment, a uniform dispersion state cannot be obtained. There is a problem that the mechanical strength of the electrolyte membrane is lowered.

JP 2006-131731 A Japanese Patent Laid-Open No. 09-110982 JP 2006-335815 A

  The present invention obtains a highly dispersed carbon nanotube that has not been highly dispersed in an aqueous solvent or a non-aqueous solvent. In addition, the present invention provides a proton-conducting material that improves the mechanical strength of polybenzimidazole (PBI), which is an alternative to a fluorine-based electrolyte and has proton conductivity and excellent heat resistance. It is an object of the present invention to provide a solid polymer electrolyte membrane suitable for a polymer electrolyte fuel cell.

  In the study of compatibility between proton conductivity and mechanical strength of the polybenzimidazole electrolyte membrane, the present inventors have a specific reinforcing material for polybenzimidazole or polybenzimidazole into which a proton conductive group is introduced. As a result of high dispersion, the mechanical strength of polybenzimidazole was improved, leakage of acid groups was suppressed, and durability was improved, and the present invention was achieved.

  That is, first, the present invention is an invention of a dispersion, (A) a polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or a polybenzimidazole derivative having a proton conductive group introduced therein, and (B) This is a dispersion containing carbon nanotubes or carbon nanotubes having proton conductive groups introduced therein.

  Conventionally, carbon nanotubes were not highly dispersed in an aqueous solvent or a non-aqueous solvent, but this time, polybenzimidazole or polybenzimidazole derivatives, polybenzimidazole or polybenzimidazole derivatives into which proton conductive groups have been introduced. Discovered that carbon nanotubes or carbon nanotubes having proton conductive groups introduced therein are highly dispersed.

  A dispersion in which carbon nanotubes are highly dispersed enables a chemical modification reaction in a homogeneous or near-homogeneous system of carbon nanotubes, which has been difficult in the past, and is useful for expanding the applications of carbon nanotubes.

  As said proton conductive group which modifies polybenzimidazole and a carbon nanotube, the acidic group containing sulfur and / or phosphorus is preferable, and a sulfonic acid group and / or a phosphoric acid group are illustrated more preferably.

2ndly, this invention is invention of the manufacturing method of the said dispersion liquid, (A) The polybenzimidazole or polybenzimidazole derivative, the polybenzimidazole or polybenzimidazole derivative into which the proton conductive group was introduce | transduced, ( B) A carbon nanotube or a carbon nanotube having a proton conductive group introduced therein is stirred and mixed in an organic solvent.
The stirring and mixing method is not particularly limited, but is preferably performed by ultrasonic irradiation.

  Third, the present invention is an invention of a proton conductive material, (A) a polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or a polybenzimidazole derivative having a proton conductive group introduced therein, and (B) It is a proton conductive material containing carbon nanotubes or carbon nanotubes into which proton conductive groups have been introduced.

  Although polybenzimidazole itself has proton conductivity, the discovery of a dispersion that highly disperses carbon nanotubes makes carbon nanotubes act as a reinforcing material, and excellent proton conductivity and mechanical properties without acid doping as in the past. Proton-conducting material with good mechanical strength was obtained.

4thly, this invention is a solid electrolyte membrane which uses said proton conductive material as a base material.
Fifth, the present invention is an invention of a method for producing the solid electrolyte membrane, wherein (A) a polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or a polybenzimidazole derivative into which a proton conductive group is introduced, (B) A method for producing a solid electrolyte membrane obtained by stirring and mixing carbon nanotubes or carbon nanotubes into which a proton conductive group has been introduced in an organic solvent to form a dispersion.
As described above, the stirring and mixing are preferably performed by ultrasonic irradiation.

  Sixth, the present invention is a polymer electrolyte fuel cell comprising a solid electrolyte membrane based on the proton conductive material.

  The discovery of dispersions that highly disperse carbon nanotubes has made it possible to perform chemical modification reactions in a homogeneous or near-homogeneous system of carbon nanotubes.

  In addition, it has become possible to obtain a proton conductive material that has improved the mechanical strength of polybenzimidazole (PBI), which is a substitute for a fluorine-based electrolyte and has proton conductivity and excellent heat resistance. Furthermore, a solid polymer electrolyte membrane particularly suitable for a polymer electrolyte fuel cell was obtained by using a proton conductive membrane of a non-fluorine resin.

  The “polybenzimidazole or polybenzimidazole derivative, polybenzimidazole or polybenzimidazole derivative into which a proton conductive group is introduced” referred to in the present invention is represented by the following general formula (I).

Here, in the general formula (I), R ¹ is a tetravalent aromatic group, R ² is an aliphatic group, an alicyclic group or an aromatic group, and R ^{3 to} R ⁴ are the same or different, and are a hydrogen atom or carbon 2 to 5 alkyl sulfonic acid groups (or salts thereof) or alkyl phosphoric acid groups (or salts thereof), and R ^{3 to} R ⁴ include 0.1 to 2 repeating units in one unit of the structural unit. A hydrogen atom, an alkylsulfonic acid group (or a salt thereof) or an alkylphosphoric acid group (or a salt thereof) is included, and n is 10 to 10,000.

Specific examples of polybenzimidazole or polybenzimidazole derivatives are shown.
Polybenzimidazole is represented by the following general formula.

  Specific examples of this polybenzimidazole include poly-2,2 '-(m-phenylene) -5,5'-bibenzimidazole, poly-2,2'-(pyridylene-3 ', 5')-5. , 5'-bibenzimidazole, poly-2,2 '-(furylene-2', 5 ')-5,5'-bibenzimidazole, poly-2,2'-(naphthalene-1 ', 6') -5,5'-bibenzimidazole, poly-2,2 '-(biphenylene-4', 4 ')-5,5'-bibenzimidazole, poly-2,2'-(amylene) -5,5 '-Bibenzimidazole, poly-2,2'-(octamethylene) -5,5'-bibenzimidazole, poly-2,2 '-(m-phenylene) -5,5'-diimidazobenzene, poly -2,2 '-(m-phenylene) -5,5'-di (ben Imidazole) ether, poly-2,2 '-(m-phenylene) -5,5'-di (benzimidazole) sulfide, poly-2,2'-(m-phenylene) -5,5'-di (benz Imidazole) sulfone, poly-2,2 '-(m-phenylene) -5,5'-di (benzimidazole) methane, poly-2,2'-(m-phenylene) -5,5'-di (benz Examples include imidazole) propane-2,2, poly-2,2 '-(m-phenylene) -5,5'-di (benzimidazole) -ethylene-1,2.

In particular, R ¹ and R ² need to contain a π-conjugated compound such as a benzene ring or a naphthalene ring. A cyclic compound is particularly preferable.

  Among these, poly-2,2 ′-(m-phenylene) -5,5′-benzimidazole represented by the following general formula is more preferably exemplified.

  The degree of polymerization (n) of polybenzimidazole is usually 10 to 10,000, preferably 20 to 5,000. If it is less than 10, the mechanical strength is inferior, while if it exceeds 10,000, it becomes a solvent. Since the solubility of the resin deteriorates, there may be a problem in moldability such as casting.

  The polybenzimidazole or polybenzimidazole derivative having a proton conductive group used in the present invention can be obtained by introducing an alkylsulfonic acid group or an alkylphosphoric acid group into the polybenzimidazole. As a method for introducing an alkylsulfonic acid group or an alkylphosphoric acid group, a known method can be adopted.

  As an organic solvent used when the dispersion of the present invention is produced, “a polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or a polybenzimidazole derivative having a proton conductive group introduced” is dissolved. If there is no particular limitation. The amount of the solvent is not particularly limited as long as it dissolves “polybenzimidazole or polybenzimidazole derivative, polybenzimidazole or polybenzimidazole derivative having a proton conductive group introduced”.

  Specific examples of the organic solvent include hydrocarbon solvents such as n-hexane, ether solvents such as tetrahydrofuran and dioxane, amide solvents such as dimethylacetamide (DMAC) and dimethylformamide, dimethyl sulfoxide (DMSO), N -Methyl-2-pyrrolidone and the like can be mentioned, and dimethyl sulfoxide (DMSO) is preferred.

  The counter ion of the sulfo group or phosphate group in the polymer is not particularly limited, such as alkali metals such as protons, lithium and sodium, alkaline earth metals such as calcium and magnesium, ammonia and organic amines. When used as a proton conductive polymer solid electrolyte, the counter ion is preferably a proton.

  The amount of hydrogen atom, sulfo group or phosphate group in the “polybenzimidazole or polybenzimidazole derivative having a proton-conducting group introduced” is usually 0.1 to 2 per unit constituting the polymer. It is a piece. If it is less than 0.1, the absolute number of proton conductive groups is small, so that sufficient performance cannot be obtained, for example, proton conductivity does not increase, and those exceeding 2 are difficult to obtain due to the structure of polybenzimidazole.

  As carbon nanotubes (CNT) used in the present invention, there are various types of carbon nanotubes (CNTs) such as single wall carbon nanotubes (SWNT), double wall nano carbon nanotubes (DWNT), and multi wall carbon nanotubes (MWNT). I don't know. Also included are fine carbon fibers (CF).

  The mixing and stirring method employed in the present invention is not particularly limited, but it is preferable to irradiate ultrasonic waves. The type of ultrasonic wave is not particularly limited, but it is more efficient to irradiate the probe type vibrator directly in the solvent than to indirectly irradiate with a bath type ultrasonic cleaner.

  Although it depends on the apparatus and the amount to be dispersed, the ultrasonic irradiation time is suitably about 1 minute to 3 hours, and particularly preferably about 10 minutes to 1 hour.

  Although the collection method of a dispersion solution is not specifically limited, The method of preferably centrifuging at 1000G-150,000G after ultrasonic irradiation, and collect | recovering supernatants is illustrated preferably. However, the presence / absence of centrifugation and the centrifugal strength are not limited thereto.

  In order to prepare the proton conductive polymer solid electrolyte membrane, for example, after blending the dispersion liquid of the present invention, a method of forming into a film by casting, a method of forming by applying pressure, and the like can be mentioned.

  Applications of the proton conductive material of the present invention include solid polymer electrolytes. Primary battery electrolytes, secondary battery electrolytes, fuel cell electrolytes, display elements, electrochromic elements (windows), various sensors, signal transmission It can be used for a medium, a solid capacitor, and the like.

  Other applications include, for example, sodium chloride electrolytic membranes, various cation exchange resins (membranes), dialysis membranes, gas selective permeable membranes, water vapor selective permeable membranes, anti-blood coagulation materials, and other medical materials, battery separators, and electrode elements. Preferred examples include an electrochemical sensor and an antistatic agent.

Examples of the present invention will be described below.
[Example 1: PBI-CNT dispersion]
20 mg of poly-2,2 '-(m-phenylene) -5,5'-benzimidazole is added to 10 ml of dimethyl sulfoxide (DMSO) and dissolved. Thereto, 0.2 mg of single wall carbon nanotube (SWNT) was added, irradiated with ultrasonic waves for 10 minutes, mixed and stirred to obtain a uniform dispersion solution.

  FIG. 1 shows a UV (ultraviolet) -vis-NIR (near infrared) spectrum of the obtained DMSO dispersion containing PBI-CNT. Originally, three different structures are known for single wall carbon nanotubes, but in the case of ordinary single wall carbon nanotube non-dispersion liquid or low dispersion liquid, these spectra draw a gentle curve. In the example, it can be seen that single wall carbon nanotubes are disperse highly dispersed from the fact that peaks are observed at three locations.

[Example 2: PBI-CNT reinforcing membrane]
As in Example 1, 50 mg of poly-2,2 ′-(m-phenylene) -5,5′-benzimidazole is added to 10 ml of dimethyl sulfoxide (DMSO) and dissolved. Thereto, 0.2 mg of single wall carbon nanotubes was added, and ultrasonic waves were irradiated for 10 minutes to disperse to obtain a dispersion solution.

  This solution was degassed and cast on a glass substrate and vacuum dried at 100 ° C. to obtain a 100 μm film.

  The tensile strength (Young's modulus) of the film of this example (0.4 wt% SWNT / PBI) was 1850 MPa, whereas the tensile strength (Young's modulus) of the PBI single film was 1630 MPa. From this comparison, it can be seen that the strength of the PBI film can be improved by mixing CNTs.

  FIG. 2 shows the UV (ultraviolet) -vis-NIR (near infrared) spectrum of the obtained PBI + SWNT cast film, as in FIG. Since the spectrum has three peaks, it can be seen that SWNTs are uniformly dispersed in PBI.

  The weight ratio of CNT to PBI (CNT / PBI (wt%)) is preferably about 0.0001 to 10 wt%, and more preferably 0.01 to 5 wt%.

  There is no limitation on the degassing method for discharging the dissolved or bubbled gas out of the liquid. Specific examples include ultrasonic waves, centrifugation, and reduced pressure. Further, this step may be omitted.

  The film forming method is not particularly limited as long as it can be extended to a required film thickness. Specifically, the solution is stretched to the required thickness by spin coating, doctor blade, casting or the like.

  The drying method is not particularly limited as long as the solvent can be removed. Specifically, there are decompression, overheating, air drying, and the like.

[Example 3: PBI-chemically modified CNT]
CNT is modified with an acid functional group, mixed with PBI, and used as a PBI electrolyte membrane that does not need to be doped with an acid, or as an electrolyte for a catalyst layer.

  By uniformly dispersing the CNTs introduced with acid groups in PBI, no acid doping is required. Since no acid doping is required, a decrease in film strength of PBI itself can be suppressed, and in addition, mechanical strength can be improved by mixing CNTs.

  The chemically modified CNT thus obtained is dispersed in PBI, the solvent is evaporated, and the solid content is used as an electrolyte membrane or a catalyst layer electrolyte. Of course, it may be impregnated with phosphoric acid in a later step.

50 mg of fluorinated carbon nanotube (F-CNT) was put into 100 ml of ethylenediamine, and stirred for 15 minutes with an ultrasonic cleaner. It was stirred at 80 ° C. for 24 hours to obtain CNT- (F) _m (NH ₂ —C ₂ H ₄ —NH ₂ ) _n . The obtained CNT- (F) _m (NH ₂ —C ₂ H ₄ —NH ₂ ) _n 10 mg and 1,3-propane sultone were stirred with an ultrasonic cleaner for 15 minutes, reacted at 125 ° C. for 3 hours, and CNT- ( _F) was obtained _{m (NH 2 -C 2 H 4} -NH 2- C 3 H 6 SO 3 H) y.

CNT- (F) _m (NH ₂ —C ₂ H ₄ —NH ₂ —C ₃ H ₆ SO ₃ H) _y was mixed with PBI in the same manner as in Example 2 to prepare an acid chemically modified CNT / PB1 composite electrolyte. I was able to get it.

  The acid-chemically modified CNT / PB1 composite electrolyte of this example does not need to be doped with an acid because it has excellent proton conductivity, but the electrolyte is impregnated with phosphoric acid or the like in a later step. Also good.

  First, CNT is modified with an acid functional group. For modification, the CNT is directly chemically bonded to the CNT (direct modification method of the CNT), or a functional group having a sulfonic acid or a phosphonic acid at the terminal is modified by a substitution reaction of the halogenated CNT with the halogen (substitution of the CNT). Modification method). FIG. 3 shows a three-dimensional schematic diagram of chemically modified CNT.

As a direct modification method of CNT, a known method may be used as long as an acid functional group bonded to the terminal can be modified to CNT, but nucleophilic reaction, electrophilic reaction, and radical reaction are desirable. As a substitution modification method of CNT, it is desirable to use halogenated CNT such as F-formation and Cl-formation as raw materials, and finally the acid functional group is modified to CNT at the terminal via substitution reaction with the halogen. If possible, a known method may be used. As the number of modified functional groups,
CNT-derived carbon number / modified functional group number (n + m or x + y) ≦ 2
It is.

[Example 4: Evaluation of acid leakage of PBI-chemically modified CNT composite film]
An experiment was conducted to determine how much acid leakage occurred from the PBI-chemically modified CNT composite film.

FIG. 4 shows a synthesis method of sulfonated SWNT (SWNT-SO ₃ ). FIG. 5 shows a method for preparing a sulfonated SWNT / PBI composite film (composite film) by mixing sulfonated SWNTs as PBI with chemically modified CNTs. Similarly, in FIG. 6, a process for producing a sulfonated SWNT / PBI composite membrane (composite film) by mixing sulfonated SWNTs as chemically modified CNTs with PBI is shown by a chemical formula.

  When the obtained sulfonated SWNT / PBI composite membrane (composite film) was not boiled, the sulfur (S) content measured by fluorescent X-ray measurement was 0.05%. When this sulfonated SWNT / PBI composite membrane (composite film) was boiled for 6 hours and the sulfur (S) content was measured by fluorescent X-ray measurement, it was 0.05%. Thus, since there is no change in the sulfur content before and after boiling, it can be seen that there was no leakage of acid. That is, it can be said that the PBI-chemically modified CNT composite film of the present invention is a system that does not leak acid.

  The discovery of dispersions that highly disperse carbon nanotubes has made it possible to perform chemical modification reactions in a homogeneous or near-homogeneous system of carbon nanotubes. In addition, it has become possible to obtain a proton conductive material that has improved the mechanical strength of polybenzimidazole (PBI), which is a substitute for a fluorine-based electrolyte and has proton conductivity and excellent heat resistance. Furthermore, a solid polymer electrolyte membrane particularly suitable for a polymer electrolyte fuel cell was obtained by using a proton conductive membrane of a non-fluorine resin.

The UV (ultraviolet) -vis-NIR (near infrared) spectrum of the DMSO dispersion liquid containing PBI-CNT is shown. The UV (ultraviolet) -vis-NIR (near infrared) spectrum of a PBI + SWNT cast film is shown. A three-dimensional schematic diagram of chemically modified CNT is shown. Shows the synthesis of sulfonated SWNT (SWNT-SO _3). A method for preparing a sulfonated SWNT / PBI composite membrane (composite film) by mixing sulfonated SWNT as PBI with chemically modified CNT is shown. A process for preparing a sulfonated SWNT / PBI composite membrane (composite film) by mixing sulfonated SWNTs with PBI as chemically modified CNTs is shown by a chemical formula.

Claims (12)

  (A) Dispersion containing polybenzimidazole or polybenzimidazole derivative, polybenzimidazole or polybenzimidazole derivative introduced with a proton conductive group, and (B) carbon nanotube or carbon nanotube introduced with a proton conductive group liquid.   The dispersion liquid according to claim 1, wherein the proton conductive group is an acidic group containing sulfur and / or phosphorus.   The dispersion according to claim 1, wherein the proton conductive group is a sulfo group and / or a phosphate group.   (A) a polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or a polybenzimidazole derivative having a proton conductive group introduced therein, and (B) a carbon nanotube or a carbon nanotube having a proton conductive group introduced therein in an organic solvent. A method for producing a dispersion, which comprises stirring and mixing.   The method for producing a dispersion according to claim 4, wherein the stirring and mixing is performed by ultrasonic irradiation.   (A) Polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or polybenzimidazole derivative having a proton conductive group introduced therein, and (B) a carbon nanotube or a proton containing a carbon nanotube having a proton conductive group introduced therein Conductive material.   The proton conductive material according to claim 6, wherein the proton conductive group is an acidic group containing sulfur and / or phosphorus.   The proton conductive material according to claim 6, wherein the proton conductive group is a sulfo group and / or a phosphate group.   A solid electrolyte membrane comprising the proton conductive material according to claim 6 as a base material.   (A) a polybenzimidazole or a polybenzimidazole derivative, a polybenzimidazole or a polybenzimidazole derivative having a proton conductive group introduced therein, and (B) a carbon nanotube or a carbon nanotube having a proton conductive group introduced therein in an organic solvent. A method for producing a solid electrolyte membrane obtained by stirring and mixing in a step and forming a dispersion film.   The method for producing a solid electrolyte membrane according to claim 10, wherein the stirring and mixing is performed by ultrasonic irradiation.   A solid polymer fuel cell comprising a solid electrolyte membrane based on the proton conductive material according to claim 6.

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