JP2003331645A - Proton conductive material - Google Patents

Abstract

(57) [Problem] To provide a proton conductive material having durability to withstand use at 100 ° C or higher. A proton conductive material comprising a polymer material having a main chain having a siloxane structure and side chains grafted to the main chain and having a silicon atom and a strongly acidic functional group. In other words, by using a polymer material having a silicon-oxygen bond or a silicon-carbon bond having a higher binding energy than a carbon-carbon bond in the chemical structure as the proton-conductive material, the resistance of the proton-conductive material to thermal decomposition is improved. can do. In addition, since the softening point and the melting point are increased, the creep characteristics are improved. Therefore, the heat resistance of the proton conductive material can be improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a proton conductive material having excellent heat resistance.

[0002]

2. Description of the Related Art As a proton conductive material that can be practically used for a polymer electrolyte fuel cell, there is a perfluorocarbon sulfonic acid type polymer material represented by Nafion (trademark).

[0003]

The disadvantages of perfluorocarbon sulfonic acid type polymer materials such as Nafion are that they are expensive because they are fluororesins, and that they creep at high temperatures of 100 ° C. or higher, thermal decomposition of the materials themselves, etc. It is known that it cannot be used and does not have sufficient heat resistance. In fuel cells, which are the main applications of proton conductive materials,
Adopting a high operating temperature increases operating efficiency. Therefore, an inexpensive and highly heat-resistant engineering plastic-based highly heat-resistant proton conductive material has been actively researched as a substitute for Nafion, but few have been put into practical use.

In the present invention, it is an object to be solved to provide a proton conductive material having durability to withstand use at 100 ° C. or higher.

[0005]

Means for Solving the Problems As a result of intensive research for solving the above-mentioned problems, the present inventor has conducted extensive research and found that a main chain having a siloxane structure and a silicon atom and a strongly acidic functional group grafted onto the main chain were formed. A proton conducting material is invented, which is composed of a polymer material having a side chain having and.

That is, carbon is used as the proton conductive material.
By using a polymer material having a silicon-oxygen bond or a silicon-carbon bond having a higher binding energy than a carbon bond in its chemical structure, the resistance of the proton conductive material to thermal decomposition can be improved. Moreover, since the softening point and the melting point are increased, the creep characteristics are improved. Therefore, the heat resistance of the proton conductive material can be improved.

It is preferable that the polymer material constituting the proton conductive material has a partial structure represented by the general formula (1) (claim 2). The structure of the general formula (1) has the advantage that the heat resistance of the proton conductive material is improved by introducing it into the polymer material, and it can be easily introduced into the polymer material and can be manufactured at low cost. There are advantages. In particular, it is preferable that this polymer material essentially has a structure represented by the general formula (1) (claim 3). The heat resistance of the proton conductive material can be further improved by making all of the polymer materials forming the proton conductive material a structure represented by the general formula (1) having a high heat resistance.

[0008]

[Chemical 3]

(In the formula (1), n> 0. R1 is independently an alkyl group having 1 to 4 carbon atoms. R2 is independently an alkyl group having 1 to 4 carbon atoms or the side chain. The symbol "*" in the formula represents the portion of the main chain into which this partial structure is introduced / bonded, and shows that unspecified elements, functional groups and polymer chains are bonded. Represent

The side chains of the polymer material preferably have a structure represented by the general formula (2) (claim 4). Since the structure of the general formula (2) can further improve the heat resistance of the proton conductive material and can be easily introduced into the side chain in the polymer material, the proton conductive material can be manufactured at low cost. Further, the proton conductivity of the proton conductive material can be improved.

[0011]

[Chemical 4]

(In the formula (2), m> 0 and R3 and R4 are each independently an alkyl group having 1 to 4 carbon atoms.)
In addition, "*" in the formula indicates that this side chain partial structure is introduced.
The main chain and / or the side chain to be bonded is shown, which represents that an unspecified element, functional group, or polymer chain is bonded.

It is preferable that these polymer materials consist of linear polymers (claim 5). By using a linear polymer, the flexibility of the proton conductive material of the present invention can be improved and good mechanical properties can be exhibited.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The proton conducting material of the present invention comprises a polymer material having a main chain and side chains grafted to the main chain. In the present specification, the “main chain” means a relatively longest chain among polymer compound molecules constituting a polymer material, and the “side chain” is a chain bonded to the main chain in the middle of the main chain. Means Here, the polymer material constituting the proton conductive material of the present invention is preferably composed of linear molecules from the viewpoint of mechanical properties such as flexibility.

The proton conductive material of the present invention may be mixed with other polymer compounds in addition to the above polymer materials. The polymer compound that can be mixed is not particularly limited, but examples include Nafion, polyethylene oxide, polyvinyl alcohol, polyacrylic acid, polysulfonic acid, silica gel, and engineering plastics.
When another polymer compound is mixed, it is preferable that the above-described polymer material of the proton conductive material of the present invention is contained in 50% or more, more preferably 60% or more, based on the entire proton conductive material. Further, the present proton conductive material can be used together with an additive such as a reinforcing material, if necessary.

The main chain constituting the polymer material has a siloxane structure. As the siloxane structure, the structure represented by the general formula (1) described above is preferable. It is preferable that essentially all of the main chain has a structure represented by the general formula (1).
In the general formula (1), R1 is preferably a methyl group or an ethyl group, and more preferably a methyl group. Also,
R2 is preferably the above-mentioned side chain or a methyl group or an ethyl group as an alkyl group, and when it is an alkyl group, it is preferably a methyl group. The ratio of side chains introduced into R2 will be described later.

The side chain constituting the polymer material is not particularly limited except that it has a strongly acidic functional group and silicon element in its chemical structure. The silicon atom contained in the side chain may be present in any manner. That is, the silicon atom only needs to exist on the side chain, and the position on the side chain is not particularly limited. As a preferable introduction position of a silicon atom, by introducing a silicon atom into a portion between the bonding portion with the main chain and the strongly acidic functional group contained in the side chain, the strongly acidic functional group is thermally transferred from the main chain. Since it can be prevented from falling off, heat resistance is improved. Further, it is sufficient if the silicon atom is contained in a part of the side chain, but it is preferable from the viewpoint of heat resistance that it is contained in all the side chains.

The strongly acidic functional group is not particularly limited as long as it has a cation exchange ability. Examples of the strongly acidic functional group include a sulfonic acid functional group, phosphoric acid, acrylic acid, silanol, carbinol and the like. As the strongly acidic functional group, a sulfonic acid functional group is particularly preferable.

The side chain is preferably one having a structure represented by the general formula (2). By adopting a siloxane structure for the side chain as well, heat resistance is improved, and at the same time, the structure represented by the general formula (2) is easily introduced into the polymer material and is easily manufactured. Here, the value of m in the general formula (2) is preferably 2 to 10.

The structure of the main chain structure other than the siloxane structure is not particularly limited. Further, the structure of the side chain structure other than the silicon atom-introduced part is not limited. For example, a general structure mainly composed of carbon-carbon bonds can be exemplified. Specifically, examples of the structure mainly composed of carbon-carbon bonds include polyolefin and fluorine-substituted olefins obtained by substituting part or all of hydrogens with fluorine, polystyrene, polyamide, polyimide and the like. The number of side chains present on the main chain is not particularly limited, but carbon-carbon bonds and / or silicon-oxygen bonds of the main chain (when the structure of the main chain is represented by the general formula (1), the parentheses The number of repeating units in the above) has a side chain at a ratio of about 2 to 10 so that the proton conductivity is improved and the strength
It is preferable from the viewpoint of improving both heat resistance and water resistance.

The method for producing the proton conductive material of the present invention is not particularly limited. For example, in the molecular chain corresponding to the main chain,
It can be produced by grafting a molecular chain corresponding to a side chain. As a method of grafting a side chain on the main chain, for example, a reaction starting point such as a radical is generated on the main chain by some method such as irradiation with high energy rays, and a monomer forming a side chain is formed based on the reaction starting point. This can be achieved by polymerizing growth or by introducing a reactive functional group on the main chain and binding a side chain to the functional group. It is also possible to add a polymerizable functional group such as a vinyl group to the end of the side chain and polymerize it with a monomer constituting the main chain to synthesize the main chain and at the same time introduce the side chain.

The siloxane structure represented by the general formula (1) can be obtained by polymerizing a corresponding dialkyldichlorosilane under appropriate conditions. Further, as shown in the general formula (2), in order to introduce a sulfonated phenyl group at the end of a side chain, a silane compound having a phenyl group bonded is used to introduce the phenyl group into a dialkylsiloxane structure, and then fuming sulfuric acid. It can be obtained by sulfonation with the like.

[0023]

(Test Example 1) (a) At room temperature and in a nitrogen atmosphere, poly H-methyl siloxane (molecular weight 2000) and terminal vinyl polydimethyl siloxane (molecular weight 2000) were used in a stoichiometric ratio of H: vinyl = 100: 1 and mixed well. Then, a platinum complex (platinum-cyclovinylmethylsiloxane complex) of 100 ppm in terms of platinum was added to the vinyl group, and the mixture was sufficiently stirred with a homogenizer to obtain a solution. Then, the solution was heat-treated in a furnace at 150 ° C. for 24 hours, gradually cooled and returned to room temperature.

(B) At room temperature under a nitrogen atmosphere, vinyl tetramethyldisiloxane and a 30% sulfonated triphenylsilanol-methylene chloride solution were mixed at a stoichiometric ratio H: OH = 1: 1 and mixed sufficiently. It was stirred. Then, 150 ppm of tin catalyst (bis (2-ethylhexyl) tin) in terms of tin was added to H, and the mixture was sufficiently stirred with a homogenizer to obtain a solution. Then, the solution was heat-treated in a furnace at 150 ° C. for 24 hours, gradually cooled and returned to room temperature.

(C) The amount of H in the solution prepared in (a) and the amount of vinyl groups in the solution prepared in (b) are mixed in a stoichiometric ratio of H: vinyl = 1: 1.5. Then, a platinum complex (platinum-cyclovinylmethylsiloxane complex) of 100 ppm in terms of platinum was added to the vinyl group. The solution was thoroughly stirred with a homogenizer. After casting this on a flat plate made of PTFE to form a film, 1 in a furnace
Heat treatment was performed at 50 ° C. for 24 hours to obtain a thin film as a test sample of Test Example 1. This thin film has a dimethylsiloxane structure in both the main chain and side chains.

Test Example 2 Vinyl tetramethyldisiloxane and a 30% triphenylsilanol-methylene chloride solution were mixed at a stoichiometric ratio H: OH = 1: 1 at room temperature under a nitrogen atmosphere and thoroughly mixed. It was stirred. Then H
On the other hand, 150 ppm of tin catalyst (bis (2
-Ethylhexyl) tin) was added, and the mixture was thoroughly stirred with a homogenizer to give a solution. Then, in a furnace,
The mixture was heat-treated at 0 ° C. for 24 hours, gradually cooled and returned to room temperature.
A styrene monomer was added to this and mixed well, AIBN was further added, and the mixture was heated at 70 ° C. for 12 hours to obtain a thin film. This was immersed in 60% fuming sulfuric acid for 24 hours to sulfonate the phenyl group, and then washed with pure water and ethanol in that order.
A thin film as a test sample of Test Example 2 was obtained by drying. This thin film has a hydrocarbon structure in the main chain and a dimethylsiloxane structure in the side chain.

(Test Example 3) At room temperature and under a nitrogen atmosphere, poly H-methyl siloxane (molecular weight 2000) and terminal vinyl polydimethyl siloxane (molecular weight 2000) in stoichiometric ratio H: vinyl = 100: 1. And mixed well. After that, 100pp in terms of platinum for vinyl groups
m platinum complex (platinum-cyclovinylmethylsiloxane complex) was added, and the mixture was thoroughly stirred with a homogenizer to give a solution. Then, the solution was heat-treated in a furnace at 150 ° C. for 24 hours, gradually cooled and returned to room temperature. Further, a 30% allylbenzene-methylene chloride solution was added under a nitrogen atmosphere (stoichiometric ratio H: vinyl = 1: 1.5). After sufficiently stirring, 100 ppm of platinum complex (platinum-cyclovinylmethylsiloxane complex) was added to H. This was cast on a PTFE flat plate to form a film, and then heat-treated at 100 ° C. for 12 hours in a furnace. Then, it was immersed in 60% fuming sulfuric acid for 24 hours to sulfonate the phenyl groups. Then, it was washed with pure water and ethanol and then dried to obtain a thin film as a test sample of Test Example 3. This thin film has a dimethylsiloxane structure in the main chain and a hydrocarbon structure in the side chain (without a silicon atom in the side chain).

(Test Example 4) A commercially available thin film (Nafion) made of a proton conductive material was used as a test sample of Test Example 4 (Test Example 5) at room temperature under a nitrogen atmosphere, and poly (H-methylsiloxane) (molecular weight 2000) was added. Vinyl-terminated polydimethylsiloxane (molecular weight 2000) was mixed at a stoichiometric ratio of H: vinyl = 100: 1 and stirred sufficiently. Then, a platinum complex (platinum-cyclovinylmethylsiloxane complex) of 100 ppm in terms of platinum was added to the vinyl group, and the mixture was sufficiently stirred with a homogenizer to obtain a solution. Then, the solution is heated in a furnace at 150 ° C. for 24 hours,
It was gradually cooled to room temperature. Next, a 30% sulfonated triphenylvinylsilane-methylene chloride solution was added to the prepared solution at room temperature under a nitrogen atmosphere (mixing ratio H: vinyl = 1: 1.5). After sufficiently stirring, 100 ppm of platinum-based platinum complex (platinum-cyclovinylmethylsiloxane complex) was added to H and sufficiently stirred with a homogenizer to prepare a solution. Cast this into a film,
A thin film was obtained by heating and drying at 150 ° C. for 2 hours in a furnace.

(Test Example 6) 1. At room temperature under a nitrogen atmosphere, poly-H-methyl siloxane (molecular weight 2000) and terminal vinyl polydimethyl siloxane (molecular weight 2000) were mixed at a stoichiometric ratio of H: vinyl = 100: 1 and stirred sufficiently. . Then, a platinum complex of 100 ppm in terms of platinum based on the vinyl group (platinum-
Cyclovinylmethylsiloxane complex) was added, and the mixture was thoroughly stirred with a homogenizer to give a solution. Then, the solution was heat-treated in a furnace at 150 ° C. for 24 hours, gradually cooled and returned to room temperature.

2. Next, at room temperature under a nitrogen atmosphere, vinyl dimethyl silane and a sulfonated triphenylsilanol-methylene chloride 30% solution were added to a stoichiometric ratio H: OH =.
After mixing 1: 1 and sufficiently stirring, 150 ppm of tin catalyst (bis (2-ethylhexyl) tin) in terms of tin with respect to H was added and sufficiently stirred with a homogenizer to obtain a solution. Then, the solution was heat-treated in a furnace at 150 ° C. for 24 hours, gradually cooled and returned to room temperature.

3.1. H amount of the solution prepared in 2. The stoichiometric ratio with the vinyl group of the solution prepared in H: vinyl =
The mixture was mixed at a ratio of 1: 1.5, 100 ppm of platinum-based platinum complex (platinum-cyclovinylmethylsiloxane complex) was added to the vinyl group, and the mixture was sufficiently stirred with a homogenizer to obtain a solution. This was cast into a film, and heat-dried at 150 ° C. for 2 hours in a furnace to obtain a thin film.
In the description of Test Examples 1 to 6, “ppm” represents the number of moles of platinum or tin in the compound to be added with respect to the number of moles of the corresponding H or vinyl group.

(Test) (Measurement of Proton Conductivity) For each test sample 1 to 4,
The proton conductivity of each was measured. Proton conductivity was measured by setting the relative humidity of the atmosphere to 90%, the temperature to 80 ° C,
The measurement was performed by the AC impedance method while changing the conditions to 100 ° C. and 120 ° C. Each test sample was kept in each atmosphere for 2 hours, and the proton conductivity was measured after the amount of water contained in the thin film reached an equilibrium state.

(Measurement of Thermal Decomposition Property) The thermal decomposition property of each of the test samples 1 to 3 was measured. The thermal decomposition characteristics are measured by thermogravimetric measurement (TG), and the measurement temperature range is 0 ° C to 40 ° C.
It was carried out under the conditions of 0 ° C. and a heating rate of 10 ° C./min.

(Results) The proton conductivity of the test sample of each test example is shown in Table 1, and the result of the thermal decomposition property measurement is shown in FIG.

[0035]

[Table 1]

As is apparent from Table 1, the ambient temperature is 80
The test samples of Test Examples 1 to 3 show a proton conductivity comparable to that of Nafion of Test Example 4, which is a typical conventional proton conducting material, at 100 to 100 ° C. In particular, the test samples of Test Examples 1 and 2 in which a dimethylsiloxane structure was introduced into the side chain exhibited remarkably high proton conductivity. When the ambient temperature was 120 ° C., the proton conductivity of Nafion (test sample 4) decreased, whereas it was revealed that the test samples of Test Examples 1 and 3 maintain high proton conductivity.

Further, as is apparent from FIG. 1, Test Example 1
Test sample (both main chain and side chain have siloxane structure)
It has been revealed that even if the ambient temperature is 150 ° C., the mass reduction is 1% or less, and the decomposition is almost zero.

On the other hand, the test sample of Test Example 2 (having a hydrocarbon structure in the main chain and a siloxane structure in the side chain) was 1
Decomposition starts at 60 ° C below 00 ° C and the ambient temperature is 15
Almost 40% of the mass loss was already observed per 0 ° C. Test sample of Test Example 3 (main chain is siloxane structure,
The side chain has a hydrocarbon structure) has an ambient temperature of 150 ° C.
Although the mass loss at 10% was about 10%, a high mass loss (about several% to 10%) was observed from a very low temperature of 100 ° C. or lower.

In other words, it was revealed that the thermal decomposition characteristics of the main chain and the side chains were deteriorated by lacking a silicon atom in the chemical structure.

(Measurement of Creep Property) Test Samples 1 and 4
The creep characteristics were measured. As the sample for measuring the creep characteristics, a test sample was cut into a 1 cm square, 20 samples having a thickness of 200 μm were laminated for sample 1, and 20 samples of Nafion 117 were laminated for sample 4.
The conditions of the creep test were as follows: after the temperature was raised to 90 ° C., the surface pressure was applied at 2.5 MPa (25 kgf / cm ² ), and the creep strain after 200 hours was measured.
Creep strain is the primary creep (2-1 after applying surface pressure)
The secondary creep strain (variation that progresses in about 10 to 200 hours after applying the surface pressure) excluding the initial variation that progresses in approximately 0 hours) was measured. The reason for evaluating the secondary creep strain is that the primary creep is due to the elastic modulus inherent to the material, not due to alteration or breakage of the material itself, and no tertiary creep is observed. Therefore, the secondary creep was regarded as the essential creep strain of the material. The creep strain is {(sample length at the time of measurement)-(sample length before applying surface pressure)} / (sample length before applying surface pressure) /
It was calculated by (surface pressure application time) × 100 (%).

The results are shown in FIGS. 2 and 3. As is apparent from the figure, the creep strain of the test sample 1 which is the proton conducting material of the present invention is lower than that of the conventional test sample 4 (Nafion) in both the primary creep strain and the secondary creep strain. Became. The secondary creep strain was 0.025% in the test sample 1 and 0.102% in the test sample 4, and the test sample 4 is the test sample 4 which is the proton conductive material of the present invention.
The value was 1/4 or less lower than that of (Nafion). The secondary creep strain is {(sample length after 200 hours after application of surface pressure)-(sample length after 10 hours)} / (10
Sample length after time) / (surface pressure application time: 190 hours) ×
It was calculated at 100 (%).

(Relationship Between Number of Siloxane Units of Side Chain Dimethylsiloxane Structure and EW Value) Test Examples 1 and 5
The EW value was measured for Sample Nos. 6 and 6. The test samples of Test Examples 1, 5 and 6 have m =
0 (test example 5), m = 1 (test example 6) and m = 2 (test example 1).

[0043]

[Chemical 5]

The symbol "*" in the formula indicates that the extended main chain is bound.

The EW value was measured by the sodium chloride titration method. Specifically, sodium chloride is added, the pH value is measured from the amount of hydrochloric acid generated, and the active sulfonic acid group is quantified. _{(* -SO 3 H + NaCl →} * -SO 3
As a result, the EW value was 850 for the test sample with m = 0 (Test Example 5), 800 for the test sample with m = 1 (Test Example 6),
In the test sample of m = 2 (Test Example 1), 620 showed a higher value as the length of the side chain was shorter, and it was revealed that the amount of the sulfonic acid group involved in proton conductivity was relatively large.
Although not shown in detail, it became clear that the measured value of the oxygen permeation coefficient increases as the value of m increases.

[0046]

The proton conductive material of the present invention has a siloxane structure in the main chain and has a silicon atom in the side chain, so that it can withstand use conditions of 100 ° C. or higher while maintaining high proton conductivity. It can exhibit high heat resistance (thermal decomposition characteristics, creep strain). Therefore, it can be suitably applied to applications where a high operating temperature is required, such as an electrode catalyst layer of a fuel cell.

[Brief description of drawings]

FIG. 1 is a graph showing an actual measurement value of TG whose thermal decomposition characteristics were measured in Examples.

FIG. 2 is a graph showing changes over time in creep strain in Examples.

FIG. 3 is a partially enlarged view of a graph showing changes over time in creep strain in Examples.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4J035 BA02 CA02U CA022 CA14U                       CA142 CA25M CA26M CA26N                       CA261 FB01 HA01 HB05                       LA05 LB20                 5G301 CA30 CD01                 5H018 AA06 AS01 EE17                 5H026 AA06 CX05 EE18

Claims (5)

[Claims] 1. A proton conductive material comprising a polymer material having a main chain having a siloxane structure and a side chain grafted to the main chain and having a silicon atom and a strongly acidic functional group. . 2. The proton conductive material according to claim 1, wherein the polymer material has a partial structure represented by the general formula (1). [Chemical 1] (In the formula (1), n> 0. R1 independently has 1 carbon atom.
~ 4 alkyl groups. R2 independently has 1 to 4 carbon atoms
Is an alkyl group or a side chain thereof. ) 3. The proton conductive material according to claim 1, wherein the polymer material essentially has a structure represented by the general formula (1). 4. The proton conducting material according to claim 1, wherein the side chain has a structure represented by the general formula (2). [Chemical 2] (In the formula (2), m ≧ 0 and R3 and R4 are each independently an alkyl group having 1 to 4 carbon atoms.) 5. The proton conducting material according to claim 1, wherein the polymer material is a linear polymer.