JP2005521777A - Ion exchange composites based on proton conducting silica particles dispersed in a polymer matrix - Google Patents

Abstract

A composite comprising acid-functionalized silica dispersed in a polymer matrix based on poly (aromatic ether ketone) or poly (benzoylphenylene), or derivatives thereof. The composite material is characterized by good water retention capacity due to acidic functionality and the hydrophilicity of the silica particles. Furthermore, good impermeability to gas and liquid fuels commonly used in fuel cell technology, such as hydrogen gas or methanol solutions, is obtained due to the presence of silica particles. The good mechanical properties of the composite material make it easier to form the material in the form of a thin film or membrane. In that form, the composite material can be used for proton exchange membranes for fuel cells, for drying or wetting membranes, for conditioning gases or solvents, or as acid catalyst membranes.

Description

  The present invention relates to an ion exchange composite material based on proton conducting silica particles dispersed in a polymer matrix. The present invention also relates to a method for producing the above composite material and to a proton exchange membrane, for example in an electrochemical instrument, in particular a fuel cell, using it as a drying / wetting membrane, for conditioning a gas or solvent, or for an acid. The present invention relates to a method for forming a film that can be used as a catalyst film.

  Ion exchange materials have many applications in several technical fields such as electrochemical instruments, environmental requirements, and chemical reactions. Among ion exchange materials, proton conducting materials have been extensively studied due to the increasing interest in clean power generation, and polymer electrolyte membrane fuel cells (PEMFC) are an important representative for clean power generation. One.

  The proton conductivity of the material can be obtained, for example, by incorporating a proton exchange group into the chemical structure of the material. The sulfonic acid functional group is the most efficient proton exchange group, but carboxylic acid groups or phosphonic acid groups can also be used for proton transfer.

  Many developments have been made on perfluorinated or partially fluorinated polymers or copolymers having sulfonic acid groups. The material of this family includes, for example, Nafion (registered trademark) (Du Pont de Nemours) (Patent Document 1; Patent Document 2), Aciplex (registered trademark) (Asahi Chemical Industry), Flemion. (Trademark) (Asahi Glass Co., Ltd.) or Gore-Select (registered trademark) (W. El Gore) (Patent Literature 3; Patent Literature 4; Patent Literature 5). It is considered that phase separation occurs between the hydrophilic acid region and the hydrophobic fluorocarbon region and contributes to good proton conductivity in the material (Non-Patent Document 1; Non-Patent Document 2). Unfortunately, water management becomes a problem at high temperatures (near 100 ° C.), mainly due to the hydrophobic nature of the fluorinated backbone of the material that causes rapid dehydration of the membrane.

  As a comparison, non-fluorinated but sulfonated polymers can also exhibit good proton conductivity with little significant dehydration effect. A strong chemical structure, preferably an aromatic based structure, is essential to give the material good stability at high temperatures. Properties of interest for fuel cell applications have already been shown for polymers based on, for example, poly (aromatic ether ketone) (Patent Document 6), poly (aromatic ether sulfone) or polyphenylene (Patent Document 7).

  Several inorganic fillers can be added to the sulfonated polymer to reduce dimensional variation between the wet and dry state of the material and improve its water retention. In that case, proton conductivity is ensured by the organic phase, while the inorganic phase helps retain water and reduces the expansion of the material (3).

  The combination of beneficial properties of the inorganic and organic phases is seen in many developments of composite materials that handle the formation of a stable continuous proton conducting phase. With these developments, alkoxysilane derivatives are polymerized via a sol-gel or co-condensation process, resulting in a structure based primarily on silicon-oxygen that is three-dimensionally crosslinked (Patent Document 8, Patent Document 9, Patent Reference 10). Although such types of composite materials are promising, their manufacture is not easy to control and is often difficult to achieve. Furthermore, such kind of structures do not readily provide any ion exchange power. Simpler composite manufacturing methods can provide an interesting solution to the challenge of electrochemical instruments such as fuel cell membranes.

  Patent Document 11 (issued on June 8, 2001, Japanese Patent Application No. 11-336986, Applicant: Toyota Central R & D Laboratory) describes a proton conductor based on a high molecular weight electrolyte containing functionalized silica. Describe. Silicas functionalized with sulfonic, carboxylic and phosphonic acid groups are described. For electrolytes, the description is limited to perfluorosulfonic acid type polymers, styrene divinylbenzene sulfonic acid type polymers and styrene-ethylene-butadiene-styrene copolymers. In the specific example using sulfonated silica and perfluorosulfonic acid polymer, the resulting membrane has a current density of 1 A / cm 2 at 0.5 V, which is not satisfactory. Data on the current density of films obtained only in other examples are not available. It is estimated that the other example membranes are substantially the same or inferior to the Example 1 membranes. Accordingly, there is a need to provide an improved film with satisfactory current density.

  Patent Document 12 (issued June 8, 2000, Applicant: University Laval) discloses an electrolytic membrane comprising a polymer matrix and a filler material that contributes to improving the proton conductivity of the membrane. In all examples, the polymer matrix is based on aromatic polyetherketone (PEEK) or its sulfonated derivative (SPEEK), while the filler is BPO4 or a heteropolyacid. This composite will not be time resistant. This is because the filler dissolves in the polymer matrix over time.

Therefore, a composite material based on an inorganic phase dispersed in a polymer matrix, which has a good proton exchange capacity, gives an excellent current density to the membrane, is time resistant, and can be easily manufactured. There is a demand for materials.
U.S. Pat. No. 3,282,875 U.S. Pat. No. 4,330,654 US Pat. No. 5,635,041 US Pat. No. 5,547,551 US Pat. No. 5,599,614 US Pat. No. 6,355,149 US Pat. No. 5,403,675 EP12223632 A2 EP 0560899 B1 US Pat. No. 6,277,304 JP 2001-155744 A Canadian Application No. 2,292,703 T.A. D. Gierke, G .; E. Munn, F.M. C. J. Wilson Polym. Sci. Polym. Phys. Ed. 1981, 19, 1687 M.M. Fujimura, T .; Hashimoto, H .; Macromolecule by Kawai, 1981, 14, 1309. "Processeds of 1998 Fuel Cell Seminar", November 16-19, Palm Spring, California

The object of the present invention is to overcome the aforementioned problems.
Another object of the present invention is to provide an ion exchange composite that exhibits an associated proton exchange capacity.
Another object of the present invention is to provide a process for producing an ion exchange composite in the form of a membrane that can be easily produced.
Another object of the present invention is to provide a composite material suitable for forming a film having a good current density.

The above and other objects of the present invention are achieved by providing a composite material comprising:
Acid functionalized silica particles,
The remaining amount is a polymer based on poly (aromatic ether ketone) or poly (benzoylphenylene), or derivatives thereof,
The composite material can provide a film having a current density of at least about 1 A / cm ² at 0.6V.
The composite material can be used in the form of a membrane.

  In the composite material of the present invention, the silica particles are preferably functionalized with sulfonic acid, carboxylic acid and / or phosphonic acid groups, with sulfonic acid groups being preferred.

  In a preferred embodiment, the composite material of the present invention typically comprises at least about 10% by weight, preferably about 20% by weight, of functionalized silica particles.

  The polymer used to construct the polymer matrix may be functionalized with acid functionalization, such as sulfonic acid, carboxylic acid and / or phosphonic acid groups, or derivatives thereof.

  The acid groups are branched into silica particles and / or polymers with, for example, linear or branched alkyl chains, linear or branched aromatic chains, or linear or linear or branched alkyl or aromatic chains, It may be covalently bonded through a combination of an alkyl chain and an aromatic chain, the chain optionally containing heteroatoms and / or halogen atoms.

In the composite material of the present invention, the silica particles have the following characteristics:
i. A surface area of 10 m ² / g to 1500 m ² / g,
ii. Silica particle size of 0.01 μm to 500 μm,
iii. Silica pore size from 0 angstrom to 500 angstrom.

The ion exchange groups are usually present in the silica particles in an amount of 0.1 to 5.0 mmol / g.
Acid groups are usually present in the polymer in an amount of 0 mmol / g to 5.0 mmol / g.

  The membranes of the present invention are preferably intended for use in fuel cells, for wetting or drying, in conditioning gases or solvents, or as acid catalyst membranes.

  Composite materials can be readily manufactured in the form of membranes that can be used for electrochemical instruments such as proton exchange membranes for fuel cells, wetting or drying membranes for gas or solvent conditioning, and acid catalyst membranes.

  Silica particles are functionalized with acid groups and, when dispersed within the polymer matrix, constitute an inorganic hydrophilic phase having proton exchange capacity. The organic phase comprising the polymer matrix may include ion exchange groups that are initially present in the chemical structure of the polymer or ion exchange groups bonded to the chemical structure of the polymer to increase the proton conductivity of the composite material. Proton exchange power is achieved by both functionalized polymer matrix and dispersed silica particles.

Some functional groups are suitable for providing proton exchange power to the material. A preferred functional group is an acid group, more preferably a sulfonic acid group (—SO ₃ H). Other acid groups such as carboxylic acid groups (—CO ₂ H) or phosphonic acid groups (—PO ₃ H ₂ ) can also be joined (grafted) to the structure to give the relevant proton conductivity.

  The ion exchange groups are preferably covalently bonded to the chemical structure of the organic and inorganic phases. The chemical bond is preferably a linear or branched alkyl or aromatic chain or a combination of both a linear or branched chain and may contain some heteroatoms or halogen atoms incidentally.

  As described above, various types of silica can be used to form the inorganic phase in the composite material. The preferred silica is porous silica, but other types may be used, including but not limited to: amorphous silica, fumed silica, spherical silica, irregular silica, structured silica, Molecular sieve silica, silesquioxane derivatives, and mixtures thereof. The amount of silica particles and their average size play an important role in the formation of the continuous hydrophilic phase and the mechanical properties of the material.

  A family of poly (aromatic ether ketones), the preferred polymer is poly (oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1) manufactured by Victrex (UK) and having the formula: , 4-phenylene) (PEEK):

  The glass transition temperature of PEEK is typically about 200 ° C. and has the necessary heat and chemical resistance, resulting in a strong composite.

  Sulfonation is a common method of altering the polymer structure by joining sulfonic acid groups that impart proton exchange power to the sulfonated material. The ability of proton mobility depends on the amount and dispersion of the acid groups in the material.

  Several studies are currently available on sulfonation of this type of structure. One of the most suitable sulfonation methods for use in the present invention is EP 8895 and later Br. Polym. J. et al. Vol. 17, 1985, page 4, using sulfonation in concentrated H2SO4. This sulfonation reaction causes less damage to the polymer than means of chlorosulfonation, since no significant chain scission or degradation occurs. Once the polymer is sulfonated, the formula corresponding to sulfonated PEEK is typically as follows:

  The degree of sulfonation corresponds to x / n, where x corresponds to the number of repeating units having one sulfonic acid group. Thus, 100% sulfonated PEEK has one acid group per repeat unit or one acid group per three aromatic rings. The number of sulfonic acid groups per gram of sulfonated polymer determines the ion exchange power (IEC) of the polymer. For example, 100% sulfonated PEEK has an IEC of 2.9 mmol / g.

  The amount of sulfonic acid groups attached to the aromatic ring depends on several parameters such as temperature, time, and the concentration of the polymer in the acid. Many properties of sulfonated PEEK (SPEEK), such as proton capacity, solubility, water retention, and expansion coefficient, vary with its sulfonation rate, ie, ion exchange capacity.

  For inorganic phases, the use of silica functionalized with sulfonic acid groups not only provides proton conductivity benefits, but also provides better efficiency in water retention than unfunctionalized silica. Typically, water retention of acid silica is twice as high as normal silica. For example, in an environment where the relative humidity is 70%, the water retention capacity of normal silica is 15%, whereas the water retention capacity of acid silica is about 30%.

  The structure of silica also plays an important role in water retention. For example, a low bulk density structure increases water retention compared to high bulk density silica, but mainly due to its high specific surface area. Typically, a low bulk density structure can take up twice as much water as a high bulk density structure. For example, the water retention of silica having a low bulk density structure at a relative humidity of 70% is about 15% compared to 7% for silica having a high bulk density structure. Furthermore, the large surface area as seen in the low bulk density structure improves the loading of acid functionality into the inorganic compound. For example, the loading of functionalized low bulk density silica is typically 1.7 mmol / g, which is typically less than twice the 0.9 mmol / g of porous high bulk density silica. .

  Low bulk density silica sulfonate can typically be produced by a co-condensation process as described, for example, in Chem. Mater. 2000, 12, page 2448. The sulfonic acid group can be bonded to high bulk density silica, for example, using the method described in J. Chromato. 1976, 117, 269. Several types of bonds are possible to bond the sulfonic acid groups to the silica particles. In the present invention, a preferred but not limited bond deals with a propylphenyl chain. The bond may also include any type of alkyl or aromatic derivative and combinations thereof, and may or may not have heteroatoms and / or halogens in the chemical structure.

  The composite material is made by adding acid silica particles into the polymer matrix and mixing both uniformly. A preferred method proceeds through the polymer solution, where silica particles or a silica suspension in the same solvent as the polymer solution or a solvent miscible with the polymer solution is added. The suspension is then homogenized and dried before being sprinkled into a uniform thin layer. Satisfactory mixtures can also be obtained without the use of solvents, as in the process based on the melt phase.

  The mechanical properties of the composite depend mainly on the mechanical properties of the polymer matrix and the silica content. Mechanical properties determine the lower limit of film thickness that can be handled without tearing. A very stiff polymer cannot fully deform a thin film without tearing, while a very flexible structure cannot hold a composite material in a thin film. Similarly, too many inorganic particles interfere with good tear resistance and make the film particularly brittle.

  The solubility of the composite material depends in particular on the solubility of the polymer matrix. As mentioned earlier, the solubility of the polymer depends on the temperature and its ion exchange capacity. The maximum temperature at which the material can be used in a hydrated state in a particular liquid, such as water, is directly related to the solubility of the polymer. Sufficient silica in the composite can be between 10 and 30% by weight, but improves proton conductivity to some extent, depending on the density of the corresponding silica used.

In the present invention, many parameters can be easily changed to adjust the properties of the final composite. Typically, the following parameters must be considered for composite formulation: solvent solubility, use temperature, final form material thickness, and expected ion exchange value. The corresponding sulfonation rate of the polymer matrix is then determined. The properties of the silica are subsequently evaluated, mainly considering the porosity requirements depending on the desired acid load and water retention.
The invention is illustrated by the following non-limiting examples.

Example 1
The sulfonated sulfonated 55 percent of PEEK of PEEK, obtained by stirring 48 hours e.g. PEEK50g of _{H 2 SO} 4 _(H 2 O in 95-98%) in a 2L at room temperature. The solution is poured into H ₂ O and the solid phase corresponding to the sulfonated PEEK (SPEEK) is washed vigorously 2-3 times in 5 L of pure water. The isolated solid is first dried in an oven at about 70 ° C. overnight, then further washed and then dried at 100 ° C. under reduced pressure for several days. About 40 g of SPEEK is obtained (yield about 80%). Elemental analysis gives the sulfur content of the sulfonated polymer and calculates the corresponding ion exchange power (IEC) next. An IEC of 1.6 ± 0.1 mmol / g is obtained, corresponding to a sulfonation rate of about 55%.

Example 2
Preparation of Composite Film a) 1 g of 55% sulfonated PEEK (SPEEK) is dissolved in 10 mL of dimethylformamide (DMF) at room temperature and filtered through filter paper. A suspension of 0.2707 g sulfonic acid conjugated silica in 2 mL DMF is added to the clear polymer solution. After stirring, the homogeneous mixture is spread on a 385 cm ² glass substrate before being dried at 70 ° C. for several days. After complete evaporation of the solvent, the film is easily removed from the glass substrate when immersed in water. Once dried, the composite film composed of 80% by weight 55% sulfonated PEEK and 20% by weight acid silica is 40 ± 10 μm.
b) 0.1755 g SPEEK55 is dissolved in 1.7 mL DMF and filtered. 0.0195 g of sulfonic acid conjugated silica is added to the polymer solution. After homogenization, the mixture is spread on a 25 cm 2 glass substrate. Once dried, a composite film comprising 90 wt% 55% sulfonated PEEK and 10 wt% acid silica has a thickness of 50 μm.

Example 3
Electrode deposition on a composite film for fuel cell testing A commercially available Pt / C electrode (Pt / Vulcan XC-72 from Electrochem) is placed on a composite film with a small amount on the sides of the two electrodes sandwiching the membrane. Laminate by spreading a 10% DMF solution (w / v) of SPEEK55. The assembly is dried under vacuum at room temperature for 1 day, under vacuum at 60 ° C. overnight, and at 80 ° C. for several days.

Example 4
Performance Comparison The performance obtained using the membrane of the present invention is compared with the performance obtained using the membrane of JP2001-155744 (Example 1).
The composite material of the Japanese reference contains 5% (w / v) inorganic phase mixed inside the polymer solution. The inorganic phase is fumed silica joined using phenylsilane as a coupling agent and then reacted with concentrated H ₂ SO ₄ (H ₂ SO ₄ cc). The organic phase is an inorganic phase binder. In this case, Nafion®, a perfluorinated polymer having sulfonic acid groups, is used. For the experiment, the fuel cell is operated at 80 deg. C in an H2 / air atmosphere at 22 psig. Under a voltage of 0.6 to 0.7 V, the fuel cell produces a current density of 0.5 A / cm ² and at 0.5 V produces a current density of 1 A / cm ² . It will be appreciated that the membrane according to the Japanese reference contains 1% by weight of silica, whereas the membrane of the present invention contains 20% by weight of silica.
The composite material of the present invention contains 10% (w / v) of an inorganic phase mixed inside the polymer solution. The inorganic phase comprises silica obtained by cocondensation and functionalized by chlorosulfonation. The organic phase is SPEEK. For experiments, the fuel cell is operated at 75 ° C. under H ₂ / air atmosphere at 20/30 psig. Under a voltage of 0.7 V, the fuel cell produces a current density of 1 A / cm ^2, a current density of 1.7 A / cm ² to 1.8 A / cm ² at 0.6 V, and 2 at 0.5 V. A current density of ² A / cm ² to 2.3 A / cm ² is produced.
Under similar operating conditions, as seen in FIG. 1, the present invention generates a much higher current density than the Japanese patent. In FIG. 1, the material used consists of 20% by weight of silica containing 1.4 mmol of sulfonic acid groups per gram and 80% by weight of SPEEK55 prepared as in Example 1.

  It will be appreciated that the invention is not limited to the above-described embodiments, and that many modifications are possible within the scope of the claims.

3 is a polarization curve of current density vs. voltage of the film of the present invention.

Claims (21)

Acid functionalized silica particles,
The remaining amount is a polymer matrix based on poly (aromatic ether ketone) or poly (benzoylphenylene), or derivatives thereof,
A composite material capable of providing a film having a current density of at least about 1 A / cm ² at 0.6V.   The composite material of claim 1, wherein the functionalized silica particles are dispersed in the polymer matrix.   The composite material according to claim 1, wherein the silica particles are functionalized with sulfonic acid groups, carboxylic acid groups and / or phosphonic acid groups.   The composite material according to claim 2, wherein the silica particles are functionalized with sulfonic acid groups.   The composite of claim 1, comprising at least about 10% by weight of acid functionalized silica particles.   6. The composite material of claim 5, comprising at least about 20% by weight acid functionalized silica particles.   The composite material of claim 1, wherein the polymer is functionalized with an acid.   The composite material according to claim 7, wherein the polymer is functionalized with sulfonic acid groups, carboxylic acid groups and / or phosphonic acid groups, or derivatives thereof.   The composite material according to claim 2 or 8, wherein the acid group is covalently bonded to silica particles and / or a polymer.   The acid group is a linear or branched alkyl chain, a linear or branched aromatic chain, or a linear or linear or branched alkyl or aromatic chain; The composite material according to claim 9, wherein the composite material is covalently bonded through a combination and the chain optionally contains heteroatoms and / or halogen atoms. The composite material of claim 1, wherein the silica particles have the following characteristics:
i. A surface area of 10 m ² / g to 1500 m ² / g,
ii. Silica particle size of 0.01 μm to 500 μm,
iii. Silica pore size from 0 angstrom to 500 angstrom.   The composite material according to claim 1, wherein ion exchange groups are present in the silica particles in an amount of 0.1 to 5.0 mmol / g.   The composite material according to claim 7, wherein the acid groups are present in the polymer in an amount of 0 mmol / g to 5.0 mmol / g.   The silica is amorphous silica or derivative thereof, fumed silica or derivative thereof, spherical silica or derivative thereof, porous irregular silica or derivative thereof, porous structural silica or derivative thereof, irregular porous molecular sieve silica or derivative thereof 2. The composite material according to claim 1, selected from the group consisting of: spherical molecular sieve silica or a derivative thereof; and silesquioxane compound or a derivative thereof.   The composite material according to claim 1, wherein the polymer is poly (aryl ether ketone) (PEEK) or a derivative thereof.   The composite material of claim 1, wherein the polymer is poly (benzoylphenylene) (PBP) or a derivative thereof.   A membrane comprising the composite material of claims 1-16.   The membrane according to claim 17, which is used in a fuel cell.   18. A membrane according to claim 17 for use in wetting or drying.   18. A membrane according to claim 17 for use in gas or solvent conditioning.   The membrane according to claim 17, which is used as an acid catalyst membrane.

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