KR20040111458A - Ion exchange composite material based on proton conductive silica particles dispersed in a polymer matrix - Google Patents

Abstract

Composites include acid functionalized silica dispersed in a polymer matrix based on poly (aromatic ether ketones), or poly (benzoyl phenylene) or derivatives thereof. The composite is characterized by good water retention due to the acidic function and hydrophilicity of the silica position. In addition, the presence of silica particles results in good impermeability to gas and liquid fuels commonly used in fuel cell technologies such as hydrogen gas or methanol solutions. The good mechanical properties of the composites allow the composites to be easily formed into thin films or films. In this form, the composite can be used in a proton exchange membrane for fuel cells, to dry or humidify the membrane for gas or solvent conditioning, or as an acid catalyst membrane.

Description

ION EXCHANGE COMPOSITE MATERIAL BASED ON PROTON CONDUCTIVE SILICA PARTICLES DISPERSED IN A POLYMER MATRIX}

Ion exchange materials are used in a variety of applications in many technical fields, such as in electrochemical devices and chemical reactions, depending on the environmental needs. With increasing interest in generating clean power, many studies have been conducted on proton conductive materials in ion exchange materials, and an important representative example thereof is a polymer electrolyte fuel cell (PEMFC).

Proton conductivity of the material can be obtained, for example, by incorporating a proton exchange group into the chemical structure of the material. Sulfonic acid functional groups are one of the most effective proton exchange groups, but carboxylic acid or phosphonic acid groups and the like can also be used for proton transfer.

Many developments have been made on perfluorinated or partially fluorinated polymers or copolymers containing sulfonic acid groups. This class of materials is described, for example, in Naflon® (Du Pont de Nemours and Co.) [US 3,282,875; US 4,330,654], Assiut Flex ® (Aciplex®) (Asahi Chemical Industry ), play lukewarm ^{TM (Flemion TM) (Asahi Glass} KK) or Gore-by Select ® (Gore-Select®) (WL Gore) [US 5,635,041; US 5,547,551; US 5,549,614, commercially available. Phase separation between the hydrophilic acid region and the hydrophobic fluorocarbon region appears to contribute to good proton conductivity in the material. See TD Gierke, GE Munn, FC Wilson, J. Polym. Sci. Polym. Phys. Ed. 1981, 19, 1687; M. Fujimura, T. Hashimoto, H. Kawai, Macromolecules, 1981, 14, 1309]. Unfortunately, at high temperatures (close to 100 ° C.) water treatment is a problem because the hydrophobicity of the fluorinated backbone of the material causes the membrane to be dehydrated quickly.

As a comparison, unfluorinated but sulfonated polymers can also exhibit good proton conductivity with less influential dehydration effect. The strong chemical structure, preferably the aromatic base structure, substantially gives the material excellent stability even at high temperatures. Valuable properties for fuel cell applications have already been demonstrated for polymers based on, for example, poly (aromatic ether ketones ([US 6,355,149]), poly (aromatic ether sulfone) or polyphenylene ([US 5,403,675]).

Certain inorganic fillers may be added to the sulfonated polymer to reduce dimensional variation between the wet and dry states of the material and to enhance moisture retention. In this case, proton conductivity is ensured by the organic phase, while the inorganic phase aids in water retention and reduces the expansion of the material ("Proceedings of 1998 Fuel Cell Seminar", November 16-19, Palm Spring, California).

The combination of advantageous properties of the inorganic and organic phases is associated with a number of developments for composites involving the formation of stable, continuous proton conductive phases. In this development, the alkoxysilane derivative is polymerized via a sol-gel or copolymerization process to lead to a silicon-oxygen based structure which is mainly three-dimensionally crosslinked [EP 1223632A2], [EP 0560899B1], [US] 6,277,304]. Composites of this kind are promising, but their formulation is not easy to control and is often difficult to achieve. In addition, this kind of structure does not readily provide some ion exchange capacity. Further simplification of the preparation of the composite may provide an interesting solution to the development of electrochemical devices such as fuel cell membranes.

Japanese Patent Application No. Hei 11-336986 [Published: June 8, 2001; Patent number 2001-155744; Applicant: Toyota Central R & D Labs, Inc. describes proton conductors based on high molecular weight electrolytes comprising functionalized silica. Mention is made of silicas functionalized with phosphonic acid groups Regarding electrolytes, there are limited descriptions as perfluoro sulfonic acid type polymers, styrene divinyl benzene sulfonic acid type polymers and styrene-ethylene-butadiene-styrene copolymers. In certain examples using sulfonated silica and perfluoro sulfonic acid polymers, the current density of the obtained film is 0.5 volts at 1 A / cm 2, but this is not satisfactory. No data have been obtained for: It is assumed that it is substantially less than the current density of the film of Example 1. Therefore, the number satisfying the current density There is a need to provide an improved membrane can be obtained.

Canadian Application No. 2,292,703 (published: June 8, 2000, Applicant: Universite Laval) describes an electrolyte membrane consisting of a polymer matrix and a filler that contributes to improving the proton conductivity of the membrane. In all examples, the polymer matrix is based on aromatic polyether ketones (PEEK) or sulfonated derivatives thereof (SPEEK), using BPO ₄ or heteropolyacids as the filler. This composite will not be time resistant as the filler gradually solubilizes into the polymer matrix.

Accordingly, there is a need for composites based on inorganic phases dispersed in a polymer matrix that can be easily produced while being resistant to time as well as providing membranes with good proton exchange capacity and good current density.

Summary of the Invention

It is an object of the present invention to solve the above mentioned problems.

It is another object of the present invention to provide an ion exchange composite that provides adequate proton exchange capacity.

It is a further object of the present invention to provide a method for producing an ion exchange composite in the form of a membrane which can be easily produced.

It is a further object of the present invention to provide a composite suitable for forming a film with good current density.

The above and other objects of the present invention

Acid functionalized silica particles,

It can be achieved by providing a composite comprising a balance comprising a polymer based on poly (aromatic ether ketone) or poly (benzoyl phenylene), or derivatives thereof, the composite being about 0.6V. A film having a current density of 1 A / cm ² or more can be provided.

The composite can be used in the form of a membrane.

The present invention relates to a composite based on proton conductive silica particles dispersed in a polymer matrix. The present invention also provides a proton ion exchange as a dry / humidified membrane or acid catalyst membrane for the control of gas or solvent in a membrane, in particular a fuel cell, which produces such composite and can be used, for example, in electrochemical devices. A method of forming a film.

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

According to a preferred embodiment, the composite of the present invention generally comprises at least about 10% by weight, preferably at least 20% by weight of functionalized silica particles.

The polymers used to make up the polymer matrix can be acid functionalized with, for example, sulfonic acid groups, carboxylic acid groups and / or phosphonic acid groups, or derivatives thereof.

The acid group is a linear or branched alkyl chain, a linear or branched aromatic chain, or a combination of linear or branched alkyl and aromatic chains into a linear or branched alkyl or aromatic chain, wherein the chain is a heteroatom and / or a halogen atom. May or may not be covalently bonded to the silica particles and / or polymers).

In the composite according to the invention, the silica particles are preferably characterized by:

i. Surface area from 10 m ² / g to 1500 m ² / g,

ii. Silica particle size of 0.01 μm to 500 μm,

iii. Silica pore diameters from 0 angstroms to 500 angstroms.

Ion exchange groups are generally present in silica particles in amounts of 0.1 to 5.0 mmol / g.

The acid groups are typically present in the polymer in varying amounts of 0 mmol / g to 5.0 mmol / g.

The membranes according to the invention are preferably for use as fuel cell, conditioning of gases or solvents for humidification or drying, or as acid catalyst membranes.

Composites can be readily prepared in the form of membranes that can be used in electrochemical devices such as proton exchange membranes for fuel cells, humidification or dry membranes for gas or solvent conditioning, and acid catalyst membranes.

When the silica particles are functionalized with acid residues and dispersed within the polymer matrix, they constitute an inorganic hydrophilic phase with proton exchange capacity. The organic phase comprising the polymer matrix may contain ion exchange groups bonded to the polymer's chemical structure to enhance the proton conductivity of the composite or ion exchange groups initially present in the polymer's chemical structure. Proton exchange capacity is achieved by both the functionalized polymer matrix and the dispersed silica particles.

Several functional groups are suitable for providing proton exchange capacity to the composite. Preferred functional groups are acid groups, more preferably sulfone groups (-SO ₃ H). Other acid groups can also be transferred to the chemical structure to provide interesting proton conductivity such as carboxyl (-CO ₂ H) or phosphonic (-PO ₃ H ₂ ) acid groups.

Ion exchange groups are preferably covalently bonded to the chemical structure of the organic and inorganic phases. Chemical bonds preferably consist of alkyl or aromatic chains or combinations thereof, linear or branched, and may finally contain some heteroatom or a halogen atom.

As described above, various kinds of silica can be used for the formation of the inorganic phase in the composite. Preferred silicas are porous silicas, but other forms may include, but are not limited to, amorphous silicas, fumed silicas, spherical silicas, irregular silicas, structured silicas, molecular sieve silicas, silesquinoxane derivatives, and mixtures thereof. . The amount of silica particles and their average size play an important role in the formation of continuous hydrophilic phases and the mechanical properties of the material.

Among the class of poly (aromatic ether ketones) preferred polymers are poly (oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl, prepared by Victrex, UK) -1,4-phenylene) (PEEK).

The glass transition temperature of PEEK is generally about 200 ° C., which has the desired heat and chemical resistance leading to strong composites.

Sulfonation is a common method of modifying polymer structure by implanting sulfonic acid groups that give proton exchange capacity to sulfonated materials. Proton mobility depends on the amount and dispersion of acid groups in the material.

Several studies have widely used sulfonation of this kind of structure. One of the most suitable sulfonation methods used in the present invention is sulfonation in concentrated H ₂ SO ₄ as described in EP 8895 and later (Br.Polym.J., Vol. 17, 1985, p.4). . This sulfonation reaction is less damaging to the polymer than the chlorosulfonation process because no significant chain cleavage or collapse occurs. Once sulfonated the polymer, the corresponding formula for sulfonated PEEK is generally as follows:

The degree of sulfonation corresponds to x / n, where x corresponds to the number of repeat units containing one sulfonic acid group. Therefore, 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 capacity (IEC) of the polymer. For example, 100% sulfonated PEEK has an IEC of 2.9 mmol / g.

The amount of sulfonic acid groups bonded to the aromatic ring depends on a number of 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 coefficient of expansion, depend on its rate of sulfonation, ie its ion exchange capacity.

For the inorganic phase, the use of silica functionalized with sulfonic acid groups not only provides the benefits of proton conductivity but also provides better efficacy in water retention than nonfunctionalized silica. Typically the moisture retention of acid silica is two times higher than that of conventional silica. For example, the moisture retention of acid silica is about 30% compared to 15% of conventional silica in an environment of 70% relative humidity.

The structure of the silica also plays an important role in water retention. For example, low bulk density structures increase water retention compared to high bulk density silicas primarily due to their high specific area. Typically, low bulk density structures can receive twice as much moisture as high bulk density structures. For example, the moisture retention of silica with low bulk density structure is about 15% compared to 7% for silica with high bulk density structure under 70% relative humidity. Moreover, the large surface area as encountered in low bulk density structures improves the loading of acid functional groups in inorganic compounds. For example, the loading of functionalized low bulk density silica is generally 1.7 mmol / g, which is generally doubled to 0.9 mmol / g for porous high bulk density silica.

Low bulk density sulfonic acid silicas can generally be prepared via a co-condensation process as described in Chem. Mater. 2000, Vol. 12, p. 2448. In addition, sulfonic acid groups can be grafted on high bulk density silica using, for example, the methods described in J. Chromato. 1976, Vol. 117, p. 269. Several bonding types are possible for bonding sulfonic acid groups to silica particles. In the present invention, the bonding is preferably made by a propylphenyl chain, but not limited thereto. Such bonds may also include any alkyl derivative or aromatic derivative and combinations thereof, with or without heteroatoms and / or halogens in the chemical structure.

The composite is made by adding acid silica particles to the polymer matrix and mixing the two homogeneously. The preferred method proceeds through a polymer solution to which silica suspension or silica particles in the same solvent or miscible solvent of the polymer solution is added. The suspension is then homogenized, then spread out to a uniform thin layer and dried. In addition, satisfactory mixtures can be obtained without using a solvent, such as a melt phase substrate process.

The mechanical properties of the composite depend mainly on the properties on the polymer matrix and on the silica content. The mechanical properties determine the lowest value of the film thickness that can be manipulated without breaking. Overly rigid polymers do not break and do not allow thin films to be sufficiently deformed, and overly soluble structures do not have composites in the form of thin films. Equally, too many inorganic particles interfere with good tear resistance, making the film very brittle.

The solubility properties of the composites depend in particular on the properties of the polymer matrix. As mentioned above, the solubility of the polymer depends on the temperature and the ion exchange capacity. The maximum temperature at which the composite can be used in certain liquids, such as water for hydration, is directly related to the solubility properties of the polymer. A sufficient amount of silica in the composite, which can vary from 10 to 30% by weight, improves the proton conductivity to an extent that depends on the density of the corresponding silica used.

In the present invention, a number of parameters can be easily changed to adjust the properties of the final composite. In general, the following parameters should be considered in the formulation of the composite: solvent solubility, temperature of use, thickness of the composite in the final form and expected ion exchange values. The corresponding sulfonation rate of the polymer matrix is then determined. The properties of the silica are then evaluated taking into account the porosity requirements, which mainly depend on the desired acid loading and water retention.

Brief description of the drawings

The invention is illustrated by the accompanying drawings.

1 is a polarization curve of current density versus voltage of a film according to the present invention.

The invention is also illustrated by the following non-limiting examples.

Example 1

Sulfonation of PEEK

55% sulfonated SPEEK was obtained, for example, by stirring 50 g PEEK in ₂ L of H ₂ SO ₄ (95-98% in H ₂ O) at room temperature for 48 hours. The solution was poured into H ₂ O and the solid corresponding to sulfonated PEEK (SPEEK) was washed vigorously two or three times in 5 L of pure water. The separated solid was first dried overnight in an oven at about 70 ° C., then washed again and then dried at 100 ° C. for several days under vacuum. About 40 g of SPEEK was obtained (yield about 80%). Basic analysis yielded the sulfur content of the sulfonated polymer and calculated the corresponding ion exchange capacity (IEC). An IEC of 1.6 ± 0.1 mmol / g was obtained, which corresponds to a sulfonation rate of about 55%.

Example 2

Composite film formulation

a) 1 g of 55% sulfonated PEEK (SPEEK55) was dissolved in 10 ml of dimethylformamide (DMF) at room temperature and filtered over filter paper. A suspension of 0.2707 g of sulfonic acid grafted silica in 2 ml of DMF was added to the clear polymer solution. After stirring, the homogeneous mixture was spread on a 385 cm ² glass plate and dried at 70 ° C. for several days. After the solvent was completely evaporated, the glass plate was immersed in water to remove the film. After drying, the thickness of the composite film consisting of 80% by weight 55% sulfonated PEEK and 20% by weight acid silica was 40 ± 10 μm.

b) 0.1755 g of SPEEK55 was dissolved in 1.7 ml of DMF and filtered. 0.0195 g of sulfonic acid grafted silica was added to the polymer solution. After homogenization, the mixture was spread on a 25 cm ² glass plate. After drying, the thickness of the composite film consisting of 90% by weight 55% sulfonated PEEK and 10% by weight acid silica was 50 μm.

Example 3

Electrode Deposition on Composite Films for Fuel Cell Testing

A commercially available Pt / C electrode (Pt / Vulcan XC-72 from ElectroChem Inc.) is fixed on the composite film, with a small amount of SPEEK55 10% DMF solution on one side of the two electrodes. (w / v) was applied to fix the film on the composite film by sandwiching the membrane between the two electrodes. The assembly was dried for one day at room temperature under vacuum, overnight at 60 ° C. under vacuum, and for several days at 80 ° C.

Example 4

Performance Comparison

The performance obtained by the membrane according to the invention was compared with the performance obtained by the membrane according to JP 2001-155744 (Example 1).

The composite of the Japanese reference patent contains an inorganic phase mixed in 5% (w / v) polymer solution. The inorganic phase is fumed silica grafted with phenylsilane as binder, which is then reacted with H ₂ SO ₄ cc. The organic phase is a binder of the inorganic phase. In this case, Nafion®, ie perfluorinated polymer containing sulfonic acid groups, are used. For the experiment, the fuel cell was operated at 80 ° C. under 22 psig H ₂ / air. Under a voltage of 0.6V to 0.7V, the fuel cell is a stylized create a current density of 0.5A / cm ^2, 0.5V was produced under the 1A / cm ^2. It can be noted that the membrane according to the Japanese reference patent contains 1% by weight of silica, while the membrane according to the present invention contains 20% by weight of silica.

The composite according to the invention contains the inorganic phase mixed in the polymer solution in an amount of 10% (w / v). The inorganic phase contains silica which is obtained by cocondensation and functionalized by chlorosulfonation. The organic phase is SPEEK. For the experiment, the fuel cell was operated at 75 ° C. under 20/30 psig H ₂ / air. Under a voltage of 0.7 V, the fuel cell produced a current density of 1 A / cm ² , produced 1.7 A / cm ² to 1.8 A / cm ² under a voltage of 0.6 V, and 2.2 A / under a voltage of 0.5 V cm ² to 2.3 A / cm ² were produced.

Under similar operating conditions, the present invention produced a much higher current density than the current density of the Japanese patent, which results in that the material used contains 20 mmoles of sulfonic acid groups per g produced as in Example 1. It can be seen from FIG. 1, which is made of wt% silica and 80 wt% SPEEK55.

It is to be understood that the invention is not limited to the above embodiments, and that many variations are possible within the scope of the appended claims.

Claims (21)

Acid functionalized silica particles, and A composite comprising a residue comprising a polymer based on poly (aromatic ether ketone) or poly (benzoyl phenylene), or derivatives thereof, A composite, characterized in that it can provide a film with a current density of about 1 A / cm ² or more under 0.6V. The composite of claim 1 wherein the functionalized silica particles are dispersed in a polymer matrix. The composite according to claim 1, wherein the functionalized silica particles are functionalized with sulfonic acid, carboxylic acid and / or phosphonic acid groups. The composite of 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 of claim 5 comprising at least about 20% by weight acid functionalized silica particles. The composite of claim 1 wherein the polymer is acid functionalized. 8. The composite of claim 7, wherein the polymer is functionalized with sulfonic acid, carboxylic acid and / or phosphonic acid groups, or derivatives thereof. 9. A composite according to claim 2 or 8, wherein the acid groups are covalently bonded to the silica particles and / or polymers. 10. The aromatic group according to claim 9, wherein the acid group is shared via an aromatic chain with a linear or branched alkyl chain, a linear or branched aromatic chain, or a combined alkyl chain which is linear or branched by a linear or branched alkyl chain or aromatic chain. And wherein the chain optionally comprises heteroatoms and / or halogen atoms. The method of claim 1 wherein the silica particles i. Surface area from 10 m ² / g to 1500 m ² / g, ii. Silica particle size of 0.01 μm to 500 μm, iii. A composite characterized by a silica pore diameter of 0 angstroms to 500 angstroms. The composite of claim 1 wherein the ion exchange groups are present in the silica particles in an amount of 0.1 to 5.0 mmol / g. 8. A composite according to claim 7, wherein the ion exchange groups are present in the silica particles in an amount of 0 to 5.0 mmol / g. The method of claim 1 wherein the silica particles are amorphous silica or derivatives thereof, fumed silica or derivatives thereof, spherical silica or derivatives thereof, porous irregular silica or derivatives thereof, porous structured silica or derivatives thereof, irregular porous molecular sieve silica or A composite material, characterized in that it is selected from the group consisting of derivatives thereof, spherical polyfunctional molecular sieve silica or derivatives thereof and silesquinoxane compounds or derivatives thereof. The composite of claim 1 wherein the polymer is a poly (aryl ether ketone) (PEEK) or derivative thereof. The composite of claim 1 wherein the polymer is poly (benzoyl phenylene) (PBP) or a derivative thereof. A membrane comprising the composite according to claim 1. 18. The membrane of claim 17 used in a fuel cell. 18. The membrane of claim 17, wherein the membrane is used for humidification or drying. 18. The membrane of claim 17, wherein the membrane is used for conditioning a gas or a solvent. 18. The membrane according to claim 17, which is used as an acid catalyst membrane.