YAMADA, Kenji (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
KUMAGAI, Mamiko (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
KUMAGAI, Kyoko (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
KAKEGAWA, Norishige (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
YAMAUCHI, Kazuhiro (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
YAMADA, Kenji (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
KUMAGAI, Mamiko (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
KUMAGAI, Kyoko (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
KAKEGAWA, Norishige (30-2 Shimomaruko 3-chome, Ohta-k, Tokyo 01, 14685, JP)
CLAIMS
1. Ion conductive materials each comprising: an inorganic layered structure including multiple layers made of an inorganic compound; and ion exchange groups bound with the inorganic layered structure, wherein the ion exchange groups are bound with every face of each of the multiple layers made of an inorganic compound. 2. The ion conductive materials according to claim 1, wherein the inorganic layered structure is made of magadiite, kenyaite or kanemite.
3. The ion conductive materials according to claim 1 or 2, wherein the ion exchange groups are sulfonic groups, carboxylic groups, phosphoric groups, phosphoric groups, or phosphonous groups.
4. An ion conducting polymer composite membrane, comprising: the ion conductive materials according to any one of claims 1 to 3; and an ion conducting polymer membrane.
5. A membrane electrode assembly, comprising: the ion conducting polymer composite membrane according to claim 4; and two catalyst layers that are in contact with the ion conducting polymer composite membrane.
6. A fuel cell, comprising: the membrane electrode assembly according to claim 5; two gas diffusion layers that are in contact with the membrane electrode assembly; and two collectors that are respectively in contact with the two gas diffusion layers.
7. A method of producing the ion conductive materials' according to claim 1, which comprises replacing with ion exchange groups protons of silanol groups on all the faces of multiple layers of each of inorganic layered structures made of an inorganic compound, with every face of each of the multiple layers having at least one silanol groups, to bind the ion exchange groups with the inorganic layered structures .
8. The method of producing the ion conductive materials according to claim 7, wherein replacing protons of the silanol groups with the ion exchange groups to bind the ion exchange groups with the inorganic layered structures comprises silylating the silanol groups to oxidize the silylated silanol groups. 9. A method of producing an ion conducting polymer composite membrane, comprising:
(i) replacing with ion exchange groups protons of silanol groups on all the faces of multiple layers of each of inorganic layered structures made of an inorganic compound, every face of each of the multiple layers having at least one silanol group, to bind the ion exchange groups with the inorganic layered structures, thereby forming ion conductive materials; and
(ii) dispersing the ion conductive materials in the ion conducting polymer membrane. |
DESCRIPTION
ION CONDUCTIVE MATERIAL, ION CONDUCTING POLYMER COMPOSITE MEMBRANE, MEMBRANE ELECTRODE ASSEMBLY, FUEL CELL, METHOD OF PRODUCING ION CONDUCTIVE MATERIAL, AND METHOD OF PRODUCING ION CONDUCTING POLYMER COMPOSITE MEMBRANE
TECHNICAL FIELD
The present invention relates to ion conductive materials, an ion conducting polymer composite membrane, a membrane electrode assembly, a fuel cell, a method of producing the ion conductive materials, and a method of producing an ion conducting polymer composite membrane.
BACKGROUND ART
As a method of improving gas barrier performance of an ion conducting polymer membrane such as a Nafion membrane (registered trade mark, manufactured by Dupont Co., Ltd.), Japanese Patent Application Laid-Open No. 2006- 327932 describes a technology of dispersing, in an ion conducting polymer membrane, ion conductive materials obtained by utilizing silanol groups of inorganic layered structures to bind sulfonic groups with the inorganic layered structures. However, in Japanese Patent Application Laid-Open No. 2006-327932, montmorillonite having silanol groups only on the end faces thereof is used as an inorganic layered
compound. Therefore, as illustrated in FIG. 1, sulfonic groups are bound with only the end faces of the inorganic layered compound, and hence, the proton conductivity of an ion conducting polymer composite membrane to be obtained is not sufficient.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an ion conducting polymer composite membrane having both a high gas barrier property and high proton conductivity, a membrane electrode assembly and a fuel cell using the ion conducting polymer composite membrane, ion conductive materials for forming the ion conducting polymer composite membrane, a method of producing ion conductive materials, and a method of producing an ion conducting polymer composite membrane.
A first aspect of the present invention relates to ion conductive materials each including: an inorganic layered structure including multiple layers made of an inorganic compound; and ion exchange groups bound with the inorganic layered structures, wherein the ion exchange groups are bound with every face of each of the multiple layers made of an inorganic compound.
A second aspect of the present invention relates to an ion conducting polymer composite membrane, including:
the ion conductive materials; and an ion conducting polymer membrane.
A third aspect of the present invention relates to a membrane electrode assembly, including: the ion conducting polymer composite membrane; and two catalyst layers that are in contact with the ion conducting polymer composite membrane.
A fourth aspect of the present invention relates to a fuel cell including: the membrane electrode assembly; two gas diffusion layers that are in contact with the membrane electrode assembly; and two collectors that are respectively in contact with the two gas diffusion layers. A fifth aspect of the present invention relates to a method of producing the ion conductive materials, which includes replacing with ion exchange groups protons of silanol groups on all the faces of multiple layers of each of the inorganic layered structures made of an inorganic compound, with every face of each of the multiple layers having at least one silanol group, to bind the ion exchange groups with the inorganic layered structures.
A sixth aspect of the present invention relates to a method of producing an ion conducting polymer composite membrane, including:
(i) replacing with ion exchange groups protons of silanol groups on all the faces of multiple layers of each
of the inorganic layered structures made of an inorganic compound, with every face of each of the multiple layers having at least one silanol group, to bind the ion exchange groups with the inorganic layered structures, thereby forming ion conductive materials; and
(ii) dispersing the ion conductive materials in an ion conducting polymer membrane.
The present invention can provide an ion conducting polymer composite membrane having both a high gas barrier property and high proton conductivity, a membrane electrode assembly and a fuel cell using the ion conducting polymer composite membrane, ion conductive materials for forming the ion conducting polymer composite membrane, a method of producing ion conductive materials, and a method of producing an ion conducting polymer composite membrane.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating an ion conductive material described in Japanese Patent Application Laid-Open No. 2006-327932;
FIG. 2 is a schematic view illustrating an example of an ion conductive material according to the present invention;
FIG. 3 is a schematic view illustrating an example of a layer made of an inorganic compound of the present invention;
FIG. 4 is a schematic view illustrating an example of
a membrane electrode assembly according to the present invention;
FIG. 5 is a schematic view illustrating an example of a fuel cell according to the present invention; and FIGS. 6A and 6B are schematic views illustrating an example of a method of producing an ion conductive materials according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention is described in detail with reference to the drawings.
The first aspect of the present invention relates to ion conductive materials each including: an inorganic layered structure including multiple layers made of an inorganic compound; and ion exchange groups bound with the inorganic layered structure, wherein the ion exchange groups are bound with every face of each of the multiple layers made of an inorganic compound.
FIG. 2 is a view illustrating an ion conductive material according to the first aspect of the present invention. In FIG. 2, reference numeral 2 denotes a layer made of an inorganic compound, and ion exchange groups A are bound with the faces of the layers 2 made of an inorganic compound. An inorganic layered structure 3 is an aggregate of the layers 2 made of an inorganic compound,
and reference numeral 1 denotes an ion conductive material. In FIG. 2, the ion conductive material 1 is composed of two layers made of an inorganic compound, with which the ion exchange groups A are bound. However, the ion conductive material 1 may be composed of two or more layers made of an inorganic compound, with which the ion exchange groups A are bound.
The ion exchange groups A are bound with every face of each of the layers 2 made of an inorganic compound. In other words, at least one ion exchange group A is bound with each of the faces of the layers 2 made of an inorganic compound. Specifically, in the case where a layer made of an inorganic compound has a rectangular solid as illustrated in FIG. 3, at least one ion exchange group A is bound with each of all the faces (6 faces) including principal faces 4 and 5 and the end faces 6 and 7. Herein, the principal faces refer to two faces having the largest areas among the faces of the rectangular solid, and the end faces refer to two faces having the smallest areas. In the case where a layer made of an inorganic compound is not a complete rectangular solid, a rectangular solid circumscribed by the layer is assumed, and a portion of the layer on which light is projected at the time of externally irradiating each of the faces of the rectangular solid with light at right angles thereto, is defined as the face of the layer.
The inorganic layered structure is an aggregate of
layers made of an inorganic compound, and includes multiple layers made of an inorganic compound. In the present invention, an inorganic compound refers to a compound containing no carbon, an allotrope of carbon such as graphite and diamond, carbon monoxide, carbon dioxide, or a metal carbonate such as calcium carbonate, hydrocyanic acid and metal cyanide, metal cyanate, and a metal thiocyanate.
In the present invention, the "layer" has an aspect ratio of at least 20. Further, the aspect ratio of a structure a is defined as (length of a line segment (A) having the largest length among line segments which can be present in the structure a) /(length of a line segment (B) having the largest length among line segments which can be present in the structure a at right angles to the line segment (A) ) . The length of the line segment (A) and the length of the line segment (B) can be found by measuring a layer made of a peeled inorganic layered compound by means of a transmission electron microscope (TEM) or an atomic force microscope (AFM) , and the length of the line segment (B) can be inferred from the chemical structure of an inorganic layered compound.
Examples of the inorganic layered structure include magadiite, kenyaite, and kanemite. Among these, magadiite is preferably used because its structure is highly stable. The inorganic layered structure generally has a configuration in which layers negatively charged made of an inorganic compound are stacked at certain intervals when
the shortage of charges is supplemented with cations present between the layers. The ion exchange groups A are bound with the faces of the layers 2 made of an inorganic compound through covalent bonds. In the present invention, the ion exchange group refers to an ion dissociative functional group, and examples thereof include sulfonic acid, carboxylic acid, phosphoric acid, phosphonic acid, and phosphonous acid. As long as at least one ion exchange group is bound with any face of the layer made of an inorganic compound, all the ion exchange groups A need not necessarily be of the same type, and ion exchange groups of different types may be present.
Next, the second aspect of the present invention is described. The second aspect of the present invention relates to an ion conducting polymer composite membrane including: the ion conductive materials according to the first aspect of the present invention; and an ion conducting polymer membrane. The ion conducting polymer membrane is formed of a polymer compound having ion exchange groups, and can hold the ion conductive materials according to the first aspect of the present invention. The ion conductive materials are preferably dispersed in an ion conducting polymer membrane. The following may be used for the ion conducting polymer membrane: for example, a perfluorosulfonic acid polymer such as Nafion (registered trade mark) , a compound
having an ion exchange group such as polyamide, polyamide- imide, polyimide, polyether ketone, polyether ether ketone, polyphenylene, polyphenylene ether, polyester, polycarbonate, polyethylene, polypropylene, polyester, polystyrene, polyacetal, polysulfone, a poly (meth) acrylic acid derivative, and a block copolymer including ion conducting blocks and non-ion conducting blocks.
The ion conductive materials used in the present invention swell upon absorbing water molecules between the layers, and therefore, when an electrolyte membrane containing a great amount of the ion conductive materials is used as a fuel cell, the output may be decreased. Thus, the content of the ion conductive materials is 50% by weight or less, preferably 30% by weight or less, and more preferably 10% by weight or less based on the weight of the ion conducting polymer composite membrane.
As the ion conductive materials contained in the ion conducting polymer composite membrane, ion conductive materials of one type or plural types may be used. The third aspect of the present invention relates to a membrane electrode assembly including: the ion conducting polymer composite membrane according to the second aspect of the present invention; and two catalyst layers that are in contact with the ion conducting polymer composite membrane.
FIG. 4 illustrates the third aspect of the present
invention.
A membrane electrode assembly 11 according to the third aspect of the present invention includes an ion conducting polymer composite membrane 8 and two catalyst layers 9 and 10 that are in contact with the ion conducting polymer composite membrane 8.
The two catalyst layers 9 and 10 (an anode-side catalyst layer 9 and a cathode-side catalyst layer 10) may each be formed from structures composed of a metal catalyst such as platinum or an alloy catalyst of platinum and metal other than platinum such as ruthenium, or a layer in which such structures are dispersed and carried on a carrier such as carbon. The structures usable for the catalyst layers may have a particulate shape or shapes other than a particulate shape, such as a dendritic shape.
When the membrane electrode assembly according to the third aspect of the present invention is formed, it is preferred that the ion conducting polymer composite membrane 8 is sandwiched between the catalyst layers 9 and 10 and subjected to hot pressing at a temperature of 130 to
150° under a pressure in a range of 1 to 40 MPa for a pressurizing time of 1 to 30 minutes.
Next, the fourth aspect of the present invention is described. The fourth aspect of the present invention relates to a fuel cell including: the membrane electrode assembly according to the
third aspect of the present invention; two gas diffusion layers that are in contact with the membrane electrode assembly; and two collectors that are respectively in contact with the two gas diffusion layers.
FIG. 5 is a cross-sectional view illustrating an exemplary fuel cell according to the fourth aspect of the present invention. The fuel cell includes the membrane electrode assembly 11 according to the third aspect of the present invention, an anode-side gas diffusion layer 14, a cathode-side gas diffusion layer 15, an anode-side collector 16, and a cathode-side collector 17.
The anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15 play a role of supplying oxygen or fuel to the membrane electrode assembly 11. It is preferred that the anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15 are composed of multiple sub-layers. In the case where the anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15 are composed of multiple sub-layers, it is preferred that among the sub-layers of the anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15, the sub-layers in contact with the membrane electrode assembly 11 have pores whose average diameter is smaller than that of pores of the other sub-layers.
Specifically, in the case where the gas diffusion layer is composed of two sub-layers, as illustrated in FIG. 5, it is
preferred that among the sub-layers of the anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15, the sub-layers 12 in contact with the membrane electrode assembly 11 are set to have pores whose average diameter is smaller than that of holes of the other sublayers 13.
In the case where, among the sub-layers of the anode- side gas diffusion layer 14 and the cathode-side gas diffusion layer 15, the sub-layers in contact with the membrane electrode assembly 11 have pores whose average diameter is smaller than that of pores of the other sublayers, the sub-layers in contact with the membrane electrode assembly 8 is hereinafter referred to as a microporous layer (MPL) in some cases. The MPL can be composed of, for example, carbon fine particles using PTFE as a binder. Examples of the carbon fine particles include acetylene black, Ketjen black, fibrous carbon formed by vapor-phase growth, and carbon nanotube. In a portion other than the MPL among the sub-layers constituting the anode-side gas diffusion layer 14 and the cathode-side gas diffusion layer 15, carbon cloth, carbon paper, porous metal, etc. may be used. Further, a gas diffusion layer with a configuration composed of three sub- layers may be used, which may be formed by stacking the MPL and two or more of carbon cloth, carbon paper, porous metal, etc., or superimposing on the MPL two or more times one of
carbon cloth, carbon paper, porous metal, etc. In the case of using a metal material for the sub-layers, it is preferred to use a material excellent in oxidation resistance. Specifically, SUS316L, a nickel-chromium alloy, titanium, etc. may be used. As the porous metal of the nickel-chromium alloy, CELLMET (registered trade mark) manufactured by Sumitomo Electric Toyama Co., Ltd. may be used.
As the materials for the anode-side collector 16 and the cathode-side collector 17, materials excellent in conductivity and oxidation resistance are used. Examples of such materials include platinum, titanium, carbon, stainless steel (SUS) , SUS coated with gold, SUS coated with carbon, aluminum coated with gold, and aluminum coated with carbon.
Next, the fifth aspect of the present invention is described.
The fifth aspect of the present invention relates to a method of producing the ion conductive materials, which includes replacing with ion exchange groups protons of silanol groups on all the faces of multiple layers of each of the inorganic layered structures made of an inorganic compound, with every face of each of the multiple layers having at least one silanol group, to bind the ion exchange groups with the inorganic layered structures.
Hereinafter, the fifth aspect of the present invention is described with reference to FIGS. 6A and 6B.
An inorganic layered structure illustrated in FIG. 6A includes multiple layers made of an inorganic compound having silanol groups on all the faces thereof. The inorganic layered structures each including multiple layers made of an inorganic compound having silanol groups on all the faces thereof are the same as the inorganic layered structures according to the first aspect of the present invention, except for having silanol groups instead of ion exchange groups . An example of the method of replacing protons of silanol groups of a inorganic layered structure with ion exchange groups A to thereby bind the ion exchange groups with the inorganic layered structure includes the following method. For example, the silanol groups of the inorganic layered structure are silylated with a silane compound having the ion exchange groups A or a silane compound having groups which are converted into the ion exchange groups A by oxidation, and the ion exchange groups are bound or the groups to be converted into the ion exchange groups by oxidation are bound and oxidized. Thus, as illustrated in FIG. 6B, an ion conductive material that is the inorganic layered structure with which the ion exchange groups A are bound can be obtained.
More specifically, for example, silanol groups of the inorganic layered structure are allowed to react with a silane compound having mercapto groups such as (3- mercaptopropyl) trimethoxysilane in an organic solvent,
thereby obtaining an inorganic layered structure with which mercapto groups are bound. Then, the mercapto groups are sulfonated with an oxidizer such as hydrogen peroxide, whereby an inorganic layered structure with which sulfonic groups that are ion exchange groups are bound can be obtained.
FIG. 6A is a schematic view illustrating as terminal groups only OH groups of silanol groups, and FIG. 6B is a schematic view illustrating as terminal groups only the ion exchange groups A in the case where the silanol groups are silylated.
In such a case, in order to carry out silylation of the silanol groups in an organic solvent, it is necessary to subject the inorganic layered material to hydrophobic treatment. When metal ions are present between the layers of the inorganic layered structure, the inorganic layered structure can be subjected to hydrophobic treatment easily by replacing metal ions with a surfactant.
Examples of the surfactant that may be used in hydrophobic treatment include amine-type surfactants such as propyl amine, octyl amine, and dodecyl amine and quaternary ammonium salt-type surfactants such as dodecyltrimethylammonium bromide, cetyltrimethylammonium bromide, and stearyltrimethylammonium bromide. The sixth aspect of the present invention relates to a method of producing an ion conducting polymer composite membrane, including:
(i) replacing with ion exchange groups protons of silanol groups on all the faces of multiple layers of each of the inorganic layered structures made of an inorganic compound, with every face of each of the multiple layers having at least one silanol group, to bind the ion exchange groups with the inorganic layered structure, thereby forming ion conductive materials; and
(ii) dispersing the ion conductive materials in an ion conducting polymer membrane. The step of (i) is the same as the step of the fifth aspect of the present invention, and thus the step (ii) is described.
As a method of dispersing the ion conductive materials obtained in the step (i) in the ion conducting polymer membrane, for example, the following methods may be used.
In the first method, the ion conductive materials obtained in the step (i) are dispersed in a solution of a monomer to be formed into the ion conducting polymer membrane to prepare a solution (a) , the monomer in the solution (a) is polymerized, and the resultant is applied to a substrate surface to form a membrane.
The polymerization is not particularly limited as long as the polymerization is not terminated by the ion exchange groups of the inorganic layered structure. For example, radical polymerization that proceeds without being influenced by the ion exchange groups is preferred. As a
radical polymerization initiator, the following may be used: a peroxide-type polymerization initiator such as benzoyl peroxide or an azo-type polymerization initiator such as azobisisobutyronitrile . A solvent for the solution (a) may be one that can disperse the inorganic layered structures and monomer, and for example, the following may be used: N-dimethylformamide (DMF) , N-methyl-2-pyrrolidone (NMP) , dimethylsulfoxide (DMSO) , γ-butyrolactone, tetrahydrofuran, 1,4-dioxane, dichloromethane, chloroform, 1, 2-dichloroethane, chlorobenzene, dichlorobenzene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, methanol, ethanol, propanol, or a mixed solvent obtained by mixing two or more of these solvents. The solution (a) after the termination of the polymerization reaction may be applied directly to the surface of a substrate. Alternatively, after the solution (a) is purified and collected, a solution obtained by re- dispersing the solution (a) in a solvent may be applied to the substrate surface. As a method of applying the solution (a) to the surface of a substrate, the following may be used: a bar coating method, a gravure coating method, a spin coating method, a dip coating method, a roll coating method, a spraying method, a casting method, etc. In the second method, the ion conducting polymer and ion conductive materials constituting the ion conducting polymer composite membrane are kneaded mechanically at a
temperature equal to or higher than the glass transition temperature of the ion conducting polymer, and the product thus obtained is applied to the substrate surface to form a membrane. In the third method, a solution (b) is prepared by dispersing the ion conductive materials in a solution including the ion conducting polymer, and the solution (b) is applied to a substrate surface to form a membrane.
As the method of applying the solution (b) to the substrate surface, the following may be used a bar coating method, a gravure coating method, a spin coating method, a dip coating method, a roll coating method, a spraying method, a casting method, etc.
As a solvent for the solution (b) , a solvent may be used which is the same as the solvent used in the first method for the solution including a monomer to be formed into an ion conducting polymer membrane.
When ion conductive materials are dispersed in a solution including the ion conducting polymer, an ultrasonic washing machine or a homogenizer may be used. By using any one of those, the dispersion of the ion conductive materials in the solution (b) can be improved. Further, the dispersion state of the ion conductive materials in the ion conducting polymer composite membrane can be confirmed easily by observation of an ultra thin slice of the membrane with a transmission electron microscope (TEM) .
Examples
Hereinafter, the present invention is described specifically by way of examples. It should be noted that the present invention is not limited to those examples. (Synthesis Example 1) Production of H-montmorillonite As clay mineral containing hydrated aluminum silicate as a main component, 5 g of montmorillonite produced in Tsukinuno, Yamagata prefecture was stirred in 500 ml of IN hydrochloric acid for 24 hours. After the reaction, centrifugation was carried out at 10,000 rpm for 15 minutes, the supernatant liquid was removed, and the resultant was dispersed in water again. Reprecipitation by centrifugation and washing with water were repeated twice, whereby H-montmorillonite was produced in which sodium ions present between the layers of montmorillonite were replaced by protons.
(Synthesis Example 2) Production of magadiite Twenty grams of silica gel (Wakogel Q63, manufactured by Wako Pure Chemical Industries, Ltd.), 3.07 g of sodium hydroxide, and 111 g of pure water were sealed in a sealed container made of PTFE and reacted at 150°C for 48 hours under the hydrothermal condition to synthesize magadiite. (Synthesis Example 3) Production of kenyaite Twenty grams of silica gel (Wakogel Q63, manufactured by Wako Pure Chemical Industries, Ltd.), 3.07 g of sodium hydroxide, and 111 g of pure water were sealed in a sealed container made of PTFE and reacted at 200 0 C for 6 hours
under the hydrothermal condition to synthesize kenyaite.
(Synthesis Example 4) Production of sulfonated magadiite
To a mixed solution of 1.8 ml of water, 100 μl of 35% hydrochloric acid and 10 ml of ethanol, 2 ml of mercaptopropyl trimethoxysilane was dropwise added, followed by stirring at 5O 0 C for one hour. The resultant solution was mixed with a solution obtained by dispersing 10 g of the magadiite synthesized in Synthesis Example 2 into 60 ml of ethanol, followed by stirring at 70° for 13 hours. Ten grams of magadiite having mercapto groups thus synthesized is stirred in a mixed solution of 40 ml of ethanol and 10 ml of hydrogen peroxide at 70°C for 2 hours, whereby the mercapto groups were replaced with sulfonic groups to produce sulfonated magadiite.
(Synthesis Example 5) Production of sulfonated kenyaite
To a mixed solution of 1.8 ml of water, 100 μl of 35% hydrochloric acid and 10 ml of ethanol, 2 ml of mercaptopropyl trimethoxysilane was dropwise added, followed by stirring at 50 0 C for one hour. The resultant solution was mixed with a solution obtained by dispersing 10 g of the kenyaite synthesized in Synthesis Example 3 into 60 ml of ethanol, followed by stirring at 70° for 13 hours. Ten grams of magadiite having mercapto groups thus synthesized is stirred in a mixed solution of 40 ml of ethanol and 10 ml of hydrogen peroxide at 70°C for 2 hours,
whereby the mercapto groups were replaced with sulfonic groups to produce sulfonated magadiite.
(Synthesis Example 6) Production of sulfonated montmorillonite To a mixed solution of 1.8 ml of water, 100 μl of 35% hydrochloric acid and 10 ml of ethanol, 2 ml of mercaptopropyl trimethoxysilane was dropwise added, followed by stirring at 50°C for one hour. The resultant solution was mixed with a solution obtained by dispersing 10 g of the montmorillonite produced in Tsukinuno into 60 ml of ethanol, followed by stirring at 70° for 13 hours. Ten grams of montmorillonite having mercapto groups thus synthesized was stirred in a mixed solution of 40 ml of ethanol and 10 ml of hydrogen peroxide at 70°C for 2 hours, whereby the mercapto groups were replaced with sulfonic groups to produce sulfonated montmorillonite.
(Example 1) Nafion/sulfonated magadiite composite membrane
A Nafion solution (5% by weight) was prepared. Then, the sulfonated magadiite obtained in Synthesis Example 4 was dispersed in the Nafion solution to prepare a mixed solution containing Nafion and sulfonated magadiite in a weight ratio of 90:10. Then, the sulfonated magadiite was further thoroughly dispersed in the mixed solution using an ultrasonic washing machine. The mixed solution was formed into a membrane by a solvent casting method in a nitrogen atmosphere. The thickness of the membrane thus obtained
was 40 μm.
Alternating current impedance measurement (voltage amplitude: 5 mV; frequency: 1 Hz to 1 MHz) was conducted by a four-terminal method, and the conductivity in the membrane surface direction of the ion conducting polymer composite membrane was calculated from the obtained resistance. As a result, the ion conductivity at a temperature of 50°C and a relative humidity of 50% was 3.12 χ lO "2 S-crrf 1 . (Example 2) Nafion/sulfonated kenyaite composite membrane
A 5% by weight of a Nafion solution was prepared. Then, the sulfonated kenyaite obtained in Synthesis Example 5 was dispersed in the Nafion solution to prepare a mixed solution containing Nafion and sulfonated magadiite in a weight ratio of 90:10. Then, the sulfonated kenyaite was further thoroughly dispersed in the mixed solution using an ultrasonic washing machine. The mixed solution was formed into a membrane by a solvent casting method in a nitrogen atmosphere. The thickness of the membrane thus obtained was 40 μm.
Alternating current impedance measurement (voltage amplitude: 5 mV, frequency: 1 Hz to 1 MHz) was conducted by a four-terminal method, and a conductivity in the membrane surface direction of the ion conducting polymer composite membrane was calculated from the obtained resistance. As a result, the ion conductivity at a temperature of 5O 0 C and a
relative humidity of 50% was 2.77x10 2 S-cm 1 .
(Comparative Example 1) Nafion/H-montmorillonite composite membrane
A 5% by weight of a Nafion solution was prepared. Then, the H-montmorillonite obtained in Synthesis Example 1 was dispersed in the Nafion solution to prepare a mixed solution containing Nafion and sulfonated magadiite in a weight ratio of 90:10. Then, the H-montmorillonite was further thoroughly dispersed in the mixed solution using an ultrasonic washing machine. The mixed solution was formed into a membrane by a solvent casting method in a nitrogen atmosphere. The thickness of the membrane thus obtained was 40 μm.
Alternating current impedance measurement (voltage amplitude: 5 mV, frequency: 1 Hz to 1 MHz) was conducted by a four-terminal method, and the conductivity in the membrane surface direction of the ion conducting polymer composite membrane was calculated from the obtained resistance. As a result, the ion conductivity at a temperature of 50°C and a relative humidity of 50% was 2.55 χ lO "3 S-cm "1 .
(Comparative Example 2) Nafion/sulfonated montmorillonite composite membrane
A Nafion solution (5% by weight) was prepared. Then, the sulfonated montmorillonite obtained in Synthesis
Example 6 was dispersed in the Nafion solution to prepare a mixed solution containing Nafion and sulfonated
montmorillonite in a weight ratio of 90:10. Then, the sulfonated montmorillonite was further thoroughly dispersed in the mixed solution using an ultrasonic washing machine. The mixed solution was formed into a membrane by a solvent casting method in a nitrogen atmosphere. The thickness of the membrane thus obtained was 40 μm.
Alternating current impedance measurement (voltage amplitude: 5 mV, frequency: 1 Hz to 1 MHz) was conducted by a four-terminal method, and the conductivity in the membrane surface direction of the ion conducting polymer composite membrane was calculated from the obtained resistance. As a result, the ion conductivity at a temperature of 50°C and a relative humidity of 50% was 5.69*10 ~3 S-ciTf 1 .
Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 and 2.
Table 1
(Example 3)
It is exemplified below how to produce a membrane- electrode assembly and a fuel cell.
As catalyst powder, HiSPEC 1000 (registered trade mark, manufactured by Johnson Matthey) was used, and as an ion conducting electrolyte solution used for a catalyst layer, a Nafion solution was used. First, a mixed dispersion of the catalyst powder and the Nafion solution was prepared and formed into a membrane on a PTFE sheet by a doctor blade method, whereby a catalyst sheet was produced. Then, using a decalcomania process, the produced catalyst sheet was transferred onto the electrolyte membrane obtained in Example 1 by hot pressing at 120°C and 100 kgf/cm 2 to produce a membrane-electrode assembly. Further, the membrane-electrode assembly was sandwiched between carbon cloth electrodes (manufactured by E-TEK Co., Ltd. ) , and thereafter, was held and fastened between collectors to produce a fuel cell.
Hydrogen gas was injected on the anode side of the produced fuel cell at an injection rate of 300 ml/min. and air was supplied on the cathode side thereof. The cell outlet pressure was set to be atmospheric pressure, the relative humidity was set to be 50% in both the anode side and the cathode side, and the cell temperature was set to be 50°C. Constant current measurement was conducted at a current density of 400 mA/cm 2 , proving that the cell potential was 810 mV, and stable characteristics were maintained even after 100 hours.
This application claims the benefit of Japanese
Patent Application No. 2008-162557, filed June 20, 2008, which is hereby incorporated by reference herein in its entirety.