JP2000256007A - Production of proton conductive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a proton conductor having excellent proton conductivity and showing no decrease in the proton conductivity even in a dry environment by bringing an acid aq. soln. having specified mol or more concn. of an acid having a group selected from phosphate group, perchlorate group and sulfonate group into contact with a silica nanotube. SOLUTION: A silica nanotube is impregnated with an acid aq. soln. such as sulfuric acid for 1 to 5 hours under the conditions of >=0.5 mol concn. of the acid aq. soln., 20 ml of the contact amt. per 1 g of silica and <=80 deg.C contact temp. to obtain a proton conductor suitable for a fuel cell, capacitor or the like. The silica nanotube is obtd., for example, by adding 1 to 3 mol of water with its pH controlled to 1 to 4 to 1 mol of tetraalkoxysilane to partially decompose the tetraalkoxysilane, adding a surfactant such as a cationic alkylammonium salt by 0.01 to 0.3 mol to 1 mol of the tetraalkoxysilane to the partially decomposed produce, stirring at 10 to 100 rpm, drying a reaction system and calcining at 600 to 700 deg.C for 4 to 10 hours.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a material exhibiting proton conductivity.

[0002]

2. Description of the Related Art Substances in which ions move in a solid have been energetically studied as materials for electrochemical devices such as batteries, and currently various materials such as Li ⁺ , Ag ⁺ , H ⁺ , and F ⁻ are used. Ionic conductors of various conductive ionic species have been found.
Among them, those using proton (H +) as a conductive ion species
It is expected to be applied to various electrochemical devices such as fuel cells, capacitors, and electrochromic display devices.
A proton conductor can be used as an electrolyte of the electrochemical device as described above. It is necessary that the proton conductor has high proton conductivity at around room temperature. Examples of such a proton conductor include inorganic substances such as uranyl phosphate hydrate and molybgophosphate hydrate, and vinyl fluoride type Organic substances such as a polymer ion exchange membrane having a side chain containing a perfluorosulfonic acid group in a molecule are known. However, the above-mentioned inorganic proton conductor is
Since the protons in the crystallization water contribute to conduction, there is a problem that the crystallization water is desorbed at a high temperature and the proton conductivity is reduced. On the other hand, since the organic proton conductor is produced by complicated organic synthesis, there are many problems in production technology such as yield, and there is a problem that it becomes an expensive material.

[0003]

DISCLOSURE OF THE INVENTION The present inventors have solved a problem described above, and have developed a production method which can easily obtain a proton conductor which has excellent proton conductivity and does not decrease in proton conductivity even in a dry atmosphere. The purpose is to provide.

[0004]

According to the present invention, there is provided a method of contacting a silica nanotube with an aqueous acid solution having a concentration of an acid having a group selected from a phosphoric acid group, a perchloric acid group and a sulfonic acid group of 0.5 M or more. And a method for producing a proton conductive material characterized by the following. Production of Silica Nanotube In the present invention, silica nanotube is defined as having an average diameter of 1
~ 5 nm, preferably 2-3 nm, average length 10-50
The silica nanotube, which is a tubular silica having a thickness of 30 nm, preferably 30 to 50 nm, is produced by partially hydrolyzing and optionally further condensing tetraalkoxysilane with water in an acidic atmosphere, then adding a surfactant and stirring. can do. Examples of the tetraalkoxysilane that can be used here include tetramethoxysilane and tetraethoxysilane. The acidity of water is preferably about 1 to 4 in terms of pH, and the adjustment of the acidity is preferably performed with sulfuric acid.

The amount of water to be added to tetraalkoxysilane is 0.1 to 1 per mole of tetraalkoxysilane.
0 mol, preferably 1 to 3 mol.

Next, a surfactant is added to the partially decomposed product of the tetraalkoxysilane. As a surfactant, C _{n
^{H 2n + 1 N + (CH}} 3) 3 X - ( where n = 8~16, X = C
Ionic (cationic) represented by (1, Br, OH)
Alkylammonium salts, C _n H _{2n + 1} NH ₂ (n = 4
To 18) can be used. In the present invention, the amount of the surfactant is usually 0.05 to 0.5 mol, preferably 0.01 to 0.3 mol, per 1 mol of the tetraalkoxysilane. After adding the surfactant to the tetraalkoxysilane, the reaction system is stirred, and the stirring speed at this time is usually 10 to 100 rpm. After completion of the stirring, the obtained reaction system is dried by air drying or vacuum drying, pulverized, and then calcined to obtain silica nanotubes. Here, the firing temperature is usually 600 to 700 ° C, and the firing time is 4 to
10 hours.

[0007] In manufacturing the present invention proton conductor, it is contacted with an aqueous acid solution to a silica nanotubes obtained above. As the acid used in the present invention, an acid having a phosphoric acid group such as phosphoric acid, perchloric acid and sulfuric acid, a perchloric acid group or a sulfonic acid group can be used, but high conductivity is obtained and drying is performed. Sulfuric acid is most preferred because of its stability in conductivity under an atmosphere. In the present invention, the concentration of the aqueous acid solution is adjusted to 0.5M or more, preferably 0.5 to 7M. In the present invention, if the acid concentration is less than 0.5 M, it becomes difficult to exhibit proton conductivity. Also, as the acid concentration increases, the proton conductivity gradually increases. However, when the concentration is 7 M or more, the effect of improving the proton conductivity is lost, and the amount of free sulfonic acid groups after the preparation of the proton conductor increases. It is not preferable because the binder polymer easily corrodes. The amount of the acid aqueous solution to be brought into contact with the silica nanotube is usually 20 ml per g of silica.

In the present invention, it is preferable to keep the temperature of the aqueous acid solution to be brought into contact with the silica nanotube at 80 ° C. or lower in order to keep the aqueous acid solution at a constant condition. In the present invention, it is preferable to impregnate the silica nanotube with the acid aqueous solution. The contact time of the acid aqueous solution is not particularly limited, but a sufficient impregnation effect can be obtained within 1 hour to 5 hours.

The proton conductor obtained as described above is
Usually, it is dried and powdered before use. The proton conductor of the present invention can be used by pulverizing, binding with a binder such as polyvinyl alcohol or rubber, and molding.

[0010]

The present invention will be described below with reference to examples. Example 1 As a starting material, tetramethoxysilane (S
i (OCH3) 4) (Tokyo Chemical Industry Co., Ltd., hereinafter referred to as TMO
S), sulfuric acid (for precision analysis, manufactured by Wako Pure Chemical Industries, Ltd.), and hexadecyltrimethylammonium chloride (first grade, manufactured by Wako Pure Chemical Industries, Ltd.) for the surfactant
(Hereinafter abbreviated as C16TAC). Water used was distilled ion-exchanged water. (1) Production of Silica Nanotubes Two moles of water were prepared under acidic conditions of PH2 using sulfuric acid, and 1 mole of TMOS was added dropwise thereto and stirred for several minutes to partially hydrolyze the TMOS. Next, C16 which is a surfactant
The sol was prepared by adding 0.2 mol of TAC and stirring at room temperature for 5 minutes. The obtained sol was spread on a glass vat, dried in a thermostat at 35 ° C. for 12 hours, peeled off from the vat, and pulverized with an agate mortar grinder to obtain a fine gel powder. This gel fine powder is spread on a magnetic dish and heat-treated at 600 ° C. for 4 hours in a muffle furnace.
Silica Nanotube Powder 50 Burned with C16TAC
g was produced. (2) Production of Proton Conductor 5 g of the obtained silica nanotube was added to 50 ml of sulfuric acid having a concentration of 0.5 M adjusted to 25 ° C., stirred for 3 hours, then filtered and dried, and the proton conductive material of the present invention was obtained. Was prepared. (3) Evaluation 1 g of the obtained proton conductive material was kneaded with 0.2 g of polyvinyl alcohol together with a small amount of water, and formed into a 0.3 mm-thick pellet using a tablet molding machine. Evaluation 1 The pellets were vacuum-dried at room temperature for 5 hours, then sandwiched between platinum electrodes, and the conductivity in a dried state under a stream of nitrogen was evaluated by an alternating current method. Table 2 shows the results. Evaluation 2 In order to examine the influence of the measurement atmosphere of the pellets and the stability of the conductivity, the relative humidity was changed from 0% (under a nitrogen stream) to 80% at a temperature of 25 ° C., and the change in conductivity was evaluated. 0% by this relative humidity change
The stability of the conductivity was evaluated by repeating the cycle of → 80% → 0% as one cycle and repeating 10 cycles.

[Examples 2 to 15 and Comparative Examples 1 to 3] In the same manner as in Example 1 except that the type, concentration and contact time of the acid aqueous solution used in Example 1 (2) were as shown in Table 1. A proton conductive material was prepared and evaluated. In addition, the comparative example 1 evaluated without the process in Example (2). Table 2 shows the results.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

The method for producing the proton conductive solid material of the present invention is simple, and the proton conductive material obtained by the production method of the present invention has excellent proton conductivity in the process.
Does not deteriorate even under dry conditions. The proton conductor obtained by the method of the present invention is useful as an electrolyte for various electrochemical devices such as fuel cells, capacitors, and electrochromic display devices.

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Claims (3)

[Claims] 1. A proton conductive material, wherein an acid aqueous solution having a concentration of an acid having a group selected from a phosphoric acid group, a perchloric acid group and a sulfonic acid group of 0.5 M or more is brought into contact with a silica nanotube. Manufacturing method. 2. The method for producing a proton conductive material according to claim 1, wherein a sulfuric acid aqueous solution is used as the acid aqueous solution. 3. The silica nanotube has an average diameter of 1 to 5 n.
2. The method for producing a proton conductive material according to claim 1, wherein the average length is 10 to 50 nm.