JP4644759B2 - Ionic conductor and fuel cell using the same - Google Patents

Description

The present invention relates to an ionic conductor and a fuel cell using the ionic conductor, and more specifically, an ionic conductor capable of improving ionic conductivity as compared with a case where an electrolyte material is an ionic liquid alone, and It relates to the fuel cell used.

As a fuel cell electrolyte membrane, a “cation-conductive / proton-conductive ceramic membrane infiltrated with an ionic liquid” has been proposed (see, for example, Patent Document 1).
This membrane is obtained by modifying so as to exhibit ionic conductivity on the basis of a porous and flexible ceramic membrane described in Patent Document 2, and then treating with an ionic liquid.
In addition, this membrane has extremely good proton conductivity or cation conductivity at a temperature higher than 100 ° C. by using an ionic liquid. Furthermore, flexibility is maintained and it can be used as an electrolyte membrane of a fuel cell.
JP-T-2004-515351 PCT / EP98 / 05939

  However, in such an electrolyte membrane in which a conventional ceramic membrane and an ionic liquid are combined, there is a problem that the ionic conductivity is not improved as compared with the ionic liquid alone.

  The present invention has been made in view of such problems of the prior art. The object of the present invention is to improve ionic conductivity and heat resistance compared to when the electrolyte material is an ionic liquid alone. An object of the present invention is to provide an ionic conductor that is high, can suppress swelling when containing water, and can be manufactured at low cost, and an energy device and a fuel cell using the ionic conductor.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by disposing an electrolyte material having high ion conductivity in the pores of the inorganic porous body. The invention has been completed.

That is, the ionic conductor of the present invention is an ionic conductor composed of an inorganic porous body formed of silica, an electrolyte material, and a pair of electrode materials,
The inorganic porous body has a plurality of spherical holes, the inner diameter of the spherical holes is substantially uniform, and adjacent spherical holes communicate with each other, and the electrolyte material is provided in the spherical holes,
The electrolyte material is an ionic liquid and includes a cation component and an anion component, and the anion component includes at least SO ₄ ^2- as a polyvalent anion ,
The electrode material sandwiches an inorganic porous body holding the electrolyte material.

  Furthermore, another preferred embodiment of the ion conductor of the present invention is characterized in that the inorganic porous body has a porosity of 70 to 90%.

Further, the fuel cell of the present invention is characterized by the formation Turkey by applying the ion conductor.

According to the present invention, a plurality of spherical holes are provided, and the spherical holes hold the electrolyte material in the pores of the inorganic porous body formed of silica having a substantially uniform inner diameter and in which adjacent spherical holes communicate with each other. The electrolyte material is an ionic liquid and contains a cation component and an anion component, the anion component contains at least SO ₄ ²⁻ as a polyvalent anion , and an electrode material sandwiches an inorganic porous body holding the electrolyte material. Since it is a conductor, the ionic conductivity is improved compared to the case where the electrolyte material is an ionic liquid alone, the heat resistance is high, and an ionic conductor that can suppress swelling when containing water can be obtained at a low cost.

  Hereinafter, the ion conductor of the present invention will be described in detail. In the present specification and claims, “%” indicates a mass percentage unless otherwise specified.

The ionic conductor of the present invention is composed of an inorganic porous material, an electrolyte material, and a pair of electrode materials.
Here, the inorganic porous body has a plurality of pores and holds an electrolyte material in the pores.
The electrolyte material includes a cation component and an anion component. This anion component contains at least a polyvalent anion.
Further, the electrode material sandwiches an inorganic porous body holding the electrolyte material.
FIG. 1 shows an outline and a photograph of the ion conductor.

As described above, by impregnating the inorganic porous material with the electrolyte material containing the cation component and the anion component, the fixation of the electrolyte material and the improvement of the ionic conductivity can be achieved at once. That is, a secondary effect of interaction acting on the interface between the immobilized electrolyte material and the inorganic porous body is obtained, and the ionic conductivity is higher than when the electrolyte material is used in a liquid state.
Moreover, since it can be comprised with an inexpensive material compared with the conventional product using a fluorine-type electrolyte etc., the ion conductor more suitable for spread is obtained.
Furthermore, by including a polyvalent anion in the anion component, a region that promotes ionic conduction can be formed at the interface between the two due to the joint effect of the inorganic porous material and the electrolyte material.

  In addition, the electrolyte material includes: Excellent thermal stability (non-volatile, zero vapor pressure, liquid in a wide temperature range), 2. 2. high ion density; From the viewpoint of a large heat capacity and the like, it is preferable to use an ionic liquid.

  As a typical ionic liquid, the cation component includes, for example, imidazolium derivatives (Imidazolium Derivatives, 1 to 3 substituents) represented by the following Chemical Formulas 1 to 3, pyridinium derivatives (Pyridinium Derivatives) represented by the Chemical Formula 4, Pyrrolidinium derivatives (Pyrrolidinium Derivatives), ammonium derivatives (Ammonium Derivatives) shown in Chemical Formula 6, phosphonium derivatives (Phosphonium Derivatives) shown in Chemical Formula 7, guanidinium derivatives (TiV), Derivatives (Isouronium Derivat ves), and the like.

  R in Chemical Formula 1 is represented by, for example, CmHn (m = 0 to 40, n = 0 to 40), and more preferably takes a combination of m = 0, n = 0, m = 4, and n = 9. obtain.

R ₁ and R _{2 in} Chemical Formula 2 are each individually represented by, for example, CmHn (m = 0 to 40, n = 0 to 40), and more preferably a combination shown in Table 1 below.

R ₁ , R ₂ , and R _{3 in} Chemical Formula 3 are each individually represented by, for example, CmHn (m = 0 to 40, n = 0 to 40), and more preferably the combinations shown in Table 2 below. It can take.

R ₁ and R _{2 in} Chemical Formula 4 are each individually represented by, for example, CmHn (m = 0 to 40, n = 0 to 40), and more preferably a combination shown in Table 3 below.

R ₁ and R _{2 in} Chemical Formula 5 are each individually represented by, for example, CmHn (m = 0 to 40, n = 0 to 40), and more preferably a combination shown in Table 4 below.

R _{1 to} R ₄ in Chemical Formula 6 are each individually represented by, for example, CmHn (m = 0 to 40, n = 0 to 40), and more preferably a combination shown in Table 5 below.

R _{1 to} R ₄ in Chemical Formula 6 are individually represented, for example, by CmHn (m = 0 to 40, n = 0 to 40), an alkyl group containing Ph, or the like, and more preferably in Table 6 below. The combinations shown can be taken.

  Examples of the anionic component include halogens represented by the following chemical formula 16, sulfates and sulfonic acids represented by the chemical formulas 17 and 18, amides and imides represented by the chemical formula 19, and amides and imides. Methanes represented by Chemical Formula 20 (Methanes), Borates represented by Chemical Formulas 21 to 26 (Borates), Phosphate and Antimones represented by Chemical Formulas 27 and 28, Phosphates and Antimonates, Other salts represented by Chemical Formula 29, etc. Is mentioned.

  In addition, as the polyvalent anion, for example, those represented by the following chemical formula 30 can be preferably used.

  In addition, these cation components or anion components can be used singly or in appropriate combination of two or more.

Furthermore, the inorganic porous body is preferably a sintered body containing a metal oxide.
Metal oxides are effective because they have high stability and many are available at low cost.
Examples of such metal oxides include alumina (Al ₂ O ₃ ), silica (SiO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), and any combination thereof.

Furthermore, it is preferable that the plurality of pores of the inorganic porous body are spherical pores, that the spherical pores have a substantially uniform inner diameter and that adjacent spherical pores communicate with each other. In other words, it is preferable that spherical pores exist three-dimensionally inside the inorganic porous body and communicate with adjacent spherical pores via a communication port. FIG. 1 shows an enlarged photograph of an ionic conductor and an inorganic porous body in which such an inorganic porous body 1 is filled with an electrolyte material 2 and sandwiched between electrode materials 3.
The inner wall surface of the spherical hole is preferably treated so that the proton donating functional group exists. Further, the electrolyte material can be filled through the communication port.

Thus, by regularly holding the electrolyte material inside the inorganic porous body, both materials are made into a composite, and the amount of ion conduction can be increased as a whole.
In the wet state, the inorganic porous body suppresses the swelling of the electrolyte material. In particular, since the spherical pores existing in the porous body have a substantially uniform diameter, the porous body receives a uniform and dispersed swelling force against the swelling of the electrolyte material when it contains water. Can be prevented from local damage. In other words, since the spherical pores of the inorganic porous body have a three-dimensional regular array structure, the swelling pressure of the electrolyte material can be supported evenly on the inorganic porous body.

The porosity of the inorganic porous material is preferably 70 to 90%. In this case, a large amount of electrolyte material can be introduced, and excellent ion conductivity can be realized.
Furthermore, the pore diameter of the inorganic porous material can be designed to be 100 to 1500 nm from the balance between ion conductivity and ease of introduction of the electrolyte material. If it is less than 100 nm, formation of a porous body using a spherical resin as a template tends to be difficult.

Furthermore, the inorganic porous body is preferably made of a material that forms an inorganic sol.
In this case, a sol-gel method, which is a simple inorganic material forming technique, can be applied. Moreover, an inorganic porous body can be obtained at low cost.
The inorganic sol-forming material is preferably an inorganic colloid. The inorganic colloid is suitable for forming an inorganic porous body using polymer particles as a template, and can form a spherical hole in which a three-dimensional ordered arrangement state is maintained.

Furthermore, the said inorganic porous body is obtained from the suspension which mixed polymer microparticles | fine-particles and an inorganic material, for example.
By applying such a suspension, a high porosity (70% or more) can be realized, so that a large amount of electrolyte material can be retained, and high ion conductivity can be expected. In addition, an inorganic porous material can be obtained using a three-dimensional regular array structure formed by stacking polymer fine particles as a template. Furthermore, an inorganic porous body having an arbitrary space can be designed by controlling the particle size and the lamination state of the polymer fine particles.
The polymer fine particles in the pores are removed by heat treatment or the like, so that a space for the electrolyte material is secured.

Moreover, as said electrode material, it is desirable to contain electrode catalyst components, such as noble metals, such as platinum (Pt) and ruthenium (Ru), rhodium (Rh), and glassy carbon, for example.
These electrode catalyst components are preferably highly dispersed through a supporting substrate such as, for example, carbon paper, carbon black, or a mixture of polytetrafluoroethylene (PTFE).

Here, the ion conductor of the present invention can be typically manufactured by a process as shown in FIG. In more detail, it can manufacture by performing the following processes.
1. 1. Step of mixing inorganic sol and spherical organic resin using solvent 2. Stir the mixed solution to make a suspension. 3. Filtration of the suspension to form a film 4. Step of removing excess water from the filtration molded membrane 5. Drying the filtration membrane 6. Step of heating and baking the filtration molded membrane to obtain an inorganic porous material 7. impregnating the electrolyte material into the spherical pores of the inorganic porous material; Process of drying and sandwiching with electrodes to form ionic conductor

  Here, an inorganic porous body in which spherical holes are three-dimensionally arranged using a spherical organic resin as a template is obtained by going through steps 1-6.

  In Step 1 and Step 2, the inorganic colloid and the spherical organic resin can be mixed in a homogeneous state. Thereby, an inorganic porous body having uniform and regular pores can be obtained.

In Step 3, filtration is suitable as a method of filling the gap with an inorganic sol using a spherical organic resin as a template. Filtration can be performed by appropriately reducing the pressure by about 10 to 60 kPa based on the size of the spherical pores of the inorganic porous material, the pore density, and the like.
As the spherical organic resin used in step 3, for example, polyethylene of about 20 nm to 1500 nm can be used.
Typically, polyolefin resin, polystyrene resin, cross-linked acrylic resin, methyl methacrylate resin, polyamide resin, and the like can be selected as appropriate. If it is smaller than 20 nm, homogeneous impregnation of the electrolyte material tends to be difficult. On the other hand, if it exceeds 1500 nm, the homogeneity of the support structure constituting the inorganic porous material may be disturbed.

Furthermore, in step 4, the drying time in the next drying step can be shortened by previously removing the solvent contained in the filtration membrane.
Furthermore, in step 5, the filtration molded membrane is previously dried at room temperature, thereby facilitating the handling of the membrane in the firing step or the like.

Next, in step 6, the inorganic porous material can be formed by baking and heating the filtration molded membrane to heat and form the inorganic material and baking and removing the template resin.
At this time, it is preferable to perform temporary baking for removing the spherical organic resin in the filtration membrane and thereafter sinter the inorganic porous body.
Temporary baking is performed at a temperature increase rate of 1 to 10 ° C./min, preferably 2 to 5 ° C./min, 400 to 500 ° C., more preferably 430 to 470 ° C., and heat treatment is performed for 30 minutes or more. Can do.
Baking can be performed, for example, at a temperature of 800 to 900 ° C. or higher for about 30 to 100 minutes. This firing may be repeated a plurality of times.

  Further, in Steps 7 and 8, the obtained porous body is impregnated with an electrolyte material and sandwiched between electrode materials, whereby a desired ion conductor can be easily obtained.

Next, the energy device of the present invention will be described.
The energy device of the present invention is configured by applying the above-described ion conductor. In this case, a system can be appropriately formed by combining with other control means.
Typically, a fuel cell (cell or stack), water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor, and the like can be given.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in full detail, this invention is not limited to these Examples.

Example 1
1. Preparation of inorganic porous material Colloidal silica having a diameter of 70 to 100 nm was prepared as an inorganic porous material.
Further, polystyrene spherical particles having an average diameter of about 500 nm were prepared for the purpose of controlling the pore diameter.

The colloidal silica and polystyrene spherical particles were mixed so that the solute volume had a predetermined film thickness to prepare a suspension solution.
As a procedure, first, 10% of polystyrene spherical particles were weighed and added to water. Further, 40% of colloidal silica was weighed and added to water. These solutions were ultrasonically stirred to uniformly disperse the particles.

  Next, the membrane filter was set in a filter holder, and the pressure was reduced to 10 kPa or less with respect to atmospheric pressure using a manual vacuum pump, and the suspension was filtered.

  After all of the suspension was filtered, excess water contained in the filter-formed membrane was removed with a water absorbing material such as filter paper. A film composed of a mixture of colloidal silica and polystyrene spherical particles was obtained by peeling off from the membrane filter after sufficiently drying at room temperature.

The obtained film was subjected to the following heat treatment.
First, as preliminary calcination, the temperature was raised to 400 to 500 ° C. at a temperature raising rate of 1 to 10 ° C./min, and heat treatment was performed at that temperature for 30 minutes or more to remove polystyrene spherical particles.
Furthermore, after pre-baking, heat treatment was performed at at least 800 ° C. for about 60 minutes to sinter colloidal silica.
Furthermore, in order to improve mechanical strength, heat treatment was performed at a temperature of 900 ° C. or higher for 15 minutes, and the temperature was slowly returned to room temperature, thereby obtaining a target silica porous membrane.

2. Impregnation with electrolyte material (ionic liquid) 50 g of N-methylimidazole and 145 g of bromoethane (EtBr) were dissolved in 1.25 L of dimethylformamide (DMF) and stirred in an ice bath for 3 days. Then, it dried under reduced pressure and removed DMF.
Then 250 mL of acetonitrile was added. Further, 5 L of diethyl ether (Et ₂ O) was added. Thereafter, the precipitate was collected by filtration and dried in vacuo at 60 ° C. for 24 hours.

Anion exchange was performed with amberlite to obtain a hydroxide compound. To this was added 116 g of sulfuric acid, and the mixture was stirred for 24 hours in an ice bath. Thereafter, the solvent was removed by drying under reduced pressure.
After dissolving in 500 mL of acetonitrile, the ionic liquid (EMImHSO ₄ ) was obtained by removing the acetonitrile by drying at 60 ° C. for 24 hours.
A porous silica membrane was impregnated with this ionic liquid to produce an ionic conductor.

3. Ion conductivity evaluation About the obtained ion conductor, ion conductivity was evaluated by the impedance measured by applying an AC wave of 10 Hz to 100 kHz. The results are shown in FIGS.
Here, the ionic conductivity was calculated based on the area in contact with the gold electrode without considering the porosity. In the measurement, the ion conductivity was measured by changing the temperature.

(Comparative Example 1)
An ion conductor was produced by repeating the same operation as in Example 1 except that the porous silica membrane was not used and the electrolyte material was only ionic liquid. Moreover, ion conductivity evaluation was performed similarly. The results are shown in FIGS.

(Comparative Example 2)
An ion conductor was produced by repeating the same operation as in Example 1 except that a polyimide film having a structure equivalent to a porous silica film (3 DOM) was used. Moreover, ion conductivity evaluation was performed similarly. The result is shown in FIG.

As shown in FIG. 3, in the ionic liquid containing an anionic component (EMImHSO ₄ ) and the porous silica electrolyte membrane, the ionic conductivity was significantly improved only in the liquid state.

Further, for the ionic liquid (EMImHSO ₄ ), the ionic conductivity of Comparative Example 1 (liquid state) was set to 1, and compared with the ionic conductivity of Example 1 and Comparative Example 2.
As shown in FIG. 4, the ionic conductor according to Example 1 using the ionic liquid together with the porous silica membrane has an ionic conductivity of about 1% compared to the ionic conductor according to Comparative Example 1 using only the ionic liquid. It was greatly improved by 3.5 times.
In contrast, in the composite film using the ionic liquid together with the polyimide according to Comparative Example 2, the ionic conductivity was lower than that of Comparative Example 1 on the contrary.

(Example 2)
FIG. 5 shows a basic configuration of an energy device (fuel cell) to which an ion conductor is applied.
It produced so that the inorganic porous body 7 holding | maintaining electrolyte material might be pinched | interposed in order by a pair of electrode material 3 and gas diffusion layer 6 which oppose.
A porous silica film was used for the inorganic porous body 7, and EMImHSO ₄ was used for the electrolyte material 2.
The electrode material 3 was platinum-supported carbon, and the gas diffusion layer 6 was carbon paper.

In addition, a gas flow path 5 is formed in each electrode using a separator 4 so that hydrogen (or a fuel gas containing hydrogen) and oxygen (or an oxidizing gas containing oxygen) can be supplied.
In addition, as for an electrode, the side which supplies fuel gas becomes an anode, and the side which supplies oxidizing gas becomes a cathode.

When power is generated by this fuel cell, each gas is supplied from the gas flow path 5 to the electrode material 3 through the gas diffusion layer 6, and the following electrochemical reaction proceeds.
H ₂ → 2H ⁺ + 2e ⁻ (1)
2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

Equation (1) shows the reaction on the cathode side of the fuel cell.
Equation (2) shows the reaction on the anode side of the fuel cell.
Equation (3) is a reaction performed in the entire fuel cell.
Thus, the fuel cell using an ion conductor can directly convert the chemical energy of the fuel into electric energy, and can be expected to have high energy conversion efficiency.

It is the schematic and SEM photograph which show an example of an ion conductor. It is a flowchart which shows an example of the preparation procedures of an ion conductor. It is a graph which shows the evaluation result of ion conductivity. It is a graph which shows the relationship between ion conductivity and temperature. It is the schematic which shows an example of the fuel cell to which the ion conductor is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inorganic porous body 2 Electrolyte material 3 Electrode material 4 Separator 5 Gas flow path 6 Gas diffusion layer 7 Inorganic porous body holding electrolyte material

Claims (4)

An ionic conductor composed of an inorganic porous body formed of silica, an electrolyte material, and a pair of electrode materials,
The inorganic porous body has a plurality of spherical holes, the inner diameter of the spherical holes is substantially uniform, and adjacent spherical holes communicate with each other, and the electrolyte material is provided in the spherical holes,
The electrolyte material is an ionic liquid and includes a cation component and an anion component, and the anion component includes at least SO ₄ ^2- as a polyvalent anion ,
An ionic conductor characterized in that the electrode material sandwiches an inorganic porous body holding the electrolyte material. The plurality of spherical holes form an arrangement structure resulting from a hexagonal close-packed structure,
The ion conductor according to claim 1, wherein the adjacent spherical holes communicate with each other through a communication port.   The ionic conductor according to claim 1 or 2, wherein the porosity of the inorganic porous body is 70 to 90%. One of the fuel cells you characterized and by applying the ion conductor formed Turkey according to the preceding claims 1-3.

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