JP2006286268A - Mixed conductor having both electron conductivity and proton conductivity and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide a mixed conductor that is inexpensive and stable without being restricted by the installation environment, and has better electron conductivity and proton conductivity in a low temperature range of room temperature to about 200 ° C.
Resorcinol, which is a starting material of an electron conductive material capable of transferring electrons, and trimethyl phosphate, which is a starting material of a proton conductive material capable of transferring protons, are combined by dehydration polymerization to form a gel. It is a mixed conductor having both electron conductivity and proton conductivity obtained by freeze-drying or supercritical drying to obtain a precursor and heat-treating the precursor in an inert gas atmosphere.
[Selection] Figure 4

Description

  The present invention relates to a mixed conductor having both electron conductivity that conducts electrons and proton conductivity that conducts protons, and a method for producing the same.

Conventionally, as a mixed conductor having both electron conductivity and ion conductivity which is a property of conducting ions, (1) CeO ₂ , ZrO ₂ , perovskite type oxide capable of moving electrons and O ²⁻ , (2) Halides (CuI), chalcogenides (Cu ₂ S, Ag ₂ S) that can move electrons and Cu ⁺ or Ag ⁺ , (3) Intermetallic compounds that can move electrons and Li ⁺ (Li-Al, etc.) In addition, oxides (such as Li _x WO ₃ ), chalcogen intercalation compounds (Li _x TiS ₂ ), graphite-based, and polyacetylene complexes are known. Mixed conductors capable of moving electrons and O ²⁻ are used in catalyst layers and catalyst carriers of solid oxide fuel cells (SOFC).

The following mixed conductors having both electron conductivity and proton conductivity include hydrogen storage alloys such as Pd and LaNi ₅ , oxides such as ReO ₃ and WO ₃ , and 2,2′-bi-1H-imidazole derivatives. Complexes using are known.

  However, there is no inexpensive and stable mixed conductor that has both good electron conductivity and proton conduction in a low temperature range of room temperature to about 200 ° C. For this reason, a conventional mixed conductor is not used in, for example, a proton transfer fuel cell that operates in a low temperature range of room temperature to about 200 ° C.

In particular, mixed conductors made of hydrogen storage alloys have (1) low proton conductivity near room temperature, (2) heavy, (3) high cost, (4) water, oxygen, CO, etc. other than hydrogen atmosphere There are problems such as being easily deactivated when used in (5) being finely divided when used repeatedly, and (6) being liable to be restricted in use in an acidic atmosphere. In addition, the hydrogen storage alloy which consists of Pd does not become a problem in deactivation other than hydrogen atmosphere, and use restrictions of acidic atmosphere. Further, the mixed conductor of ReO ₃ and WO ₃ has a low proton conductivity. The hydrogen diffusion coefficient (cm ² / sec) in Nafion (registered trademark), which is an ion exchange resin, is 11.4 × 10 ⁻⁷ (25 ° C.), and the hydrogen diffusion coefficient in a hydrogen storage alloy composed of Pd is 5 The hydrogen diffusion coefficient in the hydrogen storage alloy made of × 10 ^-7 (25 ° C), ReO ₃ is 1 × 10 ^-11 (27 ° C), and the hydrogen diffusion coefficient in the hydrogen storage alloy made of WO ₃ is 7 × 10 ⁻⁶ to 1 × 10 ⁻¹¹ . If a fuel cell is established with the hydrogen diffusion coefficient of Nafion (registered trademark), the feasibility as a fuel cell is feared with the diffusion coefficient of other substances.

  For this reason, the applicant has proposed a novel mixed conductor in Japanese Patent Application No. 2003-139431. This mixed conductor is not limited by the installation environment, is inexpensive and stable, and has both good electron conductivity and proton conductivity in a low temperature range of room temperature to about 200 ° C.

However, according to the test results of the inventors, the mixed conductor proposed previously has a specific surface area of only about 300 m ² / g. For this reason, when this mixed conductor is used for the catalyst layer of the electrode of the fuel cell, a catalyst such as platinum is likely to aggregate on the mixed conductor, so that the catalytic action is not sufficiently performed, and the fuel cell system It is thought that improvement of output is difficult to expect.

  The present invention provides a mixed conductor that is not limited by the installation environment, is inexpensive and stable, and has both better electronic conductivity and proton conductivity in a low temperature range of room temperature to about 200 ° C. This is a problem to be solved.

  The inventor has completed the mixed conductor which can solve the problems of the present invention by improving the previously proposed mixed conductor and the manufacturing method thereof, and has completed the present invention.

  That is, the mixed conductor having both electron conductivity and proton conductivity according to the present invention combines an electron conductive material made of an organic material and a proton conductive material capable of transferring protons by dehydration polymerization to form a gel. The precursor is obtained by freeze-drying or supercritical drying to obtain a precursor, and the precursor is heat-treated in an inert gas atmosphere.

  According to the inventor's recognition, the electron conducting material can comprise at least one of polyacetyl, resorcinol, phenol, 2-phenylphenol, polyaniline, polypyrrole, polythiophene, phenylphosphonic acid and phenylsilane alkoxides. It is also considered that other aromatic hydrocarbon compounds having an unsaturated bond, alkenes, and alkyne (semiconductor) hydrocarbons can be used.

  The proton conducting material may include at least one of a substance containing a proton dissociating group, a derivative of phosphoric acid, and a derivative of sulfuric acid. It is also considered that a solid acid such as tungstophosphoric acid, or an inorganic oxide such as silicon oxide, zirconia oxide, or tungsten oxide can be used.

  More specifically, the mixed conductor having both electron conductivity and proton conductivity of the present invention includes resorcinol, which is a starting material of an electron conducting material capable of transferring electrons, and a starting material of a proton conducting material capable of transferring protons. It was obtained by combining trimethyl phosphate with dehydration polymerization to form a gel, freeze-drying or supercritical drying to obtain a precursor, and heating the precursor in an inert gas atmosphere. And

  The inventor first formed a gel by combining resorcinol, which is an organic compound having π electrons, and trimethyl phosphate, which is an inorganic oxide having proton conductivity, by dehydration polymerization. This gel was once lyophilized and then used as a precursor. Thereafter, the precursor was heat-treated in an inert gas (including nitrogen gas) atmosphere to obtain a mixed conductor having both good electron conductivity and proton conductivity. This mixed conductor has both good electron conductivity and proton conductivity at room temperature to about 200 ° C.

  Since the organic compound has π electrons if it has an unsaturated bond, the organic compound according to the present invention has a double bond (SP2) or a triple bond (SP3). In addition, the proton conductive material having proton conductivity is not limited to the inorganic oxide substance, and other substances having proton conductivity may be used. These are dehydrated and condensed into a sol, and a precursor is obtained, and this precursor is subjected to heat treatment. The mixed conductor thus obtained does not drop off or elute the proton conducting portion imparting proton conductivity even in the presence of moisture.

  Therefore, the method for producing a mixed conductor having both electron conductivity and proton conductivity according to the present invention includes resorcinol, which is a starting material of an electron conducting material capable of transferring electrons, and a starting material of a proton conducting material capable of transferring protons. A first step of obtaining a gel by dehydrating polymerization of trimethyl phosphate, a second step of lyophilizing or supercritically drying the gel to form a precursor, and the precursor in an inert gas atmosphere And a third step of heat treatment.

  More specifically, in the first step, resorcinol and trimethyl phosphate are subjected to dehydration condensation polymerization to obtain a gel. In the second step, the gel is freeze-dried or supercritically dried to obtain a precursor. In the third step, the precursor is heated to 500 to 1000 ° C. in an inert gas (including nitrogen gas) atmosphere. Thereby, a mixed conductor having both electron conductivity and proton conductivity can be manufactured.

  In addition, since the gel obtained in the first step contains a large amount of water in the pores, if the gel is dried at the gel step in the second step, the pores tend to remain in the precursor and thus the mixed conductor. it is conceivable that. However, according to the test results of the inventors, when the gel is dried by a normal high-temperature drying method, the pores of the gel are easily blocked by the surface tension of water during drying, and the precursor and the mixed conductor have pores. It is hard to remain. On the other hand, if freeze drying or supercritical drying is employed, pores are likely to remain in the precursor or the mixed conductor. For this reason, supercritical drying or freeze-drying is performed at the gel stage to obtain a precursor.

  Electronic conductivity does not occur unless the precursor is heat treated in the third step. However, in the third step, it is unclear whether or not the precursor is really bonded, and the electron conducting portion and the proton conducting portion may be intercalated or may have another structure.

  When the mixed conductor of the present invention is used as a catalyst carrier of a proton transfer fuel cell such as a hydrogen-air (oxygen) fuel cell and a reaction layer is formed, an ion exchange membrane and an electrode in a conventional proton transfer fuel cell An ion exchange resin such as Nafion (registered trademark) as a binder material linking the structure becomes unnecessary or the amount of use can be reduced.

  For this reason, in this case, a catalyst such as platinum, which is a part of the electrode structure and supported on a catalyst carrier such as carbon, can be used 100% and the catalyst can be prevented from falling off.

  That is, the catalyst supported on the carbon particles as the catalyst carrier is supported on the pores of the carbon particles, assists the movement of protons, and acts as an ion as a binder for connecting the carbon particles, the catalyst, and the electrolyte membrane. By coating with an exchange resin, a battery reaction is performed based on electron conductivity and proton conductivity, and it is difficult to coat all of the catalyst supported on such carbon particles with an ion exchange resin as a binder. Some of the supported catalysts do not actually work.

  On the other hand, since the mixed conductor of the present invention has both electron conductivity and proton conductivity by itself, if the catalyst is supported on the mixed conductor, all the catalysts are contacted, so that the catalyst is used 100%. It becomes possible. Further, the catalyst covered with the conventional ion exchange resin is easy to fall off due to swelling and shrinkage of the ion exchange resin. However, if the catalyst is supported on the mixed conductor of the present invention, such dropping does not occur. For this reason, the battery performance can be improved by the effective use of the catalyst. Further, the amount of catalyst used can be reduced, and the manufacturing cost of the fuel cell can be reduced.

  In addition, since the mixed conductor maintains the pores of the gel and has a high specific surface area, the catalyst hardly aggregates on the mixed conductor, and the catalytic action is easily performed. It is considered that the diffusion is sufficiently performed and the output of the fuel cell system can be improved.

  In this case, the fuel gas supply is not hindered by the ion exchange resin, so that the battery performance can be improved.

  Therefore, when the mixed conductor of the present invention is used as a catalyst carrier in a reaction layer of a proton transfer fuel cell such as a hydrogen-air (oxygen) fuel cell, the installation environment is limited, proton conductivity is insufficient, low durability, low Battery performance and the like can be solved.

  Hereinafter, embodiments embodying the present invention will be described together with comparative examples 1 and 2 with reference to the drawings.

"First step"
As an organic compound having an unsaturated bond, resorcinol having the chemical formula shown in Chemical Formula 1 was used as the first starting material. Further, trimethyl phosphate having a chemical formula in Chemical Formula 2 was used as a second starting material as a proton conductive material.

Then, as shown in Chemical Formula 3, formaldehyde was subjected to nucleophilic addition reaction with resorcinol to obtain a first compound in which —CH ₂ OH was introduced into resorcinol. The molar ratio of resorcinol to formaldehyde is 1: 2.

  Moreover, as shown in Chemical formula 4, ethyl alcohol, water and hydrochloric acid were added to trimethyl phosphate to obtain a second compound which was a hydrolyzed solution.

Then, the second compound was added to the first compound. At this time, the molar ratio of resorcinol to trimethyl phosphate was 5: 2. After this time, Na ₂ CO ₃ as a catalyst was added to the mixture. This mixture was allowed to stand at room temperature for several hours in a sealed state, and further gelled by leaving it at 70 ° C. for 2 days in a sealed state.

"Second step"
The gel was left sealed at 90 ° C. for 1 day, cooled to room temperature, and the gel was replaced with acetone. The gel substituted with acetone was further substituted with t-butanol. The gel substituted with t-butanol was lyophilized to obtain a precursor. This precursor is presumed to have the chemical formula:

"Third step"
The precursor was heat-treated at 800 ° C. for 4 hours in a nitrogen gas atmosphere to obtain a mixed conductor of the example.

Comparative Example 1

  The gel obtained in the same manner as in the examples was sealed and allowed to stand at 90 ° C for 1 day, and then subjected to heat treatment at 800 ° C for 4 hours in an inert gas atmosphere. Thus, a mixed conductor of Comparative Example 1 was obtained.

Comparative Example 2

  A test specimen was obtained without adding trimethyl phosphate, which is a proton conducting material. Other conditions are the same as in the example.

  In order to measure the electron conductivity and proton conductivity, the mixed conductor of Example and Comparative Example 1 and the test body of Comparative Example 2 were pulverized and then pressed at 500 ° C. by SPS method (discharge plasma sintering method). The sample for a measurement of Example and Comparative Examples 1 and 2 was produced by baking.

"Electronic conductivity"
The measurement samples of Examples or Comparative Examples 1 and 2 were sandwiched between current collector plates, and the electronic specific resistance (Ω · cm) was calculated based on the voltage when a direct current of 1A, 3A or 5A was applied thereto.

  As a result, the measurement sample of Example and Comparative Example 1 was 0.35 Ω · cm, whereas the measurement sample of Comparative Example 2 was 0.65 Ω · cm, and the measurement of Example and Comparative Example 1 It can be seen that the samples for use have excellent electronic conductivity.

"Proton conductivity"
As shown in FIG. 1, the measurement samples T of Examples and Comparative Examples 1 and 2 were sandwiched between ion exchange membranes 1a and 1b made of Nafion (registered trademark). Further, carbon cloths 2 and 3 having catalyst layers 2a and 3a made of Pt on one surface were prepared, and ion exchange membranes 1a and 1b were sandwiched between the catalyst layers 2a and 3a. Then, while blocking electrons with the ion exchange membranes 1a and 1b, a voltage is applied between the carbon cloths 2 and 3 in a nitrogen and hydrogen atmosphere at 60 ° C. in a saturated humidity atmosphere, and the proton conductivity is determined from the response current. (S / cm) was calculated.

  FIG. 2 shows the relationship between applied voltage and response current over time. FIG. 2 shows that when a voltage is applied to the measurement sample of the example, no current flows in nitrogen, and a current flows when the gas is changed to hydrogen gas. For this reason, it turns out that the sample for a measurement of the Example and Comparative Example 1 which added phosphorus has the proton conductivity outstanding when the heat processing temperature is 800 degreeC. However, the mechanism of proton conduction by these is unknown. On the other hand, the response current does not flow in the measurement sample of Comparative Example 2 that does not contain phosphorus.

As a result, the measurement sample of Example and Comparative Example 1 was 1.3 × 10 ⁻³ S / cm, whereas the measurement sample of Comparative Example 2 was below the lower limit of measurement. Since this result reflects all the resistance and contact resistance of other members such as ion exchange membranes in the measurement system, it is clear that the proton conductivity of each measurement sample itself is higher than this result. It is. The proton conductivity of the measurement sample of Comparative Example 2 to which no phosphorus is added is the lower limit of measurement.

  Therefore, it can be seen that the measurement samples of Examples and Comparative Example 1 are mixed conductors having both good electron conductivity and proton conductivity at room temperature to about 200 ° C.

"Specific surface area"
The specific surface area (m ² / g) of the measurement samples of Examples and Comparative Example 1 was measured. The results are shown in FIG.

  As shown in FIG. 3, the measurement sample of the example had a higher specific surface area than that of Comparative Example 1. As a result, it is understood that the mixed conductor has a high specific surface area by freeze-drying the gel. This is presumably because gel pores are likely to remain in the precursor.

"Dispersibility of catalyst"
50% by mass of platinum was supported on the measurement sample of Example and Comparative Example 1, and the average particle size (nm) of platinum in both was measured. The results are shown in FIG.

  As shown in FIG. 4, it can be seen that the measurement sample of the example has a smaller average particle size of platinum supported than that of Comparative Example 1. For this reason, it can be seen that the mixed conductors of the examples are less likely to aggregate platinum and can support platinum with a high dispersion rate.

"Oxygen reduction activity of catalyst"
50% by mass of platinum was supported on the measurement sample of Example and Comparative Example 1, and the oxygen reduction current (A / g) of both was measured. The results are shown in FIG.

  From FIG. 5, it can be seen that the measurement sample of the example shows higher oxygen reduction activity than that of Comparative Example 1, and the catalytic action is easily performed sufficiently.

  Therefore, the mixed conductors of the examples are not limited by the installation environment, are inexpensive and stable, and have both better electronic conductivity and proton conductivity in a low temperature range of room temperature to about 200 ° C. It turns out that it is a thing.

  The present invention can be used for fuel cell systems, sensors, and the like.

It is a schematic cross section which shows the structure for measuring the proton conductivity of the sample for a measurement. It is a graph which shows the relationship between the applied voltage of a sample for a measurement, and the time transition of a response current. It is a graph which shows the specific surface area of the sample for a measurement. It is a graph which shows the average particle diameter of platinum in the sample for a measurement. It is a graph which shows the oxygen reduction current of the sample for a measurement.

Explanation of symbols

1a, 1b ... ion exchange membrane 2a, 3a ... catalyst layer 2, 3 ... carbon cloth

Claims (5)

  An electron conducting material made of an organic material and a proton conducting material capable of transferring protons are combined by dehydration polymerization to form a gel, the gel is freeze-dried or supercritically dried to form a precursor, and the precursor is an inert gas. A mixed conductor having both electron conductivity and proton conductivity obtained by heat treatment in an atmosphere.   The electron conduction material according to claim 1, wherein the electron conduction material contains at least one of polyacetyl, resorcinol, phenol, 2-phenylphenol, polyaniline, polypyrrole, polythiophene, phenylphosphonic acid, and phenylsilane alkoxides. Mixed conductor with both proton conductivity and proton conductivity.   3. The mixed conductivity having both electron conductivity and proton conductivity according to claim 1, wherein the proton conductive material includes at least one of a substance containing a proton dissociation group, a derivative of phosphoric acid, and a derivative of sulfuric acid. body.   Resorcinol, which is a starting material of an electron conducting material capable of transferring electrons, and trimethyl phosphate, which is a starting material of a proton conducting material capable of transferring protons, are combined by dehydration polymerization to form a gel, and the gel is freeze-dried or ultra-dried. A mixed conductor having both electron conductivity and proton conductivity obtained by critical drying to obtain a precursor and heat-treating the precursor in an inert gas atmosphere. A first step in which resorcinol, which is a starting material of an electron conductive material capable of transferring electrons, and trimethyl phosphate, which is a starting material of a proton conductive material capable of transferring protons, are coupled by dehydration polymerization to obtain a gel;
A second step of lyophilizing or supercritically drying the gel to form a precursor;
And a third step of heat-treating the precursor in an inert gas atmosphere. A method for producing a mixed conductor having both electron conductivity and proton conductivity.

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