JPH04345B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a positive electrode for fuel cells or air cells that has small polarization and can obtain a large current;
More specifically, in the air electrode or oxygen electrode of a fuel cell or air cell, a reactant for catalyst synthesis and an electrode current collector material are mixed to prepare the electrode,
The present invention relates to a novel method for manufacturing the above-mentioned electrode, in which catalyst synthesis is carried out by heating under a non-reactive gas, and polyiron phthalocyanine is directly supported on the electrode current collector material at the same time as the synthesis. Conventionally, various proposals have been made regarding catalysts used in air electrodes or oxygen electrodes for fuel cells and air cells. That is, as air electrode catalysts or oxygen electrode catalysts for fuel cells, metals such as copper, silver, gold, platinum, and palladium, tungsten bronze, iron or copper phthalocyanine, activated carbon, and nickel oxide doped with lithium are known. In addition, as air electrode catalysts for air batteries, noble metals such as platinum, palladium, ruthenium and silver, alloys of silver and mercury and ruthenium and gold, oxides of transition metals such as manganese and osmium, and NiFe are used. _{2O4 , COFe2O4 , NiCr2O4 _}
Spinel oxides such as COAl 2 O ₄ and COAl ₂ O 4 are known. However, among these catalysts in the prior art, noble metals are expensive and therefore uneconomical, while others are inexpensive, but the air electrode or oxygen electrode using these as catalysts has a polarization greater than that of noble metals. In addition, the electrode characteristics are not good enough, such as a considerable potential drop in the high current density region, and as a result, large currents cannot be obtained in fuel cells and air cells incorporating such electrodes. There were flaws. The present invention has been made in view of the current situation, and its purpose is to provide a high energy density device that has small polarization and can obtain a large current with almost no potential drop even in the large current density region. An object of the present invention is to provide a method for manufacturing electrodes for fuel cells and air cells. To summarize the present invention, the fuel cell of the present invention
The method for producing an electrode for an air battery is to mix an electrode current collector material with at least one of pyromellitic dianhydride, pyromellitamide, pyromellitonitrile, at least one iron compound, and urea, and then process the mixture under a non-reactive gas atmosphere. The present invention is characterized in that polyiron phthalocyanine is synthesized by a heating reaction and at the same time is supported on the electrode current collector material. Until now, there has been no example of using polyiron phthalocyanine by the above-mentioned supporting method as a catalyst in an air electrode or an oxygen electrode for a fuel cell or an air cell. According to the present invention, a novel configuration in which the electrode contains polyiron phthalocyanine by the above-mentioned simultaneous synthesis and loading method,
As will be described later, compared to the case of conventional iron phthalocyanine or polyiron phthalocyanine supported by conventional methods, the process of supporting the catalyst on the electrode can be omitted, and the polarization of the prepared electrode is reduced, making it possible to obtain a large current. This excellent effect can be obtained. The present invention will be explained in more detail. A fuel cell is constructed using hydrogen gas etc. as a negative electrode active material, and an alkaline electrolyte such as KOH or NaOH, a neutral electrolyte such as NaCl or KCl, or an acidic electrolyte such as phosphoric acid as an electrolyte. is constructed by using zinc, aluminum, magnesium, iron, platinum, or an alloy thereof as a negative electrode active material, and using the same electrolyte as the above electrolyte for fuel cells as an electrolyte. The electrode in the present invention is used as a positive electrode for the above-mentioned fuel cells and air cells. The electrode current collector material serving as the main body of the electrode may be any material conventionally used for this type of electrode. For example, it can be one or more carbon materials such as carbon powder, graphite, acetylene black, Ketchen Black EC, activated carbon, carbon fiber, and porous nickel electrode plates. To such an electrode current collector material, one or more of pyromellitic dianhydride, pyromellitamide, and pyromellitonitrile, an iron compound, and urea are added. The aforementioned iron compound may be any compound as long as it reacts with one or more of pyromellitic dianhydride, pyromellitamide, and pyromellitonitrile to produce polyiron phthalocyanine. For example, it can be ferrous chloride, ferric chloride, ferrous sulfate. The mixing amount of the above-mentioned iron compound is preferably 3.5% by weight or more based on the entire electrode material (the same applies hereinafter). If it is less than 3.5% by weight, it will be difficult to obtain the effect of the present invention, that is, to obtain a battery with better performance than conventional ones. On the other hand, the amount of one or more of pyromellitic dianhydride, pyromellitamide, and pyromellitonitrile added is preferably 10% by weight or more. This is because if it is less than 10% by weight, it will be difficult to obtain a battery with good performance. Also, urea, which is one of the reactants, is preferably
Adding 0.6% by weight or more, less than 0.6% by weight,
As in the case of iron compounds and pyromellitic compounds, it is difficult to enjoy the effects of the present invention. Optionally, a synthesis catalyst such as ammonium molybdate may be added to such a mixture. Such a mixture is reacted in an atmosphere of a non-reactive gas such as nitrogen or argon gas to synthesize polyiron phthalocyanine, which is supported on the electrode current collector material to form an electrode material. The conditions for such synthesis and support are preferably heating at a temperature of 300° C. or higher for 20 hours or longer. This is because polyiron phthalocyanine is difficult to produce at temperatures below 300°C and for less than 20 hours. The positive electrode is produced by molding and pressing a mixed powder consisting of an electrode current collector material such as a carbon material containing the above-mentioned polyiron phthalocyanine and a water repellent together with a metal mesh such as nickel or silver, and then heating and baking the mixture. be able to. The polyiron phthalocyanine in the present invention is described in the literature
A.Epsteinet.Al.J.Che m.Phys, 32, 324 (1960)
Or H.Inoueet.al.Bull.Chem.Soc.Japan,
40, 184 (1967), polycopper phthalocyanine, that is, a structure in which one or more of the four benzene rings constituting the phthalocyanine is covalently polymerized with adjacent phthalocyanines, in which copper is replaced with iron. It is something. In this publication, polycopper phthalocyanine is obtained by the following reaction. The reason why the above-mentioned polyiron phthalocyanine in the present invention is effective as a catalyst is that the most efficient four-electron reaction (for example, O ₂ + 2H ₂ O + 4e ^- → 40H ^- in an alkaline electrolyte) is selected among the positive electrode reactions,
In addition, two-electron reactions (e.g. in alkaline electrolytes)
O ₃ + H ₂ O + 2e ^- → OH ^- + HO ₂ ^- , the intermediates produced are predominant (when using an acidic electrolyte; H ₂ O ₂ ; when using an alkaline electrolyte: HO). This is thought to be due to the fact that by increasing the decomposition rate of _2- ⁾ , it is easy to supply enough electrons to make the electrode reaction proceed sufficiently smoothly in any reaction process. Furthermore, by employing the method of supporting the polyiron phthalocyanine at the same time as the synthesis in the present invention, good contact is made between the polyiron phthalocyanine and the electrode current collector material such as a carbon material (there may be some chemical bonding). ), the conductivity is improved and the supply of electrons becomes smoother. Next, the structure of the positive electrode in the present invention will be explained with reference to the drawings. That is, FIG. 1 is a schematic cross-sectional view showing a specific example of the structure of the positive electrode (air electrode or oxygen electrode) according to the present invention, in which 1 is an electrode material layer, 2 is a nickel mesh, and 3 is a hydrophobic porous layer. It is a layer. When this air electrode is assembled into a battery, it is oriented so that the electrode material layer 1 is in contact with the electrolyte and the hydrophobic porous layer 3 is in contact with the gas. As a result, a three-phase interface of electrolyte, gas, and electrode powder is formed in the electrode material layer 1. Note that the nickel net 2 has an electrode material layer 1.
and is provided as a support and a current collector for the hydrophobic porous layer 3. The hydrophobic porous layer 3 uses the same material as the electrode material layer 1 provided on the electrolyte side, but has a higher proportion of water repellent than the electrode material layer 1 (or is made of only a water repellent). (However, in this case, it only has a water-repellent effect and does not contribute to the reaction.) and increases the porosity. Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto in any way. In the measurements of the current dependence of electrode potential in Examples, potentials were evaluated using a saturated calomel electrode (SCE) as a reference electrode. The measurement is
It was carried out at room temperature of 20-25°C. Example 1 4 g of pyromellitonitrile (PN), FeCl ₂
Ammonium molybdate (NH) ₄ Mo _{7 O 24} .
4H ₂ OO.1 g, further 1 g of carbon powder (passed through 200 meshes), 3 g of acetylene black (AB), and 4 g of Kettien Black EC as electrode current collector materials were mixed well in a mortar and heated in a separate flask under N ₂ atmosphere at 500°C. It was heated for 70 hours. Thereafter, the temperature was raised to 550°C and the mixture was further heated for 2 hours. The obtained powder is
Washed by Soxhlet extraction with methanol and pyridine. After drying, 4.5 g of the obtained powder and 2.5 g of polytetrafluoroethylene emulsion (containing 60% polytetrafluoroethylene) are thoroughly mixed and formed into a sheet using a roll. After drying the sheet in the air for about 30 minutes, place a nickel mesh (50 mesh) on one side, then place a porous polytetrafluoroethylene sheet on top of it and heat it at 250℃.
Hot press at a temperature of 100 kg/cm ² for 30 minutes. It was cooled in air and cut into a circle with a diameter of 30 mm to produce an air electrode. An air battery was constructed using 1N KOH as the electrolyte and zinc as the negative electrode, and the dependence of the electrode potential (E, vs. SCE) of the air electrode in air on current density was investigated. For comparison, the same amount of iron phthalocyanine or polyiron phthalocyanine (2.5 g) as the amount of polyiron phthalocyanine thought to have been supported by the above method was added to 1 g of carbon powder with 3 ml of acetylene black.
The current density dependence of the electrode potential of an air electrode prepared in the same manner as above from 4.5 g of this mixed powder and 2.5 g of polytetrafluoroethylene emulsion, supported on a mixed powder of 4 g of Ketsuen Black EC. I looked it up at the same time. The results are shown in Figure 2. That is, FIG. 2 is a graph showing the relationship between the current density of the air electrode and the electrode potential in this example. B and C are the cases in which iron phthalocyanine and polyiron phthalocyanine were supported by conventionally known methods, respectively, and D is the case in which conventionally known silver was used as a catalyst. According to FIG. 2, when polyiron phthalocyanine is supported by the simultaneous synthesis method shown in this example, the equilibrium potential is -0.060V, 50mA/
-0.270V when ^cm2 current is applied, -0.378V when 100mA/ ^cm2 current is applied. As is clear from FIG. 2, compared to the case of iron phthalocyanine and polymer supported by the conventional method or the case of using silver as a catalyst, the present invention supports polyiron phthalocyanine by a method of supporting simultaneously with synthesis. In the case of , the equilibrium potential is high and the polarization is small, and the potential is stable without a significant drop even in the high current density region. Example 2 The same starting materials and electrode constituent carbon materials as in Example 1 were thoroughly mixed, and synthesized and supported in a nitrogen atmosphere under the temperature and reaction time conditions shown in Table 1. The obtained powder was washed and dried in the same manner as in Example 1, and then an air electrode was prepared and the dependence of the electrode potential on current density was examined.

[Table] The results are shown in Figure 3. That is, FIG. 3 is a graph showing the relationship between the electrode potential and current density of the air electrode in this example. Show characteristics. According to the measurement results in Fig. 2, the equilibrium potential of the electrodes is 50 mA/cm ² , energization,
It can be seen that the respective potentials after 100mA/ ^cm2 current are as shown in Table 2.

[Table] As explained above, the positive electrode (air electrode or oxygen electrode) produced through the method of mixing the starting material and the carbon material constituting the electrode, synthesizing polyiron phthalocyanine, and simultaneously supporting it, has a catalyst externally. It is possible to simplify the production process by omitting the step of adding from the catalyst, and it is also possible to efficiently support a sufficient amount of catalyst in the constituent materials, and its characteristics include low polarization. It exhibits superior effects compared to conventional ones, with almost no potential drop even in the high current density region. Therefore, fuel cells and air cells incorporating this electrode as a positive electrode can obtain large currents and have even higher energy densities, and have extremely high practical value compared to conventional products. can be expected.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a specific example of the structure of a positive electrode (air electrode) manufactured by the method of the present invention, and FIGS. 2 and 3 are air electrodes of examples of the present invention. 2 is a graph showing the relationship between current density and electrode potential. 1... Electrode material layer, 2... Nickel net, 3... Hydrophobic porous layer.

Claims (1)

[Claims] 1 Mix pyromellitic acid dianhydride, pyromellitamide, one or more pyromellitonitrile, one or more iron compounds, and urea together with the electrode current collector material, and react by heating in a non-reactive gas atmosphere to form polyiron phthalocyanine. A method for producing an electrode for a fuel cell/air cell, characterized in that it is synthesized and at the same time supported on the electrode current collector material.