JPH0325900B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a catalyst layer of an air electrode such as a hydrogen/oxygen fuel cell, a metal/air battery, or an oxygen sensor, and a method for manufacturing the same. It relates to a method of manufacturing at low cost. Conventionally, gas diffusion electrodes have been used as various air electrodes. Recently, this gas diffusion electrode is made up of a conductive porous catalyst layer having electrochemical reduction ability for oxygen gas and a water-repellent layer integrally attached to the gas side surface of the catalyst layer. It is configured as a layered electrode. In this case, the catalyst layer includes nickel tungstic acid with low oxygen reduction overpotential, tungsten carbide coated with palladium and cobalt; noble metals such as nickel, silver, platinum, and palladium; metal oxides such as manganese dioxide; metal phthalocyanine, A catalyst having the ability to electrochemically reduce oxygen gas, such as a chelate compound such as metal porphyrin, is supported on a base material that is a conductive powder such as activated carbon powder or graphite powder, and the resulting powder is Fluoroethylene (hereinafter referred to as PTFE),
It is a porous molded body formed into a predetermined shape (for example, a plate shape) using an electrolyte-resistant binder such as polyethylene. Alternatively, the base material may be prepared by forming a porous body using conductive powder in advance, and the above-mentioned catalyst may be supported on the base material. Now, within the pores of such a porous catalyst layer, a two-electron reduction reaction of oxygen as shown in equation (1) proceeds due to the action of the supported catalyst. O ₂ +H ₂ O+2e ^- →O ₂ H ^- +OH ^- (1) Furthermore, it is known that dimers of each of cobalt porphyrin and iron porphyrin, which are a type of metal porphyrin in the above-mentioned catalyst group, exist. However, when these dimers are used as catalysts, it is presumed that a four-electron reduction reaction of oxygen as shown in equation (2) is proceeding. O ₂ +2H ₂ O+4e ^- →4OH ^- (2) Therefore, when a dimer of cobalt porphyrin or a dimer of iron porphyrin is used as a catalyst, in the case of a catalyst that advances the reaction of formula (1) A larger current can be drawn compared to the That is, heavy load discharge becomes possible. However, metal porphyrin dimers are generally insoluble in water and alcohol, and only soluble in limited organic solvents such as benzene, pyridine, dimethylformamide (DMF), and tetrahydrofuran (THF). Furthermore, even in these organic solvents, the saturated amount of metal porphyrin dimer dissolved is as small as around 1%. Therefore, when a metal porphyrin dimer is supported on a base material that is a conductive powder or a porous molded body thereof, first, the metal porphyrin dimer powder is dissolved in the above organic solvent until it is saturated, It was necessary to repeat several times the operation of immersing the substrate in the resulting solution, then taking it out and drying it, volatilizing the organic solvent, and precipitating the metal porphyrin dimer. Therefore, in order to support a predetermined amount of metal porphyrin dimer, it was necessary to repeat the process many times and take a lot of time. Furthermore, since all of the organic solvents used are substances harmful to the human body, it is necessary to install equipment for removing or recovering the organic solvents and their vapors in order to ensure the safety and health of workers. The present inventors have conducted intensive research to resolve the above-mentioned difficulties in using metal porphyrin dimers as catalysts, and have found that by introducing a hydrophilic group into the metal porphyrin dimers, organic solvents can be removed. The present invention was completed based on the idea that it could be easily supported on a substrate in a state in which it is simply dissolved in water without using it. An object of the present invention is to provide a catalyst layer capable of heavy load discharge and a method for manufacturing the same. The catalyst layer of the present invention uses a metal porphyrin dimer having a hydrophilic group as a catalyst, and the manufacturing method thereof includes dissolving the metal porphyrin dimer having a hydrophilic group in water to form an aqueous solution; A base material, which is a conductive powder or a porous molded body of the conductive powder, is immersed in the solution; then, after the base material is taken out, it is dried or, if necessary, fired in an inert atmosphere. It is something to do. In the catalyst layer of the present invention, a metal porphyrin dimer having a hydrophilic group functions as a catalyst. As the metal porphyrin dimer to be used, cobalt porphyrin dimer and iron porphyrin dimer are preferred from the viewpoint of heavy load discharge. Various hydrophilic groups are introduced into these metalloporphyrin dimers. As a result, it becomes water-soluble.
The hydrophilic group introduced is metalporphyrin 2
Any substance may be used as long as it imparts water solubility without impairing the catalytic ability of the polymer, for example, phenylsulfonic acid group.

[Formula] or its salt with an alkali metal such as Na, K, etc.; phenylcarboxylic acid group

[Formula] Methylpyridinium base

[Formula] Methylaminophe Nyl group

[Formula], their salts, and their derivatives can be mentioned, but among these, phenylsulfonic acid groups or their alkali metal salts are preferably used because they greatly increase the water solubility of the metal porphyrin dimer. It will be done. Such a water-soluble metal porphyrin dimer is prepared as follows. That is, for example, when porphyrin tetrahydroxide is first reacted with p-chlorocarbonylbenzaldehyde, then pyrrole, and then p-carboxybenzaldehyde, a porphyrin having four organic chains bonded to each other with a benzaldehyde group at the end is obtained. . When this is refluxed with pyrrole in a mixed solvent of propionic acid and ethylbenzene, a porphyrin dimer in which two porphyrin rings are linked by an organic chain, such as tetra-meso-[p,p'-phenoxyethoxycarbonylphenyl ]strabi-bisporphyrin is obtained. The dimer thus obtained is processed under mild conditions in which the carbonyl groups and ether bonds introduced in the dimerization process described above do not react, or after masking the functional groups as necessary, for example, in concentrated Sulfonate using sulfuric acid etc. The obtained sulfonated product is reacted with a metal salt to obtain a water-soluble sulfonated metal porphyrin dimer. Now, the catalyst layer of the present invention is manufactured as follows. First, metal porphyrin 2 with a hydrophilic group
Dissolve the powder in water. The dissolved amount is hydrophilic group,
Although it varies depending on the type of metal porphyrin dimer, for example, when the hydrophilic group is a phenyl sulfonic acid group and the metal porphyrin dimer is a cobalt porphyrin dimer, the amount of water per 100 g of water is usually
This is a very large value of 5-10g. In the thus obtained aqueous solution of the metal porphyrin dimer, the conductive powder or its porous molded body, that is, the base material of the catalyst layer, is immersed. As a result, the aqueous solution of metal porphyrin dimer is supported on the surface of the substrate and its internal pores. Next, the base material is taken out from the aqueous solution, dried to volatilize water, and a metal porphyrin dimer having a hydrophilic group is precipitated on the surface or in the internal pores of the base material. If the base material is conductive powder, add PTFE to it.
It is kneaded and bound with a binder such as, and formed into a catalyst layer using a predetermined method (for example, using a rolling roll).
When the base material is a conductive porous molded body, it can be applied as it is as a catalyst layer. At this time, the base material obtained by the above method was heated at 120 to 700°C in an inert atmosphere such as nitrogen or argon.
When heated and calcined in a temperature range of remains.
The remaining metalloporphyrin dimer as described above has an increased number of conjugated bonds in its structure, and its chemical stability increases. Therefore, a catalyst layer made of a heated and calcined base material is useful because its storage characteristics (stability) are improved. Since the present invention is configured as described above, the required amount of metal porphyrin dimer capable of heavy load discharge can be supported on the base material in a single supporting operation, and therefore the manufacturing time of the catalyst layer can be reduced. It can be shortened and the manufacturing cost can be reduced. Furthermore, since no organic solvents harmful to the human body are used, safety and health issues are significantly improved and the method is useful. The present invention will be explained below based on examples. Example (1) Production of catalyst layer Sample 1: 20 g of a powder of a dimer of cobalt porphyrin having 4 phenylsulfonic acid groups per monomolecule was dissolved in 150 g of water at room temperature. 80 g of activated carbon powder having an average particle size of 100 μm was suspended in the resulting aqueous solution. After stirring the whole for 10 hours, activated carbon powder was taken. The obtained powder
Dry at 120°C. Analysis using the DTA method revealed that the above dimer was present on the surface of the activated carbon powder at 8.2
% by weight was supported. Next, this powder was kneaded with PTFE 60% Dice Version, and then rolled and
A 0.5 mm catalyst layer was produced. Sample 2: 10 g of cobalt porphyrin having two phenylsulfonic acid groups per monomolecule was dissolved in 90 g of water at room temperature. 90 g of activated carbon powder having an average particle size of 100 μm was suspended in the resulting aqueous solution. It was confirmed that 8.0% by weight of cobalt porphyrin was supported on the surface of the activated carbon powder. A catalyst layer with a thickness of 0.5 mm was produced in the same manner as in Sample 1. Sample 3: 2 g of cobalt porphyrin dimer was dissolved in 10,000 ml of pyridine. 80 g of activated carbon powder with an average particle size of 100 μm was suspended in the resulting solution. After stirring for 10 hours, the activated carbon powder was separated and the resulting powder was dried at 150° C. in an airtight dryer equipped with a pyridine recovery device. This operation was repeated 10 times to obtain activated carbon powder supporting 7.9% by weight of cobalt porphyrin dimer. Next, a catalyst layer with a thickness of 0.5 mm was produced in the same manner as in Samples 1 and 2. (2) Production of air electrodes and air batteries Each of the three types of catalyst layers described above was sandwiched between a 200μ thick PTFE sheet with a 20% distribution of pores with an average pore diameter of 10μ and a 40 mesh 0.15φ nickel wire gauze.
The whole was pressed to produce three air electrodes. Next, three air batteries were manufactured by a conventional method using these air electrodes, an electrolyte containing potassium hydroxide as a main component, and a zinc cathode. (3) Comparison of each sample The maximum discharge current density at 25°C was measured for the above three air batteries. Submit the results to sample 3.
Table 1 shows the ratios based on the values of the battery using the catalyst layer. Note that the time and cost required for manufacturing the catalyst layers of Sample 1 and Sample 2 were calculated as a ratio with respect to Sample 3, and these are also listed.

[Table] As is clear from Table 1, the catalyst layer according to the present invention (Sample 1) is comparable in maximum current density to the catalyst layer of the conventional method using water-insoluble metal porphyrin (Sample 3). First, it was found that this method was much more advantageous in terms of production time and cost, and that the maximum current density was higher than that of the catalyst layer (sample 2) obtained from a water-solubilized metal porphyrin that is not a dimer. (4) Effect of heating and calcination Three catalyst layers of sample 1 were heated in an argon stream.
It was baked for 20 minutes at each temperature of 300°C, 450°C, and 600°C. An air electrode was prepared from the obtained catalyst layer as described above, and SR44 was prepared using a conventional method.
Three zinc-air batteries were manufactured. This battery is 30
After storing at ℃ for 1 year, 5m at 25℃
Continuous discharge was performed at a current density of A/cm ² . Sample 1, which is not heated and baked, has a discharge duration of each battery.
The ratios are shown in Table 2 based on the case of an SR44 type battery with a catalyst layer of .

[Table] As is clear from Table 2, it was found that heating and firing the catalyst layer increased the discharge duration. Although the above embodiments show an air-zinc battery using potassium hydroxide as the electrolyte, other electrolytes such as ammonium chloride, sodium hydroxide, lithium hydroxide, cesium hydroxide,
It goes without saying that similar effects can be obtained by using rubidium hydroxide or the like. Also, air-
The catalyst layer of the present invention can also be applied to iron batteries. As detailed above, according to the present invention, a catalyst layer for an air electrode capable of heavy load discharge can be manufactured in a short manufacturing time, at low cost, and without causing any harm to the human body. Its industrial value is great.

Claims (1)

[Scope of Claims] 1. A catalyst layer of an air electrode using a metal porphyrin dimer having a hydrophilic group as a catalyst. 2. The catalyst layer of an air electrode according to claim 1, wherein the metal porphyrin dimer is either or both of a cobalt oporphyrin dimer and an iron porphyrin dimer. 3. The hydrophilic group is selected from the group of phenylsulfonic acid group or its salt, phenylcarboxylic acid group or its salt, methylpyridinium group or its salt, methylaminophenyl group or its salt, and derivatives thereof. Claim 1 in which both are one type of group
Catalyst layer of the air electrode described in section. 4. The catalyst layer of an air electrode according to claim 3, wherein the hydrophilic group is a phenylsulfonic acid group or a salt thereof. 5 A metal porphyrin dimer having a hydrophilic group is dissolved in water to form an aqueous solution; a base material which is a conductive powder or a porous molded body of the conductive powder is immersed in the aqueous solution; A method for producing a catalyst layer for an air electrode, which comprises drying or, if necessary, calcining in an inert atmosphere after taking it out. 6. The method for producing a catalyst layer of an air electrode according to claim 5, wherein the metal porphyrin dimer is either a cobalt porphyrin dimer, an iron porphyrin dimer, or both. 7 The hydrophilic group is selected from the group of phenylsulfonic acid group or its salt, phenylcarboxylic acid group or its salt, methylpyridinium group or its salt, methylaminophenyl group or its salt, and derivatives thereof. Claim 5 in which both are one type of group
A method for producing a catalyst layer of an air electrode as described in 1. 8. The method for producing a catalyst layer of an air electrode according to claim 7, wherein the hydrophilic group is a phenylsulfonic acid group or a salt thereof.