JPH0230142B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a porous catalyst layer that is effective for use in air electrodes of hydrogen/oxygen fuel cells, metal/air batteries, oxygen sensors, etc., and more specifically, it has a stable service life over a long period of time, and is capable of handling heavy load discharges. The present invention relates to a porous catalyst layer for an air electrode which is capable of catalyzing a gaseous process and also has excellent leakage resistance. Conventionally, air electrodes used in various fuel cells, air cells, galvanic oxygen sensors, etc. have been made by combining a current collector such as a nickel net with a porous catalyst layer having an electrochemical reducing ability for oxygen gas. A laminate with a triple structure integrally attached with a water-repellent layer made of a fluororesin or polypropylene resin such as polytetrafluoroethylene, polytetrafluoroethylene-hexafluoropropylene copolymer, polyethylene-tetrafluoroethylene copolymer It is configured as. The porous catalyst layer is made of conductive powder such as activated carbon powder, graphite powder, or various metal powders as a base material, and the surface of the base material is coated with nickel tungstic acid, palladium/cobalt-coated tungsten carbide, nickel, etc. A catalyst having an ability to reduce oxygen gas such as silver, platinum, palladium, or a metal chelate compound such as iron phthalocyanine or cobalt phthalocyanine is mixed or adsorbed, and then the obtained powder is mixed with or adsorbed to a catalyst such as a metal chelate compound such as silver, platinum, palladium, or iron phthalocyanine or cobalt phthalocyanine. A porous molded body that is formed into a plate or foil after being bound together using a water-repellent binder, and has a structure in which minute through-holes are uniformly distributed inside the body. have. In order to prevent the electrolyte from leaking from the porous catalyst layer, for example, polytetrafluoroethylene, polytetrafluoroethylene-hexafluoropropylene copolymer, polyethylene-tetrafluoroethylene copolymer is generally used. A predetermined amount of a water-repellent substance (having a large contact angle with the electrolytic solution) such as a polymer or polypropylene is mixed into the catalyst-supporting base material to form an integral water-repellent layer; Alternatively, when electrolyte leakage is not allowed, such as the air electrode of a galvanic oxygen sensor used to detect dissolved oxygen gas concentration in water, a water-repellent and oxygen gas permeable material made of the above-mentioned materials may be used. Attempts have been made to form an integral water-repellent layer by attaching a thin film of water to the air-side surface of the porous catalyst layer by an appropriate method such as heat fusion, pressure bonding, or adhesion. Now, within the pores of the porous catalyst layer as described above, a three-phase zone is formed: gas phase (air) - solid phase (catalyst and base material) - liquid phase (electrolyte). In,
The electrochemical reduction reaction of oxygen gas proceeds as shown by the following reaction equation: O ₂ +H ₂ O+2e ^- →HO ₂ ^- +OH ^- . As a result, current can be taken out via the base material (conductive) and the integrally attached current collector. However, in such a porous catalyst layer, the catalyst capable of reducing oxygen gas is simply mixed with the base material or simply adsorbed on the surface of the base material, so long-term storage and continuous discharge are difficult. If this happens, the catalyst may separate or fall off from the base material, impairing its long and stable service life. In addition, with conventional porous catalyst layers, continuous heavy load discharge (for example, 50 mA/cm ² or more) is extremely difficult, and in order to perform heavy load discharge, it is necessary to increase the thickness of the catalyst layer. As a result, the battery as a whole becomes larger.
For example, in the case of a porous catalyst layer mixed with the above-mentioned water-repellent substance, continuous discharge of about 20 mA/cm ² is possible, but the layer is thick at 0.125 to 0.5 mm, and in order to solve this problem, When the above thin film is attached to the air side surface of the porous catalyst layer, its thickness is
Although it is possible to reduce the thickness to about 12.5 μm, it is difficult to draw out a current of 10 mA/cm ² or more continuously in this case. The present inventors have conducted extensive research in order to eliminate the above-mentioned drawbacks regarding conventional porous catalyst layers, especially porous catalyst layers using metal chelate compounds having oxygen gas reduction ability as catalysts.
When the catalyst is chemically bonded to the base material and at the same time, a fluorine solvent and a perfluoro compound having oxygen gas dissolving ability are adsorbed and supported in the coexistence, in the obtained porous catalyst layer, the The present invention was completed after discovering the fact that the separation and falling off of the liquid is significantly suppressed, resulting in a stable service life over a long period of time, and that heavy load discharge, especially continuous heavy load discharge, is possible, and leakage resistance is improved. I came to the point. The present invention aims to provide a porous catalyst layer for an air electrode that has a stable service life over a long period of time, is capable of heavy load discharge, especially continuous heavy load discharge, and has excellent leakage resistance. do. The porous catalyst layer of the present invention is a conductive layer in which a metal chelate compound having an ability to reduce oxygen gas is chemically bonded, and at the same time, a fluorine solvent and a perfluoro compound having an ability to dissolve oxygen gas are adsorbed and supported. It is characterized by being a porous powder or a porous compact thereof. The metal chelate compound used in the present invention has the property of performing an electrochemical reduction reaction of oxygen gas, and includes, for example, metal phthalocyanine such as iron phthalocyanine, copper phthalocyanine, and cobalt phthalocyanine; cobalt polyphylline;
Metal polyphyllins such as iron polyphyllins can be mentioned, and in particular, at least one type selected from iron phthalocyanine and cobalt polyphyllin, and their dimers have a high oxygen gas reduction ability (4-electron reduction ability), so they are heavily loaded. It is preferred because it also enables discharge. These metal chelate compounds are preferably combined in an amount of 1 to 10% by weight based on the weight of the conductive powder or porous molded product thereof. These metal chelate compounds are chemically bonded to the conductive powder or porous molded body thereof, for example, by the following method. That is, a conductive powder or a porous molded product thereof is treated according to a conventional method for introducing functional groups to inject functional groups such as carboxyl groups, carbonyl groups, hydroxyl groups, lactones, and amino groups on the surface or internal pore walls. will be introduced. For example, if activated carbon powder, graphite powder, or a porous compact thereof is treated with a potassium dichromate solution, carboxyl groups, carbonyl groups, etc. are easily introduced onto the surface or the walls of internal pores. Furthermore, by heat-treating nickel powder or a porous molded product thereof in air, hydroxyl groups can be introduced into its surface or internal pore wall surfaces. Furthermore, in the case of introducing an amino group, a nitro group is introduced into the surface or internal pore wall using nitric acid or the like in advance, and then this group is reduced.
Alternatively, methods such as treatment with ammonia gas or mixed plasma of hydrogen and nitrogen and direct introduction can be applied. A dehydration reaction or a substitution reaction occurs between the conductive powder or its porous molded body into which various functional groups have been introduced onto the surface in this way, and a metal chelate compound having an amino group, a carboxyl group, a sulfone group, a hydroxyl group, etc. By performing this, a chemical bond such as amide, ester, carbonyl, or ether is formed between the functional group and the metal chelate compound, and the metal chelate compound becomes the conductive powder or porous molded product thereof. chemically bonded firmly to the surface or internal pore walls. As a result, the metal chelate compound is prevented from separating or falling off from the conductive powder or the porous molded body thereof. Further, the fluorine solvent used in the present invention has an ability to dissolve oxygen gas, is liquid at room temperature, has a relatively high boiling point and ability to dissolve oxygen gas, and has a relatively low surface tension. For example, Boiling point: 100~
200°C, oxygen gas dissolution ability: 40 vol% or more, surface tension: 30 dyne/cm or less is preferable. for example,
1-chloro-1,2,2-trifluoroethylene low polymer (degree of polymerization 4 to 8, molecular weight 500 to 900),
1,1,2,2-tetrachloro-1,2-difluoroethane, 1,1,2-trichloro-, 1,
Examples include 2,2-trifluoroethane. Among these, the low polymer of 1-chloro-1,2,2-trifluoroethylene has a high oxygen gas dissolving ability of more than 10 times that of water, and has excellent alkali resistance, acid resistance, and heat resistance. This is the most preferable one when applied to the present invention. Furthermore, the perfluoro compound used in the present invention is
It has the ability to dissolve oxygen gas, for example,
Examples include perfluoro-tri-n-butylamine, perfluoro-tri-propylamine, perfluorodecalin, perfluoromethyldecalin, and perfluorinated ethers. These compounds have an oxygen solubility of approximately 40 vol% (the oxygen solubility of blood is approximately
22vol%) and oxygen transfer rate is 14-26
m・sec (90m・sec for hemoglobin in blood)
sec) and large. These fluorine solvents and perfluorinated compounds are
The metal chelate compound is adsorbed and coexisted on the surface or internal pore walls of the conductive powder or the porous molded product to which the metal chelate compound has already been chemically bonded. This can be easily achieved by immersing a conductive powder or a porous compact thereof to which a metal chelate compound has already been chemically bonded into the above-mentioned fluorine solvent and perfluoro compound. In this way, in the three-phase zone mentioned above,
Metal chelate compounds, fluorine solvents, and perfluoro compounds coexist. As described above, the metal chelate compound performs an electrochemical reduction reaction of oxygen gas. Both the fluorine solvent and the perfluoro compound exhibit the ability to dissolve oxygen gas, thereby increasing the oxygen gas concentration (partial pressure) in the three-phase zone, thereby making heavy load discharge possible. Fluorinated solvents and perfluorinated compounds are
Both have similar oxygen gas dissolving ability, but
They differ in their rate of oxygen gas uptake. That is, fluorine solvents have a low oxygen gas uptake rate but have a long storage time, while perfluoro compounds have a high uptake rate but have a short storage time. Therefore, when only a fluorine solvent coexists with a metal chelate compound, instantaneous heavy load discharge is possible, but when heavy load discharge is continued for a long time, the consumption rate of oxygen gas in the three-phase zone becomes Since the fluorine solvent cannot take in oxygen gas at a rate that follows that, continuous heavy load discharge becomes impossible. On the other hand, as in the present invention, when a perfluoro compound is also present, the oxygen gas uptake rate of the perfluoro compound is high, so in the three-phase band, it is sufficient to meet the oxygen gas consumption rate during heavy load discharge. This allows for continuous heavy load discharge. In this way, the porous catalyst layer of the present invention enables heavy load discharge, especially continuous heavy load discharge, by skillfully combining the advantages and disadvantages of fluorine solvents and perfluoro compounds. It is. The fluorine solvent exhibits the above effect when 0.1% by weight or more is adsorbed and supported on the weight of the conductive powder or its porous molded product, but if it exceeds 20% by weight,
The internal resistance of the catalyst layer itself increases, and as a result, the voltage drop during heavy load discharge becomes large, which is disadvantageous.
Further, the perfluoro compound is preferably used after being dissolved in a fluorine solvent, and in that case, the perfluoro compound is preferably in a range of 0.1 to 10% by volume based on the solvent volume of the fluorine solvent. Note that these fluorine solvents and perfluoro compounds not only contribute to heavy load discharge of the porous catalyst layer, but also contribute to improving the leakage resistance of the obtained catalyst layer based on their own water repellency. have power. In the present invention, the base material of the porous catalyst layer is a conductive powder or a porous compact thereof. The conductive powder is activated carbon powder, graphite powder, or nickel powder. Also, its particle size is 50~1000μ
It is preferable that it be in a certain degree. When the base material is a porous molded body, the removal rate of oxygen reduction product ions can be increased, and as a result, a current with a high current density can be extracted, and a water-repellent layer can be formed more uniformly. The pore size is preferably about 0.1 to 10μ. Preferred methods for producing the porous catalyst layer of the present invention include, for example, the following method. A metal chelate compound is chemically bonded to the surface of a conductive powder, and then this powder is suspended in a fluorinated solvent containing a perfluoro compound to adsorb and support them. A method of kneading the kneaded product with a porous molded product (for example, a sheet) of an appropriate thickness by rolling the kneaded product, for example, and forming a porous molded product of a conductive powder chemically bonded with a metal chelate compound using a binder. A method of forming a molded body and adsorbing and supporting a fluorine solvent containing a perfluoro compound in the internal pores of the body;
Alternatively, after forming a porous molded body with conductive powder in advance, a metal chelate compound is chemically bonded to the surface and internal pore walls, and then a fluorine solvent and a perfluorinated compound are coexisted and adsorbed. However, the method is not necessarily limited to these methods. Since the porous catalyst layer of the present invention is constructed as described above, the catalyst having oxygen gas reducing ability will not separate or fall off due to long-term storage or continuous discharge, and the oxygen gas concentration in the three-phase zone will be reduced. (Partial pressure) is high, oxygen gas uptake speed is high, and water repellency is also improved, making it possible to have a stable service life over a long period of time, heavy load discharge, especially continuous heavy load discharge, and leakage resistance. It also improves and is extremely useful. The present invention will be explained below based on examples. Example (1) Preparation of porous catalyst layer Sample 1: Activated carbon with an average particle size of 150 μm was suspended in a 30% potassium dichromate solution and stirred at 30° C. for 2 hours. When this powder was analyzed by infrared absorption spectrum, it was confirmed that carboxyl groups were introduced onto the surface of the powder. Next, a dehydration reaction was carried out between this powder and the cobalt phthalocyanine into which an amino group had been introduced by a conventional method, and 5% by weight of the cobalt phthalocyanine was chemically bonded to the activated carbon powder through the generated amide bonds. This powder was mixed with 1-chloro-1,2,2-trifluoroethylene containing 5% by volume of perfluorodecalin (polymerization degree 4-6, molecular weight
500-700) suspended in a solution. The powder adsorbed 10% by weight of the above fluorine solvent. Next, add 10 to 20% by weight as a binder to this.
After adding 60% PTFE daypartition and thoroughly kneading, the mixture was rolled out to form a sheet with a thickness of 0.7 mm. The obtained sheet had a porous structure with 60% of the pores having an average pore diameter of 40 μm. Sample 2: Activated carbon powder with an average particle size of 150μ was suspended in a 20% potassium permanganate solution and stirred at 25°C for 3 hours. It was confirmed by infrared absorption spectrum analysis that carbonyl groups were introduced into the surface of the obtained powder. Next, the carbonyl group of this powder is oxidized to become a carboxyl group, and then a dehydration reaction is carried out with the iron phthalocyanine obtained by introducing a hydroxyl group by a conventional method, and the iron phthalocyanine is chemically bonded to the activated carbon powder through an ester bond. I let it happen. To this was added 10 to 20% by weight of 60% PTFE dispersion as a binder, thoroughly kneaded, and then rolled out to form a sheet with a thickness of 0.7 mm. The obtained sheet had a porous structure with 60% of the pores having an average pore diameter of 40 μm. This sheet was prepared by using a 1-containing sheet containing 5% by volume of perfluorotri-n-butylamine.
The whole was immersed in chloro-1,2,2-trifluoroethylene and dried at 60° C. under a vacuum of 3 Torr for 24 hours. The sheet was impregnated with 15% by weight of the above fluorine solvent. Sample 3: Activated carbon powder with an average particle size of 150 μm was suspended in a mixed acid of 36% hydrochloric acid and 60% nitric acid (mixing ratio: 3:1) and stirred at 40° C. for 1 hour. It was confirmed by infrared absorption spectrum analysis that nitro groups were introduced into the surface of the obtained powder. Next, this powder is treated in a mixed plasma of nitrogen and hydrogen to reduce the nitro group to an amino group, and then a dehydration reaction is carried out by a conventional method between it and a dimer of cobalt polyphylline into which a carboxyl group has been introduced. Let's do cobalt porphyrin 2
The polymer was bonded to activated carbon powder. Next, perfluorodecalin and 1-chloro-1,2,2-trifluoroethylene were adsorbed in exactly the same manner as Sample 1, and then molded to produce a sheet with a thickness of 0.7 mm. This sheet is
It had a porous structure with 60% of the pores having an average pore diameter of 38μ. Sample 4: A nickel sintered body with a porosity of 85% and a thickness of 0.7 mm was heat treated in air at 850°C for 3 minutes. It was confirmed by infrared absorption spectrum that hydroxyl groups were introduced on the entire surface and on the walls of internal pores. Next, a dehydration reaction was carried out in a conventional manner between the hydroxyl groups of this sintered body and the hydroxyl groups introduced into the cobalt phthalocyanine, thereby chemically bonding the cobalt phthalocyanine to the activated carbon powder through an ether bond. Next, a sheet on which perfluorotri-n-butylamine and 1-chloro-1,2,2-trifluoroethylene were adsorbed and supported was produced in the same manner as in the production method of Sample 2. Sample 5: Activated carbon powder with an average particle size of 150 μm was suspended in a pyridine solution of cobalt phthalocyanine, and cobalt phthalocyanine was adsorbed on the surface of the powder. Next, sample 1 was prepared without adsorbing perfluorodecalin and 1-chloro-1,2,2-trifluoroethylene.
A sheet with a thickness of 0.7 mm was prepared in exactly the same manner as in the case of . The obtained sheet had a porous structure similar to that of Sample 1. (2) Preparation of air electrodes A nickel net (current collector) was crimped on one side of each sheet of samples 1, 2, 3, and 5, and a thickness was applied on the other side.
A composite thin film of 20 μm polytetrafluoroethylene (water-repellent layer)/fluoroethylene propylene (thermal adhesive layer) was heat-sealed at 250°C to form a triple-layered air electrode with a total thickness of approximately 0.7 mm.
The nickel sintered body of Sample 4 was made into an air electrode by heat-sealing the composite thin film described above on one side thereof. (3) Performance test of porous catalyst layer Using the above five types of air electrodes, the weight ratio was 3.
% mercury amalgamated zinc powder passed through a 60-150 mesh sieve is dispersed in a gel electrolyte in which a gelling agent is dispersed in a sodium hydroxide solution, and a polyamide nonwoven fabric is used as a separator to form an air-zinc electrode. Assembled the battery. After leaving these batteries in air at 25°C for 16 hours, they were discharged for 5 minutes with various currents, and the terminal voltage after 5 minutes was 1.0V.
The current value below was measured, and this was taken as the initial performance of the battery. Next, after leaving these batteries in air at 25°C for 6 months or 12 months, measure the current value at which the terminal voltage becomes 1.0V or less using the same method as above, and determine the initial performance (initial current value) of this current value. The ratio to Furthermore, these batteries were stored in an atmosphere of 45° C. and 90% relative humidity, and the number of days until leakage occurred was measured. The discharge duration at the maximum current density of each battery was measured, and the ratio of the duration to Comparative Example 5 was calculated. These results are collectively shown in the table.

[Table] As is clear from the above table, the air battery using the porous catalyst layer of the present invention has
Its initial performance is extremely high, allowing for heavy load discharge, and the discharge duration at maximum current density is also long.Furthermore, the ratio to the initial performance is large, it has a long service life, and is also leak resistant. It turned out to be excellent. In the above example, an air-zinc battery using potassium hydroxide as the electrolyte was assembled and its performance was evaluated, but other electrolytes such as ammonium chloride, sodium hydroxide, lithium hydroxide, hydroxide It goes without saying that similar effects can be obtained by using a solution in which cesium, rubidium hydroxide, etc. are mixed with these solutions. It can also be used in air-iron batteries. As detailed above, by using the porous catalyst layer of the present invention, it is possible to easily obtain an air electrode that has a long service life, is capable of heavy load discharge, especially continuous heavy load discharge, and has excellent leakage resistance. Therefore, its industrial utility value can be said to be great.

Claims (1)

[Scope of Claims] 1. A conductive powder in which a metal chelate compound having the ability to reduce oxygen gas is chemically bonded, and at the same time, a fluorine solvent and a perfluoro compound having the ability to dissolve oxygen gas are adsorbed and supported in the coexistence. or a porous catalyst layer of an air electrode, characterized by being a porous molded body thereof. 2. The conductive powder is any one of activated carbon powder, graphite powder, and nickel powder, and the metal chelate compound is at least one selected from the group of iron phthalocyanine, cobalt porphyrin, and dimers thereof.
species, and the fluorine solvent is 1-chloro-
1,2,2-trifluoroethylene, 1,1,
At least one compound selected from the group of 2,2-tetrachloro-1,2-difluoroethane and 1,1,2-trichloro-1,2,2-trifluoroethane, and the perfluoro compound is perfluoro The air according to claim 1, which is at least one compound selected from the group of tri-n-butylamine, perfluorotri-propylamine, perfluorodecalin, perfluoromethyldecalin, and perfluorinated ethers. Porous catalyst layer of electrode.