JPH0230141B2 - - 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 a porous catalyst layer that has an electrochemical reducing ability for oxygen gas, a current collector such as a nickel net, For example, a double-layered laminate with an integral water-repellent layer made of a fluororesin or polypropylene resin such as polytetrafluoroethylene, polytetrafluoroethylene-hexafluoropropylene copolymer, polyethylene-tetrafluoroethylene copolymer It is structured as a body. 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 solution). In the obi,
The electrochemical reduction reaction of oxygen gas proceeds as shown by the following reaction formula: 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 or continuous discharge is not possible. 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 thickness of the layer is as thick as 0.125 to 0.5 mm, and it is difficult to solve this problem. Therefore, 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.
The porous catalyst layer, which is made by chemically bonding the catalyst to a base material and simultaneously adsorbing a fluorine solvent capable of dissolving oxygen gas, firstly significantly suppresses the separation and falling off of the catalyst from the base material. It has a stable service life over a long period of time, and at the same time, the oxygen concentration (partial pressure) in the three-phase zone increases due to the ability of the adsorbed fluorine solvent to dissolve oxygen gas, and as a result, the heavy load discharge The present invention was completed based on the discovery that it is possible to improve the liquid leakage resistance. The object of the present invention is 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, and has excellent leakage resistance. The porous catalyst layer of the present invention is made of a conductive powder or a porous compact thereof, to which a metal chelate compound having an ability to reduce oxygen gas is chemically bonded, and at the same time a fluorine solvent having an ability to dissolve oxygen is adsorbed and supported. characterized by something. 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 porphyrin,
Examples include metal porphyrins such as iron porphyrins, particularly at least one selected from metal phthalocyanines, cobalt porphyrins,
In addition, these dimers have a high oxygen gas reduction ability (4-electron reduction ability) and therefore enable heavy load discharge, and are therefore preferably used. These metal chelate compounds are preferably combined in an amount of 1 to 10% by weight based on the weight of the conductive powder used 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-1,2,
Examples include 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. These fluorinated solvents exhibit their effectiveness when 0.1% or more of the weight of the conductive powder or porous compact is adsorbed and supported, but if it exceeds 20% by weight, the internal resistance of the catalyst layer itself increases. However, as a result, the voltage drop during heavy load discharge increases.
The adsorbed and supported amount is preferably in the range of 0.1 to 20% by weight based on the weight of the conductive powder or porous molded body thereof. Note that these fluorine solvents contribute to the heavy load discharge characteristics of the porous catalyst layer, and also contribute to improving the leakage resistance of the obtained catalyst layer based on their own water repellency. 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. The porous catalyst layer of the present invention is prepared by the following method. An example of this is shown below. (1) Conductive powder is treated according to a conventional method for introducing functional groups to introduce functional groups such as carboxyl groups, carbonyl groups, hydroxyl groups, lactones, and amino groups onto its surface. For example, when activated carbon powder or graphite powder is treated with a potassium dichromate solution, carboxyl groups, carbonyl groups, etc. are easily introduced onto the surface thereof. Furthermore, by heat-treating nickel powder or a porous sintered body thereof in air, hydroxyl groups can be introduced onto its surface. Furthermore, in the case of introducing an amino group, it is possible to introduce a nitro group to the surface in advance using nitric acid or the like and then reduce this group, or to directly introduce it by treating with ammonia gas or a mixed plasma of hydrogen and nitrogen. method can be applied. In this way, dehydration reactions, substitution reactions, etc. are carried out between the conductive powder having various functional groups introduced onto its surface and the metal chelate compound having amino groups, carboxyl groups, sulfone groups, hydroxyl groups, etc. 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 is firmly bonded to the surface of the conductive powder. Next, this powder is suspended in the above-mentioned fluorine solvent, and a predetermined amount of the fluorine solvent is adsorbed and supported on the surface of the powder, and then kneaded with a commonly used binder, and the kneaded product is rolled, for example. It is rolled to form a porous molded body (for example, a sheet) of an appropriate thickness. (2) In addition, a porous molded body is created from the conductive powder having a metal chelate compound chemically bonded on its surface as described above using a commonly used binder, and then this is coated with a fluorine solvent. The fluorine solvent is adsorbed and carried on the surface of the molded body or the walls of the internal pores by immersion in the molded body. (3) Furthermore, after forming a porous molded body from conductive powder in advance, functional groups are introduced into the surface or the walls of internal pores by the above method, a metal chelate compound is then chemically bonded, and then a porous molded body is formed from conductive powder. The whole is immersed in a fluorine solvent to adsorb and carry the fluorine solvent. In the porous catalyst layer of the present invention, since the metal chelate compound having oxygen reducing ability is strongly chemically bonded to the surface of the conductive powder, it will not separate or fall off from the surface even when stored for a long time or subjected to continuous discharge. At the same time, since a fluorine solvent with the ability to dissolve oxygen gas is adsorbed and supported, the oxygen concentration (partial pressure) in the three-phase zone within the pores increases, and water repellency improves. , a stable service life over a long period of time, the possibility of heavy load discharge, and improved leakage resistance. The present invention will be explained below based on examples.Example (1) Preparation of porous catalyst layer Sample 1: Activated carbon powder with an average particle size of 150μ is suspended in a 30% potassium dichromate solution and stirred at 30°C for 2 hours. did. 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 in a conventional manner between the powder and the cobalt phthalocyanine into which an amino group had been introduced, and the cobalt phthalocyanine was chemically bonded to the 5% by weight activated carbon powder through the generated amide bond. This powder has a polymerization degree of 4
~6, 1-chloro-1 with a molecular weight of 500 to 700,
suspended in 2,2-trifluoroethylene;
Then, it was dried for 24 hours at 3 Torr and 60°C. The powder adsorbed 5% by weight of the above fluorine solvent. Next, add 10~ to this as a binder.
After adding 20% by weight of 60% PTFE dispersion and thoroughly kneading, it was rolled out to a thickness of 0.7mm.
It was made into a sheet. The resulting sheet has an average pore size
It had a porous structure with 60% of the 40μ pores. 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, this powder and the carbonyl group are oxidized to form a carboxyl group, and a dehydration reaction is carried out between this powder and iron phthalocyanine into which a hydroxyl group has been introduced by a conventional method.
Iron phthalocyanine was chemically bonded to activated carbon powder through ester bonds. 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 is
It had a porous structure with 60% of the pores having an average pore diameter of 40μ. This sheet has a polymerization degree of 4 to 6 and a molecular weight of
500-700 1-chloro-1,2,2-trifluoroethylene and the whole was dried at 60° C. under a vacuum of 3 Torr for 24 hours. The sheet was impregnated with 5% 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 the powder is mixed with a dimer of cobalt porphyrin into which a carboxyl group has been introduced by a conventional method. A dehydration reaction was carried out to chemically bond the cobalt porphyrin dimer to the activated carbon powder. Next, a sheet with a thickness of 0.7 mm was produced in exactly the same manner as Sample 1. This sheet is
It had a porous structure with 60% of the pores having an average pore diameter of 38μ. Then, in exactly the same manner as in Sample 1, a sheet of porous catalyst layer having a thickness of 0.7 mm was prepared. The obtained sheet had the same porous structure as Sample 1. 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 large acid groups were introduced on the entire surface and on the walls of internal pores. Next, a dehydration reaction was carried out between this sintered body and the cobalt phthalocyanine into which a hydroxyl group had been introduced by a conventional method, and the cobalt phthalocyanine was chemically bonded by the ether bond formed. Next, sample 2
1-chloro-1,2,
A sheet on which 2-trifluoroethylene was adsorbed and supported was produced. 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, a sheet with a thickness of 0.7 mm was produced in exactly the same manner as in the case of Sample 1.
The obtained sheet had the same porous structure as 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 battery. Assembled. After these batteries were left in the air at 25° C. for 16 hours, they were discharged for 5 minutes with various currents, and the current value at which the terminal voltage became 1.0 V or less after 5 minutes was measured, and this was taken as the initial performance of the batteries. Next, these batteries were placed in air at 25℃ for 6 months.
After leaving it for 12 months, the current value at which the terminal voltage became 1.0V or less was measured using the same method as above. The ratio of this current value to the initial performance (initial current value) was determined, and the ratios were collectively shown in the table in correspondence with each sample number. In addition, these batteries were stored in an atmosphere of 45° C. and 90% relative humidity, and the number of days until leakage occurred was measured, and the results are also listed in the table.

[Table] As is clear from the above table, the air battery using the porous catalyst layer of the present invention has an initial performance that is nearly 50% higher than that of conventional comparative batteries, and is capable of heavy load discharge. It has been found that all of them have a large performance ratio, have a stable service life over a long period of time, and are also excellent in leakage resistance. In the above example, an air-zinc battery using potassium hydroxide as the electrolyte was assembled and its performance was evaluated. However, 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 discharging under heavy loads, and has excellent leakage resistance. It can be said that the value is great.

Claims (1)

[Scope of Claims] 1. A conductive powder or a porous compact thereof, in which a metal chelate compound having an ability to reduce oxygen gas is chemically bonded, and at the same time a fluorine solvent having an ability to dissolve oxygen gas is adsorbed and supported. A porous catalyst layer of an air electrode characterized by: 2. The conductive powder is activated carbon powder, graphite powder, or nickel powder, and the metal chelate compound is at least one compound selected from the group consisting of iron phthalocyanine, cobalt porphyrin, and dimers thereof, and The fluorine solvent is 1-chloro-1,
2,2-trifluoroethylene, 1,1,2,2
-tetrachloro-1,2-difluoroethane,
The porous catalyst layer of the air electrode according to claim 1, which is at least one compound selected from 1,1,2-trichloro-1,2,2-trifluoroethane.