CA1273897A - Forming oxygen-cathode by joining moulded carbon sustrate with carbonaceous collector electrode - Google Patents
Forming oxygen-cathode by joining moulded carbon sustrate with carbonaceous collector electrodeInfo
- Publication number
- CA1273897A CA1273897A CA000486286A CA486286A CA1273897A CA 1273897 A CA1273897 A CA 1273897A CA 000486286 A CA000486286 A CA 000486286A CA 486286 A CA486286 A CA 486286A CA 1273897 A CA1273897 A CA 1273897A
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- Prior art keywords
- electrode substrate
- current collector
- cathode
- oxygen
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
- C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
- C25B11/031—Porous electrodes
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/042—Electrodes formed of a single material
- C25B11/043—Carbon, e.g. diamond or graphene
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/96—Carbon-based electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Abstract
TITLE OF THE INVENTION:
OXYGEN- CATHODE FOR USE IN ELECTROLYSIS OF ALKALI
CHLORIDE AND PROCESS FOR PREPARING THE SAME
ABSTRACT OF THE DISCLOSURE:
Disclosed herein are an oxygen-cathode for use in electrolysis of an alkali chloride, comprising a current collector made of a compact carbonaceous material, an electrode substrate made of a porous carbonaceous material and the catalyst carried on the electrode substrate, wherein the electrode substrate and the current collector have been joined together via the mutually facing carbonized surfaces thereof, and a process for preparing the oxygen-cathode.
OXYGEN- CATHODE FOR USE IN ELECTROLYSIS OF ALKALI
CHLORIDE AND PROCESS FOR PREPARING THE SAME
ABSTRACT OF THE DISCLOSURE:
Disclosed herein are an oxygen-cathode for use in electrolysis of an alkali chloride, comprising a current collector made of a compact carbonaceous material, an electrode substrate made of a porous carbonaceous material and the catalyst carried on the electrode substrate, wherein the electrode substrate and the current collector have been joined together via the mutually facing carbonized surfaces thereof, and a process for preparing the oxygen-cathode.
Description
~3~_3 7 BACKGROUND OF THE INVENTION:
The present invention relates to an oxygen-cathode used in a process for electrolysis of an alkali chloride, part~-cularly in a process for electrolysis of the alkali chloride while using an ion-exchange membrane or a process for electro-lysis of the alkali chloride according to SPE method, wherein a cathode reaction is caused by supplying oxygen or an oxygen-containing gas such as air into the inner part of the cathode, thereby carrying out the electrolysis of an aqueous solution of the alkali chloride without generating hydrogen in the cathode side in an electrolytic cell.
In recent years, in the industry of alkali chloride electrolysis, the diaphragm method has come to be used instead of the mercury electrode method in view of preventing the environmental pollution, and further, the ion-exchange membrane method has come to be more used in order to obtain sodium hydroxide at a higher purity and in a higher concentration.
Also the SPE method has been developed for carrying out electrolysis under a voltage as low as possible while elimi-nating the ohmic loss due to the aqueous electrolyte solution.
In order to effect the electrolysis at a still lower voltage in the above-mentioned ion-exchange membrane method or in the SPB method, various studies have been carried out, and particularly concerning the cathode used in the electrolysis, it has been recently known that in the case where oxygen or an oxygen-containing gas such as air is supplied to the cathode side from outside of the cell, the gas diffuses into the cathode, the oxygen reacts with water in an aqueous solution in the vicinity of the cathode to form hydroxide ions thus preventing the generation of hydrogen in the cathode side and accordingly, the electrolysis can be effected at a lower voltage than that of the usual case without generating a hydrogen gas in the vicinity of the cathode.
The cathode used in the recently discovered method is called the "oxygen-cathode", and must have a specified construction by which the supplied gas diffuses into the internal part of the cathode, and it is still required that the cathode is superior in cathode specificity (explained later in detail) and also in durability.
In addition, a device is also necessary for preventing the leakage of the aqueous solution present in the vicinity of the cathode through the gas-permeable cathode.
Hitherto, as the above-mentioned oxygen-cathodes, 1) an oxygen-cathode produced by mixing a hydrophobic material such as polytetrafluoroethylene with a catalytic substance, hardening the mixture and adhering closely the thus hardened product to the current collector such as a nickel grid, a reticulated material or a porous material, 2) an oxygen-cathode produced by impregnating a porous, sintered alloy with the catalytic substance and subjecting the thus impregnated alloy to the hydrophobic treatment with polytetrafluoroethylene (for instance, refer to Japanese Patent application Laid-open (KOKAI) No. 54-97600 laid open on August 1, 1979 and filed by Asahi Glass K.K. on Jan. 20, 1978) or 3) an oxygen-cathode having an improved cathode-performance by ¢ ~
lZ~;38~
adding a specific pore-forming agent to the baked material of the blended mixture of the catalytic substance and a hydrophobic substance (for instance, refer to Japanese Patent application Laid-open (KOKAI ) No. 55-28216 laid open on Feb.
28, 1980 and filed by Asahi Glass K.K. on August 18, 1978) have been known, however, in the case where the sintered alloy is used as the micropore layer, there is the disadvantage that it is difficult to control the distribution of the pore size and the thin alloy material is easy to break. In the case where the active layer of the cathode is made by hardening polytetrafluoroethylene, etc., the thus prepared cathode is still insufficient in its performance and there is a problem in joining with the current collector. In either case, contact resistance is caused between the electrode substrate and the current collector and accordingly, it is impossible to obtain a product having a sufficient performance as the oxygen-cathode for use in electrolysis of an alkali chloride.
In consideration of the above-mentioned problems, the object of the present invention is to provide an improvement of the cathode substrate to be used in electrolysis of an alkali chloride and solution of the problems on the joining ability of the cathode substrate and the current collector. As a result of studying the problem, inventors have recently attained the object of the present invention by (1) preparing the cathode substrate by using an anticorrosive and durable material in which the control of porosity and pore size is easily carried out and (2) joining the cathode substrate with the current collector into a unified body, thereby reducing the contact resistance as small as possible.
8~7 SUMMARY OF THE INVENT ION:
. ....
In a first aspect of the present invention, there is provided an oxygen-cathode for use in electrolysis of an alkali chloride, comprising a current collector made of a compact carbonaceous material, an electrode substrate made of a porous carbonaceous material and a catalyst carried on .
said electrode substrate, wherein said current collector and said electrode substrate are joined together via the mutually facing carbonized surfaces thereof, thereby forming a unified body.
In a second aspect of the present invention, there is provided a process for preparing an oxygen-cathode for use in electrolysis of an alkali chloride, comprising the steps of (1) facing a surrace to be joined of a molded mixture which is an electrode substrate before baking with a surface to be ~oined of a preliminarily baked and molded mixture which is a current collector before baking and is produced by mixing a carbonaceous material and a binding material, molding the thus obtained mixture and preliminarily baking the thus molded mixture the molded mixture being produced by mixing carbon fibers, a binding material and a micropore-forming substance as the start-ing materials and molding the thus obtained mixture under pressure and optionally subjecting the thus molded mixture to extraction with the solvent to remove said micropore-forming ~ubstance from said molded mixture, (2) heating the molded mixture as the electrode substrate and said 1~7;~7 preliminarily baked mixture as the current collector under a pressure, (3) baking the thus heated material, thereby joining the molded mixture and the preliminarily baked mixture into a unified body via the mutually facing carbonized surfaces and in the same time, compactly carbonizing the preliminarily baked mixture to form a current collector and porously carbonizing the molded mixture to form an electrode substrate, and (4) subjecting said porously carbonized electrode substrate to treatment for rendering the surface of the electrode substrate hydrophobic and coating the thus treated surface of said electrode substrate with a catalyst.
BRIEF EXPLANATION OF DRAWINGS:
Of the attached drawings, Fig. 1 is a cross-sectional view of one example of the oxygen-cathode according to the present invention; Fig. 2 is a perspective view of a current collector for use in the oxygen-cathode of Fig. l; Fig. 3 is a cross-sectional view of an electrolytic cell in the case where the oxygen-cathode shown in Fig. 1 had been applied;
Fig. 4 is also a cross-sectional view of an oxygen-cathode to which a current collector of another construction has been used; Fig. 5 is a cross-sectional view of an electrolytic cell in the case where the oxygen-cathode shown in Fig. 4 had been applied; Fig. 6 is a cross-sectional view of an oxygen-cathode to which a current collector of still another construction had been used; Fig. 7 is a A-A sectional view of the oxygen-cathode shown in Fig. 6, and Fig. 8 shows a "~
~ 3 ~9`~
result of determination of the performance of the oxygen-cathode according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION-_ .
According to the present invention, both an electrode (cathode) substrate and a current collector are formed of a carbonaceous material, thereby the joining-ability between the electrode substrate and the current collector has been highly improved.
Namely, the present invention relates to the "oxygen-cathode" ior use in electrolysis of an alkali chloride, comprisiny a current collector made of a compact carbonaceous material, an electrode substrate made of a porous carbonaceous material and the catalyst carried on the electrode substrate wherein the current collector and the electrode substrate have been joined as a unified body via the mutuaIly facing carbonized surfaces, and a process for preparing the same.
Fig. 1 is a cross-sectional view of one example of the oxygen-cathode according to the present invention for use in electrolysis, wherein 1 is a current collector made of a compact carbonaceous material; 2 is an electrode substrate made of a porous carbonaceous material and the current collector 1 is joined to the electrode substrate 2, via the mutually facing carbonized surfaces. The catalyst is carried on the electrode substrate in an impregnated state within the micropores thereof, and in case of necessity, a catalyst layer 3 is formed on the upper surface of the electrode , .
~ 3 substrate.
Each of the elements oE the oxygen-cathode is explained as follows.
Electrode Substrate:
The electrode substrate for use according to the present invention preferably has the following physical properties for use as an oxygen-cathode.
Thic~.ness is 0.2 to 2 mm, pore diameter is 5 to 100 ~m, permeability to air is not less than 5 ml/cm.hour.mmH2O, bending strength is not less than 30 kg/cm2, electric resistance is not more than 50 mQ.cm and thermal conductivity is not less than 0.5 kcal/m.hour.C.
The electrode substrate having the above-mentioned physical properties is prepared, for instance, by mixing carbon fibers,a binding material and a micropore-forming substance, molding the thus obtained mixture, subjecting the thus molded mixture to extraction with a solvent in the case where the micropore-forming substance is soluble in a solvent thereby removing the micropore-forming substance from the thus molded mixture and baking the thus treated molded mixture, thereby obtaining the electrode substrate made of a porous material. In the case where the micropore-forming substance is volatile at high temperatures, the thus molded mixture is directly baked without being subjected to extraction, thereby obtaining the electrode substrate made of a porous material.
~ 7 3 ~
The above-mentioned respective processes for preparing the electrode substra~e have been disclosed in Canadian Patents Nos 1,179,808 issued Dec. 27, 1984 and 1,181,127 issued on Jan. 15, 1985 both to Kureha Kagaku Kogyo K.K., and the concrete example of the processes is explain~d as follows.
From 10 to 80 ~ by weight of carbon fibers having from 6 to 20 ~m in diameter and from 0.05 to 2 mm in length, preliminarily baked at a temperature of higher tha~ 1500C
as an aggregate, from 10 to 50 % by weight or a substance selected from the group consisting of phenol resin, pitch derived from petroleum or coal, polyvinyl alcohol, epoxy resin and the mixtures thereof as a binding material and from 10 to 60 ~ by weight of a substance which is volatile at high temperatures and is selected from the group consisting of polyethylene, polyvinyl alcohol, polymethylmethacrylate, nylon and the mixtures thereof, or substance which is soluble in a certain solvent and is selected from the group consisting of sodium chloride, sucrose, sodium sulfate, polyvinyl alcohol, polyvinyl chloride, polymethyl methacrylate and the mixtures thereof as the micropore-forming substance are mixed together, and after molding the thus obtained mixture at a temperature of 50 to 200C under the pressure of 0.01 to 200 kg/cm2, (i~ in the case where the micropore-forming substance is soluble in a certain solvent, the micro-pore-forming substance is removed from the thus molded mixture by extraction thereof with the solvent and then the thus treated, molded mixture is baked at a temperature of l,S00 ~3~
to 3,000C, or (ii) in the case where the micropore-forming substance is volatile at high temperature, the molded mixture is directly baked at a temperature o~ 1500 to 3000C without being subjected to the above-mentioned extraction.
In the step of preparing the electrode substrate according to the present invention, the final step (baking) can be effected simultaneously with the step of baking for joining the electrode substrate before baking with the current collector before baking, as will be explained later.
The control of the micropore (pore size and porosity) and the formation thereof are easily carried out in the above-mentioned steps of preparing the electrode substrate, and the thus prepared electrode substrate is excellent in carrying the catalyst and the state of dispersion of the supplied oxygen within the electrode substrate is favorable.
Current Collector:
As has been stated, the current collector for use in the present invention is made of a compact carbonaceous material, and preferably has the following physical properties.
Permeability to air is not more than 10 7 ml/cm.hour.mmH20 bending strength is not less than 500 kg/cm2, electric resistance is not more than 10 mQ.cm and thermal conductivity is not less than 3 kcal/m.hour.C.
The compact carbonaceous material of the above-mentioned physical properties can be prepared, for instance, as follows.
~3 ~
From 30 to 90 ~ by volume of hard carbon particles having from 1 to 100 ~m in diameter and not more than 1.8 g/ml in density, from 70 to 10 % by volume of a granulated binding material having from 1 to 100 ~m in diameter of one or more than two substances selected from the group consisting of phenol resin, pitch derived from petroleum or coal, polyvinyl alcohol and epoxy resin are mixed together, and after molding the thl~s prepared mixture at a temperature of 80 to 200C under the pressure o~ 10 to 400 kg/cm2, the thus molded mixture is preliminarily baked at a temperature of from 500 to 1,500C. Instead of using the above-mentioned hard carbon particles, soft carbon particles having from 1 to lO0 ~m in diameter and a bulk density of not less than 1.8 g/ml can be used. ~n addition, as the binding material, a liquid binder selected from the group consisting of liquid phenol resin, liquid pitch derived from petroleum or coal, liquid epoxy resin, liquid polyvinyl alcohol and the mixtures thereof can be used.
The current collector is made to be in a structure by which oxygen or an oxygen-containing gas such as air can be introduced thereinto from outside and supplied to the cathode. Fig. 2 is a perspective view of the current collector for use in the oxygen-cathode of a construction shown in Fig. 1. The current collector shown in Fig. 2 has been made to be a plate-shaped body in which a plurality of ribs, for instance, of 2 to 10 mm in sectional dimension and ~3~
4 t~ ~o mm in pitch ~re provl~ed on one side. Concerning the structure of the current collector, a variety of application is considered. Fig. 3 shows a cross-sectional view of a bipolar type electrode to which the current collector shown in Fig. 2 has been applied. In Fig. 3, 4 is a unit of an electrolytic cell; 5 is the "oxygen-ca~hode"
including the current collector 1, the electrode substrate 2, the catalyst ~catalyst layer) 3 carried on the electrode substrate 2 t 6 is an anode and 10 is the passage of gaseous oxygen supplied from outside of the cell to the cathode chamber. The cathode chamber 7 and the anode chamber 8 shown in Fig. 3 are divided by an ion-exchange membrane 9. Both Fig. 4 and Fig. 6 are the respective cross-sectional views of the two oxygen-cathodes, in each of which current collectors of different structure are applied. Fig. 7 is the cross-sectional view along the line A-A of oxygen-cathode of Flg. 6. Fig. 5 is a cross-sectional view of an electrolytic cell of monopolar type to which the oxygen-cathode shown in Fig. 4 ls applied,wherein a unit 14 or 14' of the electrolytic cell ls composed of the one side of the oxygen-cathode 15 or 15', the cathode chamber 17 or 17', the anode chamber 18 and the anode 16, the chambers 17 or 17' and 18 being divided by the cation-exchange membrane 19 or 191.
In the electrolytic cell shown in Fig. 5, the oxygen-cathode ~hown in Fig. 6 may be used instead of the oxygen-cathode shown in Fig. 4.
In the oxygen-cathode shown in Fig. 6t the passage 30 ~2 7~
of gaseous oxygen on the current collector is in common with the two electrode substrates 22 and 22'.
Joining of Electrode Substrate with-Current Collector:
~ .
As has been stated above, the thus respectively prepared electrode substrate and current collector are joined together to a unified body by facing the respective two surfaces to be joined and subjecting the thus faced electrode substrate and current collector to the thermal treatment at a tempera-ture of 80 to 200C under the pressure of 0.01 to 200 kg/cm2 and then, the thus joined electrode substrate and current collector was baked at a temperature of not less than 1,500C to be in a shape shown in Figs. 1, 9 and 6, wherein the electrode substrate and the current collector are united into one body via the mutually facing carbonized surfaces.
In the case of joining the thus obtained electrode substrate by baking the molded mixture with the current collector, a binding material is necessary between electrode substrate and current collector, and as the binding material, a substance selected from the group consist~ng of phenol resin, pitch derived from petroleum or coal, polyvinyl alcohol, epoxy resin and the mixture thereof is utilized in preparing the electrode sustrate.
The thus joined electrode substrate and current collector via the binding material is baked at a temperature of 1,500 to 3000C.
7~8 I' On the other hand, in the case where the baking of the molded mixture for the preparation of the electrode substrate is combined with the baking step in the joining of the current collector with the molded mlxture for the prepa-~ ration of the electrode substrate, the baking is carried I out after joining the preliminarily baked current collector I with the molded mixture for the preparation of the electrodesubstrate. Ihe preliminary baking is carried out for I conforming t.he shrfnkage of the jolned prellminarily baked 10 1I current collector to that of the joined electrode substrate in ¦ baking step. In this case, the binding material is not indispensable, however, the same binding material mentioned ¦ above may be used. In the case where the baking of the molded mixture for the preparation of the electrode substrate is combined with the baking step for joining of the molded mixture for the preparation of the electrode substrate with ¦ the preliminarily baked current collector, one step of baking is saved and accordingly, the latter case is preferable.
By the step of baking, the porously carbonized electrode substrate is obtained and in the same time the compactly carbonized current collector is obtained.
¦ Catalyst:
After having joined the electrode substrate with the current collector into a unified body as shown above, the catalyst is coated on the surface of electrode substrate.
As the catalyst, a substance suitable as the catalyst of the 73~
oxygen-cathode for use in electrolysis of an alkali chloride, namely the substance which accelerates the reaction of formation of hydroxide ions from the oxygen introduced into the cathode and water in the aqueous electrolyte solution. Concretely, one of the known catalysts,for instance, a noble metal such as platinum and silver or Raney silver is used for the purpose. Particularly, in the present invention, those carbon black particles having their surface covered with a powdery noble metal, namely, a noble metal carried on carbon black particles is preferable.
As the method for coating such a catalyst onto the electrode substrate, a method has been known in which an aqueous suspension containing the particles of the catalyst is coated on the surface of the electrode substrate and the solvent is then removed by drying. The noble metal may be electroplated on the electrode substrate. Instead of elec-troplating, the following method may be taken wherein the electrode substrate is impregnated with an aqueous solution containing a compound of the metal which can be the catalyst, and the thus introduced compound is then~ally decomposed or reduced to the metal within the electrode substrate.
Hydrophobic Treatment:
Hydrophobic treatment of the oxygen-cathode is carried out in order to prevent the leakage of the aqueous solution in the vicinity of the cathode to the gas side of the oxygen-cathode. As the agent for use in hydrophobic treatment, ~2~3&9~
fluorine-containing polymer such as polytetrafluoroethylene is preferable, and in order to prevent the reduction in the activity of the catalyst due to the coverage of the surface of the catalyst by the thus applied agent, the agent is applied before the coating of the catalyst, and after coating the catalyst on the thus applied agent, the agent is melted and adhered to the electrode substrate.
In ord~r to avoid the reduction of electric conductivity of the electrode substrate due to the above-mentioned hydrophobic treatment, in the case of rendering the surface of the electrode substrate hydrophobic it is preferable to coat a mixture of carbon black and the particles of fluorine-containing polymer on the surface of the electrode substrate.
For instance, an aqueous emulsion containing the particles of polytetrafluoroethylene of from 100 to 5,000 A in diameter and the particles of carbon black of from 100 to 5,000 A in diameter is coated on the surface of the electrode substrate, and then an aqueous suspension containing the particles of the catalyst is coated thereon. After removing the solvent of the suspension by drying the thus coated electrode, the electrode substrate is subjected to baking at 300 to 400C, thereby sintering the particles of polytetrafluoroethylene to obtain a membrane of polytetrafluoroethylene strongly adhered to the surface of the micropores of the elec-trode substrate.
In addition, both coating of the catalyst and the agent for rendering the surface of t:he electrode substrate hydrophobic can be effected simultaneously by coating a mixture of the particles of polytetrafluoroethylene and the particles of the catalyst.
Accordi.ng to the present invention, the electrode substrate which is mainly composed of the porous carbonaceous material and carries the catalyst thereon, plays a role in dispersi.ng the supplied oxygen. The current:
collector of the present invent:ion which is mainly composed of the compact carbonaceous materi.al and i.s joined with the electrode substrate into a unified body via the mutually facing carbonized surfaces, plays the role in conducting electricity to the electrode substrate without generating electric contact resistance. In addition, in t:he case where the current collector is modifi.ed to take a suitable st:ructure, the modified current collector plays a role i.n supplying oxygen to the cathode and gas-sealing to outside of the cel1.
The catalyst carried on the electrode substrate is adhered within t:he plurality of the micropores, however, in case of necessity, the catalyst is also applied on the surface of the electrode substrate.
Furthermore, since in the oxygen-cathode according to the present invention, both the current collector and the electrode substrate are composed of carbonaceous material, and have been joined t:ogether int:o a unified body via the mutually facing carbonized surfaces, in the case where such oxygen-cathode is used in electrolysis of an 1~73~397 alkali chloride, any increase of the electrolytic voltage due to the contact resistance between the current collector and the electrode substrate is not observed and accordingly, electrolysis of the alkali chloride can be carried out at a remarkably lower voltage as compared to the conventional electrolysis of the alkali chloride.
In addition, porous carbonaceous material is used for the electrode substrate and accordingly, the electrode substrate is anticorrosive and durable. Furthermore, since a large number of micropores have been preliminarily formed with a controlled pore diameter in the electrode substrate and it is possible to carry the catalyst particles within such micropores, the catalyst is easily coated on the electrode substrate, and it is possible to obtain an oxygen-cathode which is superior in the cathode specificity.
Particularly, in the case where the electrode substrate is made from the carbon fibers, the binding material and the micropore-forming substance, it is possible to obtain an oxygen-cathode having uniformly distributed micropores with a controlled pore size and distributing oxygen gas uniformly.
The oxygen-cathode according to the present invention may be used in the electrolytic cells in the ion-exchange membrane method and also in the SPE method for electrolysis of an alkali chloride. In addition, it may be used in the electrolytic cell in which only the anode is manufactured by the mode of the SPE method for electrolysis ~389~
of an alkali chloride.
The present invention wlll be explained more in detail while referring to the following non-limitative example and comparative examples.
EXAMPLE:
1) Preparation of the current collector:
A commercialized powdery pitch derived from petroleum (made by KUREHA KAGAKU KOGYO Co., Ltd., MH-lP) was preliminarily baked in an atmosphere of nitrogen and after cooling thereof, it was pulverized to be of 6 ~m in the mean diameter and used as the hard carbon particles for aggregate.
Namely, 65 % by weight of the hard carbon particles and 35 ~ by weight of a commercialized phenol resin (more than 85 % by weight of the phenol resin passes through the sieve of 320 mesh) as the binding material were mixed, and after introducing the uniform mixture in a ribbed metal mold, the mixture was molded under the conditions of 150C in temperature and of 100 kg/cm2 in pressure, and the thus molded mixture was baked at 1,000C to be carbonized, thereby obtaining the current collector.
The present invention relates to an oxygen-cathode used in a process for electrolysis of an alkali chloride, part~-cularly in a process for electrolysis of the alkali chloride while using an ion-exchange membrane or a process for electro-lysis of the alkali chloride according to SPE method, wherein a cathode reaction is caused by supplying oxygen or an oxygen-containing gas such as air into the inner part of the cathode, thereby carrying out the electrolysis of an aqueous solution of the alkali chloride without generating hydrogen in the cathode side in an electrolytic cell.
In recent years, in the industry of alkali chloride electrolysis, the diaphragm method has come to be used instead of the mercury electrode method in view of preventing the environmental pollution, and further, the ion-exchange membrane method has come to be more used in order to obtain sodium hydroxide at a higher purity and in a higher concentration.
Also the SPE method has been developed for carrying out electrolysis under a voltage as low as possible while elimi-nating the ohmic loss due to the aqueous electrolyte solution.
In order to effect the electrolysis at a still lower voltage in the above-mentioned ion-exchange membrane method or in the SPB method, various studies have been carried out, and particularly concerning the cathode used in the electrolysis, it has been recently known that in the case where oxygen or an oxygen-containing gas such as air is supplied to the cathode side from outside of the cell, the gas diffuses into the cathode, the oxygen reacts with water in an aqueous solution in the vicinity of the cathode to form hydroxide ions thus preventing the generation of hydrogen in the cathode side and accordingly, the electrolysis can be effected at a lower voltage than that of the usual case without generating a hydrogen gas in the vicinity of the cathode.
The cathode used in the recently discovered method is called the "oxygen-cathode", and must have a specified construction by which the supplied gas diffuses into the internal part of the cathode, and it is still required that the cathode is superior in cathode specificity (explained later in detail) and also in durability.
In addition, a device is also necessary for preventing the leakage of the aqueous solution present in the vicinity of the cathode through the gas-permeable cathode.
Hitherto, as the above-mentioned oxygen-cathodes, 1) an oxygen-cathode produced by mixing a hydrophobic material such as polytetrafluoroethylene with a catalytic substance, hardening the mixture and adhering closely the thus hardened product to the current collector such as a nickel grid, a reticulated material or a porous material, 2) an oxygen-cathode produced by impregnating a porous, sintered alloy with the catalytic substance and subjecting the thus impregnated alloy to the hydrophobic treatment with polytetrafluoroethylene (for instance, refer to Japanese Patent application Laid-open (KOKAI) No. 54-97600 laid open on August 1, 1979 and filed by Asahi Glass K.K. on Jan. 20, 1978) or 3) an oxygen-cathode having an improved cathode-performance by ¢ ~
lZ~;38~
adding a specific pore-forming agent to the baked material of the blended mixture of the catalytic substance and a hydrophobic substance (for instance, refer to Japanese Patent application Laid-open (KOKAI ) No. 55-28216 laid open on Feb.
28, 1980 and filed by Asahi Glass K.K. on August 18, 1978) have been known, however, in the case where the sintered alloy is used as the micropore layer, there is the disadvantage that it is difficult to control the distribution of the pore size and the thin alloy material is easy to break. In the case where the active layer of the cathode is made by hardening polytetrafluoroethylene, etc., the thus prepared cathode is still insufficient in its performance and there is a problem in joining with the current collector. In either case, contact resistance is caused between the electrode substrate and the current collector and accordingly, it is impossible to obtain a product having a sufficient performance as the oxygen-cathode for use in electrolysis of an alkali chloride.
In consideration of the above-mentioned problems, the object of the present invention is to provide an improvement of the cathode substrate to be used in electrolysis of an alkali chloride and solution of the problems on the joining ability of the cathode substrate and the current collector. As a result of studying the problem, inventors have recently attained the object of the present invention by (1) preparing the cathode substrate by using an anticorrosive and durable material in which the control of porosity and pore size is easily carried out and (2) joining the cathode substrate with the current collector into a unified body, thereby reducing the contact resistance as small as possible.
8~7 SUMMARY OF THE INVENT ION:
. ....
In a first aspect of the present invention, there is provided an oxygen-cathode for use in electrolysis of an alkali chloride, comprising a current collector made of a compact carbonaceous material, an electrode substrate made of a porous carbonaceous material and a catalyst carried on .
said electrode substrate, wherein said current collector and said electrode substrate are joined together via the mutually facing carbonized surfaces thereof, thereby forming a unified body.
In a second aspect of the present invention, there is provided a process for preparing an oxygen-cathode for use in electrolysis of an alkali chloride, comprising the steps of (1) facing a surrace to be joined of a molded mixture which is an electrode substrate before baking with a surface to be ~oined of a preliminarily baked and molded mixture which is a current collector before baking and is produced by mixing a carbonaceous material and a binding material, molding the thus obtained mixture and preliminarily baking the thus molded mixture the molded mixture being produced by mixing carbon fibers, a binding material and a micropore-forming substance as the start-ing materials and molding the thus obtained mixture under pressure and optionally subjecting the thus molded mixture to extraction with the solvent to remove said micropore-forming ~ubstance from said molded mixture, (2) heating the molded mixture as the electrode substrate and said 1~7;~7 preliminarily baked mixture as the current collector under a pressure, (3) baking the thus heated material, thereby joining the molded mixture and the preliminarily baked mixture into a unified body via the mutually facing carbonized surfaces and in the same time, compactly carbonizing the preliminarily baked mixture to form a current collector and porously carbonizing the molded mixture to form an electrode substrate, and (4) subjecting said porously carbonized electrode substrate to treatment for rendering the surface of the electrode substrate hydrophobic and coating the thus treated surface of said electrode substrate with a catalyst.
BRIEF EXPLANATION OF DRAWINGS:
Of the attached drawings, Fig. 1 is a cross-sectional view of one example of the oxygen-cathode according to the present invention; Fig. 2 is a perspective view of a current collector for use in the oxygen-cathode of Fig. l; Fig. 3 is a cross-sectional view of an electrolytic cell in the case where the oxygen-cathode shown in Fig. 1 had been applied;
Fig. 4 is also a cross-sectional view of an oxygen-cathode to which a current collector of another construction has been used; Fig. 5 is a cross-sectional view of an electrolytic cell in the case where the oxygen-cathode shown in Fig. 4 had been applied; Fig. 6 is a cross-sectional view of an oxygen-cathode to which a current collector of still another construction had been used; Fig. 7 is a A-A sectional view of the oxygen-cathode shown in Fig. 6, and Fig. 8 shows a "~
~ 3 ~9`~
result of determination of the performance of the oxygen-cathode according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION-_ .
According to the present invention, both an electrode (cathode) substrate and a current collector are formed of a carbonaceous material, thereby the joining-ability between the electrode substrate and the current collector has been highly improved.
Namely, the present invention relates to the "oxygen-cathode" ior use in electrolysis of an alkali chloride, comprisiny a current collector made of a compact carbonaceous material, an electrode substrate made of a porous carbonaceous material and the catalyst carried on the electrode substrate wherein the current collector and the electrode substrate have been joined as a unified body via the mutuaIly facing carbonized surfaces, and a process for preparing the same.
Fig. 1 is a cross-sectional view of one example of the oxygen-cathode according to the present invention for use in electrolysis, wherein 1 is a current collector made of a compact carbonaceous material; 2 is an electrode substrate made of a porous carbonaceous material and the current collector 1 is joined to the electrode substrate 2, via the mutually facing carbonized surfaces. The catalyst is carried on the electrode substrate in an impregnated state within the micropores thereof, and in case of necessity, a catalyst layer 3 is formed on the upper surface of the electrode , .
~ 3 substrate.
Each of the elements oE the oxygen-cathode is explained as follows.
Electrode Substrate:
The electrode substrate for use according to the present invention preferably has the following physical properties for use as an oxygen-cathode.
Thic~.ness is 0.2 to 2 mm, pore diameter is 5 to 100 ~m, permeability to air is not less than 5 ml/cm.hour.mmH2O, bending strength is not less than 30 kg/cm2, electric resistance is not more than 50 mQ.cm and thermal conductivity is not less than 0.5 kcal/m.hour.C.
The electrode substrate having the above-mentioned physical properties is prepared, for instance, by mixing carbon fibers,a binding material and a micropore-forming substance, molding the thus obtained mixture, subjecting the thus molded mixture to extraction with a solvent in the case where the micropore-forming substance is soluble in a solvent thereby removing the micropore-forming substance from the thus molded mixture and baking the thus treated molded mixture, thereby obtaining the electrode substrate made of a porous material. In the case where the micropore-forming substance is volatile at high temperatures, the thus molded mixture is directly baked without being subjected to extraction, thereby obtaining the electrode substrate made of a porous material.
~ 7 3 ~
The above-mentioned respective processes for preparing the electrode substra~e have been disclosed in Canadian Patents Nos 1,179,808 issued Dec. 27, 1984 and 1,181,127 issued on Jan. 15, 1985 both to Kureha Kagaku Kogyo K.K., and the concrete example of the processes is explain~d as follows.
From 10 to 80 ~ by weight of carbon fibers having from 6 to 20 ~m in diameter and from 0.05 to 2 mm in length, preliminarily baked at a temperature of higher tha~ 1500C
as an aggregate, from 10 to 50 % by weight or a substance selected from the group consisting of phenol resin, pitch derived from petroleum or coal, polyvinyl alcohol, epoxy resin and the mixtures thereof as a binding material and from 10 to 60 ~ by weight of a substance which is volatile at high temperatures and is selected from the group consisting of polyethylene, polyvinyl alcohol, polymethylmethacrylate, nylon and the mixtures thereof, or substance which is soluble in a certain solvent and is selected from the group consisting of sodium chloride, sucrose, sodium sulfate, polyvinyl alcohol, polyvinyl chloride, polymethyl methacrylate and the mixtures thereof as the micropore-forming substance are mixed together, and after molding the thus obtained mixture at a temperature of 50 to 200C under the pressure of 0.01 to 200 kg/cm2, (i~ in the case where the micropore-forming substance is soluble in a certain solvent, the micro-pore-forming substance is removed from the thus molded mixture by extraction thereof with the solvent and then the thus treated, molded mixture is baked at a temperature of l,S00 ~3~
to 3,000C, or (ii) in the case where the micropore-forming substance is volatile at high temperature, the molded mixture is directly baked at a temperature o~ 1500 to 3000C without being subjected to the above-mentioned extraction.
In the step of preparing the electrode substrate according to the present invention, the final step (baking) can be effected simultaneously with the step of baking for joining the electrode substrate before baking with the current collector before baking, as will be explained later.
The control of the micropore (pore size and porosity) and the formation thereof are easily carried out in the above-mentioned steps of preparing the electrode substrate, and the thus prepared electrode substrate is excellent in carrying the catalyst and the state of dispersion of the supplied oxygen within the electrode substrate is favorable.
Current Collector:
As has been stated, the current collector for use in the present invention is made of a compact carbonaceous material, and preferably has the following physical properties.
Permeability to air is not more than 10 7 ml/cm.hour.mmH20 bending strength is not less than 500 kg/cm2, electric resistance is not more than 10 mQ.cm and thermal conductivity is not less than 3 kcal/m.hour.C.
The compact carbonaceous material of the above-mentioned physical properties can be prepared, for instance, as follows.
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From 30 to 90 ~ by volume of hard carbon particles having from 1 to 100 ~m in diameter and not more than 1.8 g/ml in density, from 70 to 10 % by volume of a granulated binding material having from 1 to 100 ~m in diameter of one or more than two substances selected from the group consisting of phenol resin, pitch derived from petroleum or coal, polyvinyl alcohol and epoxy resin are mixed together, and after molding the thl~s prepared mixture at a temperature of 80 to 200C under the pressure o~ 10 to 400 kg/cm2, the thus molded mixture is preliminarily baked at a temperature of from 500 to 1,500C. Instead of using the above-mentioned hard carbon particles, soft carbon particles having from 1 to lO0 ~m in diameter and a bulk density of not less than 1.8 g/ml can be used. ~n addition, as the binding material, a liquid binder selected from the group consisting of liquid phenol resin, liquid pitch derived from petroleum or coal, liquid epoxy resin, liquid polyvinyl alcohol and the mixtures thereof can be used.
The current collector is made to be in a structure by which oxygen or an oxygen-containing gas such as air can be introduced thereinto from outside and supplied to the cathode. Fig. 2 is a perspective view of the current collector for use in the oxygen-cathode of a construction shown in Fig. 1. The current collector shown in Fig. 2 has been made to be a plate-shaped body in which a plurality of ribs, for instance, of 2 to 10 mm in sectional dimension and ~3~
4 t~ ~o mm in pitch ~re provl~ed on one side. Concerning the structure of the current collector, a variety of application is considered. Fig. 3 shows a cross-sectional view of a bipolar type electrode to which the current collector shown in Fig. 2 has been applied. In Fig. 3, 4 is a unit of an electrolytic cell; 5 is the "oxygen-ca~hode"
including the current collector 1, the electrode substrate 2, the catalyst ~catalyst layer) 3 carried on the electrode substrate 2 t 6 is an anode and 10 is the passage of gaseous oxygen supplied from outside of the cell to the cathode chamber. The cathode chamber 7 and the anode chamber 8 shown in Fig. 3 are divided by an ion-exchange membrane 9. Both Fig. 4 and Fig. 6 are the respective cross-sectional views of the two oxygen-cathodes, in each of which current collectors of different structure are applied. Fig. 7 is the cross-sectional view along the line A-A of oxygen-cathode of Flg. 6. Fig. 5 is a cross-sectional view of an electrolytic cell of monopolar type to which the oxygen-cathode shown in Fig. 4 ls applied,wherein a unit 14 or 14' of the electrolytic cell ls composed of the one side of the oxygen-cathode 15 or 15', the cathode chamber 17 or 17', the anode chamber 18 and the anode 16, the chambers 17 or 17' and 18 being divided by the cation-exchange membrane 19 or 191.
In the electrolytic cell shown in Fig. 5, the oxygen-cathode ~hown in Fig. 6 may be used instead of the oxygen-cathode shown in Fig. 4.
In the oxygen-cathode shown in Fig. 6t the passage 30 ~2 7~
of gaseous oxygen on the current collector is in common with the two electrode substrates 22 and 22'.
Joining of Electrode Substrate with-Current Collector:
~ .
As has been stated above, the thus respectively prepared electrode substrate and current collector are joined together to a unified body by facing the respective two surfaces to be joined and subjecting the thus faced electrode substrate and current collector to the thermal treatment at a tempera-ture of 80 to 200C under the pressure of 0.01 to 200 kg/cm2 and then, the thus joined electrode substrate and current collector was baked at a temperature of not less than 1,500C to be in a shape shown in Figs. 1, 9 and 6, wherein the electrode substrate and the current collector are united into one body via the mutually facing carbonized surfaces.
In the case of joining the thus obtained electrode substrate by baking the molded mixture with the current collector, a binding material is necessary between electrode substrate and current collector, and as the binding material, a substance selected from the group consist~ng of phenol resin, pitch derived from petroleum or coal, polyvinyl alcohol, epoxy resin and the mixture thereof is utilized in preparing the electrode sustrate.
The thus joined electrode substrate and current collector via the binding material is baked at a temperature of 1,500 to 3000C.
7~8 I' On the other hand, in the case where the baking of the molded mixture for the preparation of the electrode substrate is combined with the baking step in the joining of the current collector with the molded mlxture for the prepa-~ ration of the electrode substrate, the baking is carried I out after joining the preliminarily baked current collector I with the molded mixture for the preparation of the electrodesubstrate. Ihe preliminary baking is carried out for I conforming t.he shrfnkage of the jolned prellminarily baked 10 1I current collector to that of the joined electrode substrate in ¦ baking step. In this case, the binding material is not indispensable, however, the same binding material mentioned ¦ above may be used. In the case where the baking of the molded mixture for the preparation of the electrode substrate is combined with the baking step for joining of the molded mixture for the preparation of the electrode substrate with ¦ the preliminarily baked current collector, one step of baking is saved and accordingly, the latter case is preferable.
By the step of baking, the porously carbonized electrode substrate is obtained and in the same time the compactly carbonized current collector is obtained.
¦ Catalyst:
After having joined the electrode substrate with the current collector into a unified body as shown above, the catalyst is coated on the surface of electrode substrate.
As the catalyst, a substance suitable as the catalyst of the 73~
oxygen-cathode for use in electrolysis of an alkali chloride, namely the substance which accelerates the reaction of formation of hydroxide ions from the oxygen introduced into the cathode and water in the aqueous electrolyte solution. Concretely, one of the known catalysts,for instance, a noble metal such as platinum and silver or Raney silver is used for the purpose. Particularly, in the present invention, those carbon black particles having their surface covered with a powdery noble metal, namely, a noble metal carried on carbon black particles is preferable.
As the method for coating such a catalyst onto the electrode substrate, a method has been known in which an aqueous suspension containing the particles of the catalyst is coated on the surface of the electrode substrate and the solvent is then removed by drying. The noble metal may be electroplated on the electrode substrate. Instead of elec-troplating, the following method may be taken wherein the electrode substrate is impregnated with an aqueous solution containing a compound of the metal which can be the catalyst, and the thus introduced compound is then~ally decomposed or reduced to the metal within the electrode substrate.
Hydrophobic Treatment:
Hydrophobic treatment of the oxygen-cathode is carried out in order to prevent the leakage of the aqueous solution in the vicinity of the cathode to the gas side of the oxygen-cathode. As the agent for use in hydrophobic treatment, ~2~3&9~
fluorine-containing polymer such as polytetrafluoroethylene is preferable, and in order to prevent the reduction in the activity of the catalyst due to the coverage of the surface of the catalyst by the thus applied agent, the agent is applied before the coating of the catalyst, and after coating the catalyst on the thus applied agent, the agent is melted and adhered to the electrode substrate.
In ord~r to avoid the reduction of electric conductivity of the electrode substrate due to the above-mentioned hydrophobic treatment, in the case of rendering the surface of the electrode substrate hydrophobic it is preferable to coat a mixture of carbon black and the particles of fluorine-containing polymer on the surface of the electrode substrate.
For instance, an aqueous emulsion containing the particles of polytetrafluoroethylene of from 100 to 5,000 A in diameter and the particles of carbon black of from 100 to 5,000 A in diameter is coated on the surface of the electrode substrate, and then an aqueous suspension containing the particles of the catalyst is coated thereon. After removing the solvent of the suspension by drying the thus coated electrode, the electrode substrate is subjected to baking at 300 to 400C, thereby sintering the particles of polytetrafluoroethylene to obtain a membrane of polytetrafluoroethylene strongly adhered to the surface of the micropores of the elec-trode substrate.
In addition, both coating of the catalyst and the agent for rendering the surface of t:he electrode substrate hydrophobic can be effected simultaneously by coating a mixture of the particles of polytetrafluoroethylene and the particles of the catalyst.
Accordi.ng to the present invention, the electrode substrate which is mainly composed of the porous carbonaceous material and carries the catalyst thereon, plays a role in dispersi.ng the supplied oxygen. The current:
collector of the present invent:ion which is mainly composed of the compact carbonaceous materi.al and i.s joined with the electrode substrate into a unified body via the mutually facing carbonized surfaces, plays the role in conducting electricity to the electrode substrate without generating electric contact resistance. In addition, in t:he case where the current collector is modifi.ed to take a suitable st:ructure, the modified current collector plays a role i.n supplying oxygen to the cathode and gas-sealing to outside of the cel1.
The catalyst carried on the electrode substrate is adhered within t:he plurality of the micropores, however, in case of necessity, the catalyst is also applied on the surface of the electrode substrate.
Furthermore, since in the oxygen-cathode according to the present invention, both the current collector and the electrode substrate are composed of carbonaceous material, and have been joined t:ogether int:o a unified body via the mutually facing carbonized surfaces, in the case where such oxygen-cathode is used in electrolysis of an 1~73~397 alkali chloride, any increase of the electrolytic voltage due to the contact resistance between the current collector and the electrode substrate is not observed and accordingly, electrolysis of the alkali chloride can be carried out at a remarkably lower voltage as compared to the conventional electrolysis of the alkali chloride.
In addition, porous carbonaceous material is used for the electrode substrate and accordingly, the electrode substrate is anticorrosive and durable. Furthermore, since a large number of micropores have been preliminarily formed with a controlled pore diameter in the electrode substrate and it is possible to carry the catalyst particles within such micropores, the catalyst is easily coated on the electrode substrate, and it is possible to obtain an oxygen-cathode which is superior in the cathode specificity.
Particularly, in the case where the electrode substrate is made from the carbon fibers, the binding material and the micropore-forming substance, it is possible to obtain an oxygen-cathode having uniformly distributed micropores with a controlled pore size and distributing oxygen gas uniformly.
The oxygen-cathode according to the present invention may be used in the electrolytic cells in the ion-exchange membrane method and also in the SPE method for electrolysis of an alkali chloride. In addition, it may be used in the electrolytic cell in which only the anode is manufactured by the mode of the SPE method for electrolysis ~389~
of an alkali chloride.
The present invention wlll be explained more in detail while referring to the following non-limitative example and comparative examples.
EXAMPLE:
1) Preparation of the current collector:
A commercialized powdery pitch derived from petroleum (made by KUREHA KAGAKU KOGYO Co., Ltd., MH-lP) was preliminarily baked in an atmosphere of nitrogen and after cooling thereof, it was pulverized to be of 6 ~m in the mean diameter and used as the hard carbon particles for aggregate.
Namely, 65 % by weight of the hard carbon particles and 35 ~ by weight of a commercialized phenol resin (more than 85 % by weight of the phenol resin passes through the sieve of 320 mesh) as the binding material were mixed, and after introducing the uniform mixture in a ribbed metal mold, the mixture was molded under the conditions of 150C in temperature and of 100 kg/cm2 in pressure, and the thus molded mixture was baked at 1,000C to be carbonized, thereby obtaining the current collector.
2) Preparation of the electrode substrate before baking:
35% by weight of carbon fiber ~commercialized after baking preliminarily at 2,000C to carbonize, made by KUREHA KAGAKU KOGYO Co., Ltd.,M 204T, 19 ~m in diameter and 250 ~m in length), 25 % by weight of a commercialized powdery phenol resin (more than 85 % by weight of the 1~73~
phenol resin pa,ses through the sieve of 320 mesh) as a binding material, 30 ~ by weight of the particles of polyvinyl alcohol (mean diameter of 120 ~m) as one of the two micropore-forming substances and 10 ~ by weight of the particles of polyethylene (mean diameter of 100 ~m) as one of the two micropore-forming substances were mixed together and after introducing the thus obtained uniform mixture on a flat metal mold, the mixture was molded under the conditions of 110C in temperature and 35 kg/cm2 in pressure, thereby obtaining the precursor of the electrode substrate which is not yet subjected to baking.
35% by weight of carbon fiber ~commercialized after baking preliminarily at 2,000C to carbonize, made by KUREHA KAGAKU KOGYO Co., Ltd.,M 204T, 19 ~m in diameter and 250 ~m in length), 25 % by weight of a commercialized powdery phenol resin (more than 85 % by weight of the 1~73~
phenol resin pa,ses through the sieve of 320 mesh) as a binding material, 30 ~ by weight of the particles of polyvinyl alcohol (mean diameter of 120 ~m) as one of the two micropore-forming substances and 10 ~ by weight of the particles of polyethylene (mean diameter of 100 ~m) as one of the two micropore-forming substances were mixed together and after introducing the thus obtained uniform mixture on a flat metal mold, the mixture was molded under the conditions of 110C in temperature and 35 kg/cm2 in pressure, thereby obtaining the precursor of the electrode substrate which is not yet subjected to baking.
3) Joining of the current collector with the precursor of the electrode substrate:
After facing the thus obtained precursor of the electrode substrate with the ribbed side of the thus prepared current collector,, the thus faced two materials were joined under the conditions of 135C in temperature and 35 kg/cm2 in pressure and, the thus joined materials were baked at 2,000C to be-unLted in one body.
~4j H~rophobic treatmen* and coating of the catalysti The open surface of the electrode substrate which had been thus joined with the current collector was coated wlth a mixture of a commercialized emulsion of polytetra-fluoroethylene (made by MITSUI Fluorochemical Co., Ltd.) and carbon black, and then the thus coated surface was further coated with an agueous suspension of carbon black .
,,., ~ ~3 ~
particles having their surface covered with powdery platinum.
After drying, the thus dried material was treated at 330c to melt the particles of polytetrafluoroethylene whereby the carbon black particles are adhered to the s11rface of the electrode substrate. The weight ratio of polytetra-fluoroethylene remaining on the surface of the electrode substrate to the electrode substrate was 0.2 : 100 and that of carbon black remaining on the surface of the electrode substrate to the electrode substrate was 0.5:100.
The amount of platinum on the surface of the electrode substrate was 1 mg/cm of the surface area.
Thus, the oxygen-cathode for use in electrolysis or an alkali chloride according to the present invention was obtained.
5) Test of the thus obtalned electrode:
The thus prepared oxygen-cathode was subjected to a test for determlning the cathode-specificity (a relationship between the current density and the cathode potential) In the following reaction carried out in an aqueous 9N
solutlon of sodium hydroxide.
, ~
; ~ 2 ~2 ~ 2+ 4 e ~ 4 OH
The test results are shown in Fig. 8 together with the test results obtained on other oxygen-cathodes shown ; in Comparative Examples below.
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3~39`~
COMPARATIVE EXAMPLE 1:
An electrode comprising a nickel wire lattice as the core material and porous carbon material reinforced with polytetrafluoroethylene and having a porous membrane of polytetrafluoroethylene on the surface through which air or oxygen is introduced thereinto, was subjected to the same treatment of painting with the catalyst and then to the same hydrophobic treatment as in the Example. The thus treated electrode was tested under the same conditions as in the Example, the results being also shown in Fig. 8.
As are seen in Fig. 8, the oxygen-cathode potential shown by the electrode of Comparative Example 1 was remarkably lower than that of the oxygen-cathode of Example at the same current density. Such a phenomenon is due to (1) the larger electric resistance of the porous carbon electrode and (2) the large contact resistance between the nickel wire lattice which also serves as the current collector and the porous carbon electrode material, and thus, the excellent properties of the oxygen-cathode according to the present invention due to its nearly-zero contact resistance have been verified.
COMPA ATIVE EXAMPLE 2:
A current collector was prepared in the same manner as in Example except for using the baking temperature ~.~. ,.
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of 2,000C instead of 1,000C in Example. An electrode substrate before baking was prepared in the same manner as in Example, and the product was baked at 2,000C to be the electrode substrate.
After subjectins the thus prepared current collector and the thus prepared electrode substrate to the same hydrophobic treatment and to the coating of the catalyst ln the same manner as in Example, the current collector and the electrode substrate were tested under the same conditions as in Example, the test results being also shown in Fig. 8.
As are seen in Fig. 8, the oxygen-cathode voltage shown by the electrode treated in Comparative Example 2 was lower than that shown by the oxygen-electrode of Example at the same current density. This fact is due to the presence of a larger contact electric resistance between the current collector and the electrode substrate ln the electrode of Comparative Example 2 than that in the electrode of the Example.
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After facing the thus obtained precursor of the electrode substrate with the ribbed side of the thus prepared current collector,, the thus faced two materials were joined under the conditions of 135C in temperature and 35 kg/cm2 in pressure and, the thus joined materials were baked at 2,000C to be-unLted in one body.
~4j H~rophobic treatmen* and coating of the catalysti The open surface of the electrode substrate which had been thus joined with the current collector was coated wlth a mixture of a commercialized emulsion of polytetra-fluoroethylene (made by MITSUI Fluorochemical Co., Ltd.) and carbon black, and then the thus coated surface was further coated with an agueous suspension of carbon black .
,,., ~ ~3 ~
particles having their surface covered with powdery platinum.
After drying, the thus dried material was treated at 330c to melt the particles of polytetrafluoroethylene whereby the carbon black particles are adhered to the s11rface of the electrode substrate. The weight ratio of polytetra-fluoroethylene remaining on the surface of the electrode substrate to the electrode substrate was 0.2 : 100 and that of carbon black remaining on the surface of the electrode substrate to the electrode substrate was 0.5:100.
The amount of platinum on the surface of the electrode substrate was 1 mg/cm of the surface area.
Thus, the oxygen-cathode for use in electrolysis or an alkali chloride according to the present invention was obtained.
5) Test of the thus obtalned electrode:
The thus prepared oxygen-cathode was subjected to a test for determlning the cathode-specificity (a relationship between the current density and the cathode potential) In the following reaction carried out in an aqueous 9N
solutlon of sodium hydroxide.
, ~
; ~ 2 ~2 ~ 2+ 4 e ~ 4 OH
The test results are shown in Fig. 8 together with the test results obtained on other oxygen-cathodes shown ; in Comparative Examples below.
:'' ~' ~' ~ ~ - 20 -',~
3~39`~
COMPARATIVE EXAMPLE 1:
An electrode comprising a nickel wire lattice as the core material and porous carbon material reinforced with polytetrafluoroethylene and having a porous membrane of polytetrafluoroethylene on the surface through which air or oxygen is introduced thereinto, was subjected to the same treatment of painting with the catalyst and then to the same hydrophobic treatment as in the Example. The thus treated electrode was tested under the same conditions as in the Example, the results being also shown in Fig. 8.
As are seen in Fig. 8, the oxygen-cathode potential shown by the electrode of Comparative Example 1 was remarkably lower than that of the oxygen-cathode of Example at the same current density. Such a phenomenon is due to (1) the larger electric resistance of the porous carbon electrode and (2) the large contact resistance between the nickel wire lattice which also serves as the current collector and the porous carbon electrode material, and thus, the excellent properties of the oxygen-cathode according to the present invention due to its nearly-zero contact resistance have been verified.
COMPA ATIVE EXAMPLE 2:
A current collector was prepared in the same manner as in Example except for using the baking temperature ~.~. ,.
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of 2,000C instead of 1,000C in Example. An electrode substrate before baking was prepared in the same manner as in Example, and the product was baked at 2,000C to be the electrode substrate.
After subjectins the thus prepared current collector and the thus prepared electrode substrate to the same hydrophobic treatment and to the coating of the catalyst ln the same manner as in Example, the current collector and the electrode substrate were tested under the same conditions as in Example, the test results being also shown in Fig. 8.
As are seen in Fig. 8, the oxygen-cathode voltage shown by the electrode treated in Comparative Example 2 was lower than that shown by the oxygen-electrode of Example at the same current density. This fact is due to the presence of a larger contact electric resistance between the current collector and the electrode substrate ln the electrode of Comparative Example 2 than that in the electrode of the Example.
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Claims (8)
1. An oxygen-cathode for use in electrolysis of an alkali chloride, comprising a current collector made of a moulded, compact carbonaceous material, and at least one electrode substrate made of a moulded, porous carbonaceous material having a catalyst carried thereon, wherein said current collector and said electrode substrate are integrated into one body consisting essentially of carbon and said catalyst, wherein said current collector has a permeability to air of not more than 10-7ml/cm.hour.mmH20, a bending strength of not less than 500 kg/cm2, an electric resistance of not more than 10 m.OMEGA..cm and a thermal conductivity of not less than 3 kcal/m.hour.°C. and said electrode substrate has a thickness of 0.2 to 2mm, a pore diameter of 5 to 100 µm, a permeability to air of not less than 5 ml/cm.hour.mmH20, a bending strength of not less than 30 kg/cm2, an electric resistance of not more than 50 m.OMEGA..cm and a thermal conductivity of not less than 0.5 kcal/m.hour.°C.
2. An oxygen-cathode according to claim 1, wherein said current collector has ribs and said electrode substrate has no ribs.
3. An oxygen-cathode according to claim 2, wherein said current collector having ribs is sandwiched between two electrode substrates.
4. An oxygen-cathode according to claim 1, wherein said electrode substrate has been produced by mixing carbon fibers, a binding material and a micropore-forming substance which is volatile at high temperatures, molding the thus obtained mixture under pressure and baking the thus molded mixture.
5. An oxygen-cathode according to claim 1, wherein said electrode substrate has been produced by mixing carbon fibers, a binding material and a micropore-forming substance which is soluble in a solvent, molding the thus obtained mixture under pressure to produce a molded mixture, subjecting the molded mixture to extraction with said solvent, thereby removing said micropore-forming substance from said molded mixture, and baking the molded mixture.
6. A process for preparing an oxygen-cathode for use in electrolysis of an alkali chloride, comprising the steps of 1) providing a current collector by mixing hard or soft carbon particles with a binding material, molding the thus obtained mixture under pressure and subjecting the thus molded mixture to a preliminary baking at a temperature of 500 to 1500°C;
2) providing a precursor electrode substrate which has not been baked by 2a) mixing carbon fibers, a binding material and a micropore-forming substance which is volatile at high temperatures, molding the thus obtained mixture under pressure, or 2b) mixing carbon fibers, a binding material and a micropore-forming substance which is soluble in a solvent, molding the thus obtained mixture under pressure and subjecting the thus molded mixture to extraction with said solvent to remove said micropore-forming substance from said molded mixture thereby forming micropores in said molded mixture;
3) facing together the respective surfaces to be joined of said current collector and said precursor electrode substrate;
4) joining said precursor electrode substrate and said current collector under pressure;
5) baking the joined precursor electrode substrate and current collector at a temperature of not less than 1500°C, thereby integrating said precursor electrode substrate and said current collector into a unitary body, and simultaneously carbonizing said current collector and said precursor electrode substrate whereby said precursor electrode substrate becomes a carbonized electrode substrate with pores formed therein, and wherein after baking, said unitary body consists essentially of carbon; and 6) subjecting said carbonized electrode substrate to a treatment for rendering the surface of said electrode substrate hydrophobic, and coating the treated surface of said electrode substrate with a catalyst, so that said current collector has a permeability to air of not more than 10 7 ml/cm.hour.mmH20, a bending strength of not less than 500 kg/cm2, an electric resistance of not more than 10m?.cm and a thermal conductivity of not less than 3 kcal/m.hour.°C. and said electrode substrate has a thickness of 0.2 to 2mm, a pore diameter of 5 to 100 µm, a permeability to air of not less than 5 ml/cm.hour.mmH20, a bending strength of not less than 30 kg/cm2, an electric resistance of not more than 50 m?.cm and a thermal conductivity of not less than 0.5 kcal/m.hour.°C.
2) providing a precursor electrode substrate which has not been baked by 2a) mixing carbon fibers, a binding material and a micropore-forming substance which is volatile at high temperatures, molding the thus obtained mixture under pressure, or 2b) mixing carbon fibers, a binding material and a micropore-forming substance which is soluble in a solvent, molding the thus obtained mixture under pressure and subjecting the thus molded mixture to extraction with said solvent to remove said micropore-forming substance from said molded mixture thereby forming micropores in said molded mixture;
3) facing together the respective surfaces to be joined of said current collector and said precursor electrode substrate;
4) joining said precursor electrode substrate and said current collector under pressure;
5) baking the joined precursor electrode substrate and current collector at a temperature of not less than 1500°C, thereby integrating said precursor electrode substrate and said current collector into a unitary body, and simultaneously carbonizing said current collector and said precursor electrode substrate whereby said precursor electrode substrate becomes a carbonized electrode substrate with pores formed therein, and wherein after baking, said unitary body consists essentially of carbon; and 6) subjecting said carbonized electrode substrate to a treatment for rendering the surface of said electrode substrate hydrophobic, and coating the treated surface of said electrode substrate with a catalyst, so that said current collector has a permeability to air of not more than 10 7 ml/cm.hour.mmH20, a bending strength of not less than 500 kg/cm2, an electric resistance of not more than 10m?.cm and a thermal conductivity of not less than 3 kcal/m.hour.°C. and said electrode substrate has a thickness of 0.2 to 2mm, a pore diameter of 5 to 100 µm, a permeability to air of not less than 5 ml/cm.hour.mmH20, a bending strength of not less than 30 kg/cm2, an electric resistance of not more than 50 m?.cm and a thermal conductivity of not less than 0.5 kcal/m.hour.°C.
7. A process according to claim 6, which further comprises after said baking step, coating said electrode substrate with an emulsion containing particles of fluorine-containing polymer and carbon black, and then coating the electrode substrate with a suspension containing particles of a catalyst, solvent in said emulsion and suspension being removed from the coated electrode substrate by drying thereof, and then thermally treating the coated electrode substrate so as to melt and adhere said particles of fluorine-containing polymer to the surface of said electrode substrate.
8. A process according to claim 6, wherein the joining of step (4) is carried out while heating said precursor electrode substrate and said current collector at a temperature of 80 to 200°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14330184A JPS6123780A (en) | 1984-07-12 | 1984-07-12 | Oxygen cathode for electrolyzing alkali chloride and its manufacture |
| JP143301/84 | 1984-07-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1273897A true CA1273897A (en) | 1990-09-11 |
Family
ID=15335568
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000486286A Expired - Fee Related CA1273897A (en) | 1984-07-12 | 1985-07-04 | Forming oxygen-cathode by joining moulded carbon sustrate with carbonaceous collector electrode |
Country Status (6)
| Country | Link |
|---|---|
| US (2) | US4675094A (en) |
| JP (1) | JPS6123780A (en) |
| CA (1) | CA1273897A (en) |
| DE (1) | DE3524604A1 (en) |
| FR (1) | FR2567543B1 (en) |
| GB (1) | GB2161833B (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4564427A (en) * | 1984-12-24 | 1986-01-14 | United Technologies Corporation | Circulating electrolyte electrochemical cell having gas depolarized cathode with hydrophobic barrier layer |
| US4643956A (en) * | 1984-12-24 | 1987-02-17 | United Technologies Corporation | Coke filled separator plate for electrochemical cells |
| US4794043A (en) * | 1985-04-30 | 1988-12-27 | Kureha Kagaku Kogyo Kabushiki Kaisha | Carbon product comprising carbonaceous materials joined together, said carbon product for electrode substrate of fuel cells and process for production thereof |
| JPS63230894A (en) * | 1987-03-19 | 1988-09-27 | Kamioka Kogyo Kk | Cathode material for electrolysis and production thereof |
| US4927514A (en) * | 1988-09-01 | 1990-05-22 | Eltech Systems Corporation | Platinum black air cathode, method of operating same, and layered gas diffusion electrode of improved inter-layer bonding |
| US5047133A (en) * | 1989-02-27 | 1991-09-10 | Metallgesellschaft Aktiengesellschaft | Gas electrode assembly for use in electrochemical cells and method |
| GB2362533A (en) * | 2000-05-15 | 2001-11-21 | Nokia Mobile Phones Ltd | Encoding a video signal with an indicator of the type of error concealment used |
| US6291882B1 (en) * | 2000-06-02 | 2001-09-18 | Siliconware Precision Industries Co., Letd. | Packaging process and structure of electronic device |
| US7043967B2 (en) * | 2002-09-30 | 2006-05-16 | University Of Dayton | Sensor device for monitoring the condition of a fluid and a method of using the same |
| US6830595B2 (en) * | 2002-12-20 | 2004-12-14 | Advanced Energy Technology Inc. | Method of making composite electrode and current collectors |
| FR2940857B1 (en) * | 2009-01-07 | 2011-02-11 | Commissariat Energie Atomique | METHOD FOR MANUFACTURING HIGH TEMPERATURE ELECTROLYSET OR HIGH TEMPERATURE FUEL CELL COMPRISING A STACK OF ELEMENTARY CELLS |
| KR101399172B1 (en) * | 2010-02-22 | 2014-05-27 | 페르메렉크전극주식회사 | Oxygen gas diffusion cathode, electrolytic cell employing same, method of producing chlorine gas and method of producing sodium hydroxide |
| EP2907184B1 (en) * | 2012-10-09 | 2018-05-02 | Oxynergy Ltd. | Electrode assembly and method for its preparation |
| US10689301B2 (en) * | 2018-05-03 | 2020-06-23 | Doosan Fuel Cell America, Inc. | Method of making a porous fuel cell component |
Family Cites Families (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE63474C (en) * | V. Graumüller und Gebrüder Harnisch in Gera, Reufs j. L | Spindle lock for web shuttle | ||
| US3395049A (en) * | 1963-07-15 | 1968-07-30 | Exxon Research Engineering Co | Method of making a porous electrode |
| US3413152A (en) * | 1965-07-30 | 1968-11-26 | Union Oil Co | Method of making carbonaceous fuel cell electrode |
| US4350608A (en) * | 1978-04-24 | 1982-09-21 | Diamond Shamrock Corporation | Oxygen cathode for alkali-halide electrolysis and method of making same |
| US4278525A (en) * | 1978-04-24 | 1981-07-14 | Diamond Shamrock Corporation | Oxygen cathode for alkali-halide electrolysis cell |
| IT1111479B (en) * | 1978-06-20 | 1986-01-13 | Fiat Spa | GRAPHITE Porous COMPOSITE STRUCTURE ELECTRODE RESIN FOR APPLICATION IN ELECTROCHEMICAL SYSTEMS |
| US4294893A (en) * | 1979-05-21 | 1981-10-13 | Centro Ricerche Fiat S.P.A. | Graphite-resin composite electrode structure, and a process for its manufacture |
| US4219611A (en) * | 1979-07-30 | 1980-08-26 | United Technologies Corporation | Fuel cell electrolyte reservoir layer and method for making |
| GB2075060B (en) * | 1980-04-23 | 1984-02-08 | Sklyariv A T | Electrode for elctrochemical processes and process for producing same |
| US4330704A (en) * | 1980-08-08 | 1982-05-18 | Raychem Corporation | Electrical devices comprising conductive polymers |
| US4456521A (en) * | 1980-10-31 | 1984-06-26 | Diamond Shamrock Corporation | Three layer laminate |
| KR830007884A (en) * | 1980-10-31 | 1983-11-07 | 앤 시이 헤릭크 | Matrix electrodes stacked in three layers |
| US4518705A (en) * | 1980-10-31 | 1985-05-21 | Eltech Systems Corporation | Three layer laminate |
| US4426340A (en) * | 1981-09-29 | 1984-01-17 | United Technologies Corporation | Process for fabricating ribbed electrode substrates and other articles |
| US4414092A (en) * | 1982-04-15 | 1983-11-08 | Lu Wen Tong P | Sandwich-type electrode |
| JPS5937662A (en) * | 1982-08-24 | 1984-03-01 | Kureha Chem Ind Co Ltd | Electrode substrate for monopolar type fuel cell with two-layer structure |
| JPS5946763A (en) * | 1982-09-10 | 1984-03-16 | Kureha Chem Ind Co Ltd | Two-layered electrode base plate for monopolar fuel cell |
| GB2128395B (en) * | 1982-10-01 | 1986-01-08 | Kureha Chemical Ind Co Ltd | Fuel cell electrode substrate having elongated holes for feeding reactant gases |
-
1984
- 1984-07-12 JP JP14330184A patent/JPS6123780A/en active Pending
-
1985
- 1985-07-03 US US06/751,525 patent/US4675094A/en not_active Expired - Fee Related
- 1985-07-04 CA CA000486286A patent/CA1273897A/en not_active Expired - Fee Related
- 1985-07-05 GB GB08517034A patent/GB2161833B/en not_active Expired
- 1985-07-10 DE DE19853524604 patent/DE3524604A1/en active Granted
- 1985-07-11 FR FR858510655A patent/FR2567543B1/en not_active Expired - Fee Related
-
1986
- 1986-01-10 US US06/817,541 patent/US4744879A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US4675094A (en) | 1987-06-23 |
| GB8517034D0 (en) | 1985-08-14 |
| DE3524604A1 (en) | 1986-01-16 |
| US4744879A (en) | 1988-05-17 |
| FR2567543B1 (en) | 1990-07-27 |
| JPS6123780A (en) | 1986-02-01 |
| GB2161833B (en) | 1988-01-27 |
| FR2567543A1 (en) | 1986-01-17 |
| DE3524604C2 (en) | 1988-04-14 |
| GB2161833A (en) | 1986-01-22 |
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