CA2451610C - Method for manufacturing gaseous diffusion electrodes - Google Patents
Method for manufacturing gaseous diffusion electrodes Download PDFInfo
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- CA2451610C CA2451610C CA2451610A CA2451610A CA2451610C CA 2451610 C CA2451610 C CA 2451610C CA 2451610 A CA2451610 A CA 2451610A CA 2451610 A CA2451610 A CA 2451610A CA 2451610 C CA2451610 C CA 2451610C
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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
- H01M4/88—Processes of manufacture
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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
- H01M4/88—Processes of manufacture
- H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
- H01M4/8896—Pressing, rolling, calendering
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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
- H01M4/8605—Porous electrodes
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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
- H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
- H01M4/8652—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites as mixture
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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
- H01M4/88—Processes of manufacture
- H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
- H01M4/8882—Heat treatment, e.g. drying, baking
- H01M4/8885—Sintering or firing
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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
- H01M4/90—Selection of catalytic material
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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
- H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
- H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
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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
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/08—Fuel cells with aqueous electrolytes
- H01M8/083—Alkaline fuel cells
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- 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
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- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Inert Electrodes (AREA)
- Catalysts (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
With the help of a method for production of a gaseous diffusion electrode from a silver catalyst on PTFE-substrate, it is endeavoured to achieve results which can be reproduced, by avoiding the disadvantages of the state-of-the-art technology, whereby this is achieved in that - the porous system of the silver catalyst is filled with a wetted fluid; - a dimension-stable solid body with a grain size above that of the silver catalyst is mixed below the silver catalyst; - the thus compression-stable mass is shaped into a homogenous catalyst band in a calender; and - in a second calender step, an electrically conductive conductor material is imprinted into the catalyst band.
Description
Method for Manufacturing Gaseous diffusion Electrodes This invention pertains to a method for manufacturing porous gaseous diffusion electrodes.
Such a gaseous diffusion electrode can, for example be based on a catalytic active silver or silver alloys for use in electro-chemical cells, particularly of choloro-alkaline electrolysis, or alkaline fuel cells.
In electro-chemical cells, the reduction of oxygen is carried out on platinum, silver or even carbon. Platinum can be used in acidic as well as in alkaline surroundings, whereas silver and carbon arc stable against corrosion only in alkaline electrolytes. However, in case of silver catalyst, even in alkaline mediums rapid deactivation occurs, which can be explained due to rearrangement of the oxidic surface of the silver. (Texas Instruments, US 35 05 129). It has been tried several times to reduce the corrosive attack of silver alloying partners. Thereby one knows of alloys with precious material like platinum, paladium, gold and mercury (DE 20 21 009), or even with non-precious substances like nickel (DE 15 46 729), copper and other materials. It has also been attempted to achieve a stabilisation ofthe silver by means of refining or also with the help of anodic corrosion protection (local elements). In case of corrosion, initially a silver oxide surface is formed. As silver oxide is relatively well soluble in lye solutions, a rearrangement of silver crystals can take place. In figures 2 and 3, REM-images of silver electrodes before and after operation have been depicted. One can very clearly identify the reduction of the inner porous structure- The catalytic activity gets reduced.
Apart from stabilisation, a method of manufacture of an active silver catalyst must also ensure that the active surface of the silver as sufficiently large, i.e. the grain size of the silver should be as small as possible. Thus, for example, from the document ((IS 3 669 101) it is known that very active silver catalysts can be attained with particle diameters of 5 to I Opm.
We also know of further methods, in which it has been attempted to manufacture the smallest particles of stable silver alloys. Adequately small silver particles are generated through precipitation procedures. Apart from controlling the phi-value, the temperature and the over-saturation, so-called crystallisation germs play an excellent role in manufacturing the smallest silver particles. We know of a method (EP 0 115 845), in which a mixture of silver nitrate and mercury nitrate are precipitated on a PTFE-dispersion by adding potash lye. In this way, a silver amalgam with smallest particle diameter is produced.
Two methods are known, in which from such hydrophobic/hydrophilic materials a thin, homogeneous gaseous diffusion electrode is rolled. According to the method (EP
0 144 002, US 4 696 872), the catalyst particles and the PTFE, are mixed in a special mixer in such a way, that a fine-meshed hydrophobic net system gets precipitated on the catalyst.
The loose mass is then rolled together in a powder roller to form a tail of approx. 0.2mm thickness. This method has proved useful for mixtures with PTFE and carbon. or PTFE and Raney-nickel. It is similarly possible to in this way roll a Raney-silver-alloy with 80%
aluminium into a porous foil. Fig. 1 shows such a calender rolling mechanism. However, it is not possible to process the ductile silver. In case of the required pressing pressure -approx. 0.01 to 0.6 t/cm2 - in such powder rollers, PTFF, and silver are pressed to form a compact, gas-imperineahle and electrolyte-impern-meable foil. The current-voltage graph for such an electrode is shown in fig. 5.
in order to nevertheless be able to produce silver electrodes, initially a silver oxide/PTFE-mixture is processed in the powder roller and subsequently reduced clectro-chemically (DE
37 10 168). The silver oxide is stable enough to withstand the pressing pressure of the roller.
Besides, the volume reduces on transition from silver oxide to silver, so that additional pores are generated in the gaseous diffusion electrodes. By means of the parameters during reduction, The grain size of the particles can be very well adjusted. The disadvantage oithis method is, that it is not yet known, how silver alloys with catalytic properties can be reduced clectro-chemically. Hence it is not possible to produce durable, stable silver electrodes by means of electro-chemical reduction.
BRIEF DESCRIPTION OF FIGURES
Further features, details and advantages of the invention are shown in the following diagrams. The following are shown:
Fig. 1 A functional diagram of a device/plant as per the invention;
Fig. 2 A microscopic image of a silver electrode before use;
Fig. 3 In the same depiction form, a silver electrode after use;
Fig. 4 A PTFE-structure embedded in a silver catalyst;
Fig. 5 A current/voltage diagram of a chloro-alkaline electrolysis; and Fig. 6 The same graph according to the parameters of the invention.
The reference characters noted in Fig. I stand for:
1 Rotary Slide Valve 2 Storage Container 3 Crusher (Hammer Mill) 4 Powder Funnel 5 Knocker 6 Light Barrier 7 Web Roll 8 Electrode Web 9 Guide Rail 10 Net Roll 11 Net Roller 12 Guide Roller 13 Conductive Net 14 Edge Stripper Spool for Electrode Band 16 Drive Motor.
5 The task of this invention is to present a method for producing a gaseous diffusion electrode, with which not only the disadvantages of the state-of-the-art technology can be avoided, but also to particularly evolve results in the process product which can be reproduced.
With the help of the method already mentioned above, this task is 1o fulfilled according to the invention, in that - The porous system of the silver catalyst is filled with a wetting fluid;
- a dimension-stable solid body with a grain size above that of the silver catalyst mixed below the silver catalyst;
- the thus formed compression-stable mass is shaped in a calender 15 to a homogeneous catalyst band; and - in a second calender step, an electrically conducting material is imprinted in the catalyst band.
According to one aspect of the present invention, there is provided a method for producing a gaseous diffusion electrode from a silver catalyst on PTFE-substrate, comprising the steps of: filling a porous system of the silver catalyst with a wetting fluid; mixing a dimension-stable solid body with a grain size above that of the silver catalyst with the silver catalyst to produce a compression-stable mass; shaping the compression-stable mass into a homogeneous catalyst band in a calender, and imprinting, in a second calender step, an electrically conducting material into the catalyst band.
According to another aspect of the present invention, there is provided the method as described herein, comprising 5% isopropanol as the wetting fluid and as the dimension-stable solid body 30% ammonium carbonate or ammonium-hydrogen-carbonate is used, and; annealing, after producing the electrode, to drive out the 5% isopropanol and 30% ammonium carbonate or ammonium hydrogen carbonate.
According to still another aspect of the present invention, there is provided the method as described herein, wherein the annealing step is carried out at 110 C.
According to yet another aspect of the present invention, there is provided the method as described herein, comprising using as the wetting fluid a tenside for penetrating into the porous system of the catalyst and for reducing surface friction, enabling the silver catalyst to glide out of a solidification zone, and the dimension-stable solid ammonium carbonate and the PTFE-substrate take up roller pressure in shaping the homogeneous catalyst band.
According to a further aspect of the present invention, there is provided the method as described herein, wherein 5% Triton* X 100 is used as the tenside.
According to yet a further aspect of the present invention, there is provided the method as described herein, wherein in the first calender step, the homogeneous catalyst band shaped has a thickness between 0.2 - 0.5 mm.
According to still a further aspect of the present invention, there is provided the method as described herein, comprising adjusting a roller gap to 350 m and setting a roller feed to approx. 2 meters per minute.
According to another aspect of the present invention, there is provided the method as described herein, comprising using as the electrical conducting material, a silver-coated nickel wire net with a string thickness of 0.15 mm and mesh width of 0.45 mm with an approx. 10 .Lm thick silver precipitate.
* Trademark The speciality of this method as per the invention lies therein, that the inner porous system of the ductile material is filled with a fluid. As this fluid cannot be solidified and, on the other hand, is fixed in the porous system by means of the capillary forces, the fluid cannot he removed from the micro-pores even at a prcssurc of maximum 600 kg/cm.'-`.
Further addition of a little powder carbon or the volatile ammonium carbonate can take up the mechanical pressure of the .powder roller even further. By means of these coarse-grained additions of typically 10 -. 100 m grain diameter, the porous system with larger pore diameter is protected from solidification. By means ofa subsequent annealing step, the fluid. as well as the ammonium carbonate can be driven out of the electrode. In this way, one can obtain large pores in the gaseous diffusion electrode, which ensures rapid gas transportation and smaller pores in the catalyst, which allow a homogeneous optimum utilisation of the catalyst.
A preferred execution of this method is depicted as follows:
first, silver or a silver alloy is produced by means of a precipitation process. Thereby, it would be advantageous to carry out the precipitation on a PTFE-dispersion. The best experiences are made with a mixture of lS%Teflon* and 85% silver. By addition of formaldehyde during precipitation, the silver hydroxide immediately gets transformed in the alkaline surroundings into a silver crystal. The precipitate mass is washed and dried.
Subsequent annealing at 200 C improves the electrical contact between the silver particles and drives out the remaining fluids.
A quantity of about 5% - 40%, preferably however 8%, of a fluid is added to this powder.
't'his fluid can penetrate into the porous system of the PTFE and the silver.
On account of the hydrophobic character of the PTFE, only isopropanol. ethanol and methanol will come into consideration. If the powder is wetted and filled with such solvents, then there could subsequently be an exchange of the fluids. For example, one can bring a powder immersed in isopropanol into a water bath, or glycerine, and thus within hours the fluids get exchanged through diffusion. In. this way, fluid enters into the porous system of the PTFE. which is generally repelled by the PTFE. The thus moistened material behaves externally like a powder because the fluid is present in the inner-porous system:
*Trade-mark Another generic type of wetting agent would be the so-called tensides. These penetrate into the porous system, and at the same time also cover the surface of the catalyst, thus reducing its surface roughness. This reduced surface roughness leads during the rolling process to the phenomenon, that the silver catalyst can move away from the solidification zone, whereas other powder components which have not been treated remain in the solidification zone and thus produce the electrode combination in which the silver catalyst is embedded (fig. 4). Such a powder could be ammonium carbonate or activated carbon, which can now be mixed to a homogeneous mass with the silver catalyst in a pulverizer, as dcwribcd in EP 0 144 002.
Subsequently, the loose mass is rolled into a foil of approx. 0 2.mm thickness by means of a powder roller.
In a second pair of rollers. a metallic support structure can be rolled in the form of woven nets or stretch-metals and thus the mechanical stability and the electrical conductivity can he improved- After this sequence, the gaseous diffusion electrode is dried.
Thereafter the electrode has a silver deposit between 0.2 kg/in2 and 1.5 kg/m"-. Generally, one endeavours lar a weight of approx. 0.5 kg/m2_ Thus, up to 75% of the hitherto required silver can be saved. In spite of the reduced silver weight, with such electrodes one obtains a current-voltage-graph t ti shown in fig.6.
Of course, this method can also be combined with others. Thus, one can do away with the environmentally harmful formaldehyde for precipitation and instead carry out the reduction after production of the gaseous difliision electrodes by means of electro-chemical methods.
In this way, one can similarly produce alloys by carrying out a co-precipitation of silver and mercury, titanium, nickel, copper, cobalt or bismuth.
Especially for the chloro-alltaline-electrolysis, changes can be effected on the ready gaseous diffusion electrode, which would enable improved removal of the occurring soda lye. For this, the imprinting of a coarse conducting system is advisable. This is possible, if a net is pressed onto the ready electrode and then subsequently removed again. The negative impression of the net forms channels, in which the electrolyte can later flow off parallel to the electrode surface.
Such a gaseous diffusion electrode can, for example be based on a catalytic active silver or silver alloys for use in electro-chemical cells, particularly of choloro-alkaline electrolysis, or alkaline fuel cells.
In electro-chemical cells, the reduction of oxygen is carried out on platinum, silver or even carbon. Platinum can be used in acidic as well as in alkaline surroundings, whereas silver and carbon arc stable against corrosion only in alkaline electrolytes. However, in case of silver catalyst, even in alkaline mediums rapid deactivation occurs, which can be explained due to rearrangement of the oxidic surface of the silver. (Texas Instruments, US 35 05 129). It has been tried several times to reduce the corrosive attack of silver alloying partners. Thereby one knows of alloys with precious material like platinum, paladium, gold and mercury (DE 20 21 009), or even with non-precious substances like nickel (DE 15 46 729), copper and other materials. It has also been attempted to achieve a stabilisation ofthe silver by means of refining or also with the help of anodic corrosion protection (local elements). In case of corrosion, initially a silver oxide surface is formed. As silver oxide is relatively well soluble in lye solutions, a rearrangement of silver crystals can take place. In figures 2 and 3, REM-images of silver electrodes before and after operation have been depicted. One can very clearly identify the reduction of the inner porous structure- The catalytic activity gets reduced.
Apart from stabilisation, a method of manufacture of an active silver catalyst must also ensure that the active surface of the silver as sufficiently large, i.e. the grain size of the silver should be as small as possible. Thus, for example, from the document ((IS 3 669 101) it is known that very active silver catalysts can be attained with particle diameters of 5 to I Opm.
We also know of further methods, in which it has been attempted to manufacture the smallest particles of stable silver alloys. Adequately small silver particles are generated through precipitation procedures. Apart from controlling the phi-value, the temperature and the over-saturation, so-called crystallisation germs play an excellent role in manufacturing the smallest silver particles. We know of a method (EP 0 115 845), in which a mixture of silver nitrate and mercury nitrate are precipitated on a PTFE-dispersion by adding potash lye. In this way, a silver amalgam with smallest particle diameter is produced.
Two methods are known, in which from such hydrophobic/hydrophilic materials a thin, homogeneous gaseous diffusion electrode is rolled. According to the method (EP
0 144 002, US 4 696 872), the catalyst particles and the PTFE, are mixed in a special mixer in such a way, that a fine-meshed hydrophobic net system gets precipitated on the catalyst.
The loose mass is then rolled together in a powder roller to form a tail of approx. 0.2mm thickness. This method has proved useful for mixtures with PTFE and carbon. or PTFE and Raney-nickel. It is similarly possible to in this way roll a Raney-silver-alloy with 80%
aluminium into a porous foil. Fig. 1 shows such a calender rolling mechanism. However, it is not possible to process the ductile silver. In case of the required pressing pressure -approx. 0.01 to 0.6 t/cm2 - in such powder rollers, PTFF, and silver are pressed to form a compact, gas-imperineahle and electrolyte-impern-meable foil. The current-voltage graph for such an electrode is shown in fig. 5.
in order to nevertheless be able to produce silver electrodes, initially a silver oxide/PTFE-mixture is processed in the powder roller and subsequently reduced clectro-chemically (DE
37 10 168). The silver oxide is stable enough to withstand the pressing pressure of the roller.
Besides, the volume reduces on transition from silver oxide to silver, so that additional pores are generated in the gaseous diffusion electrodes. By means of the parameters during reduction, The grain size of the particles can be very well adjusted. The disadvantage oithis method is, that it is not yet known, how silver alloys with catalytic properties can be reduced clectro-chemically. Hence it is not possible to produce durable, stable silver electrodes by means of electro-chemical reduction.
BRIEF DESCRIPTION OF FIGURES
Further features, details and advantages of the invention are shown in the following diagrams. The following are shown:
Fig. 1 A functional diagram of a device/plant as per the invention;
Fig. 2 A microscopic image of a silver electrode before use;
Fig. 3 In the same depiction form, a silver electrode after use;
Fig. 4 A PTFE-structure embedded in a silver catalyst;
Fig. 5 A current/voltage diagram of a chloro-alkaline electrolysis; and Fig. 6 The same graph according to the parameters of the invention.
The reference characters noted in Fig. I stand for:
1 Rotary Slide Valve 2 Storage Container 3 Crusher (Hammer Mill) 4 Powder Funnel 5 Knocker 6 Light Barrier 7 Web Roll 8 Electrode Web 9 Guide Rail 10 Net Roll 11 Net Roller 12 Guide Roller 13 Conductive Net 14 Edge Stripper Spool for Electrode Band 16 Drive Motor.
5 The task of this invention is to present a method for producing a gaseous diffusion electrode, with which not only the disadvantages of the state-of-the-art technology can be avoided, but also to particularly evolve results in the process product which can be reproduced.
With the help of the method already mentioned above, this task is 1o fulfilled according to the invention, in that - The porous system of the silver catalyst is filled with a wetting fluid;
- a dimension-stable solid body with a grain size above that of the silver catalyst mixed below the silver catalyst;
- the thus formed compression-stable mass is shaped in a calender 15 to a homogeneous catalyst band; and - in a second calender step, an electrically conducting material is imprinted in the catalyst band.
According to one aspect of the present invention, there is provided a method for producing a gaseous diffusion electrode from a silver catalyst on PTFE-substrate, comprising the steps of: filling a porous system of the silver catalyst with a wetting fluid; mixing a dimension-stable solid body with a grain size above that of the silver catalyst with the silver catalyst to produce a compression-stable mass; shaping the compression-stable mass into a homogeneous catalyst band in a calender, and imprinting, in a second calender step, an electrically conducting material into the catalyst band.
According to another aspect of the present invention, there is provided the method as described herein, comprising 5% isopropanol as the wetting fluid and as the dimension-stable solid body 30% ammonium carbonate or ammonium-hydrogen-carbonate is used, and; annealing, after producing the electrode, to drive out the 5% isopropanol and 30% ammonium carbonate or ammonium hydrogen carbonate.
According to still another aspect of the present invention, there is provided the method as described herein, wherein the annealing step is carried out at 110 C.
According to yet another aspect of the present invention, there is provided the method as described herein, comprising using as the wetting fluid a tenside for penetrating into the porous system of the catalyst and for reducing surface friction, enabling the silver catalyst to glide out of a solidification zone, and the dimension-stable solid ammonium carbonate and the PTFE-substrate take up roller pressure in shaping the homogeneous catalyst band.
According to a further aspect of the present invention, there is provided the method as described herein, wherein 5% Triton* X 100 is used as the tenside.
According to yet a further aspect of the present invention, there is provided the method as described herein, wherein in the first calender step, the homogeneous catalyst band shaped has a thickness between 0.2 - 0.5 mm.
According to still a further aspect of the present invention, there is provided the method as described herein, comprising adjusting a roller gap to 350 m and setting a roller feed to approx. 2 meters per minute.
According to another aspect of the present invention, there is provided the method as described herein, comprising using as the electrical conducting material, a silver-coated nickel wire net with a string thickness of 0.15 mm and mesh width of 0.45 mm with an approx. 10 .Lm thick silver precipitate.
* Trademark The speciality of this method as per the invention lies therein, that the inner porous system of the ductile material is filled with a fluid. As this fluid cannot be solidified and, on the other hand, is fixed in the porous system by means of the capillary forces, the fluid cannot he removed from the micro-pores even at a prcssurc of maximum 600 kg/cm.'-`.
Further addition of a little powder carbon or the volatile ammonium carbonate can take up the mechanical pressure of the .powder roller even further. By means of these coarse-grained additions of typically 10 -. 100 m grain diameter, the porous system with larger pore diameter is protected from solidification. By means ofa subsequent annealing step, the fluid. as well as the ammonium carbonate can be driven out of the electrode. In this way, one can obtain large pores in the gaseous diffusion electrode, which ensures rapid gas transportation and smaller pores in the catalyst, which allow a homogeneous optimum utilisation of the catalyst.
A preferred execution of this method is depicted as follows:
first, silver or a silver alloy is produced by means of a precipitation process. Thereby, it would be advantageous to carry out the precipitation on a PTFE-dispersion. The best experiences are made with a mixture of lS%Teflon* and 85% silver. By addition of formaldehyde during precipitation, the silver hydroxide immediately gets transformed in the alkaline surroundings into a silver crystal. The precipitate mass is washed and dried.
Subsequent annealing at 200 C improves the electrical contact between the silver particles and drives out the remaining fluids.
A quantity of about 5% - 40%, preferably however 8%, of a fluid is added to this powder.
't'his fluid can penetrate into the porous system of the PTFE and the silver.
On account of the hydrophobic character of the PTFE, only isopropanol. ethanol and methanol will come into consideration. If the powder is wetted and filled with such solvents, then there could subsequently be an exchange of the fluids. For example, one can bring a powder immersed in isopropanol into a water bath, or glycerine, and thus within hours the fluids get exchanged through diffusion. In. this way, fluid enters into the porous system of the PTFE. which is generally repelled by the PTFE. The thus moistened material behaves externally like a powder because the fluid is present in the inner-porous system:
*Trade-mark Another generic type of wetting agent would be the so-called tensides. These penetrate into the porous system, and at the same time also cover the surface of the catalyst, thus reducing its surface roughness. This reduced surface roughness leads during the rolling process to the phenomenon, that the silver catalyst can move away from the solidification zone, whereas other powder components which have not been treated remain in the solidification zone and thus produce the electrode combination in which the silver catalyst is embedded (fig. 4). Such a powder could be ammonium carbonate or activated carbon, which can now be mixed to a homogeneous mass with the silver catalyst in a pulverizer, as dcwribcd in EP 0 144 002.
Subsequently, the loose mass is rolled into a foil of approx. 0 2.mm thickness by means of a powder roller.
In a second pair of rollers. a metallic support structure can be rolled in the form of woven nets or stretch-metals and thus the mechanical stability and the electrical conductivity can he improved- After this sequence, the gaseous diffusion electrode is dried.
Thereafter the electrode has a silver deposit between 0.2 kg/in2 and 1.5 kg/m"-. Generally, one endeavours lar a weight of approx. 0.5 kg/m2_ Thus, up to 75% of the hitherto required silver can be saved. In spite of the reduced silver weight, with such electrodes one obtains a current-voltage-graph t ti shown in fig.6.
Of course, this method can also be combined with others. Thus, one can do away with the environmentally harmful formaldehyde for precipitation and instead carry out the reduction after production of the gaseous difliision electrodes by means of electro-chemical methods.
In this way, one can similarly produce alloys by carrying out a co-precipitation of silver and mercury, titanium, nickel, copper, cobalt or bismuth.
Especially for the chloro-alltaline-electrolysis, changes can be effected on the ready gaseous diffusion electrode, which would enable improved removal of the occurring soda lye. For this, the imprinting of a coarse conducting system is advisable. This is possible, if a net is pressed onto the ready electrode and then subsequently removed again. The negative impression of the net forms channels, in which the electrolyte can later flow off parallel to the electrode surface.
Claims (16)
1. A method for producing a gaseous diffusion electrode from a silver catalyst on PTFE-substrate, comprising the steps of:
- filling a porous system of the silver catalyst with a wetting fluid;
- mixing a dimension-stable solid body with a grain size above that of the silver catalyst with the silver catalyst to produce a compression-stable mass;
- shaping the compression-stable mass into a homogeneous catalyst band in a calender, and - imprinting, in a second calender step, an electrically conducting material into the catalyst band.
- filling a porous system of the silver catalyst with a wetting fluid;
- mixing a dimension-stable solid body with a grain size above that of the silver catalyst with the silver catalyst to produce a compression-stable mass;
- shaping the compression-stable mass into a homogeneous catalyst band in a calender, and - imprinting, in a second calender step, an electrically conducting material into the catalyst band.
2. The method according to claim 1, comprising 5% isopropanol as the wetting fluid and as the dimension-stable solid body 30% ammonium carbonate or ammonium-hydrogen-carbonate is used, and;
annealing, after producing the electrode, to drive out the 5%
isopropanol and 30% ammonium carbonate or ammonium hydrogen carbonate.
annealing, after producing the electrode, to drive out the 5%
isopropanol and 30% ammonium carbonate or ammonium hydrogen carbonate.
3. The method according to claim 2, wherein the annealing step is carried out at 110°C.
4. The method according to claim 1, comprising using as the wetting fluid a tenside for penetrating into the porous system of the catalyst and for reducing surface friction, enabling the silver catalyst to glide out of a solidification zone, and the dimension-stable solid ammonium carbonate and the PTFE-substrate take up roller pressure in shaping the homogeneous catalyst band.
5. The method according to claim 4, wherein 5% Triton* X 100 is used as the tenside.
6. The method according to any one of claims 1 to 5, wherein in the first calender step, the homogeneous catalyst band shaped has a thickness between 0.2 - 0.5 mm.
7. The method according to any one of claims 1 to 6, comprising adjusting a roller gap to 350 µm and setting a roller feed to approx. 2 meters per minute.
8. The method according to any one of claims 1 to 7, comprising using as the electrical conducting material, a silver-coated nickel wire net with a string thickness of 0.15 mm and mesh width of 0.45 mm with an approx. 10 µm thick silver precipitate.
9. A method for producing a gaseous diffusion electrode from a silver catalyst on a PTFE-substrate, comprising the steps of:
filling a porous system of the silver catalyst with a wetting fluid;
mixing a dimension-stable solid body with a grain size above that of the silver catalyst with the silver catalyst to produce a compression-stable mass;
shaping the thus obtained compression-stable mass into a homogenous catalyst band in a calender, in a second calender step, imprinting an electrically conducting material into the catalyst band; and obtaining said gaseous diffusion electrode having large pores in the gaseous diffusion electrode, which ensures rapid gas transportation and smaller pores in the catalyst, which allow a homogeneous optimum utilisation of the catalyst.
* Trade-mark
filling a porous system of the silver catalyst with a wetting fluid;
mixing a dimension-stable solid body with a grain size above that of the silver catalyst with the silver catalyst to produce a compression-stable mass;
shaping the thus obtained compression-stable mass into a homogenous catalyst band in a calender, in a second calender step, imprinting an electrically conducting material into the catalyst band; and obtaining said gaseous diffusion electrode having large pores in the gaseous diffusion electrode, which ensures rapid gas transportation and smaller pores in the catalyst, which allow a homogeneous optimum utilisation of the catalyst.
* Trade-mark
10. A method according to claim 9, comprising using as wetting fluid 5% isopropanol and as the dimension-stable solid body 30% ammonium carbonate or ammonium-hydrogen-carbonate, and;
annealing, after producing the electrode, to drive out the 5%
isopropanol and 30% ammonium carbonate or ammonium hydrogen carbonate.
annealing, after producing the electrode, to drive out the 5%
isopropanol and 30% ammonium carbonate or ammonium hydrogen carbonate.
11. The method according to claim 10, wherein the annealing step is carried out at 110°C.
12. A method according to claim 9, comprising using as the wetting fluid a tenside for penetrating into the porous system of the catalyst and for reducing surface friction, enabling the silver catalyst to glide out of a solidification zone, and the dimension-stable solid ammonium carbonate and the PTFE-substrate take up roller pressure in shaping the homogeneous catalyst band.
13. The method according to claim 12, wherein 5% Triton* X 100 is used as the tenside.
14. The method according to any one of claims 9 to 13, wherein in the first calender step, the homogeneous catalyst band shaped has a thickness between 0.2 - 0.5 mm.
15. The method according to any one of claims 9 to 14, comprising adjusting a roller gap to 350 µm and setting a roller feed to approx. 2 meters per minute.
16. The method according to any one of claims 9 to 15, comprising using as the electrical conducting material, a silver-coated nickel wire net with a string thickness of 0.15 mm and mesh width of 0.45 mm with an approx. 10 µm thick silver precipitate.
* Trade-mark
* Trade-mark
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10130441A DE10130441B4 (en) | 2001-06-23 | 2001-06-23 | Process for producing gas diffusion electrodes |
| DE10130441.2 | 2001-06-23 | ||
| PCT/EP2002/006706 WO2003004726A2 (en) | 2001-06-23 | 2002-06-18 | Method for producing gas diffusion electrodes |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2451610A1 CA2451610A1 (en) | 2003-01-16 |
| CA2451610C true CA2451610C (en) | 2010-11-09 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2451610A Expired - Fee Related CA2451610C (en) | 2001-06-23 | 2002-06-18 | Method for manufacturing gaseous diffusion electrodes |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US7226885B2 (en) |
| EP (1) | EP1402587B1 (en) |
| JP (1) | JP2004533544A (en) |
| KR (1) | KR100855922B1 (en) |
| CN (1) | CN1272865C (en) |
| AT (1) | ATE279023T1 (en) |
| AU (1) | AU2002325243A1 (en) |
| BR (1) | BR0210536B1 (en) |
| CA (1) | CA2451610C (en) |
| DE (2) | DE10130441B4 (en) |
| RU (1) | RU2290454C2 (en) |
| WO (1) | WO2003004726A2 (en) |
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| DE10130441B4 (en) * | 2001-06-23 | 2005-01-05 | Uhde Gmbh | Process for producing gas diffusion electrodes |
| TW558833B (en) * | 2002-09-09 | 2003-10-21 | Ind Tech Res Inst | Gas diffusion electrode and the method for making the same |
| DE102004034885A1 (en) * | 2004-07-19 | 2006-02-16 | Uhde Gmbh | Silver gas diffusion electrode for use in CO2-containing air |
| KR100682862B1 (en) * | 2005-01-11 | 2007-02-15 | 삼성에스디아이 주식회사 | Electrochemical Battery Electrode, Manufacturing Method thereof And Electrochemical Battery Using The Same |
| DE102005023615A1 (en) | 2005-05-21 | 2006-11-23 | Bayer Materialscience Ag | Process for the preparation of gas diffusion electrodes |
| ITMI20060726A1 (en) * | 2006-04-12 | 2007-10-13 | De Nora Elettrodi S P A | ELECTRIC DIFFUSION ELECTRODE FOR CELLS WITH ELECTROLYTE DISCHARGE |
| CN101191237B (en) * | 2006-11-29 | 2010-04-14 | 中国石油天然气集团公司 | A preparation method of an integrated electrode for hydrogen production and storage |
| KR101160853B1 (en) | 2009-12-18 | 2012-07-02 | 주식회사 미트 | Manufacturing apparatus of plate heating sheet manufacturing method thereof |
| CN101774666B (en) * | 2010-01-29 | 2011-12-21 | 北京化工大学 | 2-ethyl-anthraquinone modified gas diffusion electrode and preparation method thereof |
| DE102010030203A1 (en) | 2010-06-17 | 2011-12-22 | Bayer Materialscience Ag | Gas diffusion electrode and method for its production |
| DE102010039846A1 (en) | 2010-08-26 | 2012-03-01 | Bayer Materialscience Aktiengesellschaft | Oxygenating electrode and process for its preparation |
| DE102011008163A1 (en) | 2011-01-10 | 2012-07-12 | Bayer Material Science Ag | Coating for metallic cell element materials of an electrolytic cell |
| DE102011005454A1 (en) | 2011-03-11 | 2012-09-13 | Bayer Materialscience Aktiengesellschaft | Process for the preparation of oxygen-consuming electrodes |
| EP2573213B1 (en) * | 2011-09-23 | 2017-10-25 | Covestro Deutschland AG | Oxygen-consuming electrode and method for its production |
| CN102517602B (en) * | 2011-12-29 | 2014-10-29 | 北京化工大学 | Gelatin hole forming method for gas diffusion electrodes |
| AU2013328267B2 (en) | 2012-10-09 | 2018-06-28 | Phinergy Ltd | Electrode assembly and method for its preparation |
| DE102015215309A1 (en) * | 2015-08-11 | 2017-02-16 | Siemens Aktiengesellschaft | Preparation technique of hydrocarbon-selective gas diffusion electrodes based on Cu-containing catalysts |
| DE102017209960A1 (en) | 2017-06-13 | 2018-12-13 | Robert Bosch Gmbh | Method for producing an electrode, in particular for a battery |
| DE102018211189A1 (en) * | 2018-07-06 | 2020-01-09 | Robert Bosch Gmbh | Method and device for producing an electrode material strip |
| DE102019203373A1 (en) | 2019-03-13 | 2020-09-17 | Robert Bosch Gmbh | Gas diffusion layer for a fuel cell and fuel cell |
| DE102022004678A1 (en) | 2022-12-13 | 2024-06-13 | Covestro Deutschland Ag | Process for the electrolysis of carbon dioxide with prereduction of a silver oxide-containing gas diffusion electrode |
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2001
- 2001-06-23 DE DE10130441A patent/DE10130441B4/en not_active Expired - Fee Related
-
2002
- 2002-06-18 DE DE50201245T patent/DE50201245D1/en not_active Expired - Lifetime
- 2002-06-18 WO PCT/EP2002/006706 patent/WO2003004726A2/en not_active Ceased
- 2002-06-18 RU RU2004101764/15A patent/RU2290454C2/en not_active IP Right Cessation
- 2002-06-18 EP EP02758237A patent/EP1402587B1/en not_active Expired - Lifetime
- 2002-06-18 CA CA2451610A patent/CA2451610C/en not_active Expired - Fee Related
- 2002-06-18 CN CNB028123433A patent/CN1272865C/en not_active Expired - Fee Related
- 2002-06-18 BR BRPI0210536-5A patent/BR0210536B1/en not_active IP Right Cessation
- 2002-06-18 US US10/481,775 patent/US7226885B2/en not_active Expired - Lifetime
- 2002-06-18 KR KR1020037015632A patent/KR100855922B1/en not_active Expired - Fee Related
- 2002-06-18 AT AT02758237T patent/ATE279023T1/en not_active IP Right Cessation
- 2002-06-18 JP JP2003510479A patent/JP2004533544A/en active Pending
- 2002-06-18 AU AU2002325243A patent/AU2002325243A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO2003004726A3 (en) | 2003-10-02 |
| WO2003004726A2 (en) | 2003-01-16 |
| CN1272865C (en) | 2006-08-30 |
| JP2004533544A (en) | 2004-11-04 |
| AU2002325243A1 (en) | 2003-01-21 |
| US20040152588A1 (en) | 2004-08-05 |
| EP1402587A2 (en) | 2004-03-31 |
| HK1065647A1 (en) | 2005-02-25 |
| CN1526179A (en) | 2004-09-01 |
| DE50201245D1 (en) | 2004-11-11 |
| RU2290454C2 (en) | 2006-12-27 |
| RU2004101764A (en) | 2005-06-10 |
| CA2451610A1 (en) | 2003-01-16 |
| US7226885B2 (en) | 2007-06-05 |
| DE10130441A1 (en) | 2003-03-27 |
| DE10130441B4 (en) | 2005-01-05 |
| BR0210536B1 (en) | 2012-01-24 |
| EP1402587B1 (en) | 2004-10-06 |
| ATE279023T1 (en) | 2004-10-15 |
| BR0210536A (en) | 2004-06-22 |
| KR100855922B1 (en) | 2008-09-02 |
| KR20040020910A (en) | 2004-03-09 |
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