DE1812444A1 - Electrode working with gas diffusion, processes for their manufacture, and electrochemical generators and fuel elements equipped with such electrodes - Google Patents

Description

Electrode working with gas diffusion, process for its manufacture, and electrochemical generators and fuel assemblies equipped with such electrodes.

The invention relates to electrodes working with gas diffusion, which can be used in both electrochemical generators and fuel elements are, as well as a method for producing these electrodes and those with at least electrochemical generators equipped with an electrode according to the invention and Fuel elements.

It is well known that manufacturers use both electrochemical Generators as well as with 3fuel elements the simplest structure and the largest Aimed for mass and volume performance.

The aim of the invention is to give a gas electrode these properties To give. In its French patent specification no. 1,493,700 dated July 20, 1966 an electrode working with gas diffusion for electrochemical generators or fuel elements described which thereby is characterized in that it is formed by a thin llembran, which on has an active layer on both sides, under which a porous water-repellent Layer is arranged, which by contact with the active layer for the Electric current is made conductive, and that it has at least one supply line and if necessary. Has an outlet line for the gas and means for drawing electricity.

Such an electrode is preferably provided with two on its circumference electrode halves bonded to one another are formed, each of which has an outer active Layer, an inner porous layer bounded by a membrane and between them both layers has a conductive grid forming the current collector.

In the preferred embodiment, the lead electrode has the like mentioned French patent specification in a middle space, where at least £ 'at least' a lead passes through the circumference of the electrode and leads to this central space, and the inner porous layer is a barrier layer, particularly that in the French Patents r. 1,424.

432 of July 10, 1964 and 1.440.054 of April 13, 1965 or the am April 13, 1965 filed first additional application Ur.

87,730 to the first of these two patents described type, wherein these two barrier layers are made of porous polytetrafluoroethylene.

Patent No. 1,493,700 also has fuel elements and electrochemical Generators with such electrodes are the subject matter, in particular a fuel element with cathodes and anodes of the above type which are in the shape of rectangular plates have and arranged in parallel in a container made in particular of copper are, in which a liquid electrolyte, e.g. an aqueous potassium solution, the Space between the electrodes is met, being in the electrolyte between adjacent ones Electrode immersed separators and devices are provided which the Preparations of the anodes with an anode gas, e.g. hydrogen, and the lines of the Feed cathodes with a cathode gas, e.g. oxygen, which means that a Stream between the stream veins opposite polarities enables.

This patent also relates to an electrochemical generator Cathodes of the above type and anodes which are formed by an alkaline electrolyte containing divided ketallpulver are formed, and a Stromabne mer, wherein separators are arranged between successive electrodes, where the arrangement formed by the electrodes and the separators in a e.g. container made of copper is arranged, whereby facilities are provided, which feed the lines of the cathodes with air or oxygen and devices, which isolate the cathodes but not the anode current collectors from the tank, what allows, between the container forming the negative pole and the positive ones Pole-forming cathodes to remove a usable potential difference.

The electrodes according to the French patent specification No. 1.493.700 have a number of advantages, in particular the fact that they are without gas back pressure can work, i.e. with an excess hydrostatic pressure of the electrolyte, which prevents any bubble formation and any flooding of the electrode and the manufacture of crowded arrangement grooves for fuel elements and electrochemical generators enables.

However, the applicant has found that the electrodes according to French patent no.

1,493,700 have a number of disadvantages for the following reasons.

It is well known that in every electrochemical generator it requires union of two electrodes of opposite polarities (an anode and a cathode) as small a mutual distance as possible in order to avoid the ohmic voltage drop between limit the two electrodes.

This is generally achieved by -that the two electrodes after arranging a separator between the adjacent surfaces of the two electrodes are strongly pressed against each other.

It is also in the special case in which the positive gas electrodes with total anodes, in particular made of zinc powder, are combined, as in the case of that in the French Electrochemicals described in U.S. Patent No. 1,493,700 Generator, required to prevent the anode reaction products from settling, ura to avoid the creation of a concentration gradient, which occurs when recharging of the generator would be disruptive. The reaction products of the metal anode, in particular the zinc oxides, namely, show the tendency to have a larger volume than the starting products, E.g. the zinc, ingesting, creating internal tensions and pressures on the opposite Electrodes are created.

In order to reduce the ohmic voltage drops and, if necessary, the dropping In order to avoid the reaction products of the anode, it is obviously advisable to to press the electrodes strongly against each other, which when using the electrodes according to of the French patent mentioned with a middle space the Approach of the inner walls of the same causes what the entry of the gas into the Prevents the space provided for it. If the flattening of an electrode is localized takes place, e.g. under the action of the pressure of those formed in the DI-etallelectrode Reaction products, the space reserved for the gas is no longer homogeneous, and there is a partial pressure gradient in the gas supply to the active layer of the electrode, which results in uneven work.

On the other hand, a slight accidental malfunction of the system can result Regulation of the gas pressure increases the pressure in the central space within the Electrode create what one to the above, resulting from the pressing of the electrodes Deformation causes deformation of the electrode in opposite directions, i.e. swelling of the electrode, this swelling of the diffusion electrodes causing a displacement of the liquid electrolytes, so there is a risk that it will run out the vessel containing the electrodes and overflows.

There is also the risk that an electrochemical Generator according to the French patent specification No. 1.493.700 that sources the Gas electrode affects the adjacent divided metal electrode by this divided metal is locally pushed back and compressed, in particular the zinc powder contained in a gel, which makes the electrochemical work poorly System by displacing the wet.

Furthermore, the swelling of the gas electrodes can create voltages at the point the circumferential bonding of the electrodes and even generate leaks in them, so that the Gas escapes to the outside and / or the electrolyte enters inside.

Finally, the porosity of a gas electrode can be reduced by the expansion the barrier layer of the same can be changed.

The subject of the invention is a solution of the elel; troden problems raised according to the aforementioned French patent specification Kr. 1,495,700, which allows the diffusion of the gas to the active zone under excellent conditions ensured, whereby it allows a convenient manufacture of the electrodes.

It consists in an electrode that works with gas diffusion electrochemical generators or fuel elements through a porous water-repellent Layer to form which one of a number. of channels or passages for the Gas circulation is traversed and has an active layer on both sides, wherein the porous water-repellent layer for the electric current by touch with the active layer is made conductive, the electrode at least one Supply and possibly at least one discharge for the gas to feed these channels as well Has facilities for power take-off.

The invention aims in particular to be applied to the electrodes those in said French patents nos. 1.424.432 and 1.440.054 and the type described in the first additional patent No. 87,730 to the patent No. 1,424,432.

The invention is described below with reference to the drawing explained by way of example.

1 and 2 show a first embodiment of one according to the invention Electrode, namely FIG. 1 in plan view with parts broken away and FIG. 2 in section along the line II-II in FIG. 1.

Fig. 3 is a broken away plan view corresponding to Fig. 1 of parts which show a variant embodiment of FIGS.

Flight. Figures 4 and 5, which correspond to Figures 1 and 2, show in plan view under IZegbrecilung of parts or in the section along the line V-V the Pi. 4 a third embodiment of an inventive electrode.

fi. 6 shows a first embodiment of an electrochemical generator with gas electrodes according to the invention.

FIG. 7 is a section along the line VII-VII of FIG. 6.

Fig. 8 shows a second embodiment of an electrochemical Generator with gas electrodes according to the invention.

FIG. 9 is a section along the line IX-IX of FIG. 8.

An electrode operating with gas diffusion (FIGS. 1 to 5) is according to the invention produced by means of a porous water-repellent layer 1, which is of a Series of channels or passages for the gas circulation 2 is traversed and on their both sides la and Ib has an active layer 3, the porous water-repellent Layer conductive for the electric current through contact with the active layer is made, in particular by the interposition of a pantograph forming conductive grid, the electrode having at least one supply channel connected at 4 and possibly

at least one discharge channel connected at 5 for the gas as well Has facilities for power take-off.

The porous layer 1 and the two active layers 3 kötmen manufactured in the manner described in French patent specification No. 1,493,700 will.

In particular, the porous layers are barrier layers of the type described in the two other French patents mentioned and the first additional patent and both consist of porous Polyctrafluoräthlen, while the active layer th with an anode platinum, palladium, nickel or one of these three metals containing active carbon and with a cathode silver, platinum, palladium, nickel or active carbon alone or mixed with contain one of the four metals mentioned.

In the case of an electrode according to the invention, the outer sides are formed by an active layer 3, in which the electrochemical Volgange expire, wherein the two active layers by a porous water-repellent Layer 1 are connected, which in particular made of polytetrafluoroethylene or his ibkölamlingen, like Polytrifluormonochloräthylen, which is a barrier layer forms and with channels or passages (especially in the embodiment of the Fig. 4 and 5) is provided, which facilitate a natural diffusion and a Allow renewal of the gases without significant pressure drops.

The porous barrier layer 1 adheres to the active layers 3 and forms with these a whole. The pillars 6 surrounding the channels form struts, which Prevent both the flattening of the electrode and its diminution.

These struts form part of the barrier layer, i.

the electrode itself, and are porous, making a very homogeneous one Working the active layer results.

The electrodes can be a conductive grid or expanded metal between each active layer 3 and the porous layer 1 included, or only in the active layers alone, and these grids or expanded metals form current collectors.

The above electrodes can be produced by the following method according to the invention getting produced.

In a distance, the bottom of which has grooves, which are an image of the Half (or some other fraction) of that to be made in the porous layer of the electrode Are channels, between 25 and 250, preferably 30, kg / cm2 becomes an intimate mixture from 30 to 90, preferably 70 percent by weight, ammonium carbonate and from 70 to 10, preferably 30 percent by weight, polytetrafluoroethylene with a grain size of less than 100 microns, such that a density of 0.2 to 4, preferably 0.5 g / cm2.

A conductive grid may be placed on top of this pre-compressed layer or an expanded metal is placed on the electrode with the water-repellent one Layer and the active layers in contact with grids or expanded metals should have), whereupon a pressure of 30 kg / cm2 is exerted on them so that they adhere to the precompacted layer.

This is done either on the precompacted layer or on the formed by the precompacted layer and the grid or expanded metal Arrangement a active mixture spread, which e.g. from 50 to 95, preferably 90, percent by weight rane silver and 50 to 5, preferably 10 percent by weight polytetrafluoroethylene with a grain size of less than 100 microns is formed in such a way that a density of 0.25 to 2, preferably 1, g / ctn2 obtained whereupon the whole thing is compressed between 100 and 700, preferably at 250, kg / cm2 Finally, the half-electrode is shaped.

According to a first form of exercise, which is the largest industrial Seems to be of interest, the two are made in the above manner Half electrodes with their grooves placed against each other so that the finished Electrode existing channels arise, and this union of the two ileal electrodes is brought to about 4000 C in an oven for one hour to remove the polytetrafluoroethylene to polymerize, with a pressure of the order of magnitude 5 to 50, preferably 20 g / cm2 is applied. When the electrode is removed from the oven, it is she finished.

In a second exercise, each half-electrode is used alone polymerized in an oven for one hour at 4000 C without the application of pressure. To The two half-electrodes are glued together when they exit the furnace, and either on their entire contact surface (along the common active Layer forming half active layer), or only along the circumference of the electrode.

You can use the electrodes shown in Fig. 1 to 5 with different Establish geometrical relationships of the channels 2, e.g. with at both ends or longitudinal channels open only at one end (FIGS. 1 and 2), or a single meander-shaped Channel (Fig. 3), which is a labyrinthine gas flow between a rapid passage 4 and an output 5 produces. It can also be simple pillars 6a made of a porous Material are provided between the two active layers 3 (Fig. 4 and 5).

Palls electrodes with closed or open longitudinal channels at one end are to be produced, the method for producing the electrodes can be as follows be modified.

A flat-bottomed shape becomes a active Layer brought, which as in the previous case from 50 to 95, preferably 90 percent by weight rane silver and 50 to 5, preferably 10 percent by weight Polytetrafluoroethylene with a grain size of less than 100 microns, in such a way that that a density of 0.05 to 2, preferably 0.1, g / cn2 is obtained, whereupon a Pressure of 30 kg / cm2 is applied. Possibly. gets into this layer under a pressure of 30 kg / cm2 a conductive grid or expanded metal is pressed in. Then will on the precompacted layer or on that through the layer and the grid or the expanded metal assembly formed a thin layer with a density of 0.1 g / cm2 of an intimate mixture of 30 to 90, preferably 70, percent by weight ammonium carbonate and 70 to 10, preferably 30, percent by weight of polytetrafluoroethylene spread.

A stainless steel comb is polished onto this thin layer Metal placed, the teeth of which have a slight fillet and the Have the shape of the future channels of the electrode. This is followed by the arrangement with a density of 0.3 g / cm2 the above mixture of ammonium carbonate and polytetrafluoroethylene and a pressure of 125 kg / cm2 is applied. If necessary, a conductive grid or expanded metal pressed in at a pressure of 125 kg / cm2, whereupon a further layer identical to the previous active layer is applied whereupon the whole thing is subjected to a pressure of 250 kg / cm2. In the end the arrangement formed by the electrode and the metal comb is placed in a furnace brought to 4000 C for one hour in order to polymerize the polytetrafluoroethylene and the ammonium carbonate in the form of carbonic acid gas and ammonia gas, which are develop, dissipate. After the polymerisation process, the comb is pulled out, whose teeth expose the space of the canals.

The electrodes produced in the above manner as shown in FIGS. 1 to 5 can be used for the production of electrical generators, especially accumulators, and fuel elements can be used. Two examples of such generatoron, in particular Accumulators are shown in Figs. 6-9.

These generators contain positive electrodes 7 according to FIG. 1 to 5, i.e. with a double active layer, which has a porous what <J erab to send channels through coated layer surrounds, and negative Electrodes 8, e.g.

by an expanded metal (e.g. made of zinc) or a subdivided metal powder (e.g. Zin1S7 cadmium or iron powder), which is sintered or set in a gel is formed, with an alkaline electrolyte and a current collector, as described in French patent specification No. 1.408.287 of 30.

June 1964 of the applicant is described.

In the illustrated embodiments, the electrodes have a rectangular shape and are arranged next to one another in a vessel 9. You will be using air or oxygen either naturally through their upper openings 4 via one in the vessel 9 formed opening 10 / fed, or by a distribution system of the in Fig. 8 and 9 with one formed in the upper wall of the vessel and to the outside through an opening 10 opening channel 10a.

When fed with air, an electrode arrangement is preferred according to Fig. 3, there is then a discharge (at 5) for the residual nitrogen in the case strong current densities must be provided.

The electrodes are in a separator 11, e.g. a membrane made of regenerated Cellulose, or wrapped in an ion exchange membrane, which if necessary. With a the electrolyte absorbing membrane can be coated.

The connections coming from the positive electrodes 12 on the one hand and the connections 13 coming from the negative electrodes, on the other hand, become connected with each other.

As stated above, the arrangement is arranged in a vessel 9, which can be made of plastic, for example, and this vessel is aird with an alkaline Solution 14 filled, e.g. a 35% potassium solution, this being the electrolyte alkaline solution just covered the top of the negative electrodes.

The system thus formed of those shown in FIGS. 6 and 7 or 8 and 9 Art enables a significant amount of energy to be delivered, which is then reloaded can be regenerated at a voltage close to 2.10 volts.

It should be noted that the electrodes according to the invention, in particular that shown in Fig. 1 to 5 Kind of, with other electrolytes Can be used as an alkaline electrolyte, especially with salt solutions. In this way, electrodes according to the invention which work with gas diffusion and have magnesium anodes can be used combine to form e.g. a magnesium-air element, which in a saline solution works (e.g.

in an atrium chloride solution or in water). The parallel connection the electrodes working with air with channels closed at the base and The magnesium foil is inserted into a geass that contains a salt solution in a contains such amount that only the upper part of the cathodes is slightly above the level the saline protrudes to allow its ventilation.

In the case of elements working with sea water, facilities are of course used provided, which stress the arrangement so that the element is in its perpendicular position maintains.

It can also work with gas diffusion according to the invention Fuel elements provided with electrodes are produced. Such electrodes can be connected in parallel and immersed in the same electrolyte, one of them performing the task of cathodes and the other of anodes, where the former e.g. with air, oxygen, chlorine and fluorine and the second e.g. with Hydrogen, hydrocarbons, carbon oxides can be fed. Of course you can several such fuel elements are connected in series.

Has an electrode according to the invention which works with gas diffusion numerous advantages over such known electrodes, in particular the following: It can work without gas counter pressure, i.e. with an excess hydrostatic Pressure of the electrolyte, reducing any blistering / flooding of the electrode is avoided.

It has a compact structure and enables the production of crowded arrangements with the electrodes pressed against one another without the risk of a noticeable deformation, in particular without noticeable flattening of the gas inflow channels.

It should be noted that an electrode according to the invention with correct channels passing through the active layer in which a gas flows freely, clearly from the electrodes according to the French patent specification ITr. 1.433.558 from February 18, 1965 differentiates which porous electrodes have, through which a gas does not flow freely but in a Knudsen state, i.e. through diffusion through the pores of the electrode. The free circulation of the gases has the advantage of high To enable current densities and the production of large electrodes.

Claims (9)

Claims 1.) Electrode working with gas diffusion for electrical generators or fuel elements, characterized in that they are characterized by a porous water-repellent Layer (1) which is formed by a series of channels or passages (2) for a gas flow and an active one on both sides (1a, Ib) Layer (3), the porous water-repellent layer (1) through its Contact with the active layer (3) is made electrically conductive, the Electrode at least one supply (4) and possibly at least one outlet (5) for the the ducts (?) has feeding gas and facilities for drawing electricity. 2 *) electrode according to claim 1, characterized in that the porous water-repellent layers (1) on the one hand and the active layers (3) on the other according to the French patent specification No. 1.493.700. 3.) Electrode according to claim 1 or 2, characterized in that they have an electrically conductive grid or expanded metal between the porous water-repellent Layer (1) and each active layer (3). 4.) Process for the production of a sheet metal electrode according to one of the claims 1 to 3, characterized by the sequence of the following operations: in a form with Grooves that mirror half (or some other fraction) that in the electrode channels (2) to be provided, an intimate mixture of a propellant, e.g. Ammonium carbonate, and a halogenated ethylene, e.g. polytetrafluoroethylene, compressed, on this pre-compressed layer, if necessary, an electrically conductive grid is placed or expanded metal, on which a pressure is exerted, then applied to this Layer adheres to the precompacted, possibly covered with the grid or expanded metal Layer a mixture of active substances is spread out, the whole becomes one Subjected to pressure, the primary electrode obtained in this way is molded, and two semi-electrodes are combined to form the finished electrode. 5.) The method of claim 4, wherein the electrode of two lIalbele}; troden is produced, because it is characterized by the fact that the two semicircular electrodes are placed against each other with their grooves so that the channels (2) of the finished electrode arise, and that the arrangement formed by the two 11albelelectrodes on a polymerization temperature, in particular of the order of 400 ° C., during a sufficient duration is brought, in particular large order sinas sig during an hour to polymerize the halogenated ethylene, under one low overpressure. 6.) The method of claim 4, wherein the electrode of two Half-electrode is produced, characterized in that each half-electrode polyr.erisiert separately in particular at 4000 C for one hour without the application of pressure and that two half-electrodes are glued together, either on its entire contact surface, or only along the circumference of the electrode. 7.) Process for the production of an electrode containing longitudinal channels according to one of claims 1 to 3, characterized by the sequence of the following operations: an active layer is placed in a form with a flat bottom, in which is if necessary, a conductive grid or metal clip pressed in, on which if necessary the pre-sealed layer provided with the pressed-in grid or expanded metal a thin layer of an intimate mixture of a propellant, e.g. Aninoniuelkarbonat, and a halogenated ethylene, e.g. Polytetrafluörathylen, Spread out on this thin layer, a stainless steel in particular is made polished metal existing comb placed, which has teeth, which a Æ have rings and the shape of the future channels of the electrode a mixture of a propellant, especially ammonium carbonate, is added to the whole and a halogenated ethylene, especially polytetrafluoroethylene, applied, If necessary, a new conductive grid or expanded metal is placed on it, it becomes a Another active layer is applied, the whole thing is subjected to pressure and on a polymerization temperature, in particular of the order of 4000 C, during a sufficient period, in particular for one hour, for the polymerization of the halogenated ethylene and brought to the discharge of the propellant, and finally the comb is pulled out, the teeth of which expose the space of the canals. 8.) Fuel element with electrodes after a of claims 1 to 3, characterized in that they have the shape of rectangular Have plates and are arranged in parallel in a vessel (9) in which a liquid Electrolyte, e.g. a watery potassium solution, the space between the electrodes fills, with separators (11) in the electrolyte between adjacent electrodes immerse and I-i-i-i-means for feeding the channels of the anodes with an anode gas, e.g. hydrogen, and the channel of the cathodes with a cathode gas, e.g. oxygen, are provided in such a way that a current between the current collection means -n opposite Polarities can be removed. 9.) Electrochemical generator with at least one cathode after one of claims 1 to 3, characterized in that the anodes by an expanded metal or a metal powder containing an alkaline electrolyte and a current collector are formed with separators arranged between successive electrodes are, the arrangement formed by the electrodes and the Trelmglieder in a vessel is arranged, with devices for feeding the channels of the cathodes with air or oxygen.