DE1571743A1 - Electrodes and methods of making them - Google Patents

Description

Electrodes and processes for their manufacture. B B SSSB B S SB S BB ίί ^ SS-ί »B-BS BSSB BB S BSS BS & w« 3S3BS SHB

The invention relates to electrodes, in particular for fuel assemblies for gaseous or dissolved materials, which consist of a carbon fabric covered by a mixture of a polymeric substance and a catalytic agent. The invention also relates to a method for producing these electrodes

The manufacture of electrodes has already been proposed which consist of a fritted mixture of a polymeric substance and a catalytic agent * This mixture can be applied to an inert carrier. The benefits of this element "are generally moderate, due to the mediocre electrical conductivity of Gefügeβ _f and their mechanical behavior is ■ chiθoht unless incorporated nan Metallgltter that are intended

BATH

009883/1674

to collect the current and increase the strength of the electrodes.

However, the metal grids were not entirely satisfactory either.

A good carrier must meet various requirements »in particular the following:

1) It must be resistant to the electrolytes generally consist of acids or bases in concentrated aqueous solution.

2) It must be available in unlimited quantities at the lowest possible price.

These two main requirements are difficult to match to bring, especially if you use acidic media »because then only rare and expensive metals such as tantalum, niobium, tungsten and Platinum can be applied. Even in the alkaline medium, the cost of carriers such as nickel or stainless steel is high removed from it "- negligible to leg,

3) It must allow an accelerated and as uniform as possible dispersion of the catalytic component, which is necessary is to increase activity per surface iahe it iU keep.

BATH ORIGINAL '

4) Sr must have good adhesion to the mass it is bearing own.

The metallic supports, in whatever form, these third and fourth requirements bad.

5) If possible, it must be flexible for certain applications, ! fun are, however, sahi-rich metals, even in the form of fine fabrics, relatively very stiff.

It was now found that when a carbon fabric is used as the carrier, electrodes can be produced which meet the above requirements in a satisfactory manner.

The carbon fabrics are generally accelerated by Heating, preferably in the absence of air, made of fabrics formed from organic natural, artificial or synthetic threads or fibers. After heating you can the fabric more or less * be graphitized.

The initial nature of the tissue is of no great importance, since at the temperatures used in the heat treatment, for example 600 to 900 ^° C., they are converted into carbon-containing hates.

009883/1674 bathroom

As examples, fabrics made of linen, jute, cotton, regenerated cellulose, cellulose acetate, glycol polyterephthalate or Polycaprolactam are mentioned "

Pie fabrics used advantageously contain at least five loops, preferably at least 10 loops per cm, without there is an upper limit »Its thickness is below 2 nm, preferably below 0.5 mm. The warp and weft threads advantageously consist of twisted element fibers, each Pebbles are less than 50 microns in diameter, preferably less than 10 microns.

The method according to the invention for the production of electrodes consists of the following steps in sequence:

1) An aqueous dispersion is applied to a carbon fabric, which is essentially a powdery catalytic Contains agent and a powdery, normally solid polymer with various incidental additives, and

2) the resulting mass is dried and fried.

A catalytic agent is not only understood to mean a pronounced hydrogenation or oxidation catalyst, but rather also a precursor of such a catalyst, i.e. a

BAD OR / gi _Nal 009883/1874

bond, which can subsequently be converted into the catalyst in a known manner, for example by hydrogenation and / or heating to temperatures that the polymer can withstand (to temperatures below the temperature at which decomposition or melting occurs in significant hatred) _o

Examples of catalytic agents, the metals of the group can be mentioned VIII of the Periodic System "in particular those with an atomic number of at least 27 and at most 78, d _o h _o nickel, cobalt, the Metolle of platinum and palladium, as well as the metals of group Ib ₉ ie copper, silver and gold.

The metals are in pure form or preferably in the form of Precursors used, for example as oxides, carbonates, hydroxides, sulfides, selenides, tellurides, borides, molybdates, tungstates, Vanadates, chromites and generally all compounds of these metals.

All examples can be given:

Platinum black, palladium black, iridium, reduced copper, colloidal silver, Haney silver, the copper oxides, silver oxide, Nickel oxide, nickel hydroxide, cobalt sulfide, nickel boride, cobalt molybdate, Copper chromite, silver tungsten, silver vanadate, cobalt selenide, Silver selenide and nickel carbonate.

0Q9883 / 167A

The metals or the metal compounds can previously a powdery conductive carrier such as carbon, graphite, non-catalytic metal powder of metals, for example Nickel or silver.

The catalytic agents, as well as the polymer, are preferred used in the finest possible form, for example in a colloidal state. Water-insoluble agents are preferred .

"Insoluble in water" is understood here to mean that they are in soluble in an amount less than 1 per 1000 parts by weight are.

The polymer, which is used in powder form, preferably as fine as possible, or in the form of an aqueous colloidal dispersion, is preferably chosen from those polymers which are insoluble in water and have good chemical and thermal inertness generally acidic and / or basic corrosive electrolyte on the one hand must be resistant to withstand and on the other hand, relatively high temperatures are therefore Eb * polymers having a softening point above 75 ⁰ C, preferably above 15O ⁰ O preferred.

Eb especially the chlorinated and special (old fluo-

BATH ORIGINAL

ized polyolefins are mentioned, in particular polytetrafluoroethylene, polyhexafluoropropylene. Polytrlfluorochloroethylene and their copolymers. Less preferred other polymers aifai Polypropylene, polyethylene and polytrifluoroethylene.

They aqueous dispersion preferably contains 0.1 to 60 polymer and 0.1 to 3 wt ^east. ~ 5S catalytic agent, calculated as metal.

As examples of optional additives that can be used in the suspension, dispersants, thickeners or gelling agents for the aqueous media, which can be polymers, can be mentioned, for example polyethylene oxides or polypropylene oxides with low molecular weight, carboxymethyl cellulose or other modified celluloses, polyvinyl alcohol, as well the surfactants for deep impregnation of the tissues.

The method for precipitating the aqueous dispersion of the catalytic agent and polymeric binder can extend in depth over the total thickness of the carbon fabric, However, it is also because of the hydrophobic character of this tissue possible to deposit the catalytic mass only on one surface of the fabric.

009883/1674

For a better dispersion of the batch, it is recommended that the in Moisten a frame stretched fabric with pure water beforehand.

If you only want to fix it on one side, you can this side beforehand by finely atomizing pure distilled water, preferably with subsequent oil treatment moisten, if you intend to fix it in depth, soak the fabric as a whole and then let it drip off. Then it will be the catalytic dispersion is preferably applied to the moistened side (s) either by brushing or by atomization.

The solidification of the catalyst precipitate on the parsers are carried out by the fabric is first dried, then it is brought to a temperature sufficient to frit the binder, this temperature depends on the polymer and generally above 150 ⁰ C and in the case the polyhalogenated polymer is for example in the order of 250 to 350 ⁰ C. It is preferable to work in an inert atmosphere, for example under nitrogen and hydrogen. A reducing atmosphere is necessary if you want to reduce the metal compounds, for example the silver oxides.

It is clear that the temperature is litgen below the temperature must, upon decomposition or appreciable melting of the polymer entry.

BATH ORIGINAL

Q09883 / 1674

_{= J} Q -

The treatment can be carried out by calendering the electrode in to be completed by the cold «.

The final electrodes usually contain 0.1 to 300 g, preferably 1 to 100 g, of catalytic agent, calculated as metal weight, and 0.05 to 100 g, preferably 0.5 to 20 g, of polymer per square meter of surface, d, h » the content of the catalytic agent, calculated as metal, is usually from 0.1 to 60 wt ~ # _e, preferably 1 to 50 wt. = $, and the polymer content is from 0.05 to 20 wt .- ^ ₉ preferably 0.5 to 10 wt. #.

The following examples are intended to further illustrate the present invention without limiting it,

example 1

2 g of finely divided platinum black become dry with 0.2 g of colloidal Silica (inert diluent) mixed. Ea 10 cnr of distilled water and then 0.4 cnr of an aqueous polytetrafluoroethylene suspension, set to 60 #, added. This composition is made by spraying on a graphite cloth of 20 χ 20 cm, which is moistened on one side, distributed « This fabric has a thickness of 0j, 2 min, contains 11 stitches each

ρ
cm and weighs 120 g per m, the fibrils have a diameter between 5 and 10 microns,

009883/1674

~ 10 ~

After drying and heating at 300 einetündigem ⁰ C in an oven under a stream of nitrogen waeserstoffhaltigen is ETAE

Obtained electrode containing 5 mg platinum per cm.

When testing in a half-element with? .7 molar sulfuric acid as the electrolyte, the electrode used as the hydrogen electrode shows a potential of +15 millivolts, based on the normal hydrogen electrode, when the current is zero, and gives 100 milliamps per cm with a polarization of 25 millivolts away. If the electrode is used in the same electrolyte as the oxygen electrode, it shows a potential with a zero Htrora output of +800 millivolts, based on the normal hydrogen electrode, and emits 100 milliamps per cm mi "*; a polarization of 140 millivolts when in operation.

When tested in a half-element with 6 molar potassium hydroxide solution as the electrolyte, the electrode used as the hydrogen electrode shows a potential at zero current output of -875 millivolts, based on the standard hydrogen electrode, and gives im

Operate 100 milliamps per cm with a polarization of 120 Millivolts. If the electrode is used in the same electrolyte as the oxygen electrode, it gives 100 milliamps during operation

per cn at zero potential, based on normal hydrogen electrode,,

BATH ORIGINAL

009883/1674

Example 2

• χ

1.2 g of platinized charcoal places with 5 f> platinum to 2 cnr water "θ cur an aqueous solution containing 0.5 i · polyvinyl alcohol and 0.5 om a Polytetrafluoräthylensuspenaion set to # 60 added. This composition is spread with a brush on a graphite fabric of PO 20 cm, as is identical to that of Example 1 and since it is moistened on one side. After drying and one hour. Heating tinter wasßerstoffhaltigem nitrogen to 300 ⁰ C, and then calendering is obtained an electrode having despite the very low platinum content of 0.15 mg / om satisfactory properties.

When testing in a half-element with 3 _t 7 molar sulfuric acid as the electrolyte, the electrode being used as a hydrogen electrode, it has a potential with a current output of zero of +20 millivolts, based on the normal hydrogen electrode, and gives 100 milliamps per cm ^{2 in operation} If the same electrode is used as the oxygen electrode, it shows a potential of +750 millivolts with a current output of zero, based on the normal hydrogen electrode, and emits 50 milliamps with a polarization of 150 millivolts.

When testing in a half-element with 6 molar potassium hydroxide «as Electrolyte, the electrode being used as a hydrogen electrode, it exhibits a potential of zero current delivery

009883/187 4

-850 millivolts, based on the normal hydrogen electrode, for a sample simply heated in the oven, for a calendered sample this equates to -800 millivolts. In both cases, the output during operation of 100 milliamps per cm ^{2 is achieved} at a potential of -725 millivolts. When used as an oxygen electrode in the same electrolyte, the electrodes emit 100 milliamps per cm ² at a potential of »100 millivolts or -75 millivolts, based on the normal hydrogen electrode.

Example 3

3 g of finely divided silver oxide and 0.3 g of colloidal silica are intimately mixed dry, to the resulting powder 5 cnr of an aqueous solution containing 0.5 # polyvinyl alcohol, 5 cnr distilled water and 0.6 cm of a 60 # -lgen polytetrafluoroethylene suspension given. The grophite fabric that is associated with that of Example 1 is identical, is previously through in its entire thickness Immerse in distilled water completely moistened, then carefully drain and the excess water will evaporate calmly"

The mass obtained in this way is brushed onto one of the sides Tissue applied and penetrates deep into this, with this emerging slightly on the back, but the main part of the mass remains in the thickness of the layer.

BATH ORIGINAL 009883/1674

After drying and heating for two hours under hydrogen-containing nitrogen at 300 ° C., an electrode with silver oxide is made

• 2
hold, which contains 7 mg of silver per cm.

When testing in a half-element with 6N potassium hydroxide solution as the electrolyte, the electrode acting as an oxygen electrode, shows it has a potential at the current output envelope of +175 mV, based on the standard hydrogen electrode and an output during operation of 50 mA with a polarization of 200 millivolts.

Example 4

6g of graphite powdered to a grain size on the order of 1 to 5 microns is impregnated with 1 g of colloidal silver according to the following procedure: Sas colloidal silver is dispersed in 1 liter of waaser, precipitated by a few drops of nitric acid, washed on the filter and the undried The filter cake is dispersed in 50 enr methanol. This dispersion is poured suf the graphite and the combined mixture is evaporated in an oven and then re under a Stlckstoffatmosphä that VoI 5, contains -Ji hydrogen, heated to 500 ⁰ C.

To the powder obtained in this way, 20 ears of water, 20 © nr one aqueous solution with 2 wt .- ^ polyvinyl alcohol and then 2 cm 'one 50 wt .- ^ aqueous suspension of tetrafluoroethylene / hexafluoro

009883/1674

given propylene copolymer. This composition will
dusted onto a graphite fabric that has been thoroughly moistened beforehand. The application of powdered graphite containing silver amounts to 60 g / m, measured after drying.

The electrode is dried and under nitrogen, the 5th
Contains hydrogen, ^{heated to 250 0} C for one hour.

When tested in a half-element with 6N caustic soda as the electrolyte, the electrode being used as an oxygen electrode, it shows a potential with a current output of zero
«125 millivolts, based on the normal waβseretoffelectrode, and emits 300 milliamps per cm at a potential of -200 millivolts when in operation.

SAD ORIGINAL

009883/1674

Claims (8)

Claims 1. Electrode, in particular for fuel assemblies, characterized in that that it contains a thin carrier, which consists of a fabric of carbon threads of at least one Surface is covered with a fritted mixture of a normally solid polymer and a catalytic agent. 2. Electrode according to claim 1, characterized in that it 0.1 to 300 g catalytic agent, calculated as metal weight, ο
and contains 0.05 to 100 grams of polymer per square meter of surface area. 3. Electrode according to claim 1, characterized in that it contains 1 to 100 g of catalytic agent, calculated as metal weight, and contains 0.5 to 20 g of polymer per square meter of surface area. 4. Electrode according to claim 1, characterized in that it contains 0.1 to 60 wt. 5t catalytic agent, calculated as metal, and 0.05 to 20 wt% polymer. 5. Electrode according to claim 1, characterized in that it 1 to 50 wt .- ^ catalytic agent calculated as metal, and 0.5 to 10 wt .- ^ polymer contains ο 009883/1674 6. Process but production of electrodes according to claim 1, characterized in that one first looks at a carbon fabric an aqueous dispersion containing a powdery catalytic agent and a powdery normally solid polymer is applied, the resulting hasse then dries and fries. 7. The method according to claim 6, characterized in that the aqueous dispersion 0.1 to 60 wt .- ^ polymer and 0.1 to 50 Weight # catalytic agent calculated as metal contains ». 8. The method according to claim 6, characterized in that the aqueous dispersion at the same time. Contains thickener. 9 »Method according to claim 6, characterized in that the catalytic agents from group Ib or from the elements with the atomic numbers from 27 to 78 of group VIII of the periodic table is selected » _Λ « _Λ « * ^BAD ORIGINAL 009883/1674