DE2119066A1 - Process for the production of noble metal and / or noble metal oxide coated objects, in particular electrodes - Google Patents

Description

concerning:

"Process for the production of precious metal and / or precious metal oxide-coated objects, in particular electrodes."

The invention relates to a method for the deposition of noble metals or noble metal oxides Cathode sputtering on a metal support, in order to have good properties both in terms of corrosion resistance as well as the electrochemical activity. "''" ^

109845/1847

The material coated according to the invention can be used successfully for electrodes in electrolysis cells with a diaphragm or checks over cathode or in »fuel elements or Find fuel cells as well as in desalination plants.

The electrodes commonly used as anodes are often made of graphite, your use is always accompanied by some disadvantages based on electrode consumption (burn-off); this burn-up causes a Increase in the voltage required for proper operation of the electrolysis system as a result of the enlargement the distance between the two electrodes and contamination (poisoning) of the reaction medium.

It is therefore for some time been trying to develop anodes for such uses, the _s exist made of a metal a good corrosion resistance against which it has vice-Bendea medium and dije with an electrochemically active noble metal plated /, said sheet material finally an activation receives favorable treatment. These anodes are dimensionally or dimensionally stable and do not have the disadvantages mentioned above. The following have become known: From Swiss patent specification 236 579 a platinum-coated anode made of zirconium or a zirconium-titanium alloy j

US Pat. No. 2,719,797 discloses a platinum-coated tantalum or niobium anode;

from the French patent specification 1 200 841 one with Platinum-coated anode made of titanium, whereby the titanium is able to in the electrolysis solutions (electrolytes) to form an oxide barrier covering the tantalum surface protects where the platinum is porous; ο

109845/1847 - 3 -

finally an electrode made of a metal, the one Can form a barrier layer and with a precious metal oxide (French patent specification 1,479,762) or a mixture of noble metal oxides and base metal oxides (French patent 1,555,960) is coated or coated.

A variety of procedures have been used so far, around the deposited noble metal layer the adhesive properties to the carrier metal and the electrochemical To give activity. An example of a deposition process is vapor deposition Vacuum, the thermal decomposition of metal compounds and the electrochemical or mechanical deposition processes.

The. long-known working method of the cathode

especially
Atomization has proven to be suitable for producing deposits or deposits that adhere excellently to the various substrates used and result in a very uniform, homogeneous and pure layer. The working conditions under which the cathode sputtering is carried out have a special influence on the electrochemical properties of the electrodes produced in this way.

It has now been shown that when the cathode sputtering is carried out under very specific conditions Electrodes are obtained which are excellently suited for their later use.

The invention therefore relates to a method for depositing noble metals or noble metal oxides on one Metal carrier by means of cathode sputtering and is thereby.

- 4 -1098 4 5/1847

characterized in that the metal carrier is first subjected to ion bombardment in a residual inert gas atmosphere and then, without waiting for the temperature increased by ion bombardment to drop, by means of cathode sputtering is coated with a noble metal or a noble metal oxide, the cathode sputtering initially is carried out in a noble gas residual gas atmosphere and then in an atmosphere of noble gas and oxygen. Pure argon is preferably used as the noble gas.

This method of cathode sputtering belongs to the class of metal deposition by electrical means Discharge in a gas with low pressure (partial vacuum).

The required device includes a vacuum chamber, a "pumping system or pump unit, a high-voltage supply and a gas inlet system. The vacuum chamber contains the noble metal cathode and the anode consisting of the metal support to be coated. Cathode sputtering consists in that accelerated from the cathode through the bombardment with through the drop in the cathode potential (cathode fall) Ions atoms are knocked out or extracted.

The electrons released by the cathode, which is brought to a high negative voltage, are accelerated and cause the ionization of the molecules of the residual gas in the space between the electrodes. With every collision A positive ion is formed, which is accelerated again towards the cathode, and an electron, which moves towards the Anode sets up. The impact of the positive ion on the cathode changes its surface Atoms knocked out and deposited on the anode.

109845/1847

- ο -

Such a way of working is important to the extent that as precipitates or deposits of high purity are obtained "because the vacuum chamber in the High vacuum can be degassed / grounded and the composition of the ionized gas, i.e. the plasma "can be influenced that forms in the course of the discharge and that. an effect on the structure and properties of the dejected strata.

The metal carrier, i.e. the anode, is pretreated before being introduced into the vacuum chamber, namely sandblasted so that the metal has a large, developed (extensive) surface that is favorable for good electrochemical properties, and it is degreased in order to achieve the required degree of cleanliness. This carrier and the noble metal to be atomized are then arranged as electrodes in the vacuum space. During the ion bombardment, the metal carrier is switched as a cathode by applying a high negative voltage. It thus temporarily becomes the cathode and is atomized. During this work step, the precious metal is protected from the atoms knocked out of the carrier by a movable mask. The aim of this ion bombardment of the carrier is to degas and pickle the surface which is to be coated afterwards, in that the oxide layers, the traces of hydrocarbons, fats and others are removed. In this way, a support is obtained whose surface has approximated the state of the pure metal as closely as possible. This bombardment, which starts at room temperature, is of an increase in:
achieved.

Accompanying increase in temperature, the 300 to 50O ⁰ C

- 6 109845/1847

mm Q μ

The metal carrier is then quickly separated from the high-voltage source and connected as an anode, which is ready to absorb the precipitate as a result of the sputtering of the noble metal in the cathode position. The protective mask of the cathode is removed and the latter is connected to the high voltage source. This cathode sputtering onto the anode is carried out immediately afterwards and a noticeable drop in the anode temperature, which is approximately 30O ⁰ O, is avoided. This maintenance of the temperature is very important for the electrochemical properties of the subsequent electrode. The first phase of cathode sputtering is carried out in an inert gas residual gas atmosphere, preferably in pure argon, for 30 seconds up to 5 minutes. This time is also sufficient to give the subsequent electrode good corrosion resistance properties because the adhesive layer produced is very good on the. Metal support is anchored to form a microdiffusiönsschicht. The presence of the noble gas prevents the formation of a metal oxide layer on the surface of the carrier. In this way, a support is obtained in a practically metallic state, the surface of which does not contain any impurities and is coated with a hard and compact layer of noble metal.

As soon as the deposited layer is sufficiently thick to protect the metal surface of the carrier against corrosion, the second phase of cathode sputtering is carried out in a reactive gas atmosphere of noble gas, preferably argon and oxygen, the partial pressure of the oxygen in the mixture being 0.1 to 25 % is held. The introduction of oxygen at this stage of the process is of great importance because it leads to a

- 7 -109845/1847

impact of precious metal or an oxide of this precious metal of a special nature. You get one like that finely divided microcrystalline and porous material, which then no longer needs to be treated in an activating manner in order to have good electrochemical properties. It has been shown that when the noble metal is atomized in the presence of a certain percentage Oxygen in argon the metal is not oxidized and you are a porous precious metal with a lower density than normally obtained due to the adsorption of oxygen by the metal without forming the oxide. In general, a deposit of microcrystalline noble metal or noble metal oxide is obtained with a high specific Surface; this is very important because the electrochemical activity is directly proportional to this surface area is.

For the sake of simplicity, argon is predominantly indicated as the noble gas in the present description; Of course, all or part of the argon can be replaced by any other noble gas.

A metal is used as the metal carrier that forms the anode, which forms a barrier layer in the electrolyte can form, i.e. tantalum, zirconium, niobium, titanium and their alloys. It can also be a carrier can be used, which is attacked by duash corrosion, but is a good electrical conductor, for example Copper, steel or aluminum that (the) previously with a sufficient protective layer of these metals, the one Can form a barrier layer or barrier skin, has been coated.

- 8 109845/1847

The noble metals that form the cathode and are atomized onto the anode include the metals of the platinum group, i.e., platinum, iridium, palladium, ruthenium, osmium, rhodium and their alloys; the metals and / or Alloys can be used individually or in a mixture with one another. The ion shot of the connected as cathode The metal support should be made long enough to allow good degassing and pickling or cleaning to allow the surface. Generally, a period of 10 to 30 minutes is sufficient to achieve the desired result to achieve.

'The duration of the sputtering of the noble metal in pure argon residual gas atmosphere must also be sufficient to obtain a microfusion layer, the one good protection of the metal support is permitted. Generally, this desired result will be achieved in a span of 30 seconds reached up to 5 minutes. The duration of this work step can be extended; however, this is without special practical importance because it only reinforces the protective layer of precious metal, which makes it economical Machteil leads without any particular technical progress.

The second stage of cathode sputtering in an atmosphere of argon and oxygen is carried out as long as until the layer thickness of the precipitate of finely divided porous noble metal or noble metal oxide 0.1 to

1 / µm. With this layer thickness, an electrode is obtained which has a satisfactory activity or life duration owns. In general, the desired layer thickness is achieved by cathode sputtering in argon and oxygen during

2 to 30 I-minutes achieved. As soon as this precipitation

109845/1847

is completed, one leaves the erfindungsgeroäß generated Cool the anode in the yakuum chamber.

The percentage of "oxygen" is also important. A minimum of oxygen is required so that the generated electrode has good activity. But it is not necessary to have a too high percentage Use proportion of oxygen because this does not further improve the electrochemical activity of the electrode causes, however, reduce the yield of the sputtering of the noble metal or its oxide and thus the The duration of the sputtering can extend beyond the normal extent.

Cathode sputtering, which is carried out exclusively in a pure argon atmosphere, can be used to to create a metal deposit that forms a barrier layer on a highly conductive substrate such as copper, iron or forms aluminum. In this case, the conductive metal shows good passivation compared to the corrosive Substances and can serve as a metal carrier on which a precipitate of precious metal or precious metal oxide then by cathode sputtering to be complied with according to the invention Conditions is applied.

The cathode sputtering of the noble metal carried out directly in a mixture of argon and oxygen leads to an electrode that does not have a protective microdiffusion layer, which is caused by the precipitation is formed in a pure argon atmosphere. In this pallet, all of the precipitate or coating is microcrystalline and porous. An electrode made in this way shows a correct polarization curve in an electrolyte; but their lifespan is shortened and theirs electrochemical activity decreases rapidly due to the tendency to peel or peel off the generated deposit

- 10 109845/1847

schiags or cover. An electrode of the same kind is obtained, when allowed to drop the temperature to about 5O ⁰ G after the ion bombardment of the metal support before the sputtering of the Edeimetalles is made.

The following examples serve to provide a more detailed explanation the invention.

example 1

Am 30mm wide, 50mm long and 3mm thick Titanium test plaques were sandblasted, brushed off under running water and then in trichlorethylene steam degreased, rinsed with methylene alcohol and placed in the vacuum chamber; the pressure in this chamber was then brought to 10 torr.

This was used to carry out the lorsen bombardment Titanium plate connected to a direct current source with a voltage of 3000 ¥. The chamber was with

—3 pure argon up to a partial pressure of 40 χ 10 Torr filled and the removal of the surface layer of the titanium carried out for about 30 minutes under an electric

Output of 1.8 Vi per cm. The temperature of the titanium platelet was stabilized ^{at 35O 0 C at the end of this operation;} during the entire time the platinum cathode was protected by a sliding, movable mask.

The titanium plate was then separated from the high voltage source and the high voltage was applied to the platinum cathode. This process ran very quickly in order to avoid a drop in the temperature, which was 300 to 35O ⁰ C,

- 11 109845/1847

to avoid.

The first stage of the deposition of platinum on the titanium flakes was then in a pure argon residual gas atmosphere carried out for 2 minutes at a temperature of about 300.degree. The deposited platinum was very dense and not porous at all.

Oxygen was then introduced into the chamber up to an argon / oxygen ratio of 80:20. The deposition of platinum was continued until a layer thickness of 2500 Angstrg / m or 250 nm had been reached ( measured with the layer thickness meter on comparative glass plates. The two stages of platinum deposition were carried out under a voltage of 3000 V and with power

ρ
of 2 W per cm. The electrode was removed from the vacuum chamber after cooling for 30 minutes.

The second stage of the deposition of platinum in a mixed gas atmosphere of argon and oxygen makes it possible to obtain platinum in its active form, which is characterized by a low density compared to solid platinum, a considerable electrical resistivity * a very strong difference. m wrapped specific surface area, marked with reference to the catalytic activity. By means of X-ray diffraction analysis, reflection and transmission, electron diffraction analysis and IR spectrometric analysis, it was found that this active platinum is cubic platinum with centered surfaces and does not contain any oxide. The surface of the active deposit or the active deposit was ^{examined with the scanning or field electron microscope "Stereoscan 11} " and a porous microcrystalline structure was determined, which was found

- 12 109845/1847

Values for the density, the specific conductivity and the specific surface area were confirmed.

The titanium electrode coated with platinum was placed in an electrolytic cell containing a saline solution contained in a concentration of 300 g / l. The electrochemical properties were * -90 ° G through the polarization curve and the specific consumption of platinum over a longer period

2 Operation at a current density of 2 Amp / cra determined. It

were measured: * at

a minimum discharge voltage (separation potential) for * chlorine, based on the saturated calomel electrode E _n = I, 054 V / ECS (EGS = saturated calomel electrode)

U ρ

a polarization resistance of 0.120 -Π-cm a platinum consumption of less than 100 mg / t chlorine produced.

Comparison attempts 1 to 3

As in Example 1, these tests were carried out under other conditions than are to be complied with according to the invention carried out.

The pretreatment of the titanium platelets by ion bombardment was carried out under the same conditions as in Example 1. After the ion bombardment, the temperature was 300 ^° C. The conditions for the deposition of the platinum were varied.

Comparative experiment 1

The deposition of platinum was carried out immediately afterwards without cooling, but immediately in a mixed gas atmosphere of argon and oxygen in the ratio SOi20.

- 13 10984S / 1847

There was no protective, non-porous microdiffusion layer from "very dense _ ~ pia tin, special one immediately highly porous layer of active platinum. the Deposition takes place under a voltage of 3000 V with

a power of 2 V / era,. during 4 rain and led to a layer thickness of 2200 pounds or 220 nm.

The electrochemical properties of this one with platinum coated titanium electrodes were determined according to Example 1 and gave:

Minimum discharge voltage for chlorine E _n = 1.056 Y / ECS

Polarization resistance 0.105-fl-.cm

Platinum consumption 180 mg / t chlorine produced. Comparison attempt 2

After cooling for 30 minutes at a temperature of 30 ^° C., the platinum was deposited first for 2 minutes in pure argon and then for 2 minutes in a mixed gas atmosphere of argon and oxygen in a ratio of 80:20 under the same voltage and with the same output as in Example 1 and 2 performed. The thickness of the platinum layer produced was 2000 S. or 200 nm.

The electrochemical properties of this platinum-coated titanium electrode were as in Example 1 and 2 determines:

Minimum discharge voltage of the chlorine E _n = 1.065 V / ECS

Polarization resistance 0.135 Jp- · cm

Platinum consumption 600 mg / t chlorine produced.

-H-

1098A5 / 1847

Matching attempt 3

The platinum plating was carried out after 30 rain of cooling at a temperature of 30 ^° G directly in a mixed gas atmosphere argon-oxygen 80:20 under the same voltage and with the same power as in Examples 1 to 3. The thickness of the deposited platinum layer was 2200 pounds or 220 nm with a sputtering duration of 4 minutes.

The electrochemical properties of this platinum-coated " Layered titanium electrodes were determined as in the previous examples; were measured:

. Minimum discharge voltage for chlorine E _n = I, 060 V / ECS

'2

Polarization resistance 0.105-A..cm Platinum consumption 1100 mg / t chlorine produced.

This comparison clearly shows the importance of the platinum-coated titanium electrodes according to the invention, the in a significantly longer operating or useful life in the electrolyte, since the amount of consumed Platinum is extremely low.

H example 2

Exactly as in Example 1, a 30 χ 50 χ 3 ram plate made of tantalum was coated with platinum; In the first stage of the process, the platinum platelet was subjected to ion bombardment under the same conditions. The total layer thickness of the deposited platinum, ie microdiffusion layer and porous platinum, was 2000 S. or 200 nm. When this platinum-coated tantalum plate was used as the electrode according to Example 1, the following values were measured:

-15-109845 / 1847

Minimum discharge voltage for chlorine 1.062 V / ICS

Polarization resistance 0.051 -Π-icta

Platinum consumption below 150 rag / t chlorine produced. Example 3

Bin titanium flakes according to Example 1 was subjected to the above "conditions described eiflem ion bombardment The temperature it was 300 ⁰ G;. For sputtering a Rutheniumkathode was used The first stage of sputtering took 45 lake and was in pure argon at a Partialdruok of 50 X. 10

2 Torr and a power of 2.1 W per cm made; the second atomization step was carried out in a mixed gas atmosphere of argon and oxygen in a ratio of 99.8: 0.2 for 5 minutes with the same partia pressure and with one

ρ
Power of 1.9 W per cm.

was 2700 S or 270 nm.

Power of 1.9 W per cm. The thickness of the layer created

When using this ruthenium-coated titanium electrode, the following values were measured:

Minimum discharge voltage of the Ghlors E _n = 1.066 V / ECS

w 2

Polarization resistance 0.07 JLl.cm Ruthenius consumption 58 mg / t chlorine produced.

Claims

109845/1847

Claims (7)

Patent claims Process for the production of objects coated with precious metal and / or e'lmetalloxid, in particular of electrodes for electrolysis cells, fuel cells and desalination plants by depositing a noble metal or noble metal oxide on a metal carrier by means of cathode sputtering, characterized in that the metal carrier is first an ion bombardment in a residual gas atmosphere of noble gas submits and then, without waiting for the temperature increased by the ion bombardment to drop Applying layer of noble metal and / or noble metal oxide by cathode sputtering and this cathode sputtering first in a residual gas atmosphere made of pure noble gas and then in a residual gas atmosphere made of noble gas and oxygen takes. 2. The method according to claim 1, characterized in that the ion bombardment of the metal carrier is ^{carried out up to a temperature rise of up to 300 to 50O 0} C and the temperature is stabilized in this range. - 17 - 109845/1847 3. The method according to claim 1 or 2, characterized in that the ion bombardment of the Metal carrier 10 to 30 ½ inch long. 4. The method nach'Anspruch 1 "to 3, characterized in that the first cathode sputtering of the noble metal or noble metal oxide on the metal carrier in a residual gas atmosphere of pure Carry out argon for up to 5 minutes for 30 seconds, 5. The method according to claim 1 to 4, characterized in that the second cathode sputtering of the noble metal or noble metal oxide on the metal carrier in a residual gas atmosphere of argon and oxygen at a partial pressure of oxygen of 0.1-25 1 ° for 2-30 min . 6. The method according to claim 1 to 5, characterized in that the metal carrier Tantalum, zirconium and / or titanium or alloys of these metals are used. 7. The method according to claim 1 to 6, characterized in that the noble metal is platinum, Iridium, palladium, ruthenium, osmium, rhodium or their alloys or their various oxides individually or used together in Geraisch. 109845/1847