DE1909031A1 - Process for the production of electrodes containing Raney catalysts - Google Patents

Description

Process for the production of electrodes containing Raney catalysts

The invention relates to highly active electrodes containing Raney catalysts for electrochemical cells, in particular for fuel elements with reactants dissolved in the electrolyte, as well as processes for their production.

In the German patent specification 592 130 there is already a manufacturing process for electrodes, in which the electrode material is initially coated with aluminum or Zinc is alloyed and then the alloyed metal is dissolved out again by treatment with alkali hydroxide solutions. According to one embodiment of this patent specification one can now also electrolytically coat the electrode material with the additional metal and this in a neutral or reducing atmosphere burn in. However, more detailed information on a suitable aluminum deposition and alloy formation is given in this publication not included.

From the "Zeitschrift für Instrumentenkunde ^M 1959, page 155, it is also known to apply Raney alloys simultaneously or one after the other by electrolysis. It is also proposed to apply coatings made of a Ni-Al alloy by electrolytic deposition of aluminum on nickel-plated steel generate, with inorganic molten salts of these salts are used as electrolyte baths.

■ A disadvantage of the latter method is that that deposited from common inorganic molten salts

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Aluminum layers because of the high bath temperatures required to uncontrollable aluminum alloy layers. lead, which experience has shown does not result in a highly active catalyst. It has also been shown, that the Raney metals produced in this way have insufficient adhesive strength on the carrier material, as a result of which the service life of such electrodes is high is decreased.

The object was therefore to provide a process for the production of electrodes containing Raney catalysts for electrochemical cells, especially for fuel elements, by galvanic deposition of aluminum on metals find in which the disadvantages described do not occur.

The solution to the task at hand consists in next from an electrolyte of the general formula

MX · 2 AlR ₃ '^;

in which M is a sodium, potassium or onium ion * X is a halogen or cyanion and R is an alkyl radical with 1 to 12 carbon atoms. Aluminum is deposited on a metallic support below '-.-' ■ 150 ⁰ C, at a ^{temperature below 659 0} C; temperature forms a Raney alloy by diffusion, then; dissolves the aluminum and, if necessary, activates the Raney metal that has formed with one or more precious metals.,

The new process is characterized above all by the fact that when aluminum is deposited between the carrier material and the aluminum layer one which hinders the diffusion of the metals Oxide layer does not form. This ensures that during the diffusion process © ine uniform

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Alloy layer arises and during the subsequent removal of the aluminum covers the entire surface of the carrier material in the form of a Räney metal "is present.

The layers formed during the galvanic deposition of aluminum from aluminiusorganasch complex compounds show a high ductility (- «^ 20 kp / aU VH) as well as a high purity (^ 99.99 fo Al). They contain neither oxygen nor hydrogen, so that diffusion and alloy formation can take place undisturbed. As a result, the activity of such electrodes is very high.

The Raney metals produced according to the invention continue to show extremely good adhesive strength on the carrier material, which must be described as surprising. For example, even in fuel cells with Oxygen and hydrazine dissolved in the electrolyte were operated, after 6 months of operation, the Raney nickel will peel off or Raney silver from the support material was not observed will. '

The organoaluminum used as deposition electrolytes Complex compounds are already known, but it was not foreseeable that these electrolytes would be used on carrier materials such well-adhering Rahey metals can be formed. They are particularly advantageous for separating aluminum those compounds are used in which MX is an onium salt of the general formula

is, in which R ^{1 is} a Kolilenhydrogenrest, for example an alkyl, üralkyl- or aryl radical, Y is an element of b. or 6. Main group of the Periodic Table means and η 'ie assumes values 4 or 3, at least one of the hydrocarbon radicals in the onium ion being an optionally halogenated one

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Benzyl, phenyl, cyclohexyl or a heavily branched hydrocarbon radical with 3 to 12 carbon atoms, while the remaining radicals of the onium salt are alkyl radicals with 1 to 4 carbon atoms. ■ -, -. "

Such electrolytes are for example

[(CH _{3) 3} (C ₆ H ₅ CH ₂₎ n] P. 2 Al (C ₂ H ₅ O ₃ - λ

J _(CH3 J ₃ (C ₆ H ₅ CH ₂₎ Nj Cl 2 Al (C ₂ H _{5) 3} - - '■' - ^=:: '- =;.' [(C ₂ H _{5).. 5} (C ₆ H ₅ CH ₂ ) ^ Cl-. 2 Al (C ₂ H ₅ I ₃ > ■

[(C ₂ H ₅ ) ₃ (C ₆ H ₅ CH ₂ } P] P. ₂ Al (C 2 H ₅ I ₃ 'V _: /;

Of course, you can also use for aluminum deposition Complex compounds containing alkali halides are used as

) ₃

NaP. 2 Ai KP 2 Al KP. ■ « 2 Al KCl 2 Al

NaP · 2 Al (CH ₃ I ₃

Mixtures of such complex compounds can also be used, for example a mixture of _; .

. 2 Al (C ₂ H ₅ ) ₃ and NaP · 2 Al. (CH ₃

The organometallic complex compounds can both in molten as well as dissolved form as electrolyte baths are used, aromatic hydrocarbons, higher aliphatic or cyclic 'ethers can be used as solvents. Toluene and xylene are used here with particular advantage. : 7

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The aluminum is deposited from the organometallic Koiaplex compound at a temperature of 30 to 150 ° C, preferably 80 to 120 C and a current density of 1 to

20 ma / cm at a voltage of 1.5 to 12 V. The deposition conditions are of course based on the electrolyte used and the carrier material.

Sheets, porous and non-porous pollen, porous sintered bodies and nets can be used as the metallic carrier can be shaped as desired, for example round, polygonal or cylindrical. They are preferably made of nickel, Cobalt, tungsten, silver, a precious metal or an alloy these metals. The metals mentioned can also contain other known activating additives such as molybdenum and titanium.

In order to achieve good adhesive strength, it is essential that the surface of the metallic carrier is coated before aluminizing cleaned in the absence of air and then galvanically with without coming into contact with the air or water an aluminum layer is provided. The cleaning of the metallic The carrier is expediently carried out by pressure radiation with corundum powder dispersed in oil, wherein the oil can be a paraffin or a silicone oil. Then the carrier is in Hydrocarbons, e.g. perchlorethylene and / or xylene. The washing is advantageously carried out under the action of ultrasound. By using ultrasound it is achieved that the surface of the support also from traces is cleaned after adhering impurities. When using very fine metal meshes as a carrier material it is advisable to use cathodic degreasing in baths containing alkali metal cyanides instead of the pressure irradiation mentioned undertake and the so treated carrier after pickling in dilute sulfuric acid first with water and then with acetone and xylene, to wash, doing the laundry as well can take place under the action of ultrasound.

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The electrodeposited Aluminiumsehiehten are-vortexl- ^"-;. Adherent enough, 5 to 20 / um thick, the diffusion of the deposited aluminum is carried out below the melting temperature of aluminum, in particular at temperatures from 350 to 650 C, preferably in an inert or reducing atmosphere, whereby Argon, which contains about 1% hydrogen, can also be used as an inert gas. The diffusion time depends on the thickness of the deposited aluminum layer that is to be diffused in. During diffusion, the aluminum-richer alloys and are formed on the surface of the carrier metals in the deeper layers the aluminum poorer ones.

When carrying out the method according to the invention, it has proved to be advantageous, the electroplated high-purity Do not convert the aluminum layer completely into alloy form. This causes the Raney alloys against atmospheric and other corrosive effects are protected And have an excellent shelf life. Further the formation of the metal hy- " Oxide solutions not activatable low-aluminum alloy layer Niü.1 avoided. -: -

'-' ■■■■ - ■■ -: ■ y i--

The inactive component can be dissolved out of the Raney alloy formed by diffusion in a manner known per se ^ Äuf- :, aqueous-chemical way by means of alkali-hydrogen solutions "- ·" .- "■ or, according to a further invention, in an organometallic-chemical way Raney alloy is introduced into an alkyl halide, e.g. O ₂ H ^ Br, C ₂ H ^ Br ₂ , C ₆ H ₅ CH ₂ Cl or a solution of the alkyl halide, whereby the aluminum forms the sesquihalides (e.g. Al (C ₂ H ₅ ) Br ₂ · oil (C ₂ H ₅ ) ₂ Br) goes into solution and the carrier material remains in a highly active form.

According to a further embodiment of the invention, this is known Aluminum is also made from an organometallic electrochemical route the alloy are removed, in such a way that the with

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Raney alloy covered shaped bodies.in an electrolyte that delivers alkyl radicals, about ζ ( CH,) ^ ■ (TgH "CHgN ^ Cl · 2 Al (CgH ₅ ) ^ is anodically loaded, with the aluminum organi- 'see complex salts formed again as electrolyte baths for the deposition of aluminum on metallic substrates can be used.,

Purely for the production of highly active, Raney metals containing Electrodes, it can also be advantageous if the Raney metals produced according to the invention additionally with one or several precious metals are activated. Such an activation is particularly advantageous for electrodes that in fuel elements with reactants dissolved in the electrolyte be used--. Purely the anodic oxidation of hydrazine A mixture of palladium and ruthenium has proven to be special Proven suitable, the weight ratio of the two. Metals is advantageously 4: 1. The deposition of the Noble metals on the Raney catalysts can be known per se In a galvanic or currentless manner, preference should be given to the last-mentioned method.

The method is based on the following exemplary embodiments after .the invention explained in more detail.

Example 1 '

A nickel net with a wire thickness of 0.25 mm was first cleaned by pressure blasting with corundum in oil as a dispersion liquid, washed in JPerchlorethylene and / or xylene under the action of ultrasound and then hung in an electrolyte bath with the exclusion of air. The electrolyte liquid consisted of NaP · 2 Al (CpH _x -), · 3 toluene. Served as an anode

<- jj - 'η a refinal sheet. At a temperature of 90 ° C. and a current density of 7 mA / cm, it became 10 μm thick at 3 to 4 V

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Deposited aluminum layer. Then, the aluminum alloy was annealed for one hour at 500 ⁰ C to give the desired Eaney alloy was formed. The nickel-aluminum alloy was then converted into Raney nickel by treatment with aqueous KOH. On the Raney nickel was also added

0.8 mg palladium and 0.2 mg ruthenium per cm from an aqueous solution of RuCl and Na ₂ -PdCl. deposited. The solution contained 1.2 g Pd and 0.3 g Ru / 100 ml.

The current-potential behavior of this electrode is; in Pig. 1 reproduced. The temperature during the measurement was ^20.0 C. The electrolyte consisted of 6 η KOH and contained 1 mol of N ₂ H ₅ OH. The potential was measured in a half-cell arrangement against an Hg / HgO reference electrode.

For comparison, see Pig. 1, curve b _{/ the} current-potential behavior of a comparison electrode plotted, in which the electrodeposition of the Raney alloy on the nickel mesh from a solution with 10 wt. % NiSO., 3 wt .- # ZnSO ₄ and 10 wt .-% Na (CH ₃ COO) at 60 ⁰ C and 50 mA / cm ^{2 has taken} place. After the zinc had been dissolved out, a noble metal layer made of a solution of RuCl and Na ₂ PdCl was applied to the Raney layer formed, as in the case of the electrode according to the invention. deposited without current. As curve b shows, such an electrode is worse than the new electrode in terms of its current-potential behavior. Corresponding long-term tests led to the same result.

Example 2 - \ _; . /

A nickel mesh coated with 20 μm cobalt was cleaned as in Example 1 and coated with aluminum. As the electrolyte, RCH _{3) 3} was in this case (C ₆ H ₅ CH ₂₎ NJcI.- 2 Al (C ₂ H ₅ used J ₃ -2 toluene The annealing was carried out at 520 ⁰ C and about lasted · 2 ^hours...:

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the aluminum was then dissolved anodically from the Raney alloy formed in this way, with (CH ₃ ) ₃ (C ₆ H ₅ CH ₂ I ^ Cl · 2 Al (C ₂ H _5. ) ^ being used as the alky! radical "supplying substance The anodic leaching of the aluminum took place at 110 ^° C. and a current density of 12 mA / cm with vigorous stirring of the electrolyte liquid electrode in a 6 η KOH Iösung containing 1 mole of N contained ₃ H ₅ OH, measured at 20 ⁰ C. the current-potential values are given in Fig. 2 ^ wherein as the reference electrode HgO electrode was also used a Hg /.

The electrode produced in this way showed over when it was used no change in their current-potential behavior for a period of 4 weeks, which is particularly noteworthy when using hydrazine as fuel.

Of course, the invention is not limited to those in Examples given embodiments are limited. So can For example, porous sintered bodies are provided with Raney alloys according to the method of the invention and are used as gas diffusion electrodes are used.

15 claims
2 figures

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Claims (15)

PM 68/1730 ■■■■ '■ - ίο - Claims . ^ Process for the preparation of Ban.ey-Xata-lysator.en- containing Electrodes for electrochemical cells, in particular for fuel elements, 'by galvanic deposition of aluminum on metals, characterized in that from an electrolyte of the general formula MX .2 . X represents M is a sodium, potassium or Oniumiön a .Halogen- or Cyänion and R ütomen C-alkyl of 1 to 12, depositing aluminum on a metal support below 150 ⁰ C, at a temperature below 659 C. Temperature forms a Raney alloy by diffusion, then dissolves out the aluminum and, if necessary, activates the Raney metal formed with one or more noble metals. 2. The method according to claim 1, characterized in that the ■ Diffusion carried out in the presence of a reducing gas 3. The method according to claim 1, characterized in that the Diffusion in the presence of an inert gas, which optionally t contains a reducing gas, is carried out. 4. Process according to claims 1 to 3 »characterized» that the diffusion is carried out at normal or reduced pressure. ".-. '■ - ■:' 5. The method according to claims 1 to 4, characterized in that the deposition of the aluminum at a temperature of 30 to 150 ⁰ C, preferably 80 to 120 ⁰ G and a current density of 1 to 20 mA / cm ² at a voltage of 1 , 5 to 12 V is made. . . ·. 6. The method according to claims 1 to 5 «characterized in that the diffusion of the deposited aluminum at -. a temperature of 350 to 650 ⁰ G is vorgenomaen. 009837/1768: w fi =. PLA 68/1730 - 11 - 7. The method according to claims 1 to 6, characterized in that that the diffused aluminum by means of an aqueous Alkali hydroxide solution is dissolved out. 8. The method according to claims 1 to 6, characterized in that the diffused aluminum by means of alkyl halides or their solutions are extracted. 9. The method according to claims 1 to 6, characterized in that that the diffused aluminum is anodically leached out in an electrolyte which produces alkyl radicals. 10. The method according to claims 1 to 9, characterized in that that sheets, porous or non-porous foils, porous sintered bodies or mesh are used as metal supports. 11 .. The method according to claim 9, characterized in that as Carrier material nickel, cobalt, tungsten, silver, a noble metal or alloys of these metals can be used. Process according to Claims 1 to 11, characterized in that the Raney metal formed is activated with a noble metal will. 13. The method according to claims 1 to 12, characterized in that that the Raney metal with a mixture of palladium and Ruthenium, preferably in a weight ratio of 4: 1, activated will. 14. The method according to claim 13, characterized in that. the palladium and ruthenium from an aqueous salt solution be deposited without current- - 12 00 9837/1768 PIA 68/1730 - 12 - V 15. Raney catalysts prepared according to claims 1 to H. containing electrodes for electrochemical cells, in particular fuel elements. 0098 37/1768