LU84466A1 - METHOD FOR THE CATALYTIC ACTIVATION OF ANODES AND CATHODES BY "IN-SITU" MOLDING OF ELECTROCATALYSTS UNDER PROCESS-OR PROCESS-RELATED CONDITIONS - Google Patents

Description

2062 i i EUROPEAN ATOMIC ENERGY COMMUNITY (EURATOM)

Patent application

Process for the catalytic activation of anodes and cathodes by "in-situ ^ -forming of electrocatalysts under the same or near-process conditions

Inventor: Hartmut WENDT, Jürgen KUELPS,

Helmut SCHNEIDER, Hans HOFMANN

The invention relates to a method for the catalytic activation of electrodes.

Electrode activations are carried out in a variety of processes. An example of cathode activations is the coating of electrodes by cathodic deposition of an electrocatalytically active metal or a metal mixture or an alloy, one component of which - for the purpose of increasing Ή - 2 - of the specific surface can also subsequently be removed chemically or electrochemically, and the coating by plasma spraying , Called vacuum vapor deposition or ion implantation.

The so-called spray-sintering process is an example of anode activations. Solutions of the salts of metals, the ions of which are required for the formation of the often oxidic catalyst, are brought onto the electrode surface by spraying, painting or dipping, then dried and dried by heating or sintering at a controlled temperature and atmosphere in e.g. Oxide layers, which represent the catalyst and have a more or less: precisely defined composition, transferred.

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All of these methods are characterized in that the activation of the electrodes is carried out separately from the electrolysis process in terms of time and location.

Only in exceptional cases is it possible to produce a catalyst that is thermodynamically and mechanically stable when used later in the electrolysis process under the specified conditions (electrode potential, electrolyte composition, etc.).

The result is often unsatisfactory or unsatisfactory long-term stability of the electrocatalyst with the need for frequent reactivations.

The method according to the invention is characterized in that a layer of the electrocatalyst adhering to the surface of the electrode is applied directly in the electrolyzer and under working conditions (pressure, temperature, electrolyte composition, current density and / or electrode potential) which largely correspond to the normal working conditions of the desired electrolysis .

In the process according to the invention, the electrolysis is carried out or continued under only slightly changed conditions, e.g. Metal ions, e.g. Ions of transition metals or other cations or anions or molecules that are necessary for the chemical or electrochemical formation of the desired electrocatalyst, in the form of salts or complexes or in fora more or less soluble verb in fertilize in the lowest possible concentration and in the minimum amount for the formation of an effective catalyst layer is just necessary to be added to the electrolyte. To this -3 'tr - 3 - i

In many cases, it is possible to carry out the activation within a relatively short period of time without significantly reducing the composition of the electrolyte! lent to change. Through such anodic (eg of oxidic catalysts) or cathodic (eg of metallic catalysts) in-situ formation of electrocatalysts, the constituents of the catalyst reach electrolytes (via the chain s homogeneous solution, mass transfer to the Electrode, formation by cathodic or anodic formation and deposition of the electrocatalyst) on the electrodes, which is an additional mechanical operation, such as Spray on, make unnecessary.

The in-situ application according to the invention ensures that the electrocatalyst is deposited on the electrode in a form (chemical composition, modification, atomic, microscopic and macroscopic structure) in accordance with the forming conditions, which largely correspond to the working conditions of electrolysis it has the greatest possible chemical and mechanical stability under the desired working conditions.

In addition to the formation of the most thermodynamically stable phase, a mechanically very stable structure is precipitated, since the deposition of the electrocatalyst takes place under mechanical conditions (eg blistering on gas-developing electrodes or high relative movement of the electrolyte with respect to the electrode by pumping around or gas siphoning of developed gases). , which also largely correspond to the practical electrolysis conditions.

Both prerequisites a) thermodynamic stability of the electrocatalyst, b) mechanical stability of the electrocatalyst under the desired electrolysis conditions, which is made possible by the <in-situ formation of electrocatalysts according to the invention, is the greatest possible guarantee of the long-term stability of the electrocatalyst against chemically and electrochemically induced changes and Deactivation and mechanical erosion and erosion are given.

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In addition, the method according to the invention allows the electrode activation to be renewed at any time after any deactivation has occurred without interrupting the current electrolysis operation.

example 1

Simultaneous in-situ activation of anodes and cathodes for alkaline water electrolysis.

2nd

In a 4 cm micro cell with Sandvri.ch arrangement of anode, diaphragm and

Cathode is electrolyzed in 50 wt .-% KOH at 90 ° C water. The nominal ^ / 2 current density is 1 A / cm.

After 200 hours of operation, the cathode has an overvoltage of - 350 millivolts, the anode has an overvoltage of + 350 mV. Han adds cobalt nitrate solution to the electrolyte (1.50% by weight KOH) in an amount corresponding to 65 mg of cobalt. The cobalt immediately dissolves in the electrolyte in the form of a deep blue colored cobalt-II-hydroxy complex, the color of which disappears within a few minutes. After 40 minutes, the overvoltage is improved by 20 millivolts, while the improvement in the anode potential is 50 millivolts. During the next 300 hours of operation, no renewed increase in the anodic and cathodic overvoltage is observed.

For example, £ iel_2s

Activation of the anode for alkaline water electrolysis by "in-situ" deposition of a cobalt-manganese mixed oxide on the anode.

In an experiment as described in Example 1, cobalt nitrate and manganese sulfate are added to 1 l of alkaline electrolyte in an amount corresponding to 20 mg of cobalt and 20 mg of manganese after 350 hours of operation. The salts are dissolved in 2 liters of water and added to electrolytes over the course of 30 hours in accordance with the loss of water, the concentration of cobalt or manganese in the alkaline electrolyte never exceeding 10 * moles / l. Over the course of 40 hours it decreases the anodic overvoltage by 90 mV and remains unchanged for the next 200 hours.

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Example 3, Activation of the Cathode for Alkaline Water Electrolysis by "In-Situ"

Precipitation of finely divided iron whiskers on the cathode.

In an experiment as described in Example 1, 1 g of Pe20 ^ which has a solubility of about 10 ^ mol / l at 90 ° C in 50% by weight KOH is added to 1 l of the electrolyte. After 30 hours, fine iron needles have deposited on the cathode and the cathodic overvoltage has dropped by 100 mV (to - 250 mV).

Example 4

Activation of the cathode for alkaline water electrolysis by "in ^ situ’ ’- deposition of zinc on a cathode already coated with finely divided Raney nickel.

In an experiment, as described in Example 1, a 2

Perforated nickel sheet is used, on which 115 mg per cm of finely divided ranynickel (application according to [2J) is applied. After 100 hours of operation, the cathodic overvoltage (90 ° C, 5% by weight $ KOH, 1 A / cin) is 225 millivolts.

When ZnO (which immediately dissolves as a zinc hydroio complex) is added in an amount that corresponds to 0.01 mol / l zinc in alkaline electrolytes, after a temporary increase, the cathodic overvoltage falls a further 60 mV within 20 hours and remains for the next 50 hours unchanged.

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Claims (1)

- 6 - S CLAIM Process for the catalytic activation of electrodes, characterized in that a layer of the electrocatalyst * adhering to the surface of the electrode is applied directly in the electrolyzer and under working conditions (pressure, temperature, electrolyte composition, current density and / or electrode potential), which largely correspond to the normal working conditions of the desired electrolysis. * * * (fa J kBbK ^ imnM lüü 2062 & JJ II