DE2436790C3 - Use of catalysts for the cathodic evolution of hydrogen in amalgam decomposition cells - Google Patents

Description

The main patent relates to air- and storage-stable catalysts based on metal boride for the cathodic evolution of hydrogen in alkaline electrolytes with an activity comparable to Raney nickel, produced by growing X-ray amorphous, smooth boride layers by depositing the reaction product of water-soluble reducing boron compounds in an aqueous solution with nickel or cobalt ion in divalent form in the presence of a complexing agent for the metal ion at a concentration of the metal ion in the starting solution of 0.02 to 0.2 mol / l and a complexing agent concentration of 1 to 10 mol / l on a support structure made of metallic or non-metallic substances, with boranates or borazanes in a concentration of 0.02 to 0.?. Mol / l can be used as reducing agent and a concentration of free metal ions below 10 " ¹⁰ mol / l and a temperature below 6O ⁰ C are maintained during the deposition.

Furthermore, the main patent relates to the use of these catalysts for the evolution of hydrogen in alkaline electrolytes.

It has now been found that such catalysts work very well for the specific use of the decomposition of the alkali amalgam produced in chlor-alkali electrolysis.

The decomposition reaction after

NaHg ₁ + H ₂ O -> NaOH + * Hg + 1/2 H _a

is carried out in technology according to various methods. The first method uses the Reactants brought into close contact with materials on which the evolution of hydrogen is catalytically accelerated, such as. B. graphite, iron, with Metal salts contain activated types of coal, etc. Due to the violent reaction, the reaction products contain considerable amounts of mercury and catalyst wear, so that a cleaning is connected must become. The decomposition energy is lost as heat or is only used to concentrate on the Lye used.

In the second method, part of the decomposition energy is used can be used directly as electrical power

ίο made. The amalgam decomposer is used for this purpose built as an electrolytic cell with the liquid amalgam as an anode and with a hydrogen development catalyzing cathode and alkali as electrolyte and optionally separators between the electrodes. The decomposition cell can be connected in series with the primary cells of the Have chlor-alkali electrolysis or its own circuit. Usable energy can only then be obtained if the decomposer cell is also under high

»O the current still has a positive voltage, d. H. the evolution of hydrogen at the cathode must take place at a low overvoltage. The high temperature the mechanical stress caused by the strong gas development and the poisoning effect of the

»5 mercury through amalgamation make high demands to the cathode material. The previously proposed catalysts such. B. graphite, ferrous metals in plate or sintered form and Raney nickel have not been able to prove themselves.

The metal boride-based catalysts described in the main patent, the production of which is also shown in the main patent, can be obtained from a bath, the Ni ^{2+, by growing X-ray-morphic boride layers onto suitable metallic molded bodies, such as nets, sheets, tubs, plates with troughs, etc.} and / or Co ^{a +} ions in complexed form as well as boranates or borazanes and are particularly suitable in this form for amalgam decomposition in an electrolytic cell.

♦ ° In the rim of their compact metallic structure and Excellent adhesion to metallic substrates, they become mechanically through strong gas development not destroyed. In contrast to other active catalysts such as Raney nickel, they are common

♦ Stable for 5 operating temperatures around 100 ° C. As shown in Fig. 1 of the main patent, electrodes that have nickel and / or cobalt boride coatings are very highly resilient with low polarization. It was also found that the catalysts are relatively insensitive to catalyst poisons, including mercury and its compounds.

Since the catalysts can be grown directly on a metallic substrate, the catalyst-coated Electrode can have any shape.

Metallic moldings such as nets, sheets, troughs, plates with channels that run on with catalysts Metal boride-based coatings can be used successfully in amalgam decomposition cells. As an

In order to order, constructions can be selected in which the molded bodies are directly connected to the amalgam Standing touch. It is also possible to accommodate the amalgam and shaped body separately and by means of suitable ones Short-circuit bridges usable electrical energy

to win. In the latter case, there is also a series connection of primary cell and decomposer possible.

Claims (1)

Claim: Use of the air- and storage-stable catalysts based on metal boride for the cathodic evolution of hydrogen in alkaline electrolytes with an activity comparable to Raney nickel, produced by growing red-amorphous, smooth boride layers by depositing the reaction product of water-soluble reducing boron compounds in aqueous solution with nickel or cobalt ion in divalent form in the presence a complexing agent for the metal ion at a concentration of the metal ion in the starting solution of 0.02 to 0.2 mol / l and a complexing agent concentration of 1 to 10 mol / l on a support structure made of metallic or non-metallic substances, with boranates or borazanes in one concentration 0.02 to 0.2 mol / l can be used as reducing agent and a concentration of free metal ions below 10 ¹⁰ mol / l and a temperature below 6O ⁰ C are maintained during the deposition, according to patent 23 07 852.6 for the evolution of hydrogen in amalg amzersetzerzelleri.