NO160766B - STRIP SYSTEM FOR A LOAD TANK. - Google Patents

Description

Method for producing electrodes for water electrolysis.

In the case of water electrolysis tubes, the operating voltage and thus the economy depend on it

electrolytic hydrogen and oxygen production to a decisive extent of the electrodes

nature.

Methods are known for producing such electrodes, where the electrode surfaces are treated with precious metals.

Due to the relatively high precious metal prices, only electrode manufacturing has such

using base metals has become technically interesting. The vast majority of these methods use hot metal melts,

presses and sintering furnaces with protective atmosphere. All of these methods have

however, the disadvantage that they because of

relatively high device costs

rather expensive, as soon as they processed

electrodes exceed a certain size.

For the production of larger electrodes

above all, electrolytic methods have proved beneficial. This cannot

at least due to the galvanic devices due to the great demand from

many companies partly produce in series,

so that the entire facility can practically be obtained

from stock. Even used devices are on the market, and therefore expansion is

or modification of completed facilities for

other uses are always a possibility.

One of these galvanic methods is based on the separation of an alloy —

preferably nickel zinc — on the electrode surface, which is activated by subsequent release of one of the alloy com-

the ponents (zinc). The active metal is returned in porous form, in the aforementioned example nickel. This method offers a special advantage: Namely, if one wanted to produce active surface layers, i.e. layers which reduce the hydrogen overvoltage, in technically usable thicknesses (over 10 microns) directly in aqueous solution, then the layer top building would stop at the moment the first surge-reducing atomic coatings were secreted. In this case, the electric current would serve for useless hydrogen evolution, so that the layer would become very thin and delicate, in other words, this method of production would be prevented by itself.

In contrast, the cathodic separation of an alloy, which does not reduce the hydrogen overvoltage, succeeds with good current yield in practically any thickness. When activated in an alkaline medium, the reverse release reaction takes place during hydrogen evolution, and the faster the more active mass is formed.

Electrodes produced in this way, however, work unsatisfactorily at technical current densities. The electrodes age within a few weeks, and thereby lose their good properties. The most resistant layers have so far been layers which, before activation, consisted of one part nickel and two parts zinc. Significantly softer layers (too high zinc content before activation) mechanically wear down too quickly, and significantly harder layers (too high nickel content before activation ) is only very difficult to activate and, with continuous current loading, produces rising voltages with the operating time.

It was now found that even electrodes with

suitable composition of separated and activated layer is not technically durable enough, on

because the balilute, which is used as an elec-

trolyte, due to the porous nature of the activated layer, the base metal attacks iron, particularly on the anodes. Copper is not suitable as a base metal, because it

solution in the strongly alkaline electrolyte.

Nickel would be suitable as a base metal,

if the alloy layer did not regularly

they have been shown to peel off, at the latest during activation. The thin oxide layer on all nickel surfaces, also on galvanically deposited nickel-plated surfaces, prevents a sufficiently strong adhesion, even after all possible pre-treatments such as pickling or sandblasting

ler connection with the nickel-zinc layer.

The best possible bonding or connection

share with the substrate would be achieved if the composition of the layer could be varied continuously in a direction from the inside out

above, similar to a structure that is obtained by infusing inactive compo-

nents in an active metal. Such electrodes,

e.g. of iron and aluminium, are known.

Through the invention it becomes possible

to produce electrodes for water electrolysis in an economically advantageous manner. The basic idea of the invention is that the composition of the alloy layer is regulated by regulating or changing the bath composition, the temperature and the stirring, but preferably

show by changing the current density, so that the concentration of the active metal de-

comes out towards the surface, whereby after activation you get a layer that is highly porous and active on the surface, but in depth, on the other hand, is so dense and firm that it protects the basic

' the number against all electrochemical attacks.

In this way, without power consumption,

breaking and thereby without inducing a passive layer that reduces the coating strength, first a layer that is so poor in inactive alloy components that it is not attacked and does not become porous during the subsequent activation.

The subsequent layers gradually become continuous

richer in inactive components. After activation, such layers on the surface are me-

get porous and active, but inside the layer the base metal is protected due to the increasingly dense deposit. The galvanic ba-

it preferably contains nickel and zinc.,

For the regulation of layer composition

you have the following options:

1. Changing the bath composition.

2. Change in temperature.

3. Change in current density.

4. Changing the stirring intensity.

The selected regulatory area and the

The most effective method of changing the alloy composition depends on the type of bath.

A suitable bathroom with large regulation

council has the following composition:

310 g/l NiCl,. 6H20

160 g/l ZnCl, anhydrous.

(Anode material: zinc rods and nickel

staves).

The composition of the excreted le-

mitering is affected in the following way:

1. Bath composition:

Increasing the zinc concentration leads,

in the same way as reducing the nickel concentration, to a zinc-richer layer. During the galvanic precipitation, a concentration shift is obtained, as one excludes

known to use zinc anodes.

2. Temperature:

Increasing the temperature results in

separation of nickel-richer layers.

3. The current density:

Increasing the current density increases the zinc content in the layer.

4. Stirring:

An increase in the stirring intensity results in an increased zinc content in the layer.

The regulation of alloy compo-

The process is best done according to method 3,

as the other variables are then kept constant.

Based on the mentioned bath composition, at 60-70° C and not too weak stirring, when the current density is increased from 2 to 12 A/dm, alloy is deposited on iron tin cathodes, where alloy-

layer upon activation with, for example, 20-

sodium hydroxide solution is converted into durable and effective surface layers.

Surprisingly, it has been shown that so-

electrodes produced in this way are not only suitable as cathodes in the technical water electrolysis, but also as anodes. The ano-

where produced according to the new method differs from anodes with uniform porosity throughout the entire layer thickness by its high resistance to anodic corrosion. According to the existing

the method prepared electrodes are

— provided that constant zinc has been deposited

richer layer on nickel-richer layer and not the other way around — preferably durable and absolutely

relatively insensitive to peeling. With water electrolysis, it is therefore possible to achieve

nings of less than 1.8 V at current densities of

2000 A/m-.

Claims (2)

1. Method for the production of electrodes for water electrolysis by electroplating nic precipitation of an activator alloy consisting of one or more active metals such as iron, cobalt or nickel as well as an inactive chemically releasable metal such as zinc, aluminum or tin, on an electrode of the desired shape, characterized in that the precipitation of the alloy layer is regulated by controlled changes in bath composition, temperature, stirring intensity, or preferably current density, in such a way that the concentration of the active metal is brought to decrease towards the surface, whereby the layer after activation becomes highly porous and active on the surface, but increasingly denser and firmer in depth so that the base metal of the electrode is protected against all electrochemical attacks. 2. Method as stated in claim 1, characterized in that the galvanic bath contains nickel and zinc.