JPS5935690A - Low hydrogen overvoltage cathode - Google Patents

Abstract

PURPOSE:To provide a titled cathode which can maintain a low hydrogen overvoltage characteristic for a long period of time, by the constitution wherein the parts of a high hydrogen overvoltage are dispersed on the electrolytic surface placed oppositely to an anode and the deterioration of an active cathode owing to the impurities in the catholyte is prevented. CONSTITUTION:A material of a low hydrogen overvoltage such as metals of Pt groups, Ni, Co, Cu, Ag, etc., or their alloys, compds., etc. is installed by spraying or the like on an electrode base material of iron or the like, whereby an active cathode is obtd. Materials of a high hydrogen overvoltage such as metals or various compds. of Ni, Ti, Ag, etc. are adhered here and there by spraying or the like on the side of the active cathode facing oppositely to the anode. The parts of the high hydrogen overvoltage are provided preferably at about <=50% of the entire surface of the cathode, and the size of the spot is made preferably about <=20mm. and the distribution thereof approximately uniform. The impurities in the catholyte deposit as acicular crystals in these parts of the high hydrogen overvoltage, whereby the activity of the cathode is maintained for a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a low hydrogen overcharge, pressure cathode, especially in an aqueous solution.
The present invention relates to a negative ffK for electrolysis that can maintain excellent low hydrogen overvoltage characteristics over a long period of time.

Conventionally, electrolysis of an alkali metal salt solution using a diaphragm (including a porous diaphragm such as asbestos diaphragm and a dense diaphragm such as an ion exchange membrane) has been known as a technique for generating hydrogen gas at a cathode. This also applies to electrolysis, etc.

In recent years, from the viewpoint of energy saving, it has been desired to reduce the electrolysis voltage in this type of technology, and various active cathodes have been proposed as a means for reducing the electrolysis voltage.

Although these active cathodes contribute to effective pressure for electrolysis, they generally deteriorate quickly and often become unusable in a relatively short period of time. Currently, various aspects such as the selection of new coating materials, processing methods, and cathode shapes are being investigated as life-extending measures.

The present inventors have conducted various studies on the influence of impurities in the solution as a cause of deterioration of the active cathode, and have recognized that imparting specific properties to a portion of the cathode surface can contribute to prevention of deterioration.

That is, more specifically, in studying how to prevent deterioration of the active cathode due to impurities in the catholyte in alkaline chloride aqueous solution electrolysis, it was found that the side of the active cathode facing the anode tends to deteriorate;
Although the deterioration of this surface progresses over the entire y surface, it was discovered that the progress of deterioration could be significantly delayed by providing a portion with a high hydrogen overvoltage on this surface, and based on this, the present invention was completed. Ta.

The main feature of the present invention is a low hydrogen overvoltage cathode in which hydrogen overvoltage sections are interspersed on the electrolytic surface facing the anode, and this will be described in detail below.

As the electrode base material used in the present invention, many materials such as iron, copper, nickel, alloys containing these, and valve metals can be used.

Substances with cathodic activity, ie, low hydrogen overvoltage, are placed on these substrates by various methods.

Installed on the base material 4. There are many methods to do this, including pyrolysis, immersion in molten material, 1b, air plating, and adhesion.
Examples of the method for lowering the hydrogen overpressure include PT group N1 and CO. Cu A
, g metals, alloys, compounds (oxides, sulfides, carbides,
Many materials such as borides and nitrides can be used - active cathodes made from these materials can be used as is.
If used in this condition, impurities in the solution will cause deterioration. Impurities in the solution that degrade the active cathode include H.
Examples include Fe, Pb, Ni, Co, etc.

In general, many iron alloys are used as cathode materials or cathode chamber materials, and since iron has a high solubility in alkalinity, Fe is a typical impurity.
can be mentioned.

Generally speaking, the impurity concentration has no effect on the deterioration, and the degree of deterioration decreases as the impurity concentration becomes low (the degree of deterioration decreases as the impurity concentration increases, but the influence is observed even in lOOppbn-goo).

In particular, when the impurity is Fe, L in the caustic soda becomes a trap.
When i'e is 0.5 pp, in the case of an inactive cathode, while Fe has activity on the membrane surface of the cathode, it is only slightly attached to the cathode surface. Sword-shaped crystals are not recognized.

If areas with high hydrogen overvoltage are scattered on the membrane side of the active cathode, needle-shaped Fe crystals will form in these areas (however, they will not adhere to the active cathode surface unless there are areas with high hydrogen overvoltage). This decreases significantly in comparison.

Fe in caustic soda is 0. Evaluated when less than lppm [
When continuous operation is performed for a long period of time, the cathode activity continues for a longer period of time between the case of only an active cathode and the case of a cathode with scattered areas of high hydrogen overvoltage.

In this case, the part where the hydrogen overvoltage is high means the part which is higher by 0.05 V or more, or more preferably by 0.10 V or more, than the low hydrogen overvoltage part at the same W and flow density.

The hydrogen overvoltage is preferably 50 cm or less on the entire surface of the cathode, and 1-< is preferably 60 cm or less as it does not affect the cell voltage. Further, the preferable lower limit is 0.01% or more, particularly preferably 1% or more, and if the number of high hydrogen overvoltage points is too small, the effect P11 of the present invention, that is, the sustained effect of low hydrogen overvoltage characteristics, tends to not be exhibited. If the amount of backwashing is too large, the cathode itself will lose its low hydrogen overvoltage characteristics, which is not preferable.

7. The shape of the dots may be linear, circular, angular, etc. However, in the case of an active cathode having a large area, it is desirable to have a substantially uniform distribution. If the distribution is too non-uniform, the overall current distribution will be non-uniform, which will cause an increase in sliding voltage.

The size of these points (the width of the line if it is linear, the diameter if it is circular, and the length of the short side if it is square) varies depending on the application, but it is preferably 20 or less, particularly preferably 5 or less, and the preferable lower limit is about 05 or less from the viewpoint of cathode production.

The positions of the low hydrogen overvoltage part and the high hydrogen overvoltage part on the cathode surface facing the anode may be such that the high part protrudes toward the anode side, is on the same plane, or is recessed, but may be slightly Preferably, it protrudes.

One way to scatter areas with good hydrogen overvoltage on the cathode, which has low hydrogen overvoltage, is to spray a material with high hydrogen overvoltage,
Welding, plating, etc. may be used to attach dots, or hydrogen permeation may be applied.
Various methods can be adopted, such as welding a thin porous mesh such as L River, or cutting off a predetermined part of the low hydrogen overvoltage cathode to expose a high part.

Substances with high hydrogen overvoltage include Ni, Ag, and Ti.
If these substances are present, the surface should be as uniform as possible and the surface area should not increase. If the surface area is increased too much, the overvoltage will decrease due to this effect, so care must be taken.

The most suitable example of the use of the cathode of the present invention is in aqueous caustic solution, and it is used as a porous substrate (expanded metal, woven net, mesh, punched plate, etc.) to provide alkali resistance. Considering Ni-containing award 1 [1
A Ni alloy with a concentration of L% or more is preferably used, and the surface is activated to give a low hydrogen overvoltage ignition, and a hydrogen overvoltage part with high alkali resistance is formed at a desired location on the surface facing the anode. You can get good results.

As explained above, the present invention makes it possible to obtain a long-life active cathode for hydrogen generation in which deterioration due to impurities in the solution is reduced by dotting the surface facing the anode with areas with high hydrogen overvoltage. This is an invention with extremely high utility value.

The present invention will be explained below with reference to Examples and Comparative Examples.

Example 1 and Comparative Example 1 After sandblasting a 32-meter round Ni round bar, apply Ni to Komata.
-A1,6:4 weight ratio, particles with an average particle size of 2 to 3μ are sprayed to a thickness of about 150μ using plasma (-).

After bath irradiation, baking in Ar atmosphere at 650℃ x 6H, 80℃,
2411 soaked in 50% NaOH.

1 (11% was exposed, and the rest was covered using Teflon tube depth and Teflon tube.

This thing has a position of 6 o x; 2 o chi K (in use, 20
A/ds” TeHg/Hg□mJtjwo Standard 11
Cl, was measured. (Initial potential) Next, in 30% Na11 containing 40 kg of F, the opposing electrode was a Ni plate, and the current density was 10 A/dn.
2, hydrogen generation was performed 5011 times and the cathode potential was measured. (
Intermediate potential J Then, 50 H hydrogen was generated and the cathode potential was measured <4 final potential) (Example 1) N
Table 1 does not show the results for those that did not exceed 0.5"" $1 (Comparative Example 1).

Table 1 Example 2 and Comparative Example 2 φNi Marukami was sandblasted for 6.2 minutes.
Next, dilute 11 reagent with ethyl alcohol in 81/1 (R
Add rapenodar to 1 olll of solution dissolved in
111! The mixture was added and mixed to form a coating liquid, which was applied to the above-mentioned round bar and deposited in an electric furnace at 5511°C for 5 minutes. This operation was repeated 15 times, and the final firing was performed for 3D minutes.

The same experiment as in Example 1 was conducted on the round bar with a 0.5 wt Ni wire attached to 5% of the tip (Example 2) and without it (Comparative Example 2).

The results were as shown in Table 2.

Table 2 Example 6 and Comparative Example 6 Using 6.2 mm φ Nonisokel nine rods, dispersion plating was applied to it according to the following recipe and processing conditions, and Ni-8;
Plating (plating using a sulfur-containing Ni plating bath) was applied repeatedly as follows.

Dispersion plating (411 minutes) Ni-8 plating (20 minutes) → Dispersion plating (40 minutes) → Nj-8 plating (40 minutes)
Dispersion plating> Nickel sulfate 849/1 Nickel chloride 5011/1 Boric acid 50 11/
Potassium monochloride 611/1 Anomone chloride 4.5 g/l Activated carbon 20 g/l (KV-5 manufactured by Duphasical Chemical KK) Sulfur Copper 4rlO"V/l! Plating bath circle (35 Mating electrode Electrolytic nickel plate Temperature: 40°C Plating current density: 48/d 2 (Ni-8 plating) Dispersion plating with activated τ removed from charcoal and copper sulfate, replaced with urea added to a concentration of 20171, and other The conditions are the same.

From the tip of this round bar, remove the dispersed plating layer from the entire circumference for about 1 minute using a 5mm ('r-1 phantom) knife.
The Ni base material was exposed. (Example 3) Each potential was measured under the same conditions as in Example 1.

One that does not expose the Ni base material when the tip is closed (Comparative Example 3)
Table 5 shows the results compared with -1゜Table 3 Example 4 and Comparative Example 4
Made of lath net (length of the mesh in the short side force direction: 8 W) 3 m
m x mesh longitudinal length LW) 8 length x thickness t) 1
The same Ni-AI plasma spray as in Example 1 was applied to the area (mm
A 1μ coating was applied. This was calcined in the same manner, and Na ('V was removed during use).

Thus, 1] - Dot a Ni welding rod of 1 mm φ on the anode of the cathode on the 5th side at a pitch of 10 (staggered arrangement). Ta.

The size of the dots was 15 to 2.1 mm, and the crystallinity was 0.2 to 12 mm protruding from the cathode surface.The cathode 4 was installed in an ion exchange membrane electrolytic cell at 9oC and filtered at 0. %NaOH-3
(Example 4) Electrolytic operation of Na1JL aqueous solution was carried out under the conditions of lA/di. (Example 4)
The rho degree is 2.3 to 04 strokes/l, and before the start of operation and after operation 6
Sora after 01-1.

An example of electrolysis using a small cathode (
Comparative Example 4) Both are shown in Table 4.

Table 4 Example 5 and Comparative Example 5 Each plating bath of Example 6 was applied 4 times a month under the same plating conditions.
DM size 5US310s lath net (SW3mxLW5
g×t ImmxSl, 5 battles) with dispersion plating and Ni-8
The matsuki was applied repeatedly.

After plating, Ni welding of 1 mm diameter was performed in 10 pitches in the vertical direction of this cathode.

Electrolytic operation similar to that in Example 4 was carried out using such a cathode. (Example 5) The results of each potential in this electrolysis were
The results of a similar electrolysis example (Comparative Example 5) using a cathode without spot welding are shown in Table 1.

Table 5 Patent applicant name Toagosei Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. A low hydrogen overvoltage cathode with high hydrogen overvoltage areas scattered on the electrolytic surface facing the anode.