JPS58167788A - Highly durable cathode with low hydrogen overvoltage and preparation thereof - Google Patents

Abstract

PURPOSE:To keep hydrogen overvoltage in a cathode low, by coating the surface of the cathode used in electrolysis of an alkali halide aqueous solution with an active layer comprising a mixture of specific metal particles. CONSTITUTION:In preparing the cathode of an electrolytic tank used in electrolysis of an aqueous solution of an alkali halide such as NaCl, a cathode core is plated in a plating bath contg. a plating liquid having dispersed active metal particles of an alloy consisting of a component X comprising Ni or Co, a component Y being selected from Al, Zn and Mg and a component Z being the group IV metal of the Periodic Table such as Ti, Sn and the compsn. of said alloy being within a range surrounded by points A', B', C', D', E' in the drawing (A) or said alloy particles being coated by a melt coating method or a baking method on said cathode core. In this case, the composition of the alloy coated on the cathode should be in an area surrounded by points A, B, C, D, and E in the drawing (A) in order to obtain satisfactory low hydrogen overvoltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly durable low hydrogen overvoltage cathode, and particularly to a low hydrogen overvoltage cathode whose properties are hardly deteriorated even in an oxidizing environment, and a method for producing the same.

Various types of low hydrogen overvoltage cathodes have been proposed, particularly as cathodes for aqueous halide electrolysis. Among these, Japanese Patent Application Laid-Open No. 1127-1987, which the present applicant has already proposed,
Although the electrode disclosed in Publication No. 85 has greater effects in terms of lower hydrogen overvoltage and durability than previously known electrodes, the present inventors have conducted further studies. As a result, we found that some of the electrodes disclosed in the above publications do not always have sufficient durability, and as a result of our earnest efforts to solve this problem, we have arrived at the present invention.

Producing halogen gas from the anode chamber and caustic alkali aqueous solution and hydrogen gas from the cathode chamber by electrolysis in an alkali halide aqueous solution electrolytic cell is already a well-known industrial method for producing chlorine and caustic alkali. As the cathode of this electrolytic cell, the above-mentioned cathode with a low hydrogen overvoltage is preferably used, but the electrolytic cell may be stopped for various reasons during operation, and in this case, when the operation is resumed, the hydrogen An increase in overvoltage was observed. The present inventors investigated this phenomenon in depth and found that the nickel or cobalt in Raney nickel particles or Raney cobalt particles, which are electrode active ingredients, changes into nickel hydroxide or cobalt hydroxide, resulting in a deterioration of electrode activity (i.e. In order to prevent this deterioration, a known method consisting of a first component such as nickel or cobalt and a second component such as aluminum, zinc, magnesium or silver has been discovered. The present invention was completed based on the discovery that the inclusion of a third specific component in the metal particles brings about a remarkable effect. In the electrode formed by exposing on the surface of
Component Y1 selected from magnesium and component 2 selected from group Ⅰ metals of the periodic table are located at the 1-th points A, B, C, and D.
Highly durable low hydrogen overvoltage cathode A which is an alloy in the range surrounded by and E: X = ggWi% y = □wt%
Z = 1wt%13; X == 7gwt%
y = 20wt% z-Iwt%C:) (=5QW
'T;% y=20wt% Z=30wt%D:X,
= 42wt% y = 16wt% z = 42wt%: X: 5Qwt% y = □wt% Z = 50wt
% and a method for manufacturing an electrode in which a part of the electrode active metal particles is exposed on the surface of a layer provided on an electrode core, a component X consisting of nickel and/or cobalt, a component Y selected from aluminum, zinc, magnesium, and The current element z selected from Group II metals of the periodic table is at points A/, B7, C',
The electrode-active metal particles made of an alloy in the range surrounded by D/ and E' are uniformly dispersed in a plating bath and co-electrodeposited on the electrode core, or the electrode-active metal particles are co-electrodeposited on the electrode core. A method for manufacturing a highly durable, low hydrogen overvoltage cathode characterized by melt coating or baking on a core: X = 5gwt% Y =
40wt% Z = IWl;%B', X = 3g
wt% Y= 60wt% Z== Iwt%C'
; X = 25wt% y = 60wt% z
= 15wt% D/: X = 25wt%
Y-=50wt% z=25wt%"':
X==35wt% ”f=40wt% z
= 25 wt%.

Here, FIG. 1 shows a component x1 consisting of nickel and/or cobalt, a component Y selected from aluminum, zinc, and magnesium, and a component Y selected from group Ⅰ metals of the periodic table.
This is a ternary diagram of the combination of metal particles in the cathode of the present invention. The composition must be within the range surrounded by points A, B, C, and D in FIG. Preferably, the range is F, G, H. Here, points F, G, H (
7) The children of X, Y, and Z components are each k (95°0.5),
(85, 10, 5), (46, 10, 44).

The effects of the present invention are due to the inclusion of Group I metals in the periodic table as a proportion of the alloy composition, but why does the inclusion of Group N metals prevent nickel or cobalt from becoming hydroxides? The details of whether this is possible have not yet been clarified. However, the present inventor has found that it is the most suitable among the N group metals. That is, when using titanium and tin among the N group metals, it is possible to maintain a low hydrogen overvoltage for a longer period of time even under more severe environmental conditions.

The reason why it is preferable for the metal particles of the cathode of the present invention to have a composition surrounded by ABCDK in FIG. 1 is because particles having a composition outside the above range may not be able to maintain a low hydrogen overvoltage over a long period of time.

The average particle size of the metal particles mentioned above is also related to the porous dust on the electrode surface and the dispersibility of particles during electrode manufacturing, which will be described later.
A value of 0.1 μ to Zooμ is sufficient.

Among the above ranges, from the viewpoint of the porosity of the electrode surface, Fi is preferably 0.9 μ to 50 μ, more preferably Fi 1 μ to 30 μ.

Furthermore, the particles of the present invention are preferably superficially porous in order to achieve a lower hydrogen overpotential of the electrode.

This surface porosity does not mean only that the entire surface of the particle is porous, but it is sufficient that only the portion exposed from the above-mentioned metal layer is porous.

The degree of porosity is preferably as high as possible; however, if the degree of porosity is too high, the mechanical strength of the particles decreases, so the porosity is preferably 20 to 90%. More preferably 35 to 85% within the above range
, particularly preferably 50 to 80%.

The above porosity is a value measured by a known mercury intrusion method or water displacement method.

Complementary methods can be used to make it porous, but
For example, a method is preferred in which a part or all of the metal of component Y is removed from an alloy consisting of components X, Y, and Z to make it porous.

In such a case, a particularly preferred method is to treat an alloy in which components X, Y, . In the case of the cathode of the present invention, for example, when used as a cathode produced by electrolyzing an aqueous alkali halide solution to produce caustic alkali (I)7, it is not necessarily necessary to treat it with caustic alkali before installing it in an electrolytic cell. Since the catholyte used is under caustic conditions, the gold ingots of component Y are gradually removed during electrolysis and can become the desired cathode.

Various combinations of compositions of the metal particles can be used, and typical examples include N1-AI-Ti.
, Ni-Al2Sn, Ni-Zn-Ti, Ni-Zn
-8n.

Co-Al-Ti, Go-Al-8n, Go
-Zn-Ti, Co-Zn-8n.

Ni-Mg-Ti, Ni-Mg-8n, C
Possible examples include o-Mg-Ti and Co-Mg-8n.

Among these, a particularly preferred combination is Ni-Al-Ti.

Go-AI-Ti.

The conditions for such caustic alkali treatment vary depending on the composition of the starting metal particles, but in the case of metal particles with the composition described below, the caustic alkali concentration (NaOH equivalent) is 10 to 35% by weight and 1 t%, and the temperature is 10 to 50°C. It is preferable to immerse it in a water bath solution for 0.5 to 3 hours.

The reason for this is that component Y was selected to be as easy to remove as possible, and component z1, particularly tin, was selected on the condition that it was to be removed as little as possible.

The layer on which the metal particles are firmly provided on the metal substrate is preferably made of the same metal as component X constituting the metal particles.

Thus, a large number of the above particles are attached to the electrode surface of the cathode of the present invention, and macroscopically, the cathode surface is microporous.

In this way, the cathode of the present invention has a large number of particles containing nickel and/or nickel, which itself has a low hydrogen overvoltage, on the electrode surface, and as mentioned above, the electrode surface is microporous. As the active surface of the electrode becomes larger, the synergistic effect of these effects can effectively reduce the hydrogen overvoltage.

Moreover, the particles of the present invention have a layer made of the above-mentioned metal.
Since it is firmly attached to the electrode surface, it is difficult to deteriorate and can dramatically extend the durability of the above-mentioned low hydrogen overvoltage.

The electrode core of the present invention may be made of any suitable conductive metal, such as Ti, Zr, Fe, or Ni.

A metal selected from V, MO, Cu, Ag, Mn, platinum group metals, graphite, and Cr, or an alloy selected from these metals can be used. Of these, Fe, Fe alloy (Fe,
It is preferable to employ Ni alloy, Fe-Cr alloy, Fe-Ni-Cr alloy, etc.), Ni, Ni alloy (Ni-Cu alloy, Ni-Cr alloy, etc.), Cu, C:u alloy, etc.

Particularly preferred materials for the electrode core are Fe, Cu, and Ni.

The structure of the 0 electrode core, which is a Fe-Ni alloy or a Fe-Ni-Cr alloy, can be made into any suitable shape and size depending on the structure of the electrode used.

The shape may be, for example, plate-like, porous, net-like (for example, expanded metal), or blind-like, and these may be flat, curved, or cylindrical.

The thickness of the layer of the present invention depends on the particle size of the particles employed, but
20~200μ is sufficient, more preferably 25~200μ
150μ, particularly preferably 30-100μ. This is because, in the present invention, some of the particles described above are embedded in the metal layer on the electrode core and are attached in the fc state.

Is it in a state of being? For ease of understanding, a cross-sectional view of the electrode surface of the present invention is shown in FIG. As shown in the figure, a layer 2 made of metal is provided on an electrode core 1, and a portion of electrode active metal particles 3 are contained in the core layer from the surface of the layer. The proportion of particles in layer 2 is preferably 5 to 80 wt%, more preferably 10 to 5 Q wt%.
%. In addition to this state, N"i, Go, Ag, Cu is present between the electrode core and the layer containing the particles of the present invention.
By providing an intermediate layer made of a metal selected from the following, the durability of the electrode of the present invention can be further improved. Such an intermediate layer may be of the same type or different metal from the above-mentioned layer, but from the viewpoint of adhesion of the intermediate layer with the above-mentioned layer, the metal of these intermediate layers and layers may be Preferably, they are of the same type. It is sufficient for the thickness of the intermediate layer to be 5 to 100 microns from the viewpoint of mechanical strength, more preferably 20 to 80 microns, and sometimes preferably 30 to 50 microns.

A cross-sectional view of one electrode is shown in FIG. 3 to facilitate understanding of the electrode provided with such an intermediate layer.

1 is an electrode core, 4 is an intermediate layer, 2 is a layer containing particles, and 3 is the particle of the present invention.

The electrode of the present invention is the second one. As is clear from Figure 3, when looking at the surface microscopically, many particles are exposed on the electrode surface, but when looking macroscopically, the surface is porous. .

As mentioned above, the degree of porosity is also related to the reduction in hydrogen overvoltage, so the degree of porosity is 1000μF in electric double layer capacity.
/ct/ or more can sufficiently achieve the purpose. In the above range, preferably 2000μII'/crA or more,
Particularly preferably, it is 5000 pF/.d or more. The electric double layer capacity is calculated as follows when the electrode is completely immersed in an electrolyte solution.
This is the capacitance of an electric double layer formed by positive and negative ions relatively distributed over a short distance in the vicinity of the electrode surface, and more specifically, it shows the actually measured differential capacitance.

This capacitance increases as the electrode surface becomes larger.

Therefore, when the electrode surface becomes porous and the electrode surface area increases, the electric double layer capacity of the electrode surface also increases. Therefore,
The electric double layer capacity determines the electrochemically effective electrode surface area, that is, the degree of porosity of the electrode surface.

Note that the electric double layer capacity varies depending on the temperature at the time of measurement, the type of electrolyte solution, the concentration, the electrode potential, etc., so the electric double layer capacity of the present invention means a value measured by the following method.

The test piece (electrode) was soaked in a 40 wt% NaOH aqueous solution (2
A black platinum plate with an apparent area approximately 100 times that of the test piece was inserted as a counter electrode, and the cell impedance in this state d was measured using a Kohlrausch bridge. Find the electric double layer capacity.

Various methods can be used to specifically attach the electrode surface layer, such as a dispersion plating method, a melt coating method, and a baking method.

Among these, the dispersion plating method is particularly preferable because the particles of the present invention can be adhered to the method well.

The dispersion plating method is a method in which plating is performed using an electrode core as a cathode in an aqueous solution containing the metal forming the metal layer, for example, a bath in which nickel-based particles are dispersed. The above metal and particles are co-electrodeposited.

To be more specific, it is considered that the particles adsorb metal ions in the bath and adhere to the core body through charge retention and electrophoresis, and metal plating is performed at the same time. For example, when a nickel layer is used as the metal layer, a total nickel chloride bath, a high nickel chloride bath, a nickel chloride-nickel acetate bath, etc. can be used. When a cobalt layer is used as the metal layer, a total cobalt chloride bath, a high chloride cobalt bath, a cobalt chloride-cobalt acetate bath, etc. can be used.

In this case, the pH of the bath is important. In other words, the electrode-active metal particles dispersed in the plating bath generally have oxygen attached to their surfaces, and in this state, the bonding with the metal layer is not sufficient, and the particles may become loose during use as an electrode. In order to prevent this, it is necessary to reduce the amount of oxygen attached to the surface of the particles, and for this purpose, the pa? It is preferable to set it as 1.5-10.

In the case of the present invention, the metal particles include component x1 consisting of nickel and/or cobalt, aluminum, zinc,
Component Y selected from magnesium and component 2 selected from metals from group Ⅰ of the periodic table are points A', B', and
It is necessary that the alloy be in the range enclosed by C', D', and /Te. The reason for this is that if it deviates from this range, it may not be possible to ensure sufficient adhesion during the electrodeposition process, or the activity for electrodeposition may not be sufficient.

Therefore, if there is a slight deviation from the range shown by A' to E', the initial hydrogen overvoltage will be a little high and the resistance to oxidation due to short circuits, which will be described later, will be reduced. Therefore, it can no longer be put to practical use.

As mentioned above, it is preferable from the viewpoint of adhesive strength of the particle that the surface portion of the particle that comes into contact with the gold i-layer has a small amount of attached oxygen. It is preferable to form a film for stabilization. When the electrode is used as a cathode for electrolysis of an aqueous alkali chloride solution, the oxide film adhering to such particles is reduced and removed by generated hydrogen. Before use as the outer electrode, any oxide film can be removed by reduction (for example, by heating in a hydrogen atmosphere). .

The proportion of such particles in the bath ranges from 1 v/l to 2001/l
It is preferable to keep the temperature at 1 from the viewpoint of improving the adhesion state of particles to the electrode surface. Also, the temperature conditions during dispersion plating work are 20-80℃, and the current level is lA/drr? ~20A/
drrr? It is preferable that

It goes without saying that additives for reducing strain, additives for promoting co-electrodeposition, etc. may be added to the plating bath as appropriate.

In addition, as mentioned above, when providing an intermediate layer between the electrode core and the metal layer containing particles, the electrode core is first plated with N1, CO, or Cu, and then the aforementioned dispersion plating method or melt spraying is applied. forming a metal layer containing particles thereon by means of a method;

In such a case, the plating bath described above can be used as the plating bath, and a known plating bath can also be used for Cu plating.

In this way, an electrode is obtained in which the particles of the present invention are adhered to the electrode core via the metal layer.

It is also effective to attach a non-electronically conductive substance to the surface of the low hydrogen overvoltage cathode thus obtained.

When the cathode of the present invention is used, for example, as a cathode for electrolysis of a 210 alkali aqueous solution, iron ions or iron-containing ions eluted from the surrounding battery material may be present in the catholyte, and these may be present on the cathode. A discharge may occur and iron compounds (eg iron hydroxide) may be deposited on the cathode. In this case, the active surface of the cathode is lost 1 and the cathode overvoltage increases.

In order to prevent such discharge precipitation, a non-electronically conductive substance such as a fluorine-containing resin (Teflon, etc.) is attached on the cathode of the present invention and further on the metal particles protruding from the cathode surface. This is effective. As a specific means for this purpose, a method as disclosed in Japanese Patent Application No. 126921/1988 can be preferably adopted.

The resulting cathode is then optionally treated with caustic alkali (e.g., immersed in an aqueous caustic solution) to elute and remove at least a portion of the metal of component Y in the alloy particles, thereby making the particles porous. Make it.

The conditions for this case are as described above.

In addition, when an alloy of the components X, Y, and Z described above is used as particles, it is preferable to perform the caustic alkali treatment as described above, but the electrode with such particles attached is not subjected to any caustic alkaline treatment and is left as is. It may be attached to an alkali chloride electrolytic cell to actually perform electrolysis.

If so, during the electrolysis process, component Y will be eluted under the supervision of the metal force,
Electrode overvoltage decreases. However, although the aqueous caustic alkaline solution produced is slightly contaminated by the eluted metal ions of component Y, this generally does not pose a problem.

The electrode of the present invention can of course be used as an electrode for ion-exchange membrane-based alkaline chloride aqueous solution electrolysis, especially as a cathode, but it can also be used as a porous diaphragm (e.g. asbestos diaphragm).
It can also be employed as a 9-electrode for electrolysis of aqueous salt and alkali solutions using .

Next, Examples 1 to 10 of the present invention will be described with reference to Examples 1 to 10. An alloy powder (200 mesh bath) having the composition shown in Table 1 was prepared and prepared.
According to Example 12 of Publication No. 4-112785, and for Examples 9.10, Example 12ONi(:l
, -6H,O to COCl, -6H,0 (concentration aoor/
J), a low hydrogen overvoltage electrode was manufactured using a dispersion plating method based on a different plating method (however, the development temperature after plating was 50° C.) using a Ni plate anode and a '6GO plate anode.

A part of the metal particles on the obtained electrode was peeled off and its composition was investigated. The results are also listed in Table 1. Next, these electrode gold and anode f RuO2-TiO2
Fluorine-containing cation exchange membrane (CF manufactured by Asahi Glass):
CF2 and OF2. ,=CFO(CF2)3COOCH
Copolymer with 3, ion exchange capacity 1.45 meq/'
Resin) T An ion exchange membrane was used as a cathode for a salt electrolytic cell, and a short circuit resistance test was conducted. The anolyte is 3N
NaCl solution, catholyte 35% NaOH, 90
Current density 20 A/an? The following short circuit test was conducted three days after the start of electrolysis.

First, stop the power supply from the DC power supply, connect the anode and cathode outside the battery case with a copper conductor, and then
It was left for 5 hours. During this time, the current flowing from the cathode to the anode was observed. In addition, the temperature of the interstitial polar liquid was 90℃ for about 3 hours after electrolysis was stopped.
and then allowed to cool naturally. After leaving to cool for 15 hours, the 'wIL sample was taken out and the hydrogen overvoltage was measured. The results are shown in px. This is almost the same as the pre-test performance.

In addition, the electrode of Example 2 was placed in a 40-inch NaOH aqueous solution for 1 hour.
It was immersed for one week at 00°C. In order to ensure sufficient contact with air, the depth of the container was made shallow to 7α, and the top of the container was left open. The hydrogen overvoltage of this electrode was measured before and after the immersion test. The hydrogen overvoltage was 0.09V, which was almost unchanged before and after the test.

Comparative Examples 1 to 2 Comparative Example 1 follows Example 12 of JP-A-54-112785, and Comparative Example 2 follows NiCl2・0H20iCOCI□・6H20 in Example 12 of the same publication.
(+# degree 300 v/l), a plating method in which the Ni plate anode was replaced with a Go plate anode, and Ni-Al
and a Co-A1 alloy powder dispersion plated electrode was manufactured.

A portion of the obtained 1[superior metal particles was peeled off and its composition was investigated. The results are also listed in Table 2.

A short circuit test was conducted in the same manner as in Examples 1 to 10, and changes in hydrogen overvoltage before and after the test were measured. The results are shown in Table 2. Note that the hydrogen overvoltage before the test was 0.07 to 0.0 sv.

Comparative Examples 3 to 9 Cathodes were manufactured in the same manner as in the example except that the composition of the alloy powder was changed to Comparative Examples 3 to 9 in Table 2. (However, the development processing conditions were NaOH concentration 4Qwt%.

The temperature was 120°C for 5 hours. ) The results of the short circuit test conducted in the same manner as in the examples are shown in Table 2.

The hydrogen overvoltages before the short-circuit test were 0.18V, 0.18V, 0.21V, and 0.1V for Comparative Examples 3 to 9, respectively.
16■.

0.10V, 0.09V, 0.09V.

Table 1 Table 2 ■1 The adhesion strength and mechanical strength of the alloy particles were poor, and the alloy particles peeled off severely during the electrolytic work of the short circuit test. Therefore, the composition of the alloy particles and the hydrogen overvoltage after the test were not measured. There wasn't.

[Brief explanation of the drawing]

In FIG. 1, X: Ni or Ti, Y=Al or Zn. Z: The composition in the range surrounded by points A, B, C, D, and Pc in the diagram consisting of the three components of Ti or Sn indicates the composition of the electrode active particles of the cathode of the present invention. FIG. 2 is a partial cross-sectional view of the surface of an example of the electrode of the present invention, and FIG.
The figures show partial surface cross-sectional views of other examples of the electrode of the present invention. FIG. 4 shows: X-Ni or Ti, Y==AI or Zn. The composition range surrounded by points A', B/, C/, D/, and E' in the diagram consisting of the three components Z, = Ti or Sn is the composition range of the electrode active particles used in the method of the present invention. show. 111-X (%) years old/[4 years old 24 years old 3ylX Oh! + conquest

Claims (1)

[Scope of Claims] (Re) An electrode in which a part of electrode active metal particles is exposed on the surface of a layer provided on an electrode core, wherein the electrode active metal particles are composed of nickel and/or cobalt x1 aluminum An alloy in which the component Y1 selected from lzinc, magnesium, and the component 2 selected from group Ⅰ metals of the periodic table are in the range surrounded by points A; B, C, D, and E in Figure 1.
- Highly durable low hydrogen overvoltage cathode. ＼ A:X =99wt%y=oz=1wt
-%-B: ) (=7gwt%y = 20wt%
z-Iwt%C:X-50 loading%y]=zowt%z
:=: 3wt%D; X = 42wt%y
:: 16Wt,%z=42wt%K: x-s
owt% y=oz=sowt% (2) The highly durable, low hydrogen overvoltage cathode according to claim (1), wherein the Group N metal of the periodic table is titanium and/or tin. (3) In a method for manufacturing an electrode in which a part of the electrode active metal particles is exposed on the surface of a layer provided on an electrode core, component x1 consisting of nickel and/or cobalt, component Y selected from aluminum, zinc, and magnesium. and component 2 selected from group Ⅰ metals of the periodic table are points A・, B・, etc. in the figure.・
. The electrode active metal particles consisting of an alloy in the range surrounded by D' and E' are uniformly dispersed in a plating bath and co-electrodeposited on the electrode core. A method for producing a highly durable and low hydrogen overvoltage cathode, which comprises melting and applying or baking electrode active metal particles onto the electrode core. A′ 2 ](= 59”t% Y= 40
wt% Z: , wt%13/: X=3
9wt%Y=60wt%Z=Iwt%C': X
== 25wt%'f = 60wt% Z=15wt
%D': X= 25wt% Y=50wt% Z=
25wt% [/: X: 35wt%Y= 4 oet
% z = 25 wt% (4) The method for producing a highly durable and low hydrogen overvoltage cathode according to claim (3), wherein the metal of Group Ⅰ of the periodic table is titanium and/or tin. (5) The method for producing a highly durable and low hydrogen overvoltage cathode according to claim (3) or (4), wherein the plating bath contains metal ions of the same type as component X. (6) The method for producing a highly durable and low hydrogen overvoltage cathode according to any one of claims (3) to (5), wherein the plating bath has a pH of 1.5 to 3.0. (7) Electrode active metal particles co-electrodeposited, melt-coated or baked at NaOH concentration lO~35%, temperature 10~50
A method for producing a highly durable and low hydrogen overvoltage cathode which is treated in a caustic soda aqueous solution at 0.5 to 3 hours.