JPH02104686A - Cathode having low hydrogen overvoltage and high durability and production thereof - Google Patents

Abstract

PURPOSE:To obtain a cathode having low hydrogen overvoltage and high durability as a cathode for electrolyzing an aq. alkali halide soln. by coating an electrode core by plating with metal particles having activity as an electrode and contg. a hydrogen occluding metal having a specified compsn. CONSTITUTION:The surface of an expanded Ni core is electroplated in an Ni plating bath contg. fine powder of a misch metal-contg. hydrogen occluding alloy having a compsn. represented by formula I and Raney nickel or Raney cobalt to coat the core with Ni-based metal particles having activity as an electrode and contg. 5-90wt.% said hydrogen occluding alloy and Raney nickel or Raney cobalt. A cathode having low hydrogen overvoltage and hardly undergoing deterioration even in an oxidizing environment is obtd. This cathode is used in an electrolytic cell in which an aq. soln. of an alkali metal halide such as NaCl is electrolyzed to produce gaseous Cl and NaOH.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a highly durable low hydrogen overvoltage cathode, and particularly to a low hydrogen overvoltage cathode whose characteristics are extremely minimally deteriorated even in an oxidizing environment, and a method for producing the same.

(Prior Art) Various types of low hydrogen overvoltage cathodes have been proposed, particularly as cathodes for aqueous halogenated alkali solution 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 overvoltage will be low. was observed to increase. The present inventors investigated this phenomenon in depth, and found that when the electrolytic cell is stopped by short-circuiting the anode and cathode with a bus bar, the cathode is oxidized by the reverse current generated during the short circuit, and nickel and In the case of a cathode containing cobalt as an active ingredient, the electrode activity decreases due to the deterioration of cobalt into hydroxides, and the cathode does not return to its original active state even after restarting operation (that is, the hydrogen overvoltage reaches its upper limit). I found out.

In addition, even in the stopping method of stopping current supply without shorting the anode and cathode, if the cathode is immersed in high-temperature, high-concentration N, 011 for a long time, if the cathode active component is nickel or cobalt, it will corrode. It was discovered that the electrode activity decreases when exposed to electric potential (this reaction is also a type of electrochemical oxidation reaction) and changes into hydroxide.

(Problems to be Solved by the Invention) The present invention provides an electrode whose electrode activity does not decrease even under the above conditions of use, and a method for manufacturing the same.

(Means for solving the problem) Therefore, as a result of intensive studies to prevent this phenomenon, we decided to use a hydrogen storage metal that electrochemically absorbs and releases hydrogen and has a low hydrogen overvoltage as part or all of the electrode active component. When the battery is stopped as described above, a large amount of hydrogen stored in the hydrogen storage metal is electrochemically oxidized, thereby effectively preventing the oxidation of the electrode active component. The present invention has been completed based on the discovery that the electrode active metal particles can be maintained for a long period of time. The gist of the present invention is to provide a highly durable low hydrogen overvoltage cathode, a part of which is a hydrogen storage metal that can electrochemically absorb and release hydrogen, and a method for producing the above highly durable low hydrogen overvoltage cathode described below.

Here, the hydrogen storage metal that can electrochemically store and release hydrogen refers to a metal that undergoes the following electrode reaction in an alkaline aqueous solution. That is, in the reduction reaction, hydrogen atoms generated by reducing water are occluded in the metal, and in the oxidation reaction, the occluded hydrogen is reacted with hydroxide ions on the metal surface to form water. The reaction formula is shown below.

M is a hydrogen storage metal, and Mllx represents its hydride. For example, when salt electrolysis is carried out by ion removal using a cathode in which this hydrogen storage metal is used as part or all of the electrode active particles, hydrogen is present in the hydrogen storage metal due to the rightward reaction of reaction formula (1) at the initial stage of energization. When the hydrogen storage reaches saturation, hydrogen is generated on the surface of the hydrogen storage metal by reaction (2) shown below, and the original electrode reaction on the cathode proceeds.

1I20+e→Area 11□+O1+-(21On the other hand, when the hydrogen is stopped due to a short circuit in the stack, a large amount of hydrogen stored in the hydrogen storage metal electrochemically releases hydrogen through the leftward reaction of reaction formula (1). That is, by electrochemically oxidizing hydrogen and applying an oxidation current, oxidation of the electrode active particles themselves can be effectively prevented.

As described above, the vine hydrogen storage metal used in the present invention is capable of electrochemically storing and releasing hydrogen,
Specifically, MmzNia-+m□-^IxMy (M
m: Mitsushi metal, M is Mn, Cu, Cr.

One or more elements selected from Co, Ti, Nb, Zr, and Si, and 0.7≦Z≦1゜0<
x<3. O<y<3.0<x+y≦3. ) is a Mitsushmetal nickel multi-component alloy. Z＞
In No. 1, there is a problem in the corrosion resistance of the hydrogen storage metal in a caustic alkaline solution, and it cannot withstand long-term use. When x=y=o, the equilibrium pressure of the hydrogen storage metal is high, and the effect of preventing oxidation of the electrode active particles as described above is small.

Also, Z<0.7. When x+y>3, the amount of hydrogen stored and stored in the hydrogen storage metal decreases, and the effect of the present invention becomes insufficient. Therefore, 0.7≦Z≦1, 0<x<3.
O<y<3. It is necessary that O<x+y≦3,
Preferably 0.8≦Z≦0.95.0.25≦x+y≦
It is 2.5.

The electrode active metal particles used in the present invention are made of the above-mentioned hydrogen storage metal and Raney nickel and/or Raney cobalt, which have a low hydrogen overvoltage. In order to achieve the stated purpose, the hydrogen storage metal should be used in an amount of 5 to 90 w in the electrode active metal.
Preferably, L% is present, particularly 10 to 80 wt%. This is because if the proportion of the hydrogen storage metal is less than 5 wt%, the amount of hydrogen released during a short circuit is small, and the short circuit oxidizes the active components of nickel and cobalt, reducing electrode activity and increasing the hydrogen overvoltage. Also 9
This is because when it exceeds 0 wt%, the proportion of Raney nickel and/or Raney cobalt, which have a low hydrogen overvoltage, becomes small, resulting in an increase in the hydrogen overvoltage.

In addition, these hydrogen storage metals are known to cause brittle fracture and become pulverized due to absorption and release of hydrogen, so in order to prevent them from falling off due to pulverization, it is necessary to crush them mechanically or to pulverize hydrogen in the gas phase in advance. A metal that has been pulverized by repeated occlusion and release of gas may be used, or in order to prevent this from falling off, in addition to the Raney nickel or Raney cobalt as the matrix material, metal particles 1 such as nickel powder or polymer powder as a binder may be used. Good too.

The average particle size of the above-mentioned hydrogen storage metal particles is related to the porosity of the electrode surface and the dispersibility of the particles during electrode production, which will be described later, but a range of 0.1 to 100 μ is sufficient.

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

Furthermore, the particles used in 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 one particle is porous; it is sufficient that only the portion exposed from the layer made of the metal described above is porous.

The degree of porosity is preferably as large as possible; however, if the degree of porosity is excessively large, the mechanical strength of the layer provided on the electrode core will decrease.
It is preferable to set it to 0-90%. In the middle of the above range, preferably 35 to 85%, particularly preferably 50 to 80%.

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

The layer on which the electrode active metal particles are firmly provided on the metal substrate is preferably made of the same metal as part of the components constituting the 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, in the cathode of the present invention, a large number of particles having a low hydrogen overvoltage are present on the electrode surface, and as mentioned above, the electrode surface is microporous, so the active surface of the electrode becomes larger. , due to these synergistic effects,
It is possible to effectively reduce hydrogen overvoltage.

Moreover, since the particles used in the present invention are firmly attached to the electrode surface by the layer made of the above-mentioned metal, they are difficult to deteriorate and can dramatically extend the sustainability of the above-mentioned low hydrogen overvoltage.

The electrode core of the present invention is made of any suitable conductive metal such as Ti, Zr, Fe, Ni, V,
Mo.

A metal selected from Cu, Ag, Mn, platinum group metals, graphite, and Cr, or an alloy selected from these metals can be used. Among these, Fe, Fe alloy (Fe-Ni alloy).

Fe-Cr alloy, Fe-Ni-Cr alloy, etc.),
It is preferable to use Ni, Ni alloy (Ni-Cu alloy, Ni-Cr alloy, etc.), Cu, Cu alloy, etc. Particularly preferable electrode core materials include Fe, Cu, Ni,
These are Fe-Ni alloy and Fe-Ni-Cr alloy.

The structure of the electrode core can be made into any suitable shape and size depending on the structure of the electrode used. Its shape can be, for example, plate-like, porous, net-like (for example, expanded metal), or blind-like.
It may be made into a cylindrical shape.

The thickness of the layer of the present invention depends on the particle size of the particles employed, but
20μ to 2mm is sufficient, more preferably 25μ
~1 mm. This is because in the present invention, some of the particles described above are buried in a layer made of metal on the electrode core.
This is because it causes the particles to adhere. In order to facilitate understanding of this state, 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 part of electrode active metal particles 3 are contained in this layer so as to be exposed from the surface of the layer. The proportion of particles in layer 2 is preferably 5 to 80 wt%, more preferably 10 to 60 wt%. In addition to this state, Ni, Co,
By providing an intermediate layer made of a metal selected from , Cu, the durability of the electrode of the present invention can be further improved. Such an intermediate layer may be of the same type or a different type from the metal of the above-mentioned layer, but from the viewpoint of adhesion between the intermediate layer and the above-mentioned layer, these intermediate layers and the metals of the layer should not be of the same type. It is preferable that there be. It is sufficient for the thickness of the intermediate layer to be 5 to 100μ from the viewpoint of mechanical strength, etc.
More preferably 20-80μ, particularly preferably 30-5
It is 0μ.

To facilitate understanding of the electrode provided with such an intermediate layer, a cross-sectional view of the electrode is shown in FIG.

1 is an electrode core, 4 is an intermediate layer, 2 is a layer containing particles, and 3 is electrode active particles.

Various methods are used to specifically attach the electrode surface layer, such as composite plating, melt coating, baking,
Pressure forming and sintering methods are used. Among these, the composite plating method is particularly preferable because it allows the electrode active metal particles to be attached well.

The composite plating method is a bath in which particles containing, for example, nickel as a part of the alloy component are dispersed in an aqueous solution containing metal ions that form a metal layer, and plating is performed as a cathode as an electrode core. The metal and particles are co-electrodeposited on the core. In more detail, the particles become bipolar under the influence of the electric field in the bath, and when they approach the cathode surface, they increase the local current density of the plating.
It is thought that when it comes into contact with the cathode, it is co-electrodeposited onto the core by metal plating caused by reduction of ordinary metal ions.

For example, if a nickel layer is used as the metal layer, a total nickel chloride bath or a high nickel chloride bath.

Various nickel plating baths are used, including nickel chloride-nickel acetate baths, Watt baths, and nickel sulfamate baths.

The proportion of such particles in the bath is between 1 g/β and 200 g.
, l is preferable from the viewpoint of improving the adhesion state of particles to the electrode surface. In addition, the temperature conditions during dispersion plating work are 20 to 80℃, and the current density is l^/dm" to 20A/
dm'' is preferable.

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, in order to further improve the adhesion strength of the particles, after completion of composite plating, ordinary plating or electroless plating may be performed to the extent that the particles are not completely covered, or heating and baking in an inert or reducing atmosphere may be carried out as appropriate. You may go.

In addition, as described above, when providing an intermediate layer between the electrode core and the metal layer containing particles, the electrode core is first plated with Ni, Co, or Cu, and then the dispersion plating method described above or the melt plating method is applied. A metal layer containing particles is formed thereon by means of a spraying method.

As the plating bath in such a case, the various plating baths mentioned above can be used, and also for Cu plating, a known plating bath can be used.

In this way, an electrode is obtained in which electrode active metal particles containing a hydrogen storage metal are attached to the electrode core via a metal layer.

Next, another method for manufacturing the cathode of the present invention will be described.

The cathode of the present invention can also be manufactured by a melt coating method or a baking method. That is, a mixed powder of a hydrogen-absorbing metal powder and another low hydrogen overvoltage metal powder (obtained, for example, by a melt-grinding method) is adjusted to a predetermined particle size, and melted and sprayed using plasma, oxygen/acetylene flame, etc., to form an electrode core. A partially exposed coating layer of these particles is obtained on the electrode core body, or a dispersion or slurry of these particles is applied onto the electrode core body and baked by baking to obtain a desired coating layer.

The cathode of the present invention can also be obtained by preparing an electrode sheet containing a hydrogen storage metal in advance and attaching this to an electrode core. In this case, the sheet is formed by mixing particles of hydrogen storage metal and other metal particles (for example, Raney alloy showing low hydrogen overvoltage characteristics) with organic polymer particles, or by baking the mixture after forming to form a sheet. Of course, in this case the electrode active particles are exposed from the surface of the sheet. The sheet thus obtained is pressed onto the electrode core and fixed onto the electrode core by heating.

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 used as an electrode for aqueous alkali chloride electrolysis using.

When used as a cathode for alkali chloride electrolysis.

Iron content eluted from the electrolytic cell material into the catholyte may be deposited on the cathode, reducing the electrode activity.
It is an effective method to attach a non-electronically conductive substance as disclosed in Publication No. 2.

(BEST MODE FOR CARRYING OUT THE INVENTION) Examples 1 to 13 The Mitsushmetal multi-component hydrogen storage alloy shown in Table 1 was
The powder was ground in a nickel chloride bath (formerly CQ).
8・611J 300g/12. HsBO-38g/
12) at a rate of 0.75 g/Q, and commercially available Raney nickel alloy powder (manufactured by Japan-Korea Rica, formerly 50 wt%).
. The temperature was 40℃.

pl+ was 2.5, and the current density was 3A/dm''.In both cases, the eutectoid amount of the Mitshu metal nickel multi-component hydrogen storage alloy was 0.7 g/dm'', and the eutectoid amount of the Raney nickel alloy was 2. -8g/dm", that is, a composite plating layer in which Mitshu Metal Nickel multi-component hydrogen storage alloy and Raney nickel alloy coexist, where the proportion of hydrogen storage metal in the eutectoid electrode active metal particles is 20wt% and Raney nickel alloy is 80wt%. was obtained.The thickness of this plating layer was approximately 15
0μ, and the porosity was about 70%. After this sample was immersed in a 25% Na solution at 90°C for 2 hours to develop AQ of Raney nickel alloy, these electrodes were
- TiO-rich, fluorine-containing cation exchange membrane (Asahi Glass Co., Ltd.
Co., Ltd. CFi-CF, and CF, -CFO (mouth F2) 3
Copolymer with CD port C11, ion exchange capacity 1.45
A short-circuit resistance test was conducted using a cathode for a salt electrolytic cell using a ion exchange membrane (meq/g resin) as an ion exchange membrane. The anolyte was a 3N NaCf1 solution, the catholyte was a 35% Na solution, and the current density was 30^/dm at 90℃ for 20 minutes after the start of electrolysis.
The following short circuit test was conducted on day 0.

First, the anode and cathode during electrolysis were short-circuited with a copper wire to stop electrolysis, and the electrolysis was left as it was for about 5 hours.

During this time, the current flowing from the cathode to the anode was observed.

Note that the temperature of the catholyte was maintained at 90°C. Thereafter, this copper wire was removed and electrolysis was performed for one day.

This operation was repeated 5 times.

After continuing electrolysis for another 30 days after the end of the test, the electrode was taken out and treated with 35% NaOH, 90°C, current density 30A/dm.
The hydrogen overvoltage of each electrode was measured at `` and is shown in Table 1 along with the values before the test. All were almost the same as in test n1.

Comparative Examples 1 to 3 MmNi4. of Example 1. yAlo, aMno, l
MmNi5゜Mm+, +Nim, aAlo, 5c
O1. Or Mmo, aNi*, s^I021C
ow,. An electrode was manufactured in the same manner as in Example 1 except that the electrode was changed to , and the results of the same tests are shown in Table 1.

After the test, an increase in hydrogen overvoltage of 30 to 100 mV was observed.

Example + 4 The amount of metal powder added to the nickel chloride bath in Example 4 is Mm.
Nix, sAl. Composite plating was performed in the same manner as in Example 4, except that the ratio of 5cOx was changed to 5g/Q and the ratio of Raney nickel alloy powder was also changed to 5g/Q. As a result, MmN+
The eutectoid amount of s aAlo, co = 5 g/dm" The eutectoid amount of Raney nickel alloy is 2 g/dm", that is, Mm old 28
．． Eight! . , MmNim, s^Ia, 5can with a proportion of @COz of 71% and a proportion of Raney nickel alloy of 29%
A composite plating layer in which Raney nickel alloy and Raney nickel alloy coexist was obtained. The thickness of this plating layer is approximately 280 μm, and the porosity is approximately 6.
It was 5%.

The same short circuit test as in Example 4 was conducted using this electrode. After the test was completed, the hydrogen overvoltage was measured and found to be 75 mV, with no change at all.

Example 15 1mN1n, aAlo, IT+o, I powder (30μ
(below) and commercially available stabilized Raney nickel powder (manufactured by Kawamei Fine Chemicals, trade name "Dry Raney 9 Kel") in a high nickel chloride bath (NiSO4.611J 200g/Q).
.

NiC1□・6HJ 175g/12. IIJ mouth 2
40g/Q) of 10g/2 each, and while stirring well, composite plating was performed using a Ni punching metal as a cathode and a Ni plate as an anode. The temperature is 50
℃, pH was 3.0, and current density was 4 A/dm''.

As a result, MmNi4. aAlo, +Tio, +
A composite plating layer containing stabilized Raney nickel was obtained, in which the eutectoid amount of MmNin, a^1゜, +Ti'o, + was 5 g/d, and the eutectoid amount of stabilized Raney nickel was 2 g/d. dm'', that is, LaN with a proportion of MmNin, aAlo, +Tio, I in the eutectoid electrode active metal particles of 71% and a proportion of Raney nickel alloy of 29%.
A composite plating layer in which i5 and Raney nickel alloy coexisted was obtained. Further, the thickness of this plating layer was about 250 μm, and the porosity was about 60%.

Using this, the same short circuit test as in Example 1 was conducted. After the test, the hydrogen overvoltage was measured and found to be 70 mV, which was almost the same as before the test.

Example 16 Composite plating was performed under the same conditions as in Example 4 except that the Raney nickel alloy powder was replaced with expanded Raney nickel. As a result, MmNia, s^Io, 5co2. .

A composite plating layer containing expanded Raney nickel is obtained, and M
The eutectoid amount of mNii, 5Alo, 5cOx, o is 5
g/dm wealth.

The eutectoid amount of developed Raney nickel was 3 g/dm''6, that is, MmNia in the eutectoid electrode active metal particles.
, aAia, tc(la, MmNix with a proportion of 63% and a proportion of Raney nickel alloy of 37%, 5A
A composite plating layer in which Io, 5cOa, O and Raney nickel alloy coexisted was obtained. The thickness of this plating layer is approximately 4
00μ, and the porosity was about 70%. A short circuit test was conducted on this in the same manner as in Example 1. The hydrogen overvoltage after the test was 8
It was 0 mV, unchanged from before the test.

Table 1

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of the surface of an example of the electrode of the present invention, and FIG.
The figures each show a partial cross-sectional view of the surface of another example of the electrode of the present invention. 1. Indication of the case Patent Application No. 69775 of 1988 2. Name of the invention High durability low hydrogen overvoltage cathode and its manufacturing method 3. Person making the amendment Relationship with the case Patent applicant address: 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name
(004) Asahi Glass Co., Ltd. Based on the procedural amendment order dated October 17, 1999 (dispatch) (Amendment 6, number of inventions increased by the amendment None 7, brief explanation of the drawings of the specification subject to the amendment) Column 8, Contents of amendment

Claims (1)

[Claims] (1) In an electrode in which electrode active metal particles are provided on an electrode core, a portion of the electrode active metal particles are a hydrogen storage metal that can electrochemically absorb and release hydrogen. , the hydrogen storage metal has the following formula: MmzNi_5_-_(_X_+_Y_)AlxMy (where M is Mn, Cu, Cr, Co, Ti, Nb,
It is one or more elements selected from Zr and Si, and 0.7≦Z≦1.0<x<3, 0<y<3, 0<x+y≦3. ) High durability low hydrogen overvoltage cathode. (2) Claim (1) wherein some of the electrode active metal particles are particles made of Raney nickel and/or Raney cobalt.
Highly durable low hydrogen overvoltage cathode. (3) The proportion of hydrogen storage metal in the electrode active metal particles is 5 or more
The highly durable and low hydrogen overvoltage cathode according to claim 1, wherein the hydrogen overvoltage cathode is 90 wt%. (4) The highly durable and low hydrogen overvoltage cathode of claim (1), wherein the electrode active metal particles are adhered to the electrode core by plating metal. (5) The highly durable and low hydrogen overvoltage cathode of claim (4), wherein the plating metal is the same metal as a part of the components constituting the electrode active metal particles. (6) The compositional formula is MmzNi_5_-_(_X_+_Y_)AlxMy (where M is Mn, Cu, Cr, Co, Ti, Nb,
One or more elements selected from Zr and Si, and 0.7≦Z≦1, 0<x<3, 0<y<3, 0<x+y≦3. ) The electrode core body is immersed in a plating bath in which hydrogen-absorbing metal particles capable of electrochemically absorbing and desorbing hydrogen are dispersed as at least a part of the electrode-active metal particles, and the electrode is formed by a composite plating method. A method for producing a highly durable and low hydrogen overvoltage cathode, which comprises co-electrodepositing the electrode active metal particles together with a plating metal on a core. (7) Production of a highly durable, low hydrogen overvoltage cathode according to claim (6), wherein the plated metal is formed in a layer on the electrode core, and a portion of the electrode active metal particles are exposed on the surface of the layer. Method. (8) A layer containing hydrogen storage metal particles capable of electrochemically absorbing and desorbing hydrogen as at least a part of the electrode active metal particles is formed by a baking method or a melt coating method, so that some of the electrode active metal particles are A method for producing a highly durable and low hydrogen overvoltage cathode, which comprises providing a cathode on an electrode core so as to be exposed on the surface of the layer. (9) Electrode active metal particles consisting of a hydrogen storage metal that can electrochemically absorb and release hydrogen, or this metal and another low hydrogen overvoltage metal, so that a part of the particles are exposed from the surface of at least one side. A method for producing a highly durable and low hydrogen overvoltage cathode, which comprises preparing a sheet containing the particles and fixing the surface of the sheet opposite to the exposed surface of the particles to an electrode core. (10) The method for producing a highly durable and low hydrogen overvoltage cathode according to claim (9), wherein the sheet contains organic polymer particles as a sizing agent.