JPH06146046A - Cathode for electrolysis and its production - Google Patents

Abstract

PURPOSE:To provide the platinum group metal type cathode contg. a material negating the reverse current to deteriorate an electrode active material within the electrode and to enable plating of both electrode active materials discretely under optimum conditions at the time of coating two kinds of the electrode active materials by dispersion plating. CONSTITUTION:The coating layer of the cathode active material contg. a hydrogen occlusion alloy and platinum group metal or its oxide is formed on a conductive base body. The occluded hydrogen negates the reverse current and protects the platinum group metal when the hydrogen formed by electrolysis is occluded in the hydrogen occlusion alloy and the reverse current begins to be generated. This coating layer is constituted of two kinds of dispersion plating layers and the hydrogen occlusion alloy is incorporated into the plating layer on the conductive base body side and the platinum group metal into the plating layer on the outer side. Since both electrode active materials are coated and formed by the separate plating conditions, the hydrogen occlusion alloy and the platinum group metal are formable at optimum coverage, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activated cathode for industrial electrolysis and a method for producing the same, and more particularly to an industrial cathode having a high activity, less susceptible to deterioration, and easy to control the production process, and a method for producing the same. .

[0002]

2. Description of the Prior Art As an electrode used in the electrolysis industry for electrolytically producing caustic soda and chlorine from an aqueous solution of alkali chloride, particularly saline, the role of the cathode and the anode has recently been emphasized. As an activated cathode for soda electrolysis, in addition to a cathode that has been used for a long time such as nickel simple substance or Raney nickel coated on nickel, nickel or iron, and an alloy thereof as a substrate, a platinum group metal or its oxide on the surface A cathode coated with is used (Japanese Patent Publication No. 59-48872). This cathode is manufactured by dispersion-plating the substrate in, for example, a nickel plating bath in which ruthenium dioxide fine particles are dispersed. In addition to this, there is a cathode for electrolysis obtained by dispersion plating on the substrate in a plating bath containing both hydrogen storage alloy and particles active for hydrogen generation as dispersed particles (JP-A-2-258992, JP-A-2-310388, JP-A-3-36287, etc.).

A cathode coated with a platinum group metal or the like has sufficient electrode activity, but has a drawback that the anode group current, which is an electrode active substance, deteriorates when the energization is stopped and the anode current flows. A cathode proposed in order to solve the drawback of deterioration of the electrode active material in the cathode is a cathode using the hydrogen storage alloy as the electrode active material, and this cathode suppresses the deterioration as follows. In other words, the latter hydrogen gas of the hydrogen ions and the hydrogen gas generated by the cathodic reaction due to the electrolysis of water is stored inside by the hydrogen storage capacity of itself without being released into the electrolyte solution and into the atmosphere, and is stored when the energization is stopped. Degradation of the electrode active material is prevented by releasing the generated hydrogen and carrying an electric current. However, this hydrogen storage alloy was not originally developed as an electrode active substance, and the hydrogen generation overvoltage is not so low that it is difficult to say that it is sufficient in terms of electrolysis efficiency.

[0004]

It is an object of the present invention to solve the above-mentioned disadvantages of the noble metal cathode and the hydrogen storage alloy type cathode, and to obtain a cathode for electrolysis which is sufficiently satisfactory both in terms of electrolysis efficiency and in terms of electrode protection when current is stopped. It is intended to provide a manufacturing method.

[0005]

SUMMARY OF THE INVENTION The present invention is firstly a coating layer of a cathode active material containing a conductive substrate and at least a hydrogen storage alloy and a platinum group metal or its oxide formed on the conductive substrate. A cathode for electrolysis, comprising: second, a hydrogen storage alloy is plated with nickel on a conductive substrate by dispersion nickel plating, and the first cathode contains the hydrogen storage alloy and nickel.
Forming a dispersion plating layer, and then performing a dispersion nickel plating of a platinum group metal or an oxide thereof on the first dispersion plating layer to form a second dispersion plating layer containing the platinum group metal or an oxide thereof and nickel. And a method for producing a cathode for electrolysis. The present invention will be described in detail below.

An electrode using a highly active platinum group metal or its oxide as an electrode active material is a dimensionally stable electrode (DSE).
And has been widely used as an anode for salt electrolysis or the like. Since this dimensionally stable electrode promotes the anodic reaction to increase the electrolysis efficiency and has high resistance to the anodic reaction, it was sufficiently satisfactory from the viewpoint of use as an anode. However, this dimensionally stable electrode has a low resistance to the cathodic reaction, so that it has limited electrode use while being used as a cathode. This is because the platinum group metal or its oxide, which is the cathode active material, is deteriorated mainly by the reverse current that tends to occur when the energization is stopped or the operation is performed at a low current density. In order to suppress this deterioration, measures such as flowing a weak current for canceling the reverse current at the time of stopping energization or low current density operation have been attempted in the past, but in terms of operation complexity and economical efficiency. Therefore, further improvement has been desired.

The present invention meets exactly this demand, and the present invention provides an electrode which has a capability of canceling reverse current by itself and can be used as a cathode having high electrolysis efficiency without other auxiliary means. You can As the conductive substrate of the electrolysis cathode according to the present invention, nickel, iron and alloys thereof are preferably used. The shape of the substrate is preferably a porous shape that allows easy degassing, such as an expanded mesh or a punch plate.

The electrode active substance coated on the conductive substrate contains at least a hydrogen storage alloy, a platinum group metal and its oxide, and may further contain a plating component such as nickel. Hydrogen storage alloys that can be used in the present invention are all ordinary hydrogen storage alloys capable of storing and releasing hydrogen,
For example, for lanthanum-nickel based, misch metal-nickel based, titanium-nickel based hydrogen storage alloys,
The particle size of the plated particles is preferably 30 μm or less. The platinum group metal includes platinum, palladium, iridium, osmium, ruthenium and rhodium, and may be an oxide thereof or an alloy thereof, and the particle size of the plated particles is preferably 10 μm or less.

It is desirable that the electrode active material is coated by dispersion plating as a dispersion plating layer. In that case, a first dispersion plating layer containing a hydrogen storage alloy and nickel is formed on the surface of the conductive substrate, and then the first dispersion plating layer is formed. It is more preferable to form a second dispersion plating layer containing nickel and a platinum group metal or oxide thereof or nickel on the surface of the first dispersion plating layer. However, in the electrolysis cathode of the present invention, a single dispersion-plated layer containing a hydrogen storage alloy and a platinum group metal or the like may be formed, and the hydrogen storage alloy and the platinum group metal or the like may be formed by a method other than dispersion plating. You may form the coating layer of the said electrode active material containing.

However, when the hydrogen storage alloy particles and the particles of the platinum group metal or its oxides or alloys are suspended in a single plating bath and dispersion plating is performed, the dispersed particles respectively have a specific gravity, an electric conductivity and a particle size. Due to differences in diameter, etc., the amount of eutectoid in the plating layer (coating) formed when electrochemically co-deposited differs depending on the particle, and it is very difficult to control the amount of each particle deposited. Is. In other words, it is impossible to set the optimum conditions for each particle because the optimum precipitation conditions for each suspended particle are different. Further, since a plurality of particles are suspended in the plating bath, the management of the plating bath becomes complicated and the workability is deteriorated.

Therefore, in the method of the present invention, as described above, the first dispersion plating layer containing the hydrogen storage alloy is formed on the surface of the conductive substrate, and then the second dispersion plating layer containing the platinum group metal or the like is formed on the surface of the first dispersion plating layer. A dispersion plating layer is formed to manufacture an electrolysis cathode. The formation of these dispersed plating layers may be carried out in two steps according to an ordinary dispersion plating method. In order to form the first dispersed plating layer, the hydrogen storage alloy particles prepared in advance are suspended, and nickel is preferably contained as a solution of the compound (for example, nickel sulfate or nickel chloride) in a plating bath. And the conductive substrate is used as a cathode to energize. As a result, the first dispersed plating layer containing hydrogen storage alloy particles can be formed in the nickel matrix. In this case, the plating conditions are set to the optimum conditions for plating the hydrogen storage alloy particles, and the coating amount and coating thickness etc. Can be controlled to an optimum value.

Similarly, in the case of the second dispersion plating layer coated on the first dispersion plating layer, the plating bath containing the platinum group metal particles and the like prepared in advance is suspended and nickel is preferably contained as a solution of the compound. Then, the conductive substrate on which the first dispersed plating layer is formed may be dipped and the conductive substrate may be used as a cathode for energization. As a result, the second dispersion plating layer containing platinum group metal particles can be formed in the nickel matrix. In this case as well, the plating condition is set to the optimum condition for plating the platinum group metal, etc., and the coating amount and coating thickness are set. Etc. can be controlled to the optimum values. When forming the second dispersed plating layer, it is desirable to give consideration so as not to impair the characteristics of the first dispersed plating layer that has already been formed by coating.

Further, in the cathode for electrolysis of the present invention, in addition to the above-mentioned platinum group metal and its oxide and hydrogen storage alloy, polytetrafluoroethylene particles are contained in the plating layer to improve the gas separability, Activated carbon can be contained in the first dispersed plating layer to increase the surface area.

[0014]

EXAMPLES Examples of a method for producing a cathode and electrolysis using the cathode according to the present invention will be described below, but the present invention is not limited thereto.

Example 1 Prior to dispersion plating, nickel and lanthanum were arc-melted and pulverized to obtain LaNi ₅ particles having an average particle size of 20 μm, and ruthenium chloride was fired at 480 ° C. for 10 hours and pulverized to obtain a particle size of 10 μm or less. Ruthenium dioxide (RuO ₂ ) particles were prepared. On a circular nickel substrate having a thickness of 0.5 mm and a diameter of 18 mm, a composite coating layer composed of LaNi ₅ and nickel was dispersion-plated using a plating bath having the following composition. LaNi _{5 in} this coating layer was about 34% by weight.

[0015] Ni / LaNi ₅ eutectoid condition plating bath composition NiSO ₄ · 6H ₂ O 1.0 mol / l NiCl ₂ · 6H ₂ O 0.2 moles / liter H ₃ BO ₃ 0.5 mol / l plating current density 30 mA / cm ² LaNi ₅ Particle suspension amount 5.0 g / liter Plating temperature 45 ℃ pH 5.0

Further, the substrate having the coating layer formed thereon was dispersion-plated with a second composite coating layer made of RuO ₂ and nickel by using a plating bath having the following composition. RuO _{2 in} this coating
Was about 5.4% by weight. Ni / RuO ₂ eutectoid condition plating bath composition NiSO ₄ · 6H ₂ O 1.0 mol / l NiCl ₂ · 6H ₂ O 0.2 moles / liter H ₃ BO ₃ 0.5 mol / l plating current density 30 mA / cm ² RuO ₂ particles suspended Quantity 20g / liter Plating temperature 45 ℃ pH 4.0

The electrode thus prepared was used as a cathode, a platinum plate and a RHE were used as a counter electrode and a reference electrode, respectively, and a saline solution was supplied to the anode chamber and a 1 M dilute caustic soda aqueous solution was supplied to the cathode chamber at 100 mA / cm 2. Electrolysis was carried out at a current density of ² for 1 hour to produce caustic soda in the cathode chamber. The potential was read after 1 hour, the current was then reduced to a predetermined value, and the potential was read 5 minutes after the current was set. The results are shown in the graph of FIG. 1 which is a current-potential curve. As can be seen from FIG. 1, the cathode potential at a current density of 100 mA / cm ² is -180 m.
V, and no anodic current was observed when the circuit was short circuited.

[0018]

Comparative Example 1 Using only the Ni / LaNi ₅ plating bath of Example 1, LaNi ₅ particles and nickel were dispersed and plated on the nickel substrate of Example 1 to prepare a cathode. Salt electrolysis was performed under the same conditions as in Example 1 except that the cathode thus produced was used, and the potential was read in the same manner as in Example 1. The results are shown in the graph of FIG. 2 which is a current-potential curve. With this cathode, no anode current was observed even if the circuit was short-circuited, but from Fig. 2, the current density was 100 mA / cm.
Cathode potential cathodic potential than the cathode of Example at -290 mV at ² was 110 mV baser (overvoltage is greater 110 mV).

[0019]

Comparative Example 2 Using only the Ni / RuO ₂ plating bath of Example 1, RuO ₂ particles and nickel were dispersed and plated on the nickel substrate of Example 1 to prepare a cathode. Salt electrolysis was performed under the same conditions as in Example 1 except that the cathode thus produced was used, and the potential was read in the same manner as in Example 1. The results are shown in the graph of FIG. 3, which is a current-potential curve.
As can be seen from FIG. 3, the cathode in which RuO ₂ and nickel were dispersion-plated had a cathode potential of −165 mV at a current density of 100 mA / cm ² , which was superior to the cathode of Example 1, but the circuit was short-circuited. Anode current flowed when

[0020]

Example 2 20 g / in the Ni / LaNi ₅ plating bath of Example 1
A cathode was prepared by adding liters of suspended RuO ₂ particles and coating a dispersion plating layer containing LaNi ₅ , RuO ₂ and nickel mixed on a nickel substrate under the same conditions as in Example 1 using only the plating bath. . Using this cathode, salt electrolysis was performed in the same manner as in Example 1 and the potential was read in the same manner as in Example 1. As a result, the cathode potential at a current density of 100 mA / cm ² was -170 mV, and no anode current was observed even when the circuit was short-circuited.

[0021]

The present invention is characterized by comprising a conductive substrate and a coating layer of a cathode active material containing at least a hydrogen storage alloy and a platinum group metal or its oxide formed on the conductive substrate. It is a cathode for electrolysis. Of the electrode active substances of this electrode for electrolysis, the platinum group metal or its oxide has a low hydrogen overvoltage and functions as a cathode for hydrogen generation, and the hydrogen storage alloy occludes the hydrogen generated at the cathode and conducts electricity. The present invention provides a non-conventional epoch-making cathode having both high electrolysis efficiency and the ability to cancel reverse current by a single cathode because it cancels a reverse current that easily deteriorates the platinum group metal and the like when stopped. You can

Further, the hydrogen storage alloy, the platinum group metal and the like are used for the first dispersion plating layer and the first dispersion plating layer on the conductive substrate, respectively.
It is desirable that the second dispersed plating layer is separately present on the dispersed plated layer, and if the platinum group metal or the like is ruthenium dioxide, desired electrolytic efficiency can be achieved. In the method of the present invention, a hydrogen storage alloy is plated on a conductive substrate with dispersed nickel to form a first dispersion plated layer containing the hydrogen storage alloy and nickel, and then a platinum group metal or a platinum group metal is formed on the first dispersed plated layer. A method for producing a cathode for electrolysis, which comprises subjecting the oxide to dispersion nickel plating to form a second dispersion plating layer containing the platinum group metal or its oxide and nickel.

When a cathode for electrolysis is manufactured by the method of the present invention as described above, it is possible to plate the hydrogen storage alloy, which is an electrode active substance, and the platinum group metal, under different conditions. It is possible to form a coating under the plating conditions, and it is possible to obtain a cathode in which the coating amount, coating thickness, etc. are optimal values for the application.

[Brief description of drawings]

FIG. 1 is a graph of a current-potential curve of a cathode of Example 1.

FIG. 2 is a graph of a current-potential curve of the cathode of Comparative Example 1.

FIG. 3 is a graph of a current-potential curve of the cathode of Comparative Example 2.

Claims (4)

[Claims] 1. A cathode for electrolysis comprising a conductive substrate and a coating layer of a cathode active material containing at least a hydrogen storage alloy and a platinum group metal or an oxide thereof formed on the conductive substrate. . 2. A first dispersion plating layer comprising a hydrogen storage alloy and nickel formed on a conductive substrate, and a platinum group metal or its oxide and nickel formed on the first dispersion plating layer. The cathode for electrolysis according to claim 1, further comprising a second dispersion plating layer containing 3. The cathode for electrolysis according to claim 1, wherein the platinum group metal or its oxide is ruthenium dioxide. 4. A first electrode containing a hydrogen storage alloy and nickel which is obtained by plating a conductive substrate with a hydrogen storage alloy by distributed nickel plating.
Forming a dispersion plating layer, and then performing a dispersion nickel plating of a platinum group metal or an oxide thereof on the first dispersion plating layer to form a second dispersion plating layer containing the platinum group metal or an oxide thereof and nickel. A method for producing a cathode for electrolysis, comprising: