KR890003514B1 - Cathode for electrolysis and a process for making the said cathode - Google Patents

Abstract

Cathode for use in electrolysis cell consists of an electrically conducting substrate with a coating band on an oxide of a platinum group metals. The cathode also has a covering consisting of several layers of metal oxides, the surface layer consisting of the oxide of a valve metal and the intermediate layer or one of the intermediate layers being oxide of a precious group VIII metal layer. Surface layer is manufactured from oxides of only the metals concerned in another embodiment, the surface layer or intermediate layers consist of a mixed oxide of the metal concerned and a second metal in low proportion. The cathode is used for electrolysis of water or alkali metal halides, etc.

Description

Electrolytic cathode and its manufacturing method

The present invention relates to a novel cathode that can be used for electrolysis. It also relates to a method of making such a cathode. More particularly, it relates to a negative electrode which can be used for the electrolysis of particularly good alkali metal halide aqueous solutions because of its low operating voltage and chemical stability over time.

It belongs to the group of activated metal cathodes obtained by coating various activating materials on this negative electrode substrate, and a desired object is basically to lower the hydrogen overvoltage in the alkaline medium.

British Patent No. 1,511,719 describes a cathode consisting of a metal plate, a cobalt coating and a second ruthenium coating.

U. S. Patent No. 4,100, 049 describes a cathode comprising a substrate and a coating composed of a mixture of noble metal oxides and semiconductor metal oxides (especially zirconium oxide).

For example, a method of plating a coating of nickel-palladium alloy on a substrate of nickel is also described in US Pat. No. 3,216,919: According to this patent, an alloy layer is applied to the substrate in powder form and the alloy The powder is sintered.

Japanese Patent Application Publication No. 54-110,983 (U.S. Patent No. 4,465,580) discloses a dispersion of particles of nickel or nickel alloys and a coating comprising an activator consisting of platinum, ruthenium, iridium, rhodium, pallanium or osmium or oxides of these metals. The cathode is described.

Japanese Patent Application Publication No. 53-010,036 describes a cathode having a coating of a semiconductor metal substrate and at least one platinum group metal and an alloy of the semiconductor metal and a surface coating of at least one white metal as necessary.

The present invention is characterized by containing a coating composed of a plurality of metal oxide layers, a surface layer consisting essentially of a semiconductor metal oxide and an intermediate layer consisting essentially of an oxide of a Group VIII precious metal element on the periodic table, or one or more intermediate layers. A novel negative electrode, consisting of an electrically conductive substrate containing an underlying coating, can be used, in particular for the electrolysis of aqueous alkali metal halide solutions. The term " substantially " as used herein in connection with the surface layer and the interlayer refers to oxides of only the metals subjected to the above-mentioned collisions, or to mixing the metals with the corresponding metals in a lower proportion, eg, with a molar ratio of less than 1/10. It indicates that it is an oxide.

In the present invention, the expression "semiconductor metal" is used as a conventionally accepted concept, that is, metals of groups 4b, 5b and 6b on the periodic table excluding chromium.

More specifically, the present invention provides an anode comprising one or more ruthenium oxide (RuO ₂ ) layers, wherein the coating is comprised of one or more titanium oxide layers and / or one or more zirconium oxide layers. do. This relates in particular to the negative electrode whose coating contains RuO ₂ and TiO ₂ .

Notably among such cathodes is that the coating is counted from an electroconductive substrate to form one or more TiO ₂ layers contiguous to one or more RuO ₂ layers, or a series of one or more TiO ₂ layers / one or more RuO ₂ layers / one The above is a cathode composed of a TiO ₂ layer. In this series of layers are intervened with oxides of other precious or nonprecious metals, or part or bottom of RuO ₂ and / or TiO ₂ (RU _x Ti _1-x ) O ₂ [X is an electrically conductive substrate And reduced between the surface in contact with the electrolyte] is not outside the scope of the present invention. In the present invention, the term "surface layer" refers precisely to an oxide layer whose surface is in direct contact with an electrolyte, and the term "intermediate layer" refers to a layer placed between an electrically conductive substrate and the acid surface layer. In particular, the present invention provides a cathode in which part or all of the above-described oxide or the like is flaky in its coating.

In the present invention, "flake" means a part of a planar thin film, a cylinder or a sphere, or a combination of the above-mentioned shapes, and the thickness is less than 1/10 of the average of the two dimensions of the quadrilateral inscribed above the flakes. The mean of the above dimensions may be from 1 to 100 microns and more precisely from 3 to 30 microns.

As mentioned above, the coating is wholly or partly composed of one or more oxides of precious metals, ie ruthenium, rhodium, palladium, osmium, iridium, and platinum. In the present invention, ruthenium oxide or a combination of ruthenium oxide and at least one other precious metal oxide is preferred.

In the coating of the cathode according to the present invention, the molar ratio of the noble metal and the semiconductor metal oxide is generally 10/1 to 1/10, preferably 1/5 to 5/1.

The material forming the substrate can be selected from conductive materials. It may be appropriately selected from the group consisting of nickel, stainless steel and mild steel, but is not necessarily limited thereto.

The substrate may be a tube or site with or without multiple orifices or perforations, a lattice metal siting or expanded metal, or a grid, wherein the materials may be planar or cylindrical or of other forms depending on the technique used. have.

The invention also relates to a method of making these cathodes.

The method basically consists in plating a layer of a metal salt on a substrate which has been subjected to any suitable pretreatment, and subjecting the whole to a oxidized form.

Pretreatment of the substrate preferably consists of degreasing and, if necessary, mechanical and / or chemical scaling.

This method consists in continuously plating a layer of a metal salt solution on a substrate.

If the mixed oxides are plated, the same technique can be used or the layer containing the two metal salts can be plated directly. In general, metal salts are plated in solution or in suspension. Depending on the nature of the salt, the solvent or diluent may be water, an inorganic or organic acid or an organic solvent. Preference is given to using dimethylformamide, alcohols and especially organic solvents such as ethanol or 2-ethyl nucleic acidol. In general, the atomic concentration of the metal is 3 × 10 ⁻² to 3 mol / liter, preferably 1 to 2 mol / liter.

Metal salts that can be used in the present invention are generally inorganic or organometallic salts such as, for example, halides, nitrates, carbonates, sulfates or acetates or acetylacetonates. For salts to produce platinum and ruthenium oxide, hex chloroplatinic acid hexahydrate is preferred.

Plating of the salt layer described above can be carried out by immersing the substrate in solution or suspension, coating it with a paintbrush, brush or similar tool, and electrostatic spraying according to conventional methods.

The preparation and plating of solutions or suspensions is generally carried out at ambient temperature and air. If essentially necessary, the operation may be carried out in an atmosphere of nitrogen or other gases which are not reactive with the above-mentioned salts, in particular in order to facilitate the dissolution of certain salts.

The conversion of metal salts to oxides is generally carried out by heat treatment. This treatment is preferably stoving in air to remove some or all of the solvent or diluent. Stoving can be carried out at temperatures below 200 ° C, with temperatures in the range of 100 to 150 ° C being particularly recommended. This duration is typically tens of minutes. Appropriate treatment is carried out in air at temperatures between 200 and 1000 ° C., depending on the salts generally used. This operation is preferably carried out at a temperature of 400 ~ 750 ℃. The duration of this heat treatment is generally 15 minutes to 1 hour per layer. This heat treatment can be carried out after each or a final stoving.

The negative electrode of the present invention is characterized by good adhesion of the electroactive coating to the substrate.

The negative electrode of the present invention is suitable for an electrolysis cell in which water or an aqueous solution is electrolytically produced by electrolysis of hydrogen discharged from the negative electrode. This negative electrode is particularly suitable for the electrolysis of aqueous solutions of alkali metal chlorides, especially aqueous sodium chloride solutions and for the electrolysis of water, for example in the electrolysis of aqueous potassium hydroxide solutions. Although the microporous diaphragm may be used as a separator in the electrolytic cell, the cathode according to the present invention is particularly interesting in the diaphragm method.

The invention is illustrated by the following examples.

EXAMPLE

The size of the board is 200 × 10 × 0.6 mm.

Surface treatment is performed using corundum (average bead diameter 250 μm).

a) A solution of ₂ g of RuCl ₃ , xHCl, yH ₂ O containing about 38% by weight of ruthenium metal in ₂ cm ₃ of ethanol at 23 ° C is prepared.

This solution is used to coat the nickel plate. After air stove (120 ° C., 30 minutes), heat treatment in air (500 ° C., 30 minutes) is performed. Repeat the coating / stopping / heat treatment sequence after cooling.

1.4 mg / cm ₂ RuO ₂ plating having a flake shape having an average size of 3 to 30 μm and showing a RuO ₂ structure when examined with an X-ray crystal photograph was obtained.

b) In 2 cm 3 of ethanol at 23 ° C., a TiOCl · 2HCl 2.6 cm 3 solution containing 2.5 mol Ti / l is prepared.

The same coating / stopping / heat treatment procedure (two layers) as in a is performed. In this way, 0.8 mg / cm ₂ TiO ₂ is plated.

c) This electrode has an operating voltage of -1225 mV for a saturated caramel electrode (S. C. E) when tested in sodium hydroxide with a concentration of 450 g / l at 85 ° C and 50 A / dm².

d) According to the method described above, an 80 mm disc consisting of a network of expanded and rolled nickel coated with RuO ₂ / TiO ₂ is used as a cathode in the electrolytic cell of aqueous sodium chloride solution using a diaphragm method.

The working conditions are as follows.

Current strength = 30A / dm², temperature -85 ℃, sodium hydroxide 32% by weight

As a result, it can be seen that the voltage at the terminal of this cell is 300 mV gain compared to the voltage at the terminal of the cell of only nickel alloy without cathode coating, and the profit is constant at 300 mV even after 6 days of continuous operation.

Example 2

The nickel substrate is surface-treated in the same manner as in Example 1. Prepare the following two solutions at 23 ° C. Solution A: RuCl ₃ .xHCl.yH ₂ O 2 g solution in ₂ cm ₃ of ethanol of Example 1. Solution B: 1.3 cm ₃ TiOCl ₂ .2HCl solution in ₁ cm ₃ of ethanol containing 2.5 mol Ti / l.

After plating two layers of solution B on the nickel substrate according to the coating / storing / heat treatment sequence of Example 1 and cooling, the two layers of solution A and again two layers of solution B again according to the coating / storing / heat treatment sequence Plate and do the same treatment. The total plating amount of the metal oxide is 1.75 mg / cm 2 including RuO ₂ 0.6 mg / cm 2.

A negative electrode with a triple coating of TiO ₂ , RuO ₂ and ZrO ₂ is tested in sodium hydroxide as in Example 1: The operating voltage is -1240 mV for SCE and after 16 hours this voltage is -1210 mV.

Example 3

a) A Ni substrate which has been treated under the conditions of Example 1 is used.

b) Two solutions were prepared at 23 ° C .: Solution A: ₂ g solution of RuCl ₃ · xHCl · yH ₂ O in 2 cm ₃ of ethanol of Example 1. Solution B: A solution of 1 g of ZrOCl ₂ · 8H 柱 O in ethanol (2.4 cm 3) / HCl (1 cm ₃ , 1n).

c) plating two layers of solution B on the substrate according to the coating / storing / heat treatment sequence of Example 1, and then cooling, followed by two layers of solution A and again 2 The layers are plated and subjected to the same treatment.

d) The total plating amount of the metal oxide is 1.8 mg / cm 2 including RuO ₂ 0.7 mg / cm 2.

This negative electrode with a triple coating of ZrO ₂ , RuO ₂ and ZrO ₂ was tested in sodium hydroxide as in Example 1.

The operating voltage is -1210mV for S.C.E. and after 16 hours this voltage is -1200mV.

Example 4

a) Nickel substrate and solution A and solution B of Example 3 are used.

b) The two layers of solution A on the substrate are plated and the two layers of solution B are plated according to the method of Example 1 and the coating / storing / heat treatment conditions.

c) The total plating amount of the metal oxide is 1.2 mg / cm 2 including RuO ₂ 0.7 mg / cm 2.

This negative electrode having a RuO ₂ / ZrO ₂ double coating was tested in sodium hydroxide as in Example 1.

The operating voltage is -1210mV for S.C.E. After 16 hours this voltage remains unchanged.

Claims (13)

Based on platinum group metal oxides, characterized in that it comprises an intermediate layer or one or more intermediate layers consisting of a coating consisting of a plurality of metal oxide layers, a surface layer consisting essentially of a semiconductor metal oxide and an oxide of a Group VIII precious metal element substantially of the periodic table. A cathode usable in an electrolytic cell composed of an electrically conductive substrate containing a coating. 2. A cathode according to claim 1, wherein the surface layer and / or the intermediate layer or intermediate layers are oxides of only the corresponding metals. 2. A cathode according to claim 1, wherein the surface layer and / or intermediate layer or one or more intermediate layers are a mixed oxide of the corresponding metal and a small proportion of the second metal. The negative electrode of claim 1 wherein the coating is a combination of at least one ruthenium oxide (RuO ₂ ) layer and at least one titanium oxide and / or zirconium oxide layer. The method of claim 1, wherein the coating begins with the substrate and consists of one or more Tio ₂ and / or ZrO ₂ layers continuous to one or more RuO ₂ layers, or a series of one or more Tio ₂ and / or ZrO ₂ layers / one or more RuOs. Cathode characterized in that it consists of _two layers / one or more Tio ₂ and / or ZrO ₂ layers. A cathode according to claim 1, wherein part or all of the oxide or the like in the coating is flaky. The cathode of claim 1 wherein the engine is selected from the group consisting of nickel, stainless steel and mild steel. A coating consisting of a plurality of metal oxide layers, a surface layer consisting essentially of a semiconductor metal oxide, and substantially characterized by plating layers of metal salts on a substrate, optionally subjected to appropriate pretreatment, and heat treating the whole to produce an oxidized form. A method for producing a negative electrode usable in an electrolytic cell composed of an intermediate layer composed of an oxide of Group VIII precious metal element on the periodic table or an electrically conductive substrate containing at least one intermediate layer. 9. A method according to claim 8, wherein the layers of solution or suspension of metal salts are successively plated on the substrate. 9. The surface layer and / or intermediate layer or one or more intermediate layers of the negative electrode of claim 8, characterized in that the metal salts for forming the mixed oxide are plated in the form of one or more layers of the same solution. Method for producing a negative electrode of a mixed oxide. The method of claim 8, wherein the metal salts are selected from inorganic or organic salts of metals such as, for example, halides, nitrates, carbonates, sulfates or acetates or acetylacetonates. The method of claim 8, characterized in that the heat treatment at a temperature of 200 ~ 1000 ℃. 13. A method according to claim 12, characterized by stoving at a temperature of 200 ° C or less to partially or completely remove the solvent or diluent from the metal salts prior to heat treatment.