JPH0375635B2 - - Google Patents

Abstract

A substrate is coated with a solution of metal oxide precursor compounds and an etchant for etching the substrate, the metal oxide precursor compounds are thermally concentrated by removing volatiles therefrom, and the so-concentrated metal oxides precursors are thermally oxidized in-situ on the substrate. The so-formed compositions are useful, e.g., as electrode material in electrochemical apparatuses and processes.

Description

[Detailed description of the invention]

The present invention relates to a method for making an electrode and its use in an electrolytic cell, particularly in a salt water electrolytic cell. There are generally three types of electrolytic cells used in chlor-alkali production: (1) mercury cells, (2) diaphragm cells, and (3) membrane cells. Kirk-
Oihmer Encylopedia of Chemical
It is described on page 799 of Volume 1, Technology 3 edition.
Other electrolytic cells that use electrodes for aqueous electrolysis are so-called "chlorate cells" that do not use a dividing or separating device between the anode and cathode. In a mercury bath, alkali metals produced by electrolysis of alkali metal salts produce mercury and amalgam, and this amalgam reacts with water.
Generates NaOH and liberates mercury. The mercury is recovered and recycled as a liquid cathode. In most chlor-alkali electrolysis processes, an aqueous salt solution (electrolyte) is electrolyzed by passing an electric current through an electrolytic cell having a diaphragm or membrane between an anode and a cathode. Chlorine is produced at the anode, while sodium hydroxide (NaOH) and hydrogen (H ₂ ) are produced at the cathode. While brine is continuously supplied to the electrolyzer, Cl ₂ , NaOH
and _H2 are continuously removed from the bath. The minimum voltage required to electrolyze an electrolyte into Cl ₂ , NaOH and H ₂ can be calculated using thermodynamic numbers.
However, in practice this is not possible at theoretical voltage values and requires the use of higher voltages to overcome the various resistances inherent in different types of electrolyzers. In order to improve the operating efficiency of diaphragm or membrane electrolyzers, attempts have been made to reduce the overvoltage of the electrodes, to reduce the electrical resistance of the diaphragm or membrane, or to reduce the electrical resistance of the salt water being electrolyzed. The invention described herein relates to an electrode that is particularly useful as a cathode in salt water electrolysis and has substantially reduced cathode overvoltage and improved power efficiency. Millions of tons of alkali metal halides and water are electrolyzed each year, so a reduction in operating voltage of just 0.05 volts can mean significant energy savings. There is therefore an industrial need for means to reduce the required voltage. Various electrolytic cell voltage reduction methods have been developed in the development of the chlor-alkali process. Some strive to reduce the cell voltage by improving the physical specifications of the electrolytic cell, while others strive to reduce the overvoltage at the cathode or anode.
The present invention relates in part to a new method for producing an electrode characterized by a significantly low overvoltage and to the use of this electrode in electrolytic cells. It has been published that electrode overvoltage is a function of current density and its composition. (Reference PHYSICAL
CHEMISTRY, 3rd edition, WJ Moore, Prentice
Hall (1962) pp. 406-408) However, current density refers to amperes per unit true surface area of the electrode, and composition refers to the chemical and physical composition of the electrode. Therefore, an electrode surface area enhancement method must reduce its overvoltage at a given surface current density. It is also desirable to use compositions of matter that are good electrocatalysts. This further reduces overvoltages. The use of plasma or flame radiation to coat electrodes with conductive metals is well known in the art. US Pat. No. 1,263,959 sprays nickel granules onto the anode, and the particles are melted and blasted onto the iron substrate to coat the anode. The cathode is also coated with a conductive metal. US Patent No.
No. 3,992,278 describes a cathode coated with a mixture of cobalt particles and zirconia particles by plasma or flame radiation. When these electrodes are used for the electrolysis of water or aqueous solutions of alkali metal halide salts, they are said to reduce the hydrogen overvoltage for a long time. Various metals and metal mixtures have been used to coat electrodes with plasma or flame radiation. US Pat. No. 3,630,770 describes the use of lanthambolide,
U.S. Pat. No. 3,649,355 describes the use of tungsten and tungsten alloys, and U.S. Pat. No. 3,788,968 describes the use of titanium carbide or titanium nitride and at least one metal and/or metal oxide of the platinum group and a porous second oxide. Describing the use of membranes, U.S. Patent No.
No. 3,945,907 describes the use of rhenium, and US Pat. No. 3,974,058 describes a cobalt coating with a ruthenium coating thereon. The production of porous electrode membranes by similar selective leaching is also well known in the art. Sintering the nickel after coating the electrode with nickel particles is disclosed in US Pat. Nos. 2,928,783 and 2,969,315. A method for leaching one component of the alloy after electrodeposition of the alloy on a substrate is described in US Pat. No. 3,272,788.
A method of selectively leaching one or more of the coating components after compressing two or more components with or on the electrode substrate is disclosed in U.S. Pat.
No. 3427204, No. 3713891 and No. 3802878. Manufacturing process combinations involving plasma injection or flame injection followed by leaching of the electrode have also been published in this field. A process combination in which electrodeposition is followed by leaching has also been announced.
Examples of known methods are given in the following patents: U.S. Pat. No. 3,219,730 describes an electrode manufacturing method in which the substrate is coated with an oxide film and then leached to remove the substrate, and U.S. Pat. No. 3,403,057 describes a porous electrode and process by flame or plasma spraying a Raney alloy onto a substrate and leaching the aluminum from the alloy, and U.S. Pat. Or a method of plasma spraying those alloys is described. The substrate is later removed to form a porous electrode. U.S. Pat. No. 3,497,425 describes a method for making porous electrodes in which a substrate is coated with a relatively insoluble metal followed by a more soluble metal. While heat treatment is required to interdiffuse the two films, optimal conditions require separate heat treatment for each film.
The soluble metal is later leached out, creating a porous electrode. U.S. Pat. No. 3,618,136 describes a method for making porous electrodes in which a binary salt composition is coated onto a substrate and the soluble components are leached from the system. This patent emphasizes that the binary salt composition is a eutectic mixture and that optimal results are obtained when both the active and inert salts, such as silver chloride and sodium chloride, both use the same anion. It is said that there is. Dutch Patent Application No. 75-07550 discloses coating a substrate with an alloy of at least one base metal from the group consisting of nickel, cobalt, chromium, manganese and iron and a second, more base sacrificial metal and then depositing a small amount of this sacrificial metal. The present invention also relates to a porous anode manufacturing method that removes a portion of the porous anode. The sacrificial metal is selected from zinc, aluminum, magnesium and tin. The sacrificial metal is leached away with a caustic or acid solution. Japanese Patent Publication No. 31-6611 relates to a porous electrode manufacturing method in which a nickel film is electrodeposited on a substrate and then a film of zinc or other soluble material soluble in an alkaline solution is applied. This electrode is then made porous either by immersion in an alkaline solution or by electrochemical anodization to elute away the zinc and other soluble materials. Prior to dipping, heat treatment of the electrodeposited electrode is required in some embodiments. U.S. Pat. No. 4,279,709 discloses a reduced overvoltage electrode manufacturing method in which a mixture of particulate metal and inorganic particulate compound pore former is applied and the pore former is leached to create pores. Electrodes of film-forming metal substrates, particularly titanium, coated with Group metal oxides of the Periodic Table of the Elements are said to be useful as anodes in electrolytic processes such as in salt water electrolysis in combination with other metal oxides. Ruthenium oxide, platinum oxide, and other platinum metal-based oxides, in conjunction with various other metal oxides, are very popular as membranes for valve metal substrates (particularly Ti) for use as anodes. Patents relating to this anode are US 3,632,498 and 3,711,385. This coating can be applied in a variety of ways, for example in U.S. Pat. After applying a mixture of a thermally decomposable compound and a thermally decomposable organic compound of a film-forming metal and drying the film by evaporating the organic excipient, the support was heated at 400 °C.
It can be applied to a valve metal substrate by heating to -550°C to form a metal oxide. Apply repeatedly to increase film thickness. A coating of metal oxide for film formation is also applied. U.S. Pat. No. 3,632,498 discloses the use of a plasma burner to electrodeposit metals in a galvanic bath followed by heating in air by heating a substrate coated with a pyrolyzable compound of a platinum group metal and a film-forming metal. It is described that a fine oxide film of platinum group metals and film-forming metals can be formed by oxide formation between them. Furthermore, patents related to electrodes with metal oxide surfaces include U.S. Patent No. 3616445, U.S. Pat.
No. 3977958, No. 4061549, No. 4073873 and 4142005
There is a number. The use of platinum group metal oxides, especially ruthenium, in active membranes for hydrogen generation is also known. (Reference, Melendrez, Carlos A., Spring Meeting
Electro Chem.Soc., May 11-16 (1975)) Japanese Patent Publication No. 40-9130, Japanese Patent Application Laid-open No. 131474-1974, and Japanese Patent Application Laid-open No. 11178-1987 are oxides of platinum group metals and other metals. The use of mixtures of oxides as active cathode membranes has been published. U.S. Pat. No. 4,238,311 discloses that a cathode film consisting of fine particles of nickel-medium platinum group metal and/or platinum group metal oxide is useful as the cathode film. In recent years, platinum group metal oxides have been used as active catalysts for hydrogen generation in chlor-alkali electrolyzers that generally use permionic membranes.
Extreme temperatures where temperatures exceeding ℃ are not uncommon
It is known to those knowledgeable in this field that the NaOH concentration and temperature conditions are not as convenient as they are now possible. It has been found that oxide films made by the known methods age with use and, in some cases, flake off from the substrate, possibly due to substantial reduction in adhesion to the supporting metal. Catalyst membranes made of metals that inherently have low hydrogen overpotential properties can actually lose their catalytic activity due to electrodeposition of metal contaminants, such as iron, which are common in the brine and water used in electrolysis processes. It is well understood by those practicing in this field that Therefore, active membranes that may actually be convenient for hydrogen generation in modern membrane chlor-alkali electrolysers are high surface area or porous membranes and compositions that withstand chemical attack to some extent in these conditions, such as nickel or various Limited to models featuring stainless steel. In these cases, it is well known that in practice this essential surface area membrane performance is sometimes affected by the presence of large amounts of metal contaminants in the brine or water used in the electrolytic process.
In fact, the full effect of the essentially low hydrogen overpotential catalyst accessibility is not achieved, since it is reduced to the extent that is normally characterized by similar membranes with Fe.
The terfel slope that characterizes the increased electrolytic activity thus changes essentially to that of iron, ranging from 0.23 to 0.54 amp/s as in modern membrane chlor-alkali electrolysers.
The hydrogen overpotential increases especially at high current densities of 1.5 to 3.5 amp/in ² (cm ² ) and higher. On the contrary, it is desirable to preserve the original low overpotential properties of materials known to be characterized by low Tafel slopes during long-term operation in membrane chlor-alkali baths, ie platinum group metal oxides, especially ruthenium oxides. Active membranes of heterogeneous mixtures of platinum group metals and NiO when prepared by the method of the present invention exhibit low hydrogen overpotential, physical stability and long-term efficiency as brine electrolysis cathodes at high NaOH concentrations, temperatures and pressures. It has now been discovered, among other things, that it exhibits the property of not doing. It has also been discovered that the use of this electrode in the electrolytic process of producing chlorine and caustic soda under certain operating conditions such as temperature, NaOH concentration, pressure, etc. actually reduces the energy requirements not possible with other methods. The invention first comprises a layer of a conductive metal substrate and an electrocatalytically active coating deposited thereon, and the coating comprises at least one platinum group metal oxide.
Regarding an electrode for an electrolytic cell characterized by being made of a heterogeneous mixture of metal oxides consisting of NiO, the second
(a) corroding the surface of the substrate and/or the existing coating with a nickel compound that is a precursor of nickel oxide and at least one platinum group metal compound that is a precursor of platinum group metal oxide on a conductive substrate; (b) heating to remove volatile components from the substrate so coated to concentrate metal values of the precursor compounds and leaching from the substrate or existing coating; (c) further heating in the presence of oxygen, air or an oxidizing agent to a temperature sufficient to oxidize the metal values in the coating; and step (a) above; The present invention relates to a method for producing an electrode for an electrolytic cell having a substrate coated with a solution of an electrocatalytically active heterogeneous mixture of metal oxides, characterized in that steps (b) and (c) are carried out multiple times. Figure 1 illustrates the results of some of the tests described below. The electrode of the present invention comprises a conductive substrate (including a conductive coating on a non-conductive substrate such as ceramic) having a film of a heterogeneous mixed oxide of a platinum group metal and nickel. Applying a coating solution containing a soluble platinum group metal compound as a precursor of NiO, a nickel compound as a precursor of NiO, and an etchant for the substrate to the substrate,
if the substrate already has a metal oxide coating as a conductive coating, it corrodes it (thereby attacking and dissolving the least chemically resistant parts of the coating);
The substrate is then heated to concentrate and redeposit the metal values (metal values here meaning intermediate metal compounds from the soluble metal compound to the final oxide) onto the substrate, and They are produced by oxidizing them to form a substantially hard stable mixture of heterogeneous metal oxides. A preferred conductive substrate is any metallic structure that retains its physical integrity during electrode fabrication. Metal laminates such as ferrous metals coated with other metals such as nickel or film-forming metals (also known as valve metals) can also be used. The substrate may be a metal such as iron, steel, stainless steel or other iron-based alloys. The substrate may be a non-ferrous metal, such as a film-forming metal, or a non-film-forming metal, such as nickel. Film-forming metals include titanium, tantalum, zirconium, niobium, tungsten and their alloys with each other and with minor amounts of other metals, which are well known in the related art. Non-conductive substrates can also be used, especially if a conductive layer is placed thereon. The metal oxide of the present invention is applied thereon. The shape or form of the substrate used in the coating method of the present invention may be a flat plate, a curved surface, a spiral surface, a perforated surface, a woven wire, an expanded metal plate,
It may be a rod, a tube, porous, non-porous, sintered, fibrous, shaped or irregularly shaped. The novel coating method of the present invention does not require a specific type of substrate, as its chemical and thermal processes can be applied to virtually any shape useful as an electrode. Many electrolytic cells have perforated or flat plates.
These are specifically bent and spaced on substantially parallel sides to form "pocket" electrodes. Preferred substrate forms are expanded mesh, perforated plates, woven wire, sintered metal, plates or sheets, although expanded mesh is one of the best types of porous substrates. The preferred composition of the substrate is nickel, iron, copper, steel,
Stainless steel or nickel-backed ferrous metals, with nickel being particularly preferred. These substrates on which a metal oxide film is applied are themselves coated with nickel, on the underlying substrate, especially on or above the underlying substrate.
It is supported or reinforced by an underlying matrix of iron or copper. The substrate to which the metal oxide film is applied is itself an outer layer of a laminate or coating structure, optionally it may be a non-conductive substrate onto which the metal oxide is applied. Platinum group metals include Ru, Rh, Pd, Os, Ir and Pt
There is. Among these, the preferred metals are platinum and ruthenium, with ruthenium being the best. Soluble platinum metal compounds are halides, sulfates, nitrates or other soluble salts or compounds of the metal, but preference is given to halide salts, such as _RuCl3 .
Hydride, PtCl/hydrate, etc. The solutions of the present invention are capable of etching the substrate and, in the case of second and subsequent films, etching and dissolving the most chemically susceptible portions of the oxide already present, and at elevated temperatures often remove platinum from the heated mixture. At least one chemical activator capable of volatilizing with a group metal oxide precursor and a volatile anion or negative valence group from NiO. Preferred chemical activators or caustics include the common acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and hydrazine bisulfate, with hydrochloric acid and hydrazine bisulfate being the best. Generally, a preferred method of the present invention involves applying a solution of at least one platinum group metal compound, at least one nickel metal compound, a chemical caustic agent, and a volatile organic excipient such as isopropanol to the desired substrate; The excipient is evaporated to leave the corrosive agent and the dissolved metal values, and then these metal values are concentrated and the volatilized corrosive agent is substantially removed along with the anions or negative valence groups from the metal oxide precursor. heating the substrate to a temperature sufficient to expel the metal to a temperature sufficient to thermally oxidize the metal in situ on the substrate in the presence of oxygen or air, converting it to a metal oxide. . The process can be repeated many times to increase the film thickness and achieve the best effect of the invention. Additionally sometimes two or three of the metal oxide precursors are added between each thermal oxidation step.
There are benefits to be gained from having the above layers. In a particularly preferred embodiment, the electrode material consists of a nickel oxide on a nickel metal layer (which may also be in the form of a nickel layer on a conductive substrate) and a platinum group metal oxide (optionally with a modifying metal oxide, e.g. ZrO ₂ ). (a) coating the nickel metal layer with a coating solution consisting of a nickel oxide precursor, a platinum group metal oxide precursor, an optional modifying oxidation precursor, and an etchant that dissolves the most soluble portions of the nickel metal surface; (b) depositing the metal oxide precursor on the corroded nickel metal surface by heating and evaporating the volatile portion of the coating solution and (c) depositing the metal oxide precursor in the presence of air or oxygen. sufficient time to oxidize the metal
It is manufactured by a method of heating at a temperature of 300 to 600°C and (d) cooling the electrode material thus manufactured. Additional coatings are similarly applied to increase the thickness of the heterogeneous metal oxide formed on the nickel metal surface, but the etchant used to coat the second and subsequent coatings is the same as the etchant used for the first coating. However, they may also be different. Therefore, an electrode material is produced in which a heterogeneous metal oxide film consisting of a nickel oxide and a platinum group metal oxide, optionally containing a modifying metal oxide, is tightly adhered to a nickel metal layer. The platinum group metal oxide is preferably ruthenium oxide. A preferred optional modifying metal oxide is zirconium oxide. An economical form of nickel metal layer is a nickel layer on an inexpensive conductive substrate, such as steel or iron alloy. This electrode material is particularly useful as a cathode in chlor-alkali cells. The temperature at which metals are thermally oxidized depends on the metal.
Temperatures between 300 and 650°C are generally effective.
Thermal oxidation at temperatures between 350 and 550°C is generally preferred. The effect of the present invention is to produce a substantially hard deposit of a heterogeneous oxide of a particular metal. Using chemical etching methods of existing layers and/or substrates, the solubilization, concentration and in-situ deposition of the dissolved metal produce an intimate oxidation mixture that is mutually stable and electrocatalytically complementary. are within the scope of this invention. The following examples are illustrative of embodiments, but the invention is not limited thereto. Example 1 1 part of RuCl _{3.3H 2} O, 1 part of NiCl _{2.6H 2} O,
3.3 parts of H ₂ NNH ₂・H ₂ SO ₄ (hydrazine bisulfate),
A solution was made consisting of 5 parts H ₂ O and 28 parts isopropanol. First, all components except isopropanol were mixed and stirred overnight, then isopropanol was added and mixed for about 6 hours. He created a cathode made of 40% expanded nickel. After first sandblasting the cathode 1:
Etched with 1HCl. Then, it was soaked in isopropanol and air-dried. The cathode was immersed in the coating solution, air-dried, and then baked in an oven at 375°C for 20 minutes. The membrane was applied a total of 6 times in the same manner. Cathode at 90℃ with 35% NaOH
The potential was measured using a standard calomel reference electrode (SCE) and a Luggin probe by immersing it in a bath and passing an electric current through it. A cathode potential of -1145 mV was measured for SCE at a current density of 2 amps per square inch (0.31 amp/cm ² ). The cathode was installed in an experimental membrane chlorine electrolyzer at a concentration of 31-33% NaOH.
It was operated at a current density of 0.31 amp/cm ² (2 amp/in ² ) and 90° C. to produce H ₂ at the anode and Cl ₂ at the cathode. The cathode potential was checked and averaged for one week. The results are shown in the table. Example 2 A solution was prepared consisting of 1 part RuCl ₃ .3H ₂ O, 1 part NiCl ₂ .6H ₂ O and 3.3 parts concentrated HCl. This solution was mixed overnight. Next, 33 parts of isopropanol was added and mixed for 2 hours. A cathode was made by the method of Example 1. A film was applied to the cathode in the same manner as in Example 1, except that the firing temperature was 495-500°C. The membrane was applied 10 times. Cathode potential was measured as in Example 1. The potential was -1135 mV vs. SCE. A cathode was attached to an experimental chamber containing a commercially available naphionic polymer (trade name of EI DuPont de Nemaux) membrane. 90
°C, NaOH31−33%, current density 0.31amp/ ^cm2
The bath was operated at (2 amp/in ² ). The cathode potential was checked and the weekly average was calculated. The results are shown in the table. Example 3 1 part of NH ₂ OH・HCl, 5 parts of concentrated HCl, 10%
2 parts of H ₂ PtCl ₆・6H ₂ O, 1 part of NiCl ₂・6H ₂ O, and
A solution consisting of 1 part RuCl _{3.3H 2} O was prepared. After this liquid was mixed for 12 hours, 75 parts of isopropanol was added and mixed for 2 hours. A cathode was prepared in the same manner as in Example 1, and then a film was applied in the same manner as in Example 1, except that the firing temperature was 470-480°C, and the film was applied five times. After applying the sixth film, the electrode was baked at 470-480°C for 30 minutes. The cathode potential was checked in the same manner as in Example 1 and was -1108 mV with respect to SCE. A laboratory membrane chlorine electrolyzer with a commercially available membrane as in Example 2 was fitted with a cathode.
90℃, NaOH 31-33%, current density 0.31amp/ ^cm2
The bath was operated at (2 amp/in ² ). The cathodic potential and weekly average results are shown in the table. Example 4 RuCl ₃・3H ₂ O3 parts, NiCl ₂・6H ₂ O3 parts, ZrCl ₄ 1
A solution consisting of 5 parts of concentrated hydrochloric acid and 42 parts of isopropanol was prepared and mixed for 2 hours. The cathode was coated with a membrane as in Example 1. However, the firing concentration is 495 to 500
℃. After applying the 8th membrane and the 9th membrane
Bake at 470-480℃ for 30 minutes. Measure the cathode potential
It was -1146 mV versus SEC. A membrane chlorine experimental tank with a commercially available membrane as in Example 2 was equipped with a cathode. 90℃, NaOH 31−33%, current density
The cathode potential with the cell operated at 0.31 amp/cm ² (2 amp/in ² ) was tested and the weekly average values are shown in the table. Example 5 (Reference Example) A cathode was prepared as in the previous example and immersed in a solution containing 1 g of tetraisoproponol titanate in 100 ml of isopropanol. Then the cathode is 475−500
Baked at ℃ for 10 minutes. The membrane was applied three times. Example 2
Make a solution as shown below, immerse the cathode in this solution and air dry it.
Calcined at 475-500℃. The membrane was applied in 6 replicates. The cathode potential was measured as in the previous example and was -1154 mV vs. SCE. A cathode was attached to a membrane chlorine experimental tank with a commercially available membrane as in Example 2. 90℃,
NaOH 31−33% and current density 0.31amp/ ^cm2
The cathode potential was measured by operating the tank at (2 amp/in ² ), and the weekly average values are shown in the table and Figure 1. Example 6 (Comparative Example) 40% Swelling of Steel An electrode was prepared and installed as a cathode in an experimental tank using the same type of membrane as in Examples 2-5 without a membrane. The weekly average value of the cathode potential is shown in the table. Example 7 (Comparative Example) 40% Expansion of Nickel - An electrode was made, but without a membrane, and installed as a cathode in an experimental cell with the same type of membrane as in Examples 2-5. The weekly average values of the cathode potentials are shown in the table and Figure 1.

【table】

[Table] Example 8 While maintaining the anode and cathode chambers of the electrolytic cell at atmospheric pressure,
°C, NaOH 31−33% and current density 0.31amp/
The same electrolytic cell as in Examples 2-7 was operated at ² amp/in ² . Anolyte concentration NaOH180−200
Sodium chloride solution and water were fed into the anolyte and catholyte compartments, respectively, to maintain 31-33% g/g/NaOH. Internal mixing of the electrolyzer was obtained by the natural rise of gases due to the evolution of hydrogen from the cathode and chlorine gas from the anode. Data including the energy balance of the material is collected periodically during the operation of the electrolyzer.
The energy required for NaOH production was calculated. The results are shown in Table 2. Table 2 Electrodes #Cathode NWH/MTNaOH 2 With membrane 2208 3 With membrane 2221 4 With membrane 2229 5 With membrane 2259 6 Steel 2497 7 Nickel 2504 Example 9 A two-system pressure membrane chlorine electrolyzer for large-scale testing was assembled. System 1 had nickel and electrodes placed in the cathode chamber of the tank, and System 2 had the same structural specifications as the two-system electrolytic cell except that a steel wall cathode chamber and steel cathode were placed. The electrodes of line 1 were coated according to the method of the invention, while those of line 2 were not coated. A commercially available cation exchange membrane was placed in both systems as in Example 2. 90℃ in cathode chamber,
Current density 0.31amp/cm ² (2amp/in ² ) and
Two lines were run simultaneously at 31-33% NaOH. The two systems were operated at 101,325 to 202,650 Pa (1-2 atm) while circulating the anolyte and catholyte into the tank using a centrifugal pump. The ratio of catholyte flow to anolyte flow was kept above 1. Energy and material balance data were collected over 45 days and performance averages were calculated. The results show that the energy savings obtained by using the electrodes of the present invention (system 1) is 5% compared to system 2.
It was clearly shown that the above is true. It is also within the scope of the invention to use the novel electrodes of the invention at elevated temperatures in electrolyzers operated at high as well as low pressures. This electrode is also suitable for high temperature operation between 85 and 105°C. Approximately 101325Pa (1
Pressures up to 3 atm (303975 Pa) or higher can also be used, although pressures of up to 3 atm (303975 Pa) or higher are commonly used in chlor-alkali electrolysers. Although the electrode of the invention is useful in electrolytic cells where circulation within each electrolyte chamber is caused by upward movement (movement) of the product gas therein, the electrode of the present invention is useful in certain electrolytic cells where the electrolyte flows from cell to cell. Other pumping methods may be used to supplement or replace the gas upward movement. In some cases, it may be preferable to have a ratio of catholyte pump volume to anolyte pump volume greater than 1. The electrode of the present invention is useful in chlor-alkali electrolytes having an anolyte with a pH of 1 to 5, or adjusted, such as when an acid, such as HCl, is added to the anolyte.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between cathode potential and weekly average value in Examples 5 and 7.

Claims (1)

[Scope of Claims] 1. A layer of an electrically conductive metal substrate and an electrocatalytically active coating deposited thereon, the coating comprising a metal oxide comprising at least one platinum group metal oxide and NiO. An electrode for an electrolytic cell characterized by being made of a heterogeneous mixture of substances. 2. The electrode of claim 1, wherein the conductive metal substrate is nickel and the platinum group metal oxide is an oxide of at least one metal selected from Ru, Rh, Pd, Os, Ir and Pt. 3. The electrode according to claim 1 or 2, wherein the platinum group metal oxide is _RuO2 . 4. The electrode according to any one of claims 1 to 3, wherein the heterogeneous metal oxide coating contains a metal oxide that is a modifier for modifying the heterogeneous mixture. 5. The electrode of claim 4, wherein the modifier is _ZrO2 . 6. An electrode according to any one of claims 1 to 5, wherein the electrode is a low hydrogen overvoltage cathode for a chlor-alkali electrolyzer. 7 (a) On a conductive substrate, a nickel compound which is a precursor of nickel oxide, at least one platinum group metal compound which is a precursor of a platinum group metal oxide, and the surface of the substrate and/or the surface of an existing coating. (b) applying a coating solution containing a corrosive agent capable of corroding the substrate; and (b) heating to remove volatile components from the substrate thus coated to remove the metal values of the precursor compounds and any leaching from the substrate or existing coating. (c) further heating in the presence of oxygen, air or an oxidizing agent to a temperature sufficient to oxidize the metal values in the coating; and A method for producing an electrode for an electrolytic cell having a substrate coated with a solution of an electrocatalytically active heterogeneous mixture of metal oxides, the method comprising carrying out steps (a), (b) and (c) multiple times. 8. The method of claim 7, wherein the coating solution contains a metal compound that is a precursor of a metal oxide that is a modifier for modifying the heterogeneous mixture of nickel oxide and platinum group metal oxide. 9. The method of claim 8, wherein the modifier is zirconium oxide. 10. The method of claim 7, 8 or 9, wherein the platinum group metal is selected from platinum, ruthenium and alloys thereof. 11. Any one of claims 7 to 10, wherein the metal oxide precursor is selected from metal chlorides, nitrates, sulfates and phosphates, and the corrosive agent is selected from hydrochloric acid, sulfuric acid, phosphoric acid and hydrazine bisulfate. the method of. 12 The temperature at which metal valuables are oxidized is 300 to 600℃
The method according to any one of claims 7 to 11. 13. Claim 7, wherein the conductive metal substrate is nickel.
The method according to any one of ~12. 14. The method of any one of claims 7 to 13, wherein the electrode is a low hydrogen overvoltage cathode for a chlor-alkali electrolyzer.