FI75872C - Electrode for use in an electrochemical cell and its preparation - 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

75872

Electrode for use in an electrochemical cell and its manufacture

The invention relates to electrodes and to a method of manufacturing the same, as well as to their use in electrolytic cells, for example cells used in brine electrolysis.

There are three general types of electrolytic cells used in the production of chlor-alkali: (1) a mercury cell, (2) a diaphragm electrolytic cell, and (3) a membrane-10 cell. The operation of each of these cells is discussed in Volume 1 of the third edition of the Kirk-Othmer Encyclopedia of Chemical Technology, starting on page 799. Other electrolytic cells using electrodes for the electrolysis of aqueous solutions are so-called "chlorate cells", in which there is no divider or separator between the cathodes and the anodes. In mercury cells, an alkali metal prepared by electrolysis of an alkali metal salt forms an amalgam with mercury; when the amalgam is reacted with water, it forms NaOH and releases mercury, which can be recovered and recycled for further use as a liquid cathode.

In many chlor-alkali electrolysis processes, the brine (electrolyte) is electrolyzed by allowing an electric current to pass through it in a cell with a diaphragm or membrane placed between the cathode and the anode. Chlorine is formed at the anode, while sodium hydroxide (NaOH) and hydrogen (H2) are formed at the cathode. Brine is continuously fed to the cells, while Cl 2, NaOH and H 2 are continuously removed from the cells.

The minimum voltage required to electrolyse the electrolyte to C 1, NaOH and H 2 can be calculated using thermodynamic data. However, in commercial operation, the theoretical voltage is not achievable and higher voltages must be used to overcome the different resistances inherent in different cell types. In order to improve the efficiency of the operation of the diaphragm or membrane cell 2 75872, efforts may be made to reduce the overvoltages of the electrodes, to reduce the electrical resistance of the diaphragm or membrane, or to reduce the electrical resistance of the electrolyzable saline solution. The invention described herein results in an electrode that is particularly useful as a cathode in the electrolysis of saline; the cathode overvoltage is substantially reduced, leading to higher power efficiencies.

Because many millions of tons of alkali metal halide-10 volumes and water are electrolyzed every year, even a reduction as low as 0.05 volts in operating voltage brings very significant energy savings. The industry is thus seeking to find ways to reduce voltage requirements.

15 Throughout the development of chlor-alkali technology, various methods have been developed to reduce artificial voltage. Some experts have focused on reducing the cell voltage to change the physical design of the electrolytic cell, while others have focused on reducing the overvoltage at the anode or cathode. This publication relates, in part, to a new method for manufacturing an electrode characterized by a remarkably low overvoltage and to the use of these electrodes in electrolysis cells.

It has been shown that electrode overvoltage is a function of current density and electrode composition, Physical Chemistry, 3rd Edition, W.J. Moore, Prentice Hall (1962), p. 406-408), wherein current density means the current applied per unit area of the actual surface area of the electrode, and composition means the chemical and physical composition of the electrode. Therefore, a method that increases the surface area of the electrode reduces its overvoltage by a given apparent current density.

It is also desirable to use a composition of matter which is a good electrocatalyst; this further reduces the overvoltage.

It is known in the art to use plasma or flame sprays 3,75872 to coat an electrode with an electrically conductive metal; U.S. Patent 1,263,959 describes that anodes can be coated by spraying fine nickel particles onto the anode, whereby the particles are melted and pressed into an iron substrate.

The cathodes are also coated with electrically conductive metals; according to U.S. Patent 3,002,278, the cathodes were coated by plasma spraying or flame spraying with a mixture of granular cobalt and granular zirconia. When 10 of these electrodes are used in the electrolysis of an aqueous solution of water or an alkali metal halide salt, they are said to slowly lower the hydrogen overvoltage.

Many metals and combinations of metals have been used to coat electrodes by plasma or flame spraying; U.S. Patent 3,630,770 describes the use of lanthanum boride; U.S. Patent 3,649,355 describes the use of tungsten and tungsten alloy; U.S. Patent 3,788,968 describes the use of titanium carbide or titanium nitride and at least one platinum group metal and / or metal oxide and a second porous oxy-20 layer; U.S. Patent 3,945,907 describes the use of rhenium; and U.S. Patent 3,974,058 describes the use of cobalt as a coating using ruthenium as the topcoat.

Likewise, it is known in the art to prepare porous electro-rhodium coatings by selective extraction. By coating the electrode with granular nickel, followed by sintering nickel as described in U.S. Patents 2,928,783 and 2,969,315; electroprecipitating the alloy on the surface of the substrate and then extracting one component of the alloy-30 g as described in U.S. Patent 3,272,788; pressing or cementing the two or more components together or on the surface of the electrode substrate and then selectively extracting one or more coating components as disclosed in U.S. Patent 3,316,159; 3,326,725; 3,427,204; 3,713,891 and 3,802,878.

4,75872

It is also disclosed in the art to combine a plasma or flame process step followed by an extraction step to make electrodes. The combination of the electroplating step followed by the extraction step is also shown. Examples of known methods are disclosed in the following patents: U.S. Patent 3,219,730 describes coating a substrate with a multiple oxide film coating, followed by removal of the substrate by extraction to give an electrode; U.S. Patent 3,403,057 describes the flame or plasma spraying of a Raney alloy on the surface of a substrate, followed by the extraction of aluminum out of the alloy to leave a porous electrode; U.S. Patent 3,492,720 describes the plasma spraying of tungsten, titanium or their alloys together with oxides of aluminum, thorium and zirconium on the surface of a substrate. The substrate was then removed, leaving a porous electrode.

U.S. Patent 3,497,425 describes the fabrication of porous electrodes by coating a substrate with a relatively insoluble metal, followed by coating with a more soluble metal. In this case, heat treatment is required to effect mutual diffusion of the two coatings, while optimum conditions require separate heat treatments for each coating. The soluble metal is then extracted, leaving a porous electrode. U.S. Patent 3,618,136 describes the preparation of porous electrodes by coating the surface of a substrate with a binary salt mixture and extracting the soluble component from the system. The publication states that it is critical that the binary salt mixture is a eutectic mixture and that optimal results are obtained when the same anions are used in both active and inactive salts, for example silver chloride disodium chloride.

NL patent application 75 07550 describes the production of porous cathodes by applying to a substrate a coating consisting of at least one base metal selected from the group consisting of nickel, cobalt, chromium, manganese and iron, alloyed with a secondary, less noble , a galvanic metal, followed by a step of at least partial removal of this galvanic metal. In particular, the galvanic metal is selected from the group consisting of sin-5, aluminum, magnesium and tin. The galvanic metal is removed by extraction with an alkali solution or an acidic solution.

JP Patent 31,661 describes the manufacture of a porous electrode by electroplating a nickel-10 coating on the surface of a substrate, followed by a zinc coating or a coating formed by some other soluble substance that is soluble in an alkaline solution. These coated electrodes are then immersed in an alkaline solution or subjected to an electrochemical anodizing treatment to elute and remove zinc and other solutes, thus forming a porous electrode. Prior to immersion, some embodiments require heat treatment of the coated electrode.

U.S. Patent 4,279,709 discloses a method of making electrodes 20 comprising low voltage overvoltage electrodes using a mixture of granular metal and granular inorganic blowing agent and then extracting the blowing agent away to form pores.

Electrodes comprising film-forming metal substrates, especially titanium, coated with metal oxides of Group VIII of the Periodic Table of the Elements have been shown to be useful, especially in combination with other metal oxides, as anodes in electrolytic processes such as saline electrolysis. Ruthenium oxides, platinum oxides, and other oxides of the "platinum metal series", in conjunction with many other metal oxides, have gained great popularity as coatings for valve metal substrates (particularly Ti) used as anodes. Patents 35 for such anodes include, for example, U.S. Patents 3,632,498 and 3,711,385. These coatings can be applied in a variety of ways, for example, U.S. Patent 6,75872 discloses that platinum group metal oxides, combined with film-forming metal oxides, can be applied. precipitating on the surface of the valve metal substrates by applying a mixture of thermally decomposable platinum group metal compounds and a thermally decomposable film-forming metal organo compound in an organic liquid solvent, which may also optionally contain a reducing agent, on a surface of an organic solvent, by drying solvent, then heating the support in the range of 400-550 ° C to form metal oxides. The coating can be repeated to increase the thickness of the coating. The top coating formed by the film-forming metal oxide is also used. U.S. Patent 15,332,498 discloses that coatings composed of finely divided oxides of platinum group metals and film-forming metals can be prepared using a plasma torch by heating substrates coated with thermally decomposable compounds of platinum group metals and film-forming metals. followed by heating in air to form the oxide, among others.

Other patents for electrodes having metal oxide surfaces include, for example, U.S. Patents 3,616,445; 4,003,817; 4,072,585; 3,977,958; 4,061,549; 4,073,873 and 4,142,005.

The use of platinum group metal oxides, especially ruthenium oxide, as active coatings for hydrogen evolution 30 is also known (Melendres, Carlos A., Spring Meeting Electrochem. Soc., May 11-16, 1975). JP 9130/65, Applications (OPI) 131 374/74 and 11178/77 refer to the use of a mixture of platinum group metal oxide (s) with another metal oxide as active cathode coatings. U.S. Patent 4,238,311 discloses that a cathode coating consisting of fine grains of platinum group metals and / or platinum group metal oxides in nickel is useful as a cathode coating.

It is generally known to those skilled in the art that the use of platinum group metal oxides as active catalysts in the evolution of hydrogen in modern electrolytic chlorine alkali cells using permeable membranes is not appropriate due to the currently extremely difficult NaOH concentration-10% NaOH and temperature conditions. and temperatures above 95 ° C are not uncommon. Oxide coatings prepared in known ways have been found to thin in use and release from the substrate, probably in combination with substantial reduction, in some cases, to the metal form.

It is also well known to those skilled in the art that catalytic coatings composed of metals with inherently low hydrogen overvoltage properties tend to lose catalytic activity in practical applications due to the coating of metallic impurities, such as iron, which are present in the impurities. in the saline and water used in the rolysis process. Thus, active coatings which have been found by experts to be useful for the evolution of hydrogen in modern electrolytic membrane chlorine alkali cells are limited to the high surface area type or to porous coatings whose compositions are resistant to such chemical effects to some extent. or various stainless steels.

In these cases, the full effect of the catalytic nature of the inherently low hydrogen-overvoltage catalysts is not realized in practice because, as is known to those skilled in the art, the effectiveness of these substantially high surface area coatings decreases over time to 8 75872, characterized by an equivalent coating forms the predominant metallic impurity present in the saline or water used in the electrolytic process, usually iron. Thus, the steepness of the Tafel curve characterizing the electrolytic activity of the 5 coatings used changes substantially to the iron level, resulting in an increase in the hydrogen overvoltage, especially at high current densities, of 0.23-0.54 2 2 amps / cm (1.5-3.5 amps). / in) and more than 10 common in modern memembrane chlor-alkali cells. On the contrary, it is desirable to maintain the inherently low overvoltage properties of materials known to be characterized by the low steepness of the Tafel curve (i.e., platinum group metal oxides, especially ruthenium oxide) during prolonged use in membrane-chlor-alkali cells. It has now been found, among other things, that the active coatings formed by secondary electrocatalytic metals and platinum group metal oxides prepared by the process of the present invention surprisingly show low hydrogen overvoltage, high physical stability and long-term efficiency in cathode solids. , temperatures and process pressures. In addition, it has been found that the use of these electrodes in electrolysis processes that produce chlorine and NaOH at a given process temperature, a given process NaOH concentration, and a given process pressure results in lower energy requirements that are not otherwise achievable in practice. In particular, the invention relates to a method of manufacturing a low hydrogen overvoltage cathode, characterized in that a coating solution consisting of a metal oxide precursor compound or compounds and an etching liquid capable of etching any previously deposited substrate and / or surface, the substrate thus coated is heated to remove volatile constituents therefrom to enrich and redistribute the metal of the precursor compounds and the metal etched from the substrate or previous coating to the surface of the substrate or previously applied coating, and heating is continued in the presence of oxygen, air or sufficient to oxidize the metal, and wherein the coating procedure may be repeated at least once.

10 Figure 1 shows graphically the results of the experiments described later.

Electrodes treating an electrically conductive or non-conductive substrate having a coating of heterogeneous oxide mixtures of platinum group metals and secondary electrocatalytic metals are prepared by applying soluble metal compounds and an etching liquid to the substrate and, in the case of successive coatings, , in this way, such as us-20, by etching and dissolving the least chemically resistant parts of the coating, after heating the substrate to oxidize the metals, enriching and reprecipitating said metals on the surface of the substrate, and oxidizing them to obtain substantially hard metal heterogeneous oxides. , a stable relationship.

The preferred electrically conductive substrate can be any metal structure that retains its physical integrity during electrode fabrication. Metal laminates 30 may be used, such as ferrous metal coated with another metal, for example nickel or a film-forming metal (also known as valve metal). The substrate may be a ferrous metal such as iron, steel, stainless steel or other metal-35 alloy in which the main component is iron. The substrate may also be a non-ferrous metal such as a film-forming metal or a non-film-forming metal such as Ni. Film-forming metals in this field include, in particular, titanium, tantalum, zirconium, niobium, tungsten and their alloys with each other and with small amounts of other metals. Non-conductive substrates can be used, especially if they are coated with a conductive layer on which metal oxides are doped.

The substrate 10 used in this coating method may be in the form of a flat plate, a curved surface, a helical surface, a perforated plate, a tongue, a wire mesh plate, a rod, a tube, a porous, non-porous, sintered, wire-like, regular or irregular. This new coating method does not depend on the form of the substrate, since the chemical and thermal steps used are applicable to virtually any form useful as an electrode article. Many electrolytic cells contain perforated (network) plates or flat plates; sometimes these are bent to form "pocket" electrodes 20 having substantially parallel sides in a spaced apart relationship.

The preferred substrate form comprises a mesh, perforated sheet, vanadium, sintered metal, sheet or fine sheet, with the mesh being one of the most preferred porous substrates.

The preferred composition of the substrate comprises nickel, iron, copper, steel, stainless steel or ferrous metal laminated with nickel, with nickel being particularly preferred. It is to be understood that these substrates on the surface of which the metal oxide coatings will be deposited may themselves be supported or reinforced by the underlying substrate or support, especially when nickel, iron or copper is supported by or on the underlying substrate or support. The substrate on the surface of which the metal oxide coating will be deposited may itself be the outermost layer of the laminate or coated structure, and may be a potentially non-conductive substrate on the surface of which the metal oxide coating is deposited.

The platinum metal series comprises the metals Ru, Rh, Pd,

Os, Ir and Pt. Of these, the preferred metals are platinum and ruthenium, with ruthenium being the most preferred. The soluble platinum metal compound may be a halide, sulfate, nitrate or other soluble salt or soluble compound of a metal, and is preferably a halide salt such as RuCl 2 'hydrate, PtCl 4' hydrate and the like.

The secondary electrolytic metal oxide precursor of the coating may be at least one compound derived from soluble compounds of the following elements: Ni, Co, Fe, Cu, W, V, Mn, Mo, Nb, Ta, Ti, Zr, Cd, Cr, B, 15 Sn, La or Si. Preferred of these are Ni, Zr and Ti, with nickel being most preferred.

The solution of the present invention contains at least one chemically active substance capable of etching the substrate and, in the case of the second or subsequent coating 20, etching and dissolving the most chemically sensitive components of the previously formed oxides, while also, preferably raising the temperature, evaporating, in many cases, heated of the mixture, together with the vaporized anions and the negative valence radicals of the platinum metal oxide precursor and the secondary electrocatalytic metal oxide precursor. Preferred chemically active etching liquids include the most common acids, such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid; also hydrazine hydrogen sulfate, and the like, with hydrochloric acid and hydrazine hydrogen sulfate being most preferred.

In general, the preferred method of the invention comprises applying to a desired substrate a solution containing at least one platinum metal series compound 35, at least one electrocatalytic metal compound, and a chemical etching liquid, preferably 12,75872 containing a volatile organic solvent such as isopropanol; and evaporating the volatile solvent to leave the etching liquid and dissolved metal; then heating the substrate to a temperature sufficient to enrich the metals, including substantially expelling the vaporized etching fluid along with anions or negative valence radicals released from the metal oxide precursors, and heating the substrate in the presence of oxygen or air to a temperature sufficient to thermally oxidize metals into metal oxides in situ on the surface of the substrate. The steps can be repeated many times to achieve the best complete effect of the invention by increasing the thickness of the coating. In addition, it is sometimes useful to place two or more layers of metal oxide precursors between each thermal oxidation step.

In a particularly preferred embodiment, the electrode material is prepared by placing a heterogeneous metal oxide coating, said heterogeneous metal oxide coating containing nickel oxide and platinum group metal oxide (optionally a modifier metal oxide, e.g. comprising (a) applying coating solutions to said nickel metal layer containing a nickel oxide precursor, a platinum group metal oxide precursor, a possible modifier and a metal oxide precursor, and for dissolving the most soluble components of the nickel metal surface enrichment and precipitation on the nickel metal surface thus etched, (c) heating in the presence of air or oxygen to a temperature of 300 -600 ° for a time sufficient to oxidize the metals of the metal oxide precursors, and (d) cooling the electrode material thus prepared. Additional layers may be applied in the same manner to increase the thickness of the heterogeneous metal oxide coating thus prepared on the surface of the nickel metal, and the etching liquid for applying the second and subsequent coatings may preferably be the same or different from the etching liquid used for applying the first coating. Thus, an electrode material is prepared comprising a nickel metal layer to which a heterogeneous metal oxide coating comprising nickel oxide and a metal oxide of the platinum group, optionally also a modifier metal oxide, is tightly attached. Preferably, the platinum group metal oxide is ruthenium oxide. The preferred possible modifier metal oxide is zirconia. The economical form of the nickel metal layer is a nickel layer on the surface of a cheaper electrically conductive substrate, such as steel or iron alloy. Such an electrode material is particularly useful as cathodes in chlor-alkali cells.

Usually, the temperatures at which thermal oxidation of the metals is achieved depend to some extent on the metals, but a temperature in the range of 350-550 ° C is generally effective. It is generally preferred that the thermal oxidation be performed at a temperature of 350-330 ° C.

It is an object of the invention to provide a substantially hard, adhesive coating of heterogeneous oxides of soluble metals.

It is within the scope of this invention that dissolving, enriching and in situ precipitating dissolved metals using chemical etching of previously precipitated layers and / or substrate provides a homogeneous mixture of oxides in which the oxides are mutually stabilizing and electrocatalytically complementary.

The following examples illustrate specific embodiments.

Example 1 A solution containing 1 part was prepared

RuCl 2, S 2 O, 1 part NiCl 2, 61 parts, 3.3 parts I 2 NNH 3 * 14 75872 (hydrazine hydrogen sulfate), 5 parts IVO and 28 parts isopropanol. The solution was prepared by first mixing all the other ingredients except isopropanol with stirring overnight, then adding isopropanol and continuing to stir for about 6 hours.

A cathode consisting of 40% stretched nickel mesh was prepared. The cathode was first sandblasted and then etched in 1: 1 HCl. It was then rinsed, immersed in isopropanol and air dried.

The cathode was coated by immersing it in a coating solution, allowing it to air dry, then annealing it in an oven at 375 ° C for 20 minutes. A total of 6 coatings were applied in the same manner. The cathode was immersed in a heated bath containing 35% NaOH at 90 ° C. 15 Power was applied to the equipment and potential measurements were made using a standard calomel reference electrode (SCE) and a Luggin probe. The cathode potential was measured at -1145 millivolts versus SCE at a current density of 2 amps 2 per square inch (0.31 amps per cm). The cathode was placed in 20 laboratory membrane chlorine cells and operated at 90 ° C, producing C 1 at the anode and H 2 at the cathode, with a NaOH concentration of 31-33%, operating at a current density of 0.31 am-2 2 psi / cm ). The cathode potential was monitored and averaged per week. The results are shown in Table 25.

Example 2

A solution of 1 part RuCl 3 * SIMO, 1 part NiCl 2 * 6H 2 O and 3.3 parts concentrated HCl was prepared. It was allowed to stir overnight. Thereafter, 33 parts of isopropanol were added and stirring was continued for 2 hours. The cathode was prepared according to the method of Example 1. The cathode was then coated in the same manner as in Example 1 except for annealing at 495-500 ° C. Ten-35 coats were applied. The cathode potential was measured as in Example 1. The potential was -1135 millivolts versus SCE. Cathode 15 75872 was mounted in a laboratory cell containing a membrane of a commercially available NAFION * polymer (* E.I. DuPont de Nemours). The cell was operated at 90 ° C, 31-33% NaOH, and at a current density of 0.31 am-2 2 5 psi / cm (2 amps / in). The cathode potential was monitored and averaged per week. The results are shown in Table I.

Example 3

A solution of 1 part 10 NH 2 OH'HCl, 5 parts concentrated HCl, 2 parts 10% t 2 PtCl 2 * 6H 2 O, 1 part NiCl 2 * 6H 2 O and 1 part RuCl 2 '3 H 2 O was prepared. The solution was allowed to stir for 12 hours. 75 parts of isopropanol were then added and stirring was continued for 2 hours. The cathode was prepared according to Example 1. Thereafter, the cathode was coated in the same manner as in Example 1 except for annealing at 470-480 ° C. Five coatings were applied. The sixth coating was applied and the electrode was annealed for 30 minutes at 470-480 ° C. The cathode potential was mi-20 as in Example 1. The potential was -1108 milli-volts versus SCE. The cathode was mounted in a laboratory membrane-chlorine cell containing a commercially available membrane as in Example 2. The cell was operated at 90 ° C, 31-33% NaOH, and at a current density of 0.31 am-25 psi / cm (2 amps). ). The cathode potential was monitored and averaged per week. The results are shown in Table I.

Example 4

A solution was prepared containing 3 parts of RuCl 2 * 3H 2 O, 3 parts of NiCl 2 * 6H 2 O, 1 part of ZrCl 2, 5 parts of concentrated HCl, and 42 parts of isopropanol. The solution was allowed to stir for 2 hours. The cathode was then coated in the same manner as in Example 1 except for annealing at 495-500 ° C. Kah-35 dexa coating was applied. The ninth coating was applied and the electrode was annealed for 30 minutes at 16,75872 470-480 ° C. The cathode potential was measured as in Example 1. The potential was -1146 millivolts versus SCE. The cathode was mounted in a laboratory membrane chlorine cell containing a commercially available membrane as in Example 2. The cell was operated at 90 ° C, 31-33% NaOH, 2 2 and a current density of 0.31 amps / cm (2 amps / in). The cathode potential was monitored and averaged per week. The results are shown in Table I.

Example 5 A cathode was prepared as in the previous examples, then immersed in a solution of 1 gram of tetraisopropyl titanate in 100 ml of isopropanol. The cathode was then annealed at 475-500 ° for 10 minutes. Three coatings were applied. The solution was prepared as in Example 2. The cathode was immersed in the solution, air dried, and dried at 475-500 ° C. Six coatings were applied. The cathode potential was measured as in the previous examples. The potential was -1154 millivolts versus SCE. The cathode was mounted in a laboratory membrane-20 chlorine cell containing a commercially available membrane as in Example 2. The cell was operated at 90 ° C, 31-33% NaOH, and at a current density of 0.31 am-2 2 psi / cm (2 amps). / in). The cathode potential was monitored and averaged per week. The results are shown in Table I and also in Figure 1.

Example 6 (Comparative Example) A 40% stretched steel electrode mesh was prepared, but not coated, and placed as a cathode in a laboratory cell as in Examples 2-5, using a membrane of the same type. The cathode potential was monitored and averaged per week. The results are shown in Table I. Example 7 (Comparative Example)

A 40% stretched nickel mesh electrode was prepared, but not coated, and mounted as a cathode in a laboratory cell as in Examples 2-5, using the same membrane type. The cathode potential was monitored and averaged per week. The results are shown in Table I and also in Figure 1.

17 75872

Table

Negative voltage * ^ which is the average of each week for electrodes 1-7_! ^ Kon Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 No. - - - - - - - 1 1,145 1,120 1,135 1,120 1,140 1,475 1,490 2 1,150 1,120 1,150 1,130 1,130 1,460 1,475 3 1,150 1,125 1,160 1,150 1,110 1,455 1,470 4 1,155 1,130 1,150 1,155 1,080 1,455 1,470 5 1,155 1,130 1,150 1,150 1,070 1,465 1,475 6 1,150 1,130 1,180 1,150 1,060 1,475 1,480 7 1,150 1,125 1,18 1,480 1,495 8 1,150 1,125 1,180 1,160 1,060 1,480 1,510 9 1,140 1,120 1,160 1,155 1,070 1,480 1,510 10 1,130 1,110 1,185 1,160 1,080 1,475 1,510 11 1,115 1,115 1,190 1,170 1,080 1,480 1,515 12 1,100 1,110 1,190 1,165 1,080 1,490 1,520 13 1,100 1,110 1,190 1,165 1,010 14 1,100 1,115 1,190 1,170 1,080 - 1,520 15 1,095 1,120 1,190 1,170 1,090 - - 1,525 16 1,090 1,120 1,190 1,170 1,090 - - 1,530 17 1,085 1,120 1,190 1,170 1,090 - - - 18 1,080 1,120 1,190 1,165 1,100 - - - 19 1,080 1,110 1,190 1,160 1,100 - - - 20 1,080 1,110 1,190 - 1,100 - - 21 1,080 1,110 1,190 - - - - 22 1,090 - - 1,190 23 1,090 - 1,190 - - - - 24 1,100 - 1,190 - - - - 25 1,100 - - - - - - 26 1,090 - - - - - - 27 1,090 - - - - - - VES - Comparative example ie 75872 ♦ All the voltages shown in Table I were measured in the same way, using a Luggin probe, i.e. they are comparable with each other, although all are believed to be slightly lower than could be expected theoretically by calculation. Thermodynamic calculations give a true absolute reversible voltage of about -1.093V for a cell at 90 ° C in 31-33% NaOH, and a current rate of 0.31 amps cm (2 amps / in).

Example 8 The cells of Examples 2-7 were used at 90 ° C, 31-33% 2

In NaOH and at a current density of 0.31 amps / cm (2 amps-2 rpm) while maintaining the anolyte and catholyte compartments of the cell at atmospheric pressure. Sodium chloride-saline and yesi were fed to the anolyte and catholyte compartments, respectively, to maintain anolyte concentrations in the range of 180-200 grams per liter of NaCl and 31-33% NaOH. The internal mixing of the cells was carried out with a natural gas rise due to the evolution of hydrogen gas at the cathode and the evolution of chlorine gas at the anode. Data covering mass and energy balances were periodically collected over the life of the cells and the energy requirements for NaOH production were calculated. The results are shown in Table 2.

Table 2

25 Electrode Cathode KWH / MT NaOH

2 Plated 2208 3 "2221 4" 2229 30 5 "2259 6 steel 2497 7 nickel 2504

Example 9

In a large-scale experiment, two sets of 35 pressure membrane chlorine cells were constructed. The structure and design of the cells 1975872 were similar except that the series 1 cathode compartment was nickel-walled and nickel electrodes were installed in the cell catholyte compartment, while the series, called series 2, was constructed of a steel-walled cathode compartment and steel cathodes. Series 1 electrodes were coated according to the method of the invention, while series 2 electrodes were uncoated. Both kits were equipped with a commercially available cation exchange membrane as in Example 2.

Both sets were used simultaneously at 90 ° C, at a current density of 0.31 amps / cm (2 amps / in), and with 31-33% sodium hydroxide in the catholyte chamber. The kits were operated at pressures of 101,325-202,650 Pa (1-2 atmospheres) while the anolyte and catholyte were recirculated through the cells using centrifugal pumps. The ratio of catholyte flow to anolyte flow was maintained at a value greater than 1. Energy and mass balance data were collected and average performance data were calculated over a 45-day period. The results clearly show that the energy savings achieved using the electrodes of the present invention (series 1) averaged greater than a 5% energy reduction compared to series 2.

It is within the scope of this invention to use these novel electrodes at temperatures found in cells operated at pressures above atmospheric pressure, as well as at pressures at or below atmospheric pressure. The electrodes are particularly well suited for use in the high temperature range of 85-105 ° C. Pressures of about 101,325 Pa (1 atm) are commonly used in chlor-alkali, although pressures of about 303,975 Pa (3 atm) or more may be used.

The electrodes of this invention are useful in cells in which circulation in each electrolyte compartment is accomplished by gas lift (displacement) of the gaseous products produced therein, although in some cells, such as serial electrolyte flow from cell to cell, a different means of pumping is used. can be used to supplement or replace gas purchase. It was found that in some cases it was advantageous to keep the ratio of the volume of the pumped catholyte to the volume of the pumped anolyte at a value greater than 1.

The electrodes of this invention are useful in chlor-alkali electrolysis cells in which the pH of the anolyte is in the range of 1-5, such as when an acid, e.g., HCl, is added to the anolyte.

Claims (17)

21 75872 A method of manufacturing a low hydrogen overvoltage cathode, characterized in that a coating solution consisting of a metal oxide precursor compound or compounds and an etching liquid capable of etching the substrate and / or any previously applied coating is applied to the electrically conductive substrate. 10 is heated to remove volatile constituents therefrom to enrich and redistribute the metal of the precursor compounds and the etched metal from the substrate or previous coating to the surface of the substrate or previously applied coating, and continue heating from the presence of oxygen, air or oxidizing agent to a temperature sufficient to oxidize the metal; repeated at least once. Process according to Claim 1, characterized in that the metal oxide precursor compound is a metal chloride, nitrate, sulphate or phosphate. Process according to Claim 1 or 2, characterized in that the metal precursor compounds comprise at least one metal compound in which the metal is selected from the group consisting of Ru, Rh, Pd, Os, Ir and Pt, and a nickel compound and, if appropriate, a zirconium compound. Process according to Claim 1, 2 or 3, characterized in that the etching agent is hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid or hydrazine hydrogen sulphate. 5 Rh, Pd, Os, Ir and Pt, and possibly a small amount of modifier metal oxide. Process according to Claim 1, characterized in that the temperature at which the oxidation of the metal 75872 is carried out is in the range from 300 to 600 ° C and that the heating of the substrate takes 5 to 60 minutes. An electrode for use in an electrochemical cell comprising a nickel metal layer to which a heterogeneous metal oxide coating is tightly attached, characterized in that the heterogeneous metal oxide coating consists essentially of nickel oxide and a platinum group metal oxide. Electrode according to Claim 6, characterized in that the platinum group metal oxide is ruthenium oxide. Electrode according to Claim 6, characterized in that the heterogeneous metal oxide coating also contains a small amount of modifier metal oxide in addition to nickel oxide and platinum group metal oxide. Electrode according to Claim 6, characterized in that the nickel metal layer is attached to the substrate. Electrode according to Claim 6, characterized in that the nickel metal layer is attached to an electrically conductive substrate. Electrode according to Claim 6, characterized in that the nickel metal layer is attached to a non-electrically conductive substrate. Electrode according to Claim 6, characterized in that the metal oxide coating comprises nickel oxide and ruthenium oxide and a small amount of ZrO 2 as a modifier metal oxide. Electrode according to Claim 6, characterized in that the nickel metal layer is in the form of a network. 14. A low hydrogen-cathode cathode for use in a chlor-alkali electrolytic cell comprising a substrate on which an electrocatalytically active coating has been deposited, characterized in that said coating comprises a heterogeneous metal oxide mixture containing nickel oxide. and at least one metal oxide wherein the metal is selected from the group consisting of Ru, Electrode according to Claim 14, characterized in that the substrate is electrically conductive and there is a nickel layer between the substrate and the heterogeneous metal oxide structure. Electrode according to Claim 14, characterized in that the heterogeneous metal oxide mixture comprises RuO 2 and NiO and a small amount of ZrO 2 as a modifying metal oxide. Electrode according to Claim 14 or 16, characterized in that the substrate is nickel metal. 75872