KR910012344A - Improved electrocatalyst coating composition and method of preparing electrode using same - Google Patents

Abstract

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Description

Improved electrocatalyst coating composition and method of preparing electrode using same

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Claims (21)

Electrolysis of halogen-containing solutions, consisting of electrically conductive metal substrates with a coating of enhanced stability under alkaline conditions, with reduced oxygen evolution at low pH, wherein the coating of oxides present in the coating Based on 100 mole percent, it consists of 15-25 mole percent iridium oxide, 35-50 mole percent rudenium oxide and 30-45 mole percent titanium oxide, resulting in a coating of less than 1: 1 titanium. An electrode having a molar ratio of total oxides to iridium and rudenium, wherein the molar ratio of rudenium oxide to iridium oxide is 1.5: 1-3: 1. The electrode of claim 1, wherein the conductive metal substrate is comprised of a metal selected from titanium, tantalum, zirconium, niobium, aluminium, tungsten, and an alloy and an intermetallic mixture thereof. The electrode of claim 1, wherein the conductive metal substrate is comprised of titanium or an alloy or intermetallic mixture containing titanium. 4. The electrode of claim 3, wherein the conductive metal substrate is comprised of an annealed and corroded titanium substrate. The method of claim 1 wherein said coating is a non-homogeneous or smooth coating of a mixed oxide and consists essentially of 18-22 mol% iridium oxide, 35-40 mol% rudenium oxide and 40-44 mol% titanium oxide. Wherein the molar ratio of ruthenium oxide to iridium oxide is between 1.7: 1 and 2.2: 1. The electrode of claim 1, wherein the electrode is an anode in a membrane cell used for electrolysis of brine at a pH in the range of about 2 to about 4. 4. Based on 100 mole percent of the component, 15-25 mole percent of irinium, 35-50 mole percent of rudenium and 30-45 mole percent of thianium are provided. Consisting of an acidic aqueous medium containing, thereby having a molar ratio of titanium oxide to total oxide of iridium and rudenium of less than 1: 1, wherein the molar ratio of rudenium to iridium is 1.5: 1-3: 1 A coating composition suitable for providing a mixed metal oxide coating to a. 8. The coating composition of claim 7, wherein the acidic aqueous medium contains a strong inorganic acid in water and has a pH in the range of about 0.2 to about 0.8. The coating composition of claim 8, wherein said strong inorganic acid is hydrochloric acid. 8. The coating composition of claim 7, wherein said soluble component is compatible and is selected from chlorides, bromide, iodides and ammonium chloro salts. A coating composition according to claim 10, wherein all of the soluble components are chlorides and the aqueous medium contains hydrochloric acid. 8. The method of claim 7, wherein the ratio provides 18-22 mole percent iridium, 35-40 mole percent rudenium and 40-44 mole percent titanium, based on 100 mole percent of the components, wherein ruthenium to iridium A coating composition having a molar ratio of 1.7: 1 to 2.2: 1. 8. The coating composition of claim 7, wherein said coating composition provides an electrocatalyst coating of said mixed metal oxide on an electrically conductive valve metal substrate. Annealing the titanium substrate for at least about 0.25 hours at a temperature of at least about 450 ° C .: corroding the resulting annealed surface with a strong caustic to produce a roughened surface: 100 of the oxide present in the coating on the resulting stale surface 15-25 mole percent iridium oxide, 35-50 mole percent rudenium oxide and 30-45 mole percent titanium oxide, based on mole percent, with a coating of less than 1: 1 titanium oxide to iridium and Said components thermally degradable to provide a mixed oxide coating of the components in an amount such that the molar ratio of ruthenium oxide to total oxide of ruthenium oxide is 1.5: 1-3: 1 Applying an aqueous coating composition consisting of; Improved performance in chlor-alkaline cells when the electrolytic coating is present on the electrode in an electrically conductive metal substrate, consisting of heating the resulting coated substrate at a temperature of at least about 440 ° C. for at least about 3 minutes. To produce an electrode having an electrocatalyst coated. The method of claim 14, wherein the annealed substrate is cooled to at least substantially room temperature and the resulting cooled substrate is then corroded. 15. The method of claim 14, wherein the annealed substrate is corroded with a strong inorganic acid caustic. The method of claim 14, wherein the corroded surface is water washed prior to applying the coating composition. The method of claim 14, wherein the corroded surface is a rough, corroded surface. The method of claim 14, wherein the coating composition is applied to the titanium substrate by electrostatic spray application. The method of claim 14, wherein the titanium substrate is annealed at a temperature within about 600 ° C. to about 875 ° C. 16. The electrode produced by the method of claim 14, having reduced oxygen evolution at low pH during electrolysis of the halogen-containing solution while having enhanced stability coating under alkaline conditions. ※ Note: The disclosure is based on the initial application.