Electrochemical Methods

Patent #3,256,164--June 14, 1966

Donohue, John A., et al. Electrolytic Production of Ozone.

In this method of producing ozone, an electric current is passed through a liquid electrolyte, hydrogen fluoride containing not more than 10 weight percent of water, to produce a mixture of gases which contains ozone in large amounts. The procedure is carried out at a temperature of not more than 50 C but preferably between -20 C and +20 C. At least one weight percent of water must be present so that the electric current may pass through the liquid hydrogen fluoride and so that oxygen is present which may be converted to ozone.

Patent #4,316,782--February 23, 1982

Foller, Peter C., et al. Electrolytic Process for the Production of Ozone.

This patent discusses an electrolytic cell for production of ozone with current efficiencies of up to 52%. The cell uses a solution of highly electronegative anions, preferably hexafluoroanions of phosphorus, arsenic, or silicon. The anode is made of either platinum or lead dioxide, and the cathode is made or platinum, nickel, or carbon. A DC current is applied across the electrodes, ozone and oxygen are produced at the anode, and hydrogen gas is produced at the cathode.

Patent #4,375,395--March 1, 1983

Foller, Peter C., et al. Process for Producing Ozone.

This patent describes an electrolytic cell for production of ozone at high current efficiencies which uses glassy carbon electrodes. The glassy carbon electrodes are highly resistant to corrosion by the fluorine-anion-containing solutions commonly used in electrolytic cells which produce ozone at the anode. The claims are that ozone is produced at high current efficiencies when an electric current is passed through a bare glassy carbon anode and cathode in an electrolytic solution containing highly electronegative BF4- or BF6- anions. A disadvantage to this method of production of ozone is that glassy carbon electrodes are costly due to the time-consuming method of preparation.

Patent #4,416,747--November 22, 1983

Menth, Anton, et al. Process for the Synthetic Production of Ozone by Electrolysis and Use Thereof.

This patent outlines a process for production of ozone by electrolysis in which the produced ozone is used in water treatment. The anode and cathode are made of stainless steel, and between the anode and cathode is a solid electrolyte made of a plastic polymer based on perfluorinated sulphonic acids. The solid electrolyte serves as a thin ion-exchange membrane which is coated on the cathode side with a layer of a mixture of 85% by weight carbon powder and 15% by weight platinum powder. The anode side of the membrane is coated with PbO2 powder. A solution of oxygen-saturated water is fed into the cell, and ozone is produced in the solution on the anode side of the solid electrolyte ion-exchange membrane while water is formed on the cathode side. The H+ which is produced on the anode side by the decomposition of water to form oxygen and ozone migrates through the ion-exchange membrane and reacts with oxygen in the water on the cathode side to form water. The evolution of harmful hydrogen at the cathode is thereby suppressed.

Patent #4,541,989--September 17, 1985

Foller, Peter C. Process and Device for the Generation of Ozone via the Anodic Oxidation of Water.

This patent is an outline for an ozone generator using an electrolytic cell. The invention uses an air cathode to reduce the oxygen in air to water, and an inert anode to decompose the water to ozone. This patent claims to provide a method for producing ozone at levels of ten pounds per day by electrolysis using DC current.

Patent #5,154,895--October 13, 1992

Moon, Jae-Duk. Ozone Generator in Liquids.

This patent outlines a method of ozone generation in liquids which can be used in controlling biohazards in food processing, pharmaceutical chemical processing, treatment of water supplies, minor sewage disposal, and in various other disinfection techniques. The proposed ozonizing apparatus consists of one or more pairs of strip electrodes made of an oxidation-resistant metal such as Pt, PbO2, or SnO2 mounted on a substrate inside an ozonizing chamber with outer terminals extending outside the ozonizing chamber. The chamber has an inlet for a liquid such as water or solutions of H2SO4, HCLO4, HBF4, or H3PO4. An electric current is supplied to the electrodes through the terminals outside the chamber, and water molecules are dissociated at the electrodes producing ozone gas in the liquid. The apparatus

avoids the problems of ozone leakage into the air because it does not use the conventional blower to supply carrier air to the ozone generator.

Patent #5,203,972--April 20, 1993

Shimamune, Takayuki, et al. Method for Electrolytic Ozone Generation and Apparatus Therefor.

This patent is for an electrolytic cell which produces ozone. The electrolyte separating the anode and cathode is a solid electrolyte, preferably a perfluorocarbon sulfonic acid-based ion-exchange membrane. The anode is made by covering a titanium substrate first with a coat of platinum, gold, or like metal, and then with an electrodeposited layer of lead dioxide. An electric current is passed through the anode and cathode and ozone is formed at the anode in an ozone resistant anode chamber made of Teflon or titanium.

Patent #5,332,563--July 26, 1994

Chang, Shih-Ger. Yellow Phosphorus Process to Convert Toxic Chemicals to Non-Toxic Products.

This patent outlines a process which involves passing air or oxygen over aqueous emulsions of yellow phosphorus, P4, which results in the formation of P4O10 or P205, and an abundance of reactive species such as atomic oxygen and ozone (see Figure 5). The produced ozone is then used to treat solutions containing toxic inorganic or organic compounds by destroying the toxicity of the inorganic or organic components and resulting in a non-toxic solution. This process is a continuation of Patent #5,106,601, April 21, 1992. Patent #5,106,601 outlines a method for removing acid-forming gases such as NO and NO2 from exhaust gases. Ozone is produced in the process. The method involves passing the exhaust gas which contains oxygen as well as the nitrogen oxides over an aqueous emulsion of yellow phosphorus, P4. The yellow phosphorus reacts with the oxygen in the exhaust gases to form P4O10 or P205. The P4O10 then reacts with water vapor or water droplets to form phosphoric acid. When the pH of the emulsion or suspension is 3 or greater, the emulsion absorbs nitrogen oxides. When the phosphorus combines with oxygen molecules to form P4O10 or P205, a large amount of atomic oxygen is detected in area of the reaction. The atomic oxygen combines with oxygen molecules to form ozone in the presence of another molecule which remains unchanged after the reaction. The ozone produced oxidizes NO to NO2 which is more easily absorbed by the aqueous emulsion of yellow phosphorous.

Patent #5,460,705--October 24, 1995

Murphy, Oliver J., et al. Method and Apparatus for Electrochemical Production of Ozone.

This patent is for an electrochemical method and apparatus for production of ozone. The apparatus consists of an anode made up of a substrate and a catalyst coating. The substrate is made of either porous titanium, titanium suboxides, platinum, tungsten, tantalum, hafnium, niobium, or similar material, and the catalyst coating is selected from lead dioxide, platinum-tungsten alloys, glassy carbon or platinum. The cathode is a gas diffusion cathode consisting of a polytetrafluoroethylene-bonded, semi-hydrophobic catalyst layer supported by a hydrophobic gas diffusion layer. The catalyst layer consists of a proton exchange polymer, polytetrafluoroethylene polymer, and a metal such as platinum, palladium, gold, iridium, or nickel. The anode and cathode are separated by an ion-conducting electrolyte which is a proton

figure 6: Diagram of Apparatus Detailed in US Patent #5,332,563

exchange membrane with one side bonded to the catalyst layer of the gas diffusion cathode and a second side touching the anode. An electric current is passed through the anode and the gas diffusion cathode, and ozone is formed at the anode.