This invention provides electrochemical methods for producing hydroxyl free radicals and decomposing by oxidation chemical substances dissolved in water. It utilizes a novel electrode which is capable of operation at sufficiently positive anodic potential to produce hydroxyl radicals. A complete device for oxidizing chemical substances dissolved in water is described, and operating conditions favorable to the method are discussed. Examples of oxidation reactions are presented, including oxidation of an herbicide, an insecticide, toluene, cresol, and a fluoroalkyl surfactant.