The Corrosion of Carbon Black Anodes in Alkaline Electrolyte IV. Current Efficiencies for Oxygen Evolution from Metal Oxide-impregnated Graphitized Furnace Blacks

Abstract

A quantitative method for determining the number of oxygenated carbon atoms in a carbon black sample was developed and applied to the study of oxygen chemisorption on graphitized furnace blacks. It was found that chemisorption of oxygen atoms produced in a low-pressure microwave discharge of argon/oxygen results in the formation of an oxygen complex on every carbon atom exposed on the edge plane surface of these carbons. These combined procedures were then used to titrate the surfaces of a variety of graphitized furnace blacks for the number of edge atoms. The corrosion rate of these carbons was found to be directly proportional to the number of sites titrated by oxygen atom chemisorption, i.e., the number of edge atoms. The number of edge atoms exposed on the surface of graphitized furnace blacks depends on the microstructure of the precursor carbon black and the conditions of graphitization. Catalyzation of these graphitized carbons by NiO has little or no effect on their corrosion rate, which results in current efficiencies for oxygen evolution greater than 98%. The absence of an effect of NiO on the corrosion rate is attributed to the specificity of the corrosion reaction to edge plane sites and an apparent necessity for contact between NiO particles with edge planes for catalyzation of the corrosion reaction by NiO. NiO particles sitting on basal planes, which compose at least 90% of the surface area in these carbons, catalyze only the oxygen evolution reaction. © 1989, The Electrochemical Society, Inc. All rights reserved.