A new interpretation of the Acidic and Basic structures in Carbons. II. The Chromene-carbonium ion couple in Carbon

Abstract

The conflicting views of Frumkin, Shilov, and Steenberg on the chemical and adsorptive behaviour of sugar carbons activated at 800 °C (H-carbons) can be reconciled by postulating that the carbons contain chromene structures. The same is true of certain carbon blacks. The chromene system is readily oxidized at room temperature in the presence of acid to the corresponding benzopyrylium (carbonium) system, with the adsorption of the anion of the acid and the liberation of hydrogen peroxide. This reaction accounts for the dependence on the partial pressure of oxygen of adsorption of acid from dilute solutions, for the formation of peroxide from carbon with acids, and for the linear relationship between the potential of an H-carbon electrode and pH. A theoretical interpretation of the electrochemical behaviour of the chromene-carbonium ion couple is in good quantitative agreement with the observed behaviour of a cathodically polarized carbon electrode in acid solution. The ability of H-carbons to catalyse the oxidation of ferrous iron by molecular oxygen can also be accounted for by this couple, the concept of which is in agreement with the observed kinetic behaviour of the reaction.