Changes in the Surface Chemistry and Adsorptive Properties of Active Carbon Previously Oxidised and Heat-Treated at Various Temperatures. II. Electrochemical Investigations of Surface Chemistry

Abstract

Thermal treatment of oxidised active carbon under vacuum conditions led to changes in the chemical nature of its surface, e.g. a stepwise decrease in the total oxygen content and an increase in the pH of the carbon slurry. Annealing reduced the number of surface oxygen-containing groups and increased the overall number of basic groups. The results of the cyclic voltammetric studies analysed in this paper clearly indicate only a weak relationship between the presence and number of cathodic/anodic peaks, i.e. reduction/ oxidation of electroactive surface groups, forming during cyclisation and the degree of surface oxidation (regulated by heat treatment) of the carbon samples tested. The electrochemical behaviour of powdered carbon suggested electrooxidation of the surface of the electrode material with participation of adsorbed hydroxy ions and water molecules. The possible electrochemical reactions and mechanisms of the surface processes were discussed in order to explain the observed phenomena.

Mechanically activated carbonized rayon fibers as an electrochemical supercapacitor in aqueous solutions

“…The fact that, relative to the peaks registered in acidic solution, they are shifted in cathodic direction, i.e. display pH dependence as observed in [50], makes reasonable the assumption that these peaks originate also from the quinone/hydroquninone reactions.…”

Influence of the surface chemistry of modified activated carbon on its electrochemical behaviour in the presence of lead(II) ions

“…The other two peaks, with binding energies 533.5 and 534.3 eV, can be ascribed to CAOAC and C@NAO moieties, respectively, in different surface oxygen-as well as oxygen-and nitrogen-containing functional groups [45][46][47][48]. The higher relative concentration of surface carbonyl groups on ammonia-treated carbons (HTA, OPA) suggests their higher ability to chemisorb dioxygen with the formation of a superoxide species (in the first stage) and then carbonyl moieties (surface autocatalytic oxidation) according to oxygen carbon electrode action [50][51][52]. We can also see that ammonia treatment leads to a decrease in elemental oxygen (more than heat treatment in vacuum) in the carbon material.…”

“…However, this method may be useful for investigated a series of materials from a common source (relatively changes brought about by modifications). In earlier papers we showed the different ways in which metal ions could be linked to a carbon surface and the dependence of the electrochemical behaviour of such a system on the chemical structure of the powder activated carbon electrodeÕs surface [50]. The method of surface modification also influences the electrochemical properties of the same carbon material.…”