Voltammetric studies on glassy carbon electrodes I: Electrochemical behaviour of glassy carbon electrodes in H2SO4, Na2SO4 and NaOH media

Voltammetric investigations were carried out on glassy carbon electrodes in 0.5 M H2SO4, 0.5 M Na2SO4 and 1.0 M NaOH over a wide potential region from -2.5 V to +2.0 V versus a saturated calomel electrode at sweep rates up to 640 m V s-1. The results indicate three different processes. (1) In the middle of the potential region reversible surface redox processes take place. Fresh oxidation of surface carbon probably does not occur in this region. (2) In the anodic region surface oxidation as well as oxygen evolution reactions take place. This surface oxidation is probably linked with the activation of glassy carbon electrodes and hence is considered in some detail. (3) In extreme cathodic regions hydrogen adsorption takes place. The surface functional groups undergo spontaneous phase changes in both the middle and the anodic potential regions. The nature of the processes are probably controlled by pH. Preliminary studies in NaCl also indicate a substantial anion effect especially in the anodic region. A detailed discussion of glassy carbon surface behaviour is given with due consideration of earlier work in this field.