Effect of Cathodic and Anodic Treatments of Carbon on the Electrode Kinetics of VIV/VVOxidation-Reduction

Cyclic voltammetry and electrochemical impedance spectroscopy were used to examine several types of carbon electrodes in V IV /V V in H 2 SO 4 .The materials investigated included glassy carbon, graphite, carbon paper, reticulated vitreous carbon and carbon fibers.In all cases the electrode kinetics of the V IV /V V oxidation-reduction reactions are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment.Pronounced activation typically occurs at potentials more negative than +0.1 V (vs.Hg/Hg 2 SO 4 ); the effect begins to saturate at about -0.6 V. Pronounced deactivation typically occurs at potentials more positive than +0.7 V.Both activation and deactivation occur rapidly during the first ∼10 s at the most negative and most positive potentials, respectively.The activation effect saturates quickly at the most negative potentials but the deactivation effect does not saturate on the time scales investigated.There is a considerable shift (∼1.1 V) between the potentials for activation and deactivation.Activated electrodes showed no significant loss of activity after standing in the electrolyte for 3 weeks; deactivated electrodes regained about 50% of their activity.The activation and deactivation effects were observed regardless of whether vanadium was present in the electrolyte and are attributed to oxygen-containing functional groups on the electrode surface.