(Invited) Effect of Electrochemical Treatment and pH on V^IV/V^VElectrode Kinetics

Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the effect of electrochemical treatment of glassy carbon electrodes in electrolytes of various pH on VIV/VV redox kinetics. In all pH treatment electrolytes (pH 0-pH 6.3), the VIV/VV kinetics are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. For all pHs, pronounced activation typically occurs at cathodic treatment potentials more negative than ∼+0.4 V and the effect is most significant at ∼-0.8 V. It is also found that the activating effect of cathodization is enhanced significantly with increasing pH. For all pHs, pronounced deactivation typically occurs at anodic treatment potentials more positive than ∼+0.2 V and the effect begins to saturate at ∼+1.0 V. Within this deactivation region of potentials, the rate constants decrease linearly with increasing treatment potential and reach similar final deactivation rate constants. The observed effects cannot be fully explained by surface roughening effects during anodization, rather they are attributed to changes to electrode surface functional groups by electrochemical polarization. It is suggested that competing cathodic processes, the rates of which appear to be pH dependent, control the surface functional groups formed and the resulting kinetics of the electrode surface for VIV/VV.