Effect of Plasma-Assisted Electrochemical Treatment of Glassy Carbon Electrode on the Reversible and Irreversible Electrode Reactions

Resumo

A glassy carbon electrode is modified by generating cathodic and anodic electrolytic plasma near its surface. Voltage pulses of amplitude up to 250 V, pulse-on time of 10 ms, and rise time <0.5 µs in the Na₂SO₄ aqueous solution are used to form plasma. It is found that, as a result of treatment by the anodic plasma, the glassy carbon surface acquires electrocatalytic properties toward the oxygen reduction reaction, whereas the cathodic plasma has no noticeable effect as compared to the pristine glassy carbon. At the same time, a pronounced effect of plasma-assisted electrochemical treatment of surface on the electron transfer rate constants is found only for the [Fe(CN)₆]^4–/3– redox reaction. By contrast, for the outer-sphere ([Ru(NH₃)₆]^2+/3+) and inner-sphere (Fe^2+/3+) reactions, the effect is not observed. It is supposed that the observed electrocatalytic effect toward the oxygen reduction reaction is caused by the formation of carbonyl fragments of functional groups, which are active centers of oxygen reduction, on the surface of glassy carbon electrode under the action of anodic plasma. However, they have no pronounced effect on the [Ru(NH₃)₆]^2+/3+ and Fe^2+/3+ redox systems.