Electrocatalytic oxidation of ascorbic acid in the basic medium over electrochemically functionalized glassy carbon surface

In a mild acidic medium (0.10 M H₂SO₄), a pristine glassy carbon electrode (GCE) has been electrochemically activated via electrochemical oxidation which has been used for efficient ascorbic acid (AA) direct oxidation. An oxidized GCE exhibits a well-defined redox pair in 0.10 M H₂SO₄ due to development of functional groups (C=O) on the surface of the GCE during the electrochemical oxidation process. Electrochemical and X-ray photoelectron spectroscopy (XPS) have been employed to characterize the GCE surface before and after functionalization. The resultant electrode surface was employed to execute electrochemical oxidation of ascorbic acid molecules in an alkaline medium. The voltametric measurements of AA oxidation at the oxidized GCE showed that the oxidized GCE exhibited better electrochemical performance in 0.10 M NaOH compared to the pristine GCE. It was observed that oxidation of AA followed 1^st order and diffusion-controlled kinetics on the oxidized GCE surface. The hydrodynamic voltammogram analysis confirmed that oxidation of AA proceeds via a 2e⁻ transfer pathway and followed a stepwise mechanism. It was found that, for the oxidation of AA, the standard rate constant (k^o) has a value 4.47 × 10⁻³ cm s⁻¹ with a E^o value of −0.29 V vs Ag/AgCl (sat. KCl). The proposed oxidized GCE successfully decreases AA oxidation overpotentials, which enhances the possibility of using it as an anode in ascorbic acid (AA) fuel cells.