Abstract
The development of an efficient electrocatalyst for the direct oxidation of ascorbic acid (AA) has gained considerable interest since AA may be applied as an environment-friendly alternative renewable biofuel in fuel cells. In the present work, the electrocatalytic oxidation of AA was implemented at IrOx immobilized glassy carbon electrode (GC-IrOx) in an acidic medium. Prior to use, the physical properties of GC-IrOx surface were investigated by means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The XPS analysis revealed that a film of IrOx formed on the GC surface while it was cycled between 0 and 1.0 V vs Ag/AgCl (sat. KCl) reference electrode in Ir2O3 colloidal solution. The voltammetric investigations of AA oxidation at the GC-IrOx electrode revealed 4-folds higher current compared to a pristine GC electrode suggesting an excellent electrocatalytic performance. The Ir(III)/Ir(IV) redox couple is assigned for catalyzing the reaction. It was found that AA oxidation followed first order kinetics on the GC-IrOx electrode surface. The heterogeneous electron transfer (ET) kinetic study unveiled that AA oxidation reaction followed stepwise mechanism at potentials below 0.38 V and concerted mechanism above this potential with respect to a Ag/AgCl (sat. KCl) reference electrode. In this study, the standard rate constant (ko) pertaining to AA oxidation was evaluated as 7.25 × 10−4 cm s − 1. The GC-IrOx electrode exhibited reasonably excellent stability, which mounts the probability of its application as an anode in the AA fuel cells.
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