Kinetic Interpretation of a Negative Time Constant Impedance of Glucose Electrooxidation

Nickel-copper alloy modified glassy carbon electrodes (GC/NiCu) prepared by galvanostatic deposition were used for the electrocatalytic oxidation of glucose in alkaline solutions. The electro-oxidation of glucose in a 1 M NaOH solution at different concentration of glucose was studied by the method of ac-impedance spectroscopy. The impedance behavior show different patterns, capacitive, and inductive loops and negative resistances, at different applied anodic potential. The influence of the electrode potential on the impedance pattern is studied and a quantitative explanation for the impedance behavior of glucose oxidation is put forward by a proposed mathematical model. At potentials higher than 0.5 V/Ag-AgCl, a pseudoinductive behavior is observed while at higher than 0.53 V/Ag-AgCl, impedance pattern is reversed to the second, third, and forth quadrants. The conditions required for the reversing of impedance pattern are delineated with the use of the impedance model. The previously proposed electrooxidation mechanism for glucose on GC/NiCu electrode was found to reproduce the experimental impedance plots.