L-Ascorbate anion electro-oxidation on a silver electrode in hydroxide solution in the absence and presence of sodium polysulfide of concentrations from 1 × 10-5 to 4.5 × 10-4 mol/L was studied using cyclic voltammetry and electrochemical impedance spectroscopy.Both hydroxide and polysulfide ions inhibited L-ascorbate ion oxidation,with the poisoning effect of polysulfide ion being more pronounced in the potential range of-0.3 to -0.2 V/SCE.The time constants for L-ascorbate ion oxidation in the absence and presence of polysulfide were,10-3 to 1 × 10 2 s and 1 × 10-4 to 1 × 10-2 S,respectively depending on the potential used for the impedance analysis.Based on the cyclic voltammetry findings,a mechanism for L-ascorbate oxidation in the presence of polysulfide ions was proposed.Impedance calculations based on the kinetic analysis can account for the occurrence of a negative impedance in a potential region around -0.2 WSCE in the Nyquist.
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