TITLE:
Reduction Charge Smaller than the Deposited One in Cathodic Stripping Voltammograms of AgCl
AUTHORS:
Peng Tang, Koichi Jeremiah Aoki, Jingyuan Chen
KEYWORDS:
Silver Electrode, Double Layer Capacitance, Stripping Voltammetry, Chronocoulometry, Time-Dependent Charge
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.10 No.8,
August
14,
2019
ABSTRACT: A silver electrode was anodized in lowly concentrated potassium chloride solution almost under the steady state to generate a deposit of silver chloride on the electrode, and the deposit was cathodically stripped by linear potential scan to evaluate the reduction charge. Then the oxidation charge was larger than the reduction one. Since the equality was valid for long term chronocoulometry at the double potential step, the inequality is not due to any irreversibility of electrode reactions, but can be attributed to the process of the cathodic potential scan. A reason for the inequality is the negative charge of the capacitance involved in the electrode reaction, which has been observed in simple, dissolved redox species like a ferrocenyl derivative. The negative capacitive currents are conspicuous for high concentrations of redox species on the electrode because they result from the orientation of the dipoles of the redox species coupled with counterion, of which direction is opposite to that of the solvent dipoles. If a silver chloride film was thin enough to be regarded as a monolayer, we found that half of the cathodic stripping charge should be lost by the negative capacitance.