Electrochemical Oxidation of Ethanol at Nickel Hydroxide Electrodes in Alkaline Media Studied by Electrochemical Impedance Spectroscopy

Electrochemical oxidation of ethanol at nickel electrodes has been studied in 1 M KOH solution containing 0.20 M ethanol using electrochemical impedance spectroscopy. Equivalent circuits have been worked out by simulating the impedance data, and the results were used to model the oxidation of ethanol as well as the passivation of the electrode. The maximum rate of oxidation of Ni(OH)(2) to NiOOH was observed at about 0.37 V vs. Ag/AgCl reference electrode, while the maximum rate of ethanol oxidation at the Ni electrode was observed at about 0.42 V. The charge-transfer resistance for oxidation of the electrode itself became smaller in the presence of ethanol than in its absence. These results suggest that the beta-Ni(OH)(2)/beta-NiOOH redox couple is acting as an effective electron transfer mediator for ethanol oxidation. The kinetic parameters also were obtained by the experimental and simulated results.