Simultaneous oxygen-reduction and methanol-oxidation reactions at the cathode of a DMFC: A model-based electrochemical impedance spectroscopy study

A model-based electrochemical impedance spectroscopy (EIS) approach that combines an equivalent electrical circuit (EEC) method and a mathematical model derived from the reaction kinetics is proposed to investigate the simultaneous oxygen-reduction reaction (ORR) and methanol-oxidation reaction (MOR) at the cathode of a DMFC. Good agreements between the calculated results and the experimental data validated the proposed method. Detailed kinetic parameters and state variables of the cathode were conveniently extracted and the concerned reaction processes were further analyzed, which demonstrated the comprehensive applicability of this method. The results showed a significant poisoning effect on the ORR by the presence of methanol at the cathode. The results also indicated that whether the methanol permeated from the anode can be completely oxidized by electrochemical reaction at the DMFC cathode depends on the electrode design and operating conditions, even at high potentials. (c) 2007 Elsevier B.V. All rights reserved.