Electrochemical impedance was used to analyze the reaction kinetics and interfacial characteristics of an anode in a direct methanol fuel cell (DMFC). An advanced equivalent-circuit model is proposed. The new model incorporates constant phase elements (CPEs) rather than conventional capacitors in the equivalent-circuits taking into account the porous structure of the anode, particularly that in the catalyst layer and at the anode/membrane interface. It effectively simulated the electrochemical characteristics of a DMFC porous anode. The impedance model incorporates the interface factor, resulting in excellent matches between the simulation results and the experimental data in the Nyquist and the Bode plots over a wide range of frequencies. The performance of a single-cell direct methanol fuel cell (DMFC) using carbon nanotube-supported Pt-Ru (Pt-Ru/CNT) as an anode catalyst has also been investigated. In this study, the Pt-Ru/CNT electrocatalyst was synthesized using a modified polyol approach with a controlled composition very close to 20wt%Pt-10wt%Ru, and the anode was prepared by coating Pt-Ru/CNT electrocatalyst on a wet-proof carbon cloth substrate with a metal loading of about 4 mg cm-2. The membrane electrode assembly (MEA) was fabricated using Nafion 117 and the single-cell DMFC was assembled with graphite endplates as current collectors. Experiments were carried out at moderate low temperatures using 1 M CH₃OH aqueous solution and pure oxygen as reactants. The tested cell significantly outperformed a comparison cell using a commercial anode coated with carbon-supported Pt-Ru (Pt-Ru/C) electrocatalyst of similar composition and loading. High conductivity of carbon nanotube, good catalyst morphology and suitable catalyst composition of the prepared Pt-Ru/CNT electrocatalyst are considered to be some of the key factors for enhancing cell performance.

Acknowledgement

The authors would like to thank the National Science Council of Taiwan for financially supporting this research.