Impedance studies and modeling of direct methanol fuel cell anode with interface and porous structure perspectives

In this work, 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. In addition, the differences among methanol electrooxidation reaction kinetics at various operating potentials are clearly observed and satisfactorily explained using electrochemical impedance spectroscopy and the CPE-based equivalent-circuit model.