Effect of methanol crossover on the cathode behavior of a DMFC: A half-cell investigation

A half-cell consisting of a normal direct methanol fuel cell (DMFC) cathode and a membrane that contacts with an electrolyte solution was developed to investigate the effect of methanol crossover on the cathode behavior. Open circuit potentials, cyclic voltammetry profiles, polarization curves and electrochemical impedance spectroscopy (EIS), resulting from the oxygen reduction reaction (ORR) with/without the effect of methanol oxidation reaction (MOR), were measured. The transient measurements indicated that both current and open circuit potential of the electrode exhibited significant oscillations when the anodic MOR was superposed on the cathodic ORR, which explain the instabilities that may be encountered in the practical DMFC operation. The steady-state results confirmed that the presence of methanol at the cathode led to a significant poisoning effect on the ORR, especially when the DMFC operates at higher methanol concentrations and discharges at lower potentials. More importantly, the half-cell was proved to be ideal for the EIS study of DMFC electrodes because the system not only facilitates an accurate potential control but also reflects the actual mass transport process that occurs in practical DMFCs.