Measurement of polarization curve and development of a unique semiempirical model for description of PEMFC and DMFC performances

In this study, a single polymer electrolyte membrane fuel cell (PEMFC) in H-2//O-2 form with an effective dimension of 5 cmx5 cm as well as a single direct methanol fuel cell (DMFC) with a dimension of 10 cmx10 cm were fabricated. In an existing test station, the voltage-current density performances of the fabricated PEMFC and DMFC were examined under various operating conditions. As expected, DMFC showed a lower electrical performance which can be attributed to the slower methanol oxidation rate in comparison to the hydrogen oxidation. The results obtained from the cell operation indicated that the temperature has a great effect on the cell performance. At 60 degrees C, the best power output was obtained for PEMFC. There was a drop in the cell voltage beyond 60 degrees C, which can be attributed to the reduction of water content inside the membrane. For DMFC, the maximum power output resulted at 64 degrees C. Increasing oxygen stoichiometry and total cell pressure had a marginal effect on the cell performance. The results also revealed that the cell performance improved by increasing pressure differences between the anode and cathode. A unified semi-empirical thermodynamic based model was developed to describe the cell voltage as a function of current density for both kinds of fuel cells. The model equation parameters were obtained through a nonlinear fit to the experimental data. There was a good agreement between the experimental data and the model predicted cell performance for both types of fuel cells.