A transient two-phase mass transport model for liquid feed direct methanol fuel cells

Abstract

A transient two-phase mass transport model for liquid feed direct methanol fuel cells (DMFCs) is developed. With this model, various processes that affect the DMFC transient behaviors are numerically studied. The results show that the cell voltage exhibits an overshoot behavior in response to a sudden change in the current density. The magnitude of the overshoot depends on the magnitudes of the change in the cell current density and the initial current density. It is found that the dynamic change in the methanol permeation through the membrane to the cathode results in a strong cathode overpotential overshoot, which is believed to be the predominant factor that leads to the cell voltage overshoot. In contrast, the anode overpotential is relatively insensitive to the changes in the methanol concentration as well as CO surface coverage in the anode catalyst layer. Moreover, the effect of the double layer capacitance (DLC) on the cell dynamic behavior is studied and the results show that the DLC can smoothen the change in the cell voltage in response to a change in the cell current density. Furthermore, the dynamic response of mass transport to a change in the cell current density is found to be rather slow. In particular, it is shown that the slow response in the mass transport of methanol is one of the key factors that influence the cell dynamic operation.