Modeling of the Transport Phenomena in Passive Direct Methanol Fuel Cells Using a Two-Phase Anisotropic Model

Abstract

The transport phenomena in a passive direct methanol fuel cell (DMFC) were numerically simulated by the proposed twodimensional two-phase nonisothermal mass transport model. The anisotropic transport characteristic and deformation of the gas diffusion layer (GDL) were considered in this model. The natural convection boundary conditions were adopted for the transport of methanol, oxygen, and heat at the GDL outer surface. The effect of methanol concentration in the reservoir on cell performance was examined. The distribution of multiphysical fields in the membrane electrode assembly (MEA), especially in the catalyst layers (CLs), was obtained and analyzed. The results indicated that transport resistance for the methanol mainly existed in the MEA while that for oxygen and heat was primarily due to natural convection at the GDL outer surface. Because of the relatively high methanol concentration, the local reaction rate in CLs was mainly determined by the overpotential. Methanol concentration between 3 M and 4 M was recommended for passive liquid feed DMFC in order to achieve a balance between the cell performance and the methanol crossover.

Understanding Carbon Dioxide Transfer in Direct Methanol Fuel Cells Using a Pore-Scale Model

“…Therefore, early model studies focusing on the kinetics of DMFCs assumed that carbon dioxide was dissolved in liquid [8,9] or neglected the convection of methanol solution and carbon dioxide [10]. Most liquid-gas two-phase models of DMFCs neglected the impact of carbon dioxide [11] or indirectly calculated the mass fraction of carbon dioxide from the mass fractions of other species so that the summary of the total mass fractions equals unity [12][13][14][15]. Only a very small number of models have simulated the CO 2 bubble flow within flow channels [16] and counter flow of carbon dioxide gas and liquid fuel during operation [17].…”