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

Zheng Miao,Ya-Ling He,Jin-Liang Xu

doi:10.1155/2014/812706

Abstract

The transport phenomena in a passive direct methanol fuel cell (DMFC) were numerically simulated by the proposed two-dimensional 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.

Highlights

Direct methanol fuel cells (DMFCs) are electrochemical devices which can directly covert chemical energy into electricity
It is noticed that the present model is extended from the DMFC model presented in our previous work [22, 34], in which the details of the model validation against the experimental data can be found
In our former work [22], we have revealed that the local reaction rate in the anode catalyst layers (CLs) of an active DMFC feed with 1 M or 2 M methanol concentration is mainly determined by the local methanol concentration

Summary

Introduction

Direct methanol fuel cells (DMFCs) are electrochemical devices which can directly covert chemical energy into electricity. All layers in the MEA, including the GDLs, CLs, proton exchange membrane (PEM), and the microporous layers (MPLs) were considered as porous media with finite width We improved this model later by taking account of the anisotropic transfer properties of the GDLs and the detailed multistep reaction mechanism of the methanol oxidation reaction (MOR) in anode CL [34]. This modified model was used to investigate the mass, heat, and charges transport phenomena in the active DMFC [23, 26]. The physical fields related to key transport processes, such as distribution of overpotentials, species concentration, local reaction rate, and temperature, are numerically studied

Mathematical Model

Results and Discussion

Conclusions