Modeling of Coupled Multiphase Transport in Direct Methanol Fuel Cell Diffusion Layers

Abstract

A one-dimensional, two-phase model for the anode diffusion layer (DL) of a liquid-feed direct methanol fuel cell (DMFC) is developed. This model incorporates the use of Stefan-Maxwell formulation of multiphase diffusion to model the mass transport of water (H2O), methanol, and carbon dioxide (CO2) in both the liquid and gas phases throughout the porous DL. The model uses a muticomponent equation of state to model the equilibrium between each species in its gas and liquid form inside the porous medium. It is shown how the properties of the DL, including the permeability, contact angle, porosity, and thickness, affect the performance of the DMFC, in terms of ability to remove CO2 and modify the methanol concentration at the diffusion layer/catalyst layer (CL) interface. Specifically, we find that having a small permeability and a thick DL will both promote a lower methanol concentration and enhance CO2 removal, but the other parameters result in a tradeoff in performance. The preferred transport properties depend strongly on the specified operating temperature of the cell, as both methanol and water partition more preferentially to the vapor phase as the temperature is increased.