Performance study of an alkaline direct ethanol fuel cell with a reduced two-dimensional mass transport model

Abstract

A reduced two-dimensional model is presented for modeling coupled transport and electrochemical reactions in an alkaline direct ethanol fuel cell. The model considers convection-dominant mass transport along anode channel, diffusion-dominant mass transport in porous anode, diffusion-electroosmotic transport of species through membrane, two-phase flow and mass transport in porous cathode, and convection-dominant mass transport along cathode channel. After being validated against experimental data, the model is applied to investigate species transport behaviors and examine the influence of operating parameters on anode overpotential and overall cell performance. It is indicated that the local variations of reactants as well as local current density along flow channel are greatly influenced by anode flow rate. Higher anode flow rate leads to more uniform distribution of reactants and local current density, thus resulting in higher cell performance especially in high current density region. Also, it is shown that the cell performance is sensitively dependent on KOH and ethanol feed concentrations. Too low KOH or ethanol concentration leads to the sharp decrease of cell voltage in high current density region due to severe mass transport polarization. Increasing KOH or ethanol concentration, the cell voltage at whole current density region can be greatly improved due to the enhanced kinetics of ethanol oxidation reaction and the reduced mass transport loss. However, too high KOH concentration may resist the transport of OH− from the cathode to the anode and thus lead to severe ohmic loss, thus showing adverse impact on overall cell performance.