Dynamic modeling of direct ethanol fuel cells upon electrical load change

A transient, two-dimensional, and two-phase model was developed for predicting cell potential decay behavior of direct ethanol fuel cells operated galvanostatically after applying a step change in cell current density. To predict dynamic changes in anode overpotential and product distributions, a multi-step reaction mechanism based on literatures involving many adsorbed intermediates (CH3CH2OH, CH3CHO, CH3CO, OH) was incorporated into this model. The kinetic rates of reactions involving electron transfers are described by the Butler-Volmer equation. The surface coverage balance was used to determine the fractional coverage for each adsorbed species. The model also accounts for ethanol crossover through the membrane to cause cathode mixed potential. From the simulation results, a gradual increase of anode overpotential was caused by the acetyl bottleneck effect, leading to a slow decay of cell potential with time. Based on one set of model parameters, the model could accurately predict the dynamic response of cell voltage behavior after the cell current densities were stepped up as well as product selectivity.