Macroscopic Investigation of Water Transport Phenomena in PEFCs

Abstract

It is of great importance to predict and identify the water transport characteristics of polymer electrolyte fuel cells by the analytical and numerical methods for the improved fuel cell designs. In this study, comprehensive analytical and numerical analyses focusing on various water transport regimes of practical interest (i.e., anode water loss and cathode water flooding) are performed and utilized to figure out the characteristic anode and cathode water transport phenomena associated with zero water flux and water flooding. A unified water transport model assisted by the theoretical and computational approach is introduced to accurately predict water concentration profiles across the membrane electrode assembly (MEA) as a function of membrane thickness and current density. Theoretical analysis is first performed for in-depth study of the macroscopic water transport mechanism ensuring well-balanced water distribution over a fuel cell domain. Then, computational simulation is accompanied, showing that the estimated water molar concentration in the in-plane direction of a straight channel is increasing gradually for a low humidity case, which was verified by experimental data available in the literature. Finally, computational results were compared with analytical solutions in predicting those characteristics of water transport phenomena. It was found that a thinner membrane facilitates water transport in the through-membrane direction and therefore water concentration at the anode and cathode channel outlets reaches an equilibrium state particularly at low operating current densities. The results of numerical model showed a good agreement with theoretical pre-estimation in those critical characteristics.