Computational Modeling of Foreign Cation Contamination in PEFCs

Abstract

A steady-state, one dimensional computational model is developed to predict the effect of foreign cation contamination in polymer electrolyte fuel cells (PEFCs). The model solves the coupled transport phenomena of cations, oxygen, hydrogen, and water. Foreign cation (i.e. Na+) contamination in the air stream found to significantly decrease the performance of PEFC. The main effects are: (1) foreign cation replaces the proton and occupies the sulfonic acid sites in the ionomer. It can occupy up to 98% of the sites in the ionomer phase of the cathode catalyst layer (CCL). (2) It causes severe water depletion in the ionomer due to decrease in water diffusivity and equilibrium water uptake. (3) It decreases the oxygen diffusivity causing a decrease in dissolved oxygen concentration in CCL. (4) It also decreases the equilibrium potential due to reduction in proton concentration in the ionomer phase in cathode. These contamination effects on each parameter decrease protonic current density and combined effects result in a reduction of current density from 0.72 A/cm2 to 0.25 A/cm2 at a constant cell voltage of 0.7 V.