PERFORMANCE STUDY OF CATHODE CATALYST LAYER IN A PEM FUEL CELL USING AN AGGLOMERATE MODEL

Abstract

A comprehensive agglomerate model for the cathode catalyst layer (CCL) performance in a polymer electrolyte membrane fuel cell (PEMFC) has been developed. The overall transport phenomena and the electrochemical kinetics of each species namely oxygen, electrons and protons inside the CCL is considered in this model. The model is developed in such a way that it can be reduced to a pseudo-homogenous model when the agglomerate radius approaches zero. The validation of the model is done with the experimental results of Ticianelli et.al [39] .This is done by first estimating the value of agglomerate radius, ionomer film thickness and ionomer volume fraction for one set of operating conditions and then validating the model for another set of operating conditions. The agglomerate model is compared with pseudo-homogenous model. It is found that the pseudo-homogenous model over predicts the cell voltage, particularly at high current densities. The effect of two operational parameters namely operating temperature and oxygen pressure and five structural parameters namely agglomerate radius, ionomer film thickness, platinum loading, ionomer volume fraction and catalyst layer (CL) thickness on PEMFC performance is investigated. It is found that the increase in operating temperature and pressure improves the performance of PEMFC while the increase in agglomerate radius and ionomer film thickness has a negative influence on PEMFC performance. Optimum values of platinum loading and ionomer fraction is calculated for three overpotentials: 0.3, 0.6 and 0.9 V. The results show that the optimum platinum loading decreases while the optimum ionomer fraction increases with increase in overpotential. The utilization of the CL is found to decrease with increase in CL thickness.