Microstructural analysis of mass transport phenomena in a PEM fuel cell cathode

Abstract

In a proton exchange membrane fuel cell (PEMFC), the microstructure of cathode catalyst layer (CL) is critical in the performance optimization due to the sluggish oxygen reduction reaction. Nevertheless, in most of macroscale computational fluid dynamics (CFD) model, the CL has been treated as an interface or considered to be homogeneous. The CLs are composed of four phases: carbon, ionomer, binding platinum (Pt) nanoparticles and pores. One of the most important- and most difficult-factors to model in a PEMFC is the mass transport through CLs due to the complex interconnection of the phases. To describe the phenomena in the porous CLs, the macroscopic fuel cell models employ effective transport properties for reactant and charge transport, which are exceedingly difficult to measure. In this work, the CL was characterized by the focused ion beam (FIB)-scanning electron microscope (SEM); the segmented images were integrated to create the three-dimensionally reconstructed CL for the analysis of the microstructure. The structural parameters obtained from the reconstruction were implemented into a PEMFC cathode model to investigate their influence on the prediction of cell performance. In the predicted cell polarization, the reconstruction-based parameters resulted in maximum difference of 26% in the current density at 0.7 V. Consequently, it could be argued that the reconstruction method is essential for the modeling and design of the CLs to consider the realistic microstructure.