Optimization of Transports in a Proton-Exchange Membrane Fuel Cell Cathode Catalyst Layer at High Current Densities: A Coupled Modeling/Imaging Approach

Abstract

The heterogeneous nature of the cathode catalyst layer has been a major obstacle toward the comprehension of the mechanisms hindering the PEMFC performance at high current densities. To deconvolute these, an approach coupling multiscale modeling and multiscale electron microscopy characterization—allowing to move from the local to the cathode catalyst layer scale—is adopted. Here, an agglomerate scale model is developed and coupled with a MEA-scale model. Different structures are analyzed and the effects of certain structural parameters (Pt particle size, agglomerate structure and Nafion layer thickness) on the electrode performance are quantified and discussed. Reducing the Pt particle size is found to improve performance in most cases, though the improvement margin is highly dependent on the structure, and to a certain extent, on the particle spatial distribution. It is found that thickening the Nafion film is detrimental for performance only when the porosity is not sufficiently large. Performance gains upon structure rearrangement into an ideal-type structure (Nafion and pore tortuosities minimized to unity) are also quantified. These analyses have unvealed the main mechanism limiting performance when shifting to moderate/high current densities and allowed quantifying and ranking the physical phenomena hampering performance by order of importance.