Stochastic Reconstruction and Morphological Studies of Catalyst Layers of Proton Exchange Membrane Fuel Cells

Abstract

Durability is one of the main obstacles that inhibits the commercialization of polymer electrolyte membrane (PEM) fuel cells for transport applications, in which the microstructure of catalyst layers (CL) under dynamic loading conditions can be deteriorated under a long-term operation. In this study, CL’s naturally random porous medium has been stochastically reconstructed to be a three-phase microstructure consisting of ionomers, catalyst agglomerates and pores, and morphological deterioration of reconstructed CL under cyclic hygrothermal stress has been investigated. The proposed reconstruction method extracts the two-point correlation function and lineal path function from experimental images. It turns the reconstruction problem into an optimization problem by minimizing the difference between the experimental images and the reconstructed structure. Subsequently, the Finite Element Method (FEM) is used to numerically investigate CL microstructure morphological changes under cyclic loading conditions. Two major observation includes ionomer coverage loss due to delamination between the thin ionomer layer and the catalyst agglomerate, and the ionomer residual volume accumulation. It is found out that the amplitude of hygrothermal cycles is the dominating factor in both delamination onset and the ionomer residual volume accumulation. More frequent start-up/shutdown of PEM fuel cells slows down the ionomer residual volume accumulation and the ionomer coverage loss. Longer parking time in the driving cycles alleviates the ionomer volume accumulation.