Controlling cracking formation in fuel cell catalyst layers

Since cracks in catalyst layers of a fuel cell affect performance and durability, it is important to obtain the factors that control crack formation. Cracking characteristics are likely to differ due to the formation of agglomerates in catalyst inks. Herein, a critical crack thickness (CCT) is examined as a parameter for cracking characteristics by changing the formation of Pt/carbon by the presence or absence of an absorbed ionomer on Pt/carbon particles. The CCT was found to be four times greater for catalyst layers obtained from catalyst inks that are well dispersed by ionomer adsorption than for catalyst layers obtained from catalyst inks with a network of structured agglomerates. This shows that crack behavior can be controlled by ionomer adsorption into the Pt/carbon in catalyst ink. A well-dispersed catalyst ink produce a homogeneous Pt/carbon and ionomer distribution in catalyst layers with high fracture toughness, while catalyst inks with a network of structured agglomerates produce dense aggregates with small primary pores that generate high drying stress, and a self-organizing free ionomer that causes stress concentration in catalyst layers with a high risk of cracking. This research provided useful knowledge for controlling cracks and examining the effects of cracks on performance and durability.