Insight into the crack evolution and mechanism of catalyst-coated membrane undergoing freeze–thaw cycling in fuel cells

Abstract

The evolution of catalyst-coated membrane (CCM) under saturated humidity conditions during freeze–thaw cycling was investigated, with a particular focus on the evolution of initial cracks within the catalyst layer (CL) and their impact on the proton exchange membrane (PEM). A quasi in-situ fuel cell fixture was designed to enable direct observation of the CCM via scanning electron microscopy (SEM). As the number of freeze–thaw cycles increases, the initial cracks in the CL gradually propagated, with new cracks appearing around them. These CL cracks tend to extend along the larger pores, which essentially represent gaps between agglomerates. The overall trajectory of formed cracks appears to be influenced by the flow channel direction. Additionally, under freeze–thaw cycling, cracks in the CL led to the formation of cracks in the PEM. A strong correlation is found between the direction of membrane cracks and CL cracks, suggesting a direct impact of the CL defects on the structural integrity of the PEM. Furthermore, some cracks at the tips of CL cracks even penetrate through the entire membrane. This study provides valuable insights into the degradation mechanisms of CCMs under low-temperature environmental conditions and could inform future design improvements for enhanced durability.