Cross-linking network topology and durability in silicone rubber sealants for PEMFCs: the impact of curing systems and nanosilica interactions

This study investigates the durability of silicone rubber compounds employed as sealants in polyelectrolyte membrane fuel cells (PEMFCs), focusing on their cross-linking network topology. Compounds are formulated with varying curing systems, including hydrosilylation and peroxide curing, and different filler content, sizes, and surface chemistries. The findings indicate that compounds cured by hydrosilylation exhibit enhanced hardness and storage modulus, along with reduced compression set and damp factor, in comparison to those cured by peroxide. These superior mechanical properties are attributed to a homogeneous cross-linking network topology with fewer "in-elastic chains." Furthermore, strong interactions between silicone rubber and nanosilica contribute to network topology by establishing physical cross-links. Remarkably, these interactions intensify during chemical aging in a simulated PEMFC environment, resulting in increased hardness and reduced compression set. In contrast, compounds containing hydrophobic surface-modified nanosilica experience severe mechanical deterioration due to higher chain degradation during chemical aging. In summary, this study highlights the critical role of cross-linking network topology and interactions with nanosilica in determining the durability of silicone rubber compounds for PEMFC applications.