Temperature and humidity effect on aging of silicone rubbers as sealing materials for proton exchange membrane fuel cell applications

•Aging of silicone rubbers with different hardness was investigated.•Existed water molecules from humidified gases can accelerate the aging process.•Silicone rubber with hardness of 40 is more suitable as sealing materials.•Silicone rubbers can be used as sealing materials below 80°C but not above 100°C. Durability and reliability of seals around perimeter of each unit are critical to the lifetime of proton exchange membrane fuel cells. In this study, we investigate the aging of silicone rubbers with different hardness, often used as sealing materials for fuel cells, subjected to dry and humidified air at different temperatures. The aging properties are characterized by variation of permanent compression set value under compression, mechanical properties, and surface morphology as well. The results show that aging of silicone rubbers becomes more severe with the increase in subjected temperature. At temperature above 100°C, silicone rubbers are not suitable for fuel cell applications. The existed water molecules from humidified gases can accelerate the aging of silicone rubbers. Among the tested samples, silicone rubber with hardness of 40 is more durable than that with hardness of 30 and 50 for fuel cells. The change of chemical structure after aging suggests that the aging of silicone rubbers mainly results from the chemical decomposition of cross-linker units for connection of polysiloxane backbones and of methyl groups attached to silicon atoms.