Reinforced Hydrocarbon-Based Ion-Exchange Membranes for Fuel Cell Applications

摘要

Hydrocarbon-based ion-exchange membranes are seen as promising alternative to the well-established and commercially available perfluoroalkyl sulfonic acids e.g. Nafion(R). It is expected to shift the application temperature, which is approx. up to 90°C at a high humidification level for Nafion, to values well above 100°C at low humidification. In the last decades, many researchers have focused their activities on the synthesis of various sulfonated aromatic polymers that have high thermal, chemical and oxidative stability, good mechanical properties and low cost such as polyimides, poly(arylene ether)s and others as summarized in several reviews [see e.g. 1]. Due to the higher ion-exchange capacity that is needed for non-fluorinated membrane materials compared to poly(perfluoroalkyl sulfonic acid)s like Nafion~R to achieve a similar performance, these membranes have a much higher water uptake combined with a much lower dimensional stability. A second issue in ion-exchange membranes, which is closely related to swelling, is the mechanical properties in hydrated state/Since water acts as plasticizer in these materials, the membranes lose their mechanical strength on water-uptake. Several methods like chemical crosslinking [2] or ionic crosslinking [3] have been employed in the past in order to overcome swelling and mechanical property issues. These two methods may lead to more brittle materials (chemical crosslinking) and loss of ion-exchange capacity (ionic crosslinking). Reinforcement of ion-exchange membranes by incorporation of inert porous materials into the membrane has been mainly described in the patent literature [4].