(423a) New Developments in Polybenzimidazole (PBI) Membranes for Electrochemical Devices

Polybenzimidazole (PBI) polymers have been extensively studied for high temperature PEM fuel cells operating at 100-200ËšC. As part of our ongoing work in developing and using the sol-gel PPA process, we have been exploring the effects of chemical structure on membrane properties, including issues related to membrane stability and durability. Membranes produced from this process showed the ability to maintain high levels of phosphoric acid (PA) and high proton conductivities while simultaneously exhibiting low levels of PA loss during operation in many simulated duty cycles. The knowledge base created by a broad search of different PBI backbone chemistries and variations in molecular architecture (random and block copolymers, crosslinking, etc.) originally directed at high temperature fuel cells, is now being used to design PBI polymers for other electrochemical devices such as hydrogen pumps, electrolyzers, and flow batteries. In many cases, the different operating conditions of the distinct devices advocate for a specifically designed polymer structure tailored for its environment. In these devices, the general polybenzimidazole backbone structure provides outstanding chemical and thermal stability, high ionic conductivities when doped with acids, and resistance to oxidatively challenging environments. In this talk, we will review some of the emerging devices and describe a new process for producing PBI membranes with high proton conductivities, improved mechanical properties, and excellent performance in multiple devices.