(488a) 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.[1] 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.[2-5] 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.

Recently, we have developed a new process for making PBI membranes that results in much improved mechanical durability compared with the sol-gel membranes without compromising the proton conductivity or fuel cell performance. The improved mechanical durability results in membranes that operate at temperatures above 200 ËšC and are suitable for higher pressure operation that may be needed in emerging fuel cell applications such as air transportation. 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.

[1] A.T. Pingitore, G. Qian, F. Huang, B.C. Benicewicz. Durable High Polymer Content m/p-PBI Polybenzimidazole Membranes for Extended Life-time Electrochemical Devices. ACS Applied Energy Materials2019, 2, 1720-1726.

[2] L. Wang, A.T. Pingitore, W. Xie, Z. Yang, M.L. Perry, B.C. Benicewicz. Sulfonated PBI Gel Membranes for Redox Flow Batteries. J. Electrochem. Soc.2019, 166(8), A1449-A1455.

[3] F. Huang, A.T. Pingitore, T. Champbell, A. Knight, D. Johnson, L.G. Johnson, B.C. Benicewicz. A Thermo-Electrochemical Converter using High Temperature Polybenzimidazole (PBI) Membranes for Harvesting Heat Energy.ACS Appl. Energy Mater.2020, 614-624.

[4] Y. Lu, Y. Wen, F. Huang, T. Zhu, S. Sun, B.C. Benicewicz, K. Huang. Rational Design and Demonstration of a High-Performance Flexible Zn/V₂O₅Battery with Thin-Film Electrodes and PBI-based Electrolyte Membrane. Energy Storage Materials2020,27, 418-425.

[5] F. Huang, A.T. Pingitore, B.C. Benicewicz. Electrochemical Hydrogen Separation from Reformate Using High-Temperature Polybenzimidazole (PBI) Membranes: The Role of Chemistry. ACS Sustainable Chemistry & Engineering2020, 8, 6234-6242.