(75a) Synthesis of Ion Exchange Membranes for Large-Scale Energy Conversion and Storage Applications

The search for high-performance ion exchange membranes (IEM) to enable electrochemical devices continues to generate great interest in the polymer science and electrochemical communities. Emerging devices such as alkaline fuel cells, advanced electrolyzers, and redox flow batteries all require new types of ion exchange membranes beyond those available today. There has been rapid progress in elucidating the key design principles of these materials and devising new synthetic strategies to optimize the properties of IEMs for the intended application.

We have recently demonstrated new aromatic ion-conducting polymer membranes that have achieved excellent performance and long-lifetime stability in vanadium redox flow batteries, a leading technology candidate for deployment in renewable power networks and grid-scale energy storage systems with sizes ranging from 10s to 100s of megawatts. By tuning the nanoscopic self-assembly of the ionic domains in the polymers, we were able to increase the cycle life of the device by impeding vanadium ion transport through the membrane while facilitating high conductivity in the electrolyte to maintain the battery current density. For instance, by decreasing the vanadium permeability of the membrane by a factor of two, we have been able to double the lifetime of the device, which provides significant life-cycle cost savings. We have also demonstrated membranes with nearly zero vanadium permeability that show 100 % coulombic efficiency in flow battery charge-discharge cycling tests. Currently, we are working on demonstrating these membranes over 100s of charge-discharge cycles.

In another example, we have employed Ziegler-Natta polymerization to produce pendant brominated polymer backbones that can be quaternized with a variety of amines. These polyolefin-based AEMs directed towards use in fuel cells have shown competitive ionic conductivity values (greater than 60 mS/cm for hydroxide at room temperature) and good stability over 1000 h aging experiments at 80 °C in 1 M NaOH. Additionally, the use of a multication side chain boosts the properties of the materials due to hydrophilic/hydrophobic phase separation in the materials. These new polyolefin-based AEM materials can be integrated into porous support structures for high-performance membranes with superior mechanical properties.

This talk will discuss our innovations in aromatic and polyolefin-based ion exchange membranes. We will discuss both the synthesis of these new materials and show how the transport properties of the polymers can be directly connected to device performance in a number of important electrochemical applications.