Design and Synthesis of Robust Cationic Polymers for Stable and Efficient Anion-Exchange Membranes

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

Professors Kevin Noonan and Tomasz Kowalewski of Carnegie-Mellon University are supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to design and prepare new charged polymers that function as ion-exchange membranes. These membranes are sandwiched between the negative and positive compartments of fuel cells and are considered a key component of these energy conversion devices. A variety of consumer related products rely on fuel cells for clean energy generation. New cationic (positively charged) polymer membranes are synthesized using appropriate controlled polymerization techniques. Their chemical, electrochemical, and mechanical stability are assessed under fuel cell operating conditions. One of the main objectives of this work is to make durable membranes which can withstand the harsh chemical environments of a fuel cell device. If successful, fuel cells with these newly synthesized polymer membranes will not rely on precious metals for energy generation, which represents a significant economic advantage. Students from diverse backgrounds are trained and involved in this project. A "Fuel Cell Project" with educational material and demonstrations is being developed. The project is made available on the web and used to educate junior high school students about renewable energy life cycles. In this project, the PIs are exploring the chemical and electrochemical stability of cationic polymers in the presence of hydroxide ions. The information obtained is used to build robust membranes for ion-transport in fuel cells. While transport of protons under acidic conditions is well established, hydroxide transport in solid polymer electrolytes under thermal and electrochemical stress is still a significant challenge. The development of next-generation robust, long-lasting and inert cationic materials for shuttling these caustic anions requires a combination of synthesis and characterization. Controlled polymerization techniques are critical for building the polymer materials. A battery of characterization techniques is used to evaluate their structure, stability and morphology. Specifically, X-ray scattering, atomic force microscopy, transport/device measurements and computational chemistry are used to probe the properties of these membranes. Transport and mechanical properties are tailored by synthesizing well-defined polymers and block copolymers. These materials are used to establish relationships between ion transport and morphology of novel ionomers. This work provides the basis for subsequent material design to optimize anion transport. If successful, the project will result in stable and efficient anion exchange membranes (AEMs) for alkaline fuel cells that do not need precious metals for proper function. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.