Development of mechanically and chemically stable anion exchange membranes for direct borohydride fuel cells for applications in UUVs and other electrochemical technologies relevant to U.S. Navy
Abstract
Anion exchange membranes (AEMs) and bipolar membranes are crucial enabling aspect of several UUV and DNS energy sources, like direct borohydride fuel cells (DBFCs). The objective of the proposed work is to build on our work over the past 6 years under YIP funding, which has helped establish structure-property relationships for different head group cation chemistries used in AEMs and has helped ascertain how their structure influences ion conductivity and alkaline stability. The United States Navy is considering the employment of air independent energy engines with high energy densities for low rate, long duration systems such as Unmanned Undersea Vehicles (UUVs) and Distributed Network Systems (DNS). Anion exchange membranes (AEMs) and bipolar membranes are crucial enabling aspect of several such energy sources, like direct borohydride fuel cells (DBFCs). DBFCs are an appealing type of polymer electrolyte membrane fuel cell due to the relatively large standard redox potential for sodium borohydride (1.24 V vs. SHE), the intrinsic safe nature of sodium borohydride (non-flammable, high flash point), and the large energy density of the fuel of 33.5 MJ kg-1 (only 20% lower than gasoline). The objective of the proposed work is to build on our work over the past 6 years, which has helped establish structure-property relationships for different head group cation chemistries used in AEMs and has helped ascertain how their structure influences ion conductivity and alkaline stability. Over the next three years, we aim to further enhance the stability and performance of AEMs and bipolar membranes in the context of the above mentioned electrochemical applications by employing the following directions: 1. Synthesis, characterization and evaluation of AEMs and bipolar membranes with a backbone based on a tri-block copolymer (styrene-ethylene-butylene-styrene tri-block copolymer, SEBS) as highly stable, durable, conductive and scalable separators for alkaline membrane fuel cells and bipolar membranes for DBFCs. 2. Synthesis of AEMs containing Gemini cations to improve the ionic conductivity and alkaline stability of resultant membranes. The cations preselected in the proposal will be attached to a variety of backbones (PPO, polysulfone, SEBS, etc.). 3. Synthesis of perfluorinated-based AEMs by chemical modification of existing perfluorinated PEMs a. By reaction of the sulfonyl fluoride form (precursor of the PEM membrane) with a Grignard reagent followed by quaternization of the tertiary amine. b. By transforming the sulfonyl fluoride to sulfonyl iodide to easily generate radical (free radical initiator). Those free radicals can be added to a double bond in an aromatic compound (containing an amine or ammonium group) to form a C-C bond, that links the cation to the perfluorinated backbone. 4. Improve construction methods to yield more efficient bipolar membranes. The experimental methods and the strategies to be employed are described in detail in the proposal. In performing this work, the PI and his team will be greatly assisted by the instruments procured on the basis of a DURIP grant awarded in 2012.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 23, 2016
- Source ID
- N000141612833
Entities
People
- Vijay Ramani
Organizations
- Office of Naval Research
- United States Navy
- Washington University in St. Louis