Collaborative Research: A Physical Organic Chemistry Approach to the Development and Understanding of Redox Flow Batteries and Metal-Air Battery Redox Mediators

In this project, funded by the Chemical Mechanism, Function, and Properties Program of the Chemistry Division, Professors F. Dean Toste of the Department of Chemistry and Bryan D. McCloskey of the Department of Chemical and Biomolecular Engineering at University of California, Berkeley, alongside Professor Jacob S. Tracy of the Department of Chemistry at the University of West Florida, are developing strategies for creating, understanding, and optimizing new redox-active organic molecules to enable next-generation redox-flow and metal-air energy storage systems. The impacts of this work cover long duration energy storage systems, which enable overall electrical grid stability when incorporated alongside intermittent electricity generation, and ultrahigh capacity battery systems which aid heavy duty transportation applications. The project takes an interdisciplinary approach to the challenges inherent to these complex systems, combining synthetic organic and physical organic chemistry with electrochemistry and chemical engineering. Further, this project is the collaborative effort of a graduate-focused institution and an undergraduate-only chemistry department that addresses scientific training and education with impacts on students from K-12 all the way to the graduate level. Redox-active organic small molecules have an immense level of structural tunability to achieve various reduction potentials, stabilities to oxidation/reduction, and reactivities in solution and across interfaces. They have been used as active materials in nonaqueous organic redox flow batteries (N-ORFBs) and as soluble redox mediators (RMs) in metal-air (M-O2) batteries to enable or improve long-term, high-capacity performance in those systems, but holistic design rules and a mechanistic understanding of their decomposition pathways in either system remain limited. This project will take a physical organic chemistry approach to the design of both N-ORFB materials and M-O2 RMs. The broad thrusts of the RFB-focused work are (1) the design and characterization of highly cyclable, extreme-potential redox flow battery catholyte and anolyte materials and (2) development of a mechanistic understanding of how regioisomerism and intramolecular noncovalent interactions affect the voltages and long-term stability of RFB materials. For M-O2 batteries, the project focuses on (1) synthesizing new classes of mediators for Li-O2 batteries alongside mechanistic studies of their decomposition in model cell systems and (2) investigation of the fundamental electrochemistry of mediated Na-O2 and Ca-O2 metal-air cells, with a particular focus on Na-O2 discharge mediation and the ability of mediators to tune different peroxide/oxide deposition pathways in Ca-O2 cells. 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.