(Keynote) Molecular Engineering Strategies for Symmetric Aqueous Organic Redox Flow Batteries

Abstract

In this contribution we use electronic structure calculations to reveal structure-property relationships for symmetric aqueous organic redox flow battery (RFB) materials. Unlike normal asymmetric RFBs, the symmetric ones are based on bipolar electrolytes that exist in at least three oxidation states and can undergo a minimum of two distinct redox processes. We compute from first principles the redox potentials of selected electrolytes based on quinone, pyrazine, and pyridazine redox-active moieties.[1] The objective is to understand how the interaction between the redox units affects the potentials and solvation energies. We find that electronic interaction between redox units and intramolecular hydrogen bonding can be exploited to tune the difference between the redox potentials, i.e., the theoretical voltage of the battery. The redox potentials can be further fine-tuned in either direction by adding substituents. Starting from these observations, we formulate a set of rules that will help in finding improved electrolytes for symmetric RFBs.[1] R. P. Fornari, M. Mesta, J. Hjelm, T. Vegge, P. de Silva, “Molecular Engineering Strategies for Symmetric Aqueous Organic Redox Flow Batteries”, ACS Materials Lett. 2020, 2, 3, 239–246.