Molecular Engineering Strategies for Symmetric Aqueous Organic Redox Flow Batteries

Symmetric aqueous organic redox flow batteries (RFBs) are potentially an inexpensive, durable, and safe energy storage technology. Unlike normal asymmetric flow batteries, they are based on electrolytes that exist in at least three oxidation states and can undergo a minimum of two distinct redox processes. We compute the redox potentials of selected electrolytes, with the intent to understand how the interaction between the redox units affects the potentials. 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 ideal candidates for symmetric RFBs.