Solubility Trends in Pyridinium Salts for Non-Aqueous Organic Redox Flow Batteries

Abstract

Redox flow batteries (RFBs) are a strong candidate for grid-scale energy storage applications. Recent pursuits for chemical systems involve focus on organic species, due to their chemical abundance, and non-aqueous solvent systems, due to an expanded electrochemical stability window. Currently, RFBs suffer from limitations that prevent them from being economically competitive when scaled. Among the critical properties hindering RFB expansion, one limitation is low system energy densities. The energy density of a RFB system is dependent on voltage, electrons transferred, and concentration of the anolyte and catholyte. Electrolyte advancements have focused on optimizing energy density by targeting species that maximize divergence of anolyte/catholyte redox potentials, increase species solubility, and feature reversible multi-electron transfer. Strategic structural engineering of redox-active materials is necessary to tune these distinct qualities. Understanding the relationship between molecular design and these variables, and then developing strategies to predict structures with optimal characteristics could help identify promising electrolyte candidates. Our work is focused on understanding and predicting the solubility trends of pyridinium anolyte materials. The pyridiniums in this series all feature low reduction potentials and a broad range of solubility in acetonitrile. By carefully aligning experimental data to DFT and other modeled parameters we are investigating the predictive parameters involved in controlling electrolyte solubility.