Evaluation of Tris-Bipyridine Chromium Complexes for Flow Battery Applications: Impact of Bipyridine Ligand Structure on Solubility and Electrochemistry

This report describes the design, synthesis, solubility, and electrochemistry of a series of tris-bipyridine chromium complexes that exhibit up to six reversible redox couples as well as solubilities approaching 1 M in acetonitrile. We have systematically modified both the ligand structure and the oxidation state of these complexes to gain insights into the factors that impact solubility and electrochemistry. The results provide a set of structure–solubility–electrochemistry relationships to guide the future development of electrolytes for nonaqueous flow batteries. In addition, we have identified a promising candidate from the series of chromium complexes for further electrochemical and battery assessment.