Interrogation of 2,2′-Bipyrimidines as Low-Potential Two-Electron Electrolytes

As utilization of renewable energy sources continues to expand, the need for new grid energy storage technologies such as redox flow batteries (RFBs) will be vital. Ultimately, the energy density of a RFB will be dependent on the redox potentials of the respective electrolytes, their solubility, and the number of electrons stored per molecule. With prior literature reports demonstrating the propensity of nitrogen-containing heterocycles to undergo multielectron reduction at low potentials, we focused on the development of a novel electrolyte scaffold based upon a 2,2'-bipyrimidine skeleton. This scaffold is capable of storing two electrons per molecule while also exhibiting a low (similar to-2.0 V vs Fc/Fc(+)) reduction potential. A library of 24 potential bipyrimidine anolytes were synthesized and systematically evaluated to unveil structure-function relationships through computational evaluation. Through analysis of these relationships, it was unveiled that steric interactions disrupting the planarity of the system in the reduced state could be responsible for higher levels of degradation in certain anolytes. The major decomposition pathway was ultimately determined to be protonation of the dianion by solvent, which could be reversed by electrochemical or chemical oxidation. To validate the hypothesis of strain-induced decomposition, two new electrolytes with minimal steric encumbrance were synthesized, evaluated, and found to indeed exhibit higher stability than their sterically hindered counterparts.

Automated summary

As the utilization of renewable energy sources expands, the development of new grid energy storage technologies like redox flow batteries (RFBs) becomes crucial. This study focused on a novel electrolyte scaffold based on a 2,2'-bipyrimidine skeleton capable of storing two electrons per molecule at a low reduction potential. Structural-function relationships were systematically evaluated for 24 potential bipyrimidine anolytes to uncover the major decomposition pathway and validate the hypothesis of strain-induced decomposition.