Investigation of multi-electron bispyridinylidenes for symmetric organic non-aqueous Redox Flow Batteries

Thumbnail Image



Journal Title

Journal ISSN

Volume Title


University of New Brunswick


Redox flow batteries (RFBs) present a promising solution for large-scale energy storage, facilitating the proper utilization of renewable energies like solar and wind energy. Their unique advantage lies in the flexibility to separately scale up both power and energy capacity. Within the realm of RFBs, those employing organic molecules as active species are particularly promising. Most organic RFBs feature an asymmetric design, where distinct active species are used for the two electrodes. However, these systems suffer from active material crossover, reducing their lifetime. In an effort to eliminate such irreversible crossover issues, researchers have recently focused on developing bipolar molecules amenable to a symmetric RFB design. Symmetric systems utilize a single redox-active molecule (bipolar molecule) capable of existing in multiple oxidation states, enabling the incorporation of two distinct redox couples for the anolyte and catholyte. This work introduces ester-substituted bispyridinylidene bipolar molecules for non-aqueous RFBs, demonstrating the first effectively concerted two-electron oxidation and reduction processes for an organic active material. Symmetric static and flowing tests, utilizing cost-effective polypropylene separators, revealed capacity fade rates of 0.025% and 0.23% per cycle for static (2000 cycles) and flow (70 cycles) cells, respectively, signify commendable overall performance in comparison to the current state of the art. Considering the practical limits on active material solubility, this achievement represents a milestone towards the development of high energy density ORFBs. Furthermore, this study systematically categorizes five distinct classes of organic bipolar molecules utilized in both aqueous and non-aqueous solvent systems, providing a thorough exploration of their performance characteristics. Through the observation of diverse types of bipolar molecules, the study concludes by outlining the potential for designing new multi-electron redox-active molecules, which hold promise for achieving energy-dense ORFBs. Overall, the findings contribute valuable insights to the development of sustainable and efficient energy storage technologies, and pave the way for large-scale energy storage solutions in the future.