New insights into phenazine-based organic redox flow batteries by using high-throughput DFT modelling

Abstract

Identification of new redox compounds is essential for the design of new improved redox-flow batteries. Phenazines are a new class of organic compounds that have been recently used in electrochemical energy storage applications. By applying high-throughput density functional theory calculations, we investigated the redox-potentials of 200 phenazine derivatives in non-aqueous media containing various electron-donating or -withdrawing groups at different positions. We identified promising candidates for both the negative and positive sides of organic-based flow batteries. By adding an appropriate number of functional groups at the specific targeted positions, the redox potentials can be modified up to −0.65 V (for the electron-donating amino groups) and to +2.25 V (for the electron-withdrawing cyano groups) compared to the parent phenazine. The analysis of the results revealed the effect of both the functional groups and their position on the redox potential. By strategically partially functionalizing with EDGs at the appropriate positions, a redox potential equal to or even more negative than that of full functionalization can be obtained. To further accelerate the design of new improved batteries, a computational approach was used in order to assess their structural stability. The results show that the proposed compounds are predicted to have similar stabilities to other organic molecules that are used in redox-flow batteries.