Biological Anolyte Regeneration System for Redox Flow Batteries

Abstract

Redox flow batteries (RFBs) are valuable energy storage devices with applications in grid storage, and redox-active small organic molecules (ROMs) have shown promise as charge storage species for RFB applications. However, electrolyte degradation is a common mechanism in RFBs, and the chemical instability of ROMs limits their practical application in commercial RFB devices. Recently, microbial electrochemical technologies have been studied, taking advantage of the natural oxidation microbes undergo when exposed to a carbon source. Here, an aqueous redox flow battery with anolyte phenazine-1-carboxylic acid (PCA) and catholyte (Ferrocenylmethyl)trimethylammonium (FcN) is explored with a genetically engineered, phenazine-producing E. coli phzAG-SM strain. E. coli phzAG-SM is a genetically engineered bacterial strain that has phenazine gene clusters responsible for producing phenazine species, specifically PCA and pyocyanin (PYO). Standard E. coli strains like E. coli BL21 do not have genes responsible for the phenazine biosynthetic pathways that result in the production of phenazine species. This genetically engineered strain has the ability to not only excrete its own phenazine metabolites, but also to intake the phenazine species present in solution and increase phenazine production rates. In a redox flow battery, the electrolyte species are subjugated to changes in potential during charging and discharging cycles. Over time, the phenazine anolyte species can degrade or decompose. The role of the genetically engineered E. coli in the anolyte chamber is to repair the degraded/decomposed phenazine species, producing a longer lasting battery with more stable phenazine-based electrolyte species. Herein, we demonstrate the design of an RFB system where ROMs are continually regenerated by genetically engineered microorganisms to maintain RFB cycling stability. This work represents a new strategy for improving the stability of RFB systems because, under the influence of genetically engineered microbes, the anolyte species does not display degradation after battery cycling.