On the Capacity and Stability of a Biosynthesized Bis-quinone Flow Battery Negolyte

The use of naturally occurring quinones to produce more sustainable electrolytes to use for renewable energy storage in redox flow batteries (RFBs) is still a new and rarely investigated subject. In this study, we demonstrate how the putative phoenicin and its dimer (diphoenicin) influence the capacity performance of phoenicin as a negolyte in a redox flow battery. To do this, we biosynthesized phoenicin by cultivating the filamentous fungus Penicillium phoeniceum and the resulting fungal extract contained multiple metabolites, putatively related to phoenicin, including the proposed phoenicin dimer, which constituted 7% of the extract. When paired with potassium ferri/ferrocyanide as a posolyte in an RFB, the battery showed an initial capacity of 1.58 Ah L^–1. In contrast to our previous study, this corresponded to a two-electron reaction per benzoquinone group. A detailed electrochemical and chemical analysis is conducted to shed light on this discrepancy and to provide further insight into the chemical stability of phoenicin in an alkaline environment (pH = 14). A sustainable biosynthesized fungal quinone mix of phoenicin stores four electrons per phoenicin molecule in a redox flow battery negolyte.