RESUMEN
Various redox couples have been reported to increase the energy density and reduce the price of redox flow batteries (RFBs). Among them, the vanadium electrolyte is mainly used due to its high solubility, but electrode modification is still necessary due to its low reversibility and sluggish kinetics. Also, an incompatible ion exchange membrane with redox-active species leads to self-discharge referred to as crossover. Here, we report a V/Mn RFB using an anion exchange membrane (AEM) for crossover mitigation and etched carbon felt by nickel-bismuth (NB-ECF) for the vanadium anolyte. The NB-ECF significantly enhances the reversibility and kinetics of the V2+/V3+ redox reaction, attributed to inhibited irreversible hydrogen evolution by the Bi catalyst and increased carboxyl groups by nickel (etching and NiO catalyst). Notably, the V/Mn cell employed in the NB-ECF maintains a high energy efficiency of 85.7% during 50 cycles without capacity degradation at a current density of 20 mA cm-2, which is attributed to a synergistic effect of crossover mitigation and facilitated V2+/V3+ redox reaction. This study demonstrates the novel electrocatalyst design of carbon felt using two metal species.
RESUMEN
The energy density of redox flow batteries (RFBs) is generally affected by the standard electrode potential and the solubility of the redox active species. These crucial factors are closely related to the solvent in which the active materials are dissolved. Aqueous RFBs have been widely studied due to their excellent reaction kinetics and high solubility of the redox couple in aqueous media. However, the low voltage of conventional aqueous RFBs has hindered them from being candidates for practical applications. Recently, high-voltage aqueous RFBs are implemented based on the low negative potential of the Zn/[Zn(OH)4 ]2- reaction in an alkaline solution. Here, we review recent progress in the design of high energy density RFBs in both aqueous and non-aqueous electrolytes, notably focusing on the Zn/MnO2 hybrid RFBs in detail. Furthermore, strategies for inhibiting zinc dendritic growth and stabilizing manganese redox couple in the RFBs system are discussed.
