High-Capacity Economically Viable Catholyte for Alkaline Aqueous Redox Flow Battery

Abstract

Alkaline aqueous organic redox flow batteries (AORFB) show great potential as viable options for storing energy in commercial power grids. While there has been notable advancement in the development of anolytes, there has been a lack of focus on the catholyte component. In this study, we present a novel all-alkaline AORFB that utilizes a highly soluble catholyte based on manganese (Mn). The formulated combination of catholyte, MnO₄^–/NaOH, has remarkably high solubility, approximately 3.9 M, and possesses a theoretical capacity of 105 Ah L^–1. This capacity is the greatest among all reported catholytes thus far. Half-cell experiments indicate that there is a high level of reversibility and stability, with minimal capacity degradation over time. In addition to three-electrode configuration, the efficacy of MnO₄^–/NaOH is evaluated in full-cell redox flow systems utilizing alizarin as anolyte. The AORFB shows an open circuit voltage of approximately 1.3 V, which is nearly 250 mV higher than the state-of-the-art ferrocyanide-based AORFBs. This resulted in an energy and power output that is approximately 20% higher. In addition, the system exhibits consistent performance with minimal decrease in capacity (0.1% per day) while achieving approximately 85% energy efficiency and 100% coulombic efficiency. The impact of the cutoff potential and plausible degradation mechanisms of the catholyte are also discussed. The findings of this electrolyte formulation offer fresh impetus for developing high-capacity all-alkaline AORFBs.