Electrolyte Additives for Reversible Dissolution/Deposition of Mn 2+ /Mn 4+ in a Zinc-Manganese Flow Battery

AbstractDue to its adaptability in scaling up, a redox flow battery (RFB) is seen to be one of the finest options for large-scale electrical backup systems. As a result, it is feasible to create RFB systems that are both cost and performance effective. Recently, a zinc-manganese RFB that relies on Zn(s)/Zn2+(aq) and Mn2+(aq)/MnO2 redox couples has gained attention since both zinc and manganese are cheap, abundant, and eco-friendly. However, the reversibility of Mn2+(aq)/MnO2 at the positive electrode is limited by the formation of Mn3+ species upon charge/discharge (CD) cycling, resulting in severe capacity fading. Herein, this study examines the use of reducing agents as electrolyte additives to enhance the reversibility of the Mn2+(aq)/MnO2 reaction. Experimental results indicate that sulfuric acid and oxalic acid as additives can significantly improve the reversibility of the Mn2+(aq)/MnO2 reaction and the cycling stability of zinc-manganese RFBs. The acetate-based system demonstrates better reversible reaction than the sulfate-based system having more than 100 CD cycles at a current density of 10 mA/cm2. Coulombic efficiency (CE) is also seen to be higher than 90%. Overall, results lead to increased efficiency and cycling stability for zinc-manganese RFBs.Keywords: Zinc-manganese flow batteryelectrolyte additivemanganese oxide dissolution/depositionMn2+(aq)/MnO2 AcknowledgmentsThe Program Management Unit for Human Resources & Institutional Development, Research and Innovation (B16F640166), the Energy Storage Cluster, Chulalongkorn University, and Beamline 5.2 at Synchrotron Light Research Institute (SLRI) are acknowledged.Disclosure StatementNo potential conflict of interest was reported by the author(s).