Electrolyte Additives for Reversible Dissolution/Deposition of Mn²⁺/Mn⁴⁺ in a Zinc-Manganese Flow Battery

Abstract

Due 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 battery
• electrolyte additive
• manganese oxide dissolution/deposition
• Mn²⁺(aq)/MnO₂

Acknowledgments

The 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 Statement

No potential conflict of interest was reported by the author(s).