Manganese species in methane sulfonic acid as the solvent for zinc-manganese redox battery

Abstract

Abstract Manganese(II)/Manganese(III) with a standard electrode potential of 1.51 V has been identified as a potential positive electrode for redox flow cells. The current work is to evaluate the use of methane sulfonic acid (MSA) as a solvent for Manganese(II)/Manganese(III) electric pairs as cathode materials applied to redox flow batteries (RFB). The electrochemical behavior of the MSA medium in Manganese(II)/Manganese(III) was studied by linear scanning voltammetry and cyclic voltammetry. The results show that the reaction of Manganese(II)/Manganese(III) on the graphite electrode is a quasi reversible single electron transfer step. The diffusion coefficient of Mn2+ was identified as 0.982 × 10−6 cm2 s−1 in 1 M MSA. As the concentration of MSA increases from 2 to 5 M, Mn3+ would be more stable, and the electrochemical kinetics of Manganese(II)/Manganese(III) couple would be better. When the MSA concentration reached 5 M, reduction kinetics of oxidized species Mn3+ decreased obviously. The results support the selecting of 4 M MSA. When the current density was 20 mA cm−2, the average energy efficiency and coulomb efficiency of the battery were 74.0% and 92.2% respectively. The average discharge voltage was 1.91 V and the average energy efficiency was 59%, which was higher than the total V cell. At the same time, the battery got a good charging and discharging cycle performance, which indicates that the zinc manganese oxide redox battery has a wide application prospect.