Investigation on Manganese (Mn²+/Mn³+) - Vanadium (V²+/V³+) Redox Flow Battery

A novel Mn²⁺/Mn³⁺- V²⁺/V³⁺redox flow battery has been designed. The electrochemical response of high concentration Mn²⁺/Mn³⁺ couple in H₂SO₄ solution were investigated via cyclic voltammetry, steady polarization curve, electrochemical impedance spectroscopy, and charge-discharge experiments. The electrochemical and the kinetic parameters for anodic oxidation of Mn² and cathodic reduction of Mn³⁺ were measured. Performance of a RFB employing Mn²⁺/Mn³⁺ couple as anolyte active species and V²⁺/V³⁺ as catholyte ones was evaluated with constant-current charge-discharge tests. When the current density varies from 20 to 80 mA cm^-2, the average coulombic efficiency varies from 81.5% to 92.5% and the voltage efficiency varies from 93.5% to 85.3%. Accordingly the whole energy efficiency varies from 76.2% to 81.2%. Energy efficiency is about 20% higher than that of the all-vanadium battery and average discharge voltage is 1.66 V, which is about 14% higher than that of the all-vanadium battery. The energy density is calculated to be 40.8 Wh/kg, which is 60% higher than that of the all-vanadium battery. The preliminary exploration shows that the Mn²⁺/Mn³⁺ couple is electrochemically promising for redox flow battery.