Abstract
An electrochemical characteristic evaluation of the Ti-Mn electrolyte system in sulfuric acid aqueous solution was conducted in different acid concentrations with and without the mixing of TiOSO4 and MnSO4 electrolyte system for a redox flow battery application. The reaction mechanism of Mn in sulfuric acid electrolyte was studied using the cyclic voltammetry and anodic voltage hold techniques. The overall anodic behavior of the Mn system can be described by the oxidation reaction of Mn2+ to MnO2 where Mn3+ is an intermediate species. As the acid concentration increases, less MnO2 is formed on the working electrode and more Mn3+ is formed in the solution; however, due to the instability of Mn3+ in an aqueous solution, Mn3+ undergoes a hydrolysis reaction to precipitate as MnOOH in the electrolyte solution. The addition of 1 M TiOSO4 to the Mn electrolyte is suggested to lower the H+ concentration which increases the amount of MnOOH in the solution and lowers the concentration of the aqueous Mn3+ species. The MnOOH formed by the Mn3+ hydrolysis reaction is found to be electrochemically active if it is deposited on the working electrode.
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