Effect of Ti(IV) Ion on Mn(III) Stability in Ti/Mn Electrolyte for Redox Flow Battery

Abstract

The mixed electrolyte of titanium and manganese is one of the promising candidates as low-cost electrolytes for redox flow batteries. In this study, the effect of Ti4+ ion in the positive electrolyte was examined in detail. With an increase of Ti4+ ion concentration, the formation reaction of MnO2 particle was slowed down significantly, which means the stability of Mn3+ ion is enhanced. Moreover, the particle size of MnO2 precipitate became smaller in electrolytes containing certain amount of Ti4+ ion. These MnO2 particles were small enough to be flowed in the electrolyte and to be reduced to Mn2+ ion again. Ti4+ ion also affected the crystal structures of MnO2, limiting to gamma-MnO2 which is assumed to be reactive. In cyclic voltammetry study, the higher Ti4+ ion concentration was, the better reversibility of Mn redox reaction was observed. The ion interaction between Ti4+ and Mn3+ was confirmed by UV-visible spectroscopy.