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

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 Ti 4+ ion in the positive electrolyte was examined in detail. With an increase of Ti 4+ ion concentration, the formation reaction of MnO 2 particle was slowed down significantly, which means the stability of Mn 3+ ion is enhanced. Moreover, the particle size of MnO 2 precipitate became smaller in electrolytes containing certain amount of Ti 4+ ion. These MnO 2 particles were small enough to be flowed in the electrolyte and to be reduced to Mn 2+ ion again. Ti 4+ ion also affected the crystal structures of MnO 2 , limiting to gamma-MnO 2 which is assumed to be reactive. In cyclic voltammetry study, the higher Ti 4+ ion concentration was, the better reversibility of Mn redox reaction was observed. The ion interaction between Ti 4+ and Mn 3+ was confirmed by UV-visible spectroscopy.