Redox Reaction in Ti−Mn Redox Flow Battery Studied by X‐ray Absorption Spectroscopy

Abstract

We performed X-ray absorption studies for the electrolytes of a TiÀ Mn redox flow battery (RFB) to understand the redox reaction of the Ti/Mn ions and formation of precipitates in charged catholyte, because suppression of the disproportionation reaction is a key to improve the cyclability of TiÀ Mn RFB and enhance the energy density. Hard X-ray absorption spectroscopy with a high transmittance and soft X-ray absorption spectroscopy to directly observe the 3d orbitals were complementarily employed. Moreover, the Ti/ Mn 3d electronic structure for each precipitate and solution in the charged catholyte was investigated by using scanning transmission X-ray microscopy: the valence of Mn in the precipitate is mostly attributed to 4 + , and the solution includes only Mn 2 + . This charge disproportionation reaction should occur after the Mn ions in the catholyte should be oxidized from Mn 2 + to Mn 3 + by charge.

Enhanced stability and the lithium storage mechanism of oxygen vacancy-induced heterogeneous Li4Ti5O12/TiO2(B) anolytes

“…38 The peak of Ti 3+ tends to appear between t 2g and e g states of Ti 4+ , and the negative shi of peaks B and D conrms the existence of Ti 3+ . 39 The I (L 2 ) /I (L 3 ) strength ratios of LTO-TOB and LTO are 1.178 and 1.124, respectively, further demonstrating the introduction of more Ti 3+ through surface modication. 40 Four distinct peaks located at P 1 , P 2 , P 3 and P 4 can be observed at the O K-edge (Fig.…”

XAFS Analysis of Sulfuric Acid Solution Related to the Effect of Te and Sb in Suppressing the Disproportionation Reaction of Mn³⁺ in Mn/Ti Redox Flow Cells

“…Redox flow (RF) batteries are one of the most promising candidates for this purpose. [1][2][3][4][5][6] As for redox couples, titanium (Ti) and manganese (Mn) in a sulfuric acid (H 2 SO 4 ) aqueous solution are considered to be useful as the active materials in the negative and positive electrolytes, respectively. The voltage difference between the half-cell reactions of Ti 3+ /Ti 4+ and Mn 2+ /Mn 3+ is approximately 1.4 V, which is close to that realized by vanadium (V) system (V 2+ /V 3+ and V 4+ /V 5+ ) in the practical stage.…”

XAFS Analysis of Sulfuric Acid Solution Related to the Effect of Bi in Suppressing the Disproportionation Reaction of Mn³⁺ in Mn/Ti Redox Flow Cells

“…For this purpose, various kinds of redox flow (RF) batteries have been proposed, to be used as a large capacity secondary batteries. [1][2][3][4][5][6] For instance, redox couples based on vanadium (V) in a sulfuric acid (H 2 SO 4 ) aqueous solution, in which the voltage difference between half-cell reactions (V 2+ /V 3+ and V 4+ /V 5+ ) is 1.4 V, are already in the practical stage. Titanium (Ti) and manganese (Mn) are also promising candidates as the active materials in the negative and positive electrolytes, respectively, since the voltage difference between half-cell reactions of Ti 3+ /Ti 4+ and Mn 2+ /Mn 3+ is almost the same as that of the V system.…”