Vanadium‐manganese redox flow battery: Study of Mn(III) disproportionation in the presence of other metallic ions

The Mn(III)/Mn(II) redox couple with a standard potential of +1.51 V vs . SHE has drawn interest for the design of V/Mn redox flow battery (RFB). However, Mn(III) disproportionation leads to a loss of capacity, an increase of pressure drop and electrode passivation due to the formation of MnO 2 during battery cycling. In this work, we studied the influence of Ti(IV) or/and V(V) on Mn(III) stability in acidic conditions, by formulating 4 different electrolytes at equimolar ratios (Mn, Mn:Ti, Mn:V, Mn:V:Ti). Voltammetric studies have revealed a EC i process for Mn(II) oxidation responsible for the electrode passivation. SEM and XPS analysis demonstrate that the nature and the morphology of the passivating oxides layer strongly rely on the electrolyte composition. Spectroelectrochemistry highlights the stabilization effect of Ti(IV) and V(V) on Mn(III). At a comparable pH, the amount of Mn(III) losses through disproportionation is decreased by a factor of 2.5 in the presence of Ti(IV) or/and V(V). V(V) is an efficient substitute to Ti(IV) in order to stabilize Mn(III) electrolyte for redox flow battery applications.