Rechargeability of MnO2 in KOH Media Produced by Decomposition of Dissolved KMnO4 and Bi ( NO 3 ) 3 Mixtures: I. Mn‐Bi Complexes

Abstract

Bi‐doped samples produced by the slow decomposition of and mixtures at room temperature in 0.5 M nitric acid solution have stable voltammograms in 1 M KOH solution even for an extended sweep range from −1.1 to 0.7 V vs. a normal hydrogen electrode. Analysis of the voltammograms shows the existence of complexes between Mn(X) (X = IV, III, and II) and Bi(III), which implies the existence of formation reactions. These reactions take place during the first stage of the slow decomposition of , (only X = III, IV) and during the discharge or recharge when the dissolved Mn(X) species are present in the intergranular electrolyte. X‐ray diffraction studies show the absence of when Bi(III) is present. This indicates that the reactions leading to the formation of Bi‐Mn complexes prevent the hausmannite spinel lattice forming from dissolved Mn(II) and Mn(III).