RECHARGEABILITY OF MNO2 IN KOH MEDIA PRODUCED BY DECOMPOSITION OF DISSOLVED KMNO4 AND BI(NO3)(3) MIXTURES .1. MN-BI COMPLEXES

Bi-doped MnO2 samples produced by the slow decomposition of KMnO4 and Bi(NO3)(3) mixtures at room temperature in 0.5 M nitric acid solution have stable voltammograms in 1 M KOH solution even for an extended swe ep 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 format ion reactions. These reactions take place during the first stage of th e slow decomposition of KMnO4 (only X = III, IV) and during the discha rge or recharge when the dissolved Mn(X) species are present in the in tergranular electrolyte. X-ray diffraction studies show the absence of Mn3O4 when Bi(III) is present. This indicates that the reactions lead ing to the formation of Bi-Mn complexes prevent the hausmannite spinel lattice forming from dissolved Mn(II) and Mn(III).