SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF NANO FIBER HOLLANDITE-TYPE MANGANESE OXIDES USING A HYDROTHERMAL METHOD

Abstract

Hollandite-type MnO2 and its Co -substituted samples have been synthesized by hydrothermal method from MnSO4 , CoSO4 and K2S2O8 solutions. The hydrothermal products from MnSO4 and K2S2O8 solutions consisted of the hollandite-type [2 × 2] tunnel structure at 100°C–150°C for 12 h, which was transformed to pyrolusite-type [1 × 1] tunnel structure by hydrothermal treatment at 150°C for longer times of 24–48 h or at a higher temperature of 180°C. On the other hand, the hydrothermal products from MnSO4 , CoSO4 and K2S2O8 solutions at 150°C–180°C for 12–48 h consisted of the hollandite-type MnO2 phase. The Co -substituted samples showed higher initial discharge capacity (180–200 mAh (g-oxide)-1) than that of non-substituted hollandite-type MnO2 (130–160 mAh (g-oxide)-1) at 50 mA g-1.