Synthesis and characterization of hierarchically structured mesoporous MnO2 and Mn2O3

Hierarchically structured mesoporous MnO₂ with high surface area was prepared by a facile precursor route. Well-defined morphological manganese oxalate, synthesized by adding l-lysine via a hydrothermal method, was used as precursor. Mesoporous amorphous MnO₂ with high Brunauer–Emmett–Teller (BET) surface area (340 m²/g) and mesoporous Mn₂O₃ composed of nano-crystals (BET surface area 188 m²/g) were obtained by selective calcination of the oxalate precursor at 330 °C and 400 °C, respectively. Thermogravimetric and differential thermal analyses (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂-sorption analysis and X-ray photoelectron spectroscopy (XPS) were used to characterize the structure and property of products. Cyclic voltammetry (CV) and charge–discharge measurements were used to preliminarily study the electrochemical performance of the products. The range of pH value (about 5.0–7.0) in the synthesis process is apt to prepare the hierarchical structured manganese dioxide. Other types of amino acids were also employed as the crystallization modifiers and different morphologies of manganese dioxides were obtained.