Synthesis And Properties Of Nanostructured Managanese Dioxides

Based on the nanostructuredγ-MnOOH precursor,α-MnO₂ nanorods with diameters of 5-20 nm and lengths of 100-200 nm andβ-MnO₂ nanorods with diameters 50-100 nm and lengths of 5-15μm have been successfully prepared by a hydrothermal method. Furthermore, a fast microwave-heating method was introduced to synthesizeα-MnO₂ nanofibers with diameters of 5-20 nm and lengths of 2-5μm andβ-MnO₂ nanorods with diameters 100-150 nm and lengths of 5-20μm. The samples were characterized by XRD, TEM, FTIR and FE-SEM measurements. From the experimental results, the mechanism has been discussed. The catalytic and electrochemical properties of the nanostructured MnO₂ were studied fundamentally and the relationship between the nanostructures of MnO₂ and their properties were investigated.Nanostructuredα-MnO₂ andβ-MnO₂ prepared with two methods show high catalytic activities for the decomposition of hydrogen peroxide. The decomposition rates of hydrogen peroxide follow first-order kinetics. With theα-MnO₂ andβ-MnO₂ samples prepared by hydrothermal method and microwave-heating method as catalysts, respectively, the corresponding reaction rate constants are 0.0197 S^-1, 0.110 S^-1, 0.0466 S^-1 and 0.205 S^-1, respectively. Among them,β-MnO₂ seems to be more effective because of its 1×1 tunnel and well-proportioned pore size distribution.When the as-preparedα-MnO₂ andβ-MnO₂ samples are used for Li-MnO₂ battery, the discharge capacities are 208.99 mA·h/g and 155.67 mA·h/g for the two MnO₂ samples from hydrothermal synthesis, and 270.23 mA·h/g and 186.66 mA·h/g for the two MnO₂ samples from microwave-heating synthesis. The results indicate that the nanostructuredα-MnO₂ from microwave-heating synthesis has the best electrochemical property among the four samples and is more suitable as cathode material for primary Li/MnO₂ batteries.