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The influence of synthesizing temperature of manganese dioxide (MnO(2)) powders on their electrochemical reactivity in 1 M KOH was investigated. These powders were prepared chemically by the hydrothermal method by oxidation of Mn(2+) by ammonium peroxodisulphate. The observations by scanning electronic microscopy, energy-dispersive X-ray analyses, and transmission electron microscopy techniques on MnO(2) obtained at different temperatures show the formation of many nanometre scale sticks lumped together to form a spherical particle of several micrometers. The results obtained by BET and BJH methods reveal mesoporous texture, and the MnO(2) synthesized at 90 degrees C presents the largest expanded surface area. The electrochemical reactivity of these powders in 1 M KOH was characterized with microcavity electrode by cyclic voltammetry and electrochemical impedance spectroscopy. The results illustrate that the nanostructured MnO(2) powder synthesized at 90 degrees C shows the highest electrochemical reactivity in agreement with BET data. The X-ray powder diffraction identified the gamma-MnO(2), known as the most reactive species.

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An electrodeposition method based on chronoamperometry was used to develop a highly reproducible and fast elaboration method of adherent manganese dioxide thin films on a glassy carbon electrode from aqueous solutions containing sulfuric acid and manganese sulfate. The resulting films were found to have a nanostructured character presumably due rather to birnessite (G-MnO 2) than to J-MnO 2 , as suggested by their Raman and XRD signatures. They lead to modified electrodes that present an obvious although complex pH dependent potentiometric response. This sensor indeed showed a single slope non-Nernstian linear behaviour over the 1.5-12 pH range for increasing pH direction ("trace") whereas a Nernstian two slopes linear behaviour was observed for decreasing pH direction ("re-trace"). Preliminary EIS experiments carried out at a pH value of 1.8 seem to reveal a sensitivity mechanism based on proton insertion process at least at highly acidic pH values.

Chemical synthesis of hollow sea urchin like nanostructured polypyrrole particles through a core-shell redox mechanism using a MnO2 powder as oxidizing agent and sacrificial nanostructured template. Synthetic Metals, Elsevier, 2013, 175, pp.192-199. 10.1016/j.synthmet.2013 1 Chemical synthesis of hollow sea urchin like nanostructured polypyrrole particles through a core-shell redox mechanism using a MnO 2 powder as oxidizing agent and sacrificial nanostructured template AbstractHollow sea urchin shaped nanostructured polypyrrole powder was successfully synthesized chemically in an acidic medium through a core-shell redox mechanism by using a nanostructured MnO 2 powder as oxidizing agent and sacrificial template simultaneously. The morphology and the structure of MnO 2 powder based reactant and produced polypyrrole powder were characterized respectively by using FEG-SEM, TEM, EDX and XRD techniques, which led us to demonstrate clearly the formation of hollow and open microparticles of polypyrrole with the presence of nanotubes on their surface. Nanostructured polypyrrole powder was found to be rather amorphous even though the shape of the polypyrrole particles was induced by the crystalline and nanostructured sea urchin shaped MnO 2 powder on which they grew. In addition, neither MnO 2 nor any manganese based species were found within the produced polypyrrole powder, which ruled out the production of composite materials. cations as reaction products isolated after filtration of the reaction medium.

International audienceIn this investigation, Mn3O4 spinel-type oxide was synthesized at low temperature using the Pechini process. We employed a sol-gel route, in which a solution of Mn(II) in a mixture of citric acid and ethylene glycol was heated to form a polymeric precursor, followed by annealing at lower temperature. The oxide obtained was identified by X-ray diffraction, scanning electron spectroscopy, and Raman spectroscopy. The results revealed that the formation of Mn3O4 hausmannite structure with a minor secondary phase of MnSO4 occurred at or above 280 A degrees C. The sample powder consisted of fine grains with homogeneous morphology and an average size close to 1 mu m was obtained. This new preparation procedure yielded an electrode oxide which appears to be a promising cathode material for fuel cells and metal-air batteries