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Diana J. Petrovay

Bio: Diana J. Petrovay is an academic researcher from Connecticut College. The author has contributed to research in topics: Auger electron spectroscopy & Cryptomelane. The author has an hindex of 1, co-authored 1 publications receiving 243 citations.

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TL;DR: In this paper, the octahedral structure of a layered birnessite-type manganese oxides has been characterized by elemental analysis, powder X-ray diffraction, scanning electron microscopy and FT-IR spectroscopy.
Abstract: Layered birnessite-type manganese oxides have been synthesized by sol−gel reactions involving KMnO4 or NaMnO4 with glucose. These microporous manganese oxides are designated as octahedral layer materials, K-OL-1 and Na-OL-1, because their layered structure consists of edge-shared MnO6 octahedra. The interlayer regions are occupied by alkali metal cations and water molecules. K-OL-1 and Na-OL-1 have been characterized by elemental analysis, powder X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, and Auger electron spectroscopy. The empirical formula of K-OL-1 has been determined to be K0.28MnO1.96(H2O)0.19. An interlayer spacing of 7 A, typical of natural and synthetic birnessites, has been measured by X-ray diffraction. The sol−gel synthesis of K-OL-1 is carried out with concentrated aqueous solutions of glucose and KMnO4 in a 1.5:1 mole ratio. Diluted reaction mixtures produce flocculent gels or precipitates which yield other manganese oxide phases such as cryptomelane and Mn2O3. The ...

252 citations


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TL;DR: In this article, the structural features of layered manganese dioxides of the Birnessite family were studied using Raman scattering spectroscopy, which is capable of analysing directly the near-neighbour environment of oxygen coordination around menganese and lithium cations.

633 citations

Journal ArticleDOI
Xun Wang1, Yadong Li1
TL;DR: It is interesting to find that all the MnO( 2) one-dimensional nanostructures have a similar formation process: delta-MnO(2), which has a layer structure, serves as an important intermediate to other forms of MnO (2), and is believed to be responsible for the initial formation of Mn olympic nanostructure.
Abstract: Alpha-, beta-, gamma-, and delta-MnO(2) single-crystal nanowires/nanorods with different aspect ratios have been successfully prepared by a common hydrothermal method based on the redox reactions of MnO(4)(-) and/or Mn(2+). The influences of oxidant, temperature, and inorganic cation (NH(4)(+) and K(+)) template concentrations on the morphology and crystallographic forms of the final products are discussed in this paper. It is interesting to find that all the MnO(2) one-dimensional nanostructures have a similar formation process: delta-MnO(2), which has a layer structure, serves as an important intermediate to other forms of MnO(2), and is believed to be responsible for the initial formation of MnO(2) one-dimensional nanostructures. A rolling mechanism has been proposed based on the results of the series of TEM images and XRD patterns of the intermediate.

560 citations

Journal ArticleDOI
TL;DR: An asymmetric supercapacitor cell with graphitic hollow carbon spheres (GHCS) as the positive electrode and GHCS as the negative electrode can be reversibly charged/discharged at a cell voltage of 2.0 V in a 1.0 mol L−1 Na2SO4 aqueous electrolyte, delivering an energy density of 22.1 Wh kg−1 and a power density of 7.0 kWkg−1.
Abstract: Growing MnO2 nanofibers on graphitic hollow carbon spheres (GHCS) is conducted by refluxing GHCS in a KMnO4 aqueous solution aimed to enhance the electrochemically active surface area of MnO2. The stoichiometric redox reaction between GHCS and MnO4− yields GHCS–MnO2 composites with controllable MnO2 content. It is found that these ultrathin MnO2 nanofibers are vertically grown on the external surface of the GHCS, yielding a composite electrode showing good electron transport, rapid ion penetration, fast and reversible Faradic reaction, and excellent rate performance when used as supercapacitor electrode materials. An asymmetric supercapacitor cell with GHCS–MnO2 as the positive electrode and GHCS as the negative electrode can be reversibly charged/discharged at a cell voltage of 2.0 V in a 1.0 mol L−1 Na2SO4 aqueous electrolyte, delivering an energy density of 22.1 Wh kg−1 and a power density of 7.0 kW kg−1. The asymmetric supercapacitor exhibits an excellent electrochemical cycling stability with 99% initial capacitance and 90% coulombic efficiency remained after 1000 continuous cycles measured using the galvanostatic charge–discharge technique.

552 citations

Journal ArticleDOI
TL;DR: In this article, the synthesis, characterization, and applications of porous manganese oxides during the last two years have been discussed, including the synthesis of porous tunnel structures, layered structures, and related materials.
Abstract: This review concerns the synthesis, characterization, and applications of porous manganese oxides during the last two years The synthesis of porous tunnel structures, layered structures, and related materials is discussed Both microporous and mesoporous systems materials are covered here Characterization discussed here focuses around structural studies The focus of the application sections include electrochemical and catalytic studies

514 citations

Journal ArticleDOI
TL;DR: In situ XAS measurements on a bifunctional manganese oxide catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) demonstrate that the OER activity scales with film thickness, which suggests that the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film.
Abstract: In situ X-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochemical systems, with the ability to elucidate the chemical nature of electrocatalysts under reaction conditions. In this study, we perform in situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), we find that exposure to an ORR-relevant potential of 0.7 V vs RHE produces a disordered Mn3II,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs RHE, relevant to the OER, we observe an oxidation of approximately 80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged Mn3II,III,IIIO4. XAS...

467 citations