Synthesis of Nanosheet Crystallites of Ruthenate with an alpha-NaFeO2-Related Structure and Its Electrochemical Supercapacitor Property
ABSTRACT Unilamellar crystallites of conductive ruthenium oxide having a thickness of about 1 nm were obtained via elemental exfoliation of a protonic layered ruthenate, H(0.2)RuO(2).0.5H(2)O, with an alpha-NaFeO(2)-related crystal structure. The obtained RuO(2) nanosheets possessed a well-defined crystalline structure with a hexagonal symmetry, reflecting the crystal structure of the parent material. The restacked RuO(2) nanosheets exhibited a high pseudocapacitance of approximately 700 F g(-1) in an acidic electrolyte, which is almost double the value of the nonexfoliated layered protonated ruthenate.
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ABSTRACT: Exfoliated two-dimensional (2D) unilamellar nanosheets of Ca2Nb3O10–, TiNbO5–, Ti2NbO7–, and Ti5NbO143– were deposited layer-by-layer to produce multilayer films on indium–tin–oxide (ITO)-coated glass electrodes, and their electrochemical and photoelectrochemical properties were explored. The layer-by-layer assembly process via sequential adsorption with counter polycations was monitored by UV–visible absorption spectra and X-ray diffraction measurements, which confirmed the successful growth of films, where nanosheets and polycations are alternately stacked at a separation of 1.6–2.4 nm. Exposure to UV light totally removed polycations, producing inorganic films. Cyclic voltammetry on Ti and/or Nb oxide nanosheet electrodes thus fabricated showed reduction/oxidation (Ti3+/Ti4+ and Nb4+/Nb5+) peaks associated with insertion/extraction of Li+ ions into/from intersheet galleries of the films. The extent of the redox reaction is found to be governed by the cation density in the nanosheet gallery. Anodic photocurrents of the oxide nanosheet electrodes were observed under UV light irradiation. These action spectra showed close resemblance to optical absorption profiles of the colloidal nanosheets, indicating that the photocurrent was generated from the nanosheets. Their analysis indicates that the nanosheets of Ca2Nb3O10–, TiNbO5–, Ti2NbO7–, and Ti5NbO143– are all indirect transition-type wide-gap semiconductors with bandgap energies of 3.44, 3.68, 3.64, and 3.53 eV, respectively. These values are larger than those for corresponding parent layered oxide compounds before delamination, suggesting confinement effects into 2D nanosheet structure. Furthermore, the value was invariable for the films with a different number of nanosheet layers, indicating that quantized nanosheets were electronically isolated with each other. In addition, photocurrent generation was measured as a function of applied electrode potential, and the flatband potential was estimated from the photocurrent onset values as −1.12, −1.33, −1.30, and −1.29 V vs Ag/Ag+, for Ca2Nb3O10–, TiNbO5–, Ti2NbO7–, and Ti5NbO143– nanosheets, respectively, providing a diagram of electronic band structure for the nanosheets.The Journal of Physical Chemistry C 06/2012; 116(23):12426–12433. DOI:10.1021/jp302417a · 4.84 Impact Factor
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ABSTRACT: The materials properties of graphene and other two-dimensional atomic sheets are influenced by atomic-scale defects, mechanical deformation, and microstructures. Thus, for graphene-based applications, it is essential to uncover the roles of atomic-scale defects and domain structures of two-dimensional layers in charge transport properties. This review highlights recent studies of nanomechanical and charge transport properties of two-dimensional atomic sheets, including graphene, MoS2, and boron nitrides. Because of intrinsic structural differences, two-dimensional atomic sheets give rise to unique nanomechanical properties, including a dependence on layer thickness and chemical modification that is in contrast to three-dimensional continuum media. Mapping of local conductance and nanomechanical properties on a graphene layer can be used to image the domain and microstructures of two-dimensional atomic layers. This paper also reviews recent experimental and theoretical findings on the role of bending, defects, and microstructures on nanomechanical and transport properties of graphene-derived materials.Advanced Materials Interfaces 06/2014; 1(3). DOI:10.1002/admi.201300089
Annual Review of Materials Research 08/2014; 45(1):150203175635006. DOI:10.1146/annurev-matsci-070214-021202 · 15.63 Impact Factor