1,721,052 research outputs found
Electro- and photo-electrochemical water splitting as studied by In-Operando X-Rays Absorption Spectroscopy
No full textIn this work we show our most recent results obtained by in-operando X-Ray absorption spectroscopy on hydrous/amorphous [1] and on crystalline/dry [2] iridium oxide electrodes as electrocatalysts for the oxygen evolution reaction (OER). In all cases, XAS evidenced the role of Ir active sites, and the relevant oxidation states assumed during the catalytic cycle. Moreover, the local structure is not significantly influenced by the applied potential, thus suggesting a negligible reorganization energy of the catalyst.On the bases of these results, we were able to directly observe, by means of spectro-photoelectrochemical experiments, the charge transfer between a semiconductor (α-Fe2O3) and hydrous IrOx, the latter used as overlayer for generating a high performance photoanode architecture in photoelectrochemical water splitting[3]. The aim is to clarify the ambiguous role of oxygen evolving catalysts used as overlayers on top of photoanodes in photoelectrochemical water splitting cells. Previous literature suggested that the real benefit of covering hematite with overlayers like iridium or cobalt oxides is not due to an increase of the reaction rate but to a decrease of the electron density in the hematite[4] or to the storage of photogenerates holes[5]. These effects are likely more important when hydrous overlayer, that can act as adapting catalysts[6], are considered. All these hypotheses can explain the observed improved hole lifetime and reduce recombination with electrons. The experimental approach is similar to the one adopted to study Ir oxide particles electrocatalysts[1,2]. In the present case, FEXRAV [7] and XANES have been used to probe changes in the charge state of Ir while the hematite was illuminated with a 410nm diode. Thanks to this setup, we were able to observe an increase of the density of empty Ir 5d states during hematite illumination and in correspondence of water spitting in the photoelectrochemical cell. The main conclusion is that a charge (hole) transfer between hematite and iridium occurs only when the hematite is illuminated. Hydrous iridium oxide is therefore capable of withdrawing holes from the semiconductor thus increasing the probability of interface reaction rather than charge recombination.
References
[1] A. Minguzzi, O. Lugaresi, E. Achilli, C. Locatelli, A. Vertova, P. Ghigna, Rondinini S., Chem. Sci., 2014, 5, 3591-3597
[2] A. Minguzzi, C. Locatelli, O. Lugaresi, E. Achilli, G. Cappelletti, M. Scavini, M. Coduri, P. Masala, B. Sacchi, A. Vertova, P. Ghigna, S. Rondinini, submitted
[3] A. Minguzzi, O. Lugaresi, E. Achilli, F. D'Acapito, A. Naldoni, F. Malara, C. Locatelli, A. Vertova, S. Rondinini, P. Ghigna, In preparation
[4] M. Barroso, C.A. Mesa, S.R. Pendlebury, A.J. Cowana, T. Hisatomi, K. Sivula, M. Grätzel, D.R. Klug, J.R. Durrant PNAS, 2012, 109, 15640–15645
[5] L. Badia-Bou, E. Mas-Marza, P. Rodenas, E M. Barea., F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, J. Phys. Chem. C, 2013, 117, 3826−3833
[6] F. Lin, S.W. Boettcher Nature Materials, 2014, 13, 81-86
[7] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. d'Acapito, E. Achilli, P. Ghigna, Anal. Chem. 2013, 85, 7009-7013
Study of the local structure of the AuSi tips resulting from the growth of Si nanowires
No full textThis study aims to the determination, via x-ray absorption spectroscopy at the Au–LIII edge, of the local structure around Au in the AuSi tips of Au-catalysed Si nanowires grown at temperatures above and below the eutectic temperature of the AuSi alloy (Te=633 K)
XAFS study of the local structure around Er3+ ion in thin Er-doped HfO2 thin films for advanced nanoelectronic applications
No full textWe propose to perform XAFS measurements to determine the local structure of Er3+ atoms in ultra-thin Er-doped HfO2 films, which are currently investigated as high-dielectric constant (high-k) oxides for advanced nanoelectronic applications
Atomic scale ordering in Pr - Y mixed oxide heterostructures
No full textThe aim of this proposal is to determine the relative atomic ordering of Y and Pr cations in
(Y2O3)1-x(Pr2O3)x heterostructures on Si(111) using grazing incidence XAFS at the Y K- and Pr L3- absorption edges
Synchrotron radiation glancing incidence X-ray diffraction: a tool for structural investigations of ion implanted glasses
No full textAtom ic scale ordering in Pr - Y mixed oxide heterostructures
No full textThe aim of this proposal is to determine the relative atomic ordering of Y and Pr cations in
(Y2O3)1-x(Pr2O3)x heterostructures on Si(111) using grazing incidence XAFS at the Y K- and Pr L3-
absorption edges. RE (rare earth) cub-Pr2O3 and Y2O3 oxides crystallize in the bixbyite structure (space
group Ia-3) and their miscibility to form a solid solution from the powder form was demonstrated many
years ago [1]. Being the lattice parameter of cub-Pr2O3 2.7% bigger and that of Y2O3 2.4% smaller than
twice the Si unit cell, thin (Y2O3)1-x(Pr2O3)x heterostructures permit for the cost-effective integration of
lattice-matched as well as -mismatched SiGe epilayers on the Si platform for microelectronic, optoelectronic and photovoltaic applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The role of copper on colour of palaeo-Christian glass mosaic tesserae: an XAS study
No full textThis work reports mainly the results of an X-ray Absorption Spectroscopy (XAS) study carried out on coloured glass tesserae from the palaeo-Christian mosaic which decorated the votive chapel of St. Prosdocimus
(Padova) until its replacement with the current frescoes of Renaissance age, and which is one of the only two known mosaics in the Veneto region (Italy). The study aims at clarifying how the different local structure, oxidation state and quantity of copper influenced colour. Analysis of high-resolution Cu-K edge X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure
(EXAFS) spectra showed that copper is present as cuprite (Cu2O) in orange samples and as metallic copper in red and brown ones. These phases are responsible for both the colour and opacity of the samples. In
addition, Cu1+ ions linked to the oxygen atoms of the glass framework were identified in ratios of about 60% and 30% of total copper in orange and red/brown samples, respectively. In blue and green samples, copper is dispersed in the glass matrix as a mixture of Cu1+ and Cu2+ ions, and no crystalline phases are visible. In this context, the Cu1+ and Cu2+ contents in glass were also quantified thanks to suitable standards,
demonstrating that, when Cu2+ is the main chromophorous ion, colour intensity is directly correlated to its content in the glass. In particular, in green and blue samples, coloured by copper, Cu2+ content varies
from 26% to 56% of total copper, and the higher contents of Cu2+ are shown by more intensely coloured samples. It should be stressed here that the green colour of the analysed tesserae is given by the physical
interaction of blue colour, due to Cu2+ ions, and yellow colour, due to Pb antimonates used as opacifiers
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