170,368 research outputs found
Observation of charge transfer cascade in α-Fe2O3/IrO2 photoanodes by in-operando X-rays absorption spectroscopy
No full textIn this work we show the direct observation, by means of spectro-photoelectrochemical experiments, of charge transfer between a semiconductor (-Fe2O3) and a metal oxide overlayer (hydrous IrOx) as a photoanode architecture in photoelectrochemical water splitting.1 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 reaction kinetics but the decrease of the electron density in the hematite2 or the storage of photogenerates holes.3 These effects are likely more important when hydrous overlayer, that can act as adapting catalysts,4 are considered. All these hypothesis can explain the observed improved hole lifetime and reduce recombination with electrons.
The present experimental approach is similar to the one that allowed our recent disclosure of the oxidation states assumed by hydrous IrOx as catalyst for water oxidation.5 In the present case, FEXRAV6 and XANES have been used to probe changes in the charge state of Ir while the hematite was illuminated with 410nm radiation. Thanks to this in-operando 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.
1 Minguzzi A., Lugaresi O., Achilli E., D'Acapito F., Naldoni A., Malara F., Locatelli C., Vertova A., Rondinini S., Ghigna P., In preparation
2 Badia-Bou L., Mas-Marza E., Rodenas P., M. Barea E., Fabregat-Santiago F., Gimenez S., Peris E., Bisquert J., J. Phys. Chem. C, 2013, 117, 3826−3833
3 Lin F., Boettcher S.W. Nature Materials, 2014, 13, 81-86
4 Barroso M., Mesa C.A., Pendlebury S.R. , Cowana A.J., Hisatomi T., Sivula K., Grätzel M., Klug D.R., Durrant J.R. PNAS, 2012, 109, 15640–15645
5 Minguzzi A., Lugaresi O., Achilli E., Locatelli C., Vertova A., Ghigna P., Rondinini S., Chem. Sci., 2014, 5, 3591-3597
6 Minguzzi, A.; Lugaresi, O.; Locatelli, C.; Rondinini S.; d'Acapito, F.; Achilli, E.; Ghigna, P. Anal. Chem. 2013, 85, 7009-7013
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
In-situ X-ray absorption spectroscopy on (photo-)electrocatalysts for water oxidation: towards new insights on the reaction mechanism
No full textHere we introduce the Fixed Energy X-Ray Absorption Voltammetry (1), a novel in-situ/in-operando X-Ray Absorption Spectroscopy (XAS) technique for fast and easy preliminary characterization of electrodes and photoelectrodes which consists in recording the absorption coefficient at a fixed energy while varying at will the electrode potential. The energy is chosen close to a core level absorption edge, in order to give the maximum contrast between different oxidation states of an element. It follows that any shift from the initial oxidation state determines a variation of the X-ray absorption coefficient. In this work we demonstrate that FEXRAV allows to quickly map the variation of the oxidation states of the element under consideration in a desired potential window. At this purpose, we use high surface area electrodes to attain a high surface/volume ratio (nanoparticles, nanostructures, highly hydrated films) and be more sensible to any chemical phenomena occurring at the surface.
We show that FEXRAV gives important information by itself but can also serve as a preliminary screening of the potential window or, more generally, for choosing the best experimental conditions for a better targeted XAS analysis. In fact, this work includes a detailed XAS study aimed to clarify the mechanism of iridium oxide as catalyst for water oxidation: for the first time we directly observed the co-existence of more than one Ir oxidation state at E >1.23V (RHE), that is consistent with the role of Ir as center of a catalytic cycle. This represents a crucial point for a better understanding of water electrolysis and photoelectrochemical (PEC) water splitting (2).
We completed this study by time-resolved energy dispersive XAS for better understanding the time-dependence of the interfacial phenomena occurring during pseudocapacitance charge/discharge and during the water oxidation catalysis.
(1) Minguzzi, A.; Lugaresi, O.; Locatelli, C.; Rondinini S.; d'Acapito, F.; Achilli, E.; Ghigna, P. Anal. Chem. 2013, 85, 7009-7013.
(2) Minguzzi A., Lugaresi O., Achilli E., Locatelli C., Vertova A., Ghigna P., Rondinini S., Chem. Sci. 2014, 5, 3591-3597
Progetto di rilevamento tridimensionale, modellazione numerica e progettazione del supporto del cavallo di Canova.
No full textData Acquisition for Cultural Heritage Navigation: Integration of Panoramic Imaging, Terrestrial Laser Scanning and Anagliphs
No full textIn this paper some experiences about the integration of panoramic imaging and terrestrial laser scanning surveys are presented. The main goal is to produce documentation with metric information for the cultural heritage panoramic navigation; furthermore, a subordinate result is to use cheap and user-friendly 3-dimensional images for a wide range of applications like the custom navigation. Three historical sites were chosen: the main stairway of the Chancellor building at the Padua University, some ancient buildings in Venice, the Santo Sepolcro Church in Bologna. The panoramic photos acquisition is treated for all the three sites; in addition some image processing techniques are used to mosaic and to filter the raw data. The laser scanning survey is related to the Venice site using the 3D laser imaging sensor Riegl LMS-Z210 and the software Riscan Pro; the Sobel filter is used to produce detailed silhouettes and to perform edge extraction. About the Bologna site some point clouds acquired with the Leica HDS2500 3D laser scanner (re-branded Cyrax 2500 scanner) are presented with different acquisitions (point of view and resolution) in the Cyclone 5.1 environment. The creation of anaglyphs is performed for Padua and Bologna sites, using the Anabuilder software; some notes are drawn about the interpolation algorithms. The results are very useful for web-based animation purposes especially for recording indoor scenes using standard cameras for panoramic surveys, which have proven to be rather economical also in terms of computational effort
Study of photoelectrochemical behavior of copper oxides based materials using X-ray absorption spectroscopy
No full textThe use of sunlight to convert water into fuel is very attractive and ambitious since H2 is considered to be the energy carrier of the future thanks to its high mass energy density and its environmental friendliness [1,2]. Copper oxides-based photocathodes are attractive for their absorption in the visible range, low cost, high abundance and easy synthetic protocols as well as high photoactivity [3,4].
Two p-type semiconducting copper based materials has been prepared, characterized and tested as a photocathode for H2 production: CuO and Cu2O. The first one is prepared by thermal treatment of nanocrystalline CuI, which shows high efficiency in light conversion and interesting self-protection properties [5].
Cu2O instead was prepared by electrochemical deposition from a lactate-stabilized Cu++ bath [3]. Viceversa the main drawback of Cu(I) oxide is its lack of stability during photoelectrochemical conditions. For this material the influence of a metallic underlayer (Au, Cu) between the semiconductor itself and the FTO support was studied, together with the presence of a small load of Pt catalyst.
In-situ and in-operando techniques like X-ray absorption near edge structure (XANES), Extended X-Ray Absorption Fine Structure (EXAFS) and Fixed Energy X-ray Absorption Voltammetry (FEXRAV) [6] allow us to better understanding materials behavior. We observe changes in copper oxidation states upon light and/ or applied potential. Moreover, the role of methanol as hole-scavenger during photoelectrochemical experiment has been studied. FEXRAV measurements allow following the material degradation processes and defining the stability windows. With differential light and dark XANES spectra, we investigated the local changes in electronic structure upon spectroelectrochemical conditions. These results will allow us obtaining more stable system for photoelectrochemical hydrogen production.
References
[1] G. Centi, S. Perathoner, ChemSusChem. 3 (2010) 195–208.
[2] F. Malara, A. Minguzzi, M. Marelli, S. Morandi, R. Psaro, V. Dal Santo, A. Naldoni, ACS Catal. 5 (2015) 5292–5300.
[3] A. Paracchino, V. Laporte, K. Sivula, M. Grätzel, E. Thimsen, Nat. Mater. 10 (2011) 456–461.
[4] C. Li, T. Hisatomi, O. Watanabe, M. Nakabayashi, N. Shibata, K. Domen, J.-J. Delaunay, Energy Environ. Sci. 8 (2015) 1493–1500.
[5] T. Baran, S. Wojtyła, C. Lenardi, P. Ghigna, E. Achilli, S. Rondinini, A. Minguzzi, ACS Appl. Mater. Interfaces. (submitted).
[6] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. D’Acapito, E. Achilli. P. Ghigna. Anal. Chem. (2013), 85, 7009-7013
Integrazione di metodologie innovative per il rilievo panoramico
No full textIl rilievo panoramico rappresenta, oggi, una delle nuove metodologie per la produzione di documentazione finalizzata alla navigazione applicata ai beni culturali. L’integrazione di altre metodologie ormai consolidate, come la fotogrammetria e la scansione laser, fornisce al rilievo panoramico un valore aggiunto costituito dall’informazione metrica.
Il prodotto finale è quindi costituito da immagini che sono relativamente economiche dal punto di vista dell’acquisizione del dato, sono dotate di un’interfaccia user-friendly per quanto riguarda la navigazione anche in ambiente web, e che, soprattutto, sono caratterizzate da una restituzione tri-dimensionale fruibile anche da un utente comune
Da marginali a classici di oggi: le 'letterature minori' dell'area slava orientale nel panorama editoriale italiano
No full textIn this contribution we analyze how minor literatures from the Eastern Slavic area manage to enter the Italian cultural space by also using "major languages". In the case of Ukrainian and Belarusian literatures, this tendency may be seen as being in contrast with the dynamics of the respective national publishing industries, in which Russian-language authors are not very successful or may not even be considered as belonging to the national canon. On the basis of these premises, we will focus on the cases of Andrei Kurkov and Aleksei Nikiting for Ukraine, and on Sviatlana Aleksievich and Dmitri Strotsev for Belarus. In conclusion, we will touch upon broader issues of the western publishing industry in the light of the relationship between Italian cultural institutions and their Ukrainian and Belarusian counterparts
Spectroscopic Fingerprints of sp1 Hybridized C in Surface-Grown Molecular Assemblies
No full textThe advent of on-surface chemistry and molecular self-assembly opened the way to the realization of organic materials whose lack of stability in vacuo would otherwise forbid their synthesis. Recently the on-surface coupling of the precursors has also been used to synthesize adsorbed organic systems with chemically vulnerable linear carbon chains with sp 1 hybridization [1]. A notable advantage of on-surface synthesis is that the full realm of the experimental and theoretical surface science toolbox is available for the investigation. While the method of choice for surface-supported architectures is the scanning tunneling microscope and ultimate resolution is achieved by low-T non-contact atomic force microscopy, electron core-level spectroscopy can provide an even more local probe of the electronic properties of the material. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is here suggested to discriminate sp 1 /sp 2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp 1 /sp 2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials as validated by previous studies [2,3]. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp 2 systems. We then consider a mixed polymer alternating sp 1 C 4 units with sp 2 biphenyl groups, recently synthesized on Au(111) [4], as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the the presence of linear C chains [5]. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp 1 hybridization in surface-grown C structures. [1] Q. Sun, R. Zhang, J. Qiu, R. Liu, and W. Xu, Adv. Mater. 2018, 30, 1705630 [2] G. Fratesi, V. Lanzilotto, L. Floreano, and G. P. Brivio, J. Phys. Chem. C 2013, 117, 6632 [3] G. Fratesi, V. Lanzilotto, S. Stranges, M. Alagia, G. P. Brivio, and L. Floreano, Phys. Chem. Chem. Phys. 2014, 16, 14834 [4] Q. Sun, L. Cai, H. Ma, C. Yuan, and W. Xu, ACS Nano 2016, 10, 7023 [5] G. Fratesi, S. Achilli, N. Manini, G. Onida, A. Baby, A. Ravikumar, A. Ugolotti, G.P. Brivio, A. Milani, and C.S. Casari, Materials 2018, 11, 255
Mitogenomes from Two Uncommon Haplogroups Mark Late Glacial/Postglacial Expansions from the Near East and Neolithic Dispersals within Europe
No full textThe current human mitochondrial (mtDNA) phylogeny does not equally represent all human populations but is biased in favour of representatives originally from north and central Europe. This especially affects the phylogeny of some uncommon West Eurasian haplogroups, including I and W, whose southern European and Near Eastern components are very poorly represented, suggesting that extensive hidden phylogenetic substructure remains to be uncovered. This study expanded and re-analysed the available datasets of I and W complete mtDNA genomes, reaching a comprehensive 419 mitogenomes, and searched for precise correlations between the ages and geographical distributions of their numerous newly identified subclades with events of human dispersal which contributed to the genetic formation of modern Europeans. Our results showed that haplogroups I (within N1a1b) and W originated in the Near East during the Last Glacial Maximum or pre-warming period (the period of gradual warming between the end of the LGM, ~19 ky ago, and the beginning of the first main warming phase, ~15 ky ago) and, like the much more common haplogroups J and T, may have been involved in Late Glacial expansions starting from the Near East. Thus our data contribute to a better definition of the Late and postglacial re-peopling of Europe, providing further evidence for the scenario that major population expansions started after the Last Glacial Maximum but before Neolithic times, but also evidencing traces of diffusion events in several I and W subclades dating to the European Neolithic and restricted to Europe
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