The nature of the electro-catalytic response of mixed metal oxides: Pt- and Ru-doped SnO2 anodes

"This is the peer reviewed version of the following article: The nature of the electro-catalytic response of mixed metal oxides: Pt- and Ru-doped SnO2 anodes, which has been published in final form at https://doi.org/10.1002/celc.201801632. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] The catalytic behavior of metal oxides for oxidative reactions is generally classified into active or non-active, depending on whether surface redox species participate or not. In the case of mixed metal oxides, however, this simplified scenario may be more complex. Non-active oxides containing electroactive metal species, like Pt- and/or Ru-doped SnO2 electrodes, are promising anode materials for the electrochemical treatment of waste-waters. This work analyzes the effect of Pt and Ru species on the nature of the electro-oxidative catalytic response of Ti/SnO2 anodes. For this purpose, the electro-oxidation of phenol and the competing oxygen evolution reaction (OER) in NaOH have been chosen as model reactions. The different electrodes and reactions were characterized by cyclic voltammetry, electro- chemical impedance spectroscopy, and Tafel measurements. The obtained results reveal that both Pt and Ru introduce solid-state redox processes and catalyze the OER and the phenol oxidation onto Ti/SnO2-based electrodes. Nevertheless, the dopants induce quite different active behaviors in the mixed oxides. Pt practically does not affect the OER mechanism, but enhances its kinetics, so its electrocatalytic activity is associated with a specific adsorption of hydroxyl anions or phenolate on Pt sites, without participation of the irreversible Pt/PtOx couple (i.e. a "non-redox-active" behavior). On the contrary, Ru species involve various and highly reversible redox processes that accelerate and modify the rate-determining step of the OER, and that actively mediate in the phenol oxidation.Financial support from the Spanish Ministerio de Economia y Competitividad and FEDER funds (MAT2016-76595-R, IJCI-201420012) is gratefully acknowledged.Berenguer Betrián, R.; Quijada, C.; Morallón, E. (2019). The nature of the electro-catalytic response of mixed metal oxides: Pt- and Ru-doped SnO2 anodes. ChemElectroChem. 6(4):1057-1068. https://doi.org/10.1002/celc.201801632S1057106864K. Rajeshwar J. G. Ibanez (Eds.) in Environmental Electrochemistry: Fundamentals and Applications in Pollution Abatement Academic Press Inc. San Diego 1997.Martínez-Huitle, C. A., & Ferro, S. (2006). Electrochemical oxidation of organic pollutants for the wastewater treatment: direct and indirect processes. Chem. Soc. Rev., 35(12), 1324-1340. doi:10.1039/b517632hBrillas, E., & Martínez-Huitle, C. A. (2015). 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Las gramáticas dialogadas del español en el Siglo de Oro: el caso de Ambrosio de Salazar

El Espexo general de la gramática en diálogos –manual de español publicado en Francia en 1614– se ha estudiado habitualmente bajo la óptica de la historiografía lingüística atendiendo a su aportación doctrinal dentro de la tradición gramaticográfica española. De forma menos sistemática se ha aludido a sus planteamientos metodológicos, casi siempre a través de valoraciones negativas, que ya surgían incluso desde el momento de aparición del manual en el ambiente de enseñanza del español del país vecino (Oudin, Marcos Fernández)

A preliminary checklist of fungi at the Boston Harbor Islands

Between December 2012 and May 2017, we conducted a fungal inventory at the Boston Harbor Islands National Recreation Area (BHI) in Massachusetts. We extensively sampled 4 sites (Grape Island, Peddocks Island, Thompson Island, and World's End peninsula) and occasionally visited 4 others for sampling (Calf Island, Great Brewster Island, Slate Island, and Webb Memorial State Park). We made over 900 collections, of which 313 have been identified. The survey yielded 172 species in 123 genera, 62 families, 24 orders, 11 classes, and 2 phyla. We report 4 species as new, but not formally described, in the genera Orbilia, Resupinatus, and Xylaria. Another collection in the genus Lactarius may be new to science, but further morphological and molecular work is needed to confirm this conclusion. Additionally, Orbilia aprilis is a new report for North America, Proliferodiscus earoleucus represents only the second report for the US, and Chrysosporium sulfureum, a common fungus of some cheeses, was discovered on woodlice (Crustacea: Malacostraca: Isopoda: Oniscidea). We discuss our findings in the light of DNA-based identifications using the ITS ribosomal DNA region, including the advantages and disadvantages of this approach, and stress the need for biodiversity studies in urbanized areas during all seasons

Determination of pulsation periods and other parameters of 2875 stars classified as MIRA in the All Sky Automated Survey (ASAS)

We have developed an interactive PYTHON code and derived crucial ephemeris data of 99.4% of all stars classified as 'Mira' in the ASAS data base, referring to pulsation periods, mean maximum magnitudes and, whenever possible, the amplitudes among others. We present a statistical comparison between our results and those given by the AAVSO International Variable Star Index (VSX), as well as those determined with the machine learning automatic procedure of Richards et al. 2012. Our periods are in good agreement with those of the VSX in more than 95% of the stars. However, when comparing our periods with those of Richards et al, the coincidence rate is only 76% and most of the remaining cases refer to aliases. We conclude that automatic codes require still more refinements in order to provide reliable period values. Period distributions of the target stars show three local maxima around 215, 275 and 330 d, apparently of universal validity, their relative strength seems to depend on galactic longitude. Our visual amplitude distribution turns out to be bimodal, however 1/3 of the targets have rather small amplitudes (A $<$ 2.5$^{m}$) and could refer to semi-regular variables (SR). We estimate that about 20% of our targets belong to the SR class. We also provide a list of 63 candidates for period variations and a sample of 35 multiperiodic stars which seem to confirm the universal validity of typical sequences in the double period and in the Petersen diagramsComment: 14 pages, 14 figures, and 8 tables. Accepted to The Astrophysical Journal Supplement Series, September 201

Electrocatalytic Oxidation of Cyanide on Copper-doped Cobalt Oxide Electrodes

[EN] Copper and copper oxides are well-known excellent catalysts in several chemical processes, but their low mechanical and electrochemical stability restrict their direct utilization as electrodes in electrolytic processes. In this work, the incorporation of copper into cobalt oxide (CuxCo3-xO4) is presented as an excellent approach to obtain highly active and robust copper-based electrocatalysts. Particularly, the electrocatalytic performance of Ti-supported CuxCo3-xO4 electrodes (with 0 <= x <= 1.5) has been studied for the oxidation' of cyanide in alkaline media. Cyclic voltammetry and electrolysis runs show an outstanding effect of Cu on the activity, efficiency and kinetics of spinel CuxCo3-xO4 electrodes for CN(-)electro-oxidation. Despite being active oxides with high activity towards water oxidation, copper saturated (x=1.0) and oversaturated (x=1.5) spinels exhibit unprecedented 100% current efficiencies for the electro-oxidation of CN- in aqueous electrolyte. In situ surface enhanced Raman spectroscopy (SERS) reveals the specific adsorption of CN- ions on surface Cu species to be involved in the electrocatalytic oxidation mechanism. This electrocatalytic activity has been attributed to surface Cu(II) in the spinel lattice. Furthermore, the CuxCo3-xO4 electrodes also display high electrochemical stability. Therefore, they are considered excellent candidates for the sustainable electrochemical elimination of highly toxic cyanides.Financial support from the Spanish Ministerio de Economia y Competitividad and FEDER funds (MAT2016-76595-R, IJCI-2014-20012) and from the Generalitat Valenciana (PROMETEO2013/038) is gratefully acknowledged.Berenguer, R.; La Rosa-Toro, A.; Quijada, C.; Morallon, E. (2017). Electrocatalytic Oxidation of Cyanide on Copper-doped Cobalt Oxide Electrodes. Applied Catalysis B Environmental. 207:286-296. https://doi.org/10.1016/j.apcatb.2017.01.078S28629620

Dynamic screening of a localized hole during photoemission from a metal cluster

Recent advances in attosecond spectroscopy techniques have fueled the interest in the theoretical description of electronic processes taking place in the subfemtosecond time scale. Here we study the coupled dynamic screening of a localized hole and a photoelectron emitted from a metal cluster using a semi-classical model. Electron density dynamics in the cluster is calculated with Time-Dependent Density Functional Theory and the motion of the photoemitted electron is described classically. We show that the dynamic screening of the hole by the cluster electrons affects the motion of the photoemitted electron. At the very beginning of its trajectory, the photoemitted electron interacts with the cluster electrons that pile up to screen the hole. Within our model, this gives rise to a significant reduction of the energy lost by the photoelectron. Thus, this is a velocity dependent effect that should be accounted for when calculating the average losses suffered by photoemitted electrons in metals.Comment: 15 pages, 5 figure

Molecular Dynamics Simulation of Solvent-Polymer Interdiffusion. I. Fickian diffusion

The interdiffusion of a solvent into a polymer melt has been studied using large scale molecular dynamics and Monte Carlo simulation techniques. The solvent concentration profile and weight gain by the polymer have been measured as a function of time. The weight gain is found to scale as t^{1/2}, which is expected for Fickian type of diffusion. The concentration profiles are fit very well assuming Fick's second law with a constant diffusivity. The diffusivity found from fitting Fick's second law is found to be independent of time and equal to the self diffusion constant in the dilute solvent limit. We separately calculated the diffusivity as a function of concentration using the Darken equation and found that the diffusivity is essentially constant for the concentration range relevant for interdiffusion.Comment: 17 pages and 7 figure

Physico-Chemical and Chromatic Characterization of Malvidin 3-Glucoside-vinylcatechol and Malvidin 3-Glucoside-vinylguaiacol Wine Pigments

[EN] The physicochemical and chromatic features of malvidin 3-glucoside-vinylcatechol (PA1) and malvidin 3-glucoside-vinylguaiacol (PA2) adducts were investigated. Important differences between both pigments were observed. In the investigated pH range (2.0−4.5), our results suggest that PA1 could be considered as a noncovalent dimer of two pyranoflavylium ions (AH)2 which undergo a hydration reaction in two successive steps, with no proton transfer. In contrast, only proton transfer equilibrium between the pyranoflavylium ion and the quinonoid bases was observed for PA2. The hydration and acidity thermodynamic constants of both pyranoanathocyanins were determined by UV−vis spectroscopy. Pigment PA1 was shown to be less sensitive to bisulfite addition than to water addition, and PA2 seems to be largely insensitive to both water and bisulfite additions. The binding constants for the interaction between the pigments and (+)-catechin in aqueous solution and the changes in the CIELAB parameters that it provoked were also determined. The huge increase in the absorption of the pyranoflavylium ion of PA2 when it binds catechin has no equivalent for anthocyanins and nicely outlines the potential of pyranoanthocyanins in the expression of natural colors