182 research outputs found
Uncovering the Electrochemical Interface of Low-Index Copper Surfaces in Deep Groundwater Environments
Highly selective plasma-activated copper catalystsfor carbon dioxide reduction to ethylene
There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides are surprisingly resistant to reduction and copper+ species remain on the surface during the reaction. Our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper+ is key for lowering the onset potential and enhancing ethylene selectivity
Diversidad genética de cultivares de caña de azúcar determinada por marcadores de ADN y caracteres morfológicos
Un mejor conocimiento de la diversidad genética de la caña de azúcar proveerá información útil sobre el valor de los genotipos para los programas de mejoramiento y contribuirá tanto a hacer un más eficiente uso y conservación de los recursos genéticos, como a asegurar los derechos de propiedad intelectual de los creadores de nuevas variedades. Si bien los descriptores morfológicos constituyen las herramientas más tradicionales para caracterizar a las variedades, pueden presentar variaciones fenotÃpicas causadas por factores ambientales. Por este motivo los marcadores moleculares son cada vez más importantes en la identificación de genotipos y la estimación de la diversidad, debido a su precisión, abundancia e independencia de factores ambientales. El objetivo de este trabajo fue evaluar genotipos empleados como padres en el Programa de Mejoramiento de la Caña de Azúcar de la Estación Experimental Agroindustrial Obispo Colombres (EEAOC), usando marcadores moleculares (AFLP y SSR) y caracteres morfológicos y comparando los datos obtenidos con dos programas informáticos estadÃsticos (NTSys e InfoStat). Todos los cultivares se agruparon en un mismo grupo con ambos programas, cuando se emplearon al menos 150 datos. Probablemente debido al intercambio regular de germoplasma, no se observó una clara diferenciación genética entre los genotipos locales y las variedades de los EE. UU., que se agruparon juntos. Aunque los caracteres morfológicos reflejan solamente la semejanza externa, la topologÃa del dendrograma no se modificó cuando se combinaron datos moleculares y morfológicos. Estos resultados sugieren que ambos métodos de caracterización deberÃan ser utilizados para estimar la diversidad genética y que los marcadores moleculares deberÃan ser incluidos a un nivel internacional, para proteger las nuevas variedades de caña de azúcar.Better knowledge of sugarcane genetic diversity will provide useful information concerning genotypic value for breeding programs and should help to improve the use and conservation of genetic resources and the protection of sugarcane varieties by intellectual property rights. Morphological descriptors are traditional tools to characterise varieties; however, they vary phenotypically because of environmental effects. Therefore, molecular markers have become increasingly important for identifying genotypes and estimating diversity, as they are accurate, readily available, and are not affected by the environment. The aim of this research was to evaluate genotypes used as parental materials in the Sugarcane Breeding Program of Estación Experimental Agroindustrial Obispo Colombres (EEAOC), Argentina, by using molecular markers (AFLP and SSR) and morphological traits, and by comparing the data obtained with two statistical software programs (NTSys and InfoStat). All cultivars grouped in one main cluster of the dendrogram when using both programs and at least 150 data points. Local Argentine genotypes grouped together with US-varieties and no clear genetic differentiation was found, probably due to regular germplasm exchange. Although morphological traits reflected external resemblance only, the topology of the dendrogram was not modified when combining both molecular and morphological data. These results suggest that both characterisation methods should be used to estimate genetic diversity. Molecular markers should be included internationally for sugarcane variety protection.Fil: Perera, MarÃa Francisca. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Arias, Marta E.. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales E Instituto Miguel Lillo; ArgentinaFil: Costilla, Diego D.. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Luque, Catalina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales E Instituto Miguel Lillo; ArgentinaFil: GarcÃa, MarÃa B.. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Racedo, Josefina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Cuenya, MarÃa Inés. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Filippone, MarÃa Paula. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Castagnaro, Atilio Pedro. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Tucumán. Instituto de TecnologÃa Agroindustrial del Noroeste Argentino; Argentina. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; Argentin
Measuring velocity of sound with nuclear resonant inelastic x-ray scattering
Nuclear resonant inelastic x-ray scattering is used to measure the projected
partial phonon density of states of materials. A relationship is derived
between the low-energy part of this frequency distribution function and the
sound velocity of materials. Our derivation is valid for harmonic solids with
Debye-like low-frequency dynamics. This method of sound velocity determination
is applied to elemental, composite, and impurity samples which are
representative of a wide variety of both crystalline and noncrystalline
materials. Advantages and limitations of this method are elucidated
Steering the structure and selectivity of CO<sub>2</sub> electroreduction catalysts by potential pulses
Convoluted selectivity trends and a missing link between reaction product distribution and catalyst properties hinder practical applications of the electrochemical CO2 reduction reaction (CO2RR) for multicarbon product generation. Here we employ operando X-ray absorption and X-ray diffraction methods with subsecond time resolution to unveil the surprising complexity of catalysts exposed to dynamic reaction conditions. We show that by using a pulsed reaction protocol consisting of alternating working and oxidizing potential periods that dynamically perturb catalysts derived from Cu2O nanocubes, one can decouple the effect of the ensemble of coexisting copper species on the product distribution. In particular, an optimized dynamic balance between oxidized and reduced copper surface species achieved within a narrow range of cathodic and anodic pulse durations resulted in a twofold increase in ethanol production compared with static CO2RR conditions. This work thus prepares the ground for steering catalyst selectivity through dynamically controlled structural and chemical transformations
Revealing the active phase of copper during the electroreduction of CO2 in aqueous electrolyte by correlating in situ x-ray spectroscopy and in situ electron microscopy
The variation in the morphology and electronic structure of copper during the electroreduction of CO2 into valuable hydrocarbons and alcohols was revealed by combining in situ surface- and bulk-sensitive X-ray spectroscopies with electrochemical scanning electron microscopy. These experiments proved that the electrified interface surface and near-surface are dominated by reduced copper. The selectivity to the formation of the key C–C bond is enhanced at higher cathodic potentials as a consequence of increased copper metallicity. In addition, the reduction of the copper oxide electrode and oxygen loss in the lattice reconstructs the electrode to yield a rougher surface with more uncoordinated sites, which controls the dissociation barrier of water and CO2. Thus, according to these results, copper oxide species can only be stabilized kinetically under CO2 reduction reaction conditions
On the activity/selectivity and phase stability of thermally grown copper oxides during the electrocatalytic reduction of CO2
Revealing the active nature of oxide-derived copper is of key importance to understand its remarkable catalytic performance during the cathodic CO2 reduction reaction (CO2RR) to produce valuable hydrocarbons. Using advanced spectroscopy, electron microscopy, and electrochemically active surface area characterization techniques, the electronic structure and the changes in the morphology/roughness of thermally oxidized copper thin films were revealed during CO2RR. For this purpose, we developed an in situ cell for X-ray spectroscopy that could be operated accurately in the presence of gases or liquids to clarify the role of the initial thermal oxide phase and its active phase during the electrocatalytic reduction of CO2. It was found that the Cu(I) species formed during the thermal treatment are readily reduced to Cu0 during the CO2RR, whereas Cu(II) species are hardly reduced. In addition, Cu(II) oxide electrode dissolution was found to yield a porous/void structure, where the lack of electrical connection between isolated islands prohibits the CO2RR. Therefore, the active/stable phase for CO2RR is metallic copper, independent of its initial phase, with a significant change in its morphology upon its reduction yielding the formation of a rougher surface with a higher number of underco-ordinated sites. Thus, the initial thermal oxidation of copper in air controls the reaction activity/selectivity because of the changes induced in the electrode surface morphology/roughness and the presence of more undercoordinated sites during the CO2RR
The role of the copper oxidation state in the electrocatalytic reduction of CO2 into valuable hydrocarbons
Redox-active copper catalysts with accurately prepared oxidation states (Cu0, Cu+ and Cu2+) and high selectivity to C2 hydrocarbon formation, from electrocatalytic cathodic reduction of CO2, were fabricated and characterized. The electrochemically prepared copper-redox electro-cathodes yield higher activity for the production of hydrocarbons at lower oxidation state. By combining advanced X-ray spectroscopy and in situ micro-reactors it was possible to unambiguously reveal the variation in the complex electronic structure that the catalysts undergo at different stages (i.e. during fabrication and electrocatalytic reactions). It was found that the surface, sub-surface and bulk properties of the electrochemically prepared catalysts are dominated by the formation of copper carbonates on the surface of cupric-like oxides, which prompts catalyst deactivation by restraining effective charge transport. Furthermore, the formation of reduced or partially-reduced copper catalysts yields the key dissociative proton-consuming reactive adsorption of CO2 to produce CO, allowing the subsequent hydrogenation into C2 and C1 products by dimerization and protonation. These results yield valuable information on the variations in the electronic structure that redox-active copper catalysts undergo in the course of the electrochemical reaction, which, under extreme conditions are mediated by thermodynamics but, critically, kinetics dominate near the oxide/metal phase transitions
Nanostructured zinc oxide films synthesized by successive chemical solution deposition for gas sensor applications.
- …