Síntesis y caracterización de LaCoO₃±δ por el método de Pechini para su evaluación como cátodo en una CCOS

Las celdas de combustible están compuestas por dos electrodos y un electrolito sólido, que convierten la energía química a energía eléctrica, reduciendo las emisiones contaminantes y aumentando su eficiencia. En este trabajo se sintetizó LaCoO₃±δ mediante el método Pechini; el cual permite tener un buen control en la microestructura obtenida para su aplicación como cátodo. Posterior a la síntesis, el material fue caracterizado por ATG/ADB con lo que se establecieron las etapas de formación del compuesto y la temperatura de estabilización y su pérdida de masa. Con el estudio de DRX en polvos se identificó la fase estudiada, así como la completez de la reacción para posteriormente realizar el refinamiento LeBail y obtener los parámetros de celda. El análisis morfológico se realizó mediante MFA y MEB. Las características anteriores permitirán su uso como cátodo en una celda de combustible de óxidos sólidos.The fuel cells are conformed by two electrodes and a solid electrolyte, in this device the chemical energy is transformed into electric energy, by means of this method it is possible the abatement of environmental pollution and the efficiency is enhanced. In this study, the synthesis of LaCoO₃±δ was carried out by the Pechini method; this method allows having a good control in the microstructure for cathode application. The material obtained it was characterized by TGA/DSC this analysis we can obtained the stages of formation of the compound, the stabilization temperature and its loss of mass. With the powder XRD, we identified the crystallographic phase studied, as well as the reaction complete, and then the LeBail refinement was performed in order to obtain the lattice parameters. We made the morphology analysis with AFM and SEM. These characteristics and properties allow its use as a cathode in solid oxides fuel cell

Nanostructured thin films obtained from Fischer aminocarbene complexes

The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)5NH(CH2)15CH3, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium (0) or tungsten (0) as an acceptor group, are reported. These four push-pull systems formed Langmuir (L) monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves); Brewster angle microscopic images were also obtained. By using the Langmuir-Blodgett (LB) method, molecular monolayers were transferred onto glass substrates forming Z-type multilayers. LB films were characterized through ultraviolet-visible spectroscopy, atomic force microscopy and X-ray diffraction techniques. Results indicated that films obtained from 2b complex [(Ferrocenyl)(hexadecylamine)methylidene] pentacarbonyl tungsten (0) are the most stable and homogeneous; due to their properties, these materials may be incorporated into organic electronic devices

Structural, morphological and electrical characterization of ceria-based nanostructured thin films obtained by ultrasonic spray pyrolysis

In this work, the synthesis and the structural, morphological and electrical characterization of Ce1−xSmxO2−δ solid solution, with x = 0, 0.10, 0.15, 0.20, 0.25 and 0.30 mol, are reported. Nanocrystalline, homogeneous, and adherent samarium doped cerium oxide thin films were deposited onto glass (Pyrex®) substrates by a simple and cost effective ultrasonic spray pyrolysis system, at a low substrate temperature of 450 °C and further annealing treatment at 500 °C for 2 h. For all the samples, X-ray diffraction results showed the formation of single phase and well crystalline thin films, with cubic fluorite type structure. Scanning electron microscopy analyses showed homogeneous surfaces for all the samples; from SEM micrographs crystallite sizes were found to be in the range 23–37 nm. From atomic force microscopy, surface roughness in the range of 20–95 nm was measured and the formation of smooth films with an average grain size of 45 nm was observed. For the best sample in the solid solution, high oxygen ion conductivity of 1.71 × 10−1 S cm−1, at 450 °C, was determined by impedance spectroscopy, with an activation energy of 0.93 eV. Results suggest that these films may have a potential application as electrolytes in intermediate temperature solid oxide fuel cells, IT-SOFC. Resumen: En este trabajo se reporta la síntesis y caracterización estructural, morfológica y eléctrica de la solución sólida Ce1−xSmxO2−δ, con x = 0, 0,10, 0,15, 0,20, 0,25 y 0,30 mol. Se depositaron películas delgadas de óxido de cerio dopado con samario nanoestructuradas, homogéneas y con buena adherencia sobre sustratos de vidrio (Pyrex®) mediante un sistema de rocío pirolítico ultrasónico sencillo y económico, a una baja temperatura de 450 °C y con un tratamiento térmico adicional a 500 °C por 2 h. Para todas las muestras, los resultados obtenidos por difracción de rayos X mostraron la presencia de películas delgadas cristalinas monofásicas, con estructura cúbica tipo fluorita. Los análisis de microscopía electrónica de barrido mostraron superficies homogéneas para todas las muestras; a partir de las micrografías SEM se determinó que los tamaños de los cristales se encontraban en el intervalo de 23-37 nm. A partir de microscopía de fuerza atómica se midió la rugosidad superficial en el rango de 20 a 95 nm y se observó la formación de películas homogéneas con un tamaño promedio de grano de 45 nm. Para la mejor muestra, mediante espectroscopia de impedancias se determinó una alta conductividad de iones de oxígeno de 1,71 × 10−1 S cm−1, a 450 °C, con una energía de activación de 0,93 eV. Los resultados sugieren que estas películas pueden tener una potencial aplicación como electrolitos en celdas de combustible de óxidos sólidos de temperatura intermedia, IT-SOFC. Keywords: Spray pyrolysis, Thin films, IT-SOFC, Ceria, Palabras clave: Rocío pirolítico, Películas delgadas, IT-SOFC, Ceri

Propiedades estructurales y morfológicas de LaNi₀.₄Fe₀.₆O₃-δ sintetizado por sol-gel y combustión

Las celdas de combustible de óxidos sólidos, CCOS (SOFC por sus siglas en inglés) son dispositivos altamente eficientes, amigables con el ambiente, que convierten la energía química del hidrógeno directamente en energía eléctrica. Sin embargo la alta temperatura de operación limita el uso materiales en cuanto a sus componentes. Uno de los objetivos en las CCOS consiste en la búsqueda de nuevos materiales que permitan reducir su temperatura de operación y así obtener CCOS de temperatura intermedia, CCOS-TI. En este trabajo se sintetizó el compuesto LaNi₀.₄Fe₀.₆O₃-δ por los métodos sol-gel y combustión con el propósito de analizar sus propiedades estructurales y morfológicas y así determinar el método que nos permita un mejor control de ellas y que conlleve a su aplicación como cátodo en una CCOS.Solid oxide fuel cells, SOFC, are highly efficient and environmentally friendly devices that convert hydrogen chemical energy directly into electrical energy. However, the high operating temperature limits the use of materials in terms of their components. One of the objectives in SOFC is the search for new materials that reduce its operating temperature and thus obtain intermediate temperature SOFC, IT-SOFC. In this work, the compound LaNi₀.₄Fe₀.₆O₃-δ was synthesized by the sol-gel and combustion methods in order to analyze its structural and morphological properties and thus determine the method that allows to a better control of these properties and that leads to their application as a cathode in a SOFC

Síntesis de perovskitas nanoestructuradas de LaNi₀.₆Fe₀.₄O₃-δ como cátodos en CCOS-TI

Los materiales con estructura tipo perovskita presentan una gran cantidad de aplicaciones. En cuanto a CCOS, la aplicación de estos materiales, como cátodos nanoestructurados, permite una mejor conversión de oxígeno molecular a atómico, lo que conlleva a un rendimiento más eficiente en el funcionamiento de estos dispositivos y, mejor aún, con una reducción de su temperatura de operación. Debido a que las propiedades estructurales están altamente determinadas por el método de preparación, en este trabajo se sintetizó el compuesto LaNi₀.₆Fe₀.₄O₃-δ por el método sol-gel ya que éste nos permitió un buen control de la estabilidad térmica, la estequiometria y el tamaño de cristalito. Estos resultados se presentan en este trabajo, los cuales fueron determinados por difracción de rayos X, análisis térmicos y microscopias electrónicas de barrido y de transmisión, respectivamente.Materials with perovskite type structure show a variety of applications. Regarding SOFCs, the application of these materials, such as nanostructured cathodes, allows a better conversion of molecular to atomic oxygen, which leads to a more efficient performance in the operation of these devices and, even better, with a reduction in their operating temperature. Since the structural properties are highly determined by the preparation method, in this work the compound LaNi₀.₆Fe₀.₄O₃-δ was synthesized by the sol-gel method since this allowed a good control of thermal stability, stoichiometry and the crystallite size. In this work, these results are presented which were determined by X-ray diffraction, thermal analyses and scanning and transmission electron microscopies, respectively

Nanostructured Thin Films Obtained from Fischer Aminocarbene Complexes

The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)5NH(CH2)15CH3, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium (0) or tungsten (0) as an acceptor group, are reported. These four push-pull systems formed Langmuir (L) monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves); Brewster angle microscopic images were also obtained. By using the Langmuir–Blodgett (LB) method, molecular monolayers were transferred onto glass substrates forming Z-type multilayers. LB films were characterized through ultraviolet-visible spectroscopy, atomic force microscopy and X-ray diffraction techniques. Results indicated that films obtained from 2b complex [(Ferrocenyl)(hexadecylamine)methylidene] pentacarbonyl tungsten (0) are the most stable and homogeneous; due to their properties, these materials may be incorporated into organic electronic devices

Nanostructured thin films obtained from Fischer aminocarbene complexes

The synthesis of four amphiphilic organometallic complexes with the general formula RC = M(CO)5NH(CH2)15CH3, where R is a ferrocenyl 2(a-b) or a phenyl 4(a-b) group as a donor moiety and a Fischer carbene of chromium (0) or tungsten (0) as an acceptor group, are reported. These four push-pull systems formed Langmuir (L) monolayers at the air-water interface, which were characterized by isotherms of surface pressure versus molecular area and compression/expansion cycles (hysteresis curves); Brewster angle microscopic images were also obtained. By using the Langmuir-Blodgett (LB) method, molecular monolayers were transferred onto glass substrates forming Z-type multilayers. LB films were characterized through ultraviolet-visible spectroscopy, atomic force microscopy and X-ray diffraction techniques. Results indicated that films obtained from 2b complex [(Ferrocenyl)(hexadecylamine)methylidene] pentacarbonyl tungsten (0) are the most stable and homogeneous; due to their properties, these materials may be incorporated into organic electronic devices

Organic Solvent’s Effect in the Deposition of Platinum Particles on MWCNTs for Oxygen Reduction Reaction

We reported the synthesis of platinum particles anchored on the surface of multiwall carbon nanotubes (MWCNTs). The synthesis of platinum particles was carried out by microemulsion method using hexadecyltrimethylammonium bromide (CTAB) as surfactant to enhance the dispersion of platinum particles in hexane (C6), heptane (C7), and octane (C8) solutions. The effects of the microemulsion dispersion medium on the synthesis of platinum particles on MWCNTs (MWCNT/Pt) hybrid materials and their catalytic activities of the oxygen reduction reaction (ORR) in HClO4 were investigated. The anchored platinum particles showed good dispersion on carbon nanotubes surface with the average particle sizes of 2.65±0.60, 2.89±0.68, and 0.97±0.29 nm for the dispersion medium of C6, C7, and C8, respectively. The experimental results of ORR experiments indicated a relationship between the size and the dispersion media of the platinum particles; also the catalytic activity of the anchored platinum on MWCNT particles strongly depends on the dispersion medium employed in the microemulsion process