High efficiency cathodes for SOFCs prepared by spray-pyrolysis

In recent years, lowering the operating temper-ature of the Solid Oxide Fuel Cells (SOFCs) to the intermediate temperature range (500-700 ºC) has become the main challenge for this technology. The electrolyte resistance might be substantially reduced by using thin film electrolytes. However, the cathode polarization resitance is responsible for much of the loss in performance at low temperatures. Thus, the development of cathode materials with high electro-catalytic activity for the oxygen reduction reaction (ORR) is essential for this technology. Lanthanum strontium manganite La1-xSrxMnO3- (LSM) is the cathode material most widely used in SOFCs. However, LSM exhibits high activation energy for oxygen reduction reaction (ORR) and poor ionic conductivity, limiting its application at high temperatures. Alternative mixed ionic-electronic conductors, such as La1-xSrxCo1-yFeyO3-δ (LSCF) and GdBaCo2O5+x (GBC) has been investi-gated, exhibiting better performances in the inter-mediate temperature range [1]. The performance of these electrodes might be improved at reduced temperature by extending the triple phase bounda-ry length at which gas, electrode and electrolyte phases are simultaneously in contact, serving as the predominant site for the electrochemical reac-tions. To date, the preparation of electrodes via wet infiltration of a cation solution into a porous electrolyte backbone is one of the most effective methods to increase the TPB area and to improve the efficiency of the cathodes, despite the limitations of this process for large-scale manufacturing of SOFCs. In this contribution an alternative preparation method based on spray-pyrolisis deposition into an electrolyte backbone is proposed, which posses a series of advantages with respect to the classical wet infiltration process, including easy industrial implementation, preparation in one single deposition/thermal step as well as low cost [2]. The most widely used cathodes in SOFCs technology were prepared by this alternative method process: La1-xSrxMnO3- and La0.6Sr0.4Co1-yFeyO3-δ (y = 0-2) series. The electrodes were deposited on porous Ce0.8Gd0.1O1.95 (CGO) backbones at 250 ºC by conventional spray pyrolysis from an aqueous precursor solution of metal nitrates. The structure, microstructure and electrochemical properties of these materials have been investigated by X-ray diffraction, field-emission SEM (Fig. 1.a) and im-pedance spectroscopy in symmetrical cells. The values of polarization resistance (Fig. 1.b) are ex-tremely low, ranging from 0.40 cm2 for LSM to 0.07 cm2 for LSCF0.2 at 600 ºC in air, compared to those previously reported in the literature for commercial electrolytes deposited at high tempera-ture, e.g. 25 cm2 for LSM.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Ce0.8Gd0.2O2‐δ / La0.6Sr0.4CoO3 Heterostructures prepared by pulsed laser deposition

Oxide interfaces have received greater attention due to the possibility to obtain properties that are very different from bulk materials. Due to the wide variety of electronic and ionic phenomena than can be detected at the interfaces, such materials have many technological applications [1]. Attention is being drawn to oxide heterostructures, a new family of artificial materials where electronic and ionic properties can be modulated at the interfaces by varying the characteristics of the layers [2, 3]. Slight variations in the near anionic-cationic order might take place if there exists strained interfaces. The interest in multilayared heterostructures derives from the mobility deffects and the space-charge-zone effects at the interfaces. In addition, a new degree of freedom related to the capacitive and resistive contributions is provided as a consequence of the size effects of these artificial structures. In the present work, for the first time, we investigate the structure, microstructure and electrical properties of a new family of heterostructured materials with alternated thin layers of La0.6Sr0.4CoO3 (LSC) and Ce0.8Gd0.2O2-δ (CGO) deposited by pulsed laser deposition on (110) NdGaO3 (NGO) single crystal substrates. In order to evaluate the interfacial contribution to ionic-electronic conductivity and know what is actually happens at the interface of MIECs, different heterostructures were prepared by varying both the number of bilayers (N) and the total thickness of the samples (N = 2 and 5; and the thickness were 50, 100 and 300 nm).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Novel microstructural strategies to enhance the electrochemical performance of La0.8Sr0.2MnO3-δ cathodes

Solid oxide fuel cells (SOFCs) are one of the most efficient technologies for direct conversion of fuels to electricity. La0.8Sr0.2MnO3-δ (LSM) is the cathode material most widely used in SOFCs [1], however, LSM exhibits high activation energy for oxygen reduction reaction (ORR) and low ionic conductivity, which limits its application at reduced temperatures. In this material the electrochemically active reaction sites are restricted to the triple-phase boundary (TPB) near the electrolyte/electrode interface, where the electrolyte, air and electrode meet. Different strategies have been investigated to enlarge the TPB area of LSM, such as the production of nanocrystalline powders by precursor routes, preparation of composites by infiltration methods and thin films [2-4]. Here we present and compare innovative procedures to extend the TPB of LSM in contact with yttria-stabilized zirconia electrolyte: i) nanocrystalline LSM films deposited by spray-pyrolysis on polished YSZ electrolyte; ii) the addition of polymethyl methacrylate microspheres as pore formers during the spray-pyrolysis deposition to further increase the porosity of these films and (iii) the deposition of LSM by spray-pyrolysis on porous backbones of Zr0.84Y0.16O1.92 (YSZ), Ce0.9Gd0.1O1.95 (CGO) and Bi1.5Y0.5O3- (BYO) electrolytes previously fixed onto the YSZ electrolyte. The most remarkable peculiarity of this novel preparation method, compared to the traditional impregnation, is the formation of LSM thick film of 500 nm on the electrode surface (Fig. 1), which improves the electrical conductivity of the composite cathode. Thus, the optimization of this novel method would be an alternative to the classical infiltration with several advantages for the industry of planar SOFCs allowing the deposition of a wide variety of ceramic films over large areas with more uniform distribution of the catalyst, lower cost and only one deposition step is required to form the electrode. The morphology and electrochemical performance of the electrode have been investigated by scanning electron microscopy and impedance spectroscopy. Very low values of area specific resistance were obtained ranging from 1.4 cm2 for LSM deposited on polished YSZ to 0.06 cm2 for LSM deposited onto BYO backbone at a measured temperature of 650 ºC. This electrodes exhibit high performance even after annealing at 950 ºC making them interesting for applications at intermediate temperatures.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Solid Oxide Fuel Cells based on Lanthanum Tungstates Electrolytes

Lanthanum tungstate with composition La27W4NbO55- (LWNO) has been tested as proton conductor electrolyte for Solid Oxide Fuel Cells (SOFCs). For this purpose, different electrodes and composite electrodes are considered, including: La0.8Sr0.2MnO3-, La0.6Sr0.4Co1-xFexO3-, La0.5Sr0.5Cr0.5Mn0.5O3-, SrFe0.75Nb0.25O3- and NiO. Chemical compatibility between the cell components is investigated by X-ray powder diffraction (XRPD) and energy dispersive spectroscopy (EDS). Furthermore, area specific resistance (ASR) of the different electrodes is determined in symmetrical cells by impedance spectroscopy. XRPD and EDS analysis do not reveal significant bulk reactivity between most of these electrodes and LWNO electrolyte in the typical operating temperature range of a SOFC (600-900 ºC). However, minor interdiffusion of elements at the electrolyte/electrode interface affects both the ohmic losses and electrode polarization of the cells. ASR values are significantly improved by using a buffer layer of Ce0.8Gd0.2O1.9, between the electrolyte and electrode materials, to prevent reactivity. A single cell with 350 µm thick electrolyte, NiO-Ce0.8Gd0.2O1.9 anode and La0.6Sr0.4Co0.8Fe0.2O3- cathode, generates maximum power densities of 140 and 18 mWcm-2 at 900 and 650 ºC, respectively.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Compatibility and performance of SOFCs based on lanthanum tungstates

Rare-earth tungstates with general composition “Ln6WO12” have attracted great attention in last few years due to their relatively high mixed proton-electron conductivity [1, 2]. One of the main ad-vantages of these electrolytes, compared to the traditional perovskites based on BaCeO3, is that they exhibit high tolerance towards CO2 and H2S environments. Therefore, this material is a potential electrolyte for proton conducting solid oxide fuel cells (PC-SOFC). In this work, the lanthanum tungstate with com-position La27W4NbO55-δ (LWNO) has been tested as proton conductor electrolyte [3]. For this purpose, different electrodes and composite electrodes have been considered, including: La0.8Sr0.2MnO3-δ, La0.6Sr0.4Co1-xFexO3-δ, La0.5Sr0.5Cr0.5Mn0.5O3-δ, SrFe0.75Nb0.25O3-δ and NiO. Chemical compatibility between the cell compo-nents is investigated by X-ray powder diffraction (XRPD) and energy dispersive spectroscopy (EDS). Furthermore, area specific resistance (ASR) of the different electrodes is determined in symmetrical cells by impedance spectroscopy. XRPD and EDS analysis do not reveal significant bulk reactivity between most of these electrodes and LWNO electrolyte in the typical operating temperature range of a SOFC (600-900 ºC). However, minor interdiffusion of elements at the electrolyte/electrode interface affects both the ohmic losses and electrode polarization of the symmetric cells. ASR values are significantly improved by using a buffer layer of Ce0.8Gd0.2O1.9, between the electrolyte and electrode materials, to prevent reactivity. A single cell with 350 µm thick electrolyte, NiO-Ce0.8Gd0.2O1.9 anode and La0.6Sr0.4Co0.8Fe0.2O3-δ cathode, generates maximum power densities of 140 and 18 mWcm-2 at 900 and 650 ºC, respectively. Hence, lanthanum tungstates could be competitive proton conductors for PC-SOFCs with similar performance to those based on BaZrO3 if thin film electrolytes are used.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Myocardial fibrosis in congenital heart disease

Collagen biomarkers; Congenital heart disease; Myocardial fibrosisBiomarcadors de col·lagen; Malaltia cardíaca congènita; Fibrosi miocàrdicaBiomarcadores de colágeno; Enfermedad cardiaca congenita; Fibrosis miocárdicaMyocardial fibrosis resulting from the excessive deposition of collagen fibers through the myocardium is a common histopathologic finding in a wide range of cardiovascular diseases, including congenital anomalies. Interstitial fibrosis has been identified as a major cause of myocardial dysfunction since it distorts the normal architecture of the myocardium and impairs the biological function and properties of the interstitium. This review summarizes current knowledge on the mechanisms and detrimental consequences of myocardial fibrosis in heart failure and arrhythmias, discusses the usefulness of available imaging techniques and circulating biomarkers to assess this entity and reviews the current body of evidence regarding myocardial fibrosis in the different subsets of congenital heart diseases with implications in research and treatment

Spectroscopic binaries in the Solar Twin Planet Search program: from substellar-mass to M dwarf companions

Previous studies on the rotation of Sun-like stars revealed that the rotational rates of young stars converge towards a well-defined evolution that follows a power-law decay. It seems, however, that some binary stars do not obey this relation, often by displaying enhanced rotational rates and activity. In the Solar Twin Planet Search program we observed several solar twin binaries, and found a multiplicity fraction of $42\% \pm 6\%$ in the whole sample; moreover, at least three of these binaries (HIP 19911, HIP 67620 and HIP 103983) clearly exhibit the aforementioned anomalies. We investigated the configuration of the binaries in the program, and discovered new companions for HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which the latter is orbited by a $0.06$ M$_\odot$ brown dwarf in a 1-month long orbit. We report the orbital parameters of the systems with well-sampled orbits and, in addition, the lower limits of parameters for the companions that only display a curvature in their radial velocities. For the linear trend binaries, we report an estimate of the masses of their companions when their observed separation is available, and a minimum mass otherwise. We conclude that solar twin binaries with low-mass stellar companions at moderate orbital periods do not display signs of a distinct rotational evolution when compared to single stars. We confirm that the three peculiar stars are double-lined binaries, and that their companions are polluting their spectra, which explains the observed anomalies.Comment: 13 pages, 7 figures, accepted for publication in MNRA

A relação entre atividade física e saúde mental : um estudo de revisão

Introdução: Este estudo de revisão narrativa foi um caminho alternativo para o desenvolvimento do meu Trabalho de Conclusão de Curso (TCC) da graduação em Enfermagem na Universidade Federal do Rio Grande do Sul (UFRGS). O projeto de pesquisa inicial tratava dos benefícios e fatores motivacionais de um grupo de caminhada na Atenção Básica, na percepção dos participantes. Esse projeto foi suspenso por conta da pandemia, o que exigiu um redirecionamento da proposta, iniciando-se um novo estudo de revisão da literatura a fim de identificar a relação da atividade física e saúde mental, dando continuidade à temática inicial. Objetivo: Identificar as repercussões das atividades físicas na prevenção de transtornos mentais e promoção da saúde mental. Método: O artigo atual é uma revisão narrativa da literatura existente sobre as repercussões das atividades físicas na prevenção de transtornos mentais e promoção da saúde mental. A revisão narrativa é caracterizada por uma análise crítica da literatura, sob o ponto de vista teórico ou contextual, sem necessidade de sistematização. Resultados: No que se refere aos eixos a serem discutidos, foram construídos a partir dos resultados apresentados nas publicações, 6 publicações focaram atividades físicas para indivíduos com transtornos mentais, 11 em atividades físicas como promoção de saúde mental e prevenção de transtornos mentais, e 14 publicações apontam recomendações. Conclusão: A atividade física pode ser considerada um importante fator de proteção no desenvolvimento de transtornos mentais, especialmente quando se trata da prevenção de doenças como ansiedade, esquizofrenia e depressão. Dessa forma, a atividade física torna-se um método terapêutico na promoção da saúde e prevenção de morbidades psíquicas

Statistical thermodynamics of aligned rigid rods with attractive lateral interactions: Theory and Monte Carlo simulations

The phase behaviour of aligned rigid rods of length k (k-mers) adsorbed on two-dimensional square lattices has been studied by Monte Carlo (MC) simulations and histogram reweighting technique. The k-mers, containing k identical units (each one occupying a lattice site) were deposited along one of the directions of the lattice. In addition, attractive lateral interactions were considered. The methodology was applied, particularly, to the study of the critical point of the condensation transition occurring in the system. The process was monitored by following the fourth order Binder cumulant as a function of temperature for different lattice sizes. The results, obtained for k ranging from 2 to 7, show that: (i) the transition coverage exhibits a decreasing behaviour when it is plotted as a function of the k-mer size and (ii) the transition temperature, Tc, exhibits a power law dependence on k, Tc∼k0,4, shifting to higher values as k increases. Comparisons with an analytical model based on a generalization of the Bragg–Williams approximation (BWA) were performed in order to support the simulation technique. A significant qualitative agreement was obtained between BWA and MC results.Fil: Dos Santos Mendez, Gonzalo Joaquín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matemáticas y Naturales; ArgentinaFil: Linares, Daniel Humberto. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Departamento de Física; ArgentinaFil: Ramirez Pastor, Antonio Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Fisico Matemáticas y Naturales; Argentin