Chemical and electrical properties of LSM cathodes prepared by mechanosynthesis

Mechanosynthesis of La1-xSrxMnO3 (x = 0, 0.25, 0.5, 0.75 and 1) was carried out at room temperature from stoichiometric mixtures of La2O3, Mn2O3 and SrO, obtaining monophasic powders with the perovskite structure. Physical properties of these materials and their chemical compatibility with the electrolyte yttria stabilized zirconia (YSZ), which depend strongly on the La/Sr ratio, were evaluated to corroborate availability to be implemented as cathode material in solid oxide fuel cells (SOFCs). Electrical conductivity values in air ranged between 100 and 400 S cm-1 in the temperature range of 25-850 C. Samples presented low reactivity with YSZ in the working temperature range (600-1000 C) maintaining the grain size small enough to preserve the catalytic activity for oxygen reduction.Gobierno de España MAT2010-1704

Nanocrystalline cathodes for PC-SOFCs based on BCZY

Perovskites based on BaCeO3-δ exhibit the highest proton conductivity among this class of materials, however, they are susceptible to hydration and carbonation in presence of water vapor and CO2 [1]. In contrast, the chemical stability of BaZrO3-based protonic conductors is better, but they require sintering temperatures as high as 1700 ºC and suffer from high intrinsic grain boundary resistance, limiting the final performance. Partial substitution of Zr for Ce in Ba(Ce0.9-xZrx)Y0.2O3-δ allows obtaining electrolytes with both high proton conductivity and good chemical stability. The performance of a PC-SOFC at low temperatures depends significantly on the ohmic resistance of the electrolyte, although it can be lowered by reducing the electrolyte thickness. Another important limiting factor is the increase of the cathode polarization resistance due to the thermally activated nature of the oxygen reduction reaction. For this reason, it is essential to obtain high efficiency cathodes operating at reduced temperatures. In this work, BaCe0.6Zr0.2Y0.2O3-δ (BCZY) powders were prepared by freeze-drying precursor method. These powders were mixed with a Zn-containing solution as sintering additive in order to obtain dense pellets with submicrometric grain size at only 1200 ºC. After that, La0.6Sr0.4Co0.8Fe0.2O3 nanocrystalline electrodes were deposited symmetrically onto dense pellets BCZY by conventional spray-pyrolysis [3]. The structure, microstructure and electrochemical properties of these electrodes have been examined by XRD, FE-SEM and impedance spectroscopy. The stability of these electrodes at intermediate temperatures was evaluated as a function of time. These nanocrystalline cathodes exhibit a substantial improvement of the electrode polarization resistance with respect to the same materials prepared by screen-printing method at high sintering temperatures, e.g. 0.7 and 3.2 cm2 at 600 ºC for LSCF cathodes prepared by spray-pyrolysis and screen-printing method respectively (Figure). An anode supported cell with composition LSCF/BCZY/NiO-BCZY was also prepared to test the electrochemical performance.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Contenidos, metodología y alumnado : una valoración crítica de la enseñanza en BUP y COU

The aim of this study was to compare the interest of the students in Natural Science in front of three other subjects such as Mathematics, Literature and Geography & History. The selected items of the contents of every subject, and the importance of teaching as an influential factor on students were also studied. The results showed that both the selection of the contents and the methods should have been modified

Caracterización del embarazo en adolescentes menores de 15 años asistidas en el área de atención primaria El Milagro, Riochico

El embarazo en edades cada vez más tempranas se está convirtiendo en un problema social y de salud pública que afecta a todos los estratos sociales. En este trabajo se caracterizó el embarazo en las adolescentes menores de 15 años asistidas en el área de atención primaria El Milagro, Riochico, mediante un estudio cuali-cuantitativo, retrospectivo y transversal. Los factores maternos individuales predisponentes fueron menarquia entre los 10-12 años, primera relación sexual entre los 12 y 14 años, no uso de anticoncepción ni protección durante las relaciones sexuales. Los controles prenatales insuficientes, familias monoparentales, antecedente familiar de embarazo en la adolescencia y familias disfuncionales, predominaron como factores familiares y culturales, así como el abandono de los estudios dentro de los factores predisponentes de tipo socioeconómicos. Las complicaciones maternas y fetales o neonatales más frecuentes fueron el parto pretérmino, nacimientos por cesárea, sangramientos postparto, neonatos con bajo peso al nacer, con depresión al nacer, taquipnea transitoria y enfermedad de membrana hialina posterior. Se identificaron los principales factores predisponentes durante el embarazo precoz, información que puede constituir una herramienta para la educación sexual y reproductiva en aras de minimizar el impacto de esta problemática de la salud pública en el desarrollo pleno de las adolescentes y sociedad en general

Preparation of N-doped Carbon/Metal Phosphides as Promising Trifunctional Electrocatalysts Toward the OER, ORR and HER

Sustainable energy storage and conversion technologies, such as electrochemical water splitting and fuel cells, attracts increasing attention as alternative processes to advance toward a global decarbonation. However, the high cost, scarcity, and poor stability of the most active electrocatalysts, mainly based on noble metal (Pt, RuO2, IrO2,…), difficult severely their large-scale production and use. In this regard, the development of earth-abundant electrocatalysts, with high activity for the different processes, is needed. Several imidazole-containing metal etidronates, MLIm-n (M2+= Fe, Co, Ni and solid solutions; L= ETID; Im= Imidazole; n= [0, 3]), were prepared using different synthetic procedures. Thermal reduction of MLIm-n in 5%H2–Ar at different temperatures resulted on core–shell N-doped carbon/TMPs with variable content of MP and MxP as crystalline phases. Their electrocatalytic activities have been widely studied by cyclic and linear sweep voltammetry, impedance spectroscopy, transmission electron microscopy, and XPS analysis. Preliminary results reveal that factors such as the presence of the imidazole and the metal coordination environment in the precursor samples determine the final composition and electrochemical properties of the resulting pyrolyzed derivatives. So, the Co2+- derivative, CoLIm-0@800, with a composition CoP/Co2P= 80/20 wt. %, exhibited the best electrocatalytic properties toward OER/ORR/HER as well as good capabilities as anode for overall water splitting in comparison to the expensive reference RuO2 electrocatalyst

High valence transition metal doped strontium ferrites for electrode materials in symmetrical SOFCs

AbstractIn this paper we report the successful incorporation of high valence transition metals, i.e. Cr, Mo, W, V, Nb, Ti, Zr into SrFeO3−δ perovskite materials, for potential applications as symmetric electrode materials for Solid Oxide Fuel Cells. It is observed that the doping leads to a change from an orthorhombic structure (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). These electrodes are chemically compatibles with Ce0.9Gd0.1O1.95 (CGO) and La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolytes at least up to 1100 °C. Thermal annealing experiments in 5% H2–Ar at 800 °C also show the stability of the doped samples in reducing conditions, suggesting that they may be suitable for both cathode and anode applications. In contrast, reduction of undoped SrFeO3−δ leads to the observation of extra peaks indicating the formation of the brownmillerite structure with the associated oxygen vacancy ordering. The performance of these electrodes was examined on dense electrolyte pellets of CGO and LSGM in air and 5% H2–Ar. In both atmospheres an improvement in the area specific resistances (ASR) values is observed for the doped samples with respect to the parent compound. Thus, the results show that high valence transition metals can be incorporated into SrFeO3−δ-based materials and can have a beneficial effect on the electrochemical performance, making them potentially suitable for use as cathode and anode materials in symmetrical SOFC

Exploiting the Multifunctionality of M2+/Imidazole-Etidronates for Proton Conductivity (Zn2+) and Electrocatalysis (Co2+, Ni2+) toward the HER, OER, and ORR

This work deals with the synthesis and characterization of one-dimensional (1D) imidazole-containing etidronates, [M(ETID)(Im)]·nHO (M = Co and Ni; n = 0, 1, 3) and [Zn(ETID)(HO)](Im), as well as the corresponding Co/Ni solid solutions, to evaluate their properties as multipurpose materials for energy conversion processes. Depending on the water content, metal ions in the isostructural Co and Ni derivatives are octahedrally coordinated (n = 3) or consist of octahedral together with dimeric trigonal bipyramidal (n = 1) or square pyramidal (n = 0) environments. The imidazole molecule acts as a ligand (Co, Ni derivatives) or charge-compensating protonated species (Zn derivative). For the latter, the proton conductivity is determined to be ∼6 × 10 S·cm at 80 °C and 95% relative humidity (RH). By pyrolyzing in 5%H-Ar at 700-850 °C, core-shell electrocatalysts consisting of Co-, Ni-phosphides or Co/Ni-phosphide solid solution particles embedded in a N-doped carbon graphitic matrix are obtained, which exhibit improved catalytic performances compared to the non-N-doped carbon materials. Co phosphides consist of CoP and CoP in variable proportions according to the used precursor and pyrolytic conditions. However, the Ni phosphide is composed of NiP exclusively at high temperatures. Exploration of the electrochemical activity of these metal phosphides toward the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) reveals that the anhydrous Co(ETID)(Im) pyrolyzed at 800 °C (CoP/CoP = 80/20 wt %) is the most active trifunctional electrocatalyst, with good integrated capabilities as an anode for overall water splitting (cell voltage of 1.61 V) and potential application in Zn-air batteries. This solid also displays a moderate activity for the HER with an overpotential of 156 mV and a Tafel slope of 79.7 mV·dec in 0.5 M HSO. Ni- and Co/Ni-phosphide solid solutions show lower electrochemical performances, which are correlated with the formation of less active crystalline phases.A.V.-C. thanks MICIU for PRE2020-094459 student grant; M.B.-G. thanks PAIDI2020-DOC_00272 research grant (Junta de Andalucia, Spain) and R.M.P.C. thanks University of Malaga under Plan Propio de Investigación for financial support. Funding for open access charge: Universidad de Málaga/CBUA. The work at UMA was funded by PID2019-110249RB-I00 (MICIU/AEI, Spain) and PY20-00416 (Junta de Andalucia, Spain/FEDER) research projects. D.C.-L. acknowledges funding by project no. PGC2018-102047-B-I00 (MICIU/AEI/FEDER, UE). The work at UoC was funded by the Special Account of Research, Program Innovative Materials and Applications INNOVAMAT, KA 10694

Exploiting the Multifunctionality of M2+/Imidazole−Etidronates for Proton Conductivity (Zn2+) and Electrocatalysis (Co2+, Ni2+) toward the HER, OER, and ORR

This work deals with the synthesis and characterization of one-dimensional (1D) imidazole-containing etidronates, [M2(ETID)(Im)3]·nH2O (M = Co2+ and Ni2+; n = 0, 1, 3) and Zn2(ETID)2(H2O)2](Im)2, as well as the corresponding Co2+/Ni2+ solid solutions. Depending on the water content, metal ions in the isostructural Co2+ and Ni2+ derivatives are octahedrally coordinated (n = 3) or consist of octahedral together with dimeric trigonal bipyramidal (n = 1) or square pyramidal (n = 0) environments. The imidazole molecule acts as a ligand (Co2+, Ni2+ derivatives) or charge-compensating protonated species (Zn2+ derivative). For the latter, the proton conductivity is determined to be ∼6 × 10−4 S·cm−1 at 80 °C and 95% relative humidity (RH). By pyrolyzing in 5%H2−Ar at 700−850 °C, core−shell electrocatalysts consisting of Co2+-, Ni2+-phosphides or Co2+/Ni2+-phosphide solid solution particles embedded in a N-doped carbon graphitic matrix are obtained, which exhibit improved catalytic performances compared to the non-N-doped carbon materials. Co2+ phosphides consist of CoP and Co2P in variable proportions according to the used precursor and pyrolytic conditions. However, the Ni2+ phosphide is composed of Ni2P exclusively at high temperatures. Exploration of the electrochemical activity of these metal phosphides toward the OER, ORR, and HER reactions reveals that the anhydrous Co2(ETID)(Im)3 pyrolyzed at 800 °C (CoP/Co2P = 80/20 wt %) is the most active trifunctional electrocatalyst, with good integrated capabilities as an anode for overall water splitting (cell voltage of 1.61 V) and potential application in Zn−air batteries. This solid also displays a moderate activity for the HER with an overpotential of 156 mV and a Tafel slope of 79.7 mV·dec−1 in 0.5 M H2SO4. Ni2+- and Co2+/Ni2+-phosphide solid solutions show lower electrochemical performances, which are correlated with the formation of less active crystalline phases.The work at UMA was funded by PID2019-110249RB-I00 (MICIU/AEI, Spain) and PY20-00416 (Junta de Andalucia, Spain/FEDER) research projects. A.V.-C. thanks MICIU for PRE2020-094459 student grant; M.B.-G. thanks PAIDI2020-DOC_00272 research grant (Junta de Andalucia, Spain) and R.M.P.C. thanks University of Malaga under Plan Propio de Investigación for financial support. Funding for open access charge: Universidad de Málaga/CBUA (PMCID# PMC8915163

Effect of tri- and tetravalent metal doping on the electrochemical properties of lanthanum tungstate proton conductors

Metal doping on lanthanum tungstates at W2 site was confirmed by TOF-NPD. TGA and EIS demonstrated proton conductivity.</p