New Insight on the Hydrogen Absorption Evolution of the Mg–Fe–H System under Equilibrium Conditions

Mg2FeH6 is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg2FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH2 is enhanced by the presence of Fe. However, MgH2 does not take part as intermediate for the formation of Mg2FeH6 and acts as solid-solid diffusion barrier which hinders the complete formation of Mg2FeH6. This work provides novel insight about the formation mechanism of Mg2FeH6

New Insight on the Hydrogen Absorption Evolution of the Mg–Fe–H System under Equilibrium Conditions

Mg₂FeH₆ is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m³) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg₂FeH₆ under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg₂FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH₂ is enhanced by the presence of Fe. However, MgH₂ does not take part as intermediate for the formation of Mg₂FeH₆ and acts as solid-solid diffusion barrier which hinders the complete formation of Mg₂FeH₆. This work provides novel insight about the formation mechanism of Mg₂FeH₆.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Stability and Reversible Oxidation of Sub-Nanometric Cu5 Metal Clusters: Integrated Experimental Study and Theoretical Modeling

12 pags., 6 figs.Sub-nanometer Metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X-ray Absorption spectroscopy and Near Ambient Pressure X-ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion-corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude "breathing" motions. A chemical phase diagram for Cu oxidation state of the Cu5-oxygen system is presented, clearly different from the already known bulk and nano-structured chemistry of Cu.This work has been partly supported by the Spanish Ministerio de Ciencia e Innovación (TED2021-131899BI00/MCIN/AEI/10.13039/501100011033/ Unión Europea NextGenerationEU/PRTR), and the Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under Grants Nos, PID2019-107115GBC21, and PID2020-117605GB-I00; the EU Doctoral Network PHYMOL 101073474 (project call reference HORIZON-MSCA2021-DN-01); the Austrian Science Fund (FWF) under Grant P29893-N36; XUNTA DE GALICIA (Spain) (Grupos Ref. Comp. 2021 - ED431C 2021/16); ANPCyT PICT (2017-1220 and 2017- 3944) and UNLP (Project 11/X937), Argentina. This publication is also based upon work of COST Action CA21101 "Confined molecular systems: from a new generation of materials to the stars" (COSY) supported by COST (European Cooperation in Science and Technology).Peer reviewe

EXAFS and DFT study of the cadmium and lead adsorption on modified silica nanoparticles

Silica nanoparticles of 7 nm diameter were modified with (3-aminopropyl) triethoxysilane (APTES) and characterized by CP-MAS 13C and 29Si NMR, FTIR, zeta potential measurements, and thermogravimetry. The particles were shown to sorb successfully divalent lead and cadmium ions from aqueous solution. Lead complexation with these silica nanoparticles was clearly confirmed by EXAFS (Extended X-ray Absorption Fine Structure) with synchrotron light measurements. Predicted Pb–N and Pb–C distances obtained from quantum-chemical calculations are in very good agreement with the EXAFS determinations. The calculations also support the higher APTES affinity for Pb2+ compared to Cd2+.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasCentro de Investigaciones ÓpticasCentro de Investigación y Desarrollo en Fermentaciones Industriale

Role of age and comorbidities in mortality of patients with infective endocarditis

[Purpose]: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. [Methods]: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015.Patients were stratified into three age groups:<65 years,65 to 80 years,and ≥ 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. [Results]: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 ≥ 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients ≥80 years who underwent surgery were significantly lower compared with other age groups (14.3%,65 years; 20.5%,65-79 years; 31.3%,≥80 years). In-hospital mortality was lower in the <65-year group (20.3%,<65 years;30.1%,65-79 years;34.7%,≥80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%,≥80 years; p = 0.003).Independent predictors of mortality were age ≥ 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI ≥ 3 (HR:1.62; 95% CI:1.39–1.88),and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared,the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. [Conclusion]: There were no differences in the clinical presentation of IE between the groups. Age ≥ 80 years, high comorbidity (measured by CCI),and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Synthesis of Highly Stable Surfactant-free Cu5 Clusters in Water

We report the synthesis, for the first time, of small, highly monodisperse Cu5 clusters in water without any surfactant or protective agent. For this purpose, we used a new approach based on the kinetic control of the reaction, which is achieved with an electrochemical method and using a solution with almost no conductivity (i.e., without added electrolytes commonly used in electrochemical methods). This allows the application of extremely small current densities needed to focus the reaction to synthesize only one selected cluster size. Clusters were characterized by ultraviolet–visible (UV–vis) and fluorescence spectroscopies, atomic force microscopy, electrospray ionization time-of-flight mass spectrometry, X-ray photoelectron spectroscopy, extended X-ray absorption fine structure, and X-ray absorption near-edge spectroscopy, showing the presence of only Cu clusters with five atoms. Contrary to what should be expected, such clusters are very stable and remain unaltered in solution, for at least one year, because of their huge band gap (4.07 eV). Moreover, such Cu5 clusters are extremely stable to UV irradiation, temperature, and pH.Fil: Huseyinova, Shahana. Universidad de Santiago de Compostela; EspañaFil: Blanco, José. INL International Nanotechnology Laboratory; PortugalFil: Requejo, Felix Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Blanco, María del Carmen. Universidad de Santiago de Compostela; EspañaFil: Buceta, David. Universidad de Santiago de Compostela; EspañaFil: López Quintela, M. Arturo. Universidad de Santiago de Compostela; Españ

LiFePO4 CO-dopado con rGO como material catódico para baterías de ion Li: caracterización xas en condiciones "in operando"

Los estudios recientes en baterías de ion Li están dedicados a entender los procesos que se generan en la interfaz electrodo/electrolito los cuales son cruciales en la litiación/delitiación. En general, el mecanismo de intercalación de estos iones está gobernado por procesos que ocurren de manera homogénea y en diferentes escalas de tamaño, que van desde micrones hasta unos pocos nanómetros, por lo tanto, los estudios in operando surgen como una excelente forma de comprender los mecanismos que originan estos procesos. Dentro de las técnicas de rayos X, la absorción es una excelente candidata debido a que es químicamente selectiva y posee una alta sensibilidad para determinar el estado de oxidación de los átomos absorbentes. En este trabajo se sintetizaron materiales activos para cátodos, de la familia del LiFePO4 (LFP), utilizando diferentes estrategias con la incorporación de compuestos a base de carbono. Mediante estudios de caracterización avanzados (XANES in operando) se correlacionó la estructura y las características químicas de los cátodos con su capacidad de carga y estabilidad.Centro de Investigación y Desarrollo en Ciencias Aplicada