Efectos isotópicos en los procesos de producción y almacenamiento de hidrógeno

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura 21-06-200

El hidrógeno como vector energético: Mucho hecho pero casi todo por hacer

Los autores desarrollan, muy brevemente, los aspectos esenciales de lo que globalmente se denomina “Sistema Energético Solar-Hidrógeno” o a veces “Economía del hidrógeno”. El hidrógeno, obtenido por descomposición del agua mediante energías primarias renovables (solar, eólica…) se convierte en transportador de energía (vector energético) y en combustible limpio. Se discute la conveniencia del uso del hidrógeno en el contexto energético actual, así como los tres pilares fundamentales del uso del hidrógeno como vector energético: su producción usando fuentes renovables, su acumulación mediante diferentes métodos y, finalmente, su combustió

Magnesium- and intermetallic alloys-based hydrides for energy storage: modelling, synthesis and properties

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMHydrides based on magnesium and intermetallic compounds provide a viable solution to the challenge of energy storage from renewable sources, thanks to their ability to absorb and desorb hydrogen in a reversible way with a proper tuning of pressure and temperature conditions. Therefore, they are expected to play an important role in the clean energy transition and in the deployment of hydrogen as an efficient energy vector. This review, by experts of Task 40 'Energy Storage and Conversion based on Hydrogen' of the Hydrogen Technology Collaboration Programme of the International Energy Agency, reports on the latest activities of the working group 'Magnesium- and Intermetallic alloys-based Hydrides for Energy Storage'. The following topics are covered by the review: multiscale modelling of hydrides and hydrogen sorption mechanisms; synthesis and processing techniques; catalysts for hydrogen sorption in Mg; Mg-based nanostructures and new compounds; hydrides based on intermetallic TiFe alloys, high entropy alloys, Laves phases, and Pd-containing alloys. Finally, an outlook is presented on current worldwide investments and future research directions for hydrogen-based energy storag

X-ray photoelectron spectroscopy of high-throughput mechanically exfoliated van der Waals materials

X-ray photoelectron spectroscopy (XPS) is a widely used and easy accessible characterisation technique for investigating the chemical composition of materials. However, investigating the composition of van der Waals (vdW) flakes by XPS is challenging due to the typical spot size of XPS setups compared to the dimensions of the flakes, which are usually one thousand times smaller than the spot size. In this work, we demonstrate the feasibility of quantitative elemental analysis of vdW materials by using high-throughput mechanical exfoliations, which favour the coverage of arbitrary substrates with flakes of areas of the order of the cm2 using minimal quantities of materials (about 10 mu g). We have analysed the chemical composition of MoS2, graphite, WSe2 and FePS3. The high-resolution measurement of their main core levels through XPS demonstrates the absence of significant contamination during the transfer method. In the case of air-sensitive FePS3, the glove box fabrication and its degradation in air are discussed. Overall, this research opens the possibility of evaluating the purity of commercial or lab-synthesized flakes and paves the way towards a more systematic comparison between the composition of vdW materials produced and used among different laboratories.Quantitative elemental analysis of van der Waals materials can be done by XPS by using high-throughput mechanical exfoliations, which favour the coverage of large area substrates with flakes using minimal quantities of starting materials

Synthesis of Ternary Borocarbonitrides by High Temperature Pyrolysis of Ethane 1,2-Diamineborane

Ethane 1,2-diamineborane (EDAB) is an alkyl-containing amine-borane adduct with improved hydrogen desorption properties as compared to ammonia borane. In this work, it is reported the high temperature thermolytic decomposition of EDAB. Thermolysis of EDAB has been investigated by concomitant thermogravimetry-differential thermal analysis-mass spectrometry experiments. EDAB shows up to four H2 desorption events below 1000 °C. Small fractions of CH4, C2H4 and CO/CO2 are also observed at moderate-high temperatures. The solid-state thermolysis product has been characterized by means of different structural and chemical methods, such as X-ray diffraction, Raman spectroscopy, Scanning electron microscopy, Elemental analysis, and X-ray photoelectron spectroscopy (XPS). The obtained results indicate the formation of a ternary borocarbonitride compound with a poorly-crystalline graphitic-like structure. By contrast, XPS measurements show that the surface is rich in carbon and nitrogen oxides, which is quite different to the bulk of the materialSome authors (Fabrice Leardini, Lorenzo Massimi, Maria Grazia Betti and Carlo Mariani) also thank Sapienza Università di Roma for financial support under “Progetti di Ateneo”, and the Italian Ministry of Education and Research (MIUR) for the PRIN grant “GRAF” n. 20105ZZTS

Synthesis, optical band gap and thermoelectric properties of Sr1+xTiS3-y chalcogenide perovskites

Inorganic chalcogenide perovskites are semiconductors with attractive optoelectronic properties, which make them of interest in different fields, such as energy harvesting. Some of these compounds have been poorly investigated to date. For instance, very few works deal with the synthesis and characterization of Sr1+xTiS3. Here we present a novel synthesis procedure to obtain Sr1+xTiS3-y powders. Moreover, we show for the first time an experimental characterization of some fundamental properties of this compound that may be relevant for many potential applications. First, we demonstrate that this perovskite shows very high thermal stability (up to 700◦C in air and up to 1200◦C in Ar atmosphere). Next, we experimentally determine its optical band gap (about 0.97 eV) corresponding to a direct allowed transition, in agreement with previous predictions. Finally, we demonstrate a tuneable Seebeck coefficient (changing from n-type to p-type behaviour) by changing the amount of sulfur vacanciesThis research has been funded by Spanish MICINN under RTI2018-099794-B-I00 gran

Ultrathin Transparent B-C-N Layers Grown on Titanium Substrates with Excellent Electrocatalytic Activity for the Oxygen Evolution Reaction

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Energy Materials, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/acsaem.9b02339Ultrathin B-C-N layers grown on Ti substrates are investigated as efficient anodes for electrochemical water splitting. A fast and direct synthetic route has been used based on plasma-enhanced chemical vapor deposition with methylamine borane as a single-source molecular precursor. The effect of growth time on the morphological and structural properties and on the chemical composition of the layers has been investigated by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy coupled with electron energy loss spectroscopy. Flat B-C-N layers on top of an amorphous titanium oxide layer present at the Ti surface have been obtained by using short growth times, while longer growth times give rise to core/shell structures formed by vertical wall B-C-N layers and titanium carbonitride phases. The obtained layers present enhanced electrocatalytic activity for the oxygen evolution reaction in alkaline aqueous solutions. Moreover, because of their ultrathin nature, the B-C-N layers preserve the photocurrents of the underlying titanium oxide layer, acting as transparent electrodes with high conductivity for the photogenerated charge carriers and improved electrocatalytic activity for the oxidation of water to oxygen gasThis work has been funded under RTI2018-099794-B-I00 grant of Spanish MICINN and by PRIN Grant FERMAT (2017KFY7XF) of Italian MIU

Imaging the Kirkendall effect in pyrite (FeS2) thin films: cross-sectional microstructure and chemical features

This investigation provides novel data on the structure and chemical composition of pyrite thin films and new hints concerning their formation mechanism. From TEM-HAADF data, it has been found that the films are composed of two different layers: one is very compact and the other one is quite porous with many voids separating a few groups of grains. This porous layer is always in direct contact with the substrate, and its thickness is quite similar to that of the original Fe film. The average size of pyrite grains is equal in both layers, what suggests that the same process is responsible for their formation. Concentration profiles of sulfur, iron and some impurities (mainly sodium and oxygen from the glass substrate) through both layers are given in this work, and thus chemical inhomogeneities of the films are proved by the obtained stoichiometric ratios (S/Fe). Moreover, Na from sodalime glass substrates mainly accumulates at the pyrite grain boundaries and barely dopes them. The obtained results support the hypothesis that the iron sulfuration process essentially induces the diffusion of iron atoms, what leads to the porous layer formation as a manifestation of the Kirkendall Effect. Therefore, it seems that the same mechanisms that operate in the synthesis of surface hollow structures at the nanoscale are also active in the formation of pyrite thin films ranging from several tens to hundreds of nanometersMembers of MIRE Group acknowledge the financial support of the Spanish MICINN under project RTI2018-099794-B-I00. E. Flores acknowledges the intramural CSIC project 2D-MeSes funding and the service from the MiNa Laboratory at IMN, and funding from CM (project SpaceTec, S2013/ICE2822), MINECO (project CSIC13-4E1794) and EU (FEDER,FSE). Financial support through the project UMA18-FEDERJA-041 is gratefully acknowledge