1,721,115 research outputs found
Physico-chemical properties of new thin-film materials for hydrogen storage
No full textLe stockage d'hydrogène est sans doute le dernier verrou au développement à grande échelle des piles à combustible. Utiliser l'hydrogène comme vecteur énergétique, produire efficacement de l'électricité sans avoir recours aux énergies fossiles et rejeter uniquement de l'eau, il s'agit là peut-être de la prochaine révolution technologique, écologique et qui signera la fin des problèmes environnementaux en terme d'énergie.L'hydrogène gazeux est dangereux et son stockage à l'état solide représente une solution mais au détriment de la quantité stockée et des conditions d'utilisation.Dans ce contexte, la recherche de nouveaux matériaux avec des propriétés physico-chimiques nouvelles est souhaitable.Cette thèse s’inscrit dans cette démarche d'investigation : d'une part mettre en oeuvre et utiliser de nouvelles techniques de recherche structurale théorique pour explorer les possibilités qu'offrent les alliages métalliques ; ensuite entreprendre la synthèse de couches minces de métaux et d'alliages au moyen de l’ablation laser pulsé pour bénéficier des atouts de cette méthode.L'étude théorique menée au cours de cette thèse a permis de montrer l'impact des contraintes de pression sur la formation et la stabilité d'alliages dans de nombreux systèmes binaires. Des pistes sur l'hydrogénation possible de nouvelles structures ont également été présentées.D'autre part, l'adversité de l'ablation laser pulsé pour la synthèse de couches minces a été mise en lumière et de grandes disparités dans les conditions de dépôts sont à déplorer. Cette méthode permet de parvenir à des morphologies singulières, ouvrant ainsi à des perspectives dans la conception de ces nouveaux matériaux.Hydrogen storage is probably the last lock facing the development of fuel cells system.Hydrogen is a non-harmful, non-polluting that can be used as an energy vector, allowing to produce fossil fuel free electricity efficiently and releasing only water.It could trigger the next technological and green revolution, marking the end of environmental concerns related to energy.Hydrogen is the most energetic gas. These double-edged caracteristics makes it attractive and unsafe at the same time. Solid state storage can be seen as a solution in spite of a moderate hydrogen uptake and a poor desorption process.In this context, research of new materials with enhanced physico-chemical properties is desirable and represent the aim of this work.This thesis is an investigation study. On the one hand, with the help of efficient theoretical structural prediction systems, an exploration of the infinite possibilities offered by metal alloys has been performed. On the other hand, pulsed laser deposition of metal thin films has been implemented to make use of its benefits.The present theoretical study has highlighted the influence of external strains on stability and emergence of alloys in numerous binary systems. In addition, a search for potential hydrides was carried out. Informations obtained are encouraging the use of similar prediction schemes in order to identify new systems.From metallic thin films made by pulsed laser ablation, deposition difficulties and disparities in procedures have been put forward. Nonetheless, singular morphologies have been achieved by this process, opening new insights for designing novel materials
Lithium intercalation effects on the V<sub>2</sub>O<sub>5</sub> (001) surface
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Prediction of new electrodes for hydrogen production : the meeting between Darwin and Schrödinger
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New insight for hydrogen storage in the magnesium nickel and magne- sium copper systems
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Electronic and Photocatalytic Properties of Sn1−xTixO2 Alloys and (SnO2)n/(TiO2)m Superlattices under Biaxial Strain: A First-Principles and Evolutionary Algorithm Study.
No full textInternational audienceThe aim of this study is to develop more efficient semiconductor materials for photocatalytic water splitting by integrating superlattice structures and metal oxide substitutions. While metal oxides such as TiO₂ and SnO₂ show promise for water splitting, their large band gaps and rapid carrier recombination limit their effectiveness in harnessing sunlight. To overcome these challenges, the influence of biaxial tensile and compressive strains on the stability, structural , electronic properties, and photocatalytic efficiency of (SnO₂)n/(TiO₂)m superlattices and Sn1-xTixO₂ alloys are investigated using first-principles and evolutionary algorithm calculations. As a result, the variable composition evolutionary algorithm allowed us to predict four different configurations of substitution in tin dioxide by titanium atoms (Sn1−xTixO2, Sn-Ti-O). It was observed that the band gap decreases with increasing biaxial strain, along with a corresponding decrease in titanium concentration. Superlattice configurations were investigated using different stacking arrangements of nSnO2 layers and mTiO2 layers, such as (n=m), (n,1), and (1, m). The results show that the (1, m) stacking arrangement achieves the highest values for bulk modulus, Poisson's ratio, and Debye temperature. Exceptional stability was confirmed through phonon dispersion analysis for the 3(SnO2)/1(TiO2))1superlattice under both tensile and compressive strains (-5% to 5%), with other superlattices maintaining stability between -3% and 4%. Furthermore, the electronic analysis demonstrated a decrease in the band gap with increasing tensile strain, achieving a tunable band gap from 3.34 eV to 2.54 eV for 1(SnO2)/3(TiO2) using the HSE06 functional, with high carrier mobility. These superlattices exhibit favorable band edge alignments at pH = 0, 7, and 14, showcasing their potential as efficient photocatalysts
New insight for hydrogen storage in the magnesium nickel and magne- sium copper systems
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The effect of Biaxial strain on electronic properties of (SnO<sub>2</sub>/TiO<sub>2</sub>)<sub>n</sub> superlattices
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New insight for hydrogen storage in the magnesium nickel and magne- sium copper systems
No full textInternational audienc
Structural and electronic properties of layered titanate photocatalysts, Ln_2Ti_2O _7 (Ln = La or Nd)
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