The dissertation explores the electronic structures induced by the adsorption of atoms and molecules on surfaces. It focuses on the physical and chemical properties of dispersed metal atom sites on oxide surfaces and the formation of novel molecular structures at hybrid organic-inorganic interfaces. The study uses density functional theory (DFT) calculations to simulate atomic-scale behaviors and aims to contribute to understanding reaction mechanisms and enhancing catalytic activity. Part one investigates the local environments of single platinum atoms on a cerium oxide surface by analyzing their physical and electronic properties. The next part studies the local environments of single platinum atoms dispersed on a cerium oxide surface. Part two compares the water-gas shift reaction for a platinum atom coordinated with a 10-phenanthroline-5,6-dione ligand on titanium oxide with that on a single platinum atom on a titanium oxide surface. It investigates the effect of vacancies in titanium oxide on the electronic structure of platinum and its reactivity. Part three explores the electronic structure of bistable molecules and their potential as molecular switches. Part four analyzes the patterns in scanning tunneling microscope (STM) images of an organic molecule layer on Au(111) and demonstrates electron confinement despite a weak interaction between the molecular layer and the Au surface.

Cette étude porte sur la co-électrolyse de H2O et CO2 à 800°C dans une cellule à oxydessolides. Un modèle détaillé a été développé afin de rendre compte des phénomènesélectrochimiques, chimiques, thermiques et de transferts de matière, et introduisant unereprésentation macroscopique du mécanisme de co-électrolyse. Il permet d’estimer lesperformances et les compositions en sortie de cellule. Un protocole expérimental, visant àvalider les principales hypothèses de ce modèle, a été appliqué à deux types de cellulecommerciale à cathode support. À partir de courbes de polarisations, obtenues en électrolyseet en co-électrolyse, ainsi que d’analyses gaz, les densités de courant d’échange, illustrant lescinétiques électrochimiques, ont pu être estimées, et le mécanisme proposé a pu être validé.L’analyse des simulations a permis l’identification des processus limitant la co-électrolyse, laproposition de voies d’optimisation et l’établissement des cartographies de fonctionnement. / This work investigates the high temperature co-electrolysis of H2O and CO2 in Solid OxideCells. A detailed model was developed, encompassing electrochemical, chemical, thermal andmass transfer phenomena, and introducing a macroscopic representation of the co-electrolysismechanism. This model allows predicting the performances and outlet compositions in singlecell and stack environments. An experimental validation protocol was implemented on twotypes of commercial Cathode Supported Cells, ranging from polarization curves, obtained insingle and co-electrolysis modes, to micro gas analyses. These tests aimed both at determiningthe different exchange current densities, representative of the kinetics of electrochemicalreactions, and validating the simulated cell global behavior and mechanism proposed.Comprehensive analysis of the simulations led to the identification of limiting processes andpaths for optimization, as well as to the establishment of co-electrolysis operating maps.