A commercial non-contact atomic force microscope was improved to achieve utmost resolution on a routine basis. This system was used to study the (110) surface of rutile titanium dioxide. The focus was on understanding contrast formation in terms of tip-sample interaction mechanisms. Moreover, chromium and antimony-doped titanium dioxide was investigated. The implications of transition-metal doping on the surface structure of this highly interesting photocatalyst was studied at the atomic scale.

Les dispositifs thermoélectriques, basés sur la conversion d'énergie thermique, offrent des perspectives intéressantes pour le développement de systèmes autonomes. Les principaux défis pour le développement de telles technologies reposent sur l'obtention de dispositifs flexibles, écologiquement et économiquement viables pouvant alimenter des appareils électroniques à faible consommation d'énergie. Le but de cette thèse a donc été de proposer une méthodologie pour l'analyse globale de dispositifs thermoélectriques pour des applications à température ambiante. Dans un premier temps, une approche multi-échelle pour la modélisation de dispositifs thermoélectriques a été développée. A cet effet, trois niveaux d'abstraction ont été considérés. A l'échelle du système, un modèle compact a été développé afin d'évaluer les performances du dispositif dans son environnement. A l'échelle du dispositif, des prototypes virtuels de TEG ont été évalués par le biais de la simulation numérique. A l'échelle des matériaux, la DFT combinée à une approche semi-classique basée sur l'équation de transport de Boltzmann ont été utilisées afin de calculer les propriétés électroniques. La tétraédrite et la famatinite ont été sélectionnées en raison de leurs propriétés prometteuses à température ambiante ainsi que de leur abondance et faible coût. Dans un second temps, des travaux expérimentaux sur la synthèse de nanoparticules de Cu-Sb-S ont été menés. Des nanoparticules quasi-monodisperses avec des tailles inférieures à 50 nm ont été obtenues grâce à la mise au point d'un procédé basé sur la synthèse solvothermale avec surfactant, une méthode faible coût et facilement adaptable à grande échelle. / Thermoelectric devices, capitalizing on waste heat conversion, offer good prospects for the development of autonomous systems. The main challenges for technology development are to obtain flexible, environmentally friendly and low-cost thermoelectric devices with performances sufficient enough to power small electronic devices. The aim of this thesis was thus to propose a methodology for the global analysis of thermoelectric devices for ambient temperature applications. The developed methodology enables the evaluation of key parameters impact on the global system. First, a multiscale approach for thermoelectric devices modelling is developed. In this scope, three parallel levels of modeling are addressed. At the system level, a compact model is developed in order to evaluate overall system efficiency as a function of the thermal environment. At the device level, virtual prototypes of printed devices are built and their performances are evaluated via a finite-element simulation tool. Low temperature gradient has to be dealt with by appropriate architecture design. At the material level, quantum DFT is used in conjunction with semi-classical approach using Boltzmann transport theory to calculate electronic properties. Tetrahedrite and famatinite compounds are chosen due to their promising thermoelectric properties at room temperature and their relative abundance and low cost. Secondly, an experimental work has been conducted on the synthesis of sulphide nanoparticles. Quasi-monodisperse nanoparticles with a size not exceeding 50 nm have successfully been fabricated via a low cost and easily scalable surfactant assisted solvothermal technique.

Novel diorganoantimony(III) fluorides containing ligands with pendant arms, R2SbF (5), (R)PhSbF (6) [R = 2-(2′,6′-iPr2C6H3N[double bond, length as m-dash]CH)C6H4], R′′2SbF (7) and (R′′)PhSbF (8) [R′′ = 2-(Me2NCH2)C6H4], were prepared via the ionic derivatives [R2Sb]+[PF6]− (1), [(R)PhSb]+[PF6]− (2), [R′′2Sb]+[SbF6]− (4) and [(R′′)PhSb]+[SbF6]− (obtained in situ) by treatment with [Bu4N]F·3H2O. The ionic species used as starting materials as well as [R′2Sb]+[PF6]− (3) [R′ = 2-(2′,4′,6′-Me3C6H2N[double bond, length as m-dash]CH)C6H4] were obtained from the corresponding bromides or chlorides and Tl[PF6] or Ag[SbF6]. The compounds were investigated by multinuclear NMR spectroscopy in solution, MS and IR spectroscopy in the solid state. The molecular structures of the ionic species 1·2CH2Cl2 and 3·2CHCl3 as well as of the fluorides 5–8 were determined by single-crystal X-ray diffraction. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

No description available.

GeTe and Ge2Sb2Te5 alloys are potential candidates for non-volatile phase change random access memories (PCRAM). For electrical data storage applications the materials should have stable amorphous and crystalline phases, fast crystallization time, low power to switch, and high crystallization activation energy (to be stable at normal operating temperatures). Phase change memories can be tuned through compositional variations to achieve sufficient phase change contrast and thermal stability for data retention. Selenium is one of the attractive choices to use as an additive material owing to its flexible amorphous structure and a variety of possible applications in optoelectronics and solar cells. GeSb2Te3Se alloy, in which 25 at.% of Se substituted for Te, show a higher room temperature resistance with respect to parent GeSb2Te4 alloy, but the transition temperature is lowered which will affect the thermal stability. The RESET current observed for Sb65Se35 alloys were reduced and the crystallization speed increased 25 % faster with respect to Ge2Sb2Te5. Alloys of Ga-Sb-Se possess advantages such as higher crystallization temperatures, better data retention, higher switching speed, lower thermal conductivity and lower melting point than the GST, but the resistance ratio is limited to about two orders of magnitude. This affects the resistance contrast and data readability. It is with this background a study has been carried out in GeTe and GeSbTe system with Se doping. Studies on structural, thermal and optical properties of these materials all through the phase transition temperatures would be helpful to explore the feasibility of phase change memory uses. Thin films along with their bulk counterparts such as (GeTe)1-x Sex ( 0 < x ≤ 0.50) and (GST)1-xSex (0 < x ≤ 0.50), including GeTe and GST alloys, have been prepared. The results are presented in four chapters apart from the Introduction and Experimental techniques chapters. The final chapter summarizes the results. Chapter 1 provides an introduction to chalcogenide glasses, phase change memory materials and their applications. The fundamental properties of amorphous solids, basic phase change properties of Ge2Sb2Te5 and GeTe alloys and their applications are presented in detail. Various doping studies on GeTe and Ge2Sb2Te5 reported in literatures are reviewed. The limitations, challenges, future and scope of the present work are presented. In chapter 2, the experimental techniques used for thin film preparation, electrical characterizations, optical characterization and surface characterizations etc. are explained. Chapter 3 deals entirely on Ge2Sb2Te5 films studied throughout the phase transition, by annealing at different temperatures. Changes in sheet resistance, optical transmission, morphology and surface bonding characteristics are analyzed. The crystallization leads to an increase of roughness and the resistance changes to three orders of magnitude at 125 oC. Optical studies show distinct changes in transmittance during phase transitions and the optical parameters are calculated. Band gap contrast and disorder variation with annealing temperatures are explained. The surface bonding characteristics studied by XPS show Ge-Te, Sb-Te bonds are present in both amorphous and crystalline phases. The temperature dependent modifications of the band structure of amorphous GST films at low temperatures have been little explored. The band gap increment of around 0.2 eV is observed at low temperature (4.2 K) compared to room temperature 300 K. Other optical parameters like Urbach energy and B1/2 are studied at different temperatures and are evaluated. The observed changes in optical band gap (Eopt) are fitted to Fan’s one phonon approximation, from which a phonon energy (ћω) corresponding to a frequency of 3.59 THz resulted. The frequency of 3.66 THz optical phonons has already been reported by coherent phonon spectroscopy experiment in amorphous GST. This opens up an indirect method of calculating the phonon frequency of the amorphous phase change materials. Chapter 4 constitutes comparison of optical, electrical and structural investigation of GST and (GST)1-xSex films. It is well known that GST alloys have vacancy in their structure, which leads to the possibility of switching between the amorphous and crystalline states with minimum damage. Added Se may occupy the vacancy or change the bonding characteristics which intern may manifest in the possibility of change in optical and electrical parameters. The structural studies show a direct amorphous to hexagonal transition in (GST)1-xSex, where x ≥ 0.10 at.%. Raman spectra of the as deposited and annealed (GST)1-xSex films show structural modifications. The infrared transmission spectra indicate a shift in absorption edges from low to high photon energy when Se concentration increases in GST. Band gap values calculated from Tauc plot show the band gap increment with Se doping. It is noted that a small amount of Se doping increases the resistance of the amorphous and crystalline phases and maintains the same orders of resistance contrast. This will be beneficial as it improves the thermal stability and reduces the write current in a device. Switching studies show an increasing threshold voltage as the Se doping concentration increases. Chapter 5 comprises compositional dependent investigations of the bulk GeTe chalcogenides alloys added with different selenium concentrations. The XRD investigations on bulk (GeTe)1-xSex (x = 0.0, 0.02, 0.10, 0.20 and 0.50 at.%) alloys show that the crystalline structure of GeTe alloys does not affect ≤ 0.20 at.% of Se concentration. With increasing amount of Se concentration the alloys gets modified in to a homogeneous amorphous structure. This result has been verified from the XRD, Raman, XPS, SEM and DSC measurements. The possibility that Se occupying the Ge vacancy sites in GeTe structure is explained. Since Se is an easy glass former, the amorphousness increases in the alloys due to new amorphous phases formed by the Se with other elements. It is shown from Raman and XPS analysis that the Ge-Te bonds exists up to Se 0.20 at.% alloys. Ge-Se and GeTe2 bonds are increasing with increasing Se at.%. Melting temperature has found decreases and the reduction in melting point may reduces the RESET current. Further studies on switching behavior may bring out its usefulness. Chapter 6 deals with studies on (GeTe)1-xSex films for phase change memory applications based on the insight received from their bulk study. Even at low at.% addition of Se makes the as prepared (GeTe)1-xSex film amorphous. At 200 oC, GeTe crystalline structure is evolved and the intensity of the peaks reduces in the alloys with increase of Se content. At 300 oC, more evolved GeTe crystalline structure is seen compared to 200 oC annealed films whereas 0.20 at.% Se alloy remain amorphous. Resistance and thermal studies shows increase in crystallization temperature. It is expected that Se sits in the vacancies of the GeTe crystalline structural formation. This may also account for the increased threshold voltages with increasing Se doping. The band gap increase with increase of Se at.% signifying the possibility of band gap tuning in the material. Possible explanation for the increased order in GeTe due to Se doping is presented. The modifications in the alloy with Se addition can be explained with the help of chemical bond energy approach. Those bonds having higher energy leads to increased average bond energy of the system and hence the band gap. The XPS core level spectra and Raman spectra investigation clearly shows the GeTe bonds are replaced by Ge-Se bonds and GeTe2 bonds. The 0.10 at.% Se alloy is found to have a higher thermal stability in the amorphous state and maintains a gigantic resistance contrast compared to other Se concentration alloys. This alloy can be considered as an ideal candidate for multilevel PCM applications. Chapter 7 summarizes the major findings from this work and the scope for future work.

Das Phasendiagramm Sn - Mo - O wurde für 500°C und 1000°C experimentell abgeleitet. Als ternäre Phasen konnten SnMo2O8 und Sn1-xMo4-yO6-2y dargestellt werden. Die Phasen SnMo5O8 und Sn4,4Mo24O38 konnten unterhalb von 1000°C nicht dargestellt werden. Die Phase SnMo2O8 wurde über Festkörper - Gasphasenreaktion einkristallin dargestellt und auf ihr thermisches Verhalten untersucht. Anhand dieser Untersuchungen konnte das Phasendiagramm SnO2 - MoO3 abgeleitet werden. An dieser Phase wurden Einkristall-untersuchungen durchgeführt. Die Struktur der Phase SnMo2O8 wurde in der Raumgruppe Pa (a = 8,967 Å) gelöst. Die Zinnatome besetzen die Flächen - und Kantenmitten der Elementarzelle. Die Lage der Molybdän - und Sauerstoffpositionen kann über ein Fehlordnungsmodell beschrieben werden. Die Phase Sn1-xMo4-yO6-2y konnte über chemischen Transport mit Wasser einkristallin hergestellt werden. Einkristalluntersuchungen bestätigten eine Überstruktur zur NaMo4O6 - Struktur. Die Phase weist mit hoher Wahrscheinlichkeit eine Unterstöchiometrie im Zinngehalt, sowie im Molybdän - bzw. Sauerstoffgehalt auf. Diese Tatsache konnte durch Mößbaueruntersuchungen am Pulver von Sn1-xMo4-yO6-2y bestätigt werden. Eine Lösung der Struktur von Sn1-xMo4-yO6-2y war bisher nicht möglich. Die thermodynamischen Daten der Phasen SnMo2O8 und SnMo4O6 (vereinfacht für Sn1-xMo4-yO6-2y) konnten theoretisch abgeleitet werden. Das Zustandsdiagramm Sn - Mo - O wurde berechnet. Die Überprüfung der Daten erfolgte durch die Berechnung der Bodenkörper - Gasphasengleichgewichte mit dem Programm TRAGMIN. Mit den abgeleiteten Daten wurden Berechnungen zum chemischen Transportverhalten durchgeführt. Dabei wurde gefunden, dass sich die Phase Sn1-xMo4-yO6-2y über chemischen Transport abscheiden lässt. Das Phasendiagramm Pb - Mo - O wurde bis 1000°C experimentell abgeleitet. Die Phasen PbMoO4 und Pb2MoO5 konnten als einphasige Pulver hergestellt werden. Die Phase Pb0,75Mo4O6 konnte über chemischen Transport einkristallin abgeschieden werden. Beim Erhitzen auf 1250°C wurde die Zersetzung dieser Phase in die Phase PbMo5O8 und Mo beobachtet. Die thermodynamischen Daten der Phasen PbMoO4, Pb2MoO5, Pb5MoO8 und Pb0,75Mo4O6 konnten theoretisch abgeleitet werden. Das Zustandsdiagramm Pb - Mo - O wurde berechnet. Im Verlauf der Rechnungen wurde das Zustandsdiagramm PbO - MoO3 mit dem Programm CHEMSAGE berechnet und mit den Literaturdaten verglichen. Die Überprüfung der Daten erfolgte durch die Berechnung der Bodenkörper - Gasphasengleichgewichte mit dem Programm TRAGMIN. Mit den abgeleiteten Daten wurden Berechnungen zum chemischen Transportverhalten durchgeführt. Dabei wurde gefunden, dass sich die Phase Pb0,75Mo4O6 über chemischen Transport abscheiden lässt. Das Phasendiagramm Sb - Mo - O wurde bei 500°C bzw. 700°C experimentell abgeleitet. Im System existieren die Phasen Sb2MoO6 und Sb2Mo10O31. Sb2Mo10O31 konnte einphasig als Pulver hergestellt werden. Die Existenz einer Phase mit der Zusammensetzung Sb4Mo10O31 konnte nicht bestätigt werden. Es wurden Hinweise auf eine dritte ternäre Phase im System Sb - Mo - O gefunden. Die Phasen Sb2MoO6 und Sb2Mo10O31 konnten über chemischen Transport einkristallin dargestellt werden. Mößbaueruntersuchungen an Sb2Mo10O31 ergaben, dass in der Verbindung ausschliesslich dreiwertiges Sb vorliegt und somit Mo gemischtvalent sein muss. Die thermodynamischen Daten der Phasen Sb2MoO6 und Sb2Mo10O31 konnten theoretisch abgeleitet werden. Das Zustandsdiagramm Sb - Mo - O wurde berechnet. Die Überprüfung der Daten erfolgte durch die Berechnung der Bodenkörper - Gasphasengleichgewichte mit dem Programm TRAGMIN. Mit den abgeleiteten Daten wurden Berechnungen zum chemischen Transportverhalten durchgeführt. Dabei wurde gefunden, dass sich beide ternäre Phasen über chemischen Transport abscheiden lassen.

Increasing interest in an effciency enhancement of existing energy sources led to an extended research in the field of thermoelectrics. Especially skutterudites with their high power factor (electric conductivity times Seebeck coefficient squared) are suitable thermoelectric materials. However, a further improvement of their thermoelectric properties is necessary. The relatively high thermal conductivity can be decreased by introducing loosely bound guest ions, whereas atom substitution or nanostructuring (as thin films) could yield an increased power factor. The present work proves the feasibility to deposit single phase skutterudite thin films by MBE technique. In this regard CoSby and FeSby film series were deposited with three different methods: i) codeposition at elevated temperatures, ii) codeposition at room temperature followed by post-annealing, and iii) modulated elemental reactant method. The structural and thermoelectric properties of these films were investigated by taking the thermal stability of the film and the substrate properties into account. Compared to the stoichiometric Sb content of skutterudites of 75 at.%, a small excess of Sb is necessary for achieving single phase skutterudite films. It was found, that the deposited single phase CoSb3 films reveal bipolar conduction (and therefore a low Seebeck coefficient), whereas FeSb3 films show p-type conduction and very promising power factors at room temperature. The need of substrates with a low thermal conductivity and a suitable thermal expansion coefficient is also demonstrated. A high thermal conductivity influences the measurements of the Seebeck coefficient and the obtained values will be underestimated by thermal shortening of the film by the substrate. If the thermal expansion coefficient of film and substrate differ strongly from each other, crack formation at the film surface was observed. Furthermore, the realization of controlled doping by substitution as well as the incorporation of guest ions was successfully shown. Hence, this work is a good starting point for designing skutterudite based thin film structures. Two successful examples for such structures are given: i) a thickness series, where a strong decrease of the resistivity was observed for films with a thickness lower than 10nm, and ii) a FexCo1-xSb3 gradient film, for which the gradient was maintained even at an annealing temperature of 400°C.

The Phthalocyanines (Pc’s) are a group of macro-cyclic molecules, widely investigated due to the possibility to use them in a variety of applications. Electronic and geometrical structure investigations of molecular model systems of Pc’s adsorbed on surfaces are important for a deeper understanding of the functionality of different Pc-based devices. Here, Pc’s monolayers and films, deposited on different surfaces, were investigated by X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS) and Scanning Tunneling Microscopy (STM). In addition Density Functional Theory (DFT) simulations were performed. For molecular films of Metal-free (H2Pc) and Iron (FePc) Pc’s, on surfaces, it is found that the intermolecular interaction is weak and the molecules arrange with their molecular plane mainly perpendicular to the surface. Several monolayer systems were characterized, namely H2Pc and FePc adsorbed on Graphite, ZnPc on InSb(001)-c(8x2), H2Pc on Al(110) and on Au(111). For all the studied monolayers it was found that the molecules are oriented with their molecular plane parallel to the surface. The electronic structure of the molecules is differently influenced by interaction with the surfaces. For H2Pc adsorbed on Graphite the nearly negligible effect of the surface on the molecular electronic structure allowed STM characterization of different molecular orbitals. A strong interaction is instead found in the case of H2Pc on Al(110) resulting in molecules strongly adsorbed, and partly dissociated. Modifications of the electronic and geometrical structure induced by alkali doping of H2Pc films and monolayers were characterized. It is found both for the H2Pc film on Al(110) and monolayer adsorbed on Au(111), that the molecular arrangement is changed upon doping by Potassium and Rubidium, respectively. Potassium doping of the H2Pc films results in a filling of previously empty molecular orbitals by a charge transfer from the alkali to the molecule, with significant modification of the molecular electronic structure.

Les électrocatalyseurs conventionnels utilisés dans les piles à combustibles à membrane échangeuse de protons (PEMFC) sont composés de nanoparticules de platine supportées sur des noirs de carbone de forte surface spécifique. A la cathode de la PEMFC, siège de la réaction de réduction de l’oxygène (ORR), le potentiel électrochimique peut atteindre des valeurs élevées - notamment lors de phases arrêt-démarrage - engendrant des dégradations irréversibles du support carboné. Une solution « matériaux » consiste à remplacer ce dernier par des supports à base d’oxydes métalliques. Ceux-ci doivent être résistants à la corrosion électrochimique, conducteurs électroniques et posséder une structure poreuse et nano-architecturée (permettant le transport des réactifs et produits et une distribution homogène de l’ionomère et des nanoparticules de platine). Dans ce travail, nous avons donc élaboré et caractérisé des électrocatalyseurs à base de nanoparticules de platine (Pt) déposées sur du dioxyde d’étain (SnO₂) et de titane (TiO₂) texturés (morphologies aérogel, nanofibres ou « loosetubes ») et conducteurs électroniques (dopés au niobium Nb ou à l’antimoine Sb). Le support permettant d’atteindre les meilleures propriétés électrocatalytiques est un aérogel de SnO₂ dopé à l’antimoine, noté ATO. En particulier, l’électrocatalyseur Pt/ATO présente une activité spécifique vis-à-vis de l’ORR supérieure à celle d’un électrocatalyseur Pt/carbone Vulcan® synthétisé dans les mêmes conditions, suggérant des interactions bénéfiques entre les nanoparticules de Pt et le support oxyde métallique (Strong Metal Support Interactions, SMSI).Des tests de durabilité simulant le fonctionnement d’une PEMFC en conditions automobile ont été effectués en électrolyte liquide à 80 °C sur ces deux électrocatalyseurs : cyclage entre 0,60 et 1,00 V vs l’électrode réversible à hydrogène (RHE) ou entre 1,00 et 1,50 V vs RHE. Le catalyseur Pt/ATO présente une durabilité accrue par rapport au catalyseur Pt/carbone Vulcan® de référence. Cependant, de nouveaux mécanismes de dégradation ont été mis en évidence dans cette étude : tout d’abord, l’élément dopant Sb est progressivement dissout au cours du vieillissement électrochimique, ce qui implique une perte de conductivité électronique. Cette perte est en partie liée à des incursions à bas potentiel, notamment durant les caractérisations électrochimiques. De plus, entre 5 000 et 10 000 cycles de vieillissement électrochimique (entre 0,60 et 1,00 V vs RHE ou entre 1,00 et 1,50 V vs RHE à 57 °C), le matériau support perd sa structure poreuse et forme un film amorphe peu conducteur. / Conventional electrocatalysts used in proton exchange membrane fuel cells (PEMFC) are composed of platinum nanoparticles supported on high specific surface area carbon blacks. At the cathode side of the PEMFC, where the oxygen reduction reaction (ORR) occurs, the electrochemical potential can reach high values - especially during startup-shutdown operating conditions - resulting in irreversible degradation of the carbon support. A “material” solution consists of replacing the carbon with supports based on metal oxides. The latter have to be resistant to electrochemical corrosion, be electronic conductor and have a porous and nano-architectural structure (for the transport of reagents and products and the homogeneous distribution of the ionomer and platinum nanoparticles).In this work, we have developed and characterized electrocatalysts composed of platinum (Pt) nanoparticles based on tin dioxide (SnO2) and titanium dioxide (TiO2) with optimized textural (aerogel, nanofibres or loosetubes morphologies) and electron-conduction properties (doped with niobium Nb or antimony Sb). The best electrocatalytic properties are reached for an antimony-doped SnO2 aerogel support, denoted ATO. The Pt/ATO electrocatalyst has especially a higher specific activity for the ORR than a Pt/carbon Vulcan® electrocatalyst, synthesized in the same conditions, suggesting beneficial interactions between the Pt nanoparticles and the metal oxide support (Strong Metal Support Interactions SMSI).Durability tests simulating automotive operating conditions of a PEMFC were carried out in liquid electrolyte at 57 °C on these two electrocatalysts by cycling between 0.60 and 1.00 V vs the reversible hydrogen electrode (RHE) or between 1.00 and 1.50 V vs RHE. The Pt/ATO electrocatalyst has an increased stability compared to the reference Pt/carbon Vulcan® electrocatalyst. However, new degradation mechanisms were highlighted in this study: first, the doping element (Sb) is progressively dissolved during electrochemical ageing, which implies a loss of electronic conductivity. This loss is partly due to incursions at low potential, including during electrochemical characterizations. Moreover, between 5,000 and 10,000 cycles of the accelerated stress tests (between 0.60 and 1.00 V vs RHE or between 1.00 and 1.50 V vs RHE at 57 °C), the support loses its porous structure and forms a poorly conductive amorphous film.

Le développement de catalyseurs de la réaction de dégagement de l’oxygène (OER) pour les électrolyseurs à membrane échangeuse de protons (PEM) dépend de la compréhension du mécanisme de cette réaction. Cette thèse est consacrée à l'application de la spectroscopie d’émission de photoélectrons induits par rayons X (XPS) et de la spectroscopie de structure près du front d'absorption de rayons X (NEXAFS) operando sous une pression proche de l'ambiante (NAP) dans le but d’étudier les mécanismes de la réaction d’oxydation de l’eau sur des anodes à base d’iridium et de ruthénium et leurs dégradation dans les conditions de la réaction. Cette thèse montre les mécanismes différents de la réaction OER pour les anodes à base d’Ir et de Ru impliquant respectivement des transitions anioniques (formation d’espèce OI- électrophile) ou cationiques (formation des espèces de Ru avec l’état d'oxydation supérieur à IV) quelle que soit la nature (thermique ou électrochimique) des oxydes. / Development of oxygen evolution reaction (OER) catalysts for proton exchange membrane water electrolysis technology depends on the understanding of the OER mechanism. This thesis is devoted to the application of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and near edge X-ray absorption fine structure (NEXAFS) techniques for operando investigation of the Ir, Ru - based anodes. For Ru-based systems, we observe the potential-induced irreversible transition of Ru (IV) from an anhydrous to a hydrated form, while the former is stabilized in the presence of Ir. Regarding single Ir-based anodes, the analysis of O K edge spectra reveals formation of electrophilic oxygen OI- as an OER intermediate. Higher stability of Ir catalysts supported on antimony-doped tin oxide (ATO) is related to their lower oxidation. This work demonstrates different OER mechanisms on Ir, Ru-based anodes involving anion and cation red-ox chemistry, correspondingly, regardless the oxide nature.