Fabrizio Creazzo

Réaction d'évolution de l'oxygène aux interfaces d'oxides de cobalt/eau liquide : électrocatalyse hétérogène par simulations de DFT-MD et de metadynamique: Dans cette thèse, des simulations DFT-MD couplées à des techniques inno-vantes de métadynamique, sont appliquées pour acquérir une compréhensionglobale des interfaces aqueuses d'oxyde de cobalt Co3O4 et CoO(OH) dansla catalyse de la réaction d'évolution de l'oxygène (OER), et ainsi éventuellement aider à la conception de nouveaux catalyseurs basés sur des matériaux non précieux, un domaine clé de la recherche scientifique et technologique, particulièrement important pour l'économie de l'hydrogène, pour les technologies vertes dans une période de temps avec une demande toujours plus croissanteen énergie verte. Dans cette thèse, nous révélons étape par étape les mécanismes de l'OER sur les électrocatalyseurs aqueux d'oxyde de cobalt Co3O4 etCoO(OH) via de nouvelles techniques de métadynamique.Jusqu'à présent, la littérature n'a jamais pris en compte les modificationsau niveau atomique de la structure des électrodes ainsi que de l'eau interfaciale dans leur modélisation des processus OER. Ce manque de connaissances représente clairement un obstacle important au développement de catalyseurs améliorés, qui pourrait être surmonté en utilisant des méthodes capables de suivre les caractéristiques catalytiques de l'OER à l'échelle atomique. Pour la première fois, nous montrons combien il est important de prendre en considération la présence de l'environnement aqueux dans la caractérisation structurale des surfaces du catalyseur, c'est-à-dire (110)-Co3O4 et (0001)-CoO(OH) dans ce travail. Une caractérisation détaillée des propriétés chimiques et physiques des interfaces aqueuses est fournie (la structure, la dynamique, la spectroscopie, le champ électrique), pour les surfaces (110)-Co3O4 et (0001)-CoO(OH) en contact avec l'eau liquide.Une étude détaillée de l'OER est présentée non seulement du point de vue descatalyseurs, mais aussi en abordant le rôle de l'environnement de l'eau dans leprocessus catalytique, ce qui n'a pas été fait auparavant dans la littérature. En conséquence, l'OER en phase gazeuse et en phase liquide sont étudiés ici auxinterfaces aqueuses (110)-Co3O4 et (0001)-CoO(OH) en adoptant une nouvelleapproche de métadynamique d'échantillonnage amélioré, capable d'identifieret caractériser les mécanismes de réaction chimique et d'intégrer pleinement lerôle des degrés de liberté du solvant, permettant ainsi de dévoiler des réactivités chimiques d'une complexité remarquable. L'énergétique, la cinétique et la thermodynamique derrière l'OER sont donc trouvées à ces surfaces d'oxyde de cobalt à l'interface avec l'eau.

Integration of Ru(bda) [bda = (2,2'-bipyridine)-6,6'-dicarboxylate] water oxidation catalysts together with dibenzofuran, dibenzothiophene, or carbazole heterocycles within macrocycles 1-3 affords structures with different conformational preferences. The latter are dictated by noncovalent interactions of the bda oxygens with NH (hydrogen bond) or S (chalcogen bond). The different orientations afford changes in the secondary coordination sphere, thereby influencing the rate and mechanism of photocatalytic water oxidation for the three mononuclear Ru(bda)-based catalysts, with the dibenzothiophene- and carbazole-based ones favoring the unimolecular pathway (first-order kinetics), typically related to water nucleophilic attack (WNA), and the dibenzofuran one operating via a bimolecular pathway (second-order kinetics), typically related to the interaction of two metal-oxo species (I2M). NMR and single crystal X-ray analyses provided insight into the conformational preferences of the precursor macrocycles in the Ru(II) state. Photocatalytic studies including the H/D kinetic isotope effect (KIE) in deuterated water together with theoretical studies on the orientation angle-dependent energy profile for macrocycles in the Ru(V) state afforded a structure-property relationship that explains the outcome of the water oxidation experiments.

Herein, comprehensive modeling and investigation of bulk, monolayers, and heterostructures of 2D transition metal dichalcogenides (TMDs) MoSe₂ and WSe₂ have been provided by state-of-the-art spin-polarized density functional theory (DFT) simulations. This work aims to support the rational design of TMD-based (photo)electrocatalysts for water splitting by incorporating a more realistic description of the catalyst-electrolyte interface. Unlike conventional static or implicit-solvent models, an explicit water environment has been considered at the interface with MoSe₂ and WSe₂ monolayers and heterostructures, moving beyond the usual idealized vacuum modeling. Our approach allows for explicit, atomistic interactions at the catalyst-liquid interface at a given temperature, revealing a more realistic modeling and dynamic assessment of interfacial structures. Our simulations reveal that both MoSe₂ and WSe₂ exhibit water-repellent behavior, yet preferential hydrogen bonding emerges at specific surface sites. These localized interactions may enhance the catalytic surface activity, underscoring the relevance of capturing interfacial water dynamics in computational models. The study underscores the importance of accounting for explicit liquid water dynamics in DFT-based investigations aiming to engineer monolayer/heterostructure catalytic properties accurately. Here, the key ability to simulate and analyze realistic aqueous environments interacting with semiconducting 2D materials allowed predicting and tuning key interfacial properties, such as electronic structure, water organization, surface electric field, and work function, for the engineering and modeling of enhanced MoSe₂ and WSe₂-based interfaces. The lattice parameters, bulk modulus, and electronic structure were also investigated for bulk MoSe₂ and WSe₂, which yielded results that are in agreement with the available experimental data. Overall, our study demonstrates that realistic, temperature-dependent simulations of solid-liquid interfaces provide critical insight into the physicochemical behavior of 2D semiconducting catalysts. A similar approach can be applied to other complex facets and interfaces of interest and, hence, possibly help in the design of novel catalysts.

Nuclear quantum effects on the air–water interface via path-integral ab initio molecular dynamics (PI-AIMD).

DFT-based molecular dynamics simulations of the electrified air–liquid water interface are presented, where a homogeneous field is applied parallel to the surface plane. We unveil the field intensity for the onset of proton transfer and molecular dissociation; the protonic current/proton conductivity is measured as a function of the field intensity/voltage. The air–water interface is shown to exhibit a proton conductivity twice the one in the liquid water for field intensities below 0.40 V Å⁻¹. We show that this difference arises from the very specific organization of water in the binding interfacial layer (BIL, i.e. the air–water interface region) into a 2D-HBond-network that is maintained and enforced at the electrified interface. Beyond fields of 0.40 V Å⁻¹, water in the BIL and in the bulk liquid are aligned in the same way by the rather intense fields, hence leading to the same proton conductivity in both BIL and bulk water.

Within the general context of the electrochemical oxygen evolution reaction of the water oxidation/electrolysis, we focus on one essential aspect of electrochemical interfaces, i.e., the comprehension of the interaction and organisation of liquid water at the (semiconductor) (110)-Co₃O₄ surface using density functional theory-molecular dynamics simulations. A detailed characterization of the chemical and physical properties of the aqueous interface is provided in terms of structure, dynamics, electric field, work function, and spectroscopy, as a preliminary step into the modelling of the (110)-Co₃O₄ aqueous surface in more relevant electrochemical conditions. The water at the aqueous B-termination is, in particular, shown more dynamical than that at the A-termination and more “undisciplined”: the water is indeed mostly an HB-acceptor with the solid, with an orientation of their dipole moments found opposite the field generated by the negative surface charge. At both aqueous interfaces, the work function is twice lower than that at the bare (non-hydroxylated) surfaces. The SFG (Sum Frequency Generation) spectroscopy is shown dominated by the water in the diffuse layer, while the SFG signal from the binding interfacial layer reflects the single orientation of water at the aqueous A-termination and the two orientations of water at the aqueous B-termination.