Made available in DSpace on 2014-10-09T12:42:37Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:33Z (GMT). No. of bitstreams: 0 / Este trabalho teve como objetivo a combinação de ânodos e eletrólitos otimizados, para a formação de células a combustível de etanol direto (DEFC), operantes em elevadas temperaturas (130 ºC). Como materiais de ânodo, foram produzidos eletrocatalisadores baseados em PtSn/C, com diversas razões atômicas Pt:Sn, preparados pelo método do poliol modificado, essa metodologia possibilita a produção de eletrocatalisadores auto-organizados com estreita distribuição de tamanhos de partículas e elevado grau de liga. Os eletrocatalisadores foram caracterizados por DRX e stripping de CO. Os resultados mostraram que esses materiais apresentaram elevado grau de liga e Eonset de oxidação de CO em potenciais menores do que os materiais comerciais. Como eletrólito, foram sintetizados híbridos Nafion-SiO2 com a incorporação do óxido diretamente nos agregados iônicos de diversos tipos de membranas Nafion. Os parâmetros de síntese, tais como o solvente em meio solgel, a espessura da membrana, e a concentração do precursor de sílica foram avaliados em termos do percentual de sílica incorporada e da estabilidade mecânica do híbrido. Por fim, ânodos e eletrólitos otimizados foram avaliados em DEFCs nas temperaturas de 80 e 130 ºC. Os resultados mostraram um significativo incremento no desempenho de polarização (122 mW cm-2), resultado da aceleração na taxa de oxidação de etanol devido ao material de ânodo otimizado e do aumento de temperatura de operação, uma vez que o uso de eletrólitos híbridos possibilita o aumento da temperatura sem perdas de condutividade. Nesse sentido, a combinação de eletrodos e eletrólitos otimizados é uma alternativa promissora para o desenvolvimento de tais dispositivos. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Complexos polipiridínicos de rutênio mononuclares vem sendo ativamente estudados como catalisadores da reação de oxidação de água a oxigênio, mas o complexo ativado dos catalisadores mais eficientes envolve a formação de um dímero, indicando a importância da estrutura binuclear para ativação dos mesmos. Assim, nesta tese propomos o estudo dos possíveis efeitos sinérgicos em complexos binucleares de rutênio polipiridinas angulares para ativação das espécies de alta valência do tipo RuV=O e RuIV=O. Assim, foram preparadas séries de complexos polipiridínicos de rutênio empregando os ligantes tridentados derivados de terpiridinas e bidentados tipo bipiridina na forma cloro complexos e aqua complexos mono e binucleares, capazes de atuar como precursores das espécies ativas de alta valência por meio de reações de transferência de elétrons acoplado a transferência de prótons (PCET). Os complexos [RuCl(bpy)(phtpy)](PF6), [Ru2Cl2(bpy)2(tpy2ph)](PF6)2 e [Ru2Cl2(Clphen)2(tpy2ph)](PF6)2 (phtpy= 4\'-fenil-2,2\':6\',2\'\'-terpiridina, bpy= 2,2´-bipiriridina, Clphen= 5-cloro-1,10-fenantrolina e tpy2ph= 1,3-bis(4\'-2,2\':6\',2\'\'-terpiridil)benzeno) e seus aqua complexos foram sintetizados e caracterizados por técnicas espectroscópicas e eletroquímicas. Os complexos [RuCl(bpy)phtpy](PF6), [Ru2Cl2(bpy)2(tpy2ph)](PF6)2 e [Ru2Cl2(Clphen)2(tpy2ph)](PF6)2 apresentam apenas reações de transferência de elétrons onde o estado de oxidação máximo do íon rutênio é 3+. Todavia, os respectivos aqua complexos [Ru(H2O)(bpy)(phtpy)](PF6)2, [Ru2(H2O)2(bpy)(tpy2ph)](PF6)4 e [Ru2(H2O)2(Clphen)2(tpy2ph)](PF6)4 podem ser oxidados de modo a gerar complexos de alta valência com íon rutênio nos estados de oxidação 4+ e 5+ via reação de transferência eletrônica acoplada a transferência de prótons (PCET). Os complexos de RuIV=O são gerados em potenciais relativamente baixos e não apresentaram atividade eletrocatalítica significativa, enquanto que as espécies RuV=O ([RuV(O)(bpy)(phtpy)]3+ e [Ru2V(O)2(bpy)2(tpy2ph)]6+) atuam como catalisadores eficientes para a reação de oxidação da água a oxigênio. Os valores de TOF para os complexos binuclear (0,97 s-1) é cerca de três vezes maior que para o complexo mononuclear (0,32 s-1), confirmando a presença de efeitos sinérgicos que aceleram a liberação de oxigênio no complexo binuclear. As propriedades eletrocatalíticas dos complexos polipiridínicos de rutênio de alta valência foram transferidos para a superfície de eletrodos via eletropolimerização redutiva do complexo [Ru2(H2O)2(Clphen)2(tpy2ph)](TfO)4. Neste caso foram observadas a geração eletroquímica de espécies contendo o íon rutênio nos estados de oxidação 2+, 4+ e 5+, enquanto que a espécie no estado 3+ aparentemente não é estável e sofre desproporcionamento. O eletrodo modificado preservou a alta atividade eletrocatalítica do aqua complexo binuclear para a reação de oxidação da água (TOF de 0,80 s-1) e também para a oxidação de álcool benzílico a benzaldeído, com kRuIV= 14,70 L·mol-1 s-1 demonstrando o elevado potencial do material para a oxidação de substratos orgânicos. / Mononuclear ruthenium polypyridyl complexes have been studied as catalysts of oxygen evolution in water oxidation reaction, but the activated complex of most efficient catalysts assume the formation of dimers indicating the importance of the binuclear structure for their activation. Thereby, in this thesis we propose the study of possible synergistic effects in binuclear ruthenium polypyridyl complexes in order to activate species with high valence as RuV=O and RuIV=O for multi-electronic catalytic oxidation reactions. For this purpose, it was prepared a series of ruthenium polyppyridyl complexes using tridentate ligands based in terpyridine and bidentate bipyridine generating binuclear chloride complexes and aqua complexes which are able to act as precursors of the respective high valence active species generated by proton coupled electron transfer (PCET) reactions. The [RuCl(bpy)(phtpy)](PF6) and [Ru2Cl2(bpy)2(tpy2ph)](PF6)2 complexes (phtpy= 4\'-phenyl-2,2\':6\',2\'\'-terpyridine, bpy= 2,2´-bipyridine and tpy2ph= 1,3-bis(4\'-2,2\':6\',2\'\'-terpyridin-4-yl)benzene) and their respective aqua complexes were synthetized and characterized by spectroscopic and electrochemical techniques. The chloro complexes [RuCl(bpy)(phtpy)](PF6), [Ru2Cl2(bpy)2(tpy2ph)](PF6)2 and [Ru2Cl2(Clphen)2(tpy2ph)](PF6)2 (Clphen= 5-Chloro-1,10-phenanthroline) show only electron transfer reactions where the maximum oxidation state of the ruthenium ion is 3+. However, the respective aqua complexes [Ru(H2O)(bpy)(phtpy)](PF6)2, [Ru2(H2O)2(bpy)2(tpy2ph)](PF6)4 and [Ru2(H2O)2(Clphen)2(tpy2ph)](PF6)4 can be oxidized further by proton coupled electron transfer (PCET), generating high valence complexes where the ruthenium oxidation state can be 4+ and 5+. Complexes of RuIV=O are generated in relatively low potentials and do not presented significant electrocatalytic activity for oxidation of water to dioxygen, whereas the RuV=O species ([RuV(O)(bpy)(phtpy)]3+ and [Ru2V(O)2(bpy)2(tpy2ph)]6+) showed to be efficient catalysts for the reaction of water oxidation. The values of TOF for the binuclear complexes (0,97 s-1) were about three times larger than for the mononuclear complex (0,32 s-1), confirming the presence of synergistic effects accelerating the formation and release of oxygen by the binuclear complex. The electrocatalytic properties of high valence ruthenium polypyridyl complexes were transferred to electrodes surface by reductive electropolymerization of the [Ru2(H2O)2(Clphen)2(tpy2ph)](TfO)4 complex. In this case the electrochemical generation of ruthenium 2+, 4+ and 5+ species were observed whereas the 3+ species was not stable and disproportionated. The modified electrodes preserved the high electrocatalytic activity of the binuclear aqua complexes for water oxidation reaction (TOF de 0,80 s-1), and also for oxidation of benzyl alcohol to benzaldehyde with kRuIV= 14,70 L mol-1 s-1 demonstrating the high catalytic efficiency for oxidation of organic substrates.

O presente trabalho apresenta um estudo sistemático sobre a adsorção e a eletrooxidação do CO sobre eletrodos monocristalinos de platina. A partir da análise das intensidades das bandas integradas e das freqüências do Pt(111)-CO, apresenta-se uma interpretação dos efeitos de acoplamento dipolo-dipolo e de interconversão do COads.. Assim, sobre a Pt(111) os espectros de FTIR in situ mostram que o aumento na razão da intensidade das bandas integradas ACOB/ACOL e nas freqüências do νCOB quando θCO,total diminue é devido à redução do acoplamento dipolo-dipolo entre as moléculas do CO em diferentes sítios e, adicionalmente, à interconversão das formas inclinadas dos COL e COB para a forma do COB. No sentido de explicar esta interconversão, propomos um mechanism baseado nas interações dos orbitais de fronteiras do CO e do metal, associado com a retrodoação de elétrons. Nesse modelo, os deslocamentos das formas inclinadas do COL e do COB em direção à forma do COB são favoráveis provavelmente porque a retrodoação de elétrons, Ptd → CO2π* (LUMO), aumenta quando θCO,total diminui. Experimentos potenciostáticos sugerem que a cinética de nucleação e crescimento é o melhor modelo para descrever a eletrooxidação do CO. Propomos que no potencial de oxidação, ECO oxi. pode existir uma via muito rápida de formação do precursores oxigenados e que este pode lateralmente colidir com as ilhas de CO, impedindo que ocorra a dissipação das ilhas do COads. no potencial de oxidação, ECO oxi.. Apresentamos a evolução do crescimento e da oxidação de sub-monocamada de CO sobre monocristais de platina facetados. Em baixo grau de recobrimento do CO foi observado que a adsorção dessa molécula ocorre sem ocupação preferencial de sítios quinas ou terraças. Assim, sugerimos que a adsorção é um processo randômico e que depois que as moléculas do CO são adsorvidas estas não apresentam apreciáveis deslocamentos a partir de CO-(111) em direção aos sítios CO-(110). Isto significa que depois da adsorção, as moléculas do CO têm um longo tempo de residência ou que apresentam um coeficiente de difusão muito baixo. Mas, para alto grau de recobrimento por CO, os resultados mostram que é possível que laterais interações desempanham importantes papéis na distribuição de ocupação dos sítios e observamos que durante a eletrooxidação, são liberados simultaneamente sítios quinas e sítios terraços. Quanto à pré-oxidação, foi observado que quatro condições experimentais precisam ser satisfeitas para que ela ocorra sobre os monocristais de platina: (i) alto grau de recobrimento por CO; (ii) que a superfície onde oncorre a oxidação do CO tenha defeitos, como sítios quinas (110); (iii) que a camada do CO seja formada sob potenciais mais negativos do que o potencial de carga total zero do metal; (iv) e que exista pequena quantidade de CO dissolvido. As condições (i) e (ii) precisam ser satisfeitas simultaneamente para promover a pré-oxidação do CO; as condições (iii) e (iv) essencialmente contribuem correspondendo à condição (i). Observamos que a magnitude do pre-pico aumenta com o aumento do grau de recobrimento por CO. Então, isto pode ser indicativo que a pré-oxidação não tem relação com a difusão do CO em superfície porque o aumento do grau de recobrimento reduz a probabilidade de difusão em superfície. O modelo de ilhas comprimidas parece ser mais apropriado para descrever a pré-oxidação do CO. / This work presents a systematic study on the CO adsorption and its oxidation at platinum single crystal electrodes. From analysis of integrated band intensity and band frequency position of the Pt(111)-CO interface in acid, it is presented an interpretation of the dipole-dipole coupling effect and surface site inter-conversions of COads.. Thus, on Pt(111), in situ FTIR data show that the increase in both ratio integrated band intensity ACOB/ACOL and frequency of νCOB when θCO,total reduces it is indicative of reduce in dipole-dipole coupling interactions between CO molecules in different surface active sites and a mechanism where the tilted COL and COB in CO pressed adlayer displace or inter-convert in favor of increase of COB concentration. In order to explain that CO interconversion, we propose a mechanism based in frontier molecular orbitals of CO and the orbitals of the metal associated with the electron back bond donation. Thus, the displacement of tilted COL and COB on the surface towards COB is more stable because probably the back bond electron donation, Ptd → CO2π* (LUMO), increase when θCO,total diminishes. Potentiostatic experiments suggest that the nucleation and growth is the better model to describe the CO oxidation. It is proposed here that close to ECO oxi. might there is a fast pathway toward formation of oxygenated species and it might reach the CO islands by side and this hinder the dissipation of COads. islands at ECO oxi.. We report also time evolution studies of low CO adsorption coverage and oxidative stripping on stepped platinum surfaces. In low CO coverage, it was observed that there is no preferential site occupancy for CO adsorption on step or terrace. It is proposed that CO adsorption onto these surfaces is a random process, and after CO adsorption there is no appreciable shift from CO-(111) to CO-(110) sites. This implies that after adsorption, CO molecules either have a very long residence time, or that the diffusion coefficient is much lower than previously thought. But, in high CO coverage, the results show that it is possible that the lateral interaction might play important role in CO site occupancy and it was observed that during the CO electrooxidation the sites released included both terrace (111) and step (110) orientations. Among the CO oxidation a clear CO preoxidation process also occurs. It was observed four experimental conditions which were verified to be fulfilled to promote CO pre-oxidation on platinum single crystal: (i) the CO coverage is should be higher than minimum threshold; (ii) the surface where CO oxidation take place should have defects, such as (110) steps; (ii) the CO monolayer should be formed at potentials below the potential of zero total charge; (iv) and in a small amount of dissolved CO should be present in the electrolyte solution. In both conditions (i) and (ii) are necessary to take place simultaneously to promote CO pre-oxidation, (iii) and (iv) essentially contribute in fulfilling condition (i). It was verified that the magnitude of pre-peak increases with the amount of CO coverage. Thus, this might indicate that the CO pre-oxidation is not having relationship with the CO diffusion on the surface, because the increase of CO coverage diminishes surface diffusion. A picture model of compressed CO islands seems the most to describe CO pre-oxidation.

La réalisation de microsystèmes de multidétection et sans marquage pour la reconnaissance de biomolécules est d'un intérêt fondamental pour la réalisation de tests rapides dédiés au diagnostic biologique. Ces développements nécessitent une méthode d'adressage des sondes de capture sur une plateforme multiplexée associée à une méthode d'analyse sensible. Dans cette étude, la méthode de détection choisie pour les tests développés sur la puce est la voltampérométrie cyclique, et le férrocène a été utilisé pour la modification de sondes oligonucléotidiques de type tige-boucle. Une stratégie d'électroadressage a été développée sur surface d'or. Elle a été réalisée via chimie « click » entre un alcyne et un azoture. Cette réaction peut être électro-catalysée en maintenant le catalyseur cuivre sous sa forme active par l'application d'un potentiel à l'électrode. Une première entité chimique de petite taille, constituée de deux groupements dithiol phosphate et d'un groupement hexynyle a été synthétisé par synthèse supportée et greffée sur électrode d'or. Par la suite, différents éléments ont été immobilisés par chimie « click ». Un dérivé ferrocène porteur d'une fonction azoture a été utilisé pour la détermination des conditions optimales de cette chimie. Puis, cette méthode a été exploitée pour l'immobilisation de nanoparticules fluorescentes et de protéines par l'intermédiaire de la formation du complexe biotine/streptavidine. Enfin, cette méthode a permis l'électroadressage de sondes de capture oligonucléotidiques de type tige-boucle, modifiées par des ferrocènes. Des tests d'hybridation ADN ont été menés en milieu complexe avec une limite de détection déterminée à 100fM / This production of microsystem for label-free multi detection of biomolecules is fundamental for the realization of rapid tests dedicated to laboratory diagnosis. A viable method is requires to both address capture probes and to be associates with a sensitive analysis on multiplexed platform. In this study, the method chosen for detection on electrode is cyclic voltammetry, and ferrocene was used to modify stem-loop oligonucleotides. A strategy was developed for the electroadressing of probes on gold surface. It is performed through chemistry “click” between an alkyne and an azide. This reaction may be catalyzed by maintaining the correct potential to the electrode to form an active copper oxidation state on the surface. A first small chemical entity, containing two phosphate dithiol moieties and a hexynyl moiety was synthesized by supported chemistry and grafted on gold electrode. Thereafter, various elements were immobilized by chemistry “click”. Ferrocene derivative carrying an azide function was used to determine the optimal conditions for this chemistry. Then, this method has been exploited for the immobilization of proteins and fluorescent nanoparticles via the formation of biotin/streptavidin complex. Finally, this method allowed to electroaddress stem-loop oligonucleotids, designed as capture probes, modified by ferrocene. DNA hybridization tests were conducted in complex environments with a detection limit determined at 100 fM

Le dihydrogène se présente comme un vecteur énergétique d'avenir pour la diversification des sources de production d'énergie. L'électrolyse de l'eau dans le système PEMWE (Proton Exchange Membrane Water Electrolyzer) permet l'obtention de dihydrogène de grande pureté. Les atouts de cette technologie induite par l'utilisation d'assemblage membrane électrode (AME) permettent son couplage aux énergies renouvelables. Toutefois, l'amélioration de l'activité catalytique des matériaux anodiques et leur stabilité pour baisser la tension de cellule et la diminution de la teneur en métaux nobles dans la composition des matériaux sont nécessaires.Lors de ces travaux de thèse, une voie de synthèse a été élaborée pour préparer des nanomatériaux à base de ruthénium. L'ajout d'iridium a permis dans un premier temps de prévenir l'oxyde de ruthénium de la dissolution tout en maintenant l'activité du catalyseur initial. Les meilleures performances catalytiques des AMEs en termes de densité de courant, de tension de cellule et de durabilité ont été délivrées avec les matériaux anodiques dont la composition molaire en Ru est supérieure à 70 %. La substitution partielle des métaux précieux (Ru et Ir) par du cérium et du niobium dans le but de proposer des catalyseurs à moindre coût a été aussi réalisée. Contrairement au niobium qui apporte une phase amorphe dans la structure du matériau, le cérium jusqu'à une teneur de 10 % permet de conserver les performances de l'anode telles que obtenues dans le matériau bimétallique. Le cérium se présente donc comme un métal prometteur à intégrer de manière appropriée dans la composition des matériaux anodiques. / Hydrogen seems to be the most promising energetic vector in order to diversify the sources of energy production. Water splitting in a Proton Exchange Membrane Water Electrolyzer (PEMWE) provides a sustainable way of producing clean hydrogen. One of the main advantages of this technology based on the utilization of Membrane Electrode Assembling (MEA) is its potential coupling with renewable energy sources. However, the improvement of the catalytic activity of anode materials, their stability and the reduction of the noble metal content in their composition are required.During this thesis work, a new synthesis approach that consists in hydrolysis of metallic precursors in ethanol medium has been undertaken to prepare non-supported ruthenium-based nanomaterials. The addition of iridium to the nanocatalysts composition prevents the ruthenium oxide from dissolution without decreasing the initial activity of the anode catalyst. The best catalytic performance of MEAs in terms of current density, cell voltage and durability were observed with anode materials whose ruthenium molar composition is higher than 70 %. The partial substitution of precious metals (Ru and Ir) either by cerium or niobium with the purpose of decreasing the catalysts cost was also attempted. While the substitution with niobium introduces an amorphous phase in the material structure, the trimetallic materials containing cerium were shown to be crystalline. Furthermore, cerium contents up to 10 % allows maintaining the catalytic activity of the trimetallic anode close to that obtained with the bimetallic oxide material. Thus cerium appears as a promising metal to include in a suitable way on the composition of anode materials.

Ce travail a porté sur l'élaboration de matériaux plurimétalliques et l'étude de leurs propriétés électrocatalytiques. Les matériaux monométalliques (Pt/C, Pd/C, Au/C), bimétalliques à base de métaux nobles (PtxAu1 x/C, PtxPd1 x/C et PdxAu1 x/C) et non nobles (PtxNi1 x/C, PtxCo1 x/C et PtxCu1 x/C) ont été dans un premier temps synthétisés par la méthode microémulsion « water-in-oil ». Une attention particulière a été portée sur les caractérisations physicochimiques et électrochimiques des matériaux synthétisés afin d'accéder à leur microstructure, la taille moyenne de leurs particules, leur morphologie, leur taux de charge sur le support carboné ou encore la composition atomique de volume et de surface de leurs nanoparticules. Leurs propriétés électrocatalytiques et leur sélectivité pour la réaction de réduction du dioxygène ont été étudiées en milieu HClO4 0,1 M à l'aide d'une électrode à disque tournant. Il a été montré que l'ajout du palladium ou du l'or au platine conduit à une diminution progressive de l'activité catalytique à l'exception du catalyseur Pt90Au10/C. Les catalyseurs PdxAu1 x/C ont montré de faibles activités catalytiques avec l'ajout de l'or. En revanche, les catalyseurs bimétalliques PtxNi1 x/C et PtxCo1 x/C ont montré une amélioration de l'activité électrocatalytique par rapport au platine pur. L'addition du cuivre au platine (PtxCu1 x/C) a permis une légère améliorer l'activité électrocatalytique sur un intervalle de potentiel compris entre 1,05 et 0,93 V / ERH. Tous les catalyseurs ont montré une sélectivité pour la formation de l'eau à l'exception des catalyseurs PtxAu1 x/C et PdxAu1 x/C qui ont montré une sélectivité pour la formation du péroxyde d'hydrogène lorsque la teneur en or devient importante. A partir des résultats obtenus sur les catalyseurs bimétalliques, une formulation des matériaux trimétalliques (PtxMyAuz/C, M= Co, Cu, Ni, Pd) a été réalisée. Ensuite, les propriétés physicochimiques et électrochimiques de ces matériaux ont été étudiées. Les propriétés catalytiques de ces matériaux ont été étudiées. Il en ressort que le catalyseur Pt60Ni20Au20/C conduit à l'activité maximale. Tous ces catalyseurs ont montré une sélectivité pour la formation de l'eau. L'étude de stabilité par cyclage potentiométrique sur les catalyseurs trimétalliques a révélé que le catalyseur Pt60Cu20Au20/C présente une meilleure stabilité que le platine et les autres catalyseurs trimétalliques. Une ségrégation de l'or en surface a été observée sur les matériaux après cyclage potentiométrique. / This work has focused on the development of polymetallic catalysts and study of their electrocatalytic properties. The monometallics catalysts (Pt/C, Pd/C and Au/C) and the binary catalysts based on noble metals (PtxAu1 x/C, PtxPd1 x/C and PdxAu1 x/C) and non-noble metals (PtxNi1 x/C, PtxCo1 x/C and PtxCu1 x/C) have been synthesized using the « water-in-oil » microemulsion method. Investigation of the physicochemical and the electrochemical characterization of the synthesized materials has been conducted in details to findout their microstructure, their average particles sizes, their morphology, their metal loading on the carbon support or their bulk and the surface composition of their nanoparticles. The electrocatalytic properties and the selectivity toward the oxygen reduction reaction of these catalysts have been studied using a rotating disc electrode in 0.1 M aqueous HClO4 saturated with oxygen. The results demonstrate that the addition of palladium or gold to platinum (PtxAu1 x/C and PtxPd1 x/C) led to the constant decrease of the electroalalytic activity with an increase of Pd or Au ratio, except for the Pt90Au10/C. The PdxAu1-x /C catalysts showed low catalytic activity with the addition of gold. However, the bimetallic catalysts PtxNi1-x/C and PtxCo1-x/C showed improved electrocatalytic activities compare with pure platinum. The addition of copper to the platinum (PtxCu1-x/C) resulted in a slight increase of the electrocatalytic activity on a potential range between 1.05 and 0.93 V vs. RHE. All catalysts have shown selectivity for water formation except PtxAu1-x/C and PdxAu1-x/C catalysts, which showed selectivity for the formation of hydrogen peroxide by increasing of gold content. According to the results obtained from the binary catalysts, ternary catalysts (PtxMyAuz/C, M = Co, Cu, Ni, Pd) were made. The physicochemical and the electrochemical properties of these catalysts have been studied. The study of the catalytic activity of these catalysts showed that the best activity is obtained Pt60Ni20Au20/C. All of these catalysts have showed selectivity for water formation. The ageing tests have been carried out by conducting potentiometric cycling, showing that Pt60Cu20Au20/C catalyst has a better stability than the platinum and the other trimetallic catalysts. The gold segregation from the bulk to the surface of nanoparticles was observed on these catalysts, after potentiometric cycling.

Une méthode de dépôt de platine sur or a récemment été développée. Le substrat est, dans une première phase, modifié par un dépôt d’un métal moins noble que le platine, tel que le cuivre ou le plomb. Ce dépôt métallique est, dans une seconde phase, mis en contact avec une solution de sel de platine et la substitution spontanée du cuivre ou du plomb par du platine métallique se produit.<p><p>\ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Différents systèmes polyoxométallates@M-colorants ont été réalisés dans cette thèse pour électrochimique dégagement d'hydrogène catalytique et génération photocourant.• Des films hybrides, basés sur des interactions électrostatiques entre une porphyrine tetracationique et des nanoparticules stabilisées par des POMs du type POM@Pt sur ITO, ont été formés par la méthode dite couche par couche et ont été utilisés pour la génération de H2 ou de photocourant. • Pour améliorer le transfert de charge entre les nanoparticules POM@M et le substrat, la réduction de l'oxyde de graphène a été réalisée pour former des systèmes hybrides rGO/POM@Pt. Le dégagement d'hydrogène a été mesuré.• Les copolymères polycationiques bis-porphyrine ont également été obtenus par électropolymérisation avec des espaceurs bis-pyridinium. Par réaction de métathèse, l’incorporation avec divers POM de type Keggin ou des nanoparticules du type POM@Ag ont ensuite été realise. Leurs performances photovoltaïques ont ensuite été étudiées.• Enfin des films hybrides PEDOT dopés avec des nanoparticules du type POM@M ont également été fabriqués. Les performances photovoltaïques ont été examinés montrant une forte amélioration sous illumination dans le domaine du visible. L’ensemble de ces matériaux hybrides ont montré des propriétés intéressantes pour des applications photovoltaïques et la conversion d'énergie. / Polyoxometalates@M NPs-dyes molecular hybrid systems were realized in this thesis for electrochemical catalytic hydrogen evolution and photocurrent generation. • First, hybrid films, based on electrostatic interactions between the tetracationic porphyrin and POMs@Pt NPs composites on ITO slides, were formed by the so called Layer-by-Layer method for HER and photocurrent generation.• To improve the charge transfer between POMs@M NPs and the substrate, reduced graphene oxide was introduced to form rGO/POMs@Pt NPs hybrid systems. Hydrogen evolution was measured after dropping this composites onto the surface of glassy carbon electrodes.• Polycationic bis-porphyrin copolymers have been also obtained by an electropolymerization leading to the formation of new bis-porphyrin copolymers with pyridinium as spacers. Incorporation with various Keggin type POMs or POMs@Ag was then achieved, their photovoltaic performances were also studied.• POMs@M NPs doped PEDOT hybrids films have been also fabricated. The photovoltaic performances has been examined showing particularly strong enhancement under visible light. In conclusion, these polyoxometalates based hybrids materials have shown interesting properties for photovoltaic application and energy conversion.

Les travaux présentés dans cette thèse s’inscrivent dans une thématique de modification de surfaces par le biais de monocouches auto-assemblées post-fonctionnalisables. L’objectif principal consiste à élaborer une méthode générique de modification de monocouches par des motifs moléculaires variés. Pour cela, les travaux se concentrent sur la mise au point d’une plateforme générique facilement fonctionnalisable par un motif d’intérêt et greffable sur électrode modifiée. La voie retenue consiste à utiliser deux réactions de "click chemistry" de type "CuAAC". La première réaction de CuAAC s’effectue en solution et permet de solidariser plateforme et motifs d’intérêt (principalement des dérivés ferrocényles). Les ligands ainsi obtenus ont été utilisés pour la complexation d’ions métalliques (Cu2+, Zn2+). Les ligands et les complexes ont été étudiés en solution par électrochimie ainsi que par spectroscopies UV-Visibles et RPE. La seconde réaction de CuAAC permet l’immobilisation des différents complexes de cuivre sur des électrodes pré-modifiées par des fonctions azoture, généralement à l’aide de monocouches auto-assemblées. Ce greffage s’effectue selon le mode opératoire de l’"électroclick auto-induite", c'est-à-dire que le complexe de cuivre à immobiliser est également catalyseur de la réaction de CuAAC. Les systèmes ainsi immobilisés (mono-, bi- ou tri-métalliques) ont pu être étudiés en terme de cinétique d’immobilisation, de cinétique de transfert d’électrons et en réactivité. Ce dernier point a par ailleurs fait l’objet d’une attention particulière pour le cas de la réduction électro-catalytique des ions nitrite par les complexes de cuivre (I), en solution et sur surface. / This work depends on functionalized surface theme using modification of selfassembled monolayers (SAMs). The main objective consists to elaborate a new general pathway to modify monolayers with miscellaneous objects of interest. For this, we decide to focus our work to synthesize a versatile platform handling two ethynyl arms. These functions are available to operate two CuAAC reactions. The first one is use for linking platform with object of interest (in general ferrocenyl derivatives). Ligands obtained by that way were used for complexation of Cu2+ and Zn2+ ions. Electrochemical and spectroscopic (UV-Visible and EPR) studies were performed on these compounds. The second CuAAC reaction is used to immobilize copper complexes on azide modified electrode (azide derivatives SAMs on gold and ITO or direct functionnalization of glassy carbon surface). The grafting is operating through “self-induced electroclick” method; this means the CuAAC reaction is catalysed by the copper complex which is immobilized. Functionalized electrodes were characterized by cyclic voltammetry. It appears that similar complexes have closed grafting kinetic. These studies also demonstrate the both influence of copper and spacer on a second electroactive site (ferrocene moieties). The reactivity of copper centre is evaluated for complexes in solution and immobilized on surface with electrocatalytic reduction of nitrite ions by copper (I) species. The catalytic efficiency strongly depends on potential of copper reduction. Also, similar complexes show a loss of catalytic power with immobilization on surface.

The hybrid nanostructures exhibit excellent performances in various fields such as catalysis, sensing, and energy conversion as compared to their individual ones. The thesis deals with the new methods for the synthesis of different type of hybrids with doped/pristine carbon nanostructures in the form of graphene, multiwall carbon nanotubes (MWCNTs) as one component and metals nanostructures (Ag, Pd, Pt and Au), carbide (Fe3C), metal chalcogenides (Ni3S2 and Co9S8) and oxide (CoO) as the other components. Various synthesis techniques such as modified galvanic replacement reaction at room temperature, hydrothermal, microwave and pyrolysis have been explored for the synthesis of different hybrid nanostructures. Furthermore, various hybrid nanostructures have been explored for various catalytic activities such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and 4-nitrophenol (4-NP) reduction. It may be noted that the ORR and OER which are undoubtedly vital for their applications in fuel cells, metal-air batteries and water oxidation reaction. Interestingly, the catalytic activities of these hybrid nanostructures are comparable or better as compared to the commercial benchmark precious catalysts.