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Oxygen Reduction Reaction on Dispersed and Core-Shell Metal Alloy Catalysts: Density Functional Theory StudiesHirunsit, Pussana 2010 August 1900 (has links)
Pt-based alloy surfaces are used to catalyze the electrochemical oxygen reduction
reaction (ORR), where molecular oxygen is converted into water on fuel cell electrodes.
In this work, we address challenges due to the cost of high Pt loadings in the cathode
electrocatalyst, as well as those arising from catalyst durability. We aim to develop an
increased understanding of the factors that determine ORR activity together with
stability against surface segregation and dissolution of Pt-based alloys. We firstly focus
on the problem of determining surface atomic distribution resulting from surface
segregation phenomena. We use first-principles density functional theory (DFT)
calculations on PtCo and Pt3Co overall compositions, as well as adsorption of water and
atomic oxygen on PtCo(111) and Pt-skin structures. The bonding between water and
surfaces of PtCo and Pt-skin monolayers are investigated in terms of orbital population.
Also, on both surfaces, the surface reconstruction effect due to high oxygen coverage
and water co-adsorption is investigated.
Although the PtCo structures show good activity, a large dissolution of Co atoms tends
to occur in acid medium. To tackle this problem, we examine core-shell structures which
showed improved stability and activity compared to Pt(111), in particular, one consisting
of a surface Pt-skin monolayer over an IrCo or Ir3Co core, with or without a Pd
interlayer between the Pt surface and the Ir-Co core. DFT analysis of surface
segregation, surface stability against dissolution, surface Pourbaix diagrams, and reaction mechanisms provide useful predictions on catalyst durability, onset potential for
water oxidation, surface atomic distribution, coverage of oxygenated species, and
activity. The roles of the Pd interlayer in the core-shell structures that influence higher
ORR activity are clarified. Furthermore, the stability and activity enhancement of new
shell-anchor-core structures of Pt/Fe-C/core, Pt/Co-C/core and Pt/Ni-C/core are
demonstrated with core materials of Ir, Pd3Co, Ir3Co, IrCo and IrNi. Based on the
analysis, Pt/Fe-C/Ir, Pt/Co-C/Ir, Pt/Ni-C/Ir, Pt/Co-C/Pd3Co, Pt/Fe-C/Pd3Co, Pt/Co-
C/Ir3Co, Pt/Fe-C/Ir3Co, Pt/Co-C/IrCo, Pt/Co-C/IrNi, and Pt/Fe-C/IrNi structures show
promise in terms of both improved durability and relatively high ORR activity.
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Structural Studies of Pt-Based Electrocatalysts for Polymer Electrolyte Fuel Cells / 白金系燃料電池用カソード触媒の構造と活性に関する研究Liu, Chen 23 March 2021 (has links)
学位プログラム名: 京都大学大学院思修館 / 京都大学 / 新制・課程博士 / 博士(総合学術) / 甲第23346号 / 総総博第19号 / 新制||総総||3(附属図書館) / 京都大学大学院総合生存学館総合生存学専攻 / (主査)教授 寶 馨, 教授 内本 喜晴, 特定教授 橋本 道雄 / 学位規則第4条第1項該当 / Doctor of Philosophy / Kyoto University / DFAM
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Synthèse de nanotubes de carbone multi-parois sur supports pulvérulents et étude des mécanismes de croissance catalytique / Multi-walled carbon nanotubes synthesis and study of their growth mecanismBeausoleil, Julien 28 January 2010 (has links)
Produire à grande échelle des nanotubes de carbone en maîtrisant les principaux paramètres de croissance et la morphologie de ces matériaux est un enjeu important en vue de leur exploitation industrielle dans de nombreux domaines tels que l’élaboration de composites ou le stockage de l’énergie. C’est dans ce contexte que s’inscrit ce travail, basé sur la technique de dépôt chimique à partir d’une phase vapeur (CVD) mise en oeuvre dans un procédé faisant appel à un lit fluidisé de particules catalytiques (FB-CCVD). Dans un premier temps, nous avons étudié le catalyseur mis au point par la société Arkema, de sa préparation à son utilisation en catalyse pour la croissance de nanotubes de carbone multi-parois. Nous avons ainsi mis en évidence que la phase active était principalement localisée à la surface du support sous la forme d’une gangue discontinue d’hématite. Lors de la synthèse, nous avons constaté deux régimes cinétiques différents que nous avons confrontés aux évolutions physico-chimiques du matériau au cours du dépôt. Par la suite, nous avons préparé à partir du procédé Arkema différents catalyseurs bimétalliques afin d’augmenter le rendement de la synthèse de nanotubes de carbone et de diminuer leur diamètre. Un système à base de fer et de molybdène a montré une activité trois fois supérieure au catalyseur initial sous réserve de travailler à une température particulière. Enfin, dans une dernière partie, nous avons tenté de proposer une explication sur le rôle joué par le molybdène lors de la croissance des nanotubes de carbone. Nos observations nous ont mené à la préparation de catalyseurs coeur-écorce à base de fer et de molybdène présentant des activités supérieures à un système homogène. / The large scale production of carbon nanotubes associated with control of the main growth parameters and of the morphology is a challenging aim for future industrial exploitation of these nanostructured materials in numerous fields like composite production and energy storage. This work based on the fluidized bed catalytic chemical vapour deposition technique (FB-CCVD) lies in this industrial framework. At first, we have studied the catalyst produced by Arkema, from its synthesis to its use for carbon nanotubes growth. We have shown that the active phase is mainly located at the support surface in the form of a discontinuous film of hematite. During the synthesis, we have noticed two kinetic regimes that we analysed through caracterisation of the material at different times of the reaction. Then, we have prepared bimetallic catalysts using the Arkema process in order to improve the reaction yield and to decrease carbon nanotubes diameter. We have discovered thaht an iron and molybdenum based catalyst shows three times higher activity than the classic one, if we work at a specific temperature. At last, we have tried to explain the role played by molybdenum in the growth of carbon nanotubes. Our findings have lead us to develop core shell iron and molybdenum based catalysts presenting higher activity than the homogeneous sytem.
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