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Electronic structure of bimetallic systems - study of gas molecule interaction
Píš, Igor ; Nehasil, Václav (advisor) ; Bartoš, Igor (referee) ; Polčík, Martin (referee)
Bimetallic Rh-V system was studied by means of surface science experimental methods. Properties of ultra-thin Rh-V layers supported by γ-Al2O3 were compared with model systems prepared by vacuum V deposition on Rh(111), Rh(110) and polycrystalline rhodium. Formation of ordered V- Rh(111)-(2×2), V-Rh(110)-(2×1) and V-Rh(110)-(1×2) subsurface alloys and their electronic and atomic structure were investigated and models of the surface reconstructions were proposed. Influence of the subsurface alloy formation on interaction with CO and O2 molecules as well as the influence of the molecule adsorption on this alloy was investigated. The bond between CO molecules and Rh-V alloy surface was weakened due to pronounced changes in surface valence band structure. Oxygen which adsorbed on the alloy surface reacted with the subsurface vanadium at elevated temperature and blocked the interaction of the metal substrate with CO molecules.
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Study of new catalytic materials for proton exchange membrane fuel cells
Homola, Petr ; Matolín, Vladimír (advisor) ; Jiříček, Petr (referee)
Title: Study of new catalytic materials for proton exchange membrane fuel cells Author: Petr Homola Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Vladimír Matolín, DrSc. Abstract: Submitted thesis deals with study of thin layers based on platinum and cerium oxides in order to use them in fuel cells with polymer membrane (PEM- FC). A set of samples with different amount of platinum was prepared by means of magnetron sputtering. Samples were investigated by X - ray Photoelectron Spectroscopy (XPS) and results were confronted with sputtering parameters. It was found out that chemical state of platinum is related to its amount in thin layer. The less platinum was contained in thin layer, the less amount of Pt0 state was observed and amounts of Pt2+ and Pt4+ states increased. Furthermore the temperature stability of prepared layers in the interval from room temperature to 250 ◦ C was studied by means of XPS. The adsorption of carbon monoxide was measured by infrared absorption spectroscopy (IRAS). Increasing degree of adsorption on sample probably related to platinum reduction with increased tem- perature was observed. Measurements of other samples were devaluated by strong contamination with nickel carbonyls. Keywords: PEMFC, cerium oxide, magnetron sputtering, XPS, CO adsorption
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Study of the structure and of interaction with gas molecules of Rh-Sn and Rh-SnO2
Janeček, Petr ; Nehasil, Václav (advisor) ; Jirka, Ivan (referee) ; Bartoš, Igor (referee)
In this work we present the results of the analysis of the surface structures and absorption properties with respect to the CO and O2 molecules of the Sn/Rh and Rh/SnO2 model systems. In the part dedicated to the Sn structures on Rh surfaces with two different orientations - Rh(110) and Rh(111) - we have investigated the development of the core electron levels and valence band during the development of surface reconstructions and absorption of CO molecules. The surface reconstructions of the Sn/Rh(110) systems were studied for the first time. Difference in behaviour w.r.t. Sn/Rh(111) was observed and explanation offered. Finally, on in-situ prepared epitaxial SnO2 layers, the surface reconstruction (4×1) was observed. The CO adsorp- tion properties of Rh on polycrystalline and epitaxial SnO2 layers were also studied and difference in behaviour explained.
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