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Gas sensing properties of tungsten oxide thin films
Vojík, Jiří ; Mašek, Karel (advisor) ; Haviar, Stanislav (referee)
The purpose of this thesis is a study of sensing properties of pure, platinum-doped and gold-doped tungsten oxide thin films. Required films were prepared by magnetron sputtering on glass and passivated silicon. Their chemical composition was investigated by XPS. The morphology of the films was measured using AFM and SEM. Sensing response of these films to hydrogen was investigated in the range from 1,000 to 10,000 ppm and temperatures between 100 and 350 řC. It was found that platinum oxides PtO2 and PtO were partially reduced during the sensing tests. The possible encapsulation of the platinum by the tungsten oxide was discovered. The sensitivity of the metal doped films was much higher than the sensitivity of the pure films. In the case of platinum-doped films the sensitivity decreased with increasing temperature in contrast to the gold-doped films where the sensitivity increased. The gold was present in two metallic and oxidized states. The gold was reduced during the reactions with hydrogen. After the sensing tests, the size of crystalline grains increased and the platinum-doped films became coarser.
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Study of the structural properties of model ceria based catalysts
Beran, Jan
This work is concerning the study of model ceria based calalysts structure by methods of electron diffraction RHEED and photoelectron spectroscopy XPS. The influence of deposition conditions and substrate on the growth of epitaxial cerium oxide films on copper single crystals is described in detail. The work then describes the interaction of cerium and tin in model systems and the creation of SnCeOx mixed oxide and its structure. In the last chapter, the interaction of palladium with cerium and tin oxide layers is examined, and the creation of paladium bimetallic alloys is described. Powered by TCPDF (www.tcpdf.org)
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Low Platinum Content Thin Film Catalysts for Hydrogen Proton Exchange Membrane Fuel Cells
Václavů, Michal ; Matolín, Vladimír (advisor) ; Bystroň, Tomáš (referee) ; Neitzel, Armin (referee)
Novel type of catalyst for proton exchange membrane fuel cells anode is demonstrated. It is based on magnetron sputtered Pt-CeO2 a Pt-Sn-CeO2 mixed oxides. It is shown, that these materials allow to significantly decrease amount of platinum in the anode catalyst. The preparation method yields high amount of platinum in ionized form, especially Pt2+ , which is related to the high activity. Stability of these catalytic layers were investigated under conditions similar to fuel cell anode (humidified hydrogen at elevated temperature). Also interaction of hydrogen a water under UHV conditions were studied, demonstrating high stability of the Pt2+ species. In the last part of the work sputtered Pt-Co mixed catalyst were investigated to be used in the PEMFC cathode. It is demonstrated that at right conditions, the sputtered alloy catalyst improves mass activity on cathode by factor more than two.
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Novel nanocatalysts for fuel cells II: micro-fuel cells on chip
Onderková, Kristýna ; Matolínová, Iva (advisor) ; Johánek, Viktor (referee)
Title: Novel nanocatalysts for fuel cells II: micro-fuel cells on chip Author: Kristýna Onderková Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Iva Matolínová, Dr., Department of Surface and Plasma Science Abstract: The thesis examines layers of cerium oxide doped with platinum, prepared by magnetron sputtering on various types of planar substrates. The work focuses primarily on how the layers are affected by doping different amounts of platinum. The samples were studied mainly using Scanning Electron Microscopy (SEM). Using the combination of SEM and Focused Ion Beam (FIB), we have prepared thin samples (lamellae), which allow the passage of electrons. The lamellae were observed using SEM with a detector of transmitted electrons. The lamellae were prepared with the focus on parameters of the protective layer. The chemical composition of Pt-CeOx samples was studied by Energy- Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS). Keywords: Pt-CeOx, lamella, SEM-FIB, EDX, XPS 1
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Low Platinum Content Thin Film Catalysts for Hydrogen Proton Exchange Membrane Fuel Cells
Václavů, Michal ; Matolín, Vladimír (advisor)
Novel type of catalyst for proton exchange membrane fuel cells anode is demonstrated. It is based on magnetron sputtered Pt-CeO2 a Pt-Sn-CeO2 mixed oxides. It is shown, that these materials allow to significantly decrease amount of platinum in the anode catalyst. The preparation method yields high amount of platinum in ionized form, especially Pt2+ , which is related to the high activity. Stability of these catalytic layers were investigated under conditions similar to fuel cell anode (humidified hydrogen at elevated temperature). Also interaction of hydrogen a water under UHV conditions were studied, demonstrating high stability of the Pt2+ species. In the last part of the work sputtered Pt-Co mixed catalyst were investigated to be used in the PEMFC cathode. It is demonstrated that at right conditions, the sputtered alloy catalyst improves mass activity on cathode by factor more than two.
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Electronics and adsorption properties of model catalytic systems contains cerium
Cabala, Miloš ; Veltruská, Kateřina (advisor) ; Jiříček, Petr (referee) ; Polčík, Martin (referee)
Title: Electronics and adsorption properties of model catalytic systems contains cerium Author: Miloš Cabala Department: Department of Surface and Plasma Science, Supervisor: RNDr. Kateřina Veltruská, Department of Surface and Plasma Science, Abstract: The doctoral thesis contains the study of model catalyst systems based on cerium and ceria. The thesis deals with model systems of CeAg, CeO2/Cu(111), Ni- CeO2/Cu(111) a Ni-Sn-CeO2/Cu(111). We have studied these systems using photoelectron spectroscopy, ion scattering spectroscopy and low energy electron diffraction. Model systems were prepared under strictly defined conditions. The strong bimetallic interaction was observed on the CeAg layers. Molecular adsorption of carbon monoxide on CeAg was demonstrated. We also observed intensive reaction of these layers with oxygen. By measurements in different directions of surface Brillouin zone, we managed to reconstruct the band structure of the prepared CeO2/Cu(111) layer. We have shown that the Cu substrate interacts weakly with deposited CeO2 layer. This interaction results in a charge transfer from Cu into CeO2. Overall, in the valence spectrum we have identified three main electron bands corresponding to O 2p state bound in CeO2. It has been proven that the deposition of Ni on CeO2 layers leads to partial...
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Study of the structural properties of model ceria based catalysts
Beran, Jan ; Mašek, Karel (advisor) ; Olejník, Kamil (referee) ; Lykhach, Yaroslava (referee)
This work is concerning the study of model ceria based calalysts structure by methods of electron diffraction RHEED and photoelectron spectroscopy XPS. The influence of deposition conditions and substrate on the growth of epitaxial cerium oxide films on copper single crystals is described in detail. The work then describes the interaction of cerium and tin in model systems and the creation of SnCeOx mixed oxide and its structure. In the last chapter, the interaction of palladium with cerium and tin oxide layers is examined, and the creation of paladium bimetallic alloys is described. Powered by TCPDF (www.tcpdf.org)
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Characterization of highly porous Pd-modified SnO2 sputtered thin films for H2 detection
Chundak, Mykhailo ; Veltruská, Kateřina (advisor) ; Jiříček, Petr (referee) ; Šmíd, Břetislav (referee)
Title: Characterization of highly porous Pd-modified SnO2 sputtered thin films for H2 detection Autor: Mgr. Mykhailo Chundak Department/Institute: Department of Surface and Plasma Science Supervisor of the doctoral thesis: RNDr. Kateřina Veltruská, CSc., Department of Surface and Plasma Science Abstract: This doctoral thesis contains the study of tin dioxide and Pd-doped tin dioxide samples deposited by magnetron sputtering utilizing glancing angle deposition (GLAD). Influence of the deposition parameters on the change of morphology, crystalline structure and chemical state was studied. The samples were characterized by a variety of techniques, such as: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), synchrotron radiation photoelectron spectroscopy (SRPES), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Prepared samples showed high porosity which could be controlled by deposition parameters (angle of the deposition, gas pressure and power of magnetron discharge). Highly porous SnO2 GLAD samples and Pd modified SnO2 GLAD samples were deposited on the substrates at room temperature and 300 řC. These samples were found to be polycrystalline with certain fraction of amorphous contribution, given by preparation conditions. The size of the...
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Novel nanocatalysts for fuel cells I: new type bipolar fuel cells
Švenda, Petr ; Matolín, Vladimír (advisor) ; Khalakhan, Ivan (referee)
There is a greater focus on the alternative sources of energy due to the energetic crisis recently. One of the many ways are the fuel cells, which are based on generating electricity by oxidating the hydrogen. A prominent place is occupied by cells with polymer membrane called PEMFC, which are especially suited for mobile applications due to their low operating temperature. The bigest obstacle for commercial use of the PEMFC is the big amount of platinum required for their production. It is necessary to reduce their cost by means of reducing the amount of used platinum while maintaining the same efficiency. One of the ways is using platinum in alloy with another metal instead of using pure platinum. This thesis addresses the alloy of Pt-Co prepared by magnetron sputtering, which exhibits desirable properties. Adding cobalt decreases the potential barrier that must be overcome for catalytic reaction to proceed. This results in higher specific power output of the fuel cell. The goal of this thesis is to examine in more detail the properties of Pt-Co in comparison with Pt.
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Study of gas sensing properties of tungsten oxide thin films
Vojík, Jiří ; Mašek, Karel (advisor) ; Ševčíková, Klára (referee)
Purpose of this thesis is a study of gas sensing properties of pure and platinum doped tungsten oxide thin films, which are deposited on a glass substrate. Needed films were prepared by magnetron sputtering method. Chemical composition and morphology of the films were investigated by means of XPS and SEM. It was discovered that prepared films are relatively flat and homogenous. They consist of polycrystalline WO3. It emerged that platinum which is present in modified films is in form of the PtO2 and PtO oxides. During subsequent heating of the films in air, which is needed for right function of films as sensors, PtO2 partially reduced. The resistance of the films decreased after heating. Sensing properties of the films were studied at 300 řC. The platinum doped film was more sensitive to exposition of hydrogen than the pure film.
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