National Repository of Grey Literature 12 records found  1 - 10next  jump to record: Search took 0.01 seconds. 
Preparation of nanoparticles of transition metals and their oxides using gas aggregation sources
Hanková, Adéla ; Kylián, Ondřej (advisor) ; Khalakhan, Ivan (referee)
This work focuses on the synthesis of nanoparticles of vanadium, titanium and their oxides. Magnetron-based gas aggregation source was used for nanoparticle preparation. Metallic nanoparticles of vanadium and titanium deposited on substrate were heated at atmospheric pressure which transformed them into oxides. Metallic and oxide nanopar- ticles are compared in terms of morphology, chemical composition, crystal structure and optical properties. Oxidation of vanadium nanoparticles during short heating times at the temperature of 450 řC is discussed in more detail. It was demonstrated, that ideal heating time for VO2 preparation is 60 s, the most stable vanadium oxide phase - V2O5 - is formed after longer heating. The change of electrical and optical properties with tem- perature (thermochromic behaviour) was monitored for VO2 nanoparticles. The V2O5 and TiO2 nanoparticles were tested for their photocatalytic effect and possible use as substrates for surface-enhanced Raman spectroscopy (SERS). It was shown that TiO2 nanoparticles coated with a thin silver layer can be used as recyclable, enhancing SERS substrates. 1
Temperature-induced restructuring of Pt-Cu bimetallic alloy catalyst for fuel cell applications
Kučera, Jan ; Khalakhan, Ivan (advisor) ; Vorochta, Michael (referee)
Fuel cells appear as a promising technology, enabling the replacement of internal combustion engines in the automotive industry. Hydrogen fuel cells with a polymer membrane are particularly suitable for this application. Despite significant progress, this technology suffers from several drawbacks that hinder its widespread adoption. One of the main issues is the need for expensive platinum as a catalyst. A possible way to save costs is by using bimetallic catalysts based on platinum and inexpensive 3d transition metals like copper. The preparation of these catalysts can, for instance, leverage the phenomenon of thermally induced segregation. A deeper understanding of platinum segregation in bimetallic PtCu layers could contribute to the development of a better and more cost-effective catalyst. This study examined thin PtCu layers prepared using magnetron sputtering. Their structure, chemical composition, and morphology were determined, and platinum segregation was monitored by X-ray photoelectron spectroscopy, depending on the annealing temperature of the samples.
Pt-based bimetallic catalysts for polymer membrane fuel cells prepared by magnetron sputtering
Orság, Martin ; Khalakhan, Ivan (advisor) ; Paidar, Martin (referee)
The use of fossil fuels has started a climate change connected to risks such as extreme heatwaves, rising sea level, extinction of species and other catastrophes. That's why it's necessary to move to carbon neutral economics. Hydrogen fueled proton exchange membrane fuel cells (PEMFCs) can power vehicles without emitting dangerous emissions. The main obstacle to their widespread use resides on its cathode side where a sluggish oxygen reduction reaction takes place. Because of that, PEMFC cathodes require large amount of expensive platinum catalyst which moreover operates under aggressive corrosive environment. This thesis explores the possibilities of replacing platinum with a bimetallic alloy of platinum and a cheaper metal. Pt-Co, Pt-Cu and Pt-Y bimetallic catalysts of different compositions (Pt75M25, Pt50M50 and Pt25M75) were prepared by magnetron sputtering. The catalysts were thoroughly characterized and their activity and stability were tested. The results show that replacing platinum with a bimetallic alloy can significantly increase the specific power activity of the cathode catalyst in PEMFC. On the other hand, bimetallic catalysts, especially those with lower amount of Pt, are more prone to degradation. Nevertheless, bimetallic catalysts with Pt75M25 composition showed a promising...
Controllable synthesis, treatment and characterization of anodes for Direct Formic Acid Fuell Cell
Bieloshapka, Igor ; Jiříček, Petr (advisor) ; Khalakhan, Ivan (referee) ; Plšek, Jan (referee)
Title: Controllable synthesis, treatment, and characterization of anodes for Direct Formic Acid Fuel Cell Author: Igor Bieloshapka Department: Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Ing. Petr Jiříček, CSc., Institute of Physics of the Czech Academy of Sciences, Division of Solid State Physics, Department of Optical Materials Abstract: This doctoral thesis concerns the preparation of anodes with Pd-based catalysts. Anodes were deposited on a support surface with magnetron sputtering. The prepared samples were tested in a direct formic acid fuel cell (DFAFC) station. Polyaniline, graphene oxide (GO) and reduced graphene oxide (RGO) have been additionally investigated as promising support material for polymer membrane fuel cells (FCs). A scanning electron microscope (SEM) and a transmission electron microscope (TEM) were used to observe the morphological differences between the prepared samples. Elemental composition and chemical states on the anode part were studied through X-ray photoelectron spectroscopy (XPS). The results show that the power density of the prepared anodes with 3 nm of palladium thickness is lower only by 30% in comparison with chemically prepared catalysts. The highest power density results were achieved for the...
Candle soot as a support for proton exchange membrane fuel cell catalysts
Orság, Martin ; Khalakhan, Ivan (advisor) ; Yakovlev, Yurii (referee)
Burning of fossil fuels to power vehicles causes emissions of carbon dioxide and in consequence the global warming which, in turn, causes melting of glaciers, extinction of species and various other negative consequences. The only way to decrease the harmful emissions is a transition to emission-free energy sources such as fuel cells. A promising type of such fuel cells are hydrogen fueled proton exchange membrane fuel cells (PEMFCs). One of the main obstacles hindering their widespread commercialization is the production cost and poor durability of catalyst/support assemblies. The present thesis focuses on the possibility to use candle soot (CS) as an efficient and low-cost catalyst support and compares the power characteristics of the fuel cell utilising the candle soot support with the one utilizing a commercial catalyst support. The results show that Pt/CS assemblies exhibit comparable or even better power densities than Pt / commercial catalyst support, which makes candle soot a promising type of the support for PEMFCs catalyst.
Preparation and characterization of platinum-based bimetallic catalysts for fuel cells
Supik, Lukáš ; Khalakhan, Ivan (advisor) ; Kúš, Peter (referee)
1 Abstract The main sources of energy in the world are unrenewable sources. However, its reserves should last for next few tens of years and it is necessary to substitute them with alternative sources. Fuel cells are one of the most promising alternative sources of clean energy because they convert the chemical energy of hydrogen into electrical energy with the only byproduct pure water. There exist a wide range of fuel cells and the most important type is the fuel cell with a polymer membrane because it is suitable for mobile applications. One of the main problems of fuel cells is their price. Platinum catalyst enables chemical reactions and the necessity of platinum rises its price. Nowadays, the most promising strategy for overcoming this obstacle is doping platinum with other metals. Bimetallic platinum alloys increase the catalyst's activity and simultaneously decrease its price. This thesis is focused on investigation of catalyst for fuel cell made of platinum- nickel alloy. The catalyst was prepared by magnetron sputtering technique and then its other properties were measured with respect to the amount of platinum and nickel. The goal of this thesis is to study the link between chemical composition and activity of bimetallic layers.
3D tomography of thin film catalysts by means of FIB/SEM techniques
Dinhová, Thu Ngan ; Matolínová, Iva (advisor) ; Khalakhan, Ivan (referee)
One of the actual problems of today society are decreasing sources of fossil fuels. They are raw minerals and by their burning is energy produced. Regarding to the importance of energy in todays world, it's necessary to find an alternative way how to generate energy. A possible solution to this problem are fuel cells, which work on the principle of converting chemical energy into electric energy. At this moment, the development of fuel cells is in progress. In this bachelor thesis, we are concerned with morphology of catalytic layers Pt/CeO2 deposed on a polymer membrane for hydrogen fuel cells. By using of tomography method with focused ion beam system (FIB) we are creating three-dimensional models of their surface structures. 1
Controllable synthesis, treatment and characterization of anodes for Direct Formic Acid Fuell Cell
Bieloshapka, Igor ; Jiříček, Petr (advisor) ; Khalakhan, Ivan (referee) ; Čechal, Jan (referee)
Title: Controllable synthesis, treatment and characterization of anodes for Direct Formic Acid Fuell Cell Author: Mgr. Igor Bieloshapka Department/Institute: Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Ing. Petr Jiříček, CSc., Institute of Physics of the Czech Academy of Sciences, Division of Solid State Physics, Department of Optical Materials Abstract: At this doctoral thesis, anodes were prepared by novel DC magnetron sputtering technique for direct formic acid fuel cells (DFAFCs). Anode part consisted of support material and catalyst. Carbon cloth and polyaniline were used as a support. Palladium and palladium-copper bimetallic catalysts were deposited on the top of the support. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used for investigation of the morphology of the anodes. Composition and chemical states on the anode part were studied by x-ray photoelectron spectroscopy (XPS). Transmission electron microscope (TEM) together with the XPS technique were used for characterizing graphene oxide (GO) and reduced graphene oxide (RGO) as a promising support for the polymer membrane fuel cells. For decreasing the role of substoichiometric PdCx phase and other contaminations on the surface of...
Study of 3-phase catalytic layers for polymer electrolyte fuel cells and electrolysers
Fuka, Šimon ; Matolínová, Iva (advisor) ; Khalakhan, Ivan (referee)
Title: Study of 3-phase catalytic layers for polymer electrolyte fuel cells and electrolysers Author: Šimon Fuka Department: Department of Surface and Plasma Science Supervisor: doc. Mgr. Iva Matolínová, Dr., Department of Surface and Plasma Science Abstract: The diploma thesis focuses on the study of catalytic layers for Proton Exchange Membrane Fuel Cells (PEMFC) or electrolyzers based on the mixture of platinum and cerium oxide. These layers are prepared by using magnetron sputtering, their properties are studied depending on the deposition parameters or the choice of the substrate by using SEM, AFM, XPS and then tested as an anode in the fuel cell. In addition to the morphology of the catalytic layers, it has been shown that the dispersion of very small nanoparticles of the catalyst with a size of 1-2 nm has a great effect on PEMFC performance. Most of the prepared samples gave maximal and maximal specific performance much higher than the state of art values published for Pt-CeOx system. By studying properties of the layers used as the anode catalysts, this work contributes to the understanding of PEMFC fuel cell behavior and, consequently, to its potential commercialization. Keywords: Fuel cell, cerium oxide, platinum, catalyst, magnetron sputtering

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