409 research outputs found
Growth of nanoparticles in liquid medium using magnetron sputtering technique
No full textTitle: Growth of nanoparticles in liquid medium using magnetron sputtering technique Author: Josef Kučera Department: Department of Surface and Plasma Science Supervisor: Mgr. Yurii Yakovlev, Ph.D., Department of Surface and Plasma Science Abstract: This thesis investigates the preparation of platinum and platinum-ruthenium alloy nanoparticles using magnetron sputtering method on a liquid substrate. Polypropylene glycol with three different molecular weights of 425, 1000, and 4000 was chosen as the liquid substrate. The influence of the different viscosities of these substrates on the size and morphology of the nanoparticles produced in the magnetron was investigated. Dynamic light scattering and transmission electron microscopy methods were used to determine the size of the nanoparticles. Furthermore, the catalytic activity of the produced nanoparticles in an alkaline environment was investigated using the rotating disk electrode technique. Keywords: Nanoparticles, Magnetron Sputtering, Polypropylene glycol, Hydrogen Fuel Cells, Water Electrolyzers, Hydrogen oxidation/reduction reactions
Growth of nanoparticles in liquid medium using magnetron sputtering technique
No full textNázev práce: Růst nanočástic v kapalném prostředí technikou magnetronového naprašování Autor: Josef Kučera Katedra / Ústav: Katedra fyziky povrchů a plazmatu Vedoucí bakalářské práce: Mgr. Yurii Yakovlev, Ph.D., Katedra fyziky povrchů a plazmatu Abstrakt: Tato práce zkoumá přípravu nanočástic platiny a platino-rutheniové slitiny pomocí metody magnetronového naprašování na kapalný substrát. Jako použitý kapalný substrát byl zvolen polypropylenglykol se třemi různými molekulárními hmotnostmi 425, 1000 a 4000. U těchto substrátů bylo prozkoumáno, jak jejich rozdílná viskosita ovlivňuje velikost a morfologii nanočástic připravených v magnetronu. Pro určení velikosti nanočástic byly využity metody dynamického rozptylu světla a transmisní elektronové mikroskopie. Dále byla prozkoumána katalytická aktivita vytvořených nanočástic v alkalickém prostředí pomocí techniky rotační diskové elektrody. Klíčová slova: Nanočástice, magnetronové naprašování, polypropylenglykol, vodíkové palivové články, elektrolyzéry vody, vodíkové redoxní reakce.Title: Growth of nanoparticles in liquid medium using magnetron sputtering technique Author: Josef Kučera Department: Department of Surface and Plasma Science Supervisor: Mgr. Yurii Yakovlev, Ph.D., Department of Surface and Plasma Science Abstract: This thesis investigates the preparation of platinum and platinum-ruthenium alloy nanoparticles using magnetron sputtering method on a liquid substrate. Polypropylene glycol with three different molecular weights of 425, 1000, and 4000 was chosen as the liquid substrate. The influence of the different viscosities of these substrates on the size and morphology of the nanoparticles produced in the magnetron was investigated. Dynamic light scattering and transmission electron microscopy methods were used to determine the size of the nanoparticles. Furthermore, the catalytic activity of the produced nanoparticles in an alkaline environment was investigated using the rotating disk electrode technique. Keywords: Nanoparticles, Magnetron Sputtering, Polypropylene glycol, Hydrogen Fuel Cells, Water Electrolyzers, Hydrogen oxidation/reduction reactions.Department of Surface and Plasma ScienceKatedra fyziky povrchů a plazmatuMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Optimalizace svazků palivových článků pomocí ultrazvukového zvlhčovače.
No full textTitle: Optimization of the Performance of Fuel Cell Stacks Using an Ultrasonic Humidi- fier. Author: Martin Vaněk Department: Department of Surface and Plasma Science Supervisor: Mgr. Yurii Yakovlev, Ph.D., Department of Surface and Plasma Science Abstract: This work is concerned with the optimization of the performance of PEM hydrogen fuel cell stacks, a technology that opens up new possibilities for clean energy storage and restoration. We have hand-built a PEMFC open-cathode stack of 20 cells and measured its basic characteristics such as the j-V and j-P curves as well as the dependency of the temperature of the stack on power produced by the stack for constant power of the cooling fans. We have implemented and tested the performance of a new method for water and thermal management - the humidification of air via the use of an ultrasonic water fog generator. Several tests - measuring cooling efficiency, voltage variations between different cells, and j-V and j-P curves - were performed under different temperatures and with or without humidification. Keywords: fuel cell, self humidification, open cathode, performance 1Název práce: Optimalizace svazků palivových článků pomocí ultrazvukového zvlhčovače. Autor: Martin Vaněk Katedra: Katedra fyziky povrchů a plazmatu Vedoucí bakalářské práce: Mgr. Yurii Yakovlev, Ph.D., Katedra fyziky povrchů a plaz- matu Abstrakt: Tato práce se zabývá optimalizací výkonu svazků PEM palivových článků, technologie, která otevírá nové možnosti pro uskladnění a zpětnou výrobu elektrické energie. Sestavili jsme dvaceticelový sériový svazek PEM vodíkových palivových článků s otevřenou katodou a změřili jeho základní charakteristiky, jako jsou j-V a j-P křivky a také závislost teploty článku na výkonu, který produkuje za konstantního výkonu chladících větráků. Implementovali a otestovali jsme novou metodu pro správu vody a teploty článku - zvlhčování příchozího vzduchu pomocí ultrazvukového generátoru mlhy - a její vliv na výkon svazku. Provedli jsme několik testů - měření efektivity chlazení, variací v napětích na jednotlivých celách a j-V a j-V křivky - a to za různých podmínek, konkrétně při různých teplotách a se zvlhčováním či bez něj. Klíčová slova: palivový článek, samozvlhčování, otevřená katoda, výkon 1Department of Surface and Plasma ScienceKatedra fyziky povrchů a plazmatuMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Optimization of the performance of fuel cell stacks using an ultrasonic humidifier.
No full textTitle: Optimization of the Performance of Fuel Cell Stacks Using an Ultrasonic Humidi- fier. Author: Martin Vaněk Department: Department of Surface and Plasma Science Supervisor: Mgr. Yurii Yakovlev, Ph.D., Department of Surface and Plasma Science Abstract: This work is concerned with the optimization of the performance of PEM hydrogen fuel cell stacks, a technology that opens up new possibilities for clean energy storage and restoration. We have hand-built a PEMFC open-cathode stack of 20 cells and measured its basic characteristics such as the j-V and j-P curves as well as the dependency of the temperature of the stack on power produced by the stack for constant power of the cooling fans. We have implemented and tested the performance of a new method for water and thermal management - the humidification of air via the use of an ultrasonic water fog generator. Several tests - measuring cooling efficiency, voltage variations between different cells, and j-V and j-P curves - were performed under different temperatures and with or without humidification. Keywords: fuel cell, self humidification, open cathode, performance
In situ electrochemical grazing incidence small angle X-ray scattering: From the design of an electrochemical cell to an exemplary study of fuel cell catalyst degradation
No full textNowadays, electrochemistry has a considerable technological impact, involving fuel cells, super capacitors and batteries. These devices are based on complex architectures, which complicates monitoring their evolution in situ under operating conditions to reveal the reasons for reduced lifetime and performances. Here, we present a design of a multipurpose electrochemical cell for grazing incidence small and wide angle X-ray scattering (GISAXS and GIWAXS) where the environment for operating conditions can be recreated. We focus on proton exchange membrane fuel cells (PEMFCs) which operational conditions are simulated by means of potentiodynamic-based accelerated stress tests, applied to a thin film of Pt nanoparticles representing a model system of a benchmark catalyst. Two different upper potentials are used to mimic fuel cell operating conditions: at 1.0 V RHE the catalyst film preserves its initial morphology, while at 1.5 V RHE (simulating fuel cell start-up/shut-down cycles) significant coarsening has been observed. The initial dimension of the Pt particles of 4.0 nm increases to 8.7 nm due to the predominant process of coalescence and final Ostwald ripening. In parallel, the distance between the particles increases, the catalyst film (9 nm thick) becomes thinner at first and exhibit a higher roughness at the end
Capabilities of a novel electrochemical cell for operando XAS and SAXS investigations for PEM fuel cells and water electrolysers
No full textCatalyst stability is a key issue in current electrochemical devices, such as fuel cells (FCs) and water electrolysers (WEs). While for FCs, the main degradation process limiting catalyst stability have been highlighted, a clear picture is still missing concerning WEs. In this framework, in operando analyses are essential to characterize catalyst degradation over time. As X-Rays constitute the perfect probe for studying catalytic materials, we here present a reversible electrochemical cell designed for operando X-Ray Absorption Spectroscopy and Small and Wide Angle X-Ray Scattering analyses, which was used: (i) to study Pt/C catalyst degradation coupling the evolution of specific electrochemically active surface area (ECSA) with catalyst morphology, supported by the analysis of Pt oxidation state. As a result, an increase of particle (and particle cluster) size is connected to the diminishing of ECSA and to the changes in the fraction of metallic-to-oxidised Pt, underlying that changes mainly develop in the first 2000 cycles of applied stress tests. Finally, (ii) we introduce some preliminary results underlying the change in Ir oxidation state for a standard Ir/IrOX catalyst material for WEs, showing as such a change is not sufficient to induce any remarkable morphological variations within 500 cycles of stress tests
Interplay Among Dealloying, Ostwald Ripening, and Coalescence in Pt X Ni 100– X Bimetallic Alloys under Fuel-Cell-Related Conditions
No full textPlatinum-based bimetallic alloys have been largely investigated during the last few years as a valid alternative to bare Pt cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) to improve their cost-efficiency. Nonetheless, Pt bimetallic alloys are characterized by a reduced stability, which is poorly understood at a fundamental level. It is thus essential to describe the entire chain of interconnected degradation mechanisms to formulate a comprehensive model of catalyst degradation that will help interpret bimetallic alloy behavior in real complex fuel cell systems. By combining in situ inductively coupled plasma mass spectroscopy, in situ grazing-incidence small-angle X-ray scattering, and ex situ scanning electron microscopy, we have studied the morphological evolution of PtXNi100–X model catalysts with different Ni contents (ranging from 0 to 75%) undergoing potentiodynamic cycling to two different upper potentials mimicking the different operational conditions of a PEMFC: 1.0 and 1.3 VRHE. Data analysis allowed us to develop a methodology to distinguish the influence of Ni dissolution, particle coalescence, and Ostwald ripening on particle size distribution and interparticle distance and to realize time-dependent interplay maps to highlight the timeframe in which the aforementioned phenomena are prevailing or coexisting. Results show that Ni dissolution is the only phenomenon inducing morphological evolution when the lower upper potential is chosen. On the contrary, at 1.3 VRHE, Ni dissolution is rapidly overcome by particle coalescence at first and by Ostwald ripening in the later stages of the investigated time range. The onset of every phenomenon was found to occur earlier in time for larger values of Ni concentrations
The influence of deposition power during magnetron sputtering of catalysts on their activity towards oxygen evolution reaction
No full textIn the field of preparation of catalytic layers for proton exchange membrane water electrolysers (PEMWE), the magnetron sputtering seems to be an auspicious new method not yet broadly used. Because of the high cost of materials used as catalysts there is a demand to prepare the catalytic layers using less material while maintaining the efficiency of the layer at the same time; here the magnetron sputtering of catalysts seems to be a promising method. In this bachelor thesis, our task was to prepare samples and examine characteristics of magnetron- sputtered layers of noble metals in dependence on the sputtering power under which the layer had been prepared. We examined the layers in terms of their density, morphology and elemental composition and by measuring their catalytic performance via the rotating disc electrode (RDE) method
"Re-creating" Tadeusz Konwicki’s fiction : "Little apocalypse" and Yurii Andrukhovych’s "Moscoviad"a
No full textOn the basis of a comparative analysis of the worlds presented in Moscoviada by Yurii Andrukhovych and in the Little Apocalypse by Tadeusz Konwicki the article demonstrates the meaning of "metaphorical translation". Using the category proposed by Joseph Brodsky, the author of the article shows how similar characters, who search for their identities, are presented in both books
Mitigation of CO poisoning in hydrogen fuel cell.
No full textThis diploma thesis aims at studying a process of hydrogen fuel cell poisoning by molecules of carbon monoxide. Low loading platinum-ruthenium anode catalysts prepared by magnetron co-sputtering were studied. The chemical composition and crystallographic structure of the co-sputtered catalyst were analysed by X-ray photoelectron spectroscopy (XPS), energy- dispersive X-ray spectroscopy (EDX), and X-ray diffraction analysis (XRD). The process of CO poisoning was experimentally studied in half-cell and full-cell setups. Thin film catalysts were extensively studied using the rotating disk electrode (RDE) technique by analysing the desorption response of the underpotentially deposited hydrogen and copper as well as carbon monoxide stripping. Long-term and transient response to CO poisoning was investigated in the full cell setup (fuel cell operando mode) using galvanostatic potentiometry and impedance spectroscopy, respectively. A bifunctional mechanism of ruthenium in platinum anode catalyst was analysed. The mechanism of CO tolerance improvement either through adsorbed OH group formation and a change in electronic structure of alloys was discussed
- …
