225 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
Cooling rates of neutron stars and the young neutron star in the Cassiopeia A supernova remnant
No full textWe explore the thermal state of the neutron star in the Cassiopeia A supernova remnant using the recent result of Ho & Heinke that the thermal radiation of this star is well described by a carbon atmosphere model and the emission comes from the entire stellar surface. Starting from neutron star cooling theory, we formulate a robust method to extract neutrino cooling rates of thermally relaxed stars at the neutrino cooling stage from observations of thermal surface radiation. We show how to compare these rates with the rates of standard candles – stars with non-superfluid nucleon cores cooling slowly via the modified Urca process. We find that the internal temperature of standard candles is a well-defined function of the stellar compactness parameter x=rg/R, irrespective of the equation of state of neutron star matter (R and rg are circumferential and gravitational radii, respectively). We demonstrate that the data on the Cassiopeia A neutron star can be explained in terms of three parameters: f?, the neutrino cooling efficiency with respect to the standard candle; the compactness x; and the amount of light elements in the heat-blanketing envelope. For an ordinary (iron) heat-blanketing envelope or a low-mass (? 10?13 M?) carbon envelope, we find the efficiency f?? 1 (standard cooling) for x? 0.5 and f?? 0.02 (slower cooling) for a maximum compactness x? 0.7. A heat blanket containing the maximum mass (?10?8 M?) of light elements increases f? by a factor of 50. We also examine the (unlikely) possibility that the star is still thermally non-relaxe
Azygophleps junkeri Yakovlev & Witt 2017, sp. nov.
No full textAzygophleps junkeri Yakovlev & Witt, sp. nov. (Figs 6 ¯7, 15¯16) Material. Holotype: ♂, Angola, prov. Benguela, btw Cutembo & Caluquembe, 14 km E Cutembo, 13°46.901’ S 14°00.105’ E, 965 m, 2.iv.2014, leg. Naumann, Sulak & Ott (GenPr MWM: 26759; MWM). 2 ♂, same data (MWM); 3 ♂, Angola, Prov. Huambo, 2 km S Calanque, 12°52.214’ S 15°28.126’E, 1970 m, 27.iii.2014, leg. Sulak, Naumann & Ott (MWM); 2 ♂, Dzalanyama forest, Lilongwe distr., C. Malawi, 1300 m, 21.iv.2006, leg. R. Murphy (RMM); 2 ♂, Ntchisi forest, C. Malawi, 1600 m, 10.–17.v.2002, leg. R. Murphy (RMM); 1 ♂, C. Malawi, Kasungu N.P., Lifupa Lodge, 13°05'12"S 33°08'17"E, 1035 m, 22.iv.2011, leg. R. Yakovlev (RYB); 47 ♂, [Congo], Elisabethville, different data (1933¯1959), leg. Ch. Seydel (MRAC); 2 ♂, Burundi, Gitega, 20.v.1965, Dr. M. Fontaine (MRAC); 2 ♂, [Congo], Katanga, Zilo, iii.1968, Rec. V. Allard (MRAC); 1 ♂, [Congo], Zaire, Lubumbashi, 16.iii.1979, Th. Bouyer (MRAC); 1 ♂, South West Africa [Namibia], Mashare, c. 17°54’S 20°09’E, 12.iii.1978, leg. J. Ball (TMSA); 2 ♂, Tanzania, Rukwa Province, Mbizi Mts., entre Kisungu et Muze, 1415 m, 07°43.826’ S 031°32.482’ E, 14.05.2004, leg. Ph. Darge (MWM); 2 ♂, Tanzania, Rukwa Province, Kisengere / Kasimbo, 1193 m, 07°27.540' S 03°52.812' E, 17.05.2004, leg. Ph. Darge (MWM). Description. Length of forewing of holotype 21 mm (in male paratypes 19¯ 23 mm). Antenna bipectinate in proximal half, filiform in distal half. Thorax, tegula, patagia and abdomen brown. Fore wing brown with pattern of tiny fine black transverse strokes spaced rather evenly throughout the surface of the wing, narrow white area on costal edge from base to apex of wing. Hind wing brown with imperceptible pattern of fine transverse strokes, more expressed in cubital area. Anal edge pale, without pattern. Fringe pale brown, unicolorous. Male genitalia. Uncus long, triangle, with tapered uncinate apex; gnathos arms of medium thickness, ribbonlike, tapered to apices, not fused; valva simple, leaf-like, with even costal edge, obliquely cut outer edge and small notch in proximal third of abdominal edge; juxta large with narrow slit notch on dorsal surface and two long (in length equal to 2/5 of valva) lateral processes of medium thickness, directed dorsally; saccus small, semicircular; phallus thick, slightly shorter than valva, in vesica two ribbon-like sclerites in lateral surfaces, one of them two times larger and longer than the other. Female unknown. Diagnosis. The new species was erroneously determined several times by the senior author as A. aburae (Plötz, 1880) (type locality Bei Aburi [Ghana]) (Yakovlev 2011; Yakovlev & Murphy 2013; Yakovlev & Witt 2016a). The error in definition was first indicated by W. Mey (2016: 168): “The type material of A. aburae (Plötz, 1880) has not been traced so far and is probably lost. According to the original description of the species (unfortunately without illustrations), it should have an external appearance which comes close to a small individual of A. atrifasciata Hampson, 1910. The specimens identified and photographed by Yakovlev [& Murphy] (2013) as A. aburae neither correspond to the description given by Plötz (1880) nor to the colour figure in Gaede (1930). His specimens together with the present individual belong to a different species with unknown affiliation”. The new species differs well from all the known species of this genus by the following features: rather dark colour of the wings, pale narrow portion in the costal area of the forewing, two ribbon-like sclerites in the vesica, very long lateral processes of the juxta, narrow slit-shaped notch on the dorsal surface of the juxta. Distribution. Central and southern Africa: Congo, Burundi, Tanzania, Malawi, Angola and Namibia. Etymology. The new species is named after Wilhelm Junker (1840¯1892), doctor of medicine, Russian geographer and traveler, who studied the watershed of Nile and Congo, made a number of geographical discoveries, compiled the dictionary of ten ethnic groups in southeastern Africa, and gathered rich ethnographic, zoological, and botanical collections.Published as part of Yakovlev, Roman V. & Witt, Thomas J., 2017, Four new species of Azygophleps Hampson, 1892 (Lepidoptera, Cossidae, Zeuzerinae) from Africa, pp. 437-444 in Zootaxa 4303 (3) on pages 441-443, DOI: 10.11646/zootaxa.4303.3.9, http://zenodo.org/record/309464
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
Twenty Letters from St. Petersburg (epistolary heritage of A.I. Yakovlev)
No full textВ статье анализируется переписка владельца крупного уральского Верх-Исетского горного округа А. И. Яковлева с Главным заводским правлением о деятельности училища для детей служащих.Выявлены некоторые аспекты дистантных «хозяйственных распоряжений» А. И. Яковлева по учреждению и организации деятельности верхисетского заводского училища.The article is devoted to the correspondence of the owner of a large Verkh-Isetsky Ural Mining District A. I. Yakovlev main factory on the activities of the school board for the children of employees. The author points to the role of letters as a means of achieving a distant breeder its management functions. Some aspects of the distant «business orders» A. I. Yakovlev on the establishment, organization of the top-Isetsky factory school
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