The influence of the surface morphology of platinum materials on the electrocatalytic activity in fuel cells

U ovom radu ispitivan je uticaj morfologije platinskih materijala na elektrokatalitičku aktivnost za reakcije koje se odigravaju u H2/O2 (PEM) gorivom spregu. Kao platinski materijali su korišćeni monokristali platine i platinski nano-katalizatori. Rezultati ispitivanja oksidacije vodonika su pokazala da su aktivna mesta za oksidaciju vodonika platinski atomi koji nisu blokirani adsorbatima (Hupd, na niskim potencijalima i anjoni na višim potencijalima). Istraživanja redukcije kiseonika su pokazala da aktivna mesta za redukciju kiseonika i redukciju peroksida nisu ista. Aktivna mesta za reakciju redukcije kiseonika su ona mesta na površini koja ostaju slobodna od neaktivnih adsorbata na visokim potencijalima. Specijalna pažnja je posvećena ispitivanju oksidacije ugljen-monoksida koja je od presudnog značaja za pronalaženje katalizatora za oksidaciju vodonika tolerantnog na CO kao i za rešenje problema „trovanja“ u anodnim reakcijama oksidacije metanola i mravlje kiseline u gorivim spregovima CH3OH/O2 i HCOOH/O2. Kombinacijom eksperimentalnih i teorijskih tehnika kao što su: ciklična voltametrija, skenirajuća-tunelirajuća mikroskopija (STM) i infra-crvena adsorpciona spektroskopija (IRAS) i teorija funkcionala elektronske gustine (DFT) određena su aktivna mesta u oksidaciji CO. U oblasti niskih potencijala (predoksodaciona oblast) aktivna mesta su površinska ostva, niske koordinacije koja su po prvi put detektovana u ovom radu. Na višim potencijalima (glavna oksidaciona oblast) aktivna mesta su monoatomske stepenice. Prema DFT kalkulacijama atomi sa malom koordinacijom u površinskim ostrvima poseduju sposobnost da adsorbuju dva CO molekula. Jedan od ova dva CO molekula je slabo vezan i njegova zamena sa OH je energetski povoljnija na površinskim ostrvima nego na stepenicama. Korelacija oksidacije CO na model sistemima i realnim katalizatorima ukazala je na mogućnost da su ista aktivna mesta na Pt monokristalima i Pt nanokatalizatorima odgovorna za aktivnost u predoksidacionoj oblasti. Prisustvo velikog broja defekata na katalizatoru sa veličinom čestica od 30 nm je uzrok njegove visoke aktivnost u odnosu na Pt/C katalizatore.In this work the influence of morphology of a platinum material on electrocatalytic activity for the reactions taking place in a PEM fuel cell was studied. Platinum single crystals and platinum nanocatalysts were used. The results from the studies of H2 oxidation showed that the bare platinum atoms (free from adsorbents: Hupd on low potentials and anions on higher potentials) are the active sites on which the reaction is taking place. The studies of O2 reduction reaction revealed that the different active sites are involved in O2 reduction and H2O2 reduction. The active sites for O2 reduction are those sites which are free from anions on higher potentials. The special attention was paid on the CO oxidation reaction. This reaction is a key reaction for developing the catalytic material for H2 oxidation tolerant on “CO poisoning” in anodic reactions of formic acid and methanol oxidation. By using a combination of experimental and theoretical approaches the active sites for the CO oxidation were detected and their role in the reaction was defined. On low potentials (preoxidation area) the active sites are the low coordinated Pt atoms, ad-islands, while on higher potentials (main oxidation area) the active sites are the monoatomic steps. DFT calculations suggested that the atoms with low coordination are capable to bond two CO molecules. One of those two molecules is weakly bonded and can be substituted with OH. Thermodynamically this is more favorable on ad-islands than on steps. The correlation for the CO oxidation on model systems and real catalysts revealed that the same active sites are responsible for the activity on Pt single crystals and Pt nanocatalysts in the preoxidation area. In the case of 30 nm catalyst the presence of large number of defects was responsible for its superior activity compared to Pt/C catalysts

Do women in Kosovo and Metohija have their niche and the capacity for independence in the future of business?

Since the time when women cultivated the land, in order to feed their families, to this day, when numerous opportunities offered by modern life can help them fight for their financial independence, very little has changed. 107 female respondents who took part in this research stated that the primary economic activity they are engaged in is still agriculture. Fear of failure, as well as social prejudices that are increasingly highlighted as formidable and major barriers which, despite emphasizing the importance of the concept of gender equality, directly affect women's decisions about starting their own business, did not deter them from expressing their great determination and willingness to get involved in the process of switching to organic production and thus start their own business in the foreseeable future. Bearing in mind the aforementioned, it is evident that, under difficult business conditions, adequate financial and moral support from all possible relevant sources is necessary to maintain and support the entrepreneurial spirit of women in the province of Kosovo and Metohija

Between the Vinča and Linearbandkeramik worlds: the diversity of practices and identities in the 54th–53rd centuries cal BC in south-west Hungary and beyond

Szederkény-Kukorica-dűlő is a large settlement in south-east Transdanubia, Hungary, excavated in advance of road construction, which is notable for its combination of pottery styles, variously including Vinča A, Ražište and LBK, and longhouses of a kind otherwise familiar from the LBK world. Formal modelling of its date establishes that the site probably began in the later 54th century cal BC, lasting until the first decades of the 52nd century cal BC. Occupation, featuring longhouses, pits and graves, probably began at the same time on the east and west parts of the settlement, the central part starting a decade or two later; the western part was probably abandoned last. Vinča pottery is predominantly associated with the east and central parts of the site, and Ražište pottery with the west. Formal modelling of the early history and diaspora of longhouses in the LBK world suggests their emergence in the Formative LBK of Transdanubia c. 5500 cal BC and then rapid diaspora in the middle of the 54th century cal BC, associated with the ‘earliest’ (älteste) LBK. The adoption of longhouses at Szederkény thus appears to come a few generations after the start of the diaspora. Rather than explaining the mixture of things, practices and perhaps people at Szederkény by reference to problematic notions such as hybridity, we propose instead a more fluid and varied vocabulary including combination and amalgamation, relationships and performance in the flow of social life, and networks; this makes greater allowance for diversity and interleaving in a context of rapid change

Structural effects in electrocatalysis: Formic acid oxidation at model and real Pt catalysts

Formic acid oxidation was studied at low-index Pt single crystals (model systems) as well as at the platinum catalyst supported on high area carbon (real catalyst) in HClO4. The Pt single crystals were characterized by LEED. The LEED patterns obtained after a mild heating of flame-annealed crystals have shown clean, well ordered unreconstructured surfaces. Pt-C supported catalyst was analyzed by AFM and STM in air and by XRD. AFM and STM images revealed the presence of Pt-C agglomerates of several tenth of nm consisting of Pt particles ranged from 2 nm to 6 nm. The electrocatalytic activity of these catalysts in formic acid oxidation increased in a sequence: Pt(100) lt Pt(110) lt Pt-C/GC lt Pt(111)

Einfluß der Anionen bei spektrochemischer: Spurenanalyse im lichtbogen

The influence of the addition of ammonia into the arc plasma on the spectral line intensities (with background correction) of trace elements was studied. The intensity changes caused by addition of ammonium sulphate and ammonium nitrate generally do not exceed the standard deviations. But the addition of ammonium chloride and ammonium fluoride causes a depressive effect on the spectral line intensities of volatile elements. The presence of ammonia halides in the plasma has an intensifying effect on spectral lines of Ti, present in the electrode material as impurity. In this case both ammonium sulphate and ammonium nitrate have no essential influence. Possible explanations of these effects are discussed. The depressive effect of the halides could be caused by processes in the plasma, and the intensifying of Ti-lines could be explained by the change of its volatility.Es wurde untersucht wie sich in das Bogenplasma zugegebene Ammonsalze auf die Linienintensitäten (mit Untergrundkorrektion) der untersuchten Spurenelemente auswirken. Bei Zugabe von Ammonsulfat und Ammonnitrat liegen die Intensitätsveränderungen der Spektrallinien hauptsächlich innerhalb der Fehlergrenze. Die Zugabe von Ammonchlorid und Ammonfluorid schwächt dagegen die Intensitäten der Spektrallinien der untersuchten leichtflüchtigen Elemente ausgesprochen ab. Die Ammonhalogenide erhöhen aber die Linienintensitäten des als Verunreinigung in den Elektroden anwesenden Titans. Auch in diesem Falle haben Ammonsulfat und Ammonnitrat keine ausgeprägte Wirkung gezeigt. Es wurden die möglichen Erklärungen dieses Effektes diskutiert. Der Depressionseffekt der Halogenide könnte durch Prozesse im Plasma bedingt sein, und zu einer Erhöhung der Linienintensitäten von Titan käme es infolge der Veränderung seiner Flüchtigkeit

Electrocatalytic properties of Pt-Bi electrodes towards the electrooxidation of formic acid

Formic acid oxidation was studied on two Pt-Bi catalysts, Pt2Bi and polycrystalline Pt modified by irreversible adsorbed Bi (Pt/Biirr) in order to establish the difference between the effects of Biirr and Bi in alloyed state. The results were compared to pure Pt. It was found that both bimetallic catalysts were more active than Pt with the onset potentials shifted to more negative values and the currents at 0.0 V vs. SCE (under steady state conditions) improved up to two order of magnitude. The origin of Pt2Bi high activity and stability is increased selectivity toward formic acid dehydrogenation caused by the ensemble and electronic effect and suppression of Bi leaching from the surface during formic acid oxidation. However, although Pt/Biirr also shows remarkable initial activity compared to pure Pt, dissolution of Bi is not suppressed and the poisoning of the electrode surface induced by dehydration path is observed. Comparison of the initial quasi-steady state and potentiodynamic results obtained for these two Pt-Bi catalysts revealed that the electronic effect, existing only in the alloy, contributes earlier start of the reaction, while the maximum current density is determined by the ensemble effect. [Projekat Ministarstva nauke Republike Srbije, br. H-172060

Structural effects in electrocatalysis: oxidation of formic acid and hydrogen adsorption on platinum single-crystal stepped surfaces

The oxidation of formic acid and hydrogen adsorption have been measured on platinum single-crystal stepped surfaces with five orientations. A pronounced structural sensitivity of both reactions has been found. They show a sensitivity to the terrace orientation, the density of steps and to the step orientation The surfaces which are blocked for reaction by intermediates formed in the oxidation of formic acid, as the Pt(100) and Pt(110) surfaces are, become more active upon introduction of steps. The surface which are not blocked, i.e. the Pt(111) surface, become less active upon introduction of steps because more active steps increase their activity for the "wrong" reaction - the formation of blocking intermediates. Preliminary data on hydrogen adsorption show the possibility of using this reaction as a check of the degree of order and orientation of sigle-crystal Pt surfaces