Efekat osobina staklastog ugljenika na elektrohemijski nataložen platinski nano-katalizator i njegovu aktivnost u oksidaciji metanola

The effects of the properties of glassy carbon on the deposition of platinum particles and the electrocatalytic activity of platinum supported on glassy carbon (GC/Pt) for methanol oxidation in alkaline and acidic solutions were studied. Platinum was potentiostatically deposited on two glassy carbon samples, thermally treated at different temperatures, which were either polished or anodicaly polarised in acid (GCOX-AC/Pt) and in alkali (GCOX-AL/Pt). Anodic polarisation of glassy carbon, either in alkaline or acidic solution, enhances the activity of both types of GC/Pt electrodes for methanol oxidation. The activity of the catalysts follows the change in the properties of the glassy carbon support upon anodic treatment. The specific activity of the GCOX-AL/Pt electrode for this reaction in alkali is increased only a few times in comparison with the activity of the GC/Pt one. On the other hand, the specific activity of the GCOX-AC/Pt electrode for methanol oxidation in acid is about one order of magnitude higher than that of the GC/Pt electrode. The role of the substrate on the properties of catalyst is discussed in detail.Ispitivan je uticaj osobina podloge od staklastog ugljenika na taloženje platinskih čestica i elektrokatalitičku aktivnost tako dobijene elektrode (GC/Pt) u reakciji oksidacije metanola u kiseloj i alkalnoj sredini. Platina je potenciostatski taložena na dva uzorka staklastog ugljenika, termički tretirana na različitim temperaturama, koji su polirani ili anodno polarizovani u kiselom GC OX-AC/Pt ili alkalnom (GC OX-A/Pt) rastvoru. Anodna polarizacija staklastog ugljenika bilo u kiselini ili u alkaliji pre taloženja platine dovodi do povećanja aktivnosti oba tipa GC/Pt elektroda za reakciju oksidacije metanola. Aktivnost Pt katalizatora prati promene u osobinama podloge od staklastog ugljenika koje nastaju usled anodne polarizacije. Specifična aktivnost GC OX-AL/Pt elektroda u oksidaciji metanola u alkalnim rastvorima povećava se samo nekoliko puta u odnosu na aktivnost katalizatora na poliranoj podlozi (GC/Pt). Sa druge strane, specifična aktivnost GC OX-AC/Pt elektroda u oksidaciji metanola u kiselim rastvorima u poređenju sa aktivnošću GC/Pt elektroda veća je praktično za ceo red veličine. U radu je takođe detaljno diskutovana uloga podloge na osobine katalizatora

Uticaj površinske morfologije na oksidaciju metanola na platinskim katalizatorima sa podlogom od staklastog ugljenika

Platinum supported on glassy carbon (GC) was used as a model system for studying the influence of the surface morphology of a Pt catalyst on methanol oxidation in alkaline and acidic solutions. Platinum was deposited by the potential step method on GC samples from H2SO4 + H2PtCl6 solution under the same conditions with loadings from 10 to 80 mg cm-2. AFM and STM images of the GC/Pt electrodes showed that the Pt was deposited in the form of 3D agglomerates composed of spherical particles. Longer deposition times resulted in increased growth of Pt forms and a decrease in the specific area of the Pt. The real surface area of Pt increased with loading but the changes were almost negligible at higher loadings. Nevertheless, both the specific and mass activity of platinum supported on glassy carbon for methanol oxidation in acidic and in alkaline solutions exhibit a volcanic dependence with respect to the platinum loading. The increase in the activity can be explained by the increasing the particle size with the loading and thus an increase in the contiguous Pt sites available for adsorption and decomposition of methanol. However, the decrease in the activity of the catalyst with further increase of loading and particle size after reaching the maximum is related to the decrease of active sites available for methanol adsorption and their accessibility as a result of more close proximity and pronounced coalescence of the Pt particles.Platina istaložena na staklasti ugljenik (GC) korišćena je kao model sistem za ispitivanje uticaja morfologije površine Pt katalizatora za reakciju oksidacije metanola u alkalnim i kiselim rastvorima. Platina je taložena potenciostatskom pulsnom metodom na GC podlogu iz H2SO4 + H2PtCl6 rastvora pod istim uslovima u količini od 10 to 80 mg cm-2. AFM i STM slike GC/Pt elektroda pokazuju da je Pt istaložena u obliku 3D aglomerata koji se sastoje od sfernih čestica. Duže vreme taloženja dovodi do povećanog rasta Pt formi i smanjenja specifične površine nataložene platine. Realna površina istaložene platine raste sa povećanjem količine istaložene platine dostižući plato. Bez obzira na ovo, specifična i masena aktivnost platine istaložene na staklasti ugljenik za oksidaciju metanola kako u kiselim tako i u alkalnim rastvorima pokazuje vulkansku zavisnost od količine istaložene platine. Povećanje aktivnosti se može objasniti preko povećanja veličine čestica sa količinom istaložene platine, odnosno preko povećanja susednih Pt mesta dostupnih za adsorbciju i dekompoziciju metanola. Međutim, smanjenje katalitičke aktivnosti sa daljim povećanjem količine istaložene platine i veličine njenih čestica nakon postignutog maksimuma je povezano sa smanjenjem broja aktivnih mesta dostupnih za adsorpciju metanola i rezultat je smanjenja rastojanja i izraženog stapanja Pt čestica

Mikrotalasna sinteza i karakterizacija Pt i Pt-Rh-Sn katalizatora za oksidaciju etanola

Carbon-supported Pt and Pt-Rh-Sn catalysts were synthesized by the microwave-polyol method in ethylene glycol solution and were investigated in the ethanol electro-oxidation reaction. The catalysts were characterized in terms of structure, morphology and composition employing the X-ray diffraction (XRD), scanning tunneling microscopy and energy-dispersive X-ray spectroscopy techniques. The STM analysis indicated rather uniform particles and particle sizes below 2 nm for both catalysts. The XRD analysis of the Pt/C catalyst revealed two phases, one with the main characteristic peaks of the face-centered cubic crystal structure (fcc) of platinum and the other related to the graphite-like structure of the carbon support, Vulcan XC-72R. However, in the XRD pattern of the Pt-Rh-Sn/C catalyst, diffraction peaks for Pt, Rh or Sn could not be resolved, indicating extremely low crystallinity. The small particle sizes and homogeneous size distributions of both catalysts could be attributed to the advantages of the microwave-assisted modified polyol process in ethylene glycol solution. The Pt-Rh-Sn/C catalyst was highly active for ethanol oxidation with the onset potential shifted by more than 150 mV to more negative values and with currents nearly 5 times higher in comparison to the Pt/C catalyst. The stability tests of the catalysts, as studied by chronoamperometric experiments, revealed that the Pt-Rh-Sn/C catalyst was evidently less poisoned than the Pt/C catalyst. The increased activity of Pt-Rh-Sn/C in comparison to Pt/C catalyst was most probably promoted by the bi-functional mechanism and the electronic effect of the alloyed metals.Pt i Pt-Rh-Sn katalizatori na ugljeniku razvijene površine su sintetizovani poliol-mikrotalasnim postupkom u rastvoru etilenglikola i ispitivani za reakciju eletrohemijske oksidacije etanola u kiseloj sredini. Katalizatori su okarakterisani strukturno, morfološki i po sastavu korišćenjem XRD, STM i EDX tehnika. STM analiza je potvrdila da su Pt i Pt-Rh-Sn čestice uniformne veličine i prečnika manjeg od 2 nm. XRD analiza Pt/C katalizatora pokazala je prisustvo dve faze, jedne sa glavnim karakterističnim pikovima za pljosno-centriranu kubnu kristalnu strukturu platine (111, 200, 220 i 311) i druge sa difrakcionim pikom na 2q oko 25° karakterističnim za heksagonalnu strukturu vulkana XC-72R (ugljeničnog nosača). XRD analiza Pt-Rh-Sn/C katalizatora nije pokazala karakteristične pikove, što je indikacija veoma male kristaličnosti katalizatora. Aktivnost katalizatora ispitivana je potenciodinamičkim i hronoamperometrijskim merenjima. Pt-Rh-Sn/C katalizator je veoma aktivan za oksidaciju etanola sa početkom reakcije na potencijalima za oko 150 mV pomerenim ka negativnijim vrednostima i strujama koje su oko pet puta veće u poređenju sa Pt/C katalizatorom. Stabilnost katalizatora ispitivana hronoamperometrijski pokazala je da se Pt-Rh-Sn/C katalizator manje truje od Pt/C katalizatora. Mala veličina i homogena distribucija čestica mogu se pripisati prednostima mikrotalasne sinteze i modifikovanog poliol postupka u rastvoru etilenglikola. Veća aktivnost Pt-Rh-Sn/C katalizatora u poređenju sa Pt/C katalizatorom posledica je bi-funkcionalnog mehanizma i elektronskog (ligand) efekta metala u sintetizovanoj leguri

Platinum electrocatalyst supported on glassy carbon: a dynamic response analysis of Pt activity promoted by substrate anodization

In previous investigations the physicochemical state of electrochemically activated glassy carbon (GC) has been found to affect the electrochemical activity of GC-supported Pt particles. It has been assumed that carbon functional groups (CFGs) generated by GC anodization are able to renew the Pt surface through bifunctional catalysis. In order to provide evidence for the intimate electrocatalytic relationship between Pt and anodized GC and reveal the cause of CFG-induced enhancement of Pt activity, the dynamic response of Pt black supported on differently anodized GC is analysed in this paper by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in acidic solution. It was found that the capacitive properties of Pt black are not affected by modest GC anodization, but the pore resistance of the Pt layer is considerably affected. Clear evidence for the promoting influence of activated GC (i.e., CFGs) on the Pt desorption capability toward reverse hydrogen spillover at a Pt/CFGs-decorated GC interface in the Pt double layer region is elucidated by both EIS and CV measurements. The extent of GC anodization influences, in a quite similar way, both reverse hydrogen spillover desorption parameters (gained by EIS and CV) and the methanol oxidation rate as it has influence on the parameters describing the particular state of activated GC itself. Namely, the pore resistance of the Pt layer and GC resistance due to the presence of CFGs the highest when GC was moderately anodized, whereas the charge transfer resistance for hydrogen spillover desorption is the lowest. The CFGs of the anodized GC are able to "permeate" the above-applied Pt layer, thus increasing the Pt/ CFGs-decorated GC interface responsible for the enhancement of Pt electrochemical activity

Promotivni efekat Zn u platinskom katalizatoru za efikasnu reakciju elektrooksidacije etanola

Polymer electrolyte membrane fuel cells (PEMFCs) are pure electrochemical energy converters that are key components of energy sources for vehicles and for stationary and portable energy suppliers. Searching for a good catalyst for the ethanol oxidation reaction is one of the most significant issues in material science. To increase the economic potential of fuel cell technology, catalyst must be extremely active, stable, and inexpensive. Due to its high catalytic activity, structural and chemical stability, and widespread use in commercial fuel cells, platinum is still the material of choice for making cathodes. Although there is extensive continuing research to reduce the Pt concentration while keeping the high catalytic activity, its high cost remains a barrier to a wider adoption of fuel cell technology.Therefore, the potential for cost reduction lies in the optimization of the catalyst, i.e. obtaining the maximum catalytic efficiency with the lowest possible content of noble metals. The focus of this research will be on novel synthesis techniques for PtSnZn catalysts with better efficiency and durability for the ethanol oxidation reaction. This research demonstrates the potential of studying new PtSnZn catalytic materials as catalysts for the oxidation of ethanol. This study used the microwave assisted polyol technique to create PtZn and PtSnZn nanoparticles supported on high surface area carbon Vulcan XC-72R material. By using cyclic voltammetry, electro-oxidation of adsorbed CO, and the chronoamperometric method, the electrochemical behavior of synthesized catalysts was examined. X-ray diffractometry, transmission electron microscopy analysis and thermogravimetric analysis were applied to obtain the physicochemical properties of the catalyst. The advantages of microwave synthesis and carefully balanced metal alloying in the PtSnZn/C catalysts led to a high catalytic activity of the synthesized catalyst in the ethanol oxidation reaction compared to the Pt/C catalyst

Elektrooksidacija metanola na binarnim i ternarnim platinskim katalizatorima na ugljeničnom nosaču

One of the most popular alternative sources of energy are direct methanol fuel cells (DMFCs) with platinum-based catalysts due to their non-toxicity, reduced emissions of hazardous pollutants and high energy density. However, significant challenges of the scientific community related to Pt catalysts are the high cost, depletable resources and formation of poisoning species i.e. CO, during the methanol oxidation reaction. To reduce the amount of expensive Pt and susceptibility of Pt to poisoning species and simultaneously improve its catalytic performance, recent studies are focusing on the synthesis of Pt alloys in which a certain amount of platinum is replaced with less expensive metals such as Ru, Sn, Ni, Cu, Rh and Co. The usage of carbon (Vulcan XC-72R) for catalyst support enables high dispersion of metal, high surface area and good electrical conductivity improving overall performances of DMFCs. In this work, PtZn/C and PtSnZn/C catalysts were synthesized by the microwave-assisted polyol method. The structure and morphology of the catalysts were characterized by transmission electron microscopy (TEM), thermogravimetric (TG) and X-ray diffraction (XRD) analysis. The activity and stability of synthesized catalysts for methanol oxidation in 0.5 M sulfuric acid were investigated. It was demonstrated that the activity of the platinum catalysts was improved thanks to the synergistic effects caused by the addition of different metals, such are bifunctional and electronic effects

Initial stages of water solvation of stepped platinum surfaces

Catalysis and Surface Chemistr

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

A guide to ancient protein studies

Palaeoproteomics is an emerging neologism used to describe the application of mass spectrometry-based approaches to the study of ancient proteomes. As with palaeogenomics (the study of ancient DNA), it intersects evolutionary biology, archaeology and anthropology, with applications ranging from the phylogenetic reconstruction of extinct species to the investigation of past human diets and ancient diseases. However, there is no explicit consensus at present regarding standards for data reporting, data validation measures or the use of suitable contamination controls in ancient protein studies. Additionally, in contrast to the ancient DNA community, no consolidated guidelines have been proposed by which researchers, reviewers and editors can evaluate palaeoproteomics data, in part due to the novelty of the field. Here we present a series of precautions and standards for ancient protein research that can be implemented at each stage of analysis, from sample selection to data interpretation. These guidelines are not intended to impose a narrow or rigid list of authentication criteria, but rather to support good practices in the field and to ensure the generation of robust, reproducible results. As the field grows and methodologies change, so too will best practices. It is therefore essential that researchers continue to provide necessary details on how data were generated and authenticated so that the results can be independently and effectively evaluated. We hope that these proposed standards of practice will help to provide a firm foundation for the establishment of palaeoproteomics as a viable and powerful tool for archaeologists, anthropologists and evolutionary biologists