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

Synergistic Effects of the Supporting Material and Annealing Temperature on the Performance of Pt Thin Film Catalysts

The electrocatalytic oxidation of small organic molecules, such as methanol, ethanol and formic acid has been extensively studied due to their properties that make them suitable for use in fuel cells. Particularly, the electrochemical oxidation of formic acid has been comprehensively examined as the anodic reaction in direct formic acid fuel cell. The main goal in the development of the catalysts for formic acid oxidation (FAO) is to find the optimal balance between catalytic performance (activity/stability) and the catalyst cost, i.e. quantity of the noble metal used. In the work presented herein, we explored the synergistic effects of the supporting material and annealing temperature on the performance of Pt thin film catalysts for FAO in acidic media. Our results show that compared to the as-prepared Pt films, the annealed (500 oC) films show exceptional activity for FAO reaction on both Pt/Ni and Pt/Cr catalysts, with 5-fold and 15-fold improvement, respectively. The 500 oC annealed Pt/Cr catalyst was found to be the most active, the most selective and the most stable catalyst in our study. A catalyst with the best marks for all three characteristics is a very rare find in electrocatalysis in general.Lectur

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

Formic Acid Electrooxidation on Cr-Supported Platinum Thin Film Catalyst

In this study, the formic acid electrooxidation reaction was studied on a platinum thin film catalyst obtained by deposition on chromium support (Pt/Cr). In an attempt to reduce the proneness of Pt to poisoning species i.e. CO and improve the catalytic performance of Pt/Cr at low potentials in the formic oxidation reaction, the as- prepared catalyst was modified using controlled thermal treatment. The influence of thermal treatment on the electrode surface morphology was monitored using an atomic force microscope (AFM). Thus obtained catalyst was electrochemically characterized with cyclic voltammetry and oxidation of CO monolayer, while the performance of the catalyst was tested in a formic acid oxidation reaction. The improved activity on annealed Pt/Cr system is a consequence of the surface reconstruction of Pt film with predominant (111) orientation. Compared to other facets, the (111) facet selectively favors direct HCOOH oxidation, avoiding Coad poisoning at low potentials. Moreover, the Pt (111) facets offer improved stability of the catalyst compared to the as-prepared polycrystalline film. Finally, the Cr substrate also experiences improved stability after annealing, presumably due to the formation of a protective oxide layer. Thus, with the successful choice of the supporting material and annealing temperature, we were able to create a thin film catalyst with improved activity, selectivity and stability, in contrast with commonly observed activity-stability tradeoff in catalysis

The influence of substrate and thermal annealing on calalytic activity and stability of Pt thin film catalysts

In this study, we have investigated how the change in surface composition of Pt thin film deposited on Ni and Cr supports, induced by the controlled thermal treatment, reflects on catalyst performance for the electrooxidation of formic acid

Enhanced Pt@Ni catalysts obtained by galvanic displacement method for successful methanol electrooxidation

The successful development of catalysts for the electrooxidation of small organic molecules, such as methanol, requires finding an optimal balance between the catalyst's cost and its activity/stability. Thus far, platinum (Pt) remains one of the best choice for methanol electrooxidation, despite its high costs, limited supply and tendency to poison with carbon monoxide (CO). In this work, the synergistic effect of the supporting material and annealing temperature in different atmospheres on the performance of the Pt@Ni catalyst was examined. The thin film Pt@Ni catalyst was obtained through spontaneous galvanic displacement by placing a drop of hexachloroplatinic acid onto the Ni support. To mitigate platinum susceptibility to poisoning species such as CO and enhance the catalytic efficiency of Pt@Ni at low potentials in methanol oxidation, the as-prepared catalyst was modified using controlled thermal treatment in a reductive atmosphere containing 5 % H2 and in an inert atmosphere (N2). The activity of the catalysts was tested in the methanol oxidation reaction, while the influence of thermal treatment on the surface morphology was monitored using atomic force microscopy (AFM). Preliminary results have indicated that the galvanic displacement method produces ultra-thin film Pt@Ni catalysts, which were further enhanced through controlled thermal treatment. The catalysts annealed in the inert atmosphere demonstrated superior activity compared to the as prepared and catalyst annealed in the reducing atmosphere

The design of advanced thin-film catalysts for electrooxidation of formic acid

Successful development of catalysts for electrochemical formic acid oxidation (FAO) requires finding an optimal balance between catalytic performance (activity/stability/selectivity) and the catalyst cost. While platinum is one of the most active catalyst materials for FAO, it suffers from performance loss at low overpotentials due to poisoning with CO, which is one of the intermediates formed in the so-called indirect path of FAO. In this work, we explored the synergistic effects of the supporting material and annealing temperature on the performance of Pt thin films over Cr support for FAO in acidic media. In an attempt to reduce the proneness of Pt to poisoning species i.e. CO and improve the catalytic performance of Pt/Cr at low potentials in the formic oxidation reaction, the as-prepared catalyst was modified using controlled thermal treatment. The influence of thermal treatment on the surface morphology was monitored using atomic force microscopy (AFM). The catalyst was electrochemically characterized with cyclic voltammetry and oxidation of CO monolayer, while the performance of the catalyst was tested in formic acid oxidation reaction. Based on the obtained results it was concluded that the improved activity on the annealed Pt/Cr system is a consequence of surface reconstruction of Pt film with predominant (111) orientation. Compared to other facets, the (111) facet selectively favors the oxidation of HCOOH via the direct path, avoiding the formation of COad at low potentials. Moreover, the Pt (111) facets offer improved stability of the catalyst compared to the as-prepared polycrystalline film. Finally, the Cr substrate also experiences improved stability after annealing, presumably due to the formation of a protective oxide layer. Thus, with the successful choice of the supporting material and annealing temperature, we were able to create a thin film catalyst with improved activity, selectivity, and stability, challenging conventional trade-offs in electrocatalysis

General platform for hydro-information systems – a review of concept

This paper provides insight into the Institute's long-standing engagement in the design and implementation of hydroinformatics systems in Serbia and the region. The introduction provides a definition of the hydroinformatics system and different areas of application, as well as an overview of the best practices in the world. An overview of the general platform that was created based on experience in the development of different systems has been presented here. We have described the functionalities integrated into a single software platform based on mathematical models and computational services. Various practical examples of application by the Institute are presented with the specifics of implementation in line with the purpose and characteristics of the studied systems. The conclusion highlights the role of applied hydroinformatics systems and the effects of application by users. Possible further development and implementation directions in water management and hydropower systems in Serbia and the region have been also presented.Conference in the honour of 75 years of the Jaroslav Černi Water Institute, held in the Serbian Academy of Sciences and Arts, October 19-20th, 2022

Design of PtSnZn Nanocatalysts for Anodic Reactions in Fuel Cells

In order to achieve widespread application of fuel cell technology, the development of an efficient and economical catalyst is a crucial step. Reducing the diameter of catalyst particles, producing particles with a specific orientation surface, and alloying noble metals with less expensive metals are possible approaches to improve catalyst performance. This study will be focused on novel ways for creating PtSnZn catalysts that are more effective for the anodic reactions in fuel cell such are methanol, ethanol and formic acid oxidation reactions. PtZn and PtSnZn nanoparticles were produced using the microwave assisted polyol method and were supported on high surface area carbon Vulcan XC-72R material. The electrochemical behavior of synthesized catalysts was investigated utilizing the cyclic voltammetry, chronoamperometric technique, and electro-oxidation of adsorbed CO. To determine the catalyst's physicochemical characteristics, X-ray diffraction (XRD), transmission electron microscopy analysis (TEM), and thermogravimetric analysis (TGA) were used. High catalytic activity of the PtSnZn/C catalysts was achieved thanks to the benefits of microwave synthesis and carefully adjusted metal alloying

Influence of treatment of various carbon supports on electrochemical activity of Pt catalysts

Poster presented at: 4th International Congress of Chemists and Chemical Engineers of Bosnia and Herzegovina, June, 30th-July, 02nd, Sarajevo, Bosnia and HerzegovinaAbstract: [https://cer.ihtm.bg.ac.rs/handle/123456789/5215