CO and trans-cinnamaldehyde as corrosion inhibitors of I825, L80-13Cr and N80 alloys in concentrated HCl solutions at high pressure and temperature

Peer reviewedPostprin

MECHANISTIC STUDIES OF THE COMPLETE ELECTROCHEMICAL OXIDATION OF ETHANOL INTO CO2 OVER PLATINUM-BASED CORE-SHELL NANOCATALYSTS

Direct ethanol fuel cells (DEFCs) are a promising technology for the generation of electricity via the direct conversion of ethanol into CO2, showing higher thermodynamic efficiency and volumetric energy density than hydrogen fuel cells. However, implementation of DEFCs is hampered by low selectivity of CO2 generation at the anode where the ethanol oxidation reaction (EOR) happens. Therefore, anode catalysts with high reactivity for the EOR and high selectivity for CO2 generation via breaking C-C bond are highly needed. To evaluate the catalysts’ capability of splitting C-C bond of the ethanol molecule, highly sensitive CO2 detection technique was developed in this research using a CO2 microelectrode. Such an in situ CO2 measurement tool enabled the real time detection of the partial pressure of CO2 during the EOR using linear sweeping voltammetry measurements, through which electro-kinetic details of CO2 generation could be obtained. Electro-kinetics of CO2 generation were studied on the PtRh/SnO2 core-shell catalysts made by a ‘surfactant-free’ method. The results showed that Pt and Rh components located in the core were partially oxidized and therefore improved the CO2 generation at low electrical potential. In addition, in situ CO2 measurements provided the mechanistic understanding of potentiodynamics of the EOR, particularly the influence of *OH adsorbates on CO2 generation rate and CO2 selectivity. Our results showed that at low potential, inadequate *OH adsorbates impaired the removal of reaction intermediates, and thus Pt/Rh/SnO2 exhibited the best performance toward CO2 generation due to its strong ability to dissociate water molecules forming *OH oxidants, while at high potential, Rh sites were overwhelmingly occupied (poisoned) by *OH adsorbates, and thus Pt/SnO2 exhibited the best performance toward CO2 generation

Improved electrocatalytic activity of Pt on carbon nanofibers for glucose oxidation mediated by support oxygen groups in Pt perimeter

Support effects in supported metal catalysts are well studied for thermocatalytic reactions, but less studied for electrocatalytic reactions. Here, we prepared a series of Pt supported on carbon nanofiber catalysts which vary in their Pt particle size and the content of oxygen groups on the surface of the CNF. We show that the activity of these catalysts for electrocatalytic glucose oxidation relates linearly with the content of support oxygen groups. Since the electronic state of Pt (XAS) and Pt surface structure (CO-stripping) were indistinguishable for all materials, we conclude that sorption effects of glucose play a crucial role in catalytic activity. This was further confirmed by establishing a relation between the annulus of the Pt particles and the activit

Improved electrocatalytic activity of Pt on carbon nanofibers for glucose oxidation mediated by support oxygen groups in Pt perimeter

Support effects in supported metal catalysts are well studied for thermocatalytic reactions, but less studied for electrocatalytic reactions. Here, we prepared a series of Pt supported on carbon nanofiber catalysts which vary in their Pt particle size and the content of oxygen groups on the surface of the CNF. We show that the activity of these catalysts for electrocatalytic glucose oxidation relates linearly with the content of support oxygen groups. Since the electronic state of Pt (XAS) and Pt surface structure (CO-stripping) were indistinguishable for all materials, we conclude that sorption effects of glucose play a crucial role in catalytic activity. This was further confirmed by establishing a relation between the annulus of the Pt particles and the activity.</p

Selective electrocatalysis of anodic oxygen-transfer reactions at chemically modified, thin-film lead dioxide electrodes

The strategy to modify PbO[subscript]2 electrodes for electrocatalysis of oxygen-transfer (O-t) reactions is to incorporate spatially separated catalytic sites into the PbO[subscript]2 surface. The rate of ·OH radical formation is promoted at these sites, as is the rate of the O-t reaction, for the latter was demonstrated to be proportional to the former;The electrodeposition of PbO[subscript]2 was studied as a special case of a heterogeneous O-t reaction. Soluble Pb(IV) species were detected with a rotated ring-disc electrode as intermediate products of the PbO[subscript]2 deposition. These unstable Pb(IV) species are partially responsible for the catalytic activities of in-situ depositied PbO[subscript]2 electrode, as studied by voltammetry, spectrophotometry, and flow-injection analysis;Chemically modified PbO[subscript]2 is electrodeposited by addition of Bi[superscript]3+, As(III), or Cl[superscript]- to the Pb[superscript]2+ plating bath. The electrochemical stability and catalytic activity of the Bi-doped PbO[subscript]2 (Bi-PbO[subscript]2) increase with increased Bi/Pb atomic ratio in the mixed oxide which were determined by X-ray photoelectron spectroscopy;Microcracked, ultra-thin films of Bi-PbO[subscript]2 were found at Au, Pt, GC, and Ti electrodes after consecutive deposition and stripping of the thick oxide films. The ultra-thin film has higher catalytic activity and stability than the original film, due to an enhanced Bi surface concentration. The morphology and structure of the ultra-thin films were studied by scanning electron microscope and X-ray diffraction;The surface of pure PbO[subscript]2 can be modified by Bi[superscript]3+, As(V), and Cl[superscript]- by electroadsorption. The adsorption method to modify PbO[subscript]2 is fast and efficient for screening new catalysts. The catalytic activity of Bi[superscript]3+-adsorbed PbO[subscript]2 was determined to result in well-defined, mass transport-limited voltammetric plateaus for the anodic reactions Mn[superscript]2+ → MnO[subscript]4[superscript]-, Cr[superscript]3+ → CrO[subscript]4[superscript]-, (CH[subscript]3)[subscript]2SO → (CH[subscript]3)[subscript]2SO[subscript]2, and (CH[subscript]2)[subscript]4SO → (CH[subscript]2)[subscript]4SO[subscript]2. The E[subscript]1/2 values for these varied processes are virtually the same. The E[subscript]1/2 values are a function of the surface concentration of the catalyst and only slightly influenced by the identity of the catalyst;An O-t mediation mechanism was proposed for the electrocatalysis observed at the chemically modified PbO[subscript]2. The catalysts serve as O-t mediators, which are different from electron-transfer mediators by not undergoing any redox change during the catalysis. ftn[superscript]1This work was performed in Ames Laboratory under Contract No. W-7405-Eng-82 with the U.S. Department of Energy

Dye removal by nano-sized metal coated electrodes

Tez (yüksek lisans) - Anadolu ÜniversitesiAnadolu Üniversitesi, Fen Bilimleri Enstitüsü, İleri Teknolojiler Anabilim DalıKayıt no: 20884Tekstil endüstrisi gelişmekte olan ülkelerde çok yaygındır. Tekstil endüstrisinin farklı süreçleri arasında, boyama sürecinde, boyama, sabitleme ve yıkama için çok miktarda su sarf edilmektedir. Tekstil atık suyunun karakteristiği asılı parçacıklar, tuzlar, yüksek pH ve yüksek kimyasal oksijen ihtiyacı (KOİ) derişimidir. Bu toksik atık suların çevreye deşarj edilmesi önemli problemlere neden ola bilir. Nanoteknoloji teknikleri ve malzemeleri farklı alanlarda başarılı olmuştur ve atık su arıtımında bor kaplı elmas (BDD) elektrotlar renk giderim süreçlerinde başarı ile kullanılmıştır. Bu çalışmada, tıkaç akım reaktörde, bor katkılı elmas elektrotlar kullanılarak Reactive Black 5 (RB5) boyarmaddesinin elektrokimyasal yükseltgemesi gerçekleştirilmiştir. Bor katkılı elmas elektrotların yarısı anot ve yarısı katot olarak davranıyor. Farklı parametreler arıtım surecini etkiliyor ki deneyler sırasında araştırılmıştır. Akış hızı, destek elektrolit olarak sodyum sülfat derişimi (Na2SO4), başlangıç pH, akım yoğunluğu ve başlangıç boyar madde derişimi gibi deneysel parametreler incelendi. Elde edilen en iği şartlar şöyledir: akım yoğunluğu 1 mA/cm2, doğal pH, akış hızı 100 mL/min, sodyum sülfat derişimi 0.02 mol/L. En iği deneysel şartlar elde edildikten sonra sürecin güvenirliğini kanıtlamak için toplam organik karbon (TOC), KOİ ve toksisite çalışmaları yapılmıştır. Bu şartlar altında, %97 renk, ~%51 KOİ ve %29,3 TOK giderimi elde edilmiştir. RB5 boyar maddesinin toksisitesi de başlangıç toksisite oranına göre azalmıştır

Palladium electrodissolution from model surfaces and nanoparticles

Palladium (Pd) is considered as a possible candidate as catalyst for proton exchange membrane fuel cells (PEMFCs) due to its high activity and affordable price compared to platinum (Pt). However, the stability of Pd is known to be limited, yet still not fully understood. In this work, Pd dissolution is studied in acidic media using an online inductively coupled plasma mass spectrometry (ICP-MS) in combination with an electrochemical scanning flow cell (SFC). Crucial parameters influencing dissolution like potential scan rate, upper potential limit (UPL) and electrolyte composition are studied on a bulk polycrystalline Pd (poly -Pd). Furthermore, a comparison with a supported high -surface area catalyst is carried out for its potential use in industrial applications. For this aim, a carbon supported Pd nanocatalyst (Pd/C) is synthesized and its performance is compared with that of bulk poly -Pd. Our results evidence that the transient dissolution is promoted by three main contributions (one anodic and two cathodic). At potentials below 1.5 VRHE the anodic dissolution is the dominating mechanism, whereas at higher potentials the cathodic mechanisms prevail. On the basis of the obtained results, a model is thereafter proposed to explain the transient Pd dissolution.(C) 2017 Elsevier Ltd. All rights reserved

Oxidation of Methanol and Carbon Monoxide on Platinum Surfaces : The Influence of Foreign Metals

Despite of its fairly simple chemical structure, the oxidation of methanol at electrode surfaces follows a fairly complicated mechanism with parallel reaction paths and several reaction steps. Within the context of the search for better catalysts for fuel cells, the influence of various parameters such as potential, temperature, catalyst composition and structure on the single reaction steps were elucidated with the help of CO oxidation and the adsorption and oxidation of methanol on carbon supported Pt nanoparticles, polycrystalline Pt and Pt(665) as well as the influence of foreign metals such as Ru and Mo on these reactions has been studied by differential electrochemical mass spectrometry (DEMS) under continuous flow conditions. The rates and activation energies of the single reaction steps as well as the influence of the catalyst composition and structure was determined by measuring of the adsorption rate of methanol, the oxidation of the methanol adsorbate as well as the rate of the bulk methanol oxidation, where the ion current of the CO2 was detected in parallel to the faradaic current. Catalysts, and this also includes Ru and Se modified catalyst which are important as cathode material for O2 reduction in the fuel cells, were characterized by stripping of adsorbed CO and of underpotential deposition of Cu (CuUPD). It was shown that the active surface area, determined from the CO stripping, agrees with that calculated from the particle size assuming a narrow distribution and a spherical shape of the colloid particles. On the Se modified nanoparticle surfaces, it is shown that Se blocks the adsorption sites for CO, the free adsorption sites can be detected by the CuUPD). The maximum methanol adsorption rate found at room temperature at polycrystalline Pt is ca. 0.06 ML s-1, whereas at Pt nanoparticles it is ca. 0.04 ML s-1. At 50°C the rate constants of the methanol adsorption increases markedly on both electrodes. On polycrystalline Pt the maximum coverage of the methanol adsorbate amounts to 56% of a full CO monolayer, obtained by adsorbing CO from a CO saturated electrolyte. On the nanoparticles only 28% of a full CO monolayer can be obtained. The oxidation rate of the methanol adsorbate was found to be of zeroth order at polycrystalline Pt, whereas at nanoparticles it is of first order with respect to the coverage. At polycrystalline Pt and Pt(665), the rate of CO2 formation is determined by the oxidation rate of the adsorbate. At the nanoparticle electrodes, the rate of CO2 formation from bulk methanol is higher than that from the methanol adsorbate, due to the roughness of these electrodes. At Ru containing Pt surfaces the oxidation of the methanol adsorbate was shifted to lower potentials and a higher adsorption rate was observed in comparison to the pure Pt surface. It was observed that the Ru ad-atoms promote the reaction path via adsorbed CO in the low potential region. At higher potentials the Ru loses its co-catalytic activity towards methanol oxidation; possibly due to the formation of inactive anhydrous Ru oxide at higher potentials. Using isotopic labelling, the interaction of methanol and carbon monoxide with its adsorbed species on Pt and platinum based electrodes was also studied. It was shown that pure Pt surfaces modified by 0.2 ML of Ru offer different adsorption sites for CO, which can be selectively populated. On these sites, adsorption and oxidative desorption of CO can be selectively performed and 12CO at the sites with lower adsorption enthalpy can be replaced by 13CO. The additional deposition of Mo onto the Pt nanoparticle surfaces modified with 0.2 ML of Ru showed that the co-catalytic effect of Ru and of Mo in CO oxidation can be combined in a synergetic sense. On the other hand, no significant improvements on methanol oxidation were found. An enhancement of the overall methanol oxidation reaction for bulk methanol by the elevating temperature was observed and the overall apparent activation energies, determined from the faradaic current, as well as the apparent activation energies for theindirect oxidation pathway via adsorbed CO, determined from the ion current of CO2, were calculated. The comparison of both kinds of activation energies confirmed that the Ru containing Pt surfaces have a positive effect on the catalytic activity towards methanol oxidation via adsorbed CO

10 years of frontiers in carbon-based materials: carbon, the “newest and oldest” material. The story so far

While carbon in itself appears as simple an element as it could possibly get, the undeniable truth is that carbon materials represent a plethora of possibilities both from the perspective of their structure and their applications. While we may believe that carbon is “just another element”, one should never forget that its special ability to coordinate through different hybridizations with apparent ease grants the element properties that no other element may even match. Taking this one step further into the materials realm opens up numerous avenues in terms of materials dimensionality, surface and bulk functionalization, or degree of structural order just to mention a few examples. If these properties are translated into the properties and applications field, the results are just as impressive, with new applications and variants appearing with growingly larger frequency. This has resulted in over a million scientific papers published in the last decade in which the term “carbon” was used either in the title, abstract or keywords. When the search is narrowed down to the field “title” alone, the results drop to just over 318.000 scientific papers. These are figures that no other element in the periodic table can equal, which is a clear indicative that the story of carbon materials is still under constant evolution and development. This review will present an overview of the works published in the Frontiers in Carbon-based materials section during its 10 years of life that reflect the advancements achieved during the last decade in the field of carbon materials

Oxygen reduction reaction on oriented thin films: an alternative approach to electrocatalytic studies on model surfaces.

Les piles à combustible (PC) peuvent aider à atténuer les effets délétères de l'utilisation de combustibles fossiles sur l'environnement, mais leur coût élevé et leur fonctionnement limité à long terme entravent leur commercialisation. Pour résoudre ces problèmes, de nouveaux matériaux d'électrode sont nécessaires pour remplacer le platine (Pt) dans les PC, en particulier à la cathode. Des charges élevées de Pt sont utilisées comme électrocatalyseur de réaction de réduction d'oxygène (RRO) dans cette électrode. L'RRO est une réaction lente et complexe, et même sur les surfaces Pt, elle se déroule loin de son potentiel thermodynamique, provoquant des pertes d'énergie. Les voies pour résoudre ces problèmes sont soit d'améliorer les performances du Pt, soit de développer de nouveaux matériaux pour le remplacer. Pour concevoir de nouveaux matériaux pour l'RRO, les descripteurs d'activité doivent être bien compris. Dans cette perspective, les études de réactions électrochimiques sur des surfaces ayant une structure bien définie - c'est-à-dire les études modèles - représentent un outil important dans l'élucidation des mécanismes de réaction, pour l'identification des sites actifs et pour permettre la déconvolution de la réponse électrochimique des surfaces. Ainsi, les études sur des surfaces modèles ouvrent la voie au progrès d'électrocatalyse. Concernant l'RRO, traditionnellement, ces études sont menées à l'aide de monocristaux et de méthodes hydrodynamiques. Cependant, certains matériaux ne peuvent pas être évalués en utilisant les voies conventionnelles, et pour ces cas, nous avons besoin de voies alternatives pour étudier l'ORR. Dans ce contexte, l'objectif principal de cette thèse est de proposer une voie alternative pour réaliser des études électrocatalytiques de l’RRO sur des surfaces modèles. A cet effet, des films minces à orientation épitaxiale déposés par dépôt laser pulsé (DLP) sont présentés comme des surfaces modèles appropriées. Des films minces de Pt et Au ont été déposés sur des substrats de MgO(hkl) et caractérisés structurellement par diffraction des rayons-X et électrochimiquement par voltammétrie cyclique. Pour évaluer l'activité électrocatalytique de l’RRO de ces films, la voltampérométrie du courant échantillonné (VCE) est présentée et validée comme alternative à l'utilisation des assemblages électrode à disque rotatif (EDR). Les résultats présentés dans cette thèse démontrent que le DLP fournit des films minces épitaxiés qui se comportent comme des électrodes monocristallines. De plus, grâce aux coefficients de transfert de masse, il est possible d'obtenir des courbes de polarisation avec VCE semblables à celles enregistrées avec une configuration EDR. Par conséquent, une méthodologie complète pour étudier l'RRO sur les surfaces du modèle est fournie. Avec cette méthodologie, nous pouvons poursuivre la conception, la préparation et la caractérisation de matériaux avancés pour cette réaction, ce qui peut conduire à un progrès dans le domaine de la conversion énergétique en fournissant une meilleure compréhension des descripteurs d'activité pour l'RRO et en dévoilant de nouveaux matériaux. Fuel cells (FCs) may alleviate the deleterious effects of the use of fossil fuels on the environment, but their high cost and limited long-term operation hinder their commercialization. To address these issues, new electrode materials are necessary to replace platinum in the FCs, especially in the cathode. High loadings of Pt are used as the oxygen reduction reaction (ORR) electrocatalyst in this electrode. The ORR is a sluggish and complex reaction, and even on Pt surfaces, it takes place far from its thermodynamic potential, causing energy losses. The pathways to solve these concerns are either to improve the performance of Pt or develop new materials to replace it. To design new materials for the ORR, activity descriptors need to be well understood and used to devise better electrocatalysts. From this perspective, studies of electrochemical reactions on surfaces with well-defined structures – i.e., model studies – represent a fundamental tool in the elucidation of reaction mechanisms, on the identification of active sites, and the deconvolution of the electrochemical response of the surfaces. Thus, model studies pave the way for the progress of electrocatalysis. Concerning the ORR, traditionally, these studies are pursued using single crystals and hydrodynamic methods, as the rotating disk electrodes (RDE). However, some materials cannot be assessed using the conventional routes, and for those cases, we need alternative routes to study the ORR. In this context, this thesis main objective is to provide an alternative route to perform ORR electrocatalytic studies on model surfaces. For this purpose, thin films with epitaxial orientation deposited by pulsed laser deposition (PLD) are presented as suitable model surfaces. Pt and Au thin films were deposited on MgO substrates and characterized structurally by X-ray diffraction and electrochemically by cyclic voltammetry. To assess the ORR electrocatalytic activity of these films, sampled current voltammetry (SCV) is presented and validated as an alternative to the RDE assemblies' use. The results presented in this thesis demonstrate that PLD provides thin films with epitaxial orientation that behave similarly to single crystal electrodes. It was demonstrated how to obtain polarization curves with SCV akin to those recorded with an RDE setup by adjusting the mass transfer coefficients. Hence, a full methodology to study the ORR on model surfaces is provided. With this methodology, we can pursue the design, preparation, and characterization of advanced materials for this reaction, leading to progress in the energy conversion field by contributing to a better comprehension of the activity descriptors for the ORR and unveiling new materials