Surface Oxygen-containing Species Research Articles

Mechanism of surface oxygen-containing species promoted electrocatalytic CO2 reduction

Oxygen-containing species have been demonstrated to play a key role in facilitating electrocatalytic CO2 reduction (CO2RR), particularly in enhancing the selectivity towards multi-carbon (C2+) products. However, the underlying promotion mechanism is still under debate, which greatly limits the rational optimization of the catalytic performance of CO2RR. Herein, taking CO2 and O2 co-electrolysis over Cu as the prototype, we successfully clarified how O2 boosts CO2RR from a new perspective by employing comprehensive theoretical simulations. Our results demonstrated that O2 in feed gas can be rapidly reduced into *OH, leading to the partial oxidation of Cu surface under reduction conditions. Surface *OH accelerates the formation of quasi-specifically adsorbed K+ due to the electrostatic interaction between *OH and K+ ions, which significantly increases the concentration of K+ near the Cu surface. These quasi-specifically adsorbed K+ ions can not only lower the C–C coupling barriers but also promote the hydrogenation of CO2 to improve the CO yield rate, which are responsible for the remarkably enhanced efficiency of C2+ products. During the whole process, O2 co-electrolysis plays an indispensable role in stabilizing surface *OH. This mechanism can be also adopted to understand the effect of high pH of electrolyte and residual O in oxide-derived Cu (OD-Cu) on the catalytic efficiency towards C2+ products. Therefore, our work provides new insights into strategies for improving C2+ products on the Cu-based catalysts, i.e., maintaining partial oxidation of surface under reduction conditions.

Theoretical Insights into Amido Group-Mediated Enhancement of CO2 Hydrogenation to Methanol on Cobalt Catalysts.

Catalytic reduction of carbon dioxide into high-value-added products, such as methanol, is an effective approach to mitigate the greenhouse effect, and improving Co-based catalysts is anticipated to yield potential catalysts with high performance and low cost. In this study, based on first-principles calculations, we elucidate the promotion effects of surface *NHx (x = 1, 2, and 3) on the carbon dioxide hydrogenation to methanol from both activity and selectivity perspectives on Co-based catalysts. The presence of *NHx reduced the energy barrier of each elementary step on Co(100) by regulating the electronic structure to alter the binding strength of intermediates or by forming a hydrogen bond between surface oxygen-containing species and *NHx to stabilize transition states. The best promotion effect for different steps corresponds to different *NHx. The energy barrier of the rate-determining step of CO2 hydrogenation to methanol is lowered from 1.55 to 0.88 eV, and the product selectivity shifts from methane to methanol with the assistance of *NHx on the Co(100) surface. A similar phenomenon is observed on the Co(111) surface. The promotion effect of *NHx on Co-based catalysts is superior to that of water, indicating that the introduction of *NHx on a Co-based catalyst is an effective strategy to enhance the catalytic performance of CO2 hydrogenation to methanol.

Erratum to: Origin and effect of surface oxygen-containing species on electrochemical CO or CO2 reduction reactions

Erratum to: Origin and effect of surface oxygen-containing species on electrochemical CO or CO2 reduction reactions

Origin and effect of surface oxygen-containing species on electrochemical CO or CO2 reduction reactions

Origin and effect of surface oxygen-containing species on electrochemical CO or CO2 reduction reactions

Quantification of Electrocatalytic Activity of Glassy Carbon Electrode

Despite the fact that carbon represents one of the most important electrode materials today, an electrocatalysis at its surfaces is far from being understood. In the present work, a detailed investigation of electrocatalytic properties of well characterised glassy carbon (GC) surfaces prepared by defined electrochemical activation procedure was performed. In order to achieve this goal, standard rate constants of various redox couples used as probes were correlated with the information about the electrodes surface composition. In particular, the GC electrode surface was characterised by Raman spectroscopy, water contact angle, 9,10-phenanthrenequinone adsorption and X-ray photoelectron spectroscopy. Standard rate constants of Fe3+/2+, V3+/2+, Eu3+/2+, TEMPO+/• and [Fe(CN)6]3-/4- redox couples were determined by cyclic voltammetry and scanning electrochemical microscopy. Results confirmed the importance of C=O moiety as a catalytic site for Fe3+/2+ and possibly also V3+/2+ and TEMPO+/• couples. Negatively charged oxygen-containing surface species were suggested as novel catalytic sites for Eu3+/2+. An evidence was found that a redox process of 1,4-benzoquinone/hydroquinone is catalysed by the very same surface species. However, the electrocatalysis in this case seems to be influenced also by the adsorption of these compounds at the electrode. Standard rate constant of [Fe(CN)6]3-/4-, often used as a probe for electrochemical testing of electrode surfaces, could not be correlated to any of the considered surface species.

Construction of SnO2/Co3O4 n-p heterojunctions by organometallic chemistry-assisted approach

SnO2/Co3O4 n-p heterojunctions have been prepared by organometallic chemistry-assisted approach, where holy Co3O4 nanosheets and (CH3)2SnCl2were used as precursors. It is found that the surface oxygen-containing species could be regulated by changing the ratio of Co3O4 precursors and Sn-containing organic compound. Our present work is of importance because it provides a new and effective approach for construction of heterojunctions.

Biodegradable and photostable Nb2C MXene quantum dots as promising nanofluorophores for metal ions sensing and fluorescence imaging

Conventional fluorescent probes are either easily photobleached or non-biodegradable, which often leads to the unstable fluorescence signal output and long-term biological toxicity. Therefore, the development of novel fluorescent materials with both excellent photostability and biodegradability is of great significance for further broadening their application in numerous research fields. In this work, Nb2C quantum dots (Nb2C QDs) with pristine crystallographic structures of Nb2C MXene phases and surface oxygen-containing species are synthesized by an ultrasound assisted physicochemical exfoliation in tetrapropylammonium hydroxide. Detailed analyses indicate that the Nb2C QDs not only possess excellent chemical- and photo-stable fluorescence emission but also achieve successful application in fluorescence sensing of heavy metal ions and fluorescence imaging. More importantly, it is confirmed that the Nb2C QDs present high biocompatibility and unique biodegradation property responsive to human myeloperoxidase, implying the application safety of Nb2C QDs in vivo. Under the background of ever-growing and stringent requirements for biosafety and technical stability, the chemical- and photo-stability, biocompatibility, biodegradability, and most importantly the promising fluorescence sensing/imaging characteristic of the obtained Nb2C QDs may argue well for their future applications in environmental monitoring, biomedical diagnosis, visual display, and anti-counterfeiting.

Insights into the Pt/Rh(1 1 1) interface for direct ethanol fuel cells

Finding a highly efficient electro-catalyst for ethanol oxidation is the central issue in the use of direct ethanol fuel cells. Recently, fabricating interfacial sites between two phases has been reported as an effective approach to boost the heterogeneous catalytic activity. In this work, a comprehensive understanding of how the Pt/Rh(1 1 1) interface promotes ethanol electro-oxidation for direct ethanol fuel cells at atomic levels is gained by employing density functional theory (DFT) calculations. It is found that the Pt/Rh(1 1 1) interface including (1 1 1) × (1 1 0) and (1 1 1) × (1 0 0) could effectively convert ethanol to CH3CO* and the Rh(1 1 1) surface could activate water at low potentials (<0.5 V) by forming several ordered surface oxygen-containing species adlayers. Moreover, OH* is identified to be an oxidant and CH3CO* oxidation rate on (1 1 1) × (1 1 0) is faster than that on (1 1 1) × (1 0 0). It is therefore suggested that the (1 1 1) × (1 1 0) interface over Pt/Rh(1 1 1) is the active site for catalyzing ethanol electro-oxidation into CH3COOH. These results highlight the significance of metal/metal interfaces and help screen such interfacial catalysts in the design of highly active catalysts for ethanol electro-oxidation reactions.

Effects of ultrasonic treatment on dithiothreitol (DTT) assay measurements for carbon materials

The dithiothreitol (DTT) assay is the most commonly used method to quantify the oxidative potential of fine particles. However, the reported DTT decay rates of carbon black (CB) materials vary greatly among different researchers. This might have resulted from either the intrinsic toxicity of CB or the unsuitability of the DTT assay protocol for CB particles. In the current study, the protocol of the DTT assay for CB materials has been carefully evaluated. It was found that the dispersion degree of CB particles in water has a great influence on the DTT decay rate of CB materials. For CB particles (special black 4A (SB4A) and Printex U) and single-walled carbon nanotube tube (SWCNT), the DTT decay rate after sonication for 10 min became 4.2, 4.6 and 1.7 times higher than that without sonication. The rate continued to grow as a function of ultrasound time up to 30 min of sonication. Although the concentration of soluble transition metals and surface oxygen-containing species such as carbonyls increased slightly with sonication, they had no significant effects on the measured DTT activity, while the increase in the dispersion degree of aggregates was found to play a vital role in the observed enhancement of the DTT decay rates for different CB materials. Based on our results, 30 min of sonication is recommended for sample dispersion when measuring the DTT decay rate of CB materials.

A role of Au-content in performance of Pd-Au/SiO2 and Pd-Au/Al2O3 catalyst in the hydrogen and oxygen recombination reaction. The microcalorimetric and DFT studies

The thermal effects and activity of silica and alumina supported bimetallic Pd-Au catalysts (of various Pd/Au ratio) in the exothermic H2 and O2 recombination reaction have been investigated in view of their potential use in the industrial passive autocatalytic recombiners (PAR). The catalysts were prepared by the colloid-based reverse “water-in-oil” microemulsion method which provided metal particles of size in a very narrow range (4–7nm). In both SiO2 and Al2O3 − series catalysts the Pd-Au particles aggregated to some extent, especially strongly in alumina-series samples. The H2+O2 reaction has been monitored using Microscal gas-flow through microcalorimeter at temperature of 22°C and atmospheric pressure. The observed pattern of changes in both the heat evolution and the conversion of hydrogen seem to reflect the effect of water and/or other oxygen-containing surface species (like OH) on the activity/deactivation of catalysts. The nature of support and the composition of metal particles (Pd/Au ratio) played a role. Deactivation of alumina supported catalysts was stronger than silica supported counterparts. Among all studied catalysts, the best behavior was offered by low Au content-containing Pd-Au-0.1/SiO2 (Pd90Au10) catalyst. Its almost stable activity during the catalytic run may be attributed to relatively weak interactions with water molecules and/or other oxygen-containing species (like OH), intermediates formed in the hydrogen oxidation. It may be supposed that electronic modification of palladium sites by gold assisted by the surface composition of Pd-Au particles reflecting in “surface arrangement of Pd and Au-atoms” are decisive. This experimental observation seems to correlated with the DFT calculation indicating that besides the number of Au atoms, their location with respect to the Pd, e.g “surface arrangement of Au” is more important for the energy/strength of interaction with water molecules.

Coke formation and deactivation pathways on H-ZSM-5 in the conversion of methanol to olefins

The role of parallel and sequential reactions in Brønsted acid-catalyzed conversion of methanol to olefins (MTO) on H-ZSM-5 was explored by comparing the catalysis in plug-flow (PFR) and fully back-mixed reactors (CSTR). Catalysts deactivated under homogeneous gas phase in the back-mixed reactor show unequivocally that in the early stages of the reaction the zeolite deactivates via blocking of individual Brønsted acid sites and not by coke-induced impeding access to pores. While the two reactors led only to slight differences in product distribution, catalyst deactivation rates were drastically lower in the CSTR. H-ZSM-5 deactivated in the CSTR first rapidly and then at a much slower rate. During the initial phase, the rate was directly proportional to the methanol partial pressure and was caused by oxygen-containing surface species. These species were transformed to aromatic compounds with time on stream and the deactivation proceeded then via methylation of aromatic compounds, forming the typical coke species for MTO processes. The outer surface of the polycrystalline particles is virtually carbon free under these conditions. Formation of condensed aromatic species throughout the deactivation in voids between crystalline domains occurs as parallel reaction without affecting the deactivation kinetics.

Operating Alkaline Alcohol Fuel Cell (ITAAFC) in Intermediate-Temperature Range

Direct alcohol fuel cells (DAFCs) possess obvious advantages over traditional hydrogen fuel cells in terms of hydrogen storage, transportation, and the utilization of existing infrastructure. However, the commercialization of this fuel cell technology based on the use of proton-conductive polymer membranes has been largely hindered by its low power density owing to the sluggish kinetics of both anode and cathode reactions in acidic media and high cost owing to the use of noble metal catalysts. These could be potentially addressed by the development of alkaline alcohol fuel cells (AAFCs). In alkaline media, the polarization characteristics of alcohol electrooxidation and oxygen electroreduction are far superior to those in acidic media. Another obvious advantage of using alkaline media is less-limitations of electrode materials. The replacement of Pt catalysts with non-Pt catalysts will significantly decrease the cost of catalysts. Recently, the AAFCs have received increased attention. However, these fuel cells are normally operated at temperature lower than 80 °C. In this low temperature range, both methanol electrooxidation and oxygen electroreduction reactions are not sufficiently facile for the development of high performance AAFCs. Considerable undergoing efforts are now focused on the development of highly active catalysts for accelerated electrode reactions.Alternatively, increasing temperature has been proven as an effective way to accelerate electrode reactions. The changes of the reaction rates with increasing temperature are strongly determined by the values of activation energy, as described by the Arrhenius equation. More obvious changes are expected for alcohol electrooxidation in alkaline media than in acidic media since reported values of the activation energy are higher in alkaline media. Additionally, increasing temperature may decrease concentration polarization, Ohmic polarization, and CO poisoning of the catalysts. All these advantages can contribute to the performance improvement of the AAFCs.In an intermediate temperature range of 80 to 200 oC, CO is likely to spontaneously react with OH- to give formate as follows [1]: (1)Because formate produced via Reaction I is soluble and more electrochemically active than CO on Pt, surface CO formed during alcohol oxidation would be readily removed, resulting in considerable decrease in the CO-poisoning of Pt-based catalysts. Moreover, the kinetics of the alcohol oxidation in alkaline media on Pt has been suggested to be largely determined by the reaction between the surface CO and surface oxygen-containing species (OH), following a Langmuir-Hinshinwood mechanism. Accordingly, accelerated electrooxidation of CO intermediate would increase the rate of the alcohol oxidation.Further finding of increasing temperature for the methanol oxidation is that methanol can be efficiently converted with water in the aqueous phase over appropriate heterogeneous catalysts at temperatures near 200 oC to produce primarily H2 and CO2 [2]. (2)During the methanol liquid-phase reforming, trace amount of methane is the side product and the use of more basic catalyst favors H2 production. The methanol reforming indicates that sluggish methanol oxidation reaction which has plagued low temperature DAFCs, could become highly facile in alkaline media at temperatures close to 200 oC where the reforming of methanol is triggered. Substantially accelerated electrooxidation of methanol would make it possible to achieve low anode overpotentials. Therefore, driving the electrooxidation of methanol in an intermediate-temperature range over the methanol-boiling temperature (around 80 oC) and the triggering temperature of the methanol reforming (about 200 oC) would be of academic and practical importance for the development of high performance a technology.We have investigated systematically the electrocatalysis associated with the ITAAFC and demonstrated high performance of this promising fuel cell technology. Our status-of-the-art ITAAFC operating with methanol at 120 oC demonstrated a peak power density of around 250 mW cm-2 at around 700 mA cm-2.

Stability of Pt-Ru Alloy for Anode Catalyst in PEFC Fuel Cell: A Density Functional Theory Study

Pt-based material are commonly used as electrocatalysts for low temperature fuel cells. The Pt metal surface is easily poisoned by trace amount of CO, especially in fuel cells [1]. CO is also present in H2produced by stream reforming of methanol, ethanol and hydrocarbon fuels, it is also a problem in hydrogen fuel cells [2]. Among the most studied catalysts, the supported platinum based particles have been exhibited a notable efficiency for limiting CO poisoning. Most practical anode fuel cell catalysts consist of platinum nanoparticles alloyed by a second components are Ru, Mo and Sn, which have been studied in many recent surface electrochemistry studies. Among the binary systems the Pt-Ru combination has proved to be most successful at enhancing electro-catalytic activity [3].The carbon CO itself is usually assumed to follow a so-called bifunctional mechanism, originally suggested by Watanbe and Motoo. [4]. In this mechanism, Ru sites act as adsorption centers for the oxygen-containing surface species reacting with the CO to produce CO2. Attempts have been made to develop catalysts that either enhance the oxidation of adsorbed CO or simply tolerate CO better, or both, by alloying Pt with other metals. The improvement of the catalytic performance requires an understanding of the reaction mechanism at the atomistic level. There are many studies have been performed for CO adsorption and oxidation on the Pt and Pt-based alloys in order to design highly CO tolerant bimetallic catalysts but there is few studies regarding atomistic scale and dynamical phenomena of the CO adsorption and oxidation mechanism. A combined molecular dynamics (MD)/density-functional theoretical (DFT) study of the electro-oxidation of CO at the Pt-Ru alloy interface is very important to provide insights into the reaction mechanism.All calculations were performed using DFT under the generalized gradient approximation with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. A double numerical basis set augmented with polarization functions were used in the optimization. The computational method used in the present study is implemented in the DMol3 [5]. First-principles molecular dynamics is performed to know the dynamical properties of CO/Pt-Ru interface during the CO oxidation process.To simulate the mentioned first we determined the most stable initial state on each surface. The Pt(111)-(CO+O) and Pt-Ru (111)-(CO+O) system where O adsorbs on the hollow site and CO on the atop site with the carbon head closer to the surface. From previous findings it is assumed that Pt-metal alloy shows more reactivity than pure Pt for CO oxidation but very few studies regarding atomistic level and dynamical characteristics of this oxidation process. From our combined MD and DFT study we expect we will be able to examine electronic and geometric change of Pt-metal and its role of CO oxidation process. In our MD calculation we would be able to know temperature effect on Pt-Ru alloy surface as well as CO oxidation mechanism on this bimetallic surface. We also want to investigate how the Pt-Ru alloy structure change by CO and H2O adsorption using MD.Reference:H.A. Gasteiger, N. Markovic, P.N. Ross Jr., E.J. Cairns, J. Phys.Chem B. 98, 617 (1994)H. Gasteiger, N. Markovic, P. Ross, J. Phys. Chem. 99, 8945 (1995)M.Watanabe, M. Uchida, S. Motoo, J. Electroanal. Chem. 229, 395 (1987)M.Watanabe, S. Motoo, J. Electroanal. Chem. 60, 275 (1975)B. Delley, J. Chem. Phys. 92,508 (1990)

Oxygen Reduction at Model Pt Single Crystal Surfaces

Oxygen reduction reaction ORR is the main cathodic problem in electrochemistry and has a deep influence in the development of technologically relevant applications such as fuel cells. It is a complex reaction involving a nonpolar molecule with double bond breaking, 4 electron transfer and 4 O-H bond formation in different scenarios. In the reaction mechanism a possible important role can be played by intermediate peroxo species, after the exchange of only 2 electrons. To enhance reactivity, the understanding of the reaction mechanism at the Pt surfaces is necessary. Models can be used to simplify the complex reaction and from the experimental point of view such models are related to the use of single crystal surfaces with well defined orientations. For Pt(111) electrodes, the activation region is quite narrow despite the high overpotential and the process readily becomes transport controlled. Moreover, in the activation region the platinum electrode is covered by oxygenated species and it is well known the influence that these species can play in the electrode surface order, the surface stability being dependent a structure sensitive process. Possible influence of the surface oxygen-containing species, particularly as intermediates in the ORR is not clearly understood and only has been addressed at Pt(111), which likely is the most stable surface upon oxidation . On the other hand the ORR is structure sensitive, the Pt(111) being the most active in alkaline media [1] in contrast to that observed in acidic solution in which Pt(110) and Pt(hkl) surfaces with small two-dimensional domains are able to reduce oxygen at lower potentials. It is obvious that surface effects play an important role in the activation region as deduced from the marked anion effect that should be less important in alkaline solutions due to the shift in the surface charge on the metal. Another aspect that should be considered is the reactivity of hydrogen peroxide at these platinum surfaces, because its possible role as reaction intermediate [2]. In this respect if the ORR necessarily took place through the peroxo intermediate, a possible strategy would be based in the inhibition of peroxide oxidation while keeping constant ORR. Acknowledgements Financial support from MICINN (Spain) through project CTQ2010-16271 and Generalitat Valenciana (PROMETEO/2009/045, FEDER) are greatly acknowledged.

Palygorskite promoted PtSn/carbon catalysts and their intrinsic catalytic activity for ethanol oxidation

Abstract PtSn nanoparticles deposited on a stable electrocatalytic support containing conventional carbon and palygorskite are prepared using pre-treated palygorskite and are evaluated by ethanol oxidation. The electrocatalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). TEM and XRD show that the pre-treatment has an effective impact on the morphology of palygorskite, but does not destroy its architecture. XPS results imply that introduction of palygorskite can facilitate the formation of Sn oxides on the surface of catalyst. Sn oxides increase the amount of surface oxygen-containing species and in turn facilitate to oxidize CO-like species adsorbed on Pt active sites, which has been proved by CO stripping voltammetry. Cyclic voltammetry (CV) measurements show that the addition of palygorskite into the carbon as support improves the electrocatalytic activity in ethanol oxidation. The developed new composite support is catalytically more active for ethanol electrooxidation than the conventional carbon support and shows good stability, offering great potential for widespread application of palygorskite as support for electrocatalysis.

Surface‐functionalized Carbon Black as Catalyst for the Direct Production of Hydrogen Peroxide by the Oxidation of Hydroxylamine

AbstractCarbon black (CB) without micropores was functionalized by mixed acid and used to explore the surface chemistry effect on the production of hydrogen peroxide (H2O2). The CB materials were characterized by N2 adsorption‐desorption, XRD, SEM, FTIR, and TPD. The results of different characterization methods indicated that both the textural features and the surface chemical properties of CB were significantly modified by the acidic treatment. The catalytic performance of the modified CBs for hydroxylamine (NH2OH) oxidation increased with increasing the surface oxygen‐containing species. The yield of H2O2 approached 30% with the corresponding concentration of 73.9 mmol·L−1 (w=0.25%) over the most promising CB catalyst, which was much superior to the results obtained on supported noble metals. Correlations between catalytic activity and concentration of different surface functional groups on the CB samples confirmed that the quinonoid species might be the active species.

Electrocatalytic activity of Pt nanoparticles electrodeposited on amorphous carbon-coated silicon nanocones

This study pulse-electrodeposits Pt nanoparticles on amorphous carbon-coated silicon nanocones (ACNCs) and explores them as the electrocatalyst for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) for direct methanol fuel cell applications. The work prepares silicon nanocones on the Si wafer using porous anodic aluminum oxide as the template and then deposits the amorphous carbon layer on the nanocones by microwave plasma chemical vapor deposition. According to Raman scattering and X-ray photoelectron spectroscopies (XPS), the surface of the ACNC support is composed of a nanocrystalline graphitic structure, and rich in oxygen-containing adspecies. The Pt nanoparticles pulse-electrodeposited on the highly ordered ACNC support disperses well with a large electrocatalytic surface area. The Pt/ACNC electrode exhibits excellent electrocatalytic activity and stability toward both MOR and ORR. This study suggests the abundant oxygen-containing surface species and the nanometer size of the Pt catalyst as the two major factors enhancing electrocatalytic performance of Pt/ACNC electrode. The XPS study suggests the occurrence of charge transfer from π-sites of the graphitic structure to the Pt nanoparticle, thereby improving the electrochemical stability of the electrode.

Electrogenerated Chemiluminescence of the Tris(2,2′-bipyridine)ruthenium(II)/Tri-n-propylamine (TPrA) System: Crucial Role of the Long Lifetime of TPrA•+ Cation Radicals Suggested by Electrode Surface Effects

We describe the effects of electrochemical pretreatment of glassy carbon electrodes (GCEs) on the electrogenerated chemiluminescence (ECL) of the Ru(bpy)32+ (bpy = 2,2′-bipyridine)/tri-n-propylamine (TPrA) system. It has been found that the oxidation of TPrA at the anodically pretreated GCEs became more facile, while the intensity of ECL could be greatly suppressed. The contravention between the electrochemical reaction kinetics and the light emission intensity of the coreactant ECL system was reported for the first time and has been attributed to the rapid deprotonation of TPrA•+ cation radicals by the aid of oxygen-containing surface species formed on the GCE during the pretreatment. Because the lifetime of TPrA•+ was reduced, the products of the deprotonation reaction, TPrA• free radicals, would be more subject to oxidative consumption on the electrode subsequently, leading to weaker ECL signals. When the ECL was produced mainly following a catalytic route, however, the electrode surface effect was much less significant. This study suggests that the long lifetime of TPrA•+ cation radicals may be crucial for the intense light emission, which allows a sufficient amount of highly reducing intermediate radicals, TPrA•, to participate in the ECL process within a relatively thick reaction layer before being destroyed by the electrode.

A combined electrochemical and DFT study of the lattice strain effect on the surface reactivity of Pd

We report a combined study of electrochemical experiments and ab initio calculations on tuning the surface reactivity of Pd via a compressive lattice strain achieved by employing nanoparticles of Pd–Cu alloys with a Pd-rich surface. Surface oxygen-containing species were used as the probing molecule for revealing the surface reactivity. Both density functional theory (DFT) calculations and experiments showed linear relationships, with very close slopes, between the adsorption strength of OH ads and the Pd lattice constant. Not only is this work a successful realization of controllable modulation in the surface reactivity, but it also provides valuable information for the rational design of Pd-based catalysts for fuel cell applications.

XPS study of pyrite-free coals subjected to different oxidizing agents

Abstract Surface composition of two of pyrite-free coals characterized by a high organic sulphur content subjected to oxidation by peroxyacetic acid, oxygen in 0.5 N Na 2 CO 3 aqueous solution and air for 7 days at 125 °C were studied. Oxidation process followed the route: diffusion → chemisorption (formation of oxidized surface species) → further oxidation of surface species → gasification. The extent of each stage was dependent on the structure of initial coal. PAA acid was found to be the most efficient oxidizing and desulphurizing agent. The role of pyrite was discussed. The removal of pyrite influenced the results of the oxidation process following it. The oxidation ability of the used media formed a similar sequence (PAA > O 2 /Na 2 CO 3 > air/125) for coal samples with or without FeS 2 , but the numerical values of several parameters (the surface content of elements C, O, S, N; the type and number of oxygen-or sulphur-containing surface species) differed in both cases. The presence of FeS 2 increased oxidation rate but the overall effect depended on the starting amount of oxygen-containing surface species which in turn was influenced by the procedure of pyrite removal.