bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrogen Evolution at a Single Supported Nanoparticle: A Kinetic Model
Authors: Eikerling M. , Meier J. , Stimming U. 
Published: December 2003

Abstract
A kinetic model of the processes during hydrogen evolution at a single Pd nanoparticle supported on an Au substrate is studied. It builds the theoretical framework for results of currently performed STM measurements on this system. The objective of the theory is to establish relations between measured transients and underlying processes. It, thereby, helps to implement the routines for the determination of kinetic parameters from transient currents and supplements the characterization of the Pd/Au system. The balance of hydrogen involves interfacial processes on the Pd/Au substrate surface, hydrogen diffusion in the bulk electrolyte and hydrogen oxidation at the tip. The key parameter of the model is the rate of hydrogen desorption from the Pd surface. If this rate is small hydrogen will spillover from the Pd particle and diffuse on the Au surface from where it will be subsequently released. Thereby, large amounts of hydrogen can be stored on the surface. It is demonstrated, that this mechanism complies with the high turnover rates at the smallest catalyst particles and characteristic time scales observed in experiment.
Nano-Ionics: Trivial and Non-Trivial Size Effects on Ion Conduction in Solids
Authors: Maier J. 
Published: December 2003

Abstract
The significance of nano-size effects for ion transport in solids is highlighted both experimentally – by presenting various results of recent investigations – and theoretically – by considering expected size effects using a top-down approach. It is helpful to distinguish between trivial size effects (effects that equally occur at single interfaces but are augmented by the high interfacial density) and true size effects (involving local modifications due to the finite boundary conditions). The latter ones essentially include space charge overlap and structural interference leading to two characteristic sizes with respect to defect chemistry. The contribution also briefly touches upon effects of dimensionality and shape as well as of discreteness of carrier distribution.
Spontaneous and Electrodeposition of Pt on Ru(0001)
Authors: Zei M.S. , Lei T. , Ertl Gerhard 
Published: December 2003

Abstract
Pt was deposited onto a Ru(0001) electrode from a PtCl6
2−-containing HClO4 solution either electrochemically or spontaneously (i.e. without external current flow). Composition, structure and morphology of the deposit were studied by means of Auger electron spectroscopy (AES), high energy electron diffraction (RHEED), and scanning electron microscopy (SEM). At first pseudomorphic growth of a 2D-Pt adlayer takes place, while with higher coverages 3D-clusters develop for which the most densely packed [011]-rows of the Pt(111) planes are parallel with the most densely packed [1120]-rows of the Ru(0001) substrate. These Pt-clusters exhibit typical diameters between 2 and 10nm, while their average mutual separation varies with the total amount of deposit. If compared with the bare Ru(0001) surface, the samples with Pt deposits exhibit considerably enhanced activity with respect to electrooxidation of formic acid or methanol.
Structure of Electrochemically Deposited Sulfide Layers on Cu(100)
Authors: Spaenig A. , Broekmann P. , Wandelt K. 
Published: December 2003

Abstract
In-situ EC-STM has been used to examine distinct phases of electrochemically deposited sulfide layers on Cu(100). The observed structures can be clearly assigned to specific ranges of the electrode potential and the sulfide concentration in solution. The scope of the present contribution is to report the various structural phases and their potential dependence. A full description of their concentration dependence will be given in a forthcoming paper. All incipient adsorption processes have been performed exclusively at negative electrode potentials close to the on-set of the hydrogen evolution reaction in order to avoid heavy surface reactions of the copper substrate with sulfide as seen at positive electrode potentials. In a very early stage of the sulfidation first a metastable, transient p(2×2)-S layer with a nominal coverage of Θ = 0.25ML is formed which gets irreversibly replaced by an energetically more stable c(6×2)-S phase with Θ = 0.33ML. This process at constant potential is kinetically hindered and depends on the sulfide supply from the electrolyte of given concentration. All further phase transitions induced by a positive going potential sweep are influenced by the sulfide supply from the electrolyte phase as well. A low sulfide supply from a low concentration electrolyte during a positive going potential sweep provokes a uniaxial compression of the preexisting c(6×2)-S phase ending up with a striped c(4×2)-S phase. Conversely a high sulfide supply from a high concentration solution during a positive going potential sweep causes a massive reorganization of both the atomic structure and the surface morphology on a mesoscopic scale. This latter process involves a massive transport of copper material out of the topmost copper layer and is, hence, identified as an adsorbate induced reconstruction of the copper substrate. The symmetry of the resultant sulfide structure on-top of the reconstructed copper substrate is similar to a square c(2×2) arrangement but on a copper surface whose lattice constants are expanded by 9 with respect to the copper bulk structure. Hence, the atomic surface structure is denoted as a pseudo-c(2×2)-S reconstruction.
The Influence of Halide Ions on the Kinetics of Electrochemical Copper(II) Reduction
Authors: Doblhofer Karl , Wasle Sabine , Soares David M. , Weil Konrad G. , Weinberg Gisela , Ertl Gerhard 
Published: December 2003

Abstract
The cathodic reduction of copper(II) in an electrolyte comparable to technical conditions (2.2M H2SO4 + 0.3M CuSO4) is markedly affected by the presence of small concentrations of halide ions. Chloride ions accelerate the reaction, while it is slowed down by bromide. Experiments in which cyclic voltammetry is combined with an electrochemical quartz-crystal microbalance reveal the deposition and dissolution of crystalline CuCl or CuBr, respectively, on the copper surface. At the technically relevant more negative electrode potentials bulk CuCl and CuBr are unstable, however halide ions are adsorbed on the copper electrode. Although there is evidence for adsorption of the reacting Cu(II) species at the electrode surface, up to a concentration of 0.3M CuSO4 in presence as well as in absence of adsorbed halogenide, there is no evidence for limiation of the reaction rate caused by a limited coverage of the surface with this species.
The Adsorption of 2,3-Dimercaptopropane Sulfonate at the Au〈111〉 Electrode in Alkaline Solution
Authors: Yang Y. , Valet O. , Donner C. , Baumgärtel H. 
Published: December 2003

Abstract
In alkaline solution the sodium salt of 2,3-dimercaptopropanesulfonate (DMPS) is readily adsorbed at the reconstructed Au〈111〉 surface. After determining the PZC of the electrode current transients due to the adsorption have been measured at different electrode potentials. They reveal electronic charge redistribution as well as OH− desorption from the interface. From STM investigations it is concluded that the adsorption involves reorientation in the primarily formed adlayer and slow lifting of the reconstruction. The reductive desorption of DMPS has been observed at −0.97V vs. SCE.
In situ Infrared Reflection Absorption Spectroscopy Studies of the Interaction of Nafion® with the Pt Electrode Surface
Authors: Malevich Dzmitry , Zamlynny Vlad , Sun Shi-Gang , Lipkowski Jacek 
Published: December 2003

Abstract
Infrared Reflection Absorption Spectroscopy (IRRAS) has been applied to study the nature of the co-ordination of Nafion® to a Pt electrode surface. The experiments have been carried out using a Pt electrode coated with a thin film of Nafion® assembled into a thin layer spectroelectrochemical cell. The potential modulation or the subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) experiments have been performed, in order to distinguish between the bulk properties of the Nafion® membrane and the properties of the membrane at the interace with the Pt electrode. The results showed that the interaction between the membrane and a Pt electrode resembles the interaction between a Pt electrode and a sulfuric acid solution.
Stripping Voltammetry and Chronoamperometry of an Adsorbed Species with Repulsive Lateral Interactions
Authors: Koper Marc T. M. 
Published: December 2003

Abstract
In this paper a simple model is considered for the stripping voltammetry and chronoamperometry of an adsorbed species with repulsive lateral interactions. In the limit of strongly repulsive lateral interactions, the chronoamperometric transient is predicted to be hyperbolic, i.e. to have a t
−1 dependence. This dependence is confirmed by both the numerical simulation of the mean-field equations and by the Dynamic Monte Carlo simulations. However, in the analysis of the Dynamic Monte Carlo simulations, inflexion points are found in a log-log plot of the data, corresponding to the formation of ordered configurations on the surface. The stripping voltammetry exhibits broader stripping peaks with increasingly repulsive lateral interactions. An analysis of the peak potential versus the logarithm of the scan rate yields the Tafel slope, irrespective of the strength of the lateral interactions. In the Dynamic Monte Carlo simulations, strong repulsive interactions lead to multiple stripping peaks, the peaks becoming more pronounced with a faster surface diffusion of the adsorbed species. These peaks are related to the existence of ordered configurations on the electrode, whose long-range order is enhanced at faster diffusion rates.
Co-adsorption of Fluoride and Hydroxide Ions on Ag(111) in Alkaline Electrolytes: Electrochemical and SHG Studies
Authors: Danckwerts M. , Savinova E. R. , Horswell S. L. , Pettinger B. , Doblhofer Karl 
Published: December 2003

Abstract
Hydroxide (OH−) adsorption at Ag(111)/alkaline electrolyte interfaces is the initial step leading to the formation of surface oxide. We investigate how OH− anion adsorption is influenced by co-adsorption of supporting electrolyte anions (F−). Pure NaF and NaOH as well as mixed electrolytes ranging from pH=5.8 to 14 are investigated. The rotational anisotropy of the second harmonic generation (SHG) signal is measured to distinguish adsorptive processes from structural changes on the Ag surface. Our results clearly show a cross-over from F−-dominated to OH−-dominated adsorption, while both species remain charged upon adsorption. At more positive potentials, but below the reversible potential of bulk oxide growth, OH is discharged leading to sub-monolayer oxide build-up, whereas in acidic electrolyte, Ag is dissolved. At intermediate pH, the formation of a structured OH−/F− co-adsorbed layer is proposed.
Electronic Properties of LiMo3Se3-Nanowires and Mo3Se3-Nanowire-Networks for Nanoscale Electronic Devices
Authors: Heidelberg A. , Bloeß H. , Schultze J. W. , Booth C. J. , Samulski E. T. , Boland J. J. 
Published: December 2003

Abstract
Nanowires and nanotubes have attracted much interest as potential building blocks for nanotechnology. This interest can be traced to the novel structural and electronic properties of these nanomaterials. Here we describe a study that measures the electronic properties of bare LiMo3Se3-nanowires, together with wires that have been stabilized by alkylammonium- and pyridinium-ligands. The bare LiMo3Se3-nanowires consist of individual wire bundles whereas the stabilized wires form networks with an inter-wire spacing determined by the ligand. The bare wires are shown to be metallic but susceptible to electrical degradation (oxidation) in air. However, conductivity measurements at different temperature and oxidation times show that conduction in the wire networks occurs via a percolation mechanism and is activated. Moreover, the corrosion rate of the Mo3Se3-nanowires is dramatically reduced when the wires are stabilized, demonstrating that the ligands form a protective semi-insulating coating.
Adlayer Structures Probed by Distance Tunnelling Spectroscopy for Au(111)/H2SO4 + Cu2+
Authors: Nagy Gabor , Wandlowski Thomas 
Published: December 2003

Abstract
We performed a series of distance tunnelling characteristics measurements for the system Au(111)/0.05 M H2SO4 + 1 mM Cu2+ to understand, if it is possible to map the liquid part of the double layer perpendicular to the electrode surface. We found that we probed the double layer in a distance range where we do not penetrate into the inner Helmholtz layer. Nevertheless, the tip is sufficiently close to the metal surface to address adlayer features showing sensitivity toward long-range ordered structures. The bias between the STM tip and the sample drops in the inner Helmholtz layer, and electronic overlap exists between the adsorbed layer and the metal surface. Molecular contributions to the electronic structure of ordered adlayers appear to be detectable. At larger distances from the surface the average barrier height was found to be about 1 eV, practically independent on the electrode potential.
ΔS°t – as a Structural Probe – a Critical Analysis of the Method and Determination of Structure of Aquo-Alcoholic Mixtures
Authors: Gumtya S. K. , Bandyopadhyay G. , Lahiri S. C. 
Published: December 2003

Abstract
Attempts were made for a critical examination of the use of ΔS°t as a structural probe to study the ion induced perturbations on aquo-alcoholic solvent mixtures. The division of the thermodynamic properties of TATB (tetraphenyl arsonium tetraphenyl borate) in solution into equal parts is not free from defects. Naturally, the calculation of single ion values based on TATB is also problematic. Dissection of the single ion values like TΔS°t(ion) as suggested by Kundu is full of errors. Analysis shows TΔS°t(ion) to be an insensitive parameter to determine the structural characteristics of aquo-alcoholic mixtures. Structure of aquo-alcoholic mixtures should be determined from the excess thermodynamic properties of mixing, excess dielectric properties of mixing, excess polarizabilities, the correlation parameter “g” etc. Other properties like ultrasonic sound absorption, excess volume and viscosity of mixing were found to be useful. Ion induced perturbations of any solvent system will be dictated by the structure of the particular solvent system. A knowledge of the structure of the aquo-alcoholic mixtures is imperative to develop an idea regarding ion induced perturbations as mirror image relations because of compensation of ΔH° and TΔS° (and of ΔH°t and TΔS°t) will be observed in any solvent system. The thermodynamic measurements provide a summary of all interaction energies over a long time. To comprehend the rational structural details of the solvent systems, accurate thermodynamic measurements alongwith relaxation experiments providing high time and good structural resolutions are necessary.
Viscosity Properties of Electrolytes in Propylene Carbonate Based Lithium Battery Electrolyte Solutions
Authors: Wang Jianji , Zhao Yang , Zhuo Kelei , Lin Ruisen 
Published: December 2003

Abstract
Viscosities of LiClO4 and LiBr have been measured in solvent mixtures of propylene carbonate (PC) with dimethylformamide (DMF), tetrahydrofuran (THF), acetonitrile (AN) and methyl formate (MF) at 298.15K. The dependence of viscosity on the composition of the mixed solvents was fitted with an equation without adjustable parameter. Viscosity B-coefficients for lithium salts and the corresponding activation free energies (Δμ0,≠) for viscous flow have been evaluated. At the same time, viscosity B-coefficients were predicted by the dielectric friction theory. The unsuccessful prediction of the composition dependence of the B-coefficients indicates that improvements will be necessary on the theory with taking account of the short-range interaction and molecular nature of the solvents. Furthermore, solute–solvent interactions in these mixed solvents are discussed in terms of the B-coefficients and activation parameters.
Influence of Solubilized Azo Dyes on the C.M.C. Value of Cetyl-Trimethylammonium Bromide
Authors: De Vijlder Michel 
Published: December 2003

Abstract
The spectral changes in the visible absorption range of the two anionic azo dyes Methyl an Ethyl Orange in neutral aqueous solution, induced by the presence of Cetyl-trimethylammonium bromide (CTAB) micelles, are attributed to the partial solubilization of the dyes rather than to the formation of mixed micelles. The same phenomenon is not observed with the larger Orange IV (C6H5NHC6H4N=NC6H4SO3
−Na+). The c.m.c.CTAB values in the presence of dyes were obtained from spectrophotometric as well as from surface tension measurements. The reduction of the electrostatic forces within the micelles due to the presence of dye counterions initially provokes the expected progressive lowering of the c.m.c.CTAB values. In a higher dye concentration range, however, appears a systematical increase denoting a renewed strengthening of the interactions between dye and surfactant monomers that also prevail below the c.m.c. (Buwalda et al.). This assumption is supported by the observed corresponding decrease of the values for the association constant which characterize the interactions existing between the dye monomers and the surfactant micelles. At fixed dye concentrations, increasing amounts of a strong electrolyte (NaBr) lower the c.m.c.CTAB in accordance with the requirements of the Corrin-Harkins relation. Partition coefficient values have been estimated from the spectrophotometric data by using the relation proposed by Kawamura et al.. They depend on the nature and on the concentration of the solubilizate as well as on the ionic strength of the solution but their order of magnitude invariably evidences the importance of the solubilization process.
Electrical Conductivity of Some Copper Manganites
Authors: Ismail F. M. , Hamad F. F. , Faraj H. S. 
Published: December 2003

Abstract
The a.c. conductivity as a function of temperature was measured for ten prepared samples. The measurements were carried out in the temperature range 25–340°C. The sample CuMn2O4 prepared either from oxide or carbonate contains the least impurity content, while the sample Cu1.5Mn1.5O4 from oxide origin and Cu1.6Mn1.4O4 from carbonate origin contain the highest impurity content. The activation energy ΔE
1 values for the oxide origin samples are nearly the same of those obtained from carbonate origin. The variation of ΔE
2 values with concentration of copper content (x) appears to be consistent.
Thermodynamic Excess Properties of the 1-Alkylamine + Alkane and di-n-Alkylamine + Alkane Systems in Terms of an Associated Mixture Model with Equation of State Contribution
Authors: Treszczanowicz Andrzej J. , Treszczanowicz Teresa 
Published: December 2003

AbstractThe model proposed by Treszczanowicz and Benson (1985) is applied for the description and interpretation of excess enthalpyHE, excess volumeVEand excess molar isobaric heat capacityCEpof the binary systems formed by 1-alkylamines and dialkyl-amines withn-alkanes. In the model, the self-association contribution is described by an athermal associated mixture model with the continuous mode of association of the Mecke–Kempter type and the equation of state contribution described by the Flory theory. The three self-association parameters: enthalpy, entropy and volume are valid over the whole homologous series of 1-alkylamines and dialkylamines. The equation of state interaction parameters are correlated for both series of mixtures with the structure of the component molecules by using the Kehiaian–Guggenheim group contribution method. The model predicts reasonably wellHEas well asVEfor both these classes of mixtures.
Temperature Dependence of Viscosity and Density of cis-1,4/trans-1,3-Dimethylcyclohexane and Several other Commonly Used Organic Solvents
Authors: Ruth A. A. , Lesche H. , Nickel B. 
Published: December 2003

Abstract
The dynamic viscosity (η) of the glass-forming 50:50 mixture of cis-1,4/trans-1,3-dimethylcyclohexane (ct-DMCH) was measured from 293 K down to ≈ 126 K where η ~ 1.2 × 106 mPas. The viscosity measurements of several other commonly used solvents cover the range from 293 K down to ≈ 148 K (η ~ 1.4 × 104 mPas) for 1-propanol (1-Prop), to ≈118 K (η ~ 2.5 × 102 mPas) for 2-methylpentane (2-MP), to ≈ 167 K (η ~ 10.0 mPas) for isooctane (Isooct), to ≈ 183 K (η ~ 2.8 mPas) for cyclopentane (CP) and down to ≈ 98 K (η ~ 4.6 × 102 mPas) for the 30:70 mixture of cyclopentane/isopentane (CP/IP). The density (ρ) of all solvents was measured correspondingly over appropriate temperature ranges. For the solvents studied here, the temperature dependence of the viscosity can be represented by a single Arrhenius term down to ~180 K. Over a wider temperature range down to ~118K the sum of two Arrhenius terms is required, and in the low temperature regime a Vogel–Tammann–Fulcher expression is necessary to adequately describe the temperature dependence of the dynamic viscosity.
Activity Coefficients of Potassium Dihydrogen Phosphate in Aqueous Solutions at 25°C and in Aqueous Mixtures of Urea and this Electrolyte in the Temperature Range 20–35°C
Authors: Partanen Jaakko I. , Mori Yuko , Louhi-Kultanen Marjatta , Kallas Juha J. 
Published: December 2003

Abstract
Simple two-parameter Hückel and Pitzer equations were determined for the calculation of the activity and osmotic coefficients of aqueous solutions of potassium dihydrogen phosphate at 25°C up to a molality of the saturated solution (= 1.83 mol kg−1). The isopiestic data measured by Stokes (1945) were used in the parameter estimations. The resulting parameter values were tested with all thermodynamic data found in the literature for this electrolyte at this temperature. In these tests it was observed, that the Hückel equation applies to the data within experimental error up to a molality of 1.0 mol kg−1, and the Pitzer equation applies well to the data in the molality range 1.0–1.83 mol kg−1 but not very well in dilute solutions. Therefore, also a three-parameter Pitzer equation was determined that applies to all data. The activity and osmotic coefficients calculated by these three models were compared to the values suggested by Robinson and Stokes (1959) and to those calculated by the equations of Hamer and Wu (1972) and of Pitzer and Mayorga (1973) for this electrolyte. Solubility measurements of KH2PO4 at 20, 25, 30 and 35°C were made in aqueous urea solutions, and the molality of urea varied in these measurements from 0 to 2.5 mol kg−1. The thermodynamics of these studies were analyzed by using the Pitzer formalism. It was observed that only one interaction parameter between urea molecules and ions (this parameter is linearly dependent on the temperature) was needed to describe almost completely the new solubility data.
Surface Tension of the System LiF-NaF-K2NbF7
Authors: Kubíková B. , Vasiliev R. , Šimko F. , Daněk V. 
Published: December 2003

Abstract
The surface tension of the molten system LiF-NaF-K2NbF7 has been determined using the maximum bubble pressure method. The error in the surface tension measurement was estimated to be ±1%. Based on the obtained data the composition dependence of the surface tension and of the surface tension excess of the investigated system was calculated. The results are discussed in term of the anionic composition. From the surface tension excess results the negative deviation from the ideal behavior of the studied system.