DFT study of platinum and palladium overlayers on tungsten carbide: Structure and electrocatalytic activity toward hydrogen oxidation/evolution reaction

Platinum and palladium overlayers on W- and C-terminated WC(0001) surface, at coverage ranging from 0.25 ML to 2 ML, have been studied using DFT approach. Strong adhesion of metal monolayers to the WC support, accompanied by a modification of electronic structure, was evidenced. Calculated values of hydrogen binding energy on studied metal overlayers were correlated to available experimentally determined values of exchange current densities of hydrogen oxidation/evolution reaction (HOR/HER), resulting with the volcano curve with both explanatory and predictive power. None of the investigated metal/WC surfaces were found to exceed the Pt(111) surface in terms of catalytic activity toward HER/HOR. The obtained results indicate that WC may efficiently replace the precious metal support in the Pt (Pd) core–shell electrocatalyst for HER/HOR, but no synergism arising due to electronic effects of WC support was evidenced.     

Oxidation of aniline in dopant-free template-free dilute reaction media

The oxidation of aniline with ammonium peroxydisulfate in water without added acid was studied in dilute reaction media. The new nanostructured nonconducting polyaniline sulfate/hydrogen sulfate, synthesized by dilute dopant-free template-free falling-pH method, consists of network of nanorods and nanogranules. The molecular structure of polyaniline, investigated by the elemental analysis, FTIR, Raman, UV–Vis and EPR spectroscopies, was found to be significantly different in comparison with the structure of the nanostructured PANI sulfate/hydrogen sulfate prepared by dopant-free template-free falling-pH method in concentrated aqueous aniline solutions. The mechanism of the formation of nanostructured polyaniline under dopant-free template-free dilute reaction conditions is discussed.     

Computing the electromagnetic field of the system of arbitrarily positioned conductors in horizontally stratified multilayer medium

This paper presents a novel computational methodology, based on the finite element technique, for the analysis of electromagnetic field due to system of arbitrarily positioned current‐carrying conductors in horizontally stratified multilayer medium, having arbitrary number of layers with different characteristics (including air). Each soil layer is horizontally unbounded, homogenous and isotropic, whereas conductors can penetrate different layers and extend into the air. The effect of the stratified multilayer medium is taken into account by using the originally developed fixed image method. Complete electromagnetic coupling between grounding system conductors (satisfying thin‐wire approximation) is taken into account, whereas attenuation and phase shift effects are approximated. The electric and magnetic field in stratified multilayer medium are computed from the scalar electric and vector magnetic potentials, using the said fixed image method and approximations to the attenuation and phase shift effects. Copyright © 2014 John Wiley & Sons, Ltd.     

Microstructural engineering of ZnO-based varistor ceramics

In ceramic materials, special boundaries play the key role in crystal growth. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of polycrystalline materials. These effects, however, can be exploited to tailor the electronic and optical properties of the materials, as demonstrated in this review. The presented topic is related to a preparatory stage of phase transformations, manifested through the evolution of chemically induced structural faults. In non-centrosymmetric structure of ZnO, inversion boundaries (IBs) are the most common type of planar faults that is triggered by the addition of the specific IB-forming dopants (Sb₂O₃, SnO₂, TiO₂). In addition to conventional TEM techniques, new methods were developed to resolve crystallography and atomic-scale chemistry of IBs. The absolute orientation of the polar c-axes on both sides of an IB was determined by micro-diffraction, providing the most reliable identification of crystal polarity in non-centrosymmetric crystals. To determine sub-monolayer quantities of dopants on the IB, we developed a special technique of analytical electron microscopy using concentric electron probe (CEP) in EDS or EELS mode, providing more accurate and precise results than any other technique. Knowing the local crystal chemistry of IBs, we were able to design experiments to identify their formation mechanism. IBs nucleate in the early stage of grain growth as a dopant-rich topotaxial 2D reaction product on Zn-terminated surfaces of ZnO grains. Soon after their nucleation, ZnO is epitaxially grown on the inherent 2D phase in an inverted orientation, which effectively starts to dictate anisotropic growth of the infected crystallite. In very short time, the grains with IBs dominate the entire microstructure via IB-induced exaggerated grain growth mechanism. This phenomenon was used to design physical properties of ZnO-based varistor ceramics, whereas the bottom-up approach demonstrated here provides the basic tool for microstructural engineering of functional materials in virtually any system that is prone to the formation of special boundaries.     

Electrochemical behaviour of the solid electrolyte Ag6I4WO4

Electrochemical investigation of the solid electrolyte Ag₆I₄WO₄ (0.8 AgI + 0.2 Ag₂WO₄ mixture) was performed. By means of cyclic voltammetry, normal pulse polarography and ac polarography methods the electrode processes and the capacity of electric double layer on electrode/electrolyte interface were investigated at several temperature levels (room temperature, 373 K, 386 K and 423 K). It was shown that on the electrode, either a Pt or Ag one, at direct and reverse cathodic polarization, Ag⁺ ? Ag redox process occurs, and for it a substantial exchange current value was found. Hence it is concluded that the redox process at all the observed temperatures is very fast and that the rate increases with a rise in temperature. Also the passivation of the electrode at anodic polarization affecting the electrolyte decomposition voltage level considerably was pointed out. The electric double-layer capacity values found show that the structure of the layer changes with temperature and dc potential, which is manifested on the capacity.     

Electrochemical beaviour of the solid ionic conductor Ag7I4PO4

Electrochemical investigation of the solid superionic conductor Ag₇I₄PO₄ (0.8 AgI + 0.2 Ag₃PO₄) at room temperature and at 40°C were performed by means of cyclic voltammetry, cyclic chronoamperometry and cyclic chronocoulometry, normal pulse polarography and ac polarography. It was shown that the Ag⁺ ↔ Ag redox process on Pt and Ag working electrode occurs with a certain overvoltage, ie that for Ag⁺ → Ag⁺ oxidation and the return of Ag⁺ ions into the electrolyte a certain overvoltage is necessary. From the determined values of the exchange current one estimates the redox process as a rather fast one. The silver working electrode is electrochemically inactive, while only cathodically deposited silver is electrochemically active and can be oxidized to Ag⁺ ions. Chronoamperometry and chronocoulometry show that there is a certain difference in the behaviour of Pt and Ag working electrodes due to uneven passivating anodic processes. On the basis of measurements of faradaic and capacitance currents and their dependence on frequency, diagrams of complex impedance of the Pt/Ag₇I₄PO₄ interface at various anodic and cathodic polarizations of the Pt electrode were plotted. The dependence of the serial capacity of the interface on the dc potential and temperature are discussed.     

Investigation of titanium corrosion in concentrated NaOH solutions

The rate of both spontaneous and polarization assisted formation of oxide films on commercially grade titanium, DIN 3.7025, was studied in concentrated, 1–5M NaOH solutions, with particular attention to the early stages of oxide formation. Simultaneous chemical dissolution of oxides was considered. The rate of spontaneous oxide formation was examined with cyclic voltammetry as an in‐situ method. The shape of potentiodynamic curves recorded in different alkaline solutions indicated that the electrolyte concentration affects the oxide composition. Titanium electrodes were covered with oxide films of different thickness, and the time dependence of polarization resistance was measured under a fixed anodic polarization. The polarization resistance may either increase or decrease tending to attain a stationary value, which, for a fixed polarization, depends on both the initial thickness and the NaOH concentration.     

Determination of the effectiveness of the realization of enterprise business objectives and improvement strategies in an uncertain environment

This study determines the effectiveness of business objectives and key performance indicators (KPIs) of the identified business objectives for different types of enterprise. The evaluations of the relative importance of KPIs are called a fuzzy group‐decision‐making problem. The KPI weights are determined using the fuzzy analytic hierarchical process. The effectiveness of business objectives and KPIs is determined using the adopted Balanced Scorecard Designer Pro. Determination of the KPI rank with respect to each enterprise type is on the basis of Pareto analysis. The priority of management initiatives of the improvement strategy corresponds to the calculated rank, and it has a critical effect on the competitive advantage of any enterprise. The results discuss manufacturing, public and service enterprises, which exist in central Serbia. The proposed approach can also be adapted to different businesses.