Vol 52, No 11 (2016)

The rotating disk electrode technique was used to study in 0.5 M H₂SO₄ catalytic properties of products of pyrolysis of the metal-free polyacrylonitrile/carbon black composite, polyacrylonitrile/iron/carbon black composite, and also supported pyropolymers of Co(II) tetramethoxyphenyl porphyrine (CoTMPP) and Fe(III) tetramethoxyphenyl porphyrin chloride (FeTMPPCl). It is shown that the metal-free polyacrylonitrile/carbon black composite catalyzes the oxygen reduction reaction via the parallel path. Addition of up to 2% of Fe into the composite results in abrupt growth of the catalytic activity and share of the four-electron reaction, which provides the parallel–serial reaction path. The parallel reaction with no further catalytic conversion of H₂O₂ occurs on catalysts of the CoTMPP/Vulcan XC72 and FeTMPPCl/Vulcan XC72 series. The chemical composition is one of the key factors affecting activity and selectivity of CoTMPP/Vulcan XC72 catalysts. An increase in the precursor content from 5 to 30% is accompanied by an increase in selectivity k₁/k₂ from 0.14–0.30 to 0.5–1.7, where k₁ is the rate constant of the reaction of O₂ reduction to H₂O, k₂ is the rate constant of the reaction of O₂ reduction to H₂O₂.

A series of Ir_1–xNi_xO_2–y (0 ≤ x ≤ 0.5) composite oxides have been prepared by a simple pyrolysis method in ethanol system and used as the electrocatalysts for OER in acidic medium. The materials have been characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). The electrochemical performances of these Ir_1–xNi_xO_2–y composite catalysts are evaluated by cyclic voltammetry (CV) and steady-state measurements. The resulting oxides with the Ni content (x) less than 0.3 have a complex nature of metal Ir and rutile structure IrO₂ which is similar to the Ir oxide prepared by the same approach and possess the contracted lattice resulted from the Ni-doping. Although the addition of Ni reduces the electroactive surface areas due to the coalescence of particles, the catalytic activity of the Ir_1–xNi_xO_2–y (0 < x ≤ 0.3) catalysts is slightly higher than that of the pyrolyzed Ir oxide. Regardless of the surface area difference, the intrinsic activity first increases and then decreases with the Ni content in Ir_1–xNi_xO_2–y catalysts, and the intrinsic activity of Ir_0.7Ni_0.3O_2–y catalyst is about 1.4 times of the Ni-free Ir oxide mainly attributed to the enhancement of conductivity and a change of the binding energy as increasing amount of the incorporated Ni with respect to the pure IrO₂. The Ir_0.7Ni_0.3O_2–y catalyst shows a prospect of iridium-nickel oxide materials in reducing the demand of the expensive Ir oxide catalyst for OER in acidic water electrolysis.

Applying electrochemically deposited coatings is a convenient way to improve surface properties of a substrate metal. Today materials for applications are frequently selected according to their functional properties. Nowadays theoretical and practical studies of the co-deposition of tungsten with iron group metals are conducted worldwide, and interest for these studies increases. Tungsten alloys of iron group metals have a high melting point and are often considered high-performance alloys, and the attractiveness in those has been driven by their outstanding properties and multiple possible applications. That research is encouraged by the pronounced mechanical, tribological, and magnetic properties as well as the corrosion resistance of tungsten alloys. The magnetic properties of electrodeposited Co–W alloys are of interest in recording media and remotely-actuated micro-/nano-electromechanical systems. The given research presents an overview of versatile possibilities of Co–W alloys as multiscale materials obtained by electrodeposition from citrate solutions at pH 5–8 and temperatures 20–60°C. The paper discusses electrodeposited tungsten alloys as suitable candidates to meet many technological demands at macro-, micro- and nano-scale as coating films, microbumps and nanowires.

Compact CaZr_0.9Y_0.1O_3–δ (CZY) film on a porous SrTi_0.8Fe_0.2O_3–δ (STF) support is obtained using the technique of deposition from solutions of inorganic salts in ethanol. According to the data of scanning electron microscopy (SEM), the film has a nanoporous granular structure with the grain size of 0.2 to 1 μm. The thickness of the CZY film on the STF support is about 3 μm after 15-fold solution application. The results of studying the elemental composition showed that elements of the support diffuse into the film in the course of synthesis. Analysis of the data of impedance spectroscopy shows that conductivity of the CZY film is limited the grain bulk. It is assumed that the comparatively low conductivity activation energy of the film (50.3 kJ/mol) is due to diffusion of elements of the STF support that results in variation of the film composition and properties.

The total, proton, and oxygen conductivities in the CaZr_1–xSc_xO_3–α system (x = 0.03–0.20) were studied experimentally in the reductive atmospheres H₂ + H₂O + N₂ in the temperature range 600–900°C. The electric conductivity and the transport numbers of ions and protons were measured using the direct current four-probe method and the EMF method with oxygen and water vapor concentration cells, respectively. The materials under study are pure proton-conductive below 700°C in these atmospheres; at higher temperatures, a pronounced contribution of oxygen conductivity appears. The isotherms of the total and partial conductivities are symbatic and have a maximum between x = 0.05 and x = 0.10, which correlates with the position of the boundary of the single-phase state.

The problem of the radius of depleted-by-diffusion zones around the growing individual clusters during the electrocrystallization in the mode of diffusion kinetics is solved. It is shown that a decrease in the probability of nucleation in every prescribed instant of time depends on the diffusion coefficient, overpotential, and individual characteristics of deposited metal: a specific surface energy and molar volume.