Search

The existence of the AgFeS2 and Ag2FeS2 compounds in the equilibrium concentration space of the Ag–Fe–S system was established by the EMF method. Investigations were performed in the electrochemical cells (ECCs) of the type (−) С | Ag | SЕ | R(Ag+) | PЕ | С (+), where C is the inert electrode (graphite), Ag is the negative (left) electrode, SE is the solid electrolyte, PE is the positive (right) electrode, R(Ag+) is the region of Ag+ diffusion into PE. Ag2GeS3 glass was used as the solid-state electrolyte with purely Ag+ ionic conductivity. The SnS2–FeS2–Ag2FeS2 (A) phase region of the Ag–Fe–Sn–S system is formed with the participation of three-component compounds. The cross-sections AgFeS2–Ag2FeSnS4, AgFeS2–Ag2FeSn3S8, and AgFeS2–SnS2 carry out the division of (A). Spatial position of the two-phases FeS2–AgFeS2, AgFeS2–Ag2FeS2 and three-phases AgFeS2–Ag2FeSn3S8–SnS2, AgFeS2–Ag2FeSnS4–Ag2FeSn3S8 regions of (A) regarding the point of silver was used to write the equations of the overall potential-forming reactions. Reactions were realized in the positive electrodes of ECCs. PE at the stage of the cell preparation is a well-mixed composition of finely ground (particle size ~5 μm) of the compounds Ag2S, FeS, FeS2 and Ag2S, FeS, FeS2, SnS2 in two- and three-phases regions of (A), respectively. The ratios of compounds in PE of ECCs were determined from the equations of the overall potential-forming reactions in respective phase regions. The decomposition of the metastable set of binary compounds and the synthesis of the equilibrium set of phases were carried out in the nanoscale region of the PE of ECC in contact with SE, i.e. in the R(Ag+) region. The Ag+ ions displaced from the left electrode to the right one for thermodynamic reasons act as nucleation centers for the equilibrium compounds. The process of forming the equilibrium set of phases in the R(Ag+) region for the particle size of the metastable phase mixture ~5 μm and Т=580 K took less than 72 h. The linear dependencies of EMF vs T of ECCs with PE of two- and three-phases regions were established in the ranges of (455–519) K and (450–514) K, respectively. Based on these dependencies, the standard thermodynamic quantities of the AgFeS2, Ag2FeS2, Ag2FeSnS4, and Ag2FeSn3S8 compounds were experimentally determined for the first time. The reliability of the established equilibrium sets of phases that provide the potential-forming reactions in ECCs was confirmed by the coincidence of the calculated and literature values of the Gibbs energy of the Ag2FeSnS4 and Ag2FeSn3S8 compounds.

Methanol fuel cells are very promising power source due to its high efficiency and low emissions of pollutants but their commercialization is hindered by development of the effective catalysts. Bimetallic nanostructured catalysts have been used to increase the effectiveness of methanol electrooxidation. Their high electrocatalytic activity can be accounted largely by the difference in electronegativity of two metals (e.g. Pd and Au), that resulting in gradual Auδ+→Auδ– transition with the increase in Pd content. Therefore, gold-enriched bimetallic Pd-Aunano were recommended as catalysts for oxidation processes since they are characterized by the presence of Auδ+ on their surface. Deposition of Pd, Au and Pd–Au nanoparticles (~50–350 nm) were carried out in dimethyl sulfoxide by pulsed mode of electrolysis directly on electrode surface. Cyclic voltammetry was the main method to study catalytic properties of the modified electrode in the anode oxidation process of methanol. It was found that oxidation rate on the electrode surface modified by bimetallic Pd–Au nanoparticles is ~1.5 times higher as compared to that in the case of electrodes modified by Pd or Au monometallic nanoparticles individually. In order to find highly active, selective, and stable catalysts for methanol electrocatalytic oxidation reaction additional studies are needed to understand the role of electrode surface charge and local OH− ions concentration from alkali solution.

Approximately two decades ago, gold catalyst opened up a new view of their properties when they are introduced in the form of nanomaterials, since at that time, many approaches to preparation and use of gold nanoparticles started to be used in many practical applications. Today, the research activity relating to gold nanomaterials is becoming systematic and goes further to make connections between their surface structure, chemical and physical properties, and possible applications. Since electrodeposition is one of the most controllable methods used to prepare nanoparticles, nanowires, and nanoclusters of gold, the present review gives preference on their electrochemical synthesis. The relationship between catalytic activity, size, morphology and stability of gold nanomaterials is discussed in detail. Based on the properties of the prepared gold nanocatalysts, their new applications in chemical, photochemical, and electrochemical reactions have been observed.

The AgFeSe2 and Ag2FePbSe4 compounds within the phase region Ag2Se–PbSe–Se–FeSe0.96–Ag2Se (I) of the Ag–Fe–Pb–Se system were obtained from the melt. Their annealing at T

The phase equilibria of the Ag–Sn–Te system in the Ag 2 Te–SnTe–Te part were investigated by the X-ray and electromotive force method. The spatial location of the established phase regions Ag 2 Te–SnTe–AgSnTe 2 and AgSnTe 2 –SnTe–Te relative to composition of Ag were used to express the chemical reactions of decomposition and synthesis of the AgSnTe 2 compound with the participation Ag, Ag 2 Te, SnTe and Ag, SnTe, Te, respectively. The potential-forming reactions were performed by applying electrochemical cells (−) C | Ag | Ag 2 GeS 3 glass | D | C (+), where C is graphite, Ag is a reference electrode, Ag 2 GeS 3 -glass is the fast purely Ag + ions conducting electrolyte, and D is an three-element equilibrium mixture of phases (the right electrode). Components of the electrochemical cells in powder form were pressed at 10 8 Pa through a 2 mm diameter hole arranged in the fluoroplast matrix up to density ρ = (0.93 ± 0.02)× ρ 0 , where ρ 0 is the experimentally determined density of cast samples. Five-fold thermal cycling of the cells in the temperature range of 400–500 K was performed to eliminate possible defects due to plastic deformation during sample pressing. The linear dependences of the EMF of cells with positive electrodes of the Ag 2 Te–SnTe–AgSnTe 2 and SnTe–Te–AgSnTe 2 phase regions were obtained in the temperature range of 468–526 K. EMF data were used to calculate the Gibbs energy of formation of the AgSnTe 2 compound in the Ag 2 Te–SnTe–AgSnTe 2 and AgSnTe 2 –SnTe–Te phase regions, respectively: /(kJ·mol − 1 ) = −(74.41±2.89) − (21.71±0.82)·10 − 3 Т /K; /(kJ·mol − 1 ) = −(77.53±2.97) − (20.11±0.76)·10 − 3 Т /K. The calculated Gibbs energy of the ternary compound in both phase regions are consistent, which indicates that region of the solid solution based on AgSnTe 2 compound is narrow. Determined in this work standard thermodynamic functions of the ternary compound can be used for modeling of the T–x diagrams of the Ag–Sn–Te system. Keywords: Silver–based phases, Phase equilibria, Thermodynamic properties, EMF method, Gibbs energy.

Silver microparticles have been prepared by chemical reduction method onto a rotating copper disc. It was found that in the presence of polyvinylpyrrolidone (PVP) in the initial AgNO 3 aqueous solution the radius of the Ag particles decreased from 1.18 to 0.48 μm and the formation of dendritic clusters with the fractal dimension of 1.61 occurred. The two-stage modification of the surface of synthesized silver particles with bifunctional 4-thioaniline (TAn) and further grafting of polyaniline (PAn) chains to the end amino-group of formed self-assembled surface layer were carried out. The modified surfaces were studied by scanning electron microscopy and X-ray diffraction methods, the physico-chemical properties of the formed products have been investigated. The obtained results indicate that the highest thermal stability is displayed by the silver particles produced in the presence of PVP, while the sample with grafted polyaniline exhibits the lowest thermal stability among the investigated samples. The reactivity of TAn has been examined by cyclic voltammetric method. In contrast to aniline, the electrochemical oxidation of TAn did not result in the formation of an electroconductive film on Pt electrode. It was found that oxidative condensation of aniline is suppresses by the TAn: when the molar ratio of aniline/TAn is 2:1 the formation of an electrochemically active product is stopped. The phenomenon of inhibition of the oxidative polymerization of aniline with TAn is related to an impossibility of growing of polymeric chains in the result of the “head-to-tail” type of bonding of the thioaniline links.

The reaction of metals and glassy carbon with benzenediazonium tetrafluoroborate (BDFB) in aprotic solvents has been studied. During contact of Pt, Au, Ag, Pd, or V with glassy carbon in concentrated diazonium salt solution no change of color was observed. For Al, Ca, Cr, Cu, Fe, Ga, In, Mg, Li, Na, or Zn the process was accompanied by a rapid solution color change, rapid N2 release and the loss of metal sample mass. The copper metal ionization-dissolution was studied by ultraviolet and visible absorption spectroscopy, along with gravimetric and volumetric measurements. A dissolution mechanism was proposed based on kinetic, infrared, and X-ray diffraction data. The 432 nm absorption band appearing after Cu-BDFB reaction indicates formation of the mixed complex [Cu(N2C6H5·(N≡C-CH3)3]+ where the copper atom is covalently bonded to the azophenyl radical and coordinated to acetonitrile (ACN). This complex is thermodynamically unstable and decomposes slowly to a colorless crystalline and a black amorphous phase. The crystalline phase was identified as [Cu(NC-CH3)4]BF4. The amorphous phase is a mixture of products formed by azophenyl and phenyl radical condensation.

Polyaniline-palladium composite might be proposed for the electrode material in the oxidation of aliphatic alcohols (methanol, ethanol, ethylene glycol). Prepared mixture of aniline-palladium in sulfuric acid medium (0