Russian Journal of Electrochemistry最新文献

At the electrochemical deposition of alloys various phenomena are observed that lead to changes in the kinetics and thermodynamics of the processes. In particular, as a result of changing in the nature of the electrode surface, both the exchange current densities and the transfer coefficients of each of the components changed. Further, during the formation of solid solutions, the equilibrium potentials of the components change due to the non-zero enthalpy and entropy of mixing. At the deposition of eutectic-type alloys (that is, a mixture of grains of individual components), each of the metals does not deposit on the entire electrode surface but only on its own surface. In the latter case, there is a change in the diffusion pattern of the components as compared to the deposition of individual metals: it remains unchanged in the outer part of the diffusion layer but there is a condensation of the diffusion fields of the components near the surface, similar to the case of diffusion to the matrix of microelectrodes or to individual nuclei of a new phase. This also leads to a change in the diffusion part of the overpotential of the components’ deposition. The diffusion of ions of the discharging negative component of an alloy representing a mechanical mixture of the metals’ A and B grains to the grain surface of this component in the model of a partially blocked electrode is considered. At a constant potential, the local current density of the component is shown to increase as a result of the diffusion acceleration. The magnitude of the relative increase in the current and the corresponding magnitude of apparent depolarization are found, as compared between the deposition of an individual metal and the codeposition of the same component into an alloy.

A citrate–nitrate synthesis of individual materials La_0.9Sr_0.1Sc_{1 – x}Co_xO_{3 – δ} and La_0.9Sr_0.1CoO_{3 – δ} and their based composites is performed. Composite materials are obtained by solid-phase mixing in different percentages of individual phases, followed by pressing and sintering. The obtained individual and composite materials are explored by X-ray phase analysis and dilatometry. The electrical conductivity of the obtained samples is studied by a direct-current four-probe method depending on the temperature and the gas phase composition. Unique studies of the ability of composites to the ammonia direct decomposition directly at the electrode layer of the fuel cell are carried out.

Perovskite-like oxides based on lanthanum–strontium ferrites are considered to be promising electrode materials for use in various types of fuel cells, and the strategy of modifying these materials by partial substitution of iron with highly charged ferroactive cations has proved to be an efficient way to increase their chemical stability. In this work, the results of a study of the permeability of microtubular oxygen membranes based on La_0.5Sr_0.5Fe_{1 – x}Nb_xO_{3 – δ} are presented for the first time. The activation energy of oxide bulk diffusion was found (20 ± 4 kJ/mol).

Nitrogen-doped few-layered graphene structures are synthesized by plasma-assisted electrochemical exfoliation of graphite and used in the preparation of composites with phosphorene structures obtained by supersonic exfoliation of a porous black-phosphorus electrode covered with preliminarily deposited cobalt. The catalytic activity in the hydrogen evolution reaction is studied for the few-layered graphene and phosphorene structures, as well as their mixtures. The mixed electrocatalysts demonstrate the highest activity in the hydrogen evolution reaction.

The paper presents the results of studies of the structural, thermal, and transport properties of solid composite electrolytes (1 – x)(C₄H₉)₃CH₃NBF₄–xC_ND (where C_ND are nanodispersed diamonds, 0 ≤ x < 1, x is the mole fraction). It was shown by the Pawley method that the crystal structure of the low-temperature (C₄H₉)₃CH₃NBF₄ phase is described by the space symmetry group P4₂/ncm. The addition of an inert nanodiamond additive led to an increase in the electric conductivity of the composite electrolyte by four orders of magnitude to 1.3 × 10^–3 S/cm at 145°C and at x = 0.98. The theoretical dependences adequately describe the experimental data in the concentration range 0 ≤ x ≤ 0.99 at temperatures of 84 and 127°C.

This review considers the literature on electrochemical supercapacitors operating at extreme temperatures from –80 to +220°C, which is very important for practice. The influence of the following methods and factors on the efficiency of the electrochemical supercapacitors at the extreme temperatures is considered: the using of ionic liquids as electrolytes; the using of modified gel electrolyte, a combined electrolyte, aqueous electrolytes with low freezing point; the using of acetonitrile as an electrolyte solvent; the using of clay as a solid electrolyte; application of solid-state electrochemical supercapacitors; application of electrodes with optimized porous structure; the using of graphene and pseudocapacitive electrodes; the using of solar cells; using of combined techniques to create supercapacitors for extreme temperatures. Undoubtedly, this review will be of great interest both for fundamental electrochemistry and for practice.

Among all types of solid oxide fuel cells, the microtubular design demonstrated increased resistance to thermal cycling and a high power density (from 300 to 1000 W/kg and higher). Currently, one of the basic problems is the choice of a material to be used as the cathode; other problems are associated with the microstructure just within the cathodic layer of the microtubular solid-oxide fuel cells. This work is aimed at the studying of the power characteristics of microtubular solid-oxide fuel cells using Ba_0.5Sr_0.5Co_0.75Fe_0.2Mo_0.05O_{3 – δ} as a cathode material. A cathodic layer with a thickness of 65 µm, including 4 cathodic functional layers and 4 cathodic collecting ones, is optimal and allows reaching the power of a single microtubular solid-oxide fuel cell as high as 750–850 mW/cm².

Abstract

A series of ZnO/ZnWO₄ nanocomposites with different ZnWO₄ content, are electrochemically synthesized under pulse alternating current starting from ZnO and WO₃ nanopowders. A complex of physicochemical methods (X-ray diffraction analysis, Raman spectroscopy, transmission electron microscopy, energy dispersive X-ray microanalysis) was used to study the composition and structural characteristics of the obtained materials. The nanocomposite with optimal composition (ZnWO₄ ~6%) was used as a photoanode material for a flow photocatalytic fuel cell with sulfate electrolyte added with organic and inorganic fuel. The maximum values of E_oc (850 mV) and P_max (85.8 μW/cm²) are achieved using Na₂SO₄ with the addition of glucose as a fuel.