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• Russian Journal of Electrochemistry close

In this work, the method of chemical deposition from the gas phase of organometallic compounds (CVDOM) was used to obtain thin electrolyte films of zirconia stabilized by yttria (YSZ) on a supporting electrode. Tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)zirconium and tris(2,2,6,6-tetramethyl-3,5-heptanedionato)yttrium often termed as zirconium (IV) Zr(dpm)4 and yttrium (III) Y(dpm)3 dipivaloylmethanates were used as precursors for film deposition. Gas-tight electrolyte films were obtained on a supporting anode with a thickness of 4–10 μm at moderate deposition temperatures of 500–700°C. An electrochemical cell was prepared and tested using the obtained films. The cell allowed obtaining the power density values of 680, 360, and 175 mW/cm2 at the temperatures of 800, 700, and 600°C, accordingly.

It is shown that gold does not virtually dissolve in alkaline (pH 12.5) solutions containing either thiocarbamide or sodium sulfite. Gold dissolves in alkaline solutions simultaneously containing thiocarbamide (0.1 M) and sodium sulfite (0.5 M). The gold dissolution rate increases with the increase in the contents of thiocarbamide and sodium sulfite. The methods of microbalance and voltammetry are used in studying the mechanism of gold dissolution in a solution containing 0.5 M sodium sulfite, 0.1 M thiocarbamide, and 0.03 M KOH. The found relationships are explained based on the assumption that the gold dissolution in alkaline sulfite-thiocarbamide electrolytes affords gold sulfite complexes.

Anodic dissolution of steel 40Kh in a sulfuric acid electrolyte containing Cl− ions is studied by analyzing the experimental dependence of anodic current on the specimen potential. The dependences of the critical passivation current, anodic current at −0.15 to 0.55 V (Ag/AgCl), and passivation current on the concentration of Cl− ions (c) are determined. The maximum value of c for the passivation at 0.55–1.6 V (Ag/AgCl) is refined. The dependence of the specimen’s steady-state potential on c is determined and its decrease is related to an abrupt increase in the anodic current at the passivation potentials.

The regularities of electrochemical deposition and dissolution of gold in the mixed sulfite-thiocarbamide electrolytes in the absence and in the presence of sodium sulfide additive are studied by using the voltammetric measurements on a renewable electrode and quarts microgravimetry. It is shown that, in the cathodic metal deposition, an addition of sodium sulfide promotes the depolarization effect, which is caused by the presence of thiocarbamide in the solution. Under the anodic polarization of gold in the mixed sulfite-thiocarbamide solution with pH 10, the gold dissolution in the sulfite-thiocarbamide electrolyte is observed even in the solution free of Na2S additive. It is evidenced that this is associated with spontaneous accumulation of sulfide-containing species in the solution, probably, as a result of thiocarbamide hydrolysis; the rate of hydrolysis steeply increases with increasing pH value.

The effect of stirring on the kinetics of electrode processes in a chromium-plating electrolyte based on chromium(III) sulfate is studied. The electrolyte, in which thick (up to 120 μm) hard chromium coatings can be obtained, is stirred with a magnetic stirrer. Hydrodynamic conditions in the system are calibrated in a modeling solution containing the same components as the electrolyte (with the exception of chromium sulfate which is replaced by an equivalent amount of aluminum sulfate), by the reaction of discharge of hydronium ions. It is shown that reactions of discharge of hydronium ions and incomplete reduction of trivalent chromium ions occur in a diffusion mode. The Cr(III)-Cr(II) system is classified with quasi-reversible redox electrodes and is described by the known equation for diffusion kinetics. The electrodeposition of metallic chromium occurs in the mixed kinetics mode

Computer simulation was performed for the processes occurring in the basic elements of the cathode (active layer, gas-diffusion layer) and bipolar plate of a fuel cell with Nafion as electrolyte and a platinum catalyst. Current generation in the active layer was considered together with the heat exchange processes (release of the heat formed in the active layer through the gas-diffusion layer into the bipolar plate), gas and vapor exchange in the gas-diffusion layer and process of the gas reagent (oxygen) saturation by water vapor in the bipolar plate channels. Voltammetric curves and dependences on the cathode potential of the power density, vapor flow dissipated from the active layer to the bipolar plate, actual active layer temperature and reduced partial pressures of oxygen and water vapors near the interface between the active and gas-diffusion layers were calculated. Analysis is performed of the way the heating of the cathode active layer intensifies the process of current generation in it, significantly increasing the value of overall characteristics of the cathode (current and power density).

The kinetics of charging of the blocked (inert) electrode/solid electrolyte interface is studied for spherical or cylindrical electrodes by the impedance method in two modes (galvanodynamic and potentiodynamic). The case of slow diffusion and adsorption-desorption is analyzed for species of one type, namely, defects of the solid-electrolyte rigid sublattice (minor carriers). The roles that both the slow lattice defects and the fast conduction ions play in the electric double layer formation are taken into account. Calculations involve the use of both the diffusion model of a spherical or cylindrical electrode in electrolyte (proposed by Jacobsen and West) and the ac circuit of an ideally polarizable planar electrode in a solid electrolyte (developed by Grafov, Ukshe, and Bukun).

Germanium-containing quasi-binary salt systems GeSe-GeI2 and NaI-GeI2 (GeI2 is a dopant) are studied by methods of electroconductance and x-ray diffraction analysis (XRDA). The conductivity isotherms combined with the XRDA data show that the domain of restricted solid solutions in these systems comes to 3 and 1 mol % GeI2, respectively. The maximal electrolytic admittance is observed at 2 and 0.25 mol % GeI2 in GeSe-GeI2 and NaI-GeI2 systems. The GeSe system has better ceramic properties, is less susceptible to water traces, and has higher conductivity and lower activation energy for conduction.

The operational impedance technique in two modes (chronoamperometric and chronopotentiometric) was used to study the kinetics of the charging process of the blocked (inert) electrode/solid electrolyte interface in the case of small and large charging times. The case of slow diffusion and adsorption-desorption of a given species type, i.e., rigid lattice defects in solid electrolyte (minor charge carriers), is analyzed. It is shown that in the chronopotentiometric mode, analytical current-time relationships differ at small charging times and at large charging times. It is found in the chronoamperometric mode that formation of a double electric layer at the blocked electrode/solid electrolyte interface occurs much faster at large times than at small times.