Russian Journal of Electrochemistry最新文献

Abstract

The anodes based on the nickel oxide and yttria-stabilized zirconia are developed by the method of hybrid inkjet 3D-printing with laser treatment. The granulometric composition of the NiO/Zr_0.9Y_0.1O₂-composite and the rheological characteristics of its based printing pastes are determined. The printing of three-dimensional test objects using the developed ceramic paste is studied experimentally. The influence of the pore formers—graphite and potato starch—added to the paste composition on the rheological characteristics of the paste is studied. The obtained samples of supporting anodes were studied by a complex of physicochemical methods to determine their morphological and structural characteristics.

Abstract

The electrocatalytic activity of electrode materials synthesized by anodic selective dissolution of Ag–Pd alloys based on silver (4 and 8 at % Pd) was studied. Kinetic regularities of formic acid electrooxidation on palladium and anodically modified Ag–Pd alloys in an acidic sulfate solution have been established. The process includes the diffusion of HCOOH, its dissociative chemisorption, and irreversible ionization of atomic hydrogen. The conditions for formic acid anodic oxidation on Pd and Ag–Pd alloys were determined depending on the composition of the electrode system and the mode of preliminary electrochemical modification (selective dissolution) of the alloy using transient electrochemical measurements. The role of the surface development of an alloy in the kinetics of anodic degradation of formic acid was revealed. It was shown that the selective dissolution of Ag–Pd alloys contributes to a noticeable increase in the rate of the kinetic stage of atomic hydrogen ionization. A necessary condition for the activation of the anodically modified alloy in relation to the electrooxidation of HCOOH is the excess of both critical parameters (charge and potential) corresponding to the onset of morphological development and phase transformations in the surface layer of the Ag–Pd systems.

Abstract

The optimization of technology for manufacturing bilayered anode supports for planar solid oxide fuel cells (SOFCs) using precursors was performed. The bilayered anode supports for the second-generation planar SOFCs were manufactured by the tape casting method followed by the lamination. Nickel sulfate heptahydrate NiSO₄∙7H₂O was used to fabricate the composite material for the current-collecting layer containing 60 vol % NiO and the functional layer containing 40 vol % NiO (the chosen values are close to the first and second percolation thresholds). The 8YSZ/NiSO₄ composite mixture was calcined at a temperature of 1000°C. The use of this precursor resulted in fabricating durable anode support that retains mechanical stability during redox cycling. Finely dispersed NiO in a thin functional layer led to a high density of three-phase boundaries, which had a beneficial effect on the electrochemical activity of the anode. Based on these anode supports, the model samples of solid oxide fuel cells were manufactured. The samples were studied using conventional electrochemical techniques. The power density was 1 W/cm² at an operating temperature of 750°C.

Abstract

A continuous quasi-equilibrium phase diagram δ(pO₂, T) of a nonstoichiometric oxide La₂NiO_{4 + δ} with the layered perovskite-like Ruddlesden–Popper structure is obtained by the method of quasi-equilibrium oxygen release. The thermodynamic parameters are determined as a function of the oxide nonstoichiometry δ. Calculations are carried out within the framework of the localized-electron and itinerant-electron models which are used for description of the defect structure of ferrites and cobaltites, respectively. It is shown that the specific features of the phase diagram can be related to the electronic density of states near the Fermi level.

Abstract

A model of a membrane electrode assembly is considered as regards the effect of various climatic conditions on the specific power characteristics. The developed model is analyzed in comparison with a proton-exchange membrane fuel cell (PEMFC) stack operating at different ambient temperatures. The deviation (less than 10%) between the model and the experiment in the temperature range from –10 to +10°С is demonstrated. The ambient temperature of 10°C is found to be optimal for the battery operation The specific power is shown to decrease by 0.006–0.008 W/cm² every 10°C above zero, which is insignificant and can be compensated using a buffer energy storage device.

Abstract

The results of the development and study of catalysts for the anodes of water splitting electrolyzers with a proton exchange membrane are presented. To deposit catalytic layers on a titanium support, the method of magnetron sputtering of composite targets in a vacuum was used. Iridium and ruthenium are used as the principal catalysts; molybdenum, chromium, and titanium, as functional additives. The electrochemical and structural characteristics of catalytic coatings are studied. Using voltammetry methods, cyclic voltammograms and anodic characteristics of the catalytic compositions are obtained, in particular, at different temperatures of the subsequent heat treatment in air, as well as at different measurement temperatures. The Tafel slopes of the current–voltage characteristics of the composite anodes, as well as the currents at a potential of 1.55 V (RHE) are determined. The minimal slopes are obtained for the Ir–Ru–Mo–Ti catalytic composition (b = 40–63 mV/decade); the maximal currents, for the Ir–Mo–Cr catalytic composition (i = 100–110 mA/cm² at E = 1.55 V (RHE)). The magnitude of adsorption currents in the anodic potential region of cyclic voltammograms is shown to correlate with the coefficient b of the Tafel equation (E vs. logi); it determines the number of catalytic centers for the deprotonation stage in the oxygen evolution reaction. However, the catalyst activity in the oxygen evolution reaction is determined not only by the number of these centers but mainly by the functional features of the catalyst proper, i.e., the composition of the catalyst and the conditions for its preparation (including the temperature of the catalyst subsequent heat treatment in air). The iridium-based catalytic compositions added with molybdenum and chromium have higher activity in the oxygen evolution reaction. Structural studies showed that during the magnetron sputtering of the composite targets, even with small catalyst loading, dispersed structures are formed; in the real porous titanium anodes, these structures must form on the front surfaces with higher catalyst content.

Abstract

A paste composition for inkjet 3D-printing based on the NiO–Ce_0.8Gd_0.2O₂-composite is suggested and an anode billet for a solid-oxide fuel cell of planar geometry is developed using the direct inkjet 3D-printing. Effect of the printing mode and thermal annealing on the morphology and structure of the samples is studied. The anode billet is reduced and the resulting sample is characterized by a number of physicochemical methods.

Abstract

The evolution of the microstructure and the composition of Ni–Co coatings used for protecting the current collectors of stainless steel Crofer 22 APU from oxidation is studied in the operation mode of the anode chamber of a solid-oxide electrolyzer cell (SOEC). It is shown that the interdiffusion of steel and coating components and the redox reactions that proceed under the coating in the SOEC operation mode block the chromium diffusion to the current collector surface. The exploitation of the anodic chamber in the air atmosphere changes the Ni–Cr metal composition of the protective coating to a mixture of highly conductive oxides (Fe,Ni,Co)₃O₄ and (Ni,Co)O, thus changing the form of the time dependence of the surface resistivity of the junction current collector/anode. At the same time, the 7000 h tests revealed sufficiently low values, viz., ~17 mΩ cm², which means that these coatings can be used for the anti-oxidation protection of the stainless-steel current collectors in SOECs.

Solid solutions CsAg₄Br_{3 – х}I_{2 + х} (x = 0.38; 0.50; 0.68) are prepared by solid-state synthesis; the single phase of the products is confirmed using the methods of X-ray diffraction and differential scanning calorimetry. The studies of electrotransport characteristics of CsAg₄Br_{3 – х}I_{2 + х} involve measuring the ionic conductivity by the four-probe method in the temperature interval from –50 to +120°C and estimating its electronic component by the Hebb–Wagner method. It is shown that in the studied interval of compositions, the ionic conductivity of CsAg₄Br_{3 – х}I_{2 + х} solid solutions is practically independent of x, approaching the conductivity of the well-known superionic conductor RbAg₄I₅. The activation energy of conduction is found to be about 10 kJ mol^–1 for all compounds studied. The oxidation potential determined by the method of stepwise polarization for CsAg₄Br_{3 – х}I_{2 + х} solid solutions is considerably higher as compared with RbAg₄I₅, being in the range of 0.75–0.78 V (vs. Ag⁰/Ag⁺). The high electrochemical characteristics of CsAg₄Br_{3 – х}I_{2 + х} (0.38 ≤ x ≤ 0.63) and the absence of polymorphic transitions in the considered interval from –160°С to the melting point (175–178°С) make these materials promising for the use in electrochemical devices, especially in low-temperature applications.

Perovskite-like materials with mixed ionic and electronic conductivity are considered as promising functional materials for proton-ceramic electrochemical devices. In the present work, a solid-solution series La_0.9Sr_0.1Sc_{1 – x}Mn_xO_{3 – δ}, where scandium ions in the B-cation position are gradually replaced by manganese ions, was obtained and studied for the first time. The obtained materials were certified by X-ray phase analysis, scanning electron microscopy, and energy-dispersive microanalysis. The dopant influence on the studied materials’ sintering ability and morphology is elucidated. The electrical conductivity of the solid solutions as a function of temperature and gas phase humidity was investigated by the dc four-probe method.