Russian Journal of Electrochemistry最新文献

Voltammetry and chronoamperometry are used to study the effect of the solution composition on the desorption behavior of self-assembled monolayers of alkanethiols with approximately the same chain length but different terminal groups of thiols (R: –CH₃, –CH₂OH, and –NH₂). The hydrophilic properties of the terminal groups for the studied thiols increased in the –CH₃ ( ll ) –NH₂ ≤ –CH₂OH series. It is found that the anionic and cationic composition of electrolyte affected significantly the electrochemical stability and blocking ability of self-assembled monolayers of thiols with different terminal groups. It is established that the electrochemical stability and blocking ability of the self-assembled monolayers decreased in the Li⁺, Na⁺, K⁺ series in alkaline solutions regardless of the thiol terminal group. The cation nature in perchlorate and chloride solutions manifested itself only for thiol with the –NH₂ terminal group. The shape of cathodic voltammograms changed for this thiol when passing from alkaline to ({text{ClO}}_{4}^{ - }) and Сl^– medium, possibly owing to a change in the amino group protonation degree.

A comparative study of the electrochemical behavior of various forms of the antitumor antibiotic doxorubicin (DOX), both free and encapsulated in micelle-like nanoparticles of the biocompatible amphiphilic copolymer of N-vinylpyrrolidone (VP) and methacrylic acid, viz., triethylene glycol dimethacrylate (TEGDM), is carried out in aqueous neutral buffers on a glassy carbon electrode. The hydrodynamic radii R_h of the copolymer and the DOX polymeric nanostructures are determined using dynamic light scattering. Using cyclic and square wave voltammetry, for both forms of DOX at pH 7.24, the two main redox transitions are revealed namely, the irreversible oxidation/rereduction in the potential interval from 0.2 to 0.6 V and the reversible reduction/reoxidation in the interval from –0.4 to –0.7 V (vs. saturated Ag/AgCl), and their redox potentials are determined. For both redox transitions, the potential difference between the corresponding peaks does not exceed several tens (20–30) mV; and, moreover, the oxidation of the encapsulated form proceeds easier as compared with the free form, whereas its reduction is somewhat more difficult. The analysis of the dependence of the reduction current of both DOX forms on the potential scan rate shows that the electron transfer to a free DOX molecule is largely determined by the rate of reagent accumulation in the adsorption layer, whereas the electron transfer to the encapsulated form is characterized by the mixed adsorption-diffusion control. Based on voltammetric data and the results of quantum chemical modeling, it is concluded that a hydrogen bond is formed between the oxygen-containing groups of copolymer’s monomeric units and the H atoms in OH and NH₂ groups of DOX. The bond energy in these structures is calculated and shown to be close to the classical values, assuming that the carbonyl group in the VP lactam ring in the encapsulating polymer is the electron donor, and the hydrogen atoms in OH and NH₂ groups of DOX are the electron acceptors. At the same time, the bonds involving oxygen of the ester group in the TEGDM unit are extremely weak.

The effect of lithium polysulfides on the amount and ratio of electrochemically active metallic lithium, electrochemically inactive metallic lithium, and chemically formed lithium compounds in the cathodic deposits formed on a stainless-steel electrode during galvanostatic cycling in 1 М LiClO₄ solution in sulfolane at 15, 30, 45, and 60°C is studied using the method we have developed earlier. It is shown that the increase in temperature leads to increase in the Coulomb efficiency of cycling and the amount of electrochemically active metallic lithium; a decrease in the amount of electrochemically inactive metallic lithium, regardless of the presence of lithium polysulfides in the electrolyte. When lithium polysulfides have been introduced into the electrolyte, an increase in the Coulomb efficiency of the metallic lithium cycling and a change in the ratio of various forms of lithium in the cathodic deposits toward an increase in electrochemically active lithium by about 1.5 times are observed. The lithium polysulfides are assumed to contribute to the dissolution of electrochemically inactive metallic lithium, forming an interfacial “sulfide” film at the electrode, which possessed high ionic conductivity and good protective properties, the more so, at elevated temperatures.

Abstract

The applicability of calcium–borosilicate glass-ceramics with high boron oxide content as a sealant for solid oxide fuel cells is studied. Chemical composition of the studied materials is: 33 mol % CaO, 21 mol % B₂O₃, and 46 mol % SiO₂. The material is studied as an alternative to the existing calcium– and barium–aluminosilicate-based sealants because of the latters’ limited adhesion to steel interconnects in fuel cells. The studied sealant is shown to have a softening point of about 920–930°C, which allows using it for sealing of fuel cells at 925°C. Use of relatively low sealing temperature allows avoiding overheating of the cell during the sealing and avoiding the accompanying degradation of the battery operational characteristics. The studied sealant demonstrated excellent adhesion to the surface of interconnect materials (the Crofer 22 APU steel). Furthermore, the studied sealant is found to be thermomechanically compatible with the Crofer 22 APU steel and ZrO₂-based electrolytes.

Abstract

Lead Sulfide (PbS) nanoparticle-decorated silicon (Si) pyramids array on Si-based photocathodes are fabricated by using pure chemical methods. The PbS thin layers were synthesized by chemical solution deposition onto flat Silicon (Si) and pyramidal textured Silicon (SiPY) obtained from alkaline Si substrate etching. Scanning Electron Microscopy (SEM) was used to carry out the morphological characterization, while UV–Vis-NIR Spectroscopy was used to study the optical properties. The Linear sweep voltammetry (LSV) was conducted to study the catalytic activity in dark and under white light irradiation using a potentiostat station. Cyclic voltammetry in the presence of and without purging CO₂ was also investigated. The LSV investigations showed the synergy effect between PbS thin films and Si for the rising and transport of the charge carriers. The results showed a higher photocatalytic towards CO₂ reduction of PbS/SiPY compared to Silicon substrate without surface texturization and sensitization. The photoelectrode based on PbS/SiPY could efficiently be used as a photocathode for the photoelectrochemical (PEC) reduction of CO₂ to Methanol.

Abstract

The article explores the features of Pt(0) nanoparticle formation at the interface of nickel-aqueous solution of reagents and a similar interface containing nanoflakes of Co(OH)₂. The synthesis was carried out under Successive Ionic Layers Deposition (SILD) conditions, and solutions of Na₂PtCl₆, CoCl₂, and NaBH₄ were used as the reagents. Pt(0) nanolayers were produced on the nickel surface using Na₂PtCl₆ and NaBH₄ solutions, and for Co(OH)₂ nanolayers CoCl₂ and NaBH₄ solutions were used. Structural chemical studies of the samples synthesized were performed by HRTEM, FESEM, EDX, SAED, XPS, FT-IR, and Raman spectroscopy. It was shown that Pt(0) nanolayers consist of separate nanoparticles, while Co(OH)₂ nanolayers consist of nanoflakes. The main attention in the work is paid to the formation features of Pt(0) nanoparticles on a nickel surface to which a nanolayer of Co(OH)₂ was previously applied. The study of the electrocatalytic properties of such samples in the hydrogen evolution reaction (HER) during water electrolysis in the alkaline medium showed that the best properties are exhibited by nanoparticles synthesized after 20–40 SILD cycles and on nickel substrates with Co(OH)₂ nanolayers applied in advance. Also, it was found that among these samples the best properties are displayed by those containing Co(OH)₂ layers synthesized after 5 SILD cycles. One of the best examples of this series was obtained from 40 SILD cycles and is characterized by the overpotential value at 29 mV of current density at 10 mA/cm², the Tafel slope value at 29.5 mV/dec, and high stability of these values at multiple cycle potential. It is noted that the Pt(0) nanoparticles synthesized after 40 SILD cycles are 4–8 nm in size and are located on the surface of the nanoflakes at a distance of about 10 nm from each other for the nickel foam sample, on the surface of which a Co(OH)₂ nanolayer was synthesized as a result of 5 SILD cycles. These features contribute to the formation of a set of Pt(0) nanoparticle contact points with the surface of Co(OH)₂ nanoflakes, which determines the high electrocatalytic activity and stability of properties of such structures.

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.