


Vol 53, No 3 (2017)
- Year: 2017
- Articles: 12
- URL: https://journal-vniispk.ru/1023-1935/issue/view/11812
Article
Investigating interfacial parameters with platinum single crystal electrodes
Abstract
The concepts of total and free charge of platinum single crystal electrodes are revised in this paper, together with the associated concepts of potential of zero total and free charge. Total charges can be measured from CO displacement method. Results on solution of different pH are described. A novel buffer composition is used to attain pH values close to neutrality while avoiding interferences from anion adsorption processes. Stress is made on the fact that free charges are not accessible through electrochemical measurement for systems at equilibrium since adsorption processes (hydrogen and hydroxyl) interfere with free charge determination. Still, a model is described that allows, under some assumptions, extract free charge values and the corresponding potential of zero free charge for Pt(111) electrodes. On the other hand, fast measurement outside equilibrium can separate free charges from adsorption processes based on their different time constant. In this way, the laser induced temperature jump experiment allows determination of the potential of maximum entropy, a magnitude that is intimately related with the potential of zero free charge. Values of the potential of maximum entropy as a function of pH are given for the different basal planes of platinum.



Mechanistic principles of ion transport in the Na,K-ATPase
Abstract
The Na,K-ATPase is a member of the P-type ATPase family and a primary active ion transporter for Na+ and K+ ions in the cytoplasmic membrane of virtually all animal cells. Considerable progress in understanding the ion-pump mechanism of the Na,K-ATPase was gained by combining biophysical and biochemical studies of more than 30 years with structural information at atomic resolution available since recent years. Biophysical studies have revealed detailed properties of the ion movements that led to a gated-channel model which is strongly supported by structural findings obtained for the sodium pump. The basic question of how the free Gibbs energy released by ATP hydrolysis is transferred to the protein and transformed into uphill transport of the ions is still without reply.



Effect of metal nature on energy of specific adsorption of chloride ions from dimethyl formamide solutions
Abstract
The specific adsorption of chloride ions on the renewable liquid (Cd–Ga) electrode from mixed [0.1m М LiCl + 0.1(1–m) М LiBF4] solutions in dimethyl formamide (DMF) is studied with an ac bridge at the following fractions of surface-active anion m: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5 and 1. It is found that the data on the specific adsorption of Cl– anion in the system can be quantitatively described by Frumkin’s isotherm. The free adsorption energy of Cl– (ΔGads) is a quadratic function of electrode charge. The results are compared with the corresponding data for the Ga/DMF and (In–Ga)/DMF interfaces. It is shown that the adsorption energy of Cl–anions at the metal/DMF interface depends on the metal nature and increases in the series (In–Ga) ≈ (Cd–Ga) < Ga. The energy of metal–DMF chemisorption interaction, which hampers ion adsorption, increases in the same series. The analysis of the data uniquely indicates that the free energy of metal–Cl– interaction (ΔGM-CL-) increases in the series (In–Ga) ≈ (Cd–Ga) < Ga. Thus, in the series of electrodes studied, the variations in the energies of metal–Cl– and metal–DMF specific interaction are correlated: the higher the energy of metal–DMF chemisorption interaction, the higher the energy of metal interaction with Cl–.



Asymmetry of current-voltage characteristics of ion-exchange membranes: Model of charge density of fixed groups linear by membrane thickness
Abstract
The model of a finely porous membrane with a linear distribution of charges of its fixed groups along its depth is used in the work to explain the phenomenon of asymmetry of current-voltage characteristics of perfluorinated MF-4SK membranes surface–modified by polyaniline or halloysite nanotubes. A new exact analytical method of solution of a system of transport equations is suggested that is based on the assumption of the monotonous behavior of the electric potential inside the membrane and allows finding current- voltage characteristics (CVCs) of the membrane using a system of two implicit algebraic equations. Algebraic equations for limiting currents are obtained for the first time for different orientations of the anisotropic membrane in an electrodyalisis cell and existence of two inflection points in CVCs is explained when its less charge side is oriented towards the anode.



Magnetic properties of electrodeposited amorphous nickel–phosphorus alloys
Abstract
The influence of the sodium hypophosphite concentration in a sulfate–citrate electrolyte of nickel plating on the phosphorus content in electrodeposited amorphous Ni–P alloys was analyzed. The effect of the thermal treatment on the magnetic properties (coercive force and specific magnetization) of the obtained Ni–P alloys was considered; the Curie temperatures of the alloys were determined.



Hopping charge transport in amorphous organic and inorganic materials with spatially correlated random energy landscape
Abstract
The general properties of the hopping transport of charge carriers in amorphous organic and inorganic materials are discussed. The case where the random energy landscape in the material is strongly spatially correlated is considered. This situation is typical of organic materials with the Gaussian density of states (DOS) and may also be realized in some materials with the exponential DOS. It is demonstrated that the different DOS types can lead to very different functional forms of the mobility field dependence even for the identical correlation function of random energy. Important arguments are provided in favor of the significant contribution of the local orientational order to the total magnitude of energetic disorder in organic materials. A simple but promising model of charge transport in highly anisotropic composites materials is proposed.



Pt- and Ir-based disperse catalysts synthesized in a magnetron for water electrolyzers with a solid polymer electrolyte
Abstract
Disperse catalytic compositions for water electrolysis in electrolyzers with a solid polymer electrolyte were obtained by magnetron sputtering of C–Pt and Mo–Ir sectional targets. The catalysts were studied by X-ray diffraction analysis, electron microscopy, and voltammetry. The synthesized Pt–С and Ir–Mo catalysts with lowered contents of the precious component were subjected to prolonged trials in an electrolysis cell with a solid polymer electrolyte and showed high activity and stability.



Electrolyte systems for primary lithium-fluorocarbon power sources and their working efficiency in a wide temperature range
Abstract
New compositions of liquid organic electrolytes with working temperatures of up to–50°С were developed for low-temperature primary Li/CFx power sources. Five different compositions of organic electrolytes with a 15-crown-5 (2 vol %) addition and without it were studied on laboratory Li/CFx power sources. 1МLiBF4 (LiPF6) in an ethylene carbonate/dimethyl carbonate/methyl propionate/ethylmethyl carbonate (EC/DMC/MP/EMC) (1: 1: 1: 2) mixture and 1 М LiPF6 in an EC/DMC/EMC (1: 1: 3) mixture each with a 15-crown-5 (2 vol %) addition were found to be the best compositions of organic electrolytes with working temperatures of up to–50°С. The electrochemical tests at 20 and–50°С in the Li/CFx system showed that the 15-crown-5 addition increased the length of the discharge plateau at–50°С three- or fourfold. The mechanisms responsible for the increase in the discharge capacity of the CFx cathode in the presence of a crown ether addition were suggested.



The synthesis, structure, and electrochemical properties of Li2FeSiO4-based lithium-accumulating electrode material
Abstract
Different approaches to synthesis of Li2FeSiO4-based electrode materials for lithium intercalation, using low-cost and abundant Li-, Si-, and Fe-containing parent substances, are discussed. XRD, SEM, and a laser-diffraction analyzer of particle size were used for structure and morphology characterization of the composite electrode materials. Li2FeSiO4 was shown to be the main lithium-accumulating crystalline phase; minor LiFeO2 and Li2SiO3 admixtures are also present. The material microparticles’ average size was shown to vary from tenths of micrometer to 1 μm. Larger objects sized ca. 2–4 μm are the microparticles’ agglomerates. The material electrochemical properties were studied by dc chronopotentiometry (galvanostatic charging–discharging) and cyclic voltammetry with potential linear sweeping. The initial reversible cycled capacity of the best samples is 170 mA h/g. The anodic and cathodic processes manifest obvious hysteresis caused by the presence of several different lithium ion energy states in the material; the transition between the states is kinetically hindered. The dependences of the specific capacity and its stability under cycling on the current load and the conductive carbon component content in the composite were elucidated.



Electropolymerization of 2-aminophenylboronic acid and the use of the resulting polymer for determination of sugars and oxyacids
Abstract
Electropolymerization of aminophenylboronic acids proceeds by the mechanism typical of conducting polyaniline, if the substituent in the ring is the electron donor and its position favors the electrophilic substitution into the para position with respect to the amino group in the ring. For the same reason, the polymerization of meta-aminophenylboronic acid requires the presence of fluoride ions to transform the weak electron acceptor, boronic acid group into the electron-donating trifluoroborate anion. It is shown that electropolymerization of ortho-aminophenylboronic acid can be carried out in strongly acidic media in the absence of fluoride ions, in analogy to unsubstituted polyaniline. The conductivity of the resulting polyanilineboronic acids synthesized under optimal conditions increases upon their binding with sugars and oxyacids, which allows detecting the specific interactions only, while the nonspecific interactions lower down the polymer conductivity.



Degradation mechanisms of MEA characteristics during water electrolysis in solid polymer electrolyte cells
Abstract
The processes contributing to degradation of characteristics of membrane-electrode assemblies (MEA) of water electrolyzers with solid polymer electrolyte (SPE) are considered. Particularly, the life tests of an electrolysis cell with SPE reveal the migration of platinum from the cathodic active layer and its deposition in membrane’s near-cathode region. In addition to platinum, several other elements (Ti, Ir, Fe, Ni, Si) are detected in the membrane, carried there with the water-reagent from the structural elements of MEA, electrolysis cell, and its outer framing (anodic electrocatalytic layer, half-cells, tubes, water tank-separator, etc.). The observed considerable loss of platinum in the cathodic catalytic layer leads to a decrease in its activity (due to the decrease in concentration of platinum nanoparticles and the loss of their cohesion), while the appearance in the membrane of platinum and other ions that have the lower mobility as compared with hydrogen ions gives rise to modifications in the membrane structure thus increasing the electrolysis potential in the course of life tests.



Electrodeposition of thin Cu2ZnSnS4 films
Abstract
The electrochemical behavior of copper(II), zinc(II), and thiosulfate (S2O32-) ions on the molybdenum electrode in individual 0.2 М sodium sulfate solutions (рН 6.7) and with addition of either 0.1 М tartaric acid (рН 4.6) or 0.1 М citric acid (рН 4.7) is studied. A one-step electrochemical method is developed for the deposition of thin Cu2ZnSnS4 films, which is carried out on the molybdenum electrode at a constant potential in sodium sulfate solutions containing tartaric acid. The effect of the concentration of electrolyte components on the chemical composition of Cu2ZnSnS4 films is determined. The phase composition is confirmed by the Raman spectroscopy data. The surface morphology of synthesized films is studied by means of scanning-electron and atomic-force microscopes. The photoelectrochemical characteristics of Cu2ZnSnS4 films are determined. Samples of these coatings on the Mo electrode are found to be highly photosensitive.


