Oxygen electroreduction on a granulated layer of a copper-containing electron-ion exchanger

The reduction of dissolved oxygen from a flowing aqueous solution of sodium sulfite on a cathodically polarized granulated layer of a copper-containing electron-ion exchanger is studied. It is established that the polarizing current is distributed over the layer height nonuniformly. A peak current corresponding to the oxygen electroreduction is discovered. The peak shifts from the inlet into the granulated layer to the exit out of it, which is connected with the advance of the concentration front and with an increase in ohmic resistance due to partial oxidation of copper centers. The distribution of the polarizing current is analogous to the distribution of the limiting current of the oxygen reduction, which is determined from polarization curves. The reaching of a stationary position of the peak of the polarizing current and the oxygen reduction degree with time testifies to the onset of a stationary state, at which the current turns limiting and the balance between the arrival and electroreduction of oxygen is fulfilled.     

Contribution from the ion-exchange factor to the potential of a copper-containing electron-ion exchanger

The process of formation of the electrode potential of EI-21 electron-ion exchanger, composed of ultrafine copper particles and KU-23 sulfocationite, was studied. The potentials of a EI-21 powdery electrode with a platinum lead in copper(II) sulfate solutions of various concentrations (0.005–1.0 M) were measured using currentless-mode potentiometry. The potential of this electrode first shifted by 0.02–0.15 V in the negative direction with respect to a compact copper electrode, after which the shift eventually decreased to ?0.010 ± 0.003 V. It was demonstrated that the time evolution of the potential is determined by the interplay of electron and ion exchange. When EI-21 is placed onto a platinum lead, the role of the potential-determining reaction passes from Cu²⁺ + e^? ? Cu⁺ to Cu²⁺ + 2e^? ? Cu. At the same time, H⁺-Cu²⁺ ion exchange gives rise to a change in the ratio of the concentration of copper(II) ions in the internal and external solutions. The Donnan potential, which arises at the boundary between the electron-ion exchanger and the external solution, maintains a high concentration of copper(II) ions in the internal solution, a factor that facilitates the recrystallization of the particle distributed over the bulk of the exchanger. The process of recrystallization slows down with time to such an extent that the electrode potential stops changing, remaining at a level close to the equilibrium potential of the Cu²⁺/Cu pair. It was concluded that the internal stability of the system makes the potential of the EI-21 electrode sensitive to the dispersity of the metal component and the concentration of potential-determining metal ions in the external solution.     

Contribution to direct measurement of double-layer potential at the oxide/electrolyte interface

A method for direct measurement of surface-potential changes at the oxide/electrolyte interface is described. It is based upon the semiconductor effect, and, in contrast to the well-known transistor method, it uses an easier-to-prepare field-effect diode.Measurements of the systems SiO₂/electrolyte solution and Al₂O₃/electrolyte solution show, that the Nernst relation is only valid for Al₂O₃, whereas in the case of SiO₂, besides H⁺ and OH^– ions, also electrolyte ions of alkaline chlorides and MgCl₂ are potential-determining.Mitteilung Nr. 814 aus dem Forschungsinstitut für Aufbereitung der AdW der DDR, Freiberg.     

CuAg nanoparticles formed in situ on electrochemically pre‐anodized screen‐printed carbon electrodes for the detection of nitrate and nitrite anions

CuAg nanoparticles (CuAgNPs) were electrochemically formed in situ on pre‐anodized, screen‐printed carbon electrodes (SPCEs) that possessed many oxygen‐containing functional groups capable of adsorbing metal ions, namely Cu²⁺ and Ag⁺. Pre‐anodization was achieved using continuous cyclic voltammetry in the range of potential 0.3–2.0 V under a scan rate of 50 mV/s. Cu²⁺ and Ag⁺ ions were adsorbed on the pre‐anodized SPCE by immersing the electrode in solutions containing both metal ions, and then CuAgNPs were formed in situ via electrochemical reduction in a deaerated, neat NaClO₄ solution after the electrode was ultrasonicated to remove physically adsorbed metal ions. Although CuNPs showed higher activity than AgNPs toward both nitrate (NO₃⁻) and nitrite (NO₂⁻) ions, the instability of CuNPs hindered the application, so CuAgNPs were employed to achieve a compromise between sensitivity and stability. The SPCE/anodized/CuAgNP electrodes showed activity toward the electrochemical reduction of NO₃⁻ and NO₂⁻, respectively, with the limit of detection (LOD) of 15.6 μM (0.97 ppm) and 11.1 μM (0.51 ppm), which is sufficient to fit the allowed values (50 and 3 ppm, respectively) in drinking water as suggested by the World Health Organization (WHO).     

On the asymmetry of thermodynamic fluctuations of the electrode potential

The asymmetry of thermodynamic fluctuations of the equilibrium electrode potential and the asymmetry of thermodynamic fluctuations of the electrical double layer charge is characterized quantitatively on the basis of third-order noise spectra.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 131–136.Original Russian Text Copyright © 2005 by Grafov.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Electrophoretic study of the effect of ultradisperse iron powder on cotton seed proteins

The protein composition of seeds treated with a suspension of ultradisperse iron was studied using electrophoresis on PAAG. Changes were noted in the fractions with relative electrophoretic mobility (REM) 0.11 of water-soluble and REM 0.37 of buffer-soluble An-9 cotton seed proteins. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 384–385, July–August, 2006.     

金属活动性顺序的探讨——由一道初中化学试题引发的思考

列举了金属活动性顺序只能说明反应的趋势,不能说明反应速率的例子。解释了一些常见金属活泼性强,反应速率反而慢的原因。指出并举例说明了一些反应不能用金属活动性顺序来判断反应的方向。总结了在使用金属活动性顺序时应考虑的几点内容。     

Effect of ionic strength on the formal potential of the glass electrode in various saline media

We examined the variation with ionic strength (I, adjusted with KCl, KNO₃, KBr, NaCl or NaClO₄) of the formal potential (E_const) for glass electrodes exhibiting a Nernstian response (i.e. E_cell=E_const−s log [H⁺]). For this purpose, we investigated the different factors included in the formal potential, so we obtained reported values for the liquid junction potential as a function of ionic strength and determined the logarithm of the activity coefficient for the proton in various saline media, using Pitzer equations.     

Effect of solution flow rate and direction on copper electrodeposition process from sulfuric acid electrolyte on porous electrode with high electric conductivity

The effect of solution flow direction and rate on the dynamics of copper electrodeposition onto a premetallized coal-graphite VINN-250 material from a dilute copper sulfate sulfuric acid solution is experimentally studied in the direct-flow mode. A light effect of solution supply on the copper deposit final mass for high and low solution flow rates is found, while the effect of this parameter on the metal distribution within the porous electrode is significant. The most uniform copper deposit distribution throughout the porous electrode is observed in the case of intermediate solution flow rates at its rear supply. The obtained experimental data agree qualitatively with the earlier published mathematical simulation results. Small systematic deviations from numeric calculations can be due to the process disregarded in the mathematical model: the effect of gas phase formed within the porous cathode due to the simultaneous hydrogen evolution.     

膜流动电位测试中Ag-AgCl电极的制备及稳定性研究

膜的动电特性研究中,往往采用流动电位方法。该方法中,Ag-Ag Cl测试电极的质量是影响测试准确性的关键要素。本文采用正交试验设计和方差分析,着重考察电解法制备Ag-Ag Cl电极过程中,电流强度(I)、氯化时间(t)、电解质溶液浓度(CHCl)、电极来源(n)、烘烤温度(T)、活化电极溶液浓度(CKCl)等因素对Ag-Ag Cl电极稳定性的影响。得到Ag-Ag Cl电极的最优制备参数为:电流密度3.0m A/cm2,氯化时间50min,盐酸浓度0.1mol·L-1,烘烤温度120℃,活化电极溶液(KCl)浓度0.001mol·L-1;最显著影响因素为电极来源,显著影响因素为氯化时间和烘烤温度。对最优条件组合下制备的AgAg Cl电极,进行了稳定性实验,结果表明:制备的电极具有较好的稳定性,24h内电极电位漂移量小于0.10mv,7天内电极电位漂移量小于0.2mv;在聚偏氟乙烯中空纤维超滤膜流动电位测试中,流动电位与流动压差具有良好的线性和可重复性,回归曲线R20.99,变化规律符合Helmholtz-Smoluehowski公式,可以较好满足膜的流动电位测试要求。     

固态碳糊电极电位法测定利多卡因注射液

本文报道了一种以利多卡因与单质碘形成的缔合物为电活性物的全固态碳糊利多卡因电极,电极的线性响应范围5.0×10-2～4.0×10-5mol.L-1,级差电位为30mV/pC,检测下限为3.0×10-5mol.L-1。该电极响应迅速,重现性好,用该电极测定了盐酸利多卡因注射液中利多卡因的含量,结果与药典法相符。     

Determination of the Enthalpies of Formation of DyI2 and DyI3 and estimation of the Dy3+/Dy2+ standard aqueous electrode potential

DyI₂ and Dy_3I were synthesized by literature techniques. Their enthalpies of solution were determined and their enthalpies of formation calculated to be Δ_fH°(DyI₂, s, 298 K) = ?(394 ± 16) kJ· mol^?1 and Δ_fH°(DyI₃, s, 298 K) = ?(616 ± 10) kJ· mol^?1. With appropriate literature and estimated enthalpies of solution and standard entropies, the E°(Dy³⁺/Dy²⁺, aq) was calculated to be ?(2.6 ± 0.2) V. A comparison is made of the enthalpies of reduction of DyI₃ to DyI₂ and of DyCl₃ to DyCl₂.     

Generalized electronic diabatic approach to structural similarity in two‐dimensional potential energy surfaces of various topologies

Active site properties in some proteins can be affected by conformational fluctuations of neighbor residues, even when the latter are not involved directly in the binding process. A local environment thus appears to alter the relevant potential energy surface and its reaction paths. Here, some aspects of this phenomenon are simulated within a generalized electronic diabatic (GED) scheme to study the geometry and structural similarity for a class of two‐dimensional (2D) energy surfaces. The electronic quantum state is a linear superposition of diabatic basis functions, each of which is taken to represent a single (pure) electronic state for the isolated material system. Here, we describe a model reaction of isomerization by shifts in amplitudes for three diabatic species (reactant, product, and an open‐shell transition state) coupled in an external field. The “effective” 2D energy surface in the field is characterized in terms of critical points, and the amplitudes along the main reaction paths. A new feature is the introduction of a phase diagram where all possible potential‐energy‐surface topologies (consistent with three‐state systems in two linear coordinates) are matched with actual model parameters. By varying the coupling strengths between diabatic states, we classify regions of this phase diagram in terms of electronic and structural similarities; some regions comprise models whose reaction paths have geometries that belong to the catchment region of the reactant, yet are electronically akin to the diabatic transition state or product. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

硫化铜纳米粒子的合成及应用于汞离子的测定

室温下以柠檬酸三纳为稳定剂,在水相中合成了CuS纳米粒子(NP-CuS)。 用共振光散射(RLS)技术探索了不同pH值和Cu2+与S2-不同配比条件下,体系RLS强度(IRLS)的变化。 结果表明,在最佳实验条件下,在0.01~100 μmol/L范围内IRLS与汞离子浓度间呈现良好的线性关系(r=0.991),据此建立了测定水中微量汞的方法。 方法的检测限为0.003 μmol/L,样品加标测定的回收率为100.3%~103.4%。     

Effect of the nature of carbonaceous supports on the bioelectrocatalytic activity of peroxidase, immobilized on the supports, in the hydrogen peroxide reduction reaction

Electrochemical properties of such disperse carbonaceous materials as acetylene black AD-100, finely divided colloidal graphite (FCG), ultradisperse diamond (UDD), and carbon nanotubes (CNT) are examined. Effect of the nature of disperse carbonaceous supports on bioelectrocatalytic activity of adsorbed peroxidase (POD) in the hydrogen peroxide reduction reaction is investigated. It is shown that the hydrogen peroxide reduction on the biocatalysts studied proceeds in conditions of direct bioelectrocatalysis independently of the disperse-support type. It is also demonstrated that the biocatalysts’ activity depends on the structure and properties of the surface of the supports defining the magnitude of the POD adsorption in an orientation favorable for direct bioelectrocatalysis. Maximum activity is inherent in the catalysts manufactured on the basis of materials with moderate hydrophobic and hydrophilic properties. By the magnitude of the activity in the hydrogen peroxide reduction reaction, depending on the nature of the carbonaceous support, the fabricated catalysts (carbonaceous material with adsorbed POD) form the series AD-100, CNT > FCG > UDD.     

钴添加剂对发泡式镍电极的作用机理研究

分别以共沉淀和机械混合两种方式于发泡式镍电极引入钴添加剂.X射线衍射(XRD)、循环伏安、电化学阻抗谱(EIS)和恒电流充放电等测试表明,共沉淀引入的钴添加剂会降低氢氧化镍各晶面衍射峰强度并增大其半峰宽.两种方式引入的钴添加剂均能改善镍电极的电化学活性、提高金属氢化物/镍电池容量,而且以机械混合引入的CoO更有效.但由CoO氧化生成的β-CoOOH在低电位下不稳定,经强制性过放电储存后,电池容量出现不可逆衰减.     

On the standard potential of the mercury:Mercurous sulfate electrode at 25°C in aqueous solution

The standard potential of the mercury:mercurous sulfate electrode in aqueous solution at 25°C is determined in terms of the Weston saturated and Clark saturated standard cells. Eight electrode combinations involving cadmium-amalgam or zinc-amalgam electrodes and one lead-amalgam electrode are employed with the emf of the standard cells. A best value of 0.61544 V was obtained that agrees within 0.09 mV with the value previously reported by Harned and Hamer.     

Mechanism of hydrolyzable metal ions effect on the zeta potential of fine quartz particles

The effects of ion species, cation valence, ionic strength, and hydrated ionic radius on the zeta potential of quartz have been systematically studied through the measurement of zeta potential, sedimentation rate, and aggregation observation. The results show that the interaction between hydrolysis components and quartz particles results in three critical points – CR₁, CR₂, and CR₃. The results of sedimentation and aggregation observation are in good agreement with the changes of the zeta potential in 0.1?M MgCl₂, the maximum sedimentation rate being 99.26% at pH 10.85. When the pH is around 6.25 or 10.00, the sedimentation rate is relatively lower and the size of aggregation smaller. The adsorption of hydrolyzable multivalent metal ions on the quartz surface is a combination of three adsorption forms, namely electrostatic adsorption, hydroxyl complex adsorption, and hydroxide precipitation adsorption. Then the hydrolysis properties of metal ions and the surrounding environment determine the action of the hydrolysis components and the main form of adsorption.     

Effect of equilibrium potential on anodic peaks of a reversible electrode process in conditions of stripping voltammetry at a linear alteration of potential on a thin-film mercury electrode

The full contour of a stripping-voltammetry peak for a reversible electrode process in conditions of boundedly semi-infinite and symmetrical diffusion on a thin-film mercury electrode at a linearly altering potential is calculated with an exact explicit equation allowing for the equilibrium-potential effect in a broad range of values of parameter H (which are defined by the film thickness, potential scan rate, and diffusion coefficient). The height, position of maximum, and full width at half-maximum of anodic peaks are evaluated as a function of parameter H and equilibrium potential. The latter is shown to exert substantial influence on the parameters and shape of anodic peaks.To the Centennial of B.N. KabanovDeceasedTranslated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 69–75.Original Russian Text Copyright © 2005 by Nazarov, Stromberg, Larionova.     

Study on the swelling kinetics of superabsorbent using open circuit potential measurement

Open circuit potential measurement was used to trace the swelling kinetics of superabsorbent. The calibration curve and its fitting result showed the validity of the method in determining the concentration of chloride ion in aqueous solution. According to the regression analysis and theoretical derivation, the relationship between the open circuit potential change and the swelling ratio was obtained. Comparing with tea bag method, it was verified that open circuit potential measurement could be employed to trace the swelling kinetics of superabsorbent. The hysteresis effect of solute entering into superabsorbent and the overflow of soluble parts of hydrogel were also observed. Besides, we found that the entrance of solute and water were almost synchronal, and the concentration of solution absorbed by superabsorbent was lower than that of swelling medium. Moreover, the swelling model of superabsorbent in salting liquid was slightly modified.