Enhancement of the Negative Capacitance Associated with the Dissolution of Silver by Salt Concentrations by Means of Anodic Stripping Voltammetry (original) (raw)
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Electrochemical Behaviour of a Silver Electrode in NaOH Solutions
Monatshefte fuer Chemie/Chemical Monthly, 1998
Studies of the electrochemistry of metals and alloys are very important ®elds of scienti®c and industrial work. The present investigation includes detailed studies on the corrosion and electrochemical behaviour of Ag in aqueous NaOH solutions under various conditions using cyclic voltammetry, chronoamperometry, and potentiostatic techniques. It was found that the anodic polarization curve of Ag in NaOH solutions is characterized by the occurrence of ®ve anodic peaks (A1±A5). A1 is due to the electroformation of soluble [Ag(OH) 2 ] À complex species, A2 to the electroformation of Ag 2 O, A3 to nucleation and three dimensional growth of the Ag 2 O layer, A4 to the formation of AgO, and A5 presumably to the formation of Ag 2 O 3 . X-ray diffraction patterns con®rmed the existence of passive Ag 2 O and AgO layers on the electrode surface potentiodynamically polarized up to oxygen evolution.
Nanoscale, 2013
Analytical expressions for the anodic stripping voltammetry of metallic nanoparticles from an electrode, are provided. First, for reversible electron transfer, two limits are studied: that of diffusionally independent nanoparticles and the regime where the diffusion layers originating from each particle overlap strongly. Second, an analytical expression for the voltammetric response under conditions of irreversible electron transfer kinetics is also derived. These equations demonstrate how the peak potential for the stripping process is expected to occur at values negative of the formal potential for the redox process in which the surface immobilised nanoparticles are oxidised to the corresponding metal cation in the solution phase. This work is further developed by considering the surface energies of the nanoparticles and its effect on the formal potential for the oxidation. The change in the formal potential is modelled in accordance with the equations provided by Plieth [J. Phys. Chem., 1982, 86, 3166-3170]. The new analytical expressions are used to investigate the stripping of silver nanoparticles from a glassy carbon electrode. The relative invariance of the stripping peak potential at low surface coverages of silver is shown to be directly related to the surface agglomeration of the nanoparticles.
Some unusual features of the electrochemistry of silver in aqueous base
Journal of Solid State Electrochemistry, 2002
Multilayer oxide ®lms were grown on silver in base by repetitive potential cycling; however, the type of oxide obtained, as assessed on the basis of its reduction behaviour, was dependent on the lower limit of the oxide growth cycles. Using limits of 1.03±2.60 V (RHE) the oxide ®lm produced was assumed to be predominantly Ag 2 O; reduction of the latter yielded a cathodic peak at ca. 0.8 V and a surface layer of silver microparticles of diameter ranging from ca. 100 to 227 nm which, although relatively stable, were prone to rapid, extensive reoxidation. Altering the oxide growth limits to 0.7± 2.60 V resulted in the growth of a dierent type of oxide deposit which is assumed to be AgOH; reduction of the latter occurred in a negative sweep in a random manner, i.e. in the form of cathodic spikes extending to potentials as low as ca. ±0.5 V. Both types of silver oxide species are assumed to be involved in premonolayer oxidation and electrocatalysis at silver in base and the nature of the former process is discussed in some detail.
Journal of Physical Chemistry B, 2006
A novel experimental methodology for depositing and voltammetric study of Ag nanoparticles at the waternitrobenzene (W-NB) interface is proposed by means of thin-film electrodes. The electrode assembly consists of a graphite electrode modified with a thin NB film containing decamethylferrocene (DMFC) as a redox probe. In contact with an aqueous electrolyte containing Ag + ions, a heterogeneous electron-transfer reaction between DMFC (NB) and Ag + (W) takes place to form DMFC + (NB) and Ag deposit at the W-NB interface. Based on this interfacial reaction, two different deposition strategies have been applied. In the uncontrolled potential deposition protocol, the electrode is immersed into an AgNO 3 aqueous solution for a certain period under open circuit conditions. Following the deposition step, the Ag-modified thin-film electrode is transferred into an aqueous electrolyte free of Ag + ions and voltammetrically inspected. In the second protocol the deposition was carried out under controlled potential conditions, i.e., in an aqueous electrolyte solution containing Ag + ions by permanent cycling of the electrode potential. In this procedure, DMFC (NB) is electrochemically regenerated at the electrode surface, hence enabling continuation and voltammetric control of the Ag deposition. Hence, the overall electrochemical process can be regarded as an electrochemical reduction of Ag + (W) at the W-NB interface, where the redox couple DMFC + /DMFC acts as a mediator for shuttling electrons from the electrode to the W-NB interface. Ag-particles deposited at the W-NB interface affect the ion transfer across the interface, which provides the basis for voltammetric inspection of the metal deposit at the liquid-liquid interface with thin-film electrodes. Voltammetric properties of thin-film electrodes are particularly sensitive to the deposition procedure, reflecting differences in the properties of the Ag deposit. Moreover, this methodology is particularly suited to inspect catalytic activities of metal particles deposited at the liquid-liquid interface toward heterogeneous electron-transfer reactions occurring at the at the liquidliquid interface.
Electrochemical behaviour of polycrystalline silver in 0�5M NaOH containing sulphide ions
Corros Eng Sci Technol, 2005
The electrochemical behaviour of silver in 0?5M NaOH solution containing different concentrations (0?0005-0?007M) of sodium sulphide was studied using cyclic voltammetry, potentiodynamic, and current transient techniques. The anodic sweep of the voltammogram in NaOH was characterised by the appearance of three anodic peaks A 3 , A 4 and A 5 that are related to the formation of AgO 2 , Ag 2 O and Ag 2 O 2 on the electrode surface. The presence of Na 2 S in NaOH solution resulted in the appearance of two additional anodic peaks A 1 and A 2. These two peaks are related to the formation of Ag 2 S and S, respectively. The addition of Na 2 S also increases the heights of the anodic peaks A 3 , A 4 and A 5. The increase in the current density of the anodic peaks A 3 and A 4 is mainly due to surface enlargement resulting from pitting and the precipitation of sulphur on the electrode surface. Also, the large increase in the current density of the anodic peak A 5 is due to the formation of the soluble SO 22 4 compound. The morphology of the electrode surface was examined by scanning electron microscopy. Characterisation of the corrosion products formed anodically on the electrode surface was undertaken using X-ray diffraction analysis. Potentiostatic current-time transients showed that the formation of Ag 2 S, S and Ag 2 O layers involves a nucleation and growth mechanism under diffusion control.
Influence of citric acid on the silver electrodeposition from aqueous AgNO3 solutions
Electrochimica Acta, 2005
The electrodeposition of silver at 25 • C from aqueous AgNO 3 + citric acid solutions was investigated. This study shows that it is possible to obtain compact, homogeneous and coherent deposits from aqueous AgNO 3 solutions containing citric acid (H 3 Ci). The morphology as well as the roughness of the deposits was independent of the solution composition. On the contrary, deposits obtained from citrate-free solutions were neither homogeneous nor compact. All deposits exhibited a pronounced preferred orientation with a 2 1 1-texture axis. The XRD diagrams of all deposits presented an additional reflection, which cannot be indexed in terms of an fcc structure. This extra reflection was attributed to the double Bragg reflection from crystallites in twin position. The relevant chemical entity controlling growth inhibition is a neutral associate Ag 2 HCi formed in the solution between Ag + and citrate divalent anions HCi 2−. Most of the structural features of silver deposits, such as degree of preferred orientation Q 2 1 1 or intensity of the observed extra reflection, depend on the concentration of this associate. Consequently, the structural characteristics of deposits can easily be modified by: (a) changing the concentration of AgNO 3 and H 3 Ci and (b) adjusting the pH of the bulk solution by adding HNO 3 .
Journal of Applied Electrochemistry, 2004
The electrodeposition of silver at 25°C from AgNO 3 /tartaric acid solutions in binary water-methanol solvent systems was investigated. This study shows that it is possible to obtain compact and coherent silver deposits from AgNO 3 solutions only in the presence of tartaric acid (H 2 A). The relevant chemical entity controlling growth inhibition is a neutral associate Ag(HA) formed in the solution between Ag + and tartaric monoanions HA). Most of the structural features of Ag deposits such as grain size, surface roughness and degree of the preferred orientation h1 1 0i, depend on the concentration of this associate. These properties of the deposits can easily be controlled by: (a) modifying the concentration of AgNO 3 or H 2 A, (b) adjusting the pH of the bulk solution by addition of HNO 3 and (c) modifying the composition of the mixed solvent system.
Journal of Electroanalytical Chemistry, 1999
Silver voltammetric anodic stripping from stabilized rough platinum electrodes in 1 M H 2 SO 4 + c o Ag 2 SO 4 (5× 10 − 4 M5 c o 510 − 3 M) and 1 M H 2 SO 4 aqueous solutions, at 298 K, was investigated. The topography of these electrodes was determined by scanning tunneling microscopy (STM). The roughness factor, R, was varied from 10 to 71. The analysis of STM images showed that the rough structure consists of an array of nm-sized protrusions and voids as a columnar structured surface. For each value of R, the average size and volume of voids were determined. The voltammetric features of silver anodic stripping depend on R and the electrodeposited silver charge, Q Ag. The value of Q Ag (vs), the saturation value of Q Ag for voids, was estimated. The anodic stripping of underpotential deposited silver occurs in the potential range where oxygen electroadsorption on platinum takes place. By using data derived from STM imaging and equations that have been derived for the voltammetric anodic stripping reactions, in which the reactant is confined to nm-sized voids, the voltammetric behaviour of the system can be reproduced reasonably.
Monatshefte für Chemie - Chemical Monthly, 2010
A sensitive and selective procedure for the determination of silver(I) at p-isopropylcalix[6]arene modified carbon paste electrode has been developed. Silver(I) was accumulated in open-circuit design on the electrode surface via complex formation with the modifier at pH 9.00. After electrochemical reduction of silver(I), the anodic stripping wave of silver(0) appeared at ?0.04 V versus reference electrode on scanning the potential in the positive direction in 0.1 M H 2 SO 4 ? 2.0 9 10 -2 M KBr. The effects of various parameters such as preconcentration time, stripping medium, reduction potential, etc. were investigated. In the optimum condition, a linear calibration curve was obtained in the range of 5.0 9 10 -8 M to 2 9 10 -6 M with detection limit (3d) of 4.8 9 10 -8 M. Many coexisting metal ions had little effect on the determination of silver(I). Also, the proposed method was applied to the determination of silver(I) in X-ray photographic film samples. The results were in good agreement with those obtained by atomic absorption spectroscopy (AAS).