Liquid Mercury Electrode Research Articles

Role of Chemisorbing Species in Growth at Liquid Metal-Electrolyte Interfaces Revealed by in Situ X-Ray Scattering

Liquid-liquid interfaces offer intriguing possibilities for nanomaterials growth. Especially, growth at liquid metal surfaces has recently received renewed interest. Here, fundamental interface-related mechanisms that control the growth behavior in these systems are studied for the case of Pb halide compound formation at the interface between liquid mercury electrode and aqueous salt solutions, using in situ X-ray reflectivity and grazing incidence X-ray diffraction, supplemented by electrochemical measurements and optical microscopy. The nucleation and growth of these compounds at potentials in the regime of Pb de-amalgamation was investigated in NaX + PbX2 (X = F, Cl, Br) to systematically explore the role of the halide species. X-ray reflectivity studies reveal the rapid formation of well-defined ultrathin precursor adlayers in Cl- and Br-containing solution. This adlayer formation is followed by subsequent quasi-epitaxial growth of Pb(OH)X bulk crystals, that are oriented with the c-axis along the surface normal. In contrast, growth in F-containing solution proceeds by slow formation of a more disordered deposit, resulting in random bulk crystal orientations on the Hg surface. A detailed structural analysis of the Pb(OH)Br and Pb(OH)Cl precursor adlayers reveals that they determine the orientation of the subsequently formed bulk crystals, with the arrangement in the adlayer providing a template. Together with our previous results on the pseudo-epitaxial growth of PbFBr on Hg (A. Elsen, et al., Proc.Nat.Acad.Sci., 2013, 110, 6663), these data reveal the decisive role of the interface chemistry, especially the strong chemisorption of the anions bromide and chloride, in steering the formation of these textured deposits at the liquid metal surface.

ANÁLISE DA INFLUÊNCIA DA VARIAÇÃO DAS DIMENSÕES DE CORPO DE PROVA NA ANÁLISE DA RESISTIVIDADE ELETRICA VOLUMÉTRICA DO CONCRETO AUTOADENSÁVEL

The electrical resistivity is an important concrete property because it is directly related to the chloride ions penetration that cause the depassivation of the reinforcement, being a corrosion-causing agent. In Brazil, the bulk electrical resistivity test is described by ABNT NBR 9204/2012 (ABNT, 2012) which defines the specimen dimensions as Ø 150 x 150mm and the use of liquid mercury electrodes. Several studies of electrical resistivity are found using varying dimensions of specimens. This article aimed to analyze whether the variation in the specimen dimensions has a significant influence on the bulk electrical resistivity results of the same self-compacting concrete mixture. Three specimens were used for each geometry, Ø 50x100mm, Ø 100x100mm, Ø 100x200mm and Ø 150x150mm. Electrical resistivity was assessed at 28 and 90 days and statistical analysis was performed using the ANOVA program.

Fourier transformed alternating current voltammetry in electromaterials research: Direct visualisation of important underlying electron transfer processes

Recent advances in materials science have significantly broadened the range of electrodes available for use in dynamic forms of electrochemistry. In the modern era of dc voltammetry when the kinetic model of electron transfer with coupled chemical reactions was introduced, initial emphasis in theory-experiment comparison was placed on use of the ideal homogenous liquid mercury electrode with significant attention also given to polycrystalline and faceted metal electrodes. Nowadays, there are a plethora of carbon-based electrodes such as glassy carbon, edge and basal plane graphite, boron doped diamond, graphene and carbon nanotubes that may be extremely heterogeneous. These are supplemented by chemical modifications designed for example to improve the efficiency of electrocatalysis. In this review, it is shown that analysis of the higher harmonics available in large amplitude Fourier transformed alternating current voltammetry (FTacV) allows key processes to be detected, that are masked under commonly used dc voltammetric conditions. In particular it is shown how underlying fast electron processes that facilitate carbon dioxide reduction at tin electrodes and oxygen evolution at cobalt based electrodes can be directly detected and analysed for the first time. FTacV also experimentally reveals that structural defects or adatoms can give rise to well-defined higher order ac harmonics suggesting that a fast electron transfer process is associated with the active sites during electrocatalytic oxidation or reduction. Importantly, electron transfer processes often can be evaluated by FTacV in the presence and absence of the electrocatalysis, unlike dc voltammetric methods. The ability to analyse third and higher order ac harmonics that are essentially devoid of background charging current and which allow the electron transfer and catalytic steps to be resolved, presents new opportunities for fundamental advances in understanding complex electrochemical reaction mechanisms taking place at heterogeneous electrodes. Related advantages in studying electron transfer of surface confined metallo-enzymes or proteins in the presence and absence of their catalytically oxidised or reduced biologically relevant substrate partners are also surveyed. Finally, prospects for providing quantitative accounts of complex reactions at highly heterogeneous electrodes by FTacV are considered.

The Atomic scale structure of liquid metal-electrolyte interfaces.

Electrochemical interfaces between immiscible liquids have lately received renewed interest, both for gaining fundamental insight as well as for applications in nanomaterial synthesis. In this feature article we demonstrate that the atomic scale structure of these previously inaccessible interfaces nowadays can be explored by in situ synchrotron based X-ray scattering techniques. Exemplary studies of a prototypical electrochemical system - a liquid mercury electrode in pure NaCl solution - reveal that the liquid metal is terminated by a well-defined atomic layer. This layering decays on length scales of 0.5 nm into the Hg bulk and displays a potential and temperature dependent behaviour that can be explained by electrocapillary effects and contributions of the electronic charge distribution on the electrode. In similar studies of nanomaterial growth, performed for the electrochemical deposition of PbFBr, a complex nucleation and growth behaviour is found, involving a crystalline precursor layer prior to the 3D crystal growth. Operando X-ray scattering measurements provide detailed data on the processes of nanoscale film formation.

The effect of composition of solid silver amalgam electrodes on their electrochemical response

The main purpose of this work was to evaluate the effect of the silver to mercury ratio on the voltammetric responses of silver solid amalgam electrodes (AgSAE’s). For this, the AgSAE were prepared by mechanical mixing the metals in the following mass ratios of silver to mercury: 30/70, 40/60, 50/50, 60/40, and 70/30. The resulting AgSAE’s were physically characterized by energy dispersive X-ray analysis, X-ray diffraction and scanning electron microscopy, confirming the mass percentages of the silver and mercury, the total absence of liquid mercury and a globular structure of all AgSAE’s. Furthermore, it was observed that the AgSAE 30/70 contained only one single phase (Ag2Hg3), and no metallic silver or mercury oxides. Additionally, the resulting AgSAE’s were chemically characterized with respect to the influence of the electrode composition on the reproducibility and electrochemical signals of a hexamine-ruthenium (III) chloride solution by use of electrochemical impedance spectroscopy and cyclic voltammetry. The separation between anodic and cathodic peaks, and consequently, the charge transfer resistance across the electrode/solution interface, and the electroactive area were calculated demonstrating that the 30/70 composition is the best surface for practical applications. Finally, square-wave voltammetry experiments were performed in 4-nitrophenol solution, with a previous optimization of the experimental and voltammetric parameters. The calculated detection limit shows that the AgSAE 30/70 is suitable for determining any contamination by p-nitrophenol, minimizing the toxic residues in case of using liquid mercury electrodes.

ChemInform Abstract: The Determination of the Kinetic Parameters of Electrochemical Reaction in Chemical Power Sources: A Critical Review

AbstractReview: 109 refs.

Fabrication and Characterization of Solid Mercury Amalgam Electrodes for Protein Analysis

Gold and carbon electrodes have been largely used as transducers in protein and DNA sensors and arrays. Liquid mercury electrodes, with potential windows allowing detection of DNA and protein reduction processes at highly negative potentials, were considered as useless in such arrays. Here, we show that solid amalgam electrode (SAE) arrays can be prepared as a substitution of liquid mercury in the analysis of the above biomacromolecules. Vacuum metal sputtering on a glass substrate, photolithography, and galvanic mercury amalgam formation were used for fabrication of an inexpensive disposable electrode array. The resulting ultrathin (less than 1 microm) amalgam microelectrodes were characterized with respect to influence of the electrode composition and size on the reproducibility and stability of electrochemical signals. Further characterization was performed using electron microscopy and the well-established ruthenium electrochemistry. Final, optimized, design was applied in protein analysis employing the recently described electrocatalytic chronopotentiometric peak H.

Ultrasonic Effects on Electroorganic Processes (19) Cathodic Reduction and Adsorption of <i>p</i>-Methylbenzaldehyde on a Liquid Mercury Electrode

Ultrasonic Effects on Electroorganic Processes (19) Cathodic Reduction and Adsorption of <i>p</i>-Methylbenzaldehyde on a Liquid Mercury Electrode

The nature of specific adsorption of some halogen ions on mercury electrode. Quantum—mechanical approach

A model of a surface of liquid mercury electrode in the frame of thin film theory has been proposed. From the point of view of thin film approach the chemisorption problem was formulated. An attempt to explain the nature of specific adsorption on a molecular level is given. The effect of electrolyte solution at the interface is simplified; ie a boundary condition acting on the electrode surface. Based upon this theory of an electrode surface there is also the photoemission phenomenon. There is also an example of conversion of the theoretical results to those experimentally obtained.

Improvement of current efficiency in the cathodic formation of metal powders

The manufacture of metallic powders by electrodeposition is a well-documented process [1-4] which is often accompanied by hydrogen evolution, reducing the efficiency. Previous work [5] has indicated that, in some cases at least, the evolution of hydrogen occurs not at the powderelectrolyte interface but at the solid electrode surface on which the powder layer is being deposited. This suggests that it may be possible to increase the efficiency by the use of a cathode material having a greater hydrogen overvoltage than traditional materials such as the austenitic stainless steels, the hydrogen evolution characteristics of which have been reported [6-8]. Nickeltin alloy was chosen as a promising alternative material [9-12] which might be of more practical interest than the liquid mercury electrode which appears to be the only one of this type already tried [13].

A Rotating Ring‐Disk Electrode Study of the Underpotential Deposition of Mercury on Gold

The isotherm for the underpotential deposition (UPD) of mercury from solutions of mercurous or mercuric ions is the same. At the equilibrium potential of a liquid mercury electrode in either of the solutions, the surface coverage of mercury species is . However, only faradaic charge sufficient to deposit of is consumed and of appear to be adsorbed along with the UPD .

Differential capacitance and frequency dispersion on solid and liquid mercury in liquid ammonia

The behaviour of solid and liquid mercury electrodes in 0·1 M ammonium nitrate solutions of liquid ammonia is investigated. The differential-capacitance/potential curves for the solid (at −40°C) and the liquid (at −38°C) are U-shaped and have a minimum of 11·2 μF/cm 2 at 0·45 V ( vs Cd/satd. Cd(NO 3) 2 in liquid NH 3) for the solid of and 10·25 μF/cm 2 at 0·4 V for the liquid. The curves have no anodic hump. The values for the solid are about 10% higher than that for the liquid but this is still within the error of the surface area measurement. The frequency dispersion of the interfacial impedance was measured between 400 and 20,000 Hz at 0·60, 0·40, 0·10, and −0·25 V. Assuming de Levie's model of parallel grooves of depth l and aperture 2 β to be applicable, the parameter l/sin β was calculated from the data. Values obtained for the liquid mercury electrodes are 5·5–6·8 × 10 −2 cm and are attributed to shielding and solution creepage. For the solid electrodes l/sin β is 12–23 × 10 −2cm. Although these numbers are too large, the increase in l/sin β by a factor of 3 when going from a liquid to a solid surface is parallel to an increase in roughness factor to about 3 expected for this case. This suggests that l/sin β may be a useful way to measure surface roughness and/or surface roughness changes.

DL-capacitance of solid metal electrodes compared with the liquid mercury electrode

The variation of the differential capacitance at solid metal electrodes on initial electrode/electrolyte contact are reported and interpreted in terms of an equilibration. Qualitative suggestions of the equilibration processes involved are given. Relationships are suggested between the “sharpness” of the differential capacitance minimum at the pzc of a solid metal and its crystal structure and also between the value of the differential capacitance for a solid metal and its melting point.