Perchlorate Electrolyte Research Articles

Ellipsometry Study of the Adsorption of Molecules at Electrolyte Interfaces with Gold and Stainless Steel

We describe an ellipticity study of the adsorption onto gold and Type 304 stainless steel of the molecules bovine serum albumin (BSA), sodium dodecyl sulfate (SDS), and polyethylenimine (PEI) in sodium perchlorate electrolyte solutions. The ellipsometric response is made of two effects, one due to surface-charging of the metal electrodes, and the other due to adsorption. The surface-charging effect is much larger for gold than for stainless steel. Misleading estimates for the adsorption are obtained if this charging response is not taken into account. We find that for the most part the adsorbed layers are not sensitive to the applied potential, and only on one occasion did we observe reversible desorption with varying potential. The surface-charging effect is not altered by BSA (the largest molecule), but SDS and PEI show evidence for changes in the surface-charging effect (and thus in the Stern layer) and changes in conformation.

Tetrabutylammonium cation expulsion versus perchlorate electrolyte anion uptake in the electrochemical oxidation of microcrystals of [(C 4 H 9 ) 4 N][Cr(CO) 5 I] mechanically attached to a gold electrode: a voltammetric and quartz crystal microbalance study

The electrochemistry of microcrystals of [(C4H9)4N][Cr(CO)5I] attached to a gold electrode which is placed in aqueous (lithium or tetrabutylammonium perchlorate) electrolyte media has been studied in detail by chronoamperometric, voltammetric and electrochemical quartz crystal microbalance (ECQCM) techniques. Whilst chronoamperometric and voltammetric measurements show that the expected one-electron oxidation of microcrystalline [Cr(CO)5I]− solid to Cr(CO)5I occurs at the solid-electrode-solvent (electrolyte) interface, the ECQCM measurements reveal that charge neutralization does not occur exclusively via the expected ejection of the tetrabutylammonium cation. Rather, uptake of ClO4 − occurs under conditions where the solubility of sparingly soluble [(C4H9)4N]ClO4 is exceeded. This is the first time that uptake of an anion rather than loss of a cation has been detected in association with an oxidation during electrochemical studies of microcrystals attached to electrode surfaces. It is therefore now emerging that analogous charge neutralization processes to those encounted in voltammetric studies on conducting polymers are available in voltammetric studies of microcrystals attached to electrodes which are placed in contact with solvent (electrolyte) media. In the presence of LiClO4 as the electrolyte, an ion exchange process occurs leading to formation of Li[Cr(CO)5I] . X H2O which then slowly dissolves in water at a rate that is strongly influenced by the electrolyte concentration, the relatively hydrophobic nature of the [(C4H9)4N]+ cation and the poor solubility of [(C4H9)4N]ClO4.

The growth of the second underpotentially deposited silver layer on Pt(100)

The electrodeposition of Ag on Pt(100)-(1 × 1) in perchlorate electrolyte was studied by means of time-resolved in situ scanning tunnelling microscopy (STM) and cyclic voltammetry. One monolayer of Ag is deposited underpotentially (upd) ca. 500 mV positive of the Ag+/Ag equilibrium potential. Several millivolts positive of the equilibrium potential, a second well defined upd layer forms. Its growth was observed to proceed via island formation and coalescence. This process occurs in two separate stages that manifest themselves in voltammetric peaks as well as in the STM images.

Multi-method Analysis of the Metal/Electrolyte Interface: Scanning Force Microscopy (SFM), Quartz Microbalance Measurements (QMB), Fourier Transform Infrared Spectroscopy (FTIR) and Grazing Incidence X-ray Diffractometry (GIXD) at a Polycrystalline Copper Electrode

The successful application of various in situ and ex situ analytical techniques has been demonstrated at the buried interface between a metal and an electrolyte. Scanning force microscopy (SFM), electrochemical quartz microbalance measurements (EQMB), grazing incidence x-ray diffractometry (GIXD), Fourier transform infrared spectroscopy (FTIR) in the specular reflection absorption mode and electrochemical charge measurements proved complementary in the characterization of a polycrystalline copper electrode in alkaline 0.1 M sulphate, perchlorate, fluoride and chloride electrolyte contact at pH 12. The surface exhibited a mixture of Cu(111) and Cu(200) grains of the order of 100 nm. Repeated potential scanning in the double layer and passive oxide region, between -1.4 and +0.1 VMSE, resulted in a complete reorganization of the surface morphology but no detectable corrosion. The electrochemical exchange of H2O and OH− between the electrolyte and the oxide film took place reversibly in accordance with a solid-state growth mechanism. The copper atoms were redeposited at crystallographically preferred sites, generating comparatively homogeneously oriented, narrow Cu(111)-edged grain ridges of length 200 nm. In the Cu(I) potential range, the formation of several monolayers of amorphous Cu2O could be confirmed. Only after extended time periods in the Cu(II) oxide potential region, Cu2O recrystallized to a (111) phase accompanied by Cu2O(200) and Cu2O(110). In this region, one observed the formation of amorphous Cu(OH)2 concurrent with further growth of Cu2O. Strong CuOH IR stretching bands excluded the existence of CuO. At corrosive potentials of +0.25 VMSE, high anodic currents and substantial mass losses led to an electropolished surface with isolated features of <300 nm width and <70 nm height.© 1997 John Wiley & Sons, Ltd.

Multi‐method Analysis of the Metal/Electrolyte Interface: Scanning Force Microscopy (SFM), Quartz Microbalance Measurements (QMB), Fourier Transform Infrared Spectroscopy (FTIR) and Grazing Incidence X‐ray Diffractometry (GIXD) at a Polycrystalline Copper Electrode

The successful application of various in situ and ex situ analytical techniques has been demonstrated at the buried interface between a metal and an electrolyte. Scanning force microscopy (SFM), electrochemical quartz microbalance measurements (EQMB), grazing incidence x-ray diffractometry (GIXD), Fourier transform infrared spectroscopy (FTIR) in the specular reflection absorption mode and electrochemical charge measurements proved complementary in the characterization of a polycrystalline copper electrode in alkaline 0.1 M sulphate, perchlorate, fluoride and chloride electrolyte contact at pH 12. The surface exhibited a mixture of Cu(111) and Cu(200) grains of the order of 100 nm. Repeated potential scanning in the double layer and passive oxide region, between -1.4 and +0.1 VMSE, resulted in a complete reorganization of the surface morphology but no detectable corrosion. The electrochemical exchange of H2O and OH− between the electrolyte and the oxide film took place reversibly in accordance with a solid-state growth mechanism. The copper atoms were redeposited at crystallographically preferred sites, generating comparatively homogeneously oriented, narrow Cu(111)-edged grain ridges of length 200 nm. In the Cu(I) potential range, the formation of several monolayers of amorphous Cu2O could be confirmed. Only after extended time periods in the Cu(II) oxide potential region, Cu2O recrystallized to a (111) phase accompanied by Cu2O(200) and Cu2O(110). In this region, one observed the formation of amorphous Cu(OH)2 concurrent with further growth of Cu2O. Strong CuOH IR stretching bands excluded the existence of CuO. At corrosive potentials of +0.25 VMSE, high anodic currents and substantial mass losses led to an electropolished surface with isolated features of <300 nm width and <70 nm height.© 1997 John Wiley & Sons, Ltd.

Electropolishing of Al-7Si-0.3Mg cast alloy by using perchloric and nitric acid electrolytes

The aim of the present study was to find a good method for electropolishing Al-7Si-0.3Mg cast alloy. Consideration of the fundamental current density-voltage relation and limiting current density has made it possible to identify an optimum applied voltage for good electropolishing through variation of different parameters (electrolyte, bath temperature, electrode distance, surface roughness before polishing, cathode material, etc.). The significant findings of the present study are that (1) using 30% perchloric acid + 20% glycerol moderator + 50% methanol electrolyte, (2) maintaining 15 mm electrode distance and a temperature of −33 °C, and (3) electropolishing the Al-7Si-0.3Mg cast alloy at 15 V for 2 minutes reveal the microstructures clearly. The limiting current density is about 7 mA/cm 2 for the preceding conditions for attaining good electropolishing. Electropolishing can also be achieved under the same conditions even at room temperature (26 °C), but the clarity of the microstructure is not as good as that obtained through electropolishing at −33 °C.

On the suppression of zinc-copper interactions in square wave anodic stripping voltammetry in flowing solution by addition of gallium ions

The problems arising from the formation of copper-zinc intermetallic compounds in square wave anodic stripping voltammetry at wall-jet mercury thin-film electrodes in continuous flow systems have been investigated. These effects are reduced to zero by spiking the analyte solution with gallium ions and ensuring a sufficiently low value of pH, either by using acetate buffer or acidifying the generally-used sodium perchlorate electrolyte. Advantages of this approach are assessed, as are the benefits of stopping solution flow during the determination step of each experiment.

Solid State Electron-Hopping Transport and Frozen Concentration Gradients in a Mixed Valent Viologen−Tetraethylene Oxide Copolymer

This paper describes electrochemistry and electron- hopping dynamics for a novel viologen-based redox polymer (poly-V2+) formed from the copolymerization of tetraethylene glycol di-p-tosylate and 4,4‘-bipyridine. Current−potential responses and electron-hopping (i.e., self-exchange) rates have been measured for mixed valent films of poly-V2+ on interdigitated array electrodes contacted by tetrahydrofuran/acetonitrile/tetrabutylammonium perchlorate electrolyte solution and as dry mixed valent films in vacuum or dry nitrogen. Electron transfer rates vary with the mixed valency composition of poly-V2+/+ films (judging film composition from the electrolysis potential with the Nernst equation) according to bimolecular reaction theory for solvent-wetted but less well for dry films. Current−potential characteristics are also reported for mixed valent films that contain concentration gradients of the poly-V2+ and poly-V+ redox states, which we attempt to freeze into place by drying the film under a gradient-generating potential bias so as to immobilize the film's counterions. Current transients at room and reduced (−30 °C) temperature show that the room-temperature responses of films containing concentration gradients are sensitive to small changes in poly-V2+/+ oxidation state at the electrode/polymer interfaces.

Impedance investigation of the mechanism of copper electrodeposition from acidic perchlorate electrolyte

The mechanism of the copper electrodeposition from acidic perchlorate electrolyte has been investigated with polarization and impedance methods. The impedance of the copper electrode in copper perchlorate electrolytes has been measured as a function of frequency for different E dc overpotential values and different copper(II) ion concentrations. The relations between the shape of a complex plane impedance display and the copper electrode potential values as well as the concentration of Cu II ion were analysed in terms of the electrode reaction mechanism. It is shown, that the presence of the intermediate cuprous ion and its sinusoidal change of transport rate is one of the main factors determining the depressed shape of the impedance arc. The quantitative relation between the faradaic impedance and the rates of electrode reaction rates was established. The impedance arc was simulated with a set of parameters involving: rate constants, Tafel slopes, diffusion coefficient of cuprous ion and double layer capacitance. The rate constants were calculated with respect to E Cu 2 + Cu 0 0 as: k 1 0 = 6.50 × 10 −5 cm s −1, k 2 0 = 0.139 cm s −1, k −2 0 = 1.88 × 10 −7 mol cm −2 s −1.

Electrochemical Properties and Photoelectrochemical Response of Vacuum‐deposited Poly(p‐phenylene) Thin Films

The electrochemical properties of a poly(p-phenylene) (PPP) thin film prepared by vacuum deposition were investigated by cyclic voltammetry in organic and aqueous media with a lithium perchlorate electrolyte. The PPP thin film was able to undergo both n-doping and p-doping reversibly. In an aqueous medium, the cyclic voltammograms indicated the characteristic loop in a potential sweep. The loop was ascribed to the charge transfer on the PPP film surface and to an accumullation effect of the charge in the PPP film. A photocurrent was observed at the PPP film under UV light irradiation.

Interfacial Electrochemistry of Pyrite Oxidation and Flotation.: I: Effect of Borate on Pyrite Surface Oxidation

Sodium tetraborate (Na2B4O7) has been widely used as an electrolyte and pH buffer in studying the interfacial electrochemistry of sulfide minerals in relation to sulfide mineral flotation. In all the previous studies published so far, borate was regarded as an inert electrolyte/pH buffer, and its reactions with the sulfide minerals were completely overlooked. In this first part of this series papers, the complicating effects of borate on the interfacial electrochemistry of pyrite have been studied. It has been demonstrated that borate is not an inert electrolyte/pH buffer. It strongly reacts with the surfaces of pyrite. In the borate solutions, the surface oxidation of pyrite is strongly enhanced. The first and rate-determining step of the reaction between borate and pyrite has been shown to be the following irreversible reaction:[formula]This reaction appears in the voltammogram as an anodic oxidation peak at potentials of more than 0.4 V lower than the commencement of pyrite oxidation in sodium perchlorate or nitrate electrolyte solutions. As the borate concentration increases, the peak current increases linearly, while the peak potential shifts positively at 240 mV per decade. On a rotating-disc electrode, the peak becomes a plateau. The limiting current density is a linear function of the square root of the rotation speed at relatively low rotation speeds. The Tafel slope, i.e.,dE/d{logI}, is close to 240 mV per decade and is independent of the rotation speed and borate concentration. The results indicate that charge transfer coefficient (α) is 0.25.

In-situ STM investigation of Tl and Pb underpotential deposition on chemically polished Ag(111) electrodes

In-situ STM was used to investigate the adlayer formation and structure of Tl adsorbates at chemically polished Ag(111) electrodes in perchlorate electrolyte, and to study the effect of extended polarization of incomplete Tl and Pb adlayers at high initial adsorbate coverage. In the Tl+/Ag(111) system, the full first monolayer adsorbate has a hexagonally close packed structure with interatomic distances that are compressed in comparison with the bulk Tl phase. The subsequently formed second monolayer has also a hexagonally close packed (hcp) structure, but shows more pronounced disordered domains. Incomplete first Tl monolayers of high coverage have the same hcp structure as a complete monolayer, but do not extend to the very boundary of the substrate terrace. Extended polarization of such monolayers leads to a conversion of the original hcp layer into a coverage with [√3 × √3]R30 °—symmetry which is interpreted as a mixed coverage, where every third Ag atom is replaced by a Tl atom. Similar phenomena are observed during long-time polarization of an incompletely formed Pb-coverage. The results are discussed with regard to the role of the atomic steps and reveal the importance of surface singularities for the understanding of the adsorption behaviour at real electrodes.

Characterization of an electrode adlayer by in-situ infrared spectroscopy: cyanide on Pt(111)

Irreversibly adsorbed cyanide adlayers on a Pt(111) electrode in basic sodium perchlorate electrolytes were studied by infrared reflection-absorption spectroscopy. Infrared spectra obtained at saturation coverage display a single C N stretching band around 2100 cm −1, suggesting atop-like coordination of the cyanide. This band assignment is confirmed by a bismuth coadsorption experiment. The infrared data are correlated with scanning tunneling microscopy images of the surface and a real-space model is derived. The structure of the adlayer is ( 2 3 × 2 3 ) R 30 ° − 7 CN with CN molecules in atop sites, each surrounded by a hexagon of CN in near-atop sites.

A standard reference material for the measurement of particle mobility by electrophoretic light scattering

A standard reference material (SRM) was developed for the calibration and evaluation of light scattering equipment used to measure electrophoretic mobility. SRM 1980 is a positive mobility standard containing 500 mg dm −3 microcrystalline goethite (α-FeOOH) and 100 μmol g −1 phosphate in 0.05 mol dm −3 sodium perchlorate electrolyte solution at pH 2.5. The suspension is diluted prior to use. A certified mobility value (2.53 ± 0.12 μm cm V −1 s −1) was determined from a statistical analysis of round robin data from five laboratories according to NIST guidelines. This paper documents the development, characterization and evaluation of this material. Also discussed are the various contributions to measurement uncertainty and inconsistency, and appropriate protocols for dealing with these problems.

Electrochemical capacitor using polymer/carbon composites

An electrochemical capacitor fabricated by thin-film techniques is described. The active principle is based on the electrical capacitance of a polymer electrolyte/carbon interface. The flexible multi-coating device (500 μm thick) consisted of a plasticized poly(ethylene oxide) lithium perchlorate electrolyte film, two carbon composite electrodes and large area collectors. The electrochemical and electrical properties of the components and the complete cell are presented. After 5000 operation cycles the device exhibited a maximum capacitance of 2.4 F cm −3 providing an energy density of 20 kJ l −1 with a peak power about 300 W l −1.

Square-wave voltammetry of quasi-reversible surface redox reactions

Abstract A “quasi-reversible maximum” in square-wave voltammetry can be used for the determination of the standard reaction rate constant of a redox reaction between an adsorbed reactant and a product if their adsorption constants satisfy the condition 0.1 ⩽ K ox K red ⩽ 10 . By plotting the ratio of peak current and frequency as a function of frequency, the critical frequency fmax, for which this ratio is at the maximum, can be determined. Theoretically it is shown that the rate constant is related to fmax by the equation ks = κmaxfmax, where κmax is the critical kinetic parameter which depends on the transfer coefficient of the surface redox reaction. If α = 0.55 ± 0.5, κmax = 1.13, and if α is not known, the average value gk max = 1.18 ± 0.05 , which applied to 0.25 ⩽ α ⩽ 0.85, can be used. For other α values, the corresponding κmax parameters are given by the formula κmax = 1.13 + 1.13(α − 0.55)2. The method was applied to the redox reaction of adsorbed azobenzene in perchlorate and acetate electrolytes of various pH. The rate constants are ks = (62 − 12pH)s−1 for pH ⩽ 4 and ks = 28 s−1 for pH 4.65.

Intradiffusion coefficients for perchlorate ions in zinc perchlorate and zinc chloride solutions at 25�C: Comparing transport properties of zinc chloride and zinc perchlorate systems

Intradiffusion coefficients for36ClO4− have been measured in solutions of zinc perchlorate of concentration 0.1 to 3 mol dm−3 at 25°C by the diaphragm cell technique. In addition, intradiffusion coefficients for perchlorate ions in zinc chloride solutions have been measured over a concentration range at 25°C. The results confirm previous work on the effect of complexation on diffusion in zinc chloride solutions above a salt concentration of 0.1M. The present data, together with literature data for diffusion coefficients of the other species present in the zinc perchlorate electrolyte system, have enabled a simple analysis of the hydration around the zinc ions to be carried out. This indicates that the water diffusion data are consistent with the zinc ions having an effective hydration sphere of 11 (±2) water molecules. This is in keeping with values obtained for other simple divalent electrolytes using the same model. The model is extended here to allow analysis of water diffusion in zinc chloride solutions taking into account the presence of complexed chloro-zinc species. The experimental data are consistent with the effective hydration of the chloro-zinc complexes being independent of the number of chloride ligands and equal to 18±3 over a concentration range of 0 tol mol-dm−3. This postulate is discussed in terms of its consequences on the water ligand dynamics for the complex equilibria.

In situ atomic force microscopy of under- and overpotentially deposited cadmium on Cu(111)

The structure of the monolayer of Cd atoms underpotentially deposited on a Cu(111) surface in perchlorate electrolyte was revealed by an atomic force microscope (AFM). A hexagonal adlattice with a 3.43 Å lattice spacing was observed. This spacing, combined with its orientation relative to the underlying Cu(111), implies that the Cd lattice has a (4 × 4) structure. The slightly open lattice of the first Cd adlayer is possibly due to the retained partial charge of Cd adatoms. In the overpotential region, both the atomic structure and large scale morphology showed the formation of the Cd(0001) hcp crystalline structure. The crystalline domains were several hundred nanometers across and grow via a modified Stranski-Krastonov mechanism.

Infrared spectroelectrochemical study of cyanide adsorption and reactions at platinum electrodes in aqueous perchlorate electrolyte

In-situ IR spectroelectrochemistry was used to investigate the behavior of cyanide (CN −) at polycrystalline platinum surfaces in aqueous perchlorate (ClO 4 −) electrolyte. IR spectroelectrochemical data reveal the existence of a number of surface, as well as solution, cyanide species in the interfacial region. Within the double-layer potential region, there is IR evidence for several forms of adsorbed cyanide CN ads − (ν max ≈ 2070 cm −1, ν′ max ≈ 2145 cm −1, and ν″ max ≈ 2170 cm −1). When the potential is made sufficiently positive, cyanide is oxidized to form cyanate (OCN −) (ν max = 2171 cm −1). Other solution cyanide species which may be formed at the platinum cyanide solution interface include hydrogen cyanide (HCN) (ν max ≈ 2095 cm −1) and the square-planar platinum cyanide complex Pt[CN] 4 2−(ν max = 2133 cm −1) (IR-active E u mode). The interfacial electrochemistry of the Pt | CN − + ClO 4 − system was found not only to be influenced by the applied electrode potential, but also to be driven by changes in the interfacial pH, which is potential-dependent. In-situ IR spectroelectrochemistry reveals details of the potential-dependent surface chemistry of the Pt / CN − system, the complexities of which cannot easily be studied by other techniques.

Studies on Deposition and Dissolution Processes of PbO2 in Perchloric Acid Electrolytes

Electrochemical deposition and dissolution processes of layers have been studied in 1M solutions to investigate the effects of deposition potentials on the characteristics of the deposited layers. The results obtained from cyclic voltammetric, chronoamperometric, and chronopotentiometric experiments on the rotating ring‐disk electrode indicate that the oxide layers have different electrochemical behavior when deposited at different potentials. The results are explained in terms of the nonstoichiometric nature of . Results of spectroelectrochemical experiments indicate that is produced as a long‐lived intermediate species during the reduction of . A reduction mechanism is proposed based on the relationship between the peak currents and potentials observed at the ring electrode while the layer is reductively stripped at the disk electrode.