Kevin Ashley

Cation effects on the vibrational frequencies of adsorbed thiocyanate on platinum

Infrared spectra of thiocyanate adsorbed on a platinum electrode surface were obtained in the presence of perchlorate electrolytes of various alkali metal cations. It was discovered that the vibrational frequency of the C-N stretching mode is dependent upon the nature of the supporting electrolyte cation. Two bands were observed in the 2050 to 2150 cm−1 range; one band was attributed to nitrogen-bound thiocyanate, and the other to species adsorbed via the sulfur atom. Each of these bands demonstrated independent frequency dependencies on cation nature and on the applied electric field within the interfacial region. Differences were also observed in the intensity dependence of the bands on the applied potential. The results were explained in terms of changes in the distance between the outer Helmholtz plane (OHP) and the surface of the electrode, and also in terms of the possible influence of coadsorbed alkali metal cations on the vibrational frequency of thiocyanate species adsorbed through the nitrogen atom. The effects that variations in the OHP-electrode distance impart on the magnitude of the potential drop across the interface, and the influence of small changes in this potential field on the C-N stretching frequency of N- and S-adsorbed thiocyanate species, are discussed.

Properties of electrochemically generated poly(p-phenylene)

Abstract Poly( p -phenylene) (PPP) electrodes formed by anodic oxidation of biphenyl in acetonitrile solutions were examined. As a cell, we observe generally high discharge current densities and rapid discharge rates. PPP electrochemistry and cell performance were found to depend significantly on the nature of the supporting electrolyte present during electrosynthesis and doping. These electrodes were also found to catalyse O 2 reduction. Raman and scanning electron microscopic results are also presented.

INFRARED SPECTROSCOPY TO PROBE THE ELECTROCHEMICAL DOUBLE LAYER

Abstract-Infrared spectra of molecules and ions which are specifically adsorbed on an electrode surface can be used to investigate the dynamics and structure of the interfacial region. In this work we use a semiempirical method to calculate theoretical ir frequencies for model cyanide and thiocyanate adsorbates on various metal surfaces. The predicted ir energies for the surface specie8 are then compared with the observed experimental vibrational frequencies obtained by spectroelectrochemistry. The potential depen- dence of ir band frequencies (dv,/dE) for adsorbed cyanide species are also estimated using a theoretical model. Key words: infrared spectroelectrochemistry, pseudohalides, adsorption, electrodesolution interface. INTRODUCTION Since fist reported more than a decade ago[l], ir spectroelectrochemistry at fully conducting elec- trodes has been shown to be an invaluable tool for probing the electrical double layer and for investigating surfaceadsorbate interactions[2]. The methodology has been used to study a wide variety of systems of interest, including the oxidation of small organic acids[3], polymer electrodeposition[4], pseudohalide adsorption[5], and recently, diffusion layer studies of redox reactions[6], among other systems. For investigation of the dynamics of the interfacial region, it is advantageous to employ pseu- dohalide ion species (eg cyanide, thiocyanate, axide) as specific adsorbates on an electrode surface. The reason for this is that the available double layer region is much wider in pseudohalide systems than in cases where, for example, adsorbed carbon monoxide is the predominate adsorbate. With pseudohalide systems, we attain a greater range of applicable potentials over which the electrode is “ideally polar- ized”, and it therefore becomes easier to probe the potential-dependent dynamics of the interface in the absence of complications from electrode-mediated reactions. In this work we use experimental results from cyanide and thiocyanate specifically adsorbed on electrode surfaces, and employ the classical model of Korzeniewski et u1.[7] to approximate observed vi- brational frequencies of the adsorbed species. We have also modelled the potential dependence of the

Solution infrared spectroelectrochemistry: A review.

Infrared (IR) spectroelectrochemical techniques have seen extensive use in studies of electrode surface processes. They have also been employed, albeit less frequently, to investigations of redox species dissolved in solution. The application of IR spectroscopy to electrochemical solution processes represents a special challenge, for absorption of IR radiation by the solvent is a significant interference to detection of vibrational modes of dissolved analytes. It is also difficult to maintain potentiostatic control of the system in specially designed thin-layer spectroelectrochemical cells. Solution IR spectroelectrochemical experiments are important for investigations of redox systems in which it is desired to spectroscopically monitor the structures of dissolved products, intermediates and reactants involved in electrode reactions. Such experiments have been conducted on biochemical, inorganic, organic, and other systems. In this paper some examples of applications of IR spectroelectrochemical studies of solution species in the above areas are presented, and experimental aspects are discussed.

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 (ClO4−) 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 CNads− (νmax ≈ 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−) (νmax = 2171 cm−1). Other solution cyanide species which may be formed at the platinum cyanide solution interface include hydrogen cyanide (HCN) (νmax ≈ 2095 cm−1) and the square-planar platinum cyanide complex Pt[CN]42−(νmax = 2133 cm−1) (IR-active Eu mode). The interfacial electrochemistry of the Pt | CN− + ClO4− 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.

In situ infrared spectroelectrochemical studies of cyanide adsorbed on platinum and palladium

In situ FTIR difference spectra of adsorbed cyanide on polished platinum and palladium electrodes in perchlorate media are presented. A linear CN−ads moiety is observed on Pt, while on Pd four surface cyanide species are seen: linear and bridge-bound CN−ads, as well as two surface Pd-CN films.

Combined optical second harmonic generation/quartz crystal microbalance study of underpotential deposition processes: copper electrodeposition on polycrystalline gold

Optical second harmonic generation and quartz crystal microbalance techniques are used as in situ probes of copper underpotential deposition on polycrystalline gold surfaces in sulfuric acid electrolyte. The second harmonic signal from a polished bulk gold substrate is observed to decrease by >60% as a result of copper underpotential deposition on gold. Also, the mass of an underpotentially deposited copper adlayer is monitored in situ by an oscillating quartz crystal microbalance, yielding an estimated coverage of ~8.0 x 10(-10) mol cm(-2) and an electrosorption valency of 1.5 for a copper adlayer on the surface of vapor-deposited polycrystalline gold.

A conducting polymer formed from the anodic oxidation of toluene in acetonitrile

As opposed to the much harsher conditions demanded in homogeneous solutions, a conducting polymer of toluene is readily formed by anodic oxidation of acetonitrile solutions containing the precursor.