Underpotential Deposition Of Tl Research Articles

Counting surface redox sites in carbon-supported electrocatalysts by cathodic stripping of O deposited from N2O

Methods of determining in situ the electrochemically active surface area of bulk noble metal electrodes (e.g., underpotential deposition of a strongly interacting sorbent followed by columbic stripping) may not be appropriate for certain base metals supported on electroactive supports, such as carbon, because of the difficulty of finding a metal-specific titrant and because the support itself can contribute a very large background current. For example, the coulometric stripping of metal-selective sorbates, like carbon monoxide, works for the in situ characterization of certain electrode-supported metals (e.g. Pt, Pd) if applied carefully, but not for base metals, like Cu that do not strongly adsorb the titrant. Moreover, in scoping studies, we found that underpotential deposition of Tl on carbon-supported Cu failed to be selective for the copper. Here we present the use of gentle oxidation of the metal domains using N2O as the oxidant, followed by cathodic stripping of the surface oxide. The method compares approximately with XRD line broadening for characterizing ∼10 nm particles of Cu supported on graphite felt. More significantly, we show that the method usefully normalizes the rates of two electrochemical hydrogenation reactions: conversion of nitrobenzene to aniline and conversion of benzaldehyde to benzyl alcohol.

Underpotential deposition of Tl on Ag in the presence of bromide ions – Estimation of specific capacitance for design of electrochemical supercapacitors

The analysis of underpotential deposition (UPD)-based systems for the development of electrochemical supercapacitors is investigated employing the UPD of Tl on Ag in the presence of bromide ions, as an illustrative example. The specific capacitance is estimated with the help of multi-cycle voltammograms, galvanostatic charge/discharge experiments and impedance spectroscopy. The equivalent circuit for the system is constructed and the parameters are deduced from the simulation. The deduced magnitude of ∼102 F g−1 in conjunction with the satisfactory number of charge/discharge cycles obtained from galvanostatic experiments indicate the feasibility of these systems as supercapacitors.

Bromide Adsorption Induced Formation of Thallium Bromide Adlayers with Varying Composition and Structure on the Au(111) Electrode Surface

The underpotential deposition of Tl on Au(111) in 0.1 M HClO4 solution containing 1 mM Tl+ and 1 mM Br- has been investigated by using cyclic voltammetry, in situ X-ray scattering, and rotating disk-ring techniques. Three interesting phenomena for the UPD of metals in the presence of adsorbed anions are reported, viz., (i) an increase of the underpotential shift for deposition of Tl on Au(111) in the presence of Br- in solution, (ii) a formation of two mixed adlayers, surface compounds, with the stoichiometry Tl−Br2 and Tl−Br, and (iii) an exceptionally complex structural behavior of this system with five ordered phases. Bromide and thallium form incommensurate rotated-hexagonal close-packed phases at ca. 0.85 and −0.3 V, respectively. In the intermediate potential region three mixed phases exist, identified as 3TlBr2-(√13 × √13), 2TlBr-(3 × √3), and TlBr-c(p × √3).

Electrooxidation of ethylene glycol on Pt-based catalysts dispersed in polyaniline

Platinum dispersed in a polyaniline film is a better catalyst than smooth Pt for ethylene glycol electrooxidation in perchloric acid aqueous solutions. The catalytic activity of the platinum microparticles is further enhanced when Ru, Sn or both are codeposited. The PAni/Pt–Sn assembly shows the highest electrocatalytic activity of the electrodes examined. Underpotential deposition of Tl and Bi on dispersed Pt inhibits EG electrooxidation while Pb causes significant catalysis only with a specific preparation method electrocatalyst. The morphology and the identity of the metallic dispersion is examined by transmission electron microscopy.

The effects of anions on the underpotential deposition of Tl on Pt(111): a voltammetric study

The effects of anions on the underpotential deposition of Tl on Pt(111): a voltammetric study

Study of underpotential deposition of metals using the quartz crystal microbalance

Underpotential deposition (UPD) of the metals lead, cadmium and thallium, onto a polycrystalline silver substrate, has been studied. The amount of charge and mass transferred during the UPD process is examined, in situ, with voltammetry and with the quartz crystal microbalance (QCM), simultaneously. The measured charge and mass consumptions show good agreement with the expected values for Cd 2+/Ag up to 1.5 monolayers (ML) and for Pb 2+/Ag up to 0.7 ML. An anomaly occurs in the UPD of Tl +/Ag. While the measured mass change is consistent with the expected value, each Tl ion seems to contribute approximately two charges upon adsorption before the completion of the first UPD layer instead of one. In the second UPD layer the value of discharge returns to the valence number z = 1.

Structural effects in electrocatalysis: Oxidation of D-glucose on pt (100), (110) and (111) single crystal electrodes and the effect of upd adlayers of Pb, Tl and Bi

The electrocatalytic oxidation of D-glucose on Pt (100), (110) and (111) single crystal electrodes has been studied in acid solutions. Pronounced structural effects have been detected. The single crystal electrodes show much higher activity for D-glucose electrooxidation than polycrystalline Pt, particularly the Pt(111) face which appears to be less sensitive to poison formation. Foreign metal adatoms, such as Pb, Tl and Bi, deposited at underpotentials, cause workable catalytic effects as regards the oxidation current density, particularly on the Pt (100) and (110) planes. At complete adatom coverages the oxidation of D-glucose proceeds at higher overpotentials than on clean Pt surfaces, but higher oxidation current densities are obtained due to minor self-poisoning effects. In this work, the underpotential deposition of Tl and Bi on the three low index planes of Pt single crystals has also been studied.

Optical second-harmonic generation from thallium on silver.

Light which was generated at the surface of polycrystalline Ag was monitored in the specular direction at the second-harmonic energy of the neodynium-doped yttrium aluminum garnet laser incident radiation as a function of the applied voltage in a thin-layer electrochemical cell (0.05M ${\mathrm{H}}_{2}$${\mathrm{SO}}_{4}$) with and without the presence of 0.75\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$M ${\mathrm{Tl}}^{+}$. The second-harmonic generation (SHG) decreased when ${\mathrm{Tl}}^{+}$ became physisorbed prior to underpotential deposition (UPD) of a stable Tl monolayer and increased slightly upon UPD of Tl. In contrast to this, previously reported reflectance data at the first harmonic are insensitive to events preceding Tl deposition. These results point out basic differences between SHG and reflectance of the fundamental and also show that simple surface-charge-density arguments are unsatisfactory in the explanation of SHG surface phenomena.

Kinetic Features of SERS Quenching by Underpotential Deposition (UPD) of Cd and Tl on Ag Electrodes

Abstract Surface-enhanced Raman scattering (SERS) in the Ag/pyridine system is quenched through a biphasic kinetics, after completion of submonolayer underpotential deposition (UPD) of Cd. This result is elucidated by invoking a quasi-reversible transformation of the initial SERS-active site into another by an attack, via surface diffusion, of deposited Cd, followed by irreversible unimolecular decomposition of the new site. From the SERS quenching data a value of about 10−17 cm2 s−1 was derived as the surface diffusion coefficient of Cd on the Ag surface. A similar but somewhat different quenching behavior is observed by UPD of Tl.