Electrochemical Zn deposition and stripping on Cu rod and foil electrodes in 35% KOH-containing zincates were examined to study Zn/Cu interfacial processes. In the cathodic potential scan, two apparent underpotential depositions at -1.1 and -1.3 V vs Hg/HgO and Zn-Cu alloy phase formation were observed. The alloy phase growth was clearly identified by a combination of electrochemical and X-ray diffraction measurements. The alloying rate at the Zn/Cu interface was evaluated by measuring the changes in the time interval of the potential plateau in the chronopotentiometry upon aging at room temperature. A simple semi-infinitive diffusion model based on the Zn density gradient within the Cu solid region in the vicinity of the interface allowed calculation of the Zn diffusivity in the Cu bulk, which was as high as 4.4x10(-15) cm(2)/s. Such a high diffusivity of Zn atoms in Cu was attributed to the lattice vacancies commonly present in Cu specimens. (C) 2008 The Electrochemical Society.

Voltammetric curves and polarization data for air/oxygen cathodes of a commercial Pt catalyst in a 0.5 M sulfuric acid solution containing methanol clearly showed the effect of forming mixed potentials, namely significant cathodic shifts of the operating voltages from the values in the absence of methanol. Organic species of carbonyl groups were detected by attenuated total reflection infrared (ATR-IR) spectroscopy implemented for monitoring the methanol crossover products at a catalyst layer of highly dispersed Pt under various simulated conditions of operating air cathodes. The results indicated that complete oxidation of methanol was more favorable at elevated temperatures and a higher oxygen partial pressure. A real time mass spectrometry identified the organic species in the cathode exhaust of an operating single-cell direct methanol fuel cell (DMFC) to be intact methanol and partial oxidation products, i.e., formaldehyde and formic acid. Depending on the DMFC operating condition, the concentration level of harmful organic gas reached several hundred parts per million as estimated from the interference-corrected mass spectrometric data. (c) 2006 The Electrochemical Society.

Changes in the state of charge of a high-area RuOx electrode in an operating RuOx|Nafion|IrOx supercapacitor were monitored in situ by time-resolved, transmission Ru K-edge X-ray absorption spectroscopy (XAS). Linear and reversible variations in the intensity of the transmitted X-ray beam as a function of time were found by fixing the energy of the incident X-ray beam, E-i, at judiciously selected values within the Ru K-edge X-ray near edge structure (XANES), while the supercapacitor was charged and discharged at constant current. The sign of the slope of these temporal signals was found to vary, depending on the value of E-i. This behavior could be rationalized based on the spectral differences between the Ru K-edge XANES of RuOx in the fully oxidized and fully reduced states, recorded in situ from films of the material electrodeposited on a gold substrate in the fluorescence mode.

The First in situ Fe K-edge x-ray absorption fine structure study is reported on the electronic and structural properties of a nitrosyl [meso-tetrakis(p-methoxphenyl)porphyrinato]iron(II) adduct, [Fe(NO)-(TMPP)], adsorbed onto a high-area carbon electrode. This adsorbed complex displayed a remarkable stability over a wide potential range, and multiple-scattering XAFS analysis yielded bond lengths of Fe-N-p = 1.99, Fe-N-NO = 1.74, and Fe-OH2 = 2.02 angstrom, and an Fe-N-O bond angle of 15 degrres, characteristic of (FeNO)-N-II porphyrin adducts.

A technique is herein described for the acquisition of X-ray absorption spectra of electrodes fully immersed in an electrolyte solution by monitoring the energy dependence of X-ray induced photocurrents. This novel strategy made it possible to obtain in situ Au L-III-edge X-ray absorption spectra of solid Au electrodes displaying virtually identical features to those recorded simultaneously via X-ray fluorescence. The dependence of the X-ray induced photocurrents on chopping frequency and electrode potential was found to be consistent with a temperature modulation of the rate of the interfacial electron transfer (faradaic heating currents), rather than electron photoemission, as the primary source of the observed effects.

The effects of underpotential-deposited lead on the adsorption of CO on Pt(111) surfaces have been investigated in 0.1 M HClO4 by in situ infrared reflection absorption spectroscopy (IRAS). Lead coverages of about 0.4 on Pt(111) electrodes polarized at 0.1 V vs RHE prevent CO from adsorbing on multiply bonded sites, reducing the overall coverage to about a third of that observed in the absence of coadsorbed Pb under otherwise identical conditions, yielding a single, sharply-defined feature in the infrared reflection absorption spectra characteristic of atop-bonded CO. However, the integrated absorption band of atop CO at 0.1 V in the presence of coadsorbed Pb was found to be about 3 times higher than that predicted from the corresponding spectral features observed for Pb-free surfaces at that specific coverage corrected for dipole-dipole coupling interactions. Although much of this effect may be due to a Pb-induced decrease in the dielectric screening within the CO adlayer, the gains in intensity are too large to be explained solely on this basis, pointing to chemical factors, such as Pt-Pb charge polarization, as an important factor.

Interfacial processes occurring at polycrystalline gold in acidic 1-ethyl-3-methytimidazolium chloroaluminate melts at room temperature, at potentials more positive than aluminum bulk deposition, include both Al underpotential deposition and the formation of Al/Au alleys. This information complements that reported in the literature for Al electrodeposition on Au in AlCl3/NaCl melts at temperatures of 200 degrees C and higher. Cyclic voltammetry and chronopotentiometry suggest that at least two alloys farm, and there is fast phase transformation between these intermetallic compounds at room temperature in the aluminum underpotential region. This transformation with thin gold films was slower than that in bulk gold electrodes. (C) 2000 The Electrochemical Society. S0013-4651(99)07-009-3. All rights reserved.

Electronic aspects of an iron porphyrin, 5,10,15,20-tetrakis(4-methoxyphenyl)-21H iron(In) chloride (FeTMPPCl) molecularly dispersed on a high area carbon black (Black Pearls 2000, BP) and then heat-treated (or thermally activated) at 800 degrees C in a flowing inert atmosphere, were investigated in situ in 1.0 M H3PO4 by Fe K-edge X-ray near-edge structure (XANES). Profound differences were observed between the ex situ (dry) XANES of electrodes incorporating FeTMPPCl/BP before and after heat treatment and, likewise, in the case of the thermally treated FeTMPPCl/BP before and after immersion of the electrodes in the electrolyte. Monotonic shifts in the absorption edge toward higher energies were observed for heat-treated FeTMPPCl/BP as the potential was increased over a range of over 1 V. The overall magnitude of the shift, ca. 2.5 eV, was virtually the same as that obtained with non-heat-treated (or intact) FeTMPPCl/BP, which occurred in a much narrower potential range, ca. 0.2 V. In contrast to the behavior observed for the intact adsorbed macrocycle, its heat-treated counterpart displayed no affinity for CO, indicating that, to the level of sensitivity of this technique, iron sites in the thermally activated material are quite different from those in the N-4 environment of the intact macrocycle.

Changes in the Pt-L-III edge region of small Pt particles (4-5 nm diameter) dispersed in a high area carbon (XC72-R) induced by the adsorption of CO, were monitored in situ in aqueous 0.1 (M) under bar HClO4, by measuring the fluorescence intensity at fixed X-ray energies during a voltammetric cycle. This real time technique made it possible to detect a small increase in NF (<0.1) at the Pt-L-III main absorption edge (11,564 eV), following electrooxidation of CO adsorbed at saturation coverages on the high area Pt, derived from a shift In the edge toward lower energies. These in situ findings are in agreement with ex situ spectroscopic measurements of Pt surface core levels for CO adsorbed on Pt single crystals in ultrahigh vacuum environments, Also described in this work are applications of this new in situ technique to the study of hydrogen adsorption-desorption, and oxide formation and reduction on such high area Pt/XC72-R electrodes in the same electrolyte.

The reduction of bisulfite on Au electrodes in buffered aqueous solutions (pH = 5.25) was examined by in situ near-normal-incidence UV-visible reflection absorption spectroscopy on a rotating disk electrode (RDE) and in situ transmission W-visible spectroscopy downstream from a channel-type electrode. The currents associated with dithionite (S2O42-) formation obtained from the spectroscopic measurements were found to be lower than those expected for a one-electron, diffusion-controlled process. Faradaic efficiencies for S2O42- generation derived from RDE data yielded, in the range -0.60 to -0.75 V vs Ag/AgCl, values close to 100%. The advantages of rotating disk over channel-type electrodes for determining faradaic efficiencies by W-visible spectroscopic techniques are discussed.

The electronic and electrochemical properties of a carbon monoxide-FeTMPP adduct (FeTMPP = (5,10,15,20-tetrakis[4-methoxyphenyl]-21H,23H-porphine)iron(II)) adsorbed on Black Pearls (BP) high-area carbon have been examined in situ in 0.05 M H2SO4 by Fe K-edge X-ray absorption near-edge structure (XANES). This adduct was prepared by first polarizing a Teflon bonded electrode, incorporating the high-area FeTMPP/BP material, at a potential at which the adsorbed macrocycle is present in the reduced state, followed by bubbling CO into the electrolyte. The resulting in situ XANES displayed two new preedge features centered at 7112 and 7115 eV, as found for other well-characterized iron macrocycle-CO adducts, as well as a shift of the main absorption edge toward higher values (ca, 1.3 V) indicative of charge transfer from the iron to CO. Dissociation of the adduct could be achieved by polarizing the electrode at more positive potentials to yield the GO-free form of the macrocycle in the ferric state, as has been reported for solution-phase CO-Fe porphyrin adducts in nonaqueous media.