The effect of 1,3-dioxolane (DOL) based electrolyte solutions (DOL/LiTFSI and DOL/LiTFSI-LiNO(3)) on the electrochemical performance and surface chemistry of silicon nanowire (SiNW) anodes was systematically investigated. SiNWs exhibited an exceptional electrochemical performance in DOL solutions in contrast to standard alkyl carbonate solutions (EC-DMC/LiPF(6)). Reduced irreversible capacity losses, enhanced and stable reversible capacities over prolonged cycling, and lower impedance were identified with DOL solutions. After 1000 charge-discharge cycles (at 60 °C and a 6 C rate), SiNWs in DOL/LiTFSI-LiNO(3) solution exhibited a reversible capacity of 1275 mAh/g, whereas only 575 and 20 mAh/g were identified in DOL/LiTFSI and EC-DMC solutions, respectively. Transmission electron microscopy (TEM) studies demonstrated the complete and uniform lithiation of SiNWs in DOL-based electrolyte solutions and incomplete, nonuniform lithiation in EC-DMC solutions. In addition, the formation of compact and uniform surface films on SiNWs cycled in DOL-based electrolyte solutions was identified by scanning electron microscopic (SEM) imaging, while the surface films formed in EC-DMC based solutions were thick and nonuniform. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were employed to analyze the surface chemistry of SiNWs cycled in EC-DMC and DOL based electrolyte solutions. The distinctive surface chemistry of SiNWs cycled in DOL based electrolyte solutions was found to be responsible for their enhanced electrochemical performances.

The effect of FEC as a co-solvent on the electrochemical performance and surface chemistry of silicon nanowire (SiNW) anodes was thoroughly investigated. Enhanced electrochemical performance was observed for SiNW anodes in alkyl carbonates electrolyte solutions containing fluoroethylene carbonate (FEC). Reduced irreversible capacity losses accompanied by enhanced and stable reversible capacities over prolonged cycling were achieved with FEC-containing electrolyte solutions. TEM studies provided evidence for the complete and incomplete lithiation of SiNW's in FEC-containing and FEC-free electrolyte solutions, respectively. Scanning electron microscopy (SEM) results proved the formation of much thinner and compact surface films on SiNW's in FEC-containing solutions. However, thicker surface films were identified for SiNW electrodes cycled in FEC-free solutions. SiNW electrodes develop lower impedance in electrolyte solutions containing FEC in contrast to standard (FEC-free) solutions. The surface chemistry of SiNW electrodes cycled in FEC-modified and standard electrolytes were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The impact of FEC as a co-solvent on the electrochemical behavior of SiNW electrodes is discussed herein in light of the spectroscopic and microscopic studies.

In this paper we report on a novel, cost-effective fuel cell catalyst solution that meets performance as well as reliability goals set forth by the Department Of Energy for transportation applications for 2010. Our fuel cell catalyst technology is based on an inorganic, conductive nano-fiber network decorated with Pt or Pt-alloy nano-particles. The nano-fibers have diameters in the 10s of nanometers and aspect ratios of ∼100:1. The resulting large surface area, high chemical activity, and efficient electron and proton transport in the membrane electrode assembly (MEA) allow for ultra-low material loading at very high performance. Specifically, with a total loading (anode and cathode) of only 0.2mg/cm2, we have demonstrated a performance of 0.25g/kW at 0.65V exceeding the 2010 DOE goal of 0.3g/kW. We also met the DOE target for power density of 0.25 W/cm2 at 0.8V. Very important for practical applications, the initial reliability tests show that our inorganic nano-fiber-based catalysts have a lifetime performance far superior to carbon-based approaches.

The electrochemistry of gold in 50 mM aqueous sulfuric acid solutions under conditions typical of neural stimulation (cathodic-first current pulsing at 50 Hz) was studied in oxygen-free and oxygenated solutions. As the electrode was pulsed from +0.75 V vs. a reference hydrogen electrode using a 100 mu s, -500 mA/cm(2) pulse in oxygen-free solutions, (i) the initial 10 mu C/cm(2) of injected charge was stored in the double layer, (ii) the next 20-30 mu C/cm(2) was accommodated by double-layer charging plus an undetermined process consuming about 1.8 mu C/cm(2), and (iii) when the electrode potential reached approximately -0.52 V, water reduction consumed all further charge. In oxygen-saturated solution, the unrecoverable charge (associated with irreversible reactions) was not significantly different from the degerated situation throughout the pulse period, but the electrode potential was less negative, consistent with oxygen reduction. Oxygen reduction appears reversible during a 100 mu s pulse, provided the electrode is clamped back to +0.75 V immediately after the pulse. If an open-circuit period was introduced between the current pulse and application of the reversal potential, unrecoverable charge accumulated more rapidly in oxygen-saturated solution, suggesting that processes occurring during the interpulse interval of neural stimulation may produce potentially damaging reaction products. (c) 2005 The Electrochemical Society. All rights reserved.

Raman spectra of a LiMn2O4 single crystal microelectrode have been recorded in situ as a function of potential in 1 M LiPF6 ethylene carbonate (EC)/dimethyl carbonate (DMC) (1: 1) solutions at room temperature. Measurements were acquired during a linear voltammetric scan at 0.1 mV/s over the potential (E) range in which the material undergoes redox transitions, i.e., 3.6 < E < 4.4 V vs Li/Li+. Spectral data were analyzed using both classical least squares (CLS) and multivariate curve resolution (MCR) techniques. A plot of the state of charge of the LiMn2O4 single crystal microelectrode derived from the optical data vs the applied potential obtained from data collected during the reduction of the fully oxidized material displayed two well-defined steps. A similar behavior was found for corresponding plots extracted from a coulometric analysis of the voltammetric scan, except that the curves in this latter case were shifted along the potential axis by ca. 40 mV toward more negative values. This effect was attributed to the slow rates of Li+ diffusion within the lattice, allowing the surface region probed by the laser beam to reach equilibrium with the applied potential much faster than the particle as a whole. (c) 2005 The Electrochemical Society.

Modifications in the vibrational properties of a single microparticle of LiMn2O4 induced by extraction and subsequent injection of Li+ into the lattice have been monitored in situ via simultaneous acquisition of Raman scattering spectra and cyclic voltammetry data in 1 M LiClO4 solutions in ethylene carbonate (EC):diethyl carbonate (DEC) mixtures (1:1 by volume). Statistical analyses of the spectra in the range 15 < SOD < 45%, where SOD represents the state of discharge (in percent) of the nominally fully charged material, i.e., lambda-MnO2, were found to be consistent with the coexistence of two distinct phases of lithiated metal oxide in agreement with information derived from in situ X-ray diffraction (XRD) measurements involving more conventional battery-type electrodes

Key aspects of the microenvironment surrounding the Fe center in the nitrosyl adduct of iron phthalocyanine, [Fe(Pc)(NO)], have been elucidated from the analysis of the Fe K-edge extended X-ray absorption fine structure (EXAFS) of the material adsorbed on the surface of a high area carbon electrode recorded in situ, in 0.5 M H(2)SO(4). Statistical best fits to the EXAFS data place the Fe center in a five-coordinated square pyramidal configuration shifted away from the Pc plane toward the axially bound NO bent at an angle of ca. 40 degrees with respect to the normal to the Pc plane. This environment is analogous to that of Fe in the nitrosyl adduct of crystalline [Fe(TPP)], where TPP = meso-tetraphenylporphyrinato(2-), determined from X-ray diffraction.

Interests in our laboratory have focused recently on exploring various aspects of the interactions be twe n solution phase metal ions and self-assembled monola yers (SAM) bearing acid-base functionalities. 1,2 Much of the activity has centered on the use of attenuated tota l reflection Fourier transform infrared spectroscopy (ATRFTIR) as a highly sensitive and rather specific pro be of metal-ion adsorption. As has been reported in a rec ent publication, 2 the binding of Cd and Fe to carboxylate and sulfonate moieties, respectively, brings about significant changes in certain spectral features of these functional groups, providing, thereby, a useful mea ns for monitoring and quantifying metal ion uptake by the monolayer. This work describes the use of the rotat ing disk electrode (RDE) technique to the study of meta l-ion binding on SAM bearing carboxylate groups attached to the surface of iron oxide particles dispersed in th e bulk electrolyte, as a function of pH. As will be shown, the RDE provides an expedient means of detecting the amount of Cd remaining in solution, from which the extent of metal binding to the monolayer can be determined in a rather straightforward fashion.

The effect of the applied potential across a biomimetic model membrane, Δφ, on the extent of dissociation of surface bound ionizable groups has been examined theoretically using a formalism that shares common features with that recently introduced by White and coworkers (Langmuir 9 (1993) 1) to account for the occurrence of peaks in the cyclic voltammetry of self-assembled monolayers rigidly attached to an electrode surface, bearing the same type of ionizable groups facing the electrolyte. Numerical solutions of the governing coupled, highly non-linear system of equations yielded for reasonable membrane parameters, and under conditions of physiological relevance, linear changes in the extent of ionization as a function of Δφ, about Δφ=0, of ca. 0.07 units/V. Also considered in this work was a more general situation in which the contributions to the total interfacial capacity, CT, due to the diffuse double layers, CSj, and to the fixed charges Cj(fj) on each of the sides of the membrane-like assembly denoted by ‘j’, were comparable in magnitude to the potential independent capacity of the intervening hydrophobic layer, i.e. low-electrolyte concentration. In such case, plots of CT versus Δφ displayed a global minimum at Δφ=0 and two local maxima at values of Δφ slightly negative and positive to the maxima observed in the corresponding Cj(fj) versus Δφ plots. Implications of the results obtained to excitable bilayer membranes are briefly discussed.

Structural and electronic aspects of IrO2 films prepared by electrodeposition on Au substrates were investigated by in situ LIII-edge X-ray absorption and surface enhanced Raman spectroscopies in both acid and alkaline aqueous solutions. Linear correlations were found between the extent of oxidation of Ir3+ in the films determined from a statistical fit of the white line, which includes contributions from each of the sites differing by a single electron, and from coulometric analysis of the voltammetric curves. Analysis of the extended X-ray absorption fine structure (EXAFS) yielded Ir−O bond lengths decreasing in the sequence 2.02, 1.97, and 1.93 A for Ir3+, Ir4+, and Ir5+ sites, respectively. Whereas SERS provided evidence for the presence of crystalline IrO2 in the highly hydrated films, the lack of intense shells in the Fourier transform of the EXAFS function beyond the nearest oxygen neighbors indicates that the films do not display long-range order.

The affinity of selected metal ions for palmitic (PAL) and hexadecanesulfonic acid (HDSA) monolayers self-assembled onto an octadecyl silane (ODS) monolayer covalently bound to a Ge internal reflection element has been examined in situ in aqueous electrolytes by attenuated total reflection Fourier transform infrared spectroscopy. Marked changes in the bands associated with the symmetric and asymmetric stretches of the carboxylate groups induced by metal-ion binding could be discerned for PAL/ODS self-assembled bilayers (SABs) in contact with Cd2+ solutions of pH = 6 even at concentrations in the sub-muM range. Subsequent exposure of Cd2+/PAL/ODS SABs to solutions of pH < 4 devoid of Cd2+ led to the removal of Cd2+ from the bilayer leaving behind a better ordered structure, as judged by the shift of the C-H stretching modes toward lower wavenumbers. Spectral evidence for strong metal-terminal sulfonate group interactions was also obtained for HDSA/ODS SABs immersed in solutions containing Cd2+, Fe3+, and Fe2+, for which the effects on the characteristic symmetric and asymmetric modes of the terminal sulfonate moieties were found to be unique to the nature of each of the metal ions.

The electronic properties of electrodeposited Ru oxide films supported on Au have been examined in situ by Ru LIII and LII edge X-ray absorption near edge structure (XANES) in acid media. The results obtained are consistent with the main voltammetric peak centered at 0.7 V vs RHE as being attributed to a redox couple involving formally Ru3+ and Ru4+ sites in the lattice. A linear correlation was found between the extent of oxidation of the film as derived from a deconvolution of the spectral features and the charge as determined from coulomteric analysis of the voltammetric curves. This observation suggests that only two Ru-based redox states are involved in this electrochemical process.