Showing papers on "Cyclic voltammetry published in 2001"

An Asymmetric Hybrid Nonaqueous Energy Storage Cell

Abstract: A nonaqueous asymmetric electrochemical cell technology is presented where the positive electrode stores charge through a reversible nonfaradaic or pseudocapacitive reaction of anions on the surface of an activated carbon positive electrode. The negative electrode is a crystalline intercalation compound which supports the fast reversible intercalation of lithium ions. Using a positive electrode material of activated carbon and newly developed negative electrode material of nanostructured Li 4 Ti 5 O 12 we obtain a cell which exhibits a sloping voltage profile from 3 to 1.5 V, 90% capacity utilization at 10C charge/discharge rates, and 10-15% capacity loss after 5000 cycles. Electrolyte oxidation on the activated carbon positive electrode was characterized in a Li metal asymmetric hybrid cell by cyclic voltammetry. Oxidation during the anodic scan was found to decrease significantly after surface passivation at high voltage and elevated temperatures. We also introduce the asymmetric hybrid technology in a bonded flat plate plastic cell configuration where packaged energy densities were calculated to be in excess of 20 Wh/kg. In addition, a practical method for three-electrode analysis of Li cells by use of a Ag quasi-reference electrode wire is discussed.

Investigation of the Electrochemical and Electrocatalytic Behavior of Single-Wall Carbon Nanotube Film on a Glassy Carbon Electrode

Abstract: The electrochemical behavior of a film of single-wall carbon nanotubes (SWNTs) functionalized with carboxylic acid groups was studied extensively on a glassy carbon (GC) electrode. One stable couple corresponding to the redox of the carboxylic acid group, which was supported by XPS and IR experiments, was observed. The electrode process involved four electrons, while the rate-determining step was a one-electron reduction. The SWNT film-modified electrode showed favorable electrocatalytic behavior toward the oxidation of biomolecules such as dopamine, epinephrine, and ascorbic acid.

Surface modification of neural recording electrodes with conducting polymer/biomolecule blends

Abstract: The interface between micromachined neural microelectrodes and neural tissue plays an important role in chronic in vivo recording Electrochemical polymerization was used to optimize the surface of the metal electrode sites Electrically conductive polymers (polypyrrole) combined with biomolecules having cell adhesion functionality were deposited with great precision onto microelectrode sites of neural probes The biomolecules used were a silk-like polymer having fibronectin fragments (SLPF) and nonapeptide CDPGYIGSR The existence of protein polymers and peptides in the coatings was confirmed by reflective microfocusing Fourier transform infrared spectroscopy (FTIR) The morphology of the coating was rough and fuzzy, providing a high density of bioactive sites for interaction with neural cells This high interfacial area also helped to lower the impedance of the electrode site and, consequently, to improve the signal transport Impedance spectroscopy showed a lowered magnitude and phase of impedance around the biologically relevant frequency of 1 kHz Cyclic voltammetry demonstrated the intrinsic redox reaction of the doped polypyrrole and the increased charge capacity of the coated electrodes Rat glial cells and human neuroblastoma cells were seeded and cultured on neural probes with coated and uncoated electrodes Glial cells appeared to attach better to polypyrrole/SLPF-coated electrodes than to uncoated gold electrodes Neuroblastoma cells grew preferentially on and around the polypyrrole/CDPGYIGSR-coated electrode sites while the polypyrrole/CH(3)COO(-)-coated sites on the same probe did not show a preferential attraction to the cells These results indicate that we can adjust the chemical composition, morphology, electronic transport, and bioactivity of polymer coatings on electrode surfaces on a multichannel micromachined neural probe by controlling electrochemical deposition conditions

Oxidation of 4-chlorophenol at boron-doped diamond electrode for wastewater treatment

Abstract: The electrochem. behavior of synthetic B-doped diamond thin-film electrode (BDD) was studied in acid media contg. 4-chlorophenol (4-CP) by cyclic voltammetry, chronoamperometry, and bulk electrolysis. The results showed that in the potential region of supporting electrolyte stability occur reactions involving the oxidn. of 4-CP to phenoxy radical and 1,4-benzoquinone. Polymeric materials, which result in electrode fouling, are also formed in this potential region. Electrolysis at high anodic potentials, in the region of electrolyte decompn., complex oxidn. reactions can take place involving electro-generated hydroxyl radicals, leading to the complete incineration of 4-chlorophenol. Electrode fouling is inhibited under these conditions. The exptl. results were compared with a theor. model. This model is based on the assumption that the rate of the anodic oxidn. of 4-CP is a fast reaction. HPLC analyses revealed that the main intermediate products of 4-CP oxidn. were 1,4-benzoquinone, maleic acid, formic acid, and oxalic acid. [on SciFinder (R)]

A cyclic voltammetry method suitable for characterizing antioxidant properties of wine and wine phenolics.

Abstract: Phenolic antioxidants are ranked by reducing strength and characterized for reversibility using cyclic voltammetry at a glassy carbon electrode. Phenolics with an ortho-diphenol group show a first oxidation peak close to 400 mV (vs. Ag/AgCl) in a model wine solution (12% ethanol, 0.033 M tartaric acid, adjusted to pH 3.6), with a linear concentration dependence below 0.01 mM. Dilution of white wines 10×, and red wines 400×, gave first oxidation peak currents in the 1.5 to 2.2 μA range and 1.9 to 3.4 μC of charge passed by 500 mV, producing values for the concentrations of phenolic antioxidants with low oxidation potentials in the wines. Further peaks in the cyclic voltammograms of the diluted wines correspond to classes of phenolics with higher oxidation potentials, providing a qualitative assessment of wine phenolics based on reducing strength. Keywords: Cyclic voltammetry; wine; phenolics; antioxidants

Electrochemistry of CdS Nanoparticles: A Correlation between Optical and Electrochemical Band Gaps

Abstract: This communication reports novel electrochemistry of cadmium sulfide quantum dots (Q-CdS) in N,N′-dimethylformamide (DMF). During the past two decades, semiconductor nanoparticles or quantum dots (QDs), in particular those of the cadmium chalcogenides, have attracted considerable attention due to their tunable electronic properties as a function of sizesthe so-called quantum size effect. Recently, TOPO (tri-n-octylphosphine oxide)-capped Q-CdSe has been used for stimulated light emission where the laser frequency was tuned through simple variation of particle size.1 The photoelectrochemical2 and photophysical3 properties of these particles in their size-quantized states have been wellstudied. However, there have been relatively few reports on the electrochemical properties of semiconductor QDs.4,5 Using the “particle in a box” model, Brus6 has predicted a dependence of redox potential on particle size for Q-CdS. However, to our knowledge, this model has not been tested by actual electrochemical measurements of QDs in solution, largely because of the limited solvent window of many solvent/electrolyte systems and the instability of the particles. Here this is considered, and we show a direct correlation between the electrochemical band gap and the electronic spectra of CdS nanoparticles in DMF. Thioglycerol-capped, Q-CdS was chosen for study because stable monodisperse particles, which are readily soluble in DMF can be prepared relatively easily. We followed the method reported by Weller et al.7 and as-prepared particles were sizeselected8 to obtain monodisperse (<10%) fractions. The final four fractions (six to ten, denoted I-IV hereafter) were chosen for further study, and these were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-vis absorbance spectroscopy (Supporting Information). For the electrochemical measurements, CdS particle solutions were prepared in DMF with tetrahexylammonium perchlorate (THAP) as supporting electrolyte. All measurements were carried out in a helium-filled drybox, and the electrochemical properties of the dispersions were investigated by cyclic voltammetry (CV) at both Pt (A ) 0.062 cm2 ) and Au electrodes (A ) 0.3 cm2). A threeelectrode configuration was used where a Pt coil and a silver wire served as the counter and quasi-reference electrodes, respectively. The cell potential was normalized to NHE using the Fc/Fc+ couple (with the potential of this couple taken as 0.47V vs NHE). The solubility of the particles in DMF was found to be inversely proportional to their size, and the final fraction (IV) (2.4 ( 0.3 nm diameter) was the most soluble. A typical CV for IV at the Pt electrode is given in Figure 1 where it is compared with the response for the supporting electrolyte alone (Figure 1a). Increasing the amount of Q-CdS added resulted in increases in all peak currents without significant shifts in peak potentials. An identical CV was obtained with a Au electrode. Clear oxidation and reduction peaks are apparent at -2.15 V (A1) and 0.80 V (C1), respectively. The additional peaks only appear on scan reversal after traversing either A1 or C1 (Figure 1b). To show that the CV response is due to redox reactions of a solution species rather than an adsorbed film, the dependence of peak current and potential on scan rate (ν) from 10 to 500 mVs-1 was also investigated (Figure 2a). The linear fit of peak current versus ν1/2 for peaks A1 and C1 up to 100 mV s-1 indicates diffusion of solution Q-CdS to the electrode surface. The peak position shifted with increasing ν, indicating kinetic effects. The current response for the other peaks was neither clearly proportional to ν nor ν1/2. The response was stable on repetitive scanning and for several days with no evidence of fouling on either electrode surface The peak-to-peak separation between A1 and C1 is 2.96 V, a value comparable to the 3.23 eV (1s-1s transition) calculated from the electronic spectra (Supporting Information, Figure S1). Thus, these oxidation and reduction peaks can be correlated (1) Klimov, V. I.; Mikhailovsky, A. A.; Xu, S.; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A.; Eisler, H. J.; Bawendi, M. G. Science 2000, 290, 314. (2) (a) Hickey, S. G.; Riley, D. J. J. Phys. Chem. B. 1999, 103, 4599, (b) Hickey, S. J.; Riley, D. J.; Tull, E. J. J. Phys. Chem. B 2000, 104, 7623. (c) Torimoto, T.; Nagakubo, S.; Nishizawa, M.; Yoneyama, H. Langmuir 1998, 14, 7077. (d) Boxall, C.; John Albery, W. Phys. Chem. Chem. Phys. 2000, 2, 3651. (e) Boxall, C.; John Albery, W. Phys. Chem. Chem. Phys. 2000, 2, 3641. (3) (a) Burda, C.; Link, S.; Green, T. C.; El-Sayed, M. A. J. Phys. Chem. B 1999, 103, 10775. (b) Burda, C.; Green, T. C.; Link, S.; El-Sayed, M. A. J. Phys. Chem. B 1999, 103, 1783. (c) Logunov, S.; Green, T.; Marguet, S.; El-Sayed, M. A. J. Phys. Chem. A 1998, 102, 5652. (4) Hoyer, P.; Weller, H. Chem. Phys. Lett. 1994, 221, 379. (5) Chen, S.; Truax, L. A.; Sommers, J. M. Chem. Mater. 2000, 12, 3864. (6) Brus, L. E. J. Chem. Phys. 1983, 79, 5566. (7) (a) Vossmeyer, T.; Katsikas, L.; Giersig, M.; Popovic, I. G.; Diesner, K.; Chemseddine, A.; Eychmueller, A.; Weller, H. J. Phys. Chem. 1994, 98, 7665. (b) Chemseddine, A.; Weller, H. Ber. Bunsen-Ges. Phys. Chem. 1993, 97, 636. (8) Murray, C. B.; Norris, D. J.; Bawendi, M. G. J. Am. Chem. Soc. 1993, 115, 8706. Figure 1. (a) CV response in the absence and presence of thioglycolcapped CdS Q-particles (1 mg/mL of fraction IV) at a Pt electrode. Sweep rate ) 50 mV s-1 and [THAP] ) 0.05 M. (b) Variation of the initial scan direction for IV illustrating that peaks A2, A3, and C3 are related to C1 and A1; sweep rate ) 10 mV s-1.

Simultaneous measurement of dopamine and ascorbate at their physiological levels using voltammetric microprobe based on overoxidized poly(1,2-phenylenediamine)-coated carbon fiber.

Abstract: Overoxidized poly-(1,2-phenylenediamine) (OPPD)-coated carbon fiber microelectrodes (CFMEs) exhibit, in combination with square-wave voltammetry (SWV) detection mode, the attractive ability to simultaneously measure low nM dopamine (DA) and mM ascorbate (AA) in a pH 7.4 medium. The PPD polymer film is electrodeposited onto a carbon fiber at a constant potential of 0.8 V versus Ag/AgCl using a solution containing sodium dodecyl-sulfate as the dopant. After overoxidation using cyclic voltammetry (CV) in the potential range from 0 to 2.2 V at a scan rate of 10 V/s, the resulting OPPD-CFME displays a high SWV current response to cationic DA at ∼0.2 V and has a favorably low response to anionic AA at ∼0.0 V vs Ag/AgCl. The preparation of the new OPPD-sensing film has been carefully studied and optimized. The OPPD properties and behavior were characterized using CV and SWV under various conditions and are discussed with respect to DA and AA detection. The linear calibration range for DA in the presence of 0.3 m...

Surface Film Formation on a Graphite Negative Electrode in Lithium-Ion Batteries: Atomic Force Microscopy Study on the Effects of Film-Forming Additives in Propylene Carbonate Solutions

Abstract: In situ electrochemical atomic force microscopy (AFM) observation of the basal plane of highly oriented pyrolytic graphite (HOPG) was performed during cyclic voltammetry in 1 M LiClO4/propylene carbonate (PC) containing 3 wt % vinylene carbonate (VC), fluoroethylene carbonate (FEC), and ethylene sulfite (ES) in order to clarify the roles of these additives in the formation of a protective surface film on a graphite negative electrode in lithium-ion batteries. Particle-like precipitates appeared on the HOPG surface at the potentials 1.35, 1.15, and 1.05 V versus Li+/Li in PC + VC, PC + FEC, and PC + ES, respectively, and covered the whole surface at lower potentials. No evidence for cointercalation of solvent molecules was observed in the presence of each additive. It was concluded that the layer of the precipitates functions as a protective surface film, which suppresses cointercalation of PC molecules as well as direct solvent decomposition on the surface of the graphite negative electrode.

Electrodeposited iridium oxide for neural stimulation and recording electrodes

Abstract: Iridium oxide films formed by electrodeposition onto noniridium metal substrates are compared with activated iridium oxide films (AIROFs) as a low impedance, high charge capacity coating for neural stimulation and recording electrodes. The electrodeposited iridium oxide films (EIROFs) were deposited on Au, Pt, PtIr, and 316 LVM stainless steel substrates from a solution of IrCl/sub 4/, oxalic acid, and K/sub 2/CO/sub 3/. A deposition protocol involving 50 potential sweeps at 50 mV/s between limits of 0.0 V and 0.55 V (versus Ag|AgCl) followed by potential pulsing between the same limits produced adherent films with a charge storage capacity of >25 mC/cm/sup 2/. Characterization by cyclic voltammetry and impedance spectroscopy revealed no differences in the electrochemical behavior of EIROF on non-Ir substrates and AIROF. The mechanical stability of the oxides was evaluated by ultrasonication in distilled water followed by dehydration and rehydration. Stability under charge injection was evaluated using 200 /spl mu/s, 5.9 A/cm/sup 2/ (1.2 mC/cm/sup 2/) cathodal pulses. Loss of iridium oxide charge capacity was comparable for AIROFs and the EIROFs, ranging from 1% to 8% of the capacity immediately after activation or deposition. The EIROFs were deposited and evaluated on silicon microprobe electrodes and on metallized polyimide electrodes being developed for neural recording and stimulation applications.

Electrochemical Tuning of Electronic Structure of Single-Walled Carbon Nanotubes: In-situ Raman and Vis-NIR Study

Abstract: The population of valence-band electronic states of single-walled carbon nanotubes (SWCNTs) was tuned electrochemically in acetonitrile electrolyte solution. In dry and oxygen-free solution, the electrochemistry of SWCNTs is controlled by capacitive charging. Reversible changes of intensity and frequency of the Raman spectra can be monitored during cyclic voltammetry at low scan rates. Electrochemical charging of SWCNTs can be also traced via reversible bleaching of the electronic transitions in the vis-NIR region. An aprotic medium offers a broader electrochemical window for tuning of electronic properties of SWCNTs. Electrochemical charging of SWCNTs in an aprotic electrolyte solution allows easy and precise control of the electronic structure of SWCNTs. In addition to commercial SWCNTs, a material made from gas-phase catalytic decomposition of CO by the HiPco process was also studied. Selective quenching of vis-NIR and Raman spectra is a useful tool to the analysis of tubes of varying diameter and helicity.

Methylene Blue as a Novel Electrochemical Hybridization Indicator

Abstract: The interaction of double stranded DNA (dsDNA) and single stranded DNA (ssDNA) with Ru(II) complex with 2,2′-bipyridine ligand (Ru(bpy)3]2+) and methylene blue (MB) were explored by using voltammetric and spectrophotometric methods. The electrochemistry of [Ru(bpy)3]2+ and MB was also investigated at a dsDNA-modified carbon paste electrode (CPE), a ssDNA-modified CPE and a bare CPE by means of differential pulse voltammetry (DPV), and cyclic voltammetry (CV) and the increased peak currents were observed, in respect to the order of electrodes. The structure of DNA was determined by the magnitudes of the voltammetric peaks of [Ru(bpy)3]2+ and MB. The hypochromicity of the visible absorption bands of [Ru(bpy)3]2+ and MB upon the interaction with dsDNA and ssDNA was observed. Numerous factors affecting the DNA immobilization, indicator binding reactions and ionic strength were optimized to maximize the sensitivity and reduce the assay time.

Electrogenerated chemiluminescence. 67. Dependence of light emission of the tris(2,2')bipyridylruthenium(II)/tripropylamine system on electrode surface hydrophobicity

Abstract: We describe the effect of electrode surface hydrophobicity on the electrochemical behavior and electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl)/tripropylamine (TPrA) system. Gold and platinum electrodes were modified with different thiol monolayers. The hydrophobicity of the electrode surfaces changed with different terminal groups of the thiol molecules. The oxidation rate of TPrA was found to be much larger at the modified electrode with a more hydrophobic surface. The adsorption of neutral TPrA species on this kind of surface was assumed to contribute to the faster anodic kinetics. Due to the rapid generation of the highly reducing radical, TPrA., ECL intensity increased significantly at more hydrophobic electrodes. This electrode surface effect in the ECL analytical system allows one to improve the detection sensitivity at low concentrations of Ru(bpy)3(2+). The surfactant effect on the ECL process was also examined and discussed based on the change of electrode hydrophobicity by the adsorption of surfactant species.

Functionalized Self-Assembled Alkanethiol Monolayers on Au(111) Electrodes: 1. Surface Structure and Electrochemistry

Abstract: Functionalized alkanethiols (−CH3, −NH2, −OH, −COOH, −SH, −SO3H, −CN) of different lengths, self-assembled on Au(111), were studied with cyclic voltammetry and in situ scanning tunneling microscopy...

Surface Film Formation on Graphite Negative Electrode in Lithium-Ion Batteries: AFM Study in an Ethylene Carbonate-Based Solution

Abstract: In situ atomic force microscopic (AFM) observation of the basal plane of highly oriented pyrolytic graphite was performed during cyclic voltammetry at a slow scan rate of 0.5 mV in 1 mol dissolved in a mixture of ethylene carbonate and diethyl carbonate. In the potential range 1.0-0.8 V, atomically flat areas of 1 or 2 nm height (hill-like structures) and large swellings of 15-20 nm height (blisters) appeared on the surface. These two features were formed by the intercalation of solvated lithium ions and their decomposition beneath the surface, respectively, and may have a role in suppressing further solvent cointercalation. At potentials more negative than 0.65 V, particle-like precipitates appeared on the basal plane surface. After the first cycle, the thickness of the precipitate layer was 40 nm, and increased to 70 nm after the second cycle. The precipitates were considered to be mainly organic compounds that are formed by the decomposition of solvent molecules, and they have an important role in suppressing further solvent decomposition on the basal plane. © 2001 The Electrochemical Society. All rights reserved.