Showing papers on "Electrode potential published in 2002"
TL;DR: Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode, suggesting overall more efficient and effective device.
Abstract: Stimulating electrode materials must be capable of supplying high-density electrical charge to effectively activate neural tissue. Platinum is the most commonly used material for neural stimulation. Two other materials have been considered: iridium oxide and titanium nitride. This study directly compared the electrical characteristics of iridium oxide and titanium nitride by fabricating silicon substrate probes that differed only in the material used to form the electrode. Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode. Direct measurement of the electrode potential in response to a biphasic current pulse confirmed that iridium oxide uses less voltage to transfer the same amount of charge, therefore using less power. The charge injection limit for titanium nitride was 0.87 mC/cm/sup 2/, contradicting other reports estimating that titanium nitride was capable of injecting 22 mC/cm/sup 2/. Iridium oxide charge storage was 4 mC/cm/sup 2/, which is comparable to other published values for iridium oxide. Electrode efficiency will lead to an overall more efficient and effective device.
350 citations
TL;DR: In this paper, a residual slope in voltammograms is observed, which is unexpected from all simple considerations of electrochemical kinetics, and it is observed in experiments carried out with the [NiFe]-hydrogenase from NiFe hydroxide.
Abstract: Redox enzymes can be adsorbed onto electrode surfaces such that there is a rapid and efficient direct electron transfer (ET) between the electrode and the enzyme's active site, along with high catalytic activity. In an idealized way, this may be analogous to protein−protein ET or, more significantly, the nonrigid interface between different domains of membrane-bound enzymes. The catalytic current that is obtained when substrate is added to the solution is directly proportional to the enzyme's turnover rate and its dependence on the electrode potential reports on the energetics and kinetics of the entire catalytic cycle. Although the current is expected to reach a limiting value as the electrode potential is varied to increase the driving force, a residual slope in voltammograms is often observed. This slope is significant, as it is unexpected from all simple considerations of electrochemical kinetics. A particularly remarkable result is obtained in experiments carried out with the [NiFe]-hydrogenase from ...
226 citations
TL;DR: In this paper, the behavior of the TiO2−WO3 composite on an ITO electrode was examined in nonelectrolytic media, and it was shown that the composite film charged in air exhibited almost the same electrode potential as that of the film charged with aqueous NaCl.
Abstract: Reductive energy generated at a TiO2 photocatalyst under UV light can be stored in WO3 by coupling them together, and the stored energy can be used after dark. However, the reduction of WO3 requires cation intercalation for charge neutralization. Thus, behavior of the TiO2−WO3 composite on an ITO electrode was examined in nonelectrolytic media. When the TiO2 and WO3 were close to each other (less than 1 mm), WO3 could be reduced even in pure water or humid air (relative humidity ≥25%), by irradiating the composite with UV light. In dry air, WO3 was not reduced efficiently, even if the TiO2 and WO3 nanoparticles were mixed well. These results suggest that protons generated at the TiO2 surface as a result of photocatalytic oxidation of water are intercalated into WO3, and therefore ionic conductivity of the medium or the composite film surface is important. The composite film charged in air exhibited almost the same electrode potential as that of the film charged in aqueous NaCl.
213 citations
TL;DR: In this article, a low scan rate cyclic voltammetry performed over the entire electrolyte stability domain, allows for establishing the influence of the redox activity developing in the oxides layer on the electrochemical behaviour of the system and, thus, to get valuable information on the applicability of classical electrochemical techniques employed to assess corrosion of steel in concrete.
Abstract: Different electrochemical techniques (electrochemical impedance spectroscopy (EIS), ring-disk electrode, electrochemical quartz crystal microbalance (EQCM), and in situ Raman spectroscopy) have been employed to study the behaviour of the passive film formed on iron in alkaline medium simulating pore solution in fresh concrete. The study, based on low scan rate cyclic voltammetry performed over the entire electrolyte stability domain, allows for establishing the influence of the redox activity developing in the oxides layer on the electrochemical behaviour of the system and, thus, to get valuable information on the applicability of classical electrochemical techniques employed to assess corrosion of steel in concrete. The passive film is based on a magnetite-type structure which, in partially reversible processes, can be oxidised and reduced depending on the electrode potential. Those redox processes mask the corrosion process itself.
199 citations
TL;DR: In this paper, the influence of the electrode potential on the impedance pattern is studied and a quantitative explanation for the impedance behavior of methanol oxidation is achieved using a newly derived mathematical model.
Abstract: Anodic processes of methanol oxidation on Pt/C thin film electrodes are carefully examined using electrochemical impedance spectroscopy. The influence of the electrode potential on the impedance pattern is studied and a quantitative explanation for the impedance behavior of methanol oxidation is achieved using a newly derived mathematical model. Theoretical derivations agree well with the experimental results, both of which show that the impedance patterns are strongly dependent on the electrode potential. At potentials higher than 0.30 V (vs. Ag/AgCl), a pseudoinductive behavior is observed. At potentials higher than 0.42 V (vs. Ag/AgCl), the impedance pattern is reversed to the second and third quadrants. The conditions required for the reversing of impedance pattern are delineated with the use of the impedance model.
162 citations
TL;DR: In this paper, the surface treatment of p-SiC by aqua-regia-HF solution and also on electrocatalytic Pt metal islet deposition was investigated.
151 citations
TL;DR: In this paper, the charging and discharge behavior of an electrically rechargeable alkaline Zn-air battery consisting of a porous Zn/ZnO electrode on the negative side and a porous O 2 electrode on positive side has been investigated.
136 citations
TL;DR: In this article, the in situ Raman spectra of LiBF4-EC-DMC solutions were studied for the first time and it was suggested that Li ion extraction and insertion proceed as follows: the redox of Ni2+/3+ takes place in the potential range 4.4-4.7 V, and Ni3+/4+ in the 4.7-5.0 V range.
Abstract: Chemical states and structural changes accompanying the electrochemical Li extraction and insertion of LiNixMn2 − xO4
(0 < x < 0.5) thin films in LiBF4–EC–DMC solutions, studied by in situ Raman spectroscopy, are reported for the first time. Ex situ Raman measurements for the virgin electrodes revealed that the oxidation state of Ni in the pristine thin films was Ni2+. In situ Raman spectra of the thin films collected in the organic electrolyte during Li ion extraction and insertion in the potential range 3.4–5.0 V vs. Li/Li+ showed a new Raman band at 540 cm−1 appearing around 4.7 V, which is attributed to the Ni4+–O bond. In addition, from the in situ Raman spectral changes, it is suggested that Li ion extraction and insertion proceed as follows: the redox of Ni2+/3+ takes place in the potential range 4.4–4.7 V, and Ni3+/4+ in the 4.7–5.0 V range, while the redox at 3.8–4.4 V corresponds to Mn3+/4+. Furthermore, it was confirmed that these changes in the Raman spectra were reversible upon changing the electrode potential, and the Li ion extraction and insertion proceed in a reversible manner.
117 citations
TL;DR: In this paper, the authors measured impedance spectra on Au(111) electrode in aqueous perchlorate solutions containing specifically adsorbing anions (SO42−, Cl−, Br− and I−) at potentials where the dominant electrode process is the adsorption of the above anions.
116 citations
TL;DR: Mechanisms for reactions capable of displaying oscillations in species concentrations and hence in colour, electrode potential, pH and/or temperature are presented, along with the rich phenomenology that these systems exhibit.
Abstract: Chemical reactions, which are far from equilibrium, are capable of displaying oscillations in species concentrations and hence in colour, electrode potential, pH and/or temperature. The oscillation...
115 citations
TL;DR: In this article, photo-electrochemical characterization of nanocrystalline TiO 2 films deposited on titanium substrates in 0.1-M NaCl solutions was conducted and it was found that the shape of the photocurrent vs. wavelength curves depend on the electrode potential when the electrode is irradiated at energies above the optical bandgap of the films (3.2-eV for anatase single crystal), whereas at energies below the bandgap, it remains almost potential independent.
Abstract: This paper deals with the photo-electrochemical characterization of nanocrystalline TiO 2 films deposited on titanium substrates in 0.1 M NaCl solutions. These films were confirmed to contain mainly anatase crystallites by X-ray diffraction (XRD) and have n-type properties by UV-photoelectron spectroscopy (UPS). Experiments were also performed on thermal and electrochemical TiO 2 oxides formed in air or the same electrolyte, respectively, to delineate the role in the electrochemical behavior of the nanocrystalline films and differentiate their properties from the titanium substrate and its spontaneously formed oxide. Systematic enhancement of the photocurrent was observed for nanocrystalline TiO 2 films compared with the thermal oxide. This effect arises principally from the area factor but, as it was observed by UPS, capacitance and cyclic voltammetry measurements, it was not the only factor affecting the photocurrent response. It was found that the shape of the photocurrent vs. wavelength curves depend on the electrode potential when the electrode is irradiated at energies above the optical bandgap of the films (3.2 eV for anatase single crystal), whereas at energies below the bandgap, it remains almost potential independent. The capacitance measurements of the nanocrystalline Ti/TiO 2 electrodes in the dark and under illumination conditions did not show substantial changes under our experimental conditions. This fact is indicating the pinning of semiconductor bands still during illumination. The origin of this effect was related with a high rate of surface trap filling. The absorption coefficient for nanocrystalline oxide films was calculated from i ph 2 vs. V plots and a value of 1×10 2 cm −1 was obtained. The flat band potential ( V FB ) calculated from photocurrent plots was not in good correlation with the Nernstian behavior obtained from impedance measurements (Mott–Schottky plots).
TL;DR: In this article, the kinetic and transport parameters of Li-ion during its extraction/insertion into thin film LiNi0.5Mn1.5O4 (0.2 μm thick) were provided.
TL;DR: The intriguing prospect of using electrode potential to tune surface interactions and to drive surface processes, e.g., molecular self-assembly, in electrochemical systems is suggested.
Abstract: The self-assembly of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (TPyP) on Au(111) electrodes was investigated. The adlayer structure was found to depend on the electrode potential. At positive potentials (>0.5V(SCE)), a disordered layer of TPyP is formed on the Au(111) electrode. STM images showed that the disordered molecules are immobile. At negative potentials (-0.2V(SCE)), however, the molecules are highly mobile and can no longer be imaged by STM, though they remain on the surface. At intermediate potentials (-0.2 to +0.2V(SCE)), the TPyP formed a highly ordered adlayer. Once the ordered adlayer is formed, it persists even after the potential is stepped to higher values (0.5-0.8 V(SCE)). These results can be explained by the role of potential modulated adsorbate-substrate interaction and surface mobility. This suggests the intriguing prospect of using electrode potential to tune surface interactions and to drive surface processes, e.g., molecular self-assembly, in electrochemical systems.
TL;DR: In this article, a model for the electrode response is proposed based on the analysis of the time and frequency domain measurements, which shows that the intercalation rate of the RF films is not diffusion-limited, but hindered by the large charge transfer resistance, the phase boundary movement, and the hindrance by the solid electrolyte interface.
Abstract: Submicrometer LiCoO2 films have been prepared on silicon substrates with RF sputtering and pulsed laser deposition (PLD). The electrochemical activity of both types of thin film electrodes is compared using scanning cyclic voltammetry, galvanostatic and potentiostatic intermittent titration, and electrochemical impedance spectroscopy. The RF films exhibit a axis orientation and have an accessible diffusion plane alignment, unlike the c axis oriented PLD films. The preferential orientation of the host crystal lattice toward the electrolyte solution is critical for the intercalation rate and cycling efficiency. The RF films show superior electrochemical performance and faster relaxation characteristics than the PLD films. Based on the analysis of the time and frequency domain measurements a model for the electrode response is proposed. Apparently, the intercalation rate of the RF films is not diffusion-limited, but hindered by the large charge-transfer resistance, the phase boundary movement, and the hindrance by the solid electrolyte interface.
TL;DR: In this paper, the double-layer capacitance of an oxidized polycrystalline Pt surface was determined by means of impedance spectroscopy at a series of descending controlled potentials in order to avoid time-dependent effects that otherwise arise due to oxide film growth.
TL;DR: In this paper, the authors employed the thermodynamics of the perfectly polarized electrode to analyze the total charge densities for a Pt(111) electrode in solutions of H 2 SO 4 with an excess of an inert electrolyte (0.1 M HClO 4 ).
TL;DR: In this paper, the acid dissociation constant for bisulfate adsorbed at the Pt(111) electrode surface was determined by subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS).
TL;DR: In this article, the double-layer response to temperature increase is identified with the potential of maximum entropy of formation of the double layer, which is located in the doublelayer region (ca. 0.43 V vs Pd/H 2 ).
Abstract: Short pulses (10 ns) of high-power laser light produce a sudden increase in the surface temperature of a Pt(111) single-crystal electrode in acidified potassium perchlorate or sulfate solutions. The change of the electrode potential at open circuit was monitored during the relaxation of the temperature. At low pH, the potential transients in the hydrogen adsorption region exhibit a bipolar shape, which can be explained considering that the relaxation is influenced by the rate of hydrogen adsorption. With this assumption, we have estimated a value of the rate constant for hydrogen adsorption around 8 x 10 6 M - 1 s - 1 . By increasing the pH, the rate of hydrogen adsorption is reduced, making it possible to decouple the double-layer response from the hydrogen adsorption process. In this case, the potential where the double-layer response to the temperature increase is zero can be identified with the potential of maximum entropy of formation of the double layer. This potential is located in the double-layer region (ca. 0.43 V vs Pd/H 2 ) for a solution of pH 3. The relevance of this measurement in terms of the location of the potential of zero charge is discussed.
TL;DR: In this article, gold nanoparticles of a diameter of 11 nm were immobilized on a monolayer of aminoundecanethiol (1-mercapto-11-aminoundecane) coated on a polycrystalline Au electrode surface and a quartz crystal microbalance measurement of the deposition process of the Au particles revealed that the saturated deposition amount is 10% of a 2D close-packed monoparticle layer.
Abstract: Citrate-stabilized gold (Au) nanoparticles of a diameter of 11 nm were immobilized on a monolayer of aminoundecanethiol (1-mercapto-11-aminoundecane) coated on a polycrystalline Au electrode surface. A quartz crystal microbalance measurement of the deposition process of the Au particles revealed that the saturated deposition amount is 10% of a 2D close-packed monoparticle layer, and this coverage was confirmed by an atomic force microscopy (AFM) observation. The Au particle layer was characterized by the use of potential-modulated UV−visible reflectance spectroscopy (electroreflectance spectroscopy). The electroreflectance (ER) band at the plasmon absorption wavelength of the Au particles was positive-going, indicating that the plasmon absorption becomes stronger when changing the electrode potential to more negative. The plasmon absorption band shifted to longer wavelength when the electrode potential approaches to the potential of zero-charge, Epzc, of the Au electrode. The ER signal intensity also show...
TL;DR: Direct electron transfer of horse heart cytochrome c is measured at a nanocrystalline boron-doped diamond thin-film electrode and the results raise interesting questions about the necessary surface interactions of cy tochrome c for relatively rapid electrode kinetics.
Abstract: Direct electron transfer of horse heart cytochrome c is measured at a nanocrystalline boron-doped diamond thin-film electrode. A quasi-reversible, diffusion-controlled cyclic voltammetric response is observed for untreated diamond. The peak currents change linearly with the concentration, and importantly, there is no electrode fouling. The results, observed for a hydrogen-terminated and uncharged surface, (i.e., no ionizable carbon-oxygen functional groups), raise interesting questions about the necessary surface interactions of cytochrome c for relatively rapid electrode kinetics.
TL;DR: In this article, the electrodeposition of germanium on Au(111) from the GeCl4 saturated ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was investigated with in situ scanning tunneling microscopy and in part, qualitatively, with IN situI/U tunneling spectroscopy.
Abstract: The electrodeposition of germanium on Au(111) from the GeCl4 saturated ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was investigated with in situ scanning tunneling microscopy and in part, qualitatively, with in situI/U tunneling spectroscopy. Ge deposition starts in the UPD regime with the decoration of the gold steps by Ge at +1000 mV vs. Ge, then small islands that have initial heights of about 150 pm on average start growing at +950 mV vs. Ge. At +750 mV vs. Ge islands with average heights of 250 pm form, they can be removed reversibly at higher electrode potentials and holes with apparent depths between about 30 and 100 pm remain in the gold surface. Before bulk deposition of germanium starts, a thin rough layer with metallic behaviour is deposited on the surface. It can be stripped reversibly upon increasing the electrode potential to higher values. The
overpotential deposition on this layer starts with nanoclusters of 10–40 nm in diameter and some nanometres in height. They can be stabilized for hours by proper selection of the electrode potential. In situI/U tunneling spectroscopy of about 100 nm thick Ge films clearly shows semiconducting behaviour on the whole of the surface in the scanned area. The band gap of the bulk Ge determined by in situI/U tunneling spectroscopy is 0.7 ± 0.1 eV, in good agreement with the theoretical value of 0.67 eV for intrinsic microcrystalline germanium at 300 K. On a layer of approximately 20 nm in thickness we found both sites with semiconducting behaviour and sites with rather metallic behaviour.
TL;DR: In this article, the total charge densities for stepped Pt(hkl) electrodes in solutions of H2SO4 with an excess of an inert electrolyte (0.1 M HClO4) were analyzed.
Abstract: The thermodynamics of the so-called perfectly polarized electrode was employed to analyze the total charge densities for stepped Pt(hkl) electrodes in solutions of H2SO4 with an excess of an inert electrolyte (0.1 M HClO4). Three Pt single-crystal electrodesPt(10,10,9) = 20(111)×(111), Pt(7,7,6) = 14(111)×(111), and Pt(5,5,4) = 10(111)×(111)vicinal to the Pt(111) surface were employed in these studies. A complete thermodynamic analysis using the electrode potential and the charge as independent variables has been performed. The Gibbs excess, Gibbs energy of adsorption, electrosorption valency, and Esin−Markov coefficients for (bi)sulfate adsorption at these surfaces have been determined. The thermodynamic data display a dependence on the crystallographic structure of the Pt electrode surface. Both the Gibbs excess and the Gibbs energy of adsorption decrease with increasing step density or decreasing terrace length. This result indicates that adsorption of (bi)sulfate is stronger at larger (111) terraces.
TL;DR: The results presented in this work show that PM-FTIR spectroscopy, in combination with electrochemical techniques, is an extremely powerful tool for the study of the structure of model membrane systems at electrode surfaces.
Abstract: Chronocoulometry and photon polarisation modulation infrared reflection absorption spectroscopy (PM-IRRAS) have been employed to study the fusion of dimyristoylphosphatidylcholine (DMPC) vesicles onto a Au(111) electrode surface. The results show that fusion of the vesicles is controlled by the electrode potential or charge at the electrode surface (sigmaM). At charge densities of -15 microC cm(-2) < sigmaM < 0 microC cm(-2), DMPC vesicles fuse to form a condensed film. When sigmaM < -15 microC cm(-2), de-wetting of the film from the electrode surface occurs. The film is detached from the electrode surface; however, phospholipid molecules remain in its close proximity in an ad-vesicle state. The state of the film can be conveniently changed by adjustment of the potential applied to the gold electrode. PM-IRRAS experiments demonstrated that the potential-controlled transitions between various DMPC states proceed without conformational changes and changes in the packing of the acyl chains of DMPC molecules. However, a remarkable change in the tilt angle of the acyl chains with respect to the surface normal occurs when ad-vesicles spread to form a film at the gold surface. When the bilayer is formed at the gold surface, the acyl chains of DMPC molecules are significantly tilted. The IR spectra have also demonstrated a pronounced change in the hydration of the polar head region that accompanies the spreading of ad-vesicles into the film. For the film deposited at the electrode surface, the infrared results showed that the temperature-controlled phase transition from the gel state to the liquid crystalline state occurs within the same temperature range as that observed for aqueous solutions of vesicles. The results presented in this work show that PM-FTIR spectroscopy, in combination with electrochemical techniques, is an extremely powerful tool for the study of the structure of model membrane systems at electrode surfaces.
TL;DR: In this article, the authors measured the entropy of formation of the double layer formed between the Au(111) electrode and perchloric and sulfuric acid solutions and found that the potential of maximum entropy is slightly negative to the potential for zero charge, corresponding to a negative contribution of the water dipole moments to the electrode−solution potential drop.
Abstract: Illumination of the surface of a Au(111) single-crystal electrode with short pulses of high-power laser light has been used to produce a sudden increase of its temperature. From the evolution of the open circuit potential during the temperature relaxation after the laser pulse, it is possible to obtain a relative measurement of the entropy of formation of the double layer. The electrode potential, where the potential transient is zero, has been identified with the potential of maximum entropy of formation of the double layer. This methodology has been applied to study the double layer formed between the Au(111) electrode and perchloric and sulfuric acid solutions. In both cases, it has been found that the potential of maximum entropy is located slightly negative to the potential of zero charge, corresponding to a negative contribution of the water-dipole moments to the electrode−solution potential drop. In addition, in the case of sulfuric acid solutions, a sharp increase of the relaxation time after the ...
TL;DR: In this paper, the double-layer at the interface between irreversible (current-blocking) gold electrodes and yttria-stabilised zirconia (YSZ) was measured by impedance spectroscopy as a function of the applied electrode potential and YSZ content (2-8 mol%).
TL;DR: In this article, the authors used Pt(111) surfaces covered by ruthenium by a spontaneous deposition method and conducted voltammetric oxidation of chemisorbed CO in clean sulfuric acid electrolyte at 50 mV s−1 and under variable sweep rate conditions.
TL;DR: In this article, the effect of substitution of Co 3 O 4 by RuO 2 on the service life of the coatings was investigated under galvanostatic polarisation at 0.75 A cm −2 in 0.5 mol dm −3 H 2 SO 4.
TL;DR: A lead ion-selective electrode was prepared with polymeric membranes based on a calixarene derivative containing carboxyphenyl azo groups as mentioned in this paper, which exhibited high selectivity towards alkali, alkaline earth and transition metal ions.
TL;DR: In this article, the use of an aluminum substrate as an electrode and the modification of its surface by means of a thin film of palladium hexacyanoferrate (PdHCF) were developed.
TL;DR: In this article, a tentative mechanism of oxygen activation on RuxXy cluster materials is proposed on the basis of the in situ EXAFS data, which is based on the proposed mechanism of the catalytic center upon oxygen adsorption.
Abstract: Novel cluster Ru chalcogenide materials MoxRuySez and RuxTey were studied in situ using EXAFS in the transmission mode during the oxygen reduction reaction. Reversible changes in the structure of the active center were revealed for the electrochemical reaction as a function of the applied electrode potential. The shift of the potential in the anodic direction from 0.08 to 0.78 V versus rhe (reference hydrogen electrode) in the presence of oxygen resulted in an increase of the Ru−O and simultaneous decrease of the Ru−Ru coordination numbers in the first coordination shell of Ru. Along with the variation of the coordination numbers, we observed reversible changes of the coordination distances: a decrease of the Ru−O and an increase of the Ru−Ru distance with the positive polarization. These changes witness the distortion of the catalytic center upon oxygen adsorption. A tentative mechanism of oxygen activation on RuxXy cluster materials is proposed on the basis of the in situ EXAFS data.