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+ toxicity abstract The viability of living fibroblast cells cultured on a Petri dish was determined by scanning electrochem- ical microscopy (SECM). Three kinds of feedback modes for single living cells were derived with different redox couples: positive, negative and consumptive. The consumptive feedback was unique and distin- guished uptake from the response caused by cell deformation. The toxicity of Ag + ion on the living fibro- blast cells was investigated by using both ferrocenemethanol (FcMeOH) and oxygen (O2 )a s electrochemical mediators. The results showed that Ag + ions could be taken up and then reduced to form sub-micrometer and micrometer sized metal silver particles. The metal silver particles stained fibroblast cells and give a positive feedback with FcMeOH. These were also identified by the results of both SECM and energy dispersive X-ray spectroscopy (EDX). The amount of consumption of dissolved O2 decreased with time, showing the cell status as the cells died. Since O2 is directly involved in cell metabolism and the products of O2 reduction are not re-oxidized by metal silver particles trapped on fibroblast cells, it is a good SECM mediator to characterize drug effects on cell viability. The results suggest the importance of choice of redox mediator in characterizing cell viability.

An array of Pd–W alloys was fabricated, and the electrocatalytic activity of the alloys for the oxygen reduction reaction (ORR) in acidic media was screened by scanning electrochemical microscopy. The Pd0.7W0.3 showed the highest activity for the ORR, close to that for Pd0.8Co0.2 and Pt. A Pd–W electrocatalyst loaded on carbon black was formed by the NaBH4-reduction method, exhibiting high activity and stability, suggesting that it is a good candidate for the proton exchange membrane fuel cell cathode.

We observe the electrochemical formation of a silicon layer on a molybdenum (Mo) electrode at 850 °C in a CaCl2 melt containing silicon oxide (SiO2) nanoparticles (NPs). A stable electrochemical cell for high temperature molten salt was fabricated from a sealed quartz tube, with a glassy carbon counter electrode and a Ca/Ca2+ dynamic reference electrode. When SiO2 NPs are added into the CaCl2 melt, the reduction current and the generation of a new redox couple relating to the reduced silicon were observed in a cyclic voltammogram at Mo. Spectroscopic analyses confirmed the formation of a silicon layer from the reduction of SiO2 NPs. Although the deposit was not continuous, XPS shows that it is silicon of good purity and XRD shows the pattern of crystalline silicon. We also investigated the dissolved silicon species generated after the oxidation of electrodeposited silicon in CaCl2 melt, which produces a redox couple at potentials positive of the deposition potential. We tentatively attribute it to the oxidation and re-reduction of an insoluble Si–Cl surface species.

The construction and use of “dynamic potential–pH diagrams” (DPPDs), that are intended to extend the usefulness of thermodynamic Pourbaix diagrams to include kinetic considerations is described. As an example, DPPDs are presented for the comparison of electrocatalysts for water oxidation, i.e., the oxygen evolution reaction (OER), an important electrochemical reaction because of its key role in energy conversion devices and biological systems (water electrolyses, photoelectrochemical water splitting, plant photosynthesis). The criteria for obtaining kinetic data are discussed and a 3-D diagram, which shows the heterogeneous electron transfer kinetics of an electrochemical system as a function of pH and applied potential is presented. DPPDs are given for four catalysts: IrO2, Co3O4, Co3O4 electrodeposited in a phosphate medium (Co–Pi) and Pt, allowing a direct comparison of the activity of different electrode materials over a broad range of experimental conditions (pH, potential, current density). In addition, the experimental setup and the factors affecting the accurate collection and presentation of data (e.g., reference electrode system, correction of ohmic drops, bubble formation) are discussed.

After growing a thin layer of oxide (PtOx) by anodization of a Pt electrode, it changed from catalytically active for electrochemical NaBH4 oxidation into an inactive electrode. When held at a potential where the oxide film was maintained, collisions of individual 14 nm diameter Au nanoparticles (NPs) that catalyzed NaBH4 oxidation were successfully observed as discrete current pulses (spikes or blips) for each NP interaction with the modified Pt electrode via amplification from NaBH4 oxidation. The current response is affected by NP concentration and the applied potential.

The diffusion coefficient (D(O(2))), solubility (C(O(2))), and electrochemical behavior of oxygen reduction were investigated by cyclic voltammetry and transient amperometry on a Pt ultramicroelectrode in aqueous solutions containing various concentrations of NaOH (1-12 M). The results show that both D(O(2)) and C(O(2)) decrease as the solution viscosity (eta) increases significantly with increasing concentration of NaOH. The Stokes-Einstein relationship (D(O(2)) vs 1/eta) is followed, yielding a radius for the O(2) molecule, 2.8 A, that does not change over the concentration range of NaOH studied. From results reported previously for C(O(2)) in more dilute NaOH solutions and the new results here, the number of electrons, n, involved in the first step of the oxygen reduction reaction (ORR) was found to change with the concentration of NaOH, from n = 2 at low NaOH concentrations (1-2 M) to n = 1 at high concentrations (6 M), in line with the changing water activity. Scanning electrochemical microscopy (SECM) was employed as a sensitive tool to investigate the electrochemical behavior of the product of the ORR in 10 M NaOH solution, O(2)(*-), as a function of potential. The SECM approach curves depend on the substrate bias and state of the Pt substrate surface, and the apparent rate constant for the redox couple of O(2)/O(2)(*-) is determined to be about 2.6 x 10(-4) cm/s in this solution.

Electrochemical hydrazine oxidation and proton reduction occur at a significantly higher rate at Pt than at Au or C electrodes. Thus, the collision and adhesion of a Pt particle on a less active Au or C electrode leads to a large current amplification by electrocatalysis at single nanoparticles (NPs). At low particle concentrations, the collision of Pt NPs was characterized by current transients composed of individual current profiles that rapidly attained a steady state, signaling single NP collisions. The characteristic steady-state current was used to estimate the particle size. The fluctuation in collision frequency with time indicates that the collision of NPs at the detector electrodes occurs in a statistically random manner, with the average frequency a function of particle concentration and diffusion coefficient. A longer term current decay in single current transients, as opposed to the expected steady-state behavior, was more pronounced for proton reduction than for hydrazine oxidation, revealing microscopic details of the nature of the particle interaction with the detector electrode and the kinetics of electrocatalysis at single NPs. The study of single NP collisions allows one to screen particle size distributions and estimate NP concentrations and diffusion coefficients.

This review describes work done in scanning electrochemical microscopy (SECM) since 2000 with an emphasis on new applications and important trends, such as nanometer-sized tips. SECM has been adapted to investigate charge transport across liquid/liquid interfaces and to probe charge transport in thin films and membranes. It has been used in biological systems like single cells to study ion transport in channels, as well as cellular and enzyme activity. It is also a powerful and useful tool for the evaluation of the electrocatalytic activities of different materials for useful reactions, such as oxygen reduction and hydrogen oxidation. SECM has also been used as an electrochemical tool for studies of the local properties and reactivity of a wide variety of materials, including metals, insulators, and semiconductors. Finally, SECM has been combined with several other nonelectrochemical techniques, such as atomic force microscopy, to enhance and complement the information available from SECM alone.

We demonstrate a novel method of observing single particle collision events with electrogenerated chemiluminescence (ECL). A single event is characterized by the enhancement of ECL intensity during the collision of an individual platinum nanoparticle (Pt NP) on an indium tin oxide electrode, which catalyzes the oxidation of Ru(bpy)3(2+) and a coreactant, for example, tri- n-propylamine (TPrA), present in the solution. Every collision produces a unique photon spike whose amplitude and frequency can be correlated with the size and concentration of the Pt NPs. A large amplification of ECL intensity can occur by choosing an appropriate measuring electrode and using high concentrations of Ru(bpy)3(2+) and the coreactant.

Despite intense, long-term interest in organic semiconductors from both an applied and fundamental perspective, key aspects of the electronic properties of these materials remain poorly defined. A particularly challenging problem is the molecular nature of positive charge carriers, that is, holes or oxidized species in organics. Here, the unique ability of single-molecule spectroelectrochemistry (SMS-EC) to unravel complex electrochemical process in heterogeneous media is used to study the oxidation of nanoparticles of the conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole). A reversible hole-injection charging process has been observed that occurs primarily by initial injection of shallow (untrapped) holes, but soon after the injection, a small fraction of the holes becomes deeply trapped. Good agreement between experimental data and simulations strongly supports the presence of deep traps in the studied nanoparticles and highlights the ability of SMS-EC to study energetics and dynamics of deep traps in organic materials at the nanoscale.

We report in this paper a facile approach for the formation and electrochemical characterization of silver-silver oxide core-shell nanoparticles (NPs). Thus, thermal treatment at temperatures between 200 and 360 degrees C of Ag NP, in the gas phase or in an organic solvent, has been used to achieve the formation Ag@Ag2O NP. The evidence of formation of such a core-shell structure was obtained by cyclic voltammetry using a Nafion modified electrode (where Nafion containing carbon particles is used as the matrix to encapsulate the core-shell NP). Initial positive scans measure free Ag. Initial negative scans measure Ag2O, with the following positive scan, compared to the initial one, providing a measure of "trapped" or core Ag. The results presented demonstrate the utility of this approach in characterizing core-shell structures, like Ag@Ag2O, which could be extended to other core-shell forms, such as bimetallic core-shell NP.

We demonstrate the feasibility of semiconductor deposition via the electrochemical reduction of gaseous precursors by the use of an anhydrous proton-conducting membrane, the solid acid CsHSO4, at 165 °C. This membrane electrode assembly was operated within the oxidation of hydrogen on a porous Pt anode and the deposition of Si or Ge under bias at the cathode from chloride-based gaseous precursors; SiCl4 and GeCl4 in an Ar flow with a reduction potential over -1.0 V (vs RHE).

Electrochemical, spectroscopic, and mass spectrometric (MS) methods were used to probe the interaction (complexation) of silver ions and zerovalent silver species with polyamidoamine generation 1 amine-terminated (PAMAMG1NH2) and generation 2 hydroxy-terminated (PAMAMG2OH) dendrimers (DDMs). Stability constants (Kq+) and stoichiometries (q) (i.e., the number of silver ions complexed per DDM molecule) were determined from the voltammetric data, that is, shifts in potential and changes in peak or limiting current with addition of DDM. When the mole ratio of DDM to Ag+ isor = 1, Ag+ binds with PAMAMG2OH to form a dominant 1:1 complex with a value of 1.1 x 10(7) M(-1). Under similar conditions, Ag+ binds with PAMAMG1NH2, yielding a 1:1 complex with = 4 x 10(9) M(-1), which is consistent with the finding of the MS experiments. When the mole ratio is1, qor = 2. The E0' of the Ag-PAMAMG1NH2(+/0) couple shifted to a more negative value than that of the Ag(+/0) couple. The negative shift in the halfwave potential also suggests that DDM binds more strongly with Ag+ than with zerovalent silver species. Spectroscopic results suggest that hydroxyl-terminated PAMAMG2OH favors the formation of small zerovalent silver clusters after reduction while amine-terminated PAMAMG1NH2 allows for simultaneous formation of both clusters and larger nanoparticles at similar conditions. Other quantities, such as diffusion coefficients of the complexes and molar absorptivity of the Ag+ DDMs, are also reported.

Silver compounds are of interest because of their antimicrobial and other biological activity. Electrochemical and chemical (e.g., dissolution) properties of silver films of various origins, e.g., sputtered Acticoat antimicrobial silver samples, electrodeposited Ag metal and electrooxidized silver samples in various media have been studied with electrochemical techniques, quartz crystal microbalance (QCM) gravimetry, X-ray diffraction, atomic force microscopy (AFM), and scanning electrochemical microscopy (SECM). Examination of several sputtered antimicrobial silver samples with AFM reveals their nanometer grainy aggregate structures. The electrochemical results suggest that the sputtered antimicrobial films contain both Ag(0) and Ag(I) (in the form of Ag2O, AgOH, or a mixture of these). While the dissolution of metallic Ag or antimicrobial films that were completely reduced to the Ag(0) form is small in aqueous 1.0 M NaClO4 solution, films containing Ag(I) are soluble. The initial dissolution rate of an ...

The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to probe processes at a BLM and determine the kinetics of the charge-transfer process. The SECM can also be used to determine the shape of the BLM.

By using specially constructed nanometer tips of sharpened Pt-Ir wire in a wax sheath, small numbers of molecules (1−10) can be trapped between the tip and a substrate. Repeated electron transfers of an electroactive molecule as it shuttles by diffusion between tip and substrate produce a current (∼0.6 pA/molecule) that can be used to detect the trapped molecules. The tip electrode size and shape can be found from the electrode approach curves (current vs tip-to-substrate distance) based on approximate equations and digital simulations. Analysis of the observed fluctuating currents by autocorrelation, spectral density, and probability density functions is also described.

The thin film electrochemistry and electrogenerated chemiluminescence (ECL) of the title compound were obtained on Pt electrodes (CH 3 CN/0.1 M tetrabutylammonium fluoroborate). Orange luminescence (λ max =622 nm) was obtained by pulsing the potentials between +0.40 and −2.35 V versus Fc/Fc + as well as by oxidizing the system in the presence of TPAH (TPAH=tri- n -propylamine), which generates the strongly reducing intermediate TPA , and by reducing the system in the presence of S 2 O 8 2- , which produces the strongly oxidizing intermediate SO 4 −

The electrochemistry of a poly(vinylferrocene) (PVF) film of ca. 2100 A was investigated in 1 M aqueous NaClO 4 solution with electrochemical and scanning microscopic techniques. The potential-step transients show well-defined maxima that are very similar to those found for the electrochemical switching of electronically conductive polymers, e.g., polypyrrole and polyaniline. We explore here the possibility that the film resistance accompanying changes in the polymer oxidation state is a major factor in determining the shape of these transients. These chronoamperometric curves also allow the determination of an apparent diffusion coefficient. The scanning electrochemical microscope (SECM) has been used to penetrate the PVF film and to obtain directly the thickness of the film immersed in the electrolyte solution

Collisions of several kinds of metal or metal oxide single nanoparticles (NPs) with a less catalytic electrode surface have been observed through amplification of the current by electrocatalysis. Two general types of current response, a current staircase or a current blip (or spike) are seen with particle collisions. The current responses were caused by random individual events as a function of time rather than the usual continuous current caused by an ensemble of a large number of events. The treatment of stochastic electrochemistry like single NP collisions is different from the usual model for ensemble-based electrochemical behaviour. Models for the observed responses are discussed, including simulations, and the frequency of the steps or blips investigated for several systems experimentally.

The kinetics of electron transfer between electrochemically passivated chromium and several outer-sphere redox couples have been investigated as a function of passive-film thickness, d = 5 to 25/~, in 1M H2SO4. The apparent rate of electron transfer decreased exponentially with increasing thickness of the passivating overlayer. Similarly, during potentiostatic film growth, the electron-transfer rate decreased logarithmically with time, t, as a consequence of'the film-growth kinetics, since d varies with log(t). These relationships indicate an electron-tunneling controlled process. However, variations in the film thickness and defects result in electron transfer occurring at distributed sites of enhanced tunneling probability, making a meaningful quantitative analysis difficult.

In situ scanning tunneling microscopy (STM) and atomic force microscopy (AFM) were employed to examine the surface morphology of a Si(111) cathode in 1% HF or a mixed HF and H 2 O 2 solution under potential control. In the absence of H 2 O 2 , in situ STM revealed island-like features due to the native defects at the Si substrate and the subsequent dissolution of the native SiO 2 layer by the HF etchant

An electronically conductive poly-1-aminoanthracene (PAA) film was prepared electrochemically on Pt, Au, and C substrates by cycling the potential between -0.40 and +0.80 V in MeCN/BAPF 6 solutions. Adding pyridine to the solution resulted in a marked increase in the growth rate of the polymer film, as indicated by a large increase of faradaic current. A new scanning tunneling microscopy (STM) approach is also presented to determine film thickness and film conductivity through measuring the tip current vs, tip displacement

The shape of steady-state current-distance (iT-d) curves obtained by scanning electrochemical microscopy (SECM) with a submicrometer conical-type tip is substantially different from that obtained with a microdisk tip. A model is proposed to describe the iT-d curves for tips shaped as cones or spherical segments. In each case a family of theoretical working curves, computed for different values of a single adjustable parameter (the height of a cone or a segment), was used to fit the experimental curves obtained with tips approaching a conductive or insulating substrate. A good fit of the experimental and theoretical curves can be obtained only for a very narrow range of the tip shape parameters, giving confidence in the reliability of the proposed method. The shape parameters for two substantially different microelectrodes are evaluated. A 420 nm radius tip was shown to be a fairly sharp cone with a height-to-radius ratio k of 0.8. An 80 nm radius tip can be represented as either a cone or spherical segment, because of the small k = 0.2. The radius values obtained from iT-d curves agree with those estimated from steady-state current values. The cyclic voltammograms (CVs) obtained at these microtip electrodes have a regular shape with very small capacitive and resistive background. New analytical approximations for iT-d curves are also proposed for SECM with a disk-shaped tip over conductive and insulating substrates.

Dealloying of Cu~Au has been examined by in situ STM and several electrochemical methods. Three different regimes of behavior were noted. At low overpotentials, clustering of gold atoms occurs near sites of copper dissolution. This is es- sentially a two-dimensional process. The formation and smoothing of these clusters by capillary action, monitored in real time, demonstrated the highly mobile nature of the surface species. At higher potentials, the electrode is largely passi- vated by the enrichment of gold. However, there exist small localized regions of three-dimensional roughness which may be correlated to extended dealloying catalyzed by bulk solid-state defects. When the potential is increased above the critical potential (Ec), global surface roughening occurs. Correlating STM with chronoamperometric and chronopoten- tiometric results demonstrates that this transition occurs by nucleation and growth. Selective dissolution of copper de- pends on the exposure of fresh sites by the migration of passivating gold atoms. Adsorption can strongly influence this transport process, as manifest by changes in Ec. In comparison to sulfate media, chloride caused a decrease in Eo, while derivatization of CuaAu with an alkyl-thiol produced an increase in Ec. These shifts are consistent with the enhancement and inhibition of gold surface diffusion by the respective adsorbates.

The band energies of FeS 2 particles (∼10 μm) were estimated by collection of electrons generated by irradiation of the particles in the presence of a hole acceptor (e.g., tartrate ion) at an inert collector electrode. Electrons were collected directly from the particles or by the mediator Ru(NH 3 ) 6 3+ , where the resulting +2 state is oxidized at the electrode. The variation of the steady-state photocurrent in the presence of mediator as a function of pH allowed estimation of the quasi-Fermi level for electrons and located the conduction and valence band edges at −0.1 and +0.9 V vs SCE, respectively, at pH 0, and −0.9 and +0.1 V vs SCE, respectively, at pH 14. Modification of the FeS 2 surface with Pt produced a small (ca. 0.1 V) negative shift in the potential for photocurrent onset

We report the use of a micropipet-supported ITIES (interface between two immiscible electrolyte solutions, also called a liquid/liquid (L/L) or water/oil (W/O) interface) as a scanning electrochemical microscopy (SECM) tip to detect silver ion and explore Ag+ toxicity in living cells. A 1,2-dichloroethane solution containing a commercially available calixarene-based Ag+ ionophore (IV) was injected into a micrometer-size glass pipet to construct an Ag+-selective SECM tip. The local Ag+ concentration, down to the micromolar level, in the vicinity of living fibroblast cells, was monitored by SECM approach curves and through imaging of the uptake and efflux of Ag+ by living fibroblast cells in real time. The results show that several stages of interaction between Ag+ and fibroblast cells exist. Since a number of biological processes of cells are involved with non-redox-active ions, the work presented here provides a new way to explore cell metabolism, drug delivery, and toxicity assessment by SECM.

We introduce single-molecule spectroelectrochemistry (SMS-EC), a powerful new technique for studying electrochemical kinetics in highly heterogeneous systems. This technique uses fluorescence single-molecule spectroscopy to indirectly measure electrochemical kinetics one molecule at a time, offering for the first time the distribution of key electrochemical variables, such as the half-wave potential, E1/2, not just the ensemble averages. In SMS-EC, the potential of the working electrode of an electrochemical cell is linearly scanned while simultaneously measuring the florescence intensity, Ifl(t), of individual single molecules as a function of time in a wide-field microscope. SMS-EC is used herein to study the oxidation at an indium tin oxide (ITO) electrode of single molecules of the organic conjugated polymer F8BT. The results reveal both excited singlet state and ground state oxidation of F8BT. The latter process occurs over a narrow distribution of single-molecule half-wave potential values, indicating a relatively uniform electrochemical potential at the electrode.

The current-potential curve at a 2.8-nanometer-radius electrode immersed in a solution containing micromolar concentrations of a redox couple, [(trimethylammonio)methyl] ferrocene (Cp 2 FeTMA + )/Cp 2 FeTMA 2+ , shows discrete steps (a coulomb staircase) representing single electron-transfer events. Discrete potential steps are also found in the current-time curve as the electrode potential relaxes back to equilibrium after a coulostatic potential step.

The bipolar conductance, BICON, technique for the measurement of solution resistance, based on the application of microsecond current pulses, as originally described by Enke and co-workers for measurements with conventional electrodes, was extended for use with ultramicroelectrodes, with a focus on its application in scanning electrochemical microscopy (SECM). When the plateau time used to make the measurement lies within the BICON conditions, the solution conductance can be obtained directly from the output without the need for calibration curves. However, decreasing the size of the ultramicroelectrode decreases the range of values that satisfy these conditions, and one must resort to calibration curves to obtain solution conductance from the measured current, which was nevertheless found to be proportional to electrolyte concentration with electrodes as small as 5 mum in diameter. BICON/SECM approach curves over insulating substrates followed SECM negative feedback theory and approach curves in the presence of low (micromolar) or no added electrolyte are possible once the background conductivity is taken into account. Approach curves to a conducting substrate at open circuit potential are influenced by the solution time constant (solution resistance at the electrode tip x electrode double layer capacitance), which is a function of the tip/substrate distance, as well as the substrate size.

Emploi d'un microscope tunnel a balayage pour former une image de ADN sur une surface de mica dans de l'air humide. Proposition d'explication: cette formation d'image a lieu par un mecanisme electrochimique similaire a celui qui a lieu en microscopie electrochimique

Imaging of DNA, keyhole limpet hemocyanin, mouse monoclonal IgG, and glucose oxidase on a mica substrate has been accomplished by scanning electrochemical microscopy with a tungsten tip. The technique requires the use of a high relative humidity to form a thin film of water on the mica surface that allows electrochemical reactions to take place at the tip and produce a faradaic current (≈1 pA) that can be used to control tip position. The effect of relative humidity and surface pretreatment with buffer solutions on the ionic conductivity of a mica surface was investigated to find appropriate conditions for imaging. Resolution of the order of 1 nm was obtained.

We demonstrate a novel and powerful method to study electrogenerated chemiluminescence (ECL) of single nanoparticles (NPs) (r = 25 +/- 15 nm) of a conjugated polymer, F8BT, on an ITO electrode in the presence of a co-reactant, such as tri-n-propylamine (TPrAH) in acetonitrile solution. The results reveal that the maximum formation rate of ECL of individual NPs is achieved after a long "build-up" time (10-40 s after pulse application). The high number of detected ECL photons from individual NPs (1500 photons during 100 s) highlights the potential of this technique as a very sensitive analytical method. Additionally, TPrAH acts as a very efficient protecting agent against irreversible electrochemical processes occurring in F8BT, as found in photoluminescence studies. This protection mechanism probably involves the neutralization of holes at the particle surface via electron transfer by both TPrAH and TPrA radical (TPrA*).

A simple approach to prepare and characterize biomaterial-based electrocatalysts for oxygen reduction was carried out. Poly-l-histidine was used as a matrix and ligand to complex Cu2+ to mimic the active sites of laccases. A modified glassy carbon (GC) electrode with Cu2+-poly-l-histidine complex decreases the oxygen reduction overpotential as compared with the bare GC electrode. An array of Cu2+-poly-l-histidine spots with different compositions was deposited on a GC substrate, and their catalytic activity for oxygen reduction was evaluated by a scanning electrochemical microscopy-based screening technique. The electrocatalytic activities of complexes for oxygen reduction strongly depended on the mole ratio of Cu2+ to poly-l-histidine and the applied potential of the substrate.

This communication reports the findings of the investigation of the electrochemical (EC) oxidation of the important bimolecular guanosine (Gs) by scanning electrochemical microscopy (SECM) using carbon fiber ultramicroelectrodes (CF-UMEs) as the probe and substrate. The first attempt is to try to gain a steady-state voltammogram for EC oxidation of Gs at the CF-UME probe in aqueous buffer solutions with three different pH values. Experimental results indicate that due to serious adsorption of Gs on the CF-UME surface, an "S-shaped" steady-state voltammetric curve, which is required for SECM studies, cannot be obtained in aqueous solutions. To solve this adsorption problem, a series of experiments for studying the EC behavior of Gs in DMF are carried out. A well-defined "S-shaped" steady-state cyclic voltammogram (CV) could be achieved at the CF-UME in DMF containing 0.1M TBAPF6 as the supporting electrolyte. By combining several EC techniques, including cyclic voltammetry at glassy carbon (GC) macroelectrode and CF-UMEs, and chronoamperometry, the general chemical characteristics and EC behavior of Gs in DMF solution are studied. Furthermore, SECM detection of Gs*+, the radical cation of Gs electrogenerated in its first oxidation, is carried out by using feedback and tip generation/substrate collection modes in a nanogap configuration. Gs*+ has been electrochemically detected for the first time, with an estimated lifetime of

The electrochemical behavior of a single molecule can be observed by trapping a small volume of a dilute solution of the electroactive species between an ultramicroelectrode tip with a diameter of approximately 15 nanometers and a conductive substrate. A scanning electrochemical microscope was used to adjust the tip-substrate distance ( approximately 10 nanometers), and the oxidation of [(trimethylammonio)methyl] ferrocene (Cp(2)FeTMA(+)) to Cp(2)FeTMA(2+) was carried out. The response was stochastic, and anodic current peaks were observed as the molecule moved into and out of the electrode-substrate gap. Similar experiments were performed with a solution containing two redox species, ferrocene carboxylate (Cp(2)FeCOO(-)) and Os(bpy)(3)(2+) (bpy is 2,2'-bipyridyl).

We report here the electrogenerated chemiluminescence (ECL) of a red fluorophore diphenylaminospirobifluorenylfumaronitrile (FPhSPFN). FPhSPFN contains two diphenylamino groups as strong electron donors at the ends linked through a nonplanar bulky spirobifluorene linker to a common fumaronitrile group as a strong electron acceptor. The cyclic voltammetry of this compound shows two one-electron transfer reduction waves and one single overall two-electron oxidation wave consisting of closely spaced waves with a peak separation of 63 mV. Chronoamperometry with an ultramicroelectrode (UME) confirmed that each reduction wave involves a 1e transfer and that the oxidation wave contains an overall 2e transfer. The first reduction wave is Nernstian, Eo1,red = −1.09 V versus SCE, and the second reduction wave, Eo2,red = −1.50 V versus SCE, produces a film on the electrode. By comparison to a digital simulation, the oxidation is assigned to two reversible, closely spaced, one-electron processes for oxidation with Eo...

Ion transport properties of two gels made from polyacrylate and polyacrylamide (PAAM) were studied with scanning electrochemical microscopy (SECM) by using three ferrocene derivatives, which carry different charges, as the probe molecules. Ion diffusion in these gels could be nearly as fast as in aqueous electrolytes and did not adhere to the Stokes−Einstein equation. Passivation of the electrode surface in polyacrylate gels reported previously was mainly caused by the electrophoretic deposition of gel particles on the surface of the electrode. The deposited gel film can act as a cation-exchange membrane and shows permselectivity, which affects both the electrochemical and SECM behavior. No detectable film formation was found in the PAAM gel perhaps because of its neutral charge and rigid three-dimensional network structure. The small change in diffusion coefficients as a function of PAAM gel concentration and charges of the probe molecules suggest much of the transport in the gel occurs via a water-fille...

An electrochemical cell and electrode system for investigation of aqueous systems under near- and supercritical conditions is described. Cyclic voltammetry of 1.5% w/w KCl and 6% w/w KBr solutions was investigated and log current vs. potential (Tafel) plots for the chlorine and hydrogen evolution reactions are given. A study of the Cu/Cu(I)/Cu(II) system in Na/sub 2/SO/sub 4/ and KCl solutions is described and the variation of the standard potentials of the half-reactions with temperature (to ca. 300/sup 0/C) is given. The diffusion coefficient for Cu(II) was determined by chronoamperometry as a function of temperature (22-245/sup 0/C) and shown to increase from 5.4 x 10/sup -6/ cm/sup 2//s at 22/sup 0/C to 3 x 10/sup -4/ cm/sup 2//s at 245/sup 0/C. The change of diffusion coefficient with temperature was larger than that predicted by the Stokes-Einstein equation at temperatures above 175/sup 0/C. 36 references, 12 figures, 1 table.

Capacitance and voltammetric measurements were employed to investigate the electrochemical and photoelectrochemical (PEC) behavior of ,, and single crystal electrodes in aqueous solutions containing various redox couples (, , , Fe2+/ Fe3+, , and , where HV is heptyl viologen and MV is methyl viologen). In supporting electrolyte , the conduction bandedges of and , determined from the capacitance measurement, are at −0.14 and −0.44V vs. SCE, respectively, and the valence bandedge of is at 0.93V vs. SCE. A bandgap of 1.4 eV for was determined either from the photocurrent action spectrum or from the capacitance measurement. The specific effects of iodide on the capacitance and voltammetric behavior of layer‐type compounds are compared. The characteristics of several PEC cells are also described.

Description d'une cellule electrochimique a electrodes a surface presque atomiquement lisse de platine sur du mica, avec un espace inter-electrodes reglable avec une resolution de ∼1 A pour des distances entre 0 et >500 nm. Donnees sur les mesures des courants d'oxydoreduction dans le cas des solutions de Fe(CN) 6 3−/4− et du transfert d'electrons dans le cas d'un film de polymere electroactif