Cyclic Voltammetry Response Research Articles

Fabrication of Fe(CN)63− Functionalized PDDA/CdTe Layer‐by‐layer Film with Good Electron Transfer Ability

Abstract(PDDA/CdTe)n layer‐by‐layer (LBL) film immobilized with Fe(CN)63− was fabricated on the gold electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the electrochemical properties of this film. The peak current of the immobilized Fe(CN)63− increased as the number of the bilayers increased and was proportional to the scan rate. Compared with pure (PDDA/CdTe)n and (PDDA/PSS)n LBL film, Fe(CN)63− immobilized (PDDA/CdTe)n LBL film had good electron transfer ability. The immobility of Fe(CN)63− into the film was attributed to its interaction with Cd2+ on the surface of CdTe QDs. Fe(CN)63− also can interact with other metal ions, which would make Fe(CN)63− release from the film. The concentrations of metal ions will affect the CV response of Fe(CN)63− immobilized LBL film. It has provided a novel prototype of device or sensor for quantitative detection of metal ions.

Electrochemical nitrite nanosensor developed with amine- and sulphate-functionalised polystyrene latex beads self-assembled on polyaniline

Aniline doped with polyvinyl sulphonate (PV-SO 3 −) was electropolymerised on screen printed carbon (SPCE) and glassy carbon (GCE) electrodes. Then nano-structured polystyrene (PS NP) latex beads functionalised with amine (PS NP-NH 2) and sulphate (PS NP-OSO 3 −) were self-assembled on the modified SPCE and GCE. The resultant polyaniline nanocomposites (PANI|PS NP-NH 2 or PANI|PS NP-OSO 3 −) were characterised by cyclic voltammetry (CV), UV–vis spectroscopy and scanning electron microscopy (SEM). Brown–Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations of the order of 10 −8 mol cm −2. UV–vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid π–π* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that are <100 nm in diameter. When applied as electrochemical nitrite sensor, sensitivity values of 60, 40 and 30 μA/mM were obtained for electrode systems containing PANI|PS NP-NH 2, PANI and PANI|PS NP-SO 3 −, respectively. The corresponding limits of detection of the sensors were 7.4, 9.2 and 38.2 μM NO 2 −.

Nanostructured SnS/carbon composite for supercapacitor

Net-like nanostructured SnS/carbon composite was prepared by heating mixture of SnS nanoparticles and resorcinol–formaldehyde sol at 650 °C. The morphology and structure of prepared SnS and SnS/carbon composite were studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical investigation indicated that SnS/carbon composite presented superior electrochemical performances than pristine SnS. SnS/carbon composite had better capacitive response in cyclic voltammetry and could deliver larger specific capacitance of 36.16 F/g in galvanostatical charge–discharge process. Net-like structure of SnS/carbon composite and good conductivity of carbon were considered to be responsible for its preferable electrochemical performances.

Loading of Myoglobin into Multilayer Films Assembled by ZrO&lt;SUB&gt;2&lt;/SUB&gt; Nanoparticles and Phytic Acid: Electrochemistry and Electrocatalysis

Small-molecular phytic acid (PA) with its unique structure was successfully assembled with ZrO2 nanoparticles into {PA/ZrO2}n layer-by-layer films on solid surfaces, which was confirmed by quartz crystal microbalance (QCM) and cyclic voltammetry (CV) with K3Fe(CN)6 as the electroactive probe. Myoglobin (Mb) could be gradually "absorbed" or loaded into the films when the films were immersed into Mb solutions. The Mb-loaded films at pyrolytic graphite (PG) electrodes, designated as {PA/ZrO2}n-Mb, demonstrated well-defined and quasi-reversible CV responses for Mb Fe(III)/Fe(II) redox couple and good electrocatalytic properties toward oxygen and H2O2. The driving force of the film assembly and the interaction between Mb and {PA/ZrO2}n films were explored and discussed in detail. The coordination interaction between PA and ZrO2 is believed to be the main driving force for the assembly of {PA/ZrO2}n multilayer films, and the electrostatic attraction between oppositely charged Mb and the film components is the main interaction for Mb loading into the films. The loading behavior of the {PA/ZrO2}n films toward different proteins with different size indicates that while the porosity of the films is necessary for the protein loading, only those proteins with the size smaller than the average pore size of the films can be incorporated in the interior of films.

An enhanced strategy using poly( m-aminobenzene sulfonic acid) nanofibres for rapid detection of DNA oxidative damage induced by hollow TiO 2 nanocubes

A novel membrane comprising of hollow TiO 2 nanocubes and poly( m-aminobenzene sulfonic acid) (PABSA) nanofibres was constructed on the glassy carbon electrode (GCE) for detecting the oxidative damage of natural dsDNA induced by TiO 2 under UV radiation. The TiO 2/PABSA membrane was used for efficient dsDNA immobilization, dsDNA oxidation through photogenerated hydroxyl radicals, and as the platform for electrochemical sensing. The properties of the TiO 2/PABSA membrane and the immobilization of dsDNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy using [Fe(CN) 6] 3−/4− as the indicator. The resulting oxidative damage of dsDNA was detected by monitoring the CV response of an intercalated electroactive probe, namely, Co ( phen ) 3 3 + . PABSA has a profound synergistic effect with the hollow TiO 2 on the DNA damage detection and the sensor has the potential of becoming a powerful tool for the rapid assessment of the genotoxicity of existing and new chemicals.

Direct electron transfer and electrocatalysis of myoglobin loaded in layer-by-layer films assembled with nonionic poly(ethylene glycol) and ZrO 2 nanoparticles

Nonionic poly(ethylene glycol) (PEG) and ZrO 2 nanoparticles were successfully assembled into {PEG/ZrO 2} n layer-by-layer films on solid surfaces through coordination interaction between the ether oxygen groups in PEG and the Zr(IV) in ZrO 2 nanoparticles. The {PEG/ZrO 2} n films were then immersed in myoglobin (Mb) solution at pH 5.0 to load Mb into the films, designated as {PEG/ZrO 2} n –Mb. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), and scanning electron microscopy (SEM) were used to characterize both {PEG/ZrO 2} n and {PEG/ZrO 2} n –Mb films. Mb in the {PEG/ZrO 2} n –Mb films fabricated on pyrolytic graphite (PG) electrodes showed direct and quasi-reversible CV response, which could be used to electrocatalyze reduction of oxygen and hydrogen peroxide. The interaction between Mb and {PEG/ZrO 2} n films in loading was also discussed and explored. The results suggest that the electrostatic interaction is the main driving force for the loading of Mb into the {PEG/ZrO 2} n films, while hydrogen bonding and/or hydrophobic interaction are also important factors for stabilizing {PEG/ZrO 2} n –Mb films in blank buffers. The comparative experiments demonstrated that only those heme proteins whose dimension was smaller than the average pore size of the films were able to be loaded into the films and exhibited electroactivity.

A comparative evaluation on the anodic behavior of Cu and Ag electrodes in non-aqueous fluoride and fluoroborate media

The voltammetric responses of copper and silver had been extensively studied and compared in a variety of non-aqueous solvents such as acetonitrile (AN), propylene carbonate (PC) and sulfolane containing two different supporting electrolytes namely triethylaminetrishydrogen fluoride (TEA.3HF) and tetrabutylammonium tetrafluoroborate (TBABF4). The dissolution rate and surface transformation on the electrode surfaces as a result of anodic polarization was investigated using atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM), respectively. In solvent-free TEA.3HF medium, the copper electrode shows high charge recovery ratio (Q c/Q a), and the difference between the initial anodic and cathodic potentials, obtained at a current density of 2 mA cm−2, is around 0.11 V, suggesting that in this medium, Cu can certainly serve as reference electrode. On the other hand, on Ag electrode, substantial dissolution was observed leading to very high anodic (Q a) and cathodic (Q c) charges, and the surface morphology after the cyclic polarization results in roughened surface with large pores. The effects of incorporating AN and water as additives in TEA.3HF on the solubility and stability of these metal fluoride films are also reported. The dissolution pattern and film formation behavior of these two metals in the different solvents containing fluoride and fluoroborate ionic species have several qualitative similarities, as noted from cyclic voltammetry responses and SEM morphology. Anodic dissolution and precipitation process for both Cu and Ag depends significantly on the nature of supporting electrolytes as well as solvents. In AN containing 0.1 M TEA.3HF, the dissolution of Cu and Ag electrodes was very high. Fluoride salts of Cu show lesser solubility than Ag in those solvents, while fluoroborate salts exhibit the reverse trend. The AAS data suggest that for a particular salt, which may be either fluoride or fluoroborate of Cu and Ag, the relative solubility decreases in the order AN > PC > sulfolane.

Investigation on PEDOT/β-Fe 3+O(OH,Cl) nanospindles as a new steady electrode material for detecting iodic compounds

Poly(3,4-ethylenedioxythiophene (PEDOT)/β-Fe 3+O(OH,Cl) nanospindles dispersed in ethanol were dropped on a glassy carbon electrode (GCE) and their electrocatalytic properties towards oxidation of KI and reduction of KIO 3 were investigated by cyclic voltammetry (CV). Compared to bare GCE, the anodic and cathodic response currents were greatly enhanced due to the spindle-like morphology which leaded to the increase of surface area. The effect of scanning rate was also studied and obtained diffusion control to the nature of oxidation process of KI and surface control to the nature of reduction process of KIO 3, respectively. PEDOT/β-Fe 3+O(OH,Cl) nanospindles modified GCE had good stability and repeatability of CV responses and the used modified electrode could be cleaned easily by ultrasonic for several minutes. This new kind of conducting polymer/inorganic composite nanomaterials could act as a good steady and convenient electrode material for detecting iodic compounds or some other kinds of compounds.

Evidence for Concerted Proton−Electron Transfer in the Electrochemical Oxidation of Phenols with Water As Proton Acceptor. Tri-tert-butylphenol.

Proton-coupled electron transfer oxidation of phenols play a prominent role in several natural processes, and one may wonder if their high efficiency is related to the possibility that the electron and proton transfer steps are concerted. The cyclic voltammetric observation of the electrochemical oxidation and reverse reaction has allowed, with the example of 2,4,6-tri-tert-butylphenol in nonbuffered aqueous media, the clear identification of a pathway in which a phenol is directly and reversibly converted into the phenoxyl radical while the generated proton is accepted by a water molecule in a concerted manner. In very basic media, a stepwise mechanism takes place in which the phenol is deprotonated by OH- and the resulting phenoxide ion rapidly oxidized into the phenoxyl radical. As the pH decreases, this pathway progressively shuts down to the advantage of the concerted pathway. The latter assignment is confirmed by the observation of a substantial H/D kinetic isotope effect. At moderately basic pH 10.5, the contributions of the two pathways are about equal and the occurrence of the two competing routes is directly visualized in the cyclic voltammetry response.

Study of catalytic homogeneous electrochemical reactions with reciprocal derivative chronopotentiometry using exponential time currents at spherical electrodes: Discrimination between transient and stationary conditions

Catalytic homogeneous electrochemical reactions have been studied with reciprocal derivative chronopotentiometry (RDCP) using an exponential time current both under transient and stationary conditions. The general expressions for the chronopotentiometric potential–time and derivative curves obtained are applicable for spherical electrodes of any radius, including planar electrodes and ultramicroelectrodes as limiting cases. The use of this programmed current has the particularity that it enables to achieve a stationary state very quickly, even when the chemical rate constants are not very high and, under these conditions a simple and quantitative characterisation of catalytic processes can be carried out. Moreover, the RDCP response is always peak-shaped, even for very high homogeneous rate constants for which the stationary response in cyclic voltammetry has a sigmoid feature. The experimental verification of the theoretical predictions has been carried out by analysing the electrocatalytic reduction of the heteropolyanion PW 12O 40 3− in an aqueous sulphuric media with an excess of nitrite.

Sputter Deposition of Multi-Element Nanoparticles as Electrocatalysts for Methanol Oxidation

Fabrication of multi-element nanoparticles on noncatalyzed gas diffusion electrodes (GDEs) by radio frequency sputter deposition was reported. X-ray diffraction analysis of the as-deposited films indicated crystalline fcc phases while energy dispersive X-ray spectroscope confirmed their composition as Pt50Fe11Co10Ni11Cu10Ag8. Scanning electron microscopy images revealed nanoparticulate nodules growing on the carbon particles. Cyclic voltammetry (CV) was employed to analyze their methanol oxidation abilities for direct methanol fuel cells. The CV responses improved upon cycling and became stabilized after 70 cycles. The areas under the CV curves were proportional to the amount of nanoparticles deposited. In mass activities the GDE with 5 nm nanoparticles demonstrated the highest values of 400–600 mA/mg. In comparing with Pt and Pt43Ru57, the Pt43Ru57 exhibited the lowest onset potential with the highest mass activities. Our work presents preliminary information on the catalytic behaviors of multi-element nanoparticles which is likely to bring new directions in catalyst design.

Electrocatalytic oxidation of ethylene glycol on Pt and Pt–Ru nanoparticles modified multi-walled carbon nanotubes

The synthesis and characterization of catalysts based on nanomaterials, supported on multi-walled carbon nanotubes (CNT) for ethylene glycol (EG) oxidation is investigated. Platinum (Pt) and platinum–ruthenium (Pt–Ru) nanoparticles are deposited on surface-oxidized multi-walled carbon nanotubes [Pt/CNT; Pt–Ru/CNT] by the aqueous solution reduction of the corresponding metal salts with glycerol. The electrocatalytic properties of the modified electrodes for oxidation of ethylene glycol in acidic solution have been studied by cyclic voltammetry (CV), and excellent activity is observed. This may be attributed to the small particle size of the metal nanoparticles, the efficacy of carbon nanotubes acting as good catalyst support and uniform dispersion of nanoparticles on CNT surfaces. The nature of the resulting nanoparticles decorated multiwalled carbon nanotubes are characterized by scanning electron microscopy (SEM) and transmission electron microscopic (TEM) analysis. The cyclic voltammetry response indicates that Pt–Ru/CNT catalyst displays a higher performance than Pt/CNT, which may be due to the efficiency of the nature of Ru species in Pt–Ru systems. The fabricated Pt and Pt–Ru nanoparticles decorated CNT electrodes shows better catalytic performance towards ethylene glycol oxidation than the corresponding nanoparticles decorated carbon electrodes, demonstrating that it is more promising for use in fuel cells.

Layer-by-layer assembly of myoglobin and nonionic poly(ethylene glycol) through ion–dipole interaction: An electrochemical study

Nonionic poly(ethylene glycol) (PEG) and myoglobin (Mb) were successfully assembled into {PEG/Mb} n layer-by-layer films on various solid surfaces. Quartz crystal microbalance (QCM), UV–vis spectroscopy and cyclic voltammetry (CV) were used to monitor and confirm the film growth and characterize the films. The Mb in stable {PEG/Mb} n films showed a quasi-reversible CV response for its heme Fe(III)/Fe(II) redox couple, and was used to electrocatalyze the reduction of various substrates. The interaction between PEG and Mb in the assembly was investigated in detail. A series of comparative experiments showed that the ion–dipole interaction between positively charged groups on the Mb surface and electronegative ether oxygen groups of PEG would be the main driving force for the assembly of {PEG/Mb} n films, while other interactions such as hydrogen bonding and/or hydrophobic interaction may also play an important role in stabilizing the films in blank buffers.

Continuous amperometric detection of co-released serotonin and melatonin from the mucosa in the ileum

Serotonin (5-HT) and melatonin (MEL) are well known neurotransmitters and paracrine signalling molecules. Both compounds are present in enterochromaffin (EC) cells in the mucosa of the gastrointestinal tract and are thought to play a role in controlling gut motility. To date there are no real-time analytical methods for the detection of these two molecules and it is not clear if MEL is actually released from the EC cells. In this paper, I used boron-doped diamond (BDD) microelectrodes to record 5-HT and MEL overflow from EC cells in the mucosa of rabbit ileum. The BDD microelectrode was extremely stable and sensitive for measurements of both compounds when assessed using differential pulse voltammetry (DPV) and flow injection analysis (FIA) using amperometric detection. MEL release was detected in the mucosa, where it is most likely from the EC cells. Mechanical stimulation of individual villi increased 5-HT but not MEL overflow. Application of the serotonin transporter (SERT) inhibitor, fluoxetine, elevated the 5-HT but not the MEL signal. Differences in the amounts of the two gastrointestinal compounds released and the mechanism of which they are released will provide insights to the physiology of the EC cell and disease states.

Fluorinated functionalized EDOT-based conducting films

Three ethylenedioxithiophene (EDOT) derivatives bearing either perfluoro- or ether perfluoro-alkyl chains were synthesized with the objective to prepare films with dry and chemically immobilized lubrication properties. The corresponding fluorinated PEDOT films were deposited on platinum surface by electropolymerization. Cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) analyses (both quartz resonant frequency and resonant admittance) of the growing steps are described. The electroactive behavior of the films versus their doping level was followed by electrochemical impedance spectroscopy (EIS) through equivalent circuit fitting procedure and compared to their CV responses. Hysteresis in fit parameters corresponding to capacity and film resistance between the forward and the backward scans are observed and discussed. Control of the chemical structures and charge effects on PEDOT chains are followed by an XPS analysis. From these analyses, it appears that the fluorinated side-arm does not alter both the growing and the electrical properties of the films in respect to the pristine PEDOT taken as reference.

Photoelectrochemical oxidation behavior of methanol on highly ordered TiO2 nanotube array electrodes

The highly ordered titanium dioxide nanotube array (HOTDNA) electrodes were prepared in hydrofluoric acid solution by electrochemical anodic oxidation technique on a pure titanium sheet. The HOTDNA electrodes were characterized by X-ray diffraction, SEM microscopy, and UV–vis spectra. It has shown high density, well ordered and uniform titanium dioxide nanotube array film covered on these electrodes and the TiO2 structure depending on the heating condition, the anatase phase of TiO2 appeared when heating to 500 °C. The photoelectrochemical characteristics of methanol in 0.5 M Na2SO4 on the HOTDNA electrodes were investigated. The cyclic voltammetry, photocurrent-time and open-circuit photopotential response of methanol on the HOTDNA electrode were represented and significant photogenerated current was observed upon illumination in the UV regions with the light of 253.7 nm central wavelength. The effect of variables such as light intensity, applied potential, and methanol concentration on the photoelectrochemical response was investigated. It was found that the photocurrent was greatly influenced by these factors.

Cyclic voltammetry of LiCr 0.15Mn 1.85O 4 in an aqueous LiNO 3 solution

Cyclic voltammetry (CV) of LiCr 0.15Mn 1.85O 4, synthesized by rapid glycine-nitrate method (GNM), was performed in a saturated aqueous LiNO 3 (∼9 M) solution. At rather high polarization rate of 10 mV s −1 two well separated characteristic pairs of redox peaks can be clearly observed, which is not entirely the case for LiMn 2O 4 synthesized in the same way. At a reduced scan rate of 1 mV s −1, the shape and position of redox peaks evidence that deintercalation/intercalation of Li + ion is highly reversible and much faster than in the case of organic electrolytes. Faster “CV response” of LiCr 0.15Mn 1.85O 4 is in correlation with higher capacity retention (93%) in comparison to LiMn 2O 4 (88%), registered after 50 charging/discharging cycles in organic electrolyte solution (1 M LiClO 4 in propylene carbonate).

An Electrochemical Study on the Nature of Trap States in Nanocrystalline Rutile Thin Films

For monocrystalline TiO2 electrodes, capacitive currents are observed at potentials that are negative enough to induce the filling of conduction band states. Nanoparticulate electrodes exhibit, apart from these currents, an additional pair of capacitive peaks at more positive potentials, which can be attributed to charge traps in the band gap. We have taken advantage of the well-defined morphology and crystal structure of three different types of rutile electrodes to investigate the nature of these band gap states. In particular, nanostructured films composed of oriented wires, films of randomly distributed nanoparticles, and smooth single crystals have been used. The analysis of the cyclic voltammetry response reveals a strong dependence of the trap state concentration on the morphological structure of the films. On the basis of results concerning the surface modification of the electrodes, we propose a model with a location of these band gap states at grain boundaries. We report, furthermore, on a new procedure to prepare hierarchically organized nanostructures by direct deposition of nanowires onto nanoparticulate films in aqueous solutions at low temperature. From a practical point of view, this procedure allows for a systematic tuning of the inner surface area and the porosity of the original samples.

Poly-o-phenylenediamine as redox mediator for laccase

Abstract Electrocatalytic activity towards oxygen reduction of fungal laccase entrapped in poly-o-phenylenediamine (POPDA) matrix on glassy carbon electrodes was studied. Cyclic voltammetry and amperometric responses to dissolved oxygen were investigated in pH range from 2 to 6. POPDA reveals a unique ability to serve as a redox mediator for laccase and immobilizing matrix at the same time. The entrapped enzyme efficiently catalyzes reduction of molecular oxygen without any additional mediators. The electrocatalytic current reaches 0.1 mA/cm−2 per 1 μg of immobilized enzyme on cyclic voltammograms recorded at 1 mV/s in a not stirred electrolyte. Current density values are comparable with those revealed by dissolved laccase (60 μg/ml) mediated by hydroquinone and greatly higher than by the mediator less laccase/glassy carbon system. The potential of oxygen reduction is determined by the polymer redox couple. Consequently, the onset of the oxygen reduction shifts from −0.15 V versus Ag/AgCl in pH 6 to +0.05 V versus Ag/AgCl in pH 2. The laccase–POPDA layers immersed in the deaerated solution show fast amperometric responses to addition of the oxygen containing solution. The observed current values depend linearly on the oxygen concentration. Factors affecting the electrocatalytic activity of the laccase–POPDA system, including the layer thickness and the pH value, are studied. The electrodeposited laccase–POPDA films are characterized by infrared spectra. The results prove that the enzyme secondary structure remains unchanged during the entrapment procedure. POPDA matrix structure consists of the phenazine-type polymer according to infrared spectra.

An electroactive conducting polymer actuator based on NBR/RTIL solid polymerelectrolyte

This paper reports the fabrication of a dry-type conducting polymer actuator using nitrilerubber (NBR) as the base material in a solid polymer electrolyte. The conducting polymer,poly(3,4-ethylenedioxythiophene) (PEDOT), was synthesized on the surface of the NBRlayer by using a chemical oxidation polymerization technique. Room-temperature ionicliquids (RTIL) based on imidazolium salts, e.g. 1-butyl-3-methyl imidazolium X (whereX = BF4−,PF6−,(CF3SO2)2N−), were absorbed into the composite film. The compatibility between the ionic liquids andthe NBR polymer was confirmed by DMA. The effect of the anion size of the ionic liquidson the displacement of the actuator was examined. The displacement increased withincreasing anion size of the ionic liquids. The cyclic voltammetry responses and the redoxswitching dynamics of the actuators were examined in different ionic liquids.