Cyclic Voltammetric Scans Research Articles

CdS nanotubes thin film for electrochemiluminescence analysis of phenolic compounds

A CdS nanotubes (NT) thin film has been fabricated to determine phenolic compounds based on the electrochemiluminescence (ECL) quenching of the CdS NT. The CdS NT thin film coated on an indium tin oxide substrate exhibits strong ECL emission with potassium persulfate (K2S2O8) as a coreactant. The effects of pH, electrolyte concentration and cyclic voltammetric scan rate on the ECL were studied. The quenching efficiency is governed by the position of the hydroxyl moiety in the parent benzene ring which follows the trend: resorcinol (1,3-benzenediol) > catechol (1,2-benzenediol) > hydroquinone (1,4-benzenediol) ≈ phenol. Under the optimal experimental conditions of 0.010 M K2S2O8, pH 11.60 and 0.10 V s−1, the quenching of ECL by catechol (2.0–10.0 μM), hydroquinone (40.0–140 μM), phenol (10–60 μM) and resorcinol (2.0–12.0 μM) follows Stern–Volmer behaviour. The limits of detection are calculated as 0.058, 0.64, 1.7, and 0.069 μM (S/N = 3) for catechol, hydroquinone, phenol, and resorcinol respectively. The fabrication of the CdS NT film is reproducible and its shelf-life is longer than three months. The CdS NT film has been successfully applied to determine the phenol contents in various environmental water samples with satisfactory results and good recoveries. Our proposed ECL CdS NT film provides a simple and convenient method for the detection of phenolic compounds and shows potential use in the pharmaceutical industry and environmental monitoring.

Observations in the H-Pd{111} System via Stress and EQCM Measurements

The under-potential deposition (UPD) & absorption of hydrogen in thin film palladium (45–75 nm) was investigated electrochemically utilizing both EQCM and thin film stress measurement techniques. The total frequency change during H absorption (desorption) as measured by EQCM is attributed to both an increase (decrease) in mass, Δfm, as well as the associated thin film stress evolution, Δfs. In order to deconvolute these two contributions, the changes in the Pd{111} thin-film stresses were measured directly by a high-resolution cantilever curvature-based stress monitoring technique. Mass incorporation and stress generation due to hydrogen absorption were recorded during cyclic voltammetric scans of increasingly cathodic potentials as well as during chronoamperometric holds in the hydrogen UPD region. The combination of stress measurements and mass uptake of hydrogen in the purely elastic regime provided a measure of a biaxially constrained partial molar volume of hydrogen in the Pd thin films, = 0.44 cm3/mol. Additionally, the occurrence of hysteresis and dramatic changes in slope of stress vs. H concentration during loading and unloading of thin films is explained in the context of elastic-plastic transitions that occur in the film.

Self-doped polyaniline on functionalized carbon cloth as electroactive materials for supercapacitor

Carbon cloth was functionalized through cyclic voltammetric scans in 2M H2SO4 to afford functionalized carbon cloth (FC). The FC was characterized by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Self-doped polyaniline (SPAN) was deposited on FC through electro-co-polymerization of aniline and metanilic acid to get SPAN/FC which showed a specific capacitance of 408Fg−1 in 0.5M Na2SO4, based on a constant charge–discharge experiment at a current density of 1Ag−1. A symmetric model capacitor, SPAN/FC-SPAN/FC was assembled by using SPAN/FC as both of the electrodes and 0.5M Na2SO4 as the electrolyte. The charge storage property and charge–discharge cycling stability of SPAN/FC-SPAN/FC were investigated by galvanostatic experiment.

Heat treatment and electrochemical activation of titanium oxide nanotubes: The effect of hydrogen doping on electrochemical behavior

During the course of the present study, highly dense arrays of titanium oxide nanotubes (TON) were fabricated by anodization of titanium foil in aqueous fluoride solutions. The obtained TON arrays were then subjected to annealing and electrochemical treatment, followed by characterization using scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance (EI) techniques. By combining the effects of annealing and cathodic potential treatment, the cyclic voltammetry shows that the TON arrays catalyze the hydrogen evolution in acidic medium. This catalytic activity was not observed when the rutile phase started to form in TON arrays. EI results show that TON conductivity is substantially improved by cathodic potential treatment only when it contains the anatase phase. This was also confirmed by the cyclic voltammetric scan for the Fe(CN) 6 3−/Fe(CN) 6 4− couple, where a smaller peak separation between anodic and cathodic peaks was observed, rather than as-anodized TON.

Zinc sulfide surface formation on Hg electrode during cyclic voltammetric scan: an implication for previous and future research studies on metal sulfide systems

Cyclic voltammetry on the Hg electrode was used to investigate the electrochemical behavior of NaCl/NaHCO3 electrolyte solutions supersaturated with respect to Zn sulfide phases. The voltammetric results clearly show how an Hg electrode, due to exchange between Hg2+ from an HgSadlayer and Zn2+ from solution, becomes the site for surface ZnSadlayer formation in the potential range −0.45 to −0.6 V. The exchange reaction is reversible, and the surface-formed ZnSadlayer persists at the Hg electrode surface until −1.3 V during cathodic scans. Near −1.3 V, it is reduced. In the same solution, evidence for reduction of bulk Zn sulfide species including nanoparticles was not obtained. The approach emphasized here can be readily extended to any other system consisting of metal electrode and chalcogenide anions, pointing to the importance of choosing experimental conditions (i.e., deposition potential, stirring, and accumulation times) to avoid artifacts and wrong interpretation of data due to surface formation of metal sulfide species.

Electrochemical fabrication of self assembled monolayer using ferrocene-functionalized gold nanoparticles on glassy carbon electrode

Electrochemical (EC) quantification of 11-Mercaptoundecylferrocene (thiolated-ferrocene substrate, Fc-SH) onto gold nanoparticles (AuNPs) was carried out through cyclic voltammetric (CV) investigations in different base electrolyte aqueous media on glassy carbon (GC) electrode. The electrochemical data including peak current, peak potential values revealed the Fc-SH–AuNPs redox system to be adsorption controlled in terms of self assembled monolayers (SAMs). The electrochemically generated SAMs were found quite stable as these maintained the redox activity upto 3 months after repeated CV scans at 298 K. The overall output of this research can be utilized in two ways: application of electroactivity and stability of these SAMs in detection of biologically important molecules and also towards the development of EC biosensors.

Electrochemical degradation of Nafion ionomer to functionalize carbon support for methanol electro-oxidation

An effective electrochemical route to produce functional groups on carbon surface is demonstrated. Cyclic voltammetric (CV) sweeps are performed in 0.5M H2SO4 electrolyte on electrodes containing carbon cloth, Vulcan XC72R, and Nafion ionomer. With supply of ambient oxygen, the generation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomer that leads to formation of oxygenated functional groups on the carbon surface. Ion chromatography confirms the dissolution of sulfate anions upon CV scans. Raman analysis suggests a minor alteration for the carbon structure. However, X-ray photoelectron spectroscopy indicates a significant increase of oxygenated functional groups in conjunction with notable reduction in the fluorine content. The amount of the oxygenated functional groups is determined by curve fitting of C 1s spectra with known constituents. These functional groups can also be found by immersing the as-prepared electrode in a solution containing concentrated residues from Nafion ionomer decomposition. The functionalized electrode allows a 170% increment of Pt ion adsorption as compared to the reference sample. After electrochemical reductions, the functionalized electrode reveals significant improvements in electrocatalytic abilities for methanol oxidation, which is attributed to the oxygenated functional groups that facilitates the oxidation of CO on Pt.

Porous manganese oxide generated from lithiation/delithiation with improved electrochemical oxidation for supercapacitors

For manganese oxides with low manganese oxidation states, such as MnO or Mn3O4, the electrochemical oxidation during potential cycling is critical to achieve high supercapacitor performance. In this work, dense Mn3O4 thin films are prepared by pulsed laser deposition. An electrochemical lithiation/delithiation process is applied to the Mn3O4 thin film, which leads to a nanoporous structure of the film and greatly increases the porosity of the film. The nanoporous MnOx thin film electrode exhibits significantly improved supercapacitive performance compared to the as-prepared Mn3O4 thin film electrode. After 1000 cyclic voltammetric scans in 1 M Na2SO4 electrolyte between 0 and 1 V, only part of the surface of the as-prepared Mn3O4 thin film transforms into a MnO2 porous structure while the complete film of the nanoporous MnOx transforms into a MnO2 porous structure. It is believed that the nanoporous structure, which facilitates the electrolyte penetration, leads to the completion of electrochemical oxidation through the film during the potential cycling, resulting in promising supercapacitive performance of the film.

Scanning electrochemical microscopy characterization of bimetallic Pt–M (M = Pd, Ru, Ir) catalysts for hydrogen oxidation

A combinatorial screening method, combined with scanning electrochemical microscopy (SECM) in a tip-generation–substrate-collection (TG–SC) mode, was applied to systematically and rapidly identify potential bimetallic catalysts (Pt–M, M=Pd, Ru, Ir) for the hydrogen oxidation reaction (HOR). The catalytic oxidation of hydrogen on the candidate catalysts was further examined during cyclic voltammetric scans of the substrate with a tip close to the substrate. The quantitative rate of hydrogen oxidation on the candidate substrates was determined for different substrate potentials from SECM approach curves by fitting to a theoretical model. SECM screening results revealed that Pt4Pd6, Pt9Ru1 and Pt3Ir7 were the optimum composition of the catalysts from the Pt–Pd, Pt–Ru and Pt–Ir bimetallic systems for hydrogen sensors. The catalytic activity of the candidate catalysts in HOR was highly dependent on the substrate potential. The kinetic parameters for HOR were obtained on Pt4Pd6 (Tafel slope=124mV, k°=0.19cm/s, α=0.52), Pt9Ru1 (Tafel slope=140mV, k°=0.08cm/s, α=0.58) and Pt3Ir7 (Tafel slope=114mV, k°=0.11cm/s, α=0.48) and compared with Pt (Tafel slope=118mV, k°=0.17cm/s, α=0.5). Among the bimetallic catalysts studied, Pt4Pd6 exhibited the highest activity toward HOR with a high standard rate constant value in a wide range of applied potentials.

Ion transport through a porphyrin-terminated hybrid bilayer membrane

A hybrid bilayer membrane (HBM) has been prepared on a glassy carbon electrode (GCE). The HBM consists of an inner layer of n-hexadecylamine (HDA) covalently attached at the GCE and an out-layer of tetra-(N-hexadecylpyridiniurnyl)porphyrin (TC 16PyP). The HDA was covalently bounded on the carbon surfaces through its primary amine under cyclic voltammetric potential scans forming a self-assembled monolayer (SAM). The TC 16PyP forms a second layer on top of the HDA layer due to hydrophobic interaction. The TC 16PyP/HDA/GCE assembly has been utilized to study ion transport through hybrid bilayer membranes. The ion transport through this porphyrin-terminated HBM has been found to strongly dependent on pH. It allows negatively charged redox ions, Fe(CN) 6 3−, to penetrate at pH <6 while repelling positively charged Ru(NH 3) 6 3+. However, no faradaic current has been detected at pH >6 with either ions. We believe that electrostatic interaction between the redox ions and the charged membrane is the main reason for this pH dependent ion transport.

Preparation of Gold Nanotube by Direct Electrodeposition for Biosensors

A simple method to fabricate gold nanotube by means of a direct electrodeposition is constructed, utilizing anodic aluminum oxide (AAO) as a template. The performances of gold nanoelectrode have been characterized with cyclic voltammetric technique and scanning electron microscope (SEM). The SEM image of as-prepared gold nanoelectrode shows that the surface of electrode was covered with honeycomb gold tube with average pore diameter 200 nm. Its cyclic voltammetric shows the peak current is 6.25 times larger than the bare Au electrode, so the new honeycomb gold nanoelectrode was obviously better than conventional gold electrode. Microperoxidase-11 (MP-11) was immobilized on the electrode and characterized with cyclic voltammetric technique. It was demonstrated that the gold nanotube not only could offer a friendly environment to immobilize MP-11, but also enhance the electron transfer ability between protein molecules and the underlying electrodes.

Spontaneous Deposition of Pt on Carbons Activated by Cyclic Voltammetric Scans in Sulfuric Acids

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IR Spectroelectrochemical Cyclic Voltabsorptometry and Derivative Cyclic Voltabsorptometry

In this paper, we report the IR (infrared) CVA (cyclic voltabsorptometry) and DCVA (derivative cyclic voltabsorptometry) spectroelectrochemical techniques to elucidate an electrochemical mechanism. First we set potassium ferrocyanide as an example to explain the validity of this method. Then the electrochemical redox of two compounds, 1,4-benzoquinone and 1,4-bis(2-ferrocenylvinyl)benzene, was selected to be examined with this method. 1,4-Benzoquinone exhibits two single-electron waves in the cyclic voltammetric (CV) experiment, whereas two electroactive groups (Fc) are contained in p-(Fc-CH=CH)(2)BZ, but only one redox wave is observed. IR CVA results show that three IR absorption peaks in 1,4-benzoquinone, 1232 cm(-1) (the absorption of final production), 1656 cm(-1) (the absorption of original reactant), and 1510 cm(-1) (the absorption of intermediate), and two IR absorption peaks in 1,4-bis(2-ferrocenylvinyl)benzene, 1620 cm(-1) (the absorption of final oxide production) and 1589 cm(-1) (the absorption of intermediate), can be used to track the electron transfer. On the basis of the IR absorbance at the appropriate monitored wavelength (mentioned above), we can analyze simultaneously the concentration change of the corresponding redox transition during CV scans. Also the combination of the DCVA spectroelectrochemical technique with theory analysis allows reconstructing the current-potential (i-E) curve for each step of electron transfer. The reconstructed i-E curve can help us to understand the electron-transfer process. We believe IR CVA and DCVA spectroelectrochemical techniques can be applicable to the study of a wide range of complex electrochemistry processes.

Nanostructured Electrode with Titania Nanotube Arrays: Fabrication, Electrochemical Properties, and Applications for Biosensing

Titania nanotube (TNT) arrays were fabricated by anodic oxidation of titanium foil in various electrolytes and were calcined in dry nitrogen at various temperatures. The morphology, crystallinity, and chemical composition of TNT arrays were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) was employed to investigate the electrical conductivity and capacitance of TNT arrays prior to and after calcination. The results showed that the electrical conductivities of TNT arrays calcined in nitrogen for 3 hours were improved significantly as compared to the as-grown TNT arrays or annealed in air or argon. Well defined oxidation and reduction peaks were observed during the cyclic voltammetric scans at 0.1 V/s in 10 mM K3[Fe(CN)6] solution. For the application in biosensing, TNT electrodes co-adsorbed with horseradish peroxidase (HRP) and thionine chloride (Th) were studied for their sensitivity to hydrogen peroxide by means of cyclic voltammetric. The experiments showed that TNT arrays possessed appreciably different sensitivities to H2O2 due to their different conductivity. The best result was found in the TNT arrays annealed in nitrogen. Further analyses revealed that the sensitivity of TNT arrays annealed in nitrogen was increased 4-6 times compared with as-grown TNT arrays, the dynamic range on H2O2 is in the range of 2 x 10(-5) M to 3.6 x 10(-3) M at pH = 6.7 and at a potential of -600 mV (vs. Ag/AgCl).

Electrochemical codeposition of nickel oxide and polyaniline

Nickel oxide (NiOx) and polyaniline (PAni) were electrocodeposited from NiSO4 and aniline through cyclic voltammetric scans to afford PAni–NiOx composite film at controlled pH environment. The electrochemical activities of the film were investigated by cyclic voltammetry in 0.1 M NaOH and 0.1 M H2SO4, respectively. Typical redox couples of PAni in 0.1 M H2SO4 appeared at approximately 0.2 and 0.4 V vs. saturated calomel electrode (SCE); Ni(II)/Ni(III) redox couple was observed at approximately 0.4 V vs. SCE in 0.1 M NaOH. The morphologies and elemental components of the films were inspected by scanning electron microscopy and energy dispersive X-ray diffraction. The stability of nickel oxide in the films was found to be enhanced against acidic environments. Electrochemical catalytic behavior of NiOx within the composite film was conserved and demonstrated by catalytic oxidation of methanol and ethanol.

Clay Nanoparticle-Supported Single-Molecule Fluorescence Spectroelectrochemistry

Here we report that clay nanoparticles allow formation of a modified transparent electrode, spontaneous adsorption of fluorescent redox molecules on the clay layer, and thus the subsequent observation of single-molecule fluorescence spectroelectrochemistry. We can trace single-molecule fluorescence spectroelectrochemistry by probing the fluorescence intensity change of individually immobilized single redox molecules modulated via cyclic voltammetric potential scanning. This work opens a new approach to explore interfacial electron transfer mechanisms of redox reactions.

Insights into the electro-oxidation of ethylene glycol at Pt/Ru nanocatalysts supported on MWCNTs: Adsorption-controlled electrode kinetics

Electrocatalytic properties of Pt/Ru nanoparticle-electrodecorated MWCNT platform towards the oxidation of ethylene glycol (EG) have been interrogated using cyclic voltammetry and electrochemical impedance spectroscopy. Both forward and reverse oxidative reactions exhibited distinct electrochemical behaviour following changes in EG concentrations, scan rates and during repetitive cyclic voltammetric scanning. Our results suggest that the overall electro-oxidation reaction of EG is governed mainly by adsorption kinetics, with the electrochemical adsorption equilibrium constant (β) and the free energy change ( ΔG o) being 1.47 M −1 and −0.95 kJ mol −1, respectively.

Solid state spectroelectrochemistry of microparticles of ruthenium diimine complexes immobilised on optically transparent electrodes

The solid state electrochemistry and solid state spectroelectrochemistry of two ruthenium complexes, ruthenium tris-(4,7-diphenyl-1,10-phenanthroline) bis-hexafluorophosphate, [Ru(dpp)3](PF6)2, and ruthenium bis-(2,2′-bipyridine)(4,6-diphenyl-2,2′-bipyridine)bis-hexafluorophosphate, [Ru(bpy)2(dpb)](PF6)2, is described. Microparticles of the material are immobilised on ITO electrodes, and stable voltammetric signals are obtained in contact with aqueous electrolyte solution. Spectral changes monitored during a slow cyclic voltammetric scan confirm the exhaustive oxidation of the Ru2+ species to the Ru3+ form. The derivative of the absorbance signal monitored at a single wavelength during potential cycling is morphologically identical to a cyclic voltammogram with no background current. This technique is shown to be useful when peaks of small magnitude are obscured by capacitive background or when peaks close to the solvent limit are obscured by solvent electrolysis current. The technique effectively widens the electrochemical window available for voltammetric measurements. After suitable correction of the signal, the value of the voltammetric peak height (Ip) as well as peak potential (Ep) may be obtained from the derivative absorbance signal. Chronospectrometry is demonstrated to provide the equivalent to a chronocoulometric response, but is closer to the ideal simulated response. A facile method for simulating time or potential-dependant spectroelectrochemical responses using commercial electrochemical simulation software is described. Absorbance transients monitored during the electrolysis of solid particles of [Ru(dpp)3](PF6)2 show best agreement with simulated data at very short and very long timescales. This observation, in conjunction with the observations from the potential scan experiments, suggests that the absorbance, charge, or current vs. time behaviour of the system can be adequately described by a semi-infinite diffusional model at short experimental timescales and by a finite diffusional model at sufficiently long timescales.

Ionic‐complementary peptide‐modified highly ordered pyrolytic graphite electrode for biosensor application

Ionic-complementary peptides are promising new biomaterials with potential applications in bionanotechnology. In the present investigation, a typical ionic-complementary peptide, EFK16-II, was used to modify a highly ordered pyrolytic graphite (HOPG) electrode. Upon modification, peptide nanofibers, parallel or oriented 60 degrees or 120 degrees to each other, were formed on the surface of HOPG electrode. Surface wettability of the electrode was improved as indicated by a significant decrease in the water contact angle. The electrochemical response of the EFK16-II nanofiber-modified HOPG electrode for the ferricyanide/ferrocyanide redox couple was characterized. Cyclic voltammograms indicated that the presence of peptide nanofibers on the HOPG electrode did not block electron transfer at slow scan rates ( approximately 2 mV/s), but did so at high scan rates ( approximately 100 mV/s). A model enzyme glucose oxidase (GOx) was covalently immobilized onto this nanofiber-modified electrode, and its potential as an enzyme-based biosensor for glucose was examined. At an applied potential of +0.45 V (vs. Ag/AgCl), the current increased linearly with glucose concentration up to 7.5 mM and a relative high sensitivity was obtained at 11.3 +/- 1.0 nA/(mM mm(2)). The immobilized GOx showed high affinity for glucose, with a Michaelis-Menten constant K(m) of 6.8 +/- 0.9 mM. It also exhibited relatively good storage and operational stabilities, and reflected in only a small decrease (13%) in the current response after 1 month storage and negligible changes upon 50 cyclic voltammetric scans. The results presented here demonstrate an excellent potential of the use of ionic-complementary peptides to modify electrode surfaces for biomolecular sensing and diagnostics.

Electrochemical synthesis of Pd particles on poly(vinylferrocenium)

Electrochemical synthesis of Pd particles on poly(vinylferrocenium) (PVF + ) support was described. K 2 PdCl 4 was used as the metal particle precursor. Pd particles were incorporated into the polymer matrix electrochemically either by cyclic voltammetric scans (between +1.0 V and −0.8 V vs. SCE) or by reduction at constant potential (at −0.8 V vs. SCE) from aqueous solution of K 2 PdCl 4 . Scanning electron microscopy (SEM) studies showed that the Pd particles were well dispersed in the polymer matrix. Experimental parameters such as polymer film thickness, number of cycles during cyclic voltammetric scans in K 2 PdCl 4 and electrolysis time in K 2 PdCl 4 were studied. The Pd/PVF + system showed catalytic activity towards hydrazine oxidation and appreciable results were obtained when compared with the related studies.