Bare Glassy Carbon Surface Research Articles

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.

Detection of biomarkers with graphene nanoplatelets and nanoribbons

Well-defined graphene nanosheets have become increasingly popular in the electrochemical detection and quantification of small molecules. In this work, the electrochemical oxidation of biomarkers such as uric acid, ascorbic acid, dopamine, NADH and DNA bases, namely guanine and adenine, was performed using cyclic voltammetry and differential pulse voltammetry to compare the electrochemical properties of electrochemically reduced nanoplatelets (ENPs) and electrochemically reduced nanoribbons (ENRs). The graphene materials displayed better electrochemical performances than the bare glassy carbon surface. Between the two graphene materials, the oxidation of biomarkers occurred at lower oxidation potentials on the ENP surface. The sensitivities of the two graphene surfaces varied when different biomarkers were studied. The ENP surface showed enhanced sensitivities for ascorbic acid, while the ENR surface exhibited higher sensitivities for uric acid and dopamine. As for the DNA bases analysed, both guanine and adenine were oxidised at lower potentials on the ENP surface than the ENR surface. The ENP surface displayed a better sensitivity for guanine, whereas the oxidation of adenine was more sensitive on the ENR surface.

Mechanisms and kinetics of electrode processes at bismuth and antimony film and bare glassy carbon surfaces under square-wave anodic stripping voltammetry conditions

Mechanism and kinetics of anodic stripping electrode processes of Zn(II), Cd(II) and Pb(II) at bismuth (BiFE) and antimony (SbFE) film as well as bare glassy carbon (GCE) electrodes have been studied with respect to our recent published theoretical considerations developed for square-wave voltammetry (SWV). Mechanistic aspects of electrode reactions have been elucidated by a qualitative comparison of simulated and experimental data for three different electrode reaction mechanisms, i.e. simple anodic stripping mechanism, anodic stripping mechanism coupled with adsorption of metal analyte ions, and mechanism affected by interactions within the particles of the metal deposit on the electrode surface. The electrode kinetics has been estimated by the method of quasireversible maximum and by analyzing the peak potential separation between forward and backward SW components, under variation of the SW amplitude. Electrode mechanisms and kinetics are different at bismuth compared to antimony film electrodes. The electrode reactions of Pb(II) and Cd(II) at BiFE involve adsorption phenomena, while electrode processes of all three analytes are free of adsorption at SbFE. At BiFE, the electron transfer standard rate constants of all three analytes are quite comparable, ranging within the interval from 1 to 3cms−1. At SbFE the electrode kinetics of Cd(II) and Pb(II) are almost the same, while the electrode reaction of Zn(II) is significantly slower. Our results showed that the kinetics of all examined electrode reactions are slower at SbFE as compared to those observed at BiFE.

Simultaneous determination of ascorbic acid, epinephrine and uric acid at over-oxidized poly(p-aminophenol) film modified electrode

A modified electrode was fabricated by over-oxidation of polymer film after electropolymerization of p-aminophenol on a bare glassy carbon surface. A higher catalytic activity was obtained for electrocatalytic oxidation of ascorbic acid (AA), epinephrine (EN), and uric acid (UA) in pH 7.4 phosphate buffer solution (PBS) at over oxidized poly(p-aminophenol) film modified glassy carbon electrode (Ox-PAP/GCE) due to an enhanced peak current and well-defined peak separations compared with both bare glassy carbon electrode (GCE) and poly(p-aminophenol) film modified GCE (PAP/GCE). The electrode surfaces were characterized by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM). Individual and simultaneous determination of AA, EN, and UA were carried out by differential pulse voltammetry. The detection limits were individually calculated for ascorbic acid, epinephrine, and uric acid as being 1.0×10−6M, 6.5×10−9M, and 1.8×10−7M, respectively.

Study on electroactive and electrocatalytic surfaces of single walled carbon nanotube-modified electrodes

An investigation of the electrocatalysis of single-walled carbon nanotubes modified electrodes has been performed in this work. Nanotube-modified electrodes present a surface area much higher than the bare glassy carbon surfaces as determined by capacitance measurements. Several redox probes were selected for checking the reactivity of specific sites at the carbon nanotube surface. The presence of carbon nanotubes on the electrode improves the kinetics for all the reactions studied compared with the bare glassy carbon electrode with variations of the heterogeneous electron transfer rate constant up to 5 orders of magnitude. The most important effects are observed for the benzoquinone/hydroquinone and ferrocene/ferricinium redox couples, which show a remarkable improvement of their electron transfer kinetics on SWCNT-modified electrodes, probably due to strong π–π interaction between the organic molecules and the walls of the carbon nanotubes. For many of the reactions studied, less than 1% of the nanotube-modified electrode surface is transferring charge to species in solution. This result suggests that only nanotube tips are active sites for the electron transfer in such cases. On the contrary, the electroactive surface for the reactions of ferrocene and quinone is higher indicating that the electron transfer is produced also from the nanotube walls.

Electrocatalysis of Oxygen Reduction by Au Nanoparticles Electrodeposited on Polyoxometalate-Modified Electrode Surfaces

The effect of polyoxometalate monolayers on the electrodeposition of Au nanoparticles (AuNPs) on glassy carbon (GC) surfaces was examined by electrochemical and scanning electron microscope techniques. The presence of <TEX>$SiMo_{12}O^{4-}_{40}$</TEX>-layers resulted in average particle sizes of ca. 60 nm, which is larger than AuNPs deposited on bare GC surfaces. AuNPs electrodeposited on <TEX>$SiMo_{12}O^{4-}_{40}$</TEX>-modified GC surfaces for 20 s exhibited the best electrocatalytic activity for oxygen reduction. This system exhibited similar or slightly better efficiency for oxygen reduction than a bare Au electrode. Rotating disk electrode experiments were also performed and revealed that the catalytic reduction of oxygen on AuNPs deposited on <TEX>$SiMo_{12}O^{4-}_{40}$</TEX>-modified GC electrodes is a two-electron process.

Electrocatalytic Behavior of Glassy Carbon Electrodes Modified with Multiwalled Carbon Nanotubes and Cobalt Phthalocyanine for Selective Analysis of Dopamine in Presence of Ascorbic Acid

AbstractThis work describes the development, electrochemical characterization and utilization of a cobalt phthalocyanine modified carbon nanotube electrode for the quantitative determination of dopamine in 0.2 mol L−1 phosphate buffer contaminated with high concentration of ascorbic acid. The electrode surface was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy which showed a modified surface presenting a charge transfer resistance of 500 Ω, against the 16.46 kΩ value found for the bare glassy carbon surface. A pseudo rate constant value of 5.4×10−4 cm s−1 for dopamine oxidation was calculated. Voltammetric experiments showed a shift of the peak potential of DA oxidation to less positive value at 390 mV as compared with that of a bare GC electrode at 570 mV. The electrochemical determination of dopamine, in presence of ascorbic acid in concentrations up to 0.1 mol L−1 by differential pulse voltammetry, yielded a detection limit as low as 2.56×10−7 mol L−1.

Fabrication and characterization of SERS‐active silver clusters on glassy carbon

AbstractIn this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4‐aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS‐based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80–100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 × 104 relative to silver colloid, which might have resulted from the presence of ‘hot‐spots’ at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 × 107 by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface. SERS‐based Raman mapping technique in the form of line scanning further illustrates the good SERS activity and reproducibility on the silver clusters. Finally, 4‐mercaptopyridine (4‐Mpy) was chosen as an analyte and the lowest detected concentration was investigated by the SERS‐active silver clusters. A concentration of 1.6 × 10−10 M 4‐Mpy could be detected with the SERS‐active silver clusters, showing the great potential of the technique in practical applications of microanalysis with high sensitivity. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Trace analysis at a mercaptoacetic acid‐modified electrode

AbstractThe strong chelating ability of mercaptoacetic acid for certain metal ions is exploited for a new kind of voltammetric sensor. Specifically, a glassy carbon electrode (GCE) surface was covalently covered by mercaptoacetic acid. The preparation of mercaptoacetic acid‐modified glassy carbon electrode (MMGCE) under various conditions is explored. The electrodes so formed were able to chemically collect metal ions such as mercuric ions and yielded a 10‐fold greater voltammetric response than a bare glassy carbon surface. The response was characterized with respect to pH, preconcentration time, mercury(II) concentration, and other variables. For 3 minute preconcentration, the electrode gives good linearity for 1 × 10−8 mol/L to 1 × 10−9 mol/L mercuiy(II). The response can be reproduced with a 7.7% relative standard deviation. A range of analytical methods, including electrochemical, electron spectroscopy for chemical analvsis (ESCA) techniques, and alternating current (AC) polarography has been used to characterize these novel modified dectrpdes. The reaction of MMGCE to mercury ion is produced by weak adsorption.

Comparative evaluation of electrodeposition of polypyrrole on lead-dioxide-coated glassy carbon and of lead dioxide on polypyrrole-coated glassy carbon electrodes

Electrodeposition of lead dioxide and polypyrrole on glassy carbon, of lead dioxide on polypyrrole-coated glassy carbon, and of polypyrrole on lead-dioxide-coated glassy carbon electrodes was carried out by a potentiodynamic method. The morphological features of each phase were studied using scanning electron microscopy (SEM). The electrochemical activity of the phase was evaluated using cyclic voltammetry. It was found that polypyrrole-coated glassy carbon is relatively less active than lead-dioxide-coated glassy carbon electrodes with regard to further deposition on these surfaces. SEM and cyclic voltammetric studies reveal that polypyrrole growth takes place uniformly on both lead dioxide nuclei and bare glassy carbon surfaces in the case of lead-dioxide-coated glassy carbon electrodes. However, electrodeposition of lead dioxide on polypyrrole-coated glassy carbon proceeds only on active polypyrrole hemispheres, although a substantial portion of the bare glassy carbon substrate is still available for deposition. The exclusion of the bare glassy carbon surface from further deposition of lead dioxide on polypyrrole-coated glassy carbon electrode may be due to the initial growth of an invisible passive two-dimensional polypyrrole layer.

Electrochemistry at modified electrodes: Electronically conductive metallophthalocyanine coatings

The electrochemical oxidations of hydroquinone aand catechol have been studied by cyclic voltammetry at glassy carbon electrodes coated with electropolymerized films of metal phthalocyanines. Under all conditions employed, the voltammetric response seen at the polymer-modified electrode is considerably more Nernstian than that observed at a bare glassy carbon surface. For these systems, it can be estimated that the presence of the polymer coating leads to an enhancement of the heterogeneous electron transfer rate constant of two to three orders of magnitude. Similar improvement of the electrode kinetics is observed in the electrochemical reduction of Mn 2(CO) 10 in acetonitrile, demonstrating that the use of these metallophthalocyanine films is not restricted to aqueous electrolytes. Perhaps more importantly, it also suggests that such materials can be utilized for the electrocatalysis of cathodic as well as anodic processes. In view of the extremely wide range of applied potential over which these polymers remain conductive (>2.5 V), a wide variety of applications can be envisioned.