Polycrystalline Gold Electrode Research Articles

Voltammetric Study of Tin Electrodeposition on Polycrystalline Gold from Sulfuric and Methanesulfonic Acid

In this work, we have studied tin electrodeposition on polycrystalline gold electrodes from two different supporting electrolytes: sulfuric acid (SA) and methanesulfonic acid (MSA), both of them commonly used in the industry. This work aims to understand the effect of the different electrolyte anions on the deposition process. We show at least three different tin deposition mechanisms on gold: irreversible adsorption, underpotential deposition, and overpotential (bulk) deposition. Underpotential deposition leads to the formation of a layer of tin in SA and MSA with a coverage around ML (monolayer) and ML, respectively. The UPD Sn layer is however somewhat uncharacteristic as it is associated with island formation and surface alloying. Cyclic voltammograms in an extended potential range showed five distinct peaks: two cathodic peaks associated with tin underpotential and overpotential deposition, and three main anodic peaks, corresponding to the oxidation of the bulk Sn, of the AuSn intermetallic layer, and of the adsorbed Sn(II) to Sn(IV). Both voltammetric and rotating disk electrode measurements show that the kinetics of tin electrodeposition in MSA is slower than in SA, which we ascribe to Sn-MSA complex formation in solution. Slow Sn deposition in MSA promotes AuSn formation, in contrast to SA in which bulk tin deposition is more prominent. Complete Levich-type mass transport control of tin deposition in SA and MSA was only reached at low scan rate due to concurrent HER on the uncovered gold surface during the deposition process at higher scan rates. An unexpected surface-confined passivation process is observed in both electrolytes.

Revisiting the factors influencing gold electrodes prepared using cyclic voltammetry

Gold is widely used as the electrode material in different chemi- and biosensing applications while cyclic voltammetry (CV) in sulfuric acid solutions is a commonly employed method for gold surface preparation and characterization. However, as shown herein, chloride leakage from the Ag/AgCl/sat. KCl reference electrode and platinum dissolution from the platinum counter electrode can severely compromise the reproducibility and hence the reliability of the prepared gold electrodes. The aim of this work is to obtain a comprehensive understanding of the separate and interdependent effects of the aforementioned factors on the voltammetric behavior of microfabricated polycrystalline gold electrodes. It is shown that the leakage of chloride gives rise to etching of both the gold working and the platinum counter electrodes and that the chloride concentration has a strong influence on the ratio between the obtained gold and platinum concentrations in the electrolyte. The dissolved gold and platinum are then re-deposited on the gold electrode on the cathodic voltammetric scan, changing the structure and properties of the electrode. It is also demonstrated that the changes in the properties of the gold electrode are determined by the ratio between the co-deposited platinum and gold rather than the absolute amount of platinum deposited on the gold electrode. In addition, the chloride and sulfate adsorption behavior on the gold electrode is carefully investigated. It is proposed that redox peaks due to the formation of the corresponding Au(I) complexes can be seen in the double layer region of the voltammogram. The results show that the chloride leakage from the reference electrode needs to be carefully controlled and that platinum counter electrodes should be avoided when developing gold sensing electrodes. The present comprehensive understanding of the electrochemical performance of gold electrodes prepared using CV should be of significant importance in conjunction with both fundamental investigations and practical applications.

Nickel Oxide Nanoparticles Modified Gold Electrode for Fractional Determination of Dopamine and Ascorbic Acid

Dopamine and ascorbic acid has been fractionally determined at nickel oxide nanoparticles (nano-NiOx) modified polycrystalline gold electrode (poly-Au), nano-NiOx/Au, with high selectivity using voltammetric techniques. Nano-NiOx/Au electrode, fabricated electrochemically, could resolve the overlapping obtained at the bare poly-Au electrode. Nano-NiOx/Au electrode was prepared by cycling of potential of Au electrode in diluted Watts bath in the potential range between 0.0 and –1.0 V vs. Ag/AgCl (KCl sat.), and was characterized morphologically and electrochemically. Effect of loading level of nickel was examined by changing the number of potential cycles for the deposition of nickel nanoparticles, i.e., 1, 2 and 5 potential cycles were used. Also the effects of the electrooxidation of the thus deposited nickel nanoparticles and pH of the electrolyte on the voltammetric behavior were investigated. The good calibration curve of an acceptable rectilinear range is obtained at nano-NiOx/Au electrode in which nano-Ni was prepared by two potential cycles and subsequently electro-oxidized in KOH solution.

Tuning the Hydrogen Evolution Reaction on Metals by Lithium Salt

Tuning the electrode–electrolyte interfaces transiently for controlling the kinetics of hydrogen evolution reaction (HER) on metals will be highly intriguing in energetics. Here, the inherent HER activities of polycrystalline platinum (Pt) and gold (Au) electrodes are altered by different lithium salts. The HER activity of Pt is shown to be suppressed by increasing the Li+ ion concentration while inverse effect is observed in Au, and this is verified in different pH (2–13) conditions and also with different counterions (Li+, Na+, ClO4–, Cl–, and bis(trifluoromethanesulfonyl)imide) ion. A mechanistic insight is provided for this observed phenomenon, which has paramount importance in other electrocatalytic processes as well, such as carbon dioxide reduction and nitrogen reduction reactions.

Influence of argon ion beam etching and thermal treatment on polycrystalline and single crystal gold electrodes Au(100) and Au(111)

The effect of argon ion beam etching and subsequent annealing on the surface morphology and electrochemical response of poly- and monocrystalline gold electrodes was studied with the help of scanning electron microscopy, cyclic voltammetry and measurements of under-potential deposition of lead. While the samples were cleaned and restructured by the argon ion beam the following thermal treatment produced stable and very smooth highly ordered surfaces. The specific behaviour of polycrystalline and monocrystalline gold surfaces is discussed.

Synergistic electrocatalytic effect of Pd and Rh nanoislands co-deposited on Au(poly) on HER in alkaline solution

Hydrogen evolution reaction (HER) was explored on tri-metallic Rh@Pd/Au(poly) and bimetallic Pd/Au(poly) and Rh/Au(poly) electrodes in alkaline solution. Electrodes were prepared by the spontaneous deposition of either Pd or Rh and by co-deposition of both Rh and Pd on polycrystalline gold electrode. Characterization of modified electrodes was performed by cyclic voltammetry in alkaline solution, while additional information about phase analysis, chemical composition and surface morphology of tri-metallic Rh@Pd/Au(poly) electrode were acquired using X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and atomic force microscopy. Investigations of HER catalysis have shown that the activity of tri-metallic Rh@Pd/Au(poly) electrode exceeds the activities of both Pd/Au(poly) and Rh/Au(poly) electrodes, meaning that the synergism between co-deposited Pd and Rh islands is achieved. Moreover, Rh@Pd/Au(poly) electrode showed significant approach to the activities of bulk Pd and Rh electrodes for HER, especially when taking into account low activity of bare Au substrate. Synergistic effect of co-deposited Pd and Rh islands is a consequence of the strong electronic interaction between three metals in a close contact, which promotes the activity for HER by lowering the adsorption energy of Hads intermediate.

Impact of the protein myristoylation on the structure of a model cell membrane in a protein bound state

The neuronal calcium sensor protein recoverin is expressed in retinal rod and cone cells and is involved in the calcium-dependent control of receptor (rhodopsin) phosphorylation and receptor inactivation. In its Ca2+-saturated form recoverin is attached to membranes by an exposed myristoyl group and responds to oscillating changes of intracellular Ca2+-concentration by performing a so-called Ca2+-myristoyl switch. In this work we analyze changes in a liquid lipid bilayer interacting with myristoylated and non-myristoylated recoverin by employing polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) with electrochemical control. The lipid bilayer is transferred onto a polycrystalline gold electrode using Langmuir-Blodgett Langmuir-Schaefer transfer at the surface pressure π = 30 mN m−1 which ensures, necessary for the lipid-protein interaction, liquid state of the hydrocarbon chains of phospholipids. The model lipid bilayers are adsorbed directly on the Au electrode surface at transmembrane potentials −0.2 < ∆ϕM|S < 0.25 V. The interaction with recoverin leads to a stabilization of the adsorbed state of the lipid bilayer at positive transmembrane potentials. The interaction leads to a decrease in the surface charge density that accumulates on the membrane covered electrode surface, indicating changes in the lateral interactions in the lipid membrane. In situ spectroelectrochemical studies confirm orientation changes in the hydrophobic environment of the model membrane. Insertion of the myristoyl group of recoverin into the membrane is connected with an increase in the tilt of the hydrocarbon chains with respect to the surface normal and decrease in the bilayer thickness. Potential-induced pore formation and desorption of the lipid bilayer from the membrane surface is accompanied by the removal of the acyl chains of recoverin from the membrane.

Potential-induced phase transition of benzoxazole-2-thiol, naphthaleneoxazole-2-thiol and anthraceneoxazole-2-thiol monolayers on gold electrodes

In the present work we report the electrochemical characterization of self-assembled monolayers (SAMs) of N,O-heteroaromatic thiols, namely benzoxazole-2-thiol (1), naphthaleneoxazole-2-thiol (2) and anthraceneoxazole-2-thiol (3) on polycrystalline gold electrodes. SAMs were formed by immersion of pre-treated gold electrodes into ethanolic solutions of the title compounds. The modified electrodes exhibited a decrease of electroactivity, as found by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), in comparison to bare electrodes according to the length of the aromatic π-system. In addition, reductive desorption experiments confirmed that of the three compounds, 3 formed the most stable SAMs in agreement with EIS measurements which revealed better blocking properties against the redox couple in a test electrolyte indicating a charge transfer determined behaviour in the case of longer molecules. The charge transfer resistances revealed a trend towards higher resistances in the case of 3. When performing EIS at various starting potentials and different electrolyte concentrations, it was found that at certain critical potentials (Ecrit) a potential-induced structural change of the SAM occurred, with Ecrit(1) > Ecrit(2) > Ecrit(3). In the case of SAMs of 3 the nature of this alteration was investigated via scanning tunnelling microscopy and found to presumably be caused by an order-disorder-transition.

Adsorption Kinetics of WS2 Quantum Dots onto a Polycrystalline Gold Surface.

In this work, we report the adsorption kinetics of electrochemically synthesized WS2 quantum dots (QDs) (ca. 3 nm) onto a polycrystalline gold electrode. The Langmuir adsorption isotherm approach was employed to explore the temperature and adsorbate concentration dependence of the experimentally calculated equilibrium constant of adsorption ( Keq) and the free energy for adsorption (Δ Gads). Subsequently, we extract other thermodynamic parameters, such as adsorption rate constant ( Kads), desorption rate constant ( Kd), the enthalpy of adsorption (Δ Hads), and the entropy of adsorption (Δ Sads). Our findings indicate that Δ Gads is temperature-dependent and ca. -7.64 ± 0.6 kJ/mol, Δ Hads = -43.72 ± 1.7 kJ/mol, and Δ Sads = -0.126 ± 0.017 kJ/(mol K). These investigations on the contribution of the enthalpic and entropic forces to the total free energy of this system underscore the role of entropic forces on the stability of the WS2 QDs monolayer and provide new thermodynamic insights into other transition-metal dichalcogenide quantum dot (TMDQD) monolayers as well.

Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface-Enhanced Raman Spectroscopy

Development of a reproducible two-dimensional array of gold nanoparticles (AuNPs) through a guided assembly approach and sequentially using an electrochemical cleaning procedure to remove all cappi...

Electrochemical behavior of polycrystalline gold electrode modified by thiolated calix[4]arene and undecanethiol

The electrochemical behavior of polycrystalline gold electrode (PAuE) modified by self-assembled monolayers (SAMs) of thiolated calix[4]arene (C4A) and undecanethiol (C11) was investigated by voltammetric methods and electrochemical impedance spectroscopy.Coverage of the thiol SAMs and their stability was tested. The C11 layer is very stable; the desorption peak was recorded only in basic solutions of pH 12 and higher (at −1.30 V vs. Ag|AgCl (3 mol L−1 KCl)).The position of the C4A desorption peak is more pH dependent and it was recorded at −1.08 V at pH 13. Molecular coverage for C4A and C11 SAMs modified PAuE is 364 ± 52.9 μC cm−2 and 137 ± 20.0 μC cm−2 respectively.The properties of the PAuE modified by C11 and/or C4A were investigated using the model compounds hydroquinone, ferrocene and potassium ferrocyanide. It is assumed that the oxidation of the hydroquinone cannot be realized inside the C4A cavity because the hydroquinone molecule is too big to enter the cavity. Similar behavior was observed using potassium ferrocyanide.In contrast, cyclic voltammograms of ferrocene oxidation were only negligibly affected by the electrode modification. Moreover, capacitance measurements proved accumulation of ferrocenium ions at the C4A modified electrode.

Adsorption Kinetics and Thermodynamics of Hydroquinone onto a Polycrystalline Gold Electrode

The adsorption kinetics and thermodynamics of hydroquinone (QH2) onto a polycrystalline gold electrode surface in an unbuffered aqueous solution as a function of concentration have been investigated using cyclic voltammetry. The adsorption kinetics appeared to be kinetic control rather than diffusion control. The adsorption thermodynamics was represented by the Langmuir isotherm as the interaction parameter of the Frumkin isotherm was found to be 0.01, indicating small interaction between the adsorbate molecules. The saturation surface coverage was found to be 1.8 × 10−10 mol cm−2, which suggested that QH2 adsorbs on a polycrystalline gold electrode in horizontal orientation at the close packing state. The free energy of the adsorption was calculated to be –23 kJ mol−1, indicating moderate adsorption force.

Electrochemical Formation of Gold Nanoparticles on Polycrystalline Gold Electrodes during Prolonged Potential Cycling

AbstractThe voltammetric behavior of polycrystalline gold electrodes in 0.1 M sulfuric acid and the influence of prolonged repetitions of oxidation and reduction cycles at different scan rates on the surface morphology was studied. Slow (0.1 V s−1) as well as fast (1.0 V s−1) scan rates lead to an intense roughening of the electrode surface and the formation of a variety of different crystalline particles on it. These crystallites, their formation, and the influence of surface pretreatment were investigated with electrochemical methods, X‐ray diffraction measurements, and scanning electron microscopy. Additionally, an interpretation of the changing electrochemical signals of polycrystalline gold during prolonged potential cycling is given.

Design, Synthesis, and Use of Peptides Derived from Human Papillomavirus L1 Protein for the Modification of Gold Electrode Surfaces by Self-Assembled Monolayers.

In order to obtain gold electrode surfaces modified with Human Papillomavirus L1 protein (HPV L1)-derived peptides, two sequences, SPINNTKPHEAR and YIK, were chosen. Both have been recognized by means of sera from patients infected with HPV. The molecules, Fc-Ahx-SPINNTKPHEAR, Ac–C–Ahx-(Fc)KSPINNTKPHEAR, Ac–C–Ahx-SPINNTKPHEAR(Fc)K, C–Ahx–SPINNTKPHEAR, and (YIK)2–Ahx–C, were designed, synthesized, and characterized. Our results suggest that peptides derived from the SPINNTKPHEAR sequence, containing ferrocene and cysteine residues, are not stable and not adequate for electrode surface modification. The surface of polycrystalline gold electrodes was modified with the peptides C-Ahx-SPINNTKPHEAR or (YIK)2-Ahx-C through self-assembly. The modified polycrystalline gold electrodes were characterized via infrared spectroscopy and electrochemical measurements. The thermodynamic parameters, surface coverage factor, and medium pH effect were determined for these surfaces. The results indicate that surface modification depends on the peptide sequence (length, amino acid composition, polyvalence, etc.). The influence of antipeptide antibodies on the voltammetric response of the modified electrode was evaluated by comparing results obtained with pre-immune and post-immune serum samples.

Electrochemical and SEIRAS studies of urea and biuret adsorption on polycrystalline gold

The potential dependent adsorption of urea and its self-condensation product, biuret, have been studied on polycrystalline gold electrodes using electrochemical and in situ infrared spectroscopy. Voltammetry reveals that biuret displays a wider double-layer region compared to its parent compound and can only be oxidized at potentials that overlap with Au oxidation. Chronocoulometric measurements indicate that the adsorption of biuret is stronger than that of urea and the surface coverage is potential dependent. Surface enhanced infrared absorption spectroscopy (SEIRAS) experiments have been performed on both urea and biuret adsorption from neutral solutions made from heavy water. Urea provides low intensity IR signals consistent with relatively weak adsorption over a very restricted potential domain whereas biuret is spectroscopically much more pronounced. Analysis of the SEIRAS results support at least two distinct configurations of adsorbed biuret involving oxygen coordination to the metal surface. At the limit of the positive potentials studied spectroscopic evidence of the adsorption of partially oxidized biuret (ureayl-type species) is provided.

Electrochemical Impedance Spectrocopy Study Of Glucose Adsorption On Gold Nanoparticles-Graphite Paste Electrode

ABSTRACTElectrochemical Impedance Spectroscopy (EIS), is a confirmed tool for investigation of electrode/electrolyte interfaces and surface-modified electrodes. In the present work, we apply this approaching way to obtain a deeper insight into the electrochemical oxidation mechanism of the glucose in alkaline media. We studied the EIS response of gold nanoparticles embedded in carbon paste and use it as an electrode for the electro-oxidation of glucose. The results were compared with those of a polycrystalline gold electrode. In order to determine the polarization potentials for EIS tests, cyclic voltammetry is first conducted in 0.3 M KOH with 10 mM glucose, recorded at a scan rate of 1 mVs-1. Three polarization potentials were chosen, corresponding to: the open circuit potential (OCP), glucose oxidation and gold oxide formation respectively.

Broadband Sum-frequency Generation Spectroscopy Study of Electrochemical Surface Processes

As a second order nonlinear technique, sum-frequency generation (SFG) spectroscopy is forbidden, under the electric-dipole approximation, in the bulk of a medium with inversion symmetry and then generate only at the surface of such media where the symmetry is broken and appear to be highly surface-specific for interfaces between the centrosymmetric media. So far, many studies of electrochemical processes at various interfaces have been performed by using SFG, and molecular level insight like the molecular adsorption, orientation, packing, and dynamics has been obtained. We have developed broadband sum-frequency generation (BB-SFG) spectroscopy. It enables us to obtain information on in situ electrochemical systems. One of the electrochemical processes is the CO2 reduction on a polycrystalline copper and polycrystalline gold electrode. The antisymmetric C−H stretching modes of methyl group and antisymmetric C−H stretching modes of methylene group were observed on copper electrode surface, no adsorbed CO intermediate was observed. As for the process on gold electrode surface, the adsorbed CO was the main intermediate detected, and CO was observed at a relative high potential (-0.5V vs SCE). In addition, we present some other examples that investigate the electrochemical interface with SFG techniques, such as the potential-dependent nonresonant (NR) SFG. Figure 1 (a)(b) Potential-dependent BB-SFG spectra of 0.1M CO2-saturated NaHCO3 solution at poly-Cu electrode (C-H region) and poly-Au electrode (CO region). (c) Variations of the wavenumbers (black) and intensities (red) of the CO peak in (b) from the fitting data. Acknowledgement: This work was financially supported by NSFC (21327901 and 21621091). Figure 1

Phosphate-mediated electrochemical adsorption of cisplatin on gold electrodes

This manuscript reports the potential-dependent adsorption and deposition of cisplatin on polycrystalline gold electrode. It was found that this process is mediated by the adsorption of phosphate anions on the gold electrode and that the maximum coverage of Pt adsorbed is given by the maximum coverage of phosphate adsorbed at a given potential. The interaction of cisplatin with the phosphate groups was confirmed by in situ FTIR spectroscopy under external reflexion configuration. Quantitative analysis suggests that the stoichiometry of the phosphate species and the cisplatin adsorbed was 1:1. Moreover, the relationship between the charge of the Pt deposited and the charge of the electrochemical surface area of the Pt deposited on the gold electrodes indicates that 3D nanoclusters of a few atoms of Pt were formed over the gold electrode upon the electrochemical reduction of the adsorbed cisplatin.The Pt nanoclusters formed under these conditions were later evaluated for the oxidation of a monolayer of carbon monoxide. The Pt nanoclusters showed a high overpotential for the oxidation of the carbon monoxide monolayer and the high oxidation overpotential was attributed to the absence of adsorption sites for OH species on the Pt clusters: only at potentials where the OH species are adsorbed at the edge between the Pt nanocluster and the gold support, the oxidation of the carbon monoxide on the Pt nanoparticles takes place.

Large-Amplitude Fourier-Transformed AC Voltammetric Study of the Capacitive Electrochemical Behavior of the 1-Butyl-3-methylimidazolium Tetrafluoroborate–Polycrystalline Gold Electrode Interface

In this paper, the capacitive electrochemical behavior of the 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim BF4)–polycrystalline gold electrode interface is reported over the potential range from −0.37 to 0.53 V vs Fc/Fc+ (Fc = ferrocene). Experimental results are generated by analysis of data (RC model) obtained from large-amplitude Fourier-transformed alternating current voltammetry (FT-ACV) over the frequency range of 10 Hz to 1 kHz. Results suggest a parabolic, U-shaped capacitance versus potential relationship, in stark contrast to present ionic liquid (IL) electrochemical double-layer (EDL) theory. The potential range analyzed was carefully selected to be free of Faradaic current and displays minimal hysteresis with respect to the potential scan direction. Over the selected potential window spanning 0.9 V, the capacitance versus potential curve at 9 Hz exhibits a U-shape, with a capacitance minimum of 19.9 ± 1.3 μF cm–2 at 0.13 ± 0.04 V, flanked by maximum values of 21.2 ± 1.3 and 20.8 ± 1.4 μ...

Influence of Nafion on detection of glucose on a polycrystalline gold electrode from alkaline and saline solutions

The electrooxidation of glucose on a polycrystalline gold electrode from alkaline and saline solutions was investigated. The influence of Nafion on the oxidation of glucose under the same conditions was also studied. The presence of Nafion on the surface of a polycrystalline gold electrode decreased the rate of glucose oxidation in alkaline solution. The sensitivity of glucose determination was diminished. However, processes occurring at the electrode were clearly separated. Stable cyclic voltammogram of a polycrystalline gold electrode was obtained in saline solution. The addition of glucose to saline solution initiated the reaction of gold dissolution. The presence of Nafion on the electrode surface prevented the formation of hydrous gold oxide. The addition of glucose to saline solution led to the passivation of the Nafion-covered gold electrode. The gold electrode pretreated in alkaline solution and covered with Nafion was used for glucose detection in saline solution. The linear behavior was obtained in the concentration range from 2 to 10 mM with the slope of 0.0015 mA/mM and the coefficient of 0.95. The chronoampermetric response of the pretreated gold electrode covered with Nafion was also tested.