Comparative Electrochemical Behavior Research Articles

Insight into the electrochemical performance of heavy metal-free quantum dots in different buffered ferricyanide/ferrocyanide redox systems

The ferricyanide/ferrocyanide K3[Fe(CN)6]/K4[Fe(CN)6] redox couple is a widely utilized redox probe in electrochemistry. Buffering the K3[Fe(CN)6]/K4[Fe(CN)6] system has become one of the ways to generate improved electron transfer rates and stable electrochemical systems. In recent years, semiconductor quantum dots (QDs) have gained popularity as nanotags in electrochemical applications. Herein, we report on the comparative electrochemical behaviour of cadmium-free AuZnFeSeS quantum dots (QDs)-modified screen-printed carbon electrode (SPCE) in different buffered K3[Fe(CN)6]/K4[Fe(CN)6] electrolyte solutions using voltammetry and electrochemical impedance spectroscopy (EIS) techniques. Our results showed that the QDs/SPCE exhibited faster electron transfer rates, lower energy barrier and lower charge transfer resistance (Rct) in the studied buffered electrolyte solution.

Comparative electrochemical behavior of Prussian blue analogues as a host electrode for rare earth element recovery

In this paper, electrodeposited films belonging to the Prussian Blue Analogues (PBAs) family, namely, nickel-hexacyanoferrate (NiHCF) and copper-hexacyanoferrate (CuHCF), were employed as a host material for rare earth elements (REE), and the reported insertion/release study reveals a recovery capability for such valuable metals. The ion insertion/release was accomplished by adopting an electrochemically-driven process. A reversible intercalation was observed while considering both heavy and ligth rare earth elements. The amount of REEs inserted/released over the process and its kinetic evolution during the process were also studied by a chemometric approach. For CuHCF, it was seen that the intercalation of heavy rare earth elements occurs easily respect to the light ones, suggesting a possible selectivity among these ions.

Corrosion and Electrochemical Behavior of the Alloys of Ni-Re System Alloyed by Zirconium, Hafnium, Tungsten, and Palladium

The comparative corrosion resistance and electrochemical behavior in acidic, alkaline, and neutral media of both pure metals and the Ni-Re alloys doped with zirconium, hafnium, tungsten, and palladium were investigated. A positive effect of zirconium on the corrosion resistance of the Ni-Re alloy in all studied media was demonstrated. It is shown that the Ni-Re alloy doped with hafnium also improves corrosion resistance and compensates its reduction at the introduction to a tungsten alloy. It is shown that the Ni-Re alloy doped with zirconium together with palladium has the maximum corrosion resistance.

Towards a green and cost-effective synthesis of polyanionic cathodes: comparative electrochemical behaviour of LiFePO4/C, Li2FeP2O7/C and Li2FeSiO4/C synthesized using methylcellulose matrix

The polyanion cathodes for Li-ion batteries, namely LiFePO4, Li2FeP2O7 and Li2FeSiO4, were synthesized by very short high-temperature treatment (approximately several minutes) and subsequent quenching. Methylcellulose—a polymer with thermally driven water solubility—was used as the medium in which the precursor solutions were dispersed prior to high temperature treatment. The methylcellulose pyrolytically decomposes to carbon, thus producing the polyanion material/carbon composites of LiFePO4/C, Li2FeP2O7/C and Li2FeSiO4/C. The obtained powders have reduced crystallinity and significant microstructural characteristics: low crystallite size and notable microstrain. They exhibit stable electrochemical performances in both aqueous and organic electrolyte. The broadening of existing peaks in cyclic voltammetry and/or the emergence of new broad peaks was attributed to the presence of the amorphous phase in the samples. In galvanostatic charge–discharge tests, the materials provided high capacities at low current densities, while the highest rate performance was demonstrated by olivine-phosphate when compared to the other two materials.Graphical abstract

Comparative Electrochemical Behavior of Cytochrome c on Aqueous Solutions Containing Choline‐Based Room Temperature Ionic Liquids

AbstractIonic liquids have been attracting considerable interest in wide diverse fields, including biotechnology applications. Metalloproteins’ stability in such media is still a controversial subject. Divergent reports on the metalloproteins’ stability have been published, although hydrated ionic liquids seem more beneficial for achieving efficient redox transitions with the proteins’ redox centers. In the present study the electrochemical behavior of Cyt c in three choline‐based ionic liquids aqueous solutions, namely choline dehydrogenophosphate ([Ch][DHP]), choline 2‐(N‐morpholino)ethanesulfonic acid ([Ch][MES]) and choline 3‐(cyclohexylamino)‐1‐propanesulfonic acid ([Ch][CAPS]) was investigated. Cyt c formal potential and its temperature dependence, the diffusion coefficient and heterogeneous electron transfer rate were evaluated by cyclic voltammetry. The results show that Cyt c in aqueous solutions of [Ch][DHP] and [Ch][MES], retain its intrinsic redox properties.

A Comparative Electrochemical Behaviour Study of p-nitrophenol Using GC and Pt Electrode

<div><p><em>The work reports a comparative electrochemical behavior study of p-nitrophenol using GC and Pt electrode. For this purpose, Cyclic Voltammetry was employed, where the redox mechanisms could be compared for reduction processes of p-nitrophenol by analysis of the voltammetric responses. Voltammetric curves of p-nitrophenol in aqueous-methanol medium on different pH using B.R. buffer for various concentrations (0.05mM, 0.1 mM, 0.15mM, 0.2mM) and scan rates at GC and Pt electrode was obtained. The very complicated reduction of p-nitrophenol revealed three reduction peaks out of which two peaks are irreversible and one peak is reversible.</em></p><p>Equation 1</p><p>HOC<sub>6</sub>H<sub>4</sub>NO<sub>2 </sub>+ e<sup>-</sup> HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub><strong>∙<sup>-</sup></strong></p><p>Equation 2</p><p>HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub><strong>∙<sup>-</sup></strong> + HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub> HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub>H<strong><sup>. </sup></strong>+ <strong><sup>-</sup></strong>OC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub></p><p>Equation 3</p><p>HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub>H<strong><sup>.</sup></strong> + HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub><strong>∙<sup>-</sup></strong> HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub>H<strong><sup>-</sup> + </strong>HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub></p><p>Equation4</p><p>HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub>H<strong><sup>-</sup> + </strong>HOC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub> HOC<sub>6</sub>H<sub>4</sub>NO + <strong><sup>-</sup></strong>OC<sub>6</sub>H<sub>4</sub>NO<sub>2</sub> +H<sub>2</sub>O </p></div>The result obtained from GC electrode proved to be better than Pt electrode. Hence the GC electrode can be considered a suitable tool for determination of redox mechanism of p-nitrophenol.

Selective access to p-dialkyl-carbo-benzenes from a [6]pericyclynedione: the n-butyl nucleophile model for a metal switch study

The synthesis, spectroscopic properties, comparative electrochemical behavior in CHCl3 vs CH2Cl2, and X-ray crystal structure of p-di-n-butyl-tetraphenyl-carbo-benzene are described. The selectivity of preparation of the ultimate [6]pericyclynediol precursor has been examined by comparing the reactivity of the [6]pericyclynedione substrate with four n-Bu-MXn nucleophiles involving more or less halogenated metal centers MXn (0 ≤ n ≤ 2): Li, MgBr, MgCl, CeCl2/LiCl. The cerium reagent is found to be the most efficient, giving approximately twice the yield given by Grignard reagents in the target diadduct (90% vs 51%–53%). The dibutyl-carbo-benzene product happens to be soluble in both CHCl3 and CH2Cl2: cyclic voltammograms of either solution exhibit almost identical peak potentials with reduced reversibility of the redox processes in CHCl3.

Comparative Electrochemical Behavior of Proteins; Cytochrome c, Agaricus Bisporus Laccase, and Glucose Oxidase, Immobilized onto Gold-Thiol Self-Assembled Monolayer via Electrostatic, Covalent, and Covalent Coordinate Bond Methods

Comparative electrochemical behavior of three types of proteins; cytochrome c (Cyt c), Agaricus Bisporus laccase (LacAB) and glucose oxidase (GOx) immobilized on gold mercaptopropionic acid self-assembled monolayer via three different methods, including (a) covalent attachment by using EDC/NHS organic activators, (b) electrostatic interactions, and (c) covalent-coordinate binding by using Zr(IV) ion glue is investigated. Immobilization steps and electrochemical behavior of the immobilized proteins are traced by means of cyclic and differential pulse voltammetry (CV and DPV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results indicate that characteristics of the immobilized systems including; surface coverage, electrocatalytic activity and stability of the proteins are considerably affected by type of the bond formed between electrode and protein (the immobilization method), and nature of the protein. Immobilization via Zr(IV) ion resulted in higher activities for metalloproteins, i.e. Cytc with Heme active center and LacAB with T copper active center, while EDC/NHS method was more efficient for GOx having FAD cofactor. The experimental data will be presented and discussed from which the efficient immobilizing method for each case is introduced.

Preparation of titanium oxide and hydroxyapatite on Ti–6Al–4V alloy surface and electrochemical behaviour in bio-simulated fluid solution

In order to improve the bonding strength between hydroxyapatite (HA) coating and Ti–6Al–4V substrate, a uniform titanium oxide film was obtained by controlled anodic oxidation. After that an alkaline treatment with NaOH solution was used to make them more bioactive. Finally hydroxyapatite coating has been prepared on Ti–6Al–4V substrate through electrochemical deposition. Comparative electrochemical behaviour of untreated and surface modified Ti–6Al–4V alloy, in bio-simulated fluid solution was investigated by electrochemical techniques. SEM was used to observe the morphology of modified surfaces and the thicknesses of the oxide films prepared were evaluated on the cross-sections of the samples using SEM–FIB.

A Comparative Electrochemical Behaviour Study and Analytical Detection of the p-Nitrophenol Using Silver Solid Amalgam, Mercury, and Silver Electrodes

This work reports a comparative electrochemical behaviour study and p-nitrophenol analytical detection using silver solid amalgam, hanging dropping mercury, and silver electrodes. For this, square wave voltammetry was employed, where the analytical responses and the redox mechanisms could be compared for reduction processes of 4-nitrophenol by analysis of the voltammetric responses. The analytical performance of the electrode was evaluated and detection and quantification limits, recovery percentages, repeatability, and reproducibility for the silver solid amalgam and hanging dropping mercury electrodes presented similar values; the results presented for the silver electrode indicated worse analytical parameters than the other electrodes. The results indicate that the silver solid amalgam electrode can be considered a suitable tool and an interesting alternative for the analytical determination of 4-nitrophenol, as well as for the determination of other biological and environmentally interesting compounds that present analytical responses on mercury surfaces.

Comparative electrochemical study of new self-assembled monolayers of 2-{[(Z)-1-(3-furyl)methylidene]amino}-1-benzenethiol and 2-{[(2-sulfanylphenyl)imino]methyl}phenol for determination of dopamine in the presence of high concentration of ascorbic acid and uric acid

The comparative electrochemical behavior of self-assembled monolayers of two Schiff's bases, 2-{[(Z)-1-(3-furyl)methylidene]amino}-1-benzenethiol (FMAB) and 2-{[(2-sulfanylphenyl)imino]methyl}phenol (SIMP) on a bare gold electrode (Au FMAB SAM-modified electrode and Au SIMP SAM-modified electrode, respectively), was investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy in a 0.1 mol L(-1) KCl solution that contains 5.0 × 10(-3) mol L(-1) [Fe(CN)(6)](3-/4-). The results revealed that the modified electrodes showed an electrocatalytic activity toward the anodic oxidation of dopamine by a marked enhancement in the current response and lower overpotential (60 and 90 mV for the Au FMAB and Au SIMP SAM-modified electrodes, respectively) in phosphate buffer solution at pH 6.0. The Au SIMP SAM-modified electrode was applied successfully to the determination of dopamine in the presence of a high concentration of ascorbic acid. Selective detection was realized in total elimination of ascorbic acid response-a method different from the ones based on the potential separations. The detection limit of dopamine was 5.0 × 10(-8) mol L(-1) in a linear range from 1.0 × 10(-6) to 1.2 × 10(-4) mol L(-1) in the presence of 1.0 × 10(-3) mol L(-1) ascorbic acid. The interference studies also showed that the Au SIMP SAM-modified electrode exhibited good selectivity in the presence of a large excess of uric acid and could be employed for the determination of dopamine in pharmaceutical formulations, plasma samples and human urine with adequate selectivity and precision.

Preparation, Characterization and Application of Modified Surfaces with 3,5‐Bis(3,5‐dinitrobenzoyl‐amino) benzoic acid

AbstractSummary: The spontaneous adsorption of the dendron 3,5‐Bis (3,5‐dinitrobenzoylamino) benzoic acid (D‐NO2) onto gold and carbon electrodes produced conductive surfaces with electroactive chemical functions. A comparative electrochemical behavior of both electrodes after dendron immobilization led us to conclude that the self‐assembly of D‐NO2 on carbon is faster and stronger. Considering this advantage, the surface of magnetic maghemite nanoparticles (MNPs) was modified using D‐NO2. Firstly, MNPs were modified with APS as silane coupling agent and afterwards, D‐NO2 was covalently attached to the surface, achieving nitro‐functionalized MNPs. Subsequently, the immobilization of these modified MNPs onto glassy carbon surfaces was explored to generate a novel platform promising for biosensors development.

Comparative electrochemical behavior of glucose oxidase covalently immobilized on mono-, di- and tetra-carboxylic acid functional Au-thiol SAMs via anhydride-derivatization route

Comparative electrochemical study of glucose oxidase (GOx) immobilized on gold electrodes modified by three types of mercaptocarboxylic acid self-assembled monolayers (SAMs), including 3-mercaptopropionic acid (MPA), 3-mercaptosuccinic acid (MSA), and thiodisuccinic acid (TDSA), is reported. GOx was immobilized on SAMs via anhydride route to prepare (Au-MPA-GOx), (Au-MSA-GOx), and (Au-TDSA-GOx) biosensors. Steps of formation and analytical performance of the prepared biosensors were traced by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). While partial surface coverage ( θ) of gold by thiols showed the following order Au-MPA( θ = 36%) > Au-MSA( θ = 30%) > Au-TDSA( θ = 24%), inverse effect was observed for slopes (activities) of the calibration curves for glucose determination as Au-MPA-GOx < Au-MSA-GOx < Au-TDSA-GOx. This matter was explained based on advantages of multi-branch carboxylic acids (i.e. TDSA) allowing immobilization of more enzymes even with less surface coverage (24%) by thiols. Data obtained by CA and EIS methods for the entire of the study were in good agreement.

An electrochemical comparison of manganese dioxide microparticles versus α and β manganese dioxide nanorods: mechanistic and electrocatalytic behaviour

The comparative electrochemical behaviour of both α- and β-nanorods of manganese dioxide (MnO2) and microparticles of predominantly β-phase manganese dioxide is investigated at pHs close to neutral. In order to understand the observed voltammetric behaviour of all three materials the mechanisms of electrodeposition of MnO2 onto a graphite electrode surface from a solution of Mn(II) at pH 3–7 is also reported. It is proposed that two competing mechanistic pathways operate, both invoking MnOOH as an intermediate species, which are an ECE or a DISP process, respectively. At low pH values (<pH 3) the mechanism likely proceeds via a DISP mechanism whereas at high pHs (pH ∼ 7) the mechanism proceeds predominantly as an ECE process with the diffusion of protons out of the MnOOH intermediate being the likely rate determining step. The α- and β-MnO2nanorods display a ca. 30 mV difference in the observed reduction potentials corresponding to a ca. 3 kJ mol−1 difference in the Gibb’s energy between the two phases. There is also an observable difference in the reduction potential of the β-nanorods and β-microparticles, which probably reflects the differing surface or structural energies of the two materials. Finally the electrocatalytic performance of the three MnO2 materials with respect to the analytical determination of hydrogen peroxide is investigated. Both phases of the MnO2nanorods exhibited a lower limit of detection (5.0 ± 2.5 μM based on 3σ) and greater sensitivity towards H2O2 than the MnO2 microparticles, likely attributed to an increased surface area.

Comparative electrochemical study of self-assembled monolayers of 2-mercaptobenzoxazole, 2-mercaptobenzothiazole, and 2-mercaptobenzimidazole formed on polycrystalline gold electrode

Abstract Comparative electrochemical behavior of self-assembled monolayers (SAMs) of three heteroaromatic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole (MBI) are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the electrode/solution interface are considerably and differently affected by thiols constructing the SAMs. The consumed charges for reductive desorption of SAMs, which is criterion for the amount of chemically adsorbed thiol, are significantly different for these three SAMs, specially for MBT, implying that SAM of MBT is formed through both sulfur atoms; the thiol sulfur and skeleton sulfur of the thiazole ring. Desorption potentials of the SAMs have shown the following order for strength of gold–sulfur bond: MBT > MBO > MBI. Activity of the three SAMs as pH-sensitive interfaces was also investigated and their surface-p K a values derived from the EIS measurements showed this order for acidic strength of SAMs: MBO > MBT > MBI. This is the same order expected due to the difference in electronegativity of the O, S, and N heteroatoms, and confirms that the most electron-rich ring imidazole is attached to the benzene ring of MBI. A comparison of the interfacial charge transfer resistance variation as a function of gold immersion time in thiols solution reveals that kinetics of Au–MBT assembly is different from those of two others and confirms formation of Au–MBT SAM via both sulfur atoms of MBT.

First comparative reaction mechanisms of β-estradiol and selected environmental hormones in a redox environment

This work describes the first comparative electrochemical behavior of β-estradiol and selected important environmental hormones, specifically alkylphenols (APs). Most of the concerns about environmental hormones in humans center on their interference with estrogens, an ovarian steroid. APs are believed to have high affinity for biological receptors by generating conformational changes that can be detected by other macromolecules. However, no mechanistic or molecular evidence has been established for these studies. Here we show, an electrochemical mechanism of estradiol and selected APs including bisphenol-A (BPA), nonylphenol (NP), and diethylstilbestrol (DES) using cyclic voltammetry (CV), rotating disk electrode (RDE) and controlled potential coulometry (CPC). We observed a striking similarity in the electrochemistry of these synthetic xenobiotics and estradiol, a natural estrogen. The complete reaction mechanisms for the oxidation of NP, DES and estradiol were found to follow EC–EC scheme. Unlike most aromatic hydroxy phenols, our results showed that using bulk electrolysis with CPC, both estradiol and DES generated a ketone and quinone intermediate products, respectively. These products were isolated and confirmed using mass spectrometry. This study may provide insights into the origin of the in vivo molecular recognition since there is little steric or electronic hindrance expected at reactor sites between the APs and estradiol.

Comparative electrochemical behaviour of biotin hydrazide and photobiotin. Importance in the development of biosensors

The cyclic voltammetric behaviour of biotin hydrazide and photobiotin on carbon paste electrodes has been studied. Biotin hydrazide presents an anodic and irreversible process, meanwhile photobiotin presents two, adsorptive in nature. This characteristic makes photobiotin desirable for following the interaction between biotin and streptavidin, being possible to detect a streptavidin concentration of 10 −12 M. The evidence of this reaction has been shown either directly in solution or on the electrode surface. Photobiotin as the molecule portable of analytical information and carbon paste as the solid support could be applied to the development of sensors based on the oxidation of this molecule.

Part I. A comparative electrochemical study of transition metal substituted Dawson type heteropolyanions

The comparative electrochemical behaviour, in aqueous solutions, of the Dawson lacunary anion [P2W17O61]10− and of the FeIII, CuII, CoII, NiII, MnIII and MnII substituted Dawson lacunary heteropolyanions is presented. The literature concerning the latter heteropolyanions has been reviewed and completely new data are presented. The electrochemical behaviour observed for the reduction of the tungsten oxo centres, for all the heteropolyanions investigated, was found to be pH dependent. Electrochemical evidence for the presence of the FeIII, CuII, CoII and the MnII and MnIII cations in the ejected tungsten position was obtained with the NiII cation processing no electroactivity.

Comparative electrochemical behaviour of CO2 on Pt and Rh electrodes in acid solution

The electroformation of adsorbed species on Pt and Rh from CO2 dissolved in aqueous 0.5 M H2SO4 and the influence of adsorbed species on the hydrogen evolution reaction (HER) were examined for smooth and columnar structured Pt and smooth and rhodized Rh electrodes at 25|dgC. Different electrosorbed species resulting from the adsorption of CO2 on Rh were found. The electro-oxidation of these adsorbates on Rh takes place over a potential range larger than that for adsorbates on Pt, overlapping the potential range of electroformation of the O-containing layer. A part of the reduced CO2 adsorbates on Rh behaves as CO-like adsorbates. The presence of adsorbed species from CO2 influences differently the stationary HER current potential curves for both types of Pt and Rh electrodes. In the range of low current density (cd), the Tafel slope for Pt is −0.030 V decade−1. Conversely, the presence of a chemisorbed species on Rh changes the Tafel slope for the HER in the range of low cd from −0.030 V decade−1 for CO2-free solutions to −0.120 V decade−1 for CO2-saturated solution. These changes are explained by a modification in the rate-determining step of the HER produced by chemisorbed species.

Comparative electrochemical behaviour of the cis and trans azocyclohexanes

Comparative electrochemical behaviour of the cis and trans azocyclohexanes