Investigation of the electrochemical behaviour of lead dioxide in aqueous sulfuric acid solutions by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO₂ layers in contact with sulfuric acid solutions of different concentrations (1.5–5.0 M) were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers were electrodeposited on gold substrate from aqueous solutions of Pb(NO₃)₂ dissolved in nitric acid. Based on the electrochemical and the mass change responses, it was found that in more concentrated solutions of H₂SO₄, the main reduction reaction was the transformation of lead dioxide to lead sulfate. However, in less concentrated sulfuric acid media, the transformation of lead dioxide to lead(II) ion became the main reaction. These Pb²⁺ ions transformed into lead sulfate crystals later by a chemical reaction. Because the electrochemical oxidation of lead sulfate is less favourable in sulfuric acid medium of higher concentrations, thus, PbO₂ layers cannot be tested by continuous cyclization, which is necessary to study their aging parameters. Therefore, a delay step before each cyclic voltammogram was applied while the non-conductive lead sulfate dissolves or alternatively, by applying a pre-oxidation step prior to each cyclic voltammetry experiment to produce electrochemically significant amount of lead dioxide which can be reduced during the following negative potential sweep.

     

Electrochemical Characteristics of 4‐oxo‐4H‐pyran‐dicarboxylic Acid (Chelidonic Acid) and some of its Metal Complexes

A few novel metal complexes of chelidonic acid (chelH₂), namely [Ca(chel)(H₂O)₃] ( 1 ), [Cu(chel)(H₂O)₅] ⋅ 2H₂O ( 2 ) and [VO(chel)(H₂O)₃] ⋅ 2H₂O ( 3 ) were prepared, identified by elemental analysis and characterized by electrochemical methods. IR‐spectra and thermal stability in solid state are discussed as well. The electrochemical characteristics of the free chelidonic acid and its complexes 1 – 3 were studied by (cyclic) square‐wave voltammetry, on static mercury drop electrode (SMDE) and paraffin‐impregnated graphite electrode (PIGE), in aqueous media over a wide pH range. The reduction of chelidonic acid on SMDE is a kinetically controlled electrode reaction, occurring with the transfer of one electron and two protons for 1<pH<6, whereas in very alkaline media the electron transfer is pH independent, i.e . the mechanism of electro‐reduction of chelH₂ is proposed. The experimental parameters of the electroanalytical procedure were optimized and the method was applied for the investigation of the metal ion coordination preferences toward chelidonic acid. For the direct determination of solid complexes 1 – 3 , SW voltammetry of microparticles was used.     

MWCNTs/metal (Ni, Co, Fe) oxide nanocomposite as potential material for supercapacitors application in acidic and neutral media

Supercapacitive properties of synthesised metal oxides nanoparticles (MO where M = Ni, Co, Fe) integrated with multi-wall carbon nanotubes (MWCNT) on basal plane pyrolytic graphite electrode (BPPGE) were investigated. Successful modification of the electrode with the MWCNT-MO nanocomposite was confirmed with spectroscopic and microscopic techniques. Supercapacitive properties of the modified electrodes in sulphuric acid (H₂SO₄) and sodium sulphate (Na₂SO₄) electrolytes were investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic constant current charge–discharge (CD) techniques. The specific capacitance values followed similar trend with that of the cyclic voltammetry and the electrochemical impedance experiments and are slightly lower than values obtained using the galvanostatic charge–discharge cycling. MWCNT-NiO-based electrode gave best specific capacitance of 433.8 mF?cm^?2 (ca 2,119 F?g^?1) in H₂SO₄. The electrode exhibited high electrochemical reproducibility with no significant changes over 1,000 cyclic voltammetry cycles.     

Studying the effects of bismuth on the electrochemical properties of lead dioxide layers by using the in situ EQCM technique

The charge-discharge characteristics and the aging mechanism of PbO₂ layers doped with bismuth in contact with sulfuric acid solutions were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers (non-doped and doped with Bi) were electrodeposited on gold substrate from aqueous solutions of Pb(NO₃)₂ dissolved in nitric acid and they were investigated in sulfuric acid media. Based on the electrochemical and the mass change responses, it is concluded that during the electrodeposition, bismuth influences the structure of the PbO₂ formed. Bi(III) also inhibits the oxidation of lead sulfate and affects the reduction kinetics of lead dioxide. During successive cyclization (aging), the presence of bismuth accelerates the hydration of PbO₂.

     

Amperometric determination of ascorbic acid on screen-printing ruthenium dioxide electrode

Ruthenium oxide (RuO₂) is commonly used in resistive pastes for screen printing. The electrochemical properties of a screen-printing planar RuO₂ electrode have hardly been studied. In this communication, planar electrochemical sensors with a RuO₂ working electrode, an Ag|AgCl reference electrode and a RuO₂ counter electrode are fabricated by screen printing. The electro-oxidation of ascorbic acid, uric acid, and hydrogen peroxide on these RuO₂ electrodes is investigated by means of cyclic voltammetry. Compared to uric acid and hydrogen peroxide, ascorbic acid can be easily oxidized at the low operating potential (<150 mV versus Ag|AgCl). The amperometric measurement of ascorbic acid at 100 mV on a RuO₂ electrode shows fast response and good linearity in the 0–4 mM range. Meanwhile, the electrochemical interference from uric acid and hydrogen peroxide at this potential is very small.     

Gold nanoparticle-modified glassy carbon electrode for electrochemical investigation of aliphatic di-carboxylic acids in aqueous media

The electrochemical reduction of di-carboxylic acids; oxalic, succinic, malic, and tartaric have been studied on the gold nanoparticles modified electrode in aqueous media solution of 0.1 M KCl. Gold nanoparticle (Au_NPs)-modified electrodes were prepared by the electrodeposition with cyclic voltammetric method onto glassy carbon electrode in acidic media. The surface morphology of the electrodeposited gold nanoparticles was examined by SEM. Also, the electrochemical properties of the prepared electrodes were investigated with different electrochemical techniques; cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Cyclic voltammetric, chronoamperometric, and electrochemical impedance spectroscopic techniques were used for investigating the electrochemical behavior of the particulate acids. The modification of the electrode with Au nanoparticles (Au_NPs) enables the appearance of cyclic voltammogram peaks completely clear and sharp for the acids under investigation in comparison with the poor behavior of them in absence of the modification. All acids undergo totally irreversible redox reaction in neutral and acid media. The cyclic voltammetric response of the investigated acids is sensitive to pH, as well as of the scan rate. Each acid has a different reduction peak position from the other acids depending on the structure of the acid undergo the electroreduction process. Further, the lowest unoccupied molecular orbital energies of the investigated acids have been theoretically evaluated and are compared with their electroreduction potential peaks.     

PEDOT‐Modified Microelectrodes. Preparation,Characterisation and Analytical Performances

Poly(3,4‐ethylenedioxythiophene) (PEDOT) modified microelectrodes were prepared by electropolymerisation of the relevant monomer from CH₃CN or H₂O solutions. The electrochemical behaviour of the obtained coatings was investigated by cyclic voltammetry in both organic and aqueous media. The anodic responses obtained for a typical benchmark analyte such as ascorbic acid was used to test the different coatings; calibration curves were built up in order to evaluate the repeatability of the response and the reproducibility of the prepared sensing system. Moreover, the ability of the modified microelectrodes to work in low conductivity media was studied, and exploratory tests in dense food matrix was performed.     

A Hydrogen Peroxide Sensor Based on Silver Nanoparticles Biosynthesized by Bacillus subtilis

In this study, silver nanoparticles （AgNPs） were biosynthesized by Bacillus subtilis and used to construct a nonenzymatic hydrogen peroxide （H202） sensor, Scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy confirmed that the AgNPs were prepared successfully with spherical morphol- ogy. The electrochemical properties of the resulted sensor were investigated by cyclic voltammetry, chronoam- perometry and electrochemical impedance spectroscopy. It was found that the sensor exhibited good electrocatalytic activity towards H202 reduction with a wider linear range from 0.05 to 120 mmol.L-1, a detection limit of 8 gmol.L-1 and a fast response time less than 2 s. The sensor exhibited good selectivity for H202 determination in the presence of glucose, acetaminophen, ascorbic acid and uric acid.     

A Study on the Electrochemical and Electrochemiluminescent Behavior of Homogentisic Acid at Carbon Electrodes

The electrochemical oxidation and electrochemiluminescent behavior of homogentisic acid (HGA) has been studied in aqueous solutions over a wide pH range by linear sweep voltammetry, cyclic voltammetry, chronocoulometry at a glassy carbon electrode, by controlled potential electrolysis at a large area spectroscopic graphite electrode, and by spectroelectrochemistry at an optically transparent drilled holes graphite (DHG) electrode in a thin‐layer cell. The studies reveal that the electrochemical oxidation of HGA at carbon electrodes is a reversible process involving two‐electron, two‐proton transfer. In addition to the electrochemical oxidation, the chemical oxidation of HGA by dissolved oxygen was investigated by spectroscopic method combined with voltammetry. It was revealed that HGA is fairly stable in strongly acidic media but readily oxidized by dissolved oxygen in alkaline media giving rise to 1,4‐benzoquinone‐2‐acetic acid, the same product as that of electrooxidation of HGA. This oxidation product is stable in acidic, neutral and weakly alkaline media, but can further degrade in strongly alkaline media yielding oxalate as the final product. The electrochemiluminescent mechanism of HGA in the presence of Ru(bpy)₃²⁺ at a glassy carbon electrode was also investigated in detail, based on which a sensitive ECL method for determination of HGA was developed, and the detection limit was 3.0×10^?8 mol L^?1.     

Electrochemical Studies of 1,4-Bis[2-(2-pyridyl)-vinyl] Benzene and 1,4-Bis[2-(4-pyridyl) vinyl] Benzene Laser Dyes via Cyclic Voltammetry, Convolutive Voltammetry and Digital Simulation Methods

Electrochemical properties of two diolefinic laser dyes namely 1,4-bis[2-(2-pyridyl)-vinyl] benzene (2PVB) and 1,4-bis[2-(4-pyridyl) vinyl] benzene (4PVB) have been investigated using cyclic voltammetry and convolutive voltammetry combined with digital simulation at a platinum electrode in 0.1 mol/L tetrabutyl ammonium perchlorate (TBAP) in the two different solvents acetonitrile (CH3CN) and dimethylformamide (DMF). The species were reduced via consumption of two sequential electrons to form radical anion and dianion. In switching the potential to positive direction, the two compounds were oxidized by loss of one electron, which was followed by a fast isomerisation process. The electrode reaction pathway and the electrochemical parameters of the investigated compounds were determined using cyclic voltammetry. The extracted electrochemical parameters were verified and confirmed via digital simulation and convolutive voltammetry methods.     

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L ‐cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, k_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10^?5 M–2.2×10^?3 M and 1.5×10^?5 M–3.2×10^?3 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10^?5 M and 1.4×10^?6 M by CV and DPV methods.     

Electropolymerization,characterization and corrosion protection evolution of poly(4-aminomethyl-5-hydroxymethyl-2-methylpyridine-3-ol) on steel and copper

The electrochemical synthesis of poly(4-aminomethyl-5-hydroxymethyl-2-methyl pyridine-3-ol) on steel and copper electrodes was achieved in both sulfuric acid and oxalic acid by cyclic voltammetry technique. Characterization of the polymer films were achieved by Fourier transforms infrared spectroscopy technique (FTIR) and scanning electron microscope (SEM). Corrosion performance of coatings was investigated in 0.1 M H₂SO₄ by potentiodynamic polarization and electrochemical impedance (EIS) spectroscopy techniques.     

Nickel,copper and manganese hexacyanoferrate with poly(3,4-ethylenedioxythiophene) hybrid film modified electrode for selectively determination of ascorbic acid

The NiHCF-PEDOT, CuHCF-PEDOT and MnHCF-PEDOT films were prepared on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry and characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) techniques. The advantages of these films are demonstrated for selectivity detection of ascorbic acid using cyclic voltammetry and amperometric method. Interestingly, the NiHCF-PEDOT and CuHCF-PEDOT modified electrodes exhibited a wide linear response range (5 × 10⁻⁶−3 × 10⁻⁴ M, R ² = 0.9973 and 1.8 × 10⁻³−1.8 × 10⁻² M, R ² = 0.9924). The electrochemical sensors facilitated the oxidation of AA but not responded to other electroactive biomolecules such as dopamine, uric acid, H₂O₂, glucose. The difference is MnHCF-PEDOT/GCE that no response to AA. In addition, the NiHCF-PEDOT and CuHCF-PEDOT modified electrodes exhibited a distinct advantage of simple preparation, specificity, stability and reproducibility.     

Electropolymerization of Mefenamic Acid on Copper and Copper Based Alloy as a New Strategy to Control the Release of Copper Ions from Copper Containing Devices

Poly-2-(2,3-dimethylanilino) benzoic acid (PMF) coatings on copper and brass alloy were synthesized by electrochemical oxidation of 2-(2,3-dimethylanilino) benzoic acid in the presence of oxalic acid as the reaction medium. Electrodeposition was carried out using the cyclic voltammetry technique using a silver/silver-chloride standard electrode, with a scan rate of 600 mV min^–1. Smooth and well adhered PMF coatings were electrosynthesized during sequential scanning of the potential in the range–500 mV to 1400 mV on copper and brass alloy. The electrodeposited coatings were characterized by recording the oxidation peaks at 122 mV for Cu and–0.7 mV for brass, in cyclic voltammetry and using scanning electron microscopy (SEM). Corrosion inhibition efficiency of coated copper and brass alloy was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The impedance results showed that the inhibition efficiency of coated copper is 89% and for coated brass 79.4% compared to the uncoated copper and brass in 0.1 M H₂SO₄.

     

Electrocatalytic Characteristics of Ferrocenecarboxylic Acid Modified Carbon Paste Electrode in the Oxidation and Determination of L‐Cysteine

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenecarboxylic acid modified carbon paste electrode (FCMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L ‐cysteine is occurs at a potential about 580 mV less positive than that an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and catalytic reaction rate constant, K′_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear calibration curves were obtained in the ranges of 10^?5 M–10^?3 M and 4.1×10^?8 M–3.7×10^?5 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (2δ) were determined as 2.4×10^?6 M and 2.5×10^?8 M by CV and DPV methods. This method was also examined for determination of L ‐cysteine in some samples, such as Soya protein powder, serum of human blood by using recovery and standard addition methods.     

Titanium Dioxide/Multi-walled Carbon Nanotubes Composite Modified Pencil Graphite Sensor for Sensitive Voltammetric Determination of Propranolol in Real Samples

A very effective electrochemical sensor for the analysis of propranolol was constructed using TiO₂/MWCNT film deposited on the pencil graphite electrode as modifier. The modified electrode represented excellent electrochemical properties such as fast response, high sensitivity and low detection limit. The proposed sensor showed an excellent selective response to propranolol in the presence of foreign species and other drugs. The electrochemical features of the modified electrode were investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) technique which indicated a decrease in resistance of the modified electrode versus bare PGE and MWCNT/PGE. The surface morphology for the modified electrode was determined by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT-IR). Differential pulse technique (DPV) was used to determine propranolol which showed a good analytical response in the linear range of 8.5×10⁻⁸-6.5×10⁻⁶ M with a limit of detection 2.1×10⁻⁸ M. The TiO₂/MWCNT/PGE sensor was conveniently applied for the measurement of propranolol in biological and pharmaceutical media.     

Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spec-troscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers(SAMs).A carboxylic acid-terminated thiol,such as thioctic acid(1,2-dithiolane-3-pentanoic acid),was self-assembled on gold electrodes.Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63-as a probe.The surface pka of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 ±0.1 and 5.8±0.1,respectively.The method is compared with other methods of monolayer pKa measurement.     

Facile Green Synthesis of NiO/NiCo2O4 Nanocomposite as an Efficient Electrochemical Platform for Determination of Dopamine

The synthesis of NiO/NiCo₂O₄ nanoparticles by an eco-friendly, fast, simple and cost-effective approach employing Urtica extract is reported in this study. The NiO/NiCo₂O₄ nanocomposite were characterized using VSM, FTIR, XRD, and SEM techniques. Moreover, to construct a modified carbon paste electrode, NiO/NiCo₂O₄ were employed and this sensor was used for dopamine (DA) detection. Using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques, the electrochemical behavior of dopamine at the NiO/NiCo₂O₄/CPE was investigated. Analysis of dopamine, with a limit of detection (LOD) equal to 0.04 μM, in the concentration range of 0.1–100.0 μM, was facilitated by NiO/NiCo₂O₄/CPE. Moreover, the satisfactory selectivity for DA determination in the presence of uric acid (UA) and ascorbic acid (AA), was obtained. The suggested new sensor displayed a good reproducibility, sensitivity, and stability for determination of DA in drug and biological samples.     

Electrochemical characterization of PANI-Nafion membranes and their electrocatalytic activity

PANI-Nafion^® membranes were prepared by a chemical method in which the faces of a commercial Nafion membrane were contacted with two acid solutions containing an oxidant (Fe³⁺) and aniline respectively. They were then characterized by a variety of electrochemical techniques (cyclic voltammetry, chronoamperometry, ac impedance). PANI was stored mostly in the vicinity of the Nafion face exposed to the oxidant. When this face was contacted with Hg and the other with electrolyte solutions, typical electrochemical responses of PANI were detected. Electrocatalytic reduction of O₂ and oxidation of N₂H₄ were achieved on PANI-Nafion electrodes and found to be only slightly slowed down with respect to ordinary PANI film electrodes, at variance with a fast process such as Fe³⁺ reduction, the rate of which was severely limited by diffusion through the membrane.