Differential pulse anodic stripping voltammetric determination of Hg2+ at poly(Eriochrome Black T)-modified carbon paste electrode

The electrochemical behavior of Hg²⁺ was investigated in poly(Eriochrome Black T)-modified carbon paste electrode (CPE) using cyclic voltammetry (CV). Poly(Eriochrome Black T) was prepared in an alkaline medium on the surface of the CPE using a solution of Eriochrome Black T with the CV technique. The electrochemical impedance study revealed a better charge transfer kinetics at the modified electrode. The effects of variation of the experimental conditions, such as the concentration of electrolytes, pH, deposition time, and the deposition potential, which maximize current efficiency were studied. The optimum response of Hg²⁺ was observed in 1.0 M KCl solution. The differential pulse anodic stripping voltammetric technique was employed successfully to detect Hg²⁺, which gave a good linear response at low concentration levels of Hg²⁺. The detection limit was found to be 2.2?×?10^?10 M (S/N?=?3), which is comparable with that achieved in multiwall carbon nanotube-modified electrode. The remarkable electroanalytical performance of the modified electrode makes it amenable to employ it successfully as an electrochemical sensor for the determination of hazardous pollutant Hg²⁺ in environmental samples.     

Electrolytic metal deposition onto chemically modified electrodes

Some general features concerning electrochemical metal deposition onto electrodes modified with self-assembled monolayers (SAMs) of alkanethiols are discussed. Although thiols of various chain length are briefly addressed, special emphasis is placed on copper deposition onto an ethanethiol (C2)-modified Au(111) surface. The short alkanethiol blocks the surface to a great extent but does not completely suppress charge transfer. We have used in situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) to characterize the structure and the electrochemical behavior of the C2 monolayer in sulfuric acid electrolyte before and after introducing copper ions to the system. The C2 adlayer consists of domains of two different ordered structures. It is shown that the adlayer undergoes a reversible order–disorder transition at potentials slightly negative of 0 V vs. SCE, which testifies to a surprisingly high mobility of the C2 molecules within the SAM. Copper deposition on C2-modified gold electrodes shows significant differences from the same process on the bare electrode. A sharp cathodic peak at -0.18 V vs. SCE is ascribed to the insertion of a Cu monolayer between Au and the organic adlayer. At low overpotentials the Cu deposit exhibits a ramified monatomic high morphology, if the ethanethiol adlayer is dense. Three-dimensional growth starts at large substrate defects. Received: 2 May 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999     

Electrochemical response of nitrogen-doped multi-walled carbon nanotubes decorated with gold and iridium nanoparticles toward ferrocyanide/ferricyanide redox system

Novel composite films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold (AuNP) and iridium (IrNP) nanoparticles possessing diameters of 12.5 and 2.7 nm, respectively. The electrochemical responses of fabricated composite films, further denoted as N-MWCNTs/MNPs (M: Au and Ir), toward ferrocyanide/ferricyanide, [Fe(CN)₆]^3−/4− redox couple was probed by means of cyclic voltammetry and electrochemical impedance spectroscopy techniques. The findings demonstrate that both N-MWCNT/MNP composite films exhibit greater electrochemical response and sensitivity toward [Fe(CN)₆]^3−/4− compared to unmodified N-MWCNTs. The results verify that the N-MWCNT/MNP composite films are extremely promising for application in electrochemical sensing.

     

The electrochemical behavior of Dy(III) in eutectic LiF-DyF<Subscript>3</Subscript> at W electrode

The electrochemical reduction process of Dy ion on tungsten electrode at 1103 K in Dy₂O₃-LiF-DyF₃ molten system was studied by cyclic voltammetry, chronoamperometry, and chronopotentiometry methods with a three-electrode system on the electrochemical workstation AUTOLAB. The results showed that Dy³⁺ could be deposited at around ?0.75 V on inert W electrode compared with platinum electrode. The reduction process of Dy ion on W electrode occurred in a single step with the exchange of three electrons because one reduction peak was observed, and the calculated transfer electron number was three. Chronoamperograms indicated that the nucleation process of dysprosium ions was instantaneous three-dimensional nucleation on a tungsten electrode. The cathode electrochemical process on the tungsten electrode was controlled by the diffusion of ions, and the diffusion coefficient was 1.159 × 10^?4 cm²/s, which was calculated from a chronopotentiogram.     

A selective sensor for nanolevel detection of lead (II) in hazardous wastes using ionic-liquid/Schiff base/MWCNTs/nanosilica as a highly sensitive composite

An effective potentiometric sensor had been fabricated for the rapid determination of Pb²⁺ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb²⁺ carbon paste electrode for the successfully determination of Pb²⁺ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF₆, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76?±?0.10 mV decade^?1) toward Pb²⁺ ions in the range of 5?×?10^?9?C1.0?×?10^?1 mol L^?1 with a detection limit of 2.51?×?10^?9 mol L^?1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5?C8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions.     

Preparation and electrochemical performances of nanoporous/cracked cobalt oxide layer for supercapacitors

Nanoporous/cracked structures of cobalt oxide (Co₃O₄) electrodes were successfully fabricated by electroplating of zinc–cobalt onto previously formed TiO₂ nanotubes by anodizing of titanium, leaching of zinc in a concentrated alkaline solution and followed by drying and annealing at 400 °C. The structure and morphology of the obtained Co₃O₄ electrodes were characterized by X-ray diffraction, EDX analysis and scanning electron microscopy. The results showed that the obtained Co₃O₄ electrodes were composed of the nanoporous/cracked structures with an average pore size of about 100 nm. The electrochemical capacitive behaviors of the nanoporous Co₃O₄ electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in 1 M NaOH solution. The electrochemical data demonstrated that the electrodes display good capacitive behavior with a specific capacitance of 430 F g^?1 at a current density of 1.0 A g^?1 and specific capacitance retention of ca. 80 % after 10 days of being used in electrochemical experiments, indicating to be promising electroactive materials for supercapacitors. Furthermore, in comparison with electrodes prepared by simple cathodic deposition of cobalt onto TiO₂ nanotubes(without dealloying procedure), the impedance studies showed improved performances likely due to nanoporous/cracked structures of electrodes fabricated by dealloying of zinc, which provide fast ion and electron transfer routes and large reaction surface area with the ensued fast reaction kinetics.     

Synthesis and electrochemical performance of α-nickel hydroxide codoped with Al3+ and Ca2+

α-Nickel hydroxide codoped with Al³⁺ and Ca²⁺ was prepared by chemical coprecipitation method. The phase structure and surface morphology of the prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical performances of the prepared samples were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. XRD and SEM tests reveal that the Al³⁺/Ca²⁺ codoped α-nickel hydroxide has a relatively good crystallization and a very coarse surface. Electrochemical tests show that the Al³⁺/Ca²⁺ codoped α-nickel hydroxide has higher proton diffusion coefficient, lower electrochemical reaction resistance, and higher discharge capacity (395.3 mAh g^?1 at 0.2 C) than the Al³⁺ singly doped α-nickel hydroxide, which indicates its potential application as an electrode material for secondary alkaline batteries.     

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200 cycles at 50 μA μm^?1 cm^?2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1 μAh μm^?1 cm^?2) compared with that of the NCM/AZO-120s electrode (62.4 μAh μm^?1 cm^?2) and the bare NCM electrode (22.3 μAh μm^?1 cm^?2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.     

Construction of 3D polypyrrole/CoS/graphene composite electrode with enhanced pseudocapacitive performance

Herein, 3D graphene/nickel foam (GE/NF) composite matrix was successfully fabricated by using NF as template through a self-catalytic thermal chemical vapor deposition process. By using the prepared GE/NF as substrate, CoS nanosheets were deposited via a facial one-step electrochemical deposition method. Owing to the advantage of GE in boosting the electrical contact between the electroactive host material and current collector, the as-prepared 3D CoS/GE/NF electrode demonstrated a superior capacitance value of 2308 F g^?1 at 1 A g^?1 and a high rate capability of 70.49% at 20 A g^?1. After depositing the polypyrrole (PPY) film on 3D CoS/GE/NF electrode, the electrochemical performance of CoS was further greatly improved and delivered an extremely high capacitance value of 3450 F g^?1 at 1 A g^?1, with good rate capability (62.61% at 20 A g^?1) and improved cycling stability. The enhanced electrochemical performance of PPY/CoS/GE/NF electrode is closely related to the advantage of PPY film in increasing the electrical conductivity and reinforcing the integrity of electrode.     

Antioxidant behaviour of 2′‐hydroxy‐chalcones: a study of their electrochemical properties

The electrochemical behaviour of 13 chalcone analogues was systematically studied by means of cyclic voltammetry and chronoamperometry at a glassy carbon (GC), gold and platinum working electrodes using two different supporting electrolyte/solvent combinations. It was found that chalcone analogues can be easily oxidized at both GC and gold working electrodes, but not at a platinum electrode. Principal component analysis was further employed to reveal similarities/dissimilarities between oxidation potentials, chronoamperometric signals and ability of the compounds to scavenge the reactive oxygen species H₂O₂. The study reveals the inverse proportional relationship between the scavenging ability of H₂O₂, expressed as IC₅₀, and chronoamperometric signal at 800 mV using gold as working electrode. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and electrochemical performance of mixed phase α/β nickel hydroxide by codoping with Ca<Superscript>2+</Superscript> and PO<Subscript>4</Subscript><Superscript>3−</Superscript>

Nickel hydroxide with a unique mixed phase α/β-Ni(OH)₂ was prepared by partially substituting Ca²⁺ for Ni²⁺ with supersonic co-precipitating method firstly. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The results show that the Ca-substituted Ni(OH)₂ by adding PO₄ ^3? is α/β mixed phase, while the undoped Ni(OH)₂ and the Ca-substituted Ni(OH)₂ without adding PO₄ ^3? are pure β phase. Furthermore, the Ca-substituted Ni(OH)₂ by adding PO₄ ^3? exhibits irregular shape and contains many intercalated water molecules and anions as proven by SEM and FT-IR. Meanwhile, the prepared samples were added into micro-sized beta nickel hydroxide to form biphase electrode materials for Ni-MH battery. The electrochemical performances of the biphase electrodes were characterized by cyclic voltammetry (CV) and charge/discharge tests. The results demonstrate that the biphase electrode with mixed phase α/β-Ni(OH)₂ exhibits higher electrochemical activity, better electrochemical reversibility and charge efficient, higher discharge potential, and better cyclic stability. The specific discharge capacity of Ca-substituted α/β-Ni(OH)₂ electrode can retain 271.7 and 238 mAh/g after 80 cycles at 0.2 and 0.5 C, respectively. This indicates that it may be a promising positive active material for alkaline secondary batteries. The results reported in this work may be useful for the designing and synthesizing of nickel hydroxide materials with superior performance.     

Combined XPS,electrochemical and Kelvin probe measurements of NaY zeolite

In the present study X-ray Photoelectron Spectroscopy (XPS) combined with in situ electrochemical and Kelvin probe measurements was used in order to get a deeper insight on the mechanism of the cation transport through NaY zeolite and the charge transfer through the Au electrode/zeolite interface. It is shown that by imposing a potential gradient across the NaY powder which is sandwiched between two electrodes, Na⁺ ions can be electrically transferred to or from the Au working electrode area, following the direction of the applied potential between the two electrodes. Two peaks corresponding to sodium species were detected by means of in situ XPS investigation during potential application. The first peak of Na1s photoelectrons with binding energy at 1072.2 ± 0.2 eV is attributed to Na adsorbed on the grounded Au electrode with its coverage remaining unchanged upon potential imposition. The second peak is directly associated with Na present in the zeolite and upon potential application its binding energy varies proportionally with the variation of the surface potential measured by Kelvin probe. Upon varying the potential from − 4 to + 4 V between the working and counter electrode, the Na⁺ concentration decreases by ca30% at the Au/zeolite interface. However the invariant amount of Na on the Au electrode under vacuum shows that the variation in Na⁺ concentration is not due to ionic transfer onto the Au surface but instead Na⁺ accumulation can be assumed at the Au/zeolite interface. On the other hand, current or potential application under O₂ atmosphere promotes the electrocatalytic reaction of Na⁺ towards the formation of Na₂O on the Au electrode surface.     

Electrooxidation of hydrazine in alkaline medium at carbon paste electrode decorated with poly(<Emphasis Type="Italic">P</Emphasis>-phenylendiamine/ZnO) nanocomposite

In this study, poly(P-phenylenediamine/ZnO) (PpPD/ZnO) nanocomposite (NC) under ultrasonic conditions was synthesized and characterized. The presence of zinc oxide nanoparticles changed the morphology of PpPD considerably as confirmed by SEM observations. Hydrazine electrooxidation at novel modified carbon paste electrodes (CPE) with supported NC was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) techniques. Obtained results showed that the NC increases the surface catalytic activity of CPE toward hydrazine electrooxidation. The electrocatalytic current density increased linearly with hydrazine concentration, and the detection limit and sensitivity are determined to be 24 μM and 0.172 mA cm^?2 mM^?1, respectively. As revealed by the EIS measurements, the increased conductivity and decreased R _ct are owing to the presence of ZnO NPs in the PpPD matrix. The CA results indicated that hydrazine electrooxidation results in higher steady-state current density on CPE/PpDP/ZnO electrode system compared to the CPE/PpDP and CPE electrodes.     

Electrochemical synthesis and performance of PANI electrode material for electrochemical capacitor

Polyaniline (PANI) electrode materials doped with sulfuric acid (H₂SO₄) were prepared by cyclic voltammetry (CV) method in different reaction conditions. The structure and morphology of PANI samples were characterized by Fourier transform infrared spectroscopy and scanning electron microscope. The electrochemical properties of PANI samples were studied by CV, galvanostatic charge/discharge, and electrochemical impedance spectroscopy tests. Additionally, the effects of reaction conditions including aniline concentration, voltammetry scan rate, and deposition time on the morphology and properties of PANI samples were investigated in detail. The results showed that the PANI synthesized under the optimal conditions of 0.2 mol?L^?1 aniline, scan rate 20 mV?s^?1, and deposition time 50 min is in the form of nanorods with a cross-linked network structure. It exhibits an outstanding capacitive performance with good cycle stability and high rate performance. Besides, the specific capacitance of PANI is as high as 757 F?g^?1.     

Highly sensitive electrochemical detection of adenine on a graphene-modified carbon ionic liquid electrode

A new electrochemical method for the sensitive detection of adenine was established on a chitosan (CTS)- and graphene (GR)-modified carbon ionic liquid electrode (CILE). CILE was prepared by mixing 1-butylpyridinium hexafluorophosphate (BPPF₆) and paraffin with graphite powder. Due to the synergistic effects of GR, CILE, and the interaction of GR with IL on the electrode surface, the electrochemical performance of CTS/GR/CILE were greatly enhanced. Electrochemical behaviors of adenine on the modified electrode was investigated with a single well-defined oxidation peak appeared. The electrochemical reaction of adenine was an adsorption-controlled irreversible process, and the electrochemical parameters were further calculated. Under the optimal conditions, the oxidation peak current was proportional to adenine concentration in the range from 1.0 nmol L^?1 to 70.0 μmol L^?1 with a detection limit of 0.286 nmol L^?1 (3σ) by differential pulse voltammetry. The established method showed the advantages such as good selectivity, stability, and repeatability.     

Influence of NiCl2 modification on the electrochemical performance of LiV3O8 cathode for lithium ion batteries

The 5.0, 8.0, and 10.0 wt% NiCl₂-modified LiV₃O₈ materials are successfully prepared and the effects of NiCl₂ modification on the electrochemical performance of LiV₃O₈ cathode have been investigated. The structural and surface morphologic properties of synthesized materials are characterized by X-ray diffraction and scanning electron microscopy. The electrochemical properties are investigated by charge–discharge testing and cyclic voltammetry. It is found that 8.0 wt% NiCl₂-modified LiV₃O₈ shows excellent electrochemical properties. The initial discharge capacity of 8.0 wt% NiCl₂-modified LiV₃O₈ is much higher than that of pristine LiV₃O₈, and can attain 336.7 mAh g^?1 at the current rate of 0.5 C (300 mA g^?1 is assumed to be 1 C rate). Additionally, NiCl₂ modification significantly improves the cyclability of LiV₃O₈. The NiCl₂ modification is shown to be able to suppress the capacity fade of LiV₃O₈ without specific capacity expense by suppressing the characteristic phase transitions during cycling.     

Voltammetric sensor for simultaneous determination of ascorbic acid,acetaminophen, and tryptophan in pharmaceutical products

A novel carbon paste electrode modified with carbon nanotubes and 5-amino-2′-ethyl -biphenyl-2-ol was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for electrocatalytic oxidation of ascorbic acid (AA), is described. The electrode was employed to study the electrocatalytic oxidation of AA, using cyclic voltammetry, chronoamperometry, and square-wave voltammetry (SWV) as diagnostic techniques. It has been found that the oxidation of AA at the surface of modified electrode occurs at a potential of about 250 mV less positive than that of an unmodified carbon paste electrode. SWV exhibits a linear dynamic range from 2.0?×?10^?7 to 5.0?×?10^?4 M and a detection limit of 1.0?×?10^?7 M for AA. In addition, this modified electrode was used for simultaneous determination of AA, acetaminophen (AC), and tryptophan (TRP). Finally, the modified electrode was used for determination of AA, AC, and TRP in pharmaceutical products.     

Electrochemical performance of CeO<Subscript>2</Subscript> nanoparticle-decorated graphene oxide as an electrode material for supercapacitor

Cerium oxide nanoparticles and cerium oxide nanoparticle-decorated graphene oxide (GO) are synthesized via a facile chemical coprecipitation method in the presence of hexadecyltrimethylammonium bromide (CTAB). Nanostructure studies and electrochemical performances of the as-prepared samples were systematically investigated. The crystalline structure and morphology of the nanocomposites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). Electrochemical properties of the CeO₂ electrode, the GO electrode, and the nanocomposites electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) measurements. The CeO₂ nanoparticle-decorated GO (at the mole ratio of CeO₂/GO = 1:4) electrode exhibited excellent supercapacitive behavior with a high specific capacitance of 382.94 F/g at the current density of 3.0 A/g. These superior electrochemical features demonstrate that the CeO₂ nanoparticle-decorated GO is a promising material for next-generation supercapacitor systems.     

Electrocatalytic oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine at carboxylic acid functionalized multi-walled carbon nanotubes modified carbon paste electrode

The electrocatalytic oxidation of l-tyrosine (Tyr) was investigated on a carboxylic acid functionalised multi-walled carbon nanotubes modified carbon paste electrode using cyclic voltammetry and amperometry. The surface morphology of the electrodes was studied using field emission (FE)-SEM images, and the interface properties of bare and modified electrodes were investigated by electrochemical impedance spectroscopy (EIS). The influence of the amount of modifier loading and the variation of the pH of the solution on the electrochemical parameters have been investigated. Cyclic voltammetry was carried out to study the electrochemical oxidation mechanism of Tyr, which showed an irreversible oxidation process at a potential of 637.0 mV at modified electrode. The anodic peak current linearly increased with the scan rate, suggesting that the oxidation of Tyr at modified electrode is an adsorption-controlled process. A good linear relationship between the oxidation peak current and the Tyr concentration in the range of 0.8–100.0 μM was obtained in a phosphate buffer solution at pH 7.0 with a detection limit of 14.0?±?1.36 nM (S/N?=?3). The practical utility of the sensor was demonstrated by determining Tyr in spiked cow’s milk and human blood serum. The modified electrode showed excellent reproducibility, long-term stability and antifouling effects.     

Nanocrystalline Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> electrodes for supercapattery application

Nanocrystalline Li₂TiO₃ was successfully synthesized using solid-state reaction method. The microstructural and electrochemical properties of the prepared material are systematically characterized. The X-ray diffraction pattern of the prepared material exhibits predominant (002) orientation related to the monoclinic structure with C2/c space group. HRTEM images and SAED analysis reveal the well-developed nanostructured particles with average size of ～40 nm. The electrochemical properties of the prepared sample are carried out using cyclic voltammetry (CV) and chronopotentiometry (CP) using Pt//Li₂TiO₃ cell in 1 mol L^?1 Li₂SO₄ aqueous electrolyte. The Li₂TiO₃ electrode exhibits a specific discharge capacity of 122 mAh g^?1; it can be used as anode in Li battery within the potential window 0.0–1.0 V, while investigated as a supercapacitor electrode, it delivers a specific capacitance of 317 F g^?1 at a current density of 1 mA g^?1 within the potential range ?0.4 to +0.4 V. The demonstration of both anodic and supercapacitor behavior concludes that the nanocrystalline Li₂TiO₃ is a suitable electrode material for supercapattery application.