Anodic Direction Research Articles

Electrochemical determination of calcium channel blocker drugs using multiwall carbon nanotube-modified glassy carbon electrode

Abstract Background Calcium channel blockers belonging to the dihydropyridine family have been used as a potent arterial vasodilator in the management of angina and cardiovascular diseases. In the design of glassy carbon electrode coatings for the study of the same, multiwall carbon nanotubes (MWCNT) are favored. They are known for the reduction and oxidation of electroactive species towards cathodic and anodic direction with the simultaneous enhancement of the peak current. Results The MWCNT-modified glassy carbon electrode exhibited a sharp anodic peak potential at around at 0.5 V for amlodipine (AMLD) andnimodipine (NIMD), and 0.4 V for felodipine (FELD) in the cyclic voltammograms. The antihypertensive drugs were determined using a simple two-step procedure developed which comprised a preconcentration step followed by the differential pulse stripping voltammetric quantification. Concentration calibrations were linear within the range from 0.01 to 0.3 μg/mL for AMLD and FELD, and 0.025 to 0.3 μg/mL for NIMD. Conclusion The lower limit detection (LOD) was found to be very low on modified electrode. The LOD is 0.005 μg/mL for AMLD and FELD, and 0.01 μg/mL for NIMD. The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of antihypertensive drugs leading to a remarked improvement in sensitivity. An electrochemical sensor featuring the MWCNT-modified electrode was applied successfully as the result for the calcium channel blocker determination in pharmaceutical samples.

Synthesis of a low-spin iron(III) complex from its high-spin iron(II) counterpart: What causes redox potentials that disobey the expected trends?

Abstract We discuss here the chemical oxidation of a high-spin iron(II) complex containing the 1,3-bis(2′-benzimidazolylimino)isoindoline ligand (HL1) using tris(4-bromophenyl)aminium hexachloroantimonate (Magic Blue). The product was X-ray structurally, spectroscopically (Mossbauer, FT-IR, UV–vis) and electrochemically characterized and can be formulated as [FeIII(L1)2][FeIII(L1H− 2)(L1)] (1), a low-spin iron(III) 1D coordination polymer with strong H-bonds between ligands and N,N-dimethylformamide (DMF) solvent molecules in the solid phase. The redox potential of the [FeII(L1)2] complex at − 407 mV vs. ferrocene in DMF is shifted to the anodic direction only by 12 mV in the case of 1 against the expected cathodic shift upon proton loss from the ligand. The difference in the spin state of [FeII(L1)2] and 1, and the impact of H-bonds (detected in the crystal structure) that are able to facilitate proton-coupled electron transfer have been considered as plausible explanations.

Electrochemistry and in situ Raman spectroelectrochemistry of low and high quality boron doped diamond layers in aqueous electrolyte solution

In this work we report on electrochemical and in situ Raman spectroelectrochemical characterization of low quality (LQ) ultrathin nanocrystalline and high quality (HQ) polycrystalline boron doped diamond (BDD) compared especially in terms of the sp2 carbon content. The BDD films were grown by microwave plasma enhanced chemical vapor deposition and doped with various boron concentrations from 250 to 8000ppm (boron/carbon ratio in the gas phase) at different conditions. The quality (presence of graphitic or amorphous phases) and boron doping levels in the BDD films were analyzed by micro-Raman spectroscopy. From the neutron depth profiling, it was found that the boron content in the near surface region (<1μm) was in the range from about 4×1019cm−3 to 58×1020cm−3 for B/C from 250ppm to 8000ppm, respectively. The electrochemical measurements have been performed in aqueous 0.5M H2SO4 in the potential range from −2 to 2.5V vs. Hg/Hg2SO4. Cyclic voltammetry showed that the electrochemical potential window was independent on the boron doping but depended on the film quality, i.e. when the sp2 carbon content increased the width of potential window decreased. The in situ Raman spectroelectrochemistry was performed in aqueous electrolyte solution (0.5M H2SO4) in the potential range from −1.5 to 1.5V vs. Hg/Hg2SO4 using two laser excitations (633nm and 457nm). In the case of films containing high amount of sp2 carbonaceous phase (low quality), the modes belonging to sp2 carbonaceous phases changed their intensities. The intensity of the D, G and D′ Raman peaks increased in cathodic direction, while in anodic direction bleaching of these peaks was observed. The diamond films prepared with very small amount of sp2 carbon (high quality) exhibited no spectroelectrochemical changes in the potential region tested.

Nickel Multi-walled Carbon Nanotube Composite Electrode for Hydrogen Generation

ABSTRACTThe electrochemical decomposition of water is an attractive method, however, the performance of the electrodes and efficiencies are of great concern in its large scale production. In this context, we wish to report here the superior performance of Ni-multiwalled carbon nanotube composite as cathode in the decomposition of water. The current voltage curves recorded with this electrode in different media showed a significant electrocatalysis in the reduction of hydrogen ion; the background electrolysis is shifted in the anodic direction. The nanocomposite composition has been found to be crucial in the efficient production of hydrogen. A coulombic efficiency of about 68% has been obtained at this electrode with a hydrogen production rate of 130L/m2 d. This electrode is more efficient than the 316L stainless steel (composition in percentage: C 0.019, Cr 17.3, Mo 2.04, Ni 11.3, Mn 1.04, N 0.041, Fe bulk) cathode that produces 10 ml/h at an area of 20 cm2 (5L/m2.h) (2). The results obtained with different electrolytes, performance variation with electrode composition, and current densities will be presented. The trials carried out using solar panel instead of DC power source showed similar hydrogen production rates and efficiencies.

Preparation and electrochemistry of Pd–Ni/Si nanowire nanocomposite catalytic anode for direct ethanol fuel cell

A new silicon-based anode suitable for direct ethanol fuel cells (DEFCs) is described. Pd-Ni nanoparticles are coated on Si nanowires (SiNWs) by electroless co-plating to form the catalytic materials. The electrocatalytic properties of the SiNWs and ethanol oxidation on the Pd-Ni catalyst (Pd-Ni/SiNWs) are investigated electrochemically. The effects of temperature and working potential limit in the anodic direction on ethanol oxidation are studied by cyclic voltammetry. The Pd-Ni/SiNWs electrode exhibits higher electrocatalytic activity and better long-term stability in an alkaline solution. It also yields a larger current density and negative onset potential thus boding well for its application to fuel cells.

Postfunctionalization of aromatic polyamine by [2+2] cycloaddition of 7,7,8,8-tetracyanoquinodimethane with side chain alkynes

Electron-rich, side chain alkynes of an aromatic polyamine were functionalized by a [2+2] cycloaddition, followed by retro-cyclization with the electron-accepting 7,7,8,8-tetracyanoquinodimethane (TCNQ). 1H NMR studies were used to optimize the reaction conditions. Mild heating to >50 °C afforded the postfunctionalized aromatic polyamines with the desired acceptor amounts. The quantitative TCNQ addition was demonstrated by the MALDI-TOF mass spectrum and elemental analysis. Introduction of the cyano-based acceptor moieties into the polymer side chains resulted in unusually strong intermolecular interactions. In addition to the π–π interactions of the extended acceptor moieties, these intermolecular forces were supposed to improve the thermal stability of the aromatic polymers. Furthermore, the donor–acceptor chromophores formed by this postfunctionalization displayed low energy charge-transfer bands and redox activities in both the anodic and cathodic directions. The straightforward postfunctionalization technique using the alkyne–TCNQ addition is useful for the preparation of narrow band gap polymers in one step.

New Acyclic Schiff-Base Nickel(II) Complexes and their Electrochemical, Kinetic, and Antimicrobial Studies

Five new nickel(II) complexes were synthesized. All the complexes were characterized by elemental and spectral analysis. Electronic spectra of the complexes show d–d transition in the range of 500–800 nm. Electrochemical studies of the complexes show an irreversible one-electron reduction process around –0.65 to –0.91 V and an irreversible one-electron oxidation process around 0.87 to 1.00 V. The reduction and oxidation potential of nickel(II) complexes shifts toward cathodic and anodic directions, respectively, upon increasing the chain length. The catalytic activity of the nickel(II) complexes on the hydrolysis of 4-nitrophenylphosphate was determined. All the nickel(II) complexes were screened for antibacterial activity.

Fracture and physical properties of carbon anodes for the aluminum reduction cell

An experimental study with total 504 specimens has been carried out to investigate the fracture and physical properties of the carbon anode materials. The specimens were sampled from anodes produced with machined stub holes. From normal-and Weibull analysis the fracture toughness and the tensile strength showed a clear temperature dependency and orthotropic behavior. It has been found that both the fracture toughness and tensile strength increases with the temperature and are larger for the specimens directed in the horizontal direction than in the vertical direction. The variation in the tensile strength within an anode decreased with the temperature but the variation in the fracture strain increased. The tensile strain appears to be only dependent on the temperature and insensitive to the routine anode properties of the anode material. A multivariate linear regression analyses of the fracture toughness and tensile strength has been conducted and a typical correlation of R 2 = 0.5 ( R is the Coefficient of Determination) to the measured routine anode properties was found. The thermal expansion coefficient is also larger in the vertical anode direction which makes the crack initiation more sensitive to temperatures. The orthotropic studies also showed that the air permeability has a tendency to be larger in the horizontal direction in the upper part of the anode which can induce unnecessary burning from the anode sides. The influence of the processing parameters in the paste plant and baking furnace has not been presented in this paper.

Electrowetting of Molten Carbonate Electrolytes

AbstractThe wetting characteristics of various molten carbonate electrolytes were experimentally measured and the dependence of the contact angle on polarisation was thoroughly examined for various temperatures and gas atmospheres. At open circuit under an atmosphere of CO2 and/or oxidant gases, addition of alkaline earth carbonates decreases the wettability of the electrolyte. Addition of alkaline earth carbonates also tends to decrease the temperature dependence of the contact angle. Upon polarisation, the contact angle shows a complex behaviour. In an oxidising atmosphere its dependence on potential is roughly symmetric (like an electrocapillary curve) but in a reducing atmosphere this is not the case. Generally, the contact angle increases upon cathodic polarisation but decreases in the anodic direction. These changes in contact angle are interpreted in terms of interfacial tensions. The complex dependence of contact angle on polarisation can be interpreted in terms of a superimposed electrocapillary and transport effects. As such, it may be affected by specifically adsorbed species at the electrode surface (especially complex oxides), by the basicity (oxide ion activity) of the melt, and by the potential‐induced segregation of the cationic species in the carbonate melt.

High‐Yielding Alkyne‐Tetracyanoethylene Addition Reactions: A Powerful Tool for Analyzing Alkyne‐Linked Conjugated Polymer Structures

AbstractPoly(o‐phenyleneethynylene) and poly(o‐phenylenebutadiynylene) derivatives are synthesized by the Sonogashira polycondensation or oxidative polymerization of an asymmetric monomer, 3,4‐diethynyl‐N,N‐dihexylaniline. Postfunctionalization of the poly(o‐phenyleneethylene) derivatives is unsuccessful due to the occurrence of undesired side reactions. In contrast, the poly(o‐phenylenebutadiynylene) derivative is converted into the donor–acceptor type polymer without side reactions. The resulting polymer features a well‐defined charge‐transfer (CT) band in the Vis–NIR region and redox activity in both the anodic and cathodic directions. The results suggest that the oxidative polymerization mainly proceeds through the pseudo two‐step pathway. magnified image

Methanol and ethanol electrooxidation at 3D ordered silicon microchannel plates electrode modified with nickel–palladium nanoparticles in alkaline

The use of silicon microchannel plates (MCP) modified with nickel–palladium (Ni–Pd) nanoparticles by electroless plating was studied for the electrocatalytic oxidation of methanol and ethanol by cyclic voltammetry and chronoamperometry in alkaline media. The electrocatalyst was characterized by EDS, SEM and cyclic voltammetry, and the effective parameters on electrocatalytic oxidation of the alcohol, i.e. the concentration of KOH and alcohol, medium temperature and working potential limit in anodic direction were investigated. The modified electrode shows a superior electrooxidation performance with the operating temperature increasing and a strong current response to methanol and ethanol even during long-term oxidation of alcohol. All results show that the Ni–Pd/Si–MCP nanocomposite electrode is very attractive for integrated fuel cell applications.

Improvement of hydrogen embrittlement and stress corrosion cracking by annealing for Al-4.4Mg-0.6Mn alloy

With no annealing treatment, cathodic polarization trends in 5083F Al alloy revealed concentration polarization and activation polarization. However, the annealed specimens have lower current densities at corrosion protection potential compared to the non-annealed specimen. The results of SSRTs conducted in seawater at the applied potential range of −1.8 V to −0.5 V indicated that the maximum tensile strength, elongation, and time-to-fracture had high values at applied potentials of −0.7 to −1.4 V. The maximum tensile strength, elongation, and time-to-fracture decreased when the potential values were beyond this range in either anodic or cathodic direction. In general, the increased shear lip caused by annealing treatment indicates elongation. Time-to-fracture would likely increase with elongation. Potentials between −0.5 V to −0.6 V were found to be in the region of stress corrosion cracking. The corrosion protection zone was determined to be −0.7 V to −1.4 V because these potential ranges produced good mechanical properties. Potential less than −1.4 V produced a fractured surface with a mixture of dimples (ductile fractures) and a quasi-cleavage pattern resulting from the effects of hydrogen gas.

New acyclic Schiff-base copper(II) complexes and their electrochemical, catalytic, and antimicrobial studies

A new series of acyclic mononuclear copper(II) complexes have been prepared by Schiff-base condensation derived from 5-methylsalicylaldehyde, diethylenetriamine, tris(2-aminoethyl) amine, triethylenetetramine, N,N-bis(3-aminopropyl)ethylene diamine, N,N-bis(aminopropyl) piperazine, and copper perchlorate. All the complexes were characterized by elemental and spectral analyses. Electronic spectra of the complexes show a d–d transition in the range 500–800 nm, electrochemical studies of the complexes show irreversible one-electron-reduction process around −1.10 to −1.60 V. The reduction potential of the mononuclear copper(II) complexes shifts toward anodic direction upon increasing the chain length of the imine compartment. ESR spectra of the mononuclear copper(II) complexes show four lines, characteristic of square-planar geometry, with nuclear hyperfine spin 3/2. The copper(II) complexes show a normal room temperature magnetic moment value μ eff = 1.72–1.76 BM, close to the spin-only value of 1.73 BM. Electrochemical and catalytic studies of the complexes were compared on the basis of increasing the chain length of the imine compartment. All the complexes were screened for antifungal and antibacterial activities.

Creation of persistent charge-transfer interactions in TCNQ polyester

A 7,7,8,8-tetracyanoquinodimethane polyester was converted into a strongly colored polyester with low-energy charge-transfer (CT) bands by treatment with electron-rich alkyne molecules under mild conditions. The post-functionalization was monitored by its ultraviolet-visible-near infrared (IR) spectra, which suggested a quantitative addition reaction without any side reactions. This result was further supported by 1H and 13C nuclear magnetic resonance, IR and elemental analyses. The functionalized polymer retained a high thermal stability with a decomposition onset temperature of ∼200 °C and ∼63% residual soot at 500 °C. The CT chromophores in the polymer showed a clear positive solvatochromism and redox behaviors in both anodic and cathodic directions. The HOMO and LUMO levels estimated from the first oxidation potential (Eox,1) and the first reduction potential (Ered,1), respectively, were markedly elevated by this post-functionalization. The extent of HOMO elevation (1.45 eV) was more significant than that of LUMO elevation (0.44 eV). A clean post-functionalization of 7,7,8,8-tetracyanoquinodimethane polyester by a high-yielding addition reaction with electron-rich alkyne molecules provided highly colored polymer products with very stable charge-transfer bands in the visible to near-infrared region. Electrochemistry revealed elevated HOMO and LUMO levels after the post-functionalization.

CHARACTERIZATION OF NICKEL OXIDE THIN FILM — DC REACTIVE MAGNETRON SPUTTERING

Nickel oxide ( NiO ) thin films were deposited on glass substrates by reactive direct current (DC) magnetron sputtering of a Ni target in an Ar / O 2 mixture. The effect of thickness (0.2 μm, 0.4 μm and 1 μm) on the structural and surface morphological properties of NiO thin films was investigated. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). The films were cubic NiO , with preferred orientation in the (111) direction at lower deposition time (10 mins). At higher deposition time (60 mins) the preferred orientation shifted to (200) plane. Electrochemical behavior of NiO thin films for different thickness samples were analyzed between the electrode potential ‑0.2 and 0.8 V vs scanning calomel electrode (SCE) in both anodic and cathodic directions and the current responses were measured.

Imaging performance of a large-area Silicon Drift Detector for X-ray astronomy

Large-area multi-anode Silicon Drift Detectors (SDDs) have X-ray imaging and spectroscopic characteristics that make them extremely attractive in the perspective of their applications to the field of space astrophysics. We describe here the imaging performance of such a detector, originally developed for particle tracking in the ALICE experiment at LHC, as derived by laboratory measurements and Monte Carlo simulations. Despite an anode pitch of 294 μ m , we measured a position resolution as high as ∼ 20 μ m by charge weighting in the anode direction, for photon energies in the range 2–10 keV. These results are comparable to those obtained with the same detectors in particle tracking. Notwithstanding the 1-D nature of the devices, as far as their read-out is concerned, we envisaged an algorithm that exploits the charge diffusion to reconstruct the position of the photon absorption point also along the drift direction (that is, the one formally not position-sensitive). With the current set-up, the position resolution was measured as ∼ 3 – 5 mm in the same energy range as above. Such 2-D imaging capability in a 1-D detector, although asymmetric, is highly useful in space applications, where the power and the complexity requested by a 2-D read-out system is sometimes unaffordable.

Electrocatalytic Activity Analysis of PEFC Cathode by 1-D Macrohomogeneous Model of Catalyst Layer

A simple macrohomogeneous 1-D model of the polymer electrolyte fuel cell (PEFC) cathode catalyst layer incorporating ORR kinetics and including the effects of Pt surface oxide coverage, proton migration, and oxygen diffusion is introduced. In the model, both the site-blocking and the energetic effects of the Pt surface oxide are incorporated and applied to actual fuel cell data. Measured polarization curves are fitted in both the cathodic and anodic directions using a single value of the intrinsic exchange current density (that is independent of the Pt oxide coverage) representing the entire potential range of operation. By fitting with this model, the catalytic activity is broken down into the intrinsic exchange current density, the oxide coverage, and the Temkin parameter. The fitting parameters used in the model are the exchange current density, the Temkin parameter, and the transmissibility of oxygen within catalyst layer. The electrochemically active surface area and the proton conduction resistance within catalyst layer were determined using experimental diagnostic techniques. The surface charge representing oxide species was also measured experimentally and converted into a surface coverage based on an assumed species. The analysis of polarization curves using this modeling approach may help to provide a deeper understanding that could accelerates the development and characterization of new catalysts.

Novel electrochemical measurements on direct electro-deoxidation of solid TiO2 and ZrO2 in molten calcium chloride medium

A solid metal oxide cathode undergoes significant chemical changes during the molten salt electro-deoxidation process. The changes in the chemical composition lead to changes in the electrical resistivity and potential of the electrode. Two novel electrochemical techniques, based on these two parameters, have been employed to study the electro-deoxidation of solid TiO2 and ZrO2 in molten calcium chloride at 900 °C. The in situ resistance measurements carried out by the IR drop method conclusively proved that TiO2 electrode remains highly conducting throughout the electro-deoxidation process and hence is amenable for reduction. The ZrO2 electrode, on the other hand, developed very high resistance midway in the electro-deoxidation, and could not be reduced completely. The resistance measurements give strong indication that the electron-transfer reactions taking place at the cathode determine the rate and efficiency of the electro-deoxidation process to a great extent. The low-current galvanostatic electro-deoxidation of TiO2 electrodes, in conjunction with a graphite pseudo reference electrode to monitor the half cell potentials, showed that the metal oxide passes through two stages during the electrolysis; a high current, low resistant stage 1, where Ca2+ ions are inserted to the metal oxide cathode to produce different intermediate compounds and stage 2 where electro-deoxidation of the cathode take place continuously. Removal of oxygen, from the cathode, in stage 1 of the electro-deoxidation is considered to be insignificant. The anodic and cathodic voltages in this stage remained more or less stable at ~1.4 V and ~−1 V, respectively. When the oxygen ions in the melt were depleted at the end of this stage, both the anode and cathode potentials were increased in the anodic direction and this behaviour suggested that the graphite pseudo reference electrode was changed from a C/CO electrode in stage 1 to a Ca2+/Ca electrode in stage 2.

Postfunctionalization of Alkyne-Linked Conjugated Carbazole Polymer by Thermal Addition Reaction of Tetracyanoethylene.

The postfunctionalization of the main chain alkyne moieties of carbazole containing poly(arylenebutadiynylene)s was attempted by using a high yielding addition reaction between electron rich alkynes and a strong acceptor molecule, tetracyanoethylene (TCNE). After successful postfunctionalization, the polymer band gap decreased due to the intramolecular donor-acceptor interactions. The resulting donor-acceptor alternating polymer showed a very broad charge-transfer band in the visible region as well as redox activities in both anodic and cathodic directions. The optical band gap showed good agreement with the electrochemical band gap. Furthermore, the thermal stability was enhanced after postfunctionalization. These features of the donor-acceptor alternating polymer are expected to be useful for high performance activities in organic solar cell applications.

Electrochemical hysteresis and bistability in chalcopyrite passivation

A literature review of studies where the kinetic response of chalcopyrite leaching has been investigated as a function of controlled slurry potential, and the results of potentiostatic anodic polarizations, show that this mineral passivates at potentials higher than either ~ 440 mV or ~ 510 mV(SCE). These two values have been consistently observed in leaching practice regardless of the geological source of the mineral, which indicates that its passivation potential is little affected by impurity content. The factors or variables determining which one of these two passivation potentials will actually be observed remain unexplained. This paper uses steady-state sampled-current voltammetry to demonstrate that chalcopyrite active–passive behavior at high temperatures displays considerable hysteresis in response to an externally applied potential. When it is polarized in the positive (anodic) direction from the open circuit potential, the active–passive transition is observed at ~ 510 mV. When polarized in the negative (cathodic) direction, from high passive potentials to the open circuit potential, the passive–active transition (depassivation) is observed at ~ 440 mV. Hence, a potential range exists, approximately between 440 and 510 mV, where chalcopyrite presents thermodynamic bistability, and can be either passive or active depending on how it was brought to that particular potential.