Sharif Digital Repository

Nickel-modified glassy carbon electrode (GC/Ni) prepared by galvanostatic deposition was used for the electrocatalytic oxidation of glucose in alkaline solutions where different electrochemical methods were employed. In cyclic voltammetry studies, in the presence of glucose an increase in the peak current of the oxidation of nickel hydroxide is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of glucose is being catalyzed through mediated electron transfer across the nickel hydroxide layer comprising nickel ions of various valence states. Under the chronoamperometric regime, the reaction followed a Cottrellian behavior and the diffusion... 

Impedance characteristics of the negative electrode of lead-acid battery were derived on the basis of fundamental interfacial processes occurring at the electrode. The solution of the governing equations was presented in terms of a simple equivalent circuit consisting of resistive and capacitive loops in which charge transfer and sulfate layer formation and also mass transfer (Warburg) elements are considered. The kinetic parameters were deduced by fitting the theoretically derived impedance to the experimental data. Impedance at various States of Charge (SoC) was also examined  

Electrochemical deposition of aluminum from basic and acidic molten NaCl-KCl-AlCl3 mixture on a graphite electrode at 140 °C was studied by voltammetry, chronopotentiometry and constant current deposition. The deposition of aluminum was found to proceed via a nucleation/growth mechanism in basic melt, while it was found to be diffusion controlled in acidic melt. The diffusion coefficient calculated for Al2Cl- 7 ions in acidic melt by voltammetry was in agreement with the deductions of voltammetry. The morphology of the aluminum deposits was examined using a metallographic microscope and by SEM. It was shown that, depending on the current density (c.d.) and AlCl3 concentration (acidic or... 

Electro-oxidation of alcohols (methanol, ethanol, 1-propanol and 2-propanol) on nickel dispersed into a thick layer of poly-o-aminophenol on graphite electrode (GE/POAP-SDS/Ni) was investigated. Ni-doping into the polymeric film was achieved chemically followed by enrichment of Ni(III) through cycling the potential. The electro-oxidation of alcohols on GE/POAP-SDS/Ni were found to be dominated by direct electro-oxidation with some contribution from Ni(II)/Ni(III) couple. Rate constants for the electro-oxidation of methanol, ethanol, 1-propanol and 2-propanol as derived by chronoamperometry were 1.65 × 105, 1.31 × 105, 2.53 × 104 and 1.40 × 104 cm3 mol-1 s-1, respectively. Impedance... 

MWCNTs/Ag/TiO2NTs plates were synthesized via electrochemical reduction of functionalized multiwalled carbon nanotubes (MWCNTs) on Ag/TiO2NTs. The loading of silver nanoparticles was carried out by electroless reduction of Ag1+ onto TiO2 nanotubes previously formed by anodizing titanium. The SEM analysis revealed that MWCNTs were loaded significantly on the as-prepared Ag/TiO2NTs, where nanoparticles of Ag had grown on the walls of TiO2NTs. The photocatalytic activity of the synthesized plates was evaluated by the photodegradation of Methyl Orange (MO) dye under UV light irradiation. The results indicated that the MWCNTs/Ag/TiO2NTs demonstrated improved efficiency for MO photodegradation in... 

Discharge characteristics of nanorods (NRs), microsized and nanosized copper (II) oxide (CuO) particles prepared via thermal decomposition and thermal oxidation routes are examined as cathode materials of a Zn/CuO cell without membrane separators. The electrochemical discharge is examined galvanostatically at a current density of 500 mAg−1 and reveals that the first discharge cycles of all the CuO materials contain one potential plateau; subsequent discharge cycles involve three potential plateaus. Each potential plateau is due to an electrochemical reaction. The first, second, and third potential plateaus are attributed to Cu2O3, CuO, and Cu2O discharges,... 

The electrocatalytic oxidation of hydrazine was studied over Ni, Cu, Co and Ni-based ternary alloy on graphite electrodes in alkaline solution. The catalysts were prepared by cycling the graphite electrode in solutions containing Ni, Cu and Co ions at cathodic potentials. The synergistic effects and the catalytic activity of the modified electrodes were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). It was found that, in the presence of hydrazine, the modified Ni-based ternary alloy electrode (G/NiCuCo) exhibited a good catalytic activity for the oxidation of hydrazine at a reduced overpotential and it has a significant high... 

Electrocatalytic activity of electrodeposited nanocrystalline CoNiFe alloy in hydrogen evolution reaction (HER) was studied in 1 M NaOH solution. The steady-state polarization measurement and electrochemical impedance spectroscopy were used to determine the Tafel slope, the exchange current density and the activation energy. The simulation of the data obtained from these two methods, using a nonlinear fitting procedure, allowed us to determine the surface coverage and the rate constants associated with the mentioned reaction. The ac-impedance spectra measured at various overpotentials in the HER region exhibited three semicircles in the complex plane plots. The high-frequency semicircle was... 

Hydrogen evolution and electrosorption on/in TiHg alloy have been investigated in acidic solution using cyclic voltammetry, open circuit potential transient, steady-state polarization, chronopotentiometry and electrochemical impedance measurements. Comparison has been made with pure Ti. Cyclic voltammetry and open circuit potential measurements show that hydrogen absorption into the electrode material occurs during proton discharge. The steady-state polarization curves in the course of positive and negative potential scans illustrate that the formation of absorbed hydrogen slightly improves the electrocatalytic properties of the electrode. The hydrogen diffusion coefficient into the bulk of... 

Electrodeposition of aluminum onto graphite from a molten electrolyte containing AlCl3-NaCl-KCl was studied by the method of chronoamperometery. In the early stage of the deposition and at low cathodic potentials two-dimensional (2D) nucleation and growth proceeding through instantaneous and a multitude of progressive steps followed the initial double layer charging. The processes are manifested as peaks on a decaying chronoamperogram. Non-linear fitting methods were applied to obtain the kinetic parameters in the light of Bewick, Fleischmann and Thirsk (BFT) theory. Under more cathodic potentials, transition from 2D to three-dimensional (3D) processes have been observed as manifested in the... 

The processes of adsorption and absorption of H atoms on silver electrode in alkaline media has been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The potential range in the CV studies has been between -0.1 and -1.6 V /Ag-AgCl. In the first cycle, two cathodic and three anodic peaks have been observed. The H atom electrosorption current peak at ca. -0.6 V/Ag-AgCl, which appears at second cycle, is assigned to hydrogen absorption states. Nyquist plots consist of two overlapping semi-circles of variable diameters depending on the extent of the cathodic dc-potential offset. Hydrogen absorption occurs simultaneously with the hydrogen evolution reaction... 

The electrochemical adsorption and diffusion (dissolution) of hydrogen into mercury have been studied by the methods of cyclic voltammetry and impedance spectroscopy. In the potential range of -0.15 to -1.5 V (vs: Ag/AgCl) two peaks at -0.4 and -0.8 V have been observed and are associated with the adsorption and absorption of hydrogen. Impedance studies exhibit two overlapping semi-circles terminating in a straight line in the low potential region. The size of the semi-circles increases as the potential is raised and is attributed to the increased resistive effect of the dissolved hydrogen. The value of the real component upon increasing the measurement potential to -0.9 V is followed by a... 

The electro-oxidation of methanol on copper in alkaline solutions has been studied by the methods of cyclic voltammetry, quasi-steady state polarization and chronoamperometry. It has been found that in the course of an anodic potential sweep the electro-oxidation of methanol follows the formation of CuIII and is catalysed by this species through a mediated electron transfer mechanism. The reaction also continues in the early stages of the reversed cycle until it is stopped by the prohibitively negative potentials. The process is diffusion controlled and the current-time responses follow Cottrellian behavior. The rate constants, turnover frequency, anodic transfer coefficient and the apparent... 

Electrodes made of group VIII and IB metals were examined for their redox process and electrocatalytic activities towards the oxidation of ethylene glycol in alkaline solutions. The method of cyclic voltammetery (CV) and Open circuit potentials measurement (OCP) was employed. It is found that considerable electrooxidation current are observed for silver and copper but lower anodic overpotential for oxidation is obtained for gold and platinum. Oxide layer produced on the surface of all electrodes in alkaline solution under anodic scan participates in ethylene glycol electrooxidation. Oxidation current observed in the reverse scans for platinum and gold are higher than those observed in... 

The electro-catalytic oxidation of methanol on a Ni-Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0-600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10-4 cm2 s-1 and... 

Platinum microparticles electrodeposited at a glassy carbon surface (Pt/GC) and within a poly-ortho-aminophenol film formed on a GC substrate (Pt/PoAP/GC) have been used for investigating their catalytic activity towards hydrogen evolution reaction and methanol oxidation by cyclic voltammetry, impedance spectroscopy and chronoamperometry. The effect of the deposition time (t dep) of the Pt particles dispersed into GC and PoAP electrodes and of the acid anions (SO42-, ClO4- on the hydrogen adsorption/desorption peaks and hydrogen evolution reaction has been studied. It has been shown that the main cause of immediate blocking of the PoAP-SO42- pores with platinum microparticles is its smaller... 

PbS on Pb thin film (Pb/PbS) was deposited on conductive glass (CG) substrate (CG/Pb/PbS) using electrochemical techniques to investigate the Schottky junction in solution. The CG/Pb/PbS electrode was investigated by different techniques based on thermionic emission theory. Electrochemical cell consisted of the CG/Pb/PbS as a working electrode in an alkaline solution showed character of the Schottky junction. Reduction and oxidation of H2O on the CG/Pb/PbS electrode were enhanced under illumination. Water photo splitting is the main process. Study of linear sweep voltammetry at around open circuit potential (OCP) allowed proposing a model based on the Schottky junction which is charged at... 

Nickel modified NiOOH electrodes were used for the electrocatalytic oxidation of ethanol in alkaline solutions. The electro-oxidation of ethanol in a 1 mol/L NaOH solution at different concentrations of ethanol was studied by ac impedance spectroscopy. Electrooxidation of ethanol on Ni shows negative resistance on impedance plots. The impedance shows different patterns at different applied anodic potential. The influence of the electrode potential on impedance was studied and a quantitative explanation for the impedance of ethanol oxidation was given by means of a proposed mathematical model. At potentials higher than 0.52 V(vs. Ag/AgCl), a pseudoinductive behavior was observed, but at those...