Search

Abstract: The electro-oxidation of methanol on nickel and nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) in a 1M NaOH solution at different concentrations of methanol was studied by the method of ac-impedance spectroscopy. Two semicircles in the first quadrant of a Nyquist diagram were observed for electro-oxidation of methanol on GC/Ni corresponding to charge transfer resistance and adsorption of intermediates. Electro-oxidation of methanol on GC/NiCu shows negative resistance in impedance plots as signified by semi-circles terminating in the second quadrant. The impedance behavior shows different patterns at different applied anodic potential. The influence of the electrode potential on impedance pattern is studied and a mathematical model was put forward to quantitatively account for the impedance behavior of methanol oxidation. At potentials higher than 0.49V vs. Ag/AgCl, a pseudoinductive behavior is observed but at higher than 0.58V, impedance patterns terminate in the second quadrant. The conditions required for this behavior are delineated with the use of the impedance model. [Copyright &y& Elsevier]

Abstract: The electro-oxidation of glucose on nickel-modified glassy carbon electrode (GC/Ni) in a 1M NaOH solution at different concentration of glucose was studied by the method of ac-impedance spectroscopy. In low concentration of glucose (<7mM) two semicircles in the first quadrant of a Nyquist diagram were observed corresponding to charge transfer resistance and adsorption of intermediates. In higher concentration of glucose (>10mM) negative resistance is observed in impedance plots as signified by semicircles terminating in the third quadrant. The impedance data in high concentration of glucose show different behavior at different applied anodic potential. The influence of the electrode potential on impedance pattern in high concentration of glucose is studied and a mathematical model was put forward to quantitative account for the impedance behavior of glucose oxidation. At potentials higher than 0.525V/Ag–AgCl, a pseudoinductive behavior is observed but at higher than 0.4V/Ag–AgCl, impedance patterns terminate in the second and third quadrants. The conditions required for this behavior are delineated with the use of the impedance model. [Copyright &y& Elsevier]

Abstract: Nickel and nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV) and chronoamperometry (CA) were employed. The cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution. In CV studies, in the presence of methanol NiCu alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 2×10−6 cm2 s−1 in agreement with the values obtained from CV measurements. [Copyright &y& Elsevier]