A. Jannakoudakis

Gas Phase Photoelectrochemistry in a Polymer Electrolyte Cell with a Titanium Dioxide/Carbon/Nafion Photoanode

Mixtures of Ti0 2 and carbon powders are tested as photoanodes in mini-photoelectrochemical cells based on Nafion electrolyte-impregnated microporous membranes. The composite TiO 2 + C working electrode is formed onto one face of the membrane (where a Ag/AgCl reference electrode is also adhered), whereas a stainless steel mesh counter electrode is attached to its opposite face. Photovoltammetry and constant potential photoamperometry carried out under UV-A illumination in the presence of water and methanol vapors result in well-defined photoelectrochemistry, characteristic of water and methanol photo-oxidation, and point to the possibility of scaling up similar devices to be used in electrically enhanced photocatalytic air treatment.

Preparation of a Carbon Fiber-Nickel-Type Material and Investigation of the Electrocatalytic Activity for the Hydrogen Evolution Reaction

The preparation and the electrocatalytic activity of a new material of the type carbon fiber-nickel was investigated. Nickel growth on the carbon support was can-ied out through electrolysis. The kinetic of nickel deposition as a function of the electrolysis conditions was examined by cyclic voltammetry. The morphology and substitution of the nickel deposits, which at the beginning of the nickel growth proved to be of a globular type, were studied by scanning electron microscopy. It was established that a high degree of the carbon surface functionalization, achieved by double pulse oxidation, favored the nickel deposits on the oxidized carbon support. The electrocatalytic efficiency of nickel-modified carbon fiber electrodes was investigated by means of impedance spectroscopy for the hydrogen evolution reaction. The charge transfer resistance values of this reaction were significantly lower in the case of modified by nickel oxidized carbon fibers in comparison with the corresponding values for modified by nickel pristine fibers. The above values are in the order of magnitude of modified by noble metals, such as Pd and Rd, carbon fibers obtained through ion-exchange with the functional groups of the oxidized carbon fibers, and subsequent electrochemical or chemical reduction.

Electrochemical behaviour of bis(1,3-dionato)copper(II) chelates on mercury and carbon fibre electrodes

Abstract The electrochemical behaviour of 14 bis(β-dionato)copper(II) chelates was investigated in acetonitnie at Hg and carbon fibre electrodes. The reduction potentials span a range of ~ 1.1 V. Electronic effects engendered by the substituents in the chelate ring determine the potential at which reduction occurs and influence the mechanism of reduction. On the basis of the mechanism, the chelates may be classified into two subgroups: the first one comprises compounds undergoing a two-electron reduction while the second one consists of chelates reduced in two one-electron steps. The use of carbon fibres facilitates separation of the first subgroup into two classes. The reduced species, [Cu(β-dionato) 2 ] − . of chelates having aromatic substituents exists in equilibrium, with the solvated copper(I) ion, Cu + (s).

Electrochemical behaviour of tris (β-diketonato)cobalt(III) chelates on mercury and carbon fibre electrodes

Abstract The polarographic and cyclovoltammetric behaviour of a series of cobalt(III) β-diketonates in acetonitrile solution at the mercury and carbon electrodes is reported. These techniques identified one mono-electronic revsersible reduction and a two-electron electrochemical reduction step leading to elemental cobalt. The E 1 2 for the first step is shifted appreciably with ligand substituents and a linear Hammett relationship is obeyed. The presence of the -CF3 group increases the reduction potential so that Co(hfac)3, containing six -CF3 groups, acts oxidatively on hydrazine. Carbon fibre electrodes extend the study to complexes that cannot be investigated on the Hg electrode. Adsorption of reactants, especially those containing ligands with two phenyl groups, modifies the carbon fibre electrodes so that they catalyse the oxygen reduction in acetonitrile.

Structure and Electrocatalytic Activity of Ni–W Thin Films Deposited on Carbon Fiber Supports

The growth of nickel-tungsten thin films on oxidized and nonoxidized carbon fibers is carried out under potentiostatic conditions in electrolyte solution containing nickel sulphamate and high amounts of tungsten. The electrocatalytic behavior of the deposits on different substrates (oxidized and nonoxidized carbon fibers) is compared. The kinetic of hydrogen evolution on Ni-W deposits is examined in sulfuric acid by cyclic voltammetry. The scanning electron microscopy and X-ray diffraction results show a more developed structure of Ni-W deposits on oxidized carbon fibers, as the domain size is two times less than on the nonoxidized carbon fibers. The impedance spectroscopy measurements show that Ni-W oxidized carbon fiber electrodes exhibit better electrocatalytic activity for the hydrogen evolution reaction (HER) than the Ni-W nonoxidized carbon fiber electrodes. The compact films show a higher catalytic activity in comparison with an island structure deposition.