Sergio Valcher

Potentiometric investigation of the kinetics of the polyaniline—oxygen reaction

Abstract Polyaniline films electrodeposited onto glassy carbon electrodes are reversibly oxidized in acid solution by dissolved oxygen. Electrocatalytic oxygen reduction was investigated at stationary and rotating filmed electrodes. The kinetics of oxygen reduction, determined by means of potentiometric measurements, are first order in oxygen concentration and second order in the concentration of redox sites in the polymer.

Studies of Zn|ZnX2|polyaniline batteries. I. X.=Cl and Br

The cycling behaviour of polyaniline in chloride and bromide media is discussed. In both media some charge, equivalent to a charge storage capacity of 100 A h kg−1, may be stored in the first oxidation step of polyniline. Further evidence is presented that the oxidation product is emeraldine rather than the fully oxidized imine. In chloride media, attempts to store more charge led to rapid irreversible changes in the polymer and degradation in battery characteristics. In bromide media, further charge may be stored via the Br−/Br3− couple and, although the Br2 attacks the polymer slowly, the polymer retains the ability to cycle charge efficiently and gives a stable open-circuit voltage. The nature of the changes caused by Br2 attack on the polyaniline is discussed. It is concluded that bromide is the better electrolyte, but self discharge by slow exchange of Br3− in the polymer with Br− in the surrounding electrolyte remains an unsolved problem.

Polymeric salt as bromine complexing agent in a Zn-Br2 model battery

Abstract The present investigation examines the possibility of using a polymeric salt, polydiallyldimethyl-ammonium bromide, as bromine complexing agent, in a Zn-Br 2 battery. The performance of a battery model which couples the use of the polymeric salt with that of reticulated vitreous carbon (RVC) as electrode material is described.

Polyaniline as a cathode for O2 reduction−kinetics of the reaction with H2O2 and use of the polymer in a model H2O2 fuel cell

Abstract Oxygen reduction at a polyaniline cathode occurs in aqueous sulfuric acid through a chemical-electrochemical route which involves the intermediate oxidation of leucoemeraldine to emeraldine with the formation of H 2 O 2 . This paper specifically deals with the conversion of leucoemeraldine to emeraldine by H 2 O 2 whose kinetics, apparently second order on the charge exchanged, are similar to those found for the reaction with O 2 , although they occur at lower rate. The catalytic four electron O 2 reduction mediated by the Fe(III)/Fe(II) couple which decomposes H 2 O 2 is not fully achieved. However, polyaniline proved to be a reliable cathode for O 2 , sustaining the working of a model H 2 /O 2 fuel cell.

Electrocatalytic oxidation of hydrazine in acid media on polyaniline-filmed vitreous carbon

0.5 M hydrazine in aqueous H2SO4 for pHs in the range 1.5–3.75 catalytically oxidizes on polyaniline-filmed vitreous carbon, whereas the process is totally inhibited on the bare electrode substrate. The pH dependence of the reducing power of hydrazine accounts for the onset potential of the oxidation, while the currents are under pure kinetic control. A kinetic analysis of the “chemical” reduction of the emeraldine by hydrazine indicates that its rate characterizes the currents. Catalytic oxidation is faster in aprotic medium but the currents are transient owing to progressive deactivation of the polymer electrode.

Preliminary investigations on7Be as a tracer in the study of environmental processes

The usefulness of cosmogenic7Be as a tracer in a terrestrial environment has been investigated. Atmospheric fluxes and inventories of the radionuclide in grassland have been determined. Environmental behavior in connection with foliar interception and possibility of subsequent release has been studied.

Adsorption of amyl alcohol on Ag(111) electrodes : effect of electrode pretreatment and experimental technique

Abstract The adsorption of amyl alcohol on Ag(111) electrodes from 0.05 mol dm −3 KClO 4 aqueous solutions was studied by means of capacitance curves and potential steps. The results were compared with those obtained by Popov and coworkers using a capacitance bridge with differently prepared electrodes. Differences and inconsistencies are discussed in terms of experimental technique and electrode surface preparation. Amyl alcohol is less well adsorbed on Ag(111) than it is on Hg. Literature data for polycrystalline Au are also scrutinized for a comparative analysis. The capacitance under adsorption-desorption peaks is severely affected by frequency effects more at positive than at negative charges. Analysis of the peak parameters may lead to inconsistent conclusions. The superiority of the coulometric technique needs to be confirmed by further data since the physical picture is sometimes puzzling.

Polarographic study of dicyclopentadienyltitanium di-chloride (TiCp2Cl2)

The polarographic behavior of TiCp2Cl2 has been studied in water and dimethylformamide solutions. In every case the complex is reduced, at the DME, to a compound of Ti(III). In DMF, two anodic waves are also obtained; these waves enable the Kinetics of dissociation of the complex: , to be studied. The rate constant and the activation energy were evaluated by polarographic measurements.

Electrochemistry of coordination compounds

Summary The electrochemical behaviour of trans -chlorocarbonylbis (triphenylphosphine) rhodium has been investigated on the mercury electrode in 50% acetonitriletoluene containing excess of triphenylphosphine. The reduction proceeds via a two-electron step leading to a rhodium (−1) anion. Such an anion has been found to react with the starting compound forming a rhodium(0) complex. A reduction-oxidation mechanism accounting for the chemical and electrochemical results is proposed.

Studies of Zn|ZnX2|polyaniline batteries. II. X=I

The characteristics of a Zn|ZnI2|polyaniline battery have been examined. It is demonstrated that the polymer has a charge storage capacity of 143 A h kg−1 and an energy efficiency above 70%. The battery has an open circuit voltage of 1.2 V and polarization during charges and discharges at 30–120 mA were low. Self discharge is low compared to the chloride and bromide electrolyte batteries and charge recovery was 60% after 12 days stored on open circuit. It is shown that these promising characteristics may be interpreted in terms of a system where the polyaniline largely acts as a current collector and the I3−/I− couple is rapid within the film. The kinetics of the system are determined by a.c. impedance.