L.M. Peter
University of Southampton
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Featured researches published by L.M. Peter.
Journal of Electroanalytical Chemistry | 1991
M. Kalaji; L. Nyholm; L.M. Peter
Platinum microelectrodes (diameter 10 μm) have been used to study the influence of pH, ionic strength, isotopic substitution and different anions on the redox switching of electrochemically prepared polyaniline (PANI) films under first cycle and multicycle conditions. Microelectrodes reduce iR errors greatly and allow rapid scan cyclic voltammetry ( ⩾ 100 V/s) to be used in order to avoid degradation of the PANI in the region of the second oxidation peak. In all cases, the oxidation charge passed on the first cycle was found to be larger than on subsequent cycles (the first cycle effect). The multicycle switching charge was found to decrease with increasing pH, decreasing ionic strength and with increasing anion size, whereas the charge associated with the first positive scan was much less affected. More positive oxidation peaks were also obtained in DCl and D2SO4 than in HCl and H2SO4, respectively. It is concluded that the oxidation of PANI proceeds initially via rapid field driven proton egress, followed by equilibration of the oxidised phase by diffusion controlled movement of acid. Under multicycle conditions, part of the oxidized PANI film appears to remain inactive, but can be reduced if the potential is held at −0.2 V vs. SCE for several minutes. The loss of electroactivity under reduction conditions suggests that ion ingress is much more difficult than ion egress in the PANI system.
Electrochimica Acta | 1989
D.J. Blackwood; L.M. Peter
ac Impedance measurements and photocurrent spectroscopy have been used to examine the dependence on growth rate of the solid state properties of thin (<20 nm) anodic oxide films on titanium. At room temperature, the relative permittivity and defect concentration profiles in the oxide were found to depend markedly on growth rate. The effects on the photocurrent of recombination and trapping were most pronounced when the films are grown rapidly. It was found that the high defect densities associated with rapidly grown oxide films could be decresed by growing or annealing the oxide films at higher temperatures.
Electrochimica Acta | 1989
D.J. Blackwood; R. Greef; L.M. Peter
The behaviour of titanium in 3.0 mol dm−3 H2SO4 has been studied by in situ ellipsometry. The growth and subsequent dissolution of the anodic oxide under open-circuit conditions have been characterised and in addition evidence for the formation of a suboxide layer between the metal and the dioxide film has been obtained. The ellipsometric data show that thinning of the oxide film in H2SO4 at open-circuit occurs by uniform dissolution at a constant rate, rather than by localized attack. These results confirm the conclusions reached in a previous study in which the charge required to regrow the film following partial dissolution was measured by linear sweep voltammetry.
Journal of Electroanalytical Chemistry | 1981
L.M. Peter; J.D. Reid; B.R. Scharifker
Abstract Under electrochemical conditions, the formation of thin mercuric sulphide films on mercury proceeds in three distinct stages. In the first, mercuric sulphide adsorbs over a narrow range of potential to build up a monomolecular layer. This adsorbed layer subsequently rearranges in such a way that its packing density is increased. The rearrangement corresponds to a first order phase transformation, and clear evidence for the nucleation of the rearranged phase has been obtained. Finally the growth of subsequent monolayers of mercuric sulphide proceeds by the nucleation and expansion of two dimensional centres on the rearranged first layer. A variety of electrochemical techniques has been used in this study to characterise these three individual steps in detail.
Journal of Electroanalytical Chemistry | 1992
M. Kalaji; L. Nyholm; L.M. Peter
Abstract Electrochemically prepared polyaniline (PANI) films have been studied by galvanostatic charge injection. The potentiostatic-galvanostatic-potentiostati state of the polymer was well defined. The potential of the PANI film was recorded during the injection and removal of charge as well as during the sub The chronopotentiometric responses observed during the first oxidation step exhibit an overpotential maximum at short times and this is interpreted as the polymer. By contrast, the chronopotentiometric responses recorded during reduction of the conducting emeraldine form show no such effect. The open- and reduction do not coincide, mainly since the oxidation responses deviate strongly from equilibrium behaviour. The difference between oxidation and r relaxes substantially at open-circuit when the oxidation current is interrupted, whereas the open-circuit potential remains almost constant after a cat must proceed by different pathways and involve different degrees of disorder.
Journal of the Chemical Society, Faraday Transactions | 1991
M. Kalaji; L.M. Peter
The small-amplitude periodic optical transmittance response of redox polymer films is derived and related to the corresponding electrical behaviour. The combination of optical and electrical measurements allows Faradaic and non-Faradaic charging processes to be distinguished. The analysis of the modulated transmission data obtained for polyaniline films on indium-doped tin oxide coated transparent electrodes in 1.0 mol dm–3 H2SO4 indicates that the capacitance measured in a.c. experiments is associated with redox transformations in the PANI film. The a.c. capacitance was found to be lower than the pseudo-capacitance derived from cyclic voltammograms and possible reasons for this discrepancy are discussed. The absorption coefficient of the polaron has been derived from the relationship between the modulated transmittance and the film capacitance which also shows that bipolaron states are formed at potentials more positive than 0.15 V vs. SCE.
Faraday Discussions of The Chemical Society | 1989
Robert Greef; M. Kalaji; L.M. Peter
Ellipsometry has been used to characterise the growth of polyaniline films on platinum and gold electrodes by potential cycling. Analysis of the time evolution of the ellipsometric parameters allowed continuous monitoring of the growth process, and subsequent measurements of the changes in optical properties during oxidation and reduction of the PANI film were related to the electrochemical behaviour. Spectroscopic ellipsometry has been used to evaluate n and k values of the film for differing degrees of oxidation. Frequency-resolved transmission measurements have been used to show that the periodic electrical and optical responses of the polyaniline film are directly related.
Journal of Electroanalytical Chemistry | 1992
J.-N. Chazalviel; F. Ozanam; F. Paolucci; L.M. Peter; J. Stumper
The anodic dissolution of silicon in fluoride media has given rise to much excitement in recent years [l-lo], particularly concerning the intriguing current oscillations sometimes observed in the anodic region (2.5 V < Es,, < 7 V). Several authors [1,5,10-121 have found that the current exhibits spontaneous oscillations above a critical potential = 3 Vs,,. On the contrary, other authors [8,9] have found damped oscillations, which appear only upon a perturbation of the electrode potential. This has allowed them to perform a detailed investigation of the electrochemical impedance in that regime, and to propose a model accounting for their experimental results [9,13]. The origin of the discrepancy between the various authors was somewhat of a mystery. However, the compositions of the electrolytes were different in the various groups, and, interestingly, the electrolytes where sustained oscillations had been observed are in a fluoride concentration range higher than those where the damped ones had been reported. We will show here that, irrespective of the electrolyte composition in a wide fluoride concentration and pH range, the oscillations can be made intentionally damped or sustained, depending upon the value of the uncompensated resistance in series with the interface. All our experiments have been performed on low-doped p-Si electrodes (resistivity l-4 R cm). We performed two kinds of experiments. The first experiments demonstrate that, on a given interface, with damped oscillations (“steady” interface), a sustained oscillation can be created by adding an external resistor in series with the working electrode. We have taken the
Journal of Electroanalytical Chemistry | 1981
Graham Hills; L.M. Peter; B.R. Scharifker; M.I. Da Silva Pereira
Abstract The electrochemical nucleation and growth of two-dimensional anodic films on liquid electrodes has been studied by the galvanostatic method. Overpotential-time relationships have been derived from a model of the electrocrystallisation process which assumes that the rate-determining step involves incorporation of ad-molecules into the lattice of the expanding growth centres. Comparison of these theoretical curves with experimental transients has shown that non-steady state effects are important in nucleation under galvanostatic conditions. The experimental examples considered are the formation of Cd(OH) 2 on Cd(Hg), Hg 2 Cl 2 on Hg and HgS on Hg.
Electrochimica Acta | 1989
L.J. Li; M. Fleischmann; L.M. Peter
Abstract Carbon, platinum and lead microelectrodes have been used to study electrocrystallization reactions relevant to lead-acid battery electrochemistry. It is shown that single centres of α- and β-PbO 2 can be formed on carbon fibre microdisc electrodes, allowing direct measurement of the kinetics of phase growth in the absence of overlap. The validity of the analysis of current time transients has been established by examining the number, shape and size of the growth centres by scanning electron microscopy. At the same time, it has been found that the morphology of single centres of the two phases is quite different. The reductive transformation of individual α- and βPbO 2 centres to PbSO 4 has been studied as a function of sulphuric acid concentration by scanning electron microscopy, and the interconversion of lead, lead sulphate and lead dioxide has also been investigated using lead microdisc electrodes. The combination of kinetic and electron microscopic measurements at microelectrodes has revealed details of the reaction mechanisms that cannot be derived from observations at electrodes of conventional size.