Showing papers by "Andrew Hamnett published in 1993"

Electrocatalytic reduction of hydrogen peroxide at a stationary pyrolytic graphite electrode surface in the presence of cytochrome c peroxidase: a description based on a microelectrode array model for adsorbed enzyme molecules

Abstract: Electrochemical reduction of H2O2 at pyrolytic graphite disc electrodes of radius 2.5 mm occurs at readily accessible potentials (600 mV versus the standard hydrogen electrode) in the presence of yeast cytochrome c peroxidase. Introduction of the enzyme into the electrolyte solution initiates large changes in the ellipsometric angles measured for the electrode–solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electrochemical activity. Over the same time course, linear-sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type waveform. It is proposed that the time-dependent behaviour may be rationalized by use of a microscopic model for substrate mass transport, in which the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules. A voltammetric theory based on treating the adsorbed redox enzymes as an expanding array of microelectrodes is in excellent agreement with experiment.

An in situ Fourier-transform infrared study of the electroreduction of polybithiophene

Abstract: In situ FTIR spectra have been acquired for n-doped polybithiophene (PBT) films on Pt as a function of electrode potential. The spectra are qualitatively similar to those of p-doped PBT: they show a broad electronic band in the near IR and enhanced ring vibration (IRAV) modes. The variation of IRAV band intensities with potential (doping level) can be explained using a model in which carrier–carrier interactions increase linearly with carrier density. This model allows correlation of IRAV and electronic band intensities for both p- and n-doped PBT. Optically determined microscopic conductivities for n-doped PBT are similar to those for p-doped PBT. We find evidence for solvent (acetonitrile) in two types of environment within the film, and observe changes in solvent population within the film via transient (un)doping experiments.

Process for the preparation of conductive polymers

Abstract: Provided is a method for preparing a conductive polymer which is highly transparent to visible light in at least one of its conductive and non-conductive states. A solution containing a monomer component and an electrolyte is introduced into an electrochemical cell and subjected to polymerization by cyclic voltammetry. The solution is maintained at a temperature within a range of from 0° to -40° C. inclusive. Prior to the polymerization, cyclic voltammetry is firstly performed at a potential below that at which anodic or cathodic polymerization may take place, anodic and cathodic limits (A) and (B) being held at respective values. A trace of current/voltage is monitored until the trace becomes stable, and thereafter the value of the limit (B) is progressively increased until the said value reaches a critical potential having a magnitude at which anodic or cathodic polymerization is initiated.

Surface processes at electrolyte/highly doped semiconductor interfaces analysed by electroreflectance modelling

Abstract: Electroreflectance spectra from a highly doped n-GaAs sample in an alkaline electrolyte have been modelled, taking into account both Franz–Keldysh and bandfilling (Moss–Burstein) effects. Comparisons are made between theory and experiment, and the evolution of spectra calculated for a wide range of space-charge potentials is found to follow accurately that of the experimental spectra with applied potential. The proportion of the interfacial a.c. and d.c. potential differences accommodated outside the semiconductor can also be obtained from the analysis, allowing us to extract the Fermi level pinning and to associate this with possible surface chemical reactions. The importance of heavy-doping effects is also briefly discussed, and the inclusion of bandfilling in the modelling of the electroreflectance spectra of highly doped n-GaAs is shown to be essential if a quantitative fit is to be obtained.