John Daschbach

The behavior of microdisk and microring electrodes: application of Neumann's integral theorem to the prediction of the steady state response of microdisks

Abstract It is shown that Neumanns integral theorem can be used to derive the steady-state behavior of microdisk electrodes. Results obtained previously using other methods for uniform surface concentration and uniform flux boundary conditions are derived as limiting cases of a general equation which describes irreversible and quasi-reversible reaction kinetics. It is shown that the approach can be used to assess the effects of the tertiary current distribution and to predict the behavior for electrode reactions which are non-linear in the concentration terms.

The behavior of microdisk and microring electrodes. Mass transport to the disk in the unsteady state: Chronopotentiometry

Abstract The analysis of the transient response of a finite geometry disk electrode (embedded in an infinite insulating plane) to a potential step is given. The analysis makes use of the properties of discontinuous definite Bessel integrals.

The ac impedance of spherical, cylindrical, disk, and ring microelectrodes

Abstract The ac impedance for a simple redox reaction at microspherical and cylindrical electrodes is derived using conventional methods. An exact formalism is developed for the analysis of the behavior of microdisks and microrings which will allow the analysis of complex reactions using such electrode designs. The analysis here is restricted to the approximation of a uniform ac flux to the electrodes. The behavior of the various electrode designs is compared and contrasted with that of the conventional large planar systems.

Electrochemistry of Ferrocene in Acetonitrile. Evidence for Irreversible Kinetic Behavior Due to Passive Film Formation

Abstract : Montenegro and Pletcher have recently pointed out that measurement of the heterogeneous electron transfer rate constant of the ferrocene/ferrocenium couple at ultramicroelectrodes in acetonitrile solutions gives values that are several orders of magnitude larger than those measured at conventional electrodes. In addition, Bond et al. have pointed out that there is ambiguity in the interpretation of the electrochemical behavior of this couple in organic solvents. There are large discrepancies between the results from different workers on similar electrolyte/solvent systems which serves to show the difficulty in marking reliable measurements on this supposedly ideal electrochemical system. The situation is further confused since it has been proposed as a potential standard couple for non-aqueous electromechanical calibration. In his work on similar measurements on ferrocene/ferrocenium in acetonitrile at an ultramicroelectrode, Bond has discussed in detail several possible reasons for these discrepancies. Keywords: Reprints.

The behavior of microdisk and microring electrodes: application of Neumann's integral theorem to the prediction of the steady state response of microdisks. Numerical illustrations

Abstract We illustrate numerical examples of the application of Neumanns integral theorem to the steady state behavior of microdisk electrodes. Results obtained previously using other methods for uniform surface concentration and uniform flux boundary conditions are derived as limiting cases of a general equation which describes irreversible and quasi-reversible reaction kinetics. It is shown that the approach can be used to assess the effects of the tertiary current distribution. Comparisons are made with previous approximate analyses.

Time-Resolved Infrared Spectroelectrochemistry

The generation of time-resolved infrared spectra of species formed at the electrode-solution interface is reported. The methodology involves electronic pre- or post-coupling of the electrochemical experiment to the interferometer retardation timing. By the sorting of the data points in each of the resulting sets of interferograms, which are accumulated over finite intervals of time after initiation of the electrochemical experiment, spectra representing very short integrated time periods are obtained. These time discretized spectra represent the time evolution of the vibrational structure at the electrode surface.

The behavior of microdisk and microring electrodes: The chronoamperometric response at microdisk and microring electrodes

Abstract We report the theoretical chronoamperometric response for a ring electrode of finite size, and compare the experimental response to that of a disk electrode. As expected, the response of the ring electrode approaches mass transport conditions close to those for the final steady state at times which are short compared to those at which the steady state is reached for disks of similar radii. The theoretical analysis is based on the properties of discontinuous integrals of Bessel functions which give exact solutions to diffusion problems with discontinuous boundary conditions in the circular cylindrical coordinate system.

The behavior of microdisk electrodes: Chronopotentiometry and linear sweep voltammetric experiments

Abstract In this paper, we discuss the forms of the overpotential-time response to controlled current experiments at finite disk electrodes, and compare these to experimental results obtained at disk microelectrodes. With microelectrodes, fast mass transport conditions and low charging currents give rise to sharp transitions at suitably high values of the imposed flux in galvanostatic chronopotentiometry experiments, and always a transition in linearly swept flux experiments.

The infrared spectra of surface metal atom vibrations: Sniftirs studies in the far infrared region using time resolved FTIR techniques

Abstract : Studies of the vibrations of pure metals have historically been pursued by inelastic neutron scattering (which is sensitive to vibrations of the bulk crystal) and more recently by high-resolution electron energy loss spectroscopy. HREELS (which is more sensitive to vibrations of the metal surface). Direct infrared absorbance techniques provide advantages over both of these methods, since they may be used in more hostile environments (such as at the interface between metal and chemical solutions). They have rarely been applied with much success, however, because of the very effective shielding of the electromagnetic radiation by the metal conduction electrons. This results in an exponential damping of the radiation field as it enters the metal phase, with typical skin depths (1/e damping distances) of only a few tens of nm. This damping improves the sensitivity of infrared absorption measurements to the surface vibrations as opposed to bulk phonons, but limits the magnitude of the absorbance considerably. In this report we demonstrate that reflection infrared vibrational spectroscopy may be used to observe the vibrational structure of metallic species deposited on a metal surface which is under electrochemical control. Keywords: Spectroelectrochemistry, Time resolved spectroscopy, Metal atom spectroscopy, Infrared radiation.

Preliminary noteThe infrared spectra of surface metal atom vibrations: Sniftirs studies in the far infrared region using time resolved FTIR techniques

Abstract : Studies of the vibrations of pure metals have historically been pursued by inelastic neutron scattering (which is sensitive to vibrations of the bulk crystal) and more recently by high-resolution electron energy loss spectroscopy. HREELS (which is more sensitive to vibrations of the metal surface). Direct infrared absorbance techniques provide advantages over both of these methods, since they may be used in more hostile environments (such as at the interface between metal and chemical solutions). They have rarely been applied with much success, however, because of the very effective shielding of the electromagnetic radiation by the metal conduction electrons. This results in an exponential damping of the radiation field as it enters the metal phase, with typical skin depths (1/e damping distances) of only a few tens of nm. This damping improves the sensitivity of infrared absorption measurements to the surface vibrations as opposed to bulk phonons, but limits the magnitude of the absorbance considerably. In this report we demonstrate that reflection infrared vibrational spectroscopy may be used to observe the vibrational structure of metallic species deposited on a metal surface which is under electrochemical control. Keywords: Spectroelectrochemistry, Time resolved spectroscopy, Metal atom spectroscopy, Infrared radiation.