In the 1950s and 1960s fundamental developments in electrochemical methods included voltammetry and low signal techniques. A generation later, the discovery of the unusual properties of ultramicroelectrodes has opened new possibilities of analyzing electrode processes. The changes in mass transport conditions bring about extremely high current densities at ultramicroelectrodes, whereas the currents themselves become very small. This little-noticed phenomenon allows for many electroanalytical applications that are not possible with conventional electrodes, especially experiments in solutions with very low electrolyte concentrations, in nonpolar solvents, in solids, and even in gases. In addition, two factors— changes in the experimental time scale at low scan rates because of the size of the electrode, and insignificant iR effects at very high scan rates—make it possible to study very fast homogeneous and heterogeneous electrode processes.

Ultramicroelectrodes in Electrochemistry

Copper(II)-selective electrode using thiuram disulfide neutral carriers

Fast-scan voltammetry of biogenic amines

Direct determination of diffusion coefficients by chronoamperometry at microdisk electrodes

Nanometer-sized glass-sealed metal ultramicroelectrodes (UMEs) have been prepared using a laser-based micropipet puller. The tip was exposed to solution either by etching away a small portion of glass insulator or by micropolishing. The characterization of the UMEs was carried out by a combination of steady-state voltammetry, scanning electron microscopy (SEM), and scanning electrochemical microscopy (SECM). The cyclic voltammograms obtained have a regular shape with very small capacitive and resistive background. The effective electrode radii obtained from voltammetry were between 2 and 500 nm. From the SEM micrographs, the shape of polished tips appears to be close to a microdisk, while the geometry of etched electrodes is closer to conical. Accordingly, the SECM current−distance curves (iT−d) obtained with polished electrodes fit well the theory for a disk-shaped tip, while a 20-nm-radius etched electrode was shown to be a fairly sharp cone with a height-to-radius ratio of about 2.5. The experimental d...

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Nanometer-Sized Electrochemical Sensors

A method for the preparation of mercury microvoltammetric electrodes of hemispherical geometry with radii of 2.3-7.3 ..mu..m has been developed. Mercury is electrodeposited from solutions of Hg(I) onto a microvoltammetric platinum disk electrode at a constant potential sufficient to ensure diffusion limited conditions. The radius of the deposited mercury electrode is a function of the square root of the deposition time and was experimentally evaluated by applying the equation for steady-state limiting current at a hemispherical electrode to the reduction of Ru(NH/sub 3/)/sub 6//sup 3 +/ at the mercury electrode. The mercury microvoltammetric electrode has been employed in several unique applications. Anodic stripping voltammetry with these electrodes can be performed with a quiescent solution during deposition due to the enhanced mass transfer resulting from nonlinear diffusion. The stripping peaks are as narrow as those expected for thin films, and the peak current for the stripping of lead was found to be linear over the concentration range of 7 x 10/sup -10/ M to 1 x 10/sup -7/ M (5-min preconcentration interval) and to have higher precision than conventional stripping techniques. Mercury microvoltammetric electrodes also are demonstrated to be of value in fast scan cyclic voltammetry in aqueous solution. A well-definedmore » wave can be obtained for the oxidized form of ascorbic acid at pH 7.0 at a scan rate greater than 1 kV s/sup -1/. 26 references, 3 figures, 2 tables.« less

K.R. Wehmeyer

Papers

Cyclic voltammetry and anodic stripping voltammetry with mercury ultramicroelectrodes