Microelectrodes ensembles

There are three possible arrangements of microelectrode ensembles ... 

One of the earliest applications of the template method was to prepare ensanble miCTo-scopic (7, 18) and nanoscopic electrodes (116, 141). Such electrodes were prepared by electrochemically depositing noble metals within the pores of the commercially available polymeric filtration membranes. The fabrication of a microelectrode ensemble based on the electrochemical deposition of platinum into the pores of a track-etched microporous polycarbonate host membrane was first shown in 1987 by Charles Martin (7). The word ensemble was used to describe the final device because the elements in the device are not evenly spaced. The procedure is simple, and requires only routine and inexpensive electrochemical instrumentation. It was ultimately found that electroless plating allowed for more uniform metal deposition (116). Both plating methods are important for the fabrication of the array, and further considerations continue in the following. 

Choudhry, N.A., Kadara, R.O. and Banks, C.E. (2010) Cosmetic electrochemistry the facile production of graphite microelectrode ensembles. Phys. Chem. Chem. Phys., 12,2285. 

Fig. 7.35. Development of diffusion concentration profiles in ensembles of microelectrodes. Concentration distortions at very short times during chronoamperometry or fast sweep rates during (a) cyclic voltammetry, (b) intermediate times or sweep rates, and (c) long times or slow sweep rates. Voltam-metric responses are shown schematically. (Reprinted from B. R. Scharifker, Microelectrode Techniques in Electrochemistry, in Modem Aspects of Electrochemistry, Vd. 22, J. O M. Bockris, B. E. Conway, and R. E. White, eds., Plenum, 1992, p. 505.)...

A microelectrode array consists of a series of microelectrodes separated by an insulating material [36]. The microelectrodes can be regularly or randomly distributed (in the latter case the term ensemble is also used). Arrays containing hundreds or even thousands of microelectrodes wired in parallel have been... 

Arrays are ensembles of microelectrodes that may consist of regularly, or irregularly, spaced assemblies of identical electrodes, ensembles of electrodes with identical... 

The best configuration of ensembles of microelectrodes is a collection of micro discs of equal size, arranged on a uniform grid, at equal distances from each other. Sometimes this is not feasible, and ensembles containing electrodes of nonuniform size and/or distance have been considered. Ensembles of strip microelectrodes have also been constructed, and the variation of current with time for such configurations has been evaluated. 

We conclude this section by noting that ensembles of ultramicro electrodes hold more promise for future use in research and in industry than single microelectrodes. Unfortunately, neither type is yet available commercially as a standard tool, which can be employed as needed. 

Note that the current density in this case is larger by a factor of (L/r) than at short times, when Eq. 44L applies. The development of the diffusion field at an ensemble of microelectrodes is shown schematically in Fig. 20L. 

This prevents water penetration and only the exterior of the electrode is exposed to electrolytes. When used with 30 nm sized carbon black powder, the conductive area of the electrode in contact with the electrolyte consists of less than 1 % of the geometric cross-sectional area of the electrode. This has been compared with an ensemble of microelectrodes. These CCEs showed an improvement of up to three orders of magnitude in terms of Faradaic signal-to-noise compared with glassy carbon electrodes [218]. In addition, the sol gel method of preparation affords a variety of structural configurations and it has been shown that CCEs can be produced by thick film and ink jet technology, which allows for their mass production [219]. 

Similarly, it was shown by Gilleadi16 that the development of a diffusion field near the surface of an ensemble of microelectrodes occurs in the four successive steps, assuming total diffusion control of the process. The ensemble of microelectrodes consists of microelectrodes placed on the inert surface at distances between their centers larger than their diameter. The first, planar diffusion to the microelectrodes the second, spherical diffusion with no overlap the third, spherical diffusion with substantial overlap and finally, total overlap, equivalent to planar diffusion to the whole surface. 

The use of microelectrodes is impractical, but the use of ensembles of microelectrodes can be a real option. The ensemble of microelectrodes consists of microelectrodes placed on the inert surface at distances between their centers larger than their diameter. 

Assuming homogeneously distributed, equal to each other, hemispherical grains of the catalyst on an inert substrate, in a way similar to that used by Gileadi16 to describe an ensemble of microelectrodes, the surface of the macroelectrode can be presented by an idealized model, as in Fig. 2, and the number of grains per square centimeter is given by ... 

It also seems that the only way to obtain an ensemble of microelectrodes16 working independently under activation control is to form an agglomerate of dendrites, the tips of which represent microelectrodes working in the bulk solution outside any diffusion... 

In illuminated dispersions of semiconductors, light induces an electron-hole charge separation at the surface of the particles and within their bulk. Redox reactions at the solid/solution interface can then occur upon capture of the electrons and holes by an oxidant and a reductant, respectively. Since a reduction and an oxidation reaction proceed simultaneously on the same surface (at the same rate, at steady-state conditions), the dispersed system can be compared to an ensemble of semiconductor microelectrodes at open circuit (8). 

E. Gileadi (Tel Aviv University, Israel) The use of ensembles of microelectrodes for trace analysis should be considered. Recent studies in our laboratory (H. Reller, E. Kirowa-Eisner and E. Gileadi, J.Electroanal. 

A further advantage of ensembles of microelectrodes is the low solution resistance associated with the small diameter of each electrode in the ensemble. This allows electrolysis in poorly conducting solution such as tap water. 

Abyaneh, M., Fleischmann, M., Del Giudice, E. and Vitiello, G. (2009) The investigation of nucleation using microelectrodes, part I. The ensemble averages of the times of birth of the first nucleus. Electrochimica Acta, 54, 879. 

Reller H, Kirowa-Eisner E, Gileadi E (1982) Ensembles of microelectrodes. A digital simulation. J Electroanal Chem 138 65. 

Scharifker BR (1988) Diffusion to ensembles of microelectrodes. J Electroanal Chem 240 61-76... 

---