Page 146 - Analytical Electrochemistry 2d Ed - Jospeh Wang

4-5 WORKING ELECTRODES 131

FIGURE 4-24 Cyclic voltammograms for the oxidation of ferrocene at a 6 mm platinum
microdisk at different scan rates. (Reproduced with permission from reference 84.)

(85) should offer additional spatial and temporal advantages, including a closer look
at interfacial chemistry processes. The construction of such nanoscopic electrodes is
even more challenging than that of their microscopic counterparts (86).

4-5.4.3 Composite Electrodes Composite electrodes couple the advantages
of single microelectrode systems with signi®cantly higher currents due to larger
surface areas (86). Such electrodes thus address instrumental dif®culties of monitor-
ing the extremely small (subnanoampere) currents at single microelectrodes. The
surfaces of composite electrodes consist of uniform (array) or random (ensemble)
dispersions of a conductor region within a continuous insulating matrix (Figure
4-27). Examples of arrays include closely spaced microdisks or interdigitated
microband electrodes (e.g. Figure 4-28). Lithographic techniques are often used
for fabricating such arrays (with various patterning), allowing precise control of the
spacing (88). Ensembles can be fabricated by mixing or pressing a powdered