Electrode random assemblies

Fletcher S 1991 Random assemblies of microdisk electrodes (RAM electrodes) for nucleation studies—a tutorial revie w Microelectrodes Theory and Applications (Nato ASI Series) ed M I Montenegro, M A Queiros and J L Daschbach (Dordrecht Kluwer)... 

Fletcher S and Horne M D 1999 Random assemblies of microelectrodes (RAM electrodes) for electrochemical studies Electrochem. Common. 1 502... 

Instead of employing a single electrode, an array of electrodes [67] or an inter-digitated electrode [68] may be used to study electrochemical systems. Similar to advantages achieved by variations in electrode geometry, the use of several communicating electrodes poised at the same or different potentials opens up new possibilities for the study of the properties or the kinetics of chemical systems. An interesting development is the random assemblies of microelectrodes (RAM) (see Fig. II. 1.14), which promises the experimental timescale of microelectrodes but with considerably improved current-to-noise levels [69]. 

Alternatively, an assembly of microelectrodes can alleviate some of the problems associated with the individual microelectrodes. Such a random array of microelectrodes (RAM) comprises about 1000 carbon fibres (each of diameter 5-7 pm) which are embedded randomly within an inert adhesive such as an epoxy resin. (The ends of the fibres need to be widely spaced.) The net result is to generate an electrode system with a superior response time and a current which is IfKK) times that of a single microelectrode. By increasing the current in this way, the sensitivity of measurement is further increased. 

Electrode surfaces can be modified by redox polyelectrolytes via a sol-gel process, yielding random redox hydrogels or by layer-by-layer self-assembly of different redox and nonredox polyelectrolytes by alternate electrostatic adsorption from solutions containing the polyelectrolytes to produce highly organized redox-active ultrathin multilayers. 

If a stationary multiple microband electrode is used, then the collector current is rather sensitive to adventitious vibrations. If the electrode assembly is vibrated parallel to the inter-electrode gap, then although the collection efficiency is reduced the collector current is now insensitive to such random vibrations (of a non-modulatory nature). Repeatable, reliable titration using electrogenerated reagents has been demonstrated in this way [33]. 

Moreover, Shi and his group reported electrochemical deposition of PPy microcontainers onto soap bubbles associated with O2 gas released from the electrolysis of H2O in an aqueous solution of /3-naphthalenesulfonic acid (/3-NSA), camphorsulfonic acid (CSA), or poly(styrene sulfonic acid) (PSSA), which act both the surfactant and dopant [79-81]. Morphologies such as bowls, cups, and bottles could be controlled by electrochemical conditions (Figure 11.6). However, the microcontainers were randomly located on the electrode surface, which limited further applications, Shi and coworkers reported a linear arrangement of PPy microcontainers by self-assembly with gas bubbles acting as templates on a silicon electrode surface patterned by photolithography [82]. They found that capillary interactions between the gas bubbles and the polymer photoresist walls led the microcontainers to be arranged linearly. 

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