Microelectrodes, electrochemistry

Daniele, S., Bragato, C. and Baldo, M.A. (2002) Square wave voltammetry of strong acids at platinum microelectrodes. Electrochemistry Communications, 4, 374-378. 

Mokrushina, A.V., Heim, M., Karyakina, E.E. et al. (2013) Enhanced hydrogen peroxide sensing based on Prussian Blue modified macroporous microelectrodes. Electrochemistry Communications, 29, 78-80. 

A microelectrode is an electrode with at least one dimension small enough that its properties are a fimction of size, typically with at least one dimension smaller than 50 pm [28, 29, 30, 31, 32 and 33]. If compared with electrodes employed in industrial-scale electrosynthesis or in laboratory-scale synthesis, where the characteristic dimensions can be of the order of metres and centimetres, respectively, or electrodes for voltannnetry with millimetre dimension, it is clear that the size of the electrodes can vary dramatically. This enonnous difference in size gives microelectrodes their unique properties of increased rate of mass transport, faster response and decreased reliance on the presence of a conducting medium. Over the past 15 years, microelectrodes have made a tremendous impact in electrochemistry. They have, for example, been used to improve the sensitivity of ASV in enviroiunental analysis, to investigate rapid... 

Tanaka K and Tokuda K 1996 In vivo electrochemistry with microelectrodes Experimental Techniques in Bioelectrochemistry ed V Brabec, D Walz and G Milazzo (Basel Birkhauser)... 

Microelectrodes exhibit several other attractive and important properties that have expanded the possibilities of electrochemistry ... 

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.)...

There are several excellent articles which deal with the theory and practice of cyclic voltammetry.1-4 Foremost among these is the comprehensive treatise by Bard and Faulkner which gives a thorough description of the theory of controlled potential microelectrode techniques, including cyclic voltammetry.1 Particularly readable accounts of cyclic voltammetry and related techniques are given in Adams book, Electrochemistry at Solid Electrodes ,2 in Pletcher s review3 and in a series of articles which appeared in J. Chem. Educ.e>... 

Several examples of the use of microelectrodes in highly resistive media exist. The first reported measurements were an examination of the reduction of aromatic hydrocarbons such as perylene in benzene containing tetrahexylammonium perchlorate [57]. Although this electrolyte is presumably in a quite associated state in benzene (or toluene [58]), it does impart sufficient conductivity for electrochemistry to be observed. In subsequent work, this result was confirmed and extended to other low-dielectric-constant solvents [59]. Even voltammetry in hexane has been shown to be possible with a microelectrode [60]. In this sol-... 

There is, of course, a limit on the amount of solution resistance that can be overcome even with microelectrodes. Attempts have been made to perform electrochemistry in the gas phase [79] or in supercritical C02 180] with microelectrodes. In each case, however, the conduction path was shown to be not through the bulk phase, but rather across the insulating surface between the microelectrode and the counter electrode. This mechanism enables electrochemical detection in highly unusual media for voltammetry and illustrates that only very small conduction pathways are required to obtain well-defined electrochemical behavior. 

In the 1980s, it became widely recognized that there are advantages from doing electrochemistry at very small electrodes. In the 1990s, benefits from speed and access to electrochemistry in unusual media make microelectrodes quite routine. It is interesting that the microelectrodes of today are at least a thousand times smaller than the "microelectrodes" of the 30s, 40s, and 50s. What will the microelectrodes of tomorrow look like ... 

M. L. Kovarik, M.W. Li and R.S. Martin, Integration of a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis/ electrochemistry, Electrophoresis, 26 (2005) 202-210. 

Forster RJ (2003) Microelectrodes retrospect and prospect. In Bard AJ, Stratmann M, Unwin P (eds) Encyclopedia of electrochemistry, vol 3, Instrumentation and electroanalytical chemistry. Wiley-VCH, Weinheim, pp 160-195... 

It can be a further advantage of microelectrodes that they often increase the electrode resistance to bulk resistance ratio Rei/Rbuik- This is so because Re 1 frequently scales with the inverse area of the electrode, whereas the bulk resistance between a circular microelectrode and a counter-electrode is proportional to the inverse microelectrode diameter dme (see Sec. 4.1). Hence Rei/Rb iik ocbulk resistance decreases with decreasing microelectrode diameter. This is particularly helpful in order to investigate electrode polarization phenomena below the detection limit in experiments using macroscopic electrodes. (The reduced importance of the electrolyte resistance is also one of the reasons for ultramicroelectrodes to be applied in liquid electrochemistry [33, 34].)... 

Numerical simulations reveal that this effective value Rif differs form Re if the measured (simulated) Rif is smaller than Rsw (Fig. 21a). These deviations are connected with the inhomogeneous potential distribution in the vicinity of a microelectrode yielding laterally varying electrode overvoltages for small electrode resistances (Fig. 21b). In microelectrode experiments, however, the ratio Reef / Rm is often large (cf. Sec. 3.4) and hence Ra x R f is usually a reasonable approximation. In liquid electrochemistry, similar effects are discussed in the context of primary (Rei = 0) and secondary (Re > 0) current distributions [268, 269]. 

In the following, four examples of quantitative microelectrode measurements are discussed in more detail. Each reflects a typical field of solid state ionics (nonstoichiometry, highly resistive grain boundaries, highly conductive interface, electrode reactions) and thus provides evidence for the vast potential of microelectrodes in solid state electrochemistry. 

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