Electrochemistry ultramicroelectrodes

Figure 4. Electrochemistry of dendrimer 35 (a) classical CV, in the presence of 2,3-dichloronaphthoquinone as internal standard, which gives rise to the wave at negative potential (solvent MeCN, electrolyte Bu N PF" Pt electrode, versus SCE, scan rate 100 mV s )- (b) Ultramicroelectrode CV, in the presence of 2,3-dichloronaphthoquinone [solvent MeCN/CHjClj (1 1 v/v) electrolyte Bu N PF j, Pt electrode, versus SCE, scan rate 50 mV s l-...

In Chapter 21, Hawley has formulated a series of questions about the mechanism of an electrode reaction. Complete diagnosis of the mechanism includes knowledge of the electrode reaction products and the sequential steps (E and/ or C) by which they are formed. If a chemical reaction follows rapidly upon an electron transfer, the new (secondary) product may be produced close to the electrode, and may be subject to further electrochemistry. If the secondary products are formed slowly, after the primary electrolysis product has diffused away from the electrode, their formation will ordinarily not influence the electrode mechanism, except in bulk electrolysis. We limit our treatment to reactions occurring on the CV time scale, approximately 20 s to 10 ms for routine technology. Ultramicroelectrode technology (Chap. 12) extends the short-time limit to below 1 ps. 

Ultramicroelectrodes, submicrosecond electrochemistry Electrochemistry in low-conductivity media Electrochemistry under time-independent conditions... 

Amatore, C. (1995) Electrochemistry at ultramicroelectrodes. Chapter 4 in I. Rubinstein (Ed.) Physical Electrochemistry. Dekker, New York. 

Joaquin Gonzalez is a Lecturer at the University of Murcia, Spain. He follows studies of Chemistry at this University and got his Ph.D. in 1997. He has been part of the Theoretical and Applied Electrochemistry group directed by Professor Molina since 1994. He is author of more than 80 research papers. Between 1997 and 1999, he also collaborated with Prof. Ms Luisa Abrantes of the University of Lisboa. He is the coauthor of four chapters, including Ultramicroelectrodes in Characterization of Materials second Ed (Kaufmann, Ed). He has taught in undergraduate and specialist postgraduate courses and has supervised three Ph.D. theses. His working areas are physical electrochemistry, the development of new electrochemical techniques, and the modelization, analytical treatment, and study of electrode processes at the solution and at the electrode surface (especially those related to electrocatalysis). 

Ultramicroelectrodes can also greatly benefit modem microseparation techniques such as open-tube liquid chromatography or capillary-zone electrophoresis (CZE) (73). For example, cylinder-shaped carbon or copper fibers can be inserted into the end of the CE separation capillary (e.g., see Fig. 3.26). Such alignment of the working electrode with the end of the capillary represents a challenge in combining electrochemistry with CZE. 

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].)... 

Dr. Rolison is a member of the American Chemical Society, AAAS, the International Zeolite Association, the Materials Research Society, and the Society for Electroanalytical Chemistry (SEAC). She wrote Ultramicroelectrodes, the first textbook in this very active research area of electrochemistry, with Martin Fleischmann, Stanley Pons, and Peter Schmidt. She and Henry White guest-edited an issue of Langmuir devoted to the electrochemistry of nanostructured materials (February 1999). Dr. Rolison was a member of the Advisory Board for Analytical Chemistry and is a current member of the editorial boards of the Journal of Electroanalytical Chemistry and Langmuir. She is a member of the Board of Directors for the SEAC and has served since 1997 as editor of the society s newsletter, SEAC Communications. 

Refs. [i] Amatore C (1995) Electrochemistry at ultramicroelectrodes. Ire Rubinstein I (ed) Physical electrochemistry. MarcelDekker, NewYork,pp 131-208 [ii] Arrigan DWM (2004) Analyst129 1157 [iii] Bard Af (1994) Integrated chemical systems. Wiley, New York [iv] Belmont C, Girault HH (1995) Electrochim Acta 40 2505... 

Nanodes — Occasionally used term for ultramicroelectrodes with nm dimensions. It has several meanings outside of electrochemistry. The term -> nano electrodes is probably more descriptive and preferred. 

Solid-state electrochemistry — is traditionally seen as that branch of electrochemistry which concerns (a) the -> charge transport processes in -> solid electrolytes, and (b) the electrode processes in - insertion electrodes (see also -> insertion electrochemistry). More recently, also any other electrochemical reactions of solid compounds and materials are considered as part of solid state electrochemistry. Solid-state electrochemical systems are of great importance in many fields of science and technology including -> batteries, - fuel cells, - electrocatalysis, -> photoelectrochemistry, - sensors, and - corrosion. There are many different experimental approaches and types of applicable compounds. In general, solid-state electrochemical studies can be performed on thin solid films (- surface-modified electrodes), microparticles (-> voltammetry of immobilized microparticles), and even with millimeter-size bulk materials immobilized on electrode surfaces or investigated with use of ultramicroelectrodes. The actual measurements can be performed with liquid or solid electrolytes. 

Refs. [i] Bard A], Mirkin MV (eds) (2001) Scanning electrochemical microscopy. Marcel Dekker, New York, chap 3 [ii] Bard AJ, Faulkner LR (2001) Electrochemical methods, 2ni edn. Wiley, New York, chap 5 [iii] Zoski CG (ed) (2007) Handbook of electrochemistry. Elsevier, Amsterdam, chap 6,11,12,19 [iv] Fleischmann M, Pons S, Rolison DR (eds) (1987) Ultramicroelectrodes. DataTech Systems, NC... 

The RDE technique has found widespread use in analytical electrochemistry because of an excellent signal-to-noise ratio resulting from the enhanced mass transport. The RDE method has also been employed for monitoring concentrations in kinetic applications [59], as described for ultramicroelectrodes [60] and in the determination of the stoichiometry for electron-transfer reactions by means of redox titration [61]. The latter procedure will be described next. 

Heinze, 1., Ultramicroelectrodes - a new dimension in electrochemistry, Angew. Chem.-Int. Edit. Engl. 1991, 30, 170-171... 

SECM involves the measurement of the current through an ultramicroelectrode (UME) (an electrode with a radius, a, of the order of a few nm to 25 (zm) when it is held or moved in a solution in the vicinity of a substrate. Substrates, which can be solid surfaces of different types (e.g., glass, metal, polymer, biological material) or liquids (e.g., mercury, immiscible oil), perturb the electrochemical response of the tip, and this perturbation provides information about the nature and properties of the substrate. The development of SECM depended on previous work on the use of ultramicroelectrodes in electrochemistry and the application of piezoelectric elements to position a tip, as in scanning tunneling microscopy (STM). Certain aspects of SECM behavior also have analogies in electrochemical thin-layer cells and arrays of interdigitated electrodes. 

An understanding of the operation of the SECM and an appreciation of the quantitative aspects of measurements with this instrument depends upon an understanding of electrochemistry at small electrodes. The behavior of ultramicroelectrodes in bulk solution (far from a substrate) has been the subject of a number of reviews (17-21). A simplified experimental setup for an electrochemical experiment is shown in Figure 1. The solution contains a species, O, at a concentration, c, and usually contains supporting electrolyte to decrease the solution resistance and insure that transport of O to the electrode occurs predominantly by diffusion. The electrochemical cell also contains an auxiliary electrode that completes the circuit via the power supply. As the power supply voltage is increased, a reduction reaction, O + ne — R, occurs at the tip, resulting in a current flow. An oxidation reaction will occur at the auxiliary electrode, but this reaction is usually not of interest in SECM, since this electrode is placed sufficiently far from the UME... 

Exploration of electrochemistry in unconventional media. Electrochemical research has traditionally focused on measurements at electrodes fabricated from conductors immersed in solutions containing electrolytes. However, interfacial processes between other phases need to receive further attention, and they can be probed with electrochemical techniques. Electrochemistry can play a unique role in exploring chemistry under extreme conditions. The movement of charges in frozen electrolytes, poorly conducting liquids, and supercritical fluids can be experimentally measured with ultramicroelectrodes. Opportunities exist to study previously inaccessible redox processes in these media. Electrochemistry in environments of restricted diffusion... 

It is rather difficult to conduct electrochemistry in oil-continuous or W/O microemulsions because of the low conductivity, as stated earlier. Chen and Georges [34] used carbon fiber ultramicroelectrodes to study SDS-l-heptanol-dodecane microemulsions, using ferrocene... 

The decreased iR drop in voltammetric experiments at ultramicroelectrodes has been exploited to perform electrochemistry under conditions in which no or only a small concentration of supporting electrolyte is added and allows measurements in low-polarity solvents (e.g. hydrocarbons), without the presence of excess ions, or even in the gas phase [51]. This topic is discussed further in Chapter 2.5 (Sect. 2.5.5.6). In these cases, the transport of charge in the electrolyte is realized by small amounts of impurities [48], by ions of the substrate material itself [52], or those generated in the electrode reaction [39]. Thus, migration has to be considered as an additional mode of transport, in particular for multiply charged species [52]. A recent modeling study [53] has provided evidence that LSV should be best suited to deal with situations of high uncompensated resistance as compared to chronopotentiometry and chronoamperometry. 

Information concerning topology, heat, light, or the nature of the ionic species present can be readily obtained. The characterization and imaging of single cells with electrochemistry, known as SECM has recently been reviewed extensively [45] in order to explore the application of nanodes (or ultramicroelectrodes) in microscopy. In addition, there have been a variety of references to work that has... 

Dibble, T., Bandyopadhyaya, S., Ghoroghchian, J. et al. (1986) Electrochemistry at high potentials oxidation of rare gases and other gases in non-aqueous solvents at ultramicroelectrodes. The Journal of Physical Chemistry, 90, 5275. 

Heinze, J. (1993) Ultramicroelectrodes in electrochemistry. Angewandte Chemie, International Edition in English, 32, 1268-1288. 

Kwon, S.J., Zhou, H.J., Fan, F.R.F. et al. (2011) Stochastic electrochemistry with electrocatalytic nanoparticles at inert ultramicroelectrodes-theory and experiments. Physical Chemistry Chemical Physics, 13, 5394—5402. 

Cassidy, J., Khoo, S.B., Pons, S. and Fleischmann, M. (1985) Electrochemistry at very high potentials the use of ultramicroelectrodes in the anodic oxidation of short chain alkanes. The... 

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