Electrochemical characteristics electrocatalysis

This chapter is organized into sections corresponding to various electrochemical characteristics of nanometallic particles. The introduction gives a brief idea of the basics of colloids together vith related literature. Subsequently, the electrochemistry with nanoparticles and ensembles of nanoelectrodes is explained followed by the electrochemical coulomb staircase behaviour of monolayer-protected nanometallic clusters. The investigation of nanoparticles using techniques based on combinations of different spectroscopic and electrochemical techniques is then reviewed. Sensors and electrocatalysis form the next sections and finally a summary and perspectives are given. 

Figures 5.4 and 5.5 summarize results of a recent study of P. versicolor laccase electrochemistry based on cyclic and rotating disk voltammetry [60]. Figure 5.4 shows unequivocally that this laccase is voltammetrically active and gives a kinetically controlled, unpromoted four-electron peak at edge-plane pyrolytic graphite. Electrochemical reduction of 02 catalyzed by an immobilized laccase monolayer is close to reversible, and unrestricted by mass transport. The electrocatalysis follows, moreover, a Michaelis-Menten pattern (Fig. 5.5). Finally, there is a characteristic bell-shaped functional pH-profile with a pronounced maximum at pH 3.1.

The chemical stability and electrochemical reversibility of PVF films makes them potentially useful in a variety of applications. These include electrocatalysis of organic reductions [20] and oxidations [21], sensors [22], secondary batteries [23], electrochemical diodes [24] and non-aqueous reference electrodes [25]. These same characteristics also make PVF attractive as a model system for mechanistic studies. Classical electrochemical methods, such as voltammetry [26-28] chronoamperometry [26], chronopotentiometry [27], and electrochemical impedance [29], and in situ methods, such as spectroelectrochemistry [30], the SECM [26] and the EQCM [31-38] have been employed to this end. Of particular relevance here are the insights they have provided on anion exchange [31, 32], permselectivity [32, 33] and the kinetics of ion and solvent transfer [34-... 

The use of various electrode materials to explore chemical reactions in an electric field dates back to the beginning of the nineteenth century. Although the catalytic nature of some electrodes was only appreciated much later. Grove (7) recognized their chemical or catalytic action and the need for a notable surface action in early fuel cells, just a few years after the dawn of the notion of catalysis (2). When the term electrocatalysis was deliberately introduced by Grubb in 1963 (5), it did not reflect an unnecessary complication in nomenclature, but a real need to identify and comprehend the unique and characteristic features of catalytic electrode processes. How has this need been fulfilled to date Where does the field of electrocatalysis stand compared to the development of conventional catalytic and electrochemical processes What are the new directions and goals of this discipline ... 

A comparison with gas phase catalysis reveals that the electrocatalytic reduction of organic halides operates between conventional electrochemical and catalytic processes (57). However, an examination of the adsorption characteristics, identification of intermediates, or multiple surface states and kinetic results are necessary for elucidating the role of electrocatalysis in cleavage and double bond reduction. 

Understanding the activity and selectivity properties of electrocatalysts requires the characterization of catalyst surfaces, determination of adsorption characteristics, identification of surface intermediates and of all reaction products and paths, and mechanistic deliberation for complex as well as model reactions. Electrochemical and classical methods for adsorption studies are well documented in the literature (5, 7-9, 25, 24, 373. Here, we shall outline briefly some prominent electrochemical methods and some nonelectrochemical techniques that can provide new insight into electrocatalysis. Electrode kinetic parameters can be determined by potentionstatic methods using the methodology of Section II1,D,3. 

The deliberate modification of electrode surfaces by coating with one or more layers of electroactive material has been used for a variety of purposes. Solar energy conversion, electrochromism, corrosion protection, and electrocatalysis are but a few of the applications which are currently of interest. The use of in situ Raman spectroscopic studies can help to determine the structural characteristics of electrode coatings at the molecular level and can provide information on the mechanisms of electrochemical reactions occurring at modified electrode surfaces. 

Mchardy J, Bockris JO (1973) Electrocatalysis of oxygen reduction by sodium tungsten bronze I. Surface characteristics of a bronze electrode. J Electrochem Soc 120(l) 53-60... 

Since the surface must simultaneously corrode, reduce, and catalyze, it is clear that very specific substrates will normally be necessary for ordinary chemical catalytic processes. They must possess just the right combination of catalytic and reductive properties so that, when exposed to their reactive environment, they produce an electrochemical potential that gives the correct rate (bearing in mind their own electrocatalytic character) for the preparative process desired. The correct products will thereby result. Clearly, it would be much easier if the electrocatalytic and potential characteristics could be separated by the use of specialized conductive electrode surfaces, combined with a suitable electronic potentiostat, respectively. In this way, electrocatalysis could become of great future importance in certain types of preparative organic chemistry. 

The most important characteristic of electroactive polymers is that they can be electrochemically oxidized and reduced. This redox activity is the basis of many applications for these materials, such as electrocatalysis, electron transfer mediation, and charge storage. The optimization of this redox activity has been the motivation behind many studies directed at understanding and describing this phenom-... 

Shukla AK, Ravikumar MK, Roy A, Barman SR, Sarma DD, Aricd AS, et al. Electrooxidation of methanol in sulfuric acid electrolyte on platinized-carbon electrodes with several functional-group characteristics. J Electrochem Soc 1994 141 1517-22. Mukeijee S. Particle size and structural effects in platinum electrocatalysis. J Appl Electrochem 1990 20 537-48. 

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