Electrocatalysis electrode characteristics

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. 

A typical adsorption process in electrocatalysis is chemisorption, characteristic primarily for solid metal electrodes. The chemisorbed substance is often chemically modified during the adsorption process. Then either the substance itself or some fragment of it is bonded chemically to the electrode. As electrodes mostly have physically heterogeneous surfaces (see Sections 4.3.3 and 5.5.5), the Temkin adsorption isotherm (Eq. 4.3.46) is suitable for characterizing the adsorption. 

The basic characteristics of electrocatalysis will be demonstrated on several examples, in the first place on the electrode processes of hydrogen,... 

Among the several fields in which electronically conducting polymers are useful or may be so the future, are electrocatalysis, prosthetics, and electrodes suited for use with biomaterials, (d) Consider each of these areas and state the reasons you think electronically conducting compounds (those now available and those that may be synthesized) would have characteristic properties of special use in the areas mentioned. (Bockris)... 

The modification of electrode surfaces with electroactive polymer films provides a means to control interfacial characteristics. With such a capability, one can envisage numerous possible applications, in areas as diverse as electronic devices, sensors, electrocatalysis, energy conversion and storage, electronic displays, and reference electrode systems [1, 2]. With these applications in view, a wide variety of electroactive polymeric materials have been investigated. These include both redox polymers (by which we imply polymers with discrete redox entities distributed along the polymer spine) and conducting polymers (by which we imply polymers with delocalised charge centres on the polymer spine). 

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 ... 

An understanding of the mechanisms of the reactions in electrodics is provided by physical electrochemistry through the analysis of the electronic and ionic phases. For the first phase, the electronic character of the metals is important and hence solid state physics comes into focus. The quantal characteristic of the metal conductor defines the surface structure properties that are dealt by quantum electrochemistry. The concept of quantum particles is one of the main considerations of this chapter. The properties of the dual nature of this corpuscular wave produce equivocal understanding even in electrocatalysis. When a beam of electrons passes through a solid, the effective mass is the real quantity to be considered in the calculations, since the interactions of the electron with a nucleus are shielded by strong electrostatic interactions. 

Electrocatalysis can modify the composition of the electrode surfaces and the nature of the electrolytic products. The perchlorate decomposition (cathodic production of chloride) on platinum catalysts is one of the examples [57] and the IrCT decomposition during the sodium chlorate production [58]. The electropolymerization of the organic substances is critically dependent on the type of the electronic/ionic conductors, electrolyte characteristics, and the electrolysis resident time of the monomer [59]. 

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. 

Polymer-film modified electrodes are used for a variety of applications, such as electrocatalysis (5-8). analysis (9.10). and more recently for their permselectivity characteristics (11-1H). These polymer films are formed by casting the film on an electrode surface (12), using radio-frequency plasma (15), or by electropolymerization (13.16.17). Alternatively, a polymer film 1s formed as a discrete membrane Eind subsequently applied to an electrode (18). The use of both cast and discrete membrane films... 

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 unique three-dimensional aluminosilicate crystalline lattice of zeolites gives rise to three intriguing characteristics (104). These characteristics are high cation-exchange capacity, sensitive molecular recognition (size and shape selectivity), and good catalytic activity. These properties give rise to the use of zeolite modified electrodes in sensor development, and electrocatalysis (106). These and other applications are outlined in Table 8.6. More detailed descriptions can be found in recent reviews (7, 96, 102-106), with extensive lists compiled by Rolison (Table 11 in (102)) and Walcarius (Tables 1 and 3 in (105) and Table 1 in (106)). 

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. 

In order to understand the characteristics of the electrocatalysis reaction inside the nanoporous electrodes, additional analysis of the ac impedance behaviour was carried out, and the penetration depths of reactant molecules in the nanohoneycomh pores for catalytic reactions and the reaction parameters for different pore structures were estimated. The ac impedance measurements for Pt-modified diamond electrodes... 

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