Characterization of electrode surfaces

A powerful characterization of electrode surfaces can be achieved by the combined radiochemistry and electrochemistry procedures with polycrystalline materials many measurements of this type have been reported (18,20,21). A successful study of adsorption at well-defined surfaces has recently been conducted in our laboratory and it is reported below (22,23). 

A. Hamnett, Ellipsometric Techniques for the Characterization of Electrode Surfaces, J. Chem. Soc. Faraday Trat s. 89 (1993) 1593. (Review-type paper.)... 

The structural characterization of electrode surfaces on the mesoscopic scale is a prerequisite for the elucidation of mesoscopic effects on electrochemical reactivity. The most straightforward approach to access the mesoscopic scale is the application of scanning probes under in-situ electrochemical conditions. Three different applications of STM have been discussed, namely the structural characterization of model electrodes, the visualization of dynamic processes on the nanometer-scale, and the defined modification of electrode surfaces. 

TMPyP on I-Au(lll). Formation and characterization of ordered adlayers of organic molecules at electrode-electrolyte interfaces are important from the fundamental and technological points of view (14). The recently developed in situ STM and related techniques revealed exciting possibilities of the direct observation and characterization of electrode surfaces in solutions. 

The presented examples clearly demonstrate tliat a combination of several different teclmiques is urgently recommended for a complete characterization of tire chemical composition and tire atomic stmcture of electrode surfaces and a reliable interiDretation of tire related results. Stmcture sensitive metliods should be combined witli spectroscopic and electrochemical teclmiques. Besides in situ techniques such as SXS, XAS and STM or AFM, ex situ vacuum teclmiques have proven tlieir significance for tlie investigation of tlie electrode/electrolyte interface. 

Gasteiger HA, Markovic NM, Ross PN. 1995. Electrooxidation of CO and H2/CO mixtures on a well-characterized Pt3Sn electrode surface. J Phys Chem 99 8945-8949. 

Schmidt TJ, Gasteiger HA, Stab GD, Urban PM, Kolb DM, Behm RJ. 1998. Characterization of high-surface area electrocatalysts using a rotating disk electrode configuration. J Electrochem Soc 145 2354-2358. 

The chapter is divided into two subsections the first of which deals with the characterization of electrodes as prepared prior to any electrochemical treatment. The knowledge of the actual surface composition of the fresh electrodes is needed to optimize preparation conditions and to be able to correlate electrochemical performance with surface properties. In Section 3.2 the application of XPS to the elucidation of electrochemical reaction mechanisms will be demonstrated. Here XPS monitors possible changes after controlled electrochemical treatment. 

We have recently modified U7) one of the several radiochemical methods (U5) which have been used for surface electrochemistry investigations in order to characterize adsorption on well-defined, single crystal electrodes. Below, we will describe the technique and identify some challenging issues which we will be able to address. The proposed method is sensitive to a few percent of a monolayer at smooth surfaces, is nondestructive and simple to use. The radiochemical measurements can be made with all compounds which can be labelled with reasonably long-lived, preferably g- emitting radioisotopes. We believe this technique will fulfill the quantitative function in in situ surface analysis as Auger spectroscopy currently does in vacuum, ex situ characterization of electrodes. 

This resulted in a need for appropriate characterization of the structural and electronic properties of electrode surfaces and detection of adsorbed intermediates in electrode reactions. 

To a large extent, the discovery and application of adsorption phenomena for the modification of electrode surfaces has been an empirical process with few highly systematic or fundamental studies being employed until recent years. For example, successful efforts to quantitate the adsorption phenomena at electrodes have recently been published [1-3]. These efforts utilized both double potential step chronocoulometry and thin-layer spectroelectrochemistry to characterize the deposition of the product of an electrochemical reaction. For redox systems in which there is product deposition, the mathematical treatment described permits the calculation of various thermodynamic and transport properties. Of more recent origin is the approach whereby modifiers are selected on the basis of known and desired properties and deliberately immobilized on an electrode surface to convert the properties of the surface from those of the electrode material to those of the immobilized substance. 

D.P. Manica, Y. Mitsumori and A.G. Ewing, Characterization of electrode fouling and surface regeneration for a platinum electrode on an electrophoresis microchip, Anal. Chem., 75 (2003) 4572-4577. 

Determination of the optimal experimental conditions for the atomic force microscopy (AFM) characterization of the surface morphology of a DNA electrochemical biosensor obtained using different immobilization procedures of calf-thymus double-stranded DNA (dsDNA) on a highly oriented pyrolytic graphite (HOPG) electrode surface. 

It thus appears that there may be a basis for some predictions which can guide in the selection of components for composite materials, but the theoretical basis for discussions goes always back to the principles of the volcano curve in the sense that a relative increase or decrease in activity is customarily explained by recurring to the features of such a curve [92], Therefore, a theory is needed to describe the dependence of the adsorption strength of hydrogen on the electronic properties of composite materials. However, before a sound theory can be proposed, it is necessary that the experimental picture be freed from the many obscurities, ambiguities and irreproducibilities due to the scarce characterization of the surface of various materials, and to the insufficient identification of various factors which can influence electrode kinetics. 

Since the appearance of the redox [ii, iii] and conducting [iv] polymer-modified electrodes much effort has been made concerning the development and characterization of electrodes modified with electroactive polymeric materials, as well as their application in various fields such as -> sensors, actuators, ion exchangers, -> batteries, -> supercapacitors, -> photovoltaic devices, -> corrosion protection, -> electrocatalysis, -> elec-trochromic devices, electroluminescent devices (- electroluminescence) [i, v-viii]. See also -> electrochemically stimulated conformational relaxation (ESCR) model, and -> surface-modified electrodes. 

Refs. [i] Scherson DA (1988) Mossbauer spectroscopy. In Gale RJ (ed) Spectroelectrochemistry. Plenum Press, New York, p 399 [it] Eldridge JI, O Grady WE (1991) Mossbauer spectroscopy. In Varma R, Selman JR (eds) Techniques for characterization of electrodes and electrochemical processes. Wiley, New York, p 343 [iii] Holze R (2007) Surface and interface analysis an electrochemists toolbox. Springer, Berlin... 

The cleanliness and single crystallinity of electrode surfaces are not assumed even if the preparative steps outlined above are followed. The verification or identification of initial, intermediate, and final interfacial stmctures and compositions is an essential ingredient in our studies. The interfacial characterization methods employed to date have been conveniently classified in terms of whether they are conducted under reaction conditions (in situ) or outside the electrochemical cell (ex situ). In situ methods here consisted of cychc voltammetry (CV), EC-STM and DBMS. Ex situ methods included LEED, AES, and HREELS. 

Thus, the mechanistic aspects of CI2 evolution are not yet at all well clarified, although significant progress has been made during the last decade. Proper understanding of the kinetics of the O2 and CI2 evolution reactions and their relationship requires more closer scrutiny, with attention to surface characterization of electrodes. 

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