Electrochemical techniques, anodic fundamentals

The local electrochemical techniques that are used for coatings research are mainly used in the more fundamental studies of corrosion mechanisms. They can be divided into techniques in immersion (SVET end SRET) and in atmospheric conditions (Kelvin). All techniques are based on the observation that corrosion mechanisms underneath coatings are generally mechanisms in which anodic and cathodic processes take place on separated sites with a slightly different local corrosion potential. The techniques are used to visualize these differences. SRET and SVET can also be used on polarized samples to detect pinholes. 

Over the years the original Evans diagrams have been modified by various workers who have replaced the linear E-I curves by curves that provide a more fundamental representation of the electrode kinetics of the anodic and cathodic processes constituting a corrosion reaction (see Fig. 1.26). This has been possible partly by the application of electrochemical theory and partly by the development of newer experimental techniques. Thus the cathodic curve is plotted so that it shows whether activation-controlled charge transfer (equation 1.70) or mass transfer (equation 1.74) is rate determining. In addition, the potentiostat (see Section 20.2) has provided... 

At IREQ, besides the participation in the field tests run by the engineers of Hydro-Quebec (12), the main effort has been to tackle fundamental problems in the field of electrocatalysis (18-22) and of anodic oxidation of different potential fuels (23-26). A careful and extensive study of the electrochemical properties of the tungsten bronze has been carried out (18-20) the reported activity of these materials in acid media for the oxygen reduction could not be reproduced and this claim by other workers has been traced back to some platinum impurities in the electrodes. Some novel techniques in the area of electrode preparation are also under study (21,22) the metallic deposition of certain metals on oriented graphite show some interesting catalytic features for the oxygen reduction and also for the oxygen evolution reaction. 

This volume of Modem Aspects contains a remarkable spread of topics covered in an authoritative manner by some internationally renowned specialists, hi a seminal chapter Drs. Babu, Oldfield and Wieckowski demonstrate eloquently the strength of electrochemical nuclear magnetic resonance (EC-NMR) to study in situ both sides of the electrochemical interface via the simultaneous use of and Pt NMR. This powerful non-invasive technique brings new insights to both fundamental and practical key aspects of electrocatalysis, including the design of better anodes for PEM fuel cells. 

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