Controlled-current techniques charge step methods

One method for examining the corrosion behavior of a metal is to determine the E-i relationship by conducting a polarization exp eriment. The following jB-t app relationship is often expterimentally observed between applied current and potential. The expression is applicable to charge transfer controlled corrosion processes, regardless of the exact number of charge transfer controlled reactions or reaction steps. It provides the basis for the electrochemical p olarization technique [7,2,77,79]. 

Other techniques for studying protein molecnles in solntion are less infln-enced by these microscopic effects. Square-wave voltammetry is widely used due to its great sensitivity, and even a low density of productive sites on the electrode may give rise to a sharp and analyzable response [28]. The electrode may also be rotated to achieve forced convection and hydrodynamic control of solution redox species, while amperometric (and coulometric) measurements—where the current (or charge) is recorded following a potential step—enable the time and potential domains to be deconvoluted [28,29]. These options complement each other to provide a detailed picture of the thermodynamics and kinetics of redox processes. Finally, bulk electrolytic methods enable samples of a particular redox state to be prepared quantitatively for spectroscopic examination, at precise electrode potentials that may lie outside the range of conventional chemical titrants. 

The RDE has the considerable practical advantage over techniques such as cyclic voltammetry, potential step, or a.c. methods. The rate of mass transport to the electrode may be varied over a substantial range and in a controlled way without resort to a rapid change in the electrode potential which inevitably leads to the measured current having a contribution from charging the double layer. Since in most experiments with the RDE only (pseudo) steady state currents are measured, the recorded current may be unequivocably equated with the faradiac current. 

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