Nonpolarized electrodes, ideal

To begin our discussion, it is useful to consider current-voltage curves for an ideal polarized and an ideal nonpolarized elearode. Polarization at a single electrode can be studied by coupling it with an electrode that is not easily polarized. Such electrodes have large surface areas and have half-cell reactions that are rapid and reversible. Design details of nonpolarized electrodes are described in subsequent chapters. 

The ideal polarized electrode is one in which current remains constant and independent of potential over a wide range, Figure 22-6a is a current-voltage curve for an electrode that is ideally polarized in the region between A and B. Figure 22-6b shows the current-volutgc relationship for a nonpolarized electrode that behaves ideally in the region between A and H. For this electrode, the potential is independent of the current. 

FIGURE 22-6 Current-voltage curves in blue for an ideal (a) polarized and (b) nonpolarized electrode. Gray lines show departure from ideal behavior by real electrodes. 

For example, consider a cell made up of an ideal nonpolarized anode and a polarizable cathode consisiingof a small cadmium electrode immersed in a solution of cadmium ions. The reduction of cadmium ions is a rapid and reversible process so that when a potential is applied lo this electrode, the surface layer of the solution comes lo equilibrium with the electrode essentially... 

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