Properties of the Ideal Reference Electrode

Properties of the Ideal Reference Electrode. An ideal reference electrode should show the following properties (1) it should be reversible and obey the Nemst equation with respect to some species in the electrolyte (2) its potential should be stable with time (3) its potential should return to its initial value after small currents are passed through the electrode (no hysteresis) (4) if it is an electrode of the second kind (e.g., Ag/AgCl), the solid phase must not be appreciably soluble in the electrolyte and (5) it should show low hysteresis with temperature cycling. 

Because the flow of electric current always involves the transport of matter in solution and chemical transformations at the solution-electrode interface, local behavior can only be approached. It can be approximated, however, by a reference electrode whose potential is controlled by a well-defined electron-transfer process in which the essential solid phases are present in an adequate amount and the solution constituents are present at sufficiently high concentrations. The electron transfer is a dynamic process, occurring even when no net current flows and the larger the anodic and cathodic components of this exchange current, the more nearly reversible and nonpolarizable the reference electrode will be. A large exchange current increases the slope of the current-potential curve so that the potential of the electrode is more nearly independent of the current. The current-potential curves (polarization curves) are frequently used to characterize the reversibility of reference electrodes. 

Reference electrodes can be classified into several types (1) electrodes of the first kind a metallic or soluble phase in equilibrium with its ion 

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