Oxygen evolution over-voltage

Over-voltage vs Ig / curves for oxygen evolution obtained after preliminary polarization of the electrode for different periods of time [103]. 

What is the effect of silver on the anodic corrosion of lead It is revealed hy the rate of oxidation of the metal expressed in current density units (Fig. 2.45). Let us consider the case when the polarization is carried out at a constant potential (e.g., 1500 mV). When Ag ions are introduced into the solution, the oxygen over-voltage decreases. When silver is alloyed in the metal, a weaker effect on the rate of oxygen evolution is observed, but the corrosion rate of the lead—silver alloy is considerably reduced. Hence, the introduction of silver by both methods accelerates the oxygen evolution reaction, but it affects differently the anodic corrosion of the metal. 

The correlation between the rates of the two reactions (corrosion and oxygen evolution) can reveal the effect of Ag in a more clear-cut manner, eliminating the influence of the oxygen over-voltage decrease. Such a relationship is given in Fig. 2.46. 

In order to minimise, or even eliminate, the need for maintenance, the battery should operate with minimum water loss. This is achieved when the over-voltage of hydrogen and oxygen evolution on Ph and Pb02 surfaces, respectively, is very high. This is of utmost importance for VRLA and maintenance-free batteries. Hence, it is essential to reduce the rate of hydrogen evolution at the negative plates and to find appropriate methods to oxidize the evolved... 

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