The electrochemistry of lead dioxide formed on lead and lead alloys in sulphuric acid

The electrochemistry of lead dioxide has been studied using the techniques of linear sweep voltammetry, potentiostatic pulse experiments and a.c. impedance measurements. A morphological examination was also carried out using the technique of scanning electron microscopy. The formation of lead dioxide was investigated on both the flat lead/lead alloy electrode and the porous electrode which was produced by oxidation of a standard automotive positive paste on a lead/lead alloy base. The electrochemistry of the pure lead electrode (both flat and porous) was investigated and the effect on this of various alloy additions was observed. The alloys used, all of potential industrial importance, were lead-antimony, lead-bismuth, lead-calcium-tin and lead-calcium-tin-bismuth at various levels of bismuth addition. An a. c. study of Pb-Ca-Sn-Mg-Al is also included. The effect of antimony addition to lead has been isolated as the production of a secondary oxidation layer. This provides an explanation for the superior active material retention of antimony containing grids in the lead-acid battery, the relatively large material development with the antimonial alloy giving rise to a more mechanically sound function between grid and paste. The formation of this extra corrosion layer on antimonial lead may also explain the high degree of top bar corrosion which occurs in the oxygen region of the battery. The commercial significance of bismuth as a grid alloying ingredient has been highlighted and'a useful bismuth concentration range determined for both lead and lead-calcium-tin alloys.