MINOR ELEMENTS IN LEAD MATERIALS USED FOR LEAD-ACID-BATTERIES .1. HYDROGEN-GASSING AND OXYGEN-GASSING CHARACTERISTICS

Minor elements are commonly present in the raw lead materials that are used to manufacture lead/acid batteries. Although certain of these elements are known to exert, individually, a marked influence on the gassing characteristics during charging, less is understood of their collective effects. As the first stage in an experimental campaign to obtain such information, the evolution of hydrogen and oxygen has been examined on both bare (grid) and doped/pasted electrodes. With the latter electrodes, different dopants (Ag, Bi, Cd, Cr, Ni, Sb, Se, Sn, Zn) have been introduced at a level of 0.1 wt.%. The subsequent gassing rates have been determined by application of either a potential-scan or a potential-step procedure. The latter has been conducted together with gas collection. The hydrogen-evolution characteristics on bare electrodes are dependent on the chosen lead alloy. The rate increases in the order: Pb < Pb-0.09Ca < Pb-0.07Bi < Pb-0.09Ca-0.4Sn < Pb-0.09Ca-0.3Sn < Pb-0.09Ca-0.7Sn < Pb-2.2Sb < Pb-1.7Sb < Pb-5.7Sb. By comparison, the oxygen-gassing rate does not exhibit such a clear relationship with alloy composition. In general, oxygen evolution above 1.7 V increases in the order: Pb < Pb-0.09Ca-0.3Sn < Pb-2.2Sb < Pb-0.09Ca almost-equal-to Pb-5.7Sb < Pb-0.09Ca-0.7Sn < Pb-0.07Bi < Pb-0.09Ca-0.4Sn < Pb-1.7Sb. The Pb-0.09Ca-0.4Sn and Pb-1.7Sb electrodes exhibit abnormal hydrogen- and oxygen-evolution rates. This is probably due to the fact that these two alloys were made by a different manufacturer. The degree of hydrogen evolution on untreated and doped negative-material (pasted) electrodes can be classified in terms of a low, a medium, or a high rate. For elements that give a low rate, gassing increases in the order: Ag < Zn < untreated < Cd < Bi almost-equal-to Cr. The Sn- and Se-doped electrodes exhibit a medium evolution rate. Finally, Sb- and Ni-doped electrodes display the highest rate of hydrogen evolution; of these, nickel exerts the stronger effect. All the dopants enhance oxygen evolution. The gassing rate increases in the order: untreated almost-equal-to Cd < Se < Sn < Bi almost-equal-to Cr < Ni almost-equal-to Zn < Sb < Ag. The hydrogen- and oxygen-gassing behaviour of the doped electrodes is discussed in terms of the operating characteristics of valve-regulated batteries.