Bismuth oxide as an additive in pasted zinc electrodes

The effect of small additions (2–10 wt.%) of Bi2O3 to zinc electrodes has been studied using chronopotentiometry, cyclic voltammetry, and polarization studies. Methods were devised for preparing electrode samples for scanning electron microscopy so that the bismuth deposits could be clearly observed. In addition, studies were carried out into zinc deposition on bismuth single-crystals in zincate electrolytes, in an effort to elucidate the interaction of zinc with bismuth. Investigations were also carried out on silver electrodes in bismuth oxide-saturated zincate electrolytes. The chronopotentiometry results indicate that the Bi2O3 additive is essentially quantitatively reduced to bismuth prior to deposition of zinc. The reduced Bi2O3 forms a bismuth matrix in the electrode and consists of needle-like deposits. The nucleation overvoltage for zinc deposition on bismuth is ≈ 20 mV. The deposits have an hexagonal morphology. The beneficial effect of bismuth appears to accrue from the conductive bismuth matrix and the maintenance of an active deposit.