Study On Effect Of Bismuth On Electrode Reactions Involved In Lead Acid Batteries

Electrochemical behaviors of lead and bismuth in sulfuric solutions and the influence of bismuth on electrode reactions involved in lead acid battery were studied by CV, AC impedance, SEM and XRD methods. The electrode reactions include hydrogen and oxygen evolution, convertion of Pb-PbSO4, anodic corrosion of lead and convertion of PbSO4-PbO2: Following results have been obtained.1. Some irregular redox peaks appear nearby the reduction peak of PbO2 when the lead electrode potential is cycled from hydrogen evolution potential to oxygen evolution potential. These redox peaks can be ascribed to the sum of reduction current of PbO2 and oxidation current of lead under oxides.2. Two oxidation peaks are observed when bismuth is anodised in sulfuric acid solution. The first oxidation peak is corresponding to the formation of bismuth sulphate, which follows dissolution-precipitation mechanism and is controlled by ion diffusion in solution. The second oxidation peak is the second oxidation of bismuth under the bismuth sulphate film. The oxidation product is non-crystalline. At high potentials, bismuth cannot be passivated but dissolved in a big current, which is related to ion diffusion in solution.3. Bismuth accelerates the hydrogen evolution reaction on lead and decreases the reaction resistance whether it enters lead crystal lattice or deposits chemically on the lead surface. However, the influence of bismuth in lead alloys on hydrogen evolution is much smaller than the bismuth deposited on the lead surface. When bismuth is deposited chemically on lead, hydrogen evolution reaction mainly occurs on bismuth, which has a lower hydrogen evolution overpotential than lead. Bismuth in Pb-Bi alloy accelerates the hydrogen evolution through changing the microstructure of lead. The grain size of Pb-Bi alloys gets smaller with the increasing of the bismuth content in alloys. When the Bi content in the lead-bismuth alloyis lower than 0.103%, there is no significant difference in oxygen evolution on lead-bismuth alloys and lead. However, when the Bi content in the alloy is higher than 0.83% , bismuth increases the oxygen evolution current and decreases the overpotential of oxygen evolution reaction.4.There was no significant effect on the growth of PbO2 at bismuth contents less than 0.103%. However, the effect of bismuth on the growth of PbO2 depends on the anodic potential when the Bi content is higher than 0.83%. Bismuth will inhibit the growth of PbO2 at low anodic potential(l.3V) and accelerate it at high anodic potential(1.6V). This is related to the oxygen evolution. Bismuth can catalyze oxygen evolution and accelerate the growth of PbO2.5. Bismuth will decrease the corrosion resistance and accelerate the lead corrosion when bismuth contents is larger than 0.83%, which is related to the change of the structure of passivation film.6.Bismuth can accelerate the nucleation and decrease the capacity of lead sulfate when bismuth contents is larger than 0.83%. This is because bismuth will not dissolve into the solution in the region. The exist of bismuth decreases the real surface area of lead and accelerates the lead oxidation. On the other hand, bismuth can decrease the grain size, increase the active place and accelerate the nucleation of lead sulfate.