EFFECTS OF H2SO4 CONCENTRATIONS ON REDUCTION PROCESSES OF PBO LAYER

The reduction process of tetra-PbO in different H2SO4 solutions has be en studied by linear sweep voltammetry, potential step and scanning el ectron microscope (SEM) techniques. As the H2SO4 concentration decreas es, more tetra-PbO is formed on a lead electrode and the PbSO4 crystal s and the microvoid in the anodic film enlarge. This helps the mass tr ansfer of the H+ and SO42- ions and the transformation of tetra-PbO in to basic lead sulfates and PbSO4. The reduction mechanism of tetra-PbO changes from two- into three-dimensional progressive nucleation and g rowth of metallic lead with the decrease of the H2SO4 concentration. W hen PbSO4 begins to be reduced, tetra-PbO is transformed into PbSO4, w hich is then reduced. Copyright (C) 1997 Elsevier Science Ltd.