Abstract
Layers of lead dioxide, electrochemically deposited on graphite filled polypropylene, corrode rather slowly in 1 m HBF4/1 m Pb (BF4)2 under oxygen evolution with an equivalent current den sity of 1 - 4 μA/cm2. The rate of corrosion may be accelerated by a factor of 100 by localized cell action with graphite. In the presence of reducing agents like Fe++ or V+++, a significant acceleration occurs as well, which is limited by transport to the surface of the oxide. The oxidized component may be regenerated continously at a lead counterelectrode. However, hydroquinone is partially oxidized irreversibly beyond the quinone stage, and Tl+ is partially incorporated as Tl2O3.
Chemically prepared lead dioxide powders corrode slowly in 1 m HBF4 as well and tend to passivate. The passivation is only partially avoided by collision with a lead surface. However, rapid dissolution occurs in the presence of reducing agents like Fe++. The acceleration is shown to exceed the stoichiometric conversion of the redox mediator. Additional measurements with Pb3O4 powders have been performed. Consequences in regard to the lead tetra-fluoborate accumulator are discussed.
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