Abstract
The addition of a microelectrode of platinum to a lead anode polarised in sodium chloride solutions fundamentally alters the anodic behaviour. A detailed study has been made of the behaviour of lead-platinum bielectrodes in aqueous chloride electrolytes over a range of concentrations using galvanostatic, potentiostatic and microscopic techniques. In addition, studies have been made of lead, platinum and lead peroxide individually in sodium chloride solutions. It is considered that a platinum microelectrode on the surface of a lead anode limits the extent of formation of lead chloride and provides a suitable surface for the nucleation of lead peroxide. Subsequent formation of lead peroxide occurs over the surface of the previously formed lead chloride, the platinum and lead peroxide being in electrical contact. When the anode is completely covered with a film of lead peroxide, further passage of charge results in the conversion of the underlying layer of lead chloride to lead peroxide until the lead and lead peroxide are in contact, but this occurs slowly since the predominant electrode process at this stage is the discharge of chlorine at the microelectrode and on the lead peroxide. It has been shown that lead peroxide will only form and propagate satisfactorily within the range 0. 1-1. 3M NaCl, the lower limit being associated with the fact that lead will not passivate to sufficiently high potentials in solutions of sodium chloride below this concentration. It is believed that a number of factors are responsible for precluding the formation of lead peroxide at concentrations greater than 1. 3M since it was found that (a) lead peroxide is attacked when made anodic in high concentrations of sodium chloride, (b) deposition of lead peroxide on to platinum from sodium chloride solutions containing lead chloride is retarded with increasing chloride ion concentration, and (c) lead when made anodic in 2M NaCl gives rise to the formation of complex ions.