Elucidating the Cathodic Electrodeposition Mechanism of Lead/Lead Oxide Formation in Nitrate Solutions

The production of crystalline lead oxide (PbO) structures, directly on the surface of an electrode in (nitrate) solution, via electrochemical deposition of lead ions (Pb2+), is unequivocally demonstrated and the formation mechanism elucidated. Boron doped diamond electrodes are used as the deposition platform. We show the effect of electrode potential, deposition time, presence of oxygen, and temperature on the formation process. At room temperature, under both deoxygenated and aerated conditions, high-resolution microscopy reveals a predominant nanoparticle (NP) morphology. In contrast, under laser-heated conditions, both NPs and half-hexagon shaped “plates” result. Transmission electron microscopy reveals these “plates” to be crystalline β-PbO. Plate prominence, under heated conditions, increases as the driving potential and deposition time is increased. By deoxygenating the solution and applying a deposition potential such that hydroxide ion (OH–) formation is negligible, only NPs are observed, which, from cyclic voltammetry data, are confirmed to be elemental Pb. We thus propose that Pb NPs and OH– play a crucial role in the PbO formation process. Electrodeposited Pb NPs catalyze OH– generation from either oxygen or nitrate reduction (oxygen reduction occurs at a less negative applied potential than nitrate reduction) driving the formation of lead hydroxide (Pb­(OH)2) via a precipitation route. The Pb­(OH)2 subsequently dehydrates to PbO, a process significantly accelerated by temperature. Hence, by controlling temperature, potential, and solution conditions, cathodic electrodeposition of Pb2+ can lead to the preferential formation of PbO crystalline structures on the electrode surface.