Selective formation of β-PbO and α-PbO films on Pb electrodes by potentiostatic anodization in alkaline solutions

Abstract

Interesting anodic behavior of Pb electrodes at low overpotentials for PbO formation in alkaline solutions is described. It is observed that during the initial growth of anodic oxide film, β-PbO is grown selectively and continued anodization leads to a phase change or the formation of the α-PbO phase. This result is very clear particularly at low overpotentials for PbO formation (ca. between −0.7 V and −0.5 V vs. SCE). An increase in the anodization temperature and/or increase in overpotential for PbO film formation assists the rapid formation of the anodic film with clear observation of phase change. Compositional analysis of anodic oxide films by X-ray diffraction (XRD) and photoelectrochemical techniques supports the above observation since both the PbO modifications have distinct XRD patterns and photoelectrochemical responses. When this observation of anodic PbO film formation is compared with other physical methods of PbO growth, a correlation is found owing to the particular thermodynamic and/or kinetic aspect which controls the selective formation of β-PbO initially, followed by α-PbO. Further, we observe that this phenomenon is not due to acidic or alkaline conditions maintained during film formation by electrochemical methods, rather it is due to the characteristic nature of structural and thermodynamic conditions which influence the growth of one particular phase in preference to the other.