The role of a slow phase formation process in the growth of anodic silver oxide layers in alkaline solutions

Abstract

The anodic electroformation of silver (I) oxide layer on polycrystalline silver electrodes in 0.1 M NaOH was studied by using potentiodynamic and potentiostatic techniques. The growth of the silver oxide layer under a linear potential sweep or potential step measurements involves as a first step the electroformation of Ag₂O or AgOH monolayer at potentials close to the Ag/Ag₂O reversible electrode potential. This monolayer grows through a solid diffusion mechanism to form a 3-D primary silver (I) oxide. Subsequently the building up of a secondary silver (I) oxide layer is clearly noticed when the potential exceeds 0.24 V (vs sce). The formation of this layer can be described in terms of an instantaneous nucleation and 3-D growth mechanism under diffusion control. The ageing effects at the primary layer level decreases the nucleation rate so that for the growth of the secondary layer an intermediate situation between instantaneous and progressive nucleation under diffusion control can be observed. The secondary silver (I) oxide layer can be related to the aged silver (I) oxide species previously reported.