The kinetics of silver bromide film formation on the silver anode

The anodic potentiodynamic formation of an AgBr film on an Ag rotating disc electrode was studied in aqueous bromide solutions. As the electron transfer step (1) is intrinsically fast,

and as the film remains porous throughout its growth, the rate of film growth is limited by physical parameters such as ionic diffusion and migration in the solution.The anodic E/I curves for AgBr film formation were calculated quantitatively by computer on the basis of the following model of film growth. Film formation occurs initially by the nucleation of islands of film to a critical thickness, and then these islands spread laterally until only small pores remain between them. As these pores become small, the resistance of the solution within them becomes rate limiting (at the anodic current peak). After the peak, the concentration of bromide ions at the pore base falls to zero and current is then controlled by the diffusion of bromide ions into the lengthening pores of the film.This lateral spreading mechanism and the subsequent retention of the porous film morphology has been substantiated by comprehensive Scanning Electron Microscope investigations.