Reversibility and Irreversibility

Abstract

Electrodeposition onto insulating polymeric films is a synthetic route for preparing sparse metallic particles with a great variety of shapes. The nucleation of zinc on the insulating polyaniline occurs at defects in the film, which have a density on the order of 106 cm–2. The number and size distribution of the particles are related to the thickness of the film. Electrolyte concentration, cell orientation, and applied magnetic field all influence the form of the deposits. Overpotential and magnetic field control the nucleation rate, while gravity affects the subsequent crystallite growth. The concentration of the electroactive species can be used to select the growth mode between two-dimensional (2D) or three-dimensional (3D) growth of zinc; 0.1 M ZnCl2 leads to thin 2D crystallites with 6-fold symmetry and a hexagonal or flowerlike shape due to preferred growth in the 110 directions, whereas 1 M ZnCl2 produces 3D polycrystalline hemispheres or thick hexagons. Particles with a wide range of intermediate structures are illustrated.