Electrochemical synthesis of dendritic zinc films composed of systematically varying motif crystals.

Polycrystalline zinc films with new dendritic frameworks were electrodeposited from nonaqueous formamide media containing 0.01-0.3 M Zn(ClO4)2.6H2O as the Zn2+ source and 0.1 M LiClO4.3H2O as the supporting electrolyte. Formamide media offer a wider range of deposition temperatures and deposition potentials than aqueous solutions, which provides a higher degree of freedom in creating new polycrystalline architectures. The growth patterns of zinc crystals could be precisely controlled (e.g., faceted growth and dendritic growth) by changing the interplay between the growth rate and the mass transport rate. The effect of deposition potential, temperature, and Zn2+ concentration on the onset potential of dendritic growth and the detailed dendritic features were studied systematically. The zinc dendrites obtained in this study were composed of submicron-sized crystals of a uniform shape (motif crystals) that grow repetitively fused together to form three-dimensionally dispersed dendritic backbones. This unique organization achieves a remarkable physical and electrical continuity between crystals while generating high surface areas, which is difficult to accomplish simultaneously in polycrystalline films. The shape of motif crystals can be finely tuned from hexagons to fern-shaped leaves by the deposition potential applied, which in turn alters the overall degree of branching of dendritic backbones. Cyclic voltammetry of the resulting zinc electrodes with various growth patterns was carried out and discussed in conjunction with the films' morphological variation.