Morphological study of branched Sn structure formed under selected electrochemical conditions

Abstract

A controlled electrodeposition process of branched micrometric and nanometric metallic tin structures was developed. Selected potentiostatic and galvanostatic techniques were explored with the aim of forming hierarchical shaped Sn on carbon porous electrodes by a simple template-free synthesis. We have studied the influence of continuous potential steps ranging from −0.9 to −4 V versus Ag/AgCl which show a classical nucleation growth mechanism. Under high overpotentials above −1.5 V, the reaction is governed by mass transport, which enables the development of vertically aligned dendrites. Upon reaching a dendrite particle size of 2–5 µm, Sn2+ reduction is facilitated on branches extending at an angle of about 45° from the main stem due to enhanced spherical diffusion to these newly evolving sites. A competing reaction of hydrogen evolution plays a significant role during initial nucleation stages and throughout particle evolution by reducing the overall columbic efficiency. Further study of means to affect the mass transport and morphology has led us to investigate the influence of pulse deposition duty cycle as well as use of anionic (SDS—sodium dodecyl sulfate) and cationic (HDTAB—hexadecyltrimethylammonium bromide) surfactants. While short pulses and long rest time promote the formation of high surface density of small nuclei, surfactants directly influence the tin ions (SDS) or adsorbed on the negatively charged electrode (HDTBA). Finally, the study of an electrodeposition method using strong acid additives was developed. It is shown from SEM and EQCM studies that careful selection of the acid type and concentration gives rise to the formation of a much more advanced network structure promoted by selective etching and co-reduction of dissolved ions. Highly interesting two-dimensional tin films formed in this process are also reported.