Visualizing electrochemical zinc deposition and the role of a polymer additive in the crystal growth mechanism

Abstract

Electrodeposition of metals is relevant to many research fields including catalysis, batteries, antifouling, and anticorrosion coatings. Compared with hot dip galvanizing, there is significant interest in less energy and material-intense electroplating of zinc. At present, large-scale electroplating mostly uses acidic zinc solutions, containing potentially toxic additives. Alkaline electroplating of zinc offers a route to using environment-friendly green additives. Further to the previous elucidation of the mechanism by which the polyquarternium polymer (PQ) aids the deposition of negatively charged zincate, here the nature of the coating is explored. Zinc was deposited from an electrolyte including zincate and PQ, on gold model surfaces. Atomic force microscopy (AFM) and low energy ion scattering have been used to characterize the layer and explore the crystal growth mechanism that the PQ changes and, hence, improves the coating quality. We have also used AFM of the PQ on negatively charged mica to provide further evidence for the growth mechanism interpretation. Our data demonstrate that the additive is crucial to steering the growth mechanism, offering routes to optimizing deposition.