Pulse Electrodeposition in the Presence of Corrosion Reactions during the Off-Time

Abstract

Pulse electrodeposition of metals and alloys offers one route to enhance or tune material properties. However, an often-neglected period during pulse plating is the off-time, which may also influence deposit properties. Traditionally it is considered a relatively unimportant, allowing, for example, relaxation of concentration gradients, desorption of additives, recrystallization and discharge of the double later capacitance. Over the past few decades, however, studies have shown that it is possible to have ‘internal current’ processes occurring in the off-time which can strongly influence the deposit properties and composition. For example, in the pulse electrodeposition of binary alloys from aqueous solutions, displacement (corrosion) reactions have been observed in the off-time that can significantly alter the alloy composition. This has also been observed in many aqueous and molten salt systems, and appears a very general phenomenon. More recently we have observed corrosion arising from a comproportionation reactions during the pulse plating of copper from a deep eutectic solvent (DES) and noted some of their effect on deposit properties.The main purpose of this paper is to examine some of the similarities and differences in off-time corrosion caused by displacement and comproportionation processes during pulse electrodeposition. As is shown in the figure, corrosion may occur due to the presence of oxygen, or due the presence of a noble material leading to displacement reactions, as well as the presence of a stable species of differing valency in solution leading to comproportionation reactions. These differing mechanisms can produce different effects on the deposit. We will discuss how these different mechanisms can be understood and the influence on the deposit and their characteristics. Figure 1