Electrodeposition (electroplating)

What is it?

Electrodeposition, also known as electroplating, is the process of depositing material onto a conducting surface from a solution containing ionic species (salts). This fabrication technique is commonly used to apply thin films of material to the surface of an object to change its external properties such as to increase corrosion protection, increase abrasion resistance, improve decorative quality, or simply to deposit a layer which is part of a more complicated device. For example nickel metal is electroplated on automotive products so as to inhibit against corrosion, and copper metal is electrodeposited on to circuit boards to provide low resistance pathways between electronic components. Electrodeposition can not only be used for plating simple metals but also alloys (mixtures of metals) and semiconductors.

How does it work?

A typical set up for small scale electrodeposition is shown in the figure. It consists of three electrodes, namely working, reference, and counter (sometimes secondary) electrodes, respectively. The electrodes are connected to a potentiostat which is the instrument which controls the deposition process. The electrodes sit within a vessel containing a liquid which has ionic species dissolved within it, such as copper ions dissolved in water.

The working electrode is the object which will be plated, the counter electrode is used to complete the electronic circuit, and the reference electrode is used as a fixed reference point for the potentiostat. An electric field is then applied across the working electrode in such a way as to give electrons to the ions in solution so that they form uncharged elements or compounds which prefer to adhere to the surface of the working electrode rather than remain dissolved in solution. The strength of the electric field or the potential is measured versus the reference electrode, but the actual current flows between the working and counter electrodes.