How Platinum Electrodes are Used in Electrochemical Process?

How Platinum Electrodes are Used in Electrochemical Process?

Platinum electrodes resist dissolution not only because of their position in the galvanic series as a noble metal but also because it forms an electrically conductive passivating thin surface film. The dissolution rate of platinum anodes in seawater is rated as about 2 x 10-6 kg / kiloamp-hour. The high expense of platinum combined with its very low rate of wear has to lead to it being primarily used as a thin film plating over less expensive metals. The most cost effective combination has been platinum applied over titanium. Niobium and tantalum are other metals that have been used successfully as substrate metals for manufacturing platinum anodes.

Titanium has a critically important characteristic as a base metal in that it forms a nonconducting oxide over any breaks in the platinum thin film when operating as an anode. This anodic inert oxide formation by the substrate metal is very important for the successful use of platinum as a thin film anode. If platinum were applied over magnesium, for example, any breaks in the platinum thin film would lead to a concentration of current flow to the break in the thin film with subsequent rapid corrosion of the less noble magnesium substrate propagating from that point.

Platinum is most commonly applied to the substrate metal by electrodeposition in a plating bath. Coatings from 1 to 15 microns are commonly used. These platinum thin films have some restrictions in the conditions of operation if long operating life is to be maintained. Electrical ripple in the power supply will couple through the passivating thin film and rapidly corrodes the electrode. The DC current source must be well filtered. Also, the operation of a platinum coated electrode as a cathode causes rapid platinum coating loss due to hydrogen ingress into the titanium substrate. This can be very important in that any direct metallic contact between magnesium and a platinum coated electrode in an electrolyte will result in the platinum electrode acting as a cathode. This also disqualifies platinum coated electrodes from operating as both an anode and a cathode for alternating polarity.