Anodic stability and electrochromism of electrodeposited ruthenium-iridium coatings on titanium

Abstract

The anodic behaviour of galvanically plated ruthenium-iridium coatings on titanium was investigated. The dependence of the Tafel slopes and the stability of the coatings for the oxygen evolution reaction in sulphuric acid on the electrode composition was established. A change in the Tafel slope from 33 to 90 mV per decade on going from pure ruthenium to pure iridium was found. The presence of 40% Ir in the coating yielded 300 times higher stability in comparison with the coating of pure ruthenium. In addition, a square-wave pulsing between -0.25 and 1.25 V vs. the saturated calomel electrode produced an oxide film with electrochromic properties which were directly related to the charge enhancement factor of the grown oxide.