Irreversible decrease of Ir oxide film redox kinetics

Hydrous Ir oxide films have been studied using cyclic voltammetry, ac imped ance, and ellipsometric techniques. Under certain conditions of exposure af ter oxide growth, an irreversible decrease of the Ir(+III)/Ir(+IV) conversi on kinetics, also referred to as irreversible film aging, is observed. Howe ver, these films are thermodynamically not unaltered and the film charge is not lost during aging. Aging of Ir oxide films involves the detachment of oxide segments from the Ir substrate and/or cracking within the oxide itsel f. This leads to an increase in the characteristic transport length and a p ossible explanation of the altered kinetics. Furthermore, Ir oxide film agi ng can be prevented, depending on the conditions employed to grow and subse quently study them. (C) 1999 The Electrochemical Society. S0013-4651(98)06- 001-7. All rights reserved.