Hydrous Ir Oxide Film Properties at Sol‐Gel Derived Ir Nanoparticles

Abstract

Ir oxide (IrOx) films, formed on Au substrates using the sol‐gel (SG) technique, have been characterized electrochemically in sulfuric acid solution. The highest film charge densities can be reached by using higher withdrawal rates of the substrate electrode from the Ir‐containing sol solution, as well as by applying multiple successive coats. Allowing films to dry at ca. 100°C also yields higher charge densities. The kinetics of the Ir(III)/(IV) redox process are excellent, significantly higher, on a mole or mass IrOx basis, than for IrOx films formed by potential cycling/pulsing of standard bulk Ir electrodes in acidic solutions. The SG‐derived films are electrochromic, highly capacitive, appear to be particularly catalytic toward the oxygen evolution reaction, and have excellent adhesive properties at Au. It appears that small area planar substrates are preferred over curved (e.g., wire) electrodes in terms of SG‐formed IrOx film uniformity and the maximum achievable charge density. The measurement of the mass of fresh SG‐formed Ir films and the maximum IrOx charge density which can be obtained indicates that one out of every 2 to 3 Ir atoms are used in IrOx formation. © 2000 The Electrochemical Society. All rights reserved.