Comparison of Ir oxide film redox kinetics in sulfuric and p-toluene sulfonic acid solutions

Authors
Citation
C. Bock et Vi. Birss, Comparison of Ir oxide film redox kinetics in sulfuric and p-toluene sulfonic acid solutions, ELECTR ACT, 46(6), 2001, pp. 837-849
Citations number
37
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ELECTROCHIMICA ACTA
ISSN journal
00134686 → ACNP
Volume
46
Issue
6
Year of publication
2001
Pages
837 - 849
Database
ISI
SICI code
0013-4686(20010101)46:6<837:COIOFR>2.0.ZU;2-B
Abstract
Ir oxide films were grown and studied electrochemically in 0.4 M H2SO4 and in 0.3 M para-toluenesulfonic acid (TsOH). The equilibrium CV characteristi cs for films formed in these two solutions were very similar, even though t he kinetics of the Ir(+ III)/Ir(+ IV) charge transfer reaction were ca. 10 times more rapid for films grown and studied in H2SO4 versus TsOH. from the ac impedance response of these films, the same equivalent circuit was foun d to describe them both. In both solutions, the Ir(+ III)/Ir(+ IV) reaction rate was found to be inversely proportional to the square of the film char ge density (film thickness) and to increase exponentially with increasing p otential. Kinetic differences of up to 10 times were again found for films studied at the same de potential and of similar film charge density, but gr own and studied in the two different solutions. Analysis of the impedance d ata could not distinguish between an electron hopping versus a coupled elec tron-counter ion transport model. Differences in the nanostructure of the I r oxide films grown and studied in H,SO, and TsOH are believed to be at lea st partly responsible for the observed kinetic differences. Field Emission Scanning Electron Microscopy (FESEM) studies revealed a highly ordered pole structure, with pores of ca. 20-30 nm in diameter, for Ir oxide films grow n in H2SO4, while the pore size of films formed in TsOH must be much smalle r than this. (C) 2001 Elsevier Science Ltd. All rights reserved.