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
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.