ELECTROCHEMICALLY ACTIVE SURFACE-AREA - VOLTAMMETRIC CHARGE CORRELATIONS FOR RUTHENIUM AND IRIDIUM DIOXIDE ELECTRODES

Electrodes made of ruthenium and iridium oxides on titanium substrates are currently used in many electrochemical processes, in particular the chlor-alkali industry. Their electrocatalytic activity are attributed to both surface area effects and their intrinsic catalytic nature. In order to compare this intrinsic activity of candidate electrode materials, their electrochemically active surface area (EASA) must be determined. In this paper, EASA-voltammetric charge correlations are presented for RuO2 and IrO2 electrodes, using zinc ion adsorption for measuring the EASA. The correlation for RuO2 on titanium (1.5–14 mg/cm2) was found to be 2643 cm2/C (0.05–1.0V vs. SCE). In the case of IrO2 on titanium (0.88–2.7 mg/cm2), it was observed to be 3626 cm2/C. Kinetic measurements of a simple redox couple were consistent with the EASA correlation for ruO2 surfaces. However, in the case of IrO2, the use of EASA correlation gave kinetic rate constants one order below the expected magnitude. A dimensionless group comparison based on porous electrode accessibility indicates that the ru02 and IrO2 behave in a similar manner, eliminating this reason for the variation in rate constants. © 1990, The Electrochemical Society, Inc. All rights reserved.