Electrochemically Active Surface Area: Voltammetric Charge Correlations for Ruthenium and Iridium Dioxide Electrodes

Abstract

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 RuO 2 and IrO 2 electrodes, using zinc ion adsorption for measuring the EASA. The correlation for RuO 2 on titanium (1.5–14 mg/cm 2 ) was found to be 2643 cm 2 /C (0.05–1.0V vs. SCE). In the case of IrO 2 on titanium (0.88–2.7 mg/cm 2 ), it was observed to be 3626 cm 2 /C. Kinetic measurements of a simple redox couple were consistent with the EASA correlation for ruO 2 surfaces. However, in the case of IrO 2 , 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 ru0 2 and IrO 2 behave in a similar manner, eliminating this reason for the variation in rate constants. © 1990, The Electrochemical Society, Inc. All rights reserved.