Characterisation of surfaces modified by sol-gel derived RuxIr1-xO2 coatings for oxygen evolution in acid medium

The preparation of sol-gel derived RuxIr1-xO2 catalytic coatings (x = 1, 0.9, 0.7, 0.5, 0.3, 0.1 and 0) for oxygen evolution in acid media is reported. The films were deposited on titanium plates by painting the substrate with a sonocatalysed sol containing varying amounts of ruthenium and iridium acetylacetonates. This was followed by a heat-treatment at 400 degrees C for 1 h. The redox processes occurring on those films were characterised by cyclic voltammetry:at 20 mV s(-1) in 0.5 M aqueous H2SO4. The measured voltammetric charges are related to the active areas of the electrodes and increase with the iridium content going through a maximum at x = 0.5. The oxygen evolution reaction (OER) was studied through polarisation curves recorded under galvanostatic control from 10 mu A cm(-2) up to 100 mu A cm(-2). Tafel plots normalised by the voltammetric charges revealed the true catalytic effect of cm the RuO2 for the OER. The combination of electrocatalytic and roughness effects made the Ru0.7Ir0.3O2 coating the most effective for the OER. The Tafel slope values changed from 40 mV dec(-1) for pure RuO2 coatings to 60 mV dec(-1) for pure IrO2. These variations indicate a strong dependence of the Fraction pathway with the nature of the coating. Accelerated tests performed at 700 mA cm(-2) in 30% aqueous H2SO4 and 80 degrees C showed that the limiting factor in:the operational life of these electrodes is the dissolution of the active layer and that the Ru0.1Ir0.9O2 coating has the longer life-time under those conditions. (C) 1998 Elsevier Science Ltd. All rights reserved.