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 wit h a sonocatalysed sol containing varying amounts of ruthenium and iridium a cetylacetonates. This was followed by a heat-treatment at 400 degrees C for 1 h. The redox processes occurring on those films were characterised by cy clic voltammetry:at 20 mV s(-1) in 0.5 M aqueous H2SO4. The measured voltam metric charges are related to the active areas of the electrodes and increa se with the iridium content going through a maximum at x = 0.5. The oxygen evolution reaction (OER) was studied through polarisation curves recorded u nder 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 e ffect of cm the RuO2 for the OER. The combination of electrocatalytic and r oughness effects made the Ru0.7Ir0.3O2 coating the most effective for the O ER. The Tafel slope values changed from 40 mV dec(-1) for pure RuO2 coating s to 60 mV dec(-1) for pure IrO2. These variations indicate a strong depend ence of the Fraction pathway with the nature of the coating. Accelerated te sts 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 th e 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. Al l rights reserved.