107 Z ElectroanaL Chem., 352 (1993) 107-118 Elsevier Sequoia S.A., Lausanne JEC 02628 Preparation and characterization of iridium and titanium oxide layers on silica particles Anna Giatti * and Luuk K. Koopal Wageningen Agricultural University, Department of Physical and Colloid Chemistry, Dreyenplein 6, Wageningen (Netherlands) (Received 10 August 1992; in revised form 7 October 1992) Abstract Silica-supported iridium and titanium oxides were synthesized by pyrolysis of opportune salt solutions and characterized both as dry samples and in solution. Electron micrographs indicate that the layer thicknesses are about 70 nm; X-ray diffraction shows that the IrO 2 crystallizes in the form of rutile, while TiO 2 crystallizes as anatase. Different acid-base properties for supported and pure crystalline oxides are found using electrophoresis. Potentiometric titrations indicate that the oxide layers have an exceptionally high charge density, while the Brunauer-Ernmett-Teller area is negligible. An interpretation of the results has been attempted on the basis of the permeability of protons and counterions in the poorly organized microcrystalline structure of the oxide layers. INTRODUCTION Supported mixed oxides of Group VIII and Group IVa metals have an extensive technological application in the field of preparative electrochemistry [1,2]. Thermal oxides of IrO 2 and RuO2 have been proved to be catalysts for reactions such as anodic oxygen and chlorine evolution, while metal oxides, such as TiP 2, are used in combination with the IrO2 to improve wear resistance. Though these systems have received much attention in recent years, the correlation between the synthesis procedure and the final properties of supported mixed oxides is still not well * Present address: Dipartimento di Chimica dell'Universit~ e centro di Studi sulla Fotoehimica e Reattivit~ degli Stati Eceitati CC del CNR, via Borsari 46, Ferrara, Italy. 0022-0728/93/$06.00 © 1993 - Elsevier Sequoia S.A. All rights reserved