Aerogels as a tool to study the electrical properties of ruthenium dioxide

RuO2 is a well-known oxidation catalyst for electrolytic generation of Cl-2. Although bulk RuO2 is a metallic conductor, studies of mixed-oxide aerogels containing RuO2 confirm that the surface of RuO2 is a hydrous oxide and a mixed conductor. Our previous work showed that at room temperature, protonic and electronic conductivity occurs in mixed phase aerogels of RuO2 + TiO2 (designated as (Ru-Ti)O-x). Impedance measurements up to 340 degrees C demonstrate that electron hopping and/or semiconduction also occurs in (Ru-Ti)O-x aerogels. Electron hopping may occur between Ru3+ and Ru4+ ions in the ruthenia, while n-type semiconduction may be introduced into the titania by Ru3+ defects. The multiplicity of charge-transfer mechanisms measured on the surfaces of RuO2-based aerogels is indicative of the complexity of the catalytic and electrocatalytic chemistry performed on RuO2. (C) 1998 Published by Elsevier Science B.V. All rights reserved.