An EQCM investigation of charging RuO2 thin films prepared by the polymeric precursor method

An electrochemical quartz crystal microbalance (EQCM) study of RuO2 thin films, prepared by the sol-gel precursor method, is presented. The X-ray diffraction (XRD) analysis demonstrates that RuO2 films were crystallized in the rutile phase and scanning electron microscopy investigations indicated the formation of a smooth surface. Cyclic voltammetry and EQCM studies were performed simultaneously in order to investigate the charging processes of the RuO2 films in 0.1 M HClO4. The voltammetric and mass versus potential responses present three well-defined regions associated with the RuO2 redox couples. Based on these results and on the mass-charge relationships, the corresponding charging mechanisms are proposed. In the potential region governed by the Ru3+/Ru4+ redox couple, the mass-charge relation can be associated with the double-injection of protons and electrons. The other regions correspond to water release and oxyhydroxide species formation during charging.