In situ surface enhanced raman scattering of ruthenium dioxide films in acid electrolytes

Vibrational aspects of thin RuO2 films (ca. 7-8 X 10(-8) mol Ru sites/cm(2)) electrodeposited on preroughened Au electrodes were investigated in situ in 0.50 M H2SO4 aqueous solutions using surface enhanced Raman scattering (SERS). Prominent peaks could be observed for the material in the predominantly fully oxidized state (+0.80 V vs. SCE) at 456 and 710 cm(-1), and predominantly fully reduced state (+0.10 V vs. SCE) at 614 and 750 cm(-1). The first set of features is in good agreement with in situ SERS measurements reported by Chan et al. for oxidized metallic Ru films in acid electrolytes polarized at high potentials and ascribed by those authors to a hydrated form of Ru oxide in the 4+ formal oxidation state. Based on our recent in situ Ru K-edge X-ray absorption fine structure of thicker RuO2 films prepared by the same procedure employed in this work, the peaks observed for the first time for the predominantly reduced film are attributed to a highly disordered oxide incorporating Ru sites in the 3+ oxidation state. (C) 2001 The Electrochemical Society.