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 predominan tly fully oxidized state (+0.80 V vs. SCE) at 456 and 710 cm(-1), and predo minantly fully reduced state (+0.10 V vs. SCE) at 614 and 750 cm(-1). The f irst set of features is in good agreement with in situ SERS measurements re ported by Chan et al. for oxidized metallic Ru films in acid electrolytes p olarized at high potentials and ascribed by those authors to a hydrated for m 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 b y the same procedure employed in this work, the peaks observed for the firs t time for the predominantly reduced film are attributed to a highly disord ered oxide incorporating Ru sites in the 3+ oxidation state. (C) 2001 The E lectrochemical Society.