Surface-enhanced Raman spectroscopic evidence of methanol oxidation on ruthenium electrodes

Electrooxidation of methanol on Ru surfaces was investigated using in situ surface-enhanced Raman spectroscopy. Although the cyclic voltammogram did not show a significant methanol oxidation current on Ru, a Raman band at approximately 1970-1992 cm(-1) was observed from 0.4 to 0.8 V in 0.1 M HClO(4) + 1 M methanol. By comparing with the C-O stretching band (nu(CO)) of carbon monoxide (CO) adsorbed on RuO(2)(110) in the ultrahigh vacuum and on oxidized Ru electrodes, the observed spectral feature is assigned to nu(CO) of adsorbed CO (CO(ads)) on RuO(2). The formation of CO(ads) suggests that methanol oxidation does occur on Ru at room temperature, which is in contrast to the perception that Ru is not active for the reaction. The lack of significant methanol oxidation current is attributed to the competing rapid surface oxidation, which forms inactive surface oxides and therefore inhibits the methanol oxidation.