With the help of in situ multi-step FTIR Spectroscopy, two types of adsorbed geminal CO have been observed for the first time at an electrochemically modified Rh electrode. A doublet band of two broad peaks at 2166 and 2112 cm(-1) is assigned to geminal CO on Rh surface oxide (or hydroxide) produced by the electrochemical modification process, and a doublet band of two peaks near 2103 and 2033 cm(-1) is ascribed to geminal CO on surface clusters of Rh formed by reduction of Rh surface oxide. Based on the evolution of FTIR spectra with the electrode potential, the surface processes of a Rh electrode, subjected to a potential cycling treatment at 1.5 V s(-1) between -0.275 and 2.4 V for 2 min, have been elucidated. The present results at the solid/liquid electrochemical interface were compared with those obtained at the solid/gas interface, and consistent conclusions were achieved.