Over the past three decades, surface-enhanced Raman spectroscopy (SERS) has gone through a tortuous pathway to develop into a powerful surface diagnostic technique for in situ investigation of surface adsorption and reactions on electrodes. This review presents the recent progress achieved mainly in our laboratory on the improvement of detection sensitivities as well as spectral, temporal, and spatial resolutions. Various surface roughening procedures for electrodes of different metals coupled with maximum use of a high-sensitivity confocal Raman microscope enable us to obtain good-quality SER spectra on the electrode surfaces made from net Pt, Ni, Co, Fe, Pd, Rh, Ru, and their alloys that were traditionally considered to be non-SERS active. A novel technique called potential-averaged SERS (PASERS) has been developed for the quantitative study of electrochemical sorption. Applications are exemplified on extensively studied areas such as coadsorption, electrocatalysis, corrosion, and fuel cells, and several advantages of in situ electrochemical SERS are demonstrated. Finally, further developments in this field are briefly discussed with emphasis on the emerging methodology.

By using the previously developed roughening method for producing SERS-active Rh electrode, and assistedby the highly sensitive confocal microprobe Raman system, we carried out a detailed SERS study on thedissociation and electrooxidation of C1 molecules on a Rh surface. The SERS spectra obtained in a widefrequency region provide not only the vibrations reflecting the internal bonding of CO (at ca. 2000cm-1) butalso the bonding between CO or O with Rh (at ca. 450cm-1). A complementary electrochemical study wasalso performed on the roughened Rh surface in order to correlate the electrochemical and vibrationalinformation. Both electrochemical and SERS studies show that Rh has no discernible activity toward theelectrooxidation or dissociation of methanol in acidic solutions. Rh becomes active and its activity increaseswith the decrease of the solution acidity. For HCHO and HCOOH, the electrooxidation activity of Rh increaseswith increasing pH. On the basis of the result of the model CO system, discussion on the dissociation orelectrooxidation mechanisms was presented for C1 molecules on Rh.