Enhanced Raman approaches for understanding electrochemical reactivity: temporal and spatial resolution.

The development of electrochemical techniques combined to Raman spectroscopy such as electrochemical Tip- or Surface- Enhanced Raman spectroscopy (EC-TERS or EC-SERS) have attracted considerable attention over the past years by the scientific community. This spectro-electrochemical combination provides an accurate view over electrochemical processes occurring at an electrode by acquiring simultaneously local topography, and vibrational fingerprints about the material or molecules under potential control. Based on the use of an insulated TERS tip, we introduced recently a new approach that we called EC-Tip-SERS. Here, electroactive molecules are adsorbed directly onto a gold tip that acts both as working microelectrode and single hotspot for SERS. Interesting transient mechanistic information can be obtained in this configuration, for example such as those associated to the oxygen reduction reaction towards hydrogen peroxide in water using viologen SAMs as electrocatalyts. Nevertheless, there is here no spatial resolution. The latter can be obtained in TERS, but this requires to handle the Raman signal and STM feedback simultaneously in a home-made design. We will present our latest developments in that direction.