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(Invited) In Situ Electrochemical Raman Spectroscopy for Nanoscale to Macroscale Electrochemical Processes

Raman spectroscopy has been increasingly applied in studying the electrochemical processes, including adsorption and reaction, under in situ or operando condition, because Raman spectroscopy can conveniently work in aqueous solution and provide fingerprint molecular information. In this talk, I will present the recent work in my group on developing various electrochemical Raman spectroscopy for in-situ and operando studies of electrochemical systems at the limits of time and spatial resolution and sensitivity
 With the help of the plasmonic enhancement at the tip of a plasmonic material, electrochemical tip-enhanced Raman spectroscopy (EC-TERS) offers itself as the only nanospectroscopy for investigating the electrochemical interface with unprecedent spatial resolution and explicit chemical fingerprint information. We developed the electrochemical TERS both based on STM and AFM using the water immersion objective and homemade optical instrument. EC-TERS was applied to obtain the molecular fingerprint information of surface adsorption and electrochemical reaction on single crystal surfaces and monitor the plasmon-driven reaction at the nanoscale.
 Aiming at addressing the challenge of monitoring the highly dynamic changing electrochemical interfaces under potential control and presence of the electrolyte, a transient electrochemical surface-enhanced Raman spectroscopy (TEC-SERS) was developed to monitor the structural evolution of surface species at a time resolution that equals the transient electrochemical methods (e.g. cyclic voltammetry and chronoamperometry), allowing the precise correlation of Raman signal with the molecular signature information and the electrochemical current signal. He observed an interesting two-step reaction processes that are impossible to observe by conventional steady state SERS methods. A wide-field Raman imaging system was developed to offer a high imaging speed to monitor the spatial and temporal change at every point over the whole electrode surface simultaneously. The heterogeneity of electrocatalytic reaction on the electrode surface was observed. This technique offers the possibility to spatially correlate electrochemical behavior and the particular surface sites where the reaction happens.