Additionally, many techniques allow an in situ mechanistic study by monitoring reaction processes (change in ν(CO) in CO2 reduction, for example), changes in oxidation state, and shifts in bonding frequency and amplitude. Finally, recent efforts on characterizing interfacial electric fields at electrode/electrolyte surfaces using vibrational sum frequency generation (VSFG) provide a good handle on understanding the electrified interface on a molecular level. A recent comprehensive review emphasized the potential of VSFG in exploring fingerprint bands of surface-adsorbed molecular species compared with other spectroscopic techniques. Surface-enhanced Raman spectroscopy (SERS) represents another powerful tool for in situ surface characterization with a well-elaborated example published recently. To aid the interpretation of the surface-functionalized complex's performance, comparisons made between the immobilized and the homogenous species in solution using multiple techniques are highly valuable. Understanding the type of information provided by a specific method and taking advantage of those that offer complementary information allows a complete picture of the modified surface and its catalytic behavior.