Molecular Scale Assessments of Electrochemical Interfaces: In Situ and Ex Situ Approaches

Microscopic studies on electrolyte solution/electrode interfaces provide the most fundamental information not only for understanding the electric double layer formed at the interfaces but also for designing sophisticated electrochemical devices. Various types of in situ techniques, performed without taking the electrode out of electrolyte solutions, have become indispensable tools. Among them, electrochemical tip-enhanced Raman spectroscopy (EC-TERS) is considered as an ultimate tool because of simultaneous measurements of electrochemical scanning tunneling microscopy (EC-STM) and Raman spectroscopy just underneath the EC-STM tip. On the other hand, ex situ techniques, where the electrode is emersed from the solution to perform precise measurements, have been still useful because the detailed information not easy to obtain by in situ techniques is available just by combining conventional instruments, such as photoelectron spectroscopy (PES) for the analysis of electronic states. In this highlight review, we present our recent progresses with in situ (EC-TERS) and ex situ (PES combined with electrochemistry) experiments for elucidating the microscopic properties of electric double layers. Current issues and future perspective of both techniques are also discussed in detail.