In situ and ex situ approaches for molecular scale understanding of electrochemical interfaces

In recent years, electrochemical devices have become increasingly important, and atomic- and molecular-scale understanding of the electronic and ionic transfers and chemical reactions at the electrode/electrolyte interface is required. While electrochemical scanning tunneling microscopy (EC-STM) has long enabled atomic-resolution observations in real space, it is difficult to identify reaction products and evaluate their electronic states at the interface in the electrochemical environment because of various limitations imposed by the presence of electrolyte solutions in the measurement. In this perspective review, we present our recent progresses with in situ (EC-STM combined with near-field spectroscopy) and ex situ (precise measurements in ultrahigh vacuum after electrode emersion) experiments for elucidating the microscopic properties of the electrochemical interfaces. Current issues and future perspective of both techniques are also discussed in detail.