Electrochemical double layer at electrode-water interfaces: Recent advances from nonlinear spectroscopic investigations

Exploring the electrochemical double layer (EDL) at electrodewater interfaces is of both fundamental and practical importance to electrochemical technology. Current research endeavors are dedicated to unraveling the molecular-level intricacies of the EDL. In this review, we discuss the application of nonlinear spectroscopy to address this challenging task. Specifically, we present the latest experimental progress of using second-harmonic generation and sum-frequency generation to characterize the interfacial electric fields, interfacial water structures, as well as the adsorbates and reactive species. We also discuss the challenges and opportunities of employing nonlinear spectroscopy for more in-depth characterization of electrochemical interfaces.