Sum Frequency Generation Spectroscopy as a Powerful Tool for In Situ Analysis of Photo‐ and Electrocatalytic Interfaces

Understanding interfacial processes in sustainable energy conversion and environmental remediation systems has drawn considerable attention. Yet, despite advances in surface science and characterization methods, probing dynamic molecular processes occurring at reactive interfaces remains challenging. Addressing these processes requires in situ and operando surface‐sensitive tools for elucidating the interfacial dynamics that govern the performance of (photo)catalytic and electrochemical systems. Among these methods, sum frequency generation (SFG) spectroscopy is a well‐suited tool for probing interfaces under in situ and operando conditions. As a second‐order nonlinear vibrational spectroscopic technique, SFG spectroscopy combines the selection rules of infrared (IR) and Raman spectroscopy, making it inherently surface sensitive and allowing the investigation of reactions at gas/liquid, liquid/solid, and gas/solid interfaces. This review summarizes recent advances in in situ and operando studies of photocatalytic, electrocatalytic, and electrochemical interfaces, with emphasis on adsorption behavior, interfacial molecular organization, reaction intermediates, and catalytic pathways under realistic operating conditions. After outlining the fundamental principles of SFG spectroscopy, this review emphasizes recent studies on electrocatalytic interfaces, CO/CO ₂ ‐related catalytic reactions on transition‐metal surfaces, and interfacial processes at TiO ₂ ‐based photocatalytic interfaces.