Application and Development of Electrochemical Spectroscopy Methods

The theoretical and experimental technologies used for electrochemical characterization methods, which are essential for determining surface structures and elucidating electrochemical reaction mechanisms, have been significantly improved after more than two centuries of development. Traditional chemical methods like cyclic voltammetry (CV) can provide the exact electrochemical reaction rate in different potential ranges, which is beneficial for identifying the electrochemical performance of electrocatalytic materials. However, traditional chemical methods alone are often inadequate when it comes to achieving a deep understanding of reaction mechanisms. In this regard, spectroscopic methods, which are powerful tools to identify the active sites and intermediate species during electrochemical reactions, are widely applied to elucidate the electrochemical mechanism at a molecular or even atomic level. In this review, three molecular -vibrationspectroscopy -based electrochemical characterization technologies, viz., infrared (IR) spectroscopy, surface -enhanced Raman spectroscopy (SERS), and sum frequency generation (SFG) spectroscopy, are comprehensively reviewed and discussed. IR, SERS, and SFG are all non-destructive spectroscopic techniques with ultra -high surface sensitivity and are indispensable when detecting surface species during electrochemical reactions. Consequently, researchers have strived to combine these spectroscopic techniques with basic electrochemical instruments. In fundamental electrochemical research, detecting electrochemical reactions in model single -crystal systems and determining the structure of interfacial water molecules have been two major research topics in recent years. Single -crystal surfaces are important in fundamental electrochemical research because of their defined atom arrays and energy states, serving as model systems to help bridge experimental results and theoretical calculations. Meanwhile, the structure of interfacial water influences most electrochemical reaction processes, and as such, probing interfacial water structures is a challenging but valuable target in fundamental electrochemical research. Additionally, the application of electrochemical spectroscopic methods to analyze fuel cells has become important, and this review covers recent SERS studies of oxygen reduction reactions (ORR) and hydrogen oxidation reactions (HOR) in hydrogen fuel cells. Concurrently, electrochemical IR and SFG studies on the electrooxidation of small organic molecules are discussed. Finally, owing to the significance of lithium -ion batteries, studies of electrochemical spectroscopic methods on solid electrolyte interphase (SEI) and cathode -electrolyte interface (CEI) are becoming increasingly important and are introduced here. In conclusion, recent advances and the future developments of electrochemical spectroscopy methods are summarized in this review article.