ATR-SEIRAS for Single-Atom Electrocatalysis

ConspectusSingle-atom catalysts (SACs) represent a revolutionary paradigm in heterogeneous catalysis and display exceptional atom utilization efficiency with well-defined active sites. These distinctive characteristics position SACs as pivotal materials for advancing electrochemical energy conversion and storage technologies. The active center atoms are typically anchored by coordination with oxygen (O), nitrogen (N), and other functional groups on the surface of the supports. When precisely anchored onto tailored supports, these isolated active centers offer considerable promise for enhanced catalytic activity and selectivity. Nevertheless, the inherent complexity of the multistep proton-coupled electron transfer processes in electrochemical energy conversion and storage systems presents major challenges for the mechanistic elucidation and rational design of catalytic architectures to optimize reaction kinetics. Recent advancements in <i>in situ</i>/<i>operando</i> characterizations, most notably attenuated total reflection-surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), have greatly stimulated SACs research. ATR-SEIRAS amplifies the vibrational signal at the interface, enabling real-time tracking of transient interfacial species at submonolayer concentrations. Moreover, it simultaneously captures the dynamic structural evolution of single-atom motifs during the catalytic cycles.In this Account, we exemplify our recent endeavors in characterizing single-atom electrocatalysts using ATR-SEIRAS. Through the integration of the ATR-SEIRAS technique with precisely engineered SACs, we elucidate the critical structure-activity relationships of SACs in the CO/CO₂ reduction reaction (CO/CO₂RR), oxygen reduction reaction (ORR), and nitrate reduction reaction (NO₃^-RR). We begin with a fundamental analysis of the ATR-SEIRAS enhancement mechanisms, categorized into physical and chemical enhancement mechanisms. Building on this theoretical foundation, ATR-SEIRAS demonstrates the exceptional capability of tracing reaction pathways in single-atom electrocatalysis. This is achieved through vibrational fingerprint identification of oxygen-containing intermediates (O/O-H), carbonaceous moieties (C-H/C-O), and nitrogenous adsorbates (N-H/N-O). Furthermore, we discuss the role of ATR-SEIRAS in studying the stability of SACs in electrocatalytic CO/CO₂RR, ORR, and NO₃^-RR. Additionally, ATR-SEIRAS can be utilized to determine the function of active sites in single-atom catalyst motifs, which is of paramount importance for gaining a deeper understanding of the reaction mechanisms and for the rational design of highly efficient catalysts. Crucially, ATR-SEIRAS plays a vital role in monitoring the dynamic structure evolution of SACs, thereby aiding in decoding the complex interactions between catalytic structure and performance. Last but not least, we demonstrate the use of ATR-SEIRAS for verifying density functional theory (DFT) calculation results in single-atom electrocatalysis. This Account provides a comprehensive perspective on the application of ATR-SEIRAS in studying single-atom electrocatalysis. The enhanced understanding of active site dynamics and reaction mechanisms obtained shall offer valuable insights for the rational design of high-performance, durable SACs for next-generation electrochemical energy conversion and storage applications.