Nanoscale electrochemical approaches to probing single atom electrocatalysts

Single-atom electrocatalysts (SAECs) have attracted extensive attention due to their high atomic utilization, unique activity and selectivity. Compared with traditional electrochemical methods (bulk catalysis) that provide the apparent activity, nanoscale electrochemical approaches (local catalysis) can measure the intrinsic activity and explore the reaction mechanism of SAECs, which moderates the conflict between experimental measurements (i.e., apparent activity) and theoretical calculations (i.e., intrinsic activity). Here, we review recent studies of nanoscale electrochemical approaches to probing SAECs and highlight important advances in the last 2–3 years. We introduce four representative nanoscale electrochemical techniques such as single-entity electrochemistry, electrochemical scanning tunneling microscopy (EC-STM), scanning electrochemical cell microscopy (SECCM), and surface interrogation scanning electrochemical microscopy (SI-SECM), and their applications of SAECs. Meanwhile, we give insightful comments on their technical limitations. Finally, we outlook the potential hyphenated techniques which are attractive for nanoscale electrochemical studies of SAECs.