Surface interrogation of advanced electrocatalysts by scanning electrochemical microscopy: fundamentals, progress and...

In situ quantitative analysis of electrode surfaces, particularly the identification of active sites and reaction intermediates, is essential for elucidating structure-activity relationships and understanding the mechanisms underlying electrocatalytic reactions. Although conventional spectroscopic techniques are widely used to probe catalytic intermediates, they often face limitations in sensitivity, spatial and temporal resolution, and the ability to capture transient phenomena. These constraints hinder the precise quantification of catalytically active sites and the accurate assessment of electrochemical reaction kinetics. The development of surface interrogation scanning electrochemical microscopy (SI-SECM) has enabled the direct and quantitative evaluation of reactive species as well as real-time measurement of reaction kinetics at electrode interfaces. SI-SECM provides valuable insights into the adsorption behavior of intermediates, the complexity of reaction mechanisms, and the characteristics of catalytically active sites. This work introduces the fundamental principles and instrumentation of SI-SECM, with particular attention to its application in key electrocatalytic processes such as hydrogen evolution, oxygen evolution/reduction, ammonia electrosynthesis and carbon dioxide reduction reactions. The article further outlines standard operational protocols for SI-SECM and discusses future directions, including the advancement of high-throughput methodologies, expansion to a broader range of catalytic systems, and progress in multi-field coupling. These developments would collectively position SI-SECM as a versatile platform for mechanistic studies and the rational design of advanced electrocatalysts.