Electrocatalytic reactions are governed by dynamic operating states rather than by static material properties alone. Under applied potential, catalyst surfaces restructure, oxidation states shift, surface intermediates build up and disappear, and the local chemical environment near the interface evolves continuously. As a result, measurements made before or after reaction can miss the species and conditions that actually control activity, selectivity, and stability.
Operando and related in situ characterisation approaches address this challenge by probing electrocatalytic systems while they function under realistic reaction conditions. Instead of providing a single snapshot of the catalyst, these approaches capture key elements of the working state of the catalytic system: the coupled state of active sites, interfacial intermediates, local environment, and product formation that exists only during operation. Understanding electrocatalysis therefore requires observing how these components evolve and interact in real time.
This presentation discusses why access to system working states is essential for mechanistic understanding and how they can be experimentally resolved through measurements performed under operating conditions. Recent developments and adaptations of operando approaches are highlighted, including operando proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS), operando Raman spectroscopy, and in situ transient photocurrent techniques. These examples demonstrate how real-time measurements provide direct insight into reaction mechanisms and dynamic processes that remain inaccessible to conventional characterisation, offering new understanding of how electrocatalysts function during operation.