In Situ and Operando Techniques for Electrocatalysis in Renewable Energy Applications.

Electrocatalysis is essential for renewable energy conversion, yet the mechanisms governing catalytic performance remain poorly understood due to the complex nature of electrochemical interfaces. Advances in nanomaterial synthesis and high-resolution characterization now allow detailed structural and compositional analysis, but static methods fall short of capturing the dynamic behaviors of active sites during operation. In this review, we focus on the growing role of in situ and operando techniques such as optical, X-ray, and electron-based, in resolving catalytic structure and reactivity under real-life working conditions. These methods offer unparalleled access to the evolution of surface species, reaction intermediates, and interfacial topologies that govern catalytic functions. We highlight how in situ and operando studies have revealed transient phenomena and mechanistic details previously inaccessible, and discuss their critical roles in advancing systems for water splitting, CO2/N2 reduction, and fuel cells related renewable energy applications. Beyond highlighting the real-time transformations captured by operando and in situ methods, this review underscores how coupling operando datasets with theoretical modeling and machine learning can accelerate mechanistic discovery and enable rational catalyst design. By extracting hidden correlations and guiding closed-loop experimentation, data-driven approaches promise to reduce reliance on empirical trial-and-error and unlock predictive control over catalytic performance. Taken together, these developments position operando characterization, when coupled with AI-driven interpretation, as a cornerstone of future energy research, providing a pathway to accelerate discovery, design, and deployment of next-generation electrocatalysts.