Recent progress in advanced in situ/operando characterization techniques for the oxygen evolution reaction

The oxygen evolution reaction (OER) is a kinetically sluggish process in electrochemical water splitting, limiting the overall efficiency of hydrogen production. Understanding the dynamic structural evolution of catalysts and the reaction mechanisms under operating conditions remains a fundamental challenge, as conventional ex situ techniques fail to capture transient intermediates and surface reconstruction. This review highlights recent advances in advanced in situ/operando characterization techniques - including ATR-SEIRAS, Raman spectroscopy, XAFS, DEMS, and EC-AFM for probing OER mechanisms in both acidic and alkaline electrolytes. These methods provide real-time insights into catalyst structure, active sites, reaction intermediates, and gaseous products, thereby elucidating structure-performance relationships and guiding the rational design of high-performance OER catalysts. Future perspectives should focus on enhancing spatial/time resolution and integrating multi-technique platforms for correlated analysis. These advances in technology will further unravel the complex dynamics of the OER and accelerate the development of efficient energy conversion systems.