Recent Progress in the Application of In Situ Characterization Techniques for Water Electrolysis

In the global pursuit of sustainable clean energy, electrolyzed water has become a key technology for alleviating the energy crisis and promoting the green energy transition with its advantage of producing hydrogen with high purity. However, electrolyzed water has a complex chemical reaction mechanism. The changes of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and intermediate states in the microscopic process bring many unanswered questions, which bring challenges to the in‐depth mechanism study. In addition, the reaction occurs at the solid–liquid–gas three‐phase interface, making the reaction kinetics and thermodynamics difficult to grasp. Traditional methods can only provide static information before and after the reaction. They cannot track the dynamic changes in the field in real time, which hinders the understanding of the reaction mechanism and the design of catalysts. In situ characterization is a solution. It allows real‐time monitoring of physical and chemical changes during the reaction. The principles and characteristics of in situ electron microscopy, X‐ray spectroscopy, and vibrational spectroscopy, and their applications in OER and HER are discussed. These techniques can help to deeply explore the OER and HER mechanisms in water electrolysis and guide future process optimization and development of high‐performance catalysts.