Key concepts for understanding alkaline oxygen evolution reaction at the atomic/molecular scale

Understanding and improving the sluggish oxygen evolution reaction (OER) is critical for efficient water electrolysis. However, given that the OER is a multi-step, inner-sphere electrochemical reaction, understanding the OER at the atomic/molecular scale is difficult due to its complex redox chemistry and convoluted reaction mechanism. Moreover, recent discoveries of new types of active site, active species, reaction mechanism, and the driving force of the OER further complicate our understanding of the OER. Herein, a review of the key concepts of the OER at the atomic/molecular scale is given, focusing on providing their clear definitions, principles, categories, and commonalities and differences. Also, the role of each concept in determining the OER activity is discussed.