A Review on Experimental Identification of Active Sites in Model Bifunctional Electrocatalytic Systems for Oxygen Reduction and Evolution Reactions

Efficient electrocatalysis of the oxygen reduction (ORR) and evolution (OER) reactions is essential in numerous renewable energy conversion systems, such as fuel cells, metal-air batteries, and water electrolyzers. Design and optimization of electrocatalytic materials for such systems primarily rely on understanding the nature of active centers on the catalyst surface. This review focuses on several important aspects of the experimental identification of active sites on various model bifunctional ORR/OER electrocatalytic surfaces. Applications of the state-of-the-art experimental techniques are analyzed. In addition, approaches to investigate and understand the influence of some supporting electrolyte components on the ORR and OER activities are discussed.