Engineering Active Sites in Single-Atom Catalysts for Enhanced Oxygen Reduction Reaction: Strategies and Outlook

Carbon-based single-atom catalysts (SACs) combine the advantages of atomic efficiency and unique electronic configuration, making them promising candidates for next-generation oxygen reduction reaction (ORR) catalysts. Despite their notable catalytic properties, a performance gap still exists between SACs and platinum-group-metal (PGM) catalysts. Generally, two primary strategies are employed to develop high-performance SACs: increasing the density or accessibility of active sites and enhancing their intrinsic activity. This Perspective examines various approaches to improve the electrocatalytic performance of SACs for the ORR, with a focus on active site engineering. We discuss methods to increase the number or accessibility of active sites along with an overview of key synthesis techniques. Additionally, we explore strategies to boost the intrinsic activity of these sites such as incorporating synergistic elements that modulate electronic structures and optimize intermediate adsorption and desorption. Finally, we highlight the remaining challenges and prospects for advancing SACs in the ORR applications.