Applications of Atomically Dispersed Oxygen Reduction Catalysts in Fuel Cells and Zinc-Air Batteries

Due to severe energy crisis and environmental problems, green and renewable electrochemical energy devices such as fuel cells and metal-air batteries have attracted great attention, where oxygen reduction reaction (ORR) plays a vital role. The rational design of efficient and robust single-atom catalysts (SACs) is vital but challenging toward ORR. Here, recent developments of single-atom ORR catalysts in fuel cells and Zn-air batteries are systematically summarized, focusing on transition-metal-based electrocatalysts including single or dual Fe, Co, Ni, Cu, Zn, Pd, Ag, and Pt sites. At the atomic level, different synthesis methods and characterization techniques are introduced. Theoretical studies of ORR mechanisms are documented. The active sites and structure-property relationships of SACs for ORR are highlighted, and the performances of proton exchange membrane fuel cells (PEMFCs), anion exchange membrane fuel cells (AEMFCs), and Zn-air batteries are discussed. The great challenges and future directions of SACs in fuel cells and Zn-air batteries are presented.