Advanced Pt-based intermetallic nanocrystals for the oxygen reduction reaction

Proton exchange membrane fuel cells (PEMFCs) are considered ideal energy-conversion devices because of their environmentally friendly nature and high theoretical energy efficiency. However, cathodic polarization, which is a result of the sluggish oxygen reduction reaction (ORR) kinetics, is a significant source of energy loss and reduces fuel cell efficiency. Further, the need to use Pt in commercial Pt/C cathodes has restricted their large-scale application in fuel cells because of its high cost and poor durability. Thus, improvements in the activity and durability of Pt-based catalyst are required to reduce the amount of Pt required and, thus, costs, while increasing the ORR rate and fuel cell power density and promoting widespread PEMFC commercialization. In recent years, atomically ordered Pt-based intermetallic nanocrystals have received tremendous attention owing to their excellent activity and stability for the ORR. Therefore, in this review, we first introduce the formation of intermetallic compounds from the perspective of thermodynamics and kinetics to lay a theoretical foundation for the design of these compounds. In addition, optimization strategies for Pt-based ordered intermetallic catalysts are summarized in terms of the catalyst composition, size, and morphology. Finally, we conclude with a discussion of the current challenges and future prospects of Pt-based ordered alloys. This review is designed to help readers gain insights into the recent developments in and rational design of Pt-based intermetallic nanocrystals for the ORR and encourage research that will enable the commercialization of PEMFCs.