Trends of Oxygen Reduction Reaction on Platinum Alloys: A Computational and Experimental Study

The development of Pt-based alloys for oxygen reduction reaction (ORR) is an important subject to enhance the performance of polymer electrolyte membrane fuel cells (PEMFCs) and metal-air batteries. Herein, ORR on Pt alloys with smaller and larger dopants in both Pt-shelled and cored alloys have been extensively investigated from both computational and experimental approaches to rationalize the detailed mechanism. Our density functional theory (DFT) based calculations found that Pt alloying with smaller dopants (Co, Cu, Pd) is thermodynamically stable at Pt-shelled structures and their improved ORR activity originates from ligand and geometric effects. On the other hand, Pt alloying with larger and less reactive dopants, such as Au, thermodynamically favors Pt-cored structure and shows the best ORR activity through ensemble effect of surface dopant. Additionally, our results revealed that d-band center of surface Pt can be correlated to ORR activity for Pt-shelled alloys, but not to Pt-cored ones. The computational predictions were in consistent with specific and mass activity measurements in the electrochemical experiment. Our computational and experimental efforts provided the conceptual foundation for the understanding of ORR mechanism on Pt alloys in both shelled and cored forms and for the first time concluded that Pt alloying with Au will show the best ORR activity through the ensemble effect from the chemistry viewpoint.