Origin of High Activity and Durability of Confined Ordered Intermetallic PtCo Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Fuel Cell Operating Conditions

Surface carbon confinement has emerged as an efficient method in promoting the performance of Pt-based catalysts, especially in the design of ordered intermetallic Pt alloy nanoparticles. However, to what function the carbon shell associated with the ordered phase has influenced the activity and particularly long-term durability both in rotating disk electrode (RDE) and fuel cell operating conditions has not been fully understood. In this research, we designed L10 PtCo nanoparticles coated by a thin nitrogen-doped carbon shell (I-PtCo@CNx) with small particle size (about 5 nm), which exhibited almost 5 times increase in the Pt mass activity compared to commercial Pt/C. Remarkably, I-PtCo@CNx also showed improved longevity and high Co retention during the accelerated durability tests (ADT) compared with control samples. The increased performance originates from the compressed lattice of the ordered structure and the optimized electronic state by the interaction effect from the surface nitrogen-doped carbon shell (CNx) detected by ex situ and operando X-ray absorption spectroscopy (XAS), which demonstrated fewer structure changes during reaction potentials. The order phase exhibited the ability to maintain the Co component against electrochemical dissolution, while CNx suppressed the generation of the oxidation species and hindered Ostwald ripening during the degradation, which led to higher durability in both RDE and membrane electrolyte assembly (MEA) tests.